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[
"How do birds grow feathers?"
] |
[
false
] |
Is it just like how we grow hair? Can they re-grow after falling out? If so, how long does that take?
|
[
"Birds can re-grow feathers, (if one is damaged in a fight or accident) but it takes a while. If the feather is one of several needed for flight (e.g. the wing and tail feathers) a wild bird will be at a serious disadvantage. Captive birds will need to have it repaired and even then it will be weak until a new one grows in to replace it.",
"Young birds will molt or shed their feathers periodically as they grow. I think adult birds molt on a yearly basis but I'm not sure.",
"They're definitely not like human hair that keeps growing until it breaks, or falls out. ",
"Hopefully an avian expert will be along that can explain better and in more detail."
] |
[
"Cockatiel person here. I can elaborate on a lot of this.",
"Birds can re-grow feathers, (if one is damaged in a fight or accident) but it takes a while.",
"It's a surprisingly fast process, actually. They can generally get through a full molt within a week or two.",
"If the feather is one of several needed for flight (e.g. the wing and tail feathers) a wild bird will be at a serious disadvantage",
"A single feather won't slow them down. Birds are constantly losing feathers, especially during molting. It's not unusual for us to have an entire pile of feathers of all sizes after a molt, including ",
"primary feathers",
" and tail feathers. It can be a problem if they lose too many at the same time, but they have considerable redundancy.",
"Young birds will molt or shed their feathers periodically as they grow. I think adult birds molt on a yearly basis but I'm not sure.",
"True, and true. Usually some time in the spring, but different birds are different. It can happen more or less frequently, especially when they are young.",
"They're definitely not like human hair that keeps growing until it breaks, or falls out.",
"Also true, the entire feather is replaced or nothing is replaced. Basically what happens is a pin feather grows in from the hole where the old feather came out. It's essentially a spike-like feather that's covered in an outer coating of chitin (like your finger nails). The chitin breaks away, exposing the soft feather within.",
"Edit: Here's a good picture of what ",
"pin feathers look like"
] |
[
"What happens if a feather gets damaged outside of the molting period? Does the bird just have to do without it until their next molting period?",
"They lose and regrow feathers year round. They'll just lose a lot more than normal for a week or two during a molt.",
"Those pin feathers look evil, like something you'd find on an angry porcupine.",
"They are evil. They're like procupine needles, but with the sharp end pointed inward toward the bird. It's not uncommon to be preening them and they'll suddenly YELP! loudly because you stuck them with one, especially when they're molting. It doesn't discourage them from demanding more a few seconds later, though, so it can't be too bad.",
"Also, I suspect that image was from a baby bird going through one of its first molts. It isn't usually THAT bad."
] |
[
"If 100 perfect coins were flipped with identical starting conditions, would they all land the same?"
] |
[
false
] |
Assuming we have a model that the coin lands heads 50% of the time.
|
[
"There's a lot of assumptions in your question—but the spirit is that yes, coin flips, which obey Newtonian mechanics are deterministic. People have built robots that can pick which side they want their coin to land. Even more impressive, you can teach yourself to rig coin flips in your favor."
] |
[
"There are many that think that consciousness is a quantum phenomenon and not a deterministic, Newtonian process, so that we do have choice based on who we are/what we're thinking rather than initial conditions.",
"https://en.wikipedia.org/wiki/Quantum_mind"
] |
[
"But it seems to me that if we agree that humans evolved from simpler life forms than we cannot say that what we call consciousness appeared at a certain specific point in time but rather it is a spectrum or a scale and other animals just fall lower on it. Are their actions also governed by quantum processes or is it just humans?",
"Further more, I think we can both agree that singled celled organisms and even more complex multi-cellular organisms such a plants and even insects are governed by deterministic, Newtonian processes, since we definitely do not think of them as having consciousness.",
"Combining the two statements above, I would find it quite difficult to imagine that our ancestors started out deterministic and then, at some point, they stopped being so.",
"As I'm writing this, I'm starting to have doubts. Can a system governed by Newtonian physics become a system governed by Quantum phenomena or must it always remain governed by Newtonian physics ?"
] |
[
"What makes paper fresh from the copier hot? Why don't inkjet printers produce the same amount of heat as copiers do?"
] |
[
false
] | null |
[
"Laser printers and photocopiers don't work under the same principle as an inkjet printer. When you make a photocopy, the first step is to give an electrostatic charge to a special cylinder. That cylinder is coated with a material that becomes conductive when exposed to light. When the document is being scanned, a strong source of light shines on the paper and reflects on the rotating cylinder. The parts being hit by light (i.e. what is aligned with white on the original document) become conductive and allows the electrostatic charge to be grounded and discharge. What you are left with at the end of this process is a cylinder with an electrostatic charge only on areas that correspond to the dark areas on the document. The charge then picks up toner and rolls on a blank piece of paper with a heating element, which essentially melts the toner and makes it adhere to the paper. The paper then comes out of the photocopier with an approximate copy of the original document.",
"Of course, modern photocopiers and laser printers will digitize the original document and then use that digitized copy as the master to apply the charge on the cylinder and make a better copy with a single scan instead of having to pass on the original for each copy, but the core principle remains the same.",
"Long story short, the paper coming out is warm because a heating element is required to make the toner stick to the paper."
] |
[
"Photocopiers and laser printers work by applying a layer of dry toner to the page which is held in place by a static charge. The toner is then cooked onto the page using a heated roller (around 220c from memory). This is why the page is hot.",
"Inkjet printers just spray wet ink onto the page which dries naturally. No heat required."
] |
[
"Thank you "
] |
[
"What process makes drinking carbonated drinks too quickly painful?"
] |
[
false
] | null |
[
"Edit: Upon further research, both hauntedchippy and I are wrong. It isn't the acidity of carbonic acid (or else good ole' vinegar would produce the same sensation), nor is it the mechanical formation of CO2 bubbles, as illustrated by ",
"this study",
" (first result - unfortunately an online copy isn't available), where subjects at around 3 atm of pressure reported the same sensations (even though the pressure would drive the carbon dioxide to remain dissolved).",
"It is in fact a carbonic anhydrase dependent receptor that causes that sensation. So the mechanism is actually the detection of carbonic acid itself (not the acidity), mediated by the rapid conversion of carbon dioxide into carbonic acid by carbonic anhydrase. ",
"This study",
" demonstrated the effect using a carbonic anhydrase inhibitor."
] |
[
"and why does that sting?"
] |
[
"This is probably what is stinging your tongue. You probably notice it after holding the liquid in your mouth for a short time. If this is the case you shouldn't notice the pain when the drink is flat.",
"Does carbonic acid form in sugar and alcohol-free carbonated drinks, like mineral water?",
"Carbonic acid forms whenever carbon dioxide is dissolved into a water based solvent.",
"How exactly does it form?",
"CO2(carbon dioxide)+H2O(water)=H2CO3 (carbonic acid)",
"Is it always present in carbonated drinks",
"It exists in a state of equilibrium constantly changing from carbonic acid to water and CO2 and back again. At room temp approximately 0.2% of the CO2 in water exists as carbonic acid."
] |
[
"How much does using warm or hot water affect cleaning hands or dishes? Wouldn't it require almost unbearably hot water to have any anti-bacterial or anti-microbial effect?"
] |
[
false
] | null |
[
"The maximum safe temp for handwashing is about 110 for brief or occasional exposure. Higher temperatures will cause chapping and tissue damage. This isn't expected to kill germs - serious antibacterial activity is negligible below 120F and significant heat disinfection (eg contact lenses) requires 180 degrees for at least 15 minutes, which would quickly scald skin.",
"Ordinary handwashing is effective because it reduces bacterial count by removing bacteria and washing them away. Soap and surfactants help by breaking up (emulsifying) the oily film that normally covers the skin and harbors bacteria. ",
"Modern soaps emulsify pretty well at any temperature, but as a rule warm/hot water makes soap more a little more efficient. Adding antibacterials like triclosan is meant to kill germs actively but it isn't clear that this makes a big difference compared to simple soap and water. Washing more frequently with soap (at any temp) is probably better than washing less frequently with scalding water, triclosan, or handwashing gel."
] |
[
"For the record, sanitizer gel is shown to be at least as effective as soap and water, against the vast majority of microorganisms. That's why most hospitals put sanitizer dispensers outside all the rooms, and docs and nurses use that instead of washing our hands in between every patient. ",
"The rare exceptions are for certain spore-forming pathogens, because the spores aren't killed by alcohol. For instance if a patient is infected with ",
", you'll see a \"do not use\" sign on the dispenser outside their door, and everyone coming out of that room will wash their hands with soap. (They will also be wearing contact isolation gear for every patient interaction, but that's a different story.)"
] |
[
"Different bacteria have different tolerances for temperature.",
"Using hot water works better because it is better at loosening things and causing them to rinse off the plate. Cold temperatures can cause things to cling more tightly. ",
"With food it is often fat and grease and oils that cause things to stick. Hot water breaks this up better where cold water can cause it to congeal and stick."
] |
[
"Relatively larger particles and Wave-Particle duality"
] |
[
false
] |
As per this , molecules as large as buckyballs have displayed 'wave bahavior'. I can understand wave-particle duality in extremely fast paced particles like electrons and photons. But I am unable to understand this duality when it comes to molecules or even nucleons for that matter. Some further explanation would be helpful...
|
[
"Palanoid answered this, but don't think of the quantum wave as the size of a particle. This wave describes the location of the thing and as that thing gets heavier it becomes more localized in space. "
] |
[
"Everything is both wave and particle. One thing you can use to make sense of this is the ",
"de Broglie wavelength",
", which tells you the length scale over which quantum (wave) effects are important. The de Broglie wavelenth depends on the mass and velocity of the thing of interest and for a proton (the smallest atom) this is about 1 or 2 angstroms, and for a buckyball it is about ",
"2.5 pm",
", or a hundred times smaller. So you can see that as things get heavier the quantum effects occur over much smaller scales. "
] |
[
"Make sure that you don't mix the quantum wave function to waves like em-waves that transmit energy. The |ψ|",
" of position-space wave function corresponds to the probability density of finding a molecule in a given place. The size of the object affects the wavelength of the function. "
] |
[
"How does bleach work in that it strips materials of pigment?"
] |
[
false
] | null |
[
"Stains are commonly caused by the presence of organic pigments in your clothing, for example ",
"beta-Carotene",
". beta-Carotene gets its red-orange color because it absorbs blue light specifically from the long chain of carbon atoms which connect the two hydrocarbon rings.",
"This carbon chain is what we call \"conjugated,\" which basically means has molecular bonds (called pi-bonds) which allow electrons to be delocalized to anywhere along the chain. In essence, these electron wavefunction can be modeled by the ",
"particle-in-a-box",
" problem. Pigments with shorter chains absorb more energetic blue light and thus appear redder, while longer chains absorb less energetic red light and thus appear bluer. Using this simple model, you can predict that the photon wavelength whose energy corresponds to exciting beta-carotene from its highest occupied molecular energy level to its lowest unoccupied level is roughly around 480 nm... which is blue.",
"What does this have to do with bleach? Well household bleach (NaClO) is an oxidizing agent which will destroy the conjugated pi-bonds. This in turn destroys the \"box\" the electrons were previously allowed to live in. The wavelengths the molecular bonds now absorb after bleaching are no longer in the visible spectrum and thus the organic molecule appears colorless.",
"As a rule of thumb a carbon double bond (C=C) (which contains a sigma-bond and a pi-bond) will be converted from bleach to an hydroxyl and chlorine bond (OH-C-C-Cl). You might have noticed that bleach doesn't actually remove the offending pigment! It just destroyed the part of the pigment that generates color, the stain is still there, you just can't see it anymore.",
" For those playing physical chemistry at home. You might have noticed that beta-carotene should be roughly 28 nm long by counting its single and double bonds which would mean that beta-carotene should absorb 1200 nm infrared (IR) light rather than 480 nm blue light according to the particle-in-a-box energy levels! The contradiction is solved by the fact that conjugated bonds are shorter than you'd otherwise expect. Thus beta-carotene is closer to around 18 nm long."
] |
[
"Wow! Thanks! This was great!"
] |
[
"Short version - Bleach doesn't suck out dyes and colours, it chemically attacks and shatters the molecules that give things their colour. It's a quirk of how electrons work that many coloured things share a similar chemical structure so a lot of them can get broken down by bleach. "
] |
[
"How can we trust Max Planck's derived units?"
] |
[
false
] | null |
[
"Planck units are not fundamental limits. This was never assumed by Planck, nor anyone else.",
"Planck units are just units constructed out of fundamental constants related to special relativity, general relativity, and quantum mechanics.",
"The Planck length is not the \"shortest possible distance\", the Planck time is not the \"shortest possible time interval\", etc."
] |
[
"What I mean by fundamental limits is this: Take the Planck length for example, it tells us that anything equal to or shorter than that will exhibit weird quantum effects that we don't really know how to reason just yet. We also have the Planck temperature, which is supposed to give us an upper bound of sorts for temperature in the universe, since blackbody radiation will emit Planck length long wavelengths."
] |
[
"The Planck units are just scales where quantum effects ",
" should become important."
] |
[
"If visible light is just a section of a larger spectrum, why is a color wheel continuous?"
] |
[
false
] | null |
[
"Hi! This question was asked recently. You can find threads ",
"here",
" and ",
"here",
", and more by using a ",
"search",
". Check them out and let us know if you have follow up questions!"
] |
[
"Reddit search isn't the best. Glad we could help!"
] |
[
"Thanks! I tried searching, but I must not have looked hard enough. In any case, these answer my question wonderfully, thank you!"
] |
[
"Does a frozen drink have less \"effective\" calories than a room temperature one? How significant is the difference?"
] |
[
false
] |
Take two Slurpees or similar shaved ice drinks. Let one melt and keep one frozen. What is the caloric difference between consuming them? Is there a significant amount of work that my body does to melt the frozen one vs the room temperature one? Put another way, if I consumed a very predictable diet for a month and had two normal Slurpees a day during that time, then the next month I had the same diet but switched the frozen Slurpees out for melted ones, would there be any difference over time to my overall caloric intake?
|
[
"Your intake would be the same since the temperature of food doesn't affect the calories contained in the carbohydrate, protein and fat molecules. You might burn slightly more calories as the heat from your body warms the slurpee. Slurpees are basically just ice. It takes 1 kcal to heat 1 litre of water by 1 degree celcius. Let's say a slurpee is 500ml. So to raise that from 0 degrees celcius to body temperature, 37 celcius, would use only 18.5 kcal. But digesting food generates heat anyway, so you probably wouldn't have to burn calories to warm it up really anyway. ",
"Edit: assuming you did burn calories to balance out the cold, you would use 18.5 x 2 x 30 = 900 calories a month. Versus the room temperature (20 celcius) one which would use about half that. "
] |
[
"You're assuming liquid water at 0 celsius. It takes 80 kcal to melt 1 litre of water before you can start raising the temperature."
] |
[
"Really? You know I didn't know that. Well that's a bit of a bump up then. "
] |
[
"Why are trade deficits bad?"
] |
[
false
] | null |
[
"It isn't bad. A country running a trade deficit with nearly full employment and a stable inflation might be doing fine. Large trade deficits generally put a downward pressure on domestic currency which tend to make imports more expensive. This might lead to higher inflation. Again \"large\" is relative, a country with a deficit might be only importing a small fraction of goods and still have most production domestically. ",
"The other concern about trade deficits is that it represents some kind of \"failure\" of domestic manufacturing. Since manufacturing/production jobs have, in history, led to a middle-class living, the concern is that too much reliance on imports leads to fewer \"good\" jobs - leaving a low wage (MacDonald's) workforce and a very wealthy few - the \"hollowing\" of the middle class. In other words, the idea is that large trade deficits contribute to domestic income inequality."
] |
[
"Of course it can be bad --- under some conditions.",
"No country can prosper in state of perpetual trade deficit. Having a deficit implies more is leaving than coming in. To sustain this flow, you have to have enough internal financial resilience to grow your economy even as some wealth leaves it.",
"How long before it becomes a problem? Depends. Does it always imply a problem? No.",
"Perhaps cycles of surplus and deficit are the ideal --- and perhaps for a country as large as the USA a cycle of 100 years is not too much."
] |
[
"So would the US trade deficit fit under this category? They have had a pretty consistent trade deficit with the world for over 40 years. Is Trump essentially correct in his analysis that consistent trade deficits hurt the economy in the long run?"
] |
[
"If the theory of Supersymetry says there's an equal partner for every particle that we can observe, why is it that \"dark matter\" accounts for 95% of the universes mass?"
] |
[
false
] |
If every particle we could observe had an equal partner you might expect the mass to be roughly 50-50, not so ridiculously lopsided. What gives?
|
[
"Our standard model includes stuff like top quarks (which we know exist via experiment) but aren't expressed in our universe in the same ways electrons and protons are—so rarity isn't new to known physics. The supersymmetric partners in SuSy are all predicted to be quite massive (at least ~1 Tev range) and often have many decay modes available to them, in the literature you'd see lots of references to ",
"\"SuSy chains\"",
" or multiple decays which chain together. Their great mass in part is why these modes are available to them.",
"The one exception is the LSP or lightest supersymmetric particle, which is the proposed \"bottom of the hill\" particle which itself has no decay modes and should be stable. There is great interest that this particle, if it exists, might actually be the fabled dark matter. If this is true, then a SuSy partner would outnumber normal matter in mass by five times in the entire universe. ",
"Also you got your numbers a bit mixed up, the break down of matter-energy density is as follows: ",
"~70% dark energy ",
"~25% dark matter ",
"~5% normal matter ",
"Dark matter and dark energy are two entirely different things with unfortunately similar names. We actually have a good shot at figuring out dark matter in our lifetimes, dark energy on the other hand is much more mysterious and our ignorance of it is much greater."
] |
[
"Note that ",
"/u/AsAChemicalEngineer",
" did not mention anything about supersymmetry being real (he said \"predicted\", \"proposed\"). No supersymmetry has never been observed and there is no indication in Nature that it might be real. It is an hypothesis, but a very popular one.",
"Susy is less popular nowadays because its advocates have been very vocal about how great it was and how it ",
" and how we would find it for sure within 6 months of turning the LHC on. This focus on SUSY with the comedown that came out of finding no unexpected phenomena (for now) at the LHC made some people resent it as so many SUSY models (and others to be honest) became excluded. ",
"I think the doubts are more part of this general disappointment at not finding anything for now. Many \"easy\" SUSY models are excluded, but so are many non-SUSY models. I would not say SUSY is in worst shape than the alternatives, but it's simply coming back from being the star-theory to being one of the possibilities. This is a good thing because it is driving a desire on the experimental side to do more general analyses and fewer SUSY-optimized searches, which used to be the bulk of BSM searches."
] |
[
"There is about 5 times more dark matter than normal matter, as ",
"/u/AsAChemicalEngineer",
" said. If supersymmetry is true - which we have no indication of - it predicts that there is a partner ",
" for every particle ",
" we see. That does not mean that every electron in the universe has its partner super-electron somewhere in the universe. It means that if electrons exists in the universe, there is the possibility for super-electrons to exist as well. ",
"If supersymmetry exists, it has to be broken at low energy too. This means in particular that super-electrons would behave differently from electrons at low energies and in particular in many cases, it means that there should be much fewer s-electrons than electrons nowadays. In the most popular supersymmetric theory, this is true for all super-particles, none of which should be present in the universe, except for one: the neutralino - which is related to the super-photon. The neutralino is pretty different from its non-super-partner but it has one propriety that makes it special: all the other superpartner decay to it and the neutralino itself is stable. So the only leftover in the universe that susy would exist - outside the LHC - would be those neutralinos, which we call dark matter because they don't interact a whole lot with normal matter. The difference in proportion boils down to supersymmetry breaking and particles and super-particles behaving differently at low energy."
] |
[
"Why is the urge to pee more pronounced when we experience strong emotions (excitement, fear)?"
] |
[
false
] |
Is this a physiological effect? Or have we had to pee the entire time, and the emotions just make us realize it faster?
|
[
"Your sympathetic autonomic nervous system (responsible for triggering the \"flight or fight\" response) is triggered by stressors. The neurotransmitter Norepinephrine is released, which causes a number of physiological reactions, among them increased heart-rate, respiration, inhibition of digestion, and relaxation of the muscles controlling your bladder."
] |
[
"Could you cite your evidence that strong emotions such as excitement and fear increase the urge to pee. To my knowledge activation of the sympathetic nervous system inhibits one's ability to voluntarily urinate."
] |
[
"Great response, Thanks. I had no idea excitement triggered a fight or flight response."
] |
[
"If a human body suddenly got sucked up into outer space what would happen to the human body? Why wouldn’t humans flash freeze?"
] |
[
false
] | null |
[
"I'll answer the second part: a human wouldn't flash-freeze because a vacuum is an extremely good insulator. On a human scale, the thin gas of interplanetary space is so thin that it doesn't really have any temperature at all. There's no convection or conduction of heat out of your body. Instead, there's only radiation - your body is emitting infrared radiation (mostly), and that's the only way it can cool down. At the same time, it's potentially receiving radiation from the Sun, depending on if e.g. you're in the shade behind a planet, and how close you are to the Sun. You're also producing heat with your bodily functions.",
"The human body wants to be at about 37° C, but if you're in the same orbit as the Earth, after dying from exposure you'll eventually cool down to about -20°. This is the temperature where the Sun's heat and your body's emission roughly cancel each other out - although it depends on stuff like what colour clothes you're wearing and how shiny they are etc. The Earth's surface is only hotter than -20° because we have the atmosphere to insulate us.",
"It would feel cold, but more like being outside in a Canadian winter than being flash freezed."
] |
[
"Remember, the amount of pressure your internals pushing outwards on your surface is 1 atm, as our bodies are conditions to live at that pressure.\nThe equivalent would be diving to a depth of 10m in water, where the pressure is 2atm, or an increase of 1 pushing in. You hardly think we’d be crushed at that depth. We might slightly bulge in a vacuum, but far from bursting."
] |
[
"My favorite part is that due to the low pressure, the moisture on your skin will start to boil, and so will all other fluids in your body that isn't being contained."
] |
[
"Are the 'movable ribs' possessed by Draco volans, (the Flying Dragon), which form its 'wings', considered limbs/appendages?"
] |
[
false
] |
It consists of bone, presumably muscle to move the bones, and is joined in some way to the spine; what is the nature of this join, is it considered a joint? If I have misunderstood Draco volans' anatomy, and its 'wings' are not movable appendages, do they have the capacity to evolve into limbs or more recognisable wings? Thanks. I'm fascinated by this little critter, what looks like a six limbed vertebrate.
|
[
"Interesting creature. I imagine you will get some discussion if your post to ",
"r/biology"
] |
[
"I'll try there too, thanks.",
"http://www.reddit.com/r/biology/comments/vitsu/are_the_movable_ribs_possessed_by_draco_volans/"
] |
[
"No, they're not considered limbs, even though they're jointed. The vertebrate skeleton is divided into ",
"2 main parts",
": the axial skeleton (skull, spinal column, ribs) that composes the primary body axis, and appendicular skeleton (shoulder blades, pelvis, and limbs): bones that are 'draped over' or 'hung' on the spinal column. Ribs are basically elongations of vertebrae, while limbs have a distinct axis, and are attached to the vertebral column via pelvic or pectoral girdles.",
"As seen in ",
"this photograph",
", the ribs that make up the 'wing' are distinct from the limbs. In order for something like stereotypical ",
"dragon wings",
" to evolve, a third set of limbs would have to arise, possibly on the pectoral girdle or perhaps a brand new girdle, but both are extremely unlikely. The successful evolution of a third set of limbs has never arisen in vertebrates: the problem is that there isn't much 'raw material' to work with. The pectoral girdle originally evolved from the ",
"posterior skull bones of fish",
". There are no good bony precursors for a new girdle. Additionally, the developmental changes that would have to occur (say, a genetic duplication of the existing pectoral girdle sequence) would probably be severely detrimental.",
"Really cool animals though!"
] |
[
"Do other types of electromagnetic radiation 'shine' or propagate similar to how visible light does, with shadows, reflections and varying degrees of coherence?"
] |
[
false
] |
[deleted]
|
[
"Absolutely. X-ray lasers exist. I work at a facility which has one. The same rules of diffraction, refraction, reflection apply. As my old physics prof used to say, light is light is light. ",
"The really neat thing I like to think about is what it would be like if I could see in the radio spectrum. I think radio towers would appear as incredibly bright sources of light. And the world around me would appear somewhat transparent."
] |
[
"Yes actually. Any wave is subject to reflections. You'll get 'shadows' of UV light when you wear clothing hence why you get sunburned worse on unprotected areas and reflections of UV off of water can also cause burns (though to much less a degree). Coherence of light depends on the bandwidth of the light leaving the source but it is a phenomenon for all types of light. ",
"There are also other types of effects they all share such as diffraction and the photoelectric effect."
] |
[
"If you've ever received a bad sunburn in a snowy environment, you've seen one example. Ultraviolet radiation can reflect off of snow, and you can actually get an even worse sunburn during a day in the snow than you would at the beach."
] |
[
"I've got contacts that are rated for 2 weeks to a month. Now I've been really careful with them, but they haven't gotten uncomfortable at all. Can I keep wearing them past 1 month if they still feel good? (I take them out every night and put them in every morning)"
] |
[
false
] | null |
[
"I've got Acuvue Oasys Lenses haha."
] |
[
"So, first of all you should always follow the products directions. ",
"On the other hand, I was sentenced to a year in prison in 2006 and am blind as fuck. I somehow got through the fishtank without being noticed and wore them for a FUCKING YEAR!!! No contact solution or anything. My prescription is around a (-11) so I would have been fucked without them. ",
"Praise be to Acuvue Oaysis lenses!"
] |
[
"I have worn contacts for over 10 years and I always wear mine way past the recommended time frame. As long as they still feel comfortable I wear them. I have never had any consequences from it. No infections and my eyesight has not worsened any more than expected. Actually my eyes haven't gotten worse in 2 years."
] |
[
"How does navigating by Stars work?"
] |
[
false
] |
I know that in ye old times, a lot of sailors navigated with the stars. How does that work when the stars move in the sky depending on the time of night and the day of the year? I know that the North Star is a thing to help, but how can only one star be the tool for navigating the ocean? And how did people do it in the Southern Hemisphere, without the help of the North Star?
|
[
"Knowing your latitude is easy. It's equal to the angle between the celestial pole and the horizon. That's why Polaris is important, it's almost on the north celestial pole. In the southern hemisphere, you can use other stars that are close to the south celestial pole like Sigma Octantis, or you can use any other star or even the Sun if you know it's declination, you just have to wait for them to reach their highest point in the sky, that's called the transit or crossing the local meridian.",
"Knowing you longitude is way harder because, as you said, the Earth rotates. There's an awesome book called \"Longitude\" by Dava Sobel about the different solutions to this problem. It was finally solved when we were able to build clocks that were able to keep precise time while being on a rocking ship and in different temperatures. The time difference between the port where you left and where you are is equal to the difference in longitude. Say you left from Liverpool and you have a clock on board set to Liverpool time, so it marks 12 at the solar noon, when the Sun is highest in the sky. Then you sail and sail and observe than when the Sun is higher where you are, the clock says it's 2:00 pm. Since Earth does a full turn (360°) in 24 hours, you can calculate that it rotates 15° in one hour (360°/24=15°). So a time difference of 2 hours equals a difference in longitude of 30°. Since it's \"earlier\" on your ship than on Liverpool, you know you're due West (in the same sense that Pacific Time is \"earlier\" than Eastern Time in the US). Liverpool's longitude is 3° W, so that places you 33°W."
] |
[
"I know that in ye old times, ",
"Navigating by the stars was routinely done on airliners right up until the 60's. The first versions of the Boeing 747 were fitted with a sextant for taking star-shots (it somewhat resembled a small periscope in the roof of the cockpit). ",
"The US Naval Academy stopped teaching celestial navigation in the 90's, but reinstated it in 2015. It has plenty of advantages - it can't be jammed, works worldwide, uses reasonably simple equipment and doesn't emit signals that can be tracked."
] |
[
"We have 4 satellite positioning systems that work worldwide, use reasonably simple local equipment (battery-powered devices) and don't emit signals that can be tracked.",
"I would expect that a smartphone app can do celestial navigation today. It has a clock, it has an orientation sensor and it has a camera. It's probably not done because GPS is orders of magnitude more accurate normally."
] |
[
"Why do the Planetes orbit the Sun?"
] |
[
false
] | null |
[
"The solar system would have formed in a nebula. It's likely that the nebula would have been slowly spinning. As gravity contracts the gas cloud, conservation of angular momentum makes it spin faster (try sitting on an office chair and spin with your legs out, then pull them in. You'll start spinning much faster).",
"The faster spinning causes the nebula to flatten out into a shape similar to a ",
"spiral galaxy",
" (a mostly flat disk, with a bulge at the center).",
"Gravity continues to produce \"lumps\" of matter within the cloud, with the largest one in the middle. Most of the matter gets pulled into the largest gravitational well (the star forming in the center of the nebula), while clumps of matter further out \"sweep\" their orbits clean by pulling in matter from around them with gravity.",
"In summary, the orbits of the planets come from the original spinning of the nebula.",
"This site",
" has a similar explanation, with pictures to match."
] |
[
"And why did the gas rotate?",
"Excuse me, I just answered that in the text above. I'll try again.",
"The gas would be in motion already. Very few things in the universe stand completely still, due to the force of explosion of an older generation of star, gravitational effects, expansion due to heat, etc. There are many, many small forces acting on matter and causing it to move. From that point, gravity causes clumping. Some clumps of matter have a pre-existing vector of motion that is perpendicular to the gravitational force, and depending on the specifics of that vector, will either be ejected from the nebula, enter into orbit around the nebula's center of gravity, or be sucked into the center of the nebula (becoming part of the protostar)."
] |
[
"Well, that's where the original energy comes from, yes. They revolve around the sun at the speeds they do because of conservation of angular momentum as the proto-solar-system cloud collapses and condenses, and they rotate around their axes for the same reason: small forces that add together and amplify each other as many particles fall into the planet, in a smaller-scale version of what happened to form the solar system itself."
] |
[
"What was the weather/climate like during Pangea?"
] |
[
false
] |
What was the general climate during Pangea? Were there seasons? I understand it was cold on the poles but what about the equator? What about the Terrain was it completely desolate and like a dessert, a rainforest or were there mountains and constant volcanic activity?
|
[
"Seasons have more to do with tilt than continental arrangement, so there should have still been seasons. In general, the climate would have been a lot like Asia, except more so. Around the edges it would have been similar to any other continent, with ecosystem type dependent on latitude and weather patterns. Deep in the interior climate would have been much more extreme. Very hot near the equator, very cold in the winter in temperate zones. In some interior regions it may have been pretty dry. Of course, Pangaea hung around for a long time, so climate would have varied quite a bit as global climate changed.",
"Links ",
"Biome map for the carboniferious",
"http://journals.hil.unb.ca/journalimages/AGEO/2011/Vol_47/ageo47art09_fig6.jpg",
"and one for the permian on this page",
"http://palaeos.com/paleozoic/permian/permian.htm"
] |
[
"I'm really interested in that huge ocean. What was that like? Were there massive hurricanes? What about rouge waves? What kind of life could be found in the center?"
] |
[
"Our own continents are moving as we speak. These things take millions of years."
] |
[
"Where are a whale's nipples?"
] |
[
false
] |
Whales, as mammals should have nipples, correct? or do they have some other structure to deliver milk from the mammary glands? do male whales also have nipples? where are whale nipples located? how do whales "suckle" if they have no lips to create suction on the nipple? -thanks :)
|
[
"Right here",
"Additional chart",
"Another photo, the two slits beside their urogenital slit."
] |
[
"They are located in slits on either side of their urogenital slit. Whales and dolphins (I am pretty sure this includes all species) have a similar setup for the genders. Because it's all tucked up inside for hydrodynamics, a male has what is basically an 'exclamation point' (two lines in line with each other, one is the line for the penis, and the other is the anal slit), and females have a division sign (one long urogenital slit with two smaller slits on either side). The smaller slits are where the mammary glands/nipples are located. A baby approaches the mother, sticks their rostrum in the slit, and wraps their tongue around the nipple. The same way people roll their tongues is the way dolphins (at least, not sure on whales) drink milk (think of the tongue as forming a huge straw) without taking in too much seawater.",
"Source: I work with the animals"
] |
[
"From what I recall , there is a difference depending on species and sometimes even sex of the animal.",
"Here's",
" a diagram showing sex-linked differences in size and position in Orcas."
] |
[
"How does one plant a seedless watermelon?"
] |
[
false
] |
From what kind of seed do seedless watermelons grow?
|
[
"They take clippings from a living plant and grow those."
] |
[
"You sure about that? I figured it'd be like bananas where you breed an infertile triploid hybrid, which sort of ",
" like a switch..."
] |
[
"Never feel bad for trying to acquire knowledge. It is the journey, not the destination, that is important."
] |
[
"How was the sediment that forms the rocky planets formed?"
] |
[
false
] |
Where did the rocks that make up the Earth, Mars, Venus etc. come from?
|
[
"http://www.theguardian.com/science/2008/apr/28/starsgalaxiesandplanets.geology",
" has the best explanation I've come across.",
"tldr: Tiny particles from the big bang/dead stars keep smacking together until they have enough mass that their gravity starts pulling this dust together and become bigger. Eventually planets and other space stuff settle in an orbit around the sun and stop constantly crashing and assimilating into one another.",
"If you want to know where THAT dust came from, I don't know >.>"
] |
[
"Which dust are you referring to not knowing where it came from?"
] |
[
"Most of the heavy atoms, like carbon and nitrogen, that make up the rocky planets and all life on Earth, were made in stars. In the beginning of the Universe, there was only hydrogen, helium, and a trace amount of heavy elements - everything else was made later in stars.",
"When stars die, they eject their material back in to the Interstellar Medium (ISM). There, that material forms new objects like stars and planets by collapsing under the influence of gravity."
] |
[
"Can some humans see different wavelengths of light?"
] |
[
false
] |
I know the visible spectrum is from about 390-750 nm, but are there any reported cases of people with genetic variations out there that allow them to see lower or higher frequencies of light, like maybe 350 or 800 nm? I know there wouldn't be much of a difference in what they saw, but it was just a question that popped into my head.
|
[
"There are genetic variations in the color opsins that shift their frequencies, but the shift is much less than what you describe especially towards the ends of the absorption spectrums.",
"Look at this graph"
] |
[
"There is some speculation and evidence that some humans may be able to see colour differently:",
"http://en.wikipedia.org/wiki/Tetrachromacy"
] |
[
"apparently they see uv lights as a new kind of violet - it's just like\nseeing violet, but different"
] |
[
"Why can't computer RAM be phased out and replaced with larger CPU caches?"
] |
[
false
] |
I have a basic understanding of the hit or miss principle. . If the CPU can communicate with cache several times faster than RAM, will we eventually see a shift to gigabyte-sized CPU cache and removal of "the middle man" that is RAM? And further down the road, we won't need a separate hard drive at all when the CPU can link directly with the memory and that memory can be large enough to suit our storage needs. Is this at all plausible?
|
[
"Part of it comes down to cost. CPU cache memory is extremely expensive to manufacture in comparison to RAM, which is extremely expensive to manufacture in comparison to storage media like HDDs/SSDs. Then there's the logistics of fitting all that memory on the die of the CPU. Part of the reason why CPU cache memory is so fast is because it's directly accessible by the CPU, and doesn't have to be bussed, unlike RAM or HDD/SSD memory. Increasing cache size also proportionally increases latency, which defeats the advantage of the cache. Then there's the issue of it being volatile memory (it doesn't hold information when powered down). ",
"You can certainly create a RAMdrive to store your programs if you want, but it's extremely expensive in comparison to standard non-volatile memory."
] |
[
"Even if cost was not an issue (as ",
"/u/rmg22893",
" pointed out), we couldn't even come close to fitting gigabytes of cache on a CPU with current technology. As ",
"this image",
" shows, L3 cache is already takes up a huge part of the Core i7 CPU die, and what you're seeing there is only about ",
" 15 MB of cache. This is because a cache uses ",
"SRAM",
", while main memory uses ",
"DRAM",
"."
] |
[
"Sandy Bridge E has 15 MB of L3 cache right there on that picture. Just pointing out, otherwise great answer."
] |
[
"Why do \"naturopaths\" use Litmus tests with urine to determine your overall health?"
] |
[
false
] |
Does it have any meaning at all or just a gimmick? I am majoring in Nutrition with intentions of becoming a Registered Dietitian. I understand that the body has a protein buffer and also the H-H equation and that the body compensates for pH by fluctuating carbon dioxide levels (through respiration). I'm curious why it's "better" to be alkali than acidic - don't we want to be neutral?
|
[
"Because they don't know how to practice real medicine"
] |
[
"Do you know what a naturopath is? ",
"Here",
". Their techniques are not based on evidence, and their model of disease is incompatible with what we know about physiology."
] |
[
"Stay in school, you are doing it right."
] |
[
"How have oxygen levels affected evolution in the past and do they apply in any evolutionary terms today? The future?"
] |
[
false
] | null |
[
"Yes actually. Earth was originally lacking in O2, and the first forms of life were anaerobic organisms. Eventually, oxygenic photosynthesis was evolved, which produced O2. This increased the atmospheric oxygen concentration. The interesting thing about aerobic respiration (using oxygen in energy production), is that it is much more efficient than anaerobic respiration (using something else). So, when aerobic respiration was evolved, those organisms grew faster and were more efficent than the other organisms. Hence, why you see large animals roaming the earth today; anaerobic respiration cannot sustain such a large organism. Just a little tidbit i learned from my microbiology class."
] |
[
"They definitely apply today. \"During the Carboniferous and Permian periods, atmospheric oxygen concentrations were significantly higher than they are today. Prehistoric insects breathed air that was 31-35% oxygen, as compared to just 21% oxygen in the air you're breathing as you read this. Atmospheric oxygen is the single most limiting factor on insect size.\" \"During the Paleozoic era, the Earth teemed with giant insects, from dragonflies with wing spans measured in feet, to mayflies nearly 18 inches in breadth.\"",
"http://insects.about.com/od/evolution/f/Why-Prehistoric-Insects-Were-So-Big.htm"
] |
[
"so if aliens evolved in 50% oxygen earth similar to ours, they would think dinosaurs were lizards? (I know once the oxygen levels are high enough, the first asteroid that entered its atmosphere would have cause it to ignite)"
] |
[
"Do cousins whose parents are identical twins have the same genes as siblings?"
] |
[
false
] | null |
[
"If two identical males married females who were also identical twins?",
"Each child has 50% of the combined DNA of it's parents. Each child gets 50% from one and 50% from the other. Due to the number of chromosomes, chance mutations, and a phenomenon known as 'crossing over', there is effectively no limit to the number of genetic variations possible between siblings. ",
"What you are getting at, I believe, is this: Unless there is a detectable mutation between either one of the identical twin pairs, there is no way to determine which parental pair is responsible for any of the offspring. ",
"For example, if female1 cheats on her husband male1 with his twin male2 and has a child from the encounter, a DNA test will not be able to distinguish between the possible fathers. It would be a Maury Povich episode for the books."
] |
[
"Sorry, no I mean if two identical twin brothers had offspring with two different woman, if the children would have the same DNA as if they were fathered by the same parents."
] |
[
"Checking for clarification, is this what you're trying to ask?",
"A pair of identical brothers marries a pair of identical sisters. Each couple produces offspring. Is the level of genetic correlation between these offspring the same as the level of genetic correlation between siblings?"
] |
[
"How do magnets get their magnetic fields? How do electrons get their electric fields? How do these even get their force fields in the first place?"
] |
[
false
] | null |
[
"Electrons have a fundamental property called the quantum mechanical spin. This spin can be understood and described as an intrinsic angular momentum.",
"The spin creates a magnetic dipole moment with a certain magnitude. In non-interacting electrons, these dipole moments are randomly oriented such that in average all magnetic moments cancel each other and the net magnetization is vanishing. If the electrons are brought inside an external magnetic field, the spins partially align such that a rather small net dipole moment is created which is aligned in the same direction as the external field. This is called paramagnetism. As soon as the external magnetic field is removed, the electrons lose their alignment and the overall magnetization is zero again.",
"If the distance between the electrons is reduced they start to interact with each other. Either through their direct magnetic interaction between the dipoles (dipole-dipole interaction) or through a quantum mechanical effect called exchange interaction. This causes the electrons to align with respect to their direct neighbor, either in a parallel or anti-parallel configuration. In the former case (ferromagnetism) the individual magnetic moments add up and a large net magnetization is maintained, even in the absence of an external magnetic field. In the anti-parallel case, it is called antiferromagnetism and the net magetization is cancelled even in the presence of an external magnetic field.",
"In ferromagnets, the spins do align only within certain volumes, called the magnetic domains. Between these domains, these large net magnetizations may again be randomly oriented such that the overall magnetization of a piece of ferromagnetic metal is zero. If such a material is brought inside a sufficiently strong magnetic field, the domains rearrange such that all their magnetizations add up. The domains' orientations may be effectively \"locked-in\" so that when the external field is removed, the material maintains a significant amount of net magnetization and a magnet is obtained. This is called persistence."
] |
[
"This ",
"minutephysics",
" video illustrates some of these ideas pretty well, I think."
] |
[
"Each electron fundamentally has its own intrinsic dipole moment. Then the electrons and nuclei combine to form atoms, which have some total dipole moment.",
"Then many atoms assemble into a macroscopic piece of material. In a ferromagnetic material, neighboring magnetic dipoles interact strongly with each other so that an overall magnetization Can exist even if there is no external magnetic field.",
"The magnetic field that the object produces is just the sum of many small magnetic fields due to the dipole moments of the particles that make it up."
] |
[
"Why isn't the Program Counter / Instruction Pointer register directly exposed?"
] |
[
false
] |
Why isn't the Program Counter / Instruction Pointer directly exposed like the other registers? Wouldn't that make direct and relative branches/jumps possible by writing directly a value to it or add/subtract from it, without the need to have extra opcodes for unconditional branches/jumps? Would it help the compiler to have all the possibilities of the ALU to create more efficient ways of program flow? Additional Question: Would it be useful to have an opcode that causes the content of a register to be used as the next instruction? (didn't System/360 have something like that?)
|
[
"Two thoughts come to mind:",
"jmp *%eax"
] |
[
"If you look at the way that most ISAs are designed, you'll see that store opcodes typically reserve some number of bits in the opcode to designate the target register. For example, 0x1001 might mean \"store in R1\" and 0x1002 might mean \"store in R2\". ",
"If you change your ISA to treat PC as another general-purpose register, then you basically end up spending an extra bit of your opcode to allow PC to be represented; for example, in a 16-register CPU, you'd use 4 bits to represent the 16 registers, so you'd have to add a 5th bit to represent your 17th register (the PC). ",
"Now you either have to implement various arithmetic operations on your PC, which is a waste of silicon (for example, nobody in their mind will ever need logical XOR on their PC), or you end up having to special-case your PC so that only some arithmetic operations apply to it. ",
"If you do the latter, then you might as well have used different opcodes to start with. Separate opcodes would almost certainly make your overall implementation simpler.",
"Bonus answer: if you are generating executable code on the fly (which is a niche use case to start with — you're basically looking at compilers and interpreters there), then you are almost certainly interested in optimizing that executable code. To properly do optimizations at opcode level (aka peephole optimizations), you need access to multiple nearby opcodes. So you want a window into your executable code that is bigger than a single register. At that point you are looking at memory access, and optimizing that memory access with register allocation, so the ability to execute a single register's worth of code is essentially pointless."
] |
[
"Yes, I would agree with this. I think the OP however is asking why it isn't possible to do something like PC = ADD(R1,R2) or something. And the fact is, some ISA have that ability. But more importantly, doing that would make the pipeline more complicated. As it stands we have stages of the pipeline and each stage can cause problems in other stages because of needing a result from another stage or using a value that hasn't been computed or from incorrect branch prediction. By having specific jump and branch codes we can optimize the pipeline to deal with those codes in a specific way, where as using ADD we do not always want to have the same effect on the pipeline. "
] |
[
"Why are diamagnetic substances weakly repelled by magnets?"
] |
[
false
] | null |
[
"Because when a diamagnetic material is held in an external magnetic field, a magnetic field is induced inside the material which opposes the external field. See ",
"this picture",
"."
] |
[
"This picture is also instructive. Inside a diamagnet, the flux density is decreased: ",
"https://commons.wikimedia.org/wiki/File:Magnetic_Permeability-no-caption.gif"
] |
[
"Just to be sure, this is why soda cans slightly move when a strong magnet is moved near it, right?"
] |
[
"[Astrophysics] How is it that the scattered matter of the \"big bang\" isn't an even spread across our cosmos and instead, we have enormous stars, small stars, humongous galaxies, and unfathomable voids between galaxies?"
] |
[
false
] | null |
[
"It is evenly spread, on very large scales (measured in the hundreds of millions of light years). All the structure on smaller scales is the result of slight variations in density (about 1 part in 100,000) in the early universe, which have since grown through gravitational attraction.",
"edit: clarified scale of homogeneity"
] |
[
"LSS does not extend to arbitrarily large scales - again, there's a certain length scale beyond which homogeneity sets in. You can see this visually in ",
"maps of LSS from numerical simulations",
", and it is also apparent from observational measurements e.g. of the ",
"galaxy correlation function",
", which drops to 0 at the largest scales (meaning that on those scales, galaxies are just randomly distributed with respect to each other i.e. there is no structure)."
] |
[
"There are superclusters and supervoids, yes, but there aren't any structures larger than that - there are no \"super-super-clusters\".",
"So if you compare two different regions of space each big enough to contain many superclusters/voids, they will look very similar."
] |
[
"Could negative energy scalar fields be involved in spontaneous symmetry breaking?"
] |
[
false
] | null |
[
"What do you mean as the energy level of the field?"
] |
[
"Are you referring to the ground state energy? The ground state energy can be negative in a QFT. But in a pure QFT context, this is a little ambiguous because the ground state energy needs to be renormalized. This is further complicated by the fact that it is not really an observable in a QFT unless you consider quantum gravity, but in that case QFT seems to break down....",
"I've worked with QFTs in contexts where quantum gravity is not relevant but spontaneous symmetry breaking was, and in that case the actual value of the ground state energy has no effect on the physics, only differences in the ground state energy as a function of the couplings is important."
] |
[
"I suppose my question now is can a gauge field have a \"negative\" energy or is this restricted to gravity. I was assuming that the energy value in take for example ",
"The Mexican Hat Potential Figure",
" is how high or low the scalar field. But my question would be void if there is no such thing as \"negative\" energy. "
] |
[
"How do celestial bodies become tidally locked?"
] |
[
false
] | null |
[
"As they spin the side closest to the source of gravity gets slightly pulled towards the middle more than the other side elongating it slightly, as it spins the elongated side keeps changing slowing the spinning until one side stays constantly facing the centre "
] |
[
"Cheers very much, nice concise explanation 😊 So, is it essentially friction that brings the orbital and rotational periods into sync? And what happens to the angular momentum?"
] |
[
"Consider a body b1 of mass M1 with some body b2 of mass M2 orbiting it where M1 > M2. b1 will raise a tidally excited bulge that when ignoring orbital motion will align with the line of centres between the two bodies. When we consider orbital and spin motion of the body then as long as there is a mismatch between the spin period of b2 and the orbital period then due to dissipation processes (viscosity for fluid bodies) in b2 the bulge will miss-align with the line of centres. ",
"The bulge raised on b2 alters the gravitational potential of b2 which allows for an exchange of momentum's with b1. The result on b2 is that there is a loss (or gain depending on the difference in the spin and orbital periods direction) of spin angular momentum over time such that the periods of the spin and orbit end up matching. b2 is then tidally locked to b1. ",
"But this is not the end of the story as b1 does not have to be tidally locked to b2 and so there will be a continued evolution of the system."
] |
[
"We recently named elements 114 and 116. Has research begun on finding elements over 118?"
] |
[
false
] | null |
[
"It's not so much finding as inventing."
] |
[
"For those that don't get it, the newest elements have been named those funny words for simplicity's sake. The newest elements have been being simply named things like Ununtrium (113-ium) and Ununpentium(115-ium) until such time as international committees can decide on what the new names will be.",
"TL;DR They haven't picked names yet."
] |
[
"Great point. It's not like these scientists are busting out microscopes hoping to find deposits in a mine.",
"They discover them by smashing atoms together and hoping for a new one."
] |
[
"Is there a limit to the number of immunity genes bacteria can carry?"
] |
[
false
] |
Is there a limit to the genome size of bacteria that carry immunities for agents such as penicillin? In other words, if mankind continues to develop anti-bacterial drugs, will strains of bacteria be able to continue evolving immunity genes?
|
[
"Now theoretically, there must be a physical limit to the quantity of DNA that can be present in a typically sized bacterial cell (or any cell, for that matter). However, realistically it's probably never ever going to occur, due to the huge, vast quantities of DNA that can fit in one cell. The ameboid Polychaos dubium has the largest known genome of any organism (670 gigabases, that's 670,000,000,000 bases). Your average bacteria has a genome of 1mb to 10mb (megabase), and even though an amoeba cell is much bigger than your average bacterium, it can't account for such a discrepancy.",
"(Interestingly, there's absolutely no correlation between genome size and organism complexity - we only have about 3.2 gigabases in our genome.)",
"And even if you could overload a cell with DNA, the chance of it occurring in evolution is just as low - without a selection pressure genes are lost by neutral evolution and a number of other mechanisms. Unless we keep using ever bigger cocktails of antibiotics, and never retire old antibiotics even though they don't work anymore, then bacteria will not maintain every single resistance gene."
] |
[
"Maybe is the correct term to use! Now I have no idea how long it would take for a gene to be lost from a single bacterial line without any selection pressure, but it would probably be quite a long time. But even if you stopped using the antibiotic for a very long time, as soon as you start using it again, you would only need a few strains to be carrying it still to rapidly spread it throughout the population again. ",
"You have to remember that there are more individual bacteria on the planet than we can possibly imagine, and the selection pressures on each of them will all differ slightly, so the rate of gene loss won't be the same.",
"Basically, I'd have to guess that once we have a situation in which an antibiotic is entirely useless, I don't think it's realistically going to be used again (in that circumstance)."
] |
[
"Maybe is the correct term to use! Now I have no idea how long it would take for a gene to be lost from a single bacterial line without any selection pressure, but it would probably be quite a long time. But even if you stopped using the antibiotic for a very long time, as soon as you start using it again, you would only need a few strains to be carrying it still to rapidly spread it throughout the population again. ",
"You have to remember that there are more individual bacteria on the planet than we can possibly imagine, and the selection pressures on each of them will all differ slightly, so the rate of gene loss won't be the same.",
"Basically, I'd have to guess that once we have a situation in which an antibiotic is entirely useless, I don't think it's realistically going to be used again (in that circumstance)."
] |
[
"Is it rough underwater for fish while a storm is making the ocean surface choppy with big waves?"
] |
[
false
] | null |
[
"The first few feet are choppy and jerky then its much calmer. I don’t know the ratio, but based on wave turbulence, a 3 foot wave creates 1-2 foot of under current. Most fish are well below the disturbance is my guess. "
] |
[
"A particle in the water at the surface moves in an orbit in response to any waves. At the surface, the diameter of this orbital path is equal to the height of the wave, but as you say this rapidly drops off. Orbits decrease in size until the motion is essentially gone at a depth equal to half the wavelength. "
] |
[
"From my own experience it can be a bit more at the coast, i often had quite strong wave currents at 3m depth with waves that were a lot smaller. But maybe that has to do with the waves being pushed up against the coast."
] |
[
"If you dug a hole straight down to the other side of the earth, what would happen if you dropped something through it?"
] |
[
false
] |
This is pretending there’s no core or anything of that matter that would effect it. How would gravity effect it? What would happen? Would it get stuck in the middle, would it gain enough velocity to shoot out the other side?
|
[
"The object would accelerate towards the core. Once at the core, there is no gravity, so the speed of the object doesn't change at the core. So the object will shoot straight through towards the other side.",
"If there is no air resistance, the object will make it to approximately the same height that it was dropped from on the other side. At that point, it would finally come to a stop, before being pulled back down. The object would continue to oscillate between the two ends of the tunnel.",
"With air resistance, the object gets slowed down gradually and would reach a lower height with each oscillation until it finally settles in the center of the Earth."
] |
[
"To add one variable, would the earth’s rotation interfere? I’m having trouble getting my head around this. It seems that the nut (I’m imagining a knuckle-sized hex bolt) would be continue in a “westerly” direction as does the earth’s surface. So would it bonk onto the edge at some point since it isn’t pinned down to the earth’s surface?",
"Yes. It is essentially a manifestation of the Coriolis effect. In order for the object's path to be unimpeded the hole actually ",
"has to curve",
" (except in the special case where the hole is directly on the Earth's rotational axis, of course)."
] |
[
"To add one variable, would the earth’s rotation interfere? \nI’m having trouble getting my head around this. It seems that the nut (I’m imagining a knuckle-sized hex bolt) would be continue in a “westerly” direction as does the earth’s surface.\nSo would it bonk onto the edge at some point since it isn’t pinned down to the earth’s surface?",
"I guess a similar question would be if an airplane follows the earth’s rotation so the same point is below, and someone drops a nut :-), if there were no wind resistance, would the nut hit that same point, or would it over or under shoot?"
] |
[
"How was Fermat's Last Theorem eventually proved?"
] |
[
false
] |
I am more looking for an overview than an in-depth answer, as I know its extremely complicated.
|
[
" A nontrivial solution to a",
"+b",
"=c",
" in the integers would require some seriously exotic arithmetic objects. We (Wiles) proved that such objects do not exist.",
"I'm going to go a little crazy. I'm not going to go into mathematical detail or anything, more of give an overview and tell aspects of the story of it that aren't really told often. It's a good story, but you can get the \"canon story\" of it from many different places. I'm just not going to give a quick explanation that focuses on the particular idea of the proof, rather I'm gonna try to give an idea of the historical context and mathematical ideas surrounding it so that the particular ideas of the proof are not as out-of-the-blue.",
"There are more brief overviews of it ",
"Here",
" and ",
"Here",
", and there's a wonderful documentary by the BBC floating around on it that explains it very well and accessibly (I'm definitely not suggesting to use Google to search for \"BBC Fermat's Last Theorem\" and find a copy of it on Vimeo. Definitely don't do that.). I'd also recommend the book ",
" on it. I even give some explanations about it in this sub ",
"here",
" and ",
"here",
", so I'm also tired of giving the same story a little bit.",
"An equation like a",
"+b",
"=c",
" puts a lot of strain on the arithmetic of the integers, and it is hard to pin down exactly what is going on when we restrict ourselves just to integer arithmetic. A lot of weird and abstract number theory was invented in order to use more sophisticated number systems to investigate this equation. A mathematician named Kummer initially thought that he had figured it out like 150 years ago by temporarily lifting a potential solution to a more a higher order number system (called a ",
"Cyclotomic Field",
"). But what he discovered after careful work is that things that he thought he could rely on about arithmetic, particularly the unique factorization of numbers into primes, does not hold in these higher order number systems and this was a fatal flaw in his proof (though, it works well enough in some of these number systems, so he proved it for a large number of exponents for the equation, potentially infinitely many, ",
"we don't know yet",
"). But Kummer's work opened the door to modern Number Theory and Abstract Algebra, giving us a way to investigate new arithmetical objects explicitly.",
"An interesting thing happened in the early 20th Century, and that was the \"completion\" of Class Field Theory. People really started to get interested in what kinds of higher order number systems, called ",
"Number Fields",
", existed and if we could \"make\" them. Class Field Theory is a classification of the simplest type of number fields. After spending some time understanding how this classification worked, they found out how to look at it in a really good way. Essentially what happened is that there are two types of objects: One arithmetic in nature and one analytic (think: Calculus or Fourier transforms) in nature. Class Field Theory wanted to understand the arithmetic objects. The conclusion of Class Field Theory was that these two things were, in a way, actually the same thing. Somehow, this analytic object where you could do Fourier transforms and integrals, contained exactly the information needed to create these particular kinds of number fields. This explicit connection was groundbreaking, and done as a PhD thesis of the now legendary John Tate (this thesis even has ",
"its own Wikipedia page",
").",
"Largely independent from explicit investigations into Fermat's Last Theorem and Class Field Theory, other number theorists were figuring out the power of other mathematical objects. The troupe of Hardy, Littlewood, and, most importantly, Ramanujan (somewhat building off the work of Dirichlet and Riemann) discovered the power of weird functions that could encode things of number theoretic interest as properties that we usually investigate using calculus. These took advantage of arithmetic properties of infinite sums to reinterpret number theory problems as (essentially) calculus problems and Fourier problems. A lot of really big questions were investigated using these advanced analytic functions and methods. For instance, Kurt Heegner proved a ",
"famous conjecture of Gauss",
" about number theory that was really groundbreaking. It answered questions about divisibility of certain types of higher order number systems, and Heegner proved it using these special kinds of functions called, which are called ",
"Modular Forms",
".",
"Around the time that Modular Forms were really picking up, other number theorists were realizing the power of certain kinds of equations. Particularly, an equation like y",
"=x",
"+ax+b is like a conic, but more complicated. These kinds of equations and their solutions are called ",
"Elliptic Curves",
". What is surprising is that they naturally create their own kind of arithmetic on them. Moreover, this arithmetic is, in a way, more sophisticated, complex, and powerful than ordinary number systems, even higher order ones (I go into detail about this ",
"here",
"). ",
"Now, Class Field Theory uses analytic objects to understand arithmetic objects (and vice versa). Some crazy mathematicians noticed some similarities between Modular Forms and the analytic objects of Class Field Theory, but more sophisticated, moreover, Elliptic Curves had found their way into Class Field Theory, providing a slightly more explicit extension of it in very special cases. But these mathematicians posited an outlandish idea: Maybe there was a Class Field Theory-like connection between Modular Forms and Elliptic Curves? If we want to understand the complicated arithmetic of Elliptic Curves, then maybe we can do so using Modular Forms in a way analogous to Class Field Theory? (Of course, there are a lot of missing details and their conclusions were based off of a whole lot more, and there may be some inaccuracies, but this is the gist.) These were Japanese mathematicians named Shimura and Taniyama, and their conjecture is called the ",
"Shimura-Taniyama Conjecture",
".",
"Okay, at this point, we haven't said much about Fermat's Last Theorem. This is because where we left it with Kummer, mathematicians didn't really have the capability to really investigate its complexity. But now we have all this new stuff, more powerful machinery, and abstract understanding of arithmetic and number theory. This is when Gerhard Frey used a hypothetical nontrivial solution a",
"+b",
"=c",
" to create an Elliptic Curve called a ",
"Frey Curve",
". The explicit equation for such a curve is y",
"=x(x-a",
")(x+b",
"). So we have a solution to a really sophisticated equation creating an elliptic curve, an object that is capable of tremendous arithmetic power. Some interesting things about the exoticness of such an elliptic curve that seemed ",
". But no one could prove the wrongness or, even initially, precisely formulate what was wrong about it.",
"This is when the legend JP Serre came in with the ",
"Serre Modularity Conjecture",
". This basically took all these ideas and results that were around at the time (including the unmentioned work of Robert Langlands, whose ideas are still out-of-this-world) and formulated a very explicit conjecture about the kind of arithmetic information that modular forms contain. This conjecture explicitly states what is \"wrong\" about Frey curves and, if proven, Serre's conjecture would directly prove Fermat's Last Theorem in like two lines (Serre's Conjecture is now a theorem, btw, thanks to Khare and Wintenberger). Essentially, Serre's Conjecture says that a potential solution to Fermat's Equation is too powerful and would result in an elliptic curve whose arithmetic is so exotic that it can't exist.",
"But Serre's Modularity Conjecture was very ambitious for the time. It was like inventing a nuke when everyone else had just discovered gunpowder. But if Serre's Modularity Conjecture says that it is modular forms that are what put constraints around Fermat's Last Theorem through elliptic curves, then maybe we can \"simplify\" things a little bit by using the Taniyama-Shimura Conjecture, which conjectures and explicit connection between elliptic curves and modular forms? If you then assume the Taniyama-Shimura Conjecture, then you can use a simplified version of Serre's Modularity Conjecture to prove Fermat's Last Theorem. This simplified conjecture is called ",
"Serre's Epsilon Conjecture",
" (in math, epsilon usually means something really small, so it's kinda a joke). The Epsilon Conjecture was accessible and proved through genius arguments of Ken Ribet pretty quickly. It's now known as Ribet's Theorem.",
"What this means is that all you need to do to prove Fermat's Last Theorem is to prove the Taniyama-Shimura Conjecture! The only issue is that many people saw the Taniyama-Shimura Conjecture as just as impossible as Serre's Modularity Conjecture."
] |
[
"This is where Wiles comes in to the story. He needed to prove the Taniyama-Shimura Conjecture, which says that for every elliptic curve, there is an associated modular form that contains the same information as it. I'm going to try to explain the basics of his approach in an approachable way that isn't incorrect. I will probably fail at both, because it is so advanced.",
"Around this time, a mathematician name Berry Mazur found an object that was able to parameterize different kinds of complex arithmetics (of which elliptic curves are a part of). This was a fairly tangible object that we could work with. Moreover, there were also object that parameterize the modular forms in an advanced way as well. Wiles found a way to associate these two objects. Moreover, this association corresponded to the kind of association that we were looking for in the Taniyama-Shimura Conjecture. If Wiles could just show that this association accounted for all elliptic curves (of certain type), then this would prove the Taniyama-Shimura Conjecture and, consequently, Fermat's Last Theorem.",
"The way he did this was by looking at smaller, finite, parts of these parameterizing objects that were associated with each other and showing that they are the same size. This was not easy. Interestingly, he had to prove a very advanced form of a Class Number Formula which are some of the first things that Kummer looked at, and the kinds of things that Heegner's result applies to. I don't think that there is any accessible way to discuss how he proved this though, because it's a super sophisticated argument relying on very abstract connections and ideas. It's basically a sophisticated induction argument, but the base case is super-super hard.",
"Needless to say, he was able to prove his Class Number Formula. The final step was to apply it directly to elliptic curves concretely. He found that he could very easily do this for one class of elliptic curves, thanks to a groundbreaking theorem of Langlands and Tunnell a decade earlier. But there was still a final class of elliptic curves that the theorem of Langlands and Tunnell wouldn't work with. He then came up with one of the funnest arguments in Fermat's Last Theorem. He found that if you took an elliptic curve from the bad class, then you could find a different elliptic curve that was \"close\" to it that was in the good class, where you could then apply Wiles' result to. But, it turns out, that these two elliptic curves are \"close enough\" to each other that the conclusions of Wiles' result on the good one ",
" over to the bad one, allowing you to transfer the conclusion. Hence proving the Taniyama-Shimura Conjecture and, therefore, Fermat's Last Theorem."
] |
[
"If you don't feel comfortable with actually doing math problems and just want more of the story, then ",
"Fermat's Enigma",
" is great.",
"If you haven't really done advanced math (in this context, Calc1-3, Diffeq and Linear Algebra are not advanced), but are comfortable with equations and manipulations and such, then probably ",
"A Friendly Introduction to Number Theory",
" would be good. Lots of motivation and helping you through proofs and things. ",
"If you have taken advanced undergrad courses, then ",
"A Classical Introduction to Modern Number Theory",
" is good. A little dry, but covers a lot of great stuff. Also, Apostol's ",
"Introduction to Analytic Number Theory",
" is essentially an intro the other half of number theory not covered in the first book.",
"Intro number theory books can be a little dry, which I don't like, so it may be good to keep a regiment of Numberphile or 3Blue1Brown going on to boost the inspiration while you go through the books.",
"If you're more advanced, like have taken grad classes in math, then ",
"Primes of the Form x",
"+ny",
" is a really, really excellent book that covers a lot of number theory, up through Class Field Theory and the application of Elliptic Curves to it. Great for someone comfortable with math that hasn't really done number theory at all."
] |
[
"Would it be possible to create a device to generate darkness?"
] |
[
false
] |
Inspired by a bit in a kid's show my son watches, would it be possible to create a device to generate darkness? Imagine turning on a lightbulb but it instead shrouds the area in darkness. Is such a thing possible?
|
[
"Not really. Darkness isn't a substance that we can create, it is just a lack of light. In order to pull the light in a direction it wouldn't otherwise go you would need essentially a black hole, not something we can build and market very well.",
"Taking a different approach, something like a smoke bomb could potentially work. You would either need to fill all the air space between the objects being lit and your eyes, or cover all surfaces in a substance that absorbs all visible light. If light can't bounce off of an object and hit your eye then you can't see it, essentially creating darkness. Neither one of those options are quite as easy as turning on a darkness bulb but they could work."
] |
[
"I think those are called curtains. :)",
"Though something like that might be possible, but it would involve basically getting something to remove the light from a room (by absorption for instance). Though you might have other unsavory effects since that energy has to go somewhere which usually means it gets repackaged as something like heat energy. Which I'm sure you can figure out what that might do to a room. "
] |
[
"I would think it might also be feasible to create something that temporarily interferes with the signals of the optic nerve or the visual cortex. No need to eradicate photons if the people around can't detect them. Going off on a total sci fi tangent, that could be useful in a tactical situation, especially if the operatives were somehow shielded from the interference... targeted blindness grenades. "
] |
[
"How does fire act in very high pressures?"
] |
[
false
] |
For example fire in a room with 100 times athmospheric pressure.
|
[
"You know this is pretty interesting question I would say. You know how some gunpowder burn slowly when placed in ground as a single line? Same amount of gunpowder in a chamber bullet blocking the escape route of the expanding gasses from burning and you get a big boom. Same thing with engines. Fuel air mixture burns OK in atmospheric pressure, but once in the engine and compressed to around 10:1 and it's a small explosion.",
"",
"These things don't however necessarily compare to situation you are describing, but let's assume you mean like normal house fire where for example the curtains are burning. I would say that the fire would be much greater and faster than in normal house fire as there is 100x more air and oxygen for the fire to consume in the same space."
] |
[
"Based on testing that I have seen and done in ~2atm of pressure, yes the fire gets brighter, as long as there is a continual supply of fuel and oxygen. It acts similar when you fan a fire to stoke it. The fire burns larger and brighter"
] |
[
"This is the basis for how rocket engines work. There is an equation which gives the burn rate as a function of pressure; every fuel has a particular burn rate coefficient and exponent that go into this equation. At 1 atmosphere, things burn relatively slowly. When you turn up the pressure, the burn rate increases exponentially. So if you have a fire in a room at 100 atm, yes things will burn a lot faster.",
"Solid rocket motors rely especially on this principle; as it burns fuel, it generates pressure, which increases the burn rate, and so on until it reaches steady state."
] |
[
"What does it take to be considered a scientist."
] |
[
false
] | null |
[
"You have to be actively advancing knowledge of a particular field. So engineers and lab techs generally aren't scientists, although those are perfectly respectable careers."
] |
[
"Thanks, would you say a layman testing a theory could be considered a scientist then? \nAs a business major that loves science just curious as how I can contribute."
] |
[
"To be perfectly honest, it's such a specialized and technical field that it would be extremely difficult for anyone to contribute on a part-time basis."
] |
[
"Due to loss of mass via hawking radiation, could there be a black hole that has an escape velocity below the speed of light, thus visible? (Physics)"
] |
[
false
] | null |
[
"Then it wouldn't be black, would it? :) Hawking radiation reduces a black hole's mass. So the event horizon - the point where the escape velocity is the speed of light - is still there, it's just closer to the center of the black hole."
] |
[
"Short answer is that we don't know.",
"I believe the current leading theory is that it will evaporate away to nothing with a massive burst of energy in the last few milliseconds. ",
"But some predict there could be some subatomic remnant left. What that remnant is is anyone's guess. Some predict it would be a ",
"naked singularity,",
" which is a theoretical object even weirder than black holes."
] |
[
"No, he means one with the MASS of the moon. The event horizon of that black hole would be roughly the size of a grain of sand."
] |
[
"Does time reverse beneath the event horizon of a black hole?"
] |
[
false
] |
Does time reverse? If time accelerates to infinity as you approach the event horizon of a black hole, if you move beneath the event horizon, would math break down at infinity and begin reversing as some sort of law of physics? If inside this sphere, time were reversing and accelerating towards infinity, would the center represent the exact beginning of the black hole's little bubble universe? If time doesn't snap and reverse at infinity, could matter even enter a black hole without becoming trapped inside an infinite time dilation?
|
[
"If time accelerates to infinity as you approach the event horizon of a black hole, if you move beneath the event horizon, would math break down at infinity and begin reversing as some sort of law of physics?",
"No. The math does break down in ",
"Schwarzschild coordinates",
" along with a few other coordinate systems, but that's just because of the coordinate system. There are other systems where it doesn't break down.",
"Once you're inside the black hole, time points towards the singularity. Escaping the black hole, or even remaining the same distance from the center, requires moving faster than the speed of light. The exact direction that's in depends on the coordinate system. In Schwarzschild coordinates, the singularity is located infinitely far in the future, so time is generally going in the direction you expect it to go, but it might be better to think of it as time turning sideways."
] |
[
"Theoretical physics and physicists are important, and at least some 'armchair physicists' are in a state of trying to improve their understanding of those theories by trying to retell them to others. But yeah, generally it seems like they are talking out of their asses.",
"You have to go down that theoretical physics \"what if this theory were true\" chain a long ways and end up at something we could actually observe before I personally care. As far as I know, from all the black hole physics I've read, there aren't any theories advanced enough to suggest blackhole observations we should be looking for/could see. This is similar to string theory for the most part, lots of mathematical descriptions that don't result in predictions that observational physics can look for to test the theory."
] |
[
"Straightforward, practical answer: we don't know. Currently, I don't think we can know because we can't gain information from inside a black hole. There are lots of complex mathematical and theoretical physical theories that may or may not explain what happens inside a black hole, and without evidence from inside one we can't tell which ones may be right and which ones may be wrong."
] |
[
"Is there anything actually orbiting the sun along its North/South axis in our solar system?"
] |
[
false
] |
Obviously all of the planets in our solar system orbit along a somewhat flat plane (although I’d be curious to know how much distance there is between the “lowest” and “highest” planets). But given the sheer size of the solar system it’s seems absurd to me that there isn’t at least some material orbiting perpendicular to the majority of the mass. So is there anything at all orbiting in that axis?
|
[
"It is theorized there is Oort cloud out there, beyond the heliopause. It is suggested to consist of small icy objects forming a sphere around the Sun. Also, it is believed to be the source of comets. But since all those objects are very far and do not emit light themselves nobody on Earth has seen them."
] |
[
"There are objects out there with odd orbits, but generally everything is nearly along a flat plane because of the conservation of angular momentum. Given enough time, every direction but one sort of cancels out. Objects near the sun that violate this general rule were disturbed from their previous orbit, and objects far from the sun (Pluto) haven't been impacted enough to have their directions canceled out like everything else."
] |
[
"As you said, most of the planets are very close to a plane. ",
"Wikipedia has a list of their inclinations.",
" Planets make up most of the mass of the solar system (after the Sun, of course). So anything beyond that will be very small objects such as comets or asteroids.",
"Anyway, yes, there are a few asteroids with weird orbital inclinations, some of them close to 90°. ",
"https://en.wikipedia.org/wiki/List_of_exceptional_asteroids"
] |
[
"If an ape is \"genetically identical over 98%\" what does this exactly mean?"
] |
[
false
] |
I have not studied biology in high school and I've just become really interested in the study of evolution and biology and I have difficulties grasping this "gene similarity" concept. I know, for instance, that genetically, gorilla's are about 98% the same as us but I find it hard to understand this. If this similarity is this immense, why do they look, behave and think so different than us? I hope someone can answer this. Thanks a lot!
|
[
"It's not a very meaningful number. 98% ",
" like a lot, but it's not. We've got over 70% of genes in common with a sea sponge. And a significant amount in common with ",
" life form. ",
"These big differences in visible, macroscopic changes don't correspond to equally big changes at the microscopic level. At the cellular level, the differences are small. We've got a lot more in common with most eucaryotic life forms, such as yeast, than yeast has in common with bacteria, even though those are both single-celled life forms."
] |
[
"I support the above answer.",
"The thing to think about here is that all (well, almost all) life forms have to do the same things metabolically: break down and build up fats, proteins, and carbohydrates. So the enzymes are often very similar because the tasks are similar. The differences in the genome are related to environmental differences. For example, a fish at extreme depth needs a different enzyme structure to perform the same reaction as a human at sea level pressure."
] |
[
"If you take all of the DNA base pairs in humans and compare them to gorillas, 98% will be identical in the same location. ",
"As Platypuskeeper pointed out, this number isn't terribly useful because it's more important which genes are changing, not really how many total have changed. We look absolutely nothing like daffodils, but we do share a common ancestry (way, WAY back) and our genetic codes are 25% the same. Does this mean that a human is 25% daffodil? Well, no. Most of that DNA code is probably for something universal to all eukaryotes at a cellular level or somesuch thing. "
] |
[
"To what level can parasympathetic systems 'learn' or be influenced by things like psychological stimuli? (If I only Reddit while I go to the bathroom, will my body 'want' to go to the bathroom more often?)"
] |
[
false
] |
I guess my specific question is: To what level, if any, can an external (psychological?) stimulus affect a parasympathetic system (in this case, bowel movements)? Will my body make me want to poop more often so it can get its 'reddit fix'? I'd like to control my use of Reddit a little more, and one easy way to seems to be to limit myself to reading my frontpage only during the times I am using the restroom, because I don't control exactly when my body 'needs' to go. But then I got thinking, 'Maybe that would cause some issue where my body 'wants' to go more often', kind of like a learned behavior. To what level can parasympathetic systems 'learn' or be influenced by things like psychological stimuli?
|
[
"From a psychological standpoint, assuming Reddit is a significant reward to you (meaning something that you enjoy enough to seek out) then what is likely to happen is that your threshold for deciding when you need to use the bathroom will lower. ",
"In other words, if today your bathroom habits are \"I only use the bathroom when I ",
" have to go,\" if you attach a Reddit reward to it, you might use the bathroom even when you only sort-of have to go because you've conditioned yourself to view using the toilet as being pleasurable and so you will tend to seek out using the toilet more often. ",
"This is known as \"operant conditioning,\" and is not just limited to redditing on the toilet. It's one of the fundamentals of behaviorist psychology, and is the basis of a huge number of things we humans do when we try to modify our, or someone else's behavior. Parents spank their children because they want the children to associate whatever they just did with pain in the hopes that they will avoid doing it. They praise their children because they want the children to associate whatever they just did with the reward of feeling good about themselves, in the hopes they will do more of it in the future. Police give speeding tickets to condition us to drive slow, and they also hold citizen award ceremonies to condition people to help the community. ",
"This kind of conditioning works even if there is no intent behind it - i.e. if a child touches a hot stove, he'll be conditioned not to touch the stove again, even though there was no conscious objective to keep the kid from doing that because the parent (hopefully) didn't heat the stove up in order to condition him not to touch it. ",
"So from a psychological perspective, this functions independently of your intestines. You'll seek out the toilet in order to Reddit."
] |
[
"This also has some very interesting links to drug addiction, resistance, and withdraws. There was a study with rats, where two rats were hooked up to heroin pumps. One rat had a button that activated both pumps, so it \"knew\" when to expect a dose of the drug. The second rat had no reliable signals of when it would be exposed to the drug. The first rat would push the button and get its dose, it would wear off, then it would go push it again. The time between presses gradually got shorter. Mean while, the second rat was completely passed out in the cage next to it, and developed quite a bit less resistance to the drugs effects. It appears that our bodies begin to counter-act the effects of drugs even before we are exposed to them. This also helps to explain why in drug culture, prepping drugs for someone else is a big deal, because their body doesn't have as many cues to begin preparing for the drug. ",
"Our sense of hunger is connected to blood sugar drops, because our bodies release insulin at certain times every day, when it \"expects\" to eat. It also releases insulin when you see pictures of food, and when you drink diet sodas that taste sweet. This is why people tend to eat more and gain weight while drinking diet sodas, except when they drink them with meals. ",
"Tl;dr Operant conditioning makes you eat, and less high. "
] |
[
"Thank-you both for the detailed information, and the follow-up."
] |
[
"If the strength of an acid is based on concentration, why are acids like Sulfuric Acid always considered so dangerous compared to others?"
] |
[
false
] |
I was in a lap and we were working with acetic acid (vinegar) and it was highly concentrated. This idiot says something along the lines of Vinegar aint dangerous and takes a sip. I then watched him spit out his gums. Why is it that acids like Sulfuric, Nitic, etc are always portrayed as these ultimately corrosive substances despite concentration? Is there something to these "famous" acids that make them more deadly? And arent bases scarier to spill on you?
|
[
"Well some factors are:",
"A) For same concentrations, some acids are way stronger than others because they give away their protons much more easily.",
"B) Acids like sulfuric acid can “donate“ multiple protons per acid-molecule giving it more potential to turn solutions acidic.",
"But as you already noticed ofc concentration does matter. If you dillude sulfuric acid enough it will eventually be harmless as well.",
"To give a comparison: We generally consider uranium as more dangerous than tobacco yet a single radioactive isotope of uranium is nothing compared to smoking a few packs a day. "
] |
[
"One thing not mentioned yet is that how \"dangerous\" an acid is can also depend on chemical properties unrelated to acidity. Hydroflouric acid for example is a powerful poison and sulfuric acid extremely hygroscopic, two properties which make those acids risky to work with. There is no one factor all \"famous\" acids have in common, mostly it's just that these are the ones that can kill you more easily."
] |
[
"Since another poster already answered most of this I won't repeat them. ",
"To answer your final question, I'm not sure that they are necessarily \"scarier\" so much as equally horrifying. ",
"It's like asking if you prefer to be lit on fire with gasoline or on a stake, is one really that much better in the end? ",
"Strong or superbases are the opposite of acids, instead of \"donating\" protons, superbases deprotanate other atoms. In other words, they literally break apart molecules to steal protons because they want them. Look up the lithium monoxide anion if you want an idea what these things can do."
] |
[
"What is actually doing the work?"
] |
[
false
] |
It is something you learn very early on in physics that magnetic fields do no work due to a cross product being involved. However, in the case when you take a magnet, and lower it slowly down to a magnetic piece of metal, and it suddenly flies up and attached itself to the magnet, what is actually doing the work against gravity to raise it? Or is the whole "magnetic fields do no work thing" not the whole story that I should have learned before getting my degree...
|
[
"On an atomic level, electrons spinning or orbiting is what causes the magnetic field to work. The grand mystery you are asking, or perhaps trying to get to the fundamental nature of is where does the energy whichh is posessed by subatomic level come from? Not a physicist here but i got a couple of them to talk about it wih me and try to explain this exact question. I hope I did not misunderstand. "
] |
[
"Yes, I am familiar with where the magnetic fields come from, but I am asking exactly what is pulling against gravity since I have learned in 4 years of physics courses that magnetic fields ",
"do no work."
] |
[
"Since the magnetic force from the magnet and the piece of the metal is the same. Without your intervention the magnet would also be pulled down to the metal. So, is the work to lift the metal piece up to the magnet being done by you, when you hold the magnet preventing it from being pulled down to the metal piece?"
] |
[
"What kind of balance system do insects use?"
] |
[
false
] | null |
[
"I believe the OP was asking about the sense of balance or equilibrioception in insects, not fluid balance.",
"Most flying insects have what is called a ",
"Johnston's organ",
" as part of their antennae which I believe acts as a sort of 3D accelerometer. This tells them which way gravity is pulling, as well as other information while they fly. "
] |
[
"Some insects instead use ",
"halteres",
", which are basically dummy wings that flap along with the real wings. When the insect changes its flight path, these structures try to keep vibrating in the same plane. This leads to Coriolis acceleration, which creates a force that is sensed by structures at the base of the halteres. This structure is really similar to some MEMS gyroscopes."
] |
[
"Thank-you very much :D"
] |
[
"Why does blue seem to be the hardest color to achieve for so many things, such as LEDs, fireworks, and paints or dyes?"
] |
[
false
] |
What makes blue special? Also what category would this be?
|
[
"Not an answer but blue is the shortest wavelength and therefore the highest energy of the visible spectrum. And higher energy is harder all around to deal with. For example, 7,000 kelvin light bulbs emit a lot of blue spectrum and many people find them to be burning and fatiguing of their vision. Another example is radio engineering, where higher frequencies are orders of magnitude more difficult to design and have increasingly erratic behavior. So it is built in to the wavelength/frequency of the light wave and the amount of energy required to generate it."
] |
[
"Blue LEDs came along after red, yellow and green, but today white LEDs use a blue LED plus phosphors to make red and green. So production of blue LEDs is commonplace if not exactly \"easy\". ",
"Deep blue fireworks are difficult because the burning copper compounds don't emit only blue. They emit blackbody radiation as well because of their heat. That makes for a less saturated blue. The temperature is critical. Too hot means more washed out. Too cool means less blue to start with. A similar effect happens when things are heated to incandescence. At first you see deep red, then orange, yellow, and white. The red doesn't go away as other wavelengths are added. You don't see an overall green or blue hue even though both wavelengths are present in a white hot object.",
"Is blue paint or dye difficult to make? I know blue is less common in nature than red, yellow, or brown, but green is also uncommon in animals. Many bright green snakes and frogs are actually blue and yellow. The blue comes from interference, the yellow from pigment. When they die, they sometimes turn blue as the yellow pigment fades away. "
] |
[
"The sky looks blue because of the Rayleigh effect, which is where the light scatters from the atmosphere. The shortest wave we can see is blue. ",
"Same thing happens in people with blue eyes. They don't actually have melanin in their irises, so the Rayleigh effect makes 'em blue. "
] |
[
"What is the (non-aesthetic) purpose of a gradient on the edge of an automobile windshield?"
] |
[
false
] |
I've read that it has something to do with tinting and preventing the edges from going yellow. If this is true how does it prevent it? Additionally, are windows still produced with gradients or has a new, better method been put into practice?
|
[
"Reduce sun glare"
] |
[
"And some cars have a black fringe around the edges. That's for aesthetics to hide the adhesive on cars without molding."
] |
[
"Visual Aid",
"Are we discussing the black that goes the whole way around, or the blue that's at the very top?"
] |
[
"How do painkillers work on a cellular level?"
] |
[
false
] |
I am interested in how painkillers work to essentially kill pain. I take an advil, this gets dissolved by my saliva and stomach acids. The chemical(s) infused in the drug get transported in my bloodstream to all parts of my body. I assume then that this chemical (drug) binds to certain cells where the pain is emitted from. Is this only to nerve cells because that is where the pain signal is coming from correct? So this chemical (drug) will bind to nerve cells to block pain? What exactly is it binding to and for how long? Does this create changes within the cell simultaneously, for example would certain transcription factors be activated to yield the production of different proteins? So I guess I have a two part question: how does a drug (infused with a chemical) firstly accomplish its goal on a cellular level (in this case blocking pain), and by doing so does this affect the landscape of the intercellular environment - what does on inside the cell in anything when this chemical binds to the nerve cell to block pain. Thank you!
|
[
"It depends on the painkiller. Different classes of medication have different mechanisms of action- as another poster mentioned NSAIDs affect the COX pathway. Capsaicin as another example essentially depletes Substance P from the site of application, and Substance P is one of the molecules involved in the transmission of pain signals to the body."
] |
[
"Here's a ",
"paper",
" giving an overview of the alternatives to gate control theory -- specificity and intensity -- with pointers in the bibliography for going further down said rabbit hole."
] |
[
"So, NSAIDs like ibuprofen are COX2 inhibitors. They don't really bind to the cells. They actually slow down the creation of cyclooxygenase which through a few chemical changes turns arachidonic acid into prostaglandin. Prostaglandin enzymes and COX both have functional roles in the pain pathway. Check out gate control theory if you'd like to really go down a rabbit hole on pain theory."
] |
[
"50° Celcius is unbearable weather, but sitting in a tub of 50° water is relaxing. Why?"
] |
[
false
] |
[deleted]
|
[
"Water has high specific heat and efficiently conducts heat into your skin, so once you start going above 37C the warming effect is definitely perceptible and quite strong. Heating from water is so efficient that once you start going above 40C-50C it surpasses your body's ability to regulate its temperature. You're better off in 40-50C air at that point since air is a poor conductor of heat and you can benefit from evaporational cooling through sweat.",
"And I'd take exception that 50C is relaxing... that feels pretty damn hot. Most hot tubs run at about 39-40C."
] |
[
"Serious question-- then shouldn't it be comfortable to stand outside in 50c naked?"
] |
[
"50",
" Celcius is ridiculously hot for bathing water. It would not be relaxing, it would be detrimental to health. i.e. Hyperthermia. You could last much longer in air of that temperature than water, so long as it was dry (e.g. desert) heat, with fewer ill effects."
] |
[
"Are there differences between species on the neurotransmitter levels?"
] |
[
false
] | null |
[
"Yes, there are. The example that comes to mind is the use of Octopamine in Drosophila neuro systems vs mammalian neuro systems. Octopamine is very important for Drosophila/invertebrate learning + memory, but not for mammalian learning + memory systems.",
"http://en.wikipedia.org/wiki/Octopamine"
] |
[
"Sorry, completely forgot about this post, thanks for the info!"
] |
[
"The most pronounced differences are between arthropods and other animals. Histamine is an important neurotransmitter in the sensory ",
"systems of insects",
" and plays a relatively minor role as a neurotransmitter in other animals. Also, the main excitatory neurotransmitter in mammals, birds, and reptiles is glutamate, while it is ",
"acetylcholine",
" in arthropods, although mammals use it at the neuromuscular junction. This last difference is taken advantage of my many insecticides, which target insect acetylcholinesterase, the enzyme that breaks the transmitter down to stop the signal, while mostly having no effect on human."
] |
[
"What happens to bacteria when it is engulfed by a white t-cell?"
] |
[
false
] |
Once a white t-cell engulfs bacteria the bacteria "dies". What happens to the actual physical part of the bacteria? Is it expelled from the t-cell through diffusion? Just curious. Thanks in advance
|
[
"First of all you got some of your terms mixed up here. T-cells are more commonly called white blood cells, just like B-cells for example. So it is admittedly not wrong calling it a white T-cell but usually they are just called T-cells.",
"And at least to my knowledge, T-cells are not able to engulf/phagocytose anything, are you thinking of macrophages maybe?\nThere two broad classes of T-cells, helper T-cells and killer T-cells. The first one recognizes signals of macrophages that have phagocytosed bacteria, then they produce lots of signaling molecules to help activate the immune system to fight the infection. The killer T-cells on the other hand can recognize cells that have been infected by viruses and then will release a set of factors which will end up in the cells getting killed by apoptosis.",
"But to answer your general question, what happens to phagocytosed bacteria. Essentially they are engulfed by the membrane which results in them being enclosed by a vesicle inside the cell. Then this vesicle fuses with what is known as a lysosome, basically the digestive tract of a cell. The vesicle becomes more and more acidic, due to several proton pumps in the membrane which activates enzymes that are able to slowly break down the parts of the bacteria into reusable components."
] |
[
"The gamma-delta T-cell subset are capable of ",
"phagocytosis",
", but yes, conventional alpha-beta T-cells don't have that same ability."
] |
[
"The process is called ",
"phagocytosis",
" and the compartment or vacuole that engulfs the bacterium fuses with an acidic vacuole called the ",
"lysosome",
" that contains enzymes that aid in the destruction of the bacterial cell. Certain cells such as macrophages, neutrophils, monocytes (which turn into macrophages upon entering tissues), and dendritic cells of the immune system are considered \"professional phagocytes\" because that is their primary role, but others can perform phagocytosis as well. Additionally, some pathogens can actually resist being engulfed or resist killing from the digestive enzymes and then escape the phagolysosome and replicate within the cytoplasm of the immune cell. This ",
"phenotype",
" is typical of intracellular bacterial pathogens such as ",
", ",
", ",
" (TB), and ",
" (Plague) species. "
] |
[
"When it is cold outside, but not cold enough to get frostbite, are a person's extremities at risk of acute damage in any way?"
] |
[
false
] |
When my hands get cold and it's 0 to 10 C outside, what can happen? Is there any need to worry about temperatures like that besides eventual hypothermia?
|
[
"Isn't frostbite caused by cell damage when the water in the body freeze => crystalize?"
] |
[
"I though windchill just increased the rate of heat loss but not the actual temperature, and therefor wouldn't cause freezing."
] |
[
"I looked some stuff up, you are totally right, I should have looked these things up from the beginning because I clearly can't remember them right anymore, sorry, my mistake."
] |
[
"Reading recent articles, I get that we recently spotted the most distant/oldest galaxy ever, 13.4 billion light years away. With my understanding of the expansion of the universe, this galaxy was much closer to us than 13.4 bn ly, at the time it looked like what we see of it today. Am I correct ?"
] |
[
false
] |
What I understand is that in 13.4 bn years (close to the universe age) light travels 13.4 bn ly. But when photons left that galaxy to reach us, their "starting point", at that time, was closer to our today position than 13.4 bn ly. So, now, that galaxy is 13.4 bn ly away from us, but was closer then. What was the actual distance at that time? I am getting confused with articles I have read, mixing both (distance and elapsed time), but I may think I understand the expansion of the universe, while I actually do not. Please enlighten me.
|
[
"There are several ways to measure distances in cosmology. Unfortunately, the one that press releases seem to always use is the ",
" (LTD) and is arguably the worst and most misleading distance measure.",
"The LTD is defined as follows. Let t",
" be the time from today since the big bang (to be clear, this is the time as measured in the isotropic CMB frame). In plain English, t",
" is the age of the universe. Let t",
" be the age of the universe when the light from that particular galaxy was emitted. Then the LTD is simply",
"LTD = ",
"(t",
"-t",
")",
"It is the distance that light in a non-expanding universe would have traveled in the time since the emission. (Of course, the entire idea of the big bang comes about because of metric expansion, so it's a rather contradictory definition, but you can start to see why I hate it.)",
"Note that the LTD is ",
" the distance that light would have traveled from the galaxy to Earth had the universe stopped expanding after that point in time. For reference, the galaxy you mention emitted the light we just now received when it was about 2.98 billion lightyears away in proper distance (explained below). So if the universe had stopped expanding at emission, the light would have traveled 2.98 billion lightyears. But the LTD of that galaxy is actually 13.4 billion lightyears. Yes, it's confusing, and part of the reason is that the LTD doesn't really make much sense as a distance measure anyway, despite its purpose in press releases to make the science more accessible. It's better to think of the LTD as really giving the time of emission t",
", which ",
" a physically meaningful number.",
"Since t",
" is between 0 and t",
", the LTD is always between 0 and ",
"t",
", which should hint why the press often only uses the LTD. If the age of the universe is 13.8 Gyr (gigayear = billion years), then the LTD can never be larger than 13.8 Gly (ly = lightyear). So you never have to run into the problem of explaining apparent faster-than-light speeds, which come about only because of coordinate speeds in an expanding universe. The primary reason the LTD is so terrible is that it doesn't represent anything physical.",
"There are several other notions of distance in cosmology: the angular size distance, the luminosity distance, the comoving distance, the proper distance, etc. Some of these are very useful for theoretical work while others are better for practical purposes of measurement. I should also mention that the only number that ",
" ever has an unambiguous meaning is the ",
" ",
" (from which we can deduce the various distances).",
"The ",
" is what we usually think of when we think of how to measure distance. Suppose that ",
" there were a chain of meter sticks stretching out from Earth to the galaxy in question. Suppose we also have a chain of observers along those meter sticks ready to take simultaneous measurements. (In cosmology, there ",
" a notion of simultaneity and these observers would be called isotropic, co-moving observers.) At this moment now, all of these observers record how many meter sticks are in their local vicinity. The total number of meter sticks from Earth to the galaxy is the ",
" (measured in meters, obviously). That is, if the universe stopped expanding right now, that would be the distance from Earth to the galaxy from now until forever.",
"If you are interested in getting a more useful measure of distance, you can use ",
"this calculator",
" which will convert LTD to proper distance. Type \"13.2\" into the box on the left labeled \"light travel time in Gyr\" and click the button labeled \"Flat\". On the right a list of various distances and times appears. Since at t = today, the proper distance and co-moving distance coincide, you are most likely interested in the \"comoving radial distance\" (which is 31.031 Gyr according to the calculator). So this particular galaxy is, ",
", about 31 Gly away from Earth. (The edge of the observable universe is a proper distance of 46.375 Gly from Earth, for reference.)",
"If you want to know how far away (in proper distance) the galaxy was when it ",
" the light, you need to do an extra calculation yourself that is not shown on that calculator. The calculator I linked gives the redshift ",
" at the top of the list on the right. The redshift and scale factor ",
"(t) are related by the equation",
"1+z = a(t",
")/a(t",
")",
"We normalize so that a(t",
") = 1. Hence we get",
"a(t",
") = 1/(1+z)",
"This is how proper distance scales back to the time of emission, relative to today. So the calculator gives z = 9.392 for our particular galaxy. Hence a(t",
") = 1/(10.392) = 0.0962. This tells you how much smaller proper distances were at the time of emission. The proper distance of the galaxy ",
" is 31 Gly. So the proper distance of the galaxy at time of emission was (31/10.392) Gly = 2.98 Gly. That is, the galaxy was 2.98 Gly away from the Milky Way galaxy at the time of emission."
] |
[
"So you are on to a subtle point about distances.",
"As a photon is emitted from galaxy A and travels to us at B the distance increases.",
"When we say 13.4bn ly we mean the distance that the photon detected today has traveled is 13.4bn ly. 13.8bn ly as the size of the universe (radius) is the most common figure given.",
"However we do recognize that in the intervening 13.8bn years the universe has grown and as such it is currently ~45bn ly in radius (however if a photon was emitted today it would take more than 45bn ly to cross that distance since the distance would continue to grow).",
"The actual number doesn't really matter though, all that matters is that we are consistent and we generally are."
] |
[
"This comes from a conflation of two terms, the universe as a whole and the observable universe. We normally just call both the universe. The observable universe has a distinct boundary."
] |
[
"~1% of smokers die from lung cancer. What accounts for rest of the smoking deaths?"
] |
[
false
] |
[deleted]
|
[
"I feel like you're missing something here: all of the causes of death in the graph seem to be because of cigarettes in some way.",
"Like, you might die from being shot, or you die from bacteria that entered your body with/because of the bullet, but you still died because you were shot..."
] |
[
"~1% of smokers die from lung cancer",
"Where does that number come from? You quoted a study saying 1% is the lifetime risk for ",
"smokers to die from lung cancer. It also says, immediately before the part you quoted:",
"When expressed as cumulative probability rather than annual death rates, the cumulative risk of dying from lung cancer before age 85 y was 22.1% for a male smoker and 11.9% for a female current smoker, in the absence of competing causes of death.",
"That fits well to the range you estimated from other sources."
] |
[
"I might be missing something myself, but I think the 1600 in 100,000 figure was just the rate of lung cancer deaths over the course of the NLST, which seems to have been 7 years (2002-2009). It looks like the number was primarily used to compare smokers to non-smokers over that timeframe, rather than being intended as an estimate of lifelong lung cancer mortality rates of smokers."
] |
[
"Medicine: At what point is your skin compromised opening yourself up to water born disease?"
] |
[
false
] |
Just having a discussion with a friend who insists a flesh wound cannot be infected by water, only a fully opened wound that goes through all the levels of the skin. Is he right?
|
[
"Any damage to the epidermis can increase the risk of infection. A cut or a scratch can be infected if it's deep enough to draw blood. Once the bacteria in the water enters the blood flow you are at risk. However, the deeper the cut, the greater the chance of infection since there are more defenses bypasses, and most likely more surface area to collect pathogens."
] |
[
"Thank you for the well written answer"
] |
[
"just to add on, when I say 'at risk' I don't mean 'OMG WERE ALL GONNA DIE', I mean it's a viable possibility. Most healthy immune systems can fight off the bacteria in water so long as the water is relatively clean. I've had plenty of cuts and scrapes while swimming and never suffered an infection."
] |
[
"Whitebread. Where did those nutrients go?"
] |
[
false
] |
refined foods always are said to be less nutritious. Where did they go? what is involved in the refinement process of foods that removes the good part.
|
[
"One class of nutrients that are particularly sensitive to processing are the ones we would consider anti-oxidants. That includes Vitamins A, C, D, E, and K, as well as other micronutrients. Using your example,during processing of wheat into Wonderbread flour, it undergoes processes of dehulling, grinding, bleaching, and drying.",
"Each of these processes has a way of destroying some of the nutrients contained within. A lot of the fat soluble vitamins in wheat are contained in the bran, a slightly oily coating on the wheat berry. Dehulling and polishing removes this layer. What vitamins remain are in the \"white\" part of the wheat, which is then ground up and bleached, so that nobody is mislead that they might be eating whole wheat bread. These two processes expose the inner parts of the wheat to air, which can oxidize the nutrients inside. Depending on what bleaching process is used, even more can be destroyed (sunlight+air decimates vitamin C, peroxides can do the same to just about everything). Washing and drying (if necessary) completes the process. If the flour is washed with water at some point before use, it can leech out the water-soluble vitamins like Vitamin C, the B-group Vitamins.",
"To counteract all this, manufacturers usually add the missing vitamins back at the end, but they can only add in what is known to be missing. If it's some lesser-known nutrient that went away, it'll stay gone."
] |
[
"The wheat germ is where most of the nutrients are, and they get stripped away during processing. I believe bleach or some other industrial chemicals are used to get the uniform white color. What results is that the processed bread becomes very easy for your body to digest because the fiber has been stripped out, so instead of slowly ingesting everything your blood sugar spikes and then crashes."
] |
[
"It's got a nice and consistent taste and texture that people like. I love multi-grain bread, but some foods just go better with white bread. "
] |
[
"Why haven't we or why can't we domesticate bears?"
] |
[
false
] |
We've domesticated livestock, dogs, cats, etc. why can't I have a tame small bear as a pet?
|
[
"A few reasons"
] |
[
"Something that didn't come up in the previous threads:",
"A bear is strong enough that even if totally friendly it could seriously hurt you by accident or in a brief moment of anger.",
"Surely many people have experienced a pet cat scratch your face or a pet dog grab your arm. Annoying but not a big deal. But if it were much larger, ouch."
] |
[
"A brown bear can weigh upwards of 1,500 lbs. Even a playful swat could send you flying."
] |
[
"Are any of the large crater impacts (the ones that still have visible debris fields) more recent, e.g. modern times, or even within recorded history?"
] |
[
false
] |
There are some pretty bad ass crater impacts on the moon.. It's definitely taken its share of potshots...
|
[
"None of the large craters are from recent impacts. ",
"Here's",
" a nice table of craters, with size and age.",
"The ",
"Tunguska Event",
" is a popular recent event that happened just over a hundred years ago, and there's more information about recent impacts ",
"here",
".",
"Honestly, for this type of question, it's easier for you to just browse wikipedia."
] |
[
"Meteor Crater is a meteorite impact crater approximately 43 miles (69 km) east of Flagstaff, near Winslow in the northern Arizona desert of the United States.",
"The crater was created about 50,000 years ago during the Pleistocene epoch ....",
"It was probably not inhabited by humans; the earliest confirmed record of human habitation in the Americas dates from long after this impact. [citation needed]",
"http://en.wikipedia.org/wiki/Meteor_crater"
] |
[
"Im not sure, but the Sudbury Impact Crater that created the melt sheet and the whole complex resulted in several shattercones as far as Duluth...",
"I think shattercones are the greatest thing in geology.",
"http://en.wikipedia.org/wiki/Shatter_cone"
] |
[
"Since the habitable zone around the sun only grows in diameter as the sun's size increases, how is it that Mars previously had Earth-like conditions?"
] |
[
false
] |
It's further from the sun, so I would have assumed that the habitable zone will move there eventually as the sun gets larger & hotter. But this states: The new findings, just published in the journal Geophysical Research Letters, provide evidence that early Mars was saturated with water, and that it’s atmosphere was at least 20 times thicker than it is now. What's the deal?
|
[
"So does that mean the habitable zone around the sun is larger than I am assuming, or that it was located in a different spot in the past. Or neither? "
] |
[
"The habitable zone is still defined ",
"as follows",
". It doesn't necessarily have to do with which planets are habitable, it has to do with where liquid water could exist given certain circumstances. ",
"The habitable zone does not change with respect to planetary conditions, though it can change with respect to stellar conditions. For example, as the sun heats up in its old age, the habitable zone will move out farther. "
] |
[
"Okay awesome, thanks a lot. I thought the wikipedia article summed it up nicely:",
"Estimation of the Solar System's habitable zone is made difficult due to a number of factors. Although the aphelion of planet Venus and the complete orbits of The Moon, the planet Mars and dwarf planet Ceres are within the habitable zone, the varying atmospheric pressures of these planets, rather than the habitable zone, determines their potential for surface water. In the case of Venus, the atmospheric pressure is far too high, and a runaway greenhouse effect raises the surface temperature massively, and in the case of Mars, the atmospheric pressure is too low, although Seasonal flows on warm Martian slopes have not yet been ruled out. For the Moon and Ceres atmosphere is virtually nonexistent, and therefore, surface liquid water cannot exist on these worlds.",
"Really interesting stuff, will keep reading on it. Thanks again. "
] |
[
"What makes some people have a better memory than others?"
] |
[
false
] | null |
[
"Everything here people said is right. The thing you have the most control over is the technique which you employ to memorize details. However, genetics can play a role in this. This ",
"study",
" suggests that hippocampus size, the part of your brain responsible for storing memory, can have a direct relationship with short and long term retention. "
] |
[
"You seem to be suggesting that hippocampus size is genetic and static. It's not. The brain is very plastic.",
"The famous study of London taxi drivers showed that they have considerably larger hippocampi than other people. The hippocampus, among other things, is very involved in spatial navigation, and this was before the GPS era, so taxi drivers were figuring out the best route to take in a very complicated environment every day for many years. Unless only super-hippocampus humans are becoming taxi drivers (unlikely for an effect of this size), the more likely explanation is that as you develop a skill, your brain starts to reflects that.",
"Such an effect has also been observed for the motor cortex of musicians and even the visual cortex of blind people, which starts to develop other non-visual functions such as reading Braille.",
"Don't fall into the trap of believing you lack the capacity to develop a skill. While talent can give you a head start, perseverance goes a way, and as you change, your brain does, too."
] |
[
"People who engage in complex stimulus elaboration integrating new info with old remember better. The role of stimulus elaboration was shown clearly by Craik and Tulving way back in 1975 and numerous times since then. "
] |
[
"Can the US government make the big chain stores (Walmart target Lowe's etc) install solar farms on their store roofs?"
] |
[
false
] | null |
[
"Not a science question. Try a legal sub"
] |
[
"First post. Thanks. Any recommendations?"
] |
[
"No I'm not familiar with law subs... You could try googling around /seeing if ones with names you might expect exist and then see if they have others listed in their sidebar. ",
"/r/law",
" is probably a sub for example."
] |
[
"Tin cans and string: can the NSA intercept the message?"
] |
[
false
] | null |
[
"You could do it with a light sensor capable of detecting small movements of the string at about 6 kHz, which isn't impossible for an ambitious high-schooler."
] |
[
"Hey, cool, I was one of those students! I remember it being a pain in the butt to get any sort of signal - we just barely got it to work in the last week of the class, and the sound quality was pretty bad. Basically the problem is that it's really sensitive to any small vibration or movement that's not part of the actual sound. So this is not an easy thing to build if you want it to be practically useful, even though the physical principle is simple.",
"I'm sure the professionals have more robust technology though."
] |
[
"Hey, cool, I was one of those students! I remember it being a pain in the butt to get any sort of signal - we just barely got it to work in the last week of the class, and the sound quality was pretty bad. Basically the problem is that it's really sensitive to any small vibration or movement that's not part of the actual sound. So this is not an easy thing to build if you want it to be practically useful, even though the physical principle is simple.",
"I'm sure the professionals have more robust technology though."
] |
[
"Lack of a specific neuro-transmitter"
] |
[
false
] |
I am taking psychology at my high school and my teacher was discussing neuro-transmitters and then he said that a lack of a specific neuro-transmitter can cause depression and other mental sicknesses... He said this is common in teenagers and psychiatrists will sometimes prescribe medicine to get them back into balance... how accurate is this?
|
[
"I'd be surprised if there was a neurotransmitter that was completely \"lacked\" by a human being. Most neurotransmitters have far more than a single function, so if a person lacked one, I doubt they'd develop past very basic embryological stages. ",
"Cases of people who are thought to have ",
" (but still present) levels of the neurotransmitters associated with mood are probably what he meant. For instance, selective serotonin re-uptake inhibitors ",
", (oversimplification.jpg) which is thought to improve mood. However, this neurotransmitter has other, more fundamental functions. A fetus would probably not be viable if it lacked serotonin all together. ",
"Check this link out and see if it sounds like what your teacher was describing. If you have any questions, feel free to ask them here. Good question, MrChow669. ",
"http://en.wikipedia.org/wiki/Selective_serotonin_reuptake_inhibitor",
" "
] |
[
"sweet thank you... this kinda applies to me, so i was interested in this subject"
] |
[
"The serotonin depletion or “not enough serotonin” leads to depression hypothesis is promoted by psychopharmaceutical companies and many physicians including psychiatrists. It has become, perhaps, one of the biggest modern myths in medicine; although a similar myth exists about the relationship between schizophrenia and dopamine. There is simply no evidence that people who exhibit signs of depression have abnormal brain chemistries, or abnormal levels of serotonin. However, there is evidence that taking psychotropic medications such as selective serotonin reuptake inhibitors (SSRIs) causes changes in the structure and function of the brain. In addition, serotonin does not just operate in the brain, so changing its availability through the use of SSRIs has major effects (side effects) throughout the body. ",
"See for example:",
"Whitaker, R. (2002). Mad in America: Bad science, bad medicine, and the enduring mistreatment of the mentally ill. New York: Basic Books. (available at ",
"www.basicbooks.com",
")",
"Valenstein, E. S. (1988). Blaming the brain: The truth about drugs and mental illness. New York: The Free Press.",
"And this link: ",
"http://www.plosmedicine.org/article/info%3Adoi%2F10.1371%2Fjournal.pmed.0020392",
"Although the books referenced here are quite old, I have been following this issue for years, and have found no strong, reliable evidence to support the serotonin/depression connection or dopamine/schizophrenia connection. And there’s this much more recent review of this issue here:",
"Whitaker, R. (2010). Anatomy of an epidemic: Magic bullets, psychiatric drugs, and the astonishing rise of mental illness in America. New York: Crown Publishers. "
] |
[
"Answers to Vaccines? (serious answers only)"
] |
[
false
] |
Hello, . I am a father to be, yet unprepared for my child to be born in less than two months. This obviously revolves heavily around the issue of vaccinations. I'm wanting to clear the waters a bit so I can make a clear decision on my child's well being. I am other words asking for your help. I ask your patience with my responses, and take my inquiry as sincere and at face value. I'm just trying to understand what I admittedly do not fully comprehend. As of right now, I am at the beginning (only 15 pages...) of a book called "Deadly Choices" (a pro-vac book). I'm wanting to take all things into consideration. Below are a set of questions that I am trying to have answered, and in a way that I will understand. Why are there any chemicals (regardless of how safe they are) in vaccines? If a virus is already dead (thus a live sample not needed), can't the fluid simply be a saline solution or some other liquid that is void of (seemingly) unnecessary ingredients? Why was mercury ever used in vaccines in the past? Why are there actual cases where some people have incredibly adverse reactions to vaccines? Is it similar to how someone can be allergic to peanuts, but I'll be fine? With there being plenty of misinformation (perspective on where that lies), I can't make out what side is being honest about neurological development and cognitive impairment after a vaccination is given. Could someone help navigate this with me? Are there "natural" or "organic" (buzzwords) like vaccines? Meaning, vaccines that carry only the dead virus and an even more restrictive list of ingredients, even if I have to pay for it? If I decide in waiting to get vaccines for my child, what would be the latest age you would suggest? Being in the military, I've noticed that a rather large percentage of children that belong to military personnel have some type of minor or serious mental impairment, let alone physical. I finally researched the numbers a while back, and that number was actually affirmed (can't recall at the moment). Military members also have the highest rate of vaccinations for themselves AND their children. We're not talking about Agent Orange offspring, either. Now, as we know, correlation does not equal causation, but I find this correlation incredibly hard to ignore, and it freaks me out. Is there anyone who has more information about this, or the possible reasons associated? Please note that I will attempt to answer any questions that are asked honestly and with as much detail as possible.
|
[
"Chemicals are needed to stimulate the immune system and help \"present\" the vaccine to immune system in a way that will confer immunity. They are also needed to preserve the vaccine for storage and distribution as well as prevent things like bacterial contamination.",
"I believe you're talking about thiomersal, a mercury containing compound. It was used because it makes a good preservative. It was removed because it sounds scary and people thought it was linked to autism. However the removal of thiomersal from vaccines has not led to deceased incidences of autism or adverse effects and it is still used in other parts of the world. There is not really solid evidence that anything was wrong with it. ",
"It's complex and we don't understand exactly why in all cases. One possibility is that the genetics of certain people's immune system may react differently to the vaccine. If you have extensive family history of adverse effects to vaccines, consult with your MD about the risks and benefits. However, this is an even bigger reason for vaccines. Some kids CAN'T get the vaccine for whatever reason, and they rely on all their friends having the vaccines so that the virus isn't present everywhere. Imagine if your kid couldn't get a particular vaccine, but kids who could didn't. Your child would be at a huge risk of getting sick simply because the other parent's made a choice that created that risk. ",
"Also please note that, for the standard vaccines, cases of severe adverse are EXTREMELY rare (in fact in many cases they are so rare that we aren't certain the vaccine caused them). The odds are your kids aren't going to react adversely, but consult with your MD.",
"This is outside my area of expertise. However I have not read or heard of any scientific articles about this. I would be shocked if this were a serious issue and I had not heard anything about it. Hopefully another panelist can give a more thorough answer.",
"For certain vaccines, there are things like single dose injectables (often more expensive). These often lack certain preservatives since they are meant for only a single use. I honestly don't know if there is really any benefit besides peace of mind. ",
"Another thing to think about, the average \"antigenic challenge\" (bits of the virus that trigger immunity) has fallen drastically as vaccines have gotten better over the years, so many of the newer vaccines have \"less virus\" but still trigger immunity. ",
"I'll let an MD answer this, I imagine it varies for the vaccine.",
"I don't know about the particular study you're talking about. But it is several logical leaps to associate high rates of mental impairment in children of military personnel to vaccines. Even if the high rate in military children is a true and observable thing, there are so many factors that could be at play that it's quite a stretch to jump to vaccines as the cause without any other reasoning (i.e. outside of the military do vaccination rates and mental impairment correlate? I highly, highly, doubt it).",
"When you finally make the decision, I urge you to consider not only your own child's health but also the health of all the other children they will interact with. Diseases like pertussis are back in certain areas as a result of the decision to not vaccinate. The one correlation that is absolutely not in doubt is that in areas of low vaccination rates, there are higher incidences of viral outbreaks. "
] |
[
"I'm a parent, too. I understand your need to examine everything. It's really your duty as a parent to make an honest assessment about how to best take care of your kids. And as a father, you tend to focus physical safety; preventing things that will harm their ability to reach their full potential.",
"So...your questions:",
"Why are there any chemicals (regardless of how safe they are) in vaccines? If a virus is already dead (thus a live sample not needed), can't the fluid simply be a saline solution or some other liquid that is void of (seemingly) unnecessary ingredients?",
"You don't have one immune response. One kind of response is good for some threats, and another kind of response is good for others. You don't want to put a nail in using a hammer. Some of the chemicals \"nudge\" the immune response in the correct way. They essentially tell the body \"This is bad, and this is how you should kill it.\"",
"Others are there as preservatives. Antibiotics, certain salts, buffers. They make sure the vaccine stays uncontaminated.",
"Others are just byproducts of manufacture. Formaldehyde, for example, is often used to inactivate the virus. It's put \"on the label\", so to speak, even though it's only there in trace quantities.",
"Why was mercury ever used in vaccines in the past?",
"Mercury is found in thimersol, a preservative. Thimersol is toxic in large quantities, but the amount you find in a vaccine is miniscule. It's not enough to cause harm.",
"Why are there actual cases where some people have incredibly adverse reactions to vaccines? Is it similar to how someone can be allergic to peanuts, but I'll be fine?",
"Pretty much, yes. It's more complicated than that...but yes. These are exceptionally rare, though, on the order of one per thousands to one per millions. The most severe are so rare that you can't even really measure the risk. They don't happen often enough. ",
"With there being plenty of misinformation (perspective on where that lies), I can't make out what side is being honest about neurological development and cognitive impairment after a vaccination is given. Could someone help navigate this with me?",
"The study that started all of this has been shown to be a fraud. Multiple researchers tried to duplicate Andrew Wakefield's results, and none were able to. Further investigation showed that Wakefield actually conspired with at least one person in the study to use the paper to sell kits to test for autism. ",
"Are there \"natural\" or \"organic\" (buzzwords) like vaccines? Meaning, vaccines that carry only the dead virus and an even more restrictive list of ingredients, even if I have to pay for it?",
"No, because without the chemicals found in vaccines, they would be either useless or even possibly dangerous.",
"If I decide in waiting to get vaccines for my child, what would be the latest age you would suggest?",
"Sorry, but that's medical advice. Ask your doctor. Go by the guidelines.",
"Being in the military, I've noticed that a rather large percentage of children that belong to military personnel have some type of minor or serious mental impairment, let alone physical. ",
"The neurologic disorders found in military family children track very well with parent deployment. There is no known causal link between vaccines and neurologic defects. There is a known causal link between stress (e.g., a parent gone and potentially in danger) and neurologic/psychological problems. The latter seems a much more likely cause."
] |
[
"I'll piggyback onto your comment and address this question:",
"There are different variations of certain vaccines like those for the flu. Flumist is a live attenuated version of each strain predicted to be in circulation during the upcoming flu season, whereas the flu shot is a trivalent influenza subunit vaccine containing the hemagglutinin (HA) molecules from two influenza A strains, and one influenza B strain (the same strains used for Flumist).",
"You may consider Flumist to be more \"organic\" or \"natural\" due to it being the whole (but weakened) virus, but the difference in protection provided by either vaccine is negligible. The original live attenuated polio vaccine is one case where the use of a live attenuated virus (ie. \"natural\" vaccine) may have backfired somewhat. In a small number of cases, recombination could occur, and people ended up being infected with polio. Thankfully most polio infections are subclinical - meaning there are no symptoms and you don't appear to be sick - but the risk of this occurring and actually causing harm was too great for it to be used.",
"Likewise, certain vaccines against HIV using dead or attenuated virus have been tested in animal models and show protection against virus challenge in the future. For a virus like HIV however, a live attenuated vaccine, or even a killed virus vaccine is out of the question, as it is far too dangerous to risk exposing to someone to it.",
"It should be mentioned as well that even vaccines containing live attenuated versions of viruses contain chemicals that act as preservatives so that the vaccine can be transported from place to place without degrading."
] |
[
"What causes nasal congestion and why can't you just blow your nose and be clear?"
] |
[
false
] |
Not much more I can think to add, pretty clear through title. Another question that came to mind on the topic though is, why is there usually one semi-clear nostril but it will sometimes switch sides?
|
[
"The clear-vs-congested nostril switching sides is due to the ",
"nasal cycle",
". The nasal cycle is not related to pathological nasal congestion, ie happens even when you are not sick.",
"Edit: why is this being downvoted? [was at -3 for a bit]"
] |
[
"Not an expert on the matter, but usually it's not the actual mucus that causes the feeling of being stopped up. The irritation that causes the mucus also causes swelling in the nasal passages. The feeling where you can't seem to blow something out of your nose comes from that. If anyone else with more expertise cares to elaborate better, it would probably be a help"
] |
[
"This is exactly right. When you get a decongestant at the pharmacy it is a drug that causes the blood vessels in your nose and sinuses to contract, lowering the swelling and clearing your nose.\nWe have a drug that thins mucus, Guaifenisin also called mucinex, it's great for if you are coughing up lots of phlegm (mucus) but is absolutely worthless when it comes to a stuffed up nose. Think of it this way, if your nose is stuffed up its likely you also have a runny nose, that's because your mucus is already very thin and runs right out your nose. "
] |
[
"What happens when stars collide?"
] |
[
false
] |
[deleted]
|
[
"Fear not! The worst part about Wikipedia is that it's littered with articles that are either copy-and-pasted from other places, or just filled with links to sources that fall off the internet. This is one of them.",
"Blue stragglers are a real phenomenon, and explaining them as the result of a collision of two stars is still a viable theory. I saw some papers just a few months ago talking about this very topic, and it's a challenge to explain them as anything other than the result of a stellar collision.",
"Gravitational waves haven't been detected, but that's because of technological problems. LIGO has been trying to do this, but it's fantastically hard to isolate what we think are the gravitational waves from all the other things that get in the way on Earth. LISA would have done this in space, but unfortunately NASA's funding evaporated and ESA just dropped the mission a week ago. Detection of gravitational waves will probably have to wait another decade.",
"In my own research topic, Cataclysmic Variables, we see systems that are evolving in exactly the same way as would be expected if they were giving off gravitational waves. There are many other indirect lines of evidence like this.",
"White dwarfs or neutron stars merging is one possible way to make a supernova Type 1a (the \"double-degenerate\" scenario). A high mass white dwarf accreting matter from another star is another way. I don't know enough about black hole mergers off the top of my head, but I do know that LISA expected to see a lot of gravitational waves from these as well."
] |
[
"It's very, very, very, very, very, very, very (I can keep going...) rare for one star to actually collide with another. It can happen more often in globular clusters, where the average stellar density is many more times than what we have in our little corner of the galaxy. That's where we see these \"blue stragglers,\" they stick out as hot/massive stars that should have long since died out compared to the rest of the stars in the cluster.",
"As you point out, galactic collisions involve lots of \"empty\" space between stars. Most stars will just pass right by each other, though they will be heavily mixed and tossed about gravitationally creating large streams and strands. ",
"Wikipedia has a list of such features",
" of our own Milky Way (and a nice illustration, too).",
"The gas content of each galaxy will readily collide and mix, however, triggering a tremendous wave of new star formation as the gas gets compressed. When you look at ",
"this picture",
", you see two galaxies and a whole bunch of pink and blue bits; the pink and blue bits are regions forming massive stars, triggered by the collision of the gas.",
"We are headed towards Andromeda, the nearest large galaxy to us. We're about the same size, though there's some debate if one galaxy has the upper hand; it's hard to tell the mass of our own galaxy since we're riding inside of it! We've still got a few billion years to prepare, though, so if we're still around I'm sure we'll be fine. There's a ton of animations and simulations out there if you are interested."
] |
[
"When I see sentences like this on Wikipedia...",
"While much is unknown about this theory, there are new strides being made every day",
"I weep for the Wiki."
] |
[
"Could domesticated cats and dogs be considered a dependent species?"
] |
[
false
] |
If humanity were to disappear tomorrow without a trace, would cats and dogs be able to survive (and even thrive)? Would they be at a disadvantage to more feral creatures? I often see cats and dogs without a home able to survive near human habitats, but I never hear about them living in more wild environments. If they are at a significant disadvantage without humans, could that classify them as being dependent on us as a species?
|
[
"To answer your question, yes I think domesticated cats and dogs would thrive if humans were to be gone tomorrow and no I do not think of them as dependent on us. Cats and dogs survive very well without homes. Except for the animals at the zoo, which would have no way of getting out of their cages, cats and dogs would probably be near the top of the food chain (with very few predators, besides themselves). Coupled with their natural instincts, I feel they'd be just fine out in the wild. ",
"In terms of fighting off a more feral creature, it's either fight or flight. That's the case for any animal, I don't believe it'll hinder their numbers significantly. "
] |
[
"Disclosure- Just some amateur conjecture on my part",
"I think the answer is mixed, some breeds like Chihuahuas and poodles are obviously not going to do well on their own. ",
"On the other hand breeds that more closely resemble wolves will survive, they would probably be at a disadvantage when compared to coyotes and wolves but they would have a decent chance at survival.",
"The History channel had/has a documentary series, \"Life After People\" that looked at things around us and projected what would happen in X amount of time to our pets, our cities, our monuments etc..that you might want to check out for more info.",
"But I think you can say without much thought that a tea cup chihuahua isn't going to have much success hunting on its own."
] |
[
"Dogs quickly revert back to the wild to form packs (actually they're always forming packs but never really 'hunt' in the pack) and the like when they're abandoned. Their hunting skills aren't as good as their ancestors, but they can survive. ",
"This is excepting the breeds we've fucked up in the process though (chondrodystrophoids that blow out their back, bulldogs that can't hardly breathe properly, pugs that have their eyes pop out frequently, dogs with a high degree of folds of skin that are susceptible to infections, and so forth). "
] |
[
"Why does writhing help alleviate pain?"
] |
[
false
] |
I recently had a 24-hour stomach bug (or something with similar effects). My whole body, especially my stomach, ached and I was unable to get a restful sleep. During the night, I found that movement of any kind helped the pain go away a bit. Why is that?
|
[
"I am not aware of a specific mechanism involving writhing. I would expect that this is a specific manifestation of the ",
"Gate Control theory of pain",
", which says (sort of) that pain is not additive, but rather that neurons act like a pipe, and filling the pipe with non-pain sensations (or even just lower pain sensations) leaves less room in the pipe for the painful sensations."
] |
[
"No. In a gate control model of acupuncture, any benefits would end soon after the acupuncture treatment was over, whereas acupuncturists typically claim that their treatments last a few days/weeks at a time.",
"Acupuncture ",
"is based off",
" the \"traditional\" notion that the body is operated by an energy network that passes energy up and down certain pathways (analogous to blood vessels, but with chi instead of blood) and the acupuncture needles are affecting those energy passages.",
"Needless to say, western science has found ",
"no evidence",
" to support chi theory, nor has it found anything to support the idea that anything more that placebo effects are occurring."
] |
[
"No. In a gate control model of acupuncture, any benefits would end soon after the acupuncture treatment was over, whereas acupuncturists typically claim that their treatments last a few days/weeks at a time.",
"Acupuncture ",
"is based off",
" the \"traditional\" notion that the body is operated by an energy network that passes energy up and down certain pathways (analogous to blood vessels, but with chi instead of blood) and the acupuncture needles are affecting those energy passages.",
"Needless to say, western science has found ",
"no evidence",
" to support chi theory, nor has it found anything to support the idea that anything more that placebo effects are occurring."
] |
[
"If the universe is expanding at an accelerating rate, where exactly does that expansion happen? At the space between the atoms in my body, or somewhere else?"
] |
[
false
] | null |
[
"So we have two types of movement here. One is movement through space and the other is a stretching of the fabric of space itself. The common analogy is an ant on a rubber band. The ant walking on the band is traveling through space but stretching the band with an ant on either end will still result in them moving apart even if they are standing still on the surface.",
"Now the molecules in your body are stuck together very strongly. As space stretches they will slide through space and stay stuck together. In fact even gravity between galaxies is strong enough to keep galaxies stuck together, but now the stretching of the material they are on is perceptible so on average we notice things moving a bit faster away from each other or slower towards each other.",
"The only place the stretching of space dominates so that objects on it are actually all moving away is at the super galactic cluster scale. These are the largest structures in the universe.",
"edit: the bonus of why is two parts. The mechanism behind it is currently unknown. The fundamental reason behind it is that it is just the nature of the Universe we find ourselves in."
] |
[
"The only place the stretching of space dominates so that objects on it are actually all moving away is at the super galactic cluster scale. These are the largest structures in the universe.",
"Ah! Something I can visualize. I was ready to ask a few questions with the ant analogy but given the scale of galactic clusters I see it won't effect my atoms. ",
"So the strong atomic force is stronger than whatever force is causing the universe to expand? Or does the expansion happen on some kind of logarithmic scale that makes the current expansion imperceivable, but after X amount of time even the parts of the atom will move apart from each other?"
] |
[
"Space is stretching evenly. Hubble's constant is 70(km/s)/Mpc. This means that if two points in space are 1Mpc apart, in 1 second they will be about 1Mpc+70km apart (slightly more as the distance between was increasing over that second). If there are two relatively stationary objects at these points, the same thing will happen. If there is an attractive force between these two objects however, then they will still slide through space towards one another. Calculating their acceleration towards one another just becomes more complicated as you have to add in another term to account for the stretching of the space between them.",
"At the current rate of stretching I mentioned, local galactic clusters will eventually clump together and speed away from other clumps. This fate of the universe is called the big freeze. If however Hubble's constant increases over time (as some evidence points to) then there may be a time when it is so great it can rip atoms apart in what is called the big rip. edit: Don't visualize this as a force pulling them apart, but the rate of stretching of the tiny amount of space between them overcoming their speed through it due to their acceleration towards each other from the attractive force between them."
] |
[
"How were these lakes formed?"
] |
[
false
] | null |
[
"A lot of the lakes in Canada are formed in depressions caused by ice sheets during past ice ages. When the ice moved over Canada it essentially scraped indentations in the bedrock. This is especially typical in the ",
"Canadian Shield",
", more or less encircling Hudson Bay. The elongated lakes are an indication of direction in which the ice sheets moved."
] |
[
"Would you be so kind as to include the actual location in your post? Thanks a bunch!"
] |
[
"I just zoomed in on a random spot in Canada, couldn't figure out how to get the location, sorry. "
] |
[
"What happens, on a molecular level, that leads to paper becoming soft after applying water to it?"
] |
[
false
] | null |
[
"Paper consists (mostly) of cellulose fibers, i.e. a polymer of glucose molecules. These glucose molecules have free hydroxyl groups, which can form hydrogen bonds to other molecules. ",
"In dry paper, at least many of these hydrogen bonds are to neighbouring cellulose fibers, which stabilises the overall structure.",
"Water breaks up the hydrogen bonds between the cellulose fibers, so this stabilisation is lost."
] |
[
"Water breaks up the hydrogen bonds between the cellulose fibers, so this stabilisation is lost.",
"To explain a bit more, the hydrogen bonds are formed between cellulose and water, rather than between different parts of the cellulose."
] |
[
"Thanks. That explains a lot."
] |
[
"Why do batteries shut down even when they have a little bit more power on them?"
] |
[
false
] |
Why do batteries seemingly have some juice still in them when they die? For example, when a phone runs out of battery you can try to turn it on again. It might die right on the boot or even once it's turned on if you're lucky (It actually depends on the firmware, some don't try to turn but it's clear that they still have a bit of power left). Why do manufacturers do this? Is this some property of the li-ion architecture? Is this some design choice, maybe to increase battery life? Why not let the user choose to empty the battery for an emergency then? This is a question I've had for a while and I couldn't find an answer anywhere else, so let's see what's it!
|
[
"The device itself requires a minimum voltage to be able to run properly, with the voltage being synonymous with the battery's ability to deliver the amps to the device. ",
"The lower the charge in the battery, the lower the voltage given off by the battery, so a 12v battery fulled charged/recently charged may actually have up around 14.2v, and when discharged be around 11.8v. Basically the device isn't getting the amps it needs to run.",
"As to why some devices seem to run for a bit after being turned off, some batteries are able to \"recover\" their voltage a bit once the load is disconnected.",
"And some batteries are \"protected\" which amongst a few other things, means they resist going below a certain voltage, as it'd likely lead to damaging the battery (reduced capacity).",
"https://www.fenix-store.com/blog/what-is-the-difference-between-protected-and-unprotected-18650-batteries/"
] |
[
"There are three aspects to this that I can think of.",
"You're asking about LiIon/LiPo batteries, since you're asking about phones. They are sensitive to deep discharging. If you discharge too far, you risk not being able to charge it again. So there is a cut off (brown out) circuit that monitors the battery and stops if the voltage goes below a threshold.",
"However, batteries that become unused tend to increase their voltage a bit, since the internal resistance means the observed voltage decreases with higher current. It also changes with temperature (and batteries warm up when used) and time. So if you let it sit for a while, the voltage might creep up enough that the cut off circuit opens up again. Though note that the amount of energy in the battery is still really low, even if the voltage might be high enough.",
"The second aspect is this internal resistance itself. Even for non-LiIon batteries, there is a drop in voltage when used. If you have e.g. an LED connected to a NiMH battery, the voltage might drop enough that the LED doesn't have enough and it goes out. LEDs have a sharp lower voltage they need to light up. Let it sit for a while and the battery recovers, but the moment you start drawing a current, it may drop too much again. This wasn't a problem with incandescent bulbs as they don't have the sharp lower voltage limit; they'll just be dimmer as the voltage goes down.",
"Lastly, as you point out, device manufacturers might monitor the remaining battery capacity and refuse to turn on high-power peripherals (like the display or radio transmitter) if they think there's not enough runtime left to be useful. A phone without a display isn't useful, so they just refuse to turn on the phone and instead use the last energy only to notify you that you need to charge. Also, running a computer system with a power source that isn't stable may cause data corruption if you're unlucky. This last issue is actually used by hackers in what's known as power glitch attacks, where they make the power source \"glitchy\" at the right time to circumvent e.g. read/write protection on a device they have physical access to."
] |
[
"with the voltage being synonymous with the battery's ability to deliver the power (amps) to the device.",
"Just to avoid confusion, ampere (\"amps\") is ",
" a unit of power, but of current. Power would be voltage times current."
] |
[
"How many stars exploded in order to create the Carina nebula?"
] |
[
false
] |
I just saw this post: And it made me wonder. How many stars exploded to create this nebula? Or was it formed through some other process? Given how large this is, it’s hard for me to imagine that one star could create something like this?
|
[
"The most massive (and arguably, the prettiest) nebulae are giant molecular cloud complexes. Rather than being formed by an outburst of gas from a star (like a planetary nebula) or by a star going supernova (like a supernova remnant), they are not directly formed by stars at all.",
"It starts from the \"interstellar medium\", which by volume is mostly a thin medium of warm ionised turbulent gas, with a temperature of about 10,000 K, and fills the disc of the galaxy. As this gas is turbulent - stirred by supernovae and by the rotation of the galaxy - bits of gas flow together and get a bit denser.",
"Now, on Earth, if you squish gas, it heats up. But in space the opposite generally happens. The main cooling process in space is ",
" cooling. When gas particles bump into each other, they slow down a bit after the collision, transferring their kinetic energy into internal wibbles (\"excitation\"). The particles can then radiate away this internal energy as photons, which mostly totally escape the gas as it's so thin. So more collisions means you lose kinetic energy more quickly, which means the gas cools down. And the denser a gas is, the more rapidly it has collisions, and the faster it cools down.",
"So what happens is you get a ",
" process. When gas gets a bit denser, by random turbulence, it cools faster. This reduces the pressure of the gas, causing it to collapse faster. Additionally, the denser gas has more gravity, which causes it to collapse faster. And as it gets denser again, it cools faster and shrinks faster again. This gives you big clumps of cool dense stuff, formed directly from the interstellar medium. Eventually it gets cool enough that it forms dust and molecules (i.e. the hydrogen gas is not longer ionised, it's now actual hydrogen molecules, H_2), which gives a lot of interesting colours for telescopes to capture (even if the details aren't that visible to the human eye).",
"As the gas continues to collapse, gravity really takes over and dominates over the cooling/pressure effect, and the cloud fragments and collapses to form stars. These stars then heat up the gas with their winds and radiation and even by going supernovae, creating bubbles (which you can see in HST and JWST images), and stirring up and dispersing the gas again. But this isn't an even process. Some stars live shorter lives than others or are formed earlier. So you can get a really dynamic system where stars are blowing away gas in one area, and stars are still forming in another. This is part of why molecular clouds look so interesting.",
"Now, exploding stars do ",
" to molecular clouds, but they don't ",
" them. When a star goes supernova, it returns part of its gas to the interstellar medium - not all of it though, as there's usually a remnant left behind, like a white dwarf, neutron star, or black hole. This gas has been enriched with heavier elements, and spreads these heavy elements into the interstellar medium. As this is a very turbulent medium, and the supernova is expanding rapidly, it quite quickly mixes in. Instead of getting one little pocket of enriched gas, it spreads around the galaxy and enriches the whole thing. And part of that gas in the galaxy will collapse to form another molecular cloud, taking some of the enriched gas with it.",
"So: exploding stars contribute some stuff to the interstellar medium. The interstellar medium collapses under cooling & gravity to form molecular clouds. Molecular clouds collapse to form stars. These stars explode and disperse the gas, enriching the interstellar medium further. And so on!"
] |
[
"I've been wondering this for years. Love the explanation, thanks."
] |
[
"Thank you for the great answer! This was very helpful and cleared up my confusion."
] |
[
"How far back would we have to go to find the first common ancestor for all humans alive today?"
] |
[
false
] |
Also, what groups of people in the world today are the furthest relatives?
|
[
"Surprisingly, not very far!",
"http://humphrysfamilytree.com/ca.html",
"Quick notes: ",
"Quite likely every Muslim in the world today descends from the Prophet Muhammad",
"Quite likely everyone in the West descends from the Prophet Muhammad",
"Quite likely almost every Jew in the world today descends from the Prophet Muhammad",
"Quite likely everyone in the West descends from Charlemagne",
"Quite likely almost everyone in the world descends from Confucius",
"Quite likely the entire world is descended from the Ancient Egyptian royal house",
"This isn't to say that Muhammed or the Egyptian royals are the first common ancestors, but it gives you the timeframe that we are talking about.",
"The most difficulty is for groups who were isolated for a long time on an island (e.g. the australian Aborigines or isolated pacific islanders, but since all of these groups have recently interbred with the \"mass\" of humanity, this has brought the most recent common ancestor forward quite a bit.",
"Also, think about it. Take the case of the Australian aborigines. All it would have taken is one Timorese fisherman to be blown off course and then that gene pool has a chance to \"rejoin\" the mass' MRCA."
] |
[
"You are 1 generation away from your parents, 2 persons",
"You are 2 generations away from your grand parents, 4 persons",
"You are 3 generations away from your grand parents, 8 persons",
"You are 4 generations away from your grand parents, 16 persons",
"Etc, etc....",
"10 generations down the line and this would be +/- 1000 persons",
"20 generations down the line and this would be +/- 1 million persons ",
"30 generations down the line and this would be +/- 1 billion persons",
"If 1 generation = +/- 15-30 years, 10 generations = +/- 225 (150-300) years and 30 generations would be +/- 600-700 years.",
"600-700 years ago the world didnt have 1 billion people so mathmaticaly speaking everybody on the planet would share a common ancestor living +/- 600-700 years ago.",
"However, I have been making some assumptions:",
"A lower number of ancestors will make the 600-700 years number longer but still the mayority of the large continental occupants will share a common ancestor probably no older then +/- 1000 years."
] |
[
"I dont trust that website at all, the idea that DNA is not passed on over time is false, I am related to mitochondrial eve for example as is any other extant human. In terms of mtDNA mitochondrial eve is the MRCA, we are all derived from that haplogroup and therefore must all draw our mtDNA lineage back to this point. ",
"The bit of text you quoted is false, how can everyone in the world descend from confucius? Where does that leave africans? or western europeans whose lineages never travelled east upon leaving africa? How about aboriginal australians who became entrapped in the Australian content milenia before the appearance of confucius. I am sorry but pretty much everything you have stated is wrong in my view."
] |
[
"What causes \"split face\" fur patterns in cats?"
] |
[
false
] |
I have a Tortoiseshell cat and her face is split right down the middle, half black, half orange with tabby markings on the orange side. What makes this divide happen?
|
[
"This is very informative, thank you!"
] |
[
"This is very informative, thank you!"
] |
[
"The term is chimera. It's what happens when a single organism has genetically distinct cells.",
"Usually in animals it's a result of the merger of multiple fertilized eggs. Tortoiseshell cats seem to be more susceptible to this than normal."
] |
[
"Why does the Soyuz fire do its deorbiting burn with the orbital module?"
] |
[
false
] |
It seems like a waste of propellant to put the orbital module on a trajectory towards earth's atmosphere because it doesn't contain any crew, and it will burn up on its way down.
|
[
"If the deorbiting burn doesn't work you have more time to figure out what went wrong. ",
"Soyuz TM-5",
" had that problem (at that time they used the opposite order). The toilet is in the orbital module...",
"It also makes the orbital module burn up quickly instead of staying in space as waste for several more months."
] |
[
"If someone would hurry up and make solar sails practical, we could have a fleet of orbital junkyard dogs to both make us safer from space junk, and make launch planning easier, so you don't need a de-orbiter safety plan for every satellite."
] |
[
"Also, the deorbit burn causes a deceleration of only 150 m/s. That is not very much."
] |
[
"How long can a straw be before you aren't able to suck anything out of it?"
] |
[
false
] |
[deleted]
|
[
"I have a rough idea from high school physics ten years ago so apologies for any errors and problematic phrasing. The max length for a straw to work (or another kind of water pump) with water on Earth is around 30 feet. The reason it maxes out is because \"sucking\" isn't really a thing. When you suck on a straw you lower the pressure at the end of the straw that is in your mouth compared to the end in the glass. Instead of \"sucking\" up the water, the pressure of the earth's atmosphere is pushing down on the water in the glass sending it up the straw into your mouth to equalize the pressure.",
"It's the same as when you submerge a cup in a bathtub, turn it upside down, and partially lift it out of the water. The water stays in the glass above the water line because there's enough pressure to hold it up. Now if you had a 50ft long cup and did the same thing, once you pulled the cup above ~30 feet the water would max out. You could keep lifting the cup and a vacuum would form between the ~30ft mark and the bottom of the glass at say the 50ft mark.",
"The height would be different with a liquid of a different density or on a planet with a different atmospheric pressure.",
"This also assumes you have a straw that won't collapse under the pressure like when you try to drink a milkshake with a flimsy plastic straw and it flattens.",
"This link has a better explanation; if you want more google-able search terms you could try looking for the maximum depth a well pump can go.",
"http://www4.hcmut.edu.vn/~huynhqlinh/olympicvl/tailieu/physlink_askexpert/ae443.cfm.htm"
] |
[
"The suction effect is caused by a difference in pressure. The surface of the water is presumably at atmospheric pressure, which is thus the largest possible pressure difference. In other words, the atmosphere pushes down on the water, which is then pushed up through the straw because of the pressure difference between the top of the straw and the surface of the water. The longest possible straw then is simply the height of water that can be supported by one atmosphere of pressure.",
"Hydrostatic (gauge) pressure is ",
" = ϱgh, where ϱ = density of water, g = acceleration due to gravity, and h = depth of water. Substituting values of ϱ, ",
", and ",
" = 1 atm gives ",
"h = 10.33 meters, or 33.9 feet",
"."
] |
[
"You're right. Suction works by air pressure difference. If the thing you're sucking is water, then the difference between atmospheric pressure and the pressure at which water boils at room temperature gives you a maximum weight that can be supported per unit of surface area. (So regardless of the thickness of the straw, it has a maximum height, as weight scales with volume and changing the the area does not change the ratio of weight to height.) Decrease the pressure any further and the whole thing breaks down. Veritasium did a video and says around ten meters.",
"https://www.youtube.com/watch?v=HUmZrtiXDik"
] |
[
"How is location in outer space measured?"
] |
[
false
] |
My physics teacher proposed the question of how you can give directions with out a point of reference? How are coordinates assigned to objects in space? Does stuff in space have x,y,z coordinates? What would be the origin or center of space?
|
[
"Aerospace engineer here. ",
"Everything that's been said so far is absolutely true. Position and motion are both relative. However, most orbital maneuvers that we do can be approximated as taking place within the gravitational influence of a single central body. Therefore, it's easiest to define coordinate systems relative to that central attracting body (more often than not, the Earth, but these are applicable to other planets/the sun too).",
"There's a traditional cartesian x-y-z system, of course. However, this usually only gets used when a spacecraft performs some kind of orbit-changing maneuver, usually a complex one. It turns out, though, that if you start at the beginning (Newton's 2nd law, F = ma) and derive the solution to the relative 2-body problem (one planet, one spacecraft), then there is a naturally evolving set of parameters which allow us to define positions and orbit geometry in terms of angles and radii. These parameters are traditionally called 'Keplerian' coordinates, named after Johannes Kepler, who proposed the first real basis for orbital mechanics. ",
"So to answer your question, Keplerian coordinates are traditionally used to define a spacecraft's position relative to a central attracting body. This is, more often than not, what you'll find an orbit specialist at NASA using. "
] |
[
"There are no fixed points in space. Spacetime is curved, and space is expanding. We can say where other objects are in relation to our solar system, but there isn't a fixed universal reference point we can build a cartesian coordinate system around."
] |
[
"As the others have said position is relative. You ",
" give directions without a defined frame of reference. We can use earth centered coordinates within our solar system. We can use spherical coordinates centered on the earth to describe things we see in distant space.",
"The closest thing you will find to a convenient universal reference frame are comoving coordinates in which the cosmic microwave background radiation is isotropic. ",
"Space has no center or origin. Its infinite and always has been. ",
"Keep in mind in our coordinate system we need a 4th number to describe any event in space, which is time. X,Y,Z,Time."
] |
[
"Why is the consumption of chicken eggs now recommended by physicians and alike, despite the fact that until recently it was discouraged due to high cholesterol content?"
] |
[
false
] |
Why is that? What has changed? Was it the discovery of something in the eggs or rather some biomechanism that we were unaware of?
|
[
"We discovered that high cholesterol foods have less of an effect on your cholesterol than foods with a lot of trans fats and saturated fats."
] |
[
"There is no evidence that supports that the consumption of fatty foods correlates with higher cholesterol. In fact, long-term effects of ketogenic diets (little to no carbohydrates) show a decrease in LDLs and an increase in HDLs.",
"http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2716748/"
] |
[
"Because people used to think the more you ate of fat/cholesterol/calcium/protein/iron/etc the more you would have in your body, now we know its never that simple. Glycemic index and fat intake likely have more of an effect on cholesterol than actual cholesterol. "
] |
[
"Why is it such a common occurrence for people to turn down music when driving to look for an address?"
] |
[
false
] | null |
[
"Several common models of attention describe it as a finite resource that you can spread around different tasks, stimuli, senses etc. Actively ignoring some stimulus to focus on another is also a demanding task. So based on our current understanding of attention, the explanation would be that when you need to focus, you want to minimize other external demands on brain processing. "
] |
[
"It depends on the nature of the secondary task and how much attention you are devoting to the primary task. Yes, you can \"tune out\" music or TV to a certain extent... But sometimes you find yourself having read the same sentence 5 times in a row because your attention was captured by the other stimulus. In that case, the reading is sort of on autopilot. Another example of this is when you are driving along a familiar route and end up, say at work instead of wherever you meant to go. You still gave some attention to driving (enough not to crash), but not enough to go where you intended. So attention is spread across tasks and sometimes more goes to one or the other. ",
"Regarding studying in particular, and why having extra sensory stimulation may or may not help, I'm not sure. "
] |
[
"Yes these are called state dependent effects. The explanation is that when trying to recall, you are reinstating the learning context. This can be a state of the environment like whether there is music playing or whether you are in the same room or whether you are chewing gum, or emotional or other kind of state. Even imagining the room you studied in can help test performance. ",
"An example of this that we often experience during tests is if you are trying to remember some piece of information from a page of a textbook and you try to visual where on the page that info was / what was around it, it can help you retrieve the info. Here, you are also retrieving the environmental context in which you learned the material."
] |
[
"How would have our perception changed having 3rd eye? Would it be advantageous to only a pair?"
] |
[
false
] | null |
[
"Larger field of view (depending on placement). Also, potentially better stereo vision, again depending on placement. That's about it."
] |
[
"Would perception of distance and depth change?"
] |
[
"The distance to which stereo works is determined by the distance between your eyes (sort of -- technically, there is no limit, but practically, especially for small objects, we have poor stereo beyond 2 meters). The difference between the images on your retinas can provide depth information /sense of depth. For things that are very far away, they fall on similar (relative) places on you retinas. That's why, for example, your hand might look more 3D than, say, a cloud. So if we could get two eyes to be farther apart, but still have overlapping fields of view, you could get some stereo for far-off objects for which we usually don't experience it. An example of this might be a stereogram -- take two photos of the same scene from two different locations and put them in a stereoscope and things will have a greater depth than normal. Or, take two photos out of an airplane window, one after another. In between the two photos, you would have traveled a great distance. Viewing the photos with a stethoscope will make clouds suddenly appear like cotton balls held close up -- volumetric and curvy."
] |
[
"Would someone please explain, in great detail, how the young earth may have theoretically yielded the first living cell?"
] |
[
false
] |
I'm not skeptical, I'm just curious as to what chemical processes would coincide in order to create living cells from dead matter. Edit: Thanks for the great discussion guys. You seem to have sated my frustrating curiosity...for now.
|
[
"Well, I'll give you the RNA hypothesis. Firstly what are the requirements for the first proto-cells? Such proto-cells would need:",
"polymerized \"bio\" molecules (there is no biology at this point in the earth's history so we need some starting materials). ",
"Segregation of contents from the environment (some kind of membrane)",
"genetic material",
"replication",
"evolution",
"Starting materials: Clay surfaces such as Montmorillonite clay can act as catalysts for the synthesis and polymerization of biological molecules. (",
"Source",
") This mineral surface can facilitate the assembly of fatty acid molecules from carbon monoxide and hydrogen and the polymerization of nucleotides by activating the monomers. So from a pool of wet goop we can get both fatty acids and the beginnings of a nucleic acid (RNA).",
"Segregation from the environment: We need a membrane. By dividing an area from the environment local concentrations of reactants can increase (or decrease) and molecules can stay together with out dissipating out into the primordial soup; a little pool for these molecules to play in. Fatty acids will spontaneously form basic membranes in aqueous solutions in the form of micelles or vesicles. These are not the complex phospholipid bilayers of modern cells, ",
"just bubbles of fatty acids.",
" That Montmorillonite clay where the fatty acids assembled can also ",
"assist in the formation",
" of these proto-cell membranes. These membranes are very permeable and barely keep out the surrounding environment, but it's a start. More fatty acids can be added to these membranes making them larger. (",
"source1",
") (",
"source2",
")",
"Genetic material: RNA is capable of replicating in the absence of enzymes (proteins). Random sequences of RNA (synthesized on those bits of clay from before) have been shown to generate enzymatically active strands of RNA called ribozymes (",
"source Bartel & Szostak 1993 -this is a classic paper!",
") These ribozymes are not quite able to polymerize RNA, but they can stick together (ligate) strands of the nucleic acid. This is the first step in forming a proper polymerase.",
"Replication & evolution: Working ribozymes would be kept inside the proto-cell by the simple membrane. The activity of the ribozymes is slow, but faster ones will generate more nucleic acid (with replication errors -the first mutations) and thereby more ribozymes -better ribozymes. As more fatty acids join the cell it will get larger until it bursts a bit and forms two cells -each contain the same ribozymes and nucleic acid (or mutated alleles) as the original. ",
"Edit: Another vital ingredient is Time. The catalysis afforded by clay catalysts and the activity of ribozymes were improvements on rate accorded by simple random interactions. All the processes listed above are orders of magnitude slower than the enzymatic catalysis our cells enjoy today.",
"This is just a hypothesis, and there is much more to this hypothesis than I go into here (particularly in regards to ribozymes and the sugar backbones for the nucleic acid), but I hope this overview contributes to the other answers to your question!"
] |
[
"Not really.",
"This is one possible answer to \"how did our biochemistry first come about?\" Because it assumes our biochemistry, it really can't tell us much about the possibility of other biochemical setups.",
"Secondly, this only lays out the simplest of biochemical building blocks. Complex anatomy and structures may be vastly different in different environments even with this same biochemistry."
] |
[
"At first glance, this may seem like a snarky question, but you've really struck at the core of a deep and burning question that scientists are working towards explaining at this very moment. Because you say you have limited knowledge, I'm going to try to take a broad view at the kinds of chemical processes you need, and how they would react to give rise to \"active\" molecules. From these molecules, we'll proceed to \"active\" systems, which will then lead to \"biologically\" active systems, which will finds us (finally) at biological organisms. I'll be using my perspective as a biochemist and synthetic biologist to try and make these as simple as possible, without dumbing them down.",
"First, we need a few building block molecules. We'll start with sugars, because they are pretty darn simple. We find an relative abundance of H2O, CO, CO2, and NH3 in the universe (compared to other molecules outside of H2 and helium). This is particularly true on earth, where these four molecules can be found in various forms very early in the earths history. (pardon the wiki source) ",
"https://en.wikipedia.org/wiki/Carbon_dioxide_in_Earth's_atmosphere#Past_concentration",
" ",
"Given these molecules, and the chemistry that we know arises from their random interactions, we get aldehydes and sugars. There is also the possibility of an extraterrestrial origin, as detailed in this paper. ",
"http://www.pnas.org/content/112/4/965.abstract?sid=022a22d9-6d83-4c93-a7ff-e280489f295e",
" ",
"There is also the fact that we have found ribose (a sugar, and one I want you to keep in mind) in vast amounts in space. We're talking very simple molecules here, more complex than water, but much less complex than the variety of amino acids, or even the simplest protein.\n",
"http://science.nasa.gov/science-news/science-at-nasa/2000/ast20jun_1/",
"Well, that's great, but what about amino acids? The Miller-Urey experiment showed that early earth conditions favored the production of a wide variety of amino acids, and more modern experiments have yielded even better results with an even wider variety of amino acids. Just to point out, at this point, we're still talking about completely random reactions that rely on proximity and concentration. These are simple molecules, and the fact of their existence isn't really all that surprising (now knowing what early earth conditions were like). ",
"https://en.wikipedia.org/wiki/Miller–Urey_experiment",
" ",
"The next step is still a very active area of research, so pardon the cop out, but we just aren't positive yet. The formation of nucleotides is a likely next step, if we're going for an RNA world or RNA like world hypothesis. For a pretty good summary of the topic, read this (pretty dense for most people) review. ",
"http://www.chtf.stuba.sk/~szolcsanyi/education/files/Organicka%20chemia%20II/Prednaska%2010_Nukleozidy/Doplnkove%20studijne%20materialy/The%20Origins%20of%20Nucleotides.pdf",
"Well, we've got a bunch of molecules, but no activity, so what? What happens next is part of the random action of molecules reacting and interacting. Nucleotides form bonds with ribose, which has the possibility to randomly form chains by polymerizing with other ribose (using a phosphate linkage). All reasonable considering that we already have all of these molecules floating around in solution. Here's where we get to our first active molecule. RNA (or an RNA like precursor) has a really cool ability. It can form structures by interacting with its own polymer chain, and these structures can catalyze reactions with other molecules. Now we're cooking with crisco! Most of these chains won't be active in any way, but some of them will be. Here's the next cool ability RNA has: it can serve as a template to make a copy of itself.",
"If we think about this, we can imagine two RNA chains that form structures. One catalyzes the formation of more RNA nucleotides (the individual building blocks), while another can catalyze the copying of another chain. Leave these two to work, and pretty soon, you've got more and more RNA chains doing the same thing, making more building blocks, and replicating the RNA chains that make these building blocks. Every once in a while, there will be a mistake in replication that causes some change in the newly synthesized chain. Most of the time, this is bad, but sometimes, it makes a faster, more efficient, or more durable RNA chain (we can start calling these RNAzymes now). ",
"http://www.rsc.org/chemistryworld/News/2011/April/07041104.asp",
"Now, we're starting to see a wider variety of RNAzymes, and even developing new RNA structures that catalyze other kinds of reactions. Remember, there's no pressure to survive or produce any kind of useful product here, so its not a problem that we have untold amounts of useless RNA strands floating about. The only pressure is that the more efficient, stable, and quick enzymes will produce more strands of the same type.",
"Now we can get to something like a system. In the deep oceans, we have things called thermal vents, which are hot beds (haha) for organic chemistry. In particular, it is theorized that certain types of clay may have been the first \"membrane\", where molecules would get stuck to the surface, while still being biologically active. Here's what starts to look like a system, where we have multiple enzymes of different types near to each other, membrane bound, and feeding each other products (by way of proximity, not some physical link). This is a kind of active system, where the products of one enzyme are used by another.",
"Now we're beginning to see a wider variety of molecules made, as the energy of reaction is lowered by more efficient enzymes, and these systems provide more and more materials to mess around with. It is probably here that we go to proteins.",
"Proteins are just chains of amino acids, just like the RNA enzymes we were discussing are just long chains of RNA nucleotides. What great about them though is that there is a larger variety of sizes and shapes, and this can lead to a much larger variety of structures for a protein versus an RNA enzyme. This greater variety of structures can have much more efficient and durable enzymes, which can mediate a larger variety of reactions. Now maybe we begin to see other macromolecules like lipids.",
"Once lipids hit the scene, its a race to the finish, because the enzymes (RNA and protein) can exist in an enclosed micelle like structure, mediating the reactions that exist in concert with other enzymes, without as much environmental influence, and being better able to control reaction conditions.",
"Here, we find ourselves at \"biologically\" active systems, where independently replicated molecules have a proclivity to make structures that protect them from the environment. As well, we may have had ATP for quite a while by this point, meaning that these rudimentary systems could have some way of collecting energy from the environment to use in reactions that require a higher energy input. Here's the next small step.",
"These systems may contain the right mixture of components to properly replicate everything that makes them up. RNA can replicate itself, make proteins, and mediate the reactions to make the necessary molecules for these. The proteins can make a huge variety of molecules, including the lipids needed for the membrane, as well as other molecules needed for replication. This is the step from proto life to early life. In the RNA world hypothesis, DNA doesn't even hit the scene until much later, being useful because it is better at preserving a record of the genetic code. We've arrived at our destination, by way of one of the many proposed methods that early life arose. We hope you've enjoyed the ride, please stay tuned to scientists much smarter than I to actually do the research to prove or disprove any of what I've laid out here.",
"TLDR: sugars > nucleotides > amino acids > RNA strands > RNAzymes > proteins (enzymatic and otherwise) > environmental membranes > lipids > lipid membranes > enclosed systems > replication of an entire system > organism."
] |
[
"Why is it so rare to see a tetrahedron complex with a central atom that has a single charge (+1)?"
] |
[
false
] |
And are there any exceptions whatsoever?
|
[
"The ammonium cation NH4",
" is tetrahedral and is plus one charge. I would say this ion is pretty common!",
"In terms of transition metal complexes, tetrahedral geometry is most common in d",
" or d",
" complexes, so Scandium, Yttrium, Lanthanum and Actinium would be candidates for tetrahedral compounds with +1 charges with 0 d-electrons and Copper, Silver and Gold form tetrahedral complexes with +1 charges and 10 d-electrons.",
"I'm not sure I would call their occurrence rare ",
" but they are only one option of many possible structural motifs.",
"Now square planar d7 or d9 complexes, they are rare..."
] |
[
"I don't understand your question. Are you talking about the formal charge of a single atom in any tetrahedral complex, or are you talking about the oxidation state of a metal in a metallic tetrahedral complex?"
] |
[
"Sorry if my question was unclear.\nI was talking about the overall charge of the complex "
] |
[
"Articles say that getting the covid vaccine doesn’t affect rapid covid PCR results. Can someone help explain why (not)?"
] |
[
false
] | null |
[
"The vaccine is injected in your arm and the viral material stays fairly local. PCR test samples are most commonly taken from the nasal or oropharyngeal cavities.",
"Here's a review comparing ",
"intramuscular vs subcutaneous vaccine administration"
] |
[
"Adding to what ",
"u/NickWarrenPhD",
" wrote, the RT-PCR test also only detects viral RNA. The vaccine mRNA as well as the vaccine protein (which is undetectable to the RT-PCR test anyway) stays pretty localised so there is zero chance it would end up in your nasal cavity for the RT-PCR to detect."
] |
[
"The PCR might not distinguish between live virus and dead virus. Or, maybe the virus still runs a certain course through your body while the vaccine only provides enough immune response to keep you from developing symptoms. Or, maybe the test is actually detecting the vaccine particles and not actual virus particles."
] |
[
"Are house cats one species of cat or multiple species? If one species, why aren't multiple breeds considered different species?"
] |
[
false
] |
Hey there, I know almost nothing about taxonomy but I was thinking about this..to clarify a bit more, cats are wide and varied; but I seem to have only found shaky information regarding what species a cat is (wikipedia says ). Is this the only species? How can a species with so much variation within itself not be classified as a different species? If you look at something like birds it seems like they have a large number of species even with minor physical differences between the kinds of birds. To give an example, within the Macaw species of birds there are 19 subspecies alone have little physical variation (at least, I think so), so why aren't they just considered a different "breed" of Macaw? Hopefully this is clear enough.
|
[
"Contrary to what is often said, this actually isn't a criterion for classification at all. Many interspecific hybrids are perfectly fertile, including all future generations."
] |
[
"Because variation that is visible to the human eye isn't representative at all of underlying variation. Different breeds of cats have been bred to look different, but almost the ",
" differences between them are the visible ones. Genetic differences in general are very small. And in many cases, the divergence between breeds only goes back a couple centuries. ",
"Contrast this with different groups of birds, which may look similar on the surface but actually have deep underlying differences, and may be separated from each other by hundreds of thousands of years or more."
] |
[
"except that Mallard ducks, for example, can produce hybrids with about two dozen other species. Many (perhaps most) species can hybridize with at least one other species."
] |
[
"Why do we get gray hair as we get older?"
] |
[
false
] |
[deleted]
|
[
"I think it is more appropriate to say that both are right. ",
"Inside the hair follicle, there are melanocyte stem cells, and melanocytes. Melanocytes are sensitive to hydrogen peroxide levels. Where does hydrogen peroxide come from? It comes from the other prominent type of skin cell, keratinocytes. It is part of the immune system. A keratinocyte senses danger, so it secretes hydrogen peroxide. The immune cells from the blood are drawn to this like flies to stink. ",
"As we age, all sorts of inflammatory responses increase. We heal slower. Cortisol levels are higher. And hydrogen peroxide in the skin gets higher. If your melanocytes are not really good at disproportionating (look it up) hydrogen peroxide, they will die. Once the melanocyte stem cells die, it is pretty much all over for that hair follicle. The stem cells are replaceable by cells from the nerve sheath, but it is a REALLY REALLY slow process. And besides, while that process is ongoing, there is still too much hydrogen peroxide in the skin. ",
"In addition, other inflammatory markers cause melanocytes to respond much less vigorously. So they are naturally slowed. Gray hairs result from low melanin levels. White hairs result from no melanin levels. ",
"What about the future? In the future, it is easy to envision that you will be able to get a viral injection into your skin. The virus will endow melanocytes (and their stem cells) to disproportionate a LOT more hydrogen peroxide, and maintain melanin production for life. It would be cool. Today, there is pseudocatalase which can be applied topically and has a mild effect (eBay nuCyte and pseudocatalase). "
] |
[
"A theory I've heard about which sounds plausible: small amounts of hydrogen peroxide are produced in many cells in the human body, including around hair follicles. When we are young, we have lots of an enzyme called catalase that breaks the peroxide down into water and oxygen, before it can oxidize important cellular components. As we age, we make less catalase, leading to a buildup of peroxides which turn our hair grey/white (not necessarily through direct bleaching of the hair, but through oxidative damage to the cells which form the hair). "
] |
[
"I've had many grey hairs that have colored roots. Do we know if there is some controllable mechanism that regulates these processes?"
] |
[
"How did Pangaea break up?"
] |
[
false
] |
More broadly, "How does plate tectonics work?" I understand the basic theory, but I don't understand how a plate the size of a continent got halfway around the world when there were already plates there. I'd liken it to trying to trans-locate a single brick in a wall without leaving the wall itself. Did the plates in the way break up, or did they somehow go under the moving plates? Help?
|
[
"The other half of the equation is ",
"subduction",
"."
] |
[
"Yep. That's actively what's happening out here in California; the Pacific plate is subducting under the North American plate and the lighter materials melt and then float back up. That's how the current version of the Sierra Nevadas formed, there's a felsic batholith that's floating up through the crust, and when you get into the exposed rock it's mostly granite. That same subduction also caused the uplift which has formed the Coastal range.",
"EDIT: ",
"Here",
"'s a link to a map of that batholith.",
"2nd EDIT: Found a good ",
"image",
" showing the process."
] |
[
"So the plate going under would melt/break up, while the other side would be getting new material that could cool into a plate?"
] |
[
"In regards to the Quantum Zeno Effect, what defines \"observation\"?"
] |
[
false
] | null |
[
"Perturbation. Probing the system in some way so as to derive information about some element of its state, such as its position or momentum. Keep doing it to a system that would normally (for example) decay, and do it so quickly and \"thoroughly\" that you essentially lock down that observable, which is linked to its state. ",
"The way it's been done in practice to get some atoms very ",
" cold, and then you use a laser to precisely define their position. As a result the tunneling required for beta decay is suppressed for as long as you keep the system cold, and constantly ping a laser off it. For details: Perturbation. Probing the system in some way so as to derive information about some element of its state, such as its position or momentum. Keep doing it to a system that would normally (for example) decay, and do it so quickly and \"thoroughly\" that you essentially lock down that observable, which is linked to its state. ",
"The way it's been done in practice to get some atoms very ",
" cold, and then you use a laser to precisely define their position ",
"http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.115.140402"
] |
[
"I think it's better phrased as:",
"Entanglement ",
" as measurement.",
"but the two are fundamentally linked, yes."
] |
[
"In general, essentially anything that requires the quantum system to have a well-defined (i.e., classical) state counts as measurement.",
"More technically, if the state of a quantum system becomes inseparably mixed with the state of another quantum system that is too complex for us to realistically describe quantum mechanically then it is 'measured'. If we could describe the second system quantum mechanically then we'd see that the two systems actually just become entangled. This is called decoherence, and is also the source of the many worlds interpretation."
] |
[
"Can it be said that some languages are objectively easier/easier to learn than other languages?"
] |
[
false
] |
Obviously the difficulty with learning a language depends on if a person knows a similar language already. Apart from that, would it be wrong to, for example, call English easier than Finnish?
|
[
"Easier in what sense? Languages have different ",
" of complexity. ",
"So while one language might have very complex syntax, maybe its morphology is not complex at all. Another language might be really phonologically complex with a huge inventory of sounds to learn, but perhaps its syntax is not as complex. (There are fascinating theories about why languages have these tradeoffs in complexity, but that's a different issue).",
"You'd be hard pressed to find a language that is either very simple or very complex across all these levels. Not to mention the problems with quantifying learning..."
] |
[
"Yeah! OP specifically asked to disregard native language influence so that's why I didn't address it here.",
"There's a lot of fascinating work on native language influences on second language learning. Similarities & differences between languages can actually sometimes lead to unexpected effects. For example, having an L1 that has a grammatical gender system can actually lead to more difficulties when learning a language with a similar system. The idea is that you're so used to your language's grammatical gender system that it causes interference when trying to learn the new one. But if your L1 doesn't have a grammatical gender system, it can't interfere with your learning of your L2's grammatical gender system. On the other hand, there's also evidence that having an L1 with a similar phonetic inventory as your L2 helps with learning. Long story short, it's not clear why there are all of these different effects; they likely arise from a mixed bag of complex interactions.",
"(I can't for the life of me remember the authors on either of the papers I'm drawing from here, I'll try to find the sources for you! I could be getting the effects backward, so take what I say with a grain of salt.)"
] |
[
"Surely your native language is relevant to this question as well. Wouldn't foreign languages with similarities with regards to phonetics and/or grammar be easier to learn than ones that are completely different? (sorry if phonetics isn't the right word, I mean vocal sounds used in word forms)"
] |
[
"Why does sleep deprivation lead to hallucinations?"
] |
[
false
] | null |
[
"I thought DMT's role in the brain was just hypothesis as there isn't enough evidence etc or was debunked?"
] |
[
"I thought DMT's role in the brain was just hypothesis as there isn't enough evidence etc or was debunked?"
] |
[
"It is mostly speculation. No solid evidence. I haven't read his book, but Dr. Rick Strassman has a solid theory on it. Check this out for more info:",
"https://www.rickstrassman.com/",
"Again, it's mostly just speculation. But I'm not sure it was debunked."
] |
[
"Can someone please help me understand the concept of mass a little better?"
] |
[
false
] |
[deleted]
|
[
"Mass has two major properties (the two I chose might be considered arbitrary by some, but I'm choosing two for the purposes of this discussion). First, the mass of on object tells you how much force it will take to accelerate it. This is captured by Newton's second law: F = m*a. Thus, the more massive something is, the harder it is to get it moving fast. This is what we refer to as inertial mass. Secondly, mass is the property of an object which gravity \"pulls on.\" Thus, the more massive an object, the greater the gravitational pull on it. This is referred to as \"gravitational mass.\" This is what is related to weight. The more mass something has, the heavier it weighs because gravity will pull on it harder. For instance, near the surface of the Earth, gravity will pull on a mass such that it will accelerate that mass if it were dropped at a rate of 9.8 m/s",
" (or if you prefer 32 ft/s",
" ). Thus, the weight of an object is given by the equation W = m*g, where g is the acceleration of gravity. This is, of course, just a re-write of Newton's second law for the specific case of how much something weighs. ",
"It turns out that inertial mass (how hard it is to move something) and gravitational mass (how hard gravity pulls on something) are the same thing. You might think \"Of course they're the same thing, they're both mass!\" but there is no inherent reason that these must be the same. For instance, electric force determines how hard it pushes or pulls on something based on that object's charge. There is no reason that gravity couldn't pull on something based on a different property other than the object's resistance to motion. However, the fact that inertial and gravitational mass is the same is the reason that all objects on the moon fall at the same rate. The force on the object is proportional to the mass, and the acceleration is proportional to the mass, so the masses cancel out. In math: F = ma (Newton's Second Law). The force on the moon is the weight of the object, F = W = m*g. So, m*g = m* a, so a = g, independent of mass (The reason this doesn't work on Earth is because of the atmosphere slows down lighter things more than heavier). ",
"Dark Matter does provide mass, and thus gravitational \"weight\" to objects. In fact, it is required that it does so. Dark Matter is a theoretical matter which holds galaxies together. A simplified version of that. Imagine a ball on a string. If you spin the ball around, it will pull the string tight. And if you spin the ball too fast, it will pull so hard it breaks the string. So the faster you spin the ball around, the stronger a string you need. Our galaxy is spinning around, and we know how fast. So, imagine a star near the edge of the galaxy. That is like your ball at the end of the string. What is the string? The force of gravity, pulling that star in. Turns out, we know how fast that star is moving, we look at all the mass in the galaxy and we say \"Oh, the 'gravity string' holding the star on isn't strong enough, that star should fly away!\" But, of course they don't. That means, there must be something else holding onto that star, something making more gravity, to make the \"gravity string\" tougher to break. We theorize that is Dark Matter, mass we can't see which pulls on the stars in a galaxy to keep them attached. ",
"Dark Energy is even odder. We won't get into all of that, but it is energy which we believe is causing the acceleration of the universe's expansion. What does this have to do with mass? Well, according to Einstein, energy has some \"mass like\" properties. That is, objects with more energy will exhibit properties like having more mass- their gravitational field will be larger and they will be harder to accelerate. Dark Energy has this property, but so do all other energies. So it is not special in regards to this topic. "
] |
[
"(The reason this doesn't work on Earth is because of the atmosphere slows down lighter things more than heavier) ",
"You mean air resistance, not lighter vs. heavier, right?"
] |
[
"Mass is inherent, and weight is just mass by surface gravity. Inertial mass is obtained by newtons dynamics law and gravitational mass is determined by newtons universal gravitation. Dark matter is simply a gravitating, near-perfect black body. Nothing about the definition of mass and weight changes "
] |
[
"What is our current best guess of the topology of the universe?"
] |
[
false
] | null |
[
"The ",
"observable universe",
" ",
"is simply connected",
" on the scales we can observe. Anything could happen in the rest of the universe, but the simplest guess is that there's more of the same."
] |
[
"Which gives absolutely no hint on the topology."
] |
[
"Which gives absolutely no hint on the topology."
] |
[
"Are there any theories or examples of Physical Laws that are not static or immutable, and may have changed over time?"
] |
[
false
] |
It seems almost nothing in the Universe is indefinitely resistant to change, so it is possible to that the rules governing the Universe are also susceptible to change? I've never heard of any theories or examples of this, and it seems that common belief would be that the Universe follows the same rules now as it did at its beginning. Is it unreasonable to think that particles/matter/energy could have behaved differently tens of billions of years ago, and gradually came to behave that we observe today?
|
[
"There are theories that the fine structure constant, which basically determines the strength of the electromagnetic interaction, may have changed over cosmological time scales.",
"There is some experimental evidence suggesting such an effect, JK Webb's group has been doing spectra analysis of distant quasars and published several papers documenting this possibility: ",
"http://arxiv.org/abs/astro-ph/0012539"
] |
[
"I guess after reading your response, I am more interested in why the assumption that the Laws are static exists?",
"Let's say some law wasn't static, but changed with time somehow. E.g., say Newtonian gravity doubled next Tuesday. Well, we could just change the dynamic law as based off a static law F = G(t) M1 M2/r",
" in our equations and have the constant G change with time, so G(t) = G before Tuesday and 2G after Tuesday. ",
"Ultimately, the reason we believe this is that our experimental tests have largely shown that the physical constants/laws are constant as far as we have been able to test over the time ranges we see. ",
"Sure there was the ",
"announcement this summer",
" that showed evidence that alpha may have change by ~ 1 part in a million may vary based on spatial location (e.g., billions of light years in one direction it is different than what it is here and billions of light-years in the other direction), but it still has to be verified by other experiments before it will be accepted."
] |
[
"It's not that the laws themselves have changed, but the relevance. In the early universe, the equation of state for the quark gluon plasma was highly relevant; nowadays gravity is the most relevant phenomenon on the universal scale.",
"One example is Hubble's Law and Hubble's constant, where Hubble's constant changes with the age of the universe."
] |
[
"Could dark matter be explained by neutrinos?"
] |
[
false
] |
Okay, there has to be a gap in my knowledge. Which, as an armchair science enthusiast, does have many such gaps. But here's my thinking, and please let me know where I've gone wrong. 1: Dark matter interacts gravitationally, but not with the electromagnetic force. 2: Neutrinos have mass, but don't interact with matter. The only way we can detect them is when they break light speed through a material. I was also under the impression that they wouldn't interact electromagnetically, since they don't have electrons to absorb/emit photons. 3: So, if we have a bunch of neutrinos, maybe even slow-moving (is that even possible?), would they exhibit the characteristics of dark matter?
|
[
"Neutrinos ",
" a form of dark matter, but they simply do not have enough mass to explain more than a few percent of dark matter. Also, because they have such small mass, they are nearly always moving extremely fast, a property inconsistent with observations about dark matter. For this reason we call neutrinos \"hot\" dark matter, while we are searching for the unknown \"cold\" dark matter, which is more massive and not moving as fast. ETA: I should add that there are other types of particles, such as axions, that could be as light or lighter than neutrinos but still be a good dark matter candidate because, for example to make a longer story short, they are produced in a special way such that they are still moving slowly. "
] |
[
"Excellent! Thank you so much for the info, and I'm pleased to know that I wasn't all the way out in left field somewhere."
] |
[
"Thank you for the follow-up! I'll have to look into the theory behind sterile neutrinos. Dark matter is fascinating, but it's tough to keep up on the research without clickbaity garbage news clogging up the feed."
] |
[
"Why haven't aquatic mammals evolved to breathe underwater?"
] |
[
false
] |
I know that aquatic creatures eventually learned to start breathing on land, and crustaceans and amphibians can breathe both under and above water, so why cant Mammals? One of the biggest problems for whales and seals is finding an air-hole while hunting, so why haven't they adapted over time to breathe underwater using gill-like devices?
|
[
"In addition to the non-goal-drivenness others mention, there is a considerable lack of dissolved oxygen in water compared with air, or at least it's harder to get out of the water. And it takes a lot of oxygen to burn the calories to be a warm-blooded mammal. It could happen I guess, but even sea-turtles (who have been around far longer than whales) still haven't developed gills. Perhaps after a certain complexity, there's just not enough advantage getting oxygen out of the water to favor a gradual mutation that allows for such an extraction."
] |
[
"because evolution doesn't push towards a certain goal, it's a \"random walk\" of mutations, most of which are usually detrimental. So they might, if that mutation appears and is useful so it is passed on through the gene pool, but there's nothing to make it happen just because it might help."
] |
[
"granted i'm a physicist, not a biologist. I may be incorrect. This is just what I recall from similar threads on the subject."
] |
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