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[
"Does the colour of light affect a plant's rate of photosynthesis?"
] |
[
false
] | null |
[
"Absolutely. In a way it is semantics, but a different color is really just different wavelengths.",
"The worst rates of photosynthesis occur in, unsurprisingly, the green wavelengths.",
"Here's a pic",
" from the University of Miami that gives a ",
" relationship of wavelength and rate of photosynthesis."
] |
[
"Out of curiousity, is green light inherently bad for photosynthesis (less efficient, etc), or is the primary reason that green light bad for photosynthesis particularly because plants are green - and, as such, reflect green light?",
"In essence, if I managed to make a blue plant and still used white light to sustain it, would, then, green light essentially fulfill and replace the exact same function as blue light does to green plants - or is the green light inherently less efficient?",
"I guess this might by hard to answer like a \"chicken or an egg\" problem - but it's simply are plants green because green is less efficient and, as such, there's much less loss in efficiency on the plant's part from being green than there would by being red - or is green less efficient simply because plants are green and plants reflect the green light rather than absorbing it?",
"EDIT: I guess your graph would seem to imply it's more of the second - green light is not inherently less efficient, as green light kind of falls in the middle of the spectrum. It was just an interesting thought on my part."
] |
[
"It helps me understand why it absorbs two narrow bands. My question is moreover \"why are those two bands not green\".",
"The obvious answer is, of course, \"because chlorophyll green, so they reflect green light, so it wouldn't make sense for them to be highly efficient at absorbing green.\"",
"I simply am wondering is there's a reason (other than that) in which green is the color, and not red or blue. I would think (and may very well be wrong) that if there wasn't something inherently inefficient about green light in particular, we might see plants with red or blue (or other random colors) chlorophyll as random mutations that proliferate in small pockets of the world...",
"For instance, wouldn't a plant that had a mutation to where it was blue and absorbed green light with high efficiency absolutely flourish in a jungle or forest-like environment because of all of the reflected green light from other plants?",
"But that doesn't seem to be the case (that I know of - I am, by no means, a plant expert) - so I was curious if there was something inherently less efficient about green light in particular. I can definitely see why it pays to be super specialized in absorbing certain spectrums of light instead of a wide array of light - I am more curious as to why green in specific - and it's entirely possible that there's no additional explanation, I'm simply curious."
] |
[
"Why do we use Relative Humidity in all the weather reports? Surely how dry it feels is related to the Absolute Humidity? Or if how dry we feel is because of Relative Humidity, why?"
] |
[
false
] | null |
[
"Relative Humidity is a handy because it measures the ability of air to hold more water. Humidity (the moisture content of air) effects us because of its influence on the rate of evaporation. Absolute humidity measures the same thing but it is in practice a less useful scale because the saturation value changes so dramatically with temperature. The weather report could tell us the specific humidity is 1.7 grams water per kg of air, but unless they also tell us the saturation value for air at that temperature, it really isn't usually as informative as saying 25%, or 50% of 98% relative humidity. If the weather reports did routinely report absolute specific humidity and saturation values, the first step you would want to take to make it into a useful number is calculate the ratio, e.g. relative humidity.",
"If air is 100% relative humidity it is incapable of holding any more moisture and thus is lousy for providing evaporative cooling. If you sweat in 100% relative humidity air, it won't cool you down, regardless of the temperature. But if the air were relatively dry (25% humidity) than the air is capable of holding much more water and will more quickly evaporate puddles or the sweat on our skin."
] |
[
"Sling Psychrometer",
": a cleverly simple 19th century instrument to calculate relative humidity."
] |
[
"Thanks! That makes a lot of sense."
] |
[
"A question about black holes"
] |
[
false
] |
[deleted]
|
[
"Black holes are not \"drains\". They do not \"suck\" matter in. They interact (gravitationally) as any massive object (such as a star) might. For example, if our Sun was replaced by a black hole of equal mass, nothing about the Earth's orbit would change. ",
"As for the \"shape\", the ",
" of a black hole is a spherical region causally disconnected from the rest of the universe (i.e. it is the region within which you cannot \"escape\") - this is what we typically refer to as the black hole. However, the mass which causes the black hole is itself compressed into a ",
", which doesn't have any well-defined dimension to speak of (and is within the boundary of the event horizon)."
] |
[
"The event horizon of a black hole is spherical. They seem planar because clouds of gas will naturally form disks due to conversation of angular momentum."
] |
[
"There is a preferred axis about a black hole. Black holes can be completely characterized by three properties -- their mass, charge, and spin. This last one is related to your question. Since angular momentum is conserved, anything that rotates as it falls into a black hole imparts that bit of rotational energy to the black hole, so black holes have non-zero angular momentum. ",
"This means that there is an axis about which the gravitational perturbations can be found because of the black hole's spin. Disks of material falling into the black hole will align with the equatorial region of this spin axis when they're near the event horizon. The perturbations of this effect, however, are only significant close to the black hole, so the plane of the galaxy is unrelated (and could expected to be random)."
] |
[
"Does the universe have an event horizon?"
] |
[
false
] |
Before the Big Bang, the universe was described as a gravitational singularity, but to my knowledge it is believed that naked singularities cannot exist. Does that mean that at some point the universe had its own event horizon, or that it still does?
|
[
"It's more that the question itself is malformed, like asking what happens if you stand at the north pole and go north.",
"Under a Classical GR model, there is no \"before\" t=0. It's not that we just can't determine what preceded the Big Bang. It's that the notion of events preceding the first moment of time is incoherent.",
"LATE EDIT: I'm just adding to this post rather than responding to 10 different people with the same comment. For everyone who says that asking what came before the Big Bang isn't necessarily incoherent, or that there could be time prior to the Big Bang—you're right! The operative qualifier was \"Under a Classical GR model.\" You can always violate the assumptions of whatever theorem you're working with and thereby escape its implications."
] |
[
" Hmm... didn't expect this to blow up. Anyway, ",
"this is the thread I intended to link earlier",
"; it goes over all the gory details that I either skipped or summarized (possibly sloppily).",
"The big bang is the only naked singularity allowed to exist in the cosmic censorship hypothesis, which otherwise conjectures that all singualarities in nature must be behind an event horizon. (Also, just to clarify, modern physics is incapable of describing the universe before the big bang. Classical GR predicts that the universe has existed for a finite amount of time. Specifically, the universe has existed for all time t>0 and that there is a spacelike singularity everywhere in space corresponding to the limit as t-->0. It is meaningless to talk about what happens at or before t=0.)",
"In general, there are two very important horizons in cosmology, the particle horizon and the cosmic event horizon, which both exist for each point in space. (Each point in space has its own pair of horizons.) Implicit in the definitions of either horizon is that we are describing spacetime in cosmological coordinates. The particle horizon for a point P is the surface beyond which any signal emitted at the big bang could not have reached P yet. In other words, the particle horizon defines the boundary of the observable universe about point P. The cosmic event horizon is the surface beyond which any signal emitted now will never reach point P. In other words, the cosmic event horizon roughly describes the points in space we can still communicate with today. ",
"The evolution of both horizons is very important in cosmology and intrinsically linked to the matter distribution of the universe and the density of dark energy. The distance to the particle horizon is always increasing over time in comoving coordinates but current evidence shows that the distance will asymptote to some finite number. In other words, there are galaxies we will never see at all. The distance to the cosmic event horizon, on the other hand, is decreasing over time in comoving coordinates. That means that eventually all we will see in the sky are stars in our own galaxy. ",
"Note that these horizons are unlike the event horizon of a black hole. For a black hole, the horizon is a single surface in space and a universal and eternal feature of that spacetime. That is, every observer has the same horizon. The cosmological horizons are different at each point in space. ",
"I have written more details about the cosmological horizons on this sub before, so I can get the link later once I'm not on my phone. "
] |
[
"My biggest question is why is it pointless to figure out what happened before the Big Bang?"
] |
[
"Do strategic skills transfer between different games?"
] |
[
false
] |
If I play a lot of chess will I be better at go, or if I play a lot of strategy video games will it help (to whatever extent) with board games like Risk etc. or since these games have different rules, would the skills for them be mostly independent from each other?
|
[
"Speaking from experience, fighting games teach a lot about positioning, getting value from resources (like supers), setups for combos, and recognizing how an opponent \"prefers\" to play. i.e. Do they favor throws, blocks, recovery rolls, jumping or crouching?\nCertain card games (like Magic) also reward players for knowing when to use the right \"answer\" at the right time, disrupting combo setups and recognizing when the board state is in their favor to attack. To suggest that any game that has a strategy element isn't good exercise to improve at strategy in general wouldn't be right; though there is a lot to be said for practice, muscle memory and learning each game for their specific nuances."
] |
[
"Yes. Not always the individual skills themselves, but the methods you used to acquire those skills. You learn how to learn more efficiently and accurately. Abilities like pattern recognition and deductive reasoning are universal to figuring out systems you find in games. There are also some strategic principals that are universal. Like putting yourself in an opponents shoes so you can anticipate and counter their strategy."
] |
[
"Honestly your strategy doesn't really work in Starcraft either, so I'm not sure this really works as a counter-example (I don't know enough about the other games to speak to them). It sounds like you've probably never played competitively on the ladder much. Against AI or other new players you can do pretty much whatever you want and potentially win, but that's not really learning the real strategy of the game. In competitive Starcraft you need to be actively expanding your territory and reducing your opponent's territory."
] |
[
"In a crazy amount of movies, the hero is knocked unconscious and awakes hours later in captivity. How long does being knocked unconscious last?"
] |
[
false
] |
In an unbelievably large amount of fiction, someone is knocked out often for hours by a blow to the head. However, I've heard somewhere that being knocked unconscious only really lasts a few seconds; any longer than a few minutes probably means brain damage. Given how often I see someone knocked unconscious in movies, television shows and books, I can't help but wonder if any physical attack could render someone unconscious for a lengthy period of time.
|
[
"Depends on why you're unconscious. ",
"If one was hit around the head and just had a concussion ( Traumatic brain injury ) then you would expect to regain consciousness initially rather fast, in the order of minutes, although it wouldn't be unusual to be impaired somewhat for hours, days or longer afterwards.",
"On the other end of the spectrum if the trauma was more substantial and you had an intracranial bleed, you may not regain consciousness at all and just keep bleeding until the increased pressure rose high enough to cut off blood perfusion of the brain and you die.",
"neverinvalid mention the GCS scale, which is a useful clinical measure of severity if impaired conciousness, but time doesnt factor into it. If you drop less than 8, youre in trouble, with a potentially compromised airway, so may end up being intubated etc. ",
"Its most useful as a system of triage, but isnt useful on its own to predict outcomes unless its a disease specific population as a GCS of 3 might mean a huge stroke which will lead to death, but may also simply be a seizure who will walk out the door tomorrow."
] |
[
"http://en.wikipedia.org/wiki/Glasgow_Coma_Scale",
"\nThis is the GCS, and it is the standing scale for measuring unconsciousness, (although, I should mention, it has come under pressure lately, though I don't know of any other scale widely that is used at the moment.) I didn't see anything specific on the time the period lasts in this, maybe someone with more education can elaborate, but judging by the scale, complete unconsciousness is between a 3 and an 8, which is considered severe and seems like it typically does have pretty serious effects on the body.\nEdit: add information."
] |
[
"Thank you, you just saved my suspension of disbelief. "
] |
[
"Why can't the Gardasil vaccine rid you of the HPV strains you have, but can give protection from the ones that you don't have?"
] |
[
false
] | null |
[
"Gardasil contains the major capsid protein (L1) from different HPV types. Thus, vaccination results in immunity against the viral capsid (the shell of the virus), preventing new infection with HPV. ",
"However, previous HPV infection that results in viral integration (like what would cause cervical cancer, etc) drives expression of the major HPV oncoproteins, E6 and E7. Gardasil doesn’t contain those proteins, so the vaccine doesn’t induce immunity to them. However, there are several academic and industry groups developing E6 and E7 vaccines that could be used therapeutically to treat previous HPV infection/HPV-associated cancers."
] |
[
"Is there a reason why doctors refuse to give the vaccine to people at a certain age? I'm in my 30s, and I never knew this vaccine existed. When I asked for it, my doc refused because of my age, which perplexes me."
] |
[
"That's weird they refused. We give the vaccine for people up to 45 years old. The reason we don't go past 45 is that the original clinical trials were on people up to 45 years old, so we just don't have data on risks/efficacy on how the vaccine works for people older than that"
] |
[
"are fuel cells dangerous to the environment"
] |
[
false
] |
are fuel cells dangerous to the environment?
|
[
"Generally speaking, no. There are many different types of fuel cell, but the most common ones' waste products are water and heat, both of which are obviously useful and can be harnessed easily. There are hydrocarbon fuel cells which give off carbon dioxide, but these aren't very common (mainly because they're less efficient than other types).",
"Source: I used to work for a company that designed and built fuel cells. Also, the ",
"Wikipedia page",
" gives a good overview including the chemical reactions that power the cells."
] |
[
"By themselves, no because one of the fuel cells that people like to talk about the most use hydrogen and give off water as a byproduct. The big problem is where the hydrogen comes from. You could split water into hydrogen and oxygen, but on a large scale the amount of energy needed is pretty great and that energy has to come from somewhere like coal- or natural gas-fired power plants or nuclear power plants. The greatest source of hydrogen are hydrocarbons (e.g. natural gas or other types of hydrocarbons). So essentially we're still using hydrocarbons to produce hydrogen for fuel cells that were meant to get us away from using hydrocarbons. ",
"In short, the fuel cells aren't dangerous to the environment when they're being used after they're manufactured, but the hydrogen manufacturing process is dangerous to the environment."
] |
[
"thx guys "
] |
[
"Did Native Americans who lived in climates similar to Europe develop lighter skin?"
] |
[
false
] |
I was watching Pocahontas and this question popped into my head.
|
[
"No, although changes in diet may indeed have affected skin colour, it is more dependent on local environmental factors (i.e. latitude and amount of sunlight exposure) than genetic ancestry. Take a look at a ",
"map of global skin tones",
". "
] |
[
"No, although changes in diet may indeed have affected skin colour, it is more dependent on local environmental factors (i.e. latitude and amount of sunlight exposure) than genetic ancestry. Take a look at a ",
"map of global skin tones",
". "
] |
[
"This map seems to project skin tone onto a single dimension of light -> dark. How does it account for other variations, like \"red\" in Americas and \"yellow\" in Asia? Are these myths? (They don't seem to be from my experience.)"
] |
[
"could we take rhino reproductive dna and inject that into a horse to genetically create a unicorn?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"It is hypothetical or speculative in nature. We do not allow hypothetical questions because questions that cannot be confidently answered with any available data often invite non-scientific speculation. For more information regarding this and similar issues, please see our ",
"guidelines.",
"A good home for this question is our sister subreddit ",
"/r/AskScienceDiscussion",
" because of its open-ended or speculative nature. Please feel free to repost there!",
"Please see our ",
"guidelines",
".",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"understandable, but who picked that name?"
] |
[
"/r/asksciencediscussion",
"? I don't know, but probably one of the askscience mods who created it."
] |
[
"Do astronauts shave in space or do they wait till they get back? Mostly they look clean shaven - so I guess yes. However, with everything in space about 16 times more complicated than back on the planet...I just wondered"
] |
[
false
] | null |
[
"Here is a ",
"description from the Canadian Space Agency",
"."
] |
[
"I don't know if you have Netflix, but if you do, watch Part 3 of the Discovery series \"When We Left Earth.\" Go to 28 minutes in and you will see Neil Armstrong (I think, hard to tell) shaving. There's your answer. "
] |
[
"That looks like a terrible shave, and besides from that, how do they stop loose bristles that doesn't get caught in the foam from floating freely about and messing up equipment or personel in the spacecraft? According to the above link",
"Astronauts shave with foam or an electric razor, but most prefer the latter, because it doesn't require water and automatically collects hair. ",
"but the clip was of astronauts wetshaving. "
] |
[
"Density and water slides"
] |
[
false
] |
I've got a quick question about water slides. Say there are two objects of equal dimensions. One is twice as dense as the other. Both are put on similar water slides with uniform flow. Which will reach the bottom more quickly, if either? Why?
|
[
"Depends on if they're thin enough to be completely submerged, on if they're dense enough to displace the depth of water on the slide, on wind, and on the coefficient of friction between the two materials and the slide material in the presence of water. ",
"Assuming the coefficient of friction is low(it's a ",
"), both objects are big enough to contact the slide through the water and stick out the top of the water, there's no wind, the water flowing down the slide isn't powered by anything other than the change in elevation from the top of the slide, and all other variables are the same, the denser object should reach the bottom first, because it starts with twice as much energy, and the resistance that comes from the air and water does not scale directly with mass."
] |
[
"If the water is moving faster than the boxes it could cause the less dense one to win. "
] |
[
"Would the force of the moving water be factored in there at all?"
] |
[
"If a lady got pregnant by 1 identical twin, would they be able to do a paternity test to tell which twin was the father?"
] |
[
false
] |
[deleted]
|
[
"Identical twins have identical DNA. Therefore, if said paternity testing consisted of DNA testing or blood type testing, they would not be able to tell the difference"
] |
[
"Try searching. In askscience this was asked ",
"3 weeks ago",
" and ",
"3 months ago",
"."
] |
[
"Well, they'd have a few mutations. If you could find them you could distinguish them, but it's worse than a needle in a haystack. And then you'd need to be able to isolate the specific location, etc., etc."
] |
[
"Can we have twin planets like we have twin stars?"
] |
[
false
] |
How would they circle eachother and their respective star(s)?
|
[
"Yes. The Earth-Moon system is very close to a twin planet.",
"Luna in comparison to Earth is the second largest mass ratio in the solar system, I believe second only to Pluto/Charon. It is so large, in fact, that not only does the moon orbit the Earth, Earth orbits the moon. Their common barycenter is not the center of the Earth, but a point only 1,000 miles beneath the Earth's surface.",
"Unless our theories of planet migration are flawed, twin planets should be possible if uncommon.",
": And ",
"this comment",
" is cool! :) ",
"/u/dabluecaboose",
"! "
] |
[
"Another cool fact, the barycenter of the Pluto/Charon system is outside of the radius of Pluto."
] |
[
"TECHNICALLY neither are planets, so not quite. But probably the closest to what the OP was asking about. "
] |
[
"How do scientists use radiocarbon dating to determine the age of Stonehenge?"
] |
[
false
] |
Scientists used radiocarbon dating and determined that the first stones in Stonehenge were raised around 2400 B.C. How can they use radiocarbon dating to determine this? Wouldn't it only tell you how old the stone is and not when it was put there?
|
[
"Very good question, as geochronological method should not date the stones themselves in this case (which by the way are, it seems, Ordovician: ",
"http://www.sciencedirect.com/science/article/pii/S0305440310003699",
" - not through C14 but through U-Pb on zircons which is the gold standard for dating igneous rocks), but the time of erection.",
"There are several approaches to the problem, none of them direct, which when used together can set an upper and lower limit to the age of erection. Independently of the geochronological method retained (C14, thermoluminescence, etc.), the key is: what material do you date?",
"1 - one may date organic remains or perhaps charcoal immediately under the stones. This is difficult, and there will be questions of remobilisation and contamination. It will give you, with any luck, a maximum age as the stone cannot have been put up before the age of the underlying material. In this case, thermoluminescence might have good potential despite it's drawbacks, as it dates the last time material was exposed to light.",
"2 - One may date organic material such as pigments or lichen on the stones themselves. The problem here, besides contamination, is that the preservation of the oldest possible material is unlikely. This will give an upper limit to the age. ",
"Another approach is geochronology of associated organic remains. Here, the problem is reversed as there are plenty of remains but establishing which ones are associated with erecting the stones is more tenuous.",
"The more data you collect and the better you can understand the relationships between your samples, the narrower the gap between the minimum and maximum ages can get."
] |
[
"I'm just going to tack on to this comment rather than repeat most of what you just said. Another factor helping archaeologists is that people often make religious dedications when throwing up new buildings. This often involves burying some offering beneath the structure. Specifically, they've been able to date Stonehenge because of some human remains that were buried there when the monuments went up. The graves contained organic material which (obviously) contains carbon. This is especially true as many of these burial offerings were cremated, leaving easily datable ash deposits. There were also religious offerings placed at the base of early constructions there which contained animal remains, which can also be dated."
] |
[
"You could date the organic material which the rock was put ",
" and then date the first bits of organic material which well on the rock."
] |
[
"Do primates sense of humor?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"/r/AskScience",
"To check for previous similar posts, please use the subreddit search on the right, or Google site:reddit.com",
"/r/askscience",
" ",
"Also consider looking at ",
"our FAQ",
".",
"For more information regarding this and similar issues, please see our ",
"guidelines.",
"/r/askscience",
"If you disagree with this decision, please send a message to the moderators."
] |
[
"Are you honestly telling me to use Wikipedia? Wow!"
] |
[
"No, I am saying to search ",
"/r/askscience",
" in the searchbar for \"animal humor\". You will find several posts on the topic."
] |
[
"Why doesn't frozen bread get soggy when it's defrosted?"
] |
[
false
] |
It seems like there's moisture in the bag, but it doesn't make the bread soggy. Why?
|
[
"TIL what YMMV literally means, and that in the USA it's use is also idiomatic!"
] |
[
"Unless it is dehydrated, all food contains some amount of water in it. When you put packaged and sealed food items in the freezer, they won't absorb any more moisture than what they already have. If it wasn't soggy when you put it in the freezer, it won't be soggy when it thaws outside the freezer."
] |
[
"yeah if there isit any water added while freezing and the structure of the bread doesn't change enough to hold any less water then the feel of it should stay the same. if you had something which lost its structure for holding water when you froze it, and you defrosted that then it would feel soggy "
] |
[
"How closely could you suspend a particle anti-particle pair without having them annihilate each other?"
] |
[
false
] |
Obviously you couldn't get closer than the Pauli Exclusion limit, or even right up to that point, but how close could they come to each other without reacting?
|
[
"A ",
"positronium",
" is a system made of an electron and an anti-electron. It's not very stable and decays in less than a nanosecond, but at least it exists."
] |
[
"As well as all of the mesons and specifically the states of \"quarkonium\" (up/anti-up, down/anti-down, charm/anti-charm....)"
] |
[
"You actually could get as close as the Pauli Exclusion limit -- the Pauli Exclusion Principle asserts that not all the quantum numbers of two fermions can be the same. But a particle and antiparticle differ in at least one quantum number (charge or lepton number or what-have-you), so their other quantum numbers can in principle be exactly the same - at least for a little while."
] |
[
"I heard somewhere that if one could see the Andromeda galaxy in its entirety, it would look 2-3 times the size of the moon, is this true?"
] |
[
false
] |
I can't remember where I heard it, but supposedly all we are seeing when we look at it through consumer grade optics is just the bright center. Is this true?
|
[
"I've heard 6x as the number, but why don't we do a bit of calculation and figure it out?",
"The moon's angular size is about 32 arcminutes, which translates to roughly a half of a degree.",
"Andromeda is 2.5 million lightyears away and about 200,000 lightyears across. So its angular size if it was all visible would be arctan(200,000/2500000) which comes out to about 4.5 degrees. By that estimate, Andromeda could be up to 8.5x larger across than the moon in the night sky!"
] |
[
"Yes",
"!"
] |
[
"The Moon's angular diameter is listed at ~32'",
". ",
"Andromeda is listed at 190' by 60'",
"So andromeda is about 6 times wider than the Moon, and about 2 times \"taller\"."
] |
[
"I just read that Venus has about 90 atmospheres pressure at the surface. Knowing that Venus is about the same size as Earth, how can it have such a deep, or heavy, atmosphere?"
] |
[
false
] | null |
[
"Lots and lots of dense gas in the atmosphere.",
"The more gas you have, the more pressure gets developed at the bottom of the \"stack\". The denser the gas (CO2 is quite a dense gas) the heavier it will be, which contributes to the pressure even more.",
"If all the gas were replaced with H2 or He, the pressure at the surface would drop"
] |
[
"It asks why it has such a dense or heavy atmosphere not why the dense gases came to be, but that's just semantics. I'll try to answer that.",
"Scientists theorize that there used to be liquid water on Venus a few billion years ago, and it may have even been an Earth-like planet. However, a runaway greenhouse effect due to presence of excess CO2 naturally + heat from the Sun could have caused all the water to evaporate. ",
"On Earth, CO2 is trapped in biomass, in the crust, and in the oceans (a staggering amount). On Venus, these gases could be released and thus create the incredibly dense and CO2 heavy atmosphere we see today."
] |
[
"A denser core would make the planet's radius smaller for a given mass, which means that the pressure developed would be higher."
] |
[
"Is it true that the laws of thermodynamics place an upper limit on the longevity of life. If so how?"
] |
[
false
] |
I have heard that because the total amount of usable energy in the universe in decreasing there is no way life could last forever. Is this true and could you explain it a little more?
|
[
"It's all about entropy, check out ",
"Heat death of the universe",
"There is currently a lot of free energy. On earth, there are stored forms like hydrocarbons (oil), radioactive materials etc. Life is hypothesized to have been formed from pools of certain elements being struck by lightning (the energy from which forms amino acids and then proteins). Eventually, all forms all of energy like this will essentially run their course. Stars will cease to exist as all basic elements (hydrogen and helium) will have reacted via fusion to form heavier elements. I can't really say more about the topic (from lack of knowledge)."
] |
[
"The beautiful order and structure you see among the plants and animals on earth is what a physicist might call a relatively ",
" system (Baierlein's undergraduate thermal book has a great description of entropy, evolution, and life IYI). Low entropy systems tend to be highly structured, and high entropy systems tend to be 'disordered' (for a more precise idea of what entropy is, look up multiplicity). But alas, entropy always increases in the universe. Thus, eventually, the universe will have such high entropy that no ordered structure--such as a cell--could exist. No cells, no life."
] |
[
"What you've heard about is probably ",
"the heat death of the universe",
". The basic idea is that, according to the second law of thermodynamics, the total entropy of the universe is increasing, which means the energy in the universe is becoming more and more evenly distributed. The first law of thermodynamics says that work is a form of energy transfer. But if all the energy in the universe is evenly distributed, then you can't transfer energy anywhere without causing a decrease in entropy and thus violating the second law of thermodynamics, which means it's impossible to do any work, which means life can't function.",
"Wikipedia suggests that it's just a hypothesis, but I don't know anything about whether there's any sort of debate on the matter or if it's generally accepted to be true (but simply can't be proven for obvious reasons)."
] |
[
"If nothing can escape a black hole how does the universe grow from a singularity of all the mass in the universe?"
] |
[
false
] |
Already read what wikipedia says on this.
|
[
"So there's a really big difference in the \"singularity\" that we say when we say a big bang and the \"singularity\" we say when we say a black hole.",
"The equation that governs General Relativity takes a distribution of mass and energy and tells you how space and time are curved around it. If you take a spherical distribution of mass, you get a description of the curvature called the \"Schwarzschild metric.\" (if it's a rotating sphere, it's the \"Kerr metric.\") These are the solutions that have black holes. A spherically symmetric bit of matter.",
"If you take a giant region of uniform mass-energy distribution you get another description of curvature called the \"FLRW metric.\" This metric, when you evolve it back in time says that at one point the entire universe was ",
" dense. So this is a description of a giant uniform region of mass. Very different than a spherical one.",
"Now to the most common misconception of all. People improperly say \"universe\" when what they really mean to say is \"observable universe.\" See, the observable universe is all the points of history from which light can reach us. But there are many many many more points that exist far beyond our little bubble of observable universe. In fact, we can argue that given our current knowledge our observable universe is only a finite region within an ",
" universe. And the universe has ",
" been infinite, since the big bang itself. The expansion of space means that more space grows between the matter and so the universe has gone from being ",
" dense, to fairly empty now days."
] |
[
"It's not known that there was a primordial singularity. There are models that include one and models that don't, and they're all apparently consistent. We don't yet know enough about the universe as it presently exists to unequivocally discriminate between the various models.",
"That said, if there was a primordial singularity, it would have been completely different from a black hole. A black hole singularity is a point at which ",
" worldlines ",
" A primordial singularity is one at which ",
" worldlines ",
" That is, there are no worldlines — possible trajectories through spacetime — in which the primordial singularity can ever be in the future, and no worldlines in which a black hole singularity can be in the past. The use of the word \"singularity\" to describe both phenomena can be misleading, because apart from some very superficial similarities, they're really exact opposites of each other.",
"The slightly more mathematical way of saying the same thing is to point out that in the inflationary period, the geometry of the entire universe approached perfect flatness. Gravitation in general, and the existence of an event horizon around a black hole singularity in particular, is a function of the curvature of spacetime created by stress-energy. But stress-energy is not the only thing that affects the geometry of the universe. Metric expansion does as well, and in the early stages of the Big Bang, when the energy density of the universe was truly mind-boggling, metric expansion had such a dramatic effect on geometry that space remained flat, or very nearly so, despite an energy density that would result in a black hole in our more gently expanding universe today.",
"In general, I would advise caution when getting your cosmology from Wikipedia. In my experience, what's there is a sort of mish-mash of oversimplification, ",
"simplification and outdated information from now-discredited models."
] |
[
"Believe it. Though the details are still coming into focus, it's obvious that during the inflationary period at the beginning of the Big Bang, metric expansion occurred at such a monstrous rate that the geometry of space was stretched to near-perfect flatness."
] |
[
"If the Universe is expanding, does that mean that there is a greater energy cost to move \"against the flow\"?"
] |
[
false
] |
Once again, reading comments in gave me a moment of slight understanding. RobotRollCall gave a good analogy here: But this made me consider that as the universe expands, it essentially changes the rules of what is allowable to occur in physics over time. i.e During the Big Bang matter could begin to form because essentially the physical properties of the universe began to allow it to. Does this also mean that the universe is constantly changing the rules on us? Tomorrow, will it take more energy (relative to my prior existence in time) to go from point A to point B? I guess my main assumption is that mathematically this may be true (for lesser values of true), but realistically there would be no way to observe or measure this difference since I would also assume that energy itself would be different from time A to time B. Am I even making sense?
|
[
"But this made me consider that as the universe expands, it essentially changes the rules of what is allowable to occur in physics over time.",
"You're sort of right, in a sense, but it's better here to say that you're actually wrong.",
"The laws of physics do not change over time. However, the laws of physics are a bit nuanced. For example, the laws of physics tell us that if an electron associated with an atom gains sufficient energy, it will dissociate from that atom. We call that \"ionization.\"",
"So ",
" to stuff is a function of energy density. If you take a collection of matter and increase its energy density, the gross characteristics of that matter will change. Boiling water turns it into steam, for example. Increase its energy density even more, and the fine characteristics of that matter will change: if you superheat steam sufficiently, you can break the bonds holding the hydrogen and oxygen atoms together into water molecules. Increase the energy density ",
" and the individual atoms ionize, then increase it even more and the atoms start to change at the nuclear level, then increase it even more and they start to change at the ",
" level.",
"It's the same basic set of physical laws. You're just changing the parameters of the system such that different things happen.",
"As for your other question, no, it does not take more energy to traverse a larger interval in space than it takes to traverse a smaller one. But it ",
" take more energy to traverse a larger interval ",
" It takes more energy to go from London to Singapore in an hour than it takes to make the same journey in a day."
] |
[
"That's part of it. But even if we were to imagine metric expansion freezing, there would still be an eventual heat death of the universe. All the stars will burn out someday, and so on and so forth."
] |
[
"If I understand you correctly, your question can be broken down into the following:",
"If you flew to the nearest galaxy twice, once now and once in a million years, would it take more energy the second time because the distance is increasing?",
"(This is ignoring the fact that some galaxies are getting closer)",
"I believe the answer is yes, as the universe expands the distance between point A and point B will require more energy to travel.",
"The rules aren't changing, they are quite stable. ",
"You just have to factor in the rate of expansion over millions of years."
] |
[
"Is it possible for massive amounts of water to be sucked into the Earth after an earthquake?"
] |
[
false
] |
What I'm really worried about is that if an Earthquake created a huge crack in the ocean, is it possible for us to lose all or most of the water? If so, how far down would the water go? Would we be able to get it back?
|
[
"where would it go? in short no. an earthquake wont cause the oceans to drain at all. ",
"Quite of bit of ocean water is pulled under the crust every day in subduction zones. It eventually comes back to the surface as steam from a volcano or other similar venting. "
] |
[
"yea, you have to keep in mind that the Earth is really solid (minus some open spaces such as caves, or even the porosity in rocks), so there wouldn't be anywhere to store that much water. "
] |
[
"In my head, I see the cracks going pretty deep into the earth. Perhaps I should've done more research. Thank you though! "
] |
[
"Is it possible to create a formula out of a series of computer generated random numbers?"
] |
[
false
] | null |
[
"As far as I know the randomness created by a computer is never truly random, because it is created through some kind of algorithm, isn't it?",
"Yes, that's correct.",
"Is it possible to find out by those numbers, how the algorithm that created those numbers works.",
"I don't know the answer to this question, but there are people on ",
"/r/AskScience",
" who will. However this thread is a little old now, so I'd suggest resubmitting it with a more specific title.",
"Something like \"Is it possible to find the algorithm for a random number generator by studying the sequences it produces?\"."
] |
[
"What do you mean?"
] |
[
"If I have a series of numbers like \"1 5 35 23 9 3 6\" that was generated \"randomly\" by a computer. Is it possible to find out by those numbers, how the algorithm that created those numbers works. \nAs far as I know the randomness created by a computer is never truly random, because it is created through some kind of algorithm, isn't it?"
] |
[
"What geological/mechanical forces are represented in this perfect road split?"
] |
[
false
] |
I'm curious why it does this. A civil engineer weighed in at the original thread and we still didn't really reach a conclusion. Is it just coincidence that the split is so perfect so far down? Is the image a really good fake? (Doesn't seem likely, as I have seen a lot of shops in my time).
|
[
"It appears to me that this is the result of shearing perhaps. I would like you to take note of where in the foreground, the very bottom of the picture, where the left side appears to buckle up higher than the right side.",
"I would also like to say that it is most likely not so perfect a split as this particular angle and the apparent structural integrity of the asphalt would imply.",
"The only truly helpful thing I can do is confirm that it is not a photoshop job."
] |
[
"My guess is that perhaps the two lanes were laid separately creating a weak point where the two roads met in the middle which sheared under the pressure of the earth quake. "
] |
[
"I second this, if you see the way roads are originally paved the machines pave a lane at a time for convenience's sake. An earthquake could've caused some of the bedrock to sheer away and lift one lane section of the road up, appearing to make a very straight cut. "
] |
[
"How does rayleigh scattering polarize light?"
] |
[
false
] |
As far as I understand, the light from the sun is scattered with a bias towards certain polarization angles. But, the sunlight is randomly polarized and the molecules in the air are randomly oriented, so how does this bias come about?
|
[
"The polarization of sunlight (the blue sky) relies on three things:",
"So, given all that, if you look just a bit to the side of the Sun, say a few finger widths away, you're looking at molecules that are shaking roughly equally in all directions perpendicular to your line of sight, and light you see is basically unpolarized.",
"If, however, you look in the sky somewhere about 90 degrees from the sun, the sunlight has to scatter at a 90deg angle in the upper atmosphere to get to you. If you draw out the geometry and think about the \"shaking\" of the molecules as driven by the sunlight, you'll see that one (transverse electric field) polarization from the Sun shakes the molecule along the line of sight between you and the molecule. That particular shaking doesn't radiate in your direction! However, the *other* polarization from the Sun shakes the molecules perpendicular to your line of sight, so you *do* see that scattered light.",
"That's a lot of words, and it really begs for pictures to walk through it. Unfortunately I haven't found a really good set of explanatory drawings on the web to point you to. If someone else knows of a good source of such, please post!"
] |
[
"The light that reaches you is partially polarized by this effect; how polarized depends on the angle you're looking at, ie what angle the light had to scatter through to reach you. ",
"Looking at the light coming into the atmosphere, yes, there is equal amounts of scattering for the different linear polarizations. Where the scattered light goes (and therefore what a given observer sees) depends on the incoming polarization."
] |
[
"Would it be correct to say that the light that reaches me has a polarization bias. But in general, the light scattered in the atmosphere is polarized in uniformly random directions?"
] |
[
"Was always warned to stay away from windows and off/away from electronic devices (television, computer) during a thunderstorm. How valid is this claim, and how dangerous is it really?"
] |
[
false
] | null |
[
"Mythbusters tested this. If you have Netflix then you can watch it. It's the episode \"Son of a Gun\" (s01e11).",
"The phone did allow the current to go through (if the fuse wasn't grounded) and it would have killed someone.",
"They also tested if someone was in the shower \"as if they were standing on a drain, and the drain was grounded,\" and it also was \"plausible\" to kill someone.",
"Both of these happened in a \"best case\" scenario."
] |
[
"So, if there's no surge protection on between the power lines feeding your home, and the consumer electronics are plugged into the wall, a major surge can damage your electronics by briefly exposing them to currents and voltages well outside their operating ranges. If the surge is say a lightning bolt hitting a power line, that tended to be enough of a surge to burn out old-style cathode ray monitors and TVs. Due to the amount of solid state electronics in a laptop, desktop, or newer TV, you're probably decently safe just buying a ",
" lightning-arresting power strip, and running all of your sensitive electronics through the protected strip. Personally, I've only ever used a surge protecting level of protection (essentially, what's the max amount of overflow the system can handle), and in 2.5 years, the only component in my desktop/entertainment system that has died was a single stick of RAM, from standard use. A surge protector is designed to handle fluctuations of the order of a nearby factory kicking on after maintenance, a fridge or other major appliance turning on, or supply side spikes in the supply chain. There is no guarantee that it would stop lightning, there's no claim by the manufacturer to stop lightning, but a simple surge protector is sufficient for most ripples you'd see on a daily/weekly basis.",
"In terms of how dangerous is being near a window to you? Unless you have metal window frames, and are the tallest house around, and you're watching from your attic, you should be fine. In the case that you have metal window frames, are in the tallest house, and are in the attic, just don't touch any continuous strips of metal.",
" Grammarz, added a brief paragraph about people, not just electronics. Also added a correction, thanks to Enex."
] |
[
"A ",
" phone would carry a current, you've essentially got a circuit directly connected to the physical phone lines. A ",
" home phone or a mobile phone shouldn't shock you, unless something else is horribly wrong with it.",
"And, ok, don't take showers, don't wash the dishes, etc... But I feel like the grounded drain risk is inherently low. If the lightning bolt hits your house, and grounds out through a drain you are in weak electrical contact with, there is a slight risk. If the lightning bolt hits anywhere else, you're in the clear. However, I can't remember being in a structure struck by lightning personally in the last 5-10 years, so I rate the sink shock risk as negligible, personally. Is it there? Yes. Is it something you ",
" worry about? No."
] |
[
"Why is New Horizons going to flyby around Pluto and not orbit it?"
] |
[
false
] |
I read on Bad Astronomer's (Phil Plait) blog that New Horizons won't be passing by the side with 4 parallel dark spots. With all these exciting stuff coming in daily, I am more curious than ever to know more about it.
|
[
"Basically, in order to orbit Pluto it would have to massively slow down, and to do that it would have to burn a lot of rocket fuel, and it is simply not feasible for it to carry that much fuel."
] |
[
"That's true, but there's a limit to that, and that limit is the ground.",
"To be less flippant, let's do the math:",
"Pluto has a mass of 1.31e22 kg and a radius of 1.18e6 m.",
"Escape velocity v = sqrt(2GM/r) so v = sqrt(2*6.67e-11*1.31e22/1.18e6) = 1.21 km/s",
"As long as the probe is travelling faster than that, it cannot possibly be in orbit, even if it was just scraping the ground. It is currently going 19 times that speed."
] |
[
"Exactly. Apparently the probe would need the equivalent of its lift rocket (the Atlas V) to put it in orbit "
] |
[
"Why is freshly fallen snow more \"packable\" than older snow that's been on the ground for a while?"
] |
[
false
] |
when snow has been on the ground for a while, it becomes more powdery and less able to be packed into snowballs. I just don't understand why. I know that when the snow is slightly melting, it's easier to pack snow because of the surface tension with the melt-water, but it doesn't feel the same when you're packing it as when you're packing fresh snow.
|
[
"You're already onto the basics of packing snow - how wet it is matters a lot.",
"If snow just sits on the ground for a while, several things can happen to it. The water can freeze, and melt again, and freeze again, and so forth. This plays havoc with \"wetness\" and \"snowness\", and it's next to impossible to get teh great packing snow after a few cycles of this. "
] |
[
"It depends on the snow, some fresh snow is extremely low in moisture (little cottonwood canyon, I'm looking in your direction) and some is very \"wet\" ( AKA Sierra Cement) the humidity and air temperature, wind, and so on will affect how much moisture is pulled out of the snow after it has fallen, or how much is gained."
] |
[
"Wait, what? I can make killer snow balls the day after a snowfall because the snow packs so tightly. During a fresh fall, the snow is like trying to pack Splenda into a snow ball (perfect example if you've ever used it). ",
"Maybe Ohio is just weird, but I swear this is backwards. As teenagers, all of us would wait until the day after a snow fall to have a snowball fight. "
] |
[
"Why is mars so cold,-63 C, when its atmosphere is 95.3% CO2, which is considered a green house gas?"
] |
[
false
] |
Facts found at Edit: "Thanks Reddit"
|
[
"Mars' atmosphere might be mostly CO2, but it's still an extremely thin atmosphere compared to Earth's, not to mention Venus'. If you check the surface atmospheric pressure, you'll see that it's about 6 millibar, which is 0.6% of Earth standard atmospheric pressure. This is very tenuous, and not nearly enough to keep Mars at what we would consider a warm temperature. If you look at the total atmospheric mass, it's a paltry ~10",
" kg, compared to 5x10",
" kg for Earth and a whopping 5x10",
" kg for Venus.",
"Mars also receives less than half as much sunlight as Earth does."
] |
[
"Artificial structures would be necessary to live on Mars for reasons of temperature and pressure, and sometimes radiation threat from the Sun.",
"The arguments for going to Mars are varied, but mostly can be summarized as belonging to one of two camps: First, we shouldn't keep all of our eggs in one cosmic basket, that is, should something happen on/to Earth, then humans and other Earth life would still exist on Mars to continue on; and second, it's a necessary step to future exploration and colonization to somewhere we might actually find pleasant, though that is a very long term goal, since we're talking places outside our solar system.",
"While Mars is harsh by Earth standards, if we were just looking for more land to put people and things, Antarctica is far more convenient and comfortable, Mars is close and hospitable by interplanetary standards, so makes for a good first colony location."
] |
[
"While the points you make are by far the most salient, I think it's worth noting that water vapor is the most powerful of all greenhouse gases. ",
"The Earth's troposphere contains between 0.1% and 4.24% water vapor (depending on location and weather) while Mars' atmosphere contains (according to my quick calculations) about 0.021% water vapor. It's just another factor to throw onto the pile of reasons."
] |
[
"How can someone pull a plane/train with only his teeth? And even with his only strength?"
] |
[
false
] | null |
[
"Wheels make things very easy to move, the object may weigh several tons but because of the wheels he doesn't actually need to ",
" it, just get it rolling. "
] |
[
"Any relatively strong person can, try setting your car into neutral somewhere flat and give it a push. You'll find it's pretty easy to move it around even though it weighs 1000-2000lb. "
] |
[
"Train wheels are at an angle so that they can go around turns"
] |
[
"How fast are we really moving through the universe"
] |
[
false
] |
Relative to other galaxies or all galaxies together how fast are we moving? For example, the earth is rotating at the equator at 1670 km/h. We are orbiting the sun at a certain speed. The sun and our solar system is orbiting the center of the galaxy. And our galaxy is moving relative to other galaxies. So do we know how fast we humans on earth are moving through space?
|
[
"There is no objective answer to this. Motion can only be defined in relative terms -- you can ask how quickly the Earth is moving relative to another star or galaxy or supercluster, but the question of how fast Earth is moving through \"space\" is not one that is coherent in our current understanding of the universe.",
"And now for something completely different",
"."
] |
[
"This is why I've said for years that all time-machines must also be space ships.",
"Even if you travel one second into the past or the future - the Earth isn't going to be where you left it."
] |
[
"Yes. Mastery over time requires a mastery over space as well."
] |
[
"Do mirrors have \"focal lengths\"?"
] |
[
false
] |
I don't know how to put it better than asking if mirrors also can have different "focal lengths" like lenses – in some mirrors my face looks a bit wider, as if the mirror was a bit more wide angled, and sometimes it looks a bit narrower, as if my face was seen through a tele lens.
|
[
"You can also say that a flat mirror has an infinite focal length to generalize the definition; this is how it is treated in optics."
] |
[
"TL:DR Sometimes.",
"A focal length is the distance between the lens, or in this case the mirror, and where the reflected or refracted light converges. In other words, after interacting with the object, where does all of the light join up. In a plane (flat) mirror, the light never converges but if the mirror is concave, like the inside of a spoon, the light converges at a point in front of the mirror . If a mirror is convex, like the other side of a spoon, the reflected light becomes more spread out but if these rays are traced back then they will converge within the reflection, this is a negative focal length."
] |
[
"Mirrors do have focal lengths. You can think of a mirror as a lens that revert the direction in which light travels. The mirror inside your car that allows you to look behind the car (I don't know the term sorry) is curved inward to magnify a bit the image. It then looks like something is slightly closer/bigger than if you look in the outside mirrors."
] |
[
"Question about the big bang and dark matter/energy."
] |
[
false
] |
I read on wikipedia that the Big Bang started with an extremely hot and dense state. Given the new understandings of dark matter and dark energy that seems to give the universe a total energy of zero, does this require that the initial state was still extremely hot and dense or could the initial state be an unstable, cold nothing, that exploded to create matter, heat and leave negative energy? Is there a good website for the new understanding of how the universe started, in simple language?
|
[
"Dark matter and dark energy are not 'negative matter' or 'negative energy'. The energy content of the universe is not necessarily zero."
] |
[
"Could you quote a source for that statement? ",
"I'm operating under the assumption that our best model for the large scale structure of the universe is the Friedmann-Lemaître-Robertson-Walker model. In order to have a flat universe, the ",
"density parameter",
" of this model needs to be 1, which corresponds to an average (positive) energy density equivalent of roughly 5 atoms of hydrogen per cubic meter. ",
"I could easily be wrong."
] |
[
"ICWYDT",
"If one assumes that the total energy in the universe is zero, then there would have to be a way of having negative energy to balance all of the positive energy we observe (normal matter, dark energy, dark matter). The best theory I have seen is that you can write the expansion of space-time as being due to it having negative energy. All of the 'stuff' has positive energy, expanding space-time has negative energy. "
] |
[
"For exoplanets to be discovered using transit photometry, do they have to be in line with earth(does the planet have to pass between earth and its star)? If so, does this mean that planets that orbit in a plane where they don't pass between the earth and its star are undetectable?"
] |
[
false
] | null |
[
"Yes, the transiting planet should more or less pass between the our telescopes and the star, which of course is a limitation. ",
"There are some alternatives that do not require the planet's plane to intersect our line of sight, such as Astrometry. It involves measuring the wobble of the star as the planet orbits around. It directly measures the periodic change in position of the star. Since the wobble can be detected in 2 dimensions, it gives astronomers a way to measure the inclination of the planet's orbit. ",
"If the orbital plane never intersects our line of sight, we can still see the star moving around the center of mass of the star-planet system.",
"This is a nice visualization.",
" "
] |
[
"You're right that this technique works far better when the orbiting planet is fairly massive, which is obviously a limitation, but it should still be possible to detect an earth sized planet.",
"The amplitude of the stars wobble is proportional to the ratio of the planet's mass to the star's mass, so an earth sized planet orbiting a red dwarf for example, would possibly produce a large enough wobble for detection. "
] |
[
"Is it possible to detect Earth sized planets with this method? It seems like a planet would need to be huge in order to cause a noticeable effect on the parent star. "
] |
[
"How are false positive lateral flow tests possible?"
] |
[
false
] | null |
[
"Lateral flow tests typically use an antibody with an affinity for some target molecule (the virus fragments in this case), but there is always a non-zero probability that some other molecule will bind to and activate the antibody. Many drugs work by fooling a protein in the body to activate as if it was in contact with it's normal target molecule, so there are molecules present that will fool an antibody. A simple analogy is artificial sweeteners- molecules that bind to sugar receptors in your taste buds so the food tastes sweet. In the virus tests, some other molecule might have the right shape to trigger the antibodies. It is also possible that not all the antibodies incorporated into the test device are the correct ones- manufacturing is not perfect.",
"Biochemistry is inherently a probability game, and so some percentage of the time these antibody tests will trigger a positive result with no virus fragments present. On a good test that might only be 1% or 0.1% of the time. The tradeoff to be made with tests like this is sensitivity vs specificity. Sensitivity is basically your detection rate for true-positive samples. Specificity can be thought of as the detection rate for true-negative samples (how often a negative person will read a negative test). The antibodies used in these tests are never perfect, so they usually aim for the best sensitivity they can get with reasonable specificity. \"Reasonable\" is determined by the cost of a false positive- in the case of Covid, the cost would be quarantining a healthy person unnecessarily or requiring them to seek additional, more expensive tests like PCRs."
] |
[
"It's very possible. I'm a lateral flow assay developer - we are currently developing a number of LFAs for COID-19. As fossiliz3d said, false-positives and false negatives are a an inherent risk. There is always going to be a tradeoff balance sensitivity and specificity. While the antibodies themselves might good, a good assay still needs to normalize the range of conditions in samples for all the reagents to work as intended. In most cases, the sample comes from a nasal swab. The contents of a nasal swab vary greatly from person to person. This includes thickness of mucins, your hydration level, pH, particulates other cross-reacting species such as non-covid coronavirus, drugs etc... We may have an assay that works well with 99% of the population but certain donors/patients that continuously cause odd results such as false positives. A lot the early LFAs for COVID we complete junk as the range of antibodies was limited."
] |
[
"It's very possible. I'm a lateral flow assay developer - we are currently developing a number of LFAs for COID-19. As fossiliz3d said, false-positives and false negatives are a an inherent risk. There is always going to be a tradeoff balance sensitivity and specificity. While the antibodies themselves might good, a good assay still needs to normalize the range of conditions in samples for all the reagents to work as intended. In most cases, the sample comes from a nasal swab. The contents of a nasal swab vary greatly from person to person. This includes thickness of mucins, your hydration level, pH, particulates other cross-reacting species such as non-covid coronavirus, drugs etc... We may have an assay that works well with 99% of the population but certain donors/patients that continuously cause odd results such as false positives. A lot the early LFAs for COVID we complete junk as the range of antibodies was limited."
] |
[
"Are there any two foods/edible materials that are harmless when consumed separately and dangerous when consumed together?"
] |
[
false
] |
This was somewhat inspired by a friend's belief that she would explode if she ate Mentos and Diet Coke in quick succession. Having empirically showed that this is untrue, are there any foods/drinks/other materials which are safe to consume on their own, but would have side effects if consumed together?
|
[
"God damn it, My apologies."
] |
[
"Downvoted, but only because you mixed up nitrates and nitrites. It's nitrites that form nitrosamines in the presence of protein and acid, and any acid will do, including stomach acid.",
"http://en.wikipedia.org/wiki/Nitrosamine"
] |
[
"Downvoted, but only because you mixed up nitrates and nitrites. It's nitrites that form nitrosamines in the presence of protein and acid, and any acid will do, including stomach acid.",
"http://en.wikipedia.org/wiki/Nitrosamine"
] |
[
"What happens if water vapor is compressed while kept at a temperature greater than 100 degrees Celsius? Can it turn into liquid form?"
] |
[
false
] |
Sorry if this is a dumb question.
|
[
"Yes, it can. The boiling point of water is only 100 deg. C at a pressure of 1 atmosphere. At lower pressures the boiling temperature is lower and at higher pressures the boiling point is higher. You may have experienced this if you've ever gone camping at high elevations. You often have to put salt in the water to raise the boiling point so you can cook your food in a reasonable amount of time.",
"The relationship of temperature and pressure in regards to phase shifts is described in phase diagrams. ",
"Here",
" is the phase diagram for water. It can tell you what phase water will be in for a given temperature and pressure, and at what conditions phase transitions occur.",
"There are two interesting points on a phase diagram: the triple point and the critical point. The triple point describes the temperature and pressure at which all three phases can occur simultaneously. At temperatures and pressures below the triple point, the liquid phase does not occur, and the phase transitions directly from solid to gas, or vice versa.",
"The critical point describes the temperature and pressure above which phase boundaries disappear. To describe the concept, envision that beyond the critical point, the liquid phase is so energetic that it becomes similar to a gas while the gaseous phase is so dense that it becomes similar to a liquid. This is called a supercritical fluid."
] |
[
"Yes, you can up to a certain temperature. To see that, take a look at the phase diagram of water ",
"here",
". So for instance at 400K (about 130C), if you draw a vertical line going upwards (if you raise the pressure at a fixed temperature), at a certain point you cross into a region where the liquid phase is the thermodynamically stable phase. ",
"The caveat I hinted at in the beginning is that there is a critical temperature (called the critical point, which is 647K for water), where condensing the gaseous yields not a liquid, but rather a so-called supercritical fluid."
] |
[
"I forgot about the fact that boiling and freezing points are not fixed in relationship with pressure, it makes much more sense now! "
] |
[
"I have a PCL tear which never healed properly. It hurts more during the winter (New England). Is there a physiological explanation for this, or is it just my subjective interpretation?"
] |
[
false
] |
[deleted]
|
[
"I have a suspicion for this phenomenon, but it's only a hypothesis. I do not study this and this is just conjecture. Someone who knows better feel free to correct me.",
"Anyways, when you get an injury or tear to tissue, there are two healing process, both very separate from each other. The first is regeneration, in which the tissue is healed to its former uninjured status, or very near it. The second is repair, in which scar tissue invades the area, and gives the injury a kind of structural seal. Scar tissue is made of a different material and cell composition (typically collagen and fibroblasts).",
"Ok, here's where my conjecture comes in. I would imagine that the tissue and the scar tissue have different ",
"thermal expansion constants",
". I believe this is an actual problem with some dental fillings, in which going between extreme cold (i.e. snowy winter) to heat (i.e. summer) would begin to detach the dental filling from the tooth over time (for example, the dental filling might shrink faster than the tooth in the cold, and would forcefully detach itself from the tooth).",
"My suspicion is that scar tissue will expand and contract at a different rate as compared to the healthy tissue surrounding it, which would cause pain.",
"Anyways, just my intuitive guess, anyone who actually knows or can point to a peer reviewed journal that explains it, please do. I am actually quite curious about this phenomenon as well."
] |
[
"Based on my \"gut feelings\", I really like your source material (scar vs. healthy), but would like to not rule out what AnatomyGuy mentioned as a potential catalyst to the phenomenon. Barometric pressure. My gut tells me that might have more to do with it (maybe the cells expand and contract at different pressures, not just heat variations)?"
] |
[
"Hmm...this...could be possible. The problem is we have to consider what would change when pressure changes. Typically, fluid and solids (i.e. water and collagen) are considered incompressible. That would suggest that the neither the cells, or the tissue as a whole would change size in a changing pressure.",
"However...Oxygen solubility inside the tissue could potentially play a role...Not too sure how though, since oxygen solubility and concentration should be the same in both scar and healthy tissue.",
"I'll think about it, but as I said, I'm not sure. Definitely something to think about though."
] |
[
"How much CO2 do volcano's really expel on average per year, and how does that amount compare to man-made emissions?"
] |
[
false
] |
I get 300 million tonnes here : and less than half that here: What is a reliable source? It's popular myth in the Australian right wing media that volcano's emit much more carbon dioxide than humans, which is in turn used to discredit the scientific consensus on climate change. I'm looking for sources with the most solid scientific credibility .
|
[
"It's kind of irrelevant, because as you can see here (",
"http://cdiac.ornl.gov/ftp/ndp030/CSV-FILES/",
") the total estimated number of metric tonnes of CO2 caused by fuel burning is around a stately 8000 million each year. "
] |
[
"The truth is, it's hard to know exactly how much CO2 is coming out of volcanoes. You can measure the rate coming out of fumaroles and then integrate the amount coming out of soil diffusion, but then there's all the undersea volcanoes that we can't measure! That's why the number varies so much. As for an actual value, I don't really have an answer. I hope a climatologist studying volcanic forcing on climate does though!!!"
] |
[
"The argument presented doesn't really make any sense, because even if man-made contributions were dwarfed by volcanic CO2 emissions, the additional carbon from human activity would still be adding to the total, and could therefore still be sufficient to push the system over a \"tipping point\" into a new equilibrium.",
"Saying that volcanoes make human activity irrelevant is like saying that one extra straw won't hurt the camel, since there are already so many bales on its back. I think we've all heard the end to that particular story."
] |
[
"Why does an electron and a proton have the same magnitude of charge even though the electron is a lot smaller than the proton?"
] |
[
false
] |
[deleted]
|
[
"A proton is a composite particle made up of 3 valence quarks and many many more \"sea quarks\" and gluons. The charges of sea quarks cancel because there are as many sea antiquarks as there are sea quarks for any given flavor. The gluons carry no charge. So all of the charge of the proton comes from the three valence quarks, two of which have the \"up\" flavor and the third has \"down\" flavor. The up quark carries two-thirds the charge of an electron but of the opposite sign (2/3 e). The down quark carries a third of the electron charge with the same sign (-1/3 e). So it adds up as follows.\n2/3 e + 2/3 e - 1/3 e = e. ",
"For some reason, charge always comes in packets of +e/3 or -e/3. Dirac has showed that this \"charge quantization\" is a necessary condition for the existence of magnetic monopoles, but we haven't found them yet. "
] |
[
"Are the \"sea quarks\" virtual particles or real?"
] |
[
"Virtual. Constantly being pair-produced from gluons and annihilating back into gluons. \nGreat question."
] |
[
"What is the connection between nosebleeding and time traveling as seen on movies ?"
] |
[
false
] | null |
[
"It's made up because there is no such thing as time travel"
] |
[
"Maybe there is but all nosebleeding stories are made up ?"
] |
[
"There isn't and those are just movies. It's like saying most aliens in movies are depicted as green and tall and skinny so maybe they really are."
] |
[
"Is there a reason we sent the Voyager craft ahead of the solar system/into the bow shock of the heliosphere?"
] |
[
false
] |
Pretty much what it says in the title. Why that way instead of "behind" us, isn't there much there or was having instruments in the bow shock more worthwhile?
|
[
"When the voyager space craft were launched the planets in the outer solar system were in positions that allowed a single mission to do flybys of several different planets. The 2 voyager spacecraft were launched to take advantage of this, but the route they took meant that after the planetary flybys they would continue their journey outside the solar system, into the Heliosphere and beyond.",
"The route/direction they follow is dictated by the planetary alignment. That they are able to provide data about the Heliosphere is bonus rather than the original mission."
] |
[
"blobhopper's post is correct. Voyager I was launched on a trajectory that would let it observe Jupiter and Saturn, and that restricted the direction of its eventual, permanent flight path.",
"If we ",
" been able to pick a direction to investigate the heliopause, we would have chosen the direction of the theorized bow shock, just because the sheath there would be closer to us. As the sun moves \"forward\" through the thin interstellar medium, the pressure of the incoming matter would push the heliopause inward to some extent.",
"However, earlier this year it was determined that the sun appears to have no bow shock. We are moving too slowly through the interstellar medium for there to be a significant effect, and our heliosheath is most likely close to spherical."
] |
[
"Ahhhhhh ok then, thank you"
] |
[
"Is it possible to use a set of units for measurement (length, time etc.) that would negate the need for universal constants?"
] |
[
false
] |
We currently define a meter as a set certain length, and a second as a set certain amount of time. This means in formula like the law of gravity, we must use the Gravitational constant to make the math work. If we had different definitions for mass, length and time etc. then this constant would also be different. So could we use a 'universal set of measurements' that would eliminate the need for such constants. Downside, all future discoveries would be slightly disappointing if the scientist couldn't be able to name them after his/her self. But on the up side we wouldn't need to calculate such a constant in the first place and lazy science students with poor memory skills wouldn't need to spend so much time memorizing them. Or would changing one set of measuring units cause another set to change, meaning we will always need some universal constants somewhere?
|
[
"The Planck units do this.",
"There is still some room for interpretation over which equations you shrink and which constants you eliminate. For example, in the Planck units, Coulomb's law has no constant, but the unit for charge is not an integer multiple of the fundamental charge.",
"The Planck units are also pretty much useless for actually measurements, except momentum."
] |
[
"No. We can eliminate many of them using the Planck units, but there's nothing we can do about ",
"dimensionless physical constants",
". For example, the fine structure constant is about 1/137. It's not 1/137th of a meter or something. Just 1/137. It doesn't matter what system of units you use, because there's no units here."
] |
[
"Cheers for the answer"
] |
[
"Is it possible to generate propulsion of a wavelength using a laser?"
] |
[
false
] |
[deleted]
|
[
"I don't understand the question. A \"wavelength\" is not an object, it is a property of something. You can create light at a certain wavelength. You can use a laser to create light at a certain wavelength.",
"Also, I don't know what you mean by \"a laser doesn't technically disturb the wavelengths around it\". What a laser does is create coherent light at a specific wavelength. I'm not sure how this is relevant to your question."
] |
[
"A wavelength isn't an object, it's a size. How do you push a size?"
] |
[
"In general, photons don't interact. Unless they're high energy ones in which case they can interact to pair produce particles and anti-particles."
] |
[
"FTL Communication"
] |
[
false
] |
Hypothetical time! Say I built a gigantic, gigantic building - I'm talking reaching into space tall. In that building I have a long rod that goes from the top to the bottom. If I tapped the rod at the bottom level, would the top of the rod instantly move up (presuming the strength to move such a rod)? Could I use a lot of these rods (and perhaps some sort of automated pressing system) to transmit data faster than light?
|
[
"Mechanical signals travel at the speed of sound. For wood, this is a few kilometers per second."
] |
[
"This question is asked pretty often around here. Check out ",
"this entry",
" in ",
"/r/sciencefaqs",
" and see if that answers your question. "
] |
[
"Thank you."
] |
[
"Illustrations of dinosaurs often depict volcanoes in the background. Were erupting volcanoes once so common that this a probable scene if one were to look at a typical dinosaur during its era, or is this a cliche that's an artifact of compressing our perception of extremely long time-scales?"
] |
[
false
] | null |
[
"It is just dramatic effect.",
"Science often describes the effects of increased volcanism, in the Jurassic for example, and this is certainly part of what you describe. There are theories about geology, and the breakup of supercontinents, ",
"Associated middle to late Jurassic volcanism and extension in southern South America",
". There are also theories about the impact of changes in volcanism on flora/fauna, ",
"Floral changes across the Triassic/Jurassic boundary linked to flood basalt volcanism",
".",
"However, even if volcanism were to increase by an order of magnitude (a huge stretch), then you would only be ten times more likely to see an active eruption at any particular place and time.."
] |
[
"There's also the hypothesis that a supervolcano (like the one beneath yellowstone national park) was the cause or a significant contributor to the extinction of dinosaurs. "
] |
[
"I think you're talking about the eruption of the Deccan Traps, which happened around the end of the Cretaceous. Here's the ",
"wikipedia",
" page for it, but if you want a pretty good description of its effects on the climate (and life on earth at that time), I think ",
" by David Beerling actually did a really good job."
] |
[
"How are the effects of molecules' spatial orientation on reaction kinetics studied?"
] |
[
false
] |
In general chemistry I recall learning that certain spatial orientations of molecules are more favorable for producing a reaction than others. Presumably when two molecules, A and B, are approaching, it is more favorable if the reacting group of A is oriented towards B and vice-versa, rather than the reacting groups being oriented away from each other. This concept sounds reasonable, but is it experimentally determined? In aqueous solution? In the gas phase? How are the relative orientations of molecules in space determined or manipulated?
|
[
"You are asking about the Frequency Factor, specifically one component of that which is the Orientation Factor. OK, let's back up:",
"We're talking about Collision Theory for chemical kinetics, where the rate constant (k) is described via the ",
"Arrhenius Equation",
":",
"In this equation A is the Frequency factor, Ea is the activation energy, R is the gas constant, and T is the absolute temperature. Your question relates to the Frequency Factor and how it is determined through experimentation. The Frequency Factor is best defined as \"",
".\"",
"This begins by determining the value of the rate constant at a variety of temperatures (and there are a variety of methods of doing this), plotting the data, and applying a best-fit line/curve to the data (I can elaborate more on this later if you like). By this method we can get the value of Ea and more importantly A, the Frequency Factor.",
"That is not the answer to your question, though :)",
"The Frequency Factor is a combination of 2 values that are difficult to separate by experimentation: A=Z*P=(expected frequency of collisions)*(probability of being in the correct orientation)... so in order to find the value of only 1 of those variables requires you to have somehow found the other. And to my knowledge the only way to determine the value of Z (the average frequency of collisions) is through ",
"some theoretical calculations",
"/Kinetics/06%3A",
"-_Pre-exponential_Factors) that take into account the average speed of the reactants, volume of the particles, etc. Best to do this for the gas phase where the intermolecular interactions are minimal. If we had A and Z, we could then find P. ",
"So we can experimentally determine A, but finding P is harder and to date requires estimation of Z."
] |
[
"Lyotropic Nematic and Lamellar liquid crystals may be used to study orientation effects on certain reactions, see- V. Ramesh and M.M. Labes Journal of the American Chemical Soc. vol 109,3228 (1987) ,ibid Vol.108, 4643 (1986).",
"Reactions at monolayer surfaces are discussed by H. Kuhn in Modern Trends of Colloid Science in Chemistry and Biology Edited by Eicke (Birkhauser Verlag Basel 1985). UV spectroscopy is the primary tool used in the first two studies above. The latter paper discusses polymer formation at surfaces and photoinduced electron transfer of molecules adsorbed or contained within biomembranes. It also includes some theoretical discussions on rates of reaction. Most of the above are confined to aqueous solutions of the constituents. If you have access to a university research library these references should be available.",
"In the liquid crystal cases the reaction is observed by the change in absorption bands parallel and perpendicular to the predetermined liquid crystal matrix orientation as the molecule changes shape before and after reaction and reorients itself within the micelle or on the surface of the micelle.",
"Hope this helps.",
"edit- changed adsorption to absorption in the last paragraph."
] |
[
"Are molecular beams of any value here? Is there any way to control the orientation of a beam of molecules using such technology? I am totally speculating here, but would an electric field applied to the beam orient the molecules in a particular way, making that parameter a known experimental quantity? Would this work only for, for instance, polar molecules?"
] |
[
"Followup to: What is the distribution of numbers picked at random by people?"
] |
[
false
] |
Original thread by iamayam . Gist of the question: I want each person in a large group of, let's say, 50 people to choose a number from 1 to 4. Each person picks his/her number silently, so that no one else knows who has what number. What is the likely distribution of those picking 1, 2, 3, or 4? I then made a quick . Since quite a few people (well...64) responded, I thought I'd let everyone know what the results were: While not very scientific at all (you can see the results before voting, you might have read a comment on the thread saying which ones people tend to go for), there is a noticeably smaller number of people picking 4. This was predicted in the comments section in the original thread. Science(ish) in action. : As pointed out by nicksauce below, the figure of 14% (the proportion of people who picked 4) is not far enough away from the expected 25% to actually be statistically significant. So the answer to the original question seems to be "flat". nicksauce's analysis is apparently incorrect, see discussion in comments
|
[
"There's something in game theory call a beauty contest, where you tell people to pick a number between 1 and 100 and that a prize will be awarded to whomever picks closest to two thirds of the average of all the numbers. If you assume everyone is an idiot and guesses randomly then the average should be about 50 and the winner would guess 33.3. If you assume everyone assumes everyone is an idiot, the average would be 33.3 and you should guess 22.2. But then if you assume that everyone assumes that everyone assumes...etc...equilibrium is reached when everyone guesses 0."
] |
[
"EDIT:\nAs nicksauce incorrect analysis is still getting upvoted, I guess I didn't explain myself properly, so I've expanded my explanation significantly.",
"Nicksauce doesn't factor in the number of bins (4 bins as 4 numbers you can guess). If there were 16 bins and 64 total votes, he'd still say there is a 12.5% error on each bin, which means that even though the average count in a bin is 4, he'd need to see 12 votes before its a sigma aberration high, or -4 votes before its 1 sigma low. My simple analysis (given next paragraph) would say with 16 numbers, the average in each bin is N=4 votes, and hence expected error is 2 (sqrt N), so if you received more than 6 or less than 2 in a specific bin you ",
" expected to be high or low that would start be significant at roughly the 1 sigma level. ",
"This is called ",
"Shot noise",
" where you take if N is the mean number of counts averaging over an ensemble of experiments, sqrt(N) is the standard deviation you'd observe. Shot noise is derived from the Poisson distribution, a distribution of random discrete events that can occur with some (unknown) underlying frequency. Poisson distributions are described by one parameter lambda. The mean (mu), the expected value if you repeated the experiment many times is equal to lambda, as is the variance (the standard deviation (sigma) squared) which describes how far the spread of values will be.",
"The observed count of 9 votes for #4 is a statistical anomaly by this analysis (7 votes or 1.75 sigma below the mean). A 1.75 sigma deviation only should happen ~4% of the time as arising from chance",
"[1]",
"), giving you a 96% confidence.",
"However, this was oversimplified on three counts. ",
"First there were four numbers that could each be the lowest number. No one predicted that 4 would be the least frequently picked #, so we have to factor in our study could have found multiple interesting statistical results. Roughly speaking if you do 3 studies of a non-existing effect, on average 1 study will have a 1 sigma effect. If you do 20 studies, on average 1 will have a 2 sigma effect (95% confidence). Thus when you do a study and look at more things that could be findings, you must set a higher threshold to call something a statistically significant finding.",
"{ASIDE: One person said #1 and #4 would be least frequently picked, but those had a total of 27 votes which is less than 1 sigma from the expected mean for two numbers using 32 +/- sqrt(32)=32+/- 5.6. Though a more accurate analysis uses binomial distribution, which has a variance 16, or the expected value is 32+/- 4, so its slightly more than ",
"1.25 sigma",
" by that analysis (11% prob of arising from chance).} ",
"Second I really should be using the ",
"Multinomial distribution",
", as each trial results in one of 4 results (vote for 1,2,3,4). Under multinomial the std dev is smaller than 4 (sqrt(64",
"3/4) = 3.46), so 9 appears as a 2.6 sigma effect.",
"But since any number could be the least frequent #, we should say what is the likelihood that any one of the 4 numbers could be the smallest # occurring 9 or less times. This is easiest to demonstrate by doing a simulation of a few hundred thousand experiments. (Otherwise you are likely to make silly mistakes). You find that 10% of the time you find one number occurring 9 or less times when none are favored.",
"Now the final analysis (which I'd suggest you'd read the ",
"NYTimes quote",
" below first) factors in how the frequentist interpretation overestimates confidence in results. We didn't measure the least frequent number occurring less than 9 times, we measured it least frequently occurring exactly 9 times. Thus we should compare our null hypothesis (all numbers are equal) to some alternative hypothesis (the number 4 occurs with a specific lower frequency than other numbers) subject to the experimental data of it occurring exactly 9 times. If we do the calculation to any specific alternative hypothesis, we find that the alternative hypothesis is favored by at most 2.6 to 1. This isn't strong evidence in favor of the alternative hypothesis (e.g., if you had to say it was a confidence it would be at most 72% confidence)."
] |
[
"First, method was flawed by letting people see poll results prior to the poll being concluded. (E.g., one could vote multiple times to twist the dataset).",
"Second, with 64 #s you may ask what percentage of the time do you get a # less than or equal to 9 from a uniform distribution? A quick Monte Carlo shows about 10% (repeating the experiment 100 000 times using Mersenne Twister in scipy found 10 031 where the minimum # was less than or equal to 9) and wouldn't be that difficult to analytically calculate. But only 5608 of the tries had the least picked number be picked exactly 9 times.",
"We should be careful about our interpretation ",
"[1], go to the \"Consider this following example\"",
". It does not simply mean we have a 10% chance of seeing this fluctuation happen by chance, a Bayesian approach should be taken. Say compare what is the chance of observing exactly 9 on one # if it is a fair distribution, vs if one # only shows up 9/64 of the time and the other numbers are equiprobable. (I do this by generating random #s in the range of 1-192 and assign 55 of the numbers to be 1,2, or 3 and assign 27 of the #s to be 4.) Doing this experiment, you find only about 15% of the cases had exactly 9 as the minimum number picked (despite it being the most likely). Thus the Bayesian interpretation is that data favors the 9/64 probability of 4 over uniform probability by a factor of ~at most 2.6 to 1 (or at most 72% confidence). This is pretty weak evidence for the number 4 being selected 14% of the time.",
"Now unless there was a mountain of previous data that somehow favored the view that 4 would be selected 14% of the time the logical conclusion is to say the null hypothesis (that #s are equally probable) has not been rejected.",
"Python code:",
"#!/usr/bin/python\n\nimport scipy\n\ndef one_trial():\n nums = scipy.random.randint(0,4,64) \n totals = []\n for i in range(4):\n totals.append(sum(nums==i))\n if min(totals) == 9:\n return True\n else:\n return False\n\ndef one_flawed_trial():\n nums = scipy.random.randint(0,192,64) // 55\n totals = []\n for i in range(4):\n totals.append(sum(nums==i))\n if min(totals) == 9:\n return True\n else:\n return False\n\nfair = 0\nunfair = 0\ntotal = 0\n\nfor x in range(100000):\n total += 1\n if one_trial():\n fair += 1\n if one_flawed_trial():\n unfair+=1\n\nprint fair/(1.0*total), unfair/(1.0*total)\n",
"Finally, when asked to guess a random # in a range (say) 1 and 4, I usually guess a complicated irrational #. Something like pi - e + 1.1. Just to be different."
] |
[
"What factors affect the rate in which marijuana metabolites are excreted from the human body?"
] |
[
false
] |
[deleted]
|
[
"Unsurprisingly, it's metabolism and excretion (peeing/sweating/etc). You need to increase your metabolism to burn the fat cells which contain the metabolites, and then you need plenty of water to flush the released metabolites from your system. ",
"If you're looking to get rid of the most metabolites as fast as possible, you need a zero carb zero sugar diet (to prevent fat storage) with 30-60 mins of exercise (cardio) and roughly a gallon of water a day. Nothing else will work. "
] |
[
"Sorry didn't realise."
] |
[
"Nope. The relevant information would be some crazy cellular analysis, not mention require some metabolic tests, assuming you want the information to be accurate to your unique situation. No \"guide\" or anything will tell you exactly how to calculate it for yourself. It's so highly depending on so many unique factors that you're better off just hitting the diet and exercise ASAP and hitting it hard. "
] |
[
"Which has more complexity as far as the number of physical operations happening in one time, a 200 foot commercial fishing vessel (minus crew) or a single celled organism?"
] |
[
false
] |
I'm sitting on my boat in the Bering Sea, thinking about what defines life (we do a lot of philosophical thinking out here) and if you could say that the boat is alive. I mean power is created by burning energy, there are a huge number of computers, transformers, fans, pumps, winches, even the two sets of washers/dryers, dishwasher and wifi routers are running right now. So what's a more complex system, my boat, or a single cell of cyanobacteria?
|
[
"I don't know much at all about boats, but I feel pretty confident saying its a single celled organism, and I'll try to explain why. Proteins are created from a DNA template in two steps. First, the DNA is ",
"transcribed",
" into mRNA. Then, the mRNA is ",
"translated",
" into a protein by a package of proteins and RNA called a ribosome. In eukaryotes like plants and animals, that's two separate processes. In bacteria, they can be coupled: an mRNA strand can have transcription started on it before the whole thing is translated. Moreover, a single strand of mRNA can have multiple ribosomes on it at the same time, all performing translation.",
"Take a look at ",
"this picture",
" showing coupled transcription and translation. That thin line on the bottom with all the \"strands of pearls\" on it is DNA. The \"string\" in each strand of pearls is mRNA that is being transcribed, while each \"pearl\" is a ribosome. In bacteria, RNA can be produced at ",
"80-90 nucleotide bases per second",
" while amino acids (the building blocks of proteins) are added to a growing strand at a rate of ",
"4 to 22 per second",
". Now it looks like there are about 12 mRNA strands coming off the DNA (not counting the really little ones) each with at least 15 ribosomes on it. So taking the more conservative estimates for speed, just in this picture we're looking at (12*80)+(12*15*4)=1680 operations/second in this picture-and that's without breaking \"add one nucleotide\" or \"add one amino acid\" into their own component steps. ",
"That may not seem like a lot, but this is looking at one small piece of DNA; there will be many other places across the genome where the exact same thing is happening. Not to mention some enzymes work extremely fast. For example, ",
"ATP synthase",
" is used by the cell to make ATP, which is the basic unit of energy used in many other processes. ATP synthase lets protons move through it from one side of a membrane to another and uses the energy to produce ATP. Part of the protein spins, at an average of ",
"nearly 400 revolutions/second",
" and each revolution produces three ATP-each ATP synthase is responsible for 1200 operations/second, and one cell will have hundreds or thousands. ",
"Carbonic anhydrase",
" interconverts water and carbon dioxide to bicarbonate and a proton and has a rate of 10",
" to 10",
" reactions per second.",
"Basically, there are so many copies of so many enzymes working so quickly that I think its pretty reasonable to say that a single celled organism is more complex."
] |
[
"Snarky: The boat is clearly more complex, since it contains at least one cell of cyanobacteria, as well as other stuff.",
"Not-snarky: Presumably there is some implicit feature size - where the questioner would say \"that's not my boat, that's the natural microcrystalline structure of steel\" or \"that's not my boat, that's a rat living on my boat\". My point is, the question is ill-specified unless we know that dividing line."
] |
[
"I don't think it's fair to count the sub-processes of one body and not the other. You could count the the combustion of all the fuel molecules and every stroke of a mop and get quite far with the ship's count as well. Then again, what level organization and indeed what organization at all would offer a fair comparison? Intra-cellular communication is far more complex than intra-ship communication on the scale of individual signals, but could be quite comparable on the scale of entire signal systems of some definition.",
"So we could put the question this way: All intra-body processes considered, which involves more functions: keeping a cyanobacterium alive or keeping a ship running?"
] |
[
"What causes people to procrastinate and what do you have to change to stop it?"
] |
[
false
] |
A lot of people procrastinate. I'm an expert at it. I'm trying to figure out the underlying causes of it, both biologically and psychologically. What can one do to actively stop it from happening permanently?
|
[
"Check out ",
"temporal motivation theory",
", which outlines four factors in determining motivation at any given time: expectancy, value, impulsiveness, and delay. The rationale for those factors make intuitive sense:",
"Expectancy: if you expect to succeed in a task you'll be more motivated to do it - e.g., if I get a D in every quiz in a topic I'd not be willing to invest much time studying for the next one.",
"Value: if the reward of successfully completing the task is high you'll be more motivated to do it - e.g., going out with friends is much more rewarding than studying for the quiz, so I'm more motivated to go out.",
"Impulsiveness: some people are more impulsive than others, meaning they value short-term reward over long-term reward",
"Delay: regardless of how impulsiveness a person is, there is ",
" a natural, innate human tendency to priorities tasks with a short delay for reward - e.g., going out with friends ",
" and having fun ",
" is much more attractive than studying for the quiz ",
" and doing well ",
".",
"For some reading material you can also check out ",
"The Procrastination Equation",
", a book based on that theory. It is geared towards general audience but is very well sourced. The idea behind the book isn't to eliminate procrastination - because it is impossible to do so. The argument is that humans have ",
" to be procrastinators. So rather than hopelessly trying to eliminate it all together, it's best to recognize how it works and what you can do to increase motivation for the desired tasks."
] |
[
"Check out temporal motivation theory[1] , which outlines four factors in determining motivation at any given time: expectancy, value, impulsiveness, and delay",
"Sounds really interesting. I'll check it out tomorrow or whenever I get around to it..."
] |
[
"There are many explanations for why people procrastinate, from the relative value of things now vs. in the future, to the meaning success (or failure) might hold for a person. ",
"Some possible avenues for reducing procrastination are ",
"temptation bundling",
", cognitive-behavioral therapy, or time management techniques. Temptation bundling is a variation on tried and true behavioral therapy techniques of pairing a reinforcing, fun, or otherwise enjoyable activity with something you don't like to do. Although temptation bundling is a new spin, the ",
"idea has been working since the '60s",
".",
"Cognitive-behavioral therapy techniques would help you understand why it's hard for you to do what you need to do. Sometimes, procrastinating can actually be self-protective. For example, if I am afraid of failing my math test, and I don't study, I can attribute my failure to not working rather than being stupid. This doesn't happen consciously, and may not apply to you, it's just an example of maladaptive thinking that can underly a pattern of procrastination.",
"I sometimes use the Pomodoro method. I don't think there's anything magic about it, but it's simple. You work for 25 minutes, then take a 5 minute break. Repeat 4 times then take a 15 minute break. You can find ",
"timers online",
" for using it. I find that 25 minutes isn't too long or too short, and 5 minutes is enough to get a little break. It also allows me to structure my work time.",
"BF Skinner, the famous behaviorist, had an electric switch in his desk chair. When he sat down, the light on his desk turned on, and he got right to work. If he needed to take a break, he would go into another room. He claimed he trained himself to respond to the stimuli to work so well that he could accomplish in 4 hours what it would take others days to do. We can't all be intellectual giants like Skinner, but we can learn from his principles. Organize your work space, and don't do non-work stuff (like Reddit) when you're there. When you take a break, go somewhere else. Having cues to start working, like Skinner's desk light, might also help.",
"To summarize:",
"Take one or two things you like to do. Never do them unless you are simultaneously doing your target activity (e.g., never watch TV unless you are at the gym), or immediately following a successful session of the target activity (e.g., reward yourself with an hour of TV after you study for 4 hours).",
"Take some time to think about what success or failure might mean to you. Don't be afraid to see a therapist. A CBT therapist will be very focused on immediate behavior change. A psychodynamic therapist will help you understand the underlying causes and meanings in more depth.",
"Structure your time spent doing the target activity. Make goals, use a timer to track on-task times and breaks.",
"Organize your work area and don't do non-work stuff in that space.",
"I wouldn't necessarily try all these things at once. Successful behavior change usually involves setting goals, tracking your progress, and making sustainable changes. That said, I would do what you think would be helpful. If you can do all of them, go for it."
] |
[
"What is actually going on when you have a \"crick\" in your neck?"
] |
[
false
] |
What is happening physiologically that causes that feeling of stiffness/soreness in one's neck?
|
[
"Some of the muscles around the neck or shoulder area have become tight and shortened so that there is no longer enough space in the neck for the vertebrae to turn freely. There are endless different factors that can cause the muscles to shorten."
] |
[
"Yeah, that makes sense aye! I don't have one at the moment, I was just curious about it in general.",
"Thanks!"
] |
[
"Yeah, that makes sense aye! I don't have one at the moment, I was just curious about it in general.",
"Thanks!"
] |
[
"Would a rainbow on a planet that orbits a different colored star have a different hue?"
] |
[
false
] |
Edit: it should be range of colors instead of hue
|
[
"A rainbow doesn't have a single hue, so it doesn't make much sense to say that it would have a different or similar hue. However, let's assume you can still see the same visible range of light but were on a planet orbiting a red star. Since a star is basically a giant blackbody, the star would still emit some non-zero amount of light at other parts of the visible spectrum, but it would be more heavily skewed toward the red end of the spectrum. ",
"On Earth, a rainbow is most visible at the center of the visible spectrum where the suns emission spectrum peaks (since our eyes evolved to see wavelengths around this peak). A rainbow on a red-star planet would have more dominant reds and oranges than blues and violets, which may be faint enough to be effectively invisible, depending on the temperature of the star. The colors would still be there, and assuming the atmosphere is similar in composition to Earth, the spacing of the colors would be similar, but the intensities would be different."
] |
[
"If wavelengths of light are absent from the spectrum of the star, then they will be absent from the rainbow. The rainbow's colors come from refraction, due to bending of light at the surfaces of water droplets. Our sun's peak intensity is roughly in the middle of the visible spectrum, so we get very nice complete rainbows (this is no coincidence, our eyes likely evolved to see this range). A star with an output shifted to the red or blue sides would likely produce more monochrome rainbows."
] |
[
"Light from a source, most sources at least, comes in many different wavelengths, different colors. The light from each star would be different depending on the temperature of that start. OK? ",
"So from the Sun we get different amounts of energy at different wavelengths, from infrared to ultraviolet. We see a segment of all that light. When it is all mixed together it is a sum that we recognize as, that we call white.",
"So a rainbow separates out the colors. It takes the blue from the white and the green and so on. We get the spectrum laid out from long to short, from red to orange to yellow to green to blue.",
"If you did this on a different star with a different color profile you would have a different set of colors. Still the same order but maybe more red or more ultraviolet."
] |
[
"Question about Apoptosis in Heart. Your response is highly appreciated!"
] |
[
false
] |
[deleted]
|
[
"Apoptosis is a series of events not an instantaneous change in a cell. It takes a surprisingly long amount of time to occur. See ",
"Suzuki et al (2001)",
" for an example in rat cardiomyocytes. DNA fragmentation peaked at 14 hours in that study."
] |
[
"Thanks for your reply. However I dont know what exactly does bolded statement mean in relation to study."
] |
[
"Arrhythmia can persist for a long period of time. Like days, weeks, etc. "
] |
[
"Why does magnetism not appear on electromagnetic spectrum?"
] |
[
false
] |
[deleted]
|
[
"The electromagnetic spectrum simply isn't measuring on a scale that magnetism should appear on, any more than magnetism should appear on the top 100 schools by grades list.",
"All electromagnetic waves are ultimately composed of little energy bundles called photons, which exhibit both wave-like and particle-like behaviour in accordance with quantum mechanics. The EM spectrum is a way of describing photons in terms of their energy (which, following QM, also means in terms of their wavelength or frequency). Radio waves have little energy, and a large wavelength. Gamma rays have very large amounts of energy per photon, and a very small wavelength. In real life terms, the way we perceive light colours is directly related to the energy of the photons making up the light.",
"The photons themselves are disturbances in electromagnetic fields. One way to think of it is that if you jiggle the electric field, this causes the magnetic field to change (a changing electric field induces a magnetic field), but the opposite is also true so the magnetic field causes an electric field. This change self-propagates in a little bundle of energy which is the photon.",
"The electromagnetic fields are inseparable in principle, as they are manifestations of the same thing. They even 'change' into one another as you move through reference frames - what appears as an electric field effect to one person might look like a magnetic field effect to someone moving past with some speed!",
"So, overall, the 'electromagnetic' in 'electromagnetic spectrum does ",
" mean that the spectrum contains electricity and magnetism. It actually is a spectrum of the different energies that ",
" in these combined fields may have.",
"Of course, we can compare magnetism and gravity if we want to, but they are very different things and are very separate. For instance, magnetism is well understood in terms of a force carrying particle (which is actually the photon, which is also the force carrying particle in electric fields, which is part of why they're manifestations of the same thing). Our best theory of gravity, though, describes it in terms of the curvature of spacetime - a completely different thing! We'd quite like to unify these and describe gravity with a force carrying particle as well, but this is very hard for various reasons, and is a major unsolved problem in physics."
] |
[
"The electromagnetic spectrum describes the frequency of ",
"electromagnetic radiation",
". Electricity and magnetism are interacting phenomena which produce electromagnetic radiation. What you're asking is a similar question to 'what colour is a photon'."
] |
[
"To expand on what OrbitalPete said, we know this because the speed of light is calculated to be 1 over the square root of the permeability of free space (magnetism) multiplied by the permittivity of free space (electrostatics): ",
"c = 1 / (√µ(naught)ε(naught))\n",
"This shows how magnetism and electrostatics interact and can be both described through "
] |
[
"Most of the world's gold is found in sea-water, is it possible to extract this?"
] |
[
false
] |
Could you use Electrolysis to extract gold atoms? * Tuning the Electrolysis-apparatus to the frequency, to which Gold clings to Cathodes or Anodes. * Placing these gold-extractors on oil-rigs or ships. * Taking the power for the Electrolysis-apparatus from solar, wind and wave energy-sources. Is this possible or is it naive science fiction?
|
[
"There are ",
"several ways",
" to extract gold from seawater; I'm not sure about electroysis, though. The problem is that none of those methods are currently economically feasible - they all require vast expenditures of energy to obtain a minute amount of gold."
] |
[
"It is possible to extract gold from seawater. People are unlikely to do it as the cost and the energy needed far exceeds the amount of gold they receive."
] |
[
" especially since these might be gold atoms. Gold by itself is a remarkably unreactive metal, the only solution known to dissolve gold is a concentrated solution of HCl and HNO3, also known as Aqua Regia (royal water). In order to get the atoms, I think Haber's idea might be effective but you would have to centrifuge several kiloliters just to get a noticeable amount of gold."
] |
[
"How is the shingles vaccine any different from the chicken pox/VZV vaccine? Is it any different?"
] |
[
false
] | null |
[
"They’re very different currently. ",
"The chicken-pox vaccine is a live attenuated virus vaccine, described ",
"here",
":",
"VARIVAX [Varicella Virus Vaccine Live] is a preparation of the Oka/Merck strain of live, attenuated varicella virus. The virus was initially obtained from a child with wild-type varicella, then introduced into human embryonic lung cell cultures, adapted to and propagated in embryonic guinea pig cell cultures and finally propagated in human diploid cell cultures (WI-38). Further passage of the virus for varicella vaccine was performed at Merck Research Laboratories (MRL) in human diploid cell cultures (MRC-5) that were free of adventitious agents. This live, attenuated varicella vaccine is a lyophilized preparation …",
"The shingles vaccine is an adjuvanted subunit vaccine, described ",
"here",
":",
"SHINGRIX (Zoster Vaccine Recombinant, Adjuvanted) is a sterile suspension for intramuscular injection. The vaccine is supplied as a vial of lyophilized recombinant varicella zoster virus surface glycoprotein E (gE) antigen component … The gE antigen is obtained by culturing genetically engineered Chinese Hamster Ovary cells, which carry a truncated gE gene, in media containing amino acids, with no albumin, antibiotics, or animal-derived proteins. The gE protein is purified by several chromatographic steps, formulated with excipients, filled into vials, and lyophilized.",
"The older shingles vaccine, Zostavax, was much more similar to the chicken-pox vaccine, but it’s no longer available in the US as of 2020. The difference between Zostavax and chicken-pox vaccine was that Zostavax had a ",
" higher dose, at least 14 times higher. ",
"Here",
" is a now-obsolete info page about Zostavax."
] |
[
"I'm 37 and had Shingles, was not fun. Doctor said no Shingrex till I'm 50 unless I get single a few more times. Why is 50 the magic age?"
] |
[
"The one thing I'm aware of is the older you are, approximately 60+, there is a greater possibility following shingles of neuralgia. The nerves infected by the virus remain extra sensitive to stimulation and are exceptionally painful. My FIL at 73 had shingles, and it affected the nerve on his nose and forehead. Afterwards he couldn't even go out in the wind, as a slight breeze would aggravate those nerves and he'd be in extreme pain. At the time, the neurologist prescribed morphine and Fentanyl for the pain. The neuralgia still affected him until his death 6 years later. ",
"My SO and I got our Shingles vaccine as soon as we were eligible and we definitely didn't want the neuralgia my FIL experienced!"
] |
[
"Why does time dilation occur when traveling at near light-speed?"
] |
[
false
] | null |
[
"Time dilation follows directly from the constancy of the speed of light from all reference frames. I.e. if light appeared to travel faster or slower depending on how fast you were travelling, then there would be no time dilation. It really boils down to the tact that we observe A, therefore B must occur."
] |
[
"It is a logical consequence of the constancy of the speed of light. ",
"If you stand near some train tracks and see Michael Jordan riding a train toward you, when he tosses a basketball at you, the two of you will disagree on the speed of the basketball. ",
"Yet if he shines a laser pointer at you, the two of you could not, and would not, disagree on the speed of his laser's emanating light beam. This is a fact of life we must all grapple with. Light has this property.",
"Time dilation is a logical consequence of this fact. The simplest derivation of time dilation I know of is by use of a common example called ",
". It is described ",
"Here",
". ",
"Look around for other explanations of the light clock - there are many, and we all have different learning styles. This is one of the most accessible results in fancy physics and could be appreciated by almost anyone. Go for it!"
] |
[
"Let's give a view from from the view of conserving \"some quantity\". Let's discuss \"Euclidean three space\" (just \"ordinary space\" you are used to). You would say, it makes no sense that an object's length, width, or depth has, in this space a (line) length is conserved, and is written as \"(length)",
" = x",
" + y",
" + z",
" Boring trig that you are just told \"is true\" in class.",
"\nThe reality is that that isn't true. It depends on what we call the \"metric\" of the space. You might say that a metric is \"how you measure things in this space\". You might also describe it as how the space is curved. For example, if we were 2 dimensional creatures, living on a three-dimensional sphere, we would not live in \"Euclidean two space\". It may be approximately true (if the sphere is very large compared to whatever we are interested in). A consequence to these creatures would be that a triangle would not have its angles add up to exactly 180 degrees (as it did your geometry class).",
"\nEuclidean space certainly is simple and nice, and fortunately for us, at very low relative velocities (compared to c) we can say the spatial dimensions are Euclidean to more precision than necessary. We really live in an approximate Minkowski space (plus other distortions from mass, but let's keep it as simple as possible).",
"So how to do we measure the length of a line in Minkowski space. Well, if we call this additional fourth dimension \"ct\", we get something like \"(length)",
" = x",
" +y",
" + z",
" - (ct)",
" This means that \"duration\" (length in \"time direction\") is a measurable quality of a physical object. And why call this thing the \"right way to measure things\"? Because if you had a line, and \"rotated\" it in these four dimensions, ",
". We call this length the \"invariant interval\"- it represents the \"length\" between two \"events\", and it is constant no matter what. It may be helpful to think of an \"event\" as a \"time and a place\".",
"\nSo what about your question? If you are asking about an object moving at high speed between two \"events\", what does that look like? Let's say you happen to move only in one such dimension of space and throw a ball upward. The first event is \"you threw a ball up\". Where and when did this happen- let's say at x=0 and t=0. The second event is \"You caught the ball\". But this time is later, and you were walking in between. So, let's say now you exist at x=L and t=t_1. The \"invariant interval\" (let's call it S):",
"S",
" = L",
" - c",
" t_1",
"This is only what I saw. What did you see?",
"Think this way- you never see yourself away from where you are. Yes, it's a really stupid sentence, but it's absolutely true! So when/where do you see yourself exist? Well, never away (x=y=z=0) but you certainly \"feel\" different times. So while you were moving the events \"You threw a ball\" happened at x=0, t=0 (we have a bit of freedom to choose this to coincide with when/where I saw you first exist, but let's leave that be for now) and also later \"you caught the ball\" at x=0 (remember that stupid sentence I said) and t=T. What's important is that this time is different than before, but represents that same thing- it's when you caught that ball! Yes, this means I saw you catch it at t=t_1, and you saw it at t=T. But what is the \"invariant length\" you measure?",
"S",
" = - c",
" T",
"We already said this has to be the same as my \"invariant length\":",
"So S",
"= S",
"\nL",
" - c",
" t_1",
" = - c",
" T",
"Solve for t_1",
"t_1",
" = T",
" - (L/c)",
"What does that mean? The time I saw you take (t_1) was shorter than the time \"you saw yourself take (T)\". So if I ever see you moving, you will feel more time than I measure you for!",
"The idea that the invariant interval in Minkowski space is \" x",
" + y",
" +z",
" - c",
" t",
" is not universal. There is another, equivalent metric that measures the interval as \"c",
" t",
" - x",
" - y",
" - z",
" Both are fine for physics, as long as you remain consistent.",
"Some intervals have special names. For instance, that time \"T\" you saw yourself for; this would be called the \"proper time\". Similarly, if you ask about the \"length\" of an object, you really might mean the \"proper length\"- it's length when viewed at rest.",
"An event doesn't need to be anything happening at all. I used the names \"throwing a ball\" for instance to give a frame to understand why I was doing that math. \"This box exists\" is a valid idea for an event. So it just saying \"this point and space and time happened\".",
"\nThe interval, S, between two spacetime events in Minkowski space is conserved by all viewers:",
"S = x",
" + y",
" + z",
" - c",
" t",
"If I see you move, some of \"your interval that I measure\" exists in space. Since I have to have the same interval as you measure for yourself (which is ONLY in time), I have to add more time to bring it back down to what you measure."
] |
[
"How does heat dissipate in solid materials? Does it move away from gravity like hot air, or uniformly outwards?"
] |
[
false
] |
Bonus question: What decides the speed of dissipation in a material?
|
[
"The key word to learning more about this subject is \"heat transfer\". ",
"The laws of thermodynamics (and physics) determine how it behaves. ",
"Hot air moves around due to convection currents. The different buoyancy of hot air to cold air causes this circulation. This cannot occur in solids, since the cold/hot segments of the solid cannot move (although their density will change, given room to expand/contract). ",
"So, how dos it function if it cannot move like air? Well, first is that the heat goes from hot areas to cold areas, not the opposite. You'll never (well, essentially never) see a cold object get colder on its own. ",
"The mollecules vibrate, and that vibration moves around the solid. Higher vibrations =higher temperature! Try to visualize how jello would behave if you pinged the center of it, creating just one wave. This is quite similar to how ",
"heat moves through a solid object.",
". Also, see ",
"this one",
"Now, how fast does this go, how much heat can go through an object. WHY IS MY CHAIR SO COLD!",
"These are all questions that can be answered with extremely complicated equations (math majors specialize in heat transfer equations). But, there are simpler ones so people like mechanical engineers can model stuff quickly. These equations all depend on constants, which depend on the material. As you know, an aluminum pan will heat up faster than a cast iron pan. The speed depends on the material. One constant very important to a material is the ",
"thermal conductivity",
". So, there is no absolute speed of heat transfer. The fundamentals of the speed depends on how quickly the molecules can transfer their vibrations. I suppose you could examine the inertia of the molecules...There's so much more to go about explaining, but I highly recommend reading up on ",
"heat transfer",
"You'll go over your head occasionally, but there's a lot to be learned!"
] |
[
"Thanks for that ",
" answer. But one thing seems strange to me: If heat is vibrations, why does it travel slower than macro-level vibrations (ie. sound) through that material? Is heat really vibrations in the same sense?"
] |
[
"Sound works like a wave. It ripples quickly through mediums because it doesn't leave much behind, One molecule whacks another and all the energy is transferred (most). Heat (molecular vibrations), leaves energy behind when it travels. The vibrations are not like a sound wave, they're much 'finer', so when you press an object with a lot of heat up against an object with less heat, these 'finer' vibrations even out much slower than the speed of a sound wave through the objects. "
] |
[
"How do handheld police radar guns work while the operator is driving?"
] |
[
false
] |
I'm assuming they need to be synced with sensors on the patrol car and add the relative velocity between the patrol car and the target car to compute the actual speed of the target car? Also, some guy on Youtube was saying that you could aim a standalone radar gun at the interior of your own car and somehow measure your own speed using the Doppler effect. There's no way you could do this without directly measuring your relative velocity with the road, right?
|
[
"EDIT: and I just noticed you said \"handheld.\" I don't think most handheld radar guns have a \"moving radar\" mode, the technique I describe is used by dash-mounted speed radars, which seem to be getting more common in police use anyway. I don't think there's any reason it *couldn't* be built into a handheld radar, it's just a matter of having the right computer logic to detect and add/subtract the background speed, so I bet there are handheld models out there that can do this. A typical handheld radar probably could tell you the speed it's moving at (it'd display it as approaching speed) because it would pick up the same background echo, but I think the computer logic might reject the echo and not display it because of it being stronger than expected and associated with an off-angle \"lower tail\". Newer models have a lot of filtering to avoid showing spurious numbers because of weird echos.",
"Most modern speed radar systems work by doppler effect, meaning that they function by detecting the shift in echo to a single pulse rather than a difference in echo timing across multiple pulses. This mostly just results in a faster result with less sensitivity to aiming. The radar might still use multiple pulses though, to help determine whether vehicles are moving in same or opposite direction.",
"So what about the moving patrol car? Doppler radar allows a neat trick here. Doppler radar can detect the speed of multiple objects by examining the echo in frequency domain - basically there will be a peak corresponding to each speed at which objects are moving. When the patrol car is moving at, say, 65 mph, the largest peak should be reflection off the ground, signs, guard rails, etc shifted according to the speed at which the patrol car is moving - the speed of the environment moving relative to the radar. In reality there will also be a sort of decaying set of frequencies received downwards that correspond to things which are not straight ahead but off to the sides (and so the received echo is shifted not due to the full vehicle speed but due to the component of it in the forward direction), but directional antennas and electronic logic are used to minimize that effect.",
"So there will be other peaks in the frequency response that correspond to things that are moving at speeds other than the patrol car. Someone who is driving, say, 75mph in the same direction as the patrol car will result in a small frequency shift due to the 10mph difference in relative speed. The controller in the radar picks out these shifts for display. How exactly this is done depends on configuration and most units offer multiple modes, but the simplest (and most common) is to only show the speed of the person driving fastest.",
"People driving slower than the patrol car can be detected in a similar way, but the shift will be in the other direction because they are relatively coming nearer.",
"There's a trick though: a vehicle moving at the *same* speed as the patrol car will result in an echo not shifted at all, which radar will ignore because it blends into the noise that comes from the antenna being imperfect and so on. So most of these radars say in the spec sheet that vehicles need to be going a few percent faster or slower than the patrol car to be detected at all.",
"Things are a bit complicated by oncoming traffic. If our patrol car is doing 65mph and someone approaches at 65mph in the other lane, an echo is received with a very high shift due to the 130mph relative speed difference and the \"background\" shift must instead be subtracted. Older radar require the operator to switch to specific modes for vehicles going opposite way or same way and faster or slower, but modern versions use computer logic and a fancier RF receive side to automatically detect any of these cases. This is of course based on some assumptions, but a patrol car won't be doing 130mph faster than someone in the same direction.",
"And the final point, yes, a dash-mounted radar can detect how quickly the patrol car it's installed in is moving. Think about it this way: the radar actually detects the *relative* speed between the patrol car and a target ,10mph in my example earlier. But to be more convenient, they also determine the \"background\" speed, which is the speed of the patrol car, or 65mph. Then they calculate 65 + 10 to show 75mph as the target speed. So yes, a radar can display the speed of the vehicle it's mounted in, but it has to be put into a specific mode, otherwise the background speed is just used as the basis for calculating target speeds.",
"One of the reasons LIDAR doesn't seem to have caught on too much is because it isn't really made in dash-mounted versions due to the need for relatively precise aim, but also because there's no \"easy trick\" to get the speed of the moving vehicle with LIDAR. It's conceptually possible to build a dash-mounted LIDAR but it'd be more complicated, it'd probably need to use some kind of high-precision external speedometer like police patrol cars had back in the '50s."
] |
[
"For lidar it seems like a mems accelerometer + GPS through a kalman filter really isn't that hard."
] |
[
"I don't know exactly how radar guns work but I imagine using it in the car would be as simple as the officer driving the speed limit and measuring the relative velocity of the target car to determine how much above or below the speed limit the target car is.",
"It's technologically possible for a radar gun to measure the velocity of the car relative to the road or even to sync with the car's own speed but I don't know whether radar guns have bothered to invest in that technology.",
"The guy on YouTube is wrong, what he's referring to is the Doppler shift the radio waves from the gun would experience due to the motion of the car, what he's not understanding is that that shift would only be observable to someone measuring the wavelength outside the car (like how an ambulance siren has obvious Doppler shift if you get passed by it on the highway but has no Doppler shift for the passengers). If Doppler shift was constant and didn't depend on relative velocity, radar guns would be unusable because any measurements of speed you tried to take of passing cars would be drowned out by the Doppler shift of the Earth hurtling through space at mind-boggling speeds."
] |
[
"Why is the speed of light so important?"
] |
[
false
] |
I understand E=MC and why you can't go faster than C. But why is it C in that equation, and not some other number/speed?
|
[
"The easiest answer for that kind of question is to read the ",
"derivation",
" of the expression in question."
] |
[
"It's not that the speed of light is important, but more that the 'natural' unit for velocity is ",
"."
] |
[
"It's a human conceptual problem. ",
"If you had grown up with C being randomly assigned to a different number, perhaps you would ask the same question. "
] |
[
"how \"hazardous\" are the chemicals used in zara clothing that the current green peace campaign is aimed at removing?"
] |
[
false
] | null |
[
"The answer is that they aren't.",
"The chemicals they found on the clothing are not hazardous, they're widely used plasticizers found in many synthetic fabrics. Probably wouldn't want to chug a bottle, but they aren't harmful in clothing. Greenpeace is concerned that these chemicals, after being dumped ",
" will decay into carcinogenic and toxic materials in rivers."
] |
[
"thanks, this is what I thought. It is LOW concentrations. But i am not a chemist/bio-chemist/medic, and a buddy of mine is convinced that it could be harmful to people wearing the fabrics. "
] |
[
"Ignore Greenpeace, they are more about violent political action than a source of consumer aid."
] |
[
"South-west Astrakhan, Russia, has some interesting geographical features I've never seen before. Is there a name for this phenomenon, and how is it formed?"
] |
[
false
] |
Was just looking around on Google Maps when I came upon Tried to look up information about it but couldn't really find anything. It can be found at .
|
[
"These are referred to as \"Baers Mounds\" or \"Baers Knolls\" after the scientist who first described them in detail in the mid 1800's. There have been a large number of hypotheses put forward to explain their formation, with aeolian (wind blown sediment) being one of the more popular as they do have a similar form to some windblown features, but subsequent work has shown that their internal structure and sediment characteristics are inconsistent with this. At present, there is still not a single explanation for their formation as far as I know, but recent publications have suggested they may be related to deposition during flow of water in a former connection between the Black and Caspian Seas, i.e., the Manych Strait (e.g., ",
"Badyukova, 2018",
") or as a result of deposition during rapid fall of the level of the Caspian Sea (e.g., ",
"Melnikova & Pokazeev, 2020",
")."
] |
[
"Thank you for answering! It's pretty fascinating that it's still sort of a mystery. The longitudinal (?) striations are quite striking and I thought my browser had glitched when I saw it at first."
] |
[
"This has a similar feel to it as the Carcross Desert and the Athabasca Sand Dunes (among others in Northern Canada)",
"https://en.wikipedia.org/wiki/Carcross_Desert"
] |
[
"What about quantum chromodynamics? Is this theory still around today?"
] |
[
false
] |
[deleted]
|
[
"That's literally all I study. ",
"Edit: But they're all just different names for the same thing. The strong force is one aspect of QCD, and color charge is another aspect of it. In general, though the whole theory is QCD. When we do some numerical simulations (since it's bloody difficult to actually solve), it sometimes gets called pQCD (perturbative QCD) or QCD on a lattice (where we put a bunch of particles at certain points within space, then iterate forward in time). We have other useful mathematical tools to help us understand the larger theory of QCD, one of my favorites being AdS-CFT duality (Anti-deSitter - Conformal Field Theory), a really interesting bit of maths that fell out of studying string theory, and allows us to simplify some of the aspects of QCD and other systems like it. Note that this doesn't imply that string theory is \"right\" it just happens to have found a new mathematical tool that is useful in non-string theory cases."
] |
[
"Yeah I realized that after I made my initial post of one sentence. Yes, color force is still used within the field. But usually (from my experience at least) if someone says something like \"color force\" they mean something akin to the electric force, and then there's a \"color magnetic force\" the force from color charges in motion, akin to the magnetic force being the force of electric charges in motion. And together, they just form the strong force or strong interaction like the electric and magnetic forces form the electromagnetic force or electromagnetic interaction."
] |
[
"OP is asking about the terminology more than the theory. Of the terms in the OP's post I see \"strong force\", \"quantum chromodynamics\", \"strong interaction\", and \"color charge\" (my addition) used frequently. I see the term \"color force\" used infrequently. Does that accurately reflect the current trends?"
] |
[
"What would we see with the naked eye if Betelgeuse were to Supernova?"
] |
[
false
] |
With the recent dimming of Betelgeuse and speculation that it might go supernova, I'm curious what one would see looking up at the sky with the naked eye? Would we just see brightness or could we make out the bubble from the expanding gas? How quickly would such a nebula form, and on what sort of time scale?
|
[
"You would see a very bright star.",
"The nebula would form pretty quickly, but it would be long, long time before you would be able to perceive it even theoretically with the naked eye, as it would have to be at least a few lightyears across to appear large enough in the sky to be resolved by your eye.",
"How long it would take to reach such a size depends on the speed of the expansion, which would probably in the range of a few thousands kilometers per second at most (based on the expansion rate of comparable nebulae like the Crab nebula).",
"Even when the nebula has reached a large enough size, visibility depends of course on its brightness, which is hard to predict. Most existing nebulae from supernovae are too faint to be visible with the naked eye, though."
] |
[
"You would just see Betelgeuse gradually get brighter for a few weeks until it is as bright as the full Moon, and then gradually get dimmer over a span of months until it disappears from the sky. It would never look like more than a very bright star to the naked eye."
] |
[
"A week ago someone estimated that Betelgeuse's nebula will become too dim for the naked eye after just a year or so. 5% the diameter of the Moon would be 0.25 light years or so, at 2% the speed of light that needs 10-15 years. Bad luck."
] |
[
"Can a geneticist or a bio-chemist walk us through the differences between genomes, proteomes, transcriptomes etc?"
] |
[
false
] |
Additional explanations on how these different classes of chemicals interact would be welcome too! (fyi i have taken a bio-101 course in uni so I don't know much more than that)
|
[
"Simple answer:",
"The relationship between these three things is fairly straightforward, though as with everything in biology there are exceptions to ",
" I’m about to make. I won’t go into those exceptions here, as it’ll make the explanation into a textbook :D.",
"Every cell in an organism contains the same set of genes, which are recorded in DNA form. Every organism has a unique genome, but every cell in one organism has the same genome. Side note: When we refer to ‘the’ human genome, it’s really the composite genome of lots of people, and every single person will have a difference somewhere.",
"Some genes are protein coding genes, which are used to make proteins, and the collection of proteins in a cell is called the proteome. To turn a gene into a protein, you first make a copy of the gene, which is then used to make the protein. The copy of the gene is called a transcript, and is made out of messenger RNA, or mRNA for short. The collection of mRNA in a cell is called the transcriptome.",
"While every cell contains the same set of genes, they don’t use these genes identically. Every cell transcribes a different set of genes at different times – a stomach lining cell makes different proteins to a bone cell, and both of those cells will make different proteins at different times. If you break a bone, the nearby cells change what proteins they make to fix your bone, for example. ",
"This means that while the genome is identical in every cell throughout an organism’s life, this is not true for the transcriptome and proteome. The transcriptome and the proteome are in continual flux in every cell of your body, as the cells adapt to changes in your environment. Also, while the transcriptome and proteome are very closely related to each other, they’re not identical. Each mRNA is turned into a protein at different speeds, and each protein has a different lifespan. This means that you get a different view of what’s happening in the cell depending on whether you look at the transcriptome or proteome.",
"Source: PhD in molecular biology, looking at how bacteria turn genes into proteins.",
"Edited to clarify that only some genes code for proteins."
] |
[
"Good point - I should have said \"",
" genes are protein-coding genes...\""
] |
[
"That's fine, but if every time a layperson asks this type of question and gets a severely watered-down answer like \"genes code for proteins,\" public understanding of modern research will never improve. ",
"It's like saying every body that orbits the sun is a planet. Why can't we be more specific? We can give a more accurate answer that not necessarily more confusing, like \"genes sometimes code RNA that get translated into proteins, and sometimes code for RNA that doesn't get translated. This untranslated RNA can have a variety of functions. However, the definition of what a 'gene' itself is remains hotly debated.'\" ",
"I don't think that's so bad. "
] |
[
"Why isn't the Winter Solstice the coldest day of the year?"
] |
[
false
] |
If the Winter Solstice has the least amount of direct sunlight, then why is it typically warmer than say, January or February?
|
[
"A lot of variables control temperature. Different air masses, cloud cover, and wind mixing are just as important to regulating temperature as radiative heating is. ",
"Assuming a constant air mass, a noticeable time lag in the global radiative heating balance appears. As summer progresses, more heat is entering the Earth and that continues well into the fall when a eventually a balance between the heat gained and the heat loss reach an equilibrium. As fall progresses into winter, more heat is expected be lost but the swing between heat gain and heat loss takes awhile and then it takes more time for the heat loss to become dominant around January or so. "
] |
[
"Why isn't my drink instantly cold when I put it in the fridge?"
] |
[
"Wow, that was fast. Thank you, this question popped in my head at the bar last night and sadly we did not have a Atmospheric Science/Forecast Meteorology expert to help. "
] |
[
"Suppose instead of a giant pool, the Olympic swimmers had their individual lanes of water seperated from each other. Would this affect their swimming, and if so by how much?"
] |
[
false
] | null |
[
"One of the issues in a giant pool is that backwash off of the side creates more turbulent water for the swimmers on the sides of the pool as opposed to the swimmers in the middle (this is why swimmers with the fastest heat times are placed in the middle; kind of a \"seeding\" of sorts). This does slow the outside swimmers a bit. However, this issue has been remedied to a great degree by deeper pools, flow gutters and more separation between the outside lanes and thew all. From a physics standpoint, the times probably wouldn't change much, if at all.",
"However, a non-scientific reason separating the swimmers might change their times is that they wouldn't be able to see the other swimmers as easily. This might actually have the effect of ",
" down times, as the adrenaline burst obtained from having to chase someone would be largely taken out of the equation."
] |
[
"Can anyone explain the 'riding the wave' lore that exists within swimming? That seems to have some advantage.",
"Look at ",
"this video of Jason Lezak",
" where he is actively swimming as close to his opponent's wake as possible."
] |
[
"I can't speak quantitatively, however there are a few effects at play:",
"Lane lines (the floating dividers) significantly absorb the wakes from the swimmers, reducing the amount of turbulence each swimmer sees.",
"Hard walls reflect the wake, increasing the turbulence seen. ",
"Heats are populated with the fastest swimmers at center, out to the slower swimmers at the edges (causing those to go slower, due to increased turbulence). I've seen pools with lane lines at the edges, but it's apparently not used in Olympic events (as far as I can tell by looking at photos) ",
"If you built a series of 1 lane wide pools, everyone would have an equal amount of turbulence, which would make things a bit more even. However, overall times would be slower for two reasons:",
"It would be harder to see who you were racing against, causing you to not go as fast. (This could be solved with transparent dividers instead of solid concrete)",
"Increased self-induced turbulence would cause everyone to go slower. ",
"To wit:",
"I've swam in pools that didn't have lane lines (coaches were too lazy one morning to put them in, so we practiced without them), the increased turbulence was crazy",
"Anecodtally, it's physically harder to swim in an edge lane than a middle lane. Not just when competing, but also during solo practice. "
] |
[
"How effective are programs like Fold at Home?"
] |
[
false
] |
This is a protein folding program that supposedly helps find cures to cancer, Alzheimers, etc. I was wondering how effective these distributed computing systems are. Thanks!
|
[
"Define effective. ",
"The site lists over 120 papers that have resulted from access to these donated computing resources. Without doubt this has been invaluable to the groups who use the service. This kind of project is of critical importance to groups who work at smaller institutes and don't have local access to large scale distributed computation. Also it saves money for groups that use it (as you don't have to pay running and administration overheads) which is always a bonus when grant money is tight. ",
"If the question is really \"to what extent has this program brought us closer to a cure for a disease?\"this is a very difficult question to answer. Many of the conditions listed are among the most difficult and intractable to study and develop treatments. And much of the work that comes from computational study is at the more theoretical/modelling end of the analysis, rather than the drug discovery/testing work which would need to come later. For each disease you'd have to be on top of the literature on each of those fields to understand the importance of the contributions. But in the main any given single scientific paper is rarely more than an incremental step forward in knowledge. Without doubt our slowly accumulating knowledge of protein misfolding has shed a great deal of light on the mode of action for amyloid/plaque diseases (Alzheimers, CJD, etc) and I can't imagine we'll get to a cure or therapy for those without such knowledge. ",
"For the slightly more rarefied question of \"solving the protein folding problem\" I wouldn't say that fold@home has contributed a great deal, all atom MD simulations remain a bit of a side show for protein ",
" folding. "
] |
[
"Quantum computing allows you to run quantum algorithms. In the main these are a class of algorithms that will run in polynomial time (quickly) on a quantum circuit where they would run in super-polynomial time (exceedingly slowly) on a classical circuit.",
"https://en.wikipedia.org/wiki/Quantum_algorithm",
"If some part or all of your folding simulation can be expressed in terms of an existing quantum algorithm then quantum computation will help speed up the simulation. If it's not the case that the simulation steps can be expressed in terms of a quantum algorithm then a quantum computer is of no additional help.",
"Of course this is somewhat moot as there are no generally available quantum computers and of the few in existence none have the capacity to simulate protein folding.",
"Edit: For some of the folding simulations we do we might generate 500 models of our target with each one taking 1hr to complete. Having access to 500 cores means that we can finish these simulations in about an hour. If you could give me a quantum algorithm enabled simulation that could generate a model in 1second then I could generate my 500 models on one machine in <10mins. Of course if I had that kind of speed up available I would probably want to generate 50,000 models instead...",
"Edit 2: And of course having access to very, very fast simulation doesn't mean that the simulation is correct. There are still big open questions about what is important to simulate to get folding right. There are plenty of known factors that are currently ignored with ",
" folding (binding partners, heat shock proteins, cellular crowding etc...) because we don't know how to incorporate them in to today's simulations."
] |
[
"Foldd@home has not contributed much in relation to what we need, or it has not contributed much in relation to other methods?"
] |
[
"Is mercury in canned fish a real issue?"
] |
[
false
] |
I was reading about eating canned tuna in and it reminded me about the fact that there is mercury in canned fish. How much can you safely consume? Somebody mentioned that the more expensive cans are from younger fish who haven't had time to accumulate larger levels of mercury like the older fish of the cheaper cans.
|
[
"The real danger with mercury is Biomagnification. ",
"Wiki has a nice picture of it listing human monthly intake levels: ",
"http://en.wikipedia.org/wiki/Mercury_in_fish"
] |
[
"The FDA provides an excellent ",
"table",
" concerning a broad range of fish and their mercury levels.",
"Worth noting: salmon have much lower levels than those of many other fish."
] |
[
"As a panelist/expert I strongly endorse this table, and endorse minding it for seafood choices. As fish is extremely healthy (omega 3s and all that), as a personal choice my family eats seafood twice/week that's low on the list but limits anything high on the table to very occasional (and completely avoided when pregnancies/small children were part of said family).",
"Edit: The comment on tuna is correct but you have the prices backwards! \"Canned light\" is lower in mercury and cheaper while \"canned white\" (listed as albacore on the chart) is higher in both mercury and price. ",
"It's actually a species difference and not just age. \"Canned light\" is skipjack tuna that grows faster, is more plentiful, eats lower on the food chain, and doesn't live as long compared to \"canned white\" albacore. Skipjack doesn't have big white chunks of flesh so is seen as less in-demand ($.99/can versus $1.79/can in quick spot check on Amazon). Personally I disagree, I like my tuna on the more dark mackerel-flavor side than in the big bland white chunks!"
] |
[
"How are filters of specific pore sizes manufactured, especially those on the micron scale?"
] |
[
false
] |
I was thinking specifically of filters that have specific molecular weight ranges, such as 15 kDa or 30 kDa.
|
[
"The general area is Sol-Gel processing. \"Sol\" stands for solution and \"Gel\" stands for gelation. Essentially, you mix two chemical solutions together and reactions occur such that long chains start to form and the liquid solution turns into a soft solid, like gelatin. You can then dry these gels using different drying methods to preserve the porous structure of the solid network. The result is a solid material that has a very porous internal structure. The pore sizes are often tailored by adjusting the temperature at which the reaction takes place or the pH of the chemical solutions. You can analyze the pore size by using Brunauer–Emmett–Teller (BET) apparatus and theory.",
"I should note that this is one of many ways to make a material with defined porous structure."
] |
[
"Sol-gel is not based on long chains it is all about particles, it has been proven beyond a doubt even though some text books still try to teach it like you are describing."
] |
[
"This might be a good question for ",
"/r/askengineers",
" ",
"A lot of times finding the public information online about things like this is knowing the terms to google like ",
" filter manufacturing.",
"High level page: ",
"http://www.millipore.com/membrane/flx4/filter_manufacture_hm&tab1=3#tab1=3"
] |
[
"What is the role of norepinephrine in comorbid ADHD and anxiety?"
] |
[
false
] |
I'm going to try my best to provide sources, but a lot of them disagree with each other which is pretty much why I'm asking this question. So apparently ADHD is linked to a deficiency of norepinephrine ( ). Norepinephrine is also linked to the fight or flight response, and increases heart rate, blood pressure and anxiety ( , ). Comorbid ADHD and anxiety are also very common ( ). I've heard anxiety (specifically GAD) described as a permanent/extended fight or flight response where there is no danger but the brain/body still thinks there is. Since norepinephrine raises with anxiety/the fight or flight response, it is higher in those with anxiety or extended stress than without ( ). It seems to me that ADHD has a chronic deficiency of norepinephrine, while those with chronic anxiety generally have too much. How can these two things be true at the same time? Would it be possible for someone with ADHD to also have a condition that results in elevated norepinephrine, such as hyperPOTS, pheochromocytoma, or chronic stress? I'm pretty sure that chronic stress doesn't cure ADHD, but wouldn't it balance out your levels if they were already low? A sudden scare can trigger a release of epinephrine/norepinephrine (adreneline rush). But I don't think that purposely scaring ADHD people helps them focus? Conditions that increase norepinephrine (specifically hyperPOTS and pheochromocytoma) are partially diagnosed by a blood test to test the norepinephrine levels in the blood ( ). If a blood test can accurately find out if there is too much norepinephrine, why can't a blood test that tests for low levels be used to diagnose ADHD? Finally, SNRIs seem like a common treatment for anxiety. However, they increase norepinephrine. Isn't this the last thing you would want if you are already feeling anxious? TL;DR: ADHD and anxiety are often comorbid. But ADHD has a chronic deficiency of norepinephrine, while chronic anxiety can lead to high levels. How can both be true at once?
|
[
"In neuro chemistry the goal is to get the brain in a certain balance, too much or too little of a neurotransmitter can cause problems.",
"If you are deficient in norepinephrine your attention will suffer because you aren't stimulated enough, if you have too much you are stimulated to a point that you will be pushed into anxiety. You want to reach a level somewhere in the middle.",
"Absence or excess of stimulating neurotransmitters can cause attention like symptoms however ADHD is more than just a problem of attention, it is also an impulse control problem."
] |
[
"Yeah, but how can someone have anxiety and also ADHD then? How do you simultaneously have too little and too much of the neurotransmitter?"
] |
[
"The ",
", lack of or excess of is what causes the symptoms.\n",
" of norepinephrine will cause concentration and impulsivity issues.",
"Also some neurotransmitters work together, if one is too low or too high then it can effect other neurotransmitters. This is a hard thing to get exactly right.",
"For example I increase my serotonin levels too high, in theory I should feel great but I feel flat. I feel flat because when I increased my serotonin my norepinephrine went down. To fix this I increase both of them to a nice level. If I were to push those further I might get hyper stimulated.",
"Getting the balance right is trial and error for each individual. Not too high, not too low and in the right combination."
] |
[
"How does a planet get its axis?"
] |
[
false
] |
[deleted]
|
[
"If you have a ball, any ball, you can make it rotate around different axes. The axis isn't anything concrete until you make the ball rotate. And once you do, there is a single axis around which it rotates. So the axis of planets is just determined by how they rotate.",
"All planets in the Solar System do orbit the Sun in the same direction. Though this isn't strictly required by the laws of physics. It's just that due to the way a solar system comes into being it's almost certain that at least initially this is the way things end up being.",
"Same with planets rotating around their own axis. Most of the planets in the Solar System rotate in the same direction, but not all. Venus is the prime example here, it is rotating in the opposite direction of other planets. Uranus is also technically retrograde rotation but it's a bit more interesting case.",
"The axis of Uranus is tilted roughly 90 degrees, so it's rotating kind of sideways, which I think is what you meant by your last question. But that doesn't mean that half of it is constantly in the darkness. One pole will stay in darkness for half of the (Uranus) year, and then stay in sunlight for the other half.",
"Other spots on the planet will have more or less normal day and night cycle, depending on how close to the poles they are and time of year. If you move a bit away from the pole, then you'll be in darkness almost half a year, then you have a short while where you have a distinct day and night, and then you're in sunlight again almost half a year. Close to the equator you have a day and night cycle for almost the whole year, but time of year will still strongly influence how high the Sun rises, just as it does on Earth, but to a much higher degree on Uranus."
] |
[
"Can there be a planet that revolves around a sun and has an axis so that half of it would always be dark constantly?",
"Yes, a planet can be ",
"tidally locked",
" to the star it orbits - although no planets in the solar system are tidally locked, it's thought that some of the extrasolar planets that are in tight orbits are locked"
] |
[
"no planets in the solar system are tidally locked",
"Although, many moons are tidally locked wrt their planet."
] |
[
"Why does the search for extraterrestrial always have to be on earth like planets?"
] |
[
false
] |
I've always wondered why nasa searches for earth like planets when looking for signs of life? Why does life have to be exactly like it is here on earth?
|
[
"They search for earth-like planets for other reasons, including the ability of humans to live there. It's interesting if we find life on Venus, but we aren't moving there.",
"Also, they are using a standard scientific approach. We know for a fact that life can and has evolved under conditions like those found on Earth. We don't know that life can evolve on other types of planets at this point. So if you were going to make an educated guess at the planets most likely to contain life, you'd pick planets similar to Earth. Yes, you can look at all planets but cost is a big issue.",
"It's the same methodology used in every scientific field. If I work on a gene with a known function and a closely related gene is discovered, my first thought is that the new gene likely has a function similar to the old one. That very well may be incorrect but it's a reasonable starting point given the information we have."
] |
[
"Why does life have to be exactly like it is here on earth?",
"It doesn't have to. But we have no means of directly detecting the presence of life from afar, so the best we can do is to detect conditions/environments which we know can support some form of life. Since we have only the template for life on Earth to go by, that's been pretty much all we can look for."
] |
[
"I've always had a beef with this, too, because I personally would be more interested in anything that evolves, whether or not it uses carbon (or even chemistry for that matter). For example, there might be self-reproducing, mutating, and surviving patterns in electromagnetic radiation that we are not aware of because we aren't looking for it. Heck, you could even say languages evolve (i.e. they are parasites that use humans as a host).",
"That said, the reason people search for carbon-based life forms is that for that special case we would probably know what we are looking for and we already have evidence that it is possible."
] |
[
"Why hitting the bottom of my coffee cup (and yours probably...) does this ?"
] |
[
false
] |
Hello ! been wondering since a while now and didn't take time to ask you physics pro. I think video is self-explanatory but here is the thing: As I keep hitting the bottom of the cup the sound is getting higher and higher. It looks like it's linked to the coffee movement. What is the physic phenomenon here please ? I'm not into this but it looks like Doppler thing or something ? had i searched better, i would have found this : TL;DR : resonating frequency varying as sound speed increase due to bubbles leaving ! :)
|
[
"This is essentially the Hot Chocolate Effect. ",
"When you first start stirring the coffee air bubbles get trapped inside the coffee reducing the speed of sound in the it lowering the frequency. As the bubbles begin to get released from the coffee sound travels faster in the liquid and the frequency increases again.",
"Here is a short wikipedia article that goes into a bit more detail. ",
"http://en.wikipedia.org/wiki/Hot_chocolate_effect"
] |
[
"This is absolutely correct! I am really happy to see that the correct answer floated up to the top this time. Usually people have some silly conversation about temperature and the speed of sound in water or some nonsense, but ",
" are the right answer.",
"To elaborate on this, sound speed is given by c = √(B/ρ) where B is the bulk modulus (inverse of compressibility) and ρ is the density. To make a long story short, when you have air and water, the water is much much less compressible than the air, and the air has much much less mass than the water. Thus, when you combine them together, you end up with an effective fluid with the density of water and the compressibility of air. In other words, B is small and ρ is large, so c becomes very small.",
"Worth noting is that the water/air mixture can have a much lower soundspeed than either the air or water together. In fact, for a bubbly water mixture, the soundspeed can go as low as 10 m/s! This is compared to 343 m/s in air and 1500 m/s in water."
] |
[
"Check out ",
"this big thread",
" about a year ago, on this exact topic."
] |
[
"Why can we compare numbers to infinity although we do not consider infinity a number in itself?"
] |
[
false
] | null |
[
"Do you have a particular context in mind?"
] |
[
"It is mostly just convenient notation: \"n < ∞\" just means that ",
" is finite.",
"However, we can extend the real numbers ",
" by adding two elements, -∞ and +∞, to form R-bar, the ",
"extended real numbers",
". The elements +∞ and -∞ are not real numbers, but are defined so that +∞ is greater than all other elements in R-bar, and -∞ is less than all other elements in R-bar. Some arithmetic operations can also be extended to suitable domains of R-bar. For instance, a+∞ = +∞ for any ",
" in R-bar, except -∞. The set R-bar is not a group, ring, or field. The primary value in using the extended real numbers is that many statements in analysis can be made without qualification, which would otherwise just add clutter to the theorems. For instance, many limits can be extended from R to R-bar to make many functions (like the logarithm) continuous on R-bar.",
"There are other senses in which we can treat +∞ as a number, although necessarily not a real number. Other contexts are one-point compactifications, ordinal numbers, etc."
] |
[
"any positive number compared to +INF is \"<\" than it ( ex : n < inf ) but why can we compare a number to something which is not a number technically"
] |
[
"Do different people see different ranges of the visible light spectrum?"
] |
[
false
] |
Different people, of course, can hear different ranges of frequencies of sound waves, as we learn in middle/high school science. I was wondering if the same happens with light? Are there some very low frequencies of red light, or high frequencies of violet light, that some people can see and some others can't? Does this, perhaps, change with age?
|
[
"Although (aside from the color blind) all humans have nominally the same three color receptors, there does exist natural variance in the genes encoding these. These variants do not have exactly the same activity profiles. Now, this wouldn't have a significant effect on the visual spectrum, but it could cause slight changes in the ability to discriminate certain colors. It's even possible for a person to have more than three distinct color receptors in their genome - to have four is known as tetrachromacy, though it is disputed whether such persons can see more colors. These extra colors would not be outside the visual spectrum, but would instead just represent a greater variety within the visual spectrum.",
"There is one way the visual range can be extended, however. Our photoreceptors are actually responsive to ultraviolet light, but ultraviolet is mostly blocked by the lens of our eye. A person who lacks a lens can thus see much shorter wavelengths than someone with normal eyes. However, this is not a good thing, since ultraviolet light is not something you really want in your eyes."
] |
[
"Do you know how insects deal with UV then, since they are able to see and use it? Or do they just don't live long enough for the UV to have impact?"
] |
[
"So, i actually don't know, and I don't know if the answer is known at all. I would hazard a ",
" it's simply that they are evolved for it since they use it, and we are not because we don't.",
"Insect eyes do not have anywhere near the focusing power of vertebrate eyes, so the total intensity falling on any one region of photoreceptive tissue is much smaller than we would experience (even without a lens, the human eye still behaves optically like a lens, just with a more fixed focal length). Thus, it's not as much of a problem for them to begin with.",
"On top of this, even though insects do not have pupils, they do have methods to protect their eyes from intense sunlight. Specifically, compound eyes can increase the depth and steepness of their ommatidia, and darken the tissue that lines them. So it's not like they're totally defenseless, they would just need to adjust until it's not a harmful amount of light, but still enough they can see.",
"There ",
" some mammals that can see UV. Usually cited are rats, bats, and of all things, reindeer. So clearly it's not impossible for mammals, just uncommon."
] |
[
"Baby Talk and Language Acquisition"
] |
[
false
] |
We are babysitting my brother's niece. He and his wife are adamant about not using baby-talk around her; they insist it will damage her in some way. My parents baby-talked (baby-spoke?) the two of us, and I like to think that we turned out just fine. What is the askscience take on how a baby begins to apprehend language? Will baby-talk hinder this in some way, or matter whatsoever? the child is less than one year old.
|
[
"It has also been speculated that baby talk helps emphasize basic phonemes involved in the language spoken. ",
"http://www.ncbi.nlm.nih.gov/pubmed/9235890",
"In the early months of life, infants acquire information about the phonetic properties of their native language simply by listening to adults speak. The acoustic properties of phonetic units in language input to young infants in the United States, Russia, and Sweden were examined. In all three countries, mothers addressing their infants produced acoustically more extreme vowels than they did when addressing adults, resulting in a \"stretching\" of vowel space. The findings show that language input to infants provides exceptionally well-specified information about the linguistic units that form the building blocks for words.",
"Edit: this is likely quite sensitive to age - babies in that study were about 5 months old."
] |
[
"My impression from when I studied linguistics is that kids who are exposed to language use will learn to speak despite anyone's best efforts to the contrary. If you want better terms to search on, you could try \"motherese\" or \"child-directed speech\". From what I've seen, it is generally thought to improve language learning."
] |
[
"Although my field is computational linguistics, I have heard some about this from generic linguistics classes.",
"As far as I've been taught, child-directed speech is actually better for the child. There may be studies on either side but as far as I know it's scientific consensus that it aids the acquisition of speech in the child: they are more attentive to the sounds and are more likely to start picking up the language as a result.",
"You might consider asking on ",
"/r/linguistics",
" as there may be many more people who are actually experts in this particular thing."
] |
[
"Can someone please explain how the NERF Firevision products work?"
] |
[
false
] |
I am very intrigued by the product description, but I am also very curious how it works and how well it works. Key phrases that make it interesting/mystifying: What I can surmise is that the light emitted by the frames is caught and brilliantly reflected by the ball. What I can't figure out is the apparent 'special effects' that can only be seen while wearing the frames. The video wasn't much help, so maybe it's not that amazing and I'll just have to buy it to see it in person (and be disappointed).
|
[
"As far as I can tell, the ball simply has retro-reflectors ('microprism technology') and the glasses have red LEDs. The retro-reflectors on the ball reflect the light back to the source, with a bit of scattering. Similar to road signs, roadwork vests, and the like. ",
"Each tiny retroreflector is shaped like corner of a cube, it reflects the light back to the source (typically using total internal reflection). Other kind of retro-reflectors uses spheres of glass with coefficient of refraction of 2.0 , with reflective coating on the back.",
"More info here: ",
"http://en.wikipedia.org/wiki/Retroreflector"
] |
[
"The light from the glasses is directly reflected towards the wearer of the glasses. This is because the reflectors use a corrugated mirror to reflect the light, using the same principal as ",
"bicycle reflectors",
". The special glasses have lights and in the details it states: ",
"\"Requires 4x 'A76' batteries, included.\""
] |
[
"looks like a cool toy, but what I don't get is why companies make up totally stupid technobabble for stuff like this . . . Microprism Technology lol",
"I wonder if there's a way to adapt the retroreflection and head mounted light source to work with infrared or polarized light . . . It might be cool to have a glowing ball that only the players can see"
] |
[
"There are over 200 types of Cancer that negatively affect humans, is it possible for the disease to manifest in a way that would be positive?"
] |
[
false
] |
At it's core Cancer as I understand it is a mutation affecting cell growth. There are over 200 different types of Cancer that all negatively affect humans. Would it be possible for the disease to mutate or change in a way that would make it helpful rather than harmful? And if that happened, would it be a step forward in human evolution?
|
[
"Another note to add: we are finding that different locations within the SAME tumor can possess different markings and genetics. Essentially, there is no such thing as a single \"type\" of cancer, each is kind of its ecosystem of genetic mutations."
] |
[
"No, probably not. Cancer isn't exactly a conventional \"disease\". What happens is, mutations occur over time in individual cells. Most of them are fixed either directly, or via apoptosis of the cell (the cell \"commits suicide\" and materials are recycled). If a single cell escapes termination or repair and enough mutations build up, the cell can start dividing uncontrollably. Basically normal cells are limited in division by 2 things: 1) proximity to other cells and 2) the length of telomere ends. The proximity thing, called contact inhibition, is not experienced by cancer cells; in other words, the cancer cells will not stop dividing, even if they are surrounded on all sides by other cells. And this is one reason cancer is very dangerous: it physically destroys neighboring cells by forced compression, and when excess tumor cells slough off from the main pile, they can metastasize (migrate through the bloodstream to new tissues/ different parts of the body). If they get stuck somewhere else, they will begin killing cells in the new area as well. Cancer cells are eerily similar to pluripotent stem cells, and I won't get into anything else. Sorry for the long-winded response, for some good reading check out \"Molecular Biology of the Cell, 5th edition chapter 20 by Alberts\". There may or may not be a torrentable pdf available on the internet of this entire textbook."
] |
[
"Cancer is uncontrolled cell growth. Not all the time does the cancer become malignant and spread everywhere. I remember an autopsy studying stating that a majority of men over the age of seventy die ",
" but not from prostate cancer. They never knew they even had it. So you can have a tumor that sits there and essentially minds it's business, for a time. But overall Cancer is a removal of the mechanisms that control cell growth. Your body is a well ordered place, when rogue cells start swimming around and taking up space in an uncontrolled manner, it's not good."
] |
[
"What happens when lightning strikes in the ocean?"
] |
[
false
] |
Typically, when electric current goes through a small body of water, like a bathtub, the water carries current and results in someone sitting in the tub being shocked. However, obviously when lightning strikes the ocean, the whole world doesn't get electrocuted. So... How far does the ocean (or any large body of water) carry current? What determines this?
|
[
"Wait, hang on - does that make any sense at all? You can't say \"a lightning bolt consists of 100 kV\"... Voltage is the potential difference ",
" points. I would figure that wikipedia is saying that the voltage ",
" by 100 kV between the lightning source and the ground.",
"That wikipedia article even tells you that the electric field hits several hundred volts ",
"...",
"Also, I don't think you can just plug in V=IR even if you had the right voltage. If you pass current through an ohmic resistor, the voltage drops across it, but the current is constant. So in this situation you are hitting 0 V, but you still have 30 kA flowing somehow. It doesn't really make sense.",
"Now I don't really know how I'd do the actual calculation, but I'm pretty sure that assuming that it's a simple circuit does not really apply here.",
"Edit: as was pointed out below, it looks like you need to really look at ",
" dissipation, not voltage - as the current \"spreads out\", it decreases to basically zero. The geometric factor you didn't take into account is actually the most important thing here!"
] |
[
"According to Wikipedia, an average lightning bolt consists of 30KA and 100KV, thus when it strikes the water it will need to go through 3.33 Ohms of resistance before dissipating. A meter of salt water at 20 Degrees C has 0.20 ohms, so assuming a straight path down, worst case scenario (think a string of resistors in a series circuit) will reach a depth of 16.65 meters. This is assuming that the lightning doesn't dissipate in more than one direction which is unlikely."
] |
[
"I remember doing ",
"these calculations in class",
". I'm not sure if I can properly explain it here, but I'll try. I'm going to throw some concepts at you, keep them in mind, then I'll put them together at the end. ",
"When you want to know if you're going to get shocked or not it depends on voltage potential of two points. If there is a voltage, then there will be current until that voltage goes to zero. If you're heart is in the way, and that current is above ",
"100mA",
" then you may have a very bad day.",
"Now as electrons are flowing through things, they drop in potential, it's called a voltage drop, I love it when names are obvious. So as an example if hook up a car battery to the top and bottom of a strip of PURE water, if you measure the top and bottom of that strip of water, you would read 12 volts. If you measure half of that distance you may read 6 volts. ",
"At the point of the strike the voltage potential is very high and electrons will dissipate away from that potential. The farther away you get from the strike the the less current there is to dissipate, it drops relatively quickly, it's the ",
"surface of a hemisphere equation",
" so it's like a 1/r",
" like a drop. As it dissipate the voltage will drop across this hemisphere. The voltage drop across any distance D to delta r, will determine if the current flowing through any objects in the water, and this my friend will determine if you shall survive or not in a lightning strike in the water. ",
"Given these numbers (in my link) and a sea water resistivity of ",
"0.2 ohm meters",
", you are only guaranteed death via lightning strike if it's closer than 6 meters. It seems that salt water is so conductive current would prefer to flow around you than through you. ",
"Note: Technically in the case of lightning potential is reversed, but those are details in orientation. ",
"Edit: some of my grammar.",
"Edit2: added clarity. Also fun fact. Cheers!"
] |
[
"Why aren’t/can’t non-recyclable plastics be processed and used as aggregate in construction applications?"
] |
[
false
] | null |
[
"That depends on the types of plastics in question.",
"For some plastics I'm sure this would work fine. There are others however, that aren't going to meet compaction standards for fill, and further others that may leach chemicals into the ground as they slowly decompose."
] |
[
"research on alternative aggregates is ongoing, at least one grad student in my program is working on a parallel idea. a few things that come to mind would be thermal expansion factors as well as interactions with the concrete mix and additives. strength and uniformity/dependability of the aggregate is important, curing time and of course, cost.",
"https://www.giatecscientific.com/education/concrete-mix-design-just-got-easier/",
"http://news.mit.edu/2017/fortify-concrete-adding-recycled-plastic-1025",
"https://ascelibrary.org/doi/10.1061/%28ASCE%29MT.1943-5533.0001765",
"https://www.ncbi.nlm.nih.gov/pubmed/26970843",
"edit ",
"ohh yea and undergrad concrete canoe. most teams use packaging peanuts(among other things ie woodchips) as an aggregate ",
"http://www.asce.org/event/2019/concrete-canoe/"
] |
[
"Couldn’t this be a viable solution to at least part of the problem of non recyclable plastics? I understand not all of them would be suitable, but..."
] |
[
"Are planets and stars limited to how big they can get?"
] |
[
false
] |
[deleted]
|
[
"Well, if a \"planet\" gets too big it starts undergoing fusion and is a star."
] |
[
"Yes, there are limits on the mass that a star can naturally attain. There is a number called the \"Eddington limit\" that discribes the maximum size that a star can obtain (150 solar masses for MOST stars, with rare exceptions for suspected Population III metal-free stars like R136a1).",
"The Eddington limit basically discribes an equalibrium between gravity/degeneration pressure that supports the star against collapse, and the outward solar wind that whisks away solar mass."
] |
[
"Sure. The size of stars is limited by the Eddington luminosity (with luminosity being related to size). If they get too big and bright, radiation pressure starts blowing them apart more and more.",
"If planets becoming too big, they start undergoing fusion and stop being a planet."
] |
[
"Whats the difference between Osmosis and Capillary Action?"
] |
[
false
] |
I thought water moves from higher concentration of water to low concentration of water ( I maybe wrong about this) and that is why water will pass through a permeable membrane of different concentration. Isn't capillary action similar to this in the sense that the water is moving to an area where there is lower concentration of water? Please explain to me the differences and where I am wrong. Thank you :D!!
|
[
"Capillary action is to do with surface tension, where for instance water is attracted more so to a glass tube and will have a curved surface and rise up a tube, ",
"look here for diagrams",
"\nCapillary action is not a change in concentration.",
"You are pretty much on the right track with osmosis from what I can recall. "
] |
[
"No, water moves to the area of higher solute concentration. OP was right but phrased it in an odd way."
] |
[
"Osmosis is where water moves from an area of lower solute concentration to one of higher concentration. So OP just phrased it differently.",
"EDIT: Thanks to chemistree for finding my herpderp error."
] |
[
"How does Shazam work?"
] |
[
false
] | null |
[
"I actually worked with Shazam for a while when my employer at the time was partnering with them. They generate a \"fingerprint\" of the audio and then I assume they segment that in a way that you can then search on parts of songs.",
"It's probably similar to this project ",
"https://github.com/worldveil/dejavu",
"More descriptive blog post: ",
"http://willdrevo.com/fingerprinting-and-audio-recognition-with-python/"
] |
[
"Sorry for the mobile link.",
"Shazam and others like it use a variation on Fourier Transforms to generate a fingerprint that is extremely compact and easy for a computer to analyze. ",
"This is also part of the secret that allowed mp3 files to be so compressed and yet play back at high quality.",
"https://en.m.wikipedia.org/wiki/Fourier_transform"
] |
[
"I have read a bit about the general procedure of fingerprinting songs, and a few friends of mine worked on developing their own version of the software. DejaVu, the software linked in another comment, has an excellent description of the process, complete with visuals. For those who don’t want to look it up, I can provide an overview. ",
"The software most likely starts by converting whatever audio input it gets directly into a “wav” file or something equivalent. These files are a time series of amplitudes of diaphragm compression from the mic. This is a map of a sound signal in the time domain. This is pretty common way to represent sound, and is most likely what you’ve seen if you work with any software like GarageBand or the like. ",
"Then, the software takes a discrete Fourier transform of the data. The method used to do this is the FFT (Fast Fourier Transform). If you’ve never heard of this process, it can be difficult to conceptualize. In essence, it takes data in the time domain and maps it into the frequency domain. This means that it calculates the amount of the signal that is made up of different frequencies. This is possible because any signal can be created by a combination of different frequencies at different amplitudes. The FFT extracts those amplitudes. ",
"I lied a little in the last step. Instead of taking the FT on the entire time stream at once, we take it on small amounts at a time. Maybe a second or so. This is often called the “bin” size. The bin size is arbitrary, and there are advantages and disadvantages to making it larger or smaller. So, for a three minute song, using a bin size of half a second, we would have 360 bins. For each bin, the frequency information is extracted. Now, we have a series of bins, chronologically ordered, and the frequency information extracted from them. ",
"With this information, we can begin to implement fingerprinting techniques. The most common way to do this is to finding “peaks” in the data for each bin. This means finding local maxima. There may be (and most likely ",
" be) several per bin. The reason we do this is that peaks tend to survive noise. In the presence of static, as long as there is a sufficient signal to noise ratio, the peaks ought to retain their relative locations to each other (location meaning how many bins away it is from another peak). ",
"The collection of local maxima and their locations with respect to one another is the fingerprint of the song. You can then calculate this fingerprint for many songs. ",
"To identify a song, record a small sample of audio, and then apply the same process to this sample. The local maxima locations will partially match with a previously calculated fingerprint. The better the match, the greater our confidence in the identification. ",
"There are many different things to consider when using this method:\n- Windowing functions for the FT of the bins\n- Bin size\n- Peak finding techniques (and acceptance and denial of peaks)"
] |
[
"Are there chemicals that, once ingested, will never leave the body?"
] |
[
false
] |
I've heard that ingesting certain chemicals (either by breathing them, absorbing through the skin, or consuming with food) have a cumulative effect on the body because they don't leave with the rest of the bodily waste (This is evidently what people who claim "detoxing" works are supposed to be curing.) How true is this? I was under the impression that the body slowly replaces all of its cells in a few years. If so wouldn't it be the case that in that time any residual chemicals would also leave the body? If not how does that persistence work?
|
[
"\"Never\" might be a bit of a strong word for something that's ultimately statistical. But yes, some things can stay in your body effectively forever, the technical term for this is ",
"bioaccumulation",
". These tend to be compounds (such as heavy metals) which end up in your fat tissue, (and will remain there as long as the fat is there) and things which bind chemically bound to your bones, and similar. These are things that are not replaced very rapidly. Nor are your cells replaced, much of the stuff that makes up most the cells are replaced continually. ",
"Things can also bioaccumuate even if they leave the body relatively quickly, if they're being taken in faster than they can be excreted. So it both depends on the compound and the concentrations.",
"Is there a cumulative effect? Yes, that's how things like (chronic) heavy metal poisoning work.",
"However, \"detoxing\" with ginger root or whatever does ",
" work, and has no scientific support. (note that it's always vague and unspecific 'toxins' those things supposedly remove). There is really only one case where something like that works, which is using chelating agents (compounds that bind strongly to specific things, usually metal ions) which can bind up metals in the case of ",
" poisoning (getting a lot at once), and help keep them from getting stuck in your body. It does nothing to remove things that are already 'stuck'. Chelation therapy is a dangerous medical procedure (an extreme measure for an extreme situation), because it is not entirely specific to the heavy metals it's supposed to remove, and will bind and remove needed mineral ions from the body as well. On a similar note, some antidotes work in a similar way, by chemically reacting with a toxin into some less harmful compound. Those are also specific to specific toxins, but not so specific that they don't tend to damage other stuff. Obviously, taking antidotes as a preventative measure is ",
" a good idea.",
"This lack of specificity is why \"detox\" stuff can easily be dismissed: \"Toxins\" is not a specific thing (even whether something is toxic or not can depend on the dose). There does not exist any chemical property that all or even most toxins have in common, and especially not any property they don't share with compounds that are supposed to be in your body. On the contrary, things are often toxic ",
" they're chemically very similar to things that are supposed to be there, and thus get integrated into your body, but then not quite similar enough to serve the same purpose. They're like parts that fit into the machine but don't work.",
"So there ",
" exist, even in principle, any 'detoxifying' agent that targeted 'toxins' in general. Even targeting one single compound with great specificity is extremely difficult. For instance, it's considered a bit of a marvel of nature that the potassium channels in cells ",
" allow potassium ions to pass through them, when sodium atoms are near identical except for being slightly ",
". Figuring out how that worked was a Nobel-prize winning discovery (MacKinnon, 2003)."
] |
[
"So by losing weight, and thereby reducing my body fat, I'm washing the heavy metals previously stored in my fat tissue... where? Back into my blood?"
] |
[
"Back into the blood. I'm not sure of the extent to which that happens with heavy metals (as they can end up in other places as well), but ",
"that does happen",
" for fat-stored, bioaccumulated toxins like PCBs and DDT."
] |
[
"In hunting, poison-tipped arrows are used. Is the animal's flesh treated in some way to render the poison harmless?"
] |
[
false
] | null |
[
"Curare is what South Americans use. It's ",
"not effective if taken orally",
", so it's safe to eat your kill.",
"Curares are used medically when muscles need to be relaxed or paralyzed for certain procedures. In ophthalmology, it's used to paralyze the eye muscles while replacing a cataractic lens, for example. The half life in the body is one to two hours."
] |
[
"Some are effective only when introduced to the blood stream (e.g. ",
"Curare",
" and ",
"chrysomelid beetles",
"."
] |
[
"I once met an indigenous tribe in Borneo, they still used poison blow darts to hunt with, they told me a small amount about what they used. Apparently as long as it didn't get into your blood stream it wouldn't kill you. \nHowever before eating a kill they would cook it and cut out and discard its heart.\nNow how much of this is accurate or true I don't know, but this was what I was told by people who still used poison tipped blow darts to hunt with. "
] |
[
"I see a lot of people arguing over the validity of \"The China Study.\" Can someone provide me with an unbiased critique?"
] |
[
false
] |
The China Study was a study conducted throughout the 1970's and 1980's in which researchers monitored the health and lifestyles of the rural population in China. Many people tout it as evidence for a vegetarian lifestyle, others say the study is garbage. The issue is, I can't find any comments on it from unbiased sources. What do you guys know about it? Here is a link to the There was also a
|
[
"Disclaimer: this is not my field, but I have followed the literature on this topic in some depth. The China Study is an observational epidemiological study. You can't infer causation from those studies, but you can rule out and rule in some hypotheses. It is consistent with quite a bit of other data suggesting that vegetable-rich diets are good for overall health and longevity. It does not prove that meat, per se, is bad for you. There is a lot of evidence that a hamburger-hotdog diet is bad for you, but very little evidence that a balanced diet with reasonable sized portions of all kinds of meat is bad for you. But there is experimental research showing that switching to a strict plant based diet is a healthy transition for many Americans (but not proof that the benefits are for lack of meat--most of the evidence just think it's healthy because it is high in vegetables, not because it is zero in meat). Hope this isn't "
] |
[
"Here is a blog post by Robb Wolf, ",
"\"The China Study: Junk Science and Lies\"",
" that links to some articles \"refuting\" the work of the China Study, in particular this link to a ",
"rebuttal by Loren Cordain",
", which is extra interesting as it contains comments by Campbell, which are not very convincing."
] |
[
"http://rawfoodsos.com/2010/07/07/the-china-study-fact-or-fallac/"
] |
[
"What kind of information can I get on my own with my \"uninterpreted raw genetic data\"?"
] |
[
false
] |
For example, like the data I can get from 23andMe. I'm interested in using open source software to help interpret the data.
|
[
"Google prometheus. They can interpret the raw data for $5 and their website should give you a description of what they offer. "
] |
[
"You get the complete raw data, so you can get the same info you could prior, just with a different service. A friend of mine just did it a week ago."
] |
[
"The site is ",
"https://promethease.com/",
".",
"My understanding is that 23andme used to provide quite a bit of health risk information, but were shut down by the US FDA who deemed the service an unapproved medical device. It looks like this site can import their data and match it up with the SNPedia -- an open database relating SNPs to traits.",
"I'm not sure what kind of data you can get out of 23andMe's service anymore, though. It's probably best to send them an email and tell them you plan to upload it to promethease -- I'd guess they'd be sympathetic. If you do get a response back, please update us!"
] |
[
"Have the measurements of time always been standard?"
] |
[
false
] |
[deleted]
|
[
"This might be worth cross-posting to ",
"/r/AskHistorians",
". From my (very limited) understanding, there were many, many ways of dividing time before the invention of clocks, each with different units.",
"Since mechanical clocks were invented in a particular time and cultural context (16th century Western Europe) we took 24 hours in day from the greeks and 60 minutes / 60 seconds from the babylonians and ran with it. ",
"So it's not at all that there was an efficiency contest, thinking that this method is better than the other, just that at that time we used those concepts from our historical heritage and they just kind of stuck since. ",
"Part of the reason they haven't gone away is that 1/60 is also quite handy for doing maths and divides up the day neatly.",
"(Nice Wikipedia article on ",
"the whole thing",
". Also ",
"metric time",
")"
] |
[
"I vaguely remember from a documentary that a Chinese astronomer divided the day up into something like 100 units (14.4 minutes) in order to track star movements. It could have been Yi Xing or Su Song. See 3rd pargraph ",
"http://en.wikipedia.org/wiki/Unit_of_time"
] |
[
"Much like how the concept of unit measuring in metric is more efficient than the imperial measurements",
"I'm not sure that's strictly true... I think a prime example of why metric isn't always the best choice for units is, in fact, ",
"decimal time",
". While a good idea in theory, in practice, it's untenable in part because our two natural units of time (the day and the year) don't relate by a clean number. Try as we might, we've as yet been unable to change the relationship between these two units, making any system of time inherently not easily convertible to a metric system (a year will never be 100 days).",
"Of course, that also means that the opposite of your hypothesis is what actually happened in history (i.e., the \"less efficient,\" non-decimal time is what prevailed). I'm sure there's an interesting history there that someone could expand on, and I suspect the French Revolution had a lot to do with all of it."
] |
[
"In domestic violence, why do victims stay with their abusers?"
] |
[
false
] |
[deleted]
|
[
"In short, it is because the circumstances under which abuse take place make it very difficult for the victim to leave. ",
"The abuser almost always makes certain that the victim is ",
" before actually engaging in abusive behavior. This can take several forms:",
"Financial dependence: The abuser is the only one with income, and isolates the victim from the ability to provide for themselves. Now the victim must stay with their abuser in order to survive.",
"Social isolation: The abuser cuts off the victim from friends and family. This is the classic \"Where else do you have to go/Who else will take you in\" dilemma.",
"Blackmail: The abuser has power over the victim due to embarrassing material or some secret the victim does not want revealed.",
"Of course, these are extremely overt abusive behaviors. And there is a more common reason: ",
" Most domestic violence occurs in a recognizable cycle:",
"The Honeymoon phase: The couple first meets, gets married, things go well, and there is no suggestion of violence or abusive behavior. There may be a power differential, but it is not enough to cause any problems. ",
"Tension. Something is wrong in the relationship. This could be the result of a single catalyst or a slow decline in relationship quality as the abuser's power grows and tendency toward abuse grows. Many times, victims feel as if they are \"walking on eggshells\" around their abusers. There are no overt abusive behaviors here, but neither is the relationship healthy. Covert abuse might take place here; mind games, gaslighting, etc.",
"Violence. Outright abuse occurs--physical, emotional, mental--and the victim experiences the dependence listed above, making it extremely difficult to leave. In addition, the victim often looks back on the Honeymoon phase as an example that there is hope for change. This is often also called the \"explosion\" phase, because the violence can be extreme.",
"The cycle begins again with the Honeymoon phase. The abuse stops, either because the abuser is caught or the victim seeks help. The relationship approximates a healthy one again as the abuser seeks to keep the victim near and re-establish the power differential. Meanwhile, the victim feels relief and validation that the abuser does love them.",
"The more times the cycle restarts, the shorter the cycle becomes. For example, the first full cycle may take years. The next cycle may take months, and eventually it may only take days. Abuse finally stops when the victim is made aware of this cycle and is able to find a way to overcome the power differential and isolation, and seek assistance.",
"EDIT: You may also want to read this ",
"very informative journal article by Sarah M. Buel, a lawyer and domestic violence advocate, who lists 50 reasons why victims stay with their abusers.",
". You may recognize the patterns of power differential, isolation, and victim belief systems she illustrates!"
] |
[
"Alright, let me see if I can answer those adequately.",
"The concept of protecting minors and the elderly from abuse is a legal one, and stems from the fact that children and elderly adults do not have the same capacity to protect themselves as healthy adults. In minors, this is because of a lack of experience/naivete and a lack of physical strength. In the elderly, it is because of declining health/mental ability. It should be noted here that middle-aged adults may also be abused due to diminished mental capacity; I have several clients that I am helping to coordinate with Adult Protective Services in order to file complaints.",
"The so-called \"insanity defense\" doesn't really apply to domestic violence. It is much less common in reality than in police procedural shows like Law & Order, for the simple reason that the punishment for being found not guilty by reason of insanity is not that preferable to being found guilty: those that are declared mentally unfit are remanded to their local locked-ward psychiatric facility for long-term treatment. They do not get off lightly.",
"What I believe you're asking about is the effect of trauma on brain and mind, which--luckily enough--is my forte! The extent of changes to an individual's mental state after prolonged abuse is far, far too lengthy to detail in its entirety, but some of the main features are:",
"Hypervigilance. In the context of domestic abuse, this is the aforementioned feeling of \"walking on eggshells,\" but dialed up to 11. Victims are constantly aware of their propensity to be abused or to trigger their abuser to harm them, and so they experience vastly increased anxiety, paranoia, and depression.",
"Changes in self-image. Victims of prolonged domestic violence often internalize their abuser's reasoning for abusing them. The cliche illustration of abuse is the husband beating his wife for burning dinner; the abused wife may actually internalize this reasoning and begin to believe that her husband beats her to \"correct her bad behavior\" and that if she pleases him, he will be loving and stop abusing her. ",
"Social isolation. As I stated above, this is usually initiated by the abuser, but the victim may perpetuate social isolation because they are ashamed of their status as a victim. They would much prefer to let people believe the illusion of a happy family than suffer the embarrassment of others knowing they are being abused.",
"While these changes all serve to perpetuate the abusive relationship, it must be noted that ",
" They simply continue to engage in decision-making that perpetuates the abuse cycle because the alternative is overwhelming. It is not that they ",
" choose to stop the cycle, it is that they ",
" This is why advocacy centers, abuse centers, and counseling are so important: They provide a safe space for the victim to orient themselves outside the influence of their abuse, and allow them to make the hard decision."
] |
[
"Alright, let me see if I can answer those adequately.",
"The concept of protecting minors and the elderly from abuse is a legal one, and stems from the fact that children and elderly adults do not have the same capacity to protect themselves as healthy adults. In minors, this is because of a lack of experience/naivete and a lack of physical strength. In the elderly, it is because of declining health/mental ability. It should be noted here that middle-aged adults may also be abused due to diminished mental capacity; I have several clients that I am helping to coordinate with Adult Protective Services in order to file complaints.",
"The so-called \"insanity defense\" doesn't really apply to domestic violence. It is much less common in reality than in police procedural shows like Law & Order, for the simple reason that the punishment for being found not guilty by reason of insanity is not that preferable to being found guilty: those that are declared mentally unfit are remanded to their local locked-ward psychiatric facility for long-term treatment. They do not get off lightly.",
"What I believe you're asking about is the effect of trauma on brain and mind, which--luckily enough--is my forte! The extent of changes to an individual's mental state after prolonged abuse is far, far too lengthy to detail in its entirety, but some of the main features are:",
"Hypervigilance. In the context of domestic abuse, this is the aforementioned feeling of \"walking on eggshells,\" but dialed up to 11. Victims are constantly aware of their propensity to be abused or to trigger their abuser to harm them, and so they experience vastly increased anxiety, paranoia, and depression.",
"Changes in self-image. Victims of prolonged domestic violence often internalize their abuser's reasoning for abusing them. The cliche illustration of abuse is the husband beating his wife for burning dinner; the abused wife may actually internalize this reasoning and begin to believe that her husband beats her to \"correct her bad behavior\" and that if she pleases him, he will be loving and stop abusing her. ",
"Social isolation. As I stated above, this is usually initiated by the abuser, but the victim may perpetuate social isolation because they are ashamed of their status as a victim. They would much prefer to let people believe the illusion of a happy family than suffer the embarrassment of others knowing they are being abused.",
"While these changes all serve to perpetuate the abusive relationship, it must be noted that ",
" They simply continue to engage in decision-making that perpetuates the abuse cycle because the alternative is overwhelming. It is not that they ",
" choose to stop the cycle, it is that they ",
" This is why advocacy centers, abuse centers, and counseling are so important: They provide a safe space for the victim to orient themselves outside the influence of their abuse, and allow them to make the hard decision."
] |
[
"If both parents weren't overweight and obesity doesn't run in your family.. What are the chances an offspring will be obese ?"
] |
[
false
] |
[deleted]
|
[
"It depends on the child's diet. Although he will have no predisposition to obesity, he can still become obese."
] |
[
"Why higher than average if both parents are not overweight if the child is influenced by them? "
] |
[
"Sorry, read that wrong. I thought it read \"were overweight, but it didn't run in the family\""
] |
[
"I hope this isn't a dumb question but, how do calculators work?"
] |
[
false
] |
It seems pretty intuitive that when adding 1 and 1, the calculator would maybe put one dot next to another dot and then count the sum. Or something like that. But once you get to higher level operations, such as larger scale multiplication, powers, or trigonometric operations of decimals, my idea is obviously wrong. This is absolutely baffling to me. edit: thank you, all! you all were quite helpful. :)
|
[
"Imagine an incredibly simple electronic calculator: one that can only add together 2 2-bit binary numbers and produce a 3-bit binary output.",
"The first number is represented by nothing more than 2 toggle switches, which can be either up or down (on or off, 1 or 0). Thus you can represent 0: 00, 1: 01, 2: 10, and 3: 11. The second number is represented in the same way, and the result is represented by 3 lights which can be either on or off.",
"The rules for adding 2 binary numbers are incredibly simple, you just go from right to left adding digits at the same level and carrying over as necessary. 0 + 0 is obviously 0, 1 + 0 is the same as 0 + 1 or a result of 1, 1 + 1 is 0 with a 1 carried over to the next highest digit, and then there are 4 more sets of rules for those cases but where the carried in digit is 1. The ",
"electronic adder circuit",
" is very straightforward, with 3 inputs and 2 outputs and only 5 logic gates. All you need to do is set up 2 such adder circuits, one for each digit, connect up the carry from the 1s addition to the 2s addition and then wire the carry output directly to the 4s column of the result output.",
"From there it's a simple matter to increase the length of the binary numbers up to arbitrary levels just by adding more components. Also, one might imagine adding in other functions and wiring up a simple multi-way switch which hooks up one set of circuits at a time so that only the adder is active or only the multiplier is active, etc. And, of course, one could imagine adding circuitry to translate the display and input of the numbers from/to binary to decimal. At that point it's just a matter of adding additional functions and niceties to get to a calculator you know and recognize."
] |
[
"http://www.lifeslittlemysteries.com/1408-how-calculators-calculate.html",
"You can always google straightforward questions. Feel free to ask questions about specifics and understanding. If you've never seen anything about circuits or binary before this might get a little confusing."
] |
[
"that's about right. electronics only have the capacity to perform elementary operations (addition, subtraction, multiplication, division, and division with dividends). fortunately, all the other functions out there, like sine or natural log, can be approximated using such methods as taylor series. when a calculator calculates one of these functions, it actually calculates a numerical approximation based on a series."
] |
[
"If you have two peas in a vacuum and one is moving 100 mph away from the other pea (assume they start touching eachother), given an infinite amount of time will they come back together?"
] |
[
false
] | null |
[
"They will never come together. Their relative velocity is much greater than their mutual escape velocity, even if they start out touching each other. Even though gravity has infinite range, and will always be accelerating each one towards the other, they have more than enough kinetic energy to escape."
] |
[
"So would it be similar to subtracting 1 from 10, then .1, then .01... ect going on forever. You are getting a smaller number each subtraction but you will never hit zero."
] |
[
"Yes, it's like that."
] |
[
"Why do quantum physicists operate their testing equipment on earth?"
] |
[
false
] |
[deleted]
|
[
"You're acting like it's no big deal just to pop into space and get'er done."
] |
[
"They are planning to do it in space",
", it's just that everything is much more expensive and complicated in space. It takes much more planning, research, and time invested to send an instrument into space, which is why the usual pattern is that we perform the experiment here on Earth first as best we can before we launch anything."
] |
[
"Ah, thanks! It was something I thought up earlier today, and was kind of plaguing my mind. I'm glad there is a project in works to try it."
] |
[
"What exactly is \"Information\"?"
] |
[
false
] |
In many other posts they say that information can not travel faster than the speed of light, but what exactly is information and what can be considered not information.
|
[
"At its most fundamental, information is any propagation of cause and effect within a system. The degree to which the the past state of one part of the system can be known through observation at another part of the system. Effect can only propagate at the speed of light (since nothing can go faster).",
"Information is carried in a \"signal\", which is the variation of any physical property, over time, against the backdrop of random variation (entropy). ",
"Different fields discuss information in different contexts. E.g. in physics you'll probably be talking about the propagation of cause and effect. In information theory, you're probably talking about formal logic, statistics, signalling, bandwidth, [edit: also, should include language, coding, compression, cryptography, etc.] etc."
] |
[
"I thought of calling it 'information', but the word was overly used, so I decided to call it 'uncertainty'. [...] Von Neumann told me, 'You should call it entropy, for two reasons. In the first place your uncertainty function has been used in statistical mechanics under that name, so it already has a name. In the second place, and more important, nobody knows what entropy really is, so in a debate you will always have the advantage.'",
"-- Claude Shannon "
] |
[
"Information theory was basically created by turing, Shannon and Von Neumann (most prominently) in the 40s-50s. Since then it's been pretty widely accepted. So depends on your definition of new."
] |
[
"Does smoking (vaporizing) alcohol affect the liver and body the same as drinking it?"
] |
[
false
] | null |
[
"Yes, alcohol arrives at your liver via the blood. Whether it gets to the blood through the intestines or through the lungs wouldn't make any difference, except to your stomach and intestines. Most metabolism of ethanol doesn't begin until it reaches the liver."
] |
[
"Not entirely accurate. When drugs are delivered directly to the blood stream they may or may not reach the liver. If they are ingested to the intestines they reach the liver through the \"portal\" circulation and make it to the liver where they are metabolized. This is called the \"first pass\" metabolism. Drugs that skip this 'portal' circulation do not get metabolized, which is often the point of parenternal administration of drugs (IV). Vaporized alcohol would go into the pulmonary circulation, to the heart, and throughout the body to the tissues and not reach the liver until they have made it to the entire body's tissues. People would get drunker faster. ",
"This is the same reason why crazy college kids do stupid shit like soak tampons in vodka and put them in their vaginas or why people put drugs like ecstasy in their butt. All these areas skip liver metabolism and reach the tissues without liver metabolizing them first "
] |
[
"People would get drunker faster",
"True, I was thinking more about the effect on the liver. Eventually wouldn't the alcohol would reach there and be metabolized just the same as if it had gone through the intestines?"
] |
[
"I am allergic to some dogs. Can a dog be allergic to me?"
] |
[
false
] |
Can animals be allergic to humans?
|
[
"So here's the setup:",
"All an allergy is is an \"inappropriate\" immune response of a given kind. (\"Appropriate\" is relative. That's whatever we want to happen. Killing bacteria and stuff, mostly.) Most seasonal/animal/dust allergies are the result of Th2 T cells triggering your B cells to produce IgE, a certain kind of antibody, that \"arms\" mast cells to excrete a lot of histamine and other inflammatory agents. ",
"Here's a picture that takes up less space than my verbal diarrhea.",
"All you, or any animal with an advanced enough immune system, needs is to be sensitized to a compound in your/its environment. (Obviously there are some common suspects - there is actually some research on why people tend to have allergies to the same small subset of chemical compounds... that's another story for another day.) And dogs, as mammals, have the same ",
" machinery as we do, so it's safe to assume they have T cells, B cells, and mast cells. ",
"In short: dogs are capable of having allergies, and allergies can be in response to a variety of compounds. Since you're an animal that sheds a whole bunch of stuff into the environment, it's plausible that a dog could be sensitive to, say, your dandruff, or something in your spit or snot.",
"I've never ",
" of an allergy like that, but it is possible."
] |
[
"Yes. Veterinary Technician here. We routinely send allergy panels on dogs and cats to the lab, and one of the allergens on the list is human dander. I have seen one case of a cat that was allergic to her human! This is treated with twice daily injections produced at the lab."
] |
[
"Oh, okay - well, absolutely. Most immune responses are/can be mounted against single molecules. An antibody/B cell receptor recognizes a bacterial cell by binding to one region of one molecule (called an \"epitope\") - you could definitely get them to do the same thing in the absence of all the other crap attached to it. In fact, that's how the T cell receptor works ",
" the time - other cells grab the whole antigen, chew it up, and stick little pieces of it back on their surfaces for the TCR to find. ",
"The major histocompatibility complexes are probably the coolest shit ever to grace our bodies.",
"That's how a lot of vaccines work, too. You inject the antigen alone, not as part of a whole cell/virus particle, so there's no danger of actual infection, but the antibodies can grab it and trigger the immune response that leads to memory B and T cells being formed.",
"EDIT: So to answer your question, yes! If you isolated the specific proteins that provoke the immune response to intestinal parasites, and then injected them into the skin of a bunch of people, the vast majority would display an \"allergic\" (Th2/IgE/mast cell degranulation) response - a big swollen bump and a patch of pink, itchy skin. We just don't call it an allergic response when it happens in the intestine, because then it's not an allergy, it's just the immune system doing its job :)",
"EDIT again: I am stupid and wrote Th1 when I meant Th2. ",
" cells mediate parasite immunity."
] |
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