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[
"Could Enigma code be broken today WITHOUT having access to any enigma machines?"
] |
[
false
] |
Obviously computing has come a long way since WWII. Having a captured enigma machine greatly narrows the possible combinations you are searching for and the possible combinations of encoding, even though there are still a lot of possible configurations. A modern computer could probably crack the code in a second, but what if they had no enigma machines at all? Could an intercepted encoded message be cracked today with random replacement of each character with no information about the mechanism of substitution for each character?
|
[
"As with most cryptographic systems, the flaw was never the cipher algorithm, but the humans using them."
] |
[
"As with most cryptographic systems, the flaw was never the cipher algorithm, but the humans using them."
] |
[
"It's worth mentioning that, as famous as the Enigma machines were, Germany used other encryption machines such as the ",
"Lorenz rotor stream cipher machines,",
" which were cracked by British cryptanalysts despite their never having gotten their hands on a physical example. As with the Enigma, though, this was made possible by a German operator's procedural mistake."
] |
[
"Why Can't the brain interpret the image it sees to make things clear to people who need glasses?"
] |
[
false
] | null |
[
"Yes the brain makes us ignore blind spots, this is not the same as filling in the missing visual information. With blind spots we just don't notice that nothing is there and if we do it is usually just a white or black spot or a kind of smear of the images around it.",
"Maybe you multiple images idea would work if we had compound eyes but it side steps the problem of the brain processing a 'low resolution' image into a 'high resolution' one. In other words, no matter what software (brain) you have it will be limited by the hardware (eyes)."
] |
[
"No, this is akin to CSI type shows using computers to zoom in on or clean up images, in reality the image resolution prevents this. The brain cannot fill in the visual info it is not getting. "
] |
[
"The brain cannot fill in the visual info it is not getting.",
"The brain does this all the time, with our blindspots and bloodvessels infront of our eyes.",
"Also it's possible to build up a higher resolution image from several lower resolution images taken from different angels, which is how the police make out faces from lower quality video from surveillance cameras etc. A brain \"configured\" like that could basicly work the same process, but faster and \"live\".",
"Although I doubt by the time we're able to \"modify brains\", returning eyesight will be a big problem for the modern medicine."
] |
[
"How do we have images of the Milky Way Galaxy?"
] |
[
false
] | null |
[
"We don't. We have pictures of other galaxies. We know that the milky way is a spiral galaxy. So pictures of spiral galaxies stand in for the milky way."
] |
[
"Pictures of the Milky Way from an outside perspective are just artists impressions."
] |
[
"Ah. Thanks for the answer. I'm not really all that familiar with images of the cosmos so they looked extremely convincing to me."
] |
[
"Why is colorblindness specific combinations of colors or a certain amount of colors?"
] |
[
false
] |
[deleted]
|
[
"There are 7 types of color blindness. You have three types of cones that help you to see different colors. If any one of them are not there or does not work correctly you get different types of color blindness. Different combinations lead to different color blindnesses.",
"Because you only have three types of cones that can see all colors in existence, it is not possible for any unknown color blindness to exist. With the exception that because our eyes are made of millions of different cells in different orientations, our perception of colors is not 100% identical."
] |
[
"That was a journalistic exaggeration. Actual research shows that people who use different names for colors differentiate them a bit faster, if they are not given parallel linguistic task."
] |
[
"Yes.",
"Look up the Himba tribe color perception experiments, they might blow your mind."
] |
[
"How many unique selves are implied by the major histocompatibility genes?"
] |
[
false
] |
From my understanding, there are about 6 major genes that are considered during transplant matching, and at least two of these - HLA-A and HLA-B both have thousands of variants leading to millions of permutations. So if we considered all of the major histocompatibility genes and the # of known variants, how many unique immune signatures would we get? If the immune system sort of defines "self", does this then give us an upper bound of the number of unique "selves"? Here's a quote from The Song of the Cell talking about the variants: Humans have multiple “classical” major histocompatibility genes, and potentially many others, of which at least three, and possibly more, are strongly related to graft compatibility versus rejection. One gene, called HLA-A, has more than a thousand variants, some common and some very rare. You inherit one such variant from your mother and one from your father. A second such gene, HLA-B, also has thousands of variants. You might have guessed already that the number of permutations between just two such highly variable genes is mind-boggling. The chances that you’d share such a barcode with a random stranger you met in a bar are vanishingly small (and all the more reason not to fuse with him or her).”
|
[
"There may be thousands of individual genes per locus (ie 7712 for A locus currently), but only about 100 of them are common. Many are caused by synonymous mutations or are found in the non-coding regions (introns). Also there is strong linkage disequilibrium between B-C as well as DRB1-DQB1 as those genes are ver close together on the chromosomes. There are still a lot of possible combinations. Thirty percent of the population will have a matching sibling and most others can find a non related match.\nThe only thing that might reach the level of permutations that you seek would be in VDJ recombination seen in the repertoire of antibodies/B cell and T cell receptors."
] |
[
"There are three genes for MHC I, namely HLA-A, HLA-B, and HLA-C. You'll have one allele of each of them on each of your copies of chromosome 6. Last I checked there were 2041 alleles of HLA-A, 2668 alleles of HLA-B, and 1677 alleles of HLA-C. The number's probably higher now.",
"But that's just MHC I. There's also MHC II, where the situation is even more complex. ",
"Here's",
" a chapter about it from an immunology textbook - the numbers are seriously out of date as it's an old edition, but you get the basic idea.",
"I'll leave the combinatorial math to you, because it gets kind of ridiculous."
] |
[
"That's really cool, thanks. So i suppose the actual numbers both of total possibilities and commonly encountered possibilities would be hard to estimate? Are there estimates anywhere? How do you define matching like is it based on how similar the output proteins are even if the genes might be very different?"
] |
[
"Are fish and other aquatic animals able to see regularly underwater or do they have the same blurring in their vision that humans have?"
] |
[
false
] |
If they can’t see regularly underwater do they have other senses to make up for it?
|
[
"When the prehistoric creatures moved out of the water, their eyes adjusted over time to the air. The way that fish and other aquatic animals see underwater is equivalent to what we see on land. Over time our eyes have adapted to our surroundings. "
] |
[
"Well, most animals that regularly go between land and ocean such as reptiles or birds have a transparent eyelid that slides over their eye and protects it from irritation and salt while allowing them to see. I think I've heard/read that humans might have also had one but it stopped being useful and all that remains is our eye duct. I'm not sure on that so don't quote me. I'll try to look up the correct answer after finals.",
"Most fully aquatic animals have evolved to be used to it. They may not perceive light and shapes exactly the same as we do, but for them it is normal. Creatures that have poor eyesight may be more active at night or have some other lifestyle where vision is not the most useful. In that case, smell, sound, and touch are the senses that usually make up for it. Especially since sound and smell can travel very far in water while certain wavelengths of light wash out relatively quickly in the water column (red light especially)."
] |
[
"Does that mean that if a fish was out of water it would have blurry vision like us underwater?"
] |
[
"Why do we swing our arms when we walk?"
] |
[
false
] | null |
[
"You swing your arms for balance. Try running with your arms straight down to your sides. (Don't actually do this)"
] |
[
"I assume its angular momentum? The same reason why a bike doesn't fall over when in motion?\nBut then why do we do it when we walk."
] |
[
"It's a counter-balance measure for during the swing phase of walking. Walking can be divided up into two phases, swing and stance, in which stance is when both feet are firmly on the ground and swing is when one foot is in the air. The swing phase generates some rotation on the body, which is counteracted by swinging the upper limbs in the opposite direction. ",
"Loss of arm swinging while walking can be a sign of loss of function in the red nucleus in the brain stem, which could be a sign of a stroke."
] |
[
"Why doesn't the Earth build up a positive charge from cosmic rays?"
] |
[
false
] |
We are continually bombarded with lots of cosmic rays, which are mostly bare protons. Shouldn't this mean that the Earth accumulates an excess positive charge over time?
|
[
"Cosmic rays are not the majority of particles striking Earth. In quantity they are greatly outnumbered by the particles of the solar wind, which are both positively and negatively charged. ",
"If the Earth does happen to acquire a slight positive charge, it will tend to repel positively charged particles and more strongly attract negative ones. If Earth acquires a negative charge then the opposite will happen. This means that over time, the charge of a large object will tend toward neutral."
] |
[
"will tend toward neutral.",
"Well, more precisely it would tend towards equilibrium. Even under your model, that equilibrium may have a net charge."
] |
[
"That's correct. Thanks for catching it."
] |
[
"Can you have two colds at once?"
] |
[
false
] | null |
[
"You definitely can be infected with two viruses which cause the common cold at once, although it's probable that one will dominate over the other before long, with only one surviving and continuing the symptoms.",
"The epidemiology of the wintertime respiratory viruses (the viruses which cause the common cold) is one of the most fascinating, complex, and least understood topics in medical science, and there are a lot of unanswered questions. One of the things that is known is that knocking out one pathogen can sometimes open up an \"ecological niche\" for another one to proliferate. An interesting phenomenon which has been observed for decades is that when a new strain of influenza emerges, one of the old strains just sort of magically disappears. This is likely due to the new strain \"out-competing\" one of the old strains within a population as a group of people, but the core battle happens within individual hosts, one person at a time, where someone is co-infected with both viruses, but only one dominates and survives in the end (until your immune system figures out how to get rid of it, at which point you get well).",
"But co-infection with two cold viruses at once for at least a little while is pretty common.",
"Here's a study looking at the incidence:",
"https://link.springer.com/article/10.1007/s10096-012-1653-3",
"The Health Protection Agency Public Health Laboratory (HPA PHL) Birmingham, UK, routinely uses polymerase chain reaction (PCR) to detect common respiratory viruses. ",
". A total of 4,821 specimen results were analysed. Of these, 323 (",
", 22 (",
". Reciprocal patterns of positive or negative associations between different virus pairs were found. Statistical analysis confirmed the significance of negative associations between influenza A and human metapneumovirus (HMPV), and influenza A and rhinovirus. Positive associations between parainfluenza with rhinovirus, rhinovirus with respiratory syncytial virus (RSV) and adenovirus with rhinovirus, parainfluenza and RSV were also significant. Age and temporal distributions of the different viruses were typical. This study found that the co-detection of different respiratory viruses is not random and most associations are reciprocal, either positively or negatively. The pandemic strain of influenza A(H1N1) was notable in that it was the least likely to be co-detected with another respiratory virus.",
"",
"So if you've had at least 10 colds in the past over the course of your life, you've probably had two at the same time at least once."
] |
[
"Yes, of course. Not just colds, you can be infected by multiple pathogens at once, which is one of the reasons why doctors might sometimes prescribe antibiotics to someone who is afflicted with a cold - to eliminate any bacterial infections potentially active even if it won't affect the virus. That's also the point of broad-spectrum antibiotics, when doctors prescribe that, it's because they suspect that a patient is infected by multiple bacterial infections at once."
] |
[
"That's not typically why a broad-spectrum antibiotic is prescribed. It's often done to start treatment before the bacteria can be cultured and classified. Or for prophylaxis where they are trying to prevent an infection (e.g. due to surgery) but they don't know in advance what you might be exposed to."
] |
[
"In Journey to the Center of the Earth one of Jules Vernes characters argues that the earth can't have a molten core. How can it?"
] |
[
false
] | null |
[
"Hi t7been thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
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"/r/AskScienceDiscussion",
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" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Planetary Sci."
] |
[
"'Planetary Sci.'"
] |
[
"Do any of the transition metals have negative charges? If so, why?"
] |
[
false
] | null |
[
"What do you mean by negative charges?"
] |
[
"It sounds like you're asking if they have a lower oxidation states.",
"Being a simple organic chemist who really only cares about transition metals as they have relevance to coupling chemistry, the short answer is \"No.\" Metals like to donate their D-shell electrons lending to higher oxidation states, adding extra electrons to that shell is energetically difficult.",
"However, I believe that there are some specific cases where lower (negative) oxidation state metal complexes have been observed, or calculated to exist, but these examples are rare.",
"Hopefully some inorganic chemist will come along and expound on this - or correct it."
] |
[
"Overall the short answer is no. When you have a bulk amount of a transition metal they have delocalized electron interactions which lead to \"positive nuclei.\" As for transition metal complexes, one in which you have a central inorganic atom that has formed a compound with some ligand structure, The total charge on the transition metal will be positive. You could potentially induce a negative charge through some sort of polarization scheme but this would destabilize the complex and it would break apart. In general, transition metal complexes are finicky with their typical positive charges in terms of stability; trying to induce a negative charge just isn't going to happen."
] |
[
"A2 Physics coursework unexpected result? (LASER + Diffraction Grating)"
] |
[
false
] |
Whilst trying to get data for my A2 physics coursework (measuring the wavelength of light by the bending through a diffraction grating- not the best, but the alternative was literally paint-drying), I've been having some troubles with the diffraction grating; I should expect to see the brightest spot being straight ahead of the laser hitting the diffraction grating, a lá Phasor theory- however instead I'm getting the brightest dot offset to one side (dependant on the rotation of the grating, but not which side it's going though). Even more strangely, the offset between the brightest and the straight ahead is slightly more than between either and the next dot out. That is, between '0' (middle/straight on) and l1 (brightest dot) there's 1.6cm, whilst between l1-l2 and 0-r1 the gap is 1.5. (l2-l3 and r1-r2's 1.7 cm). I could take pictures if my wording isn't sufficient, but it'll have to be later as I'm about to go out. Please help me to explain this counterintuitive result! My teachers couldn't explain it either, putting it down to diffraction within the grating until I realised that it would always bend the same way, independant of the normal. They then were puzzled again. (The diffraction gratting is 300lines/mm, the laser is 532nm, but also happened with a 650nm. The behaviour was witnessed with several gratings of the same type, but a 15000line/inch (different make) and an unknown spacing grating I got for free from a uni visit don't have the behaviour).
|
[
"I'm doing my Ph.D in laser spectroscopy, so I think I can help you. Sadly I'm not sure I fully understand your premise. Maybe a cartoon would help ?"
] |
[
"Here ya go; ",
"http://imgur.com/a/tAhbk",
"\nIf MS paint scrawlings aren't good enough, I'll get out the camera and take pics."
] |
[
"Hello from a month in the future, just coming back to say that no-one could figure it out, although we now have a tentative explanation (although I don't like the explanation, I need to conclude the cwk somehow)."
] |
[
"I remember reading somewhere that major cities that experienced catastrophic fires (ones that burned down the majority of the city) converted to gridded road systems, whereas those that had no major fires didn't. Is there any truth to this statement?"
] |
[
false
] | null |
[
"Not really any truth to this statement. London is the perfect example to demonstrate this. London burned completely to the ground in 1666, but yet the road layout in the center of the city is over a thousand years old. In the days after the fire there were lots of plans to completely redo the road system, and the entire layout of the city. The plans still exist in a museum in the city. All these plans were dropped. Why? For two main reasons: Firstly, to redraw the entire map was going to cause a legal nightmare. Buildings may have been burned down, but people still owned all the land, and it was not possible to simply build a new road through someones land. Even in London centuries ago, the state didn't have the power to arbitrarily redraw maps Secondly: the city needed to get back to business and life as normal, and the quickest way of doing so was to simply rebuild all the houses/businesses in the same places as before. Bakers etc. simply had their shop rebuilt and opened selling bread again a few weeks later. ",
"In the case of London, all that the officials achieved was a slight change to the building codes stating how wide roads had to be. The roads were made a little wider. "
] |
[
"Actually I was talking about the City of London, which lies within the city Greater London. They have their own mayor, governing bodies, and police force separate from Greater London. They control the Port of London's health authority which includes London Heathrow airport.",
"I wouldn't call that completely meaningless."
] |
[
"I'm guessing you mean the City of Westminister? While this is legally an independent city, in reality those laws have no meaning. It is just part of the quaint idiosyncrasies that is English Law. England has no written constitution, but rather a thousand years of legal case law, acts of parliament, traditions and conventions which evolved over time. Some old laws are kept around for ceremony, others simply because no one could be bothered to remove them, and many other laws exist only as traditions and have never been written down. ",
"It may be a little surprising, but there is not even such a position as \"Prime Minister\" in England. David Cameron is \"First Lord of the Treasury\". That's what the sign on his door says, and that is what his monthly pay cheque says. But because of centuries of tradition and convention a de-facto position of Prime Minister exists, even though there is no law creating that position or describing what powers the position has. "
] |
[
"How does oxygen go from lungs into blood? Could you explain in details and simply?"
] |
[
false
] |
Thank you in advance
|
[
"Think of it as a wall with 1-way valves in the shape of oxygen (into the bloodstream) and CO2 (out of the bloodstream)",
"There's no directed \"valve\". Diffusion there is just a matter of the different concentrations on both sides."
] |
[
"It's not an overly complicated system really",
"You breathe in, air enters your lungs, eventually reaching a part of the lungs called the alveoli. The alveoli are 'fluffy', so as to have a high surface area, and surrounded by capillaries (small blood vessels). ",
"The barrier between the alveoli and surrounding capillaries is very thin - 1 cell thick, .000039 inches), and has a permeable membrane that allows oxygen and carbon dioxide to pass in and out of the bloodstream. Think of it as a wall with 1-way valves in the shape of oxygen (into the bloodstream) and CO2 (out of the bloodstream)",
"Oxygen enters the blood stream, CO2 exits, you exhale"
] |
[
"Can you oxygenate a person (or mammal that uses lungs) in any other way besides the lungs?",
"What I’m getting at is, how do babies in the womb breath or get their oxygen from via the umbilical cord?"
] |
[
"Is there adequate evidence, beyond the anecdotal, to suggest that the internet has lowered attention spans, memory and/or patience?"
] |
[
false
] | null |
[
"You may be thinking of ",
"this Science article",
", which reports:",
"This is preliminary evidence that when people expect information to remain continuously available (such as we expect with Internet access), they are more likely to remember where to find it than to remember the details of the item. One could argue that this is an adaptive use of memory—to include the computer and online search engines as an external memory system that can be accessed at will. "
] |
[
"One could certainly be smart with a short attention span, however."
] |
[
"One could certainly be smart with a short attention span, however."
] |
[
"In terrestrial contexts, cooler flames are red while hotter flames are white/blue. How can it be that stars also exhibit this characteristic?"
] |
[
false
] |
I've heard many times that cool flames are red/orange while hotter flames are white/blue. I've also heard that the difference in colour between red dwarf stars and white dwarf stars is caused by difference in temperature. How can it be that a star - which is presumably much hotter than, say, burning alcohol vapours in a flambé - is cool enough to still be red for the same reason? Do the color "thresholds" change depending on the condition (vacuum of space vs. sea level on Earth)? Or maybe red dwarf stars really are that cool?
|
[
"Red dwarf stars--- or at least their surfaces--- really are that cool. "
] |
[
"The sun looks orange yellow ... because it is made up of mostly superheated hydrogen ... releasing a single wave length of light, which is orange-yellow. ",
"Are you sure about this? ",
"Here",
" is the solar spectrum. It is nearly a black body spectrum (T ~ 5500 K). The biggest deviation is at ",
"500 nm, which is green",
", not orange-yellow"
] |
[
"The sun looks orange yellow ... because it is made up of mostly superheated hydrogen ... releasing a single wave length of light, which is orange-yellow. ",
"Are you sure about this? ",
"Here",
" is the solar spectrum. It is nearly a black body spectrum (T ~ 5500 K). The biggest deviation is at ",
"500 nm, which is green",
", not orange-yellow"
] |
[
"What happens when a particle loses all energy? Can you drop below the ground state? [physics]"
] |
[
false
] | null |
[
"The ground state is, by definition, the lowest energy state a particle can be in. If it was possible to drop lower then that lower state would ",
" the ground state. ",
"Depending on the situation, the ground state may be zero energy, or some small finite nonzero energy."
] |
[
"I read somewhere that even in ground state, particles still maintain some kinetic energy, is it possible to lose ALL energy?"
] |
[
"That was what my last statement was. There are some cases where the lowest possible energy (the ground state) is not zero. But by definition those situations it can not lose it, it is the lowest possible, it can not lose it.",
"Other situations, it can lose all energy. The ground state of a particle is defined by its surroundings. If you put a particle in empty space completely isolated from everything else, in a completely empty universe, then the ground state would be zero kinetic energy. However if the particle is forced to be stuck in some region (like there are walls, such as other particles near by) then the ground state generally is not zero."
] |
[
"What can we use bronze for today and why?"
] |
[
false
] |
I was wondering what we use bronze for today and the reason for it. I cant seem to find a reason for using bronze in industrial and non-industrial purposes.
|
[
"Bronze type alloys are often used in places where you want low friction with steel parts. The most common example are oil infused bronze bushings for rotating parts. They are cheaper and take less space than roller bearings. "
] |
[
"The propellers on ships are commonly made from a bronze alloy. Mainly because it is very resistant to corrosion and has good machinability."
] |
[
"The most common example are oil infused bronze bushings for rotating parts.",
"To elaborate, this type of bushing is a porous cylinder sintered from powder, then filled with a wax/oil/mix. Capillary action and heat draw the lubricant to the surface, but surface tension keeps it from actually going anywhere. Wax and heavy oils are used to prevent evaporation.",
"And not only are they cheap, for high-force low speed applications they're straight up better than rollers. They can take a much higher pressure over the same area, and the high quality ones are practically immune to contamination. Unlike ball bearings there's no way for grit or dust to get into the tiny gap between the rod and bushing. They can also be more accurate in some circumstances, but that varies.",
"In general when you're designing a part, the prime consideration for picking bearings is cost. Sometimes the environment or space will dictate your choice, but bearings nowadays are incredibly good. You ",
" get most kinds of bearings to work for most applications, but there's an art to picking which is cheapest for all considerations.",
"Bronze is an excellent bearing material in addition to being quite hard. When you need low friction and very high force, there are few substitutes. Self-lubricating plastics have replaced some low-force bearings, but nothing lasts at high surface pressure like bronze. Well, except for sapphire, but that's obviously a little pricey. ",
"Brass (copper + zinc) is obsolete as an engineering material, although I think it still has designated specs. It's almost purely decorative nowadays. Funny that bronze outlasted it."
] |
[
"Does Earth tilt/seasons affect the amount of moonlight we get like it does with the sun?"
] |
[
false
] |
Like… do we get more hours of moonlight per day in the summer vs the winter? Or maybe it's the other way around? Or does it not matter and we always get the same amount?
|
[
"No.",
"Seasons exist because the axis of rotation of the earth isn't \"vertical\" to the earth's orbit around the sun, and the axis doesn't really change. So for large parts of the orbit, the northern hemisphere points slightly away from the sun, and gets less sunlight. Half a year later, the sun has moved \"around\" the earth (relatively speaking), and the southern hemisphere now points away. ",
"The moon, however, moves \"around\" the earth (also relatively speaking) once a month, so earth's lunar \"seasons\" are about a week long."
] |
[
"So you're saying the moon is in the sky for the same amount of time each day/night no matter where you are on the planet?"
] |
[
"I think there is a big misunderstanding between you two. Although viscence is correct, i think the OP was asking for each phase. In that case, the moon would be indeed at different places over the year. ",
"For example, the full moon on the northern hemisphere will be very low over the horizon in june/july, because it is at the opposite side of the ecliptic than the sun. The new moon in the same month is at the same side like the sun, so it will be very high above the horizon, but invisible and on the daylight side. ",
"In december and january, the full moon will be high above the horizon, because it is again on the other side of the ecliptic than the sun. The new moon in these month will be low above the horizon, for exactly the same reason stated above. ",
"So it is correct: The moon is indeed the same amount above the horizon each month. However, each phase will be visible at different places and different periods of time in ",
" month. A full moon in winter will be longer above the horizon than one in the summer. "
] |
[
"Is absolute motionlessness impossible in the universe?"
] |
[
false
] |
Let's say I get in a spacecraft and travel to the area between our galaxy and Andromeda, then just stop. As I understand it the galaxies would still be moving away from me due to the expansion of space, and relatively speaking I'm also moving away from the galaxies due to the expansion of space. Does mean that it's impossible to be perfectly motionless since everything is moving relative to each other?
|
[
"You are motionless in your rest frame. You are moving in another equally valid frame of reference. There is no absolute frame of rest.",
"Consider two objects that are not at rest relative to another. You can either be in a reference frame in which one is moving, the other is moving, or both are moving."
] |
[
"This question is actually bugging me a bit, let me try and explain my issue.",
"Consider two objects that are not at rest relative to another. You can either be in a reference frame in which one is moving, the other is moving, or both are moving.",
"I suppose you know about the ",
"twin paradox",
" , so if the 2 objects you mention are the twins, why only the one traveling is being affected ? if it's all relative to the reference frame, the twin staying at home is moving relative to he's traveling brother ?",
"The only difference I see is one of them have been accelerated. ",
"So to rephrase the original question, is it possible for an object to never have been accelerated, or be decelerated enough to put it at rest ?",
"When we say an object is moving, can we refer to how much it was accelerated rather than its speed relative to something else ?"
] |
[
"If you have two twins moving relative to each other, they do not necessarily have to agree on the sequence of events. Simultaneity is not guaranteed between reference frames, and this is one of the more confusing aspects of special relativity (look up the ladder paradox, for example). So in this case, one could see the other aging slower and vice versa, and there is no problem or paradox.",
"When one of them turns around and comes back, then there would naively be a paradox, which is resolved as you suggest by the acceleration breaking the symmetry."
] |
[
"How do accents form?"
] |
[
false
] |
I was talking to my dad about this today. How does an accent come about, and why do they exist? I was thinking specifically about somewhere like Australia or America, where it was colonised by British settlers. Thanks in advance!
|
[
"I would like to add a follow up question:",
"Are accents just precursors to new languages? If Donald Trump built a wall around the former Confederate States, would the southern accent eventually become another language in a few centuries?"
] |
[
"While groups of people who share an accent speak alike, no two individuals speak exactly alike. There's natural variation. When a language community is isolated from other speakers of that language, it is free from reinforcement from outside and those variations are allowed to evolve independently and gain their own distinctive character. ",
"It's not just accents either. Together with vocabulary and grammar, they make up a dialect. There are several examples of vocabulary differences between UK and US English, e.g. loo vs. toilet, lorry vs. truck, etc."
] |
[
"If there was no interaction ",
" (no migration, no media, no internet) between the two regions, then ultimately, the languages spoken by those inside the wall and those outside would diverge, but not because the ",
" are different, not the ",
". If something new were invented that was visible from both inside and outside the wall (such as a spacecraft), then the two communities would come up with different names for it. New concepts would also need new names. Over time, the language spoken by the two communities would diverge and eventually become different.",
"This is what has been happening gradually with British and American English. Americans say \"cilantro\"; Britons say \"coriander\". You say \"cellphone\"; I say \"mobile\". You spell it \"maneuver\"; I spell it \"manoeuvre\". And so on. But British and American are just dialects of English, not distinct languages. However, it's unlikely that they ever will become separate languages, given the amount of communication between the two countries. For that to happen, Britain and the US would have to become completely isolated from one another."
] |
[
"Why do particles with no mass have to travel so fast?"
] |
[
false
] | null |
[
"Physics"
] |
[
"Physics"
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"guidelines",
"Please see our ",
"list of related subreddits",
" for other options for your question.",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"Psychologists and/or psychiatrists, what is the difference between dissociative identity disorder and alter ego?"
] |
[
false
] | null |
[
"An alter ego has no psychological definition, and as a result refers to many things. Many of those things are engaged in willingly by the person, such as:",
"A second family",
"A pseudonym",
"Superhero civilian personas",
"Dissociative identity disorder involves an individual possessing an alter ego, but it is one that the person cannot control."
] |
[
"So basically it's Sasha Baron Cohen/Ali G. vs. DR. Jekyll and Mr. Hyde?"
] |
[
"Yeah, kinda. As said an alter-ego is more of a chosen identity, Dissociative personality disorder is what used to be called multiple personality disorder - it's more of a fragmentation of personality that the suffer switches between without conscious choice. Someone playing the role of their alter ego know that it is not the \"real\" them (the superhero is the alter ego and the \"hidden identity\" is the true identity), someone suffering DPD switches between the two involuntarily and suffers memory lapses from times and events that don't correlate to one or both identities."
] |
[
"Why does a spine have protrusions on it? What causes this and how are they evolutionarily useful?"
] |
[
false
] | null |
[
"The ",
" that protrude from each vertebra in the spine have two main purposes. The longer ones are attachment points for ligaments and muscles, giving muscles more area to attach, and also acting like long levers to help the muscles bend, straighten, and rotate the spine. There are also smaller protrusions, called ",
", that help each vertebra fit together with the vertebrae above and below it."
] |
[
"Or spikes weren't sexy, so non-spikers got more and out reproduced the spikes."
] |
[
"Or spikes weren't sexy, so non-spikers got more and out reproduced the spikes."
] |
[
"Why can I hear a snapping/popping sound when scuba diving or snorkeling near coral reefs? What makes that noise?"
] |
[
false
] |
My best guess is that it is small organisms popping in and out of coral. I am curious what the real answer is. Can anyone help me?
|
[
"Underwater organisms are loud! There are lots of crustaceans and fish making various noises down there cracking shells with their claws, crunching hard shelled organisms with their teeth and communicating to each other via all manner of sound producing organs..."
] |
[
"Also, the sounds carry differently in water."
] |
[
"There is a type of Crustation called a Mantis Shrimp. It kills its prey by smashing their Shells in and eating them. (Unless they are the the Spearing kind). ",
"And the Pistol Shrimp can also be an explanation. \nMantis is more likely though. "
] |
[
"Question on Time Dilation"
] |
[
false
] |
So I finally read up on special relativity and I'm a bit confused right now. Using the analogy of two spaceships, if one space ship moves at 0.9c relative to the other, the moving one would have its time slowed down from the reference of the second. However, because velocity is relative, the second spaceship would also be observed to have a slower time relative to the first. Here's where my confusion comes in. So when both spaceships suddenly travelled at equal velocity such that both are of zero relative velocity to one another and thus of equal reference, which one would have the slowed time?
|
[
"You've discovered ",
"the twin paradox",
".",
"The answer is that you can't have the spaceships \"suddenly\" be at rest with each other. Either one or both must undergo acceleration. In the case of one spaceship accelerating and becoming at rest with the other, the accelerating spaceship has its time dilated. If they both accelerate at the same rate to reach the same frame of reference, then neither's time is dilated - symmetry is conserved.",
"In the case that the spaceships never attempt to reach the same frame of reference, ",
" views are valid."
] |
[
"I see the light now. Thanks!"
] |
[
"He understands all that, you completely missed the point of his question."
] |
[
"How do Feynman Diagrams work?"
] |
[
false
] |
[deleted]
|
[
"Not a very detailed question. To give a simplified answer, then:",
"When you do the math of quantum mechanics (in this case the part known as quantum field theory/quantum electrodynamics), you end up with equations you can't solve exactly, mathematically. ",
"But there's an approximation method, known as ",
" (PT), that exists for solving the stuff. Basically you start with idealized (for instance, non-interacting) systems. The criterion here being that it's something which you can solve that's still relatively similar to your original system. You remove whatever little mathematical term is making stuff unsolvable for you, and start with that. Then you calculate the changes as you 'perturb' them by allowing that term back in. What you get, is a sum of terms to calculate - basically you let all the possible states of your non-interacting things (electrons, photons, what-have-you) interact with each other 'one at a time' so to speak. ",
"What you're looking for, the actual answer, is a sum of an infinite number of these terms (because there are an infinite number of states). But if you chose the right starting point for your PT, then you don't need to include that many to get an accurate enough answer. (The 'right' place to start here being that the thing you initially neglected and then put back in as a 'perturbation', is a small part of the energy compared to everything else)",
"In quantum field theory, there's an additional problem: Some of the terms were infinite! And the solution to this (called renormalization) basically amounted to throwing out those terms. (Something that angered Paul Dirac: \"Sensible mathematics involves neglecting a quantity when it is small – not neglecting it just because it is infinitely great and you do not want it!\") By 'cancelling out' the infinite, you (surprisingly, perhaps) got the right results. ",
"Now we get to Feynman diagrams. They enter here, with perturbation theory, as a way to simplify doing PT calculations. They're diagrams that you draw according to particular rules, whose topology (how the lines are connected) show you what the contributing (non-infinite) terms in your sum look like. In other words, it's a way of graphing a mathematical expression. -Contrary to the impression easily given, that they're a visualization of the actual physical process.",
"Perturbation theory is a general method, not limited just to quantum field theory, or even to quantum physics. (you can use the same general method ",
"even for classical mechanics",
") Although it's used mostly for quantum stuff. So people also extended these kinds of diagrams to other situations where it's used. There are, for instance, ",
"Hugenholtz diagrams",
" and ",
"Goldstone diagrams",
", for dealing with many-body problems (like the kinds of calculations I do). They're drawn with different rules and look a bit different, but the principle is the same - they're for describing the terms in your perturbation theory calculation. "
] |
[
"They are also used in polymer physics to get a better picture of how polymers orient themselves in space. ",
"See for example figure 7"
] |
[
"If you say so :) ",
"On a cursory reading I recognize the general formalism, but can't say I have the foggiest idea about what they're doing with it, there."
] |
[
"Theoretically, how small can a nuclear warhead be made?"
] |
[
false
] | null |
[
"It's called the ",
"Special Atomic Demolition Munition",
". But the W54 warhead is possibly the smallest nuclear device capable of being fired from a weapon with a yield dial-able between 10 tons and 1 kiloton."
] |
[
"Small enough to fit in a backpack and be carried by one man. Since the minimum size for a non-pressurized chain reaction that just melts seems to be about the size of a baseball implosion with neutron reflective material seems to make it possible to do with even smaller quantities than that, with a powerful enough conventional explosive."
] |
[
"Thanks. I am amazed at the information the internet is making readily available."
] |
[
"If terrestrial plants get the majority of their mass from the carbon dioxide in the air, where do aquatic plants get their mass from?"
] |
[
false
] | null |
[
"Carbon dioxide in the water. Water can have gasses dissolved in it, so pretty much the same processes happen in water as in air. Plants suck dissolved CO2 out of the water, break it apart and react it with water, then spit out excess O2. Fish and plankton absorb this oxygen, then expel CO2."
] |
[
"Are you thinking of algal blooms?",
"These usually occur when nutrients (often fertilizer runoff from farming) get into a water supply and give algae the nutrients they need to rapidly proliferate (called ",
"eutrophication",
"). This results in reduced dissolved oxygen for a number of reasons, but essentially they algae create an initial bloom of O2 which cascades into an extreme depletion of O2 as sunlight becomes less available and other organisms heterotrophic organisms bloom in respose."
] |
[
"Aren't there water plants that absorb O2? I thought I read something that they could be dangerous if they grow too much in numbers for the animals living there."
] |
[
"Will two engines with the same HP but with different engine displacement consume an equal amount of fuel?"
] |
[
false
] |
[deleted]
|
[
"If one engine is a 2.0 and the other is a 4.0, they are by definition not the same type (unless by type you mean \"gasoline-powered.\")",
"Broadly speaking, the 4 liter engine will have higher torque output at a lower RPM range, while the 2 liter engine will have a horsepower advantage at high RPM (a rev speed that the 4.0 engine may or may not even be able to get to without destroying itself). ",
"To put this into real world perspective examples, an indy car's engine (I'm using 2011 and before here for this example) is a 2.2 liter 8 cylinder motor that puts out somewhere around 650hp and 300ft/lb of torque. ",
"The 5.4L V8 in a 2008 F150 puts out 300 hp and 365ft/lb of torque. ",
"So, basically, there's no way to get the indy car engine to put out the numbers of the F150 engine. You can cut the indy car's horsepower by limiting how much throttle can be applied, but you can't up the torque number (at least, not appreciably). ",
"In short, what you've asked really isn't possible, and you're only thinking about horsepower, whereas torque is also important when it comes to performance, and the torque output of identical-except-for-displacement engines is not going to be the same."
] |
[
"I'm not an engineer, so someone feel free to jump in, but this is my take on it...",
"The efficiency of the engine goes well beyond the displacement, and what you're asking is purely about efficiency. ",
"Gasoline releases 19,000 BTU's of energy per pound, or about 112,480 per gallon, and one horsepower is 2545 BTU's per hour. So if your engine uses 1 gallon per hour then it's capable of producing about 44 horsepower. Most of that is lost as heat through the exhaust or cooling system, but the point is that gasoline has a specific amount of energy and it doesn't matter what size engine you use to burn it, it will always have the same amount of energy.",
"The problem for the larger displacement engine is that engines are designed to run at a stoichiometric 14.7:1 air/fuel ratio, depending on load and throttle position. Since there is more ",
" for air in the cylinders it will necessarily have to add more fuel to bring it to that ratio. That's why rpm-for-rpm a smaller displacement engine will burn less fuel, but at the same time they're producing less power at that RPM - all things equal. In other words, with both engines at 2,000rpm (both of the same aspiration/tech) the smaller displacement engine will use less fuel, but will also be making less power. ",
"To take it one step further, time is a factor when calculating horsepower, which means you can produce horsepower through burning more fuel per stroke, or more strokes per minute. Large displacement engines typically don't rev very high but will produce a lot of horsepower because they're burning more fuel per stroke. Smaller displacement engines typically have to rev much higher to produce the same amount of horsepower, in which case they're burning roughly the same amount of fuel, but instead of gulping it down 5,000 times per minute they're 'nibbling' it 9,000 times per minute. ",
" "
] |
[
"Upvote for a complete and clear answer, but as a physicist I am compelled to point out that \"ft/lb\" is not a torque, it is an inverse spring constant (a measure of spring softness). You want \"ft-lb\", or (even better) \"Nm\"."
] |
[
"Do 'normal' cats have the same wrinkles that sphinx cats have under their fur?"
] |
[
false
] |
Does this apply to other mammals with fur? Also, is there an evolutionary advantage to the large amount of wrinkles sphinx cats have?
|
[
"Yes, sphinx cats are just hairless cats and I don't think there's a real advantage to it.\nThey get cold very quickly so owning one they must always have clothing, they also have no hair to groom so they get stinky pretty easy and needs baths every 2-3 days.\nSource: I'm a vet nurse trainee, just had one come in the other day"
] |
[
"Note: Sphynx cats were developed through selective breeding in the 1960s. This artificial selection means the question of \"evolutionary advantage\" doesn't really come into play, unless you consider it an advantage in being selected by humans to breed.",
"As for other mammals, here are pictures of some examples (including some birds) ",
"without hair",
". Note that most of these animals have lost their hair through disease or mutation, and is most likely a detrimental condition."
] |
[
"The advantage to having the extra skin(that ends up in wrinkles) is partially in stretching-gives them rooms to expend when running, and in fighting it lets them twist around under their skin and escape.\nBut these apply to all cats not just hairless ones. "
] |
[
"How did Houston communicate with the astronauts on the moon?"
] |
[
false
] | null |
[
"USB",
". But not the adapter type. Radio waves - the general method of communication in space for basically everything (laser links are a very recent development).",
"By changing the amplitude or (better) the frequency of the radio waves you emit many times per second you can transmit information."
] |
[
"The carriers were neither amplitude nor (except TV) frequency modulated by the Apollo Unified S-Band transceivers. The vast majority of their communication utilized Phase Modulation."
] |
[
"Like those times Ensign Kim got caught in the transporter?"
] |
[
"In a theorized multiverse, how are \"universes\" separated from one other and can they influence each other?"
] |
[
false
] | null |
[
"Which 'multiverse' are you talking about?",
"One view of the multiverse is that the big bang was a point origin of our universe, but there may be other point origins far removed from ours. This is the ",
" multiverse. These universes are separated from each other by immense distances. They can never influence each other.",
"In the ",
" multiverse theory, the universe branches off every time a quantum effect settles on a random number. (Or possible only certain quantum effects.) This is where you find your parallel universes where anything that could have happened somewhere did happen. They are not really separated from each other; in this theory, all possibilities exist somewhere, but we humans are only able to follow and understand one of time's infinite threads. There may be faint interactions between these universes, and we can speculate that may lead to one possible universe being able to influence another.",
"The ",
" theory leads to a multiverse separated by distance in one of the ten dimensions of space-time, as described by certain quantum string theories. They do influence each other, sharing some gravitational wells and possibly other phenomena -- recently it's been speculated that dark matter is a brane interaction. But these other universes are alien and probably without the same physical laws, so it's not as if you'll see people living there.",
"And then there are theories where all these possibilities (as well as other multiverses, such as the holographic universe) are all true ",
". When the theory gets that complicated it's impossible to say what can and cannot interact.",
"tldr; We don't know whether there is a multiverse, or which of several theoretical multiverses may actually exist. Some allow interaction between universes and some don't."
] |
[
"I can answer from a physics/mathematics perspective.",
"Our perspective is limited to 3 dimensional space. In a multiverse philosophy, there is basically a 4th spatial dimension. So imagine that all 3 of our dimensions were squashed flat into 2 dimensions. There would other universes above and below us that are literally parrellel, and at no point touch the plane of our universe.",
"In theory these universes could be inches apart. As for how they influence each other, high energy or density areas of the universe could have forces that act in the extra spatial dimension. Kind of like how a magnet can act on a metal without touching it. So things in our universe could effect a nearby parallel universe.",
"Edit: A different comment pointed out that this is the ",
" multiverse, and there are also other multiverse philosophies."
] |
[
"Like kburger said, there is no way to know since we would have no contact or perception of the extra dimension. If large forces were capable of acting in the extra dimension we could possibly notice physics abnormalities in our own universe. However, there is still so much that we don't understand about physics, so if we did see an abnormality, it would be more likely to be caused by something in our own universe that we do not understand.",
"Since there is no way to observe this hypothesis, it is more philosophy than science. All we can say at the moment is that it is not impossible."
] |
[
"Using two video cameras, getting two different angles of a flying object what could you prove?"
] |
[
false
] |
Given a flying object, of unknown size, speed and distance, being filmed by two stationary cameras, with a known distance between the cameras and hopefully known angles that the camera are set at what could you prove regarding the flying object? I dont really want to talk specifically about the case below, but more in a general fashion. Lets say I was out in Nevada at Area 51 (its just convenient for the description). Me and my buddy TinFoil have the exact same cameras (Red One) and we have set up on two different points of the same height etc and we have measured the angles of where our cameras are pointed. Out of nowhere something appears, we film, and it goes away. THen we sit down with our footage, we sync it up 100% good, and we start doing the math. What could we for sure prove about the object? Since the distance to the object, the objects size, and the objects speed are all unknown variables, and since the object is in the sky, during day time, making it more difficult to find an anchor point to fix it too. How much more could we prove with more cameras at different focal points. This question was fully inspired by this reddit post I read today [ ]
|
[
"With the angle and knowledge of the camera lenses and FoV we can determine the precise location of the object with triangulation. We can also determine the cross-section from both angles, and given some maneuvering of the craft, an accurate measure of its shape. Since we can determine its location we can also determine speed while it is in view of both cameras, but once we have its size we can calculate range and position (and thus speed) from a single camera if we assume it is of a fixed size."
] |
[
"Careful, though. Don't convince yourself your calculations are more precise than they are. From a theoretical standpoint, any two cameras at any two places (well, almost...) shooting the same object will give you this information. Thus, stereoscopic cameras placed inches apart would suffice. In the real world, the parallax would be impossibly small for a distant object, and thus your \"measurements\" would be meaningless.",
"It's also important to approach the problem rigorously; simply drawing lines on a video wouldn't suffice. The effects you have to account for (including things like focal length, lens shape, shutter speed, sensor effects, etc.) may well be important in an analysis like this.",
"If you ",
" do an analysis like this rigorously, you could wind up with errors on the order of 100%. Depending on your goals, this isn't necessarily a problem, but you should be aware that a poor analysis may be worse than worthless."
] |
[
"I would love to try and read up on the math behind it. \nAny links to suitable material?"
] |
[
"Does tire pressure change when they are in motion (rotational)?"
] |
[
false
] |
I know that there is only one point of the tire that touches the ground at once and it applies a static force to the ground forcing the vehicle forward, but does this force cause a compression (significant or insignificant) to the tire itself. If it does, how much? Thank you!
|
[
"The ",
"weight of the car will cause a miniscule pressure change in the tire",
" (as compared with an unmounted tire), but typical acceleration and velocity will not cause any further changes.",
"The force that moves the car forward is a result of torque at the axles. This torque is transmitted through the wheel and tire to the contact patch. Tires are extremely stiff in the rotational direction, so there won't be much deformation as torque is applied, and what deflection does occur will be a very slight \"twisting\" of the sidewalls such that the wheel will be slightly \"ahead\" of the outer surface of the tire. This deflection, however, won't have any significant change on the volume of the tire.",
"Edit: I assumed OP was not asking about effects as a result of the tires heating from rolling friction. This is obviously the dominant factor causing changes in tire pressures while driving."
] |
[
"Unless of course you're talking about a ",
"Top Fuel Dragster",
", but that's probably not what the op is asking."
] |
[
"Friction generating heat. Yes."
] |
[
"What would happen to the stiffness of a spring if you would cut it in to two equal pieces?"
] |
[
false
] | null |
[
"The spring constant of a spring is inversely proportional to the length. ",
"Look up “Hooke’s law” and you'll find a bunch of info."
] |
[
"For a bit more detail, the stiffness k can be calculated like so:",
"k = G d^4 / 8 D^3 N\n",
"where",
"k = spring stiffness",
"G = shear modulus of the material",
"d = diameter of wire",
"D = diameter of spring",
"N = number of turns",
"Source",
"Chopping the spring in half is basically like cutting the number of turns in half with all else being held constant."
] |
[
"If I am thinking about this right, this means the total force a spring exerts at a specific percentage length change doesn't depend on the number of turns, right? Since the absolute length change per relative length change is proportional to the number of turns, and the spring constant is inverse with the number of turns."
] |
[
"Is there any evidence linking the period of heavy nuclear testing (1940s to 1970s?) to increased rates of cancer, either locally, nationally, or globally?"
] |
[
false
] | null |
[
"Yup, Castle Bravo. Was supposed to be about 6 megatons, instead it was 15. The problem was that Lithium-7 (which makes up most natural Lithium) is basically inert at low to medium neutron energy levels, the sorts of neutron energies which come out of fission reactors, for example, and were used for studying the properties of isotopes at the time. But at high neutron energy levels, the sorts that come out of fusion reactions, Li-7 breeds Tritium quite readily. That means that instead of just the 40% of Lithium-6 in the enriched Lithium fusion fuel, almost 100% of the Lithium could participate in fusion reactions via Tritium production. This is only half the story though, because it boosted the fusion yield of the bomb from about 3 MT to 7.5 MT, but the bomb was surrounded by a U-238 jacket. U-238 can't be used to make bombs or reactors on its own because, just as with Li-7, it doesn't react much with neutrons that are in the energy range of fission reactions, so it can't participate in a fission chain reaction (the neutrons it produces aren't energetic enough to fission further U-238 atoms). But when bombarded with an external source of neutrons, especially high energy ones, it'll fission quite easily, which is an easy way to double the yield of thermonuclear weapons. So an additional 7.5 MT of fission reactions occurred, and an additional 7.5 MT of fission fallout spread across the contamination area.",
"In comparison, when the 100 MT Tsar Bomba was tested they used an inert jacket instead of U-238, so it had a yield of 50 MT, avoiding contaminating the Soviet countryside with 50 MT of fallout."
] |
[
"There arę, at least locally. After one of tests went wrong (castle bravo? Might be wrong but iirc that one. Had to do with additional fuel breeding during detonation, pushing the yield from expected few megatons to over 15mt) local population was subjected to fallout. That has caused very high cancer rates later."
] |
[
"It's been looked at in ",
"a couple of dozen studies",
", most focusing on high-risk areas like the Marshall Islands and the Semipalatinsk Nuclear Testing Site in Kazakstan but with a few looking more generally.",
"A number of studies found a slight increase in leukemias in the US:",
"The entire United States population exhibited an increasing leukemia rate during and for several years after the open air nuclear testing and fell sharply thereafter. Regional differences in leukemia rates correspond to a composite exposure index that used 90Sr concentrations in food, cow's milk, and human bone. The calculated leukemia risk per rad for children was similar to that calculated for Japanese A-bomb children survivors.",
"--",
"Association of nuclear fallout with leukemia in the United States.",
"A Scandinavian study found a smallish increase in thyroid cancer:",
"These results are compatible with an increased risk of thyroid cancer during childhood and adolescence for subjects exposed to radioactive fallout early in life. Alternative explanations for the pattern of incidence are discussed.",
"--",
"Incidence of thyroid cancer in Scandinavia following fallout from atomic bomb testing: an analysis of birth cohorts.",
"In the higher-exposure areas, the risk was greater:",
"A part of the Altai Territory of Russia has been subjected to radioactive contamination from nuclear testing. Cancer morbidity in neighboring areas has increased 15-27%",
"--",
"Oncology education and cancer prevention in a high-risk region of Russia.",
"Findings suggest that cancer is the second-leading cause of death in the RMI and is, in part, a consequence of 12 years of nuclear testing in this region of the Pacific.",
"--",
"Cancer in the Republic of the Marshall Islands.",
"Overall, there does seem to be a link, but the number of cancer cases due to testing, in most places, would be quite small -- a two-fold increase ",
" means only a handful of cases.",
"As a complicating factor, the 1940s to 1970s covers the period (in the US, and much of the Western world) during which smoking became very widespread, and of course this led to a huge increase in many forms of cancer, the effects of which are just recently starting to fade away."
] |
[
"How come Nuclear Pasta is the strongest material on the universe?"
] |
[
false
] | null |
[
"Yeah, they'd explode. They only exist because of the enormous pressure inside the star. Take them out and they decompress and produce regular nuclei like you find on earth."
] |
[
"Basically, it's because nuclear pasta is so dense. Nuclear pasta is nearly as dense as atomic nuclei- in a neutron star matter reaches densities a hundred trillion times anything on earth.",
"This results in really extreme properties. Denser things will general be stiffer (which is what's meant by \"strongest\" here, having large elastic moduli and breaking strains), so long as they aren't totally fluid. So unless neutron star cores contain some exotic phase of solid matter we can guess that nuclear pasta is probably the densest sort of material in the universe. And also, for the sake of citing sources: ",
"link."
] |
[
"To be clear, if you somehow could bring these materials to the earth, they probably wouldn't maintain their properties right? They would fall into lower energy states where they were less dense?"
] |
[
"What is the largest known non-aquatic arthropod?"
] |
[
false
] |
[deleted]
|
[
"The largest organisms",
": \"The coconut crab (Birgus latro), also a crustacean, is the largest land arthropod and the largest land invertebrate, up to 40 cm (1.3 ft) long and weighing up to 4 kg (8.8 lb) on average. Its legs may span 1 m (3 ft).\"",
" \"Was either the eurypterid (sea scorpion) Jaekelopterus or the Carboniferous millipede Arthropleura, which were both between 2.5 and 2.6 m (8.2–8.5 ft) in length and weigh 180 kg (400 lb). They were closely followed by Pterygotus, an aquatic eurypterid that was up to 2.3 m (7.5 ft) in length. The closest living relatives of Eurypterida are the arachnids, horseshoe crabs, and sea spiders\""
] |
[
"According to the internet, among currently living arthropods, it's the ",
"coconut crab",
". If we allow for extinct species, the largest known would be from the genus ",
", related to centipedes and milipedes.",
"Edit: and now I feel silly, posting 2 minutes after someone gave the same answers. We need to get some kind of auto-update on reddit."
] |
[
"haha I feel the same way!"
] |
[
"Why aren't gravitational batteries viable on large scale?"
] |
[
false
] |
[deleted]
|
[
"This is an excellent idea and is therefore already used in practice at many places. It is called pumped-storage hydroelectricity. Thereby, water is pumped up into a reservoir at higher elevation with electric pumps. If needed, the water is used to generate electric power using turbines. \nAs you can pump hundreds of tons of water hundreds of meters up, that is of course on a much bigger scale then any counterweight inside a powerplant can be.",
"On a much smaller scale, this form of energy storage is used for pendulum clocks or ",
"gravity lights",
"."
] |
[
"https://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity"
] |
[
"Just as a scale thing: the total installed \"battery\" capacity in TWh, of which the vast majority is PSH, along with the maximum power generation from PSH, is about 0.8% of world annual energy consumption/average power generation. ",
"We don't have a good way to store energy on a large scale. PSH is the best we have, and even PSH isn't very good because of the weakness of gravity."
] |
[
"Why do microwaves damage circuitry?"
] |
[
false
] | null |
[
"Microwaves, or any light for that matter, are oscillating EM fields. In the case of MW its on the same size order of most of these objects so the fields couple very well.",
"These fields then induce a current which then proceeds to short or melt various parts of circuits."
] |
[
"The metal inside your electronics acts as an antenna for the microwaves - the induced current (which is probably on the order of hundreds of watts) shorts and melts various parts of the circuitry."
] |
[
"Came here to say this... But then I started to explain how dielectric heating works, got confused, and had to lay down for a few hours. You left it where you should have."
] |
[
"Do females and males have different amounts of rods and cones in their eyes?"
] |
[
false
] |
Do females and males have different amounts of rods and cones in their eyes? I have heard it as a back up to a theory that women and men see colour differently, but I don't remember there being any differences in anatomy from biology class.
|
[
"There is an important gender effect on cones - the L/M wavelength cones use a photopigment that relies on genes located on the X chromosome. when that gene is defective, you generally have red-green colorblindness. since women have two X chromosome, they are far less likely to be r-g colorblind, since they'd need to have inherited 2 defective copies of the gene (only ~2% of X chromosomes in human circulation carry the defect).",
"a further thing on this phenomenon - the L/M pigment genes can be defective in several different ways. usually the defect results in undifferentiated pigments in the L/M cones (colorblindness), but sometimes it results in a ",
" that is sensitive to wavelengths a little different from the normal L/M sensitivities.",
"when this happens in a man, he is merely 'color anomalous', meaning he has trichromatic (Red-Green-Blue) color vision, but just a little different from normal. but in a woman, it's possible to get ",
" color vision, meaning there is effectively a fourth type of cone in some human female retinas. this phenomenon was only discovered very recently and I don't think it's thought to really have very significant perceptual consequences, but it's not inconsequential.",
"summing up: most men and women probably have similar forms of trichromatic color vision. ~1-2% of men are r-g colorblind, and far fewer women (.01%) are, because of the sex-linked L/M pigment. some women might be tetrachromats, but it's not clear how this really affects how they see colors. So, we mostly see colors the same way, but there's lots of room and reason for differences on a gender basis."
] |
[
"The genes for color blindness are on the X chromosome, not the Y. People with XX chromosomes (females) almost always have another gene to correct this. People with XY chromosomes (males) do not have an extra X chromosome to correct the color blind genes on the Y, so they end up color blind. The genes for hemophilia act similarly: they're carried by mothers and the traits appear in their sons.",
"Females who are color blind will always have a father who is color blind and a mother who is either a carrier or color blind herself."
] |
[
"Not sure about the cones thing, but men have a higher chance of being color blind because certain types of color blindness are sex-linked recessive on the Y chromosome. Most bio females (there are some rare exceptions such as Swyer Syndrome) dont have a Y chromosome so they cannot possibly express the gene for color blindness. However, they can still be a carrier of the trait and pass it to their male children. "
] |
[
"Since space isn't a complete vacuum does light ever actually travel at the speed of light?"
] |
[
false
] | null |
[
"No, but it travels close. Due to free electrons in the interstellar medium, light waves undergo ",
"dispersion",
". Dispersion is the same optical effect that you see when white light goes through a prism and splits into different colors of the rainbow. In practice, dispersion only affects radio waves measurably but it does affect all light. The time delay is proportional to the density of electrons along the entire path the waves travel, given by the ",
" (DM) quantity, and inversely proportional to the frequency of light squared. So, the higher the frequency is, the less of a delay, which is why this doesn't practically impact frequencies above radio light. ",
"So, if there was a vacuum, then DM = 0 and so you'd get some extra delay = 0, that is, the light is just moving at c. But, since space is not a perfect vacuum, then there is some extra delay and it moves at a speed slightly less than c. This is a bit backwards though since the dispersive delay is ",
" from the fact that the group velocity of the waves is less than the speed of light given a frequency-dependent index of refraction."
] |
[
"Good question. Yep, it'll speed back up, just like if you have optical light going through a bunch of prisms with different refractive indices and it goes from one to another with the right properties. You can also think about this in terms of the DM being the integral of the electron density along the path. So, you can consider the time delays through segments of length L but with different DMs, then the time delay equation applies to each and you can probably convince yourself that the time is shorter through segments of the same length L but with lower DM (so lower electron density).",
"When I give talks, I always make sure to say that redder light (longer wavelength) is \"delayed more\" than bluer light (shorter wavelength) rather than saying that bluer light \"moves faster.\" Because while that's technically true, I worry that it gives the impression that bluer light somehow speeds up compared to the case where there would be no medium, which can't be true since you can't go faster than c, rather than in the case you're specifying. Again, nothing wrong with what you're saying since the bluer light will move faster than the redder light, and more so when it goes through a lower DM, I always just worry about giving the wrong ideas!"
] |
[
"Would photons 'speed up' when moving from an area with a certain DM to an area with a lower DM? Or would they retain the same speed, but it would be comparatively lower to the c number for the current, lower, DM?"
] |
[
"Do the lattice constants of NaCl and KCl change when water is added, if so do these changes remain when the water is removed or do the lattice constants return to their original lengths?"
] |
[
false
] |
[deleted]
|
[
"Do you mean when you dissolve them in water? ",
"When a salt dissoves in water, the Na is attracted to the negative oxygen while Cl is attracted to the hydrogen in turn splitting the salt into Na+ and Cl-. Because of this the salt no longer has a crystalline structure so it doesn't have lattice constant.",
"edit Oxygen has a partial negative charge."
] |
[
"The water would pull apart as many NaCl molecules as it can. The lattice would remain unchanged. It will either exist in crystalline form or as a solution."
] |
[
"The water would pull apart as many NaCl molecules as it can. The lattice would remain unchanged. It will either exist in crystalline form or as a solution."
] |
[
"Would a biological radio be possible?"
] |
[
false
] |
I thought about the amazing senses we have and wondered if it would be possible for a sufficiently advanced race to communicate telepathically via radio waves, also i'm going to split this into two parts for ease of understanding. Is it possible to have a biological radio transmitter/reciever I.E a radio organ at all? If possible would a average size mammal be able to produce enough power to transmit over meaningful distances, say 10-100 meters. In essence, if both of these are true, telepathic communication would be possible right?
|
[
"Well, it surely wouldn't be impossible. There are animals featuring ",
"electric organs",
". Also, it seems that some of them can already communicate modulating weak electric fields (",
"see here",
" for example), which is probably the closes thing we have to radiocommunicating animals. To do that long-distance and well modulated like radio would probably require a lot of evolutive jumps that I can't honestly fathom now, however. If someone with experience on radio technology can tell us what are the essential requirements for a radio, we can begin to wildy speculate :)"
] |
[
"Considering how simple a ",
"crystal radio",
" receiver is, it doesn't seem too implausible that somehow there could be a \"receiving\" organ, even if it were very inefficient (but maybe still effective for short distances). Just need an organic diode, mainly, and maybe something in the brain to interpret the result as sound. ",
"Disclaimer: I am not a scientist, but am a licensed amateur radio operator (which totally qualifies me to talk about biology and anatomy, of course...)"
] |
[
"This seems implausible, magnetic field drop-off rates would mean unless one organisms sensing organ was directly adjacent to the other organisms transmitting organ, it would be phenomenally difficult to get a useful signal. Additionally, this totally glosses over the difficulty of organically building such a powerful magnet. The organism would need to either ingest magnetic material and assemble little magnetic bits at the nanometer level or be able to make powerful electrical currents. If it can already produce powerful electric currents, it seems more feasible that it would power a transmitter of some sort. "
] |
[
"Are there any residential scale carbon capture technologies available?"
] |
[
false
] |
I’m considering adding an non-grid tie solar system to my home. As solar is somewhat variable in energy production the system would need to be sized for poor production times of year/days. Are there any electrically based carbon capture technologies that could be run with excess electricity production? I’ve seen some diy solutions but by the time I’ve purchased and had shipped the needed chemicals then disposed of them I’ll have spent all the carbon I would have captured.
|
[
"If you want to personally remove some carbon from the air, grow corn, sorghum, or some other C4 crop, make charcoal from the inedible parts, and bury the charcoal in your garden. Charcoal degrades very slowly in the soil, so the carbon it contains will stay out of the air for a long time, and the internal surface area of charcoal particles in soil is good for plants. ",
"If you want a use for your electricity that benefits the world, run your air conditioner or heater extra hard when you have extra electricity so that you don't have to spend grid energy on climate control at night, or run a computer and donate the computing power to folding@home."
] |
[
"To literally sequester carbon, the suggestions you've gotten about trees and biochar are good options. As far as beneficial uses for excess electricity towards reducing climate change, assuming the grid in your region still uses fossil fuels, one of the best things you can do is connect to the grid and send your excess back into the grid to displace that fossil-fuel use."
] |
[
"Biochar",
" might be one practical DIY method of carbon capture and storage. ",
"But take a step back and consider the objective - to reduce climate change. Perhaps you would achieve a larger reduction by helping other people install solar systems if you are becoming skilled at this activity. ",
"You can store excess solar as thermal energy - hot or cold depending on your climate - for example ice for AC, or a domestic hot water tank."
] |
[
"What is the speed of time?"
] |
[
false
] | null |
[
"1 second per second."
] |
[
"Speed is a measurement relative to time. ",
"You can't measure something with relativity to itself. "
] |
[
"Can you clarify/expand on the question?"
] |
[
"Could a brown dwarf sustain a life-bearing planet/moon and if so what would be the goldilocks zone?"
] |
[
false
] |
I'm curious about Arthur C. Clarke's idea of Jupiter becoming a brown dwarf and it's Galilean moons becoming habitable (I think this was from the novel 2010?). I wondered how realistic that was, or if they would be too close. Also for bonus points: what do we call a body that orbits a brown dwarf - is it a planet or a moon?
|
[
"The problem with brown dwarfs is that, unlike stars, they don't provide a constant source of light, but rather one that diminishes greatly over time.",
"When first formed, a brown dwarf is pretty hot and easily rivals the brightness of a small star. However, it quickly burns through its deuterium reserves (and potentially lithium), but isn't massive enough to fuse regular hydrogen...at which point it begins cooling for the rest of its life.",
"So, for the first ten million years a brown dwarf might have a temperature close to 3000 K, and a reasonable habitable zone to go with that. However, by the time it reaches 1 billion years old, that temperature has dropped to somewhere around 1500 K, pulling the habitable zone inwards by a factor of 4x. ",
"Planets that were once reasonable candidates to harbor liquid water and maybe even life will become frozen, permanently icy worlds. Bear in mind that we think life took a few hundred million years to get started here on Earth, so you might be able to get a few microbes before they get encased in ice. At the opposite extreme, planets just entering the habitable zone around this time will have been baked for most of their early life; by the time they're finally reaching a temperature that liquid water could exist, most of it would have already evaporated away into space.",
"Depending on the mass of the brown dwarf, by the time it reaches the age of our Sun, it might not even have a habitable zone. For example, ",
"WISE 0855−0714",
" (which is also one of the closest objects in our stellar neighborhood, less than twice the distance to Alpha Centauri) has a temperature colder than Earth - it's literally incapable of maintaining a habitable zone.",
": Brown dwarfs spend most of their lives cooling, meaning the habitable zone around them is constantly shrinking until it just disappears entirely. That's not a good candidate in the search for life."
] |
[
"Most likely a dwarf planet",
"The planet / dwarf planet distinction is based on whether the object has cleared its orbit, not what kind of star it orbits."
] |
[
"I don't know, I haven't read the book OP mentioned. Presumably a hyper-advanced spacefairing civilization dragged a bunch of hydrogen in from nearby stars or something like that. "
] |
[
"Can we pull a reflected image off a \"nonreflective\" surface?"
] |
[
false
] |
Can we pull a reflected image off a "nonreflective" surface? Reflectiveness is relative. A dirty mirror could be called reflective. A cracked or distorted mirror too. But how about white sheet of paper? Or a rock? It may not be an image that our eye or mind can appreciate, but maybe we could run the reflected light through a noise filtering algorithm. So I guess the real question is, how good are our reflected light image extraction algorithms? What's the limit on extractability?
|
[
"Yes, if you're willing to use a specialized time of flight camera and pulsed light source.",
"Here's a ",
"cute short video that explains and demonstrates",
". You can see the latest work from those researchers on ",
"their webpage",
"."
] |
[
"there was no technical explanation of this, so i'm going to think out loud here -- i'd be interested to hear your ideas about this!",
"this is surprisingly similar to the process of creating a hologram, except in this case the recording medium might instead be a scanning photodiode of some kind.",
"from what i understand from watching the video, they are firing a pulsed laser beam which is expanded by some optics. it would be pulsed to eliminate movement as a possible variable, and possible to increase the SNR from the photodiodes perspective. the laser would likely be operating in a single longitudinal mode (single wavelength), as this makes the task of recovering the backscattered image much easier.",
"essentially first they fire the laser with no figurine and record this as the reference. then they put the figurine in place and record the backscattered laser light from that.",
"because the nature of the laser beam is so stable and predictable, it is possible to quite accurately work backwards from the backscattered light and build a recognisable image of the subject."
] |
[
"If you can run a calibration of a known point source of light on the surface you want to image from, you can do optical signal processing on the new reflection. For instance, as far back as the 1960's they could recover a clear image from a camera that was set out of focus. This was primarily developed by the military. You don't want to have to refly over enemy territory because some technician mis-set the camera on a reconnaissance aircraft.",
"https://www.raymond.cc/blog/how-to-correct-or-fix-blur-and-out-of-focus-photos/"
] |
[
"How small can a radio receiver get?"
] |
[
false
] |
In addition, does the size of the receiver have any bearing on the number of frequencies it can distinguish?
|
[
"In terms of the antenna that must be within 1/4-1/2 of the wavelength of light in order to efficiently receive/emit.",
"That being said there are fractal antennas that fold upon themselves to create a long length in a short space, as well as short lengths for multi frequency reception."
] |
[
"Must it be 1/4 or 1/2?",
"Can it be multiples of these ratios, i.e., 1/8, 1/16 of wavelength?"
] |
[
"usually its a value between 1/4 and 1/2 of the wavelength. Those are just the values that allow the electric field to couple efficiently to the antenna. Smaller and the light wont couple at all, larger and the light will couple in multiple places and create interference. "
] |
[
"How long after the Big Bang did the first supernovas happen?"
] |
[
false
] |
[deleted]
|
[
"Don't forget, in astronomical terms, millions of years later ",
" \"shortly\" :) The first stars are thought to have formed roughly 100 millon years after the Big Bang. These would most likely have been incredibly massive, a few hundred times or even a thousand times more massive than the Sun. Stars this massive can't form today, because the clouds that form stars are filled with heavy elements that quickly cool the gas as it collapses. But these heavy elements were created by stars, so the first stars had no such impediment.",
"The more massive a star is, the shorter its lifespan - a dim red star, less massive than the Sun, will have a lifetime longer than the present age of the Universe, lifespans of tens of billions of years or longer, while these extremely massive first stars would have only been able to survive for a few million years. So the answer to both of your questions is yes - the first supernovae happened very shortly after the first stars formed, only a few million years later :)"
] |
[
"Right. Keep in mind this only applies on dim red stars, not read stars in general. Any red dwarf that has ever formed is still in existance, except the ones, which were involved in few star collisions. No red dwarf has died by age so far. "
] |
[
"The more massive a star is, the shorter its lifespan - a dim red star, less massive than the Sun, will have a lifetime longer than the present age of the Universe",
"Does this mean there are no dim red stars that have \"died\" yet?"
] |
[
"Question about the future of human evolution"
] |
[
false
] |
[deleted]
|
[
"For speciation to occur, two populations of a single species must be physically separated for a very long time. This is not likely to occur in humans."
] |
[
"I'm not really sure I understand the question. Are you asking me why I don't think humans will fragment into separate, non-interbreeding populations?"
] |
[
"I'm not really sure I understand the question. Are you asking me why I don't think humans will fragment into separate, non-interbreeding populations?"
] |
[
"What actually is the dial up internet noise?"
] |
[
false
] |
What actually is the dial up internet noise that’s instantly recognisable? There’s a couple of noises that sound like key presses but there are a number of others that have no comparatives. What is it? Edit: thanks so much for the gold.
|
[
"Everything you need to know about the acoustic modem handshake can be found here on this map: ",
"https://oona.windytan.com/posters/dialup-final.png",
"Then you can listen to the actual handshake and follow along:\n",
"https://www.youtube.com/watch?v=abapFJN6glo",
"Yes, this is what network engineers still do with packet sniffers and other protocol analyzers on various types of layer 2 networks like ethernet, PPP, MPLS.. etc."
] |
[
"Sometimes I miss that sound. For years it meant I was about to talk to or play games with good friends."
] |
[
"That first image you linked is amazing. Thank you."
] |
[
"Do larger animals have a bigger chance to get cancer?"
] |
[
false
] |
Larger animals have more cells, and since cancer is a defect cell, more cells should mean a higher chance at cancer, right?
|
[
"In general, larger animals are not more prone to getting cancer, and this is known as ",
"Peto's Paradox",
", after Richard Peto:",
"These may be nicely illustrated by a comparison of mice and men: A man has 1000 times as many cells as a mouse (although the ratio of our epithelial stem-cell numbers is not known), and we usually live at least 30 times as long as mice. Exposure of two similar organisms to risk of carcinoma, one for 30 times as long as the other, would give perhaps 30",
" or 30",
" (i.e., a million or a billion) times the risk of carcinoma induction per epithelial cell. However, it seems that, in the wild, the probabilities of carcinoma induction in mice and in men are not vastly different. Are our stem cells really, then, a billion or a trillion times more \"cancerproof\" than murine stem cells? This is biologically pretty implausible; if human DNA is no more resistant to mutagenesis in vitro than mouse DNA, why don't we all die of multiple carcinomas at an early age? Presumably some concomitant of our evolved ability to grow big and to live for threescore years and ten is involved.",
"--",
"Richard Peto. Epidemiology, multistage models, and short-term mutagenicity tests",
" ",
"Peto's Paradox has been ",
"discussed widely",
". One summary of the various arguments is ",
"Peto’s Paradox: how has evolution solved the problem of cancer prevention?",
". ",
"There are likely many solutions to Peto’s Paradox in nature, because large body size has evolved independently so many times across the history of life. We know that whales did not evolve the extra copies of TP53 like elephants [8, 9]. In fact, there is no evidence that whales evolved extra copies of any tumor suppressor gene—even the gigantic bowhead whale (Balaena mysticetus), which has a lifespan of over 200 years [9]. ... Since many lineages faced the trade-off between large body size and cancer risk during their evolution, there have likely been many different pathways in which cancer suppression has evolved."
] |
[
"No. Elephants for example are massive but have more oncogenes and cancer suppressor genes do they are less prone but a large margin. Similarly many sharks don’t get cancer as well bc of suppression genes as well"
] |
[
"Sharks ",
"do get cancer",
" and that myth has to do die."
] |
[
"Knowing that we are all stardust is there a way to find out from how many is, approximately, each person made?"
] |
[
false
] | null |
[
"I think on average, each human is made from roughly 75 kg of stardust. Depends on the weight of the person.",
"No, honestly, how do you define stardust? We do probably consist entirely out of stardust (depending on your definition).",
"You could say that stardust is everything that once was in a star. That means that every element except hydrogen is surely stardust. The fraction of hydrogen that has not yet been in a star is probably also very low. A very rough estimate then says that you consist to at least 80% out of stardust (probably much closer to 100%, but I am no astronomer)."
] |
[
"But how many stars? How many stars exploded resulting in the cloud of dust that our solar system aggregated from? Can that be measured?"
] |
[
"Sorry, I had misread your question. For this I can not really give an answer. Most of your atoms will probably come from a single star, but of course you will have some that are from completely different ones. How the ratio between those two is would depend on how far out a supernova distributes the atoms of its star on average."
] |
[
"Why at airports can they complete the detection for drugs quickly and accurately, and yet medical results and such can take weeks for results?"
] |
[
false
] | null |
[
"For scanners that you walk through, they search for an isotope of nitrogen (for example) because many explosives contain a lot of it, and if the particular isotope is out of balance with what should be present, it's a good bet a follow up is warranted. Certain nuclides can be detected easily because even tiny amounts will produce gamma radiation with certain energies that can be simply tested (Assuming decay of the nuclide produces gamma radiation, obviously)",
"If you get randomly selected to get your hands wiped, that is a form of mass spectrometry. MS is not a long process, but it is destructive and can't be done in the body.",
"Also as mentioned in prior responses, airport tests are usually concerned with binary existence and not with concentrations. Concentrations are hugely important in health determinations."
] |
[
"At airports, they often use Biosensors and other sender's that detect drugs and explosives based off of their residue. ",
"They usually use ion mobility chromatography coupled with MS to detect different substances. ",
"it's described here",
" and the machines where they put in the fabric they used to wipe off your hands works the same way."
] |
[
"At airports, they often use Biosensors and other sender's that detect drugs and explosives based off of their residue. ",
"They usually use ion mobility chromatography coupled with MS to detect different substances. ",
"it's described here",
" and the machines where they put in the fabric they used to wipe off your hands works the same way."
] |
[
"What is the trade-off that requires astronauts to be able to withstand several Gs during launch?"
] |
[
false
] |
I know about escape velocity, but in my mind it doesn't help much in knowing about the acceleration during launch, especially why the acceleration couldn't be made less. As a side question, how much as far as Gs during launch does it matter if we are headed to LEO or headed to the moon or beyond?
|
[
"It's a matter of efficiency. Consider the following thought experiment: What if you have a rocket that can just barely accelerate under gravity (it provides enough thrust to fight gravity, and just a little more)? After 10 seconds, it has only picked up a few m/s of velocity, but it has spent 10 seconds worth of fuel fighting gravity. By the time you reach orbital velocity (or escape velocity, or whatever velocity you want), you will have to have spent a great deal of fuel just resisting gravity.",
"Now consider a high-g acceleration rocket. If it accelerates at 4G, then 1G goes to countering gravity and 3G goes to increasing velocity. It needs less time to reach the desired velocity, so it doesn't have to fight gravity for as long (once you are in orbit, you don't need to fight gravity any more).",
"A high acceleration rocket is much more efficient for liftoff. Once you're in orbit, it doesn't matter as much (for reasons I'll skip for the time being), so there are other factors that determine efficiency in orbit. But for liftoff, higher accelerations are more efficient (until you reach the point where atmospheric friction becomes significant, but that's another problem), regardless of final destination."
] |
[
"If you want a great intuitive understanding of the tradeoffs, download ",
"Kerbal Space Program",
" and try to reach orbit with the least fuel possible.",
"The basic answer to your question about tradeoffs though is: if acceleration is too low, you'll spend most of your fuel essentially hovering in place; if your acceleration is too high, then you'll spend most of your fuel fighting air resistance.",
"To get a bit more technical, as soon as your rocket has left the ground, it ",
" to spend 1g of thrust just opposing earth's gravity. Any additional thrust will either fight air resistance, or accelerate the rocket. Ignoring acceleration for a moment (we will add it back in later) - suppose you just want to find the most efficient way for your rocket to ascend at constant gravity (1g) and constant atmospheric pressure - there will be some ideal speed of ascent, with a corresponding ideal rocket thrust to maintain this constant speed. What are the ideal speed and thrust?",
"Remember, that at constant speed, the rocket is not accelerating, so thrust is going only two places: 1g of thrust opposes gravity, and some amount of thrust will be opposing air resistance (to keep the rocket at constant speed), and our task is to find the best balance of these. There is a deep principle of optimization that when you are trying to optimize the sum of two things, try making them equal (this is a very general principle, and worth keeping in mind; you can justify it with calculus; it works far more widely than you would suspect) - so thus we might guess that the most efficient rocket ascent has 1g of thrust opposing gravity, and 1g of thrust opposing air resistance. This is thus an answer to your question: if the atmosphere were uniform (instead of pressure decreasing with altitude), then you should set the engine to 2g of thrust, and inside the rocket, you would feel 2g of force under the most fuel-efficient ascent. (As a side note, what velocity will your rocket be going at? The same velocity that air resistance would let your rocket ",
", if 1g of gravity were pulling it down, with no engines. Thus, the optimal ascent velocity ",
" terminal velocity if you just dropped the rocket. This is a surprising fact about rockets.)",
"Now to add back in the fact that the atmosphere gets thinner: as you get higher in the atmosphere, the most fuel-efficient ascent velocity will increase (namely, the terminal velocity if you dropped the rocket in thinner atmosphere would be higher). Thus the rocket, in addition to spending 1g of thrust opposing gravity and 1g of thrust opposing air resistance, should also spend additional thrust accelerating. (The rocket, of course, also starts stationary on the ground, so at launch it would ideally accelerate up to terminal velocity as quickly as possible to save fuel, with very high acceleration.)",
"In short, the most fuel-efficient ascent requires thrust somewhere above 2g, with the specifics depending on the aerodynamics of the rocket. Even with all this attention to efficiency, modern rockets still can only get about 1/40th of their launch weight into low-earth orbit. Namely, if you have a million pound rocket, maybe it can launch 25,000 pounds to orbit. This huge ratio hints that space travel is still barely at the edge of the impossible, and is why efficiency is so important - if you're buying a million pounds of rocket, you want to get as much cargo into orbit for your money as possible.",
"One other point: rocket engines are quirky like car engines. If you floor the pedal in your car, you won't get an even acceleration. Thus even if the \"mathematically ideal\" rocket thrust is some certain number like 2.2g, physical limitations on how rocket engines are built may mean that the actual thrust in flight varies from 1.5g to 3.5g, and thus the higher limit of these fluctuations, maybe 3.5g, is what the astronauts (and cargo) must withstand to reach orbit."
] |
[
"Rockets launch straight up and slowly turn over until they are parallel to the ground. Most of the fuel is used while the rocket is parallel to the ground so it can build up enough speed to reach orbital velocity.",
"A low thrust rocket would need to hover the entire way into space so it doesn't fall back to earth.",
"A high thrust rocket can get enough speed earlier so it has time to reach orbital velocity before falling back to earth. This ends up using less fuel because once orbital velocity is reached the rocket doesn't need to fight gravity and high thrust rockets reach that much faster."
] |
[
"Does the brain have or require a human equivalent of RAM?"
] |
[
false
] |
[deleted]
|
[
"Computing analogies are often dangerous when applied to the brain. The RAM/Hard drive one is particularly bad.",
"You see, one of the better ways to actually make a computational analogy is to remove the hard drive from the computer altogether. If we take a very simple computer, where RAM directly interacts with the CPU (i.e. no Cache), then we have something much more akin to the brain. I.e. the storage and the computation upon the storage stop really being separate things, that is, a Digital 1 or 0 is as much a stored state as it is an input to a transistor. In the same way, the activity of a brain cell is as much an representation of historical activity as it is input to the next cells in the circuit. Similarly, the activity of a CPU is dictated in equally important fashion both by the state of the RAM (which bits are high and low) as the pattern in which the transistors are connected. Likewise, the activity of the brain is dictated both by which neurons are activity, and how they are wired up.",
"Now, I appreciate this probably isn't the answer you were looking for. So more along those lines: there is no doubt that there is short term memory storage in the brain. But saying it is RAM, and long term memory is like a hard drive is not a particularly helpful analogy (or at least, it isn't given what we think we know about the brain). That is to say, there isn't much evidence that long term memory works by impinging it's activity pattern onto some short term storage system, which then interacts with a computational core. The computation core and the storage are one and the same in the brain!"
] |
[
"RAM is a particularly good analogy because if the brain loses power it tends to lose all its data :)"
] |
[
"Holy shit that was a great answer!"
] |
[
"What happens when an object enters Earth's atmosphere traveling faster than its terminal velocity?"
] |
[
false
] |
As a side question, what would happen if something enters another planets atmosphere, say, Jupiter, faster than it's relative terminal velocity?
|
[
"What happens when an object enters Earth's atmosphere traveling faster than its terminal velocity?",
"Drag slows it down toward its terminal velocity.",
"As a side question, what would happen if something enters another planets atmosphere, say, Jupiter, faster than it's relative terminal velocity?",
"Same thing, just with its terminal velocity on Jupiter."
] |
[
"Terminal velocity is the speed at which gravity and atmospheric friction cancel each other out. So if an object enters the atmosphere faster then terminal velocity, earths gravity will not be able to speed up the object enough to prevent the atmosphere from slowing it down. As a result, the object would lose speed - until it either disintegrates from the heat of atmospheric friction, surface impact ('though technically that makes its speed zero) or it's speed being equal to terminal velocity."
] |
[
"To add to the other answer, terminal velocity itself depends on altitude and projectile orientation. As altitude increases, air density decreases and terminal velocity increases, towards an extremely high value in outer space much faster than any natural object. Therefore any object that has come from outer space ",
" \"enter Earth's atmosphere\", something that is itself not sharply defined, faster than its terminal velocity.",
"Most objects hitting planetary atmospheres are not travelling straight down either. The Earth Impact Effects Program states the most common angle for meteor impacts as 45 degrees. Orbital spacecraft making a re-entry, either controlled or uncontrolled, typically enter at much shallower angles. On the other hand sounding rockets follow a trajectory that's appoximately straight up and down."
] |
[
"Does putting on sound-canceling headphones decrease the amount of noise my ears, or add it it?"
] |
[
false
] |
If I put in sound-canceling headphones, is it adding noise to my ears, like if I had 110 units of sound (forgive my lack of knowledge on the subject) and I put on sound cancelled, and I still taking in 110 units, just quieter? Interpreted quieter? Or is the music I then put on making it 170 or so? (again, it's just for understanding)
|
[
"The noise cancelling headphones detect the ambient sound and then emit the exact opposite of that waveform causing ",
"destructive interference",
"#Mechanism). This reduces the movement of the air in your ear and so decreases the noise, I hope that's the right question I've answered, it was a little confusing."
] |
[
"It reduces the intensity level (the noise would be 0 if it were perfectly opposite). You can't just add the intensity of the two waves, because they are out of phase."
] |
[
"Oh I understand that, I was wondering if that counter-noise adds to the total noise, hurting my ears, or cancel the noise and all potential damage it could do. Like if I stood next to a jet engine at, let's say 200 decibels, would the counter noise at 200 make the total 400 and potentially damage my ears, or do the opposite and make it 0?"
] |
[
"How do we know that dark matter interacts weakly with other matter. Isn't it possible that it doesn't interact at all?"
] |
[
false
] |
Isn't it possible that it only interacts gravitationally?
|
[
"Yes, it's absolutely possible. That's a terrifying prospect that people obviously avoid talking about, but it's there.",
"In most reasonable scenarios for dark matter and grand unification though, there's hardly any way of avoiding some very weak interaction with SM particles. A completely non-interacting DM is pretty hard to fit in most theories beyond the SM, so we stay hopeful."
] |
[
"If dark matter interacts only via gravity, it will be extremely difficult to learn more about it. For example we would have no hope of detecting or producing individual dark matter particles in the foreseeable future, because gravity is an extremely weak force."
] |
[
"Why is it terrifying?"
] |
[
"There are several \"health products\" becoming increasingly popular such as the ionic foot detoxer, water ionizer, nanosilver water, and ozone generators. Could these \"health products\" actually be harmful?"
] |
[
false
] |
The pamphlets that I have read for these products describe how they can make you healthy. For example, read the very scientific-sounding explanation of how the ionic foot detoxer works, I am obviously skeptical of the validity of their claims but I do not know enough (Chemistry, Biology, ect.) to understand why these products wouldn’t have the stated health benefits. Can anyone ELI5? Even more important, can these products be harmful to a person’s health?
|
[
"Yep for sure they have the potential to be harmful! There is tons of research that is going into this currently! Though right now I think they're working on the physiological effects of fish gills (and therefore certain ion pumps that are critical to our respiratory and circulatory functions similar in humans). ",
"If you want to look up some articles, I know that Dr. Greg Goss (from the University of Alberta) does a lot of collaborative work with other professors in the States to research toxicology of silver nanoparticles on physiology (i.e. zoology, cause at this stage they can really only test on model animals)."
] |
[
"this was a quick search and i didn't look into the sources too closely (it's late, i wanted to at least give you a starting point), so i cannot speak to their veracity, however the claims of most of these products are wholly unsubstantiated through research and as you suspect they may actually prove harmful rather than helpful. ",
"ionic foot detoxer",
", ",
"nanosilver toxicity",
", ",
"ozone toxicity",
". there are a ton of resources ",
"here",
" and ",
"here",
"; they go far beyond your inquiry but they hit plenty of similar topics and may stimulate more skepticism. i also highly suggest this ",
"podcast",
" if you've never listened to it. they delve into plenty of these \"alternative medicines\" and promote science-based medicine. and speaking of ",
"science-based medicine",
". i hope you'll find something helpful and enlightening somewhere in this post! :)",
"edit: this ",
"episode",
" specifically discusses colloidal silver supplements (from what i can tell nanosilver is the same, it's hard to tell sometimes with the different terms used by snake oil salespeople...)",
"edit2: i tried to link to articles with full-text available, but if you have trouble getting any and would like them, PM me"
] |
[
"I presume that \"nano-silver\" is a new, buzzwordy name for colloidal silver. Silver is a legitimate external antiseptic (for disinfecting wounds, for example), but internal use is dangerous quackery.",
"There are no proven benefits to ingesting colloidal silver, and in addition to having several risks, large doses eventually ",
"turns patients' skin blue-grey",
", which can be socially debilitating, not least because it slightly resembles death. Also, it is usually promoted as an alternative to antibiotics, despite being ineffective, putting users at risk from untreated infections.",
"Fascinatingly, while there are many possible complications from silver consumption, it is possible to turn completely grey without side-effects. ",
"More information on the man in Wikipedia's photo",
"."
] |
[
"Can therapy really cure mental illnesses or is it an outdated method?"
] |
[
false
] |
As I've understood, a lot of mental illnesses can be connected to an unbalanced production of neurotransmitters, e.g too much dopamine and too little serotonin leading to OCD. Can all mental illnesses be cured simply through drugs, either existing or potential? Are mental illnesses simply due to a chemical imbalance? Or is therapy a modern, effective and recognized approach to these disorders?
|
[
"Many mental illnesses are indeed caused by physical differences in the brains of the sufferers from the baseline population. However, at the moment, our knowledge of the mechanics of the brain is not so great that we can simply fix that; the many interlocking systems mean that adjusting one part will quite often lead to other parts becoming unstable.",
"In these cases, what therapy does is allow people to work around their illness and develop routines and techniques that allow them to function close to normal. It is unlikely to fix many more severe mental illnesses on its own in the sense that most people would understand as curing the illness, but often that is less important than allowing people to simply act normally.",
"There are also illnesses that are much less due to unusual brain chemistry or structure, such as phobias. Therapy is generally much better at treating these than medication, because they are part of a normal and healthy human mental function (in this case, fear) simply taken to an extreme in one case. Rather than just knocking out the entire system with medication, it is easier to use therapy to just target the problem areas.",
"If I am allowed to guess, I would say that this question arises from a misunderstanding of what therapy is in modern psychology. One of the most common forms of therapy (Cognitive behavioral therapy) is focused less on understanding the root causes of the illness, as the stereotypical 'tell me about your mother...' therapy is, but about simply learning to control the aberrant thought patterns. CBT is used for (and I'm going to take the liberty of quoting wikipedia because this passage makes a nice point):",
"CBT has been applied in both clinical and non-clinical environments to treat disorders such as personality conditions and behavioral problems. A systematic review of CBT in depression and anxiety disorders concluded that \"CBT delivered in primary care, especially including computer- or Internet-based self-help programs, is potentially more effective than usual care and could be delivered effectively by primary care therapists.\"",
"In adults, CBT has been shown to have a role in the treatment plans for anxiety disorders; depression; eating disorders; chronic low back pain; personality disorders; psychosis; schizophrenia; substance use disorders; in the adjustment, depression, and anxiety associated with fibromyalgia; and with post-spinal cord injuries. There is some evidence that CBT is superior in the long-term to benzodiazepines and the nonbenzodiazepines in the treatment and management of insomnia.",
"In children or adolescents, CBT is an effective part of treatment plans for anxiety disorders; body dysmorphic disorder; depression and suicidality; eating disorders and obesity; obsessive–compulsive disorder; and posttraumatic stress disorder; as well as tic disorders, trichotillomania, and other repetitive behavior disorders. - ",
"Wikipedia.org"
] |
[
"It is also not particularly productive to think of therapy as a \"cure\" in a medical sense, and at the same time, it is very helpful to consider that mental illness, while certainly a disease rooted in physiological causes, manifests in symptoms that alter the way that you see and understand yourself and the world. While medication for mental illness has come a long way, the bottom line is, drugs such as SSRIs, anxiolytics, and antipsychotics, are still \"drugs\" in the colloquial sense: they alter perception. ",
"What I'm trying to explain is that the purpose of psychotherapy in this day and age is not to cure the disease ",
", but to provide a secure and private interpersonal dynamic for a patient - a person who is beset by both his own haywire neurochemistry along with the artificial neurochemistry provided by his medication - to make sense of his experience, to gain some welcome perspective and professional sympathy, to help him grow as a person. ",
"Source: I am aspiring to become a therapist for patients of debilitating mental illness."
] |
[
"It should also be emphasized that therapy doesn't 'cure' mental illnesses. As Syreniac correctly pointed out, modern day therapy is about controlling or correcting bad behaviors. CBT came out of cognitive and behavioral therapies which used to be separate, they came together because they both were founded upon empirical studies and are proven effective. CBT usually only lasts a few months (~8 weeks). CBT is very useful and helps a great number of people every day.",
"On the flip side, you're asking about drugs. To say that mental illness is caused by a chemical imbalance is at best grossly simplified and at worst wrong. While most serious mental illnesses are a result of genetics (or are heavily influenced by individual genetics), their symptoms form in the brain. Nearly all drugs treating mental illness have been discovered by accident, the simple reality is that we don't understand enough about the causes of these diseases to actually create a drug that treats them.",
"For example, serotonin is often associated with depression because selective serotonin reuptake inhibitors (SSRI's) are used to treat depression. However, anti-depressants often also affect norepinephrine and sometimes even dopamine (tricyclic anti-depressants). Further, if depression was simply caused by to little serotonin, the symptoms would alleviate as soon as the SSRI's started to take effect (within hours) instead of the many weeks most anti-depressants take to actually work. Because of this, it is often believed that while SSRI's can treat depression, they do so in a round-about manner. And even still, there are individuals who respond to therapy but not pharmaceuticals, and those who benefit from receiving both.",
"Now, while CBT is heavily evidence based, other therapies are founded on less scientific grounds. Psychodynamic (Frued) therapy tends to lack evidence, however it's efficacy has been examined in a few populations. For anxiety disorders, CBT should always be used, and I would say it is more effective than drugs simply because of the side effects of anti-anxiety mediation, however in depression, Psychodynamic tends to be equally effective as CBT, or at least very close to it. On the other end, Schizophrenia is treated amazingly well with anti-psychotics, however the disease itself isn't 'curable' under current science.",
" So basically, therapy is still useful when it is the result of scientific inquiry and when paired with diseases that it can actually treat. We know very little about the chemistry of the mind and because of that struggle to develop drugs that even treat the symptoms of mental illness, much less cure it.",
"It's worth keeping in mind that therapists with a Ph.D. will have a stronger background in the science than those with a Psy.D. That's not to undermine Psy.D.'s but rather that those programs often place less emphasis on research.",
"Edit: Sorry this is a little long!"
] |
[
"Do planets in pictures of gaseous looking galaxies actually have gas in the space around them?"
] |
[
false
] | null |
[
"\"Gaseous-looking\" is kind of both right and wrong. They might look gaseous because galaxies have a LOT of stars. Interstellar space is quite empty, but most of the stars might blend together in the picture and make a bright fog. More clarity means you can see more stars in said fog.",
"On the other hand, interstellar space is not totally empty either. Just very close. So yes, there is gas, but no it doesn't make a huge difference in images."
] |
[
"Even the crowded parts of space are empty. The densest nebulae contain about ",
"10,000 molecules per cubic centimeter",
", which is a quadrillion times less dense than air at sea level. ",
"If you link to a picture then other Redditors and I can tell you what you're looking at in a bit more detail. In some images the whisps of what look like gas or smoke are just lots and lots of stars."
] |
[
"The planets don't, as per your question, but the spaces in between stars has a ",
" sizeable quantity. The planets mostly just have their own atmospheres and there is whatever intrastellar dust is around their parent stars...which isn't much, just like her, but it's enough to ",
" like a lot on a picture, especially a false color picture (say IR downscaled to visible)"
] |
[
"How can I identify a bird simply by its call?"
] |
[
false
] |
Every morning between one and two a.m I hear an amazing bird call, and I would love to find out what it is. I live in the southeastern United States, but I'm sure that doesn't help but so much if at all. I once heard on NPR that an app was being worked on similar to Soundhound to identify bird calls, however who knows when that will come out . I searched for an ornithological based /r/, but couldn't find one especially using my phone, so I figured this may be a good place to start.
|
[
"A quick google search gave me these:",
"-",
"eNature",
"-",
"Birding by ear",
"-",
"Guide to NAm birds and songs",
"-",
"iBird"
] |
[
"Record it and post the sound"
] |
[
"There is an iPhone app called \"Chirp!\" that has calls based on region. My daughter has been using it to learn the birds in our area, she's gotten pretty good."
] |
[
"Did Antarctica's land wildlife go extinct? Or did it evolve into the marine wildlife that lives there presently?"
] |
[
false
] |
Given that was temperate and presumably inhabited by land animals, and , where did all the animals go as Antarctica became colder/drier? Did they go entirely extinct, or are some of the pinnipeds/cetaceans/birds that live there now descended from antarctic animals? )
|
[
"Seals originated in or near the ",
"arctic",
" and cetacians originated in ",
"Pakistan",
", so they aren't from Antarctica at all. Penguins did ancestrally live in the southern hemisphere, however they were flightless and aquatic long before Antarctica got it's glaciers. See this early penguin from New Zealand, for example ",
"http://en.wikipedia.org/wiki/Waimanu",
"The stuff that used to live on Antarctica went extinct. It's a shame, there was probably an interesting batch of marsupials living there. We don't know much about them though, because of the difficulty of digging for fossils."
] |
[
"I think it wasn't so much that the speed exceeded their ability to adapt-rather, the endpoint was just too harsh for anything to survive. Not only is Antarctica incredibly cold year round, it's nearly devoid of plant life (2 flowering plant species, I think, and they only live in a few places around the edges) and covered in kilometer thick sheets of ice. There's just not much to live on. It's a crazy place."
] |
[
"Thank you! ",
"It's interesting to think that, at some point in Antarctica's history, the rate of climate change exceeded the animals' abilities to adapt. And not just for some of them, but ",
" of them. Especially considering how slow continental drift is.",
"It's too bad we can't easily search for fossils there, I'm sure the continent's bio-history would be quite fascinating."
] |
[
"Why do some countries (Japan, Norway, etc.) which have reasonably good economies have such low exchange rates with USD?"
] |
[
false
] |
Question is fairly self-explanatory. I guess I've always sort of interpreted a currency having a low exchange rate with the US as a sign of the country in question being economically weak, but I'm noticing that countries which seem reasonably prosperous, like Japan and Norway, also have this going on. For example: 1 Norwegian Krone: $0.04 1 Japanese Yen: $0.0098 I know the prices of things in these countries is often similar to the items' price in the US, once you convert (e.g. Japanese vending machine prices vary from 50 to 3000 yen according to Wikipedia, which is between about $0.49 and $29.40). Do some countries prefer to just have a single unit, rather then doing the dollars/cents thing? Is there some historical reason? Am I just horribly misinformed about these countries' economic state? Please enlighten me, this has been bugging me for awhile.
|
[
"You numbers are wrong. 1 krone is 0.16 US$. ",
"Until 1933 i US1$ equaled 1.5 grams gold. Norway had 1 krone equaled 0.4 gram gold until 1931. So at that time the rate was 1 krone was 0,26 US$. Since that time, deflation, inflation, differences in real trade and financial trade and differences in interest rate levels have moved each currency up and down. Norway has been seen as a European safe haven when there is probelms with the Euro, and German investors love to put their money here. It moves the currency up; that hinders export, and the Norwegian central bank try to press it down. And on and on it goes. Currencies never started 1=1, and there are no right level. A currency is hard if it has been moving upward for a long time. But it may still be 0,00XY something. Some countries have no cent. Norway have øre, but there no longer exist any physical coins, so if paying in cash, you will get to closest krone. ",
"Do no mix the currency and the price level of some single consumer good. Local prices may be higher or lower than in the US, but that is a completely different discussion."
] |
[
"It doesn't matter what their exchange rate is with the dollar, ultimately. If I have a \"dollar\" coin, or a 100-yen coin, or a 10",
" space bucks coin, but they all buy me the same thing, the difference doesn't much matter. I mean, the difference is kind of obvious with the Yen and dollar. Replace \"Yen\" with \"Cents\" (a fractional currency we need, since a dollar is too course grained for pricing) and things are fairly even-parity.",
"What matters more is how they trade over time. If I can get 1.5 yen on the penny now, and then a penny for a yen later, I buy up yen now, and trade them in for pennies later. "
] |
[
"You numbers are wrong. 1 krone is 0.16 US$. ",
"Actually, my numbers were correct as of last night. It appears that there was some kind of weird spike sometime last night.",
"Thank you for the explanation, though."
] |
[
"Can someone explain Quarks in a simple manner?"
] |
[
false
] |
I've been curious about the subject, but any time I try to look up the page on Wikipedia, I always get too confused by the terminology. So since I'm such a slow person, I'd like a simpler explanation as to what Quarks are, and what they actually do.
|
[
"Quarks are (as far as we can tell) fundamental constituents of matter, so they are not themselves made of something else. They possess mass, electric charge",
" (±1/3 or ±2/3) and what we call \"color\" charge of green, red, blue. Or if they are antiquarks they can have, antigreen, antired, and antiblue.",
"While the forces between the electric charges are mediated by the electromagnetic field (via photons or light), the color force is mediated by the gluon field. The gluons of the gluon field are massless like light, but carry one color and one anticolor.",
"Quarks can form combinations of color which make the overall particle \"colorless.\" This is due to a process called confinement where color forces ",
" with distance which prevents free quarks from existing. There are two main types of quark combinations (though others exist): ",
"Mesons: Quark—antiquark pairs with a color and anticolor or some superposition of such combinations.",
"Baryons: Three quarks or three antiquarks each with a different color. This is what protons and neutrons are. Adjacent neutrons and protons still feel \"residual\" color force which allows them to bind together forming atomic nuclei, the process can by approximated by this animation:",
"\n",
"https://upload.wikimedia.org/wikipedia/commons/3/35/Nuclear_Force_anim_smaller.gif",
"This is a lot to take in, so if you need some words defined, feel free to ask.",
" More technically we can talk about weak hypercharge which is how the quark's interaction with both electrical forces and weak forces can be united in electroweak theory.",
" We've ignored their spin which is 1/2 making them fermions. Fermions have half-integer spins and Bosons have integer spins. They behave very differently, for instance fermions cannot occupy the same quantum state together.",
" More technically we can talk about how they combine into 8 distinct states that are a superpositon of different combinations of color and anticolors."
] |
[
"Doesn't this mean that there is actually an extremely small amount of actual matter in us? Is matter even the right word I'm looking for?",
"I don't think there is a word for what you're looking for.",
"In a strictly illustrative sense, yes, if you added up the individual masses of all the fundamental particles which you consist of, you would have around 1% of the mass that you actually do. That's not a useful or meaningful thing to do, though, because it's not how mass works. Mass necessarily involves the interactions between those particles, because mass is just a form of energy.",
"Quarks and electrons are also \"massless\" in another purely illustrative sense. They have mass because they couple to the Higgs field, but a \"totally naked\" quark or electron (ie a quark or electron in a universe with only quarks or electrons and nothing else) has no mass either. Mass isn't an intrinsic property of ",
", it always arises out of interactions between two or more things."
] |
[
"Okay so protons and neutrons are composed of 3 quarks. Are electrons composed of anything or are they still considered to be fundamental constituents of matter?",
"Electrons are leptons, which are considered fundamental. The fundamental fermions are the six leptons (electron, mu, tau, and the electron/mu/tau neutrinos) and the six quarks (up, down, strange, charm, top, and bottom). There are also the fundamental bosons, which are the photon, W",
" and Z, and the eight gluons which ",
"/u/AsAChemicalEngineer",
" mentioned.",
"Also, quarks have mass yet after googling I read that quarks have SIGNIFICANTLY lower mass than a proton/neutron. It seems to me that the sum of the masses of 3 quarks should equal the mass of a proton/neutron, but that doesn't appear to be the case. How is it possible that the mass of something composed of 3 things is not equal to the sum of the masses of those three things?",
"It takes lots of energy for the gluons to hold the quarks together. E=mc",
" says that that \"trapped\" energy has the appearance of mass. 99% of the proton/electron mass comes from the gluon energy holding the quarks together. Gluons themselves are massless, so the other 1% is from the quark masses."
] |
[
"Do photons experience any form of time?"
] |
[
false
] |
After reading , I began wondering if this is a legitimate understanding of the implications of relativity theory. So is it true that because photons only travel at the speed of light, they experience infinite levels of "time dilation" and "length contraction"? I understand the claim about time slowing down as one approaches the speed of light, but are the claims about photons experiencing zero time merely conjectures? Or are they legitimate implications of relativity theory?
|
[
"We know of absolutely no tachyonic particles. And we have good reason to suspect that such things cannot exist. (they'd cause logical paradoxes)"
] |
[
"First off, tachyons are only hypothetical and probably do not exist.",
"Secondly, you cannot \"pass\" the threshold... there are 3 cases:",
"Even if they exist, is makes no sense to talk about what tachyons \"experience\" because they are a particle that we cannot communicate or \"use\" in any fashion. ",
"when you pass the zero threshold the tachion affect beginsas you pass zero everytrhing then reverses backward time travel",
"It is like asking what size hat the color purple wears... the words are all right but don't convey anything answerable...."
] |
[
"you can't speak of any observer moving at the speed of light. But in the limit that an observer ",
" the speed of light, the length along the line of motion contracts away to zero. How long does it take to cross zero length? Zero time."
] |
[
"What would happen if a bee/wasp stung me on the eyeball?"
] |
[
false
] |
Let's assume the person in question has no allergy to bees/wasps/whatever does the stinging. In what ways would the effect differ from being stung on skin? Would blindness result? Would the effect of stings (edit: the effect of the stinger's penetration has been pretty well handled; how about the effects of the toxins?) on the white, iris, or pupil be different from each other in any appreciable way?
|
[
"Not necessarily. I had a stick go through the pupil of my eye and I don't have a 'scar' on my eye. (It only went through the front of the eye. If it had hit the back then I'd likely be blind. But I don't think a stinger is big enough to hit the back.)",
"I would think the poison would be the real problem."
] |
[
"happened to me when i was 10.",
"fuckin hurt. a lot. little fucker dive-bombed me. ",
"i managed to snap my eye closed a fraction of a second before he got me, so the stinger went through my eyelid and into my eyeball (sclera). had my mom pull the stinger out (while crying/screaming in pain).",
"no lasting damage, but that eyelid stays a little more closed than my other - can't attribute it to the sting, could just be a natural thing.",
"EDIT: only treatment given was an ice pack. i'm pretty sure it went into my eyeball because my mom said she could see it moving around when i would look around with my good eye (i figure if it was just in the eyelid, it wouldn't move in tune with my eyeball). definitely no issues with sight - had my eyes checked about 5 years ago, came back 20/10."
] |
[
"I remember this happened to a friend of mine in like kindergarten, he didn't go blind but did stay out of school for about a week iirc. Of course, I don't know/remember where exactly this happened, probably on the sclera (white part). I would imagine if it happened on the pupil/cornea it would cause some scarring that would obscure vision similar to a cataract. ",
"(layman speaking)"
] |
[
"How possible is it for a habitable planet to have a larger land surface area than Earth, but have about the same gravity on the surface (i.e. have a lower density)?"
] |
[
false
] |
[deleted]
|
[
"Tldr: just under double before it starts becoming a gas giant and a whole new problem."
] |
[
"The surface gravity g is equal to GM/R",
" , where G is the gravitational constant, M is the mass of the planet, and R is the radius of the planet. So, if the surface area goes up, R increases, and as long as the mass goes up as the square, then it's okay, e.g. if R increases by 3, M increases by 9, or if R changes by a factor x, then M changes by x",
" .",
"Assuming the planet has a uniform density and is a sphere, then the density ρ=M/V = M / (4/3 π R",
" ). So, if R changes by the same factor x and M changes by x",
" you might see that ρ changes by x",
" on top and x",
" on the bottom, so ρ changes by a factor of 1/x. So the planet would be less dense.",
"Our current model of planet formation, however, is that once it gets too massive, it will have enough gravity to start gathering more lighter gases. This is a bit of a runaway effect, which is how gas giants form. You could consider one possible limit on how massive a non-gas planet could be, before it gets to the gas-collecting regime I mentioned, would be about 10 times the mass of the Earth (see ",
"mega-Earths",
"). However, in order to keep the same surface gravity, based on the math above, is mass changes by the factor x",
" = 10, then radius must increase by x = sqrt(10) ~ 3.16 and density must decrease by x ~ 3.16. That much of a decrease basically means you can have a density consistent with a rocky planet. So in reality, the mass range in which you could get the same surface gravity is probably smaller. ",
"This site",
" suggests a density between 3 and 8 g / cm",
" , but these are simplifications. For reference, Earth's density is 5.51 g / cm",
" and is a mix of rock/metal. So, to make a larger planet, you might be able to change the density by maybe a factor of ~1.83 (density from 5.5 to 3.0), which would increase the radius by 1.83 and the mass by 1.83",
" ~ 3.36."
] |
[
"Additionally, you can still have continents that don't touch one another on an Earth-sized planet. Assuming that it was geologically identical to Earth, it would depend on what stage of the supercontinent cycle it was in and on the age of the planet."
] |
[
"What happens to mosquitoes when they suck your blood while you are intoxicated?"
] |
[
false
] |
I apologize if this has been asked before, my attempts at google and reddit search have not shown any actual studies or questions asked on this. So does the alcohol in your blood have any affect on a smaller mosquito? I'm assuming that either the alcohol is not concentrated enough to affect the mosquito, or the sac that the mosquito stores the blood in does not absorb the alcohol? Maybe a better understanding of how mosquito store blood would render this whole question moot. This could also go for any type of substance in your blood. Like if I drank some sort of human safe DEET. Could I be mosquito's destroyer of worlds?
|
[
"Scientists routinely puff ethanol vapors at insects and measure their sensitivity with devices called inebriometers. Bugs are no lightweights, often withstanding vapor concentrations of 60 percent alcohol, far more than what’s in our blood after a couple beers. “Someone who’s had 10 drinks might have a blood alcohol content of 0.2 percent,” says entomologist Coby Schal of North Carolina State University. To a mosquito, a blood meal that contains 0.2 percent alcohol is like drinking a beer diluted 25-fold.",
"Source"
] |
[
"The article is very vague and for all it says it may very well be fruit flies (which feed off of sometimes rotting fruits) that can handle such a high amount of alcohol, unless I am missing something"
] |
[
"It's not great but gives a good ball park. The other problem I have is that vapor pressure does not translate to BAC."
] |
[
"How big can a crystal get?"
] |
[
false
] |
I'm sure many of us have heard about some planets being discovered that could basically be giant diamonds. (And that's a whole other complicated can of worms, but let's not open it here.) I think a lot of people probably hear "diamond" and think that this is the type of thing where you'd be able to see some sort of crystaline structure from space - facets, planes, etc. I assume that that's not possible, because that would require the crystals to form at a massive scale. However, I don't actually know if my assumption is correct, nor why. What prompted this line of thinking was a discussion in another sub where an of the Omega/Swan/Horseshoe nebula was being (needlessly) debunked by Phil Plait. It's clearly fake, but it got me wondering how large a crystal formation can actually get. There are those amazing ones in the , though obviously there's a huge difference between a crystal that's 39ft tall and one that's 15 light-years tall. Is there an upper-boundary for how big a crystal can get? Gravity and mass are probably the biggest factors, of course. And even if you had the material and conditions to form a 15 light-year tall crystal formation, the mass would probably collapse into a black hole. But let's speculate a little. Could a mile-long crystal exist, for example? If we ignored mass and/or gravity (except for what is needed for crystal formation in the first place), and assumed a limitless supply of source material, could a crystal theoretically grow forever? I really don't know anything about crystallography, or even anything beyond the most basic mineralogy. (I'm a web designer.) I apologize if I'm using terms incorrectly. Thanks!
|
[
"Without knowing the exact answer, at the high end you'll be limited by gravity and general relativity. Crystals by definition are materials with repeating units (the \"unit cell\"). That can only repeat indefinitely in \"flat\" space. For example, a crystal is only a crystal if the axes of the unit cells in the crystal remain perfectly parallel to each other. ",
"(I'm open to corrections if I've misstated relativity here)",
"If you have enough material that it starts to induce relativistic effects - distortions in space - then the axes will bend inward, won't be parallel any more, and the crystal stops being a perfect array. ",
"If you're willing to tolerate some deviation from ideal, you'll still run into gravity, where the force packing your molecules or ions into the crystal is eventually overcome by gravity and collapses. I'm pretty sure you'd end up with gravitational collapse and formation of a neutron star or black hole before you get to the theoretical perfect crystal destroyed by distortions in space-time. Though I'm not certain on that one.",
"In the intermediate size range, you're probably more practically limited by things like purity (impurities can distort the crystal lattice), stress and strain. "
] |
[
"No crystals are perfect. All crystals have equilibrium point defects due to entropy and most have some concentration of line defects, which are non-equilibrium, but low enough energy that they are easy to produce and difficult to completely remove (more so in metals than in ionic and covalent crystals). Most solids have some types of pressure induced phase transformations at sufficiently large pressures, so in most cases you would run into a situation where the core of the crystal would have to transform into a different phase than the exterior. ",
"In theory, there are not constraints on growing large single crystals, but it is difficult because phase transformations occur by two processes nucleation and growth. To grow single crystals, you need to suppress the nucleation rate such that you only get growth. The larger your system is the more difficult it becomes to only get 1 nuclei."
] |
[
"This is a single crystal",
". A planetary diamond would be spherical due to the gravity that allows the crystal to form. Also it will have to have something over the top of it providing the pressure to form the crystals, so it will never look like one big crystal.",
"I don't have enough knowledge to say if its a single crystal under whatevers on top of it. I think its probably possible since it would have taken a long time to cool off, but I don't know."
] |
[
"I recently quit using tobacco after 10 years of use. My family is telling me that I need to do a cleanse. Is there any scientific evidence to say that these detoxifying cleanses work or are they BS?"
] |
[
false
] |
I've heard a lot about body cleanses and detox but I'm wondering if there is any legitimate scientific research done on the subject? For example, members of my family do a cleanse where they drink lemonade/maple sugar/cayanne pepper for a week straight with no food, claiming it detoxes them. When I search for information on the matter all I can find are new age/holistic websites that I do not trust to be unbiased. Thank you for any relative information. EDIT: BTW I was a chewing tobacco user.
|
[
"The first question I ask about anything like that is whether they can name the specific \"toxins\" that are supposedly being removed. They generally do not get specific because they're not actually doing anything helpful."
] |
[
"It's complete bullshit. And unhealthy."
] |
[
"Obviously I'm just here to lend my grey tag to the answers. (/sarcasm) Cleanses are bullshit. If we needed cleanses we'd have died out as a species long ago. "
] |
[
"When we view distant cosmic bodies, do relativistic effects cause us to see their changes at a slower rate since they are moving so fast relative to us?"
] |
[
false
] |
I was under the impression that galaxies are flying apart from each other at a pretty rapid pace. I was also under the impression that time slows down for fast moving objects. If we can see the light from one of these galaxies as it is soaring away, wouldn't that mean that from our vantage point that they would move/change very slowly? For example- Say we observed a distant galaxy rotating while is is soaring away from us at speeds close to the speed of light. Would the rotation speed we see correspond to the rotation speed measured by an inhabitant of that same galaxy? If this is already a thing, how does it affect our assumptions and observations about distant objects, and how to we compensate for it?
|
[
"You're using a speed almost 3 orders of magnitude too large. Objects receding at about the speed of light are at a redshift of about 1.5."
] |
[
"Realistically this isn't an observational effect, because to look far enough away/back in time for the object to be receding at relativistic speeds you will be looking at redshifts where galaxies haven't formed yet. We can't see even primordial structures here because they are 1) too faint, and 2) obscured by neutral hydrogen (i.e we would be looking at things ",
"pre-reionisation",
" era). ",
"Let's double-check my statements: Just roughly, using a simplified Hubble's law, d = v/H_0, so if v = 2.5x10",
" km/s, and H_0 = 70.2, then d = 3.6x10",
" Mpc (approx). Plugging this in to ",
"Ned Wright's cosmology calculator",
" (the go-to for lazy cosmologists), this corresponds to a redshift of about 265. Reionisation ends at z ~6, and the first galaxies are thought to have formed at about redshift 10 so yeah, not visible.",
"For arguments sake however, let's pretend we can observe a relativistic galaxy, and we try to measure the rotational velocity via the doppler shift of the emission lines on either side of the disk. In this case, the period of rotation will be adjusted by the gamma factor according to special relativity. T` = gamma x T. ",
"Made a stupid unit-related error. Thanks to ",
"/u/mhwalker",
" for pointing it out. Cbf fixing it - see posts below for details :)",
" Upon further consideration, it is only the ",
" velocity that affects the special relativistic time dilation. The ",
" recessional velocities can be relativistic and even superluminal but in reality they will never be significantly time dilated since the large majority of that velocity is due to expansion. Without expansion (i.e. in comoving coordinates), on average every galaxy we observe is stationary relative to us, the light emitted that we are now observing was emitted by an object ",
" receding from us at relativistic speeds. The fact that the object now appears to be receding at speeds close to c is not relevant. That said, there are some phenomena in the universe where relativistic effects need to be accounted for. Examples of this are relativistic jets from accreting black holes, and relativistic shock waves from supernova. "
] |
[
"Can you elaborate please? How do you get this? Are you talking about taking into account the redshift dependence of H?",
" Oh god you're right - what a retarded mistake to make! I'm so used to working with 3x10",
" km/s - I got my wires crossed with 3x10",
" ",
"/s :)",
"Repeating with v = 2.5x10",
" km/s, proper distance is 3560Mpc, corresponding to z ~2.5. So yeah, you're right - my bad :)"
] |
[
"What is the most accurate measurement?"
] |
[
false
] |
Hello askscience, I am a chemistry undergrad in an analytical/instrumental chem course, and just learned about one of my professor's research topics that is a method with detection limits theoretically in the parts per quadrillion, which got me thinking. I was wondering: what is the most accurate measurement technique out there? In terms of detection limit, or measurement uncertainty, or whatever. I realize that I'm asking a question that could be taken several ways, as you can have accuracy in looking for a concentration, a distance, or a whole host of other things, but I feel like it would be really cool to hear about things from a variety of fields. Thanks all!
|
[
"The quantity that is often cited as being the best measured is the magnetic moment of an electron (related to how an electron responds to magnetic fields). It is very close to two, and half the deviation from 2 has been measured as 0.00115965218073(28), where the brackets indicate uncertainty on the final digits. This means the magnetic moment has been measured to a part per trillion.",
"The theoretical value, based on quantum electrodynamics, is .001159652180{85(76)}, where I put curly brackets where it deviates from the experiment (within the uncertainties). This is the most accurate verified prediction in science."
] |
[
"This is the current winner in the verified predictions category, but in terms of percent measurement error, ",
"LIGO",
" should be capable of detecting a change of length on the order of one part in 10",
" Using interferometry to measure a 1064 nm laser over a distance of 600 km is basically cheating, but I guess that's kind of the point, isn't it.",
"Edit: Cheating because the error is independent of the measurement distance. So if you double the distance without actually changing anything about your sensor, the \"percent error\" decreases by half."
] |
[
"A very ",
"recent experiment",
" managed to make a measurement with an accuracy approaching the Heisenberg uncertainty limit. This means that the uncertainty associated with this measurement is roughly as small as is physically possible, because quantum mechanical considerations preclude precise knowledge of the state of a system at higher accuracies. ",
"This measurement was of the interference of two photon that were only slightly out of phase with one another."
] |
[
"Are there any studies or can anyone explain to me in the most objective way possible why some people can smoke all their lives and never get any kind of cancer?"
] |
[
false
] |
My girlfriend's grandmother has been smoking UNFILTERED pall malls since she was in her early 20's/late teens, and she is 80 now and is still healthy. WTF?
|
[
"There is hardly anything that has a 100% guaranteed chance to cause cancer. Cancer development is an extremely complicated process which requires successive mutations in cell populations over your lifetime.",
"Smoking increases your RISK of cancer. ",
"According to the CDC",
" lifetime smoking increases your risk of having lung cancer by a factor of 10-20."
] |
[
"Smoking increases the probability that you will get cancer, but there is always a chance that you will not."
] |
[
"Just because something is likely to happen doesn't mean it will. "
] |
[
"Is it possible for us to catch 2 or more variant of covid-19? If so, can those variants inside our body fuse/combine to mutate into another variant? or mutate individually?"
] |
[
false
] | null |
[
"This is a about segmented viruses. Influenza is segmented, Covid is unsegmented. So this doesn't apply."
] |
[
"Yup. ",
"A little known fact is that viruses can “have sex”, all out “orgies” to be a bit more precise. ",
"When two or more viruses enter a cell, it’s possible for their genes to combine/interact/exchange/affect or otherwise mix with each other resulting in hybrid viruses, some of which can remain viable. ",
"Some viruses actually rely on this mechanism and would not be viable without it. ",
"https://www.nature.com/articles/6889110.pdf?origin=ppub"
] |
[
"More than one coronavirus can infect the same cell, and when that happens the coronaviruses can recombine. That is, as their genomes replicate, the replication factors can jump from one genome to another, so that you end up with part of the progeny genome coming from one parent, and another part coming from another parent. (This is technically quite different from the reassortment seen with segmented viruses like influenzaviruses, though there are similar concepts.)",
"This is almost always completely undetectable, because almost always when a cell is infected with two coronaviruses, they are the same strain. If one parent has sequence ABCDEF and another has sequence ABCDEF, then recombining gives ABCDEF -- no change.",
"Even if there are moderately different strains infecting the same cell, you may not be able to tell the difference. If you infect with ABCDeF and ABCDEF, recombining gives you ABCDeF and ABCDEF. But certainly it ",
" happen that you infect with AbCDEF and ABCDeF, and get a few versions of AbCDeF out of it. ",
"The frequency of this in SARS-CoV-2 is hard to estimate because the virus mutates relatively slowly. Without a lot of diversity among genomes, you have the ABCDEF problem, where you can't distinguish recombinants from their parents. (In large databases, simple sequencing errors also complicate analysis.)",
"The detection of ongoing recombination from a sample of genetic data is, in general, a very challenging problem. Only a fraction of recombination events significantly change the shape of a genealogy, and even then, mutations must occur on the correct branches of the genealogy ... Coronaviruses are known to have relatively high recombination rates (Su et al., 2016), and cell culture studies indicate that this holds true for SARS-CoV-2 (Gribble et al., 2021). This suggests that ongoing intra-host recombination since the start of the pandemic should be commonplace, but detection efforts are thwarted by the slow accumulation of genetic diversity.",
"--",
"Ongoing recombination in SARS-CoV-2 revealed through genealogical reconstruction",
"But it definitely does happen:",
"Our results clearly indicate the presence of recombination in the history of the analysed SARS-CoV-2 sequencing data, suggesting a recombination rate greater than around 4 · 10",
" per site per year. ",
"--",
"Ongoing recombination in SARS-CoV-2 revealed through genealogical reconstruction",
"Is this a major concern for development of new variants in SARS-CoV-2? Probably not, though it can't be ignored. The background mutation rate is probably more significant. But of course the solution to this potential concern is the same as for generic mutations -- reduce the number of circulating viruses, using vaccination and masking etc, and you'll reduce the opportunities for mutation and for recombination.",
"Importantly, recombination is potentially more important in the big jumps of virus preference. One of the leading theories for the origin of SARS-CoV-2 is that a bat coronavirus recombined with a pangolin coronavirus, in some unknown host, leading to a progeny virus with new features. See ",
"Genomic recombination events may reveal the evolution of coronavirus and the origin of SARS-CoV-2",
", for example."
] |
[
"What keeps an object in orbit at the same distance instead of being pulled toward the source of the gravity?"
] |
[
false
] |
Eg what keeps an satellite at the same distance from earth? and why is it not pulled in? What keeps earth from being pulled into the sun?
|
[
"We ",
" being pulled towards the major source of gravity in our Solar System (the Sun), but the reason why we don't fall into the star is because our planet is moving at a pretty high rate of speed relative to it, with the vector of our travel being roughly 90 degrees tangent to the Sun's center of mass - our planet's tendency to maintain the same direction of travel offsets this force - per Newtonian law and also due to the conservation of angular momentum, which originated from the proto-planetary disc which formed before fusion even commenced in the Sun billions of years ago.",
"Anyway, this creates a scenario in which the force that is keeping our planet in orbit around the Sun also happens to maintain our relative velocity while travelling around it, and also our distance from it rather steady.",
"Try playing around with ",
"this simple online orbital simulator",
" and you'll begin to understand how it all works."
] |
[
"this diagram may help clarify your point"
] |
[
"It's falling with a lateral speed that makes it constantly \"miss\" hitting the planet. "
] |
[
"This may be a dumb question, but if losing weight requires simply eating less calories than your body burns, what are the biggest differences from eating healthy or poorly?"
] |
[
false
] |
If I understand correctly, if your body burned, say, 2500 calories a day, and you ate 2000 calories of fast food, you'd lose weight. If you ate 3000 calories of extremely healthy food, you'd gain weight. Obviously eating healthier food is better, but why exactly?
|
[
"This is complicated because your question isn't entirely clear. If by \"health\", you mean weight gain/loss, it is very hard to overeat truly healthy food. have you ever tried eating 3000 calories of meat and vegetation? your stomach and satiety hormones simply won't let you. healthier food also tends to impact insulin levels and sensitivity, controlling blood sugar and thus, hunger.",
"If \"health\" for you goes beyond just weight control, there are many vitamins and minerals that we must eat to maintain proper health, and junk food tends to be extremely low in these, as well as plant-based compounds that are very good for you (think fruit phytochemicals and leafy greens). ",
"while it is true that the sheer number of calories matters for weight loss, it is clearly easier and healthier to eat higher-quality foods for these calories than lower-quality ones."
] |
[
"It's definitely not a dumb question. ",
"Some things to consider/bear in mind:",
"Eating \"healthily\" is a poorly defined concept, and the many items can be both healthy in one regard and unhealthy in another (for example, the association of certain types of fats, omega-3's, with both improved metabolic health and a small increased risk of prostate cancer)",
"\"Healthy\" eating is invariably dependent on how much of a particular nutrient you consume; compounds in red wine improve cardiovascular (heart and circulation) health, but drinking 2 bottles a night won't make you healthy. ",
"Certain classes of compounds worsen metabolic measures. For example, a type of fat compound very similar to the omega-3 fats (which are highly beneficial), the omega-6 fats, are linked to increased inflammation, which drives many disease states including obesity, diabetes and cardiovascular disease. Trans-fat consumption is even more strongly linked to these disease risks.",
"It's also worth saying that calorie content is not accurate for many foods, due to the method of estimation used. This often fails to accurately account for inefficiencies in digestion, which can, for example, be altered by the bacteria in the intestines (the microbiome). The ",
"wiki article",
" discusses some issues."
] |
[
"being healthy is not maximized by minimizing weight, thats the first point it guess, also every kind of \"unhealthy\" is only a matter of dosage. For example protein is considered healthy. But too much protein is unhealthy. Sugar is considered unhealthy but without it(or it being split out of more complex carbs) you have no short term energy. The only thing thats is kind of out of that principle is water since it can't be essentially unhealthy when consumed in mass but its unhealthy to consume too little. Also too little diversity in food can lead to not having enough substances to process certain types of food. I can't really describe this any better since english is not my main language."
] |
[
"When our epidermis grows with our size, does the number of nerve endings increase to maintain a constant density, or are they simply spaced further apart?"
] |
[
false
] |
And is the phenomenon the same or different between adolescent body growth/adult weight gain? EDIT: Thank you for the responses! Looks like my question has been answered quite thoroughly. This is why I love , I'd been wondering about this for ages, and may have gone one wondering if you guys hadn't explained it. Great work!
|
[
"the number of sensory nerves innervating your skin is determined by the number of neuronal cell bodies in the dorsal root ganglia. During gestation this number increases through division (some die off) and reaches a stable number. Neurons are 'post-mitotic' and do not divid further. The neuronal cell bodies by then have extended their peripheral terminals out to the skin.",
"However, the branching of sensory nerve terminals in the target organs (e.g. skin) continues to be plastic throughout life. Thus you have the same number of nerves, but the branching or arborization of the terminal can adjust to your size."
] |
[
"Seems unlikely. The sensation you get from stimulating your skin sensory nerve terminals is the result of 2nd and higher order processing in the brain. So it seems likely to me (although I'm a peripheral nerve man not a CNS guy) that the brain will have already calibrated to your particular state of arborization/skin size."
] |
[
"Seems unlikely. The sensation you get from stimulating your skin sensory nerve terminals is the result of 2nd and higher order processing in the brain. So it seems likely to me (although I'm a peripheral nerve man not a CNS guy) that the brain will have already calibrated to your particular state of arborization/skin size."
] |
[
"Will light be refracted by any glass like object? Can it be treated to decrease the amount of refraction?"
] |
[
false
] |
I'd like to think I remember this topic from my classes but I have been asked this question in such a way that it made me question my knowledge. As far as I know any glass like object will refract light that passes through it to a certain degree. Can this effect be controlled by the manufacturing process of said object? Here is the actual situation I'm dealing with. I am a customer service rep handling warranty claims on motorcycle helmets. I have a customer who is complaining to me that the visor on his helmet refracts light and distracts him and could pose a safety risk. I had thought that any glass like material will do this. Can this effect be lessened by the way it is manufactured? Thanks for your time guys.
|
[
"Light is refracted whenever the light encounters a medium with a different refractive index at any angle other than normal incidence (anything other than perpendicular to the surface). Typically this means the surface is curved like a lens or tilted, etc. but it can also happen when the light is coming into, or going out of focus. This is very much dependent on design on the material (glass, plastic, crystal, liquid, gas... pretty much anything can refract as long as its at least partially transparent). The amount the light is refracted is very wavelength dependent, but most optical materials used for applications like helmets are specifically chosen to have small changes in the refractive index over the visible wavelengths (dispersion). ",
"Manufacturing processes can the refractive index of most optical materials, specifically if the material is injection or compression molded (both of which require the material to be slightly fluid, then rapidly cool it down to a manageable temperature). If you take some plastic safety goggles and put them between two crossed linear polarizers, you can see the effects of how the stress in the glasses is distributed, and that can give you an idea of how the refractive index also changes. But that being said, we still dont notice that level of a difference in refractive index very readily. ",
"For your warranty issue...what do you mean (in this case) by 'refracts the light'? Is the visor causing a lensing (magnification) effect, or is it acting like a prism, where the colors are being separated?"
] |
[
"I may be using the wrong terminology. It looks as if the visor is acting as a prism. The white light is being separated into a spectrum."
] |
[
"Flat sheets will not bend light (or rather they will refract the light back by an equal amount into the original direction and the total effect is very small). This probably wouldn't help in making a helmet visor, sadly. There's not really any way to prevent refraction in general through a material, especially hard clear materials. In fact if it were possible, this would result in basically invisible materials since the light would pass right through."
] |
[
"Why doesn't an alpha decay release a huge amount of energy like nuclear fission?"
] |
[
false
] |
I've heard the word "tunneling" used in this context, but don't really understand what's going on...
|
[
"The idea of interest for this is ",
"Nuclear binding energy",
". The total energy of the nucleus is the mass of all of the nuclei ",
" the binding energy of all the nuclei. ",
"As you increase the number of protons and neutrons (A) in the nucleus, the amount of binding energy per nucleon (proton or neutron) holding the nucleus together ",
" (on average) until you hit Iron-56. That is the most strongly bound nucleus (in this sense) in the universe.",
"As you add more nucleons, the binding energy per nucleon drops. It's like they stick more and more tightly until you pass Iron-56, then the whole thing gets less sticky each time you add another nucleon. This is important: as you keep going, this effect gets worse and worse (a nucleus with 200 nucleons is stuck together much more poorly than a nucleus with 100 nucleons) For these heavy elements, then, the total energy can be lowered if they can ",
" nucleons.",
"Alpha decay decreases the total number of nucleons by 4. The binding energy per nucleon goes ",
", so everything is stuck together better and more stable. And as I noted above, since the binding energy goes up, the total energy goes down and you've released energy. On the other hand, fission will split the nucleus into two nuclei with about half (ok, not really, but close enough for our purposes) of the nucleons. So you've decreased the number of nucleons by a LOT more than 4. So you've increased the binding energy per nucleon by a LOT, thus getting more energy out."
] |
[
"That's just where the equilibrium point happens to be.",
"Let's say you are selling hot dogs. At $1, you sell a whole lot, but for not much profit per unit. At $2, you sell fewer at a large profit per unit.",
"So you have two competing forces, volume and profit margin. Some where in the middle, say, $1.38, is the point that maximized your profits. There is nothing magically different between it and $1.37, it just happens to be the maximal point where the two forces balance out.",
"Iron-56 is the same way, it is just where the energies of fusion and the energies of fission are minimized."
] |
[
"There are 3 effects that are important for understanding this.",
"First, the strong force by itself tends to favor bigger nuclei. So you gain binding energy by adding nucleons. But as you go up to bigger nuclei, the effect of adding one more gets smaller.",
"Second, since protons and neutrons are fermions, they cannot be in the same quantum state. This means that as you add protons, the lower energy states get filled up first, so you have to put them in higher energy states. The effect of this is that it costs energy to have more neutrons than protons or vice versa. So you can't just build a stable nucleus out of neutrons - there will be less binding energy if some of the neutrons beta decay, so they will.",
"Finally, since protons have charge, they repel eachother. So every time you add a proton, there is a downward effect on the binding energy (the interaction of the protons makes the nucleus less stable). This effect gets bigger every time you add a proton.",
"So for light nuclei, the total charge of the nucleus is small (there aren't many protons), and so the binding energy gets larger and larger because the repulsion of the protons isn't important enough. Eventually though, the effect of the protons gets strong enough that it starts paying off to have more neutrons than protons. Finally, as you continue to add nucleons, the effect of the protons repelling gets more and more important. It just happens to start dominating around Iron-56"
] |
[
"Any chemists in the house? Can fluoride really cause hypothyroidism?"
] |
[
false
] |
Is this legit? If so, what does this have to do with the autoimmune disease Hashimoto's thyroiditis (which causes low thyroid levels because of an attack by antibodies on TSH and TPO receptors on the thyroid gland). It would seem that this is an entirely different path to hypothyroidism. I looked for epidemiological evidence of thyroid disease on the rise, but because of changes in testing procedures and disagreement on proper lab ranges, it's hard to say how many people have thyroid disease now, much less how many had it 60 years ago before the time of ubiquitous fluoride...
|
[
"There is a LOT of pseudo-science around fluoride use in drinking water, and I'm sure you've found it by conducting Google searches. Many of them ignore basic concepts (dose-dependence is a big one i.e. taking the results of a high dose study and implying a low dose has the same effect) or cherry-pick research without giving the full story or noting the limitations of the research. All peer-reviewed studies are not created equal, and should not carry equal weight, and in the case of anything medical is nature, one study does not allow for a general conclusion.",
"Here's a reference put out by the ADA:",
"QUESTION 30.\nDoes the ingestion of optimally fluoridated water adversely affect the thyroid gland or its function?",
"Answer.",
"There is no scientific basis that shows fluoridated water has an adverse effect on the thyroid gland or its \nfunction.",
"p. 34 of ",
"http://www.ada.org/sections/newsAndEvents/pdfs/fluoridation_facts.pdf",
"The document contains references for making this statement.",
"Also from the CDC(",
"http://www.cdc.gov/fluoridation/pdf/pollick.pdf):",
" ",
"In the literature reviewed, doses appropriate for caries reduction were not shown to negatively impact thyroid function. Studies in which humans received doses significantly higher than the optimum fluoride intake for long periods of time showed no negative impact on thyroid function.",
"Claiming that the ADA and the CDC are involved in a giant conspiracy to cover up the health effects of fluoride is frankly laughable, these are serious professionals who do their jobs ethically and responsibly. People who claim a conspiracy are basically telling you they don't have a real argument or data to present.",
"Also, contrary to a lot of the claims of the anti-fluoride websites, it is quite easy to conduct studies comparing fluoridated water to non, there are a lot of communities that do not fluoridate their water in the USA, but for a more basic reason: they don't want to spend the money on it.",
"Edit: here is a page from the CDC summarizing Fluoride research over the years by the National Research Council \n",
"http://www.cdc.gov/fluoridation/safety/nas.htm"
] |
[
"There is a LOT of pseudo-science around fluoride use in drinking water, and I'm sure you've found it by conducting Google searches.",
"I just want to second this. Flouride ",
" in water is a very long running psuedo-science. Going back at least far enough to have been mocked in the movie Dr. Strangelove. ",
"here is a good, short little article",
" that talks a bit about how to tell if a conspiracy theory is BS or not. I think OP should read it. ",
"Edit: oops"
] |
[
"Take it from a chemist, their opinion is not equal to the findings of the CDC, not even close. The CDC doesn't have an \"agenda\" beyond public health, implying that they do is ignorant and some what offensive to serious scientists. "
] |
[
"Does wiping off your sweat prevent the body from cooling down?"
] |
[
false
] |
Does the cooling effect come from the sweat absorbing the heat on its way out or should you leave it and not wipe it to lower your temperature more efficiently?
|
[
"Yes, sweating is based on evaporative cooling, where the phase change from liquid to gas absorbs heat energy from its surroundings (including your skin and the warm blood carried by the ",
"superficial veins",
" from deeper tissues. So yes, wiping off sweat actively hinders your body's natural cooling mechanism, however, it's not the secretion of sweat itself that does anything, but the subsequent evaporation. So taking a shower or just rinsing your skin with water, and letting it dry naturally, has largely the same effect, and won't dehydrate you so fast as a bonus."
] |
[
"All correct, however you can actually hinder your ability to cool by sweating too much. If you're absolutely dripping sweat, like totally soaked, there will not be much evaporation taking place (the phase change that's most important). Instead, you're just warming up your sweat a bit before it drips off you, gets wiped up, or gets soaked into your clothes. If you're this sweaty, it's actually more effective to wipe/blot away excess drippings so you can expose your damp skin to moving air to kick start evaporation."
] |
[
"I'd add that when dripping sweat, the sweat droplets are mostly spherical, ans as such have a small surface area where phase change happens. By wiping off the sweat, you'r effectively smearing it, greatly increasing the surface area and accelerating evaporation and cooling."
] |
[
"How do we know the structure of molecules?"
] |
[
false
] | null |
[
"This has been asked a few times, so you may want to do a search.",
"In short, chemists use a variety of tools to determine the structure of molecules. These techniques include:",
"A chemist looking to determine the structure of an unknown molecule would use a combination of these tools to come to a conclusion."
] |
[
"In addition to the methods outlined by ",
"/u/Joe_Q",
", there are some new techniques coming out in the microscopy world. The most notable is cryo electron microscopy (cryoEM) which actually ",
"won the 2017 chemistry Nobel Prize",
"With cryoEM, you can use a transmission electron microscope to essentially take thousands of pictures of the same type of molecule in different orientations and then reconstruct the 3D structure with high resolution. ",
"While the resolution is heavily influenced by the image processing after data acquisition, the newest generation of cryo microscopes can get resolutions down to ~1.5 angstroms."
] |
[
"I agree that it is powerful, but in organic chemistry at least (which is where I go when I hear \"the structure of molecules\") it is not at all a common structure-determination tool."
] |
[
"How long do you have to be exposed to the sun to get the same dose of vitamin D as your daily supplements?"
] |
[
false
] | null |
[
"It will depend on the strength of sunlight, but ",
"this study",
" found >1hr per day was sufficient in their study population in India. However, it seems that time of day and latitude would have a significant impact on duration needed to achieve healthy levels of vitamin D production."
] |
[
"Depends on your genes and how dark your skin is/how much melanin. And there is many different amounts of vitamin d supplements. I take 5000iu a day. Usually 20-30 mins a day of full exposure is adequate. Making sure you get enough K2 is important."
] |
[
"Strange that an important factor is not mentioned which is how much skin is exposed, as in how much clothing they're wearing. This study is in India so there's going to be more sun than in North Europe. ",
"Considering its hot in India, usually, they probably weren't wearing much, but if it's colder, not only is there usually less sun, people also wear more clothes so that decreases the required exposure duration a lot, one can assume."
] |
[
"Would science in general (I mean in academia in practical terms) benefit from discarding all prior assumptions in every field and trying to formulate fresh sets of hypotheses based solely on observations to date?"
] |
[
false
] | null |
[
"This isalready practiced in science, to the benefit of scientifical progress. My favourite example of this is Newton's law of universal gravitation, which is known to be imprecise in some regards, but still accurate enough to describe most cases."
] |
[
"Some Examples for discarding and refining of prior \"knowledge\" in science:",
"The latter point is explained at length ",
"on Wikipedia",
"."
] |
[
"Some Examples for discarding and refining of prior \"knowledge\" in science:",
"The latter point is explained at length ",
"on Wikipedia",
"."
] |
[
"Can individuals evolve with respect to Epigenetics?"
] |
[
false
] |
[deleted]
|
[
"Totally agree with your first part, great explanation. +1.",
"In regards to transgenerational epigenetic inheritance, in humans/mammals the evidence definitely isn't great, but some epigenetic marks survive meiotic reset in animals, plants, and other eukaryotes, particularly those where the germ line isn't sequestered. When heritable epigenetic marks modulate gene expression and affect phenotype, they can be selected for just like anything else in Darwin's paradigm."
] |
[
"Totally agree with your first part, great explanation. +1.",
"In regards to transgenerational epigenetic inheritance, in humans/mammals the evidence definitely isn't great, but some epigenetic marks survive meiotic reset in animals, plants, and other eukaryotes, particularly those where the germ line isn't sequestered. When heritable epigenetic marks modulate gene expression and affect phenotype, they can be selected for just like anything else in Darwin's paradigm."
] |
[
"Epigenetics is a method of gene regulation. It's a way of turning genes on and off. That's all. Your own genes are turning on and off in response to outside stimuli ALL THE TIME. Gene regulation isn't a new thing; it's been known about for a long, long time.",
"Epigenetics is getting lots of attention only because we've discovered that epigenetic changes can be passed on from one generation to the next, which is new and interesting and cool. But now you're asking about epigenetic changes within an individual, so you're throwing away the only unique and interesting thing about epigenetics.",
"Epigenetic changes are NOT evolution. Allele frequencies are not changed over time. DNA sequences are not changed at all. It's not evolution.",
"This is a pet peeve of mine - I think the lay media are blowing this up into something way bigger than it actually is.",
"So, anyway, to your question, your own genes are constantly changing expression levels all the time based on environmental and developmental signals. Epigenetics doesn't add anything to this picture. It's not individual evolution. It's just \"staying alive\"."
] |
[
"Electronics on Airplanes"
] |
[
false
] | null |
[
"Bit of your own medicine, Doctor. From the first link in your search:",
"It is not, contrary to popular opinion, to force you to pay attention to the safety briefings. If that was the case, you wouldn't be allowed to have books out, and you couldn't sleep - neither of which is prohibited.",
"http://en.m.wikipedia.org/wiki/Mobile_phones_on_aircraft#section_1",
"[ABC came to conclusion] the primary reason for the ban on cell phone use in flight was that neither the FAA nor the FCC were willing to spend the money to perform conclusive safety tests.",
"Most people who do an overview of the situation come to similar conclusions. ",
"The culprit is \"regulatory inertia\", not passenger safety."
] |
[
"http://money.cnn.com/2012/12/09/technology/in-flight-cell-phones/"
] |
[
"That's not the issue, it's passenger safety and cost for testing to prove the regulations are overly conservative.",
"\"the cost of an accident, should one occur, could be extremely high in terms of human life and the risk is completely avoidable in that no one absolutely needs to use their mobile phone in flight. The regulatory agencies and aviation industry take the position that any increased risk is unacceptable if it is avoidable.\"",
"Please do a search to see if your question has been asked before posting next time.",
"http://www.reddit.com/r/askscience/search?q=phone+plane&sort=new&restrict_sr=on&t=all",
"Edit: quote."
] |
[
"How can computers calculate sines so accurately?"
] |
[
false
] |
I've been learning about rewriting a function as a series in my Calculus class, and my professor mentioned that computers need to use series to approximate the values for functions such as sine. To calculate a sine accurately, you need a good number of terms, and even with that, the error from using a series with a finite number of terms increases by quite a lot as the sines argument (for lack of a better word) distances from zero. I wrote a rather simple calculator program to compare the time of executing the Taylor series with <0.01% error to the built in program, and found that the built in program is much faster, especially as the input numbers got larger. How does a computer calculate these functions so quickly and accurately? Is it even using a Taylor series, or some other approach?
|
[
"First of all, you can (and really should) always arrange the argument of your sine or cosine to be between 0 and π/4 by using periodicity and identities. In this small interval the error in the series expansion is much smaller, and controlled.",
"However, computer implementations (like C built-in functions) do not usually use the series expansion. They tend (there's actually a different function for each architecture) to use an algorithm called ",
"CORDIC",
".",
"CORDIC is better on hardware because it reduces mostly to multiplications and divisions by powers of 2, which can be done with bitshifts and so are faster than floating point operations."
] |
[
"It looks like GNU libm (standard sin() on linux) uses a combination of techniques, depending on the input (at least for x64 - there are different implimentations for different architectures). The code is mostly black magic to me, but it does seem to involve a Taylor series.",
"https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/ieee754/dbl-64/s_sin.c;hb=HEAD#l281"
] |
[
"There's also CORDIC in there in one of the cases, though it's barely legible. If the angle is pretty small, you can gst away with only two or even one Taylor term and that might be faster than CORDIC in that case"
] |
[
"does the vitamin c from my lemon tea breaks down when i'm boiling it?"
] |
[
false
] |
i heard that vitamins are destroyed when cooked so i googled it but haven't found any thing that satisfied my curiosity. i found the melting and boiling points for vitamin c but i have no idea what to make of them so im asking for your counsel. p.s. sorry for any grammar mistakes and punctuation errors
|
[
"Vitamin C doesn't decompose until around 370°F/190°C so boiling water alone won't destroy it. It does, however, react with oxygen in the air. The oxygen in the water combined with the high temperature will probably lead to some of the ascorbic acid being oxidized but unless you're leaving it out boiling for a very long time I think it's safe to say any loss of vitamin C would be rather minuscule. One thing worth noting is that because vitamin C is soluble in water, after boiling most of the vitamin C will stay in the water instead of in the lemon. If you're drinking the tea this ends up being a benefit, but if you were cooking vegetables and throwing out the water afterward you would be losing it with the water."
] |
[
"It depends on the kind of tea pot you have. Copper catalyzes vitamin-C ",
"http://en.wikipedia.org/wiki/Vitamin_C#Food_preparation",
" and ",
"http://www.ncbi.nlm.nih.gov/pubmed/3595980",
". ",
"Apparently ",
"copper teapots are a thing",
" so this is quite possible.",
"Traditionally someone boils the ",
" and ",
" the tea and then adds the hot water to the tea so the vitamin-c would not be catalyzed in the pot, but that isn't exactly what you said.",
"I would correct what you have heard to be, \"vitamins are destroyed when cooked ",
"\"."
] |
[
"well thanks, i do boil my water but the tea i drink is pretty tasteless anyway "
] |
[
"Why do your arms float up after pressing outwards on a door frame with locked elbows?"
] |
[
false
] |
I make educational science videos and I wanted to make one about this phenomenon a while ago, but I was unable to find any satisfactory explanations. My understanding is that it's a generalized muscle effect - you can induce something similar by making a fist and squeezing really hard for a while, then gently trying to open your hand. It will feel 'locked up'. I saw various sources claim different effects were responsible: that excess calcium buildup was stimulating the muscle fibers, that muscle spindles were somehow getting confused and setting a false equilibrium point for muscle lengths, or that the opposing set of muscles were getting tired trying to oppose the anticipated movements leading to mismatched muscle tone. Can anyone shed some light on the accuracy of any of these claims? I'd love to make a video about it if I can get a well-supported explanation. Thanks for your help!
|
[
"EDITS: Here is how I Think it happens, and here is a picture for reference : ",
"http://imgur.com/PaYsC",
"When you contract the triceps (extrafusal muscle), an intrafusal muscle also contracts, wich slows down signaling along the 1a sensory neuron. A gamma motor neuron then activates to stretch out the intrafusal muscle fiber (IF) again. This alows the brain to tell if there is further contraction. If you release your arms, the signal to the gamma motor neuron will also stop. This causes the IF to shrink to its normal size slowly, which tells the brain that your arms are raising. However, now its contracting on its own, without the triceps actually contracting. The sensory sytem sends collaterals to the motor system, telling it the arm is raising, which in turn makes your arms raise. The brain wants sensory and motor systems to be in synch, which is why unless you try to stop it, if you feel your arms rising, they will rise. ",
"It can't be muscle memory as it is a form of procedural memory that involves consolidating a specific motor task into memory through repetition. This works first time.",
"It also can't be fatigue, as your arms travel the SAME direction you were pressing. You were using the Extensor (triceps) to push the door jam, and they continue to contract afterwards. This is not like a reflex, or sensory adaptation. It is a result of the IF muscle fibers resetting after extended periods of load."
] |
[
"I created this account to comment on this. From what I can tell you're on the right track, but if I recall correctly it works more like this: The first thing to remember is that nerve signals are sent in pulses, and your brain reads changes in pulses (speeding up or slowing down) as corresponding sensory signals (i.e. hot and cold). What can occur if a signal is sent constantly is what is called habituation, or basically an ignoring of the sensory input (as in why you don’t constantly feel your clothes.) When a signal goes long enough, the signal is then believed by the brain to be the new baseline, and so a drop to the previous baseline nerve pulse signal (or tone) can then be interpreted as a change, even if it is actually a return to the original baseline. \nIn this case, when you're pressing against the door frame you are using your \"up\" muscles (you're pressing outwards with palms facing in, activating muscles to lift your arms up) which along with sensory neurons that send proprioception information (where your body is in space), change their tones accordingly and if held long enough (say around a minute), your brain becomes habituated to the tone.\nThen, when you let your arms relax, the tone sent from your muscles and sensory neurons return to their original baseline, but this return to baseline is interpreted by the brain as a change in position (in this case arm going down) and adjusts your arm position accordingly."
] |
[
"I appreciate the responses I've gotten here so far, but ironically I now have two people supporting two different options out of my original three. As in all of science, the truth is probably some combination of my conveniently separate options. Still, it would be really great to have someone provide definitive support for one explanation being the main cause over the others.",
"It's also quite likely that as my research hinted, we simply don't know yet. The problem there is that it's very difficult to find someone knowledgeable enough to know that this is the case."
] |
[
"Would everything on an extrasolar planet be dark to human eyes?"
] |
[
false
] | null |
[
"Other suns might have their peaks at completely different frequencies",
"Yup, it depends on the temperature of the star (and a couple of other things because they aren't perfect ",
"black bodies",
", but that's not really important here)",
"and not much light of the kind that we are used to seeing.",
"Not necessarily so - whilst a hotter object has a higher peak frequency, it will emit more light at ",
" wavelength that a cooler object (",
"pretty graph time!",
"). Conversely, a cooler object has a lower peak frequency ",
" emits less at every wavelength that a hotter object.",
"It would only be in the case of very cool stars (which emit mostly in the infrared) or planets very distant from their host stars (for obvious reasons!) that you would really be lacking in visible light."
] |
[
"Other suns might have their peaks at completely different frequencies and not much light of the kind that we are used to seeing.",
"Not really. The Sun is a ",
" average star, and there are tons similar to it. Most stars have peak frequencies in the visible range anyways, so it wouldn't be as extreme as you're thinking."
] |
[
"Every bona fide star emits visible light in a more or less thermal spectrum, like the sun."
] |
[
"What is happening physiologically when we feel so happy our heart feels like it will burst?"
] |
[
false
] | null |
[
"Sometimes when I am extremely happy, my breath catches and my chest feels so full. Alternatively, when I feel very emotional or sad, my chest actually aches. What is going on in my body? "
] |
[
"I'm not a cardiologist (However I am working on my ACLS certification), but I'll take a shot based on what I've learned from what I've taught about the heart and related tissues, and what I've learned in my ACLS studies.",
"That \"ache\" is a result of a combination of many things, and is called a Palpitation. Although palpitations usually indicate more serious abnormal heart activity are and associated with serious myocardial arrhythmias, they can ",
" happen as a result of an intense emotion triggering a CNS-mediated reaction in your body. Chemicals from the brain associated with pleasure and excitement, namely dopamine and epinephrine, rush into your blood stream after they are released by glands in your body's endocrine system. If the heart is mid-beat when these chemicals enter the cells of the heart through the blood, they can cause the parts of the heart to become \"desynchronised\" in a way and not beat in an orderly fashion that pumps blood in an effective manner, although this is ",
" rare. More often than not, epinephrine's effects as a vasopressor cause the heart to beat faster in a short amount in time, and the rapid muscle constrictions cause chest pain, along with airway constriction as the SNS is stimulated.",
"Source",
" for the details regarding the nervous system and epinephrine.",
"td;dr: Adrenaline makes your heart go nuts and beat faster, and the ache is just your heart muscles increasing in activity very rapidly."
] |
[
"You are experiencing premature ventricular contraction (PVC), also known as your heart \"skipping a beat\""
] |
[
"When flying away from earth at the speed of light, why does \"my\" time stop passing and not the earths?"
] |
[
false
] |
Since there is no magical static grid covering the universe that tells us how fast we travel, speed can only be measured between two observable objects i.e. inertial systems. So if I fly away from earth at the speed of light, there is a relative speed c between me and earth. Couldn't one say that earth is flying away from me at the speed of light instead of vice versa? What is the difference between me and the earth that makes "my" time stop?
|
[
"Because when you come back to earth, you change your frame of reference while the earth remains in the same frame of reference. You change your direction of travel. This causes the symmetry to stop working as before."
] |
[
"Let's make it so that you're travelling close to c and not at c so the good folks here at ",
"/r/askscience",
" don't get all mad.",
"When you're travelling away from earth, the people on earth view your time as passing slower than on earth. However, you view earth's time passing slower than yours. This is vital because it fits your statement:",
"Couldn't one say that earth is flying away from me at the speed of light instead of vice versa? ",
"In fact, that is precisely why the effect of time dilation is dependent on who is doing the observation. That fact would always make the other party's time seem to be passing slower."
] |
[
"That isn't a solution of the twin paradox that IS the twin paradox (or rather one of them). It arises because the special relativity arguments used to make the statement do not include acceleration, which is necessary to get the twins back into the same frame."
] |
[
"working on hourly basis on grant money instead of Physics RA?"
] |
[
false
] |
So I plan to start grad school in Physics this upcoming fall, but for the summer, I have nothing to do, so I'm willing to work for a prof as a volunteer research assistant. I missed the deadline to work under an RAship for the summer. I've already agreed to work as a volunteer, but is it possible to get hired on an hourly basis with the prof's grant money, so I could work for him even if it isn't officially an RA? Could I work out an hourly wage that would be comparable to an RA stipend? I mentioned this in one of my previous emails to this prof, along with talking about renegotiating the deadline for an RAship, but he just told me the dept is strict about deadlines. So I don't know if he actually read my question about trying to work out a salary but not work officially as an RA.
|
[
"r/askacademia",
" is probably a more appropriate place for questions like this."
] |
[
"I think only your professor can really answer this question..."
] |
[
"There is also a difference in the answer depending upon what country you are in. There are tax differences between most RAships and hourly pay. There is also the difference between different titles on your resume, provided the work is of the same nature."
] |
[
"What is the temperature of a particle moving near the speed of light?"
] |
[
false
] |
Such as particles in the LHC.
|
[
"Temperature is a statistical property of an ensemble. A single particle doesn't have a temperature in any meaningful sense."
] |
[
"temperature if a transfer of energy between things.",
"You're mistaken. Heat is a transfer of energy. Temperature is (basically) a system's tendency to give off heat. More generally, it's defined in terms of a partial derivative of entropy, which means that every system has a temperature, not just ones for which a temperature can be measured."
] |
[
"Particles in the LHC do not technically have a temperature until they collide, to be specific. ",
"Soronume pointed out a flaw in that analysis, that heat is the transfer of energy, which is different from temperature. Thanks.",
"Additionally, the particles are not \"heating up\" in the traditional sense when they're zipping around the LHC tubes, as they're doing so in a near vacuum; air resistance is needed to generate heat via friction, if that's what your question was aiming at. ",
"However, when those particles do collide and transfer their energy, they've managed to generate a maximum temperature of 5.5 trillion degrees Celsius (about 10 trillion Fahrenheit). I'm not sure how well this answers your original question, but the idea I'm getting at here is that a particle traveling at near the speed of light has an absolutely massive amount of potential energy, which would translate to a significantly high temperature. "
] |
[
"Would we be better at mathematics if we weren't bought up using a base-10 number system?"
] |
[
false
] |
Decimal may be an easy-to-grasp concept because of the whole ten fingers thing, but would we be at mathematics if, for example, we were taught from a young age to use hexadecimal (base-16) instead?
|
[
"Very little mathematics has anything to do with the base for decimal representations of numbers. (For that matter, a lot of mathematics isn't really about numbers at all!)"
] |
[
"Not really. How we represent numbers does not really have anything to do with the math behind it. ",
"Ten digits are easy to remember. We have ten fingers and can use them to learn the ten digits. The word digit stems from the latin word for finger. It might be more work to remember 16 digits and have a unique symbol for each. ",
"Another property to think about is division. In base 10 you can easy divide by 2, 5 and 10. Base 12 is often proposed to be better in this category. It is easy to divide by 2, 3, 4, 6 and 12 in base 12. ",
"I am not sure about any other properties."
] |
[
"By \"we\" do you mean a particular country or humanity in general? Because we, as in the human race, have advanced mathematics quite a bit. If you mean we as in the US, Canada, or wherever you might be from, there are plenty of other countries that use the same base-10 number system and have higher proficiency numbers than those countries.",
"Edit: According to ",
"this",
" Canada is top 10 for math, bravo!"
] |
[
"How do fish and other marine animals survive the crushing pressure of the abyss?"
] |
[
false
] |
I was reading on the recent discovery of the Airbus that had crashed off of Brazil a few years ago, I think it's about 2 1/2 miles down -I thought wow, that's a lot of pressure. Then I began to wonder how ocean life can survive such crushing depths...any ideas? relevant link:
|
[
"Well the pressure inside them matches the pressure outside.. They're kinda equillibriated with their surroundings, and hence they should be fine. The structural properties maybe very slightly different but I don't see any reason why any biological process should happen in a different manner under very high pressure as long as the pressure is equal everywhere. Thats why its almost impossible to actually bring these animals back up, since the pressure difference will be so great they will just disintegrate!"
] |
[
"Liquids are notoriously hard to compress. As organisms are mainly made up of liquids their intracellular pressure simply matches the pressure of the surrounding liquid. The size of the organism is less important than the gasses in it's system. Most marine organisms don't have large pockets of gasses that would change in response to pressure. Most that do either stay at one depth or change the size in response to the change in pressure. ",
"Marine mammals are one of those exceptions and they have a slew of adaptations to help them. Whale's don't usually get the bends because they only breath at the surface whereas divers breath continuously. Collapsing their lungs helps maintain the branched structure that could be damaged due to pressure changes. The slow their heart rate and limit activity in secondary organs. And a high concentration of hemoglobin helps keep the oxygen in the bloodstream."
] |
[
"Liquids are notoriously hard to compress. As organisms are mainly made up of liquids their intracellular pressure simply matches the pressure of the surrounding liquid. The size of the organism is less important than the gasses in it's system. Most marine organisms don't have large pockets of gasses that would change in response to pressure. Most that do either stay at one depth or change the size in response to the change in pressure. ",
"Marine mammals are one of those exceptions and they have a slew of adaptations to help them. Whale's don't usually get the bends because they only breath at the surface whereas divers breath continuously. Collapsing their lungs helps maintain the branched structure that could be damaged due to pressure changes. The slow their heart rate and limit activity in secondary organs. And a high concentration of hemoglobin helps keep the oxygen in the bloodstream."
] |
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