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[
"Is radiation from electronics really dangerous?"
] |
[
false
] | null |
[
"In 99.9% of cases, no. And it's not real radiation. Electronics do not emit radiation. They emit EM signals. There are exceptions to this- anything that employs very high voltage can actually emit x-rays which are considered ionizing radiation. Some plasma TV's, x-ray tubes, vacuum tubes, and air ionizing machines can be harmful if they are not properly shielded. Cell phones only emit radio waves. Radio waves are not ionizing radiation. Microwave ovens (if they are properly shielded) emit very low levels of microwaves, which are also not ionizing. Both microwaves and radio waves can cause localized heating of tissue in large doses- but as far as chronic exposure, you will be harmed more by a simple sunburn than by standing in front of a running microwave with your pants full of ringing cell phones for a year straight.",
"http://en.wikipedia.org/wiki/Mobile_phone_radiation_and_health",
"Mobile phones use electromagnetic radiation in the microwave range.",
"\"to date, no adverse health effects have been established as being caused by mobile phone use.\"",
"mobile phone radiation as Group 2B - possibly carcinogenic",
"http://en.wikipedia.org/wiki/Ionizing_radiation",
"the lower ultraviolet part of the electromagnetic spectrum, visible light (including nearly all types of laser light), infrared, microwaves, and radio waves are considered non-ionizing radiation.",
"By the way: \"Group 2B carcinogen\" is in the same carcinogen risk category as Coffee and pickled vegetables. Group 2A, the next level up, includes solar radiation (UVA, B, and C). Alcohol ranks in Group 1 (most carcinogenic). "
] |
[
"Thank you for your thurrow answear. \nVisible light is electromagnetic radiation: ",
"http://en.m.wikipedia.org/wiki/Electromagnetic_radiation",
"All EM waves is EM radiation\nYou even wrote it yourself :)"
] |
[
" and ",
" are not the same thing. "
] |
[
"Why does inhaling steam decongest lungs and sinuses"
] |
[
false
] |
I've done this when im really sick. I'll run the shower at a higher temp, steam up the bathroom and breath the steam with long breaths. within a couple of minutes i can feel my sinuses and lungs free up. any reason why? does water in the vapor form bond with something else to create some super decongestant?
|
[
"If the sinus passages are constricted or inflamed then you get the \"stuffed up\" feeling.",
"It can cause dilation of the sinus passages, effectively acting as a (relatively very poor, in my opinion) decongestant (not in the same way a medication would)."
] |
[
"You're watering down your mucus. Mucus that is more viscous doesn't clear as easily out of your lungs/nasal cavity/throat. Viscous mucus, and your body's inability to clear it, is what causes problems in ",
"Cystic Fibrosis",
".",
"The more watery your mucus, the easier it is for it to be cleared out of blockages in your nose and lungs."
] |
[
"Question: Is mucus discarded from your system only via the nasal passage? Does watering down mucus mean you'll have a runny nose?"
] |
[
"regeneration?"
] |
[
false
] |
So I know that certain species can regenerate. Such as Starfish, but if you cut a starfish's appendage off and then cauterize the wound will that appendage still grow back? If not are they're any organisms that you can cause limitless damage to and regeneration still be possible?
|
[
"Can't answer your starfish quesiton, but ",
"planaria",
" are the most regenerative creatures I know of. The smallest visible chunk cut off a planarian will form a small worm which will grow back to full size if properly fed.",
"They're able to regenerate this way because stem cells are stored more or less equally throughout their entire bodies. Obviously, if you manage to cut out a microscopic chunk that lacks a stem cell it won't grow into a worm, but other than that they are amazingly resistant to physical damage. However, if you treat them with sufficient radiation, you'll kill the stem cells and the worms lose their regenerative properties (and will die a few days later)."
] |
[
"so if you cut a planaria in half you'll eventually have two?"
] |
[
"If you cut one into 20 pieces you'll eventually have 20 new planaria. If you slice it halfway down the middle it will grow two full heads attached to one tail. The lab down the hall works on them. At the end of the day, they chop up a bunch of worms to replace the ones they used in experiments."
] |
[
"Will the Voyager probes foreseeably be overtaken by other probes and if so when?"
] |
[
false
] |
[deleted]
|
[
"Despite RRC saying it is impossible, I strongly believe otherwise. Here's one proposal from NASA, which may or may not materialize, that would send an ion-thruster equipped spacecraft through gravitational slingshots to reach 37km/s compared to Voyager's 17km/s. It would pass Voyager 1 in 2047 if the proposed launch window is used.\n",
"http://interstellarexplorer.jhuapl.edu/index.php"
] |
[
"The most recent similar probe is New Horizons, which is not going fast enough to overtake it."
] |
[
"It's more that a probe needs to have a lot of velocity to get that far out in the solar system, but then it's hard to get rid of that velocity once you arrive. You can't aerobrake, and you can't bring enough fuel to cancel out your velocity."
] |
[
"Will a transplant limb work on its own DNA or adapt to the patients DNA?"
] |
[
false
] |
So if you got a hairy hand put on your right arm but your original hand was not as hairy. Or would a slightly darker natural tone eventually even out? Or will it always be obvious?
|
[
"The arm is still made out of the original donors’s cells, so it will keep the same DNA. All that changes during a transplant is where the energy for the arm comes from. As long as it gets blood from the patient, the arm should act as if it’s still on the original person.",
"Although, that’s disregarding the possible rejection that the patients immune system would have."
] |
[
"Well DNA is a lot more complicated than a single long strand. It’s compacted into 23 pairs of chromosomes, each made up of huge coils of DNA. They pretty much stay in the nucleus of the cell, unless a cell dies. In that case, all the bits that made up the cell are shredded and recycled into new ones. So any rouge DNA would probably be scrapped for parts before it could get into another cell. ",
"I’m not sure about the blood thing, I would assume that the original donor’s blood would be drained and replaced with compatible donated blood just before it’s attached, but I couldn’t find much about it online."
] |
[
"Not likely, as most of the cell replacement takes place by division of the nearby cells in a relatively \"endogamic\" process. Near the place where the arm was attached there migth be come cells going from one place to the other, but truth be told, I don't think it would be even detectable."
] |
[
"When the Big-Bang happened, was the energy that exploded traveling at the speed of light? [More related questions inside]"
] |
[
false
] |
[deleted]
|
[
"Try starting with ",
"inflation."
] |
[
"the big bang wasn't an explosion of matter - it was the start of the expansion of space. ",
"we aren't moving \"out\" anywhere - we are in the same place in the universe, but the universe has been stretching since the big bang - increasing the space between galaxies"
] |
[
"because there is no \"center\". the universe isn't like a balloon being blown up - where you can observe an edge and measure the distance from the edges to the centre. ",
"the ",
"universe is isotropic",
" (the same in every direction). we could say that ",
" are the centre of the universe, which could be true - and everything is moving away from us at the same speed, in every direction. similarly we could be on a planet at the other side of our observable universe, and say that ",
" was the centre of the universe and make all the same observations. ",
"no the earth isn't being stretched - it isn't mass being stretched, only space. the latest theory is that ",
"dark energy",
" is what is pushing everything apart, as the expansion of space is actually increasing - mass is held together by gravity and is still much stronger than dark energy. "
] |
[
"If humans could live healthily for hundreds of years, what effect would that have on our brains?"
] |
[
false
] | null |
[
"If you are looking for hypothetical / speculative / open-ended answers, please post to our sister-sub ",
"/r/asksciencediscussion",
" which was made for just such questions!"
] |
[
"We don't know."
] |
[
"That’s a fair answer ",
"But from what we ",
" know, can anything be hypothesized?",
"Like I understand learning means more neural connections and new cells, and therefore more mass. I understand that it also develops the folds as a way to have more surface area in a confined space.",
"If the time in which we could continue learning was extended, say indefinitely, would that not require an expanded cranium eventually? Or would the brain, in its constant quest to prioritize what’s important, just eventually kill off that which is too old to matter anymore?",
"That second question, I get how it wanders into unknown territory since we have at best people at 120 who can remember their distant pasts well enough to tell their stories, so there just isn’t any data to tell at what point such an information culling would begin to take place, but physiologically, we could make predictions, couldn’t we?"
] |
[
"Could normal flora be considered as a part of our immune system?"
] |
[
false
] |
We have a lot of bacteria that live in and on our bodies. Would a healthy person then possibly have "healthy" bacteria that competes for resources with "bad" bacteria?
|
[
"Yes, absolutely. That is one of the many ways that gut flora and other forms of bacteria we associate with are mutualistic. While they do serve other purposes, many of these mutualistic bacteria help reduce the persistance of 'exotic' or 'foreign' strains by outcompeting them for resources. This is called the barrier effect. They mention it briefly in this ",
"wikipedia article"
] |
[
"A great example of this is the fact that most adults can eat honey (which relatively often has C. botulinum in it) but infants cannot. This is because infants don't have well developed gut bacteria yet. Adults have well developed gut bacteria that can easily out compete the C. botulinum. "
] |
[
"Fun info of the night. The bacteria in your gut are responsible for the initial exposure to the other blood types. When you give an A person B blood for the first time, the transfusion reaction occurs because they already have antibodies against the B antigen, but this requires an exposure prior to that transfusion. During infancy and the development of your immune system the initial exposures occur due to your normal flora's presence. ",
"Speaking of blood types, there are also normal flora types that divide us up into three groups. ",
"As to your question, a lot of immunologists (ime) consider your normal flora a vital part of a fully functional immune system, and they often keep us free from harm by direct competition and the production of bacteriocins which kill off invaders (neosporin inside your gut at all times is nice). Loss of these due to antibiotics can lead to some nasty opportunistic infections. "
] |
[
"Why do naturally occurring chemicals affect our brains? Is there an evolutionary link or is it just a lucky accident?"
] |
[
false
] |
E.g. pscilocibin, THC, DMT. Have our brains evolved to process these chemicals in a certain way that changes our experience of the world or is it mere fluke that these chemicals have a seemingly profound affect on our perception and consciousness?
|
[
"Plants can't flee, so they evolve chemical defenses. They employ foul-tasting compounds, antinutritional factors, and toxins (which are generally variations on metabolic compounds that interfere with normal metabolic processes). For example, psilocybin is derived from the amino acid tryptophan, but is structurally ver similar to the neurotransmitter serotonin. A byproduct of a variation in tryptophan metabolism suddenly renders the fungus toxic to organisms that would consume, enhancing its fitness and selecting for the trait."
] |
[
"Everything co-evolves within an eco-system, but most likely the fungi have adapted defences mainly against some other creature, and those defences just happen to have the effect they do on humans. I don't think humans and magic mushies have exerted major selection pressures on each other. [edit] - unless our ancestors in the forgotten past once cultivated magic mushies, which is not that implausible."
] |
[
"\"Have our brains evolved to process these chemicals in a certain way?\"",
"It's more like the other way around. The kinds of drugs you're talking about have their effects because they mimic (or inhibit) certain neurotransmitters that are already in the brain, like what FellowConspirator was saying. This is actually a very important part of neuropharmacology: studying the effects of drugs on behavior can give us important clues to how the brain works. This may seem obvious, but if a substance can have an effect on your brain, then it must have a chemical analogue somewhere in the brain, otherwise the substance wouldn't be able to act on any of our neurotransmitters. ",
"That's actually how endorphins were discovered. A lot of the research that went into that discovery started out as research on opium addiction, which led to the question of how opiate binded so strongly to the brain. Turns out it's because opiates have an action that is strongly similar to what your brain produce when enorphins are released (More here: ",
"http://www.pbs.org/wgbh/aso/databank/entries/dh75en.html",
") ",
"So like FellowConspirator, I'm inclined to believe it's a fluke of nature that certain plants can cross the blood-brain barrier and act on neurotransmitters. But it could well be that it's evolutionarily advantageous to develop these traits. I'm speaking a little outside my field now, but it seems likely that organisms which could have an intoxicating effect on humans (or other animals) would be more likely to survive, as they would be more likely to be cultivated or at least get spread to a wider area by animals who may carry the seeds etc. to new environments. "
] |
[
"Do other species have “early birds” and “night owls,” or is this a uniquely human/ primate trait?"
] |
[
false
] |
[deleted]
|
[
"The tendency for an individual to be active during particular parts of the day is called the cronotype, and it varies as a continuum across members of a species and across their lifetimes. It has been shown in ",
"macaques",
" and ",
"rodents",
", and is related to the difference between an individuals intrinsic circadian rhythm and the day-night cycle."
] |
[
"What do you mean by abberations? Chronotype is like height - it's just a feature. Some of us are just at the tails of the distribution. "
] |
[
"In other words you are saying that there could be \"early birds\" night owls ?"
] |
[
"Can you do 100 edits on a single (human) genome with CRISPR, or is the number limited ?"
] |
[
false
] |
I'm interested in both theoritical limitations and practical ones. I can't seem to find something about it in the litterature. This is a question that is in a context of eugenics : would it be possible for parents to edit as many genes as they want, or would too many just be impossible (too long, too much errors, ...) ?
|
[
"I'm actually working with CRISPR right now, although in plants, so I'll try and give a shot at answering this question. \nThe actual 'gene editing' part of CRISPR is done by the interaction between the Cas9 protein and a strand of guide-RNA which targets a region just upstream of a 'PAM' site (a 3bp sequence used to target). When the Cas9/gRNA complex binds to the DNA it makes a double strand break, which can then be repaired in two ways. The first is non-homologous end joining (NHEJ), which essentially just sticks the two strands back together, it's quick and dirty, but prone to errors. This method is commonly used to induce an indel frameshift or nonsense mutation to deactivate a gene. The other method of DNA repair is homology directed repair (HDR), which uses a template strand to copy off. The advantage of this is that you can insert novel DNA into the genome, the downside being twofold: that you have to have the template DNA present, and the rate of HDR is super low. Recently, ",
"the Corn lab",
" came up with a method exploiting the mechanics of ",
" Cas9 induces the DSB, which increases the frequency of HDR into the region of 40%. ",
"So the problem for trying to do 100 edits on a human genome start to come together. If you want to do proper gene editing, you probably want to do HDR. The absolute best method we currently have for HDR has a 40% rate of occurring at all, with a lower chance of actually being successful. Not only that, but you have to figure out a way to get 100 template strands and 100 guide RNAs into the right cell to do their work, when most people aren't using any more than one or two of each. Even if you did manage to get all the template and all the gRNA, the chances of each just not working starts to add up. ",
"I can't say I'm familiar with human gene editing with CRISPR, either. In plants you either work on the germline, or regenerate from a single cell. I don't know how you edit human, whether it's sperm, or embryo, or what. ",
"So TL;DR summary answer to your question, probably not, the tech is still in the infant stages and people are trying to make it better."
] |
[
"This is a fantastic description, kudos. ",
"From my experience, I used CRISPR to generate a knock-in mouse and the current methods leave additional caveats that would also apply in humans. ",
"First, in order to modify the whole mouse, we had to microinject the cas9 mRNA, guide RNAs, and repair plasmid for HDR into single cell fertilized embryos. The trauma of the injections caused around 30-40% of the embryos to die within the next 24h, so that's challenge 1. ",
"Next, the embryos had to be inserted into a surrogate mouse, and just like with in Vitro fertilization in humans, the successful implantation of an embryo is a fairly low probability event. You end up inserting many embryos and seeing what sticks.",
"Finally, when you have offspring born is when you can see if the CRISPR worked. We screened over 100 mouse pups before we got a single successful mouse. These pups came from embryos that survived the microinjection and got implanted successfully.",
"Combine the mammalian difficulties with trying to edit 100 sites and the picture gets even more daunting! There are certainly people more adept at CRISPR than I am, with better success rates, but it's still a difficult process even for single gene edits, at least for HDR."
] |
[
"This is why I'm glad I work with cell lines. All I need to do is culture cells, nucleofect the guide vector and repair template and grow single cell clines. Then it's just a simple matter of applying my selection to the clones and sequencing the positives. It takes about 3 weeks from the inital subculture to having identified a successful knock-in"
] |
[
"Why is it that we can tell the difference between a note, ie. a Gmajor played on a violin and the same not played on a piano. even if the soundwaves are the same frequency and the same note."
] |
[
false
] | null |
[
"The note that we perceive we hear say, G natural, (G major is actually a chord, i.e. a set of notes) is the lowest frequency of the note. A pure note is really dull, listen to an A440 ( ",
"http://en.wikipedia.org/wiki/A440_(pitch_standard)",
" ). It sounds digital because it basically takes a computer to produce a pure tone. However, notes that musical instruments make don't just consist of a pure frequency, they also consist of a number of \"harmonics\". The different loudnesses of all of the harmonics is what causes the notes to sound different. Harmonics are multiplications of the base frequency. For example, for an instrument playing A440 (the standard tuning note of the orchestra), it also produces sounds at 880 hertz, 1760 hertz, 2640 hertz, etc. As ee58 mentioned, in music, we call the different qualities of the same base pitch \"timbre\".",
"Sounds that we perceive as noise (for example coming out of an airplane or from radio static) are composed of notes at a lot of frequencies, not just a number times the base frequency. As such, we don't perceive it as a nice standard tone, but as a crazy mess of tones, which it is.",
"Another fun tidbit is to look at the first few harmonics.\n440 hz -- A; \n880 hz -- Also an A; \n1760 hz -- an E; \n2640 hz -- a C#; ",
"A+ C# + E are the tones which make up the A major scale. Major scales sound so pleasing because they \"match up\" with the base harmonic and its overtones.",
"Vi Hart has a really good video on this ",
"https://www.youtube.com/watch?v=i_0DXxNeaQ0",
"Edit: Whoops, messed up the scale. Thanks Die_Fuherin! A-C#-E is the major scale (and the hertz numbers listed), A-C-E is the A minor scale. "
] |
[
"Good post, but you made A minor mistake (badum tshh). You gave the notes for the A minor chord. The A major scale is A, B, C#, D, E, F#, G#, A, where the '#' signifies sharp i.e. the note is raised a semitone. The chord A major is A, C# and E.",
"EDIT: I'm afraid I spotted another mistake - 1760Hz is the A two octaves (or 4 times freq) above the first A, not an E as you stated. See ",
"this",
" wikipedia article for some interesting information on the frequencies of notes using twelve-tone equal temperament."
] |
[
"In the context of music the difference is called ",
"timbre",
"."
] |
[
"How much are clouds effected by gravity?"
] |
[
false
] |
Is there movement in the sky effected by earth's pull?
|
[
"None of the current comments (2 total) are correct in stating that clouds are \"less dense\" than air. Simple observation tells us that liquid water, and ice, are in fact a factor of approximately 780 more dense than air at standard temperature and pressures. Clouds on Earth are composed primarily of droplets of water or particles of ice, or some mixture thereof.",
"The correct answer is that cloud particles do fall, but their fall speeds are slowed by upward and turbulent air motions. Due to their small mass, the force imparted on cloud droplets (as opposed to rain droplets) by air is more effective at slowing their vertical descent. In convective storms, the vertical updrafts are are sometimes strong enough to shoot cloud drops/ ice particles into the stratosphere. In very stable atmospheres, clouds droplet size precipitation can reach the surface (commonly as heavy fog or light drizzle). ",
"So clouds, composed of cloud droplets, are affected by gravity and the motions of air in an approximately balanced fashion. If one could construct a cloud of bowling balls, air motion in all but the strongest storms would be negligible compared to the force imparted by gravity on the bowling balls. "
] |
[
"They are less dense so there's a difference in Fg so they float. The same as any other mass, but there's the buoyant force counteracting it. "
] |
[
"*affected, presumably."
] |
[
"What are the characteristics that make blood types different?"
] |
[
false
] |
What is the science behind finding out blood types and their differences?
|
[
"The surface of your cells is not smooth - every cell membrane is studded with tons of proteins, many of which have strings of sugars attached to them (they're called \"glycoproteins\"). The way that these sugars are added is a bit complicated, but while the proteins are being made, some sugars are added in a specific order, and then some are trimmed in various ways. What's important to know is that all this addition and modification is mediated by enzymes, which are basically protein machines inside the cell. Also important to know: these enzymes are coded for by genes.",
"A and B blood groups refer to specific types of sugar modifications on surface glycoproteins, mediated by two different alleles (variations) of a particular enzyme called glycosyltransferase. If you're type O, both copies of this gene that you inherited are a version that doesn't work. If you're type A, you inherited a version that likes to add a specific type of sugar to these glycoproteins and if you're type B, your enzyme likes to add a different type of sugar. Type AB people have one of each type of functional enzyme, so they have some glycoproteins on the surface of their cells with the one sugar added, and some with the other sugar added.",
"The reason this matters is because our immune system can make antibodies against these different forms of sugar modifications. If you have the A modification, your immune system is trained to ignore it, but if you don't, and you get a blood transfusion with cells that have the A modification, your immune system will attack and destroy all those new cells. As for how we test it, we have ways of using antibodies in the lab to test a sample for these blood groups."
] |
[
"Proteins on the outsides of the blood cells - protein markers."
] |
[
"Not exactly - the blood groups are the arrangement of sugars added to cell surface glycoproteins, not the proteins themselves."
] |
[
"What would happen if a Nuclear bomb went off in space?"
] |
[
false
] |
Just listened to a podcast talking about the Star Wars program and it got me quite curious.
|
[
"I'd refer you to: ",
"http://en.wikipedia.org/wiki/High-altitude_nuclear_explosion"
] |
[
"Thank you!"
] |
[
"Actually, there have been five nuclear explosions in space as defined by the Fédération Aéronautique Internationale, one of which being Starfish Prime:",
"http://en.wikipedia.org/wiki/Starfish_Prime",
"Hope that helps, OP."
] |
[
"How do antibodies pass to the baby during breastfeeding? Why the antibodies aren't simply digested?"
] |
[
false
] | null |
[
"As sockstuff pointed out, its possible that protein-digesting enzymes in the baby's system is not as strict on proteins as adults' systems are (I don't know the fact on that)..",
"What I do know is that levels of antibodies in the breastmilk can be quite high too so that even if there are proteases that cleave proteins in the system some of the antibodies can still make it to the small intestine. ",
"This is especially striking in some mammals like the cow: the first time a cow secretes milk after giving birth the antibody concentrations in that milk go to 50 milligrams per liter (thats a real, REAL lot of protein, leave alone antibody) to the extent that the mother's blood antibody levels go down significantly because of this transfer. The milk itself is brownish and tastes wildly different (trust me :P ). At least in that case the concentrations are so high that even a normal digestive system will still struggle to digest all the antibodies in that milk."
] |
[
"This first secretion after childbirth is known as the colostrum, if it helps anybody wanting more information."
] |
[
"It's not digested because, IIRC, the babies GI tract has protease inhibitors present (it's either in the GI tract of the child or in the colostrum itself, I forget which). Additionally there are antibody transport channels present in the child's GI tract which allow for the absorption of the antibodies themselves (primarily IgG in apes). These disappear after 24 hours which makes it critical that the baby receives their first milk from the mother. ",
"It really has little to do with concentration present on whether it's digested or not, BUT concentration ",
" important in terms of immunity. The child can absorb too little (and 'too much' but that's more of a case of maternal interference with things like vaccines) and not be able to survive. ",
"What's more is that in some species, such as the cow, they have a temporary diverticulum in the neonate that allows the colostrum to bypass certain areas of the their stomach where bacteria that are present would break down the antibodies or have them bind so that they were 'soaked up' so to speak and never reach the gut. "
] |
[
"Why is it I can watch hours and hours of TV programming with little to no latency, but I have to buffer a two-minute movie trailer?"
] |
[
false
] |
I'm assuming it has something to do with codecs and compression technology and all that, but it seems like the internet could move at least as fast as the cable TV signal coming in, right? I never have to let NBC or FOX buffer. The TV doesn't hiccup between commercials.
|
[
"Someone else can fix or add to this but I'll get the ball rolling.",
"Tv signal is more like water into your house. Somewhere a company is just cramming a bunch of it into the system and the instant you turn on your tap, boom, water. Same with your neighbors.\nBut for the internet signal to get to you each junction has to be switched to direct that water to your house for your use. (series of tubes joke here)",
"The second and probably bigger reason is because of how this works, and your streamed show not being communal, you require dedicated space in the Internet to watch a stream. If you can pay enough money, and buy a good enough Internet connection, and pay a high enough price to a company like Netflix, they would be happy to give you a tv like experience. I have put incredibly high res movies on servers that I host with and streamed them to myself before. It's possible. To talk about the real costs of this and market demands is just speculation so hopefully someone with some knowledge about the business side can tell you why there aren't premium services out there.",
"Have a nice day."
] |
[
"It doesn't have to due with codecs or compression or anything like that. The cable company owns the wires going to your house and to everyone else's house that is getting cable TV. They're sending the same signal to everyone: all of the video that is on all of the channels are going to everyone's house at the same time. To watch a certain channel on your TV, your cable box decodes that one channel from the signal that contains all the channels. That's why there's no waiting or hiccups on cable TV; the signal is always on, always there.",
"On the internet, everyone gets different information at different times. So if you want to watch a TV show streamed from the internet, your computer has to request that show, and the site has to stream it to you. Rather than sending it to you as a continuous signal, like cable TV, the site breaks the show up into lots of separate packets and sends you the packets. It has to do that; that's just the way the internet works.",
"Some of these packets might get lost or delayed as they're transmitted to you, so your computer \"buffers\", or stores, enough of them so it can play your show for several seconds while it's waiting for the next packets. If it didn't buffer, or doesn't buffer enough, the show would pause or hiccup every time a packet got lost."
] |
[
"Well, this isn't really a science question. This is more of an engineering question, specifically communications. Simply put, TV is broadcast, the internet is delivered as on-demand packets. ",
"A poor analogy: TV service is to internet service as a water line is to buying groceries. "
] |
[
"How can we freeze something to the temperature near the absolute zero?"
] |
[
false
] | null |
[
"Heat is mechanical motion, so if you slow down that motion it will cool down. Basically the light is \"pushing\" in one direction because of the different wavelengths of the light, and they position lasers pointing into the same point from a bunch of directions. They all point into the same spot, and the targets are held in position by all these opposing forces. As they are held in position, they slow down, and as they slow down, they cool."
] |
[
"http://en.wikipedia.org/wiki/Magnetic_refrigeration",
"This technique involves a thermodynamic cycle where by applying a strong magnetic field and allowing previously randomized magnetic domains to realign causes a decrease in entropy. This allows temperatures on the order of 10-100 of mK",
"A similar method can be used on nuclear spins for even lower temperatures. This method can allow temperatures as low as uK"
] |
[
"Just FYI Freeze != absolute zero."
] |
[
"How do we know super-earths aren't binary planets?"
] |
[
false
] |
Can we tell the difference given current technology, or could the combined gravitational pull of a binary planetary system be perceived as a "super rocky planet"?
|
[
"Using the ",
"radial velocity",
" method of detecting planets, you wouldn't be able to tell the difference. All you're getting out of that is the total mass of the planet(s) and moon(s) in that particular orbit.",
"Using the ",
"transit method",
" though, we ",
" be able to tell the difference. It would basically depend on how high the signal to noise is of the planet transit.",
"See for example ",
"this figure",
" taken from ",
"Lewis et al. (2015)",
". The red and cyan show the transit shapes we've come to expect from normal planets, while the purple and dark blue show what you get for different types of binary planets. So the shapes are different, it's just a matter of if it's different enough to be detectable. And also can you prove it's actually a binary planet and not something else causing the changes in transit shape (e.g. starspots can be a big problem that look somewhat similar)."
] |
[
"But sunspots wouldn't be periodic, though, would they? So if you get the same profile over multiple transits, that would allow you to say it isn't a sunspot, right?"
] |
[
"Exactly right, the problem is that transits can take a long time to occur. The orbital period of Jupiter is just under 12 years. So to an outsider they'd only see Jupiter's transit every 12 years and that's assuming they're in the same plane as Jupiter's orbit."
] |
[
"Is a bugs \"old age\" death similar to a humans? In that they die of organ failure or cardiac arrest?"
] |
[
false
] |
If so, why do some bugs live only a few days then die... are their cells dividing much more rapidly than a humans?
|
[
"Entomology grad student here.",
"Some insects, like cicadas, don't eat as adults; they live off energy reserves they built up as larva and die when they basically starve to death. However, the majority of adult insects do eat, and here the length of time an insect lives can vary wildly. Ant and bee queens, for example, can live for years, while other insects can overwinter and survive for a year or two. It has a lot to do with the climate (hard winters will kill insects regardless of how biologically \"old\" they are), predation (many insects don't die of old age because something eats them), what they're eating (nutritionally poor foods like nectar mean insects may run out of certain key nutrients - or just proteins), and what they're doing (flying around a lot eats up tons of energy and causes a lot of wear and tear on the insect).",
"As for what death is like, that depends. For butterflies (for example), a lot of the proteins they accumulate as caterpillars are saved by the adults for egg or sperm production. The nectar butterflies drink is a bad food source (rich in carbs but poor in protein and fats) and is mostly used to feed the flight muscles. If you dissect very old butterflies, you'll find that their flight muscles are pretty destroyed: heavy use damages them, but they don't have the resources to repair them because they can't get more proteins in their diet.",
"Adult insects tend to save resources they get from food for reproduction and sustaining themselves long enough to find mates. I don't know for sure, but I suspect in a lot of cases, adult insects waste away when they get old as they deplete their stored energy on reproducing."
] |
[
"very interesting!!"
] |
[
"agreed, excellent and enlightening response."
] |
[
"Why do rockets produce a crackling noise?"
] |
[
false
] |
This is what I am referring to:
|
[
"The gases coming out of the exhaust jets are travelling faster than the speed of sound. You know how when lighting strikes, you hear a sonic boom? If you're standing close enough to where the lightning strikes, it'll sound a lot more like a crack than a boom. So imagine that except tons of miniature ones. You can hear similar things from fighter jets when they have the afterburners on, you can sorta see it happening ",
"here",
"."
] |
[
"I can't seem to find the sources at the moment, but the crackle you hear is actually quite complex and the answer isn't as simple as sonic booms. Multiple studies have been done and we've learned a lot about how the sounds come to be but they still have not reached a satisfactorily full answer."
] |
[
"This is something that confused me as well, so I'll use the example that was used to explain it to me.",
"Think about a rock and a pond. If you toss the rock in the pond, it's going to sink. Pretty much common sense. But if you throw it at the right speed (with the right angle), a rock will skip across the water. Think of the air as the water, and the exhaust gases as the rock. Those gases are hot and pressurized and want to expand, but they're moving so quickly that they'll \"bounce off\" the surrounding air and sort of reflect back into the exhaust stream, creating those little diamonds of even higher temperature and pressure. Obviously this is a simplified explanation."
] |
[
"What differences are there between a deuteron (proton/neutron) and a bound Δ++/ Δ- pair?"
] |
[
false
] |
Both bound states include 3 up and 3 down quarks and have the same symmetries (as far as I can see). I haven't learned any chromodynamics though. Is there some reason for partitioning a deuteron as a proton and neutron? Any answers are appreciated!
|
[
"The Deltas have spin 3/2, while the nucleons have spin 1/2."
] |
[
"Yes, they would be different because the Δ baryons also have isospin 3/2, while the nucleons have isospin 1/2."
] |
[
"And the masses would be different as well. If you look at the Delta",
" and the proton, both of which are (uud), you'll see the Delata",
" has about a 30% larger mass."
] |
[
"What causes the mutation in evolution?"
] |
[
false
] |
Feel free to get technical, I'd like to know any details!
|
[
"Any random event that changes a molecule of DNA. Some examples are transcription errors when a cell divides, or damage/alteration caused by radiation. Some organisms (unicellular) even have built-in mechanisms that create more transcription errors in times of extreme ecological stress in an attempt to create a mutation which will let the species survive.",
"There are many potential sources, but this is the basic idea."
] |
[
" things",
". Since there's about a dozen listed there feel free to ask about specific ones. This mostly covers damage. In addition to these we've got some built-in mechanisms that ensure variability as well.",
"DNA repair mechanisms",
" are not 100% effective, so damage to DNA sometimes results in a permanent change. Sometimes a few strands break and are re-attached at the wrong points (your immune system does this intentionally to make highly variable antibody cells). Sometimes DNA polymerase, the enzyme that copies DNA, doesn't copy it perfectly either, so you get mutations the longer your cells are around. ",
"Other sources of mutation include the ",
"cross-over events that occur during meiosis",
" - the creation of sex-cells, wherein chromosomes criss-cross and trade material with one another.",
"Viruses insert their DNA into our DNA creating new sequences. ",
"We also have elements within our genomes ",
"called transposons",
" that essentially copy themselves then re-insert the copy of themselves into our genome, again breaking up genes and adding to existing sequences.",
"When many eukaryotic (i.e. non bacterial) cells divide they actually fail to properly replicate the end-points of their chromosomes. Many organisms have built in buffer zones called ",
"telomeres ",
" that they can afford to lose. Some organisms possess an enzyme which replenishes these, humans do not have this enzyme. If a cell line replicates enough it can lose its telomeres and start eating into actual genes. ",
"You can also get errors during meisosis where chromosomes are broken or attached to places they wouldn't normally be, you can get non-disjunctions where they don't split up properly. ",
"Really its a wonder how DNA manages NOT to mutate."
] |
[
"Thanks!"
] |
[
"Is the Moore's law going to fail soon?"
] |
[
false
] |
[deleted]
|
[
"This is correct. 'Moore's law' is really more of a target goal (particularly for Intel). There are some arguments about how far we can take Moore's law, but nobody expects it to continue indefinitely."
] |
[
"This is correct. 'Moore's law' is really more of a target goal (particularly for Intel). There are some arguments about how far we can take Moore's law, but nobody expects it to continue indefinitely."
] |
[
"Moore's law isn't a law, in the sense that it will remain true for the foreseeable future- it is an observation that is actually starting to break.",
"There are several major problems that will be faced in the next couple generations in silicon-based IC manufacturing.",
"Firstly, it is the case of quantum tunneling- creating unwanted leakage currents in and between the field effect transistors that will switch 'on' and 'off' states",
"Secondly, heat. Running a current through wires creates heat ",
" ",
" . With an increase in number of transistors, there is parallely an increase in the number of integrated wires, all of which need to be somehow cooled to prevent crystallographic defects from being created. ",
"Thirdly, the technologies used to actually make the chips need to have significantly higher resolution. Intel struggled to get the 14nm Broadwell processors- going smaller will require revamps in the IC manufacturing processes, namely in the stereolithographic portions. ",
"There are probably more problems than the ones that I listed, but I am not up to date on my electronic materials- it has been a couple years. ",
"New technologies- quantum dots, nanotubes, graphene, silicene, phosphene, and gallium-arsenide, upon others, are all being actively researched to be a suitable replacement for silicon based integrated circuits. ",
"if you have any specific questions, I can attempt to answer, but I am by no means an expert in this field. "
] |
[
"Does it take longer for the temperature of water to be raised by one degree if it is initially hot, rather than cold?"
] |
[
false
] | null |
[
"Depends. If it's at 99.5 degrees, raising its temperature by 1 degree will take a heck of a lot more energy than if it's at 98 degrees."
] |
[
"This essentially boils down ",
" to a question about the temperature dependance of the heat capacity of water. if Q is heat in joules, del_T is a change in temperatue and Cp is heat capacity: Q = del_T * Cp. ",
"The heat capacity for pure water at 20C is 4,181.6 J kg",
" C",
" . For water at 60C the value is 4,200.7, so for an equivalent amount of added energy, Q, the change in temperature will be slightly less for warmer water.",
"Update: Above for 1 atm pressure. Also, the variation of Cp(T) is not linear so the answer depends on the speciic temperatures in mind. Here is a ",
"graph",
". The biggest increases are above 70C."
] |
[
"You may not have been downvoted if you had said 99.5 C. ",
"I think your point was too subtle for the downvoting fanatics to recognize, not taking into account the heat of vaporization."
] |
[
"Explanation of magnetism induced by currents"
] |
[
false
] |
Veritasium (a great educational physics YouTube channel) posted an of how currents induced a magnetic field using Lorenz contraction. However there is one point of the explanation which I am not sure I follow. At 1.22 ( ) he explains that if a charged particle is at rest with respect to a wire with no current, then the particle is not attracted to the wire. Then he proposes that if there were current in the wire, the charges are still balanced, so the particle is not attracted to the wire. Finally, he suggests that if the charged particle were moving (in the same direction as the current), then the positive charges in the wire are Lorenz contracted from the particle's perspective and therefore less dense, creating an electrostatic force between the wire and the moving charge. Okay, this agrees with experiment, but I am puzzled why moving electrons in the wire are not Lorenz contracted when the charged particle is at rest (relative to the wire) and the electrons are moving. If his explanation is correct, shouldn't it imply that a static positive charge would be attracted to a wire with current running through it? (I am guessing that there is something about electrons already being in motion, but I don't have a clear image.) Many thanks.
|
[
"The argument is subtle (the original derivation is in Griffiths \"Introduction to Electrodynamics\" if anyone want to consult the original source for mathematical detail), and you have to be very careful with the argument. Let's have another look at things:",
"1) When the charges in the wire are at rest the negative and positive charges balance (another way to say this is that they have equal charge densities in space). So if a positive test charge is at rest nearby it feels no net force.",
"2) Now both charges in the wire start moving simultaneously, and you have to be VERY careful when you define the way that they move. The positive charges in the wire move to the left at the velocity v while the negative charges in the wire move to the right with the ",
" velocity v. ",
"If a charge is at rest nearby it will see that both the moving positive charges and the moving negative charges ARE Lorentz contracted by the exact same amount. The effect will cancel because the positive and negative charge densities increase by the same amount for each charge so there is no net charge seen by the resting test charge. So the test charge at rest feels no force like before.",
"3) Let us do 2) again, but now let's have the test charge move to the right at velocity v. The negative charges in the wire will now appear to be at rest relative to our test charge and there will be no Lorentz contraction for them. However, the positive charges are still moving to the left and WILL be Lorentz contracted even more so than before. The net result in this case is that the Lorentz contraction causes the positive charges to contract only, this increases the positive charge density over the negative charge density in the frame of the test charge, and the test charge is repelled.",
"Edit: I looked it up in Griffith's and his argument isn't exactly the same as above. The interested reader should consult section 10.3 in \"Introduction to Electrodynamics 2nd Edition\". I do agree that there is something not quite right with the video's description."
] |
[
"Your guess is basically correct. Where the video goes wrong is in implying that you start the derivation with defined linear charge densities at rest and then speed them up. When the derivation is done in textbooks (my favorite is \"Electricity and Magnetism\" by Purcell) they define the charge densities in the \"lab\" frame with the electrons already moving."
] |
[
"I have a few comments:",
"The argument is subtle (the original derivation is in Griffiths \"Introduction to Electrodynamics\" if anyone want to consult the original source for mathematical detail), and you have to be very careful with the argument. Let's have another look at things:",
"The approach using Coulomb's law, charge invariance and special relativity is much older than that. Griffiths cites \"Electricity and Magnetism\" by Purcell and Purcell cites a 1912 paper L. Page as the earliest exposition of the approach he knows of.",
"1) When the charges in the wire are at rest the negative and positive charges balance (another way to say this is that they have equal charge densities in space). So if a positive test charge is at rest nearby it feels no net force.",
"True, but this a different situation than is used as the starting point for the derivations and there is not a straightforward connection between it and what you're calling #2. (As I said in my top level comment, this is where the video is misleading.)",
"2) Now both charges in the wire start moving simultaneously, and you have to be VERY careful when you define the way that they move. The positive charges in the wire move to the left at the velocity v while the negative charges in the wire move to the right with the same velocity v.",
"There is nothing fundamental about the charges moving with equal and opposite velocities. Purcell uses the more realistic situation where the positive charges are stationary and the electrons are moving. I haven't read Griffiths's derivation carefully but I think the only reason for using equal and opposite velocities is to make the math work out a little more cleanly.",
"If a charge is at rest nearby it will see that both the moving positive charges and the moving negative charges ARE Lorentz contracted by the exact same amount. The effect will cancel because the positive and negative charge densities increase by the same amount for each charge so there is no net charge seen by the resting test charge. So the test charge at rest feels no force like before.",
"Both Griffiths and Purcell define the charge densities with the charges already in motion so the force with the test charge stationary is zero by definition. There is no Lorentz contraction to speak of."
] |
[
"Why does the Boron group generally react poorly with Aluminum?"
] |
[
false
] |
[deleted]
|
[
"Ah, I have made a critical mistake. The chemical shown to be poured on to aluminum foil was BROMINE. I was careless and I remembered the wrong element.",
"Which means the BORON group doesn't react with aluminum, it reacts with the halogens. And I see that all the halogens are the same group. ",
"It does seem like many elements react with aluminum though. Would that be simply because aluminum is cheap and easily accessible? Or does aluminum have a trait that makes it so?"
] |
[
"Well, if it was really liquid boron being poured on the foil, the foil was simply melting and burning from the extremely hot temperatures. Boron is one of the hardest elements to melt, at 2300 C.",
"So if it wasn't really hot, it was likely a solution of some boron compound. Do you have more information?"
] |
[
"Bromine is a very electronegative element. Aluminum has three valence electrons and the ionization point of the first electron is very low which makes it very easy for bromine to react with it. This reaction would be comparable to reacting Gallium with Fluorine. "
] |
[
"Why are clouds flat on the bottom? And when it rains do clouds get smaller?"
] |
[
false
] | null |
[
"Generally speaking (that is, the common/simplified model of cloud formation), because the \"bottom\" of clouds usually represents the condensation line where rising moist air has cooled enough to condense into cloud droplets. ",
"While it looks like a \"hard\" line, it's not like one side is moist and the other is bone dry. It's just on one side it's not quite cool enough to condense droplets out of air, on the other it is."
] |
[
"Two parts: ",
"Part 1: Temperature decreases with rising altitude: 3.3 F lower temperature for every 1000 feet of increased altitude (also expressed as 9.8 C per 1000 meters of increased altitude). ",
"Part 2: Dew Point: for a given humidity level, there is a temperature at which the water vapor present in the air will begin to condense out. ",
"As you increase in altitude, the temperature is lower as you rise. At a certain altitude, you reach the dew point, an voila', there's cloud above that point. "
] |
[
"Are you saying that when I see a cloud moving across the sky it's not the wind pushing it but instead a temperature/pressure difference moving that is condensing and.... dissipating? evaporating? behind it?"
] |
[
"Would a rubber bouncy ball bounce higher when dropped from equal heights if it was to hit concrete or bouncy material (the same material as the ball itself)?"
] |
[
false
] |
I hope I explained that well enough in the question itself, if not I can clarify.
|
[
"This!",
"In an ideal case it would not matter. For large impact speeds you would get differences because you enter the non-linear regime and then it would depend on the properties of the bouncy material (the concrete will be far from the non-linear regime at the point where the bouncy ball just breaks into many pieces)"
] |
[
"I suspect it would not matter.",
"The energy expended in deforming two identical surfaces is the same as the energy expended deforming one surface. Thus the elastic rebound energy is close to the same but divided between the ball and the \"bouncy\" surface. If the two surfaces rebound simultaneously against each other, the net bounce effect should be the same."
] |
[
"How would you calculate the energy regained by the \"spring\" effect, since rubber would bounce back fairly quickly."
] |
[
"Why is the price of gold so high relative to its actual uses?"
] |
[
false
] |
[deleted]
|
[
"The value of gold has little to do with utility. It was the base unit of trade for most money systems in history, up to this century. Precious metals is the ",
" speculative bubble that never burst. Fiat currency is not likely to be the second, so the price can be expected to rise with inflation."
] |
[
"It doesn't corrode, which worth every penny for things like medical or military equipment. Basically, if you are building something very expensive, you would rather use gold than something cheaper that might corrode and fail."
] |
[
"Really appreciate the response. I am wondering though, why is it so commonly used as historical currency (today as well, I suppose). Is it ONLY because of its rarity combined with its intrinsic beauty, lack of corrosion, etc? ",
"Why would the value of Gold be so much more than silver which has very similar properties?"
] |
[
"How do we know that pi is irrational?"
] |
[
false
] | null |
[
"If you're into the maths, ",
"wikipedia",
" has a nice little article on proofs of pi's irrationality. They're beyond me, but one of the approaches taken is that certain formulas pump out answers that we know to be false if we assume that pi is ",
" (answers such as 'an integer exists that is greater than 0 but less than 1'). This method is called proof by contradiction."
] |
[
"True, but the two are clearly equivalent here."
] |
[
"Math major here. This is a pretty good answer. Proof by contradiction is how mathematicians prove things like sqrt of 2 is irrational. Like ",
"u/YouGotTheTouch",
" just said; proof by contradiction works for proving pi is also irrational."
] |
[
"Why are there so few blue, green, or purple mammals?"
] |
[
false
] |
Why do we see only really see white/black/red/orange/yellow/grey/brown/pink but little to no blue/purple/green based mammals? With Green and Blue being such prominent colors in nature, I would think they would be go to colors for camouflage. I honestly couldn't think of any mammals except the Blue Whale, but they are more grey-ish than blue... Any insight would be welcomed. -Blue- Whales, Dolphins, Mandrills
|
[
"This column",
" has an in-depth answer, focusing specifically on the absence of the color green. But as it turns out, mammals are only capable of generating brown-black pigment (the melanin that gives skin its tan) and reddish-yellow. These are the dyes which, in various combinations or absences, are responsible for the limited mammalian color palette. ",
"It turns out, amazingly enough, that other terrestrial vertebrates can't create blue or green pigments either! The array of ",
"cool colors",
" we see in birds, amphibians, and the like (as well as many brilliantly-colored insects like tropical butterflies) are actually caused by microscopic structures in their feathers or skin. These structures refract the light that bounces off of them, like a prism or a CD, causing us to perceive them as a particular color."
] |
[
"isn't all colour due to light scatterng?"
] |
[
"This Mammal",
" seems to be capable of creating blue pigment, no?",
"Edit: image url changed. Points to all who knew what it was anyway!"
] |
[
"Extremely fast space travel is possible, right?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"/r/AskScience",
"/r/askscience",
"For more information regarding this and similar issues, please see our ",
"guidelines.",
"If you disagree with this decision, please send a message to the moderators."
] |
[
"To add, the speed of light is a fundamental speed limit. You cannot travel faster than light."
] |
[
"I wasn't thinking lightspeed, but the possible speeds we could reach if we had the fuel capacity to keep burning thrusters "
] |
[
"Why do our sex drives hit at ~17 for males, and ~30 for females?"
] |
[
false
] |
[deleted]
|
[
"Lots of speculatation, here.",
"(orgasms increase the change of conception).",
"Citation needed."
] |
[
"Not really, no. Unless you are also the sort of person that needs a citation when people suggest puppets can't speak on their own."
] |
[
"Only true for men because their libido/hormone levels are higher at late teens/early 20s. Alfred Kinsey Ph.D found woman have more orgasms in their 30s and that might just be related to either having more confidence and being comfortable with their bodies and partners, and therefore having better sex. Or it could be a natural reaction to try and conceive before it becomes increasingly dangerous to do so (orgasms increase the change of conception)."
] |
[
"What is the universe expanding in respect to?"
] |
[
false
] | null |
[
"Please see the Astronomy FAQ.",
"https://www.reddit.com/r/askscience/comments/qk58k/what_is_space_expanding_into/c3y7opc"
] |
[
"That question is also is in the FAQ..."
] |
[
"That question is also is in the FAQ..."
] |
[
"Have any animals evolved scent camouflage in the way that many animals have developed visual camouflage?"
] |
[
false
] | null |
[
"A semi example I can think of is the parrot fish, which secretes a mucus bubble to avoid detection of a non-visual source.",
"here's an image ",
"https://www.google.ca/search?q=parrot+fish+mucus+bubble&espv=2&biw=1280&bih=701&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjLzv3l0onMAhXkuoMKHXC8AIMQ_AUIBygC#imgrc=V640Y9Vb-w1MmM%3A",
"\nsorry for the massive link",
"Edit: File fish also do something similar by ingesting corals so that they can secrete a smell similar to the seemingly non-nutritious coral they eat. This effectively acts as an olfactory camouflage. here's an article that should explain it. ",
"http://blogs.discovermagazine.com/d-brief/2014/12/10/fish-coral-smell-camouflage/#.Vw067xMrKRs"
] |
[
"Additionally, a frog is able to use this ability to survive amongst ants.",
"http://www.ncbi.nlm.nih.gov/pubmed/24349157"
] |
[
"Additionally, a frog is able to use this ability to survive amongst ants.",
"http://www.ncbi.nlm.nih.gov/pubmed/24349157"
] |
[
"When we say space is expanding, what is that relative to?"
] |
[
false
] |
Or is it somehow an intrinsic quantity of the space?
|
[
"I feel like this is probably an outstanding answer, but I understood none of it except the part about imagining clocks. :("
] |
[
"There is a set of observers that see the Universe as homogeneous and isotropic. These are the comoving observers, and they are stationary with respect to the CMBR (i.e. they see the temperature of the CMBR to be isotropic, whereas we see a dipole anisotropy because we are moving at a few hundreds km/s wrt it).",
"Imagine all of these observers carry a clock. Say, for example, that all clocks are started at the Big Bang. Then the clocks define a global time coordinate called cosmological time.",
"Define the proper distance between two comoving observers at cosmological time t as this: take the straight line of comoving observer connecting A and B and have them all use a ruler as soon as their clock displays t. Summing all the measured length gives the total proper distance. More mathematically, just integrate the length element on a hypersurface of constant cosmological time.",
"Now, it turns out that as a function of t, proper distance between two given observers grows. Not only, all proper distances between all pairs of comoving observers grows in proportion; if one doubles between t1 and t2, all of them double.",
"That's all there is to metric expansion. Or better, this is the kinematics; I haven't told you about exactly this expansion is determined, which is the dynamics. "
] |
[
"Maybe how we discovered the expansion of the universe will be illuminating.",
"When things move quickly away from you they appear redder than before, just like the Doppler effect shifting the pitch of a moving car. The spectrum of light emitted by stars has certain dark bands (caused but absorption of light by certain elements) that are always created at the same wavelength. This means that you can quantify the amount of \"redshift\" and determine how fast you and the star are moving apart from each other. This works for galaxies, too, as they are just big aggregations of stars.",
"If you look at galaxies near to ours, you'll find that the movements are kind of random. Some are moving closer (Andromeda, in particular) and some are moving away. But as you look at galaxies further and further away, they get redder and redder. For large distances Hubble's law applies: the further you are from a galaxy, the faster you're moving away from it. ",
"You could interpret this as earth being some kind of special repulsive body, but it's pretty unlikely we're special. That means that everything is getting further away from everything else, which is pretty weird. At any point in the universe (as far as we can tell, assuming the universe is roughly homogeneous) you'll see the same relationship, where everything appears to be getting further away from you. ",
"Over short distances the strong and weak nuclear forces are more important than this expansion, so we don't get torn apart. Gravity is stronger than the expansion over somewhat longer distances, so galaxies and small clusters of galaxies tend to clump up. This might not be the case forever, as the expansion is accelerating. Eventually (very far into the future) the expansion could get powerful enough to tear apart atoms in à process called the big rip. ",
"TL;DR: the expansion is relative to wherever you observe it from, because everything is trying to get further apart from everything else."
] |
[
"After inhaling air into the lungs, how are our bodies capable of holding that breath under pressure? It seems possible to hold back a strong exhale, for example."
] |
[
false
] | null |
[
"Please do not quote me on this, but it seems to be the soft palate which can block airflow. The soft palate also blocks airflow when swallowing.",
"Reference",
"https://pubmed.ncbi.nlm.nih.gov/3368631/"
] |
[
"Inhalation is actually the exact opposite of pressurizing air. The diaphragm and intercostal muscles expand the lungs, so the pressure inside the lungs gets ",
" than the pressure outside of the lungs. This forces air in.",
"When exhaling, lungs are slightly compressed, making the pressure inside the lungs higher than the pressure outside the lungs, forcing air out."
] |
[
"Hey thanks. My question was referring more to exhaling, however. How can we hold our breath, and fight the feeling of pressure from exhalation?"
] |
[
"Wing suits and G-force"
] |
[
false
] |
Ok, so from what I understand of flight... the faster you are traveling the more g-force is exerted on your body while doing maneuvers. In fact most pilots who fly jets have actual "G-suits" which air up to prevent blood pooling and eventually cause a black out. My question is... if you do a loop in a Wing Suit could you pull enough G's to pass out and eventually plummet to your death?
|
[
"Well, that question is highly dependent on the wing-loading capability of the aircraft. The reason why fighter pilots have to wear G-suits is because the planes they are flying are very high performance machines that can fly into extreme maneuvers at high speeds, and it is pretty easy to enter a climb/bank which makes the plane want to enter travel in a different direction than you are very quickly.",
"If the wingsuit was constructed to the same degree of that a fighter jet, then yes it would be possible. However, you need to have a pretty solid airframe in order to withstand this degree of loading. Otherwise, the suit would simply rip apart well before it could apply any significant force to the pilot in order to make them black out."
] |
[
"Well the super structure of the wing suit would be the human body. So I think it would depend on how strong the pilot of the suit is. Since the wing suit seems pretty much made of fabric it should be able to flex according to the body and wind resistance, right?",
"Then again the wing suit has no real thrust/power or substantial lift to maintain the physics through the loop. Essentially my theory is if someone attempts this towards the top of the loop they will \"stall\" and maybe plummet to their death if they can't recover."
] |
[
"I have no knowledge of g-forces and such, but i do know that one would not be able to do a loop in a wing suit. The suits don't provide substantial lift, rather, they just direct you while you're falling."
] |
[
"What are those darker (squishier) area on some bananas and why do they occur?"
] |
[
false
] |
I'm talking about after you peel it and the edible part might have dark to black spots on it, the parts that most people don't like to eat
|
[
"sweet thanks a lot man"
] |
[
"sweet thanks a lot man"
] |
[
"Thanks follow up, is there anything wrong with eating the bruises, like belly ache or something"
] |
[
"Can someone exaplain the new covid brain damage study?"
] |
[
false
] |
I'm not scientifically literate enough to full understand this study. Can someone please tell me, What was the average amount of brain loss? Is this a big deal or relatively minor? Will these effects be permanent or does the brain normally heal? Can you assume this data would be similar in young people or would I have to wait for another study?
|
[
"Basically they looked at 401 people who had imaging done before and after they got COVID and compared it to 384 people who did not have covid. The 3 main results they found are:",
"The overall reduction in brain size has a mean difference of 2%. Whether this is small or large is sort of subjective based on what you consider \"small or large\" but it does lead to cognitive decline compared to the control group. They do not know if this change is permanent, they'd need to follow the patients longer to know. Since the age of this population is 51-81, it's hard to tell whether these results extrapolate to younger populations without studying them also.",
"",
"Edit: Since people have been asking, thought I'd also add that the paper did not look into vaccination status or severity of illness. They did account for hospitalizations, but there were only 15 hospitalizations out of the 401 covid participants."
] |
[
"Also this was for the alpha variant I believe. Other variants might have lesser or greater impact"
] |
[
"A small correction, but with a significant impact.",
"The overall reduction in brain size has a mean difference of 2%",
"The information I read says: ",
"\"...",
"...\".",
"https://www.bbc.com/news/health-60591487",
"\"...",
"...\".",
"https://journals.lww.com/neurotodayonline/blog/breakingnews//pages/post.aspx?PostID=1215",
"Looking at the actual article in ",
", those ranges would appear to be reasonably represented by the graph.",
"https://www.nature.com/articles/d41586-022-00503-x"
] |
[
"Why can't we remember our memories when we were a baby?"
] |
[
false
] | null |
[
"Infantile amnesia is not well understood, partly because we still have a lot to understand about memory, and also because for obvious reasons there is only so far we can go studying infants and young children without some sort of ethics problems.",
"There is some evidence that memory is linked to language. Studies have shown that children exposed to more 'memory' related talk seem to have earlier first memories that not. Also the development of retrievable long term memories seems to correlate somewhat with language acquisition.",
"However there is still a big unknown in the area - a couple of little factoids to help blow your mind:",
"typically children 0-5 will show day-to-day memories (i.e. remember what happened yesterday) yet will not be able to recall their childhood once they're older",
"The range of infantile amnesia appears to change throughout the life-span, more most of our adult years more of our childhood is inaccessible and often more younger memory returns as people reach elderly ages",
"Sauces: 4th year developmental psyc."
] |
[
"My question here then would be what about children who don't learn language? Like in cases of feral children or children that were abused and didn't learn language acquisition until much later. Do they have memories of their time before they learned to speak?"
] |
[
"My understanding of most children in these circumstances have notable learning disabilities which confounds the issue somewhat. I doubt that memory is entirely dependent on language however its also unlikely to be completely separated either."
] |
[
"Will audio-video capture and display technology within the next several decades get to the point where our eyes and ears cannot distinguish it from the real thing? If so, what effects will that have on us?"
] |
[
false
] | null |
[
"I'm involved in film and post-production and have attended some training courses on stereoscopic filming so here's what I think, given what I know about the current state of things as far as the visual side goes: ",
"We don't yet have anything that can capture an image with the same characteristics and qualities that the human eye has, cameras work very differently in many way than our eyes do, so the character of the image is 'colored' by the mechanism that captures it, often in ways that are noticeable. (lens flairs, grain, framerate artifacts). It would be difficult to overcome these issues, but I think this would be trivial compared to the real problem: The display technology. No matter how clear the image is, the current 3D display systems will never 'fool' the eye completely. A big reason for this is because your eye still has to focus on a flat plane - even though there is the illusion of depth, there is no getting around the fact that optically, you are focusing on a flat plane. Also, with current systems you cannot choose which objects to bring into focus with your eyes - the depth of field is 'baked' into the image when the image is captured. ",
"I don't think we will overcome the issue with reproducing 3d images in the next ten years - the solution will require something vastly different then a simple incremental improvement over the current stereoscopic fidelity. We would have to wander into the realm of volume displays and the like, before we start to get close at all. ",
"Now, I think it is very possible that we could have displays that look very very real when we close one eye, or under some limited sets of circumstances. If you have any follow up questions I'll do my best to shed some light on them. "
] |
[
"I'm involved in audio engineering and recording. Currently, the closest thing we have to sound recording technology that truly sounds like you're there is binaural recording, where two microphones are placed at approximately the same distance and pointing in the same direction as human eardrums. In higher-end binaural recording rigs, the microphones are placed in a dummy head. It can produce some astonishing results - as long as you listen through headphones. It doesn't work any better than normal stereo recording through speakers.",
"There's also the problems with audio recording of how various kinds of microphones color the sound, the fact that sound is a three-dimensional compression wave and a microphone element moves in two dimensions, the frequency responses of the speakers, the fact that you don't know what kind of speakers are going to be listened with or how they'll be placed. And there's the physiological differences that cause differing perception of sound - the shape of the outer ear strongly influences how you perceive the directionality of sound, and the condition of the inner ear influences how loudly you perceive different frequencies. "
] |
[
"Relevant."
] |
[
"Is there a reason strings and not blades are used for Weed Eaters? Why don't we see strings on Lawn Mowers?"
] |
[
false
] |
Does this have to with the rate at which you would have to spin the string at a large circumference?
|
[
"I have not actually used either but have seen how the work. It is my understanding that string is used for weed wackers because weed whackers are made more for areas that you cannot get a lawn mower to. The strings are designed to hit these obstacles without breaking but while still being able to cut the plants you are aiming for. Plus, if the string does break, its on a spool so you just pull out some more, i believe. Lawn mower blades are a bit more sensitive and expensive and would be much more of a hassle to replace should you hit the edge of a sidewalk. "
] |
[
"There isn't a big reason as you can purchase blades (metal or plastic ones) to outfit them just like cord. \nCord is a lot softer than steel and so you can push right up to the very edge of an object to cut away grass and weeds without having a spinning metal blade take a nice chunk out of it."
] |
[
"The main reason is to minimize damage to things you don't want to chop down, like a fence. They make plastic hinged blades for them, but that will scratch up a fence significantly more than a plastic string.",
"To minimize damage to things like fences you want the weakest, softest cutting attachment you can use that will still cut what you want, if you're cutting grass against a fence then string that wears rapidly when cutting light grass is what you want. If you're using it to clear small saplings then a stronger bladed attachment is what you want."
] |
[
"What is the significance (if any) of being the fastest sperm?"
] |
[
false
] |
I read motivational posters that talk about being the fastest sperm. The reason for the millions of sperm cells is for high success rate in terms of fertilization, but is there a difference (in terms of development of embryo) between the fastest sperm fertilizing the egg and the slower sperm fertilizing the egg?
|
[
"In many species, a female will mate with many partners when she's \"in heat\". Having the fastest and strongest sperm means that you are more likely to supply the lucky sperm that gets to fertilize the egg, meaning that you beat out your competitors, which is what this procreation business is all about.",
"There's actually a correlation where if many males mate with one female (say chimpanzees for example), their sperm will be stronger and faster than that of a male from a species where one guy gets all the girls (say gorillas for example).",
"The above was experimentally verified on 2008 by ",
"Berns et al",
". This is actually a pretty cool study because they used laser tweezers and optical trapping to measure sperm speed and swimming strength."
] |
[
"No, it's just that the fastest sperm (for the sake of argument) reaches the egg first. "
] |
[
"\"So what do you do for a living?\"",
"\"Oh, I shoot gorilla sperm with lasers.\"",
"Seriously though, I would also think that even with mating with one partner a lot of natural selection still goes on in the sperm race. All kinds of different combinations of factors that affect sperm morphology are going to generated during meiosis, and any that result in a slower sperm won't tend to propagate. Any sperm cells with serious genetic abnormalities would also be likely to be malformed in such a way that they would be less likely to reach the egg in time. Of course not every possible abnormality in the offspring would manifest itself in the sperm's morphology, but it seems like that would weed out some portion of them. I'm don't know of any actual research in this area, however.",
"It's also been shown that sperm from a single male deer mouse (which mate with many females) will recognize each other and ",
"cooperate to reach the egg first."
] |
[
"How can entropy be the reason?"
] |
[
false
] |
So today I had my second lecture of 'introduction to biophysics' and the topic of protein folding came up. The prof emphasized that the folding is happening mainly due to entropic reasons, saying that the water molecules around the protein would have more possible states when the hydrophobic parts were being folded away. Since entropy = number of possible states of a system, this maximizes it which is what entropy 'wants' to do. I kind of understand that explanation, but I can't see how you can call the reasons for the folding . To me, the reasons are all kinds of electromagnetic forces, or Brownian motion or the like, that are acting on the protein, and not some kind of omnipresent abstract that strives to maximize itself. How much of a theory is 'entropy'? Am I neglecting its importance and presence in nature? I am a physics student, but I have to say I am not a thermodynamics fan (even though I know it is very very useful) and don't have the best understanding of that part of physics.
|
[
"Symmetry and conservation laws are useful tools in physics because they often let you figure things out about your system (such as an equilibrium state), in an easier way than by more direct, but complicated methods (such as figuring out exactly how the system gets to the equilibrium state from some initial state).",
"Consider a much more intuitive system such as a ball resting on a \"U-shaped\" slope like a half-circle or a parabola. Suppose that the system includes friction so that as the ball rolls it dissipates energy. We know that if the ball is given an initial velocity it will roll around for a while, but eventually come to rest at the bottom of the slope. We know this because we can use the concept of energy. The ball can convert it's potential energy to kinetic engery by rolling downhill, but as it's rolling it's loosing total energy to friction, and thus it can't roll back up hill as high as it started. We expect that as the ball rolls its maximum height will decrease until it eventually stops at the lowest point in the slope.",
"Now, you could have done the problem in a different way: by calculating the exact path of the ball as it rolls by consideirng the forces that are exerted on it. You would be able to solve for the exact position of the ball at all times after you gave it its initial velocity, and you should find that the final position after a long enough time will be at the bottom of the slope.",
"You can now ask ",
" the ball stopped at the bottom of the hill. Is it because the complicated series of forces which eventually pushed it to that position, or was it because of energy conservation and dissipation? Of course, both are valid explanations that use different mathematical tools. The first explanation is a dynamical explanation, where you figure out how a system evolves over time, and the second is a explanation that uses the concept of energy. If you take an upper-year classical mechacnics course you will learn that energy and energy conservation are related to an abstract kind of symmetry, and so I would say that the second explanation takes advantage of the symmetries of the system.",
"Back to your question about entropy and protein folding, the situation is analagous. It's true that the shape of a protein is ultimately determined by the electromagnetic forces that the different atoms exert on each other, and ",
", it should be possible to calculate the shapes of proteins this way. Of course, in practice, this is stupidly complicated and not a very efficient way to figure out the shape. Ultimately, you don't care how the protein got to the shape it ended up in, you just want to know what the shape will be (similar to the way you don't really care how the ball rolled to it's eventual resting potision, you just want to know what that position is). Similar to the way that energy is a concept that is useful in the study of mechanical systems, entropy is useful in the study of thermodynamical systems. We were able to ague that the ball on the hill wanted to end up at the lowest point on the slope, i.e. the point that minimized its potential energy. By using ideas of thermodynamics, you can argue that a protein will want to end up in a position that maximizes its entropy.",
"The point is that dynamical explanations are just as valid as explanations that use concepts like energy and entropy, but the later are often much more efficient, depending on what kind of questions you're asking."
] |
[
"To me, the reasons are all kinds of electromagnetic forces, or Brownian motion or the like, that are acting on the protein",
"That's probably true. However, it would be impossible to calculate the position and motion of every single atom due to these forces, so their values are, for all practical purposes, random.",
"some kind of omnipresent abstract that strives to maximize itself.",
"That isn't what entropy is. Entropy is simply the the number of microstates consisent with a given macrostate. The microstates are the exact position and velocity of every single atom in the system, which we have no hope of keeping track of. Macrostates, however, consist of measureable quantities like internal energy. There can be many microstates consistent with a given macrostate. Naturally, if the probability of being in a given microstate is essentially random, then the most likely macrostate is the one with the highest number of microstates. Put another way, entropy tends to increase."
] |
[
"A chain in a thermal environment will experience an entropic shortening force, because the number of conformational states with a short end-to-end distance is much greater than the number of extended states. DNA is a molecule that displays this entropic elasticity. Proteins are a lot more complicated, because of the attractive interactions between different amino acids. The extended state is one of low entropy, so a stretched protein will retract, but among the compact states there isn't the same degeneracy as there is with an ideal chain. ",
"The protein's folded state is the one that minimizes electrostatic energy; it's not purely entropic, but I'm not as familiar with proteins as DNA."
] |
[
"Can you have causation *without* correlation?"
] |
[
false
] |
The original quote is so overused, I was just curious what the answer might be. And as a follow up; are there any practical examples where this is the case? thanks
|
[
"This is not a straightforward question to answer as given.",
"You have to define what you mean by \"correlation\". Statistically there are many many tests that seek to quantitatively define how \"correlated\" N variables are. Unfortunately there isn't a test that is foolproof in all cases. For a given set of data many of the tests may well disagree (depending on the nature of the underlying correlation - linear, exponential, etc).",
"In real data if there is an observed causation then by definition I would think there must exist some form of correlation quantifiable or not. So it boils down to being a problem of defining the correct metric to uncover quantitatively the correlation. Though hidden in this statement is the inherent problem of \"observing\" the causation without first having a metric to suggest one exists via the data..."
] |
[
"I'll let someone else give you a more solid answer, but if you mean correlation on any specific test (e.g Pearson's correlation), then yes of course. If you look at the first figure on here: ",
"http://en.wikipedia.org/wiki/Correlation_and_dependence",
" then you will see many examples of U shaped or cyclic phenomena that could have a causal relationship, but would get a linear correlation of 0. Anything where the causal relationship varies by a function symmetrical about the y axis, your correlation will be 0. "
] |
[
"Imagine that a drug reduced the risk of heart disease in a dose-dependent manner. If the dose was just right, the risk would be a minimum. If the dose was 0, heart disease risk was 5%, if the dose was perfect, the risk would be 1%, and if the dose was at the maximum measured, the risk was back up to 5%. This is a U shaped curve. Imagine the shape of the U was perfectly symmetrical. If you approached the question of the relationship between dose and risk with a linear model, you would find no significant relationship (no correlation), despite the dose-dependent causal link between drug dose and disease risk. If you allowed your model to look for a quadratic component to risk (a U shaped curve), the relationship would be significant, and once again, causation would come along with correlation. If you could make an edit to the title of your presentation, please state that you are asking about \"statistical dependence\" not just linear correlation. And read the wikipedia article that I linked to before. "
] |
[
"Do speakers use less/no electricity when there's no sound?"
] |
[
false
] |
Inspired by , I've always wondered if I leave my computer/home theatre speakers on when there's no music or audio playing, does it actually consume much electricity? Bonus: if so, do speakers use more electricity the higher the volume?
|
[
"Here's some empirical evidence:",
"I used a Kill-A-Watt meter to measure the power consumption of a set of computer speakers. When the speakers were off, they use 0 W. When they are on with no sound coming out, they used 8 W. When they were playing normal volume music, they used 9 W. When the music was really loud, they used 10-12 W.",
"I leave my computer/home theatre speakers on when there's no music or audio playing, does it actually consume much electricity?",
"Yes",
"do speakers use more electricity the higher the volume?",
"Yes"
] |
[
"For even more empirical data I attached my oscilloscope to the terminals on a set of stereo speakers. When the amplifier is off there was no voltage waveform present, when on but not actively playing sound there was some very slight <3Hz oscillations with total power hovering in the milliwatts, when playing it was the spectral content of the audio and total delivered power in the 2-3 watt range.",
"I think it's safe to say the amplifier used will dominate the measurements. The speakers themselves aren't going to use any significant power when not moving but the amplifier can do whatever it wants."
] |
[
"While this is true and answered the question the way it was put forward, I think it disregards one of the most important factors in the system: The amplifier.",
"There are several types of amplifiers, some which use next to no energy when there is no sound signal and some which use their full amount of energy, regardless of the signal. So the answer to wether or not it is reasonable to leave your system turned on all the time is: it depends :)"
] |
[
"Is the sparking that occurs when metal is put in a microwave the photoelectric effect?"
] |
[
false
] | null |
[
"...and even if it didn't damage the unit or spark, metal conducts heat well, so you're going to have a piping hot spoon (from the heated food) when you pull it back out."
] |
[
"...and even if it didn't damage the unit or spark, metal conducts heat well, so you're going to have a piping hot spoon (from the heated food) when you pull it back out."
] |
[
"Is this the same reason grapes produce that glow?"
] |
[
"Why do mentally disabled people often sound alike?"
] |
[
false
] | null |
[
"I've removed this post not for being offensive but for asking us to try to explain an observation that may not even be true. If you want to resubmit it, you could try something more along the lines of \"why are some learning disabilities associated with unusual speech patterns and facial structures?\""
] |
[
"Thank you for the more politically correct way of stating it :) You can expect a resubmission soon, would you also like me to change the description accordingly or is it ok currently?"
] |
[
"You might just want to boil it down into one succinct, cohesive question and avoid adding baggage with apologies and clarifications."
] |
[
"Why do black holes become less dense when they grow in size?"
] |
[
false
] | null |
[
"When people say that large black holes are \"less dense\" than smaller ones, they're using a funny definition of density. They are taking the total mass of the black hole divided by the spatial volume contained by the event horizon. Since the radius of the event horizon is proportional to mass, you quickly find",
"density ~ (mass)/(mass",
") ~ 1/mass",
"so a larger mass results in a \"less dense\" black hole.",
"I say that this is a funny definition because the mass of the black hole is not distributed throughout the inside of the event horizon so you're not really talking about a mass-density. For a Schwarzschild (non-rotating steady-state) black hole, the mass is concentrated at the singularity at the center of the black hole. In classical general relativity the mass-density is infinite (a finite amount of mass is concentrated in zero volume)."
] |
[
"The singularity is certainly an artifact of the breakdown of general relativity. Eventually, at high enough energy scales (which will get reached close enough to the singularity), we will need to replace GR with a full quantum gravity theory to get correct results. Perhaps there will be a finite volume that the mass is in, and this finite volume changes in some way as the total mass increases. But right now there is really no way to know how the mass is actually distributed - this is unknown physics."
] |
[
"The singularity is certainly an artifact of the breakdown of general relativity. Eventually, at high enough energy scales (which will get reached close enough to the singularity), we will need to replace GR with a full quantum gravity theory to get correct results. Perhaps there will be a finite volume that the mass is in, and this finite volume changes in some way as the total mass increases. But right now there is really no way to know how the mass is actually distributed - this is unknown physics."
] |
[
"How strong would a laser have to be to burn a visible line on the moon from earth?"
] |
[
false
] | null |
[
"Funnily enough, there is a ",
"relevant XKCD",
" about this very topic."
] |
[
"The article actually gives you a decent ballpark approximation though. The laser you need lies somewhere between the last (which vaporises the moon) and the second last (which simply lights it up very brightly).",
" more precisely, the article does say that 40 Mj of energy is enough to vaporise a killogram of rock and that moon rocks are about 3kg/litre. All you need to do is then work out how big a mark would be visible from Earth.",
"Looking ",
"here",
", with the Hubble telescope, you can resolve about 100m size object on the moon. Clearly, with the naked eye, you can't see objects that small.",
"Looking at ",
"Wikipedia",
", it seems as though the craters in the Gissendi region are visible to the naked eye from Earth. The smallest of those is 200m deep and about 3km in diameter, that's probably not visible though but we'll use those figures for the lower bound. ",
"The volume of that crater is roughly: 1.413 x 10",
" m3\nThe total volume of lunar rock to be excavated is roughly: 1.413 x 10",
" litres\nMass conversion: 3 kg/l",
"So we need a total of 18.849 x 10",
" Mj of energy. There's no meaningful deposition of dust on the moon on short timescales so you could certainly take even a year to carve out your monument. Let's call it 31.557 x 10",
" seconds.",
"You need a laser with power: ",
" which is as close to the National Ignition Facility confinement laser as makes no difference. You don't need 5 billion of them, unlike the article's example, just one will do the trick if you have a year to burn your mark into the Moon.",
"EDIT: corrected units for clarity & correctness"
] |
[
"I don't mean shine a light on it, I mean burn a line into it."
] |
[
"Why aren't we using thorium as a primary source of energy?"
] |
[
false
] |
[deleted]
|
[
"You have to be careful what you watch on the internet. There are lots of YouTube videos making LFTR reactors seem like they’re perfect, and better than other nuclear reactor designs, but there’s always a trade-off.",
"Both of your two bullet points could be said about coal and uranium, for some definitions of “incredible” and “extremely”.",
"Nuclear power is always going to have much higher energy density than power based on chemical reactions (like combustion). Thorium is more abundant than uranium, but uranium is not exactly scarce at this time.",
"We still have plenty of uranium, and we have plenty of newer-Generation reactor designs with a lot of the same benefits as LFTRs, but can still be fueled by uranium.",
"These videos tell you that LFTRs are meltdown-proof because the fuel is already liquid, and that they have the advantage of operating at atmospheric pressure, so there’s no large pressure difference between inside and out of the primary loop.",
"Those are true, but what they ",
" tell you about LFTRs is that they require you to work with corrosive chemicals, which can cause damage over time. Better materials are needed to be engineered so that the plants don’t frequently go down for maintenance.",
"Collectively we have thousands of years worth of man-hours operating and researching light water reactors with enriched uranium fuel.",
"You can read a much more extensive list of advantages and disadvantages of LFTR on the ",
"Wiki article",
".",
"Overall, LFTRs look pretty good once all the details are figured out. But then again, so do ",
" newer-generation (III+ and IV) designs. LFTRs are not a magic solution to our problems, but they are ",
" of the many good options that modern nuclear reactor designs offer."
] |
[
"One of the arguments against that I've often seen glossed over is Thorium reactors can be made to easily breed Uranium 233 which can be used for nuclear weapons. This seems like a simplistic or not fully explained, but perhaps U233 is more easily separated from spent fuel than either P239 or U235 "
] |
[
"Coal is not corrosive to the atmosphere it just releases some pollutants. Corrosive refers to a substance that has the power to cause irreversible damage or destroy another substance by contact. Pollution caused by coal is a problem but it doesn't physically attack the materials in the power plant, similarly with uranium reactors. And while the waste is highly toxic and radioactive, so is the waste from thorium reactors, as is uranium and thorium itself"
] |
[
"Do birds have taste buds?"
] |
[
false
] |
Birds mostly eat seeds which are almost tasteless unless chewed. But birds don't chew their food they just swallow it. I've been wondering if birds have any tasty foods or they just eat for energy and nutrients. Also the question applies for animals(wild animals).
|
[
"There is research that animals are able to taste or at least able to differentiate between different foods.",
"",
"In a study in fruit eating birds, three bird species were given the ability to select from 3 different diets composed of different sugar levels (8%, 10%, and 12%). Three tanager species (",
"a bird family",
") preferred the high sugar diet. Now I guess it is up to debate to see if they actually \"taste\" the difference versus another way to differentiate, but they can tell the difference."
] |
[
"We used to feed our chickens foods with capsaicin. Capsaicin is responsible for the spicy sensation in food like jalapeños, or hot peppers. Chickens would gobble it up - their taste buds aren’t susceptible to capsaicin, so they don’t taste the heat. ",
"I don’t know how many taste buds a chicken has, but I googled ",
"this article."
] |
[
"In the previous comment, the attached article says chickens do have taste buds(if i read it correctly) but from ur information it seems like they do lack some specific taste buds which senses the spiciness or maybe some enzymes in their mouth dissolves capsaicin just like fat dissolves capsaicin."
] |
[
"What are some interesting finite numerical sequences?"
] |
[
false
] |
Most "general interest" mathematical sequences we hear about are infinite. What are some mathematical sequences which are of general interest?
|
[
"The Heegner Numbers",
": 1, 2, 3, 7, 11, 19, 43, 67, 163. If D is a Heegner number, and we take the integers, and look at the number system that consists of the (square-free) integers and sqrt(-D), then this number system has the property that every number can be written as a unique product of the primes in this system. These are the only numbers that do this. For instance, if we include sqrt(-5), then we can write 6=2*3=(1+sqrt(-5))(1-sqrt(-5)), and 2,3,1+sqrt(-5) and 1-sqrt(-5) are all different prime numbers in this system. So 5 is not a Heegner number. ",
"These pop up in a few interesting places. Firstly, perhaps you've heard that the polynomial x",
"+x+41 gives prime numbers for x=0,1,...,39. This is a ",
"Prime Generating Polynomial",
". It has been proved that x",
"+x+p is a prime generating polynomial if and only if 4p-1 is a Heegner number.",
"Another place that it pops up is that if p is a Heegner number, then e",
" is ",
" an integer. This is most clear with p=163, the largest Heegner Number, where e",
" is within a trillionth of the integer 640320",
"+744.",
"We can form a ",
" version of Heegner numbers, by saying that d is a positive Heegner number if when we add sqrt(d) into the integers, then we get the unique factorization into primes. The first few entries in this list are",
"This list goes on for a while though, we don't know how long. The real question is then \"Is this list finite?\" we do not know the answer to this question. It could be very long and still be finite. We were able to answer this affirmatively for the negative Heegner numbers because we can use very sophisticated techniques involving ",
"Elliptic Curves",
", called ",
"Complex Multiplication",
", that cannot be used in the positive case.",
"The way that it was proved that 163 is the last Heegner Number is interesting. Gauss originally conjectured that it was the last Heegner Number (not called such at the time) in the 1800s, and it was a long standing open question for ~150 years. Then ",
"Kurt Heegner",
", an German amateur mathematician and engineer, came up with an ingenious way to prove it using very modern techniques for the time, in the 1950s. He published the proof, but there was a mistake in it and, since he was an amateur, it was quickly forgotten and no one really heard of it. Then, in the late 60s, after Heegner's death and 17 years after Heegner originally proved it, another mathematician named ",
"Harold Stark",
", an American mathematician, proved it independently using the same ideas as Heegner. After he published it, it was accepted, but he heard of Heegner's original work and took a look at it. He then published another paper that showed that his and Heegner's ideas were the same and that the mistake in Heegner's paper was actually a mistake in the book he was using written by Weber (a prominent mathematician), and that this mistake was inconsequential to the work. We then call this theorem the Heegner-Stark Theorem, and the objects created to prove it are called \"Heegner Points\" in honor of Heegner. And today, Heegner points have great significance in much more contemporary settings.",
"Also, ",
"here is the OEIS",
" complete list of finite sequences. Have fun!",
"EDIT: I'm going OEIS crazy. ",
"Here",
" is an interesting one: 1, 2, 6, 42, 1806. These are the numbers N so that for every other number m we have that m",
"-m is divisible by N."
] |
[
"Division with remainder doesn't always work in a ring. The ring has to be \"nice\" enough; the rings that allow division with remainder are called Euclidean domains. I can talk about that more but I don't want to go too far on a tangent.",
"We are defining a new ring by taking the ring of integers and adding in the element sqrt(-5). I'll explain how this ring can be defined. It's a little bit long but hopefully I'm not too unclear.",
"First, we consider the ring of polynomials in an arbitrary variable with integer coefficients. This ring is called Z[x] (Z indicates the integers and x is our variable). This ring has elements that look like 1, 7, x, 5x",
" +2x",
" +1, etc. This ring Z[x] is what you get when you want to adjoin an element x to the ring of integers (you can see that Z[x] contains the integers as well as all combinations of integers and multiples of x). ",
"Okay, now we are going to consider Z[sqrt(-5)] instead. This is the ring of all polynomials in sqrt(-5) (instead of in x) with integer coefficients. So elements of Z[sqrt(-5)] might look like 15, sqrt(-5), 8+5sqrt(-5), 1+3sqrt(-5)+2sqrt(-5)",
" , etc. The difference between Z[x] and Z[sqrt(-5)] is that there is a relationship between sqrt(-5) and the integers, i.e. that sqrt(-5)",
" = -5 which is an integer. So sqrt(-5)",
" can be reduced to an integer if n is even, and if n is odd then sqrt-5)",
" can be reduced to something of the form b*sqrt(-5) where b is an integer. Then we see that any element of Z[sqrt(-5)] can be reduced to the form a+b*sqrt(-5) where a and b are integers. It's important to note that polynomials are defined as having only a finite number of terms, so we don't have to worry about any infinities showing up when we reduce things to that form.",
"So this was a long-winded way of explaining how to adjoin a new element to a ring. In this specific case, we end up getting the nice-looking set of elements of the form a+b*sqrt(-5). It's easy to check that this satisfies the definition of a ring with addition and multiplication defined as you expect."
] |
[
"4, 6, 8, 12, 20\n",
"and",
"6, 12, 12, 30, 30\n",
"A platonic solid is a convex polyhedron whose faces are all the same convex regular polygons. Familiar ones include the tetrahedron, which has 4 equilateral triangles for faces, and the cube, which has 6 squares for faces. You might (I would, at least) naively think that there might be a whole lot of these solids—maybe even infinitely many. But it turns out that there can only be 5. If you list the number of faces of each solid in increasing order, ",
"you end up with this short and rather surprising-looking finite sequence",
". If instead, you count the number of ",
" of each of the platonic solids, you end up with ",
"the second sequence above",
"."
] |
[
"If I captured a photon with energy hv inside a perfectly reflective sphere, what mass increase would I measure for the sphere (provided that I had perfect scales)?"
] |
[
false
] | null |
[
"Approximately hv/c",
". Slightly less, because of conservation of momentum."
] |
[
"Can you explain the \"slightly less\" part?"
] |
[
"Momentum is conserved. So some energy is carried away by the motion of the center of mass afterwards, and doesn't contribute to the mass of the system."
] |
[
"If there is energy coming to Earth from the sun's radiation, and leaving it from heat that radiates out from the planet into space, what is the net change over time? Is it perfectly balanced, or does the Earth cool down/heat up over a long enough timeline?"
] |
[
false
] | null |
[
"Perhaps the most accurate way of saying it is it's always driving towards balance. There's a self-correcting feedback at play driving back towards balance should the system leave it. The amount of IR light (i.e. thermal radiation) the Earth radiates away to space is proportional to the Earth's temperature (to the power of four). If at any given moment IR(out) doesn't balance Sun(in) then the Earth's temperature will rise or fall until it does. At the most fundamental level, that's what the concern over global warming is. We're hampering our IR emission thus Sun(in) is greater than IR(out) and thus the Earth is accumulating energy and this drives the Earth's temperature to rise so that IR(out) can increase until it again matches Sun(in)."
] |
[
"Yeah, but that's a ",
" small imbalance.",
"The Solar flux (essentially the intensity of sunlight at Earth) works out to be 1367 watts per square meter. When averaged over the entire planet, that's 342 watts per square meter, of which about 240 Watts is absorbed per square meter, and thus must be re-radiated back out into space.",
"By comparison, the extra heat added due to geothermal sources is about 3000x smaller, at about 0.087 Watts per square meter - or an extra 0.036% that must be re-radiated out to space. ",
"In terms of temperature - which scales as the fourth root of flux - that means geothermal sources add an extra 0.02° C to the temperature of the planet, or some 50 times smaller than the amount the temperature has already risen due to human-caused climate change."
] |
[
"Also, thank the heavens for Earth's magnetic field. Without it, the atmosphere would have been stripped away eons ago, leaving Earth, much like Mars.",
"Yeah, that's not true.",
"The idea that a magnetic field is necessary for atmospheric retention is the \"conventional wisdom\" that's often repeated in layman-level literature, but doesn't really work out to be factually correct.",
"Venus has no intrinsic magnetic field, yet maintains an atmosphere 92x thicker than Earth's. Somewhere along the way, the very true statement \"Mars' lack of magnetic field hastened its atmospheric loss\" turned into the very untrue \"All atmospheres need a magnetic field for atmospheric retention.\"",
"It turns out that planetary mass, mean atmospheric molecular mass, upper atmospheric temperature, and atmospheric replenishment mechanisms are all more important than the existence of a magnetic field for retaining an atmosphere - it's just that Mars was a marginal case for all of those, while Earth is not. We have an ample atmosphere because our planet has a high escape velocity, reasonable atmospheric molecular weight, and active replenishment from volcanoes.",
"A magnetic field protects against atmospheric loss only by preventing solar wind sputtering...but also causes atmospheric loss by producing a polar wind outflow, charge exchange, and raising the temperature of the upper atmosphere. Earth loses many tons of oxygen off the poles every day because we have magnetosphere."
] |
[
"If 5 pounds of C4 was detonated in an indestructible sphere measuring 2 foot in diameter, what would happen?"
] |
[
false
] |
[deleted]
|
[
"The c4 reaction would complete but since it stays compressed inside the sphere and all of the energy is converted to heat you would have a super hot ball of plasma inside the sphere... a nuclear bomb inside an indestructible spere? Not to sure about that one. The explosion would definitely complete. Actually. When a nuclear bomb is detonated, the entire fission reaction is mostly complete before the radioactive material even starts to expand. If would imagine that the indestructible sphere could be viewed like the gravity from a large star. You would just have a hot ball of material inside the sphere that would just radiate heat until it cooled to the surrounding temperature. "
] |
[
"Ok thanks, will re-post it there!"
] |
[
"Thanks for the reply!",
"/u/changetip",
" 1000 bits"
] |
[
"Inspired by another question: why don't Martian explorer robots include wipers to wipe dust from the solar panels, thereby making the robot more reliable?"
] |
[
false
] |
[deleted]
|
[
"\"We looked at all sorts of ways to try to keep the panels clean: windshield wipers, transparent plastic that you could put on rollers and you could roll it off to bring new plastic into place. All of the different techniques that we looked at were big, complicated, heavy,\" Squyres says."
] |
[
"Quis custodiet ipsos custodes",
"But then who will wipe the dust from the wipers ?"
] |
[
"Actually, given that the little guys far exceeded their design life as is, I would assume not. It isn't ",
" a problem."
] |
[
"Can optical elements be arranged to robustly redirect ambient light towards a desired direction?"
] |
[
false
] |
I hope this makes sense; it's something I toyed around with and don't know if it's been considered before or what it'd be called. It'd be interesting if there were an "unpowered book light" that could (partially) redirect isotropic ambient light in such a way that lit up a particular direction more than other directions. The idea being, you could use it in an ambient isotropic low-light situation as a weak flashlight or booklight that didn't need batteries. It would be made of some combination of mirrors, lenses, prisms, and other optical elements. When you try to make sketches of how this might work, however, you get the sense it's probably impossible. If you put a mirror here, it adds exactly the amount of light in your desired direction as it blocked. If you try to redirect the blocked light, other light gets blocked. Lenses don't seem to play well either. It's like trying to fit a too-small sheet on a bed. Is there a physical law at work here? Is this truly impossible? Thanks for reading
|
[
"This is a classic application of ",
"Etendue",
". The ambient light input has a high Etendue and you want all of the light focused and going on to your book (a low Etendue output). The basic theorems of radiometry and the Lagrange invariant say that Etendue can never decrease in a system that has passive optical elements so you are stuck. Your system cannot be a collection of lenses, mirrors and prisms.",
"There may be special materials that absorb light energy isotroptically and then can be stimulated into re-emitting the light in a particular direction (as in a flash-lamp pumped ruby rod laser) that could be useful, but I am not a materials person. I can just tell you that you can't to it with class linear optics. "
] |
[
"This question has been getting some really off the mark responses so I thought I'd give it a go...",
"Firstly, the answer is a resounding YES. You can use passive optics to take ambient light and redirect it to a particular direction. Proof? It's been done:\n1) ",
"http://www.nature.com/nature/journal/v339/n6221/abs/339198a0.html",
"Your first response might be- \"But they used the sun! That's not even the same thing!\". Actually, it is. More on that shortly.",
"First though, I'd like to point out that I chose this particular example because they actually achieve the thermodynamic limit (discussed inaccurately elsewhere on this thread). The physical limit for concentration on Earth occurs when you've brought the receiver temperature up to the effective surface temperature of the sun. This is because once it's that hot it re-radiates the same amount of energy it receives as black body radiation and you can't heat it up any further. This level of concentration is an astounding ~50k times the ambient power flux here on Earth (luckily) and the U of Chicago group have manged reaching it.",
"Secondly, the etendue argument. Very broadly etendue states that you can't make a beam both narrower and less divergent using just passive optics. Or, said the other way around, if I take a beam of light and try to make it narrower it will also try to spread out more. The relevant restriction etendue places on the question is the theoretical limit on the concentration that is possible. This value is: \n C = (beam width in)/(beam width out) ~ 1/sin(a)",
"Where \"a\" is the half angle that limits the acceptance of the optics, i.e. beams of light striking the input optics at an angle greater than \"a\" will not be admitted to the system (and I've left a number of irrelevant factors out). Etendue is conserved in our case by making the output beams be very divergent forming a very distorted image - but since we're only interested in the energy of the light-rays we don't care.",
"You can see that we can make the output beam width arbitrarily small (so long as we don't approach wavelength dimensions) by limiting the input angle. Of course, accepting smaller and smaller half angles of beams makes us lose some of the energy but we never wanted it arbitrarily small anyways, just book size. If the input light is isotropic (as OP stated) then we are screwed because trying to double the concentration of energy by halving the input angle will also halve the input energy. However this is the worst case scenario and in the real world, light is hardly every isotropic but much more often nearly completely collimated as is the case for natural sources e.g.- starlight, moonlight or really anything that is far enough away from you. This has already become somewhat longer than I expected so I'll just state the bottom line: making the input angle smaller will negligibly affect the energy entering the system but will allow us to concentrate it further.",
"Lastly, let's do an order of magnitude calculation to see why at the end of the day this isn't going to be feasible. Basically our simplified setup is a big (really big) lens accepting (collimated) starlight at the input and our book is placed at the output focus. Let's say the book is 1 m",
" and that you need around 10",
" photons per second per m",
" to read somewhat comfortably. Starlight gives us around 10",
" photons per second per m",
" (sources: ",
"http://en.wikipedia.org/wiki/Lux",
", ",
"www.wolframalpha.com",
"). This means we need the area of the input lens to be around 10",
" m",
" - about 10 football fields. \nSo, in theory- yes, in practice- no."
] |
[
"Unfortunately one way mirrors do not work like that. The boundary always reflects equal proportions of light on both sides. The \"one way mirror\" effect is created by dimming the lights on one side of the mirror."
] |
[
"Do crickets coordinate their chirping with each other?"
] |
[
false
] |
When you listen to chirping crickets at night, you usually only hear one voice. Is this because they chirp at the same time, or are you simply hearing the nearest cricket.
|
[
"Crickets, like all other insects, are cold-blooded. They take on the temperature of their surroundings. Many characteristics of cold-blooded animals, like the rate at which crickets chirp, or the speed at which ants walk, follow an equation called the Arrhenius equation. This equation describes the activation energy or threshold energy required to induce a chemical reaction. For instance, crickets, like all other organisms, have many chemical reactions occurring within their bodies. As the temperature rises, it becomes easier to reach a certain activation or threshold energy, and chemical reactions, like those that occur during the muscle contractions used to produce chirping, happen more rapidly. As the temperature falls, the rate of chemical reactions inside the crickets' bodies slow down, causing characteristics, such as chirping, to also slow down.",
"Source"
] |
[
"Cricket chirping actually has to do with the outside temperature. The hotter it is, the more they chirp"
] |
[
"Thanks, but temperature aside, I'm more asking whether or not a group of crickets will chirp at the same time.."
] |
[
"How can an Ergosphere drag space faster than the speed of light?"
] |
[
false
] |
How can a dense rotating object drag the local frame of reference faster than the speed of light (speed of light measured by an observer “at infinity”)? I'm, mostly, unclear as to the the mechanism. Mostly it bothers me that something which, by definition, must be traveling slower than the (local) speed of light (such as a dense rotating neutron star), can drag time-space enough to create the ergosphere which, again by definition, causes space to “travel” faster than the speed of light. I understand how this can happen at cosmological scales (relative velocity between stars) given the expansion of space, but how can this occur locally, within the region of a sufficiently dense rotating object?
|
[
"For the ergosphere to exist (extended past the event horizon) it ",
" drag space-time faster than light. This doesn't mean matter will be dragged at this speed but describes the warping of space-time (matter in this region will experience time dilation... edit: and rotation).",
"Let's impale the rotating body with a stake at the equator! Our stake is made out of rigid space-time. The mass of the rotating body warps space-time but our stake is firmly buried in the equator and it stands upright. The stake extends past the event horizon. To extend this far requires superluminal frame dragging and it is a product of the rotation and distance from the object. Our space-time stake is rigid due to the mass of the object warping space-time and achieves great speed at distance due to the rotation and rigidity. Space-time is not matter and so this doesn't violate relativity.",
"This is the best i can do with some pretty incomplete understanding of the subject. My apologies is this is incorrect and i encourage someone with greater insight to contribute.",
"Edit2; I havent changed the wording but it's definately a mistake to reference ",
" than light. At light speed is accurate - not faster. My bad."
] |
[
"What would an observer experience if they were in the superluminal bit of space-time?",
"Since they can't move at super-luminal speeds, it would mean spacetime would be moving away from them, so would they measure a larger-than usual expansion metric or something?"
] |
[
"Not faster than; AT! AT the speed of light.\nI believe the boundary is defined by the surface where a photon, striking the equator tangentially and moving opposite the body's rotation direction, would freeze in place with respect to an outside observer."
] |
[
"Can a prism split more than just visible light?"
] |
[
false
] |
We always see prisms splitting white light into a rainbow, but are they also dividing other forms of electromagnetic radiation by wavelength? If not, are there materials that do?
|
[
"This is how infrared light was discovered. William Herschel ran sunlight through a prism, and noted that it could heat a thermometer even when the thermometer was held just beyond the red end of the spectrum",
"Link"
] |
[
"A prism will split light into all its wavelengths. If you used a prism to split sunlight, the infrared would be refracted to the red side of the rainbow, and the UV is refracted to the violet side. This happens whenever you split light, but you just can't see those wavelengths. \nYou theoretically could prove this by sunbathing underneath a huge prism. You would only feel warmth just beyond the red, and only get tanned above the violet strip of the rainbow.\nFurthermore, radio waves and microwaves are refracted even further in the red direction, and vise versa with X-rays and gamma rays."
] |
[
"that depends on the transmittance of the material at those wavelengths : for example, normal soda-lime glass does not transmit UV light, it would get absorbed, not refracted. I also highly doubt microwaves and radio waves interact with glass at human scales, their wavelengths ore just too big and if anything they should diffract around the small obstacle more than refract through it. Finally, Highly energetic photons like x-ray and gamma interact with matter in other ways (Compton scattering and pair production) and do not refract (though you ",
" refract X-rays using an Al prism).",
"So your answer ",
" makes sense for an arbitratily large prism of a material ttransparent to all wavelengths, but there is no such material."
] |
[
"When pollen reaches the stigma, how does it get to the ovules?"
] |
[
false
] | null |
[
"One of the most interesting details of plant biology is the fact that they have life cycles which involve ",
"alternation of generations",
". Unlike humans and most other animals, which are multicellular diploids for our entire lives (with the exception of an extremely brief unicellular bottleneck at fertilization), plants go through ",
"multicellular diploid and haploid phases",
". The haploid gametophyte phase produces gametes through mitosis, while the diploid sporophyte produces spores through meiosis. To make an analogy, is sort of like if humans gave birth to testes and ovaries that became self-sufficient entities rather than parts of our bodies, and then these went on to make new humans by themselves. In the earliest plants that colonized land, like mosses, the haploid gametophyte phase dominates the life cycle, with the ",
"sporophyte depending on it",
" for nutrients. Later plants like ferns developed separate ",
"gametophytes",
" and ",
"sporophytes",
":max_bytes(150000):strip_icc()/GettyImages-521606980-5a7b3f7cc064710037c365fd.jpg) that are both more self-sufficient, and this became a general ",
"trend towards increasing dominance of the diploid sporophyte",
" stage in more derived groups of plants. Ultimately, this trend has reached a peak with angiosperms (flowering plants), in which the pollen produced in male flowers is actually a large number of extremely reduced and simplified gametophytes that are incapable of surviving on their own.",
"That probably seems like a lot of build-up before getting to your actual question, but it's an interesting topic and I wanted to provide some background. The point of everything I just explained is that pollen is ",
" actually a plant's gametes (which would make it equivalent to sperm), but is in fact more accurately thought of as a multicellular (though very small) individual plant which ",
" gametes. So, just like any larger plant, pollen is capable of germinating and growing in a way that a single-celled gamete like sperm cannot, and this is exactly what it does upon reaching the stigma of a compatible plant of the same species. It grows a ",
"pollen tube",
" which travels down the stigma to the ovule and connects with it. Then, the pollen releases not one but ",
" individual male gametes down this tube, in a process called ",
"double fertilization",
". One of the male gametes ",
"fertilizes the female gamete",
" to produce a diploid zygote that will grow into an embryo, while the other one merges with two additional haploid cells to make a ",
" cell that develops into the endosperm. The endosperm is basically the equivalent of a yolk that sustains the embryo while it develops, and for many plants with edible seeds (e.g., cereal crops like corn, wheat, rice, etc.), this is actually the ",
"main part that is consumed",
"."
] |
[
"I'm really glad I don't have to write a test about this! ",
"Thanks a lot for the thorough explanation though."
] |
[
"How does the endosperm help the embryo ?"
] |
[
"Can it rain sand?"
] |
[
false
] |
I live a few miles from the coast and sand is on everything. I know the winds are responsible for most of it but I was wondering if any of it comes down with raindrops from being evaporated out of the ocean.
|
[
"You might get some very fine sand entrained in the wind and suspended on especially windy days that will travel several miles from the coast (or other source), larger sizes grains will creep and saltate inland over time with wind. ",
"Very fine dust particles do become suspended in the atmosphere to quite high levels where they can act as condensation nuclei, creating clouds and eventual precipitation thereby 'raining' the dust out. After dust storms the rain drops can actually impact and absorb enough suspended dust particles as they fall to colour the rain drops. I've had red rain here in Australia before. "
] |
[
"Similarly in Northern Europe, every now and again when the winds are blowing up from Sahara, they take sand with them into the atmostphere. When it then rains, the rain drops will leave sand with them on the ground.",
"\nHere's an article from last year: ",
"http://www.telegraph.co.uk/news/weather/11525166/Blood-rain-to-fall-on-Britain-as-red-Saharan-dust-blows-in-from-Africa.html"
] |
[
"I was pretty sure the answer was no... but it's yes! (",
"source",
")",
"Desert dust can actually travel quite far in the winds! (",
"source",
")"
] |
[
"Why did we cultivate onions even though we couldn’t eat them the same way as apples or oranges?"
] |
[
false
] | null |
[
"Its more of an historical questions then biology. As you can very well eat an onion just like an apple -> if you use one that is not as strong in flavor like red onions. You can also eat it raw and make pickles...Onions where used hundreds of years before... to spice up food. As regular food (as it holds quite well on storage - so you can use it as rations for long journeys).Therefore cultivation occurred naturally - but regarding the original onion -> it went extinct so we don't have enough info on it.",
"Wikipedia already explains it quite well (Quoting) :",
"Because the wild onion is ",
"extinct",
" and ancient records of using onions span ",
"western",
" and ",
"eastern",
" Asia, the geographic origin of the onion is uncertain,",
"[17]",
"[18]",
" with likely domestication worldwide.",
"[19]",
" Food uses of onions date back thousands of years in China, ",
"Egypt",
" and ",
"Persia",
".",
"[17]",
"[18]",
"[19]",
" ",
"Traces of onions recovered from Bronze Age settlements in China suggest that onions were used as far back as 5000 BCE, not only for their flavour, but the bulb's durability in storage and transport.",
"[20]",
"[19]",
" ",
"Ancient Egyptians",
" revered the onion bulb, viewing its spherical shape and concentric rings as symbols of eternal life.",
"[19]",
" Onions were used in Egyptian burials, as evidenced by onion traces found in the eye sockets of ",
"Ramesses IV",
".",
"[21]",
" ",
"Pliny the Elder",
" of the first century CE wrote about the use of onions and cabbage in ",
"Pompeii",
". He documented Roman beliefs about the onion's ability to improve ocular ailments, aid in sleep, and heal everything from oral sores and toothaches to dog bites, ",
"lumbago",
", and even ",
"dysentery",
". Archaeologists unearthing Pompeii long after its 79 CE volcanic burial have found gardens resembling those in Pliny's detailed narratives.",
"[19]",
" According to texts collected in the fifth/sixth century CE under the authorial aegis of \"Apicius\" (said to have been a ",
"gourmet",
"), onions were used in many Roman recipes.",
"[19]",
" ",
"In the ",
"Age of Discovery",
", onions were taken to ",
"North America",
" by the first European settlers,",
"[17]",
" only to discover the plant readily available, and in wide use in ",
"Native American",
" gastronomy.",
"[17]",
" According to diaries kept by certain of the first English colonists, the bulb onion was one of the first crops planted by the ",
"Pilgrim fathers",
".",
"[19]",
""
] |
[
"If the wild predecessor of cultivated onions is extinct, then what were the Native Americans eating in that last paragraph?",
"Does it mean that onion cultivation pre-dates the migration across the Bering Strait to populate the Americas?",
"Or does it mean that onion cultivation spread so quickly from the very first European contact with America that later (but still early) European migrants encountered onions spread from there? Do we know if it came from Spanish contact in the Caribbean or from the Norse settlements in Newfoundland?",
"Or is this evidence of the supposed ancient Egyptian commerce with the Americas that some people think led to pyramid-formed structures being found in both the old and new worlds?"
] |
[
"For one, you can very well eat onions as a main ingredient, but you have to cook them. Onion soup and Onion Cake are both tasty af. ",
"",
"For another, Onions as a plant can be grown together with other plants to reduce the effects of pests. When you look up biological agriculture, you'll find out that a lot of plants are grown specifically next to each other because they benefit each other. Be it through exchange of nutrients or through offering a protective shield against a pest. ",
"",
"Onions are also said to have health-benefits an to be boosting the immune system. They store very well in cold dark places and spring-onions can be harvested very early and are a delight, especially grilled with some balsamico glacé on top. "
] |
[
"Are invasive species ever beneficial to their new environment(s)?"
] |
[
false
] |
EDIT: I'm not condoning the act of releasing a species into a new ecosystem, as I'm well aware of the dangers involved. I'm just wondering if the opposite can be true as well. Edit 2: Some of you have asked what I mean by "beneficial." I realize that word may be a bit arbitrary, since ecosystems are incredibly intricate. However, I'm looking for examples of invasive species who have filled previously empty niches or those that have replaced a native species and are better in that niche than the native one was, if this clears things up. Also, thank you all for your answers!
|
[
"Define \"beneficial to an environment\"."
] |
[
"The introduction to of foreign dung Beatles to Australia has been reasonably successful. It was done properly by scientists and used to limit problems caused by other introduced species. They chose varieties that only bred in dung to stop them getting out of control. ",
"The Cactus moth was introduced and successfully reduced the numbers of invasive prickly pear plants. "
] |
[
"It really depends what you mean by beneficial. However, in general most ecosystems are in a sort of an equilibrium. Different species at different parts of the food chain are able to sustain over generations as if they didnt they would have gone extinct a long time ago. Introducing a new species throws and spanner in the works and disrupts the ecosystem which can then lead to a cascade of species extinctions. Eventually a new equilibrium will be reached. You can't real be more equal than a equilibrium, so generally introducing a new species will not have any benefit to the ecosystem, only to specific species. An exception might be where an species has already been introduced, or some other environmental disturbance has taken place, and another introduction may help to solve that, another commenter has pointed out a few examples of these."
] |
[
"If a small force was applied on a heavy object over a large number of times, would it break?"
] |
[
false
] |
[deleted]
|
[
"I believe you are talking about ",
"fatigue",
". A object can be loaded repeatedly and survive, then one day the same loading causes catastrophic failure. A famous case was the turbofan in ",
"United 232",
". I was on that flight the day before it crashed..."
] |
[
"To some extent yes. You are referring to fatigue. However, there is a threashold stress which much be obtained before small stress high frequency loading fatigue can affect a material. There's also high stress low frequency fatigue. Also, some materials are better under repeat loading than others. Steel is excellent when considering fatigue, while aluminum is an extremely poor material under repeat loading."
] |
[
"each application of force",
"That is dynamic loading.",
"But at some point, all your imperfections will have grown as much as they are ever going to for the force you're applying",
"That isn't the way fatigue failure works. Repeatedly applying the same load will eventually cause failure if the load is sufficient to overcome any hardening of the material that occurred as a result of the previous deformations. "
] |
[
"When I shine a black light onto tonic water, what is actually occurring to make it glow blue?"
] |
[
false
] | null |
[
"The phenomenon is called ",
"fluorescence",
". Fluorescence occurs when incident light excites the electrons within a molecule to a higher energy level, and these excited electrons relax to emit a photon, often of lower energies.",
"Tonic water contains ",
"quinine",
", which is a highly fluorescent compound. Your black light emits ultraviolet light, which is absorbed by quinine, and visible light is emitted when the excited electrons relax."
] |
[
"The system that fluoresces is the conjugated aromatic system of the quinine ring. Essentially, electrons are free to move about this pi system. Thus, the least energetic transition between the highest occupied molecular orbital and the lowest unoccupied molecular orbital is relatively low-energy. An UV photon can excite it to even higher states, and it immediately decays by shedding the extra energy as visible light photons. Because the transitions follow from quantum mechanics, they have very well-defined energies, shown as a single wavelength or color."
] |
[
"To add to ",
"/u/rupert1920",
" and ",
"/u/RRautamaa",
", it is the ",
"quinine",
" in the tonic water that is ",
"able to fluoresce",
" under the black light. The ",
"key absorption bands of quinine",
" are at 350 nm in UVA and 310 nm in UVB range. The fluorescence you see is the emission wavelength of 460 nm, which gives a blue/cyan color under UV light.",
"\n - some vitamins (Vitamins A and B)\n - Chlorophyll A - Glows reddish/orange. Easiest to see if you have some plant-infused oils (ex. olive oil)\n - Milk\n - Ripe bananas due to ",
"Breakdown of chlorophyll",
" during the ripening process releases some fluorescent versions.\n - More foods can be found ",
"here",
" and ",
"here"
] |
[
"Is there a limit where the size of a particle accelerator returns fewer benefits?"
] |
[
false
] |
I know that's badly worded... It seems that the larger the accelerator the better. If we could build an accelerator that was about the same size as the orbit of Mars, would building one that was the same size as the orbit of Pluto be better for us to experiment with?
|
[
"I think it depends somewhat on the development of physical theory, but I would say that no, there's no limit to how large of an accelerator that we might someday want to build.",
"The diameter of a synchrotron is set by the interaction of the intensity of the magnetic field (which causes the particles to curve), and their speed/momentum/energy level (which tends to cause them to spiral out).",
"A larger-diameter ring can contain higher-energy particles at a given magnetic field strength, so it makes sense to make ever-larger rings to allow experiments at higher & higher power levels. I know that there's some loss in energy from synchrotron radiation when charged particles move in a curved path. That might produce some kind of practical upper limit for a synchrotron's diameter, though you could always use more-massive particles to minimize that effect.",
"The reason I say it depends on the development of physical theory is that there may be \"flat spots\" in the energy levels associated with phenomena predicted by theory. In other words, there are all sorts of interesting questions that the LHC may be able to answer, or provide data on. There are also experiments that will require just a ",
" more energy to verify. So, if there are \"interesting\" experiments to be performed at energy levels 100 times what the LHC can produce, and nothing after that until you get to 1,000,000 times, there might not be much point in building that Mars-orbit-sized accelerator."
] |
[
"Yes and no. As particles travel around a storage ring, they're constantly losing energy to radiation (circular orbits at fixed speed are constantly accelerating [velocity is changing direction], accelerating charged particles radiate, and radiation carries off energy). The amount of radiation is very sensitive to the energy of the accelerated particle(",
"equation 8 for synchrotron radiation",
"), so for a fixed radius, there is a point where the amount of energy we can give the particle per orbit via the acceleration system is balanced by the loss of energy to radiation. Increasing the radius, and thus decreasing the amount of radiation per orbit, increases where that maximum energy will be.",
"Looking at that second to last version of that equation, we see that we want to use the heaviest particles possible, and we want the biggest radii possible. Unfortunately, heavier particles (smaller gammas due to more rest mass) tend to probe for different effects. Colliding two electrons is a relatively simple event compared to colliding two protons. When protons collide, you randomly get a collision of their constituents. When heavy ions like lead and gold collide, you get a random collision of many protons and neutrons, adding even more chaos to what actually collided. However, heavy ion collisions probe high energy densities much more effectively than protons or electrons can. So what you collide isn't as free a parameter as we may hope: we need to identify what phenomena we want to study, then decide on what the most effective things to collide are, and that sets our energy.",
"Getting back to your question, the answer is yes: a bigger accelerator is a better accelerator. However, there's a downside to a bigger accelerator: cost. The bigger the accelerator, the more material it requires (would you rather build a thin tube of superconducting magnets the radius of Mars' orbit or Pluto's?), and the more power it takes to run, as there's simply more places where energy is dumped into the beam or leaked as inefficiencies out of the system. So, when we build a new accelerator, yes, we want the biggest one possible, but the design constraint tends to be more in the \"how much energy can we afford to put into the beam per orbit\" and \"how much accelerator can we afford to build\" departments than the \"how big do we want to go\" department.",
"There is also a question of diminishing returns. At the moment, the Standard Model doesn't really predict any more particles. Yes, there are problems with the Standard Model, and yes, there are extensions or alternatives to the Standard Model that do predict the existence of more particles. But, given that the world scientific community has a limited budget, new flagship accelerators tend to be concerted, major leaps forward. So, if you could build any collider you want, build the biggest, most energetic one. In all likelihood, your costs will somehow be proportional to 2",
"r, so you tend to build the biggest accelerator you can afford that can legitimately probe new areas of physics inaccessible to your previous equipment. That's also why a lot of the big tunnels that house collders get reused: cheaper to build the LHC in an existing tunnel than to dig out a new several km wide circle deep underground."
] |
[
"From what I've always been told, bigger accelerators mean more energetic collisions, which mean you can observe smaller things better. \"More is less\" so to speak. However, the \"law\" of diminishing returns states that the return on an investment gets lower and lower the more you invest, sort of. Basically, more money spent on building bigger accelerators doesn't mean you'll get a proportional benefit. "
] |
[
"Is there a reason your own \"young\" bone marrow couldn't put in storage for an immune system \"restoration\" when you are older?"
] |
[
false
] |
It seems a reasonable hypothesis that a portion of the "problems" with an aging immune system come from aging stem cells in your bone marrow. Obviously bone marrow extraction is very painful, but other than that hurdle, is there some reason I am not seeing that storing your own bone marrow on LN2 for later wouldn't be a way to restore the "youth" of your immune system later on in life?
|
[
"Yes. Benefits are not proven, and the procedure is VERY expensive, and carries it's own risks. (Either you have to puncture bones with a big needle to aspirate bone marrow, or take drugs to make your bone marrow cells divide too much and spill into blood stream then collect them by apheresis.) And then storage costs money too, and takes up space. (I work in apheresis and bone marrow transplant.)",
"And to do the transplant you would need to ablate existing bone marrow using chemo or total body irradiation. I work at a hospital, trust me, you don't want to do that.... This in of itself carries Very significant risks."
] |
[
"You need to free up space for new bone marrow to engraft, otherwise only a tiny portion will."
] |
[
"And to do the transplant you would need to ablate existing bone marrow using chemo or total body irradiation. I work at a hospital, trust me, you don't want to do that.... This in of itself carries Very significant risks.",
"If the current bone marrow wasn't cancerous, why would you need to kill it off when replacing it with a younger copy? Wouldn't the implanted bone marrow be 100% compatible with the current one?"
] |
[
"Are neutrons really completely neutral in charge?"
] |
[
false
] | null |
[
"According to ",
"http://prd.aps.org/abstract/PRD/v37/i11/p3107_1",
", the charge of a neutron is experimentally limited to within 10",
" electron charges of zero. This would seem to be the best result to date; it's cited in ",
"http://pdg.lbl.gov/2011/listings/rpp2011-list-n.pdf",
"."
] |
[
"There is also a theoretical reason to expect this result. The neutron is (as VT237 mentions) the bound state of an up quark and two down quarks (and lots of gluons holding them together). The requirement of gauge anomaly cancellation requires precise relationships among the charges of the different particles (see section 3 of ",
"this",
"), which in turn leads to a neutron with electric charge exactly, not approximately, zero."
] |
[
"Yes. They consist of one up quark and two down quarks. An up quark holds a +2/3 charge, whilst a down quark holds a -1/3 charge. 2/3 - 2*(1/3) = zero.",
"At least this is how I understand it. If a quantum physicist comes by and says otherwise, I will bow to his/her greater knowledge and experience."
] |
[
"Could the Chicxulub have ejected complete creatures into space? If so, is it possible they are still preserved in space?"
] |
[
false
] |
How awesome would that be to find?
|
[
"In order to reach space and stay there, you need to give something an awful lot of energy - from the surface in order to escape the planet's gravity well, you'd need to be accelerated to over 11km/s (slightly less will get you into orbit). We achieve this in a fairly gentle manner with rockets by continuing the acceleration over a long period, but this isn't possible with an impact event. Certainly the scale of the event will cause the rock to deform in such a manner the acceleration won't be quite instant, but it's still not going to be gentle.",
"Even if your organism survives the initial acceleration intact, it also needs to have survived the blast and heat from the atmospheric impact, and subsequently needs to avoid colliding with any of the other debris that was kicked up or coming into contact with any high temperature debris.",
"You'd have to run some very complicated simulations to be totally sure, but the sheer violence of the event and number of exciting different ways to be obliterated during it renders the chance of surviving intact vanishing."
] |
[
"Chicxulub event..."
] |
[
"If by \"complete creatures\" you mean \"complex multicellular organisms\", the answer is that the forces in the event would have destroyed them. However, if a complete single-cellular organism is acceptable, it's certainly possible that they might have been ejected into space without being destroyed. As for where they'd have ended up, see ",
"this recent paper",
"."
] |
[
"What happens to the bits of particles that fly off during atom smashing?"
] |
[
false
] |
Quarks and such, do they exist freely in nature? Do they spontaneously reassemble into their respective particles? Could you fill a bucket with them? It would probably have to be a very dense bucket but you get the idea. Can you collect enough of them to make an observable mass? Can you make things out of them besides particles? There are probably a few dumb questions in there but please let me know where I am thinking incorrectly.
|
[
"Quarks won't exist freely. Quarks are really cool in that as you pull one out of something like a proton, the energy you have to expend to pull it out ends up creating new particles that \"dress\" the quark. They really can't exist on their own. Now we have done some cool stuff creating \"Quark-Gluon plasmas\" where you have a whole mess of quarks and gluons floating around in one big ball at something like 4 Trillion degrees. ",
"Everything made of quarks will decay except for the proton (most likely. there's still a tiny tiny chance the proton may decay).",
"Then there are the leptons like electrons, muons, and tau particles (and their respective neutrinos). The latter two will eventually decay into electrons and various neutrinos. The neutrinos rarely interact with matter, but they oscillate between various states (not really the same as decaying).",
"Okay this should just be a start. Feel free to ask more questions."
] |
[
"On the first, yes. In fact, much of the energy goes into new particles' mass. Not just from quark \"dressing.\" I mean the simplest collider is electron on electron. Those both have extremely tiny masses, but when we accelerate them to tremendous energies and collide them, we get a lot of particles that are each much much more massive than the electron.",
"But yes, in the case of quarks, the energy from the strong force binding will create the new quarks to dress the outgoing one",
"On the second topic, yes it's radioactive decay. Particles changing from one type to another via exchange/release of the weak force bosons. That radioactive decay often involves the transformation of mass energy into kinetic energy or the release of photons."
] |
[
"So on the first part, it's all about matter just being one form of energy. We can move energy from one form to another. And that's really cool in my book. The picture that usually gets used in more general science talks is two strawberries smashing together and out pops a whole fruit salad of stuff. Bananas and grapes and oranges and whatnot. That's high energy particle physics for you.",
"As for micro black holes... doomsday scenarios get media attention. As do black holes. So if you're outside the physics community and you want to get your name known... why not claim both of those things will happen at once? I mean... I dunno, it's something that's maybe slightly possible from some far outside the accepted field of physics hypothesis. But no one really thought it'd happen, and they certainly haven't been observed to happen."
] |
[
"Why do I get a sharp pain when metal touches my alloy filling?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"We do not offer ",
"medical advice",
" on ",
"/r/AskScience",
". Please see our ",
"guidelines.",
" If you have concerns about your health, you need to speak to a medical professional.",
"Questions based on personal anecdotes or isolated events tend to invite speculation and more anecdotes, which are not allowed on ",
"/r/AskScience",
".",
"For more information regarding this and similar issues, please see our ",
"guidelines.",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"Respectfully, I'm not asking for medical advice. I did not comment asking for treatment recommendations or for advice on actions to take to alleviate my symptoms. I specifically asked for an explanation as to why metal touching my filling would cause sudden pain.",
"Secondly, a Google Search will show that this is a common issue, and hardly anecdotal. You will also see that, according to Google Search results, many of the explanations for this common issue point to Oral Galvanization, which is also claimed to be debunked on Wikipedia an in other search results.",
"I am simply asking for a scientific explanation for what happens when many people touch metal to their metal fillings and experience pain. ",
"As such, I ask that you reinstate the post."
] |
[
"Hello,",
"You are asking for a diagnosis. We do not address ",
"such questions",
" in ",
"/r/askscience",
" - doctors and health professionals do.",
"Cheers."
] |
[
"Does a species on Earth really go extinct every 20 minutes? This seems ridiculous."
] |
[
false
] |
[deleted]
|
[
"Most of the species that go extinct are not very widespread to begin with (and by definition they are not anymore at the point they go extinct).",
"Of course, there are also some large animals that went extinct due to over-hunting (dodos, stellers sea cow, etc.) and some dolphin species that will go extinct soon as a direct result of human activity (mostly trawl nets and pollution). These extinctions are very visible, but only a small part of the overall picture.",
"The ecosystem is undergoing rapid change due to the presence of humans. Animals are hunted and fished and plants and animals are bred and domesticated. Forests are cleared, farming land created, swamps drained, cities are built. In addition to these direct influences, there are also indirect ones like pollution and climate change. It is clear that this corresponds to the disappearance of many ecological niches and whole local ecosystems.",
"Plants as well as animals go extinct all the time. This is simply the nature of a non-static system like earths ecosystem is. New species evolve, old ones migrate or grow. This in turn changes local ecosystems. Mankind simply one example of new species that spreads over the planet and changes local ecosystems, isn't it? So is this all just the natural state of things?",
"Well, in my opinion, 'naturalness' is a meaningless word. What is certain is, that right now, the extinction rate is 10000 times as high as it's 'background level' (standard extinction rate between mass extinction events). While we certainly can't push this down to the 'normal' levels anytime soon, we should at least try to minimize our impact.",
"For more info, look at the ",
"wikipedia article for holocene extinction",
".",
"[Edit:] This is actually not my area of expertise, so take everything with a grain of salt and read the wikipedia article."
] |
[
"Also worth remembering that when ever any animal goes extinct you also lose all of it's parasites. So when you lose 1 organism you also lose many, many times more additional ones"
] |
[
"Only if those parasites are host-specific. "
] |
[
"How does algae reproduce in mountain streams without being \"flushed out\"?"
] |
[
false
] |
I've been taught that algae reproduce either asexually or through spores. How then do algal populations persist in mountain streams? Without a means of upstream dispersal, it seems that any population would be flushed downstream within a number of generations.
|
[
"Just being pedantic here, but vegetative and asexual reproduction is the same thing."
] |
[
"Have you ever taken a rock out of a stream? Algae stick to it in my. experience. Though although I don't know how the very first algae of a stream found its place every other will be hit by spores of the previous ones. "
] |
[
"Algae have 2 forms of reproduction. Asexual and sexual. The asexual form can be vegetative and can reproduce by fragmentation or budding by growing off the parent strand and then coming off and becoming independent. Vegetative reproduction is what typically occurs in the fast flowing streams. Also some algae like diatoms have adherence mechanisms that allow them to colonize the fast moving streams. Source: ",
"http://docdro.id/LZruYNt"
] |
[
"Human languages evolve and change over time. Is there any indication that the same is true of animal languages?"
] |
[
false
] | null |
[
"The only other animal that has been demonstrated to show the ability to vocalize complex and novel concepts vocally is the crow. We don't know anything about the languages (or even if you could call it a language) and dialects of crows, how complex they are, what kind of syntax they use (if they even have a syntax), we are totally ignorant there. There are a few other animals that we think can vocalize novel concepts (elephants, dolphins) be we haven't demonstrated this yet experimentally.",
"With crows, since they are creating new vocalizations for new novel concepts and teaching this to their offspring and peers, than that necessitates the \"language\" would change over time as new concepts are added (and presumably others are forgotten). I don't think what crows are doing would be comperable to humans though, it's almost impossible they are transmitting even close to the amount of data human language can, or that what they say is capable of carrying as complex of meanings. But I'd be surprised if there weren't definitive dialects and changes over time to these dialects in crow societies. I don't even see how it would be possible for this not to happen."
] |
[
"Yeah, it does beg that question. With humans we are fundamentally wired to learn language, there are behaviors engaged by parents (and other adults around an infant alot) to help facilitate language acquision in the infant. It's not only instinctual to learn language for infants and children, there are also instincts at work in full grown adults (especially parents). With crows we don't know if their use of vocalizations to label novel concepts could even be considered a language (though it wouldn't be a minority viewpoint to assert as such), we simply don't know much about it. So we don't know enough to even begin questioning if this ability to label concepts with novel calls is instinctual (like human language) or simply a biproduct of their intelligence.",
"The experiment to identify novel concept labeling on vocalizations in crows was quite simple: Experimenters harassed crows using a specific type of mask. The crows being harrassed created a new caw used to alert other crows when this mask was sighted (the call was not used when other masks were worn, and this call was not heard before or in any other context). These crows taught this new call to offspring and peers, and these other crows that never had contact with the masked assailent were seen to use this new call when aproached by an individual using a mask. That's pretty complex, somehow a small group of crows was able to not only formulate a novel call to associate with the mask, but they were able to explain what the mask looked like to peers and offspring in a reasonably accurate way so that crows that never saw the mask before were able to identify it without ever seeing it before. But so far as I know that's the only experiment done on crow \"language\". There is alot more to learn here, this is probably only the tip of the iceberg."
] |
[
"This is amazing really. It begs the question whether it is a language (dialects and therefore different languages adapted through time), or whether different groups of the bird, due to their intelligence, develop their own response to certain calls from their peers."
] |
[
"Why does the ball in this gif go in the direction it does?"
] |
[
false
] |
Here: I know the bernoulli's theorem, that where the speed is high the pressure is low and vice versa. So here when the guy spins the ball inwardly, the speed of air on the near side is higher and so the pressure should be lesser. This means that the ball must move backward,i.e. opposite to the direction it moved in.
|
[
"Here's",
" the video that gif came from. The Magnus Effect is what they're demonstrating. The video does a good job explaining what's happening, but here's a short version: the ball moves through air, but because it's spinning the interaction with the air is different depending whether the air is moving with the spin or against it. Those two different \"sides\" of the ball result in different forces on those different sides. The force on the side where air opposes the spin moves the ball in a direction (like you saw in the gif/video)."
] |
[
"Once falling, the air on the near side is actually being slowed down by the texture of the ball pushing back against the oncoming wind. This gets more pronounced as the ball falls faster. The far side air is being sped up by that side of the ball going in the same direction as the passing air. ",
"This results in the higher pressure building up on the near side of the ball, lower pressure on the far side and the ball heading outwards as a result."
] |
[
"Wait, so there was a video ezplaining an effect, and they used this as an example. Then, someone took a segment of the video, made a .gif out of it, and posted it online. Some curious soul finds it and doesn't know what's going on in it, and you link him to the original... as an explanation.",
"I love the internet."
] |
[
"How do Earth's continents move?"
] |
[
false
] | null |
[
"The continents are the parts of tectonic plates that stick up above sea level. Tectonic plates are large sections of the earth's crust that float on molten rock, the mantle. Since the mantle's heat is uneven there are convection currents which carry the tectonic plates around.",
"Here's an animation"
] |
[
"Good basic answer, but the vast majority of the mantle isn't molten rock. It's solid, but acts as a fluid over geologic time. Only very small amounts of melt are present in the mantle, mostly at divergent plate boundaries and subduction zones."
] |
[
"Do you know what causes some parts of the mantle to be hotter than other parts (referring to mantle plumes and the like)?"
] |
[
"Could we measure the age of an organism by looking at its DNA?"
] |
[
false
] |
The ends of DNA get shaved off every time they’re copied, as far as i remember. So could we measure the age of an organism by looking at its DNA? For cases where we don’t have the birthday.
|
[
"Those are teleomeres. But to do what you’re talking about would require having an sample of the DNA sequence at the literal moment of conception / first cellular division of the organism in question. As well as a known rate of teleomere loss.",
"The first is essentially impossible. The second is likely to vary for every organism and also essentially impossible to determine."
] |
[
"Not just by looking at telomeres, and not to the year by any known method.",
"Telomere shortening is not a continuous effect with a known rate, and most organisms have an enzyme called telomerase that's job is to actually rebuild those telomere \"caps\". The effectiveness of this repair process varies and can be affected by oxidative stress as well. So you're unlikely to get a very accurate estimate of age from this measure alone. ",
"A better measurement of cellular age is likely to be DNA Methylation. Check out the Wikipedia pages for ",
"Epigentic clock / Horvath's clock",
" and ",
"Senescence",
". ",
"Just as with telomere length, DNA methylation varies considerably among individuals and is affected considerably by various factors like stress and exercise. ",
"If you were to compare person who is 40 years old, but who eats healthy, exercises daily, and lives a low stress lifestyle with a 35 year old who is obese and has been working 12hr night shifts for a decade you may very well find that the 40 year olds cells are younger in terms of telomere length and DNA methylation."
] |
[
"Aren't there also external factors that speed up the rate of decay and damage, such as sunburn on skin cells?"
] |
[
"Why isn't urine more concentrated?"
] |
[
false
] |
I'm aware of what urine is and why we have to filter certain compounds out of our bodies, but we waste so much water every time we pee. Why is urine so relatively dilute? It seems like it should be much more concentrated. Out in nature, drinkable water can be hard to come by, but even when we get dehydrated we still pee out a fairly large volume of otherwise usable water which is just being used as a vessel to expel these chemicals. It seems to me that if our bodies didn't waste so much water in that process, we would need to drink a lot less water and could go much longer without drinking, which has obvious and extremely significant benefits when considering humans outside of modern civilization.
|
[
"Ammonia is not acidic it is basic."
] |
[
"Ammonia is not acidic it is basic."
] |
[
"Water intoxication",
" doesn't really directly increase blood pressure, nor does it cause cells to 'burst'. Water is stored in the body in 3 areas.",
"Inside the cells of the body.",
"Between the cells and the vessels (Colloquially called the third space)",
"Inside the Vessels.",
"If you add water to the stomach it's rapidly moved through to the vessels, but because it has made the blood hypo-osmotic in comparison to cells at such a rapid degree that it moves into them at a rapid rate, causing them to swell, not burst. This can increase intracranial pressure, which causes a number of syptoms, one of which is an increase in blood pressure with a reflexive bradycardia."
] |
[
"Do \"self rewards\" after performing a behavior stimulate more of that behavior?"
] |
[
false
] |
An example of this is a pattern of rewarding oneself after studying hard or working hard on a project actually increases the likelihood that you will do so in the future, or whether having control over the reward changes something about the result. Thanks!
|
[
"This isn't specifically about self reward, but it touches on your question about whether having control over the reward changes anything. It's been shown with humans and other animals that if rather than giving a reward every time a desired behavior is seen, you only sometimes give out the reward in a random fashion, that results in much better training of that behavior. The reason is that if the animal knows every time they do something, they'll get a reward, then they may feel comfortable choosing not to participate in the behavior at certain times if they feel they don't currently need the reward (e.g. they aren't hungry). If it's uncertain whether or not they'll get the reward, though, then they'll take every opportunity to get that reward, because who knows when they'll get another chance.",
"Emulating this might be difficult with self rewarding, though, because even if you do something like flip a coin to see if you reward yourself or not, you're still aware that your chance of getting the reward is the same this time as it will be the next time."
] |
[
"Definitely works. ",
"Here's an old study",
" showing that self-reward is effective in weight loss.",
"Rewards are very simply things that cause dopamine to be produced, which is a neurotransmitter associated with pleasure (ok, the system is a lot more complicated than that, but that's the easy way of explaining it). If you constantly associate a reward, even one you give yourself, with an activity, as long as that reward is causing a dopamine release, it should work to influence behavior. If you want more information on all the details of how an effective reward schedule works, look into what's called operant conditioning. This was a huge topic in psychology back in the '50s and basically spawned the field of behavioral psychology."
] |
[
"so good!"
] |
[
"Since it takes complex, highly evolved Enzymes to decode information from RNA, why do we consider the origin of RNA the origin of Life?"
] |
[
false
] | null |
[
"Because there are some RNA molecules that can self assemble without protein based enzymes.",
"I must also correct one point. It takes highly evolved enzymes to decode information from RNA ",
". It is believed that there once existed more primitive enzymes that were less accurate but much simpler."
] |
[
"You are referring to the ",
"ribosome",
", the enzyme that translates RNA into proteins. In some cases, RNA itself function as an enzyme. The name for this is a ",
"ribozyme",
". Specifically, there are enzymes like ",
"RNA polymerase ribozyme",
" which can catalyze their own synthesis under certain conditions."
] |
[
"Ribozymes",
" are RNA that is catalytically active."
] |
[
"If we grew a tree in a perfectly sterile environment, would it make it?"
] |
[
false
] |
As I understand, trees and plants in general greatly benefit from other organisms in an ecosystem. But imagine a room completely sterile, sterile soil and water. Would the tree grow to its full potential?
|
[
"Well, the sterile soil is where this would likely go wrong. Because, by definition, if the substrate contains no organisms it is not ",
"soil",
":",
"Soil is the mixture of minerals, organic matter, gases, liquids ",
"But if we take that soil out of the mix then you have no real impediment. I worked growing axenic plant specimens for tissue culture work. Anything from redwoods to tobacco grows perfectly fine in contained sterile environments absolutely devoid of other organisms. So long as the plant has access to the appropriate nutrients, provided mostly by the sterile nutrient solution in which it is grown, the vast majority of plants are perfectly happy and healthy; indeed, some plants grow ",
" more effectively in sterile environments, even when being prepared for field transplants.",
"A major concern becomes size, I am not aware of how one would contain a full grown redwood tree within a sterile environment. If one could acquire a large enough glass cylinder and enough nutrient media, it would be theoretically possible (though you would also need an autoclave large enough to sterilize the vessel)."
] |
[
"It would really depend on the species. Most plant species are symbiotic with either fungus or bacteria and rely on them for nutrient absorption/nitrogen fixing and they have a huge impact on plant health. I don't personally know of any trees without these relationships but the extent to which they are dependent on these relationships greatly varies depending on soil conditions and species."
] |
[
"Without supplementation, yes, it would die. The source of nitrogen for plants is ammonia produced by soil bacteria carrying out a process called nitrogen fixation. Without them, your plant can't grow. These bacteria are also responsible for the tree line seen on mountains. Above a certain altitude, the temperature is too low for these bacteria to do their job effectively and the soil gets depleted quickly."
] |
[
"If mass exponentially increases as you approach the speed of light, how is CERN stable?"
] |
[
false
] | null |
[
"A few things:",
"The mass of particle is the same no matter how fast it's moving.",
"The energy of a particle increases very rapidly with speed at relativistic speeds, although the dependence is not exponential.",
"The LHC produces beams of protons and lead-208 ions, no electrons.",
"But yes, the particles in the beam have very high energies, microscopically speaking. But if you compare their energies to macroscopic objects, each individual particle has an energy comparable to the kinetic energy of a mosquito in flight."
] |
[
"So objects do not increase in mass as they approach the speed of light?",
"Correct, mass is Lorentz-invariant. That means that it's the same in all inertial reference frames."
] |
[
"Ok, I must've gotten my facts muddled up. So objects do not increase in mass as they approach the speed of light? "
] |
[
"Which Odd-Toed Hoofed Mammals Chalicotherium Most Closely Related To?"
] |
[
false
] |
Are they most closely related to Tapirs, Rhinos or Horses? I'm confused because in this video at 6:00 the guy claimed that they belong to the same radiation as tapirs: Did he mean that they're tapirs themselves or they share a common ancestry with them?
|
[
"Its very unlikely that they were tapirs (strictly speaking).",
"Ive done a bit of reading and its controversial how they relate to other perissodactyls, different studies have them more closely related to different perissodactyls. On top of that (and this may just be my bias as a geneticist) trying to determine the relationships of animals from their morphology (bones etc) alone is pretty speculative apart from the broad relationships. For example, once we started sequencing genomes, the relationships between different mammalian orders were revised dramatically, so I don't put to much weight on the taxonomy of extinct animals even when its uncontroversial. ",
"It may be that they are a sister group of modern tapirs, as some studies suggest. But its extremely unlikely that they would be classified within the modern tapir family, all modern tapirs are from a single genus and thus closely related and share a fairly recent common ancestor.",
"Did he mean that they're tapirs themselves or they share a common ancestry with them?",
"This depends on what you mean by tapir, but even if they are a sister group I would not think its correct to call the tapirs as they would not be placed in the Tapir genus and very unlikely to be placed in the Tapir family.",
"Hope that makes some sense and doesnt make you more confused."
] |
[
"Ok, he seems more confident in the placement of them then what I saw in the literature, but I'm not expert, so happy to take his word for it! If its true that they are a sister taxa of modern Tapirs, than the question of whether they can be called tapirs or not is a bit of a semantics one, and in terms of taxonomy depends on what is the convention in the literature. Unless it has been established in the literature that they are commonly called tapirs, (again I can't see any evidence of that) I would not call them tapirs. The -oid ending means 'resembling', like asteroid which means 'star-like', so Tapiroids are animals that are 'Tapir-like'. If they are classified as tapiroids they could be described as Tapir-like, but not strictly tapirs, unless in the future they are placed in the Tapir family itself."
] |
[
"I just want to know whether or not Chalicotheres were tapirs or not."
] |
[
"Why are oxides so colorful?"
] |
[
false
] |
Recently I've began taking an interest in chemistry (specifically relating to every day life) and I've noticed that what seems to come up all the time when it comes to pigments is oxides. Within the table of the elements, out of the solid materials out there, most really aren't that colourful - so why are the oxides?
|
[
"Oxides can be colorful, but very frequently are not.",
"Examples: Aluminum Oxide, Zinc Oxide, Titanium Oxide, Calcium Oxide, silicon oxide....",
"Oxides are one of the most ubiquitous classes of compound, so it should come as no surprise that some of them are colorful. Usually this has to do with either band-like behavior of the metals leading to a visible-bandgap semiconductor or dopants which act as impurities. ",
"Examples of this: Copper(II) Oxide, Amethyst, Ruby/Sapphire, etc."
] |
[
"I wouldn't say that oxides are colorful in general, since most oxides tend to be white.",
"When you get to some of the transition metals (and the rare earths) however, the presence of extra electrons in \"closely packed\" energy levels gives rise to transitions between those energy levels that result in the absorption and emission of light in visible range."
] |
[
"This doesn't apply only to oxides. Any time a transition (or rare earth) metal binds to ligands (groups with lone pairs of non-bonding electrons), certain wavelengths of light get absorbed as the electrons in the d orbital of the transition metal either move up to higher energy levels, or move to an empty ligand orbital, resulting in the compound appearing to be the opposite color of the light that was absorbed. While using different transition metals will significantly change the color of the compound, using different ligands can also change the color due to the differing electronic conditions."
] |
[
"Why can't ethanolamines be detected by spectrophotometry?"
] |
[
false
] |
A very specific question, I know. I don't have a chemistry background, so all the research reads like a weird combination of wizardry and facts to me. I learned about ethanolamines last week. I was rather intrigued by one molecule being both a primary alcohol and a primary amine. If I understand it correctly, this molecule is literally two-faced. Now, I read about its use as a 'cleaner' and I'm thinking about experimenting. This could be the perfect molecule to use in an eco-toxicology experiment. Problem is, I need to measure the levels before and after. Before will simply be the amount I decide to use. After... well, I don't know how to measure that. This will be a field-experiment, so gas-chromatography is pretty much out of the question. Same with HPLC. The simplest way to go (I thought), would be spectrophotometric. But I can't find anything on ethanolamines. So... to make a long story even longer: Why can't amines/alcohols be measured directly through spectrophotometry? I know this question is waaaaay too specific, and I probably should just ask of professor or such, but maybe there is someone out here who might have an answer. I've got this nagging feeling I'm missing something rather obvious about this.
|
[
"Photometry is a collective term meaning ultraviolet-visible (UV/VIS) and infrared (IR) spectroscopy.",
"Ethanolamine isn't UV active because it does not have any double bonds, so it has no detectable bands in the UV/VIS region. It certainly has IR peaks, but so does pretty much every other compound. So if you have pure ethanolamine, it's certainly possible to obtain an IR spectrum. But quantification in some solvent or other matrix is difficult due to the high background signals given by the other compounds in the mixture. Thus, IR is often used for identifying pure compounds, but hardly ever for quantification.",
"As for using ethanolamine in some field experiment: no idea what you're actually planning to do, keep in mind however that ethanolamine is fairly basic (pKA of ethanolamine-H",
" is 9.5).",
"If you truly want to use ethanolamine, the best idea might be to take samples to later analyze in a lab with GC. HPLC will be difficult, since the common photometric detectors won't find ethanolamine. Refractive index detectors or a mass spec detector might work.",
"If that is not an option, tell us more about what you want to do. Maybe another organic substance is an option."
] |
[
"It's not so much about whether you can identify if ethanolamine is present in the sample so much as being able to quantify it with IR, which is the crux of the problem. While as you say, you can compare obtained IR spectra with a reference of a pure compound, quantification with IR as Greek0 says is typically difficult especially in a complex chemical matrix (such as an environmental study) because the intensity of these vibrational bands in ethanolamine could be indeterminably altered by the absorption from other amines in particular. ",
"When attempting to use IR quantitatively, you would then require extensive calibration techniques to ensure you identify how much of the absorption is distinctly ethanolamine. However, chromatography could still be a viable option as while ethanolamine may not be UV/vis active you can derivatise the primary amine to give a compound which is and run that via HPLC. By derivatisation with something like FMOC-Cl (9-fluoroenylmethoxycarbonyl chloride) or many others available, you effectively add a UV/vis absorbing \"handle\" to the molecule which will have a specific retention time and so on and so forth"
] |
[
"Amines, alcohols, and ethanolamines are most definitely detectable using spectroscopy. There are a ",
" of types of spectroscopy, of which spectrophotometry is only one.",
"In spectrophotometry, you're looking at absorption in the visible spectrum, the near-UV, and the near-IR.",
"For organic compounds, molecular vibrations are going to fall well into the infrared, while electronic transitions fall well into the UV (unless there is an extended pi-system). Visible light is too energetic to cause a vibrational transition, but not energetic enough to cause an electronic transition. A mostly-saturated alcohol, amine, or amino-alcohol is not going to absorb much in the range of ~350-700 nm.",
"If you're trying to measure something on a surface in the environment, I'd think about Raman spectroscopy. The theory behind it is a little less straightforward than spectrophotometry, but suffice it to say that this technique is well-suited to what you want to do. Unfortunately, you'd need to find a way of getting a portable Raman spectrometer."
] |
[
"How do scientists measure the diameter of a distant planet?"
] |
[
false
] |
I've been reading "Finding Habitable Worlds Around Other Stars" by Geoff Marcy and one of the graphs shows the diameters of various planets. How would somebody go about measuring the diameter of a planet outside the solar system?
|
[
"I actually remember reading this but I am not entirely sure I am remembering it correctly. They can tell what the planet's apparent diameter is from our vantage point because they measure the amount of dimming that occurs as the planet crosses in between its parent star and us. This is called the \"transit method\".",
"The planet blocks out some portion of the light of the host star, say 1%, and we can measure that with our instruments -- from that we get the planet's ",
" size.",
"But getting from apparent size to actual size requires us to know how far away the planet is from its host star.",
"But we can't really know how far away it is unless we know the planet's orbital period and the mass of the host star.",
"We know the orbital period, of course, from the transit method (we observe the 1% or whatever dimming every X years, and that's the orbital period).",
"Knowing the mass of the star is trickier and requires knowing a lot about how stars work.",
"They calculate the mass of the star using astroseismology, which involves observing the patterns of intensity changes in the light the star puts out. Those intensity changes are the result of seismic waves inside the star, and plugging that data into fancy models of how stars work tells us basically how massive the star must be for the observed seismic waves to be what they are.",
"So, once you know the mass of the star (and thus its gravity) and the orbital period of the planet, you basically can deduce how far away the planet must be from its star for the observed orbital period to be what it is. Then you have all you need to turn your ",
" size measurement into an actual real size for the planet.",
"Does the above help? And, can an actual astrophysicist or similar confirm whether I am remembering this correctly?"
] |
[
"Your post is in the right direction, but I've got something to add as well.",
"We don't need the distance between the planet and the star, the percentage is what matters. We can use the temperature of the star to deduce its size, which we use again to find the size of the planet."
] |
[
"from that we get the planet's apparent size.",
"What you describe is more like the planet's relative size to the star. Based on some pretty robust models of stellar evolution (with help from things like astroseismology), we know the size of many stars. So finding the planet's size is just a matter of comparing it to its host star.",
"Here's an example:\nIf the transit results in the star dimming by 1%, then the area of the planet must be 1% of the star's. Since area is proportional to the radius ",
" (A=pi*r",
" then the radius of the planet must be the square root of 1% of the star's radius. This comes out to the planet's radius being 10% of the star's radius.",
"Edit: grammar"
] |
[
"How is a singularity possible?"
] |
[
false
] |
[deleted]
|
[
"That's right. In fact we have almost no understanding of singularities. While they are a fairly logical extrapolation of GR - we have no physical models that can describe the behaviour of infinitely dense matter.",
"Quantum Mechanics suggests that infinitely dense matter simply isn't possible. Heisenberg's uncertainty principle says we cannot know both position and momentum beyond a certain degree - but a singularity is a mathematical point. Nor is it clear how energy (heat = kinetic energy of particles = movement) can be expressed in a singularity."
] |
[
"That's right. In fact we have almost no understanding of singularities. While they are a fairly logical extrapolation of GR - we have no physical models that can describe the behaviour of infinitely dense matter.",
"Quantum Mechanics suggests that infinitely dense matter simply isn't possible. Heisenberg's uncertainty principle says we cannot know both position and momentum beyond a certain degree - but a singularity is a mathematical point. Nor is it clear how energy (heat = kinetic energy of particles = movement) can be expressed in a singularity."
] |
[
"A singularity is a logical consequence of General Relativity taken to an extreme. However, GR only describes gravity - there are three other forces described by Quantum Mechanics. At a singularity the scale becomes one at which Quantum Mechanics is generally regarded as more relevant than General Relativity.",
"As such, a genuinely infinitely dense point of matter should be taken with a grain of salt.",
"Having said that - a singularity occurs when the force of gravity overwhelms the Strong Nuclear, Weak Nuclear and Electro-magnetic forces. While gravity is very weak in general terms compared to the other forces, it sums in a way that the other forces do not and thus sufficient mass can overwhelm the other forces.",
"On the other hand, matter heading towards a singularity takes an apparently infinite amount of time to reach the event horizon. With angular momentum thrown in it isn't clear how matter can reach the singularity to form it in the first place.",
"TL;DR our understanding of singularities lies at the extreme of two theories that fundamentally disagree with each other. And in any case there is no way of directly (or indirectly) observing a singularity. By contrast the Event Horizon (black hole bit of a black hole) is much better understood."
] |
[
"If a photon does not experience time or space, how is it able to have varying properties?"
] |
[
false
] |
Some expansion on the title question, I think an example might help clarify. Imagine a photon, from our perspective it is moving through space. During its flight it passes through a blue plane of glass (which would alter its wavelength, correct?). From our perspective, the photon was once of a "white" wavelength and now it is of a "blue" wavelength. But... from a photons perspective there is no time or space. So... was the photon always both white and blue? How does this work? Thanks!
|
[
"/r/AskScience",
"This answer is wrong and misleading.",
"Photons ",
" have varying properties.",
"As for the OP's example, there ARE white photons.",
"Consider a broadband laser emitting white light. If we choose one photon from this source, we have no information about it except that the emitter is capable of emitting all colors. Since any mode of the classical field is a valid single photon mode, this is a ",
".",
"Now, it passes blue glass. We have some information about it. It is no longer a white photon. If it was absorbed, we'd also learn some information about it.",
"You have to always consider that photons are quantum mechanical objects and sometimes exist in superposition states. Information determines what those superpositions are and how they evolve subject to measurements.",
"The way it was phrased below ",
" correct. \"A single photon cannot appear white.\" Yes, if it is measured by a wavelength-discriminating detector (the eye), then it cannot be multiple wavelengths at once. However, before it is measured, the lack of information says that it must be all colors corresponding to the distribution it was derived from. The OP is asking a question that gets to the heart of quantum mechanics and deserves a thoughtful discussion about it rather than a repetition of 1800s-style \"photons are bullets of light\" answer."
] |
[
"Photons don't have varying properties. If a photon appears to change its properties it really got absorbed by something (an electron usually) and got reemitted with a different energy, polarization or direction. It won't change any of its properties on its own.",
"As for your example, there are no white photos. What we percieve as white is a particular mixture of colors of the rainbow which our brain interprets as white based on the interaction they have with the visual perception cells in our eyes. So your example works like this: A number of photons of different colors (which visually add up to white for us humans) enter the blue glass pane. The ones that are ",
" in the color circle (which in the case of blue is yellow) get absorbed by the coloring agent in the glass, whereas the other photos pass through either unchanged or get absorbed and reemitted unchanged. What leaves the glass is light that is lacking in yellow (which you can regard as \"anti-blue\" as far as our eyes and our visual perception are concerned), and that is why we see that light as blue. ",
"Have a read ",
"here",
" for some background on how color vision works for humans. "
] |
[
"Please don't downvote this response just because you think it doesn't fit the high-school explanation of what a photon is. Please read ",
"http://www-3.unipv.it/fis/tamq/Anti-photon.pdf",
" (written by Lamb - the one responsible for discovering the Lamb shift) about what a photon ",
" means to a modern physicist before judging pfigbash's comment."
] |
[
"Is there a simple explanation of this exploit \"Heartbleed\"?"
] |
[
false
] | null |
[
"http://xkcd.com/1354"
] |
[
"To expand a little bit for people who aren't familiar with buffer overrun attacks, it's a common operation for a piece of software to be asked to produce the contents of a chunk of memory (indicated by the starting address of that chunk of memory and the size of the chunk). Properly written software should do a sanity check on the size of the chunk being requested to ensure that it doesn't start reading the contents beyond the chunk it's asked for and start reading the contents of adjacent chunks. OpenSSL neglected to perform this check in one spot and thus, if you ask OpenSSL for more memory than you're allowed to see, OpenSSL will start reading the contents of other things that it has stored in its memory and return them to you.",
"Specifically, OpenSSL does this in its \"heartbeat\" code. Part of the SSL specification is that you're allowed to make a heartbeat request to an SSL server, asking it to echo back to you whatever you like. Part of this heartbeat request is the length of the contents you want back, which is where OpenSSL neglected to make its check.",
"The most serious (IMHO) bit of memory that OpenSSL can give you that it shouldn't is its private key. OpenSSL needs to keep its private key in memory so that it can perform encryption, but it should never allow anyone else to see that private key. If you can trick it into giving you its private key (which Heartbleed allows you to do), then you can eavesdrop on communications and impersonate the server you stole the key from."
] |
[
"The most serious (IMHO) bit of memory that OpenSSL can give you that it shouldn't is its private key. OpenSSL needs to keep its private key in memory so that it can perform encryption, but it should never allow anyone else to see that private key. If you can trick it into giving you its private key (which Heartbleed allows you to do), then you can eavesdrop on communications and impersonate the server you stole the key from.",
"The private key issue is serious, but I'd hesitate from calling it the most serious, since beside capturing the private key, you need to either passively capture the communication, or actively perform man-in-the-middle attack. Both require you to take some additional steps (unless you've managed to sniff stuff over an open wifi, or hub-running lan). The ability to read session cookies (",
"see link",
") is I think even more serious, since with just one step, you can access some unsuspecting stranger's account."
] |
[
"When you grow and your birthmark stretches, how do the new skin cells know to be discolored?"
] |
[
false
] |
As you grow or get fat, your birthmark stretches. As it stretches, the boundary of the birthmark grows, and it gets filled in with new discolored skin. This doesn't seem to happen with moles for example. How exactly do discolored birthmarks expand?
|
[
"Birthmarks or Cutaneous Hermangiomas are essentially tumors, allbeit harmless in most cases. As such cell replication produces more tumorous cells. ",
"http://jamanetwork.com/journals/jama/article-abstract/656904",
" "
] |
[
"If you are referring to Poliosis Circumscripta, that isn't a birthmark. "
] |
[
"Then how do you explain my white spot of hair as a birthmark?"
] |
[
"How do we treat radiation poisoning? We can't repair the DNA damage, can we?"
] |
[
false
] | null |
[
"Acute Radiation Lethality can be broken into 3 categories: Hematologic, Gastrointestinal, and Central Nervous system. The short answer is that they only real \"treatment\" is a bone marrow transplant if you fall into the Hematologic category since it's the first stage. Usually if you've received a radiation dose to put you in Gastrointestinal or Nervous system you probably won't survive. The cells in the lining of your stomach are not very radiation resistant, when you couple that with the fact that stem cells will die before the cells lining your stomach and intestines it spells death because the stem cells will need to become the new lining of your gut. This will lead to dehydration and electrolyte imbalance. Supportive therapy like IV's hydration doesn't work since there are no cells to help regulate the flow of fluids in your intestines. The dose needed to put you into Central Nervous System is usually so high you'll die within a few days, since nerve cells are some of the most resistant cells in your body to radation. I'd be happy to answer more questions",
"source: \"Radiologic Science for Technologist\", Stewart Buschong"
] |
[
"There is an \"anti-radiation pill\" to protect against fallout, but it's not what most people assume.",
"Much of fallout's risk is not the immediate radiation, but in absorbing radioactive elements in the dust from eating, drinking, or inhaling it. It will integrate into body tissue and release radiation over the coming weeks or months it takes to flush out, and when it decays it turns into inappropriate elements for that tissue.",
"Radioactive cesium-137 and iodine-131 are the more notable offenders. Cesium chemically acts much like potassium (same column on the periodic table) which is 0.2% of the human body, and iodine-137, like any other iodine, tends to concentrate in the thyroid, which creates a risk of thyroid cancer.",
"The \"anti-radiation pills\" are fairly simple- they're a potassium iodide supplement, nothing more. They saturate the blood with nonradioactive potassium and iodine. This dilutes the pool of radioactive iodine and cesium. The body will not absorb more than it needs, and when it grabs an iodine atom to absorb it will be less likely to be the dangerous iodine-131. The ingested radioisotopes are still radioactive, but it takes a long time for them to decay. If the body does not integrate them into tissue, it will simply be excreted (peed out) in a short time. ",
"Iodine-131 has only an 8-day half-life, it's quite radioactive and unfortunately delivers a lot of its damage in the hours it takes to excrete. However, in the presence of abundant nonradioactive iodine, it's not concentrated in the highly vulnerable thyroid and does little damage overall.",
"Unfortunately, potassium iodide:",
"cannot protect against direct radiation; for example standing next to exposed nuclear material which irradiates you with beta, gamma, or neutron radiation. Or x-rays emitters, even.",
"prevent radioisotopes from decaying. It's not a radiation magnet or shield.",
"protect against radioisotopes in general- only cesium and iodine. Other notable elements of fallout like strontium-90 are completely unaffected.",
"heal radiation sickness, except in speeding excretion of cesium-137 and iodine-131 which would be helpful, if it's part of the problem. But past damage cannot be fixed."
] |
[
"Radiosensitivity is dependent on cell cycle and the ability of the cell to repair. It must first be noted that the target for radiation damage in a cell is DNA. If the DNA is damaged, when the cells tries to divide problems arise, e.g. cell death or cancer. If exposed to a high enough doses of radiation more and more cells end up dying making it more difficult for you to survive. ",
"Radiation damage can be repaired and if the cell cannot repair itself it instructs itself to commit suicide (apoptosis). These repair mechanisms need time and the right conditions to work effectively. The time component is why radiosensitivity is so highly dependent on the cell cycle. If a cell is damaged by radiation and tries to divide before it has enough time to divide, then there are issues. For these reasons, cells are least sensitive when in the S phase, then the G1 phase, then the G2 phase, and most sensitive in the M phase of the cell cycle. As a result of this, rapidly diving cells like tumor cells are very sensitive to radiation, they are so active that they do not have time to repair. Cells in the GI tract and the hair are also very sensitive. Less active cells like muscle cells are less sensitive.",
"The presence of oxygen in the microenvironment also plays a vital role in radiosensitivity. In short, the presence of oxygen interferes with repair mechanism by binding to the damaged part of the DNA, not allowing it to repair and making permanent. This is why hypoxic (low pO2) tumors are harder to treat with radiation, there is no oxygen to \"fix\" (make permanent) the damage and allows the cells to repair themselves. ",
"I can keep on but that's roughly how radiosensitivity is defined"
] |
[
"Are superconductors protected from EMPs?"
] |
[
false
] |
What would the effect of an EMP be on a superconductor?
|
[
"Ideal SC materials would shield their own interiors against any value of EMP.",
"But real SC materials have a threshold current density where, if exceeded, the material switches to normal conductivity. That's why the currents in the surface of an SC block aren't infinitely thin, and why we can't transmit tera-amperes on SC wires thinner than spiderweb.",
"A large enough EMP might exceed the threshold and become trapped (pinned) in the SC material, and leave it with a large circulating current and large static b-field."
] |
[
"What is the current density necessary to overload a typical superconductor used today? Btw have you done your phd in elec eng?"
] |
[
"The same as an EMP hitting a wire- a large current spike. Even larger though, since a superconductor has no resistance.",
"It's not the conductors you worry about in an EMP situation, it's the semiconductors, which cannot handle large voltage/current spikes. It's npt the wires connecting microchips, but the chips themselves that are of concern."
] |
[
"Are animal products bad for you?"
] |
[
false
] |
[deleted]
|
[
"This is a juvenile way to respond."
] |
[
"This is a juvenile way to respond."
] |
[
"Um, no. You can get Vitamin B12 through vegan B12 supplements. And the body does recycle its own B12 - I got a B12 blood test and my levels were well within the normal range.",
"Also, the fact that vegetarians and vegans can live just as long as meat-eaters is sufficient enough in itself to ",
" that you don't need meat to live. I'm not even trying to make the stronger claim that they live longer than meat-eaters. "
] |
[
"Why is it I can bear the sunlight fine with one eye open, but I have to squint like Mr McGoo with both, if I've been inside? (crosspoint)"
] |
[
false
] |
Crossposting this in hopes of more people, with better knowledge, having an answer: I find it odd that if I've been indoors, and I enter the waking world, I can have one eye practically all the way open and be fine. No tearing up. No sun-blindness shock. No problems. But the minute I open the other eye, it's a complete overload, an I go back to my Popeye face? I'm assuming it's just too much for our eyes/brain to process at one shot, but why would that be? Any takers for a nerdy explanation? Link to original (I hope...):
|
[
"This is called photophobia. It's particularly severe in some medical conditions (e.g. migraine), but (almost) all of us experience it in the sort of situation you describe, e.g. waking up in a dark room, and immediately going into a bright light.",
"It turns out that this whole phenomena is poorly understood. For instance, is photophobia mediated by the usual pain sensing neurons in your body, ",
" the neurons that convey visual info to your brain? At first glace, the former is more complicated, since you need a story for how the pain sensing neurons \"find out\" that you're looking at a bright light, and this story will probably involve ",
" the neurons used for vision -- at least the ones in your eye.",
"~~~~~~~~~~~~~~~~~~~~~~~~",
"First off, a couple of interesting anecdotes (the second one being unreputable, but still fun) to ease us into the topic:",
"(1) There's a rare condition called Congenital insensitivity to pain (CIP) that selectively effects pain neurons. However, other neuronal functions, like motor control, vision, hearing, cognition, are all (largely?) intact. CIP folks can occasionally feel certain types of pain, though. It's an interesting topic, because these sorts of pain might therefor be mediated by non-pain neurons. Danzigera & Willera(, 2005. Pain 117) have a case study of a CIP woman with a headache titled \"Tension-type headache as the unique pain experience of a patient with congenital insensitivity to pain\". In introducing the case, they write that",
"Despite partial or total sensory loss for pain, many patients with CIP can experience pain during their life, especially in HSAN I (Dyck, 1993, p. 1069). Such patients can have phantom pain in amputated extremities, lancinating pains due to inflammation within nerves containing actively degenerating fibres, mechanical allodynia in partially denervated areas and stimulus-independent pain that may be of central origin (anonymous reviewer, personal communication). We report the case of a 32-year-old woman with a severe and generalized congenital insensitivity to pain caused by HSAN, who experienced physical pain for the first and unique time in her life shortly after the sudden loss of her brother.",
"They don't mention photophobia, here (either in the examples of pain in CIP, or for this woman \"who experienced physical pain for the first and unique time\"). That's ",
" the omission unless CIP people don't experience photophobia. The authors didn't simply ignore or forget about the phenomenon of photophobia, either: They specifically asked if she experienced it during her headache, and she didn't.",
"If people with CIP don't experience photophobia, then that strongly suggests that photophobia is mediated by the usual pain sensing neurons in your body, ",
" the neurons that convey visual info to your brain.",
"(2) Someone caliming to have CIP ",
"posted an AMA awhile back",
". ",
"I specifically asked about photophobia",
", and he said he didn't experience it.",
"(3) Amini, Digre, and Couldwell's 2006 \"Photophobia in a blind patient: an alternate visual pathway\" (Journal of Neurosurgery, 105)",
"In this report, we describe a blind patient with a history of pituitary adenoma and apoplexy who suffered from photophobia. [...] On physical examination, the patient had no light perception in either eye; however, she reported discomfort in her eyes with exposure to light. The discomfort was so severe that the room lights had to be turned off and the windows covered. The patient’s pupils were 9 mm and nonreactive bilaterally.",
"This person is completely blind, to the extent that her pupils don't constrict in response to light. This is because she has a big tumor (pituitary adenoma) crunching down on the neurons travelling between the eyes and the brain. Yet, she experiences photosensitivity. Clearly, the usual pathways for sending light info back to the brain are unnecessary for photophobia. They say as much, later.",
"The most likely anatomical localization of photophobia is at the site where the visual and pain pathways converge. The signaling pathway for photophobia seems to be anatomically and functionally different from the neural pathway associated with vision. Initially, it was thought that functioning optic and trigeminal nerves were needed for photophobia. However, by demonstrating the presence of light sensitivity in patients with a damaged optic nerve, Custer and Reistad showed that a functioning optic nerve is unnecessary for photophobia symptoms.",
"Nonetheless, trigeminal innervation of the eye and brain does play an important role in photophobia. Lebensohn showed that an intact trigeminal nerve is necessary to experience the disorder. Eckhardt and colleagues showed that direct irritation to the trigeminal afferents of the eye surface (cornea and iris) can produce photophobia when those structures are exposed to light. They concluded that surface sensitivity must be present for the disorder to occur. Moreover, direct irritation to a nonocular portion of the ophthalmic branch of the trigeminal nerve can also induce photophobia. These authors injected sodium chloride into the frontalis muscle above the supraorbital margin and concluded that irritation of the trigeminal nerve—anywhere along its course or its ophthalmic division—can produce increased light sensitivity.",
"So, it looks like trigeminal innervation is the key. ",
"But the mystery remains... ",
"In mutated blind mice with near-complete degeneration of rod and cone photoreceptors, most of the nonvision lightregulated functions such as the circadian clock, pupillary light reflex, and photic suppression of melatonin have been retained despite the absence of vision. Recently, Berson, et al., identified unique inner retinal ganglion cells that function as photoreceptors providing photic information to the brain. These authors specifically showed that these retinal ganglion cells provide nonvisual photic information to the circadian systems. [...] Perhaps in patients who have no visual photic perception, as in the patient in the present report, the retinal ganglion cells function as photoreceptors providing the photic signal to the hypersensitized trigeminal system. Although the specific site of interaction between the retinal ganglion cells and the trigeminal system is not known, one possible site can lie at the retinal level where the ophthalmic branch of the trigeminal system provides rich afferent enervations of the choroid and blood vessels of the retina.",
"~~~~~~~~~~~~~~~~~~~~~~~~",
"If photophobia were simply a matter of light intensity, the relationship between light sensitivity and color (e.g. how intense the red vs. green light must be for us to see it) should have the same patterns as the relationship between photophobia and color (e.g. how intense the red vs. green light must be for someone to squint in pain). This also should happen if our normal photoreceptors (rods and cones) are responsible for photophobia.",
"However, photophobia is presumbed to have an evolutionary advantage. Crudely: keeping your retina from getting a sunburn. In this case, photophobia should be greater for lower wavelength (higher frequency) light.",
"This was measured in a small 2003 study by Stringham, Fuld, and Wenzel, called \"Action spectrum for photophobia\" (Journal of the Optical Society of America A, 20(10))",
"After accounting for the absorption of light by (non-vision-related) pigments in your eye (which tend to absorb high-frequency/low-wavelength light that can damage tissue), they see a ",
" relationship between wavelength and photophobia: Doing their best adjustments to try and equate things, lower-wavelength (more potentially-damaging light (violets)) light hurts most.",
"(an interesting aside: in that paper, the authors mention some hypotheses that pupil constriction is related to the pain. That is, you perceive bright light, this causes your pupil to constrict, and rapid constriction might be painful. ...This hypothesis is probably wrong, esp. because of cases of photophobia and unreactive pupils in bind people, but it's interesting to see how creative people were at trying to figure out how the light-insensitive trigeminal system is responding to light.)",
"~~~~~~~~~~~~~~~~~~~~~~~~",
"In this paper ",
"(pdf)",
" the authors proport to identify, in rats (in gritty detail), the neuronal link between light perception and pain. Just glancing at it, it looks really interesting. Basically, though, ",
"In this paper ",
"(pdf)",
" they argue that melanopsin-positive intrinsically photosensitive retinal ganglion cells (ipRGCs) are responsible. These differ from your normal photoreceptors (rods and cones) in that they don't help you see, per se, but instead help influence pupil responses to light and entraining your circadian rhythms to light. It's not a bad argument... (as they reference) people who have lost most of their normal photoreceptors due to retinitis pigmentosa still show photophobia (but people e.g. that have had both of their eyes removed, do not). "
] |
[
" (I went over the word limit!):",
"I'm assuming it's just too much for our eyes/brain to process at one shot",
"Your brain is processing just fine. It's more that a certain level of stimulation for the trigeminal nerve triggers the sensation of pain. Opening your other eye (or stimulating other parts of the trigeminal nerve) puts you over the threshold. This sensation of pain would have some evolutionary advantages (but, as always, difficult to link this to evolution in any non-speculative way).",
"This is an odd phenomenon, because your pain pathways aren't themselves light sensitive (no photopigments), and the light-sensitive pathways aren't themselves pain-causing (if they were, there would be different results for retinitis pigmentosa blind people, the lady with pituitary adenoma shouldn't be photophobic, and the color-to-pain relationship would match the color-to-light-sensitivity relationship). So, the pathways must be linked somehow. Based on available data, it appears that intrinsically photosensitive retinal ganglion cells detect light, and (somehow) convey this information to pain pathways neurons. This communication happens somewhere in your eye, not back in your brain."
] |
[
"So some animals have pupils that dilate independently of each other. Humans do not. So one eye open and one close gives an average intensity that isn't so bright. Both eyes open give a much higher average intensity. While I don't know for sure, I would assume that the other physiological responses you describe as sun shock operate on the same basis. ",
"You can test this yourself by being in a bright room with a mirror. If you close one eye and look at the pupil of the other, and then open the one eye, you'll notice that the pupil of the eye that was open the whole time will get smaller as the other eye opens, even though there's no change in the light going in that eye."
] |
[
"Do we have any reason to believe multiple universes actually exist?"
] |
[
false
] |
Or is the theory more just kind of a "what if" scenario?
|
[
"There's actually several hypotheses that may be described as multiple universe models. All of them, at least for now, are either purely speculative or are simply conceptual tools. However, I wouldn't describe them as simply \"what if scenarios.\" They were all developed to better understand or better model known physics. Some may be testable (eventually) and some will never be.",
"Three of the main ones are:",
"The infinite Universe, as mentioned by rmxz. Basically, the Universe is probably infinite, but the part we can observe and interact with, our ",
", is finite and always will be. So it stands to reason that their are other causal domains out there that will never intersect ours. Those may as well be other universes, in a sense. Even if our Universe is finite, there are almost certainly \"outside\" regions like this.",
"The many worlds interpretation of quantum mechanics, as mentioned by DevestatingAttack. This is actually more of a conceptual tool than a theoretical prediction.",
"Brane theory. This arose out of string theory. The idea is that our Universe is the (10-dimensional) surface where two higher dimensional structures called ",
" collided. Since branes collide all the time in this \"brane world\" (of which our Universe is a tiny part), universes should be forming all the time.",
"Here's a Wikipedia article."
] |
[
"There are multiple \"mainstream interpretations\" of quantum mechanics, which are basically hypotheses that are generated in an attempt to explain what's happening with quantum phenomena. One of these is the \"many-worlds\" interpretation. While that interpretation is mainstream, so far there is no solid reason to prefer that interpretation to the Copenhagen model, which has long been the most popular. Until more theoretical work is complete it's impossible to rule out Many-Worlds as a consistent interpretation of quantum mechanics. "
] |
[
"Dr. Andrei Linde from Stanford gave a talk at a physics colloquium a few weeks back. He discussed the 30 year cosmological theory of universe inflation. It is essentially based around the idea that the premature universe experienced a stage of extremely quick expansion (referred to as inflation) in a vacuum-like state. The very existence of this phase has apparently solved several problems of the original big bang theory.",
"It was this inflationary theory that provided several testable cosmological predictions. As of now, all of these predictions are in a good agreement with the available observational data. His inflationary theory is actually a variant of cosmic inflation, which proposes that the false vacuum is eternally inflating in exponential growth powered by repulsive constant random zero point dark energy of negative pressure. He compared this false vacuum to a supersaturated steam in which liquid bubbles of more stable vacuum form Higgs-Gladstone fields that describe the coming together of the pre-inflationary random dark energy into a smooth fabric of curved spacetime. ",
"According to Linde, our universe is but a mere casual part of a single bubble, and there are something like 10",
" bubbles. This, in fact, led to the multiverse portion of his talk which claims there to be 10",
" universes like ours on a single bubble which is more like an expanding infinite sheet than a finite spherical surface (picture a flattened and stretched soccer ball). ",
"His theory, in combination with string theory, leads to a picture of the universe that consists of many exponentially large parts with different laws of physics operating in each of them. This was a very interesting talk to say the least. "
] |
[
"Why did humans evolve the visual spectrum to what it is?"
] |
[
false
] |
I know other animals can see parts of the electromagnetic spectrum that are invisible to us and presumably we can see parts that other animals cannot, so why is ours or any organism's vision restricted to what it is?
|
[
"This article tackles precisely this question, though you might not be able to access it unless you have an affiliation with an institution that has a subscription, or you yourself are subscribed:",
"http://iopscience.iop.org/0031-9120/42/1/002/pdf/0031-9120_42_1_002.pdf",
"I can summarise for you though; there are a number of reasons. Primarily, it's to do with the emission spectrum of the sun: This provides different intensities of light at different wavelengths, and objectively, it's a fairly simple step to assume evolution would favour the ability to see the most abundant wavelengths, since those would provide the most utility.",
"Reasons we can't see far into the UV spectrum include the fact that photons with shorter wavelengths (towards the UV end of the spectrum, and beyond), have significantly higher energies. For us to see, a photon much be absorbed by a molecule in your eye, and affect its energy level in a way that can be reversed. UV radiation is simply too energetic, and will damage the molecule in the eye, and furthermore, the tissues in the eye.",
"Infra red radiation on the other hand, doesn't really have quite enough energy, in comparison with chemical bonds. Also, from a more physics-related perspective, infra red radiation has far longer wavelengths, which would make creating a small system for focusing would be very difficult. If you want to detect big wavelengths, you need a big lens and a big detector; that's why radio telescopes are made up of many ",
" dishes. Focusing a long wavelength with a small lens will also lead to optical aberrations."
] |
[
"I have a point to add. Naturally, for eyes to work (at long ranges) they have to operate at wavelengths where the atmosphere is transparent. From the wikipedia article on the visible spectrum, ",
"this diagram",
" shows the transparency of the atmosphere at different wavelengths. As might be expected the visible spectrum lies around a local minimum.\nNow as can be seen, the atmosphere is even more translucent at radio-frequencies. However as the parent post points out, radio-eyes needs to be huge in order to work which would not be a feasible evolutionary path to take.",
"I can't access the article, so forgive me if I just reiterate points in the article."
] |
[
"For us to see, a photon much be absorbed by a molecule in your eye, and affect its energy level in a way that can be reversed. UV radiation is simply too energetic, and will damage the molecule in the eye, and furthermore, the tissues in the eye",
"Don't atoms in our retinas (and skin) absorb the UV photons and jump to an higher energy state regardless of the information being discarded?",
"My guess is that if they didn't, UV radiation would be harmless. What am I missing here?"
] |
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