title
list | over_18
list | post_content
stringlengths 0
9.37k
⌀ | C1
list | C2
list | C3
list |
|---|---|---|---|---|---|
[
"Is a \"global compass\" a marketing gimmick or is it true that most compasses are \"balanced\" for the portion of the earth they're used in?"
] |
[
false
] |
A friend of mine (in the US) is buying his daughter a special "global compass" for her trip to Australia. He says that the earth's magnetic field varies so much that a compass needle that's balanced for the US will get stuck in Australia. Is this true? EDIT: I'm not referring to declination i.e. the difference between magnetic north and true north which varies based on your location. The claim is that "the horizontal and vertical components of the earth's magnetic field vary considerably in different locations, a compass needle that "balances" perfect in North America will drag or stick in South America."
|
[
"http://en.wikipedia.org/wiki/Compass#Compass_balancing",
"You're right in your explanation of how compasses work, but wrong about compass design. Simple compasses don't read well off the horizontal plane, so balancing must be done to make sure they don't get stuck when held flat."
] |
[
"http://en.wikipedia.org/wiki/Compass#Compass_balancing",
"You're right in your explanation of how compasses work, but wrong about compass design. Simple compasses don't read well off the horizontal plane, so balancing must be done to make sure they don't get stuck when held flat."
] |
[
"No, but they also used very inaccurate compasses and knew that they were using very inaccurate compasses. This is why they mostly used celestial navigation. Compasses were for rough direction finding while walking around between taking more accurate measurements.",
"EDIT: This was in response to someone claiming that this must be a marketing ploy because early explorers 'clearly' (unsourced) didn't switch compasses while travelling the world. I suspect that this same person also downvoted my main comment below."
] |
[
"Does the body produce Vitamin D in the presence of moonlight similar to sunlight?"
] |
[
false
] | null |
[
"No, Vitamin D requires UV radiation to produce, and moonlight has negligible amounts of this. See:",
"http://legacy.adsabs.harvard.edu/full/1974Moon....9..295C"
] |
[
"It‘s the ultraviolet portion of the Sun’s spectrum that causes vitamin D production in skin cells. Moonlight is merely reflected sunlight, so if the Moon reflects ultraviolet it will also cause vitamin D production in the skin, though to a far smaller degree since the Moon is much much dimmer than direct sunlight."
] |
[
"It‘s the ultraviolet portion of the Sun’s spectrum that causes vitamin D production in skin cells. Moonlight is merely reflected sunlight, so if the Moon reflects ultraviolet it will also cause vitamin D production in the skin, though to a far smaller degree since the Moon is much much dimmer than direct sunlight."
] |
[
"Is holding your breath as an infant a learned reaction or one you are born with?"
] |
[
false
] |
Got into a heated argument with my biology teacher whether or not it's one you are born with. She says that it is learned because when a baby gets water in it's lungs it "learns" to not do so again.
|
[
"The Mammalian Dive Reflex is what causes babies to hold their breath in water. The sensation of cold and pressure on the face, among other things, triggers an involuntary breath hitch, which passively leads into breath holding. Keep in mind, babies develop in a liquid medium without breathing, since they get all their oxygen via the umbilical cord, so their ability to breathe ",
" is \"learned\" immediately after birth.",
"Human babies are born with many reflexes, including the mammalian dive reflex. Newborns don't have the conscious, logical ability to connect the unpleasant stimulus of aspirating/choking on water to the idea that ",
" so I think the idea that they would be able to \"learn\" not to try to breathe underwater is silly."
] |
[
"Most newborn infants instinctively hold their breath underwater. But this instinct drops out by around 6 months and they have to relearn it.",
"So depending what age you are talking about, you could both be right.",
"Pedroso, F. S., Riesgo, R. S., Gatiboni, T., & Rotta, N. T. (2012). The diving reflex in healthy infants in the first year of life. Journal of child neurology, 27(2), 168-171."
] |
[
"Babies don’t develop without breathing, they “breathe” the amniotic fluid to develop their diaphragm. They also hiccup a bunch for the same reason. When they are born and first breathe in air all the liquid that was in their lungs gets absorbed into the blood stream.",
"You are right that they get all their oxygen from the placenta though."
] |
[
"How does a photon provide a physical force to objects like solar sails when it has no mass?"
] |
[
false
] |
[deleted]
|
[
"The momentum."
] |
[
"what is p?"
] |
[
"what is p?"
] |
[
"According to a recent study at Oxford, only 8.2% of DNA is functional. In theory, could we remove all the 'junk' and create a more efficient genome?"
] |
[
false
] | null |
[
"Would you mind posting the article? I'd like to read it. ",
"In the meanwhile, look up \"junk\" or \"non-coding\", it's actually believed to be more useful than one might initially think. And also, just because we don't know the biological function, doesn't mean it doesn't have one. :-)",
"http://www.scientificamerican.com/article/hidden-treasures-in-junk-dna/"
] |
[
"Efficient in terms of cell division, yes probably. DNA replication goes incredibly fast for how many bases need to be duplocated, but it does still take hours to finish. Bacteria given lots of extra plasmids to copy divide slower than thise that just have their own chromosomes to copy.",
"Efficient in terms of other things, probably not. Genes are activated based on sequences relatively close to the start of the gene, which transcription factors go right to, they don't read through from the beginning.",
"You'd also expect if it were going to be much of an advantage and not much of a disadvantage that evolution would have already done it. Doesn't prove it of course, but the fact that there are a lot of organisms out there with a lot of DNA suggests it's not much of a burden.",
"Getting back to the cell division thing, cells dividing faster alone would likely mess up development. For one thing, the embryo would probably run out of nutrients faster, unless placental development were also sped up."
] |
[
"No, not all. That seemingly junk DNA is what allows variation and epigenetic regulation. Worms have ~ 20,000 genes and humans have ~23,000 genes. Humans and worms have a lot of the same genes. We also have a lot of repeats of the same genes. One role the repeats have is to be able to mess up or experiment with new variants of genes without messing the whole organism up. It's tough to mess with a vastly complex organism without it having a number of fail-safes.",
"Another role is in the form of promotor and silencer regions. Basically a Cis protein can bind to a trans-acting element which is a region upstream or downstream from a coding sequence that will help the RNA polymerase complex form faster or block it from forming at all. In this way, that non-coding junk is actually a big player in affecting how much of each protein is made. This is a hug deal when you are a complex organism comprised of protein after protein building blocks.",
"We could remove a lot of DNA without huge developmental impact, but in doing so we would certainly lose some ability to evolve as a species.",
"edit: ",
"http://en.wikipedia.org/wiki/Noncoding_DNA",
"\nhere is a fuller answer. \"Initially, a large proportion of noncoding DNA had no known biological function and was therefore sometimes referred to as \"junk DNA\", particularly in the lay press. However, it has been known for decades[citation needed] that many noncoding sequences are functional. These include genes for functional RNA molecules (see above) and sequences such as origins of replication, centromeres, and telomeres.\""
] |
[
"How much is known about Oarfish?"
] |
[
false
] |
It seems, to the casual observer, that there has been a recent rash of Oarfish washing up on beaches. How unusual is this? Any indication of this being something more, like perhaps a result of the deep oceans warming? How much do we know about these strange creatures?
|
[
"Not a terrible amount. We know for a fact that oarfish are pretty well distributed around the oceans of the world because they've been historically washing up everywhere for hundreds of years. The sea serpent is a good example of sailors mistaking the oarfish for a monster.",
"Oarfish, however, like other deep sea fish, are tough to study for the reason being that they are deep sea fish and usually they they are not particularly good eating. We know best of the fishes we tend to eat the most of. However, there have been fishermen that have caught these guys while recreational fishing. They are a nice catch.",
"Records for oarfish in the scientific realm tend to be based off only what people bring back to the laboratory for examination. I remember one report from a Croatian scientist where he cites that in 10 years, only 4 records of oarfish had been written up for that region in the Adriatic sea. Crazy if you think about it. ",
"Because we know nothing really about the life of oarfish, we can only postulate on what's going on. However, I think the current spate has more to do with the fact that news spreads fast and when the media picks up something juicy, they'll run with it. As far as I know as a fisheries scientist, this isn't abnormal at the moment. It could be that the oarfish are just doing really well and that more are dying because there's just more. Or there could be something going on in terms of bad environment in the deep sea. We really don't know because other than morphometric and occurence data... nothing's really been done to intensively study the life history of these large animals. "
] |
[
"This happens all the time in the fisheries realm. Fish are weird animals and they come in all kinds of shapes and forms. An animal that's about 40 feet long and is not a whale, a shark, or a jellyfish is just too cool to pass up. It's also this kind of exposure that helps us expose these animals to the public spotlight for conservation efforts.",
"So as much as the media may pick up stuff like this to warrant us being concerned that many are dying, the other side of the coin is that it helps us be aware that, \"Hey, these animals exist too!\"."
] |
[
"On slow news days, the media LOVES reporting stuff like this. \"Big dead fish washes up on the beach\" becomes \"Mysterious deep-sea monster discovered off the coast!\"."
] |
[
"Question per Richards Dawkins book: Is glass a liquid with very high viscosity or a solid?"
] |
[
false
] |
Per Richards Dawkins book "The magic of reality" on page 78 or so, he states that glass is a liquid with a very high viscosity. I have read studies previously that this was a myth due to cites sources being incorrect. (Medieval church windows being thicker at the bottom, however, there were indeed designed this way.) so... Solid or liquid? So based on the multitude of responses I get the general feeling that the answer is something like "special case solid." Followup; Was Richard Dawkins in error to state it as a fluid?
|
[
"Yay! Something right up my specialty! This never happens!",
"So here is the deal: The problem with the terms Gas/Liquid/Solid is that these are forms of matter, they are not ",
" of matter. The distinction that I am making seems trivial, but the difference I am drawing is whether or not you're in equilibrium. Gas/liquid/solid is a statement about the properties of a material. Gas/liquid (",
"fluids",
", more precisely) flow on fast time scales (note the use of the word fast, it will come up later) and will change their shape to accomodate their container. ",
"Solids",
" are rigid and resist changing shape.",
"Glass is, under those definitions, clearly a solid. Its rigid and it resists changing shape.",
"So why the constant confusion on this issue? It goes back to the question of equilibrium. When most people talk about solids, what they really are thinking about are ",
"crystals",
". Crystals are equilibrium solids -- that is to say, they are solids that are in thermal equilibrium and obey the laws of thermodynamics. That doesn't mean glasses can't be solids too!",
"Glasses, both common window glass and all other variations, are ",
" in equilibrium, and are made by cooling liquids below their melting point. Instead of crystallizing, you get a ",
"supercooled liquid",
". As you continue to cool that liquid, eventually the molecules are no longer able to respond to the changes in temperature (thermal expansion) on the timescale of your cooling. We're not talking about fast cooling either -- my experiments, for example, use 1 degree per minute. The point at which the liquid stops being able to keep up is dependent on the rate at which you're cooling (which makes sense because of the temperature dependence of the motion of molecules and is usually measured by ",
"dielectric relaxation",
"). Whatever that temperature happens to be is called the ",
". Below that, you have a glass. Glasses ",
" obey the laws of thermodynamics, and they are not in equilibrium.",
"Regarding the viscosity thing: One of the great unsolved mysteries in condensed matter physics is the origin of the ",
"glass transition",
". I phenomenologically described it above, but no rigorous theoretical treatment has fully managed to predict it. Even the correlation with molecular motion times isn't perfect from system to system.",
"One of the original and long standing pieces of thought on the glass transition is that it would be caused by the viscosity of the material growing extremely large at whatever temperature the material was at, so that it would behave like a solid on the time scale of working with the material. Viscosity, via the ",
"Debye-Stokes-Einstein relation",
" relates directly to molecular diffusion and might give you an idea of how molecules were moving based on a bulk measurement. This relationship, however, is also qualitative and does not fully explain why the glass transition happens."
] |
[
"Thanks for the awesome response. I immediately thought about the famous ",
"\"Pitch Drop Experiment\"",
", which is actually still ongoing (there used to be a webcam set up to view it, but I don't have the time now to look for the link). Essentially, to prove that certain \"solids\" are indeed just supercooled liquids, as you define them, Dr. Thomas Parnell (UQD) took tar pitch, let it settle into a funnel, and then let the tar pitch slowly drip out of the bottom at a rate of roughly 1 drop per decade. The interesting thing is that tar pitch is essentially a solid. Like glass, you hit it with a hammer, and it shatters."
] |
[
"I'm going to allow this, because its awesome."
] |
[
"If a pregnant woman is given a vaccine does the unborn child also gain immunity?"
] |
[
false
] |
Just kind of popped into my head.
|
[
"For some, yes. Flu shot and whooping cough vaccines provide some protection to the unborn baby for a period of time after birth (e.g. 6 months). That is part of the reason that pregnant women are encouraged to get those two vaccines while pregnant. Not sure about others."
] |
[
"Live vaccines such as the MMR (measles, mumps, and rubella) vaccine and the varicella (chickenpox) vaccine are contraindicated in pregnant women due to the theoretical risk of transmission to the fetus."
] |
[
"To be a little more specific, the vaccine doesn't pass directly to the baby, like through the placental barrier. The mom gets the vaccine, and the antibodies she develops from having had the vaccine will then pass through the blood supply to the baby, giving the baby some natural defenses. Babies don't have significant immune system responses at birth, so those defenses aren't long-lasting, and babies are scheduled for their own vaccines a few weeks after birth, once their systems are strong enough to handle receiving the vaccines and their systems are prepared to replicate antibodies of their own."
] |
[
"Why does RNA have Uracil instead of Thymine?"
] |
[
false
] | null |
[
"Unfortunately, you've got it backwards and it's a common misconception since we make RNA off our DNA. However, a better question would be Why does DNA have Thymine instead of Uracil?",
"RNA is considered the evolutionary precursor molecule to DNA. RNA is simpler in structure than DNA (single helix vs double) and not as stable. An unstable genome is not conducive to hardy life. If you take Uracil and add a single methyl group, it becomes Thymine. The methylation changes the chemical structure allowing DNA's double helix to form properly. ",
"Additionally, the removal of Uracil from DNA increased the replication efficiency. From Wiki:",
"Uracil is rarely found in DNA, and this may have been an evolutionary change to increase genetic stability. This is because cytosine can deaminate spontaneously to produce uracil through hydrolytic deamination. Therefore, if there were an organism that used uracil in its DNA, the deamination of cytosine (which undergoes base pairing with guanine) would lead to formation of uracil (which would base pair with adenine) during DNA synthesis. ",
"Uracil-DNA glycosylase",
" excises uracil bases from double-stranded DNA. This enzyme would therefore recognize and cut out both types of uracil – the one incorporated naturally, and the one formed due to cytosine deamination, which would trigger unnecessary and inappropriate repair processes.",
"The simple change allowed for an extra layer of genetic data storage. DNA is like an archive. Specific enzymes read the archive and copy it down on mRNA. mRNA is the working copy which travels to the ribosomes. The ribosome (also made up of rRNA and proteins) is a copy center reads the working copy and prints a protein with the help of tRNA. Several ribosomes can read a single mRNA strand at the same time, they all start at the same end due to the way the mRNA fits into the ribosome. After a short while, the mRNA deteriorates. The data is lost, but it doesn't matter because the info still exists back in the archives of DNA and the protein(s) are made."
] |
[
"Just to add on something, you said \"RNA is simpler in structure than DNA,\" but the complete reverse is true. Infact, there are a large variety of RNAs in the cell which involve themselves in essentially every biological process known, and adopt complex secondary and tertiary structures which can give them functionality (including catalysis) of a level which is more usually associated with proteins. "
] |
[
"It may be a simple matter of difference of opinion, but I feel that the 6 foot long strand of double helix DNA, wrapped around histones, rolled up into nucelosomes, further coiled into a chromatin, and then supercoiled into chromosomes to fit inside the nucleus of the cell is a more complex structure than the on-average 200 nt in length RNA. RNA does have a myriad of forms and functions I completely agree, it is a much more versatile molecule. The versatility of RNA is hand in hand with its instability. RNA is an excellent molecule for its job, otherwise it wouldn't be ubiquitous. As a stable store of genetic material, though, a more complex structure was necessary.",
"This",
" has some cool visualizations. "
] |
[
"Why don't we shield exposed reservoirs?"
] |
[
false
] |
Whenever we have droughts I always see news articles with shocking pictures of reservoirs at their lowest levels yet. But they are always fully exposed to the blistering sun. Why don't we cover them with reflective material when there is no rain? Wouldn't this significantly reduce evaporation?
|
[
"i think with questions like these its best to think of a simple cost vs benefit system.",
"so the costs are:",
"-it will cost a lot of money to cover the lake.",
"-it will cost a lot of money to maintain the cover, be it either a dome or some form of fabric laid on the top.",
"the benefits:",
"by taking rough numbers you can see that instead of covering the reservoir and improving the capacity by 5%-10%. You could spend that money on another reservoir and increase capacity by 100%."
] |
[
"Some places do, but in most cases the added cost and maintenance of the balls seem to be considered more than is reasonable to put the cover into place.",
"I have heard of municipal drinking reservoirs doing that, but can't find a link back to that article, so here is a ski resort, and a manufacturers websites for reservoir covers:",
"http://www.prnewswire.com/news-releases/ski-resort-first-mt-baldy-ski-lifts-adopts-unique-reservoir-evaporation-reduction-method-234061171.html",
"http://www.awtti.com/reservoir_floating_cover.php"
] |
[
"Yes. Water quality would diminish greatly, requiring additional effort to purify for drinking. Maintaining the reservoir as a fresh water habitat is essential to keep the water from turning into a cesspool.",
"The real issue with the reservoir being at their lowest levels is usage, without resupply. We are using the water without it being restocked by rain way faster than any loss due to evaporation. ",
"Adding to the issue are areas that are using the water from reservoirs that cannot sustain themselves. Los Angeles is a great example of this. There are more people in LA than fresh water available, so water sources from other areas are tapped, and diverted into reservoirs for LA, which intensifies a droughts effects."
] |
[
"Why do the prongs on an electric plug normally stay cool even after heavy use?"
] |
[
false
] |
[deleted]
|
[
"The prongs are made of a pretty non-resistive metal (copper perhaps). Resistance would generate heat and waste energy, both of which would be terrible qualities in a plug. The metals and wires chosen are designed to cause as little resistance as possible, for safety and to maximize the power usable by the device (your vacuum, in this case)."
] |
[
"The prongs are generally made of brass, which is an alloy of copper and zinc."
] |
[
"Not only that, but they have considerable more mass in them than the wires that they connect. If your fuses/CBs didn't function, you would melt the wires before you would see any damage/heat on the (relatively speaking) massive prongs of the plug."
] |
[
"Is there a certain pitch that humans interpret as \"loudest\"? If so, why?"
] |
[
false
] |
For example, a drum has a certain pitch, and when you play that pitch, it vibrates a little more than usual. Does the eardrum do the same thing? I thought of this because I was listening to the radio and during one note the song seemed abnormally loud.
|
[
"Yes, it's around 3 kHz. The Wikipedia page on ",
"Equal-loudness contours",
" has a nice figure showing this; for a 20 Hz (barely audible on the lower end) sound to be \"as loud as\" a 3 kHz sound, it needs to be 60 dB higher, which is 1,000 times more energy.",
"The \"why\" is harder to answer... It may have to do with human speech, but on the other hand, speech may have evolved in this range because we're better at hearing it. There's a correlation, but causation would be difficult to prove.",
"Edit: The drum has a ",
"resonance",
" at that frequency, probably due to the (0,1) mode of the drum head. It's also probably the frequency that will have the highest energy if you play the drum directly. ",
"Wikipedia page on vibrations of a circular membrane",
", or skip to the ",
"pretty pictures",
"."
] |
[
"Our ears are more sensitive to certain frequencies than others. For an explanation refer to the Wikipedia entry on ",
"equal loudness contours",
" or dave_casa's answer.",
"I have not seen evidence that drums in general transmit through the body in any significant way. There would need to be a lot of energy entering the body for it to match the intensity of the sound simply entering your ears. This small amount of energy would be easily masked.",
"I don't want to sound like a jerk, but please refrain from layman speculation in this subreddit."
] |
[
"Our ears are more sensitive to certain frequencies than others. For an explanation refer to the Wikipedia entry on ",
"equal loudness contours",
" or dave_casa's answer.",
"I have not seen evidence that drums in general transmit through the body in any significant way. There would need to be a lot of energy entering the body for it to match the intensity of the sound simply entering your ears. This small amount of energy would be easily masked.",
"I don't want to sound like a jerk, but please refrain from layman speculation in this subreddit."
] |
[
"Is it more efficient to have multiple grocery lines and people choose which to wait in, or to have one long \"feeder\" line and have a person wait until the next cash teller is available?"
] |
[
false
] |
This is a thought experiment I've had for some time. Consider two situations of identical grocery stores, with five cash registers available each. In Store A, each cash register has its own line of customers in queue. An individual who wants to buy their items walks up and waits in a specific line for a specific cash register. In Store B, there is one long line that people wait on for all five cash registers. As each of the five cash registers becomes available, the next person in line walks up to one available. Assuming that people do not switch lines in Store A (and an individual will always go to the line with fewest individuals), and that all other factors are identical between the stores, which store will have a more efficient check out scheme? Will it even make a difference?
|
[
"Ignoring lading of groceries, the layout of supermarkets and the difficulties calling people to a register for a moment (which all complicate the problem):",
"This is called an M/M/c queue.",
"https://en.wikipedia.org/wiki/M/M/c_queue",
"In ",
"queueing theory",
" (again, remember I'm ignoring the problems listed above) it is the most efficient (highest server utilisation) and the most equitable (consistent wait time) way to handle a queue under almost all circumstances. It is efficient because:",
"You don't have servers being idle because their queue is empty even though others are full.",
"You don't have stalls in service due to a single customer being slow",
"All customers wait approximately the same time.",
"So why isn't this done in supermarkets?",
"Physical space. Single queue layouts take a lot of space and obstruct aisles. They require huge snaked queuing areas. This is less a problem for \"12 items or less\" areas (since customers don't usually have trolleys) so these often have single queue layouts.",
"People don't follow single queuing rules well.",
"With more than about 6 queues people can't always see all servers, you start needing start to dispatch queued shoppers (I've seen a few airport check-ins with dispatch staff for this purpose). Again, this point is less relevant for small clusters of queues, like a dedicated 12 items of less cluster of servers.",
"Humans do a little mental load balancing when choosing between queues which gives them a multi-queue advantage over theoretical random people. Humans don't simply queue at a random line and do attempt to judge how many items each person has. We also switch queues if there is an obvious advantage. Of course, it doesn't always save us (are we a subject to various biases that can make our judgment worse) but on the whole, we're not too bad."
] |
[
"I strongly believe you're speculating here, the dynamics of queues aren't always the way your intuition tells you."
] |
[
"If I remember correctly, the motivation behind the shared queue is that while total time for all customers is about the same, average time goes down because quick customers go through more quickly.... something along those lines anyway. People, however, psychologically feel like it's slower."
] |
[
"What are the benefits of having an AI learn through human interaction; rather than teaching it beforehand?"
] |
[
false
] |
[deleted]
|
[
"There was a big project a couple of decades ago (the name, unfortunately, eludes me right now) to do just that. The goal was to create (or at least enable) AI by instantiating a set of rules to enable parsing and \"understanding\" of natural language. I believe that after many years of effort, the attempt was either abandoned or vastly scaled back. ",
"It turns out that the task is ",
". Much of \"natural\" language interpretation relies on contextual cues, sometimes multiple contextual cues. To be able to understand what is meant by a phrase or sentence, it is often important to understand many other things about the world, society, physics, etc., not to mention the situation, the intent of the speaker, etc. Trying to put those understandings in place created a requirement for ever growing areas of knowledge to also be instantiated. ",
"The researchers working on the project found that virtually every time they encountered a situation where contextual knowledge was needed and put it in place, it uncovered many more such areas. It was like peeling an onion, except every time you peeled off a layer, the underlying layer was larger. The task seemed to simply grow almost exponentially. ",
"I don't think that implies that the task was impossible, just that it was very difficult. Certainly humans have only a finite understanding of such things, but it is simply very large, complex, and interconnected. We also rely on \"fuzzy\" logic systems and feedback loops that themselves may be chosen contextually, and may even be self-modifying. ",
"It might be easier to do such a thing today with the resources that have been developed such as Wikipedia, large data mining techniques, etc. Certainly IBM's Watson has been able to be successful in certain areas. ",
"But as a result of this effort and others like it, most researchers decided that it simply doesn't make sense to try to create a huge body of information beforehand, but to instead rely more on a learning-based technique. ",
" - It is \"better\" to teach the AI how to fish rather than giving it an ocean's worth of fish. "
] |
[
"By \"hard wire\" do you mean e.g. personally program how cleverbot should react and what cleverbot should say? This is an exceptionally difficult task due to the extremely complicated nature of language.",
"Or do you mean give a bunch of data sets of conversations rather than requiring actual humans to provide this data? This is a very reasonable approach, but the amount of data you can receive by public interaction is much greater than the amount of data you can otherwise find. Unless you're google or something, you won't have access to terabytes upon terabytes of sample data to learn with, so crowdsourcing this data is a very smart move."
] |
[
"No, that was developed by IBM (and I referenced it above). It predated Watson. It was government funded, or maybe a consortium. I just can't remember. (I need machine augmentation for my memory, obviously.)"
] |
[
"Does something like codon degeneracy also exist for RNA genes?"
] |
[
false
] |
Codon degeneracy exists because there are multiple ways to code for a given amino acid. This means that a sequence with different DNA could in principal produce the same protein. RNA genes are non-coding genes. They are transcribed from the DNA strand but never translated into a string of amino acids in order to produce a protein. But is it still possible for some other form of redundancy to exist? Could two different RNA molecules achieve the same goal with the same efficiency? Let us say that their job was to influence gene expression for example.
|
[
"RNA is a transcript of DNA. Transcription of DNA to RNA is based on base pairing rules (A <--> T/U, G <--> C). There is no degeneracy there. ",
"When it comes to functional redundancy, the answer is a firm and decisive \"well that depends.\" Are you talking about comparing non-coding RNAs from different species? Then, just like proteins, there will be families with some ",
"differences",
" and some ",
"similarities",
". They all do the same job, even with their sequence variations. ",
"I'm beating around the bush. \"Could two different RNA molecules achieve the same goal with the same efficiency?\" That's a bit of a hypothetical, but sure, there's nothing stopping that from happening. "
] |
[
"Calling RNA genes non-coding is going to upset a lot of Biochemists. RNA genes code for ribosomal RNA, tRNA, and numerous small, medium, and long RNAs that are all functional in the cell, (RNA decay, survalance, regulatory mechaisms). ",
"But I know what you mean, these are not translatedi into protein. ",
"The answers so far have been \"no there is no degeneracy.\"",
"While this is sort of true, based on the A--T, G---C base paring, its important to remember that RNA is actually A--U, and G---C. Now The copying of the DNA code to the RNA code is faithful, but once we are in the RNA world secondary structure is hugely important for function. Tertiary structure is also important, but it relys on secondary. ",
"In this case, A to U and G to C are no longer the only base pairs possible. G and U can pair. In addition non-Watson-Crick base pairing is common. So if while this is not redundancy in the same way it exists in the codon language, the pairing options are expanded when you are looking at RNA. "
] |
[
"To add to some of the answers here, the fundamental basis of codon degeneracy is that RNA transcribed from DNA must be translated, and the dictionary that is used to translate has many words that mean the same thing. RNA genes are fundamentally different because they are not translated at all. They simply are transcribed and then function based on their folding. To ask if there is degeneracy is not a very poignant question because degeneracy refers to interpretation, of which there is none in RNA genes. "
] |
[
"When people have a high pain tolerance, are experiencing less pain, or are they just better at \"sucking it up?\""
] |
[
false
] |
Basically, is people's pain tolerance all psychological?
|
[
"No, it is not all psychological.",
"Pain may be mediated by a number of factors, including:",
"\n* Sleep deprivation",
"1",
"\n* Sex",
"2",
"3",
"\n* Humour",
"4",
"\n* Depression and/or Anxiety",
"5",
"6",
"\n* And very likely countless others. ",
"Is there likely a significant psychological component? Yes.",
"\nIs pain a very multifactorial experience? Yes. "
] |
[
"First it is important to understand the difference between tolerance and threshold, and I think the answer is there are 2 kinds of people you are asking about. One with high tolerance and one with high threshold.",
"A high pain threshold means that you can sustain a (relatively) high amount of damage to your person before you feel pain. ",
"A high pain tolerance means that you can have a lot of pain and continue to do normal tasks.",
"So to answer your specific question those who have a high pain tolerance are better at \"sucking it up.\" They can deal with a lot of pain and continue to function. Those with a high pain threshold do not feel pain unless more severely injured."
] |
[
"Cultural",
"1",
" influences are becoming prevalent. A difficulty in finding reliable reporting tools is that there are cultures that prize emotive responses to give validity to a situation as well as those that value minimal expressiveness."
] |
[
"How do cosmologists equate relativistic mass of galaxies moving away from us (the observer)?"
] |
[
false
] |
I recently asked/proposed the question/idea about the expansion of the universe as noticed by galaxies moving away from us (the observer) and how it might be true that these galaxies are actually shrinking, causing them to look like they are moving away because the edges closest to us are actually moving away from us (and, because they are moving away from us, they must be travelling in time at a different rate than us because of our differences of momentum - and because space is not independent of time). So I looked up how we determine the mass of a distant galaxy. If these galaxies are moving away, then they must be (relativistically speaking) shrinking according to the observer due to the special theory of relativity. If that is so, then they must also be gaining mass. Therefore, we must allow for this increase in mass when calculating the mass of the galaxy in question. I've done some research and have found no mention of this additional mass being considered. Is it considered? If so, how so? And if not, why not?
|
[
"A few things going on here. One is that the concept of relativistic mass doesn't translate into an actual mass. It's something that was used to explain the concept of relativistic momentum, but isn't a physical quantity. The only relevant mass is the rest mass. Another is that when we're considering the internal dynamics of galaxies only their rest frame matters; relativistic effects are only seen by external observers. Another is that galaxies generally don't move very fast compared to light (relative to a rest frame where the cosmic microwave background is anisotropic), only a few hundred kilometers a second. There is also cosmic redshift, but that doesn't translate into galaxies moving fast through space."
] |
[
"It was my understanding that the physical and real effects of relativistic mass is a key to understanding why objects cannot accelerate to and subsequently exceed the speed of light.",
"Not really; it just shifts the question around a bit, which sometimes satisfies lay-persons.",
"In relativity, accelerating an object that is already close to the speed of light requires significantly more energy than accelerating one that is going slow. This required energy becomes infinite if you actually want to ",
" the speed of light. Now, relativistic mass shows up by someone saying something like \"when things get faster, their mass increases, so you need more energy to accelerate them\", but that just raises the question of why their ",
" should increase. ",
"More to the point, it turns out that the \"relativistic mass\" is just the total energy expressed in units of mass instead of energy, but that already has a perfectly good name (total energy). As such, there's no reason to confuse the issue by calling it a mass.",
"You said that galaxies generally don't move very fast compared to light, but everything else that I've learned about the subject says otherwise (a number of them moving faster than light, even). Who am I to believe?",
"They aren't ",
" very fast compared to light. Their distance from us is increasing, but this is because of cosmological expansion: an object at rest some large distance away right now will nevertheless be ",
" away in the future, despite not changing its position. You might find ",
"this comment",
" helpful.",
"And the original question, is relativistic mass ever taken into account and calculated?",
"Ever? Maybe. ",
"? No. It's not a physically useful or relevant quantity, so there's no ",
" to \"calculate it\" or \"take it into account\"."
] |
[
"Relativistic mass is an outdated concept. Massive objects can't reach ",
" because their momentum goes to infinity as their velocity goes to ",
".",
"iorgfeflkd is right that galaxies don't go near the speed of light ",
". An observer in any given galaxy will see the CMB as being shifted by only a few to several hundred km/s in some direction, for example we see it as redshifted by about 600 km/s (if memory serves). However, since we do observe cosmological redshift (due to the expansion of space), distant galaxies that are redshifted ",
" also appear time-dilated, meaning that processes appear to move more slowly there. ",
"An example is this paper",
", which shows that supernovae appear to happen more slowly in high redshift galaxies.",
"But relativistic mass is not used, because all calculations should be done in a galaxy's rest frame."
] |
[
"Which is more efficient? Insect flight or avian flight?"
] |
[
false
] |
I'm an undergrad biology student and I've been learning about the evolutionary advantages of being bipedal, so I was wondering... Weight for weight, in general, which is more efficient?
|
[
"Dynamic soaring, as first observed in ",
"Nature",
" is a method of flying employed by some sea birds to fly huge distances with virtually no flapping needed. However some ",
"moths",
" use the jetstream to migrate. To really say which of these is more efficient, you would need to clarify what you mean my efficient. And also what kinds of birds and insects you are talking about. The dynamics of a moth with huge wings are going to be quite different from a horsefly that has much smaller wings with respect to its body. Likewise a hummingbird flies very differently than a vulture, one needing to rapidly flap and the other often using thermals to gain altitude while just gliding."
] |
[
"i'm assuming its energy output to distance flown w/ respect to its weight"
] |
[
"Efficient in what sense? Energy/distance? Energy/height? Energy/speed? Cargo transportation?",
"The first one is easy - eagles, vultures and other gliders will outperform any insect in that sense. ",
"Second...can be tricky. Fleas are fuckn efficient when it comes to gaining height. ",
"As for speed, speed/weight prize should be given to insects. Some dragonflies reach 50 mph, and weight a fraction of the fast birds types (also of similar speeds). ",
"For lifting and cargo...I've seen a wasp steal a cherry. I doubt any bird can beat that. "
] |
[
"Are there any multicellular organisms which are not symmetrical?"
] |
[
false
] |
I can't think of any. Every animal, every plant, every living thing on this planet is symmetrical in some sense, except apparently for sponges. Is there a reason for this, or is this just a mystery? Is it reasonable to assume that a planet in another solar system with life would also be symmetrical?
|
[
"Many plants are not symmetrical, nor are the main mass of most fungi (mushrooms are just small fruiting bits).",
"EDIT: As for why things are symmetrical, I can think of two main underlying reasons. First, if you are going to move around, it helps to be symmetrical, because otherwise one side tends to move more easily than the other and you go around in circles. Second, symmetry is the natural result of an ordered program of growth keeping it simple. It's simpler to just express the same genes in the same pattern on both sides of the body or in regular intervals coming off the growing tip of a plant. This provides various sorts of symmetry.",
"I'd very much expect to see most alien mobile life as symmetric, and most plant analogs showing the kind of semi-symmetry that plants show (with parts being symmetric, if not the whole plant)"
] |
[
"Sponges have no symmetry. "
] |
[
"I can think of some crabs which have one huge claw and another smaller one on the opposite side. They'd be asymmetrical right? "
] |
[
"Why do whales and dolphins die on shore?"
] |
[
false
] |
Couldn't they get air like regular mammals?
|
[
"They can still technically breathe, but the weight of their bodies is what kills them, by crushing their organs and even limiting how much air their lungs can breathe in. Their bodies are designed to be in the water all the time and as such the distribution of weight/organs with their bodies relies on the water to provide support. They are literally crushed under their own weight."
] |
[
"This, and they also can't properly thermoregulate on land. They quickly overheat."
] |
[
"depending on the species, thermoregulation failure is the biggest killer. keep them wet!"
] |
[
"Question about Special Relativity, time dilation and length contraction"
] |
[
false
] |
Using the Wikipedia as a reference. Assume John is stationary and is observing Bill traveling at 0.9c This means that Bill travels at 269,813,212.2 m/s. So he covers X=269,813,212.2 m in T=1 s. Now I want to work out the time (t) that John sees has passed for Bill, and the distance (x) that John sees Bill has traveled: t = T / √ (1-v x = X * √ (1-v √ (1-v = 0.4359 t = 1 / 0.4359 = 2.294 x = 269,813,212.2 * 0.4359 = 117608852.6 So Bill has traveled, from John's point of view 117608852.6 m in 2.294 seconds, which means his velocity is 51264510.32 m/s or 0.171c. But I did the calculation with his velocity as 0.9c to work out the time dilation and length contraction factor. How can his velocity be both 0.171c and 0.9c? What am I doing wrong?
|
[
"Your mistake is applying the time dilation equation the wrong way.",
"First let's work in units where c=1 light-sec/sec, and I'll use gamma = 1/sqrt(1-v",
" ~ 2.3 for simplicity.",
"Remember, proper time (the clock of someone who views themselves at rest) can only get dilated (its time dilation if you view something appearing to move) and objects in frames moving relative to you get length contracted.",
"So Bill thinks he's at rest at sees John moving at 0.9c and in 1s of Bill's time, John will move 0.9 light-seconds (according to Bill). Now during that same spacetime interval, John has aged less than 1 second, because his proper time was dilated when observed by Bill. Thus John has aged only tJ ~ t/gamma ~ 1 second/gamma ~ 0.43 s. During that time John has traveled a length contracted distance of xJ ~x/gamma ~ 0.9 light-seconds/gamma ~ 0.39 lt-sec. (Remember the distance that Bill saw John move between at rest was 0.9 light-seconds; thus John who is moving will see that distance be length contracted.)",
"So xJ/tJ ~ 0.9c again."
] |
[
"Let's just ignore numbers because they make things more confusing.",
"In reference frame A, Bill travels a distance d from x to y in a time t, with velocity d/t.",
"In Bill's inertial frame B, point y moves toward him until it passes him in what he experiences as time t' which is equal to g",
"g. He calculates the velocity of A with respect to B as d",
"g=d/t=v."
] |
[
"Doesn't length contraction mean the length would be shorter?",
"This is where the numbers help.",
"With my numbers above:",
"γ = 1 / √ (1-v",
" = 1 / 0.4359 = 2.294157339",
"So if d' = γd, then the length would be longer. This doesn't appear contracted, but elongated.",
"I thought it was t'=γt and d'=d/γ",
"Which would give you v'=d'/t' = d / tγ",
"Still confused."
] |
[
"How large a colony must be in order to be genetically diverse?"
] |
[
false
] |
Operating on a example - how many people would be required for a colony to avoid inbreeding? Or to rephrase - how many generations must pass so offspring from the same n-grandfather could mate without consequences?
|
[
"The homo-sapien population is theorized to have dropped from around 21,000 to around 618 breeding individuals around 195,000 years ago. Due to the Long glacial stage known as Marine Isotope Stage 6 (MIS6) that lasted until roughly 123,000 years ago. This explains the lack of genetic diversity in modern humans. ",
"They managed to produce 7.2 billion of us, with only 618 individuals."
] |
[
"How did they get the number 618? That seems pretty specific. "
] |
[
"There's no hard and fast rule, and no one can get you an exact number. It depends on a lot of factors, including the exact genetic makeup of the founding population - how many harmful recessive alleles are floating around, etc; how much and what kinds of environmental pressures are acting; mutation rates; and so on and so forth.",
"For example, the current cheetah population is thought to have descended from a very small population (bottleneck) during the last ice age. Did they succeed? Did they manage to continue \"without consequences\", as you put it? Well, they're still here, so arguably yes. Would they be healthier as a species if they hadn't had that bottleneck? Probably. So would that count as a win or a loss? What if they end up going extinct in the next century? How much of that is due to their inbreeding?",
"Hopefully, that illustrates why it's impossible to just draw a line and say \"on this side, you're good; on that side, you're in trouble\"."
] |
[
"What is the purpose, if any, of the second and third generations of matter?"
] |
[
false
] |
It seems to me that if a top quark, for example, only exists at very high energies and is too unstable to really do anything other than (and for a very brief time at that) that the particular event that created it might as well have just generated a cascade of lower generation particles. Do the second and third generations have a justification in the current model or do we only include them because they are observed to exist?
|
[
"there's not a \"purpose\" to any particle's existence. They just are."
] |
[
"No it doesn't really predict 3 generations of matter exactly. Maybe in the future we'll have an argument for why there \"must\" be only 3, but at the moment it seems to just be the case."
] |
[
"What I mean to say is, does the standard model predict multiple generations of matter or was it just made to accommodate them because we know they exist? I know the strange quarks were known (sorta) before the standard model was formulated, but what about the rest of the second and third generation particles?"
] |
[
"What would happen if you carved grooves into a fresh vinyl record at random? Is it possible to replicate music simply by carving out the right kind of grooves?"
] |
[
false
] | null |
[
"In the same way that it's theoretically possible that a room full of monkeys on typewriters could write out Hamlet."
] |
[
"Okay, but I'm not fundamentally wrong in thinking it's possible? Like, there isn't anything that would physically prevent a person from creating Abbey Road from scratch, even if they'd never heard it or seen it etc?",
"I get that it's practically impossible, but is it physically impossible? "
] |
[
"Right. A phonograph record just has grooves of different depths in the material. You could in theory do that by hand."
] |
[
"Ask Anything Wednesday - Biology, Chemistry, Neuroscience, Medicine, Psychology"
] |
[
false
] |
Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...". Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists. Please only answer a posted question if you are an expert in the field. . In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away!
|
[
"The monolith in Utah, how is that formed?"
] |
[
"artists"
] |
[
"Whatever happened to the vaccine against tooth decay I read about in the late 1980s.?"
] |
[
"What exactly is vacuum energy?"
] |
[
false
] |
I have read bits and pieces here and there but i really don’t understand it still. From what I understand its an insanely high density energy found in the vacuum of space and Its still a theoretical quantum physics theory. Thats about it (wikipedia only goes so far) My main questions are Where did the energy originate from? Big bang? How certain are we of its existence? If we were able to harness it what would that look like and how far off are we from being able to do so? I am not a physics major by any means but don’t let that hold you back in your explanations!
|
[
"Zero-point energy is just the minimum energy that some given quantum system can have, and it's not necessarily zero. Vacuum energy is the zero-point energy of the vacuum state (the state with zero particles) of a quantum field theory.",
"We are certain of its existence because it has measurable consequences, like the Casimir effect. And by definition we can't harness zero-point energy because it's the minimum possible energy of the system. You can't take energy out of something which is already at its minimum energy."
] |
[
"A useful analogy is to think of the fields in nature (every particle is associated to a field) as a pond, and the particles are (specific types of) ripples on the pond. ",
"You shouldn't imagine the pond as perfectly still when there are no ripples in this case though, it is always fluctuating up and down.",
"The fact that the pond isn't still even when there are none of the ripples means it has some energy. The vacuum (no particles) has some energy"
] |
[
"Oh. For some reason i thought i remembered reading something that said it had a crazy high density energy. Have i mistaken this for something else?"
] |
[
"What algorithms exist to find a set of *n* points within a cube that are at maximally displaced from one another?"
] |
[
false
] |
A colleague of mine has brought in the dodecahedral equivalent of the Rubik's cube today. The faces are coloured red, orange, yellow, lime green, medium green, dark green, light blue, dark blue, mauve, white, grey, and pink. This led me to wonder how they chose the colours, and whether there is an algorithm for finding (in this case, 10) colours that are as different from each other as possible, in other words, for finding points at maximum distance from each other in an RGB colour cube. One way would be an iterative method that attempts to minimise a cost function summing the distances between all pairs of points. Is there a direct method? For small , the answer is easy: for = 2, put the points in opposite corners; for = 3, set the origin at one corner and then choose the points at the ends of the x-, y- and z-axes, but after that it gets more complicated (for = 4, we could choose the corners of a tetrahedron, but what is the largest tetrahedron that fits into a cube?). EDIT 1: Please ignore the redundant "at" in the title. EDIT 2: Added the two missing colours... I don't think anyone noticed :)
|
[
"We do this in our simulations to make clean initial conditions. It's what's called a \"glass\". You set up a bunch of particles, and run a simulation where every particle has a repulsive force on every other particle. You slowly remove kinetic energy from the system (\"anneal\" it), until everything settles down. When everything is basically stationary, everything should be pretty spaced out.",
"It is, as you say, an iterative method, but it works pretty well, even for very large numbers of particles. We usually do it with periodic boundary conditions, so you'd have to do some tricks to take the finite-size of the cube into account, but that's basically the algorithm."
] |
[
"It should be added that algorithms like these sometimes find local minima that aren't the globally best answer...just pretty good answers."
] |
[
"True true true... but when you have a million particles, the landscape is so bumpy that the absolute minimum isn't necessarily the most important thing..."
] |
[
"Can underwater currents be remotely sensed from the surface or just under the surface of the water?"
] |
[
false
] | null |
[
"There is (sort of) another technique for looking at currents throughout the water column, namely seismic oceanography (e.g. see ",
"this review",
"). Whilst this does not allow you to solve for water velocity, it does allow you to remotely infer the density structure of the water column, potentially giving insight into water mass structure and possibly more interestingly, small-scale turbulent structures. This is an emerging technology and it's not clear how useful it will be, but it certainly is interesting."
] |
[
"This is a big problem in oceanography: there's basically no way to measure subsurface currents from the air or from space. There are some indirect methods, like measuring the shape and temperature of the sea surface and using a computer simulation to predict what's below, but there's a lot of ways that can go wrong.",
"But you also asked for a way to measure deep ocean currents from \"just under the surface\", and there ",
" a way to do that. Ships can be fitted with an \"acoustic doppler current profiler\" (",
"ADCP",
"): it sends out beams of sound into the ocean, which bounce off tiny particles in the water colum. Just like a police radar, the ",
"Doppler",
" frequency shift of the reflected waves tells you the speed of the water the particles are in, and the time it takes the waves to bounce back tells you the depth.",
"However, ADCPs typically only work down to 1 km depth or so: beyond that you need to actually put some sort of instrument or robot down there."
] |
[
"Underwater ocean currents are typically measured directly by \"deep water drifters\" or other types of probes. It's also possible to remotely measure the speed of water relative to a device known as an \"Acoustic Doppler current profiler\". These have a range of up to one kilometer, depending on model and conditions."
] |
[
"How do Jet Engines Work?"
] |
[
false
] | null |
[
"The basic concept was described by my university Aerospace Propulsion professor as Suck, Squeeze, Bang, Blow. ",
"The first stage of a modern jet engine pulls the air into the engine with a large fan (Suck). Behind the fan, this high velocity air is compressed by a series of compressors (Squeeze). Next, the high velocity, high pressure air is mixed with fuel and ignited in the burner (Bang). This high velocity, high pressure, high temperature air is then forced through a series of turbines, which are used to power the fan and the compressor. Finally, all the air is expelled through a nozzle at the back, producing thrust (Blow).",
"It obviously gets a bit more technical if you want to actually design one, but this is the gist of it."
] |
[
"A lot of fighter jets have an additional step called after burner, where more fuel is pumped into the exiting high velocity, high pressure, high temperature air which can be toggled on and off and is used for short bursts of speed.\n",
"http://www.youtube.com/watch?v=qZKKeg7lOr8",
"\n@2:30"
] |
[
"Not true, I'm afraid. Yes, when the plane is static on the ground, the engine does suck air in. When it's at operational speed, the air is pushed into the engine. In either case, most or all of the thrust comes from the pressure of the exhaust pushing on the turbine blades at the back of the engine (or on the back of the fan in a turbofan engine).",
"That transition from the engine sucking to being force-fed makes a lot of difference. The extreme case is Concorde: on the ground, the engines only made 5% of the power they did at full speed because of the reduced amount of air they can take in by sucking. So little power, in fact, that they had to use reheat (afterburner) to get off the ground. "
] |
[
"Is there a compound that can be found naturally but cannot be made artificially?"
] |
[
false
] |
[deleted]
|
[
"Insulin absolutely can be synthesised, and in fact it was one of the first peptides to be produced by solid-phase peptide synthesis. It's just not a practical route for the vast majority of proteins due to their sizes and post-translational modifications, since it is very time consuming, yields would be very low, and purification difficult."
] |
[
"Depends in what way you mean by 'made artificially'. Proteins and enzymes are very complex structures that can't really be made by standard chemical reactions, and require a living organism such as bacteria to be produced in a lab. ",
"A good example is insulin, a hormone used to treat diabetics. It was originally isolated in the early 20th century by harvesting it from the pancreas of a dog, but nowadays its produced by specially cultivated bacteria.\n It's not currently possible to synthesise insulin chemically (along with a lot of other biological compounds) as the molecules are so complex. Edit:",
"More info about insulin",
"Edit2: I just learned that insulin can in fact be synthesised! See below comment. "
] |
[
"From a theoretical standpoint, no. Potentially anything that is possible in nature (on earth) we could theoretically produce artificially.",
"From a practical standpoint, absolutely. There are countless natural compounds we do not know how to produce, and papers get published all the time by some organic chemist demonstrating a route to produce said compound."
] |
[
"What stops an aircraft from reaching specific altitudes?"
] |
[
false
] |
So I was reading a bit about an aircraft (MiG 21 or otherwise known as the Fulcrum) and found that the maximum altitude it can reach is specificly 18013m. My question is what stops the MiG from going an extra, say 1000m? Or even better, why exactly 18013 and not 18015 or just 18000?
|
[
"An aircraft flies at a constant altitude when the sum of the forces acting on that aircraft in the up direction is zero. There's two forces acting in the up direction on aircraft: gravity and lift. From ground level to the altitude airplanes can fly, gravity is basically a constant (it decreases a little bit with height, but you have to be very far away before you see much change. For instance, at the altitude of the ISS orbit, gravity is still ~90% as strong as it is at sea level). So really, the question comes \"at what altitude can the airplane have enough lift to counteract gravity?\"",
"Well, the amount of lift a plane can produce is decreases with altitude because the density of the atmosphere decreases with altitude. With less air passing over the wing, less lift is produced. This is partially offset by the fact that the thinner the atmosphere, the faster the jet can move forward, due to decreased drag but the overall effect is that lift is decreased. ",
"That altitude is the altitude that the two forces cancel out. "
] |
[
"They're not floating around. They are constantly freefalling towards the Earth, but travelling sideways fast enough that the rate of which they fall equals the curvature of the earth."
] |
[
"Astronauts are weightless while in orbit not because there is no gravity there (if there was no gravity, nothing would hold them in orbit) but because orbits are free-falls. So, the astronauts and the space station (of shuttle or whatever) are all falling together, so it appears as if they are \"floating\""
] |
[
"How empty of a vacuum can we make? How are the more \"pure\" vacuums made?"
] |
[
false
] |
I imagine it is either impossible or very difficult to remove every last molecule from a given space, so how empty are we capable of making something? Say for example we wanted a 1 m cube with no air or anything inside of it. How would we go about doing so? How much of the air could be pumped out/what other methods would be used to make it a total vacuum? How many/what percent of air (or any other) molecules would remain?
|
[
"First you have to take into account that perfect vacuums do not exist. Even in outer space, there are a few atoms per cubic meter. A perfect vacuum - with a gas pressure of exactly zero - can not be artificially obtained.",
"There are designations for \"qualities\" of vacuum. What's called \"ultra high vacuum\" has a pressure of less than 10",
" Pa but more than 10",
" Pa (for comparison, normal atmospheric pressure is just over 10",
" Pa). Ultra high vacuums can be achieved in laboratory conditions, and in such cases hydrogen atoms will be most of the atoms remaining in that space. Achieving ultra-high vacuum is quite a challenge because you need a series of different and efficient vacuum pumps, and you have very strict limitations for everything from temperature to materials used. ",
"Wiki",
" gives a nice overview of some of the steps required for an ultra-high vacuum, that should hopefully illustrate how challenging it is."
] |
[
"Of course, there are certain areas which happen to contain no atoms at a given time. But atoms not being stationary, that area will have some atoms later. Since this perfectly atom-free area isn't at all isolated from everything else around it, it makes little sense to talk about it separately in physical terms."
] |
[
"You could never get the piston to touch all of the walls and top so perfectly that there is no existing volume in the cylinder, and that volume will contain some atoms."
] |
[
"Using freezing point depression how does adding salt to ice (0 C) reduce the temp (to <0 C)? or does it?"
] |
[
false
] |
I understand how freezing point depression works with the salt ions disrupting ice crystal lattice formation. However, when I'm looking at pages for homemade ice cream they say that adding salt allows for the mixture to be below the freezing point of water. While I can see that adding salt to the ice will melt some of the ice and water will allow for more heat transfer from the cream to the brine (than just ice alone), I don't see how the temperature can be reduced below 0 C. There is nothing colder around it to remove heat from the mixture and everything around it is warmer and will be adding heat to the brine. How does the brine become colder than 0 C?
|
[
"When you add salt and lower the freezing temperature of the solution, ice will begin to melt because it's then above the freezing temperature. However, ice requires a lot of energy when it melts, which it will take from it's surroundings and therefor decrease the overall temperature."
] |
[
"The ice cools it. It takes quite a bit of energy to melt ice. ",
"But if you have a mixture of pure water and ice at 0 C, then it'll stay that way, the proportion of ice/water won't change - some water will freeze and some ice will melt, but it's at the same rate. ",
"If you mix water above 0 C with ice, then there will be more melting than freezing, and the energy for that is coming from the heat of the water, which drops until it has melted enough ice to bring them both down to 0 C. ",
"Same thing if they're both at 0 C and you add salt and depress the freezing point. You shift that balance. The water is now above the freezing point (for that solution, not for pure water), so the water doesn't freeze at the same rate as the ice is melting anymore. So you have a net melting of the ice and the temperature of the water solution will drop until it reaches the new, depressed, freezing point."
] |
[
"Melting is an endothermic process, which means it takes energy from the environment to melt.",
"When you add salt to ice, the ice melts, and the temperature of the system lowers. This is how ice baths - down to about -20 C - can be prepared in the laboratory with ice, water and salt alone."
] |
[
"What will scientist and doctors use once we run out of helium?"
] |
[
false
] |
I know helium is very important for medicine and science. What will we do when helium runs out? Make more? Replace it with something else? It's just a scary thought. Do I have any reason to be scared or worried about this?
|
[
"Hydrogen, Neon, Nitrogen.. They'll figure it out. Also, to the people saying Helium isn't used in medicine and science; Helium is used in GC/MS.",
"Edit: Before anyone comments, I'm linking forensics to medicine. Yes, it's a stretch, but the link is there."
] |
[
"For many applications, a high temperature superconductor would significantly reduce the need for helium. For example, the LHC uses tonnes of liquid helium to cool the superconducting magnets."
] |
[
"It's used in MRI magnets."
] |
[
"Are there any currently existing species that evolved or diverged from any other currently living species?"
] |
[
false
] |
Creationists love to ask 'If we evolved from apes, why are there still apes?' Of course the answer is that we did not evolve from apes, that we and apes share a common ancestor. My question is if there any current species who at some point diverged biologically from a species that stayed relatively static and still exists. The only way I can think of for this to have happened, would be for a subset of a species to be in a different environment to the rest of the herd. E.g. because of migration.
|
[
"First off, I'd say that \"still exists\" is sort of a difficult thing to tease apart. If you mean that these two species have been living and interacting within any particular environment, then I would say no, there are probably no species that have remained as static as you would probably consider sufficient.",
"Some species do maintain more of their ancestors' traits than others. Sphenodon punctatus (Tuatara) is a reptile that is often studied because it is considered to have many 'ancient' traits, sharing a common ancestor with other squamates 230 million years ago (or so). I would suggest looking up 'living fossils' and starting there. ",
"This",
" is an example paper on Tuatara and Squamates.",
"However, if this isolated species could be in a 'stasis'-like state and still count as an answer to your question, then I would suggest that you check ",
"this",
" out. Plant seeds from the species Silene stenophylla were found in Russia and, despite being 30,000 years old, were successfully grown in a lab. The resulting plants were similar to, but phenotypically slightly different from the modern day version of the same species. "
] |
[
"http://www.talkorigins.org/faqs/faq-speciation.html",
"http://www.talkorigins.org/faqs/speciation.html",
"describes several recent speciation events",
"the wikipedia page on speciation gives examples of each type - some of those may be relevant."
] |
[
"Yeah, after thinking more about this, for a situation like what I've described to occur, you'd need some members of a species to stay static for a long period of time while others evolved. The problem with that isn't really the divergence, it's the idea of a species staying so static as to be considered 'still the same species it was X years ago' (where x is obviously quite large), which would be pretty unlikely.",
"That said, the Tuatara does seem to fit the bill to some extent. I only read a little bit of the wikipedia article, but it does seem that they have changed from their common ancestor ",
" than lizards and snakes, which is certainly in the ball park of what I was looking for. Cheers."
] |
[
"Why do ladybugs follow a drawn line?"
] |
[
false
] | null |
[
"Hi zeetotheex thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Biology"
] |
[
"Biology"
] |
[
"Most galaxies have a black hole at their centre, does this mean that galaxies form around black holes?"
] |
[
false
] |
Given enough time, will enough matter and stars accrete around a black hole to form a galaxy?
|
[
"More likely the opposite: Given enough time, a galaxy will form a supermassive black hole in its center.",
"Galaxy formation can be simulated well from the dynamics of dark matter alone. Visible matter and black holes just follow the dark matter clumps."
] |
[
"In terms of dynamics this is true, because even supermassive black holes make negligible contributions to the total gravitational potential of galaxies.",
"But we do believe black holes play important roles in regulating the cool gas content of galaxies, and hence the rate at which they can form stars. This happens not through gravity directly, but via the energetic outflows (\"feedback\") produced from material spiralling toward the black hole."
] |
[
"All sufficiently massive galaxies are expected to have a central SMBH. But where that mass threshold lies, and what the origin of the material the BH initially forms from is, are both still somewhat uncertain."
] |
[
"If your visual cortex is damaged, can you see in your dreams?"
] |
[
false
] |
Particularly, can a patient in a coma dream if the auditory or visual cortex is damaged?
|
[
"I don't have any direct evidence but I would assume no, based on the following reasoning: losing the part of the visual cortex that allow you to see colour (eventually) makes you unable to imagine colour. More generally, mental imagery activates the same parts of the cortex that are activated through corresponding perception/action (but weaker). There are both imaging studies and reaction time studies to show this. So since there is no possibility for imagery, your dreams would probably be visionless if you lost your (entire) visual cortex.",
"However! Sometimes partial damage to the occipital lobe is associated with people who are in fact cortically blind, but still claim/believe that they can see!\n",
"https://en.m.wikipedia.org/wiki/Anton–Babinski_syndrome"
] |
[
"by definition, if you're in a coma you are unconscious i.e. not dreaming.",
"as for dreams with visual cortex damage: there's been no systematic study of this, possibly because every patient is different and would report different things. but also because, i guess, the right people haven't gotten together to collect the data?",
"i have worked with a number of hemianopia patients (blind in half the visual field due to primary visual cortex lesion), and talked with them about their experience including dreaming. most thought that their dreams were similar to their waking experience; I think one or two believed they could see more in their dreams. a problem there is that, with cortical blindness (even with retinal blindness) it is difficult or impossible to \"see what you can't see\" - everything may actually look normal, and yet you keep walking into furniture and bumping into doorframes. so it would probably be very difficult (but not impossible) to get convincing data about this question from a dreamer.",
"that said, considering that visual cortex is the substrate of visual experience, you would have to expect ",
" of visual experience to be missing in a cortically-blind dreamer. what part, exactly, can be guessed by the ostensible function of a brain region, but it's never really that simple..."
] |
[
"by definition, if you're in a coma you are unconscious i.e. not dreaming ",
"So are the dreams people who have been in a coma experience all the result from brain activity during waking up from the coma?"
] |
[
"Why can't we communicate faster than light using entanglement?"
] |
[
false
] | null |
[
"See the ",
"physics FAQ",
":",
"Special Relativity - Can quantum entanglement be used to communicate information faster than the speed of light?"
] |
[
"Hi! thanks for your answer. I did read those threads and it makes a lot of sense. I still don't understand how it actually plays out in this circumstance I'm proposing. I don't really understand the implications of entanglement, and that's what I'm trying to understand. ",
"What I'm asking is, if there is a continuous flow of entangled particles to both sides, what they see would be random. But if one side changes the spin of the incoming particles into meaningful pattern, can't the other side see the pattern as well, albeit with noise?"
] |
[
"But if one side changes the spin of the incoming particles into meaningful pattern, can't the other side see the pattern as well, albeit with noise?",
"From the very first link in the FAQs:",
"Because you're measuring a fundamental aspect of a particle (let's say spin in this case), and you then know that its entangled partner has the opposite spin, but you cannot ",
" your particle to have any particular spin, which is what would be necessary to actually send information.",
"This answer is echoed in pretty much every link in that FAQ comment."
] |
[
"Melting Ice"
] |
[
false
] |
Every day I freeze a bottle of water and let it melt all day the next day so that I have cold water to drink. I keep the bottle in an insulated carrier so that the ice doesn't melt too fast. I have noticed that the ice melts faster from the bottom up. By the time I leave work, the ice is in a cone shape with the apex at the bottom and the flat face at the top. Why does the ice melt faster at the bottom of the bottle than at the top? The insulated carrier leaves the top inch of the bottle exposed. On a barely related note, why is the center of the ice in my bottle filled with tiny holes? The outside of the ice is smooth and as it melts it exposes a rough texture with many tiny holes. What causes this? Thank you all for answering my questions. I'm still curious about the properties of freezing water and why it does what it does.
|
[
"It could also be that more heat is transferred by conduction from the ground/surface it is resting on than conduction with the air. So the bottom is melting quicker as it has more heat transferred to it."
] |
[
"I would make the educated guess that as the ice melts, the water travels to the bottom. This water located near the bottom is a worse insulator than the air above which causes the bottom of the ice to melt quicker. As more and more water builds up it travels up the ice block melting as it goes giving it the cone shape you're talking about."
] |
[
"Thank you. I always thought the heated air in the room was warmer than the surface of the desk."
] |
[
"Do racing games improve your driving abilities?"
] |
[
false
] |
Do games that include a closed racing circuit that rely on reflexes and braking, such as F1 2013, Forza Motorsport, etc.. improve your real life driving abilities?
|
[
"Are you asking whether it can in general, or whether it does for you specifically if you play driving games?",
"It's been shown to make a difference for people already, where those with extensive game time in Forza or GT can drive a track for the first time in RL and put up a significantly better time and display of skill than a person otherwise totally inexperienced. "
] |
[
"It's been shown to make a difference for people already",
"Reference?"
] |
[
"Short answer, ",
"yes",
". Long answer, it's arguable that such people were bound to be good drivers naturally, but just as pilots train in simulators, a sufficiently realistic game should test/build up your reactions/reflexes that can translate to actual driving. In more realistic games like the Gran Turismo series, you will learn much more about how to pick a racing line as well and in general get a better grasp on how cars react to steering/braking/etc and changes to the traction. Of course, there will be a few real life things that simulators won't be able to emulate.",
"That and many racers and other with hefty experience in real racecars have often spoken highly of the realism of some games like ",
"GT",
" and ",
"iRacing",
". In fact iRacing claims some racers even use it sometimes to get a feel of a track before they can actually drive there (though take it with a grain of salt like most promotional statements).",
"IIRC I think the biggest challenge from that one guy who went from winning the GT competition to an actual race in a real race car was that he wasn't ready for the forces you can experience and his neck hurt from the lateral g's."
] |
[
"How Exactly Does Light and the Ionization of Hydrogen Cause Emission Nebulae?"
] |
[
false
] | null |
[
"where a star is sending out light energy that ionizes the hydrogen atom, is it really losing or gaining an electron? If H loses an electron, does it emit light in the process?",
"In an H II region the hydrogen is ionised into H",
" it loses an election. When astronomers says something is ionised they usually mean it has lost electrons. H II means singly ionised, H I is neutral hydrogen and to illustrate further C IV is carbon which has lost three electrons. ",
"Light is not emitted in the process of photoionisation (as far as I know). The light we see from H II regions doesn't come from the ionisation, but from recombination. As the electrons are bouncing about they can be recaptured by a proton if they don't have enough energy. When they are recaptured they are captured to an exited energy level. When they fall to lower energy levels (excited states generally aren't stable) they emit the atomic hydrogen lines. One nice feature of this is that the ratio of the different lines (for example the Balmer series) is determined by atomic physics. By measuring the ratio of the lines one can therefore work out if there is dust in the way which preferentially scatters bluer light, changing the ratios of the lines. "
] |
[
"Yes. Recapturing can release photons but these aren't the ones that dominate the light of H II regions. "
] |
[
"Yes. Recapturing can release photons but these aren't the ones that dominate the light of H II regions. "
] |
[
"How come my green laser pointer changes color when pointed at this specific book?"
] |
[
false
] | null |
[
"I'm not sure what the natural color of the book is, but green laser pointers typically double the frequency of a near infrared light source. I believe in the US, a filter is required to reduce the IR emissions for safety (as the battery dies, you may get only/mostly IR. The eye does not adjust to reduce its intensity and depending on power level, it can permanently damage your retina if shone into the eye.) Cheap Chinese green lasers often lack this filter. I have a 50mW pointer like this and when the battery is almost dead, I see a similar brown-red color to what is in your picture.",
"So this is a hypothesis, but perhaps the other color is on the edge of IR? Many cameras will not show this as the eye sees it though, and will instead show white, pink, light blue, or another semi-random artifact color, as it is harder to make a CMOS camera NOT see IR than to see it on purpose."
] |
[
"I also want to add, 5mW, maybe 10 is what you'd find in a \"safe\" pointer. If it is any more than that, exercise extreme caution not to shine it on reflective surfaces, and if you can, even get safety goggles to filter the specific frequency out. Depending on strength, some lasers can cause permanent blind spots before you can even blink. My 50mW green, and 500mW(!) red ones are absolutely into a dangerous range and while you may find places that sell them cheaply and without restriction, they can actually be quite dangerous, even looking at the dot for too long."
] |
[
"Interesting - I was thinking this couldn't be right - because the frequencies are usually 1064 nm, frequency doubled to get to the 532 nm green light; The light at 1064 nm shouldn't be visible to the eye at all. However, a web search found ",
"this report",
" which suggests the near IR laser is actual driven by a pump laser at 808 nm. It seems more likely that is what you are seeing.",
"That page has an interesting link to a NIST report that describes a little DIY experiment to see what actually is in the laser - basically, use a CD as a diffraction grating and look for spots separate from the green spots, that might only be visible to a digital camera (might need to remove a near-IR blocker on the camera to make it work.)",
"So, back to the OP - it seems plausible that the book might be absorbing the green light and leaving the pump laser, if your laser does not have the right spectral filter. If the laser is properly filtered, so the beam is really just the green light, I'm really baffled as to why the beam would \"change colors\" like that. The spectral width of cheap commodity solid state laser is pretty crummy by laser standards - but even so, there is no way the spectrum would be wide enough to include the seemingly red colors that are in your image."
] |
[
"When you have a solution, how come the [OH-] x [H3O+] value always has to equal 1x10^-14? Specifically, why is there always some H+ or OH- left in very basic/acidic solutions?"
] |
[
false
] |
Sorry if this question is too simple... I've just been wondering since I'm learning about it in chem (well, to clarify, learning about it for the 3rd time, but he first two times I wasn't intuitive enough to care)... EDIT: I guess another example is why Water has to have OH/H+ in it (although I'd assume that's because water ionizes to some extent in... water...)
|
[
"Any molecule of water is identical and indistinguishable at chemical level from any other molecule of the same compound. One volume of pure water is identical to the same volume of water. Under equal conditions (temperature, pressure...) their chemical and physical behavior will be the same. So if a volume of water have some properties derived from its composition that characteristic will be the same for any other volume of water in the same conditions. Ionic product at laboratory conditions is one of that characteristics.",
"While water molecules are normally stable at laboratory temperatures when you have trillions of trillions of them on every tiny drop (10²³ molecules on 18g of water); a nonzero probability that some of them dissociate into [OH-] and [H3O+] exists .",
"The combination of cohesive forces, the momentary local alignment of the distribution of electrical charges, combined thermal impacts... all can cause sudden ionization of some molecules. These ion pairs exist only for a moment and then reshape into \"water\", but the process does not stop and at all times there is a minimum amount of these ions.",
"As by the amount of dissolved ions and pH we can infer the conductivity of a liquid, we can also do the opposite and apply conductivity measurements to determine the ionic product of pure water. The result is 10⁻¹⁴ in laboratory conditions, which is consistent with theoretical calculations."
] |
[
"That whole thing chages if you have deuterated water, it's really quite cool how such a tiny change can affect so much."
] |
[
"Thanks for such an in depth answer. If I understand correctly, there will always be OH-/H3O+ present because there is a real chance that H2O will ionized into those parts [due to its high amount of molecules], and even if OH- and H3O+ come back together then other H2O's will ionize. This holds true at no matter what level, assuming equal conditions.",
"If you don't mind, I have a follow up question:"
] |
[
"A couple of questions on evolution by selective breeding"
] |
[
false
] |
[deleted]
|
[
"It is possible, but it is probably fairly unlikely, or at least, very difficult. In part it depends on how reproductive isolation occurs. If it is a result of incompatibility between the dirty bits then you might be able to breed individuals with more compatible naughty parts. If it results from some sort of incompatibility between the sperm and eggs at the actual point of conception, or some sort of genetic problem that causes the embryo to abort, then it would be much more difficult to actually selectively breed compatibility back, but not impossible.",
"Sure, all you have to do is look at the modern diversity of species and then look at their ancient ancestors to see it's possible.",
"No. You will never go back \"down\" the evolutionary tree, you'll only go forward. The tree is a model of relatedness between individuals, so to go backwards you'd be implying that the two species suddenly have a much closer relationship to one another than they actually do. What you're trying to do is to make the traits more similar, not to change the traits.",
"Ultimately what you propose in #3 is possible, but you'd have to (probably) generate novel mutations that would permit the traits to develop. The basis of leaves require thousands of genes, from the meristem, the vasculature, the support and chlorophyl. To generate that ",
" in an animal (a dog for example) would require millions of years if you were simply breeding, and there are very real structural problems you'd have to overcome (blood vessels are not tracheids for example). The traits you were trying to develop would probably only look like leaves, but have completely different origins."
] |
[
"I'm a little curious what is driving these three questions. Are you trying to selectively breed a giraffe from a palm tree grove?",
"http://en.wikipedia.org/wiki/Reproductive_isolation",
"Recombine also has a technical definition in biology, so I assumed you meant \"two resultant populations [can] reproduce\"? ",
"http://en.wikipedia.org/wiki/Genetic_recombination",
" (very cool biological event).",
"2, 3. Evolution is based on the idea that all life shares a common ancestor. Keep in mind the idea of a species is a practical convenience that has many shortcomings which were recognized even before Darwin (",
"http://en.wikipedia.org/wiki/Species",
"), so a species isn't a single organism but a loosely defined population. The difference between an ancestor and its descendant can be described by a series of small changes. In nature, these changes occur over finite time in an uncontrolled environment. If you inverted the evolutionary changes that differentiates one species (e.g. a dog) from a common ancestor (e.g. a fish) in the exact same order then applied the changes required for a descendant on a different evolutionary branch (e.g. a giraffe), you could achieve this. The main idea is that you would have to travel down one branch of an evolutionary tree to a common ancestral species then travel up the branch to another species.",
"We are no where near close to knowing what changes must occur to induce a specific change in a population. What is more likely to happen is we would select for similar traits to the ancestor, miss the mark, and invent a new phylogenetic branch.",
"However, the chances of correctly breeding something like this given infinite time is equal to 1 (similar to the idea of infinite monkeys at typewriters producing Hamlet).",
"Hope this helps!"
] |
[
"Thanks for the answer. Your answers for 1 and 2 are pretty much in line with what I thought the case would be. The third one I had no idea about at all!"
] |
[
"What's the point of grand unifying theory?"
] |
[
false
] |
[deleted]
|
[
"So then, there is no difference between the gravitational interaction and the other three? "
] |
[
"So the gravitational interaction isn't mediated by any gauge bosons, but the other three are, how does one fit this into a framework of some theory of everything? So far in my exposure to the quantum world, physics is mediated by the bosons."
] |
[
"You're at a party and everyone is expected to wear green hats, Gravity shows up with a boat on his head.",
"People just like uniformity and patterns, gravity breaks away from the mold known as the standard model entirely. The question whether gravity does conform to this mold is one worthy of study and pursuit. Right now, it looks like gravity will be the successful odd man out in physics whose interactions are governed by ideas which do not involve gauge bosons. ",
"But who knows what the future will bring? I wouldn't call anyone's pursuit of getting closer to the truth pointless, such an attitude would prevent growth and the development of knowledge.",
"cue RRC :D",
"EDITS; I wouldn't say we have no confirmation of gravity not being one of the fundamental forces, in fact force is a bit of an archaic term. Gravity is certainly one of the fundamental interactions, otherwise you wouldn't exist, so it must be a pretty damn important thing matter is subject to just like the other interactions."
] |
[
"Can anything have wave and particle properties? Just like light."
] |
[
false
] | null |
[
"Yes, as long as by 'anything' we're talking about matter. Matter exhibits wave-like properties according to the de Brogile wavelength (wavelength = h/p, ",
"http://en.wikipedia.org/wiki/Matter_wave",
"). This applies to the fundamental particles just as much as anything else. The wavelength of a person or a planet just ends up being very small since Plancks constant is so small in comparison.",
"This can be shown in the double slit experiment with all sorts of things, not just light. Electrons and even molecules with many atoms show an interference pattern."
] |
[
"All matter (even ordinary matter composing everyday items) have wave and particle propertied when described from a quantum point of view. This quantum description is necessary if one wants to obtain its macroscopic properties from its microscopic description.",
"For instance, it would be impossible to compute the speed of sound inside a crystal without describing its inner structure (mainly the electronic structure) from a quantum point of view.",
"As one of the other posters said, it is all a matter of scale. Everything should in principle be considered as a \"wave and a particle\", but if we are on a different scale, one can often take a classic approximation. For instance, if one wants to compute with a computer the bulk modulus of a salt, one can safely consider the atomic nuclei as classic static objects (even if this is not correct in principle)."
] |
[
"The largest molecule thus far that has been successfully diffracted in a double-slit type experiment had 810 atoms:",
"http://pubs.rsc.org/en/Content/ArticleLanding/2013/CP/c3cp51500a#!divAbstract",
"So yes. Quantum mechanics is a WAVE theory and all matter is described in this language. However, as many different waves (i.e. particles) come together they will statistically come together in a meaningless way that adds to wash out their net waviness which is why we don't observe it in the macroscopic world. However, if you're clever you can make them add their waviness in a reinforcing way, this is called coherence. An example of this is something like a laser or a Bose-Einstein Condensate.",
"EDIT: Spelling"
] |
[
"How do Led Lights/semi conductors function?"
] |
[
false
] |
Hi, I 'm trying to learn how led/semiconductors work. What I understand so far is that there are 2 sides of the led. one contains negatively charged particles and the other positive. there are gaps in the atoms in the negative side, so the electrons from the positive side go to the other. By changing energy levels, energy has to be lost and it is lost by giving off light. depending on how much energy it is losing, the color changes. Is this correct? Additionally, I was wondering how electrical discharge differs from leds. electrons flow from one side to the other side, and collide with gas particles which produces light. why does this method of lighting require gas, while leds only need the movement of electrons? Thanks
|
[
"Why doesnt the P side eventually turn neutral? Should the electroms eventually fill up all the empty spaces and make both sides neutral?"
] |
[
"Keep in mind the LED is connected to a circuit. The electrons are pulled from one end and added at the other."
] |
[
"I know this is pretty old, but I want to stress that both sides of the pn junction ARE neutral."
] |
[
"Does soda maintain carbonation better in warm or cold temperatures?"
] |
[
false
] |
What would be the optimal temperature for storage, and why?
|
[
"Colder, by far. Around its freezing point, water has the highest affinity to dissolve carbon dioxide. That's why warm soda seems to always taste flatter and has more bubbles; the carbon dioxide is bubbling out of solution very fast."
] |
[
"It will hold carbonation worse in warm temperatures. When the bottle is warm, the solubility of CO2 in the liquid goes down, and the gas pressure increases. This causes it to diffuse faster."
] |
[
"Storage doesn't matter. When you open it though, colder is better. "
] |
[
"Why are all particles bosons or fermions?"
] |
[
false
] |
Why is it not possible for a particle to be neither symmetric nor antisymetric on exchange? If a particle can have 1/2 integer spin why can't it have 1/3 , 1/4 etc.
|
[
"Excellent questions - the answers are very subtle.",
"First of all, let's look at your first question, why exchange has to be symmetric or antisymmetric. You may be surprised to know that It's actually a peculiarity of having 3 (actually, just of having more than 2) spatial dimensions.",
"To see why this is, let's think first about how to implement particle exchange. A careful way to do this is to imagine that you start with two particles and slowly drag one of them around the other one until it's on the other side, then slide both particles over so that they are in the initial positions. You should try to draw this if my description is confusing. The statistics shouldn't depend on ",
" you drag one particle around the other, just that you complete one half loop.",
"Now, suppose you exchange the particles twice. That's the same as dragging one particle halfway around the other, and then doing it again, that is, having one particle make a full loop around the other one. Now here's the key point: again, the result here shouldn't depend on the exact shape or size of the loop, only that the particles have been exchanged twice. In two dimensions, this loop must contain the other particle, and you cannot shrink the loop to zero size without crashing the first particle into the second at some point. However, in three dimensions, you can push the loop out of the original plane - in fact, you can shrink the loop to zero size while always keeping the first particle far away from the second particle. (Sorry I don't have pictures! Try drawing some.) This means that two exchanges ",
" have the same effect as doing nothing at all, since the statistics shouldn't depend on what the loop looks like! That is, a single exchange can ",
" either give you a minus sign or no change at all, so that you get no change upon doing it twice. In 2D, this is not true - in fact, you can get ",
"anyons",
" in 2D.",
"This exhausts my expertise for lay explanations to your questions - unfortunately I don't have a non-technical answer to the others. Hopefully someone else can fill in. But I'll give a couple of starting points.",
"Your second question, of why a particle can't have other spins. ",
" (EDIT: Important correction given as a response.)",
"And finally, the connection between the two - the ",
"spin-statistics theorem",
" tells you that bosons have integer spin and fermions have half-integer spin. This again relies on special relativity and having 3 spatial dimensions."
] |
[
"Your second question, of why a particle can't have other spins. It's a result of putting special relativity and quantum mechanics together, actually, in 3 spatial dimensions. For the mathematically inclined, it has to do with the fact that 1/2-integer and integer spins are the only allowed representations of the Lorentz group (which is the set of symmetries of spacetime in special relativity).",
"Actually, plain old rotational symmetry in 3D will give you the restriction to half-integer and integer spins. Adding special relativity will give you the notions of chirality and helicity, as well as the spin-statistics theorem."
] |
[
"It follows from the fact that identical particles can't be distinguished. Consider a system of two particles, with wavefunctions Ψ(x1) and Ψ(x2). The wavefunction of the system is:",
"Ψ(x1,x2)",
"The square modulus of the wavefunction is the probability density function, relating to the probability of finding the particle in some place:",
"ρ = |Ψ(x1,x2)|",
"Since the two particles are indistinguishable, we can interchange x1 and x2 and the probability density should remain the same:",
"|Ψ(x1,x2)|",
" = |Ψ(x2,x1)|",
"Taking the square root of both sides yields two equations:",
"Ψ(x1,x2) = Ψ(x2,x1)",
"and ",
"Ψ(x1,x2) = -Ψ(x2,x1)",
"Since a quadratic equation has two roots, e.g. x",
" = 9 means x = -3 V x = 3.",
"The first of these equations yields a symmetric wave function upon exchange (bosons), the second one antisymmetric (fermions). If a particle were to be neither fermion nor boson, it would need to be distinguishable from its fellow particles.",
"This works for three dimensional space, but in 2-dim space, a particle be something called an ",
", which alternates between acting like a boson and a fermion.",
"At least, this is how it was explained to me in my intro quantum class. A more experienced person can probably provide a better explanation."
] |
[
"Please explain it like I'm five. What is the gist of the Pauli Exclusion Principle?"
] |
[
false
] |
I'm in a Chem 105 class and everywhere I look online explains it to me like I'm in a majors level Physics class. Help me please!
|
[
"Two electrons can't occupy the same orbital (energy state) and have the same spin. That's all."
] |
[
"If you're in Chem 105 then you're probably 18 and not 5. This isn't explainlikeimfive, we treat each other like adults here.",
"Basically it says that two fermions can't occupy the same energy state. An analogy is if you imagine dropping marbles down into a narrow cylinder, their energy is the gravitational energy given by their height, but you can never have two marbles at the same height, because one marbles presence excludes another from being at that height. It's a bit more complicated and subtle for subatomic particles. In the context of your chemistry class, the energy levels are different states the electron can have around the nucleus, characterised by four numbers: the energy level (n), the angular momentum (l), the direction of the angular momentum (m",
" ) and the spin state (m",
" ). The Pauli principle tells you that no two electrons in the atom can share all four of these numbers."
] |
[
"I like this. Succinct."
] |
[
"How is the calorie content of food determined?"
] |
[
false
] |
How can we found the amount of energy that a human body can obtain from a given food? Can this slightly change from person to person?
|
[
"A calorie is a unit of energy, specifically how much energy is needed to heat one gram of water 1 degree celsius. I should note that if you're American, when talking about food, what's measured is actually a different unit, kCals, which measures the energy required to heat one kilogram of water by 1C (so one calorie in the US = one kCal).",
"You can calculate the amount of calories in food by literally burning the food completely and measuring the resulting change in water temperature. ",
"How many calories are in food stays constant, but how well the body is able to process them varies dramatically. If you have a diet high in refined sugars, you will be better able to process sugary foods and take in more of the potential energy than someone with a different diet. ",
"1"
] |
[
"Thanks, good answer. This is what I was suspecting. ",
"How much variability are we talking about? ",
"How can then we trust nutritional charts?",
"(sorry, but the access article is only through a license). "
] |
[
"Out of interest, how accurate is this with materials the body can't really digest (like fibre)? I can imagine that certain things might burn quite well but give very little energy to a human."
] |
[
"How Is Light Slowed Down?"
] |
[
false
] |
A few years ago research results were released which showed the ability to slow and even stop light. What exactly is happening when this happens? I've browsed Wikipedia but I still have a few questions, mainly: Thanks!
|
[
"The slowing down of light can be undestood by assuming that matter is composed of small dipoles, like positive and negative charge on a string which act like an oscillator. Almost like a mass on a string.\nWhen light enters the medium, it drives the oscillators. And the driving frequency is different than resonant frequency of those oscillators, so the oscillators oscillate with a phase shift.\nAnd oscillating dipole radiates, but it radiates the waves with the phase shift given by the driving frequency.\nSo in the end it all adds up and it looks like the wave is slower because of all the internal oscillating and radiating.",
"Waveguides are different. Through solving wave equation, or helmholtz equation, you get different modes for a waveguide with different propagation constants, so that is the dispersion.\nYou can imagine that like you have two mirrors facing each other in parallel, and then you have rays at different angles bouncing between the mirrors as they propagate in the same direction. These are exactly the modes of such waveguide.",
"I can't give you an answer in this.",
"In regard of stopping light, look up photon echo. It is not exact stopping of the light, but it is similar to it."
] |
[
"Wow, So I got them completely inverted. The waveguide is more like things bouncing around and the refractive index is more like waves being phase shifted. In any case It doesn't sound like my scenario in 3 would happen."
] |
[
"In the wave picture of light passing through a refractive medium there is the front velocity which is the Propagation of the first non-zero disturbance of the wave. This is always c just as massless particles travel at c. Nothing can slow a photon down and no valid reference frame can be constructed for particles at c so the last question in 3 is moot"
] |
[
"With today's technology, how fast can a human-made object go in space?"
] |
[
false
] | null |
[
"Sounding rockets can get to space (100 km+) in just over a minute while carrying a several hundred pound payload. The one example I can get while not at work hit 100 km in 75 seconds: ",
"https://www.youtube.com/watch?v=GLhaNd_H5bM",
". There are probably some that went a bit faster but I don't have access to the data right now.",
"However, we typically don't launch rockets just to see how fast it can get to space, so we could probably go faster if that was our only goal as we wouldn't have to carry a payload.",
"Source: I work with sounding rockets",
"Edit: Misread your question as how fast can a human-made object go ",
" space. My bad."
] |
[
"In the old racing mantra, \"Speed costs money. How fast do you want to go?\". ",
"NASA's Solar Probe mission will go just over 0.1% of the speed of light -- most of that speed comes from falling all the way down the Sun's gravity well. Helios was a probe that was launched in the 1970s and achieved 250 km/sec (0.08% of the speed of light). The current record holder for fastest launch is the ",
" spacecraft, which left the Earth at 16 km/sec on direct departure (i.e. all its speed was from rocket thrust).",
"It's very hard to get going faster than about 30 km/sec with direct thrust and chemical rockets. The Rocket Equation tells you how much mass it costs to get going up to a certain speed, with a given quality of rocket engine. It is exponential in your final delta-vee -- every time you increase your speed by an amount equal to the speed of your rocket exhaust, it costs you a factor of about 3 in mass. So to go twice as fast as your rocket exhaust costs a factor of 9. Ideal hydrogen-oxygen combustion gives a rocket exhaust speed of about 4 km/sec, so getting up to 32 km/sec requires a reduction in mass by a factor of about 6500 - i.e. every kg of payload going at 32 km/sec costs you 6.5 tonnes of initial vehicle mass (most of that being fuel). But if you were willing to spend as much on your mission as we spent on the Bush Wars, you could do better than that. Famously, our occupation of Iraq would have funded an Apollo style moon landing about every two weeks for 8 years, for a total of perhaps 200 landings (neglecting economies of scale). If you used that much cash to build an orbiting depot and launched from orbit, you could conceivably get a probe up to maybe 45km/sec with direct thrust.",
"You can get quite a lot of boost by flying by heavy planets, if you time your shot correctly. That's how Voyager got up to its current speed of 17 km/sec. ",
"Getting up to hundreds of km/sec feasibly would require using exotic technologies like ion thrusters, which have much higher exhaust speeds. Those technologies are also energy-inefficient, since you have to pay for the kinetic energy of the fast-moving exhaust -- so either nuclear power or solar power is required. There are some technology hurdles to be overcome to make that type of system work for very high delta-vee, though, so it probably doesn't qualify."
] |
[
"Your question had me thinking. While fastest speeds will almost always come from taking advantage of the Sun's gravity accelerating a craft, how much speed can we get \"departing Earth\" out of just the rocket engines we currently (or used to) possess?",
"Here's an exploration of a possible merged launch vehicle. These are all rockets that humans have built, but might take some doing to merge them properly.",
"The Saturn V is the highest payload launch vehicle ever successfully launched. It can place a 118,000 kg payload into low earth orbit; Assuming an Apollo-style launch, that payload will be 118 miles up and travelling at 7.7 km/s relative to the earth's surface.",
"For orbit changes once launched, many Atlas and Titan launches today use a Centaur upper stage rocket. The Centaur normally has a unfuelled mass of 2200 kg, while carrying 20830 kg of fuel & oxidizer. Let's plan on replacing that 118,000 kg payload of the saturn with a massively upscaled Centaur.",
"Since we're only increasing the tank size, let's assume that the dry mass doesn't quite scale 1:1 - larger tanks usually require slightly different bracing. To use nice round numbers, we'll call the dry mass on the upsized Centaur 18,000 kg. We'll also reserve 10,000 kg for a \"post-centaur payload.\" That gives us 90,000 kg of fuel and oxidizer.",
"To go for optimal efficiency, we'll replace the rocket usually used on the ",
"Centaur",
" with the upgraded but almost identical russian ",
"RD-0146",
" that was just developed, which gives a rocket exhaust velocity of 4.611 km/s; plugging the information above into ",
"Tsiolkovsky's rocket equation",
" says that the Centaur can place itself and the 10000 kg payload on an escape trajectory at roughly 14.333 km/s relative to Earth. Now let's look at that payload.",
"10000 kg is a bit large to push around with ion thrusters if you're going for a \"departing earth orbit\" speed record. Let's go with another chemical rocket. This time we'll use the same engine, and assume the same mass fraction as the normal centaur - so our 10000 kg remaining rocket is about 1100 kg dry mass and the rest is fuel. We fire this \"mini-Centaur\" stage as soon as the oversized centaur is out of fuel and separated. Plugging all that into the rocket equation again, we get a final \"goodbye, earth\" velocity of 24.511 km/s.",
"Real rocket design would involve fine-tuning of the two centaur stages to get the optimal mass fraction out of both, and could give you a few km/s better speed - but this is the ballpark estimate of how much speed humanity's chemical rockets can manage, from launch to interplanetary departure. Once the US is launching its SLS (block 2) or China is launching its Long March 9, we will have launchers capable of placing 130,000 kg in low earth orbit. You can go back and play with various values for orbital stages to see what that additional size in Centaurs would do to the maximum speed."
] |
[
"Why was it much harder to develop blue LEDs than red and green LEDs?"
] |
[
false
] | null |
[
"Gallium nitride (GaN), which is the material used to create blue LEDs, is hard to grow. In order to make an LED you need to make a P-N junction, meaning a layer of p-type material (positively doped) on top of n-type material (negatively-doped). \"Doping\" a material is the process of changing the carrier concentration (number of electrons or holes) and this can be done by adding other elements with a different charge state, such as silicon (adds an electron) or magnesium (takes an electron). Unfortunately, adding these \"dopants\" introduces defects into the host material. Defects are bad and GaN is very sensitive to certain types of defects. Nakamura and others won the Nobel for figuring out how to grown GaN and effectively dope it p and n-type such that the material was still highly-crystalline and thus had excellent optical properties.",
"tl,dr: crystals are good for LEDs. blue LED crystals were hard to grow since they are more sensitive to defects in the material.",
"about me: PhD Materials Scientist who grows GaN and other semiconductor materials. ",
"Sources: ",
"Nakamura's original paper: ",
"http://iopscience.iop.org/1347-4065/30/10A/L1705",
"p-type doping of GaN from Akasaki and Amano (free): ",
"http://iopscience.iop.org/1347-4065/28/12A/L2112",
"Nakamura's Science paper, good overview (free): ",
"http://www.sciencemag.org/content/281/5379/956.short",
"Characterization of GaN PN junctions: ",
"http://scitation.aip.org/content/aip/journal/apl/73/7/10.1063/1.122057",
"Good comprehensive overview of III-nitride semiconductors (free): ",
"http://scitation.aip.org/content/aip/journal/jap/87/3/10.1063/1.371971",
"Also, Nakamura has written an entire book on the subject, some of which you can read on google: ",
"http://books.google.com/books?hl=en&lr=&id=AHyMBJ_LMykC&oi=fnd&pg=PA1&ots=-TWn5KcSiy&sig=J5q-IvF8kHBFelwJIPu9PDoaAjc#v=onepage&q&f=false",
"edits: literature citations"
] |
[
"The light given off by a solid state device is individual photons that correspond to an energy gap. The energy gap is the 'height' that the electron falls into a hole in the emmissive layer of an LED. ",
"Blue photons have a higher energy than red or green photons. This means that you have to have a large hole for an electron to drop into. The problem lies with designing a material that the electron will drop the energy difference in a single move, rather than 2 smaller drops (which might make 2 * red photons for example). ",
"To get a pure colour, you also must reliably get the same energy difference consistently. ",
"Caveat: I don't know the fine details of this beyond this point, and I haven't formally studied condensed matter, so a lot of this is educated speculation based on what I do understand."
] |
[
"Nah you can run blue LEDs at whatever brightness you like, everyone just started using ultrabright blue LEDs because apparently blinding blue light = \"future\" :|"
] |
[
"How come there are two planets able to support life in our solar system (counting Mars too, as it theoretically was in the past), when our star is just like any other of its class and this kind of planets are seemingly hard to find alone as far as our spectrometers can measure?"
] |
[
false
] | null |
[
"These kinds of planets are ",
", but they probably should be common. There has been an explosion of exoplanet observations over the last couple of decades, and we've found that there are planets of all sorts of sizes in all sorts of environments. However, it's typically easiest to detect really massive planets, and/or planets very close to their parent star. We haven't been able to find many planets around Earth's mass and orbit just because they're small and not super close to the star. But each time we get a better instrument, we can observe smaller planets and planets further from their star. There's no compelling reason to believe that this will stop, and we should expect to observe more and more Earth-like planets as our sensitivity improves."
] |
[
"Well, rocky planets with roughly similar gravity, and the right temperature to have liquid water may be fairly common. But the Earth's atmosphere is the result of billions of years of biological influence, so we're not likely to find a planet with a similar atmosphere unless it already has similar life on it, and we really have no idea how common life is. Whether \"right gravity but wrong atmosphere\" is \"easily terraformable\" will come down to what terraforming technology you are imagining, which is getting very speculative at this point."
] |
[
"We have no idea how likely life evolves on these planets. Anything from \"almost guaranteed\" to \"less than 1 in 10",
" is possible."
] |
[
"How long does it take to digest food? What are the major factors that affect this and how do they affect it(e.g. water, protein, fiber, carbohydrate, fat content, etc.)? Also what does the literature say about buildup of bad stuff in the intestines due to the average westerner's diet?"
] |
[
false
] |
I am very short on money for the coming fortnight, and haven't eaten in about 24 hours. I've been passing solid waste consistently for the past month, but today it felt like those little pelets you get sometimes, but looked like brown salsa. I'm not asking for medical advice, I'm just curious about the mechanics of why this happened, and any relevant things. Could it have been because I just ran out of poop? Also: I remember reading that someone was having black tarry stools while fasting for an extended period, and it made me concerned that they had an iron defficiency as that is a major symptom of it. They claimed that it was from the buildup of garbage in their intestines being liberated. Is there such an obvious buildup of bad stuff in the average american's intestine? What has the literature found on this subject?
|
[
"I'll address the second part. There is no intestinal build up from food in normal, healthy individuals. Your entire GI tract is coated in very slick mucous which makes it very difficult for things to stick. Peristalsis throughout the intestines is occuring constantly, squeezing things along. "
] |
[
"Two thoughts to add to what mobeilehypo gave you. Normally, about 30% dry weight of your feces is bacteria. Even if you are fasting, they are still there, and you'd still need to defecate some of them out. ",
"You also defecate out dead red blood cells. So again, even if you are fasting, they still need to be defecated out."
] |
[
"So the new age hippy types that claim there's toxins built up in your intestine from eating meat are wrong?",
"What are your thoughts on the whole fasting for a long time and shitting out the toxins thing? I think it's internal bleeding from an iron defficiency, but I'm not expert."
] |
[
"How does deep sea life maintain the pressure to not be crushed and how does it effect their life cycle."
] |
[
false
] |
Man needs heavily reinforced steel to dive to the bottom, yet whales do it casually to hunt squid, while there are entire ecosystems at the bottom of the mariana trench. Excluding whales, how do these animals maintain the pressure to not be crushed, while still being able to (i assume) lay eggs. As a side question; If the mariana trench is the deepest part of the ocean and thus under the most pressure and we have been able to explore it with submersibles, what is stopping the rest of the waters from being explored in search of the giant squid or those mysterious sounds?.
|
[
"The biggest issue for us is that we need sea-level type air pressures for our respiratory system to work. ",
"Deep sea animals don't have that limitation (they rely on gases dissolved in fluid, which is in equilibrium with their ambient pressure)",
"As far as your last question - nothing is stopping us, but it is a hugely expensive thing to do, and who's going to pay for it? Visibility down there is pretty terrible, so a single well equipped submersible might be expected to map a square kilometre in perhaps a week. The ocean bottom is about 335,258,000 sq km"
] |
[
"No rover is targetted at mapping that kind of area though. Opportunity has covered 30 km in 8 years, and only really observed a narrow strip of that length. ",
"James Cameron has been famously quiet about how much his little sojourn to the bottom of the Marianas Trench cost, but simply chartering the support ship ran into costs of ~ ",
"$1 Million per month",
".",
"So, ignoring any development / maintenance / staffing etc, and assuming a single support ship per mapping area, and we'll increase the mapping rate by a factor of 100 - so will assume we can cover ",
" square km in a month, the project cost would be somewhere in the region of $840,000,000,000 (i.e. $840 billion). Total cost of the MSL mission which included Curiosity was $2.5 billion."
] |
[
"The pressure inside the deep-sea organisms is the same as the pressure outside, as long as they do not descend or ascend rapidly. Thus, they do not have to withstand pressure in the same sense that a human diver with hollow lung-space would. There is an equilibrium between their bodies and their surroundings. If you were to rapidly bring a deep-sea creature to the surface, it would most likely burst and die, as it would be unable to reduce its internal pressure to match the much lower external pressures it would be experiencing on and after the ascent.",
"When fishing, if you catch a fish deeper than 30m, and pull it to the surface too fast, you will often find its eyes are bulging out of its face, due to the sudden drop in external pressure.",
"The Sperm Whale is the deepest known diving mammal, with some observed to dive to 2500m. Their lungs and ribs are designed to collapse and fold up under the pressure, which prevents damage."
] |
[
"How can a 100 solar mass black hole be \"too big\"?"
] |
[
false
] |
Reading the recent news just causes me confusion, I thought the black holes at the center of galaxies have billions of solar masses? How can there be a limit? Won't stuff just keep falling in and increasing the mass?
|
[
"Basically they have very different formation scenarios and exist in very different places. Black hole binaries observed by LIGO are a completely different population than supermassive black holes."
] |
[
"Lone blackholes that keep moving around (stellar mass and intermediate mass\n black holes) are usually small compared to the supermassive blackhole we have at center of the milky way \"sagittarius A*\"",
"The difference is supermassive blackholes like sagittarius A* are not that massive from start , their main source of growth is merging with other blackholes. And these supermassive blackholes are usually found at centers of galaxies",
"Without these mergers it's incredibly unlikely for a blackhole to get that big by just eating gas and stars. ",
"What the news mentioned should be that they saw formation of a blackhole which was much more massive than a stellar mass blackhole from the start."
] |
[
"Stars in the range of 100 black holes are thought to completely destroy themselves in ",
"massive explosions ",
" , before achieving the critical density. So astronomers seem to be missing a link in the sequence of stellar collapse."
] |
[
"Does drafting take energy from the car in front of you, or is it just using energy that would otherwise be wasted?"
] |
[
false
] | null |
[
"While this is correct, it doesn't explain why BOTH cars go faster. In addition to the effect you describe the second car creates bubble of air pressure that literally pushes the lead car forward.",
"Interestingly, NASCAR teams have recently taken to actually touching the car in front of them and pushing them, effectively making one long car with 2 engines, but the air resistance of one. After a little while though decreased airflow to to back car starts to overheat the engine and they have to switch place."
] |
[
"Neither. You are using less energy to drive in the partial vacuum created by the passage of the lead vehicle through the atmosphere."
] |
[
"I see. But would a more aerodynamic would have a smaller vacuum? Doesn't creating that vacuum slow the vehicle down?"
] |
[
"How do you measure the effectiveness of vaccines without a controlled experiment?"
] |
[
false
] |
Working on these of data on flu vaccine effectiveness, I had some questions about how these estimates are made. First, whats the difference between vaccine effectiveness, and vaccine efficacy? Second, this data come from studies using the described below: Under the test-negative design for influenza VE, study subjects are all persons who seek care for an acute respiratory illness (ARI). All subjects are tested for influenza infection. Influenza VE is estimated from the ratio of the odds of vaccination among subjects testing positive for influenza to the odds of vaccination among subjects testing negative. How can you get an accurate measure of effectiveness by only evaluating sick people? The assumption is that people do not differ in ARI rates across the vaccine and no-vaccine groups, but is that realistic?
|
[
"The only way you could test the number of people it definitely worked on would be to purposely expose people to the virus. Hardly ethical.",
"I mean that's been done and it's considered perfectly ethical, with informed consent. ",
"But of course it's not the only way to test vaccine efficacy. You don't have to deliberately expose people to flu, because people get naturally exposed to flu every day.",
"You could \"simply\" do a randomized controlled trial, as you do for virtually every clinical intervention. You collect a few hundred thousand people, randomize them into \"vaccine\" and \"no vaccine\" groups, wait through a flu season or two, and then ask which group had fewer cases. (Obviously it's more complicated than that, but the principle is straightforward.) ",
"But you're exactly right in the point of the test-negative design. Millions of people are naturally vaccinated, millions of people are naturally exposed to flu, without being part of a formal randomized controlled trial. The test-negative studies are approaches that take advantage of these natural experiments, without the huge cost and trouble of even a small RCT.",
"Vaccines are tested in RCTs all the time, but test-negative studies are the next best thing, and give much more bang for the buck."
] |
[
"Efficacy is basically how well it works under perfect conditions while effectiveness is how well it works in practice. A medicine can have high efficacy but if people have trouble using it, the effectiveness might be low. e.g. A drug might have a 100% chance of killing a particular virus (which makes it very efficacious) but if it requires being injected into a very specific vein while your blood sugar is exactly 5.2,during a full moon then it's probably not very effective. ",
"A negative control like the one described is still a control, just not as good. But you work with what you've got. You compare the number of people who got sick that got a flu jab vs the number that didn't. The only way you could test the number of people it definitely worked on would be to purposely expose people to the virus. Hardly ethical. "
] |
[
"I don’t think you understand the system. They absolutely know if they’re vaccinated and they absolutely know what strain they’re infected with. That’s the “test” part of the “test negative design”. ",
"Edit to explain: they’re testing people with flu-like symptoms, but since there are many viruses that cause flu-like illness they’re not just testing “failures”; even in flu season something like 90% of ILI is not flu. If (simplified) 60% of ILI patients without flu are vaccinated, and 20% of ILI patients with test-positive flu are vaccinated, then you’re seeing a protective effect and controlling for the two biases I mentioned in my other answer. "
] |
[
"Why do some types of bread grow mould, while others become hard?"
] |
[
false
] |
I was chewing on some rock-hard french bread when this thought occurred to me the other day
|
[
"Bread going hard is due to staling. It was originally thought to be due to loss if moisture from evaporation, but staling is now understood to be a manifestation of starch retrogradation, the recrystallization, water migration out of the granules, and hardening that take place when cooked starch is then cooled. In other words bread can go stale even when moist. This type of staling coupled with temperature and spore exposure allows fungi to prosper.",
"Some breads have the correct starch crystallization to facilitate rapid water migration, which means dry stale, which doesn't lend itself to hosting fungi."
] |
[
"So if I store my bread on a refrigerator it will go stale quicker, but I would avoid mould from growing on it?"
] |
[
"Yep, that's about right. Other than freezing bread, one of the best ways is to keep it in an unglazed clay pot with a lid on. It is counterintuitive but what is happening when bread goes stale is that the starch molecules in the bread are crystallizing, which requires moisture as does any mould spores. The clay will absorb any excess environmental moisture thus keeping your bread nice and fresh. Try it! "
] |
[
"Why is DNA made up of adenine, thymine, cytosine, and guanine?"
] |
[
false
] |
It is common knowledge that DNA is what "codes" many biological functions. But why is it made up of the famous ATCG nucleobases? Is there some chemical property behind them that made them "ideal" for playing an important role in life? Was it something that occured when life was just being formed on the earth that led to some kind of primitive natural selection for these bases? Could some other molecules replace these ones and lead to a different type of DNA? I am a university biochem major but I have yet to take O-chem, so any background info or additional reading would be helpful too. Thank you.
|
[
"The nucleotide bases are particularly good for storing infomation. They have 3 bonding positions, 2 are used to create the main chain, the last to form a weak bond with a matching base. This makes them particularly good at storing information, being read and being copied. Other chains have some of these properties, but DNA wins out on them.",
"From memory, I believe there are 20 or so possible bases that form naturally. (Evolution was a take what you can get game back then) Some of them are better than others at the job. Some bond to weakly, some to strongly, others interact with other chemicals. At least 4 were particularly good for the job, at least back when it evolved.",
"Why 4 bases? We don't really know, but we can make some guesses. \n* It might just be fluke. The first system to work well had 4 bases and simply overwhelmed the other versions. \n* It could also be that only those 4 bases were suitable at the time and so they came to dominate. \n* The third option is that 4 bases has a particular benefit. 2 bases give the lowest ambiguity to the data (hence why computers are binary) but 20 give maximum information storage ability. 4 Might just be a good balance point.",
"There is an intreaguing thing about the 4 bases thing though. In quantum computing Grover's algorithm only takes 1 computational check to match a base. 4 times faster than a traditional sorting algorithm. At 5 bases it takes 2 checks on average. DNA copying is one of the most critical tasks a cell does, it also happens to be faster than it 'should' be almost 4 times faster. It is also done on the same scale that current quantum computers can work on the same algorithms. Might be fluke, but there would be a huge advantage to it.",
"As for why we still have 4 bases. The DNA coding system is highly conserved. It's akin to a computer language. You can change the code and make slight changes, that might be better. But if you change the way the code is interpreted and compiled, it will likely break it. In sort, once the DNA/RNA system became established, changing away became almost impossible. Any change to it would be deadly."
] |
[
"RNA came before DNA, but since RNA is less stable than DNA (RNA has an extra oxygen which makes it prone to strand breakage) DNA became the long-term store for genetic information, while RNA is used (mainly) as a transient message in the cell. I'm not sure what you mean by \"why didn't the change from RNA to DNA break it?\".\nDo you mean change the bases used? If so, RNA has pretty the same ",
" as DNA (only thymine is replaced with the very similar uracil). It's only the presence of an extra oxygen on the ribose sugar that distinguishes the two"
] |
[
"RNA is easier to make proteins from, but a lot less stable. DNA can be coded into RNA though.",
"It's akin to a computer with RAM and a HDD. The RAM (RNA) is fast but unstable, the HDD (DNA) is better for long term storage and can be dumped to RAM for use."
] |
[
"Why do some people suffer mentally, when spending extended periods of time with other people?"
] |
[
false
] |
Some people can spend time with others indefinitely, whilst others need to take time away, alone, to recharge or cool off. Why is this a problem for some people and not for others?
|
[
"As is the case with most things in psychology, there is no defined answer that seems to totally fit as an explanation. There are two explanations I can think of for this and one is related to personality and the other is a neurological function. In short you're asking a question on what causes the social aspect of \"introversion\" and \"extroversion\" (which in itself most psychologists will probably say people are somewhere in the middle and don't quite live on either extreme). ",
"Now there are several theories on what emphasizes these attributes. The go-to answer most psychologists will say is it comes down to both \"nature\" and \"nurture\". The nature aspect says some people are simply born to be more socially adept and desire to be more social (wanting to live in a community, desire human interaction in everything they do) while others are born to be more independent (you can find nature documentaries that show these mannerisms in other social animals, like monkeys, as well). \nThe nurture aspect states that the way you are raised as a child and the experiences you undergo will highlight and enhance certain aspects of your personality. Some theories suggest it has to do with whether your parents were overprotective or if you were not properly socialized as a child (i.e. you were an only child, didn't have many children around you, etc). ",
"That explains the personality aspect. The neurological aspect has to do with the frontal lobe and its ability for executive function and inhibition control. Everyone is susceptible to needing to get away to \"recharge\". Even if you are the most social person if you spend a week of vacation with a friend you'll often find by the time you're on the plane back home you can go a LONG time without seeing them again. In general when we are around people we need to use our executive function and inhibition control to sort of control how we behave so that we don't give off bad impressions. (Note: executive functioning is a general term to mean anything that requires management; inhibition, time management, attention and focus, etc). A person only has a finite amount of \"executive functioning\" they can perform in a day, after which time it recharges through sleep. (in fact, if you don't get enough sleep this is why many people report not being able to focus or they start to lash out at others) So, if you're in a social setting and are actively monitoring your own behavior this may result in a feeling of being overwhelmed and the desire to get away will be enhanced. ",
"Edit: I should note, in my opinion, any mental \"suffering\" that occurs from having to be in a social setting is a different issue and not related to the above explanations. If you are an individual that actually \"suffers\" from social interaction that is likely indicative of another issue (usually a personality/behavioral issue). "
] |
[
"When talking about extraversion-introversion, Eysenck's theory is one of the most popular ones.",
"\nWhat Eysenck basically said is that introverted people get aroused ",
" easily by stimuli, while extraverted people get aroused ",
" easily by stimuli.",
"\nThe effect of this is that an introvert will get overstimulated far quicker than an extravert, and is more likely to avoid stimulating environments because of this.",
"\nExtraverts on the other hand, actively seek out stimulation, to sort of get their dose of excitement. ",
"So an introvert would then be drained more quickly and would need time alone to recharge. The extravert is able to stay in company for longer.",
"A short note; I'm talking about extraversion and introversion as binaries, while in reality they happen on a spectrum. "
] |
[
"I liked the neurological explanation, I never considered it that way. I always thought in terms of personality. ",
"So you're saying that neurologically, some people have more \"energy/stamina\" for executive functioning than others? (I say energy/stamina for want of a better word)."
] |
[
"Could the lithification process expand/shrink the original fossil size?"
] |
[
false
] |
Meant petrification*, the process by which fossils are formed.
|
[
"Fossils can be deformed, but that doesn't have anything to do with the actual process of fossilization. It's typically due to tectonic activity that flattens or shears fossils. ",
"The page you linked to is a gross oversimplification of the process by which fossilization occurs, which may be leading to your confusions. Wikipedia actually has a nice overview of different types of fossilization ",
"here",
". What's notable about these explanations is ",
" these processes occur. They're not just chunks of bone-shaped rock (although these can exist as natural casts in the fossil record).",
"In permineralization, original material remains while spaces are filled in with minerals. In replacement, the original material is replaced bit-by-bit with minerals. Both of these can actually preserve cell structure, so we can take thin sections of bones and look at growth lines in them, for example. We can count tree rings. We can look at cell walls in plants. We can look into minerals incorporated into teeth and bones as they grew, telling us what sort of plants the animals ate or what the climate was like at that time (this is what can be affected by ",
"diagenetic alteration",
". All of these features aren't always preserved, but they are enough of the time that we know that what we're looking at represents the morphology that was present in the original organism.",
"To answer your question below, no, fossils from the past aren't bigger because they grew during the process of fossilization. In some cases there were terrestrial animals larger than are alive today. There are various reasons for this (see: ",
"why sauropods may have gotten so big",
" and ",
"what happened to larger mammals",
"). ",
"However, there were certainly smaller organisms or those perfectly in line with what you see today. They are more difficult to preserve in the fossil record (because they break or get destroyed), more difficult to recover (because they're small and hard to find), and honestly, a lot of early paleontologists weren't looking for them. You often have to bring sediment back to the lab and sort through it under more controlled conditions, and transporting that sediment may not be possible from the field. These are called ",
"taphonomic biases",
". Some of these logistics are now more feasible, and there is an increased interest in the microfaunas of the past. This means we are starting to spend a lot more time looking for these smaller fossils!"
] |
[
"Both diagenesis and lithification tend to involve dewatering and compaction. So if anything any changes in size might be expected to be reductions. Getting bigger is basically out of the question."
] |
[
"Lithification is the process by which fossils are formed.",
"Ahhhh. I think you might be mistaken, and are actually asking about taphonomy?",
"Lithification is certainly one process that is very important. And there are unquestionably biases imparted to the fossil record due to taphonomy. But the reduction in size is not something I would worry about biasing fossil reconstructions ",
" absent evidence to the contrary (which in specific cases there very well could be!).",
"Can I ask what prompted this question?"
] |
[
"I read the story on the front page about Mount Fuji's imminent eruption, what global implications does this have if the eruption is as big as the say it potentially will be?"
] |
[
false
] | null |
[
"A quick point on reading articles about volcanoes.",
"If they use the word 'overdue', start treating it as an overhyped piece of garbage.",
"To deal with it point by point:\nWe know Fuji is active - an eruption at some point in the future is almost inevitable. We cannot at any point use the word overdue, and any volcanologist worth their salt would not use that word. It is a word crap journalists who don't understand what they're writing about use. Volcanoes do not obey nice simple patterns of erupotion behaviour. There is no such thing as being 'due' an eruption.",
"Equally, steam, boiling mud and other hydrothermal indicators are situation normal for such a volcano. They do not indicate an imminent eruption - all they indicate is shallow magma. Which we know is there in any case.",
"The fault discovery is simply odd to bring up. Just because it was recently discovered does not mean it was recently formed. indeed, a 34 km long fault does not just appear - it forms over time. Given it's subduction zone location, it also suggests it's relatively deep. The fact they provide no reference whatsoever for the 'experts' suggesting it offers a risk of collapse is also odd.",
"What's ",
" odd about that bit of information is that all I can find with 5 minutes of searching is ",
"this",
" and a reuters piece, neither of which quote any peer reviewed work. Now, it shoudl come as no surprise to anyone that there's a fault down there - Fuji is smack-bang on top of an active subduction zone. The problem is that I can't find ",
" solid info ",
" suggesting it has any influence on the volcano.",
"What I find really bizarre is that they're reporting greater internal pressure than the 1700 eruption. Anything we have inferred about the 1707 eruption is just that- inference. We certainly didn't measure the stress regime inside the volcano.",
"The 0.1 megapascal minimum eruption pressure is a red-herring being thrown in there with no context; an open vent will allow eruption at any pressure high enough to force the magma out. It's a function of many many different variables. 1.6 megapascals is certainly a big number, but 4 or 5 megapascals is not out of the question to even begin to force material from a shallow felsic magma chamber. That pressure increases with depth too.",
"Finally, the source article is here: ",
"http://english.kyodonews.jp/news/2012/09/180633.html?searchType=site&req_type=article&phrase=Mt+Fuji",
"You have to have a subscription to that newspaper, so I can't see it. There doesn't appear to be any peer-reviewed publication to refer to that I can find.",
"TLDR: Meaningless numbers are meaningless, overhyped press release is without content or merit, scaremongering is inevitable and wrong. Fuji is going to erupt, this we know. This reporting brings nothing to the discussion and does nothing but promote a kind of undirected and uninformed fear."
] |
[
"Not sure what article you're looking at. Link would be appreciated.",
"But all that has been reported is that there is a higher pressure regime under there than there has been for some time.",
"That does not mean an eruption is imminent. It also gives no information on potential eruption volume. Fuji tends to erupt VEI 5 or less (i.e. same size or smaller than Mt St Helens 1980 eruption of 1 cubic kilometer), with the smaller ones being the most common."
] |
[
"http://www.wired.co.uk/news/archive/2012-09/06/mount-fuji",
"This was posted in ",
"r/worldnews",
"."
] |
[
"When I cook food in the oven, what does hotter temperatures versus a longer cooking time do to the physical structure of my food?"
] |
[
false
] |
This is something I wonder about whenever I fire up my toaster oven. How does turning the heat up versus leaving it in for longer affect my food? Do they have discrete properties that affect the food? Or is it just a mathematical function? heat x time = heat energy radiated into my food. Could I halve the cooking temperature and double the cook time and have the same result? I see how some kinds of food like meat or fish would only cook at a certain temperature, so some recipes would necessitate a certain cook temp. What combination results in the most even cook? As in, the inside of the food heats up at the same speed as the outside. Why are almost all recipes either 350F, 375F, or 400F? Why is nothing at 200F or 800F?
|
[
"Although you can sometimes tweak the temperature and time ratios in a recipe to get the same result, cooking is a ",
" process -- this means that there are some specific, critical temperatures above/below which certain processes will/won't happen. ",
"For example, meat/fish items usually have to be cooked in such a way that the entire object reaches some minimum temperature (160F, or so) in order to ensure that dangerous bacteria and the like have been destroyed. ",
"Heat flow equations tell us that if we want the core of an object to reach a certain temperature, there are two extreme ways we can do this. If we want to do it quickly, we just have to make the outside really hot (the rate of heating will increase with the magnitude of the temperature gradient), but this might end up burning and/or drying out the food. The other extreme is to make the oven temperature equal to what we want the inside of the food to be, and wait for the temperature throughout the entire object to reach equilibrium (which will probably take a really long time). Balancing these two extremes tends to mean heating things in the temperature ranges you mentioned; 200F would take way too long, and 800F would probably end up burning the food before the inside got hot enough to be \"done\". "
] |
[
"For example, meat/fish items usually have to be cooked in such a way that the entire object reaches some minimum temperature (160F, or so) in order to ensure that dangerous bacteria and the like have been destroyed. ",
"This isn't totally accurate. At 160F, bacteria die instantly. That is from what I understand why the USDA uses this value. If your food reaches that temp, all that stuff is dead.",
"However, it's not the only way to kill it. At about 135F those things start to die. If you hold your food there long enough, you can achieve the same level of killing things as you would as if you got it to 160F. The advantage of doing this is that you don't overcook your meat.",
"In the past this has been difficult, since you don't really know what temperature your food is at as you are cooking it, so it's hard to measure how much time it is spending at what temperature. Nor is it easy to hold your meat at an exact temperature when you are cooking in the oven/grill/pan, etc. However, with sous vide cooking becoming more popular and doable for more people, things are starting to change. Sous vide is basically putting your food in a bag, removing the air, and then putting it into a water bath that is held at a specific temperature, so your food can reach that exact temperature from end to end and all the way through. ",
"This article",
" has some more information on that and how it relates to chicken breasts. You can cook a chicken breast to 140 degrees and make it just as safe as one that has been (over) cooked to 165 degrees by making sure it remains at 140 degrees for 35 minutes. It is also delicious and will completely change your mind on what a chicken breast can be. ",
"There's a ton more info out there on food safety and sous vide that is easily found. ",
"This",
" is a commonly sited source. "
] |
[
"Go find and watch Good Eats with Alton Brown. He goes into the specifics of the affects of certain cooking techniques on the foods featured.",
"For instance, if you are cooking meat that has a lot of fat and connective tissue (like ribs and pork shoulder) you want to cook it for a long time at a lower temperature to allow those connective tissues to loosen, making the meat tasty and tender. But if you had something like a fat free chicken breast, you would need to cook it hot and kinda fast to keep it from drying out."
] |
[
"I just read a research paper about \"downregulation of cannabinoid receptors in daily cannabis smokers\". Does that mean that cannabis actually does have a mechanism for physical addiction?"
] |
[
false
] |
Full disclosure, I am a cannabis smoker myself. We've always liked to tell ourselves that weed isn't addictive like caffeine or heroin that have direct chemical effects on your brain, it's just psychologically addictive like anything else you enjoy, like TV or shopping. But I recently found this study, and I'm wondering if it means that entire commonly repeated view is maybe not so accurate? Reversible and regionally selective downregulation of brain cannabinoid CB1 receptors in chronic daily cannabis smokers I don't know what role "cannabinoid" receptors normally play in the human body, but it sure sounds like cannabis is downregulating a neuroreceptor in your brain, sort of like caffeine does to norepinephrine, right?
|
[
"So there's a few things we should clear up first. The terms \"physically addictive\" and \"psychologically addictive\" are not great. They lead to people misunderstanding how addiction and dependence works. What you are calling \"physically addictive\" is the idea that when people use certain drugs for some period of time, and then stop taking them, they become sick in some way. This is not addiction. There are many drugs which do this, (corticosteroids being a good example, where you can die if you stop taking it when you've been on a high dose), but are not addictive at all. People do not necessarily feel an urge to continue to take these drugs. This is called \"dependence\" and the sickness you get when you are dependent on a drug and stop taking it is called \"withdrawal\".",
"Addiction on the other hand is the strong compulsion to perform an action, even when you don't want to perform that action, or when it is having a detrimental effect.",
"Some drugs can cause dependence , but are not addicting, like corticosteroids. Some drugs are addicting, but basically don't cause dependence, like nicotine. And some drugs cause dependence and addiction, like alcohol and heroin.",
"It is ",
"well established",
" that heavy cannabis users experience mild withdrawal symptoms, specifically in terms of lack of sleep, lack of appetite, stomach pain, anxiety and irritability. And as you've read, cannabis use causes a down-regulation of CB1 receptors. In humans, if you block CB1 receptors you get lack of sleep, lack of appetite, stomach pain, anxiety and irritability. So it certainly seems like cannabis withdrawal is caused by the downregulation of CB1 receptors.",
"Just FYI, caffeine works by blocking the adenosine A2A receptors (as well as a few other things), Blocking the A2A receptors has numerous effects, but one is to increase the release of norepinephrine/noradrenaline."
] |
[
"To add, downregulation or desensitization of a receptor when exposed to high levels/prolonged levels of an agonist (or partial agonist as with THC) is nothing extraordinary, rather is something to be expected in the pharmacology world. The decrease in receptor number and a decrease in signaling efficacy certainly plays a role in the establishment of tolerance to cananbinoids that is observed. But that’s not indicative of addiction, more so just a homeostatic response of the system.",
"\nSince you (OP) asked, generally cannabinoid receptors in the central nervous system are found presynaptically. They’re a G Protein Coupled Receptor (Gi), tended to be thought of as an inhibitory GPCR. Activation of the receptor decreases neurotransmitter release, both through second order messenger pathways (reduction in cyclic AMP levels -> decreased PKA activity) and direct membrane deliminated actions (inhibition of voltage gated calcium channels, activation of inward rectification potassium channels via the beta/gamma subunits). "
] |
[
"Why do you say nicotine doesn't cause dependence? Or are you just speaking relatively to stronger drug related dependencies? I certainly notice I become irritable and often get headaches (similar to caffeine withdrawals, but worse) if I haven't had nicotine in a while (usually about a day). I don't have a strong addition, but I'm definitely addicted, although I've been trying to work on that lately. "
] |
[
"If we could travel and c+1, what would happen if I outpaced the expansion of the Universe."
] |
[
false
] |
What would be in the zone that would eventually be filled later by the expansion of the universe. I realize this might be a stupid question.
|
[
"First, everything we know about the universe tells us that nothing can change position faster than the speed of light. If your question requires us to assume that you ",
" change position faster than the speed of light, then your question cannot be answered.",
"Second, the rate at which an object is receding from us due to expansion is ",
" limited to the speed of light. This is because rather than the objects' position in space changing, space itself is expanding. There are many objects we can see that are receding at rates significantly above c.",
"Third, there is no \"zone that would eventually be filled later\". The expansion of the universe isn't carrying a bunch of stuff out into some empty void. Rather, the entire universe is already filled with stuff and that stuff is just getting more and more spread out."
] |
[
"You seem to have asked several questions at once, but I am not really sure what you are asking. What does c+1 mean?"
] |
[
"This question is ",
" somewhat related to ",
"\"What is the universe expanding into?\""
] |
[
"How can quadriplegics breathe?"
] |
[
false
] |
I've always heard the phrase "paralyzed from the neck down". Is this really the case? If so, then how does the heart beat? And how does digestion work? I'm assuming this isn't the case, so why is it only the arms and legs that are affected?
|
[
"It depends on the level of paralysis. The diaphragm is innervated by the ventral roots of the cervical roots from C3/C4/C5, so lesions at or above those levels may indeed result in loss of diaphragm function, and thus require mechanical ventilators to breathe. ",
"The heart functions fairly autonomously (since its contractions are mediated by the SA node), and is thus able to beat independent of spinal influences. However, there are a number of parasympathetic and sympathetic inputs to the heartbeat, such that damage to the vagus nerve (unlikely in a purely spinal lesion, since the vagus nerve is a cranial nerve) may result in tachycardia, and damage to the sympathetic ganglia may result in inability to modulate inotropy. ",
"Digestion is similarly largely governed by neurons of the enteric nervous system, which function fairly independently of higher-order inputs. There is some parasympathetic and sympathetic signal to the gut, which may indeed affect digestion, but my understanding is that those factors aren't as important as the native enteric nervous system."
] |
[
"CN 3, 4, 5 keeps you alive."
] |
[
"Many quadriplegics ",
"require breathing equipment",
" to force air in and out. (Injuries to C1-C2 necessitate this)",
"A large percentage of patients die due to pneumonia as they are unable to evacuate fluid from their lungs. ",
"Digestion and heartbeat are entirely separate functions, governed by brainstem and similar tissue structures. ",
"Relevance: Surgeon's Assistant"
] |
[
"If the Milky Way collided with another galaxy, would our solar system be affected? Would Earth change?"
] |
[
false
] |
I've heard about galaxies colliding but due to the massive size, would anything likely happen?
|
[
"Generally speaking, two galaxies colliding wouldn't be a collision that you would fit in the every day sense of the word. Despite the immense amount of material in a galaxy, the density of that material is still reasonably small since it's spread out in structures with diameters on the scale of hundreds of thousands of light years across. Because if this, effects from the merging of the two galaxies would be seen on more of a galactic scale as opposed to a solar scale."
] |
[
"We might get hurled out of the soon-to-be singular galaxy, or we might get hurled into the center. At worst I could imagine the gravity of a passing star disturbing orbits, I doubt direct collisions are likely, though."
] |
[
"I remember seeing something about this somewhere. It was a TV show. ",
"You have to remember the distances between stars are immense. The closest star (other than the sun) to us is Proxima Centauri, at 4.24 light years away. That's 2.49248392 × 10",
" miles away (24,924,839,200,000 miles).",
"So the chance of a collision is extremely, extremely small. The solar system could be put into an erratic orbit or gravity from an object could disrupt the Earth's orbit from the Sun, but even then that's also an extremely small chance."
] |
[
"How would one explain Slowing of a mechanical clock as satisfactorily as the photon clock?"
] |
[
false
] |
I understand how a photon clock, placed perpendicular to motion, slows down and also the fact that since one clock is slowing down all others must as time, a physical phenomenon, must behave the same. But how would one explain exactly HOW a mechanical clock would slow in relativistic conditions?
|
[
"You would have to know ",
" specifically how the clock works. Which is why it's much easier to just point out, hey, all clocks in a single reference frame should agree."
] |
[
"The thing is, it feels like you're assuming the slowing of a photon clock is the explanation for time dilation, when it's actually the converse - time dilation is an explanation for why a photon clock will slow down.",
"The photon clock example, while relatively easy to understand, is still highly counter-intuitive. The entire concept behind it from the invariant speed of light is very weird to envision, and I honestly feel the photon clock makes you think you understand the phenomenon ",
". I'm not saying this is a bad thing, since some understanding is better than none.",
"Here's how you should think of the photon clock: with respect to your reference frame, moving [inertial] reference frames experience time more slowly than you do. If you examine the phenomenon of a photon bouncing back and forth at a certain rate, you can conclude through separate means that the rate is slowed by the same factor relativity says time is slowed. That's just independent verification, ",
" an argument for the cause of the dilation. Time slows in a moving reference frame, therefore both a mechanical clock and a photon clock must slow in that reference frame.",
"There isn't going to be a way to explain ",
" the mechanical clock slows down, just like there isn't a way to explain ",
" radioactive particles that are moving decay more slowly than their stationary counterparts. Relativity doesn't tell you ",
", it says that this is how the laws of nature work, and these are the equations that make them work. And it came from something very different than photon clocks or poles and barns.",
" - The photon clock is another way to look at the time dilation effect with ",
" (the photon). It doesn't explain dilation, nothing does. Dilation happens, period. It must happen for the laws of physics to be the same in all reference frames such that light speed is invariant, because it is. Period."
] |
[
"This is an excellent excellent answer. I understand that dilation isn't BECAUSE of the clock slowing down, rather it's the dilation slowing the clock down. But there appears to be a very definite way in which the photon clock is slowing down however I fail to find such a mechanism behind more conventional clocks. ",
"I also like your idea that the photon clock is letting me believe I know how time dilation works when I haven't the slightest idea. BUT, the clock seems to explain how time is dilating for it. What am I reading too much into?"
] |
[
"Does the removal of leaves from suburban land very year cause damage to soil quality?"
] |
[
false
] |
I was watching the town trucks pick up leaf piles curbside and it got me wondering. non-science person here, sorry if im misunderstanding some basic concept. Every year*
|
[
"Generally leaf litter is a positive contributor to soil health in a number of ways, including but not limited to:",
"Recycling elements such as carbon dioxide and nitrogen to be absorbed again by plants, and playing a part in the nitrogen cycle.",
"Providing important food to microflora and fauna, which in turn work the soil, thereby increasing soil aeration.",
"Helps to break down clay soil, aiding drainage and aeration. ",
"So removal of leaf litter prevents these and other benefits from happening, but to be fair, it's not on a large enough scale to be noticeably detrimental. Various things happen throughout the seasons which add to & subtract from soil health."
] |
[
"Most likely you would be able to detect very minute changes over long spans of time (say decades) but if you look at what percentage of a tree actually comes from the soil and not the air then you would have a much better perspective. Over 90% of the tree comes from the air not the soil, this is in the carbon that is pulled from the air and subsequently turned into various products in the tree. This is why trees are very good at temporary carbon sequestration. See here ",
"http://entirelysubjective.com/what-are-trees-made-of/"
] |
[
"Removing leaf litter is also a recommended practice for managing plant pathogens; they tend to overwinter in this stuff."
] |
[
"Why is it so satisfying to rub our eyes for long periods of time? And why do we see all the pretty \"shapes and colors?\""
] |
[
false
] | null |
[
"I don't know why it's so satisfying, but the pretty 'shapes and colors' are called an 'endoptic phenomenon'. It's caused by applying pressure to the eyeball, which raises the intraocular pressure, or the pressure inside the eye which in turn affects blood flow to the capillaries that feed the retina, causing strange retinal activity which the optic nerve interprets as pretty flashing lights and colors. It's basically the same idea as wiggling your monitor cable until your computer monitor starts flicking and doing weird things. "
] |
[
"That satisfying, calming feeling that occurs when you rub your eyes is due to the oculocardiac reflex. Pressure being applied to the eyeballs or the extraocular muscles can decrease an individual's heart rate. In turn, this results in a calming, relaxing sensation."
] |
[
"To further elaborate on the strange shapes and colors, increasing the intra-ocular pressure stimulates the rods and cones in your eyes (the photoreceptors responsible for seeing color and brightness). As it stimulates them, it causes them to send signals to your brain perceiving the sensation of colors or shapes. "
] |
[
"Why are lions and tigers considered separate species if they can produce fertile offspring?"
] |
[
false
] |
Isn't the ability to produce fertile offspring the defining characteristic of a species? This is why all dogs are the same species, while horses and donkeys are separate, right?
|
[
"No, ",
", for example, can produce fertile offspring but are different species. Same with domestic cats and several species of jungle cats. ",
"Some of the ways speciation can happen is through geographic separation (eg, migration to island) or behavioural separation (eg, one group mates in winter, other in summer).",
"However, species is not a clean-cut word. There are problems defining it among experts. You can read more ",
"http://en.wikipedia.org/wiki/Species_problem",
"EDIT: I guess I didn't answer the actual \"Why\" of your question. The reason tigers and lions are different species is because of different behaviours, different habitats, different social hierarchies, and they each have their own subset of genes that they share within their species (like the genes for stripped fur or for manes)."
] |
[
"Dogs and wolves are the same species, but different subspecies (Canis lupus familiarus vs. Canis lupus lupus, respectively). ",
"So speciation happens due to myriad causes, which all eventually lead to reproductive isolation. As virkon points out, this doesn't have to be inability to produce fertile offspring. It can be speciation by geographic distance/barriers, it can be life history barriers including reproductive timing. In the case of African Lions and Asian Tigers, it's probably geographic isolation. ",
"Worth noting is that the species concept isn't terribly rock-solid and isn't agreed upon by scientists. For my masters work, I studied two species from the same genus that could reproduce, had the capacity to generate viable hybrid offspring, and co-occurred geographically and ecologically. They didn't have reproductive timing differences. But because hybrids were a rare occurrence in the natural systems, they're considered different species. With the revolutions coming so rapidly in genome sequencing, I imagine we'll be able to come up with a genomic definition of what a species is to add to the long list of species definitions. "
] |
[
"Isn't the ability to produce fertile offspring the defining characteristic of a species?",
"It depends on your definition of a species. What you're describing is the popular biological species concept. However, that is simply one of about ",
"26 or so definitions."
] |
[
"Why we can't use supercaps as a battery alternative?"
] |
[
false
] |
I know that caps can provide a huge power within a short period of time, while common batteries can provide power over a long range of time. But why we can't just put a into the circuit with the supercap to make the discharge time longer and to use it then as a battery alternative?
|
[
"You can delay the discharge of any capacitor (or supercap) by increasing the resistance of the circuit. However, there are two things that need to be considered: "
] |
[
"Batteries also have a much flatter discharge curve (their voltage stays relatively flat from 100 to 0 percent). A cap has a much steeper curve. Nothing a simple power control circuit can't rectify (hehe), but that just adds cost and complexity. "
] |
[
"I think its not just about the discharge time, but also charge duration, as in amp-hours. You would need lots of capacitors to provide the same total amount of watt hours, which ends up costing lots of money.",
"This is currently done in applications where cost isn't a big factor, like the SAE's Formula Hybrid competition where college students develop electric and hybrid formula race cars. They all use supercaps because its about performance, not cost. "
] |
[
"Radiocarbon Dating seems the most popular form of dating objects. What are it's flaws and what other options of dating are available?"
] |
[
false
] |
[deleted]
|
[
"ACtually, carbon-14 is only used for dating relatively young things. For other methods used in archaeology ",
"this wiki article",
" is probably a good place to start. The ",
"wiki article on radiometric dating",
" covers a huge array of methods used in geology and cosmochemistry for dating older mateirals and discusses the potential problems.",
"Regarding carbon-14, ",
"this part of the TalkOrigins site",
" responds to claimed problems with the method. Practically everything you want to know about carbon-14 dating is presented ",
"here",
". Check out the \"Pretreatment\" section for discussions of contamination."
] |
[
"Thanks for responding. I've read this article on radio metric dating and the flaws aren't easily detectable. Can scientists explain the flaws with the scientific methods of dating objects? Where are the objective scientists who challenge scientific methods?"
] |
[
"Radiometric dating is so well tested that it is accepted in the scientific community."
] |
[
"Question about DNA phosphodiester bond?"
] |
[
false
] |
Hi, I'm in a microbio course right now in college, just started. I feel like my question is just an issue in wording, but here's the reading: "Nucleotides have a 5’ phosphate group at one end and a 3’ hydroxyl group at the other end. When nucleotides are polymerized, the 3’ hydroxyl group of the first nucleotide is joined to the 5’ phosphate group of the second nucleotide. The resulting dinucleotide will have a 5’ end (the 5’ phosphate of the first nucleotide) and a 3’ end (the 3’hydroxyl of the second nucleotide), joined by a This means that they are directional molecules and one end is not the same as the other end. The resulting sugar phosphate chain is called the backbone of the nucleic acid, with the bases sticking out to the side." The phosphodiester bond part is what confuses me. It says that the two nucleotides connect in a phosphodiester bond, then it clearly shows that they connect with a Hydrogen bond. Does it mean that the phosphodiester bond is the 3' end of one nucleic acid as well as the 5' end of the other nucleic acid connecting to the sugar-phosphate backbone?
|
[
"Hydrogen bonding is what happens between the two complimentary stands of DNA. The phosphodiester bond in the DNA backbone is at the phosphate group. What is circled ",
"here"
] |
[
"To add to the post by ",
"/u/NeuroBill",
", the 3' and 5' refer to standard numbering of the ",
" of each nucleotide. In DNA, the phosphate group connects the 3' carbon on one deoxyribose unit to the 5' carbon on the next deoxyribose unit. ",
"This is all about the covalent connectivity of a single strand of DNA."
] |
[
"take a look at nucleotide structure - a phosphate group attached at the 5-position of (deoxy)ribose, with the nucleobase attached to the 1-position of the ribose.\nso the monomeric nucleotide has the ribose 3' position vacant.",
"the 'diester' part indicates that two carbon chains attach to the phosphorous, one from to the nucleotide to which it belongs (via 3'), and the other to the next nucleotide's ribose (via 5').",
"the term 'phosphodiester bond' is a little misnomer, it is a phosphodiester 'group', and this involves two phospho-ester bonds."
] |
[
"I have a science presentation for inter-city middle schoolers coming up, looking for some cool ideas."
] |
[
false
] |
I'm a PhD student and volunteer at a Boys and Girls club. I've been asked to put on an hour-long presentation for some 10-15 year-olds, and I'm hoping to blow their socks Bill Nye style. I have a large, well-funded lab at my disposal. Initial ideas include an invisible ink station (pH dependent), some kind of liquid nitrogen experiment, and maybe a combustion experiment (like soaking a dollar bill in ethanol and lighting it on fire). I'm looking for some great ideas to get these kids excited.
|
[
"When we did these science demonstrations in college we bubbled propane through soapy water in a bucket to make propane bubbles, then scooped them up in our hands and set them on fire. You get a neat little fireball mushroom up from your hand and it has that 'wow factor'.",
"If you do this, remember to soak your arm in the water/soap solution really well. The water acts as a barrier to protect your skin because of it's high heat capacity. The flame is short-lived but it could singe your hair if you're not careful. Also sometimes bubbles will fall off your hand (on fire), so just be careful where you do it.",
"The liquid nitrogen examples are always great. We froze flowers then shattered them. Also we put in balloons and showed them shrink and expand w/temperature. Try to get thick balloons though because sometimes they pop.",
"Another popular one is \"Elephant toothpaste\" (I've never done). Or \"Screaming Gummy Bears\" if you have some of the more exotic chemicals at your disposal."
] |
[
"Check out ",
"http://www.unitednuclear.com/experindex.htm",
" for some cool chemistry experiments (they sell the chemicals, but explain the entire procedure with no purchase necessary). I've personally done ",
"http://www.unitednuclear.com/negx.htm",
" with great results. You mix a few dry, powder reagents together. Add a couple drops of water and the whole pile erupts into a brilliant flame."
] |
[
"Get a water cooler bottle (the giant ones) and make a 10 ft or more rail with four PVC pipes at the corners so the bottle can slide easily along the rails but wont deviate from the path of the rails. Build plywood bulkheads at either end one with a hole drilled out of the middle so the bottom end of the bottle pokes through it.",
"Now, take an easily atomized propellant like rubbing alcohol and put it in a spray bottle (not a squirt bottle). Spray some in the water cooler bottle, spin it around to increase the surface area of the small amount of liquid so it evaporates quickly. Take a long lighter and touch off the flammable gases at the bottle's mouth. ",
"The fuel/air inside will burn rapidly and exhaust out the back generating thrust and rapidly propelling the bottle to the end of the rails. Congratulations, you've just demonstrated all the science involved with rocket propulsion including newtonian mechanics, chemistry of combustion, etc... And the large water cooler bottles are thick-walled enough that they can be reused for a long time and you can basically repeat the experiment as long as you have fuel.",
"It's loud enough to be cool but not so loud you need hearing protection. Also it involves fire and the little pyro in every 10-15 year old will eat it up like forbidden Halloween candy."
] |
[
"The way, when witnessing an object fall into a black hole, it seems to slow to a halt. Does this mean that if you were to fall into a black hole, by the time you got beyond the event horizon you would have outlasted the universe?"
] |
[
false
] | null |
[
"The infalling observer reaches the singularity in finite proper time."
] |
[
"I did answer your question. Someone hovering outside the black hole never sees the object fall past the horizon. The infalling object reaches the singularity in finite proper time. It does not see all of the universe's future."
] |
[
"Ohh okay I didn't realise I would be wrong. So the time that appears to go by on the outside from the infalling observer point of view, it speeds up but not infinitely? ",
"Edit: I read up on proper time. It is the time measured by the clock held by the infalling observer. And yes, the proper time to fall in the black hole is finite, short even. But you haven't amswered my question."
] |
[
"Why are the boosters on the Atlas V arrayed asymmetrically?"
] |
[
false
] |
. Is it to help with gravity turning?
|
[
"Its because originally the Atlas V rockets weren't designed to accommodate solid boosters. They were added later upon request. However, the main engine section on the Atlas V has important features running down its side in fixed places (oxygen supply and electrical stuff IIRC). Therefore the boosters cannot simply be placed wherever and results in an asymmetrical orientation. Scott Manley just released a great video on this, which also shows how gimbaling engines are used to control the offset boosters: ",
"https://www.youtube.com/watch?v=f-o6BLBzsUA"
] |
[
"Do they adjust thrust levels, or thrust vector via gimbals to keep the center of thrust through the center of gravity?"
] |
[
"So that they could attach additional boosters incrementally depending on the desired thrust. The attachments are in the same location whether there is one or five being added. These boosters control vertical thrust only, there would have been other thrusters to control the direction laterally. "
] |
[
"What exactly gives certain materials the ability to better cope with different kinds of stress?"
] |
[
false
] |
For example, concrete is great at handling compressive stress, but awful at handling tensile stress. Why?
|
[
"This is a complex, interesting question in general, but concrete specifically is very simple. Concrete is a mixture: solid aggregate bonded together with cement. Cement is weaker than concrete and the bond between the aggregate and the cement is even weaker. When you pull on concrete it breaks that bond and the concrete falls apart. When you crush concrete, there's nothing trying to break that bond and it stays strong. It's kind of like how it's very hard to crush a stack of bricks, but easy to lift the top brick.",
"A related phenomenon is the ",
"angle of repose",
" of a pile of granules. The particles ",
"jam",
" together which prevents them from being crushed effectively- the pressure causes them to interlock more tightly and resist being spread out. If you take a scoop out of the pile, there's no pressure to interlock the granules, and they don't resist you at all.",
"That jamming phenomenon basically explains how even pretty homogeneous materials, like plastics, glass, and cement, can be weaker under tensile stress. The extreme example is ",
"reinforced earth",
", where a unidirectional mesh holds earth so it's strong in only 1 or 2 directions. The large majority of the time, the compression strength will be higher than the tensile strength, but you can engineer it so the compressive strength is weaker. Carbon fiber constructions are like this sometimes- they're extremely strong when you pull on the fibers, but if you press on them they ",
"buckle",
" and split apart. Fibrous materials in general, like wood, some plastics, ceramics and composites, can do this.",
"Even on the smaller scale you still have the same things. Metals are both highly crystalline and highly granular, and crystals are directional. That leads to anisotropic materials that are stronger in particular directions and different types of load even though they look totally homogeneous. "
] |
[
"It mostly comes down to the molecular structure of the individual material. For, example with a lot of metals, they are fairly ductile and can stretch elastically and plastically under a tensile load before they finally break. That is because the electron sharing in ",
"metals allows the atoms to slide across one another",
" but this again depends a lot on the structure of the specific metal. It is also the structure of crystals which are made up of multiple atoms and have internal structure that inherently affects strength. Certain metals are much more brittle than others, such as cast iron and other high carbon steels due to the carbon atoms in the crystalline structure being very rigid, whereas ",
"structural steel",
" is very low carbon and can deform significantly, not to mention any pure metal like gold or copper can be drawn into thin wires or flattened into foil. As for the resistance and thus the strength of the materials when this is happening, the metal crystals can slide across eachother but will eventually snag and reach an ultimate strength, which is called work hardening then at a certain point the material will fracture.",
"As for concrete, it is basically a bunch of rocks glued together with ",
"calcium and silica",
". Rocks and sand used which make up the aggregate tend to be brittle themselves and the cement matrix itself is quite brittle. I cannot give a very detailed answer, but essentially the cement makes a mineral precipitate crystalline structure which binds the aggregates inside of it. ",
"Here are some good images.",
" So far as I understand, there is significant strength in compression mostly just in the ultimate shearing strength of the cement paste and the aggregates combined. Whereas in tension it is mostly the strength of the cement paste matrix around the aggregates and whatever small amount of adhesion there is between the aggregates and the cement. ",
"Practical engineering is doing a series on concrete atm",
" and they're pretty good videos to go check out. ",
"I know very little about plastics and ceramics exept that some plastics have very high tensile strength and are very hard (i.e. scratch resistant) and a lot of that is due to the structure of polymers being smaller molecules attached to one another leading to very strong bonding throughout the material.",
"Wood is actually a quite similar to plastics, in that much of its strength is due to ",
"lignin",
", essentially a natural cellulose polymer. Timber has very good tensile strength and is able to take repeated high dynamic loads, in addition to being super light. ",
"There's a lot more to be said, about specifics and other aspects of material response to stress and to material failure, notably creep and visco-elastic behavior, but simply the answer comes down to specifics of the internal structure of the material itself."
] |
[
"For homogeneous materials, it mostly comes down to the bonds between atoms in a material. Ceramics, which are typically good in compression and very bad in tension, are predominantly formed with ionic bonds, which are the transfer of valence electrons between two oppositely charged ions. This makes the bond very very strong, but very very brittle, i.e. once you break it, it's broken. Now think about stresses on that bond. A tensile stress will stretch it until the bond breaks, and then it's broken. A compressive stress just pushes the atoms closer, which doesn't actually break the bond. Therefore, ceramics tend to perform better under compression than tension.",
"Metals, on the other hand, have a different, special kind of bond, called metallic bonding. This is a sort of sharing of free electrons among a lattice of metal atoms. It's an omni-directional type of bond, so it's easier to reform a bond if it breaks. And that's why metals typically fare better in tension. If a bond breaks due to tension, it can reform much easier than in an ionically bonded ceramic. ",
"There are, of course, other kinds of bonds, but I'm using these two as demonstration. And this isn't getting into other things like alloying, heat treatments, dislocations, fracture, or composite materials. But for the most part, it all comes down to the atomic bonds a material has."
] |
[
"How do the proteins that manage RNA and DNA know exactly what to do without having their own DNA?"
] |
[
false
] |
They make RNA, replicate, etc... but how can a simple protein be able to know and do all those complex cells without having any organelles or anything?
|
[
"This is a great question!",
"The simple answer is that there are many many many proteins involved in these processes. Thousands and thousands. ",
"Each performs a very specific function. For example, in DNA replication, you have initiator proteins, primases, RNases, DNA helicases, DNA polymerases, each of which has many subtypes. Check out ",
"wikipedia",
" for an overview of replication.",
"I think what you're really asking though, is how does each protein \"know\" what it needs to be doing?",
"Well, it doesn't! Biology is a huge numbers game, all based on physics and chemistry. Every protein is made up of a string of amino acids, whose interaction give it a very specific shape. This shape is usually key to its function - for example, enzymes have \"active sites\", which are regions where substrates can \"dock\" and a reaction can be facilitated. One great example of how physical this can be is gated ion channels, which sit in the cell membrane. ",
"The hair cells of the inner ear are connected such that deflection of the hairs by the endolymph causes the protein gates to actually be pulled open mechanically! Take a look at ",
"this diagram",
".",
"I know that's a bit away from your point, so I'll get back to it. Ultimately, there are a huge huge huge number of proteins floating around in a cell at any time. This means that proteins often meet their targets purely by random chance (in fact, the cell relies on this being true!). For mechanisms such as DNA replication, where the process needs to be tightly regulated, there are an enormous number of regulatory proteins. ",
"One great example is ",
"CREB",
" the cAMP Response Element Binding protein. This protein is a ",
"transcription factor",
" which means it is a special protein which floats around waiting to be activated (there are a huge number of proteins that perform functions like this!). When conditions are right, CREB will bind to cAMP Response Elements on the genome, which will allow other proteins to bind, which in turn will allow other proteins to bind, and so on. ",
"Complicated processes in cells are thereby gated by a complex interaction of huge numbers of proteins. Some will change shape or activity in response to changes in the environment (or time, or cellular energy level, or whatever needs to be regulated), and these will set off a chain of downstream processing, which activates other proteins, allowing the next step in the chain to activate, and so on. ",
"So. Sorry to go on and on! At high school, you get taught there are only a small number of proteins involved in each process. Unfortunately, that's super wrong! There are huge numbers of proteins, and huge numbers of regulatory proteins, which govern the whole process. Since there are so many, each of them can be quite simple. It's the interaction which produces the complexity you see in life.",
" - There are just way way more proteins than you think."
] |
[
"Hey! It's nice to see my comment reached someone!",
"I know there's a bit of confusion in the responses to your comment so I'll try to put things straight a bit. Like ",
"/u/arrein",
" says, there are about 20,000 coding genes (give or take). But ",
"/u/happytime1711",
" isn't wrong! ",
"It's not at all true to say there are only 20,000 proteins. Many genes don't code for whole proteins but actually code for polypeptide subunits of proteins - a whole protein might be made of 4 or 5 such subunits (or more, or less) which might all be different, or might all be the same. This means that there is huge scope for combination. ",
"For an example, check out the ubiquitous ",
"sodium ion channel",
". As you can see there are several genes for each subunit (called α and β in this case - subunits are often named after greek letters), and while each doesn't combine with every other, there are still lots of options!",
"Even more complicated still is the process by which antibodies are generated - since there are infinite possible antigens that your body might encounter, and since the genome couldn't possibly be large enough to carry data on an antibody to counter each of them, each white blood cell performs ",
"V(D)J recombination",
"J_recombination) where it randomly creates a new gene for an antibody by cutting apart its genes and sticking them back together. The vast majority of these are failures of course (the process is random after all) but there is a very strict process which makes sure that these antibodies don't react to your own cells and are stable in the cell which created them. I won't go into how this works or what happens next though, because I could write a whole different (and huge) post on that topic alone! ",
"On top of this, proteins often undergo a process called ",
"post-translational modification",
" in which they have sections added or taken away which affect their function. For example, one type of PTM involves the addition of a long-chain fatty acid molecule, which will cause the protein to locate itself to the membrane (since fatty acids are hydrophobic and so is the inside of the membrane). The same protein however might also be able to undergo a different PTM which changes its function in a different way.",
"Also, RNA can be modified before being changed into proteins (",
"post-transcriptional modification",
".",
"This means then that there are a huge number of possible arrangements of polypeptides which can be used by the body - I couldn't put a number on it, but it's certainly not a 1:1 gene:protein relationship.",
"Another thing people forget is that a cell isn't empty - everything is bashing into everything else all the time! Everything in the cell is packed together like balls in a ball pit, all being shaken around at once. In addition, diffusion at the distances we're talking about here is almost instantaneous at any timescale we can comprehend (it would have to be, wouldn't it!).",
"So I'm afraid I haven't answered your question with any actual numbers, I'm sorry! Still I hope you can start to get a feeling for how this sort of thing works - because we learn about proteins and what they do individually, it's easy to think about them working in a big open space with nothing nearby, but actually that's pretty much the furthest from the truth you can get! ",
" - There's loads and loads of proteins and I didn't actually give you any numbers.",
"Edit: Thanks for the Gold! I'm glad I could help! "
] |
[
"While there are some other good answers already here, I thought I'd try to stay as much on topic of your question as possible. ",
"without their own DNA?",
"Every protein is encoded by DNA, transcribed to RNA, and then translated into a long chain of amino acids that eventually adopts a three-dimensional shape. As others have mentioned, protein function is directly related to its structure (this is why we strive so often to get the structures of all of these proteins prior to other biochemical work). ",
"Others have said proteins \"don't know what they're supposed to do,\" and I agree with this statement to a point. I like to think of it as an analogy. Think of a protein as a key. Think of the DNA as the metal used to make that key, as well as the exact blueprint used to cut the grooves into the key. The keymaker uses his knowledge of the blueprint and metal (his messenger RNA), to carve the key into the correct shape (thus, he is like the ribosome). Like keys, proteins tend to have one particular function. However, there are some keys that unlock multiple different doors -- the same is true about proteins.",
"Everything points back to the DNA encoding the protein. Natural selection has chosen fortuitous mutations in the DNA of bacteria, viruses, dogs, cats, and people that allow them to function ",
" than our peers. These mutations allowed for proteins to work differently, perhaps a little better, perhaps on a different substrate in the environment, etc. It all goes back to the instructions ingrained in the DNA.",
"DNA and RNA binding proteins are no different from proteins that have nothing to do with RNA/DNA. They are still encoded by DNA and therefore have their structure determined by this code and thus their function as well. "
] |
[
"How long would it take to upload/download 1 gig of data to/from a mars rover?"
] |
[
false
] |
Basically I'm wondering what kinda bandwidth NASA is working with when sending and receiving transmissions to satellite probes and such.
|
[
"http://www.msnbc.msn.com/id/4269545/ns/technology_and_science-space/t/mars-rovers-get-bandwidth-boost/#.Tr6V2VaGWvk",
"Post-February: 256,000 bits per second; (1 gigabyte) / (256 000 bits) = 33 554.432; 33 554.432 seconds = 9.32067556 hours = 0.388361481 days",
"Pre-February: 128,000 bits per second; (1 gigabyte) / (128 000 bits) = 67 108.864; 67 108.864 seconds = 18.6413511 hours = 0.776722962 days",
"That is assuming that it's a constant transmission, and that the article is correct (or correct still). There are probably a number of factors that limit the amount of transmission time, error correcting, and the like."
] |
[
"You forgot propagation delay. The first bit takes:",
"(225 million kilometers) / the speed of light = 12.5086536 minutes",
"to reach earth (according to google calculator). ",
"Where 225 million km is the average distance between Earth and Mars according to this: ",
"http://www.universetoday.com/14824/distance-from-earth-to-mars/"
] |
[
"but it will significantly lengthen the time taken to transmit the data.",
"This is highly doubtful, unless you have sources to back it up. NASA engineers are not idiots, and most likely will know better than to use standard TCP on an interplanetary connection.",
"Reasons why acknowledgements might not significantly lengthen the time of transmission:"
] |
[
"Does it take more energy to open a door when applying force close to the hinge?"
] |
[
false
] |
An interesting question which caused a on Stackexchange. Assuming an ordinary hinged door (M=3Kg, L=1m), would it take more to open it when applying force in the middle of the door (point b: r=50cm), rather than at the end of the door (point a: r=100cm), where the door knob is? What about the situation where you forcefully push the door open (J=10kgm/s), rather than pushing it with the same acceleration throughtout the whole movement?
|
[
"It requires the same amount of energy to move the door, but it's 'harder' for a person to apply the force required when you get closer to the hinge. It takes more energy for a person to create a large force over a short distance than it does for a person to create a small force over a long distance. This is specifically in reference to the door question.",
"A comparable analogy would be lifting a 50 kg box 10 cm in the air vs a 5 kg box 100 cm in the air. They require the same increase in potential energy, but lifting 50 kg off the ground would require a lot more energy for most people as they strained their muscles when compared to lifting 5 kg."
] |
[
"Energy consumed is the same assuming the distance opened is the same. The force required to open at different points of the lever are different and decreases as you move away from the hinge. Remember that energy in this scenario is work applied over a distance. Closer to the hinge the amount of force required is greater but you're applying that force over a shorter distance and vice versa as you move away."
] |
[
"Ignoring friction. The only thing that happens when you put more energy in the door is that it will move faster. It doesn't matter where you insert the energy.",
"\nIf you push closer to the hinge you apply more force over a short distance. But when you push farther from the hinge you apply less force over a large distance. Assuming you want the door to rotate equally fast in both cases, the energy used is the same. ",
"TLDR: More energy = faster door."
] |
[
"What exactly is Anti-Matter?"
] |
[
false
] |
I have seen some YouTube videos but really couldn't grasp what exactly antimatter was. Any explanation would be awesome.
|
[
"Both neutrons and antineutrons have charge 0.",
"The opposite charge thing is just ONE of the differences between matter and antimatter. It's usually given as the only difference in ELI5 explanations. ",
"There are some other, more complicated differences between matter and antimatter.",
"For example, a neutron is composed of one up quark and two down quarks. An antineutron is composed of one up antiquark and two down antiquarks. A neutron has Baryon number +1, and an antineutron has Baryon number -1."
] |
[
"Both neutrons and antineutrons have charge 0.",
"The opposite charge thing is just ONE of the differences between matter and antimatter. It's usually given as the only difference in ELI5 explanations. ",
"There are some other, more complicated differences between matter and antimatter.",
"For example, a neutron is composed of one up quark and two down quarks. An antineutron is composed of one up antiquark and two down antiquarks. A neutron has Baryon number +1, and an antineutron has Baryon number -1."
] |
[
"Matter that has the opposite charge on its particles. So it would contain a positive electron. (A positron) *along with all the atom's other subatomic particles"
] |
[
"If electrons had a spin of 3/2 instead of 1/2, why would there be 4 Pauli-slots for different spin orientations instead of 2 for a given set of n,l,m numbers? Intuitively I would still think there are 2, +3/2 and -3/2."
] |
[
false
] | null |
[
"A spin of 3/2 can have a projection along any given axis of +3/2, +1/2, -1/2, and -3/2."
] |
[
"Okey, thanks. Whats the theoretical explanation for that?"
] |
[
"If the spin is J, the projections are -J, -(J-1), ..., (J-1), J. So (2J + 1) total.",
"For J = 3/2, that’s 4."
] |
[
"Mars has little atmosphere while Venus has a very thick atmosphere yet both planets don't have a magnetosphere. Why?"
] |
[
false
] |
From my understanding a planet that has no magnetosphere will eventually have their atmosphere stripped away due to solar winds. Both of these planets have no magnetosphere but are complete opposites from one another. Whats going on here?
|
[
"Due to Venus' lack of magnetosphere, it is currently experiencing significant atmosphere loss. As to why it has more of an atmosphere than Mars in the present day, I would expect it to be a combinations of:"
] |
[
"Volcanic activity usually suggests a liquid core, but there are three requirements for a planetary core to act as a dynamo: conducting liquid, rotation, and convection. It's thought that because the first two requirements are satisfied (though the rotation is slow), that there's no convection. We aren't sure of the exact cause, though.",
"No convection » no dynamo » no magnetosphere."
] |
[
"Wouldn't volcanic activity imply an active core, which would generate a magnetic field?"
] |
[
"Is it possible that some virii are created from mutations in the replication of DNA in more complex life forms?"
] |
[
false
] | null |
[
"I would just go with 'viruses'.",
"What you're describing is the escape hypothesis, which says rather than viruses having developed before complex and truly reproductive capable DNA holding organisms, viruses are the result of the escape of some lower bound threshold of replication capable components that could infect cells to replicate, instead of reproducing.",
"Following these citations",
" should give you some better reading material. ",
"I'm also sure this question will attract some microbiology/evolutionary specialists better suited to expand on what I've said, and set right any wrong implications I may have made."
] |
[
"Virii is what's known as a ",
"hypercorrection",
". The correct plural is viruses."
] |
[
"Thank you."
] |
[
"Do changing magnetic fields induce current in the air?"
] |
[
false
] |
Title says it. Changing magnetic fields can induce current in nearby conductors so there should be a minimal amount of it in the air everytime a magnet moves around. Is that correct or do the currents possibly cancel each other out?
|
[
"Air is a really bad conductor."
] |
[
"Air isn't a conductor. If you took a general physics class, air is modeled accurately when looking at dielectrics in capacitors. Air is a dielectric with permativity of e0. ",
"The most that happens is momentary polarization."
] |
[
"Lightning can happen because it ionises the air, enabling the flow of electrons."
] |
[
"Is there a way to tell the charge remaining on individual batteries?"
] |
[
false
] | null |
[
"Do you mean the state-of-charge remaining in the batteries? I think you may be able to estimate it from the open circuit voltage based on discharge curves."
] |
[
"You can measure the potential difference and current between two batteries quite easily given a known resistance. I'm curious as to what you mean by \"",
" remaining on individual batteries\"? Also your definition of \"battery\" if you don't mind."
] |
[
"For example, if I have a remote control that stopped working, would there be a way for me to tell which battery lost charge more?"
] |
[
"I've heard that we can't see the atom and will never be able to. Is that true? If so, why?"
] |
[
false
] |
The exact phrase was "it's not about technology, we just can't see the atom directly and will never be able to, despite all the technology that is available to us now and will be available in the future".
|
[
"It really depends on what you mean by \"see.\" If you mean see with the unaided eye, then no we cannot. If you mean unambiguously detect and visualize, then we can.",
"https://www.physicsforums.com/insights/can-see-atom/"
] |
[
"We can't 'see' atoms with wavelengths our own eyes are sensitive to. We never will because the diffraction limit of visible light is still much larger than a single atom, no matter how powerful your microscope. ",
"We can use other technology to 'see' atoms by having a computer interpret the results from say electron microscopy, as the wavelength and diffraction limit can be made much smaller."
] |
[
"Yes, they do interact with atoms in a practical way. X-rays are diffracted by electrons, so you can use them to study the structure of crystals. ",
"X-ray crystallography",
" is an extremely powerful tool for that. But again, you do not directly \"see\" atoms with that method, but rather some ",
"interference patterns",
" between the atoms (or rather, the electron density around them) that make up the crystal. I think it's the closest you will come."
] |
[
"At what ratio of salt to water does it cease to be hydrating?"
] |
[
false
] |
[deleted]
|
[
"Which is about a 3% saline solution (for reference, a 0.9% saline solution is isotonic, which means it's equivalent to the osmolarity of your blood which is important so your cells don't lyse [explode] or crenate [shrivel]), or 3 grams of salt per 100 ml water. "
] |
[
"Which is about a 3% saline solution (for reference, a 0.9% saline solution is isotonic, which means it's equivalent to the osmolarity of your blood which is important so your cells don't lyse [explode] or crenate [shrivel]), or 3 grams of salt per 100 ml water. "
] |
[
"If you are thirsty, you aren't supposed to drink stuff like salt water and soda because the salt will actually make you more thirsty. OP is probably asking the maximum level of saltiness such that you will be less thirsty."
] |
[
"Where does the heat in our bodies come from ? Are we generating heat intentionally or is it a byproduct of our internal activity ?"
] |
[
false
] |
[deleted]
|
[
"to add to prior comments, we also have '",
"futile cycles",
"' with the sole purpose of maintaining a core temperature. these futile cycles are regulated by varying the concentrations of the products or substrates, allowing temperature to be modulated. "
] |
[
"ATP (which is the chemical used to provide energy in many cellular reactions) breaks down to provide the energy from its bonds. For many cellular processes, the match up between energy released by the ATP and the energy actually needed leaves a little left over which is 'heat'. Also ATP can be broken down without doing any 'work' so it is all released as heat (like in brown adipose tissue)."
] |
[
"This is why wrapping yourself in a blanket does not actually \"warm\" you, rather, it merely keeps more of your own body heat closer to you."
] |
[
"Why is it that when you hear yourself on a recording, you sound different than what you thought? Also, which one is what you actually sound like? What you hear when you talk, or what you hear on a recording?"
] |
[
false
] | null |
[
"When you talk, part of what you are hearing is the vibrations through your facial bones. When you hear others (or a recording of yourself), this component is not present.",
"If you record your voice on a high quality recorder, what you hear from the recorder is what other people hear."
] |
[
"Would that mean that it's impossible to just hear it the way other people hear it without it being a recording? Because I hear myself sometimes and it sounds like it does on a recording. Sometimes just randomly while speaking, but I can also specifically listen and hear it the way I assume other people are hearing it (and the way I've heard myself on a video or something before).",
"I would think that if I'm hearing the vibrations this would be impossible, unless I'm just listening so intently that I'm picking up on the voice specifically and not those vibrations?"
] |
[
"Yes. \"Bone-conducted\" vs. \"air-conducted\" sound. When you hear yourself speak, you are receiving input from both sources, when you hear a recording, you are only receiving the air-conducted source. There is actually a certain type of hearing aid which is sort of a vibrating implant. It can help people who have certain types of hearing loss. I would give more detail, but I am just a third-year psych student taking a \"sensory systems\" course and wouldn't want to overreach my knowledge... sorry!"
] |
[
"Do the meals you eat always get expelled in the same order?"
] |
[
false
] |
This question came up when I was considering people who hide small objects by swallowing them. Can they somehow prolong how much time that object spends inside them? Maybe by eating it with something oily?
|
[
"I dont entirely agree with this answer and find it too simple. The lumen of the gastrointestinal tract is not completely full nor are its contents entirely solid. Moreover, the different constituents of your food are all digested at different rates depending on voluntary and involuntary mechanical digesting and the presence or absence of specific digestive enzymes. So while I would generally agree that time of ingestion largely determines the time and order of excretion, I think the idea of temporally separate meals coming out in an exact order is misleading and doesn't appreciate the mixing of contents and different rats of digestion. I think the pyloric sphincter would also also have a bottle nose effect allowing meals to mix in the stomach if they are within a few hours of each other.",
"Edit: you probably could alter the rate at which you excreted such an object, but to get the effects you described - slowing down the passage of an object - you would have better success by suppressing the parasympathetic nervous system which largely regulates the peristalsis (contractions of the intestines) that moves food, than by eating a specific type of food. This would be achieved by activation of the sympathetic nervous system (fight or flight) by something like exercise. The stress caused by smuggling stuff in this fashion and the fear of getting caught could perhaps even contribute to this. "
] |
[
"To answer your title, for the most part things get crapped out in the same order the get consumed. There might be a bit of leeway here and there (say, having a solid breakfast and a liquid lunch and having the liquid slide by the solids), but for the most part more recent food just pushes the food that was ingested earlier. Not sure if there is any way to feasible manipulate one meal over another in regards to digestion speed.",
"To answer your actual inquiry, you can slow down digestion ",
" by various means, such as activity (via adrenaline) or some drugs that have the side effect of constipation via slowing peristalsis (opioids, I think?). However, these techniques don't select one meal over another, but stall everything."
] |
[
"Since the gut is a simple long tube, there is no anatomical means for today's lunch to bypass today's breakfast (if that is what you mean)."
] |
[
"If Nitrogen is the most abundant element in our atmosphere, why did organisms adapt to breathe oxygen instead?"
] |
[
false
] |
If Nitrogen is the most abundant element in our atmosphere, why did organisms adapt to breathe oxygen instead?
|
[
"First thing is that O2 has a lot of free energy available in the context of O2-->H2O. Life gets energy by very regulated transfers of electrons to terminal electron receptors like oxygen, and electron transfers tend to be in the form of pairs of electrons, usually accompanied by a proton. This works well for oxygen, where this reaction has a E0 of about +800mV. A similar reaction using N2 requires that N2-->NH2OH-->NH3, which has an E0 of about +300 if I recall rightly. It's much less energetically favorable, and the synthesis of hydroxylamine (NH2OH) can be dangerous, as it is a powerful mutagen. Additionally, getting N2 to NH2OH also involves an intermediate step that yields a free radical. Microbes and other organisms which do nitrogen metabolism using N2 have evolves relatively high cost solutions to dealing with the free radical problem, such as large amounts of periplasmic space for the reaction (to limit exposure to the intricacies of the cytoplasm). ",
"All in all, it is much less energy intensive to deal with oxygen and the sorts of problems ir brings as opposed to the intermediates of nitrogen metabolism. "
] |
[
"It's much harder to make a living on N2 than O2, because N2 is so much less reactive because of its strong triple bond. However, there are ",
"nitrogen fixing bacteria",
", which take N2 out of the air and convert it to ammonia, which is then used for other purposes."
] |
[
"There are organisms that get by on far less favorable redox couples than that of dioxygen. The main impediment is not the smaller energy gain from the reduction of ammonia, but rather the incredibly high activation energy. ",
"Organisms that utilize dinitrogen don't use it as a terminal oxidant, as you said, and actually have to waste energy to convert it into ammonia. By the way, where do you find that nitrogenase proceeds through a hydroxylamine intermediate? I've seen hydroxylamine as part of the denitrification leg of the nitrogen cycle (in which nitrogen compounds ",
" used as terminal oxidants), but not during fixation."
] |
[
"Why is carbon the element that all organisms have in their organic molecular structure?"
] |
[
false
] |
I want to know why carbon, why not some other element. What makes carbon special?
|
[
"Well, molecules based with carbon can form ridiculous numbers of variety from the same constiuent species. They chain together in repeating (or nonrepeating) units that can be broken at room temperature. DNA, the code for all known life, (unless you want to be pedantic and count things that soley use RNA) is a huge polymer of millions of carbon atoms bonded with a many different functional groups. No other element can create that level of interconnectivity. I believe (sorry there is no strong source - my google fu is weak) that sulfur can make linking structures of around 21 sulfur atoms long. That is simply not long enough to create the necessary instructions for life (DNA). Carbons ability to form 4 bonds and to form endless chains is the reason why carbon is so special and is apart of all life on earth."
] |
[
"Carbon has four valence electrons; ",
"forms chains easily",
"; and makes stable molecules with abundant elements like hydrogen, oxygen, and nitrogen.",
"According to ",
"this article",
", silicon can form chains but they are reactive with water so they wouldn't survive on Earth. Phosphorous can form long chains too, but these are much more reactive than carbon-based molecules.",
"Without long chains, you'd have a hard time making membranes which are important for compartmentalization. It would be difficult to have storage medium that could recursively recreate itself like DNA does.",
"You also have to consider the ",
"electronegativity of carbon in relation to other elements",
".",
"This is just an brief overview, though, ",
"here's a more thorough discussion",
" of hypothetical alternatives to carbon-based life."
] |
[
"It is hypothesised that other forms of life on other planets could be based on silicon and the likes, but it just so happens that where we live the atmospheric conditions favour carbon. There was alot of 'behind the scenes' carbon-chemistry happening early on in the development of our planet though, long before the existence of 'life' as we know it now. Spontaneous self-assembly of carbon and hydrogen into hydrocarbons, then into sugars and amino acids, then into polysaccharides and polypeptides, then slowly shifting toward things like organisms. It's not like bacteria just turned up and went \"hey carbon, we choose you!\""
] |
[
"Does the Heisenberg Uncertainty Principle describe a literal or figurative effect?"
] |
[
false
] |
At the most basic level, the Heisenberg Uncertainty Principle is usually described as observing something changes it. Is this literal, as in the instrument you use to observe it bumps it and changes its velocity/location etc? Or is this a more woo woo particle physics effect where something resolves or happens by the simple act of observation? If you blindfold a person next to a pool table, give them a pool cue, and have them locate the balls on the table with the cue (with the balls moving or not), they will locate them by hitting them, but in the act of "observing" (hitting them), their location is then changed. Is this a representative example of the Heisenberg Uncertainty Principle? There is a lot of weirdness and woo woo around how people understand what the Heisenberg Uncertainty Principle actually is, so a basic and descriptive science answer would be great.
|
[
"Your statement of the \"most basic level\" for the uncertainty principle is the heart of your misunderstanding. You cannot take this at the most basic level. You gotta stop thinking about very small objects as particles. They are wave-particles, and the uncertainty principle arises from the wave nature of matter.",
"Imagine dropping a pebble into a still pond. A wave results, and that wave spreads out as it travels away. That's what waves do, and this part is not strange. But then I ask you \"where is the wave?\" and you point to the wave, \"no... where in the wave is the wave?\" and this question makes little sense to you, because the wave IS the wave. And yet this question is at the heart of the uncertainty principle and the wave-particle duality of matter.",
"An electron is a wave-particle, existing somewhere in its orbital around the nucleus. But to ask \"where in the orbital is the electron?\" is akin to asking \"where in the wave is the wave?\" The former question sounds reasonable, the latter absurd, and yet they are the same question.",
"Quantum-sized object are small and so their uncertainty is large relative to their size; for bulkier objects the uncertainty seems smaller (and also we're talking about billions of uncertainties and only concerning ourselves with the average). The uncertainty of a single atom makes it impossible to determine the exact location (so we only talk about probability); however when you consider a baseball, even though each atom in the baseball has uncertainty in its own location or movement, the baseball as a whole moves and behaves as the average of all these. In this way, large objects are knowable in their location and momentum, but very small objects are not.",
"if I take a single 6-sided die and roll it, I will get a random number between 1 and 6 and which result I get is unpredictable. but if I roll 10^24 dice and sum them all, we can safely dispense with probabilities and assume only the average is obtained each time"
] |
[
"At the most basic level, the Heisenberg Uncertainty Principle is usually described as observing something changes it.",
"That’s not an accurate description, maybe some pop science articles say that but no actual physics lesson would. ",
"The Heisenberg uncertainty principle is a simple truth about how wavefunctions work. If there’s less uncertainty in a particle’s position, there must be more uncertainty in its momentum. It doesn’t matter how you measure it, quantum mechanics is inherently probabilistic."
] |
[
"The neat thing about the HUP is that it goes for ",
" waves, not just quantum mechanical particles. Take a simple sine wave extending forever. It's made up of just one frequency, but is so very spread out that you can't pin down one single location and call it \"the wave's position\". Frequency is well defined, and that means position is not well defined.",
"The opposite would be what's called an impulse function, or the ",
"Dirac Delta Function",
". This can be described as a spike, and it's composed of a combination of sine waves of varying frequencies. For the ideal case, it's made up of ",
" frequency. This gives us a spike with a very well defined position, but ",
" well defined frequency.",
"Quantum mechanics enters the picture because for a quantum mechanical particle, its momentum depends directly on its frequency. Hence, if your particle-wave is very localized in terms of its position, its frequency (and therefore momentum) is not well defined. And vice versa."
] |
[
"Every time I put gas in my car, the tank isn't completely empty. Does that mean there is a trace of gas from the very first fueling in it?"
] |
[
false
] |
Although incredibly diluted, is there any reason that some gas from the very first fueling of the car isn't in the tank?
|
[
"It doesn't matter whether you're talking classical or quantum physics. The impossibility of telling two identical molecules apart doesn't change the actual probabilities in the calculation he gave above. So the question as asked can be answered very easily: ",
"No, the fact you don't fully empty the tank doesn't mean that some of the original fuel is still there. ",
"There's a small but non-zero chance that some is there if you've refilled more than 44 times but there's a high probability that none is left."
] |
[
"That is interesting and wanders off into quantum teleportation in fairly short order.",
"I'm reminded of an essay called ",
"'What colour are your bits'",
". This byte here is from a blockbuster movie and is unquestionably the property of the copyright holder. This ",
" byte is from your rather shabby fanfic and is completely your property, even though both bytes are the same value."
] |
[
"Well you could perform a hypothetical experiment with isotopically labelled fuel which would be fairly close to identical."
] |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.