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[
"When transition metal ions absorb visible light of certain colours wouldn’t they de-excite to emit photons of the same colour?"
] |
[
false
] | null |
[
"Not necessarily. For example if you excite an electron from level 1 to level 5 it could just go back down and emit the same photon, or it could go down any series of steps (allowed by the spin of the energy level) like 5-3-1 or 5-4-2-1, etc., emitting a series of photons with different wavelengths than the original light. This is similar to how fluorescence works: a high-energy photon, usually UV or x-ray, frees an electron in a low energy level, so electrons in higher levels fall down to fill the empty state, emitting lower-energy photons that can be in the visible spectrum."
] |
[
"Yes they can. It's not the only possibility but they definitely can."
] |
[
"Thanks for answering :)"
] |
[
"Is it possible to get multiple different colds/flu viruses at the same time? If so, what are the effects?"
] |
[
false
] |
What are it effects on the body, and how does the body defend itself, would it take longer to fight off? Is it more difficult to fight off different viruses vs just one type? Do the effects compound on top of each other?
|
[
"Yes, this is called a \"superinfection.\" ",
"The effects will vary quite a bit depending on the details. Many of the responses of the immune system to an infection are general - if you get infected with two rhinoviruses (one of the virus types that causes \"colds\") of the same type or two rhinoviruses of different types, the cells around the area of infection will respond in essentially the same way - principally by activating inflammation and something called the \"antiviral state.\" ",
"The response of your adaptive immune system (T-cells and B-cells) will be a bit different, since there would be two sets of activating signals with a co-infection, but it's hard to max out an immune response, and to some extent the different viruses will be competing with each other. It's possible that it will take you longer to recover, but I'm not aware of any solid data on this.",
"On the other hand, if you are co-infected with two different ",
" of infection, say a bacterial and a viral infection, this can cause serious problems, since the immune response necessary to deal with viruses and the response necessary to deal with bacteria can be quite different, and the response to one can be counterproductive to the response to the other. In fact, most people that die \"of the flu\" actually die from bacterial infections of the lung that were able to gain a foothold because of the immune response to the flu virus. "
] |
[
"A fungal infection in the skin is not likely to effect the immune response in, say the lung. Again, it depends a lot on specifics, and some infections can have systemic consequences, but as I said before, it's hard to run out of immune response. The reason that having two different kinds of infections in the lungs is an issue is not because you're running out of immune response, but because the immune environment is different.",
"Think about it this way - say you're the military and you're trying to combat an invading army and also rescue hostages being held by terrorists. If the invasion is in Boston and the terrorists are in New York - no problem. You can bomb the army and send in SWAT for the terrorists. If the terrorists are in a building surrounded by the invading army, then getting SWAT into the building is going to be impossible, and bombing the army is going to kill your hostages. Different immune responses are necessary to combat different types of infections, and they're not always mutually compatible. But if the infections are in different places, the immune system is more than capable of local responses. "
] |
[
"Would having a fungal infection of say... of the skin decrease the effectiveness of the immune systems ability to fight a bacterial and or viral infection at the same time?"
] |
[
"Would an obese person, provided with enough water and nutrients, become completely skinny before starving to death?"
] |
[
false
] | null |
[
"This has actually been done... year without food:",
"http://pmj.bmj.com/content/49/569/203.abstract",
"Doesn't eat for over a year, poops every 42 days and lost 275 pounds. "
] |
[
"Rather than nutrients, I think he was reaching for trace elements in the diet like \"vitamins and minerals\" --i.e. if an obese person was surviving on a diet of water and diet supplements, would they lose all their fat before starving to death? Or, would the lack of proteins and readily convertible carbohydrates kill them before all the fat was used up?"
] |
[
"The paper (without a paywall) can be found ",
"here"
] |
[
"Would it be possible to use GFP to create glow in the dark tattoo ink?"
] |
[
false
] |
[deleted]
|
[
"Not \"glow in the dark\" but fluorescent (i.e. visible under UV (black) light), yes, absolutely. You'd need to use a virus to transfect your cells. If you just injected GFP your body would break it down.",
"There are rumors everywhere about scientists who accidentally injected themselves with GFP transfecting viruses and have little fluorescent points on their fingers."
] |
[
"Not \"glow in the dark\" but fluorescent ",
"For true \"glow in the dark\" you would need all of the enzymes that make ",
"luciferin",
" plus the lusiferinase enzyme."
] |
[
"Splicing the gene that codes for GFP into skin cells might work, but there would be a risk of dermatitis if your immune system attacks the foreign protein."
] |
[
"Why is it that we start to forget a dream soon after we wake up? Why don't we remember them like everything else?"
] |
[
false
] | null |
[
"The more impressive your dream or thought, the more likely you are to remember it.",
"Quoted from ",
"this",
" article"
] |
[
"Would it be possible to \"introduce\" the norepinephrine hormone while someone is dreaming to allow them to remember their night of dreams as clearly as if they were recalling the previous day's events?"
] |
[
"I've currently quit smoking and I wear the nicotine patch when I dream. My dream recall has never been better in my life, and I surmise that the cause is increased norepinephrin in my brain while I'm asleep, a reason that nicotine is addictive. Norepinephrin belongs to a group of chemicals called the catecholamines which are excitatory neurotransmitters that participare in addiction. Other members are dopamine and epinephrine."
] |
[
"How come a solar eclipse could blind you?"
] |
[
false
] | null |
[
"Looking at the sun will blind you. Any time, anywhere. Including when you look at the sun during the partial phases of a solar eclipse. Naturally, people who don't know any better are more likely to look at the sun during a solar eclipse. They should not. One can look at the sun safely only during \"totality,\" that brief period during an eclipse when the moon completely hides the sun. ",
"During the upcoming eclipse, that period of totality, when it will be safe to look at the sun, will last a maximum of 2 minutes. The rest of the eclipse (all of the partial phases before and after totality) will be dangerous to look at. If you are not directly in the path of totality, there won't be ever be a safe time to look at the sun during the eclipse."
] |
[
"Because the sun is really bright, so bright in fact that you cannot focus your eyes on it. However, during an eclipse, it's much easier to focus on the sun, because the moon is dimming some of the light, but since the sun is just as bright as before, if you focus your eyes up there, it'll ruin your eyes, just as it will with any camera "
] |
[
"TL;DR: ",
"Eclipse Eye Safety",
"It can blind you if you try to observe any partial stage of the eclipse through ",
" Not all dark filters are equivalent. ",
"Even if a filter blocks enough ",
" light to allow observation, it may still be allowing a dangerous amount of UV and IR light to painlessly enter and damage your eyes. One recommended material is number 14 welder's glass.",
"Direct (without a filter) observation of a solar eclipse is only safe during the total phase when the Sun's photosphere is completely, totally, ",
" by the Moon (not 99%, not 99.9%). ",
"If there is no total phase, then it is ",
" to look at a solar eclipse without an adequate filter."
] |
[
"What is the highest number of beats per minute that the human ear can discern?"
] |
[
false
] |
How many beats can the human ear discern before it just sounds like one, continuous note/sound. And is it different for different sources of sound?
|
[
"Not a scientist, but a musician. 20Hz is about the lowest tone most people perceive as a, well, tone. Lower than that and you hear the individual cycles as beats (or you hear nothing at all). Similarly, if you take a percussive beat and play more than about 20/second, it will transform from a beat pattern into a tone. There's electronic music that uses this to great effect.",
"I believe this 20Hz cutoff is independent of the source or type of sound - it's more a result of how our ears work. \nMaybe a scientist can chip in on ",
" this happens?"
] |
[
"Our ears have three bones call the ",
" (latin for hammer), ",
" (anvil), and ",
" (stirrup) connected to the tympanic membrane, the outermost source of detection of longitudinal waves in air pressure that we know as sound.",
"The vibrations are transferred from the membrane to each of the three bones in the order listed, in the process intensifying the signal from the high surface area -> small surface area transition.",
"The ",
" moves against an inner opening called the ",
" which has a fluid-filled conch-like spiral structure on the other side called the ",
". The cochlea has three chambers, two of which, the scalas ",
" and ",
", sandwich a membrane with sensitive hair cells. These hair cells are moved by the fluid movement induced by the stapedius' vibration.",
"When the hair cells move, they tilt over, and tiny ",
" hairs on the surface of the cells also move. The stress on the stereocilia causes tiny channels in the hair cells to open, allowing the gradient that is normally maintained by ion pumps to be relaxed, resulting in potassium flowing into the cells. This in turn induces another channel to open, but this one is ",
", meaning it is sensitive to changes in the electrical gradient, and the end result is that calcium, a commonly used ion for cell signal transduction, flows into the cell.",
"The calcium causes achetylcholine to be released into the synapse and stimulates cranial nerve VIII, which we will eventually interpret as sound.",
"The ability to distinguish two different beats very close together depends not only on the ability of the hair cells to \"recharge\" via maintenance ion pumps after the relaxation of the ion gradient, but also on achetylcholine reuptake and synthesis.",
"If our hearing was based entirely on electric and ionic processes, then we might be able to distinguish shorter intervals, but there is chemical neurotransmitter signal transduction at this step, which is generally slower to act and slower to recover than purely electrical signals."
] |
[
"Lower than that and you hear the individual cycles as beats ",
"Just to clarify, this would be 1200BPM."
] |
[
"Could a power generator in geostationary orbit transfer power to us via wire?"
] |
[
false
] |
Some context, when I was way younger in a physics class we were discussing having a nuclear reactor in orbit and the advantages and disadvantages, when posed the question of how we'd get the power down to earth and I suggest, well, a wire. Now everyone looks at me like I'm a moron, I know the 'correct' answer was to be some form of wireless energy transfer, I believe the example in the book used electromagnetic radiation for it. But now I'm older and have a better understanding of physics and I'm still not sure why this wouldn't work.
|
[
"In theory it would work. In practise we don't have any materials that are strong enough to make the wire. It would also be incredibly expensive...enough that a wireless solution would be far better even if constructing the wire was feasible."
] |
[
"It's called a ",
"space elevator",
". Basically the only thing preventing us from building it is having a light and strong enough material for the wire."
] |
[
"Huh, I'd heard of space elevators but had always thought them a silly idea due to bad explanation, plus the name is a bit iffy. I had always thought it would just be a huge tower with all the support coming from the base.",
"This is exactly what I was thinking of, thank you."
] |
[
"As our solar system/galaxy moves is it possible that time could slow or speed up depending on our position?"
] |
[
false
] |
[deleted]
|
[
"Stars are sufficiently spaced apart that as we orbit around the centre of the galaxy we never really get close to anything else. We basically just feel the average gravitational field for this radius. Our orbit is not perfectly circular, but that's a fairly small effect. If you're looking at time dilation, the biggest effect is that the orbital velocity of the sun around the centre of the milky way is a couple of hundred kilometres a second, so if you were an observer \"stationary\" with respect to the galaxy, you'd see a little bit of time dilation from our orbital motion."
] |
[
"Time dilation only really has a measurable effect in extremely strong gravitational fields and at extremely high speeds. These aren't common.",
"Also, stellar mass black holes (i.e. black holes that formed from dead stars) don't actually have exceptional gravity! Gravity basically only depends on mass, and a black hole can't have more mass than the star that formed it. The difference is that if you get ",
" close to a black hole, things get weird - time slows down etc. But \"really close\" is ",
" close. Like we are more likely to have a head-on collision with a star than bump into a solar mass black hole. So yes, if we were close enough to have strong time dilation from a black hole, it would have totally disrupted the solar system.",
"There is however, a ",
" black hole in the centre of the galaxy. However, its Schwartzchild radius is still less than the orbit of Mercury, and it's not likely we've passed anywhere near that close, seeing as we're in a nice fairly circular orbit."
] |
[
"Time dilation only really has a measurable effect in extremely strong gravitational fields and at extremely high speeds. These aren't common.",
"Also, stellar mass black holes (i.e. black holes that formed from dead stars) don't actually have exceptional gravity! Gravity basically only depends on mass, and a black hole can't have more mass than the star that formed it. The difference is that if you get ",
" close to a black hole, things get weird - time slows down etc. But \"really close\" is ",
" close. Like we are more likely to have a head-on collision with a star than bump into a solar mass black hole. So yes, if we were close enough to have strong time dilation from a black hole, it would have totally disrupted the solar system.",
"There is however, a ",
" black hole in the centre of the galaxy. However, its Schwartzchild radius is still less than the orbit of Mercury, and it's not likely we've passed anywhere near that close, seeing as we're in a nice fairly circular orbit."
] |
[
"With all the covid tests going on are we getting any non-covid related data from the tests?"
] |
[
false
] |
I would imagine all personally identifiable information(PII) would be stripped, but this would be a huge waste of an opportunity to do some other research if we didn't collect the data.
|
[
"Probably not exactly what you’re looking for but I know a study was done to determine if maternal covid during pregnancy impacted long term infant development. There was no measurable difference between babies born to mothers who had covid during pregnancy compared to those who didn’t. However, instead what they found was overall, there was a big increase in developmental delays of all 2020 babies when compared to those born prior to the pandemic. They believe maternal stress could be a big contributor."
] |
[
"Or I also read, could be contributed to baby's lack of early socialization."
] |
[
"If the organization doing the testing got permission (written, explicit) regarding how information was to be used, things like age, race, employment, etc could be used for a study.",
"Given the small quantities of sample -- most places don't use the same sample for PCR and Antigen -- any other testing and results would require additional samples. And permission."
] |
[
"Why does metal have a smell?"
] |
[
false
] | null |
[
"If you're referring to the metallic smell that is frequently associated with coins, it is actually the oxidation of oils and other components found on your skin that transfers to the metal. The metal acts as a catalyst in the oxidation of these components.",
"An experiment you can try yourself is to wash a bunch of coins with gloved hands and smell them afterwards, they won't have a scent. Only after you remove your gloves and handle them will you be able to smell them."
] |
[
"THANK YOU! this solves a 40+ year old puzzle."
] |
[
"You're not smelling an engineering metal; they aren't volatile enough (meaning that they don't evaporate quickly enough) for there to be available molecules to interact with your olfactory system. However, you may be smelling a relatively volatile material coating the metal or produced by a chemical reaction with the metal or produced by microbes on the metal."
] |
[
"Why are there two bones in your lower leg and only one in you upper leg?"
] |
[
false
] |
[deleted]
|
[
"Well the lower leg has a different function then the upper leg. While both are supporting your weight, the lower leg also is in control of your foot. By having two bones, it allows you to \"roll\" your foot. This can be seen also on your arm. The forearm is made up of two bones which allows you to move your wrist in many directions. "
] |
[
"They both have a wide range of motion (due to the ball and socket joints) but they can't rotate like the lower limbs. For example, if you keep your bicep still, you can turn your forearm so that you can see the top an bottom of your wrist. You cannot do that same motion to your upper arm especially when you keep your forearm still. This motion comes from the two bones in the forelimb having the ability to twist over each other. Twist might not be the best word to describe the motion but it gives the general idea of what the two bones do."
] |
[
"It adds a whole new degree of freedom to the system. A degree of freedom is basically a definition of how many directions something can move in space. They are in layman's terms, up-down, left-right, forward-backward, and a rotational direction around each of those three axes, for a maximum total of 6 degrees of freedom for any particular joint.",
"Your shoulder joint, being a ball and socket joint is free to rotate around all three axes, but cannot translate. It has 3 degrees of freedom. So, if you only had one bone from your arm to your hand, your hand could reach all of the points in a sphere with a radius the same length as your arm, but it could never reach within or outside of that sphere. Adding a single degree of freedom joint in your elbow (a hinge type joint) allows your hand to move in and out from the outer edge of that original sphere of possible reach. You've now got the ability to reach anywhere in a solid sphere.",
"But why two bones in the forearm/lower leg. We could achieve this with just one bone.",
"Well, the more degrees of freedom there are, the more possible movements are available allowing your hand to become much more flexible and have a much much higher range of motion in order to grab things in different orientations.",
"This still doesn't quite answer the need for two bones. That comes down to stability. If our arms had two ball in socket joints (one at shoulder, one at elbow) it would have an immense range of motion, but would be inherently unstable. Muscles and tendons are only so good at keeping things in line (that's why muscle strains and injuries of the shoulder are much more common than those near the elbow). By having two bones in the forearm, we allow our hand to rotate a limited amount around that axis defined by the length of your arm while maintaining the inherent stability of the hinged elbow joint.",
"The human arm/hand and leg/foot systems have an immense number of degrees of freedom allowing for a huge range of different motions while maintaining a pretty stable structure.",
"This is a big deal in robotics. Of course in robotics, we can have pin in slot type translational joints as well as rotational joints. It's just that biological systems tend to the much simpler rotational joints. You'll note that no parts of your body allow for 'telescopic' motion like Inspector Gadget's legs."
] |
[
"Does the post-1945 increase in background radiation have any effect on our health?"
] |
[
false
] |
From what I understand, after 1945, because of the nuclear tests, the background radiation has increased in a significant enough amount to contaminate steel production noticeably. Does this increase affect human life and health?
|
[
"Luckily the numbers of background radiation are really low. I wouldn't mind if it were, say, doubled. IIRC a dose of 500 mSv is correlated to a 3% risk. Background radiation is merely 3-6 mSv per year."
] |
[
"after 1945, because of the nuclear tests, the background radiation has increased in a significant enough amount to contaminate steel production noticeably.",
"You have a source for this? How much (numbers) has it increased?",
"Anyway, assuming the above is correct, for stochastic health effects at least according to the ",
"Linear no-threshold model",
" (whose name pretty much says it all):",
"The probability of developing a cancer is directly proportional to the dose absorbed.",
"The sum of multiple small exposures is equivalent to a large exposure.",
"There is no minimum dose that can be considered safe. A negligible dose carries a negligible but still non-zero probability."
] |
[
"You get ",
" more radiation put through your body every time you fly in a 737. It's certainly not enough to worry about."
] |
[
"Is watching a bright screen (computer/TV) in the dark damaging to your eyes?"
] |
[
false
] |
By in the dark, I mean without any lights in the background. If it's damaging, why is that?
|
[
"Reddit has a pretty mediocre search function so don't feel too bad."
] |
[
"This question has been asked several times before. You may be interested in the following responses:",
"http://www.reddit.com/r/askscience/comments/1gijxx/has_there_been_any_observed_damage_to_the_eyes/",
"http://www.reddit.com/r/askscience/comments/z6qh4/is_sitting_in_front_of_a_computer_staring_at_the/",
"http://www.reddit.com/r/askscience/comments/z4v2g/question_about_eyestrain_and_low_light_situations/",
"A lot of really interesting questions and good answers get buried because of the high volume. The searchbar is a great way to explore some of the interesting content on ",
"/r/askscience",
"!"
] |
[
"I tried searching, apparently not hard enough. Thank you very much, I'll mark this as answered.",
"Edit: Apparently I cannot mark it as answered, too bad."
] |
[
"What is the tensile strength of human ligaments? Is it constant? If not, can they be strengthened by working out?"
] |
[
false
] | null |
[
"resistance training can increase the cross sectional area and tensile strength at the insertion site of human tendons and ligaments",
"http://www.rehab.research.va.gov/jour/00/37/2/wren2.html",
"http://www.rehab.research.va.gov/jour/00/37/2/wren2.html"
] |
[
"this is actually a link to a theoretical model of how tendons/ligaments may adapt to a stimulus (ie resistance training), but it is based on animal models where the exercise loading was not described very well. ",
"This to me is not very high quality evidence that resistance training does provide actual increases in strength/cross sectional area in humans. ",
"As opposed to the following study, where actual cross sectional area was examined following resistance training and showed increases in cross sectional area.",
"http://www.ncbi.nlm.nih.gov/pubmed/17524067",
"In short, it does look like strength training increases tendon cross sectional area and strength"
] |
[
"I feel I might have a unique perspective on this question. The tensile strength of human ligaments varies widely depending on the ligament in question. This is due to the different composition of ligaments in the body. ",
"There are some interesting factors to consider when discussing ligament strength. For example, the ",
" of load applied will alter the amount of elasticity in the tissue. In general, higher rates of applied force lead to lower elasticity (the same is true in bone tissue, yes bone has elastic properties). Also, the orientation of collagen fibers in the ligament will have a dramatic effect on the tensile strength. Collagen is typically oriented along the axis of greatest load, so the tensile strength of a tendon in different directions will vary. Another factor to consider when discussing tensile strength in connective tissues is what is known as the 'toe region' of the stress-strain curve. This is a nonlinear region of the curve where fiber recruitment occurs. When first placed under load, not all of the fibers are under tension, as the load increases, more and more fibers are stretched to length and then put under tension (this has an effect on the rate-related tensile strength as well). Additionally, the type of collagen plays a major role in tensile strength (with type 1 collagen being most abundant in the musculoskeletal system)",
"Despite what some others have mentioned IIT, tendons and ligaments ",
" be strengthened, but the overall strength increase is something along the lines of a 10-15% gain in overall tensile strength. ",
"Tendons and ligaments are avascular and aneural, meaning they have poor blood supply and not many nerves. This makes them notoriously hard to repair or regenerate once injured. Fibroblasts (the main cell type in this tissue) have specialized mechanical receptors that respond to loads. Higher loads on the cell result in higher transcription of collagen products. "
] |
[
"I recently learned that some insects release a pheremone when they're killed that attracts other insects to their corpse. What is the reason for this? Wouldn't it make more sense to release a chemical than warns of danger?"
] |
[
false
] |
[deleted]
|
[
"Ants for example have a graveyard where all the dead ants go. When an ant dies, it releases a pheromone which attracts other ants, who bring the dead ant to the graveyard. I assume having all dead ants, some of them probably dangerous because of infectious diseases, in one place that the ants never visit except to bring more dead ants, is less of a risk than having the corpses lie around where they died and have fungi and bacteria grow on them and attract predators."
] |
[
"On a side note this is an interesting undertaking by using oleic acid on a live ant and observing surrounding ants take him to the ‘graveyard’ while still alive. ",
"https://youtu.be/ZPw9dSV6y2c"
] |
[
"https://phys.org/news/2015-12-arms-social-wasps-alarm-pheromones.html",
"In the case of wasps, if one wasp has been killed the killer may well pose a risk to the whole hive. It's to the hive's advantage to be proactively defensive, and the pheromone marks the potential enemy - rather in the way explosive dye capsules can be used to mark thieves/stolen items."
] |
[
"Why is it that when propellers reach a certain speed they seem to slow down?"
] |
[
false
] |
I've seen this phenomenon plenty of times. is a great example. You can clearly see the propeller speeding up, but once it gets fast enough, it seems almost stationary, or that it slows down tremendously. Why is this?
|
[
"Ahhh this is a funny phenomenon. It has to do with aliasing.",
"Aliasing is an effect of sampled signals.\nYou know that a camera takes shots every few milliseconds right?\nWhat happens is that we piece together the frames you get a smooth film. But with symmetric objects we get a special effect.",
"Imagine a cartwheel with 6 spokes. it turns a full circle in a second at the start.",
"Our camera can take 24 shots each second. So we have 24 shots of a turning wheel each second, which so far gives a smooth image. ",
"Now when the wheel reaches a certain speed, in this case 4 rotations a second. Now we have only 6 shots of each rotation. \nThus each shot of the wheel is after it has made 1/6th of a turn.",
"Due to symmetry of the spoked wheel it looks like it's not moving at all. As turn a spoked wheel 1/6th and it would look exactly the same as the previous shot. Thats why it looks like its standing still!",
"Or lets say you go even faster, the wheel rotates 24 times each second. So the wheel is only shot once every turn, in exactly the same position.",
"The slowing down is as you approach this effect.",
"TL:DR Every image the camera takes is exactly as fast as as a full rotation, or a point-symmetric looking shot."
] |
[
"...what about with the human eye? It's not just cameras that this effect appears."
] |
[
"Hm to be very fair, I thought its not relevant for human sight, when we cannot capture it it blurs for us, but we never suffer the image by image effect as eyes send a continuous signal to the brain."
] |
[
"Is there a theoretical maximum resolution of a digital image made from scanned film? What determines this?"
] |
[
false
] |
Obviously there are constraints with currently available hardware and cpu power, but does film itself have infinite resolution?
|
[
"It depends how big the film is, and how fine the crystals in the film grain are. It's also apples and oranges.",
"Film is made up of tons of tiny, light-sensitive particles. Different types of film have very differently sized particles. The smaller they are, the more detail they can capture (but also, the less sensitive the film is).",
"Films with very fine grain can resolve quite a lot of detail, but the best and fanciest digital cameras beat them... ",
". That's because film comes in tons of sizes. The most common type of film is probably 135 format film (commonly called 35mm), which is the same size as \"full frame\" digital sensors are: 24x36mm.",
"Saying it's like 4K in quality is a bit silly, since 4K is a video resolution and 35mm film is capturing still images. They're also different aspect ratios; 4K is 16:9, while film is a somewhat more square-looking 3:2. That means that with the same width, film is capturing more resolution on the top and bottom. It's also a bit of a hard question, since you could scan it down to the molecule - but film isn't recording ",
" down to that level.",
"To get an actual number from 35mm film... Again, depends on the film, but nobody quite seems to agree. Some say it's as low as 8 megapixels, and I've seen folks claim 40 megapixels. I doubt it's that high, although who knows what Kodak was making for the SR-71s in the cold war. Most folks seem to agree it's ",
" higher than 4K, and at 3:2 aspect ratio, 4K is about 11 megapixels. To notice a difference, you'd need at least a few more megapixels. I'd think 14-20 megapixels is probably a fair ballpark for the best films with the best conditions. Under anything less than ideal settings or the finest-grained films, that number falls quickly. In practice, it's probably less than that. I think 12 is a good ballpark for real-world films with fine grain, even if the theoretical max is somewhat-to-substantially higher.",
"All this goes out the window when you ask about ",
" size film. The above was for film that's 24x36mm, or very roughly 1x1.5 inches. You can get film that's 8x10 inches, which is more than 59 times the area of the above. Rounding the above way down to 12 megapixels, we're now talking about a single film exposure pushing 719 megapixels of resolution.",
"Put very simply, large format film is the king of resolution.",
"Theoretical maximum in resolution? Well, what's the theoretical maximum size film you could use? Multiply that by roughly 1.5 gigapixels per square foot."
] |
[
"The light sensitive particles in film are known as grain, and they have a specific physical size. ",
"There is generally a relationship between the size of the grain particles and the sensitivity of the film; film with bigger grain is more sensitive but has less resolution. ",
"Very roughly, 35mm film is around 5K in video terms, so something around 5600 x 3600"
] |
[
"The light sensitive particles in film are known as grain",
"Note: the size of the clumpy spots visible in film (grain) is ",
"significantly larger than the actual light-sensitive particles",
". Because the light sensitive particles are randomly distributed, and the human visual system tries to extract meaning from noise, we perceive it more like large grains than a bunch of overlapping irregular tiny spots. In silver halide there are tens of actual photosensitive crystals per grain.",
"There is generally a relationship between the size of the grain particles and the sensitivity of the film",
"When a silver halide crystal is hit by a bunch of photons, it only causes a few molecules to react and turn into silver metal. The development process causes the metal spot to grow and convert the rest of the crystal into dark silver.",
"If you take a very fast picture, a lot of crystals won't be hit by enough photons to have any metal spots. If you make the crystals larger, the spots that ",
" hit are able to convert a larger amount of silver during development, making the image more exposed."
] |
[
"Was my physics teacher right about soda gas behavior?"
] |
[
false
] |
[deleted]
|
[
"Yep. What matters is the volume of air relative to the volume of liquid.",
"The way a coke \"goes flat\" is this: Carbon dioxide is a ",
" gas - it dissolves in liquid - and there is dissolved carbon dioxide gas in the soda. That's what makes it fizzy. Molecules of a soluble gas, when dissolved in a liquid, are still constantly leaving the liquid and going back into the gas phase(this happens pretty slowly. The molecules of co2 that are touching the surface of the liquid sometimes \"break free\" of the liquid and go into the air). ",
"This is constantly happening, and it lessens and lessens the amount of co2 in the liquid. However, at the same time, the molecules of co2 that are in the gas phase in the air are also constantly going back into the liquid. Eventually the leaving and entering of the co2 reaches ",
" with the air portion of the container. In other words, when it fills the air with enough gas(in this case, carbon dioxide gas), that the speed in which co2 molecules are leaving the liquid equals the speed in which co2 molecules are entering the liquid). Once you reach equilibrium, the coke does not get any flatter. Think of an NFL game. There are always 22 players on the field and 84 players on the sideline. Players come off the field, but other players always go on to replace them. \"22 players\" is the ",
" of an NFL game. In gas, the equilibrium is measured in pressure, not players. Each gas has its own equilibrium vapor pressure. (Sorry. I really wanted to try an analogy out.)",
"Ergo, lessen the volume of space that the gas has to fill up to get to this point, and you lessen the amount of co2 that ends up leaving the liquid. So, press in the sides to lessen the volume. If you squeeze it all the way until the coke is all the way to the top, and put the cap on, no co2 will leave the liquid. This is obvious, as there is no where for the co2 to go. ",
" Sorry, this is wrong, as a couple of people pointed out, as the coke bottle isn't rigid. The gas can leave and \"push\" against the walls of the container, bending it back.",
"This means that, no matter how new the soda is and no matter how fast and completely you close it, if you drink 99% of a 2 Liter of Coke and put it back in the fridge, it will go basically completely flat. The .02 liters left of coke do not contain nearly enough co2 to fill up all of that empty space. Unless you press in the sides.",
"Out of curiosity, why didn't you believe your teacher?"
] |
[
"Ergo, lessen the volume of space that the gas has to fill up to get to this point, and you lessen the amount of co2 that ends up leaving the liquid. So, press in the sides to lessen the volume. If you squeeze it all the way until the coke is all the way to the top, and put the cap on, no co2 will leave the liquid. ",
"But the 2-litter bottle squeezed in half is not a fully rigid structure. As gas escapes, would having the bottle squeezed in half allow more room for the gas to expand (via the expanding bottle) outwards?"
] |
[
"I've been dying to ask a similar question, especially because (if you've ever tried this), the soda will often \"re-inflate\" the 2-liter bottle which I assume will mean that there are ",
" carbonation losses than if that space had been filled with some room air to begin with.",
"I don't have an answer for you, but I hope whoever answers your question addresses the reinflation issue as well... it seems to happen to me more often than not."
] |
[
"How has light had time to reach us from distant stellar phenomena?"
] |
[
false
] |
More precisely what I mean is, if our universe is only 13-14 billion years old, how has light from objects that are 40 billion light years away reached us. I understand that expansion got them so far out but I don't understand how the light has reached us in a fraction of the time it should take: it should take 40 billion years but the light only has had 13 billion.
|
[
"More precisely what I mean is, if our universe is only 13-14 billion years old, how has light from objects that are 40 billion light years away reached us.",
"The objects were much, much closer when they emitted the light. Over time, the distance between us and the light and the distance between us and the object expanded. As a result, the light took 13 billion light-years to reach us, and the object got to be 40+ billion light-years away."
] |
[
"Roughly, you look at the rate at which distant objects are receding, note how that recession speed depends on distance, and then calculate how far into the past you would have to go for all of those distant objects to be located here. To do this properly, you use the mathematical machinery of the general theory of relativity, with certain parameters chosen to fit observational data. Then you modify that result to account for new data from things like the Planck and WMAP missions, for example."
] |
[
"Hold on, if the star was 13 billion light years away when it produced the light",
"I didn't say it was 13 billion light-years away when it produced the light; I said it was much, much closer than it is now. In fact, making some reasonable assumptions and using the current best fit data, if we're currently receiving 13 billion year old light from some source then that source was approximately 3.5 billion light-years away when the light was emitted.",
"and it is now 40 billion light years away from us",
"Actually, I was being very rough with those numbers. Using our above source, from which we are receiving 13 billion year-old light, the distance to the source now is about 29 billion light-years away.",
"which means it exceeds the speed of light. How is that possible?",
"It's possible because there are no in-principle constraints on the rate at which cosmological expansion can increase the distance between two objects. See my comment ",
"here",
" for details."
] |
[
"Does cold weather lower your immune system's capability to defend against disease?"
] |
[
false
] |
I know that colds are not caused by a drop in temperature, but someone once told me that one reason colds are more common in the winter is that your immune system weakens from the cold, and therefore you are more likely to get a disease.
|
[
"Unless you become pathologically cold (hypothermia), the cold does not affect your immune system. There are many reasons as to why we seem to become sick more often when it's cold. We tend to confine ourselves to smaller, enclosed spaces, surrounding ourselves with people who are potential carriers of disease. The winter months are often stressful, which can lower immunity. Sometimes we just pay more attention to symptoms in the winter and something that we may pass off as a runny nose or a cough in the summer becomes \"the flu\" in the winter.",
"tl:dr Cold by itself does not affect your immune system, but there are many reasons why we appear to get sick more often when it's cold."
] |
[
"Does humidity matter as well as heat? I've heard that cold/flu viruses survive longer in cooler, drier environments."
] |
[
"Not sure about humidity, but temperature does matter. Rhinovirus (the virus that causes about half of all colds) proliferates at about 90 degrees F, not your body's internal temperature of 98.6 degrees. This is why it attacks the upper respiratory tract (nose, mouth, throat), which is much cooler than the rest of your body."
] |
[
"How do I calculate the \"heat transfer\" function for a tank of gas?"
] |
[
false
] |
I have some sensors installed on a carbonation system that's installed in a remote location, effectively outside. Specifically, we'd like to be able to estimate the amount of gas remaining and track usage in the tank. The tank in question is what I would call a 280 of CO2: the tank holds about 280 cubic feet at atmospheric pressure, but is a heavy steel tank about 300mm in diameter and about 1.5m tall. You can estimate tank fill by measuring the tank pressure-- at about 1000psi, the tank is full. At 0psi, the tank is empty. All that said, we're seeing dramatic changes in tank pressure based on the air temperature. These changes are completely masking the gas usage. We can still determine when the tank needs to be replaced, but I'd really like to be able to estimate gas usage on a daily or weekly basis. -- top is pressure in psi, bottom is temperature in C. The temperature sensor is near to the tank. Visually, you can see that the tank pressure generally follows the temperature, but it lags a bit due to the thermal mass of the tank. The gas isn't getting pulled out fast enough for the evaporation/decompression cooling to really affect stuff. Given all that: is there a way to model or estimate the "heat transfer function" of the tank so we can remove the temperature signal from the pressure? Raw data is here if you want to play:
|
[
"ChemE here. In those conditions the CO2 is in a mix of liquid and gas, the vapour pressure of the liquid depends on the temperature. Therefore, you can't really use the pressure to know the %fill of the tank since as long as the tank contains liquid CO2 the pressure depends only on temperature, and when the tank does not have liquid CO2 anymore it is close to being empty. A better approach would be to put a flow totalizer at the outlet of the tank. Or, if the tank is small enough, mount it on load cells.",
"CO2 P-H diagram",
"In the two phase region, the isotherm lines are flat, which means that the pressure will not depend on the %fill of liquid CO2 in the tank, but on temperature only. The critical point of CO2 is around 1000 psig, the pressure of your tank varies close to this value, therefore it is certain that at some point you have liquid CO2 in the tank, which makes using the ideal gas law incorrect."
] |
[
"A CO2 'gas' cylinder contains both liquid and gas phases. The liquid occupies the bottom of the internal volume and it slowly decreases as the gas is removed from the top. This happens in order to maintain a constant vapor pressure when the two phases are in equilibrium. Once there is no longer enough moles in the tank to maintain a condensed phase, the tank becomes just a gas phase and the pressure starts to decrease until its fully discharged. So the tank pressure is not a reliable indicator of the remaining mass content until its almost empty. External temperature changes will influence the pressure because the ",
"saturated vapor pressure",
" of the liquid is a strong function of temperature. This is not a 'heat transfer function' per se, its just vapor pressure, but it does require heat to change vapor to gas, hence there will usually be a lag between the external temperature influence and the internal pressure change. You can ignore these fluctuations for the most part by installing a mass flow meter on the output and integrate that flow rate to get the total mass of CO2 discharged."
] |
[
"But what you're saying is that I'm going to see relatively flat pressure (if I compensate for temperature), and then a rapid drop off once the liquid is gone?",
"Yep. You don't need statistical analysis to compensate for temperature. The pressure will be at the saturation pressure for CO2. ",
"https://www.ohio.edu/mechanical/thermo/property_tables/CO2/CO2_PresSat2.html",
"Once the pressure is below the saturation pressure at the current temperature, you know you have to fill the tank."
] |
[
"How can you possibly see an object freeze in time as the object crosses the event horizon of a black hole?"
] |
[
false
] |
[deleted]
|
[
"Imagine you're sending a probe into a black hole. And its a super super simple probe to test for just this idea. It's a very bright lightbulb on a blinking circuit. It blinks 100 Hz, eg. As it falls closer and closer to the black hole, you find that the rate of blinking slows to 1 Hz, then to .01 Hz and so forth. And as the rate slows, the light gets redder and redder. Eventually you get one blink, deep red, maybe radio wavelength. Then the next one is billions of years later, even lower in energy. Then some insanely longer time after that, and barely energy at all. Each successive blink takes a longer amount of time and has less energy. In the limit as time goes to infinity, eventually the next blink both never comes and has 0 energy. (ignoring black hole evaporation)"
] |
[
"my understanding was that, for an outside observer, objects falling into a black hole never crossed the event horizon, like an asymptote (I'm proud to have remembered this word) "
] |
[
"Oh. I don't recall that exactly, but I think the Schwarzschild metric dt",
" term seems to imply it goes like 1-1/r where r is the distance to the center of the mass. So I'd say it's more like exponential, where there's a divergence at the event horizon where the dilation goes ",
" infinity."
] |
[
"If a person gains weight gradually, will their leg muscles (quadriceps, hamstrings, calves etc) grow proportionally to support the added weight?"
] |
[
false
] |
I expect that they will grow as the increasing weight simulates a slim person doing leg workouts with gradually increasing weights.
|
[
"They would have to, otherwise you wouldn't be able to walk. On the other hand, it depends on what kind of weight you are gaining. Obviously gaining muscle mass will cause your muscles to grow. On the other hand, gaining a lot of weight in the form of fat has other consequences. The fat gets deposited all over the place, including within the muscle, and certainly within the walls of your blood vessels, limiting blood flow. ",
"Your muscles may get stronger to carry the weight, but the restricted blood flow limits the ability of the muscle to perform for long periods of time, because it doesn't get enough oxygen for oxidative phosphorylation. While overweight people may have an increased amount of glycogen providing the muscle with a larger \"fuel tank\" if you will, the muscle still will quickly be forced to switch to anaerobic metabolism. This is less efficient, and causes lactic acid to build up (which gives you cramps). Your heart beats faster to deliver more blood to the tissue, but it isn't getting there effectively because of the fat clogging up the blood vessels. You start to hyperventilate (technically speaking this is a misnomer, it would likely be hyperpnea in this case) to compensate for the increased oxygen demand and the increased acid load created by lactic acid. ",
"The consequence of this is that you walk less, and of course, without using the muscle, it gets weaker again, and you may end up with a weaker muscle as well as body fat that you cannot carry. ",
". ",
"See: ",
"In ",
"this paper",
", the results conclude that obese women are stronger than their lean counterparts, but only in terms of absolute strength. When you control for body weight, every muscle is weaker on a pound for pound basis in the obese women, with the exception of trunk flexors, which were stronger. Presumably, this might be because many obese women carry the weight in the abdomen and chest. ",
"Edit: tl;dr: Yes, gaining weight makes your legs stronger. But there is a diminishing return on this, and the growth is not linearly proportional. This does more harm than good. "
] |
[
"If say you're a semi fit person wise average weight. Maybe 6' tall and 190lbs and you gain 110lbs to be 300 lbs. Stay at that weight for maybe a year. Then lose all of the fat weight you gained. Would you be stronger than before gaining all the weight"
] |
[
"Still no. The same hormones that are active when you burn fat also promote the breakdown of muscle. This is why people who do cross fit aren't usually as \"ripped\" as people who focus solely on strength training, although every body is different. From a medical perspective, doing something like this intentionally is not good for your health."
] |
[
"A chicken egg is 40% calcium. How do chickens source enough calcium to make 1-2 eggs per day?"
] |
[
false
] |
edit- There are differing answers down below, so be careful what info you walk away with. One user down there in tangle pointed out that, for whatever reason, there is massive amounts of misinformation floating around about chickens. Who knew?
|
[
"Chickens are omnivores, but free-range chickens eat a great many insects, and insect exoskeletons are similarly rich in calcium. They'll also eat just about anything else, including small mice, voles, moles, lizards, etc., bones and all.",
"In a commercial setting, they are supplemented with oyster shells, or whatever source is cheap. Home chicken keepers sometimes feed old eggshells back to their chickens.",
"Chickens fed more calcium will lay eggs with thicker shells, and they can accept a fairly wide range, but a deficit will yield fragile eggs."
] |
[
"Home chicken keepers sometimes feed old eggshells back to their chickens.",
"Yes, but you have to be careful to mash up the eggshells small enough so that the chickens don't recognize them as eggshells, or else they'll start to eat their own eggs after they lay them."
] |
[
"Chickens will also eat their own eggs if the chicken is deficient in calcium."
] |
[
"Even though Jurrasic Park is fictional, is the science possible to make extinct animals alive once again using extremely old DNA?"
] |
[
false
] |
How would it work? Does DNA go bad? What would be the errors in creating extinct animals?
|
[
"The half-life of DNA is such that you'd never get a decent enough sample of a dinosaur to clone it. A mammoth though? Sure.",
"Assuming we did, by sheer dumb luck, somehow find a dinosaur so well-preserved that we could somehow extract a complete enough genome to use to clone the animal though, a new set of problems would arise. Firstly, you need some kind of similar creature to bear the organism as a surrogate mother. With a mammoth, an elephant should do just fine, but a dinosaur? There aren't any reptiles large enough to lay a T-rex egg. Even if you did somehow grow the dinosaur in-vitro in a prosthetic egg or something, you'd still only have a genetically similar (not identical since some damage is inevitable which must be repaired with, for example, frog DNA) creature, not an exact replica. For example, you'd have no way to teach it how to be a T-rex, since we have no idea how T-rex behaved and no similar animals to be a surrogate mother. "
] |
[
"SMURG is right, I'd just like to drop an expansion onto his comment.",
"Cloning is hard. To get a clone to survive takes a lot of work, a lot of genetics, and a lot of luck.",
"Take a look at the Pyrenean ibex, the first animal to become extinct and then ",
". An Pyrenean ibex is an ungulate (hooved animal) that was native to the Iberian peninsula, meaning Spain and Portugal. In the late 90s to early 2000s, the species went extinct. Fortunately, scientists took cell samples from one of the last remaining individuals before it's accidental death.",
"In this case, the surrogate used for the process was a species of goat. Very closely related to the ibex and of similar size and build, a goat was deemed a good match. So they used the DNA to make and fertilize eggs, placing roughly 50 of them into different surrogate mothers.",
"In 2009, one was successfully born from the surrogate goat. Thus creating the first un-extinct animal in history. So why don't we see Pyrenean ibex bounding through the news, history books, and mountains? It died a few minutes later, thus becoming the first species to become extinct twice.",
"So they had DNA about ten years old, with a species they knew and had experience working with, and the process still ultimately failed. Imagine that with DNA a few hundred years old, now a few thousand. Now add in a species you've never actually seen in real life who's DNA might or might not have degraded quite a lot.",
"Basically, cloning is very hard. Hypothetically possible, but absurdly unlikely."
] |
[
"Which doesn't even touch on whatever gut fauna the creature had which would be completely impossible to reproduce."
] |
[
"What are the effects of vaccine mandates on vaccination rates?"
] |
[
false
] |
In King County, WA USA there appears to be no effect as vaccination rates are relatively unchanged since the August 9th mandate announcement by the Governor and County Executive. August 9th Announcement: Vaccinations in King County by date:
|
[
"They were talking about this on CBC radio here in Canada the other week. They said basically, people who aren't vaxxed fall into a couple of groups. Those that intend to get it at some point but are really in no rush, people who rather indifferent to getting it or not, people who are hesitant (sometimes with language barriers), people who haven't been able to because of working hours/logistics, anti-vaxxers, and those who cannot get it. They estimated the last two groups are very small percentage wise.",
"They see mandates as being effective at moving the needle on those first 2-3 groups as has been seen in some other jurisdictions (I think they mentioned Quebec and somewhere else)."
] |
[
"Small percentage wise, yet inordinate amount of attention given to these people by the media"
] |
[
"If you are talking about COVID specifically - This may affect some sub populations more than others.",
"It is also hard to dissociate the FDA approval , and fear of variants (and other factors) from mandates as many of them came at near the same time. ",
"It is also really too soon to evaluate - many of the mandates are literally weeks old.",
"Washington post says vaccine rates are rising ",
"https://www.washingtonpost.com/nation/2021/08/24/covid-delta-variant-live-updates/",
" but typically gives no numbers or real source.",
"However , historically (",
"https://www.sciencedirect.com/science/article/pii/S0264410X20312342",
") many countries /regions have had vaccine mandates for things other than COVID in place. This can include special mandates for particular classes of people (like flu vaccines may be required for hospital workers but not the general population). So if your question is more general about any vaccines there is reasonable data that vaccine mandates have historically improved vaccination rates. If it is for COVID only it is really probably too soon to tell.",
"There were for example, mandatory vaccination requirements at many borders, including Ellis island. Small pox vaccinations were required in some regions and this paper indicates a 20 fold difference in vaccine rates based on mandates. ",
"https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(21)00267-1/fulltext",
".",
"There was not, alas , such rabid and ignorant antivax movements as you see now in some places. People were really pretty glad to not die of polio and not to have their kids throats close up from diptheria. It may well be that there are pockets of unrelenting people who will be moved by neither overwhelming data, logic, human empathy or mandates."
] |
[
"Why is random dispersal of matter more energetically favorable than if matter is clumped in one spot (question of entropy)?"
] |
[
false
] |
Disclaimer: I'm a biology major, not a physicist. I am going back over osmosis/passive diffusion and Gibb's free energy, and I don't understand why the same amount of matter (therefore, same energy) is more favorable in one configuration (random/dispersed) versus another (clumped or all on one side).
|
[
"They have the same energy (barring some sort of interaction potential) but there are many more ways for particles to be randomly dispersed than clumped together, so if the particles are found in any equally-likely configuration, there is a high chance that that configuration is random-looking."
] |
[
"Find this a very good short written explanation. The answer is similar to saying that: How is it more favorable for a 1000 dice to have every number of eyes come up a roughly equal amount of time. "
] |
[
"So instead of thinking of it as an energetically more favorable state, is it more correct to say that it's more probable for particles to arrange randomly (because there's more ways for them to be randomly arranged) than clumped in one spot (only so many ways in a finite space that they could arrange in a clumped fashion)?"
] |
[
"How do astronomers determine how far newly or past discovered stars are? Like how do they know one twinkling star is 8ly and another is 150ly?"
] |
[
false
] | null |
[
"Distance calibrators are a giant topic in astronomy. I'll give you the most simple example that requires only geometry, it's called parallax. You can make a triangle with three points: Sun, Earth and star. If the star is not so far away (or you have a really good/big telescope) you take a picture of the star in March and one in September, for example. You then measure the tiny angle on the sky that is the difference between the apparent positions of the star in six months. You then have a completely solvable triangle because we know the distance Sun-Earth."
] |
[
"Wikipedia has a nice description of the different techniques used for different distances.",
"https://en.wikipedia.org/wiki/Cosmic_distance_ladder",
"Out to about 100 light years, an Earth-based telescope can estimate the distance based on how much the stars seem to move when seen from one side of the sun vs. the other. Using a satellite like Hipparcos extended that to 1,000 LY and the Gaia mission will extend it to 20,000 LY or more.",
"Beyond that, other, indirect methods get used. For example, the brightness of a Cepheid variable star is related to its period, so if you see one in another galaxy, you can measure the period and then compute the brightness (and, hence, the distance)."
] |
[
"From the angle that you deduce you put one over said angle and you get a big number in parsecs (the reason this works is the angle is usually a decimal) and the you have the distance in parsecs. you can times that number by 3.26 for light years or 1.92*10",
" for miles!"
] |
[
"Do other animals commit suicide, and does it seem like it's ever due to something similar to depression?"
] |
[
false
] | null |
[
"There are numerous instances of dolphins committing suicide. ",
"The main figure in the movie \"The Cove\" detailed the suicide of dolphins under his watch in captivity. Stranded and stressed dolphins in the wild have also said to have committed suicide. ",
"At work so not many links, but a 1-minute google search will get you there. "
] |
[
"In China there have been reports of bears who commit suicide or attempt to in order to escape the torture of bile collection. Here's a story of a mother bear who killed her cub to save it from a life of pain and torture:",
"http://ingenira.hubpages.com/hub/A-Teary-Mother-Bear-Killed-Her-Baby-and-Committed-Suicide-A-Heart-Breaking-True-Story",
"Edit: autoincorrect"
] |
[
"That just breaks my heart."
] |
[
"Is there anything (Natural substance, man-made medicine, specific injury, etc.) which can completely negate all pain?"
] |
[
false
] |
I tried googling this, rephrasing it multiple times, but it turned up nothing. Does anyone here at know the answer?
|
[
"You've clearly never been ",
"anesthetized",
"."
] |
[
"Any spinal cord injury that affects your ",
"spinothalamic tract",
" is going to completely sever the neurons that are sending pain up to your brain. Brainstem lesions along that tract or the ",
"trigeminothalamic tract",
", which is the same thing but for pain from your face, will cut out pain.",
"Enkephalins",
" are your bodies main way of downregulating pain. They prevent the transmission of pain afferent messages.",
"Your somatosensory cortex",
" is the part of your brain that deals with all your incoming sensations. Area 3b within the cortex is the one most correlated with pain.",
"EDIT: Also, local anesthesia will absolutely get rid of all pain sensation, it just needs to be a high enough dose. There's no reason to push the healthy limit for anesthesia when you don't need to. That's why you felt some slight dull pain."
] |
[
"There are some rare disorders known as ",
"congenital insensitivity to pain",
". People with these do not experience physical pain which typically causes them severe physical injuries from childhood: e.g. burns, lip-biting, walking on a broken limb etc. "
] |
[
"Can you tell me what dangerous animals are in Jamaica?"
] |
[
false
] |
I know, for example, Hawaii has giant centipedes, which are poisonous. I'm curious which animals and insects are in Jamaica which are dangerous/venomous. Water creatures count too.
|
[
"Picking the low hanging fruit here, but ",
" are extremely dangerous. Seriously. Most of them are fine and wont bother you if left unprovoked, but a small percentage are very aggressive."
] |
[
"Mosquitos. Sharks. Jamaican Boa. "
] |
[
"Jamaican boas only seem to get to 6ft; that really isn't big enough to fuck your shit up. It'll be able to give you a nasty nip, sure (what animal can't?), but for a constrictor to actively endanger the life of a grown person you're looking at it being 9ft and upwards."
] |
[
"What do babies think about?"
] |
[
false
] | null |
[
"is that you speaking as a layman or you speaking with some expertise/knowledge?"
] |
[
"is that you speaking as a layman or you speaking with some expertise/knowledge?"
] |
[
"I'm assuming he was speaking as a layman? That's disappointing I actually wonder this very often."
] |
[
"Can plants get cancer from the sun like humans can get skin cancer?"
] |
[
false
] | null |
[
"Skin cancer is cause by damage to to our DNA by UV light, usually the UV light creates cross-links between the base pairs. Plants have a really cool enzyme called photolyase, which is light powered enzyme that breaks these cross-links and repairs the DNA. "
] |
[
"For that reason, cancers tend to occur on the trunk. Since that is less exposed to sunlight due to the thick bark layer, it is possible that rates of sun-induced cancer in plants are pretty low, even if it is theoretically possible.",
"This is mostly guesswork though, since there's no empirical backing here."
] |
[
"For that reason, cancers tend to occur on the trunk. Since that is less exposed to sunlight due to the thick bark layer, it is possible that rates of sun-induced cancer in plants are pretty low, even if it is theoretically possible.",
"This is mostly guesswork though, since there's no empirical backing here."
] |
[
"Does infection produce different kinds of antibodies than vaccination?"
] |
[
false
] |
I know that for example Hepatitis B vaccination produces different antibodies than infection. This is because the vaccine does not contain certain structural components of the virus. Does something similar happen with SARS-CoV-2 as far as we know?
|
[
"For the current vaccines for Covid-19 in the US (Pfizer, Moderna, JJ) they’re expressing only the spike protein. There are plenty of other protein epitopes you could generate antibodies to via an actual Covid-19 infection.",
"In fact, this rapid antigen test uses both spike and nucleocapsid protein to look for antibodies in the blood- ",
"https://www.fda.gov/media/139792/download",
"This doesn’t mean the vaccines are less protective than a natural infection would be. ",
"Here’s a paper talking about why the spike protein was chosen- ",
"https://translational-medicine.biomedcentral.com/articles/10.1186/s12967-020-02392-y"
] |
[
"Your body is constantly refining the antibody response, keeping the B cells that make the highest affinity ones."
] |
[
"Upon infection, does the body just allow any antibody to be generated and keeps around all of them? Or is there some sort of logic in there or possibly selection"
] |
[
"If we flip flop between glacial periods and non- glacial periods (ice ages) why then is global warming considered so dire? Wouldn't it mitigate the severity of the next ice age?"
] |
[
false
] |
I have been reading a lot about ice ages recently and the different hypothesis to what causes them, the massive ice sheets covering North America (2miles thick) and how devastating an Ice age would be to human population and civilisation. Also during history when the planet warmed humans done really well. I know C02 is a catalyst to warming but is not the only factor in warming, going off history is seems like a relatively small part in a very complex equation. I know about feed back loops and climate models predicting hotter planet but the earth has been a lot hotter before will more carbon in the atmosphere yet we the planet still went into ice ages. So are Humans this time solely responsible for this ice age ending? Or is the planet on a natural heating cycle anyway and humans are just making it worse?
|
[
"Portions of my answers below are borrowed from an answer I wrote to another, semi-related question.",
"Are humans this time solely responsible for this ice age ending?",
"Technically we are still in an ",
"ice age",
", and what we're talking about is the transition from glacial to interglacial periods within an ice age (for the lay person, this appears to be mostly semantics, but it's kind of an important distinction when thinking about the range of behavior in climate over geologic time). With that out of the way, let's consider what happens during normal glacial-interglacial cycles. ",
"This page",
" from NOAA gives a nice summary. Ultimately, the primary driver for glacial-interglacial cycles are changes in Earth's orbit, which change the amount of solar radiation reaching the Earth's atmosphere/surface, i.e. ",
"Milankovitch cycles",
", which in turn cause cyclic changes in average global temperature. There are some additional important processes that act as either negative or positive feedbacks during these natural cycles, e.g. a small amount of warming driven by a gradual change in orbital parameters / incoming solar radiation drives a release of CO2 from the ocean, which increases the greenhouse effect, which drives more rapid warming. CO2 and other greenhouse gases (along with lots of other feedbacks, e.g. ",
"dust",
") play important roles in modulating the temperature changes during glacial/interglacial periods and are especially important in controlling the transitions between glacial and interglacials, but the underlying primary driver are changes in solar radiation (",
"e.g. more discussion of this from Wikipedia",
"). With this in mind, we can say that the end of the ",
"last glacial period that occurred ~14,000 years ago",
" happened without human intervention and was driven by a combination of factors as discussed above, with primary one being the progressive change in Earth's orbit.",
"Is the planet on a natural heating cycle anyway and humans are just making it worse?",
"In the modern, anthropogenic climate change is being driven by our direct and rapid input of massive amounts of CO2 and other greenhouse gases that have been largely sequestered for 100s of millions of years (i.e. carbon stored in fossil fuels representing carbon pulled from the atmosphere by marine microorganisms, or terrestrial plants if we're talking about coal, and buried largely during the late Paleozoic or Mesozoic periods) into the atmosphere. This addition of greenhouse gases is essentially swamping out a lot of other natural processes and initiating other feedbacks (e.g. warming drives melting of permafrost which potentially drives release of more greenhouse gases sequestered in the permafrost driving more warming, etc). As to what would be happening in regards to the climate without human influence, it's been suggested that we'd expect another glacial period to occur in ",
"50,000 years",
" (non-paywalled link through ",
"ResearchGate",
"). They don't explicitly show temperature in their model results, instead tracking ice volume, but it shows a pretty steady low amount of ice for the next ~50,000 years. When the human CO2 contribution is added in, it's been suggested that the Earth will not experience ",
"another glacial period for 100,000 years",
", i.e. our modification of the climate either causes us to skip the next glacial or pushes it back another 50,000 years depending on your perspective. So, in summary we would still be in an interglacial regardless, but we are making things much warmer by adding additional CO2 (we'd be in an interglacial, but the expected CO2 concentration would be closer ~290 ppm, compared to the 400+ ppm it's sitting at today).",
"Finally, a few important points with regards to statements/ideas like \"CO2 has been higher before\" or \"temperatures have been higher before\" etc and thus the current trend is not problematic:",
"(1) The entire history of our civilization has occurred during an incredibly stable period of the climate compared to various episodes throughout the geologic past. The warming induced by our addition of millions of years worth of sequestered CO2 to our atmosphere (injected essentially instantaneously when considered on a geologic time scale) is driving various aspects of the climate (e.g. temperatures, precipitation, etc) toward increased variability. What the affect of that will be on our civilization (e.g. for things like our agricultural systems which are largely predicated on the idea of climate not changing) is uncertain. ",
"(2) Rates are important. Arguments fixated on the idea that our atmosphere has hosted comparable or higher concentrations of CO2 in the past or that the average global temperature has been as warm or warmer in the past largely ignore that outside of things like mass extinction events (e.g. ",
"the end Permian",
", which may have been precipitated by rapid, and massive injections of greenhouse gases into the atmosphere)) that in natural cycles, these concentrations / temperatures were reached over 100,000s to millions of years, not over a few centuries as they are now. When things change very rapidly, this means that basically very few organisms have the ability to adapt to the changes in temperature, precipitation, etc patterns (which in turn change vegetation ranges, etc). A crude analogy is acceleration and velocity. The argument that high values in the past are fine with no consideration of the rate of change getting us there is like arguing that humans can safely travel at several hundreds of miles per/hour (e.g. in a plane) so it's immaterial whether you reach that velocity over a few minutes via low acceleration or over a fraction of a second via extremely large accelerations."
] |
[
"Thank you greatly for the in depth and easy to understand response, you have definitely enlightened me and have put to bed my pessimism, on of how much humans are making an impact. I work in a dirty fossil fuel industry and my guilt has me researching if it is all really as bad as scientists say, I am convinced that we need to deal with this situation ASAP thanks again"
] |
[
"The fossil fuel industry has deliberately tried to muddy the waters, so it makes sense that people are confused. See: ",
"https://exxonknew.org/timeline/"
] |
[
"When spacecrafts need to change to a higher orbit, do they burn sideways or downwards?"
] |
[
false
] |
Both make sense in my head - burning sideways (rocket exhaust pointing away from where you're going) seems like it should work, by enlarging your orbit. But then I thought about how your velocity is lower when you're in a higher orbit. So if I burn sideways, would my orbital height increase while my speed decreases? Can you be super fast in a high orbit? And then I thought - what if you just burn down, not changing your sideways velocity? Your spaceship would climb, no? And since higher orbits are slower, you should be able to reach the desired orbit by burning downwards? Help, reddit, I am very confused.
|
[
"Well, the thing to keep in mind is that when you're orbiting you're not floating around the earth, you're hurtling around it at high speed. So, let's say you're orbiting towards the earth and point your thrusters downward. You'd gain a little vertical velocity, but in order to get into a higher, circular orbital path you'd have to burn again to cancel out your vertical velocity, or it would result in a more elliptical orbit. ",
"You're right, though. Increasing your speed also sends you into a higher orbit, and that's how most orbital transfers are done because they're more fuel efficient. ",
"So, there are a few different ways to get into another orbit, but obviously fuel efficiency is critical in spaceflight so that's a central concern. ",
"One great way to get an intuitive sense of how orbits work is play Kerbal Space Program. Seriously, I went to space camp and studied physics in undergrad and I understand orbits much better due to that silly video game. :)",
"See: ",
"http://en.wikipedia.org/wiki/Orbital_mechanics#Orbital_transfer"
] |
[
"Strictly speaking, the correct answer is \"yes and yes.\"",
"Either one will accelerate you to a higher orbit. However, \"buring sideways\" is the method used in a ",
"Hohmann Transfer Orbit",
", which is the most fuel-efficient way to enter a higher orbit. It works like this:",
"Assume you start in a circular orbit. Accelerating in the direction of your orbit (what you refer to as \"burning sideways) speeds up your orbital velocity. So now you're moving too fast for the orbit you're in, at least a circular one.",
"Because you're moving too fast for the orbit you're in, you end up no longer being in a ",
" orbit, and instead you end up in an elliptical orbit where the perigee of the orbit has you moving at the increased velocity at the old height of your orbit, and the apogee has you moving much slower. It's when your craft reaches that peak height that you accelerate a ",
", ",
" in the direction of your orbit, to speed the craft up so now it's lateral velocity corresponds to the velocity of a circular orbit, only now at the higher altitude. Poof, you've just reached a stable, circular, higher orbit.",
"All other accelerations besides \"burning sideways\" can affect a craft's orbit, but they're rarely used because they're inefficient compared to burning sideways. ",
"Edit: There's some claim on Wikipedia that a \"bi-elliptic transfer\" can somehow be more efficient than a Hohmann in certain corner cases. Dunno how that'd work, but I suppose it's not IMPOSSIBLE.",
"Nope, that ain't it. Still dunno how it's more efficient.",
"It also should be noted a \"Bi-Elliptic Transfer\" also \"burns sideways\" as you mention, it just does so three times instead of two."
] |
[
"The bi-elliptic transfer is more efficient because of the ",
"Oberth effect",
". Burning at higher velocities is more efficient than lower velocities, so if you're making a ",
" change in orbit, a bi-elliptic transfer biases the burns to be done at higher velocities: a big burn at high velocity, a smaller one at low velocity, and another larger one at high velocity again."
] |
[
"Askscientists- show us your favorite figure!"
] |
[
false
] |
Science is all about communicating and a picture is worth a thousand words- at least. Share with us your favorite figure or graph from a scientific paper. Ideally it should be self-explanatory, but it might be helpful if you informed us why it is so important or interesting to you or your field. Please link to the actual image so everyone can enjoy it!
|
[
"This is almost as hard to answer as \"what's your favourite science fact\" but right now I'll go with the ",
"decay of the Hulse-Taylor binary system",
" because it's so cool.",
"What you're seeing is the orbit of two pulsars slowly decaying because they're emitting gravitational radiation."
] |
[
"ive always liked ",
"this",
" cardiac physiology graph.",
"It contains more information about how your heart works and the actual mechanics and pressures than dozens of pages. It makes it easy to understand murmurs, reflux, back flows and abnormal pressure changes, and allows you to predict the signs and symptoms you could expect with such changes.",
"the only way to make it more perfect would be to add flow velocities."
] |
[
"Ah I love that one too- I once saw a couple of lectures by a cardiac tissue engineering guy who had an animated version of that figure, scanning from left to right. It made everything so much more clear than anything else he had said in the 20 minutes previously. "
] |
[
"Why is it critical to have extremely accurate time, for Electricity distribution networks to function?"
] |
[
false
] |
I over heard a couple of Engineers at an Electrical power plant discuss the importance of having extremely accurate time through atomic clocks (something like 1 second of error over 3,000 years is minimum acceptable). Hoping some one could explain, exactly why such time accuracy is required, what does it enable?
|
[
"Well, strictly speaking your premise is false: large-scale electrical grids have been around long before atomic clocks. So the pedantic answer is \"it's not necessary\".",
"When multiple generators are connected to the same power line, their phases have to be carefully matched. In a typical AC generator, the oscillating voltage/current is actually determined by the physical rotation speed of the rotor. If the output voltages of two generators aren't matched, or if they peak at different times, the resulting voltage imbalance causes huge currents to flow, which in turn exerts a force on the generator. So when bringing a generator online, you can't just flip a switch; you have to ",
"match the frequencies, voltages and phases",
", so that when you close the circuit, the phase difference is small. You don't need a clock for this, though; you can just compare the two voltage curves to each other, independent of any time reference.",
"However, there's another reason for using accurate clocks that has nothing to do with the functioning of the power grid itself. By keeping the frequency very stable, it can be used as a reference point for other equipment that needs to keep accurate time. For example, cheap alarm clocks can keep time very accurately if they're plugged in, simply by counting the cycles. The frequency can vary slightly from 60Hz over the short term -- for instance, if the power demand increases faster than the generators can keep up, the frequency drops slightly. If that happens, the power plant operators can make up the difference later, so that the total number of cycles per day or per year is still accurate. In this case, the \"1 second of error over 3,000 years\" is simply the target accuracy that they've decided they want to maintain."
] |
[
"You can watch the US grid frequency changes as the loads are shared.",
"http://fnetpublic.utk.edu/frequencymap.html"
] |
[
"/u/teraflop",
" gets the facts right - AC power grids do not need atomic clocks to operate. Grids involving multiple generators (power plants) must only be synchronous, meaning that they operate at the same AC frequency, nominally 60 Hz, or 60 cycles per second. Synchronization can be achieved using analog devices and measurements. For example, you can use [regular light bulbs](",
"https://www.youtube.com/watch?v=RGPCIypib5Q0",
" to determine sync. You can measure and accurately time 60Hz AC signals with any basic electronic test equipment, as this frequency is very 'slow' by electronics standards.",
"The modern grid does use ",
"atomic clock-based devices",
" to perform additional measurements to enhance the stability, reliability, and visibility of the grid. These devices are only now becoming widespread, and many electric utilities still aren't totally sure what they are useful for, or how to process and make sense of the huge volumes of data they produce (source: I work in the high-voltage power transmission industry). There are a lot of research papers each year claiming to find new uses for PMUs, but in practice they are not really necessary for basic grid operations."
] |
[
"How are air pockets formed?"
] |
[
false
] |
So, my sister asked me to explain this, but I found that I can't. How are air pockets created, by air pockets I mean the air that is trapped when say, a cave fills with water, but raised areas in the ceiling retain air. The example that brought it up is from the original Pirates of The Caribbean when Will and Capt. Jack use the canoe to sneak aboard and commandeer the ship. Any help in explaining this would be greatly appreciated.
|
[
"The canoe in PotC was presumably pulled down from the surface and the air doesn't escape because the canoe is fairly airtight, and because for the air to go down around the hull it would have to lift water (which requires energy) so it stays where it is. ",
"The canoe scene is completely impossible in real life because the air-filled canoe could be so much lighter than the surrounding water that it would be pushed upward by several tons of buoyant force that no human could overcome."
] |
[
"Ok, thanks for the explanation."
] |
[
"Also, an extremely generous calculation based on the size of the boat says there's only about 5 minutes worth of air in that thing, even if the two were at rest. There's no way they could breath for the time it takes them to walk that distance, even if they were exerting no effort."
] |
[
"Why does isometric transition only occur with gamma rays?"
] |
[
false
] |
Question about gamma decay. Is there any reason why when a radioactive isotope in an excited state emits gamma radiation over x-rays? I understand that gamma decay is the fastest way to get rid of the excess energy but is it possible that if an excited nucleus didn't have enough energy to emit gamma rays that it would emit x-rays
|
[
"Not if they had the same energy. The photon retains no memory of where it came from."
] |
[
"There are some circles in which \"gamma rays\" refer to higher-energy photons than \"x-rays\", but despite often being taught in high school, this is not actually the usual terminology.",
"In astrophysics we make a distinction. There are x-ray experiments and gamma-ray experiments based on how energetic the photons are."
] |
[
"if you had a gamma ray photon and an x-ray proton could you tell which is which, without knowing their origin? "
] |
[
"If beef is properly prepared, wouldn't that practically eliminate the risk of e coli causing foodbourne illness?"
] |
[
false
] |
This question mainly comes from the massive recall of beef products in Canada. If beef is cooked to an internal temperature of over 160 degrees Fahrenheit, wouldn't that kill off the bacteria? Is this meat too tainted to eat even after thorough cooking?
|
[
"I thought this was true. In, theory of the meat is cut properly then searing the outside alone is good enough because there is no opportunity for bacteria like ecoli to get inside. Ground meat is a problem because the outside and inside get mixed up...",
"Apparently (at least here in Canada) Costco has been stabbing their steaks with pins to tenderise them, effectively requiring the steak to be cooked thoroughly. So, always read the labels (and shame on them if it wasn't labelled properly...)! I would have never thought that this was done to my steak! :("
] |
[
"Its safe to eat many raw meats, provided you kill surface contaminants, or eat it right off a fresh kill. Beef especially, but even pork is processed in such a way that its misconception or paranoia that leads people to believe parasites are still a problem. Trichinosis was just about eliminated in the 60s and hasn't been reported in the US since. So if you get pork that's slightly under cooked and sort of pink, its going to be safe to eat.",
"However, Ground beef mixes the surface with the interior. Cook thoroughly. ",
"This article applies not just to beef, but most grazing animals we get our meat from."
] |
[
"Yes, it would kill off the bacteria. Though, there are certain products or chemicals of bacterial metabolism that can still make you sick, and those don't go away with heat."
] |
[
"How is the force on light particles conceptualized?"
] |
[
false
] |
If the characteristic equation for Force is , and photons have no mass, how is it that we can conceptualize a photon's interaction with other particles? Do we use the observed change in momentum of the massive particle and then deduce what kind of force was exerted by the photon retroactively? Or is there some formula that can characterize how much force a photon is able to exert?
|
[
"F = ma is a simplification/special case of a Newtonian principle that only applies to certain classical systems.",
"First, Newton's second law is actually that F = dp/dt, which is to say that the force applied to an object is equal to the rate at which its ",
" (represented by p) changes. If you have an object of constant mass, then dp/dt = ma, but, as I said, that's a special case.",
"Second, photons are fundamental particles; their interactions are governed by quantum dynamics. In quantum theory, the whole notion of force becomes rather ambiguous and one tends to just work with momentum and potentials directly. We can still define force analogously to Newton's equation, but it doesn't take on the same fundamental role."
] |
[
"I should also say that, at least in my experience, most people who do work in classical mechanics don't use Newton's formulation either. They tend to use ",
"Lagrangian",
" or, more often, ",
"Hamiltonian",
" formulations."
] |
[
"Ah, okay that answers my question pretty well. Thanks!"
] |
[
"Why does wind whistle when it blows through objects like doors, trees etc?"
] |
[
false
] | null |
[
"Wind howls when it’s broken up from passing through or around objects, such as trees. The gust of air will split up to move around the tree and then comes back together on the other side. Due to factors such as the surface of the tree and the air speed, one side of the wind is going to be stronger than the other when the currents rejoin. The mixing of the two currents causes vibrations in the air, which produce that ghostly howling noise that gives us the creeps."
] |
[
"This also explains why wind whistling and howling tends to be much more pronounced during the winter months. Without leaves to catch the wind, all those branches will have a lot more turbulent air rushing around and past them."
] |
[
"It's due to a concept known as ",
"vortex shedding",
". In short, it's a fluid dynamics effect that can happen within a range of Reynolds numbers when a viscous fluid flows around a disturbance. The sound you hear is related to the frequency of the vortices being shed. ",
" (partially true). You can see slower examples of vortex shedding where water flows around a rock or behind a slow boat."
] |
[
"Why are we discouraged from giving suspected shock victims water to drink? And why are they thirsty?"
] |
[
false
] |
Please be specific. I am studying for my Nursing registration exam (in Canada), and have come across this bit of advice annually in first aid recertification and often in reference to emergency nursing care. I want specific rationale. As in, microbio/biochemistry/cellular biology level explanation. Go deep, Reddit. I'll understand. Quick note: No, of course I don't need to know this level of knowledge for the registration exam... I just want some rationale for .
|
[
"Shock is a hypotensive/hypoperfusion state, depending on the exact cause of shock, they will need specific treatment. ",
"Being hypotensive the body is going to draw fluid into the vasculature from the third space, and the cells, to attempt to maintain BP, and then it's going to start shutting down peripheral vasculature to maintain central BP. ",
"The stomach is one of the first places that gets shut down, so giving him water is liable to just make him puke. This gives you aspiration to deal with, and now you're dumping his acid and making him alkotic. Yay for making it worse!",
"I don't really think you need deep micro levels to understand this, the above should be plenty adequate, but if it isn't, feel free to ask what you want clarity on."
] |
[
"1",
"\n",
"2",
"Any good first aid course nowadays should tell you not to give anything to anyone injured by mouth, it's just a terrible idea period."
] |
[
"The decreased blood flow to the stomach makes emesis more likely. Filling it while it's non-motile makes this risk increase.",
"If you dump their acids, you're likely to cause hypokalemia as well (remember your pathways here) and then some arrythmia's (do you know which?)"
] |
[
"What kind of damage would a collapsing space elevator do to earth?"
] |
[
false
] |
In a few anime a falling space elevator has a potential to destroy the planet but what kind of damage would it really do if the elevator was 60,000 miles high?
|
[
"A space elevator consists of three parts: the terminus up at geosynchronous orbit (or a little higher), the car that moves up and down, and the cable.",
"The terminus wouldn't fall. It's essentially just like a satellite that orbits freely. ",
"The car that moves up and down would most likely mostly disintegrate on entering the atmosphere, in much the same way that the Space Shuttle Columbia did. In terms of effect, you can probably compare it to the meteorite that landed in Russia a while back.",
"I think the largest risk is going to be from supersonic whiplash from the cable, which would be under tension. How that behaves depends on where it breaks."
] |
[
"To clarify the danger from the cable: it would be moving far more slowly than a meteorite, have a far higher surface area to volume ratio, and presumably not be very dense. We don't have materials strong enough to make a space elevator cable, but the question would be 'would most of the cable burn up before it even hit the ground' rather than 'would it destroy the earth'."
] |
[
"The usual material of choice for the cable when discussing space elevators is carbon nano tubes, and they have very high heat resistance. So a cable made of that material would likely make it to the ground."
] |
[
"If we ever build a space elevator, would I be able to climb into orbit without making escape velocity?"
] |
[
false
] |
This has been bugging me for a while. Pretend we built a space elevator. Pretend there is a ladder on the side in case of emergencies. Pretend I am in good shape and want to climb the ladder cause it'd be a hootenanny of a good time. I know the shuttle needed something like 26kmph to reach escape velocity to leave the earth and get into orbit. If I just slap on a pressure suit and commence to climbing, would I be able to get to the top of the ladder without having to increase my speed, or would I get yanked off due to centripetal force of the ladder flinging itself around the planet the same speed it's currently travelling in space? Or, would I end up dying somewhere on the ladder due to something that I have completely overlooked? I know the materials must be under a huge amount of stress, so is there a chance that would somehow get transferred to me and I'd go flinging off into the sunset like a live action Wile E. Coyote?
|
[
"For starters, you'd have to climb 22,000 miles to achieve orbital velocity (this is the altitude of geostationary earth orbit). Jump off any lower and you ",
" fall back to earth.",
"The earth is spinning and the space elevator with it. As you climb the ladder, you get further from the center of the earth so you travel further on each revolution. With each step higher you are gaining horizontal velocity despite only moving yourself vertically relative to the elevator."
] |
[
"The idea that you need escape velocity to enter orbit is a common misconception. Even without a space elevator, you can enter orbit (and in fact get arbitrarily far from Earth) at any speed you choose. Escape velocity is the speed necessary to avoid ever being totally stopped by the gravity of a body ",
" through space. If you have a rocket system capable of lifting you up from Earth's surface at a constant 1m/s you will eventually reach orbital altitude even though this is nowhere near escape velocity.",
"EDIT: as the chaps below have pointed out, orbital ",
" is germane - you would need a separate system to accelerate up to a speed that would keep you from falling back to Earth."
] |
[
"Orbital mechanics are counter-intuitive and fun to learn.\nIf you are into video games I suggest go grab:",
"https://kerbalspaceprogram.com/",
" a great fun, toy like \"space-sim\". Subreddit: ",
"/r/KerbalSpaceProgram",
"http://orbit.medphys.ucl.ac.uk/",
" \"orbiter\" a free and realistic space flight simulation if you want to go hardcore. Subreddit: ",
"/r/Orbiter/",
"Have fun."
] |
[
"What happens to a gravitational wave when it crosses a black hole ?"
] |
[
false
] | null |
[
"Gravity isn't transported by gravitational waves any more than static electrical charge is transported by light. The static forces are from the field itself, which exists both inside and outside the black hole. This is why a black hole can be electrically charged but no light escapes, and why a black hole impacts the rest of the universe via gravitation, but not via gravitational waves from below the event horizon.",
"Changes in the gravitational field are transported by gravitational waves. They cannot escape the event horizon. It doesn't matter what is happening below the event horizon, none of that can impact the rest of the universe. Its gone."
] |
[
"The same thing that happens to everything else. It falls into the central singularity.",
"Gravitational waves are impacted by gravity in the same way as all other waves. The difference being that gravitational waves are only impacted by gravity, and nothing else."
] |
[
"gravitional waves are basically ",
" in the Gravitational Field (or geometry of spacetime) . The gravitational field of a static black hole is static. It doesn't need any gravitational waves to \"be\". It just \"is\" what it is, based on an equation you can just punch the numbers of the situation into.",
"When we start moving objects around or changing their energy distribution, then this changes the gravitational field (or spacetime geometry) around them. These changes are local, but because of self-interaction, they cause ripples out into the rest of the universe, where they may be observed later and farther out by instruments similar to the ones at LIGO.",
"LIGO isn't trying to detect the gravitational field of these objects: it's trying to detect ",
" in them, manifesting as these self-interacting self-propagating ripples.",
"So, gravitational waves not being able to escape a black hole doesn't mean that we can't feel the gravity of these black holes, because gravity doesn't come from gravitational waves. Rather, it means that we can't ever detect any of these ripples from any internal \"rearrangement\" of things inside the black hole. If you move around stuff inside a black hole, that will still cause spacetime ripples, but those ripples will only go as far as the event horizon.",
"To further relate this to what you wrote, light doesn't actually carry an Electromagnetic Field. It carries information about ",
" in the EM field. Light isn't going to bring you EM field, it's only going to bring self-interacting ripples in it."
] |
[
"Do different language make lying easier or harder?"
] |
[
false
] | null |
[
"Yes and no. Even if you reduce it down to binary signals, one signal could be yes and the other could be no. Sending an incorrect signal for any given situation makes it a lie.",
"In the complexities of human language it is still no different. Giving a false response is always still possible.",
"The degree to which how \"easy\" or \"hard\" it is to lie depends on the multitude of meanings you can express. Basically what that means is: ",
"It is possible for certain languages to make lying ",
", but no laguage can really make lying any ",
" in relation to the most basic level of communication. "
] |
[
"That's definitely one aspect of what makes it easier or harder to lie. Another aspect might relate to how sentence structure and conjugation is altered when lying, depending on the kind of lie being told. In English, the difference between \"I did that bad thing\", and \"she did that bad thing\" is relatively easy to change the story in your speech with only altering one word. In spanish for example, Hice algo malo and Ella hizo algo malo it requires 2 ( sort of ) words to be altered. I'm not sure which languages are generally considered more complex in conjugation."
] |
[
"I would personally say this is also a Psychology question. Most \"good\" lying is going to be based on training yourself (or being taught to) hide psychological cues that show you're lying, ie. Looking away, blinking, a twitch, etc. The Language cues that show you're lying are change in voice tone (sudden high voice), shaky voice, etc. ",
"Theorizing: Based on languages like chinese where a lot of the word differences are based on tone of voice, or inflexion of voice, you could theorize it might be harder in chinese since you change tone so much, or you could theorize the other way. ",
"I'm a Biologist though, so most of this is based off what I've studied from Psychology and what little I know of languages, hoping someone can articulate better for me or expound on my ideas a little better."
] |
[
"How do individual cells know what shape to arrange themselves into to form a multicellular organism?"
] |
[
false
] |
I know that it's "in the DNA", but logistically, how do kidney cells know to arrange themselves into a kidney shape? How do the cells on the outside edge of an organ know to stop expanding outward and changing the organ's shape? Cells can't possibly have spacial awareness, can they? I know there is some rudimentary communication between cells, but organizing cells into complex shapes seems like it would require more complex communication that what could be passed via chemical triggers. EDIT TO CLARIFY: So when an embryo is developing, it starts off as all stem cells. At some point, one or more of these cells somewhere in the middle say "OK, I'm gonna be a kidney!". Then it divides into more kidney cells. How does cell in that area know it should be a kidney cell, how does it know what shape the final organ should be, and how does it know when it's a big enough kidney and should stop getting bigger? The final arrangement of the cells in the organ seems like it would need an external perspective or at least some very complicated communication between the cells of the organ. What prevents a human from developing a hexagonal kidney located in the lower calf area?
|
[
"This a pretty big topic, but I will try to simplify it for you and then you can ask more specific questions.",
"When you think of cell division, you usually think of a parent cell dividing to produce two identical daughter cells. However, during embryonic development, not all cells divide evenly. This is called ",
"asymmetric cell division",
". ",
"Here is an ",
"illustration of this type of division",
" as we understand it in ",
", but same basic idea applies to humans. Each of those cells has a different cellular fate because of the uneven segregation of cytoplasmic determinants, which can be proteins, RNA, or mRNA, during cell division. In humans, embryogenesis proceeds through morula, blastocyst, and gastrula stages. The gastrulation stage is really the first step to answering your question. ",
"Gastrulation is the process of forming the three germ layers - ectoderm, mesoderm, and endoderm. Since you asked about a kidney, let's just focus on that one aspect. The mesoderm produces the urogenital system, which includes the kidneys. ",
"Humans go through a few stages of transient kidney types. Starting around day 22 of embryonic development, the pronephric duct is formed, which gives rise to the nephric duct (Wolffian duct), which induces formation of the mesonephric kidney. These early transient kidney types eventually give rise to the metanephros. You can look up all the anatomy of it from that point, but that isn't the real basis of your question.",
"So how do the kidney cells know to do all those things? And how do they know where to form? Well, the simplest answer is ",
"a lot of cell signalling",
".",
"First, let's look at how they know where to form. Signals from the paraxial mesoderm induce primitive kidney formation in the intermediate mesoderm. In the article linked above, they did an experiment in chick embryos where they cut the embryos such that the intermediate mesoderm wasn't in contact with the paraxial mesoderm on one side of the body, but left the other side intact. The intact side showed normal kidney development, but the cut side didn't form a kidney. So a big part of the equation here is signals coming from \"established\" parts of the embryo. In other words, it's not some cells just floating around and suddenly deciding to become kidneys in the middle of the calf muscle. ",
"More specifically, the Pax2 gene, which has been shown to be a highly conserved tissue-specific transcription factor involved in kidney development, along with Lim1 and Pax8, cause the intermediate mesoderm to start forming the kidney. Furthermore, if you take those genes and express them in other tissue types, you can ",
"induce ectopic kidney formation",
". There are other papers that do similar experiments, let me know if you want links to more of those.",
"So as far as specific placement, for example, in chick embryos as described in the articles above, those genes are expressed in the intermediate mesoderm at the level of the sixth somite (trunk of the body). And that is why the kidneys form there instead of elsewhere.",
"Second, how they know how to form a kidney. Again, the answer is cell signalling. ",
"Here is a good review of nephrogenesis",
". If we expand upon the first point, where the Pax2, Lim1, and Pax8 genes signal the intermediate mesoderm to start forming the kidney, you can kind of take it from there that those cells will then signal the next cells, and so on. In short, there is a very complex and highly regulated (by transcription factors, protooncogenes, growth factors, etc.) process that results in a step-wise formation and progressively increasing complexity in the developing cells and eventually tissues. ",
"If you want more detail than that, you can just read the article. It's a pretty big beast of a process.",
"As far as the other part of your question - how do they know when to stop? That may be better left to an A&P person, but here is my take.",
"The ",
"Hippo pathway",
" is one of the pathways involved in organ growth and size regulation. If you read the article, you will find that, while we know some things about this pathway, some things are still being studied. In short, the Hippo pathway is a cascade of protein kinase signalling that is involved in regulating the cell cycle. The review linked above mentions a couple of studies where mutations in Hippo pathway components led to adults with overgrown organs.",
"Since I am not especially familiar with the Hippo pathway or how it regulates organ size, I am just going to leave it at that and hope someone else with more insight can chime in here.",
"Please let me know if I have misstated something or can clarify anything for you.",
"Edit to cite non-internet sources, two of my favorite textbooks: ",
"Developmental Biology",
", 9th edition, Scott F. Gilbert 2010",
"Molecular Biology of the Cell",
", 4th edition, Alberts et al. 2002",
"Something else I wanted to say... when you are talking about how something forms correctly and wondering why they don't do it another way or somewhere else - they do. ",
"Here is the March of Dimes page on birth defects",
". If you read their statistics, 1 in 6000 babies are born without kidneys, and between 1 in 500 and 1 in 1000 babies are born with a single kidney. Then you also have structural defects with kidneys that do form.",
"The people you see walking around out in the world are largely the products of the \"correctly formed\" embryos. It's estimated that as many as half of pregnancies end in miscarriage, many of them before a woman knows she is pregnant, and these are often due to genetic or cell division problems. ",
"I'm not sure what my point was with adding this, it's just something I always think about when people ask how these developmental things always happen the right way, because they don't."
] |
[
"People like you who take the time to give such a thorough answer just to satisfy someone's curiosity is the reason this is my favorite subreddit."
] |
[
"Thanks for that! And I love talking about this stuff anyway :-) It makes me happy when people are curious about biology!"
] |
[
"How does temperature affect London Dispersion Forces?"
] |
[
false
] |
I don’t how to word it, Im basically asking why do the London dispersion forces occur between two non-polar molecules to form a super cold liquid like liquid nitrogen?
|
[
"My approach to answering this may not be the direction you were taking this but it is how I think about van der waals forces (London dispersion). I work in a lab that does biomolecular modeling and this force is most often represented by the Lennard-Jones potential. This potential is good at approximating these forces as purely a function of distance, it is a weak force and decays very quickly - on the order of nm. In my modeling we define the cutoff for vdw as 14-16 angstrom.",
"The role temperature plays in this is that kinetic energy is directly proportional to temperature and as temperature increases the effects of vdw force become increasingly transient. When you cool nitrogen down enough it becomes a liquid not because of vdw forces but because the kinetic energy is low enough that the nitrogen cannot exist in the gas state anymore."
] |
[
"This is ultimately a statistical mechanics problem. I would say that how you put it is essentially correct but it would be more accurate to say that it is more probable that atoms are nearer to their contact distance. Once you get to a small enough level everything reduces to statistics and quantum mechanics"
] |
[
"This is ultimately a statistical mechanics problem. I would say that how you put it is essentially correct but it would be more accurate to say that it is more probable that atoms are nearer to their contact distance. Once you get to a small enough level everything reduces to statistics and quantum mechanics"
] |
[
"What is the purpose of creating synthetic elements?"
] |
[
false
] |
Elements such as Californium and Tennessine, what is their purpose?
|
[
"Most of them are just for research purposes, and no element past Fermium has been synthesized in useful quantities. Pretty much everything past there decays in less than a second.",
"It’s mostly just ",
" but research like this isn’t useless. Far from it. Learning more about the universe is always important, there may be incredible discoveries just around the corner, but we’ll never know unless we try to find them.",
"Maybe there is a use for some super-heavy synthetic element, we just don’t know yet. There is a theorized “island of stability” for some super-heavy elements, where they may last long enough to be useful. But again, we won’t know unless we try to find it."
] |
[
"Well californium-252 is a great laboratory fission source. We use it because it produces neutrons. For the superheavies like tennessine and oganesson, we just produce them to learn about nuclear, and possibly atomic physics."
] |
[
"It decays some of the time by spontaneous fission, and some number of neutrons are emitted in the process."
] |
[
"How do we know that the climate change we see today is not just part of a natural cycle?"
] |
[
false
] |
The earth has gone from hot to cold and vice versa without human intervention. How can scientists tell if this isn't just part of a natural cycle?
|
[
"For one thing, we have ",
"direct evidence",
" that increased CO2 means more radiative heat is trapped in the atmosphere:",
"Both series showed the same trend: atmospheric CO2 emitted an increasing amount of infrared energy, to the tune of 0.2 Watts per square meter per decade. This increase is about ten percent of the trend from all sources of infrared energy such as clouds and water vapor.",
"We also know that ",
"atmospheric CO2 is increasing year by year by around 2.5 ppm",
" because humans are burning 3 cubic miles of oil equivalent per year. Actually the amount of fossil fuel we burn would be enough to increase atmospheric CO2 by around 5 ppm per year, but about half of it is absorbed by the oceans and the biosphere, decreasing the alkalinity of sea water.",
"We also know what the other drivers of total atmospheric energy are, and that ",
"they haven't changed rapidly or drastically enough to account for the rapid and drastic increase in temperature we have seen",
".",
"And of course there's the ",
"correlational evidence of rising CO2 compared to rising temperature",
"."
] |
[
"One example would be that if you look at the charts for frequency of tropical storms, severity of the storms, and quantity of CO2 in the atmosphere, there is a linear increase up until the 1800's when the industrial revolution took place."
] |
[
"i wonder the same thing. I strongly suspect that there is no way to distinguish between the natural cycle of ice ages followed by umm, thermal ages(?), and the deviation from that cycle contributed by human activities.",
"An interesting side question tho is, even if we halted/reversed all currently suspected behaviors negatively affecting global climate, and still noticed an increased warming and/or change in the climate, what could we do?",
"Can we artificially counter-act whatever processes are in play that cause the 50k year cycle of warming and cooling?"
] |
[
"Physics problem that has been plaguing me since high school."
] |
[
false
] |
Hypothetical situation. Lets say you have a fighter airplane that flies at a maximum velocity of (just throwing numbers out there) 100 m/s. This plane can fire missiles, which travel at 200m/s. If the plane is flying at 100m/s and fires the missiles, the missiles would travel faster than 200m/s, right? Ok. So what happens if the same missiles are equipped on a jet fighter that can travel 500m/s. If the jet fighter is flying at 500m/s and fires a missile, will the missile now be able to travel faster than 500m/s or would it trail behind the jet fighter, kind of like when you throw a ball out the window of a moving car (I know its an entirely different phenomenon). I don't know how air resistance would play into this, assuming there is or isn't any. Also, assume the missile is loaded under the wing of the aircraft (not in some tube that could jam). This hypothetical situation has seriously been giving me headaches for about 10 years because I simply can't wrap my mind around it. I'd appreciate some clarification!
|
[
"The question at hand is: What causes the speed limit on the motion of the missiles? Is it air resistance (as is the case for airborne missiles)? ",
"If so, then firing a missile (limited to 200 m/s velocity in air) from a jet (traveling at 500 m/s in air) will cause the missile to fly backward at 300 m/s from the perspective of the jet pilot. Imagine throwing a beachball from the window of a rapidly moving car. The air catches it going \"above its speed limit,\" and drags it back down pretty quickly. ",
"If all of this is happening in outer-space, where there is no air resistance, whatever speed limit is imposed won't be with respect to the air, so you're the pilot will likely see the missile move forward in the expect fashion. "
] |
[
"Remember that the missile is not travelling at 200m/s relative to the plane as it is released, or it would probably rip a wing off with it!",
"The missile will detach and fire. Its initial speed will be that of the plane, but if it cannot maintain this speed then it will slow down.",
"Obviously in reality missiles are far more aerodynamic and have much higher thrust/weight ratio than a plane so the missile is likely to have higher speed!",
"EDIT: To add to this, consider 3 phases:",
"Phase 1, Missile attached to plane, travelling at the same speed as plane",
"Phase 2, Missile detaches and reduces in speed due to air resistance",
"Phase 3, Missile fires and its speed increases upto and beyond that of the plane (for a real world missile)."
] |
[
"That makes sense, but for a \"practical\" clarification: missiles are generally fairly aerodynamic, which means that the slowdown from jetVelocity+launchVelocity to 200m/s would be pretty slow, so I think you would see the missile speed out ahead of the plane at first, and then gradually the plane would overtake it."
] |
[
"We're used to burning natural gas in air. What if you reversed things and tried to light a stream of air piped into a natural gas atmosphere?"
] |
[
false
] |
[deleted]
|
[
"If the air stream was lit, perhaps from a Bunsen burner, it would appear to burn in the natural gas (mostly methane) atmosphere. But it would be much more difficult to light and maintain a flame, and the flame would have a different appearance...",
"Composition of natural gas: ",
"http://www.beg.utexas.edu/energyecon/lng/LNG_introduction_07.php",
"Why it's basically the same: The \"Burning\" of hydrocarbons like natural gas produces carbon dioxide, water, and heat energy. This heat causes the carbon dioxide and water molecules to glow, which we observe as a flame. The hot gasses rise, which is why the flame goes up.",
"There is an important concept in chemistry called the \"limiting reagent\". If you consider boys and girls pairing off at a dance, and there are more boys than girls, then once everyone pairs off, there will be some boys without partners. In this case, girls are the \"limiting reagent\". When you light a natural gas flame in the atmosphere, there is an abundance of oxygen, so the methane is the limiting reagent. If you light an oxygen stream in a methane atmosphere, oxygen is the limiting reagent, but the reaction is the same. Whether there are too many girls or too many boys, there's still a lot of dancing going on.",
"Why it's different: methane gas has a higher specific heat than air. That means that it takes more energy to heat up methane than air. The methane atmosphere will therefore act as a heat sink, and it may be more difficult to maintain hot enough temperatures to support the flame. The flame would likely be smaller since heat would leak off into the methane atmosphere.",
"http://www.engineeringtoolbox.com/specific-heat-capacity-gases-d_159.html",
"Also, methane is half the weight of air (nitrogen/oxygen) so the rising of the hot gasses would be less dramatic, reducing the height of the flame and increasing its width. This is similar to how a helium balloon would lose buoyancy if it was placed in a lighter atmosphere. (50:50 air and helium)",
"Natural gas is mostly methane, but air is only ~20% oxygen. That's a lot of non-reactive nitrogen gas getting in the way. The nitrogen gas would sap the reaction of heat energy even more than the methane atmosphere. This would make the flame very difficult to light.",
"Finally, the burning (oxidation) of hydrocarbons is actually a multi-step process. Hydrocarbons that are surrounded by oxygen will rapidly proceed through all steps. It's possible that an excess of hydrocarbons will allow for only partially oxidized (burned) hydrocarbons to escape. This will change the appearance of the flame, and reduce the heat produced, and further inhibit the maintenance of the flame."
] |
[
"Please do not do this. But to answer your theoretical question....",
"An air to fuel ratio for Natural Gas of 10:1 seems to be the standard. So for every ten cubic feet of air pumped into the room, 1 cubic foot of gas would be consumed.",
"http://sagemetering.com/combustion-efficiency/air-fuel-ratio-effect-on-combustion-efficiency/#.VZ0N_Lxk_CI"
] |
[
"Maybe this doesn't answer your question, but there are industries that use the perfect ratio of pure gas/oxygen to heat industrial processes. I know that glassmaking is one of those. ",
"To try and answer your question, it would explode pretty dramatically, or if you could do the math regarding flame stability and supply of air, you would get a flame stream, but it will not burn completely or cleanly. If there is \"too much\" gas, the incomplete combustion would leave you with a lot of CO instead of CO2, since there is not enough oxygen. The resultant gas exhaust would be very toxic."
] |
[
"How do we know how far light has traveled when it gets to earth?"
] |
[
false
] |
I suppose this will be an easy one, i searched for an answer here. My question is simply How do we know that the light from the farthest galaxy away is 12.91 billion light years away? What about light lets us say its traveled 12.91 billion years?
|
[
"Redshift, the wavelengths of light from distant galaxies are shifted to the red end of the spectrum, the amount of redshift is proportional to the distance."
] |
[
"A red shift is when an object is moving away relative to the observer. Blue shift is moving towards the observer. ",
"We can use this in a way to measure the distance to stars and objects by looking at emission spectra of the object. For example, a stars emission spectra will have sharp absorption peaks which correspond to certain elements. Because we know the value of wavelength which corresponds to this absorption value. We can calculate the difference in the wavelength received by looking at how far these absorption lines are shifted from their true values."
] |
[
"Thanks for answering. The red blue shift is from the object in question moving towards or away from us correct? Similar to the way we found planets around suns? "
] |
[
"Does the body in any way distinguish between intentionally self-inflicted injuries and other injuries?"
] |
[
false
] |
Do they heal in the same way in the same amount of time and/or generate the same amount of pain? Or, in the same way that it's nearly impossible to tickle oneself, does the conscious realization of the injury somehow lessen or change the body's reaction to it?
|
[
"Self inflicted injuries ( and other 'safe' damage) will trigger a flood of endorphins to counteract Your natural adrenalin response. this is why people become addicted to cutting, and similar behaviors."
] |
[
"I meant I choose to pinch myself somewhere else on my body with my other arm while I wait for the pins and needles to go away. It explains why that method works at distracting me."
] |
[
"During essay exams I bite my left hand really hard when I feel my right starting to cramp."
] |
[
"Can vaccines be inherited?"
] |
[
false
] |
If lets say the mother ( lets name her Karen) of the child had aquired the MMR vaccine during her childhood, but does not want her child to get vaccinated with the same vaccine as she got, is it possible for the child to have inherited the vaccine or is the only possible way for the child to be protected by having the vaccine itself?
|
[
"Short answer - No",
"Long answer - Really, really no. ",
"Vaccines work by producing antibodies in the host which provide protection against pathogens. ",
"There's no gene stuff involved, so this \"protection\" cannot be inherited. ",
"Can this be passed on (mother-baby blood exchange)? - No. "
] |
[
"IgG crosses the placenta and IgA is transferred in breast milk. So there is limited protection for a short time. But definitely no true inheritance. "
] |
[
"Newborns benefit from acquired maternal immunity. This is a temporary condition that can last from 6 to 18 months after birth and bridges the gap before the babies own immune system becomes strong enough to start fighting a lot of common infections in its own. From this we know that natural immunity is stronger than vaccinated immunity. My example is measles virus; if the mother had measles as a child and is naturally immunized, the acquired immunity in the child is stronger and makes it more likely that child will be resistant. If the mother’s immunity comes from a vaccination, there is still a protective effect to the newborn child, but it is known to be somewhat less effective.",
"Any acquired immunity wears off after a point in time, leaving the child open to contracting the viruses they may have formerly been immune to. And they then must develop their own immunity or be vaccinated to protect against.",
"Remember, always vaccinate your kids folks!"
] |
[
"Why do planets rotate on the same plane?"
] |
[
false
] | null |
[
"Frequently Asked Questions."
] |
[
"Thanks!!!"
] |
[
"Why do all planets rotate around the sun on roughly the same plane?",
"They don't. There are variations in the orbits which planets take around the Sun. Most of the 8 planets in our solar system have a small angle of elevation off the plane of the ecliptic. However, the angle is not constant for every planetary body. For example, Mercury revolves around the Sun on a plane tilted 7 degrees from the ecliptic. Some dwarf planets, such as Pluto (17 degrees from the plane of the ecliptic) and Eris (40 degrees from the plane of the ecliptic) have very tilted orbits.",
"Why don't we see some planets rotating on different planes/axis where potential planetary collisions would be possible?",
"Well, we don't see the planets bashing into each other because our solar system was lucky. Here, stable planetary orbits began to form from the disk of dust and gas (which eventually birthed our planets). This was caused by accretion for the terrestrial planets and jovian (outer) planets. ",
"Planetary collisions are possible, but not in our solar system at the present time--the activity has died down. Way back when, roughly 4.5 billion years ago, there was likely a collision with Earth, with a large object, possibly even the size of Mars. This object hit the Earth, and after some exchange of material and after bombardment of meteorites ended, both the Earth and the newly-formed Moon began to cool. The other planets in the solar system did the same in a general sense."
] |
[
"If a certian chemotherapy drug was created that functioned like all chemo drugs (killing dividing cells) to which no cells could develop resistance to, would that effectively cure all cancers?"
] |
[
false
] |
[deleted]
|
[
"What you are saying is \"if I magically create a substance that kills cancer and has no side effects, would that cure cancer\". Yes, it would. Also, it's impossible. The whole reason that cancer is hard is that a) what is broken are mechanisms that are essential to normal cell functioning and b) they can be broken in hundreds of different ways. You can't create a single drug that magically handles that.",
"It's like saying \"if we created a screwdriver that fits every screw, could I disassemble everything?\". Yes, if you created that, you could disassemble everything, but you can't possible create that, because a tool that is small enough to handle iPhone screws is not strong enough to handle bolts on a shipping container. "
] |
[
"Not necessarily, there would still be a problem of toxicity, as this wouldn't be specific to the cancer but would also target, skin, intestine, etc. That's also the problem with most chemotherapy treatment, you can increase dosage and kill the cancer but you'd also likely kill the patient."
] |
[
"My basic point is that everything is dose dependent, even cyanide or ricin won't kill you with a low enough dose. That's why there's a lot of research into immunotherapy, which should Theoretically decrease toxicity and increase effectiveness. Today's drugs as you say kill the cancer more effectively than normal healthy cells, your hypothetical drug would be a step back due to the lack of targeting and would be more comparable to radiation."
] |
[
"Is there a limit to how long a radio wave can be? Would extremely long waves be of any use?"
] |
[
false
] | null |
[
"Frequencies lower than 1 oscillation within the age of the universe don't produce anything you could call an electromagnetic wave, and similarly wavelengths longer than the Hubble length are not meaningful waves. Apart from that there is no limit, it just gets harder to detect radiation the lower the frequency gets."
] |
[
"The longest I've heard of is ELF, used to communicate with subsurface submarines. The extremely low frequency, 76 Hz, allows the signal to penetrate hundreds of metres of seawater, which as a conductor shields against most higher frequency radiation. However, this comes at the cost of terrible bandwidth, a few characters a minute at most. Also, it required huge (tens of kilometres) antennae arrays and megawatts of power. So no mobile transmitters existed. Basically it was a way to tell a sub to surface so it could communicate with a high frequency satellite connection.",
"\nEdit for conversion: 76hz equates to a wavelength of 4000km."
] |
[
"Your home wiring is broadcasting EM waves at 50 or 60Hz depending on where you live. In fact guitar pickups are basically antennas and can pick it up. "
] |
[
"Why are some units measured with negative powers?"
] |
[
false
] |
Examples: kiloJoules per meter squared per year---kJ m yr Biomass is measured in grams per meter per year g m yr Why are the exponents negative? wouldn't those signify the reciprocal of a year or 1/meter Am I thinking to strictly mathematical in a scientific field or is my math incorrect?
|
[
"I don't quite follow your question. Writing kJm",
"yr",
" is the same as writing kJ/m",
"yr- perhaps the former is sometime preferred because it only takes a single line, but they are identical statements. "
] |
[
"Thanks, I was thinking about the math wrong. I gotcha now"
] |
[
"Biomass is measured in grams per meter per year g m",
" yr",
"Biomass is measured in grams (or kg).",
"Biomass ",
" is measured in grams per square meter.",
"Biomass density ",
" is measured in grams per square meter per year.",
"The units of m",
" and yr",
" do not exist on their own (at least, not meaningfully), but within the context of other units."
] |
[
"Differences between the Pfizer/BioNTech vaccine and Sputnik V?"
] |
[
false
] |
Yesterday's news seem to have given everyone a much-needed dose of optimism. Understandably, when Russia announced its own COVID vaccine a few months back, the reaction was much less enthusiastic. I'm from Moscow, and, although anecdotal, don't know a single person who is planning to inject Sputnik V, primarily due to a deep lack of trust in our government and everything related. Russians, for the most part, don't think it's safe, or at least that it's too early to say. Now, I know very little about the actual science behind these vaccines. With the information we currently have, is it possible to compare the two? Do they operate on the same principle, or are they inherently different? I have a feeling that for most Russians, Sputnik V will be the default/only option for some time, so would really like to know if what we're getting is in at least the same ballpark as the supposedly world-saving BioNTech vaccine. Greatly appreciate any info.
|
[
"off the top of my head I don't know the science behind the Sputnik, but I do know that the original trial only tested it in 73 patients, whereas the Pfizer vaccine has now been tested in over 43,000 patients.",
"Sputnik could end up working fine and being safe, the issue - for the scientific community - is that the process, the way it was developed, was not in line with the accepted international clinical research guidelines - which were developed after, and in an effort to prevent further, disasters such as thalidomide (experimental drug which caused foetal deformities) and others.",
"So while there may not be anything to suggest Sputnik is unsafe, there is not enough to give real confidence that it is safe (i.e. you are taking a higher risk than if you took a vaccine that had been tested in large numbers (about 500 for normal medicines, but vaccines need more people - e.g. a few thousand at least - or a longer time to get good data), in three phases and assessed for safety and efficacy by an independent regulatory body). I hope it works and is safe, but this will be down to a bit of luck."
] |
[
"They do work somewhat differently, yes.",
"Sputnik V is and adenoviral vector vaccine. A vector is a virus that has been modified to remove the genes that allow it to reproduce in the body so it can't make the recipient ill, but it still has the structures/genes that allow it to enter the body and permeate the cells. The Sputnik uses two adenovirus vectors to encapsulate a gene coding for SARS-CoV-2 S protein. The vector will allow the S protein gene to be transferred into the cells, and the body will then continue synthesizing the S protein and build immunity to the virus that way.",
"Pfizer's vaccine is an mRNA based vaccine. Pfizer's contains a strand of mRNA that codes for the spike protein (the protein on the outside of the virus that allows it to penetrate the cells). The body will then replicate the spike protein on it's own, and consequently learn to build immunity to it.",
"So, these two vaccines work by somewhat different delivery mechanisms and will produce an immune response to different COVID proteins. These differences don't inherently make the Pfizer one better. In theory they could both be very effective. I think it's just like the other commenter described, most people don't believe Russia's initial trial was enough to prove it was both safe and effective, and a lot of people/countries just don't trust Russia at all.",
"Sources:",
"https://sputnikvaccine.com/about-vaccine/",
"https://www.fastcompany.com/90573488/how-pfizers-covid-19-vaccine-works-mrna"
] |
[
"One big difference between the two is that human adeno vector vaccines have been tested since the 80's on long term adverse effects, and that's why they being released only for some years. This is not the case for mRNa vaccines, we shouldn't call the \"new vaccines\", but prototypes.",
"mRNA vaccines have potentially more serious effects, like cancer, auto-immune illnesses or modification of the DNA of the receiver when in presence of another virus.We all hope that these potential adverse effects will never occur, but without long term studies, we simply don't know."
] |
[
"We have different types of speech in different parts of the world, do animals as well?"
] |
[
false
] |
Say a Bengal tiger raised in Africa compared to a Bengal tiger raised in China. Would they both make the same sounds as each other?
|
[
"Similar question from a few months ago",
"Birds, whales, dogs and possibly cows have been found to have \"regional accents\".",
"I imagine the rarity of a tiger makes studying something like this a bit difficult but I wouldn't be surprised at all if they had 'accents' as well."
] |
[
"An important caveat here is that various species differ appreciably in terms of (1) the diversity of their vocalizations and (2) the degree of biological preparedness they display for those vocalizations. I doubt very strongly that two ",
"lyrebirds",
" raised in different environments would sound similar."
] |
[
"Wow. Really interesting thought. I have nothing to add but I just wanted to thank you for giving me something new to think about and look into. "
] |
[
"Why don't neutrinos interact with matter?"
] |
[
false
] | null |
[
"They only interact via the weak force and gravity, so the cross sections (basically the probabilities) for any scattering or reaction processes are extremely small."
] |
[
"Piggybacking onto this, they don't interact electromagnetically because, unlike electrons, they don't have any electric charge (nor magnetic moment?), and they don't interact via the strong force because, unlike quarks, they don't have any 'colour charge'."
] |
[
"Thanks"
] |
[
"If you exposed a conducting battery to light, would the reaction occur faster?"
] |
[
false
] |
Would the electrons move quicker and therefore produce more work and cause the battery to die sooner?
|
[
"Well, light wouldn't do anything more than the same amount of heat; it's not a photochemical reaction. But heating it would cause it to react faster. Not due to the electrons moving faster, but because the molecules would bump around faster and so the chemical reaction would occur at a faster rate."
] |
[
"It would increase the power, but not the amount of energy in total. Specifically, the voltage drop for a given load would be smaller. You'd have a higher current because of that, so a greater number of electrons flowing for a while, but the total number of electrons transferred in the reactions is the same no matter what rate it occurs at."
] |
[
"But since the chemical reaction occurs at a faster rate, would that increase the energy output like if you were to measure the amperes? If so, is this because there's more electrons flowing at any given time because the chemical reaction occurs faster?"
] |
[
"How does a computer know how much is 1 second?"
] |
[
false
] |
[deleted]
|
[
"Computers use a hardware device on the motherboard, usually an integrated circuit that is constantly powered, to keep time. Most real-time clocks count seconds using a crystal oscillator. This is a device that operates by converting the mechanical resonance of a vibrating crystal (like quartz) into an electrical signal with a precise frequency."
] |
[
"Yes there is a tiny quartz crystal that vibrates at a known frequency when an electric current is passed through It. This is the same mechanism that is used in most non mechanical clocks, e.g. a battery powered wrist watch.\n",
"https://en.wikipedia.org/wiki/Quartz_clock?wprov=sfla1"
] |
[
"Yup. Quartz is how Seiko, Timex, Casio, Texas Instruments, etc. almost killed the Swiss watch industry."
] |
[
"If a person were to be taking antiviral drugs when taking a viral vector vaccine, would that ruin the effect of the vaccine?"
] |
[
false
] | null |
[
"It would depend on the kind of antiviral. Since the viral vector in the vaccine does not reproduce any antiviral that operates to reduce reproduction would be moot. An antiviral that happens to block the receptor site where the virus can interact with the cell could prevent the virus from actually delivering its payload into the cells as designed; which could reduce the effectiveness of the vaccine. Meanwhile an antiviral that boosts the immune system might actually help the vaccine function (again depending on the kind of boost the antiviral drug provides).",
"In the case of covid the MRNA vaccines would have none of this problem, and probably would be preferable .",
"But I would ask the person who prescribed the antiviral drug whether or not it will have any effects or interactions with the vaccinations you may need or want.",
"At the viral scale the organic chemistry is a mix of solving puzzles and playing Lego. It's extremely mechanical. There's a lot of fitting and prying and meshing and twisting. So a drug that is designed to (say) clog one spot would completely ignore the spot right next to it that a different substance is going to interact with. So it an antiviral interacts with point A, and the vector virus latches on at point B, then it would have no effect. But if the vector needs spot A it mi might bounce around looking for an open A. The longer the vector bounces around unmatched the more likely it is to run into something and be destroyed before it can find an open A.",
"So just as any medication only does whatever it does and doesn't do the things it can't mesh with.",
"So the exact answer varies."
] |
[
"No.",
"“Because the current vaccines used in the U.S. are not live vaccines, no virus is produced and, therefore, an antiviral medication would not be expected to alter the response to the vaccine. However, if an individual is still experiencing symptoms from the viral infection for which the medication was prescribed, they may consider delaying vaccination so that the cause of any symptoms can more easily be determined.” — ",
"Children’s Hospital of Philadelphia"
] |
[
"Viral vector vaccines rely on a virus to penetrate cells and to deposit DNA that encodes a protein, typically the spike protein, of the virus that the vaccine targets in order to stimulate an immune response.",
"The mechanism of most antiviral drugs is to prevent the virus from entering a cell and therefore the effect of the vaccine would be diminished. The effect would not be entirely ruined since no drug would 100% prevent cell entry of the vaccine."
] |
[
"Can someone help me gain a more quantitative understanding of the concept of invariance of the speed of light?"
] |
[
false
] |
Hello askscience, So I've heard and even explained a lot of the more qualitative, analogical, and heuristic takes on special relativity and time dilation and such. I'm by no means mathematically sophisticated, but I'm studying math and economics in school and I've done some linear algebra and multivariable calculus and such, but I've never applied anything to physics except insofar as physics is applied to math problems in math classes (mostly things about springs). But I'd like to understand this stuff a little better cause it fascinates me. I understand that having a constant speed of light basically means that the time between emission from my flashlight to perception by your eyes is a function of the distance between my flashlight and your eyes, and not of anything else. But I don't fully understand how this works, so maybe you can help me work out a basic problem: I'm travelling at 0.5c, following you in a straight line. You're going at 0.6c. I turn on my flashlight at time t=0. How do we work out when you perceive the light from my flashlight when our distances are changing with time? If you'd rather not work out the full problem, pointing me to online resources from which I can study this stuff would be greatly appreciated too. This stuff is a lot more interesting than my linear programming homework that I ought to be working on.
|
[
"The speed of light is constant in all reference frames. Time and space distort to keep it constant (compared to your preconceived notions of them). Since light is a wave, this actually says something deep about physics - wave speed is calculated from a springlike term (the energy required to make an electric field) and a momentumlike term (the energy required to make a magnetic field). Those two quantities are constant in every laboratory, no matter where or how fast it be moving, ergo local physics is independent of position and motion."
] |
[
"Hi, I'll have a go at this, but I don't have a huge amount of time. A first remark: you need to specify that everything is measured with respect to some fixed reference frame R. As a direct consequence, if you measure the speed of your buddy, you will ",
" measure 0.6 c - 0.5 c = 0.1 c, but you need to use the ",
"velocity addition formula",
".",
"Let's get down to the math. Say that at time t = 0 you're at the point x = 0. Then the trajectory of the light is described by x(t) = c t. Now you'll remark that that formula doesn't depend on your own velocity v = 0.5 c. Odd, isn't it? However, it's not an issue. If you use the above velocity addition formula, you'll see that in ",
" reference frame, moving at 0.5 c, you'll still measure that light moves away at a velocity v.",
"Now suppose that your buddy starts out at x = L at t = 0. To find the time t at which he sees the light (no pun intended), just solve",
"c t = L + 0.6 c t --> t = 2.5 L/c.",
"That seems almost to simple to be true. That's because the time t is measured in the fixed reference frame R. If you want the values in your frame R' or your buddy's frame R'', you need to apply a Lorentz transformation. The formulas (and a decent explanation) are given on ",
"this excellent site",
". Since it's very late, I won't plug in the numbers, and I think it's a good exercise to play with the formulas a bit.",
"If you're more of a visual person, you can also use ",
"space-time diagrams",
" to draw the problem. It's very easy, helps you overcome conceptual issues and it's in fact a rigorous method (you can prove everything in special relativity using them).",
"Hope this helps you out a little - apart from the hyperphysics site I don't know that many web resources. There are tons of textbooks that explains the stuff at the undergrad level though, i.e. knowing what a vector/matrix/square root is should suffice."
] |
[
"As a layman, this is the way I like to think of it:",
"1) Light traveling from the sun to the Earth takes 8 minutes to reach you. ",
"2) From the perspective of a photon the trip is instantaneous.",
"3) The faster you travel, the closer to instantaneous your movement becomes from your perspective."
] |
[
"What causes gender dysphoria?"
] |
[
false
] | null |
[
"Gender dysphoria is incredibly controversial. ",
"First, some background biology is in order.",
"Genotypic sex essentially refers to the presence of the Y chromosome in men. Throughout development in utero, all individuals have both mullerian and wolffian ducts. In individuals with a Y chromosome, the wolffian ducts are preserved, but they regress in individuals without testosterone, barring androgen insensitivity.",
"Phenotypic sex refers to the expressed sex based upon development. Some individuals with certain mutations (those with androgen insensitivity for instance) are phenotypically female but genetically male. This is quite rare overall.",
"Gender is an entirely social construct based upon the norms associated with being a man or a woman. It has essentially no biological basis.",
"As an aside, sexual identity and expression is not related to either sex or gender.",
"To my knowledge, there is no documented cause for gender dysphoria, but most hypothesize that there is a combination of genetic and social factors that lead to a person's gender expression not coinciding with their genotypic sex.",
"Many more progressive members of the medical community would like to see it removed from the DSM. We believe that it only reinforces the binary gender model, which once again has no biological basis.",
"As social mores change, it will likely become obsolete. Homosexuality was once listed as a disorder as well, but now its an accepted form of sexual identity.",
"Credentials: I'm a physician, but not a psychiatrist."
] |
[
"No, you need two sexes to reproduce. You could think that you are a badger for all the difference it makes, your sperm or your eggs still function normally."
] |
[
"No, you need two sexes to reproduce. You could think that you are a badger for all the difference it makes, your sperm or your eggs still function normally."
] |
[
"If we know how tectonic plates moved in the past, can we accurately predict how they will move going forward?"
] |
[
false
] |
Im not sure this information would be useful to us in any way because of the amount of time it will take for the predictions to come to fruition, but are the movements of the plates predictable or random?
|
[
"We can project the future motion of the plates, but only up to a point with any accuracy. To back up, through a variety of techniques we can measure and reconstruct average plate motions and directions in the past, e.g., from plate circuits, paleomagnetic data, reconstructions from sea floor spreading, etc. (e.g., ",
"Müller et al., 2019",
") and similarly from things like GPS we can measure the geologically instantaneous rate and direction of current plate motions (e.g., ",
"DeMets et al., 2010",
"). Plate motion is not random, it is driven by clearly demonstrable forces and processes (e.g., ",
"this FAQ",
") and thus it is certainly possible to extrapolate recently past and current motions into the future and expect these to hold for a while, basically as long as the forces themselves driving the plates hold. The trick becomes how long \"a while\" is. ",
"In much the same way that we can only accurately forecast the weather a little bit into the future, the same is largely true for plate motions (and largely for many of the same reasons, i.e., the complicated dynamics of nonlinear systems and incomplete knowledge of all of the necessary variables), but because of the ",
" slow rates in comparison to things happening in the atmosphere, our projections of current conditions for plates can hold for a few million years. One of the biggest challenges is that it's generally hard (bordering on impossible) to project possible plate reorganizations. A plate reorganization is a geologically rapid changes in the direction and magnitude of the velocity of multiple tectonics plates, and these can be regional (seriously impacting only a few plates) or a true global reorganization. In general, things like the initiation of mantle plumes or large-scale collisions (e.g., like the collision between India and Eurasia forming the Himalaya) are events thought to be able to initiate global plate reorganizations (e.g., ",
"Muller et al., 2016",
", ",
"Olierook et al., 2020",
"). In a recently published paper ",
"Gurer et al., 2022",
" nicely demonstrate how a change in the interaction of two plates (e.g., through the initiation of a plume) can cascade into a larger plate reorganization. In terms of the frequency or regularity of these global plate reorganizations, that's a bit harder to answer. They are not uncommon in the geologic record, but are also not always happening or periodic. However fundamentally, many of these are not generally predictable, or at least, the outcomes are not predictable. For example, we don't really have a way of projecting when and where a new mantle plume might develop, so possible plate reorganizations driven by plume origination are a \"random\" occurrence. For reorganizations caused by large-scale collisions, we can extrapolate when and where these might happen (based on current rates and directions of plate motions), but ",
" the plates reorganize as a result of the collision is unclear (and this of course assumes that some other reorganization process doesn't preclude the projected collision from happening in the first place).",
"Sort of bound up with plate reorganizations is just generally that any individual plate boundary evolves for a variety of reasons. Effectively, as a primarily edge force driven process (i.e., plate motion is ",
" driven by forces acting along the edges of the plates), anything that modifies those edge forces will change the motion of a plate. Just thinking about subduction, as the most important of the forces driving plate tectonics, a whole range of processes can change the details of subduction which may influence the rate and direction, which in turn can force a change in plate motion, and a break from a simple extrapolation of current motion into the future. Not all of these necessarily rise to the level of a \"plate reorganization\", but even small changes to lots of plate boundaries add up over time, progressively making extrapolation of current rates less and less accurate.",
"All of the above is why, when we consider projected plate motions more than a few million years out, the future position of the plates/continents become non-unique. The most common representation of this is the range of different projections for the next expected supercontinent in ~250 million years (e.g., ",
"this FAQ",
"). The different projections discussed there are vastly different and rely on very different pathways (e.g., closure of the Pacific ocean vs closure of the Atlantic ocean) and is a relatively clear representation of the compounding uncertainty that develops when projecting future plate motion."
] |
[
"There is a lot we don't know about mantle plumes, but modeling suggests that they operate on scales between 500 million years and 2+ billion years, making them somewhat \"stable\" in that sense, with only a handful (around a dozen or more?) active today. Though we dunno how quickly a new one might form or old one fizzle out, or how to predict it.",
" This line is too simplistic, see comment below.",
"This is even ",
" to predict, especially on these time frames. The best we can do in our predictive models in regards to these dynamics is to assume they're static through the timeframe, which is likely incorrect. We could imagine them doing all sorts of things and model that specifically, but it'd be no more likely to be correct.",
"However, even just 50 million years from now a lot can change from more well-known tectonic processes without dipping too much into the timescale mantle plumes operate on, so we probably have some half decent models on the 10s of millions scale which, geologically, isn't particularly long but it's not nothing!"
] |
[
"However, an existing plume doesn't mean an erupting plume - which is what is believed to cause massive basalt floods (such as Deccan Traps, famously) which are a major source of continental reorganization as new crustal material is formed.",
"This isn't really accurate though. Flood basalts and other large igneous provinces are associated with the initial interaction of the plume head with the lithosphere, but plumes continue to drive melting and volcanism (albeit at reduced rates compared to LIP eruption) after the dissipation of the plume head. If this was not the case, hotspot tracks would not be observed."
] |
[
"Are there potential applications (even if theoretical) for the Bose-Einstein condensate? And really, what is Bose-Einstein condensate?"
] |
[
false
] |
I learned about this peculiar state of matter only recently (and only learned that it exists - nothing more). I don't exactly understand what it is. I gather that it is a special state of matter that does not occur in nature, and can only be achieved at temperatures close to absolute zero. I guess I'd just like to hear some general thoughts on Bose-Einstein condensate. What does it do? How does it differ from the other four states of matter? What can we do with it? Or is it one of those things that is nice to know about, but has no practical application? My inclination is to believe that it could be useful in superconductivity (simply an uneducated guess due to the role of cold in superconductivity)... Anyone have thoughts for me? I was an English major, so my physics background is, suffice it to say, weak. I'm just curious.
|
[
"Possible applications as an accelerometer to use for navigation in spaceships."
] |
[
"I've heard some talk of using BECs in atomic interferometry, typically in the context off gravitational wave detection. Imagine that you have a coherent BEC beam which you can split into two, and later recombine somewhere down the line. If the two beams pass through different gravitational fields, they will pick up different phases which will constructively or destructively interfere with one another when they are recombined. This is the same principle behind a Mach-Zehnder interferometer for light. The reason that you would need a BEC, rather than say, a laser, is that if you have a large enough condensate, gravity will couple to it more strongly (i.e. bend it more) than it would light.",
"To answer some of your fundamental questions, a BEC is a coherent quantum state that is comprised of a large number of bosonic particles. Bosonic matter has the special property that the constituent particles are very friendly, i.e. they like to occupy the same state. Fermionic matter is the opposite (i.e. fermions can't occupy the same state). When I say that it is a coherent quantum state, I mean that the constituent particles of the BEC (typically cold atoms) all fall into a state that can readily be described by a single wavefunction. Because there are so many particles in this state, a lot of the weird quantum properties that you have probably heard about can be observed on a macroscopic scale. This motivates interest from a purely scientific perspective. ",
"Otherwise, there are some fundamental similarities between the superconducting state and the Bose-Einstein condensate, in so far as the former is characterized by the condensation of Cooper pairs, i.e., bosonic quasiparticles (2 electrons paired by a phonon/lattice vibration). While I'm not 100% up on it, the crossover between BEC and BCS (superconductivity) is a relatively active area of research. The essential difference between the 2 states is the strength of the pairing interaction, from what I understand."
] |
[
"How?"
] |
[
"Is it possible for a tectonic plate to crack into two?"
] |
[
false
] |
I got bored and was looking at plate tectonic map on Google. I noticed the tip of africa was sandwiched between plates. I wondered if a situation was to occured that caused that piece to snap off
|
[
"This question comes up from time to time. It's known as rifting and it's a routine process. Fairly slow though. Geological forces stretch and thin the plate. If it's stretched and thinned enough the underlying mantle that fills the space melts and erupts, creating a new oceanic spreading ridge.",
"I'm not sure which \"tip of Africa\" you are referring to. The East African Rift Valley is active, the African plate is in the process of splitting in two there, and expected to complete the split in about 10 million years."
] |
[
"Besides the mechanism cantab mentioned, you get oceanic plates breaking apart when subducting under continentals. Like on the North American west coast, where you'll find several small plates that are thought to be remnants of old plates that have been pushed under America. Same probably goes for the mess that is the Philippines. ",
"See here"
] |
[
"Yes indeed. It’s called rifting. The opening of the Atlantic, known as the ‘Atlantic rifting’ about 200 million years ago is one of the best known examples. The fossil record of the Atlantic rifting is what gave rise to Wegner’s theory of plate tectonics."
] |
[
"So when I close my eyes, I don't 'see' anything, but I still see something black. Do blind people also see something black?"
] |
[
false
] | null |
[
"IIRC from an article I read once, people born blind never develop the visual cortex so they literally have no concept of vision. It would be like a Dolphin asking us what we perceive with our lack of Sonar.",
"If you lose your vision later in life then supposedly you see \"black\" "
] |
[
"I remember on an AMA a long time ago that someone said if you were born blind, it was like seeing out of your elbow. You just don't."
] |
[
"I'm deaf. There's no such thing as silence for me."
] |
[
"How much pressure is necessary to form a bruise?"
] |
[
false
] |
Is there any typical value? What would be your approach to this kind of problem? Edit: Yes, about human bruising. How about approximating a fall on a knee/elbow?
|
[
"There are way too many variables to be able to say, \"This amount will bruise.\" When we're in school we learn all about platelets' function, which is clotting blood. That is such an incredibly simplified version.",
"The coagulation cascade",
" is a complicated process in which each step's functionality has a certain baseline, but there is variation. This variation depends on diet, overall health, medications and herbal supplements, and actual functional disorders. So, if one of the steps is a little off you may bruise more than average or less than average. ",
"Sorry there's no real cut and dry answer! "
] |
[
"I don't know about people, but for fruit the \"bruise threshold\" is measured in how high you need to drop it from to bruise it. According to ",
"this",
", it's about 2 cm."
] |
[
"Look a bruise is just internal bleeding, this will depend on what kind of tissue it is affecting, what it is being hit with and what the properties of that area, and the person who it belongs to"
] |
[
"What amount of impact energy did medieval siege weapons reach?"
] |
[
false
] |
I am thinking about battering rams (logs suspended from frames, not the ones that were carried), trebuchets, catapults, ballistas, and so on. I've been searching the web for a bit, but there seems to be no real information on this...
|
[
"Using these numbers: ",
"http://en.wikipedia.org/wiki/Trebuchet",
"In 1421 the future Charles VII of France commissioned a trebuchet (coyllar) that could shoot a stone of ",
", while in 1188 at Ashyun, rocks up to 1,500 kg were used. Average mass of the projectiles was probably around 50–100 kg, with a range of ca ",
".",
"Calculating speed from a 45 degree trajectory reaching 300m:",
"http://www.wolframalpha.com/input/?i=trajectory+distance+traveled+300m+initial+speed",
"Calculate kinetic energy using that speed and mass of 800kg:",
"http://www.wolframalpha.com/input/?i=kinetic+energy+54.24+m%2Fs+800kg",
"We get about ~1.1 MJ (about the explosive energy of a stick of dynamite).",
"EDIT: Arrg 2 late and almost exactly the same answer."
] |
[
"Lets look at the trebuchet (",
"http://en.wikipedia.org/wiki/Trebuchet",
") as an example that should provide one of the higher energies. Wiki says: ",
"Average mass of the projectiles was probably around 50–100 kg, with a range of ca. 300 meters.",
"Let us make the assumption for simplicity that there is no friction and the trebuchet is at ground-level, and firing at the ideal angle of 45°. We can then compute the initial velocity v0 = sqrt(g * R) = 54.25 m/s. Using the mass of 100 kg, this gives us a momentum of p = 5425 kg*m/s, and thus, E = p²/2m = 147,2 kJ. \nOf course, the Energy probably was a little lower than that, due to friction and everything. Also, Wiki says",
"in 1188 at Ashyun, rocks up to 1,500 kg were used.",
"Assuming they still went 300 meters far (unlikely), we suddenly have an impact energy of 2.207 MJ! ",
"What about today? ",
"The record-holder in that contest for trebuchets is the Yankee Siege II, which at the 2011 WCPC Championship tossed a pumpkin 2,326.6 feet (709.1 m). The 51-foot-tall (16 m), 55,000-pound (25,000 kg) trebuchet flings the standard 8–10-pound (3.6–4.5 kg) pumpkins,[19] specified for all entries in the WCPC competition.",
"Disregarding the height of the trebuchet (it should still only make slight changes to the angle and such and not influence our results greatly), this will result in impact energies of a whopping 15.7 kJ! Somehow, the frenchmen did that a lot better ;)",
"I didnt calculate any other siege weapons, but I assume the trebuchet should be the most powerful. Hope this helps =)"
] |
[
"For comparison, a modern hand grenade (M67) has a yield of ~750 kJ, equivalent to a large (but not the largest) trebuchet.",
"Edit: The trebuchet would still be much more effective for destroying walls than the M67 grenade. The grenade is a weapon designed to throw shards of metal in all directions, while a trebuchet projectile concentrates the energy at a point, and is very directional."
] |
[
"If our ears locate the direction which a sound comes from by the time lag between our two ears, how does it determine if it's in front or behind of us?"
] |
[
false
] | null |
[
"Observe your reaction next time you hear a sound whose source is not visible or immediately apparent. You’ll notice that — while you will likely have an initial impression of which side it comes from — you will instinctively react by turning/angling your head to some degree, which is the process that really allows you to pinpoint the location. Quick bangs and other instantaneous sounds don’t allow for this process to play out, and are thus much more difficult to precisely locate without a visual cue."
] |
[
"The various shapes and indentations of the earlobe affects soundwaves in ways the brain already knows. By working backwards from the received sound, the brain can figure out which features of the earlobe the sound traversed"
] |
[
"It's a good question. ",
"When using stereo headphones, you certainly don't get any sense of \"front\" or \"back\", so how does this work in real life? The simple answer is, there is more to \"hearing\" than just the ears. Sound vibrations are also picked up by the skull itself, and this information transmitted to the brain. Because of this, we are also able to distinguish \"front\" and \"back\" point sources of sound.",
"https://www.imperial.ac.uk/news/153374/scientists-explain-more-detail-hear-bones/"
] |
[
"If a glass jar free falls and shatters on the floor, can any shards fly higher than the altitude from which the jar fell?"
] |
[
false
] | null |
[
"There's no physical law forbidding it, but the center of mass of the shards will never be higher than the center of mass of the original object at the drop point.*",
"*Assuming a regular system in which potential energy constitutes the entire available energy (e.g., no explosive chemical reactions, etc.)."
] |
[
"As a proof of the basic concept, see ",
"The Galilean Cannon",
"."
] |
[
"An individual shard can go higher, since the energy needed is much less than potential energy from the entire jar.",
"The collection of shards will not."
] |
[
"How have our bodies evolved to metabolize chemicals such as pharmaceutical drugs that would never be found in nature?"
] |
[
false
] | null |
[
"Well, it's not that we evolved to metabolize drugs but rather we design drugs that can be effectively metabolized and used by our specific physiology. ",
"Other chemicals that our bodies may come across are usually dealt with by nonspecific ligand receptors, meaning receptors that tend to recognize a class of molecules, rather than a specific one. "
] |
[
"I used to work in a toxicology lab, and there are a variety of reasons that we can be naturally resistant to non-natural compounds. Two big reasons are the ",
"Cytochrome P450",
" system which can ",
" a compound and the ",
"ABC Transporter system",
" which can ",
" a compound.",
"This nice image",
" shows how some cytochrome 450 families such as 3A4/5 in humans metabolize a large percentage of pharmaceuticals. These families have naturally evolved over time to defend us from natural compounds in nature, and by chance any one of them will have a substrate pocket that may fit your pharmaceutical. These proteins don't just have one substrate, they can accommodate a range of molecules of a certain characteristic.",
"The ABC transporter system is an ATP driven motor that spans the membrane, and its job in the case of detoxification is to pump a drug from inside the cell to the outside. Again these are a diverse family that has formed over time to deal with naturally occurring compounds. ",
"This cool page",
" allows you to search for terms such as drug and find the most common drug transporting transporters in a human."
] |
[
"We possess many enzymes for for detoxifying compounds, courtesy of our vegetarian ancestors. We can eat many things that would kill pure carnivores such as cats and dogs. Some animals, such as rats, possess an even more powerful set of detoxifying enzymes, and they can eat many things that would kill even us."
] |
[
"How much have we evolved as a species over the past 100, 200 or 500 years, in contrast to how much we have evolved over the past 200,000+ years?"
] |
[
false
] |
We've certainly changed over the past few hundred years. Per Wikipedia, our anatomically similar ancestors came into being 200,000 years ago while we reached full behavioral modernity about 50,000 years ago. Is the rate of our evolution changing, either slower or faster? Rather, are we evolving at an exponential rate? Cheers, folks.
|
[
"There is a whole lot of debate among anthropologists how much it's appropriate to apply evolutionary theory right now.",
"Some evolutionary-minded folks want to recode all of anthropology and history in evolutionary terms; they say everything's \"evolution\". Ideas, people, ethnicities, etc.",
"As for actual physical evolution - it's pretty hard to say on such short time scales. There's more intermixing of different previously-separate groups, that's for sure."
] |
[
"I've always pondered whether or not the fact that we now modify our environments to suit ourselves rather than vice versa, coupled with the fact that in a lot of places natural selection is essentially non-existent, would more or less mean that natural evolution wouldn't continue. I imagine that because of the amount of intermingling and lack of isolated gene pools would also make it harder for any mutation to take hold in the public at large."
] |
[
"Who adapts faster than humans? Nobody.",
"Bacteria."
] |
[
"How are Countries named in their non-native languages?"
] |
[
false
] |
Even in multi-lingual countries, how did they decide what the place should be called in the different languages? Where does the English name for Germany or Austria come from when their German-language names are vastly different in pronunciation and literal interpretation? Who took "Nippon" and said, "yeah, that's 'Japan', now."??
|
[
"For your specific examples: Germany was a \"region\" of many small kingdoms, duchies, counties, principalities, etc. long before it became a single country in the 1860s. The word \"Germany\" was based on what the Romans called part of the area ",
". Germany has different names in different languages, partly because different outside groups ended up referring to it using the names of different former constituent places or tribes, e.g. ",
" in French after the Germanic tribe known as the ",
". ",
"https://en.wikipedia.org/wiki/Names_of_Germany",
". ",
"This is an example of a country getting its name from specific real or historical places or groups within them. The informal English name \"Holland\" is also kind of an example of this. Another example is how English and many other languages use the name \"China\" (based on an ancient dynasty that controlled much of the modern country) while Russian uses the name ",
" (\"Cathay\") (based on a different not-as-ancient group that also controlled much of the modern country).",
"\"Austria\" comes from an attempt to render ",
" into Latin. Lots of country names come from this kind of process, trying to make the name easier to pronounce in the destination language -- think ",
" \"Spain\".",
"\"Japan\" seems to come from a combination of Portuguese explorers hearing Malay traders call it ",
" and Venetian explorers hearing Chinese people calling it ",
". It seems that these were how the kanji characters, which are read as ",
" in Japanese, were vocalized in some Chinese dialect. Same characters, different pronunciation.",
"A somewhat related example to this might be how we pronounce \"Mexico\" based on how the letter \"x\" is pronounced in English, even though the \"x\" represents a different sound in modern Spanish, and the whole thing is an approximation of the original Nahuatl name which sounds like "
] |
[
"For Japan in particular, you google \"etymology of Japan\", and you get this page ",
"https://en.wikipedia.org/wiki/Names_of_Japan",
"in summary, basically the Kanji Nippon is read as Re Ben, which sounds like Jepang to Malay and Indonesian, and the European first heard about this country from them, and so it ended up with Japan in English.",
"Many countries have their own unique history of how their name changes and spread and get mis-heard by other cultures."
] |
[
"As you say, ",
" is a Latinization of Old High German ",
", but that itself is likely a translation of Latin ",
"!",
"In regards to Germany being a region of many small principalities (the ",
"), there was no real question from the emergence of the Ottonians-on that \"Germany\" was a \"thing\". There has been no point in recent history where some state or organization representing \"Germany\" has not existed - the Kingdom of the East Franks (colloquially ",
") within the Empire, Napoleon's Rhine Confederation, the German Confederation (briefly the ",
", the North German Confederation, and finally the German Empire. Even during Roman times, tribal confederations existed which could be considered to constitute nascent ethnogenesis: the Franks, the (Old) Saxons, and the Alamanni in particular, if we're only counting West Germanic tribes. They certainly already recognized themselves as related, had terminology to refer to themselves (Þeodiskaz/Þeodisca in Common Germanic and West Germanic) and for foreigners (Walhaz/Walhs). ",
"Most of the foreign names are ",
" than the ethnogenesis of Germany in the Early Middle Ages. So, I would say that the ",
" doesn't have much impact in this case - when most foreign names were adopted was well before that situation, back when ",
" was still largely tribal."
] |
[
"What is the biological reasoning behind humans gaining pleasure from adrenaline-inducing activities like amusement parks and skydiving while other events like car crashes and impending danger do not give the same pleasure? Do other species of animals gain the same pleasure?"
] |
[
false
] |
[deleted]
|
[
"It's exactly the same feeling except there's safety measures built into things like extreme sports and amusement parks which are missing from actual danger. They're designed to give the experience of danger, and the reward for surviving the danger, without actually putting yourself in harms way.",
"The reason people don't want to replicate a car crash for the thrill is just because it's too risky, the danger is real."
] |
[
"It'll vary, if they trust the person enough and have the personality for it they could enjoy it."
] |
[
"So when people take animals sky-diving, those animals are actually terrified?"
] |
[
"Are quantum entangled particles subject to time dilation?"
] |
[
false
] |
Let's suppose you have two twin astronauts as described in the Twin Paradox thought experiment. Each of them is given one particle of a quantum entangled pair for safekeeping. One twin remains on Earth, while the other flies away for several years traveling at nearly the speed of light. When he returns to Earth he is younger than his brother. The entangled particles have experienced the same effect as the brothers have, and are brought back together. Are the particles both still entangled in the same time reference to one another? If you collapsed the wave function of one particle would the other "end" collapse at the same time, or would it seem to happen with some sort of delay in relation to the time dilation effect that had been imposed?
|
[
"Just going to copy my post below:",
"This the exact opposite of what entanglement is. You're just describing classical information, do you think there would be all this fuss over quantum mechanics if a quantum state was just classical information (left and right handed gloves placed in separate boxes)? What you're describing is a local hidden variable theory, which is precisely something quantum mechanics isn't.\nQuantum entanglement is a quantitatively subtle effect, which is a big reason that it is so difficult to convey to layman, see for example the difference in predictions for a spin singlet between classical and quantum mechanics:\n",
"https://upload.wikimedia.org/wikipedia/commons/e/e2/Bell.svg",
"\nIn fact the two theories coincide when the detectors are at \"round\" angles like 0, 90, 180, 270 and at other angles the difference is non-zero but not huge. However, you can see that the whole point is that there IS a difference between quantum mechanics and classical information (gloves in a box).",
"Specifically, the difference between the blue and red lines IS a correlation. That's the whole point, they're correlated in some NON-classical way, that's why quantum mechanics was invented, because the behaviour is non-classical."
] |
[
"Depends on your interpretation of QM. We've proved there aren't local hidden variables, but there are still non-local deterministic interpretations. Many-worlds, pilot waves, etc."
] |
[
"I take some issue with this statement.",
"Nothing is \"collapsing\" but our ignorance of the actual state",
"Isn't it a core tenet of quantum mechanics that it is NOT deterministic? The particles are not in some defined/\"actual\" state that we don't know yet, they are genuinely probabilistic until observed or measured. I agree with your conclusion about OP's question, though."
] |
[
"What molecular properties make a substance a good or bad conductor of electricity?"
] |
[
false
] | null |
[
"It's related to the ",
"electron orbitals",
" of a given substance.",
"Metal atoms have D-Orbitals, which are large, easily polarized (Deformed), and well shielded from the nucleus. Because of this electrons can move fairly freely through metals while still being stabilized by the metal nuclei at the core.",
"Materials like graphene have a similar but distinct property: they have a large system of overlapping P orbitals (called a conjugated pi-bonding system) that allows electrons to flow in a similar fashion across the surface without disrupting the sigma bonds between the individual carbon atoms. This sort of conjugated pi system and the stabilizing effect it has on the ",
"band gap",
" is also often responsible for the color of substances.",
"Ionic liquids are different, electricity flows through these materials because individual ions actually migrate through the liquid carrying electrons and passing them off between each other. "
] |
[
"How do f-block metals fit into this then? Also, this seems to apply to pure substances only... are alloys not used as conductors? "
] |
[
"Metallic bonding",
". Metals are essentially nuclei awash in a sea of delocalized electrons. It is easy to make these electrons move (conduct)."
] |
[
"How did they discover that a photon was the smallest unit of light, and how did they fabricate an instrument that could shoot individual photons?"
] |
[
false
] | null |
[
"It really started with the \"Ultraviolet Catastrophe\": classical physics predicted that black bodies should emit light at all frequencies, with the intensity going up for higher-frequency light. However, around the ultraviolet range, the classical prediction broke down and didn't explain the black body spectra observed. Max Planck showed this could be explained by a quantized form of light - light energy being carried in individual \"packets\" of energy. Einstein would go on to propose the photon (although he did not give it its name) when he described the photoelectric effect, for which he won the Nobel Prize in Physics. In the photoelectric effect, light shines on a metal and electrons in that metal are ejected. Einstein noted that if photons were discrete particles, then the intensity of photons (number per area) should control the number of electrons being ejected, and the energy of the photons should determine if electrons are ejected at all. Specifically, if light below a certain frequency shines on a particular metal, no electrons would be ejected. These properties of the photoelectric effect were demonstrated and this was taken by the scientific community as proof that light must exist in discretized particles - the photon was discovered."
] |
[
"The catastrophe of it was that it was predicted that radiating bodies should radiate an infinite amount of energy, since they would emit radiation at all frequencies. Something red-hot, for example, has a peak at the wavelength of red light, but classical physics predicts that it will emit some infrared radition, some microwave radiation, some ultraviolet radiation, and so on - all at lower intensities, but when you add them all up you end up with an infinite total amount of radiation being emitted.",
"That's problematic, to say the least, but the discovery of the photon meant that light could only be emitted in packets, which sort of \"pixellates\" the emission spectrum and makes the total energy non-infinite."
] |
[
"Could you explain the UV catastrophe a bit more for the non scientifically literate?"
] |
[
"What kind of information can we obtain from mars with the new MSL cameras?"
] |
[
false
] |
As in the title, i would like to know what kind of scientific information we can obtain from using the MSL cameras and their new high definition panoramas. Will it just be simple geographic observations, or can maybe some 'hard science' be done to. Thanks.
|
[
"If you don't get your answer here, try ",
"/r/geology",
"."
] |
[
"What makes you say geographic observations aren't hard science? "
] |
[
"I knew i would get this comment. I know you can get hard geographic observations and geology is hard science, but i was wondering whether this could be obtained from photos alone, or could you only make general/sweeping statements about the geology."
] |
[
"How did DNA, such an extremely efficient coding system for the development and functioning of all organisms, just happen to come about?"
] |
[
false
] |
It seems like its too perfect for it to just happen by chance. The universe is about 13 billion years old. First life on earth is 4 billion years ago. So in just 9 billion years, random chemicals mixing around just happened to come together to create such a beautiful mechanism for life? I'm just wondering how something so complex and the basis for all life can just happen? Can someone explain how it originated?
|
[
"Not only is 9 billion years a huge amount of time for humans, who experience time on the orders of seconds/hours/decades, but for individual atoms and molecules, it's significantly longer.",
"The typical vibrational frequency of an atom is 10",
" times per second. And in a crystal lattice, the amount of times an atom jumps spots in the crystal is around 10",
" times per second. Near the melting temperature in a solid, an atom (~10",
" meters) can travel ",
" in total distance over the course of a few hours. Mind-boggling.",
"9 billion years is 10",
" seconds. And each atom is moving around roughly 10",
" times ",
". And there are 10",
" atoms in ",
" (12 measly grams) of carbon.",
"The numbers that come out of something like this are entirely unfathomable to a human brain."
] |
[
"So in just 9 billion years, random chemicals mixing around just happened to come together to create such a beautiful mechanism for life?",
"I don't think you comprehend just how long 9 billion years is. I don't think any human really can.",
"Can someone explain how it originated?",
"We don't know. There are theories about panspermia, theories about deep sea vents, theories about clay crystals, etc.",
"Correct me if I'm wrong, but the most accepted proposed mechanism is that RNA came first. RNA can store genetic information but also act like a protein. So RNA covers both requirements for early life as we understand it (information and metabolism), which makes abiogenesis much more likely.",
"Evolution, rinse, and repeat for billions of years..."
] |
[
"The immense dimensions of time are so truly mind-boggling to me.",
"Now if all ",
", all of human history, all our wars and peaces, conquests and discoveries could happen in the past 10,000 years (a mere 500 generations), and all our evolution since the demise of the ",
" could happen in the past 65,000,000 years, and the immense changes that shaped us out of ",
" could happen in 1,000,000,000, then ",
" a few thousand atoms could arrange to reproduce their structures in the same amount of time, no?",
"Time is wide, and time is vast, and it knows nothing of the word \"improbability\"."
] |
[
"Do matter and antimatter always annihilate instantly on contact, or does the process have some kind of a 'half-life' like particle decay?"
] |
[
false
] | null |
[
"The latter is more correct. Consider, for example, positronium, which is an \"atom\" of an electron bound to a positron. It has a half-life of about 120 picoseconds."
] |
[
"Positronium can be excited into metastable states that last longer. It can also form a molecule with hydrogen, positronium hydride.",
"They are all examples of a higher energy quantum state decaying into a lower one. "
] |
[
"Thanks for the response! Do we know of any other matter-antimatter bound states that last longer, perhaps for timescales on the order of what humans can perceive?",
"Also, as an interested layman, I'm a bit curious if my intuition is correct in assuming that annihilation and particle decay are related in some way. Is there a fundamental relationship between the two, or is it just coincidence that both involve particles turning into different particles?"
] |
[
"Can you make a nuclear bomb with any element?"
] |
[
false
] |
Could you use an element like gold, or sodium, instead of uranium?
|
[
"No. There are a few basic requirements that a nuclear package should meet in order to be useful. First, you need nuclear reactions that release energy, and as much of it as possible. Second, you need this reaction to be as easy as possible to initiate; you don’t want a large energy barrier to overcome. In broad strokes, this already limits you to fission of very heavy nuclides, and fusion of very light nuclides. In the case of fission, you want to maximize the probability of each fission reaction occurring, so this further limits you to ",
" fuel. Fissile nuclides are defined by the fact that they can fission in the presence of neutrons of arbitrarily low energies. In other words, there is no energy threshold for neutron-induced fission. This generally implies that the probability of a neutron causing the nucleus to fission is proportional to 1/sqrt(E), and it’s very large in magnitude compared to other cases. In the case of fusion, you want to minimize the energy barrier required for the reaction to occur. The Coulomb barrier is proportional to Z",
"Z",
", where the Z’s are the atomic numbers of the target and projectile. So obviously the lowest Coulomb barrier will be for hydrogen on hydrogen reactions.",
"If you want to use fissile nuclides for a fission bomb, this limits you to a handful of heavy species. Engineering/practical constraints further limit you down to uranium-233, uranium-235, plutonium-239, and plutonium-241.",
"If you want to use hydrogen fusion for a thermonuclear weapon, you’re limited to deuterium and tritium.",
"For a sense of scale, the DD and DT fusion reactions used in thermonuclear weapons release about 10 MeV of energy per reaction, and neutron-induced fission of uranium-235 releases an average of 200 MeV per reaction (it’s an average because there are many possible exit channels).",
"So to summarize, ",
", you can’t just use whatever you want if you want your bomb to actually work, and satisfy a few basic requirements desirable for a weapon."
] |
[
"There are other fissile nuclides. ",
"Here",
" is a chart.",
"Lower down in that article, under “Nuclear fuel”, they mention the criteria I had above, as well as some of the more detailed ones that I swept into the catch-all of “engineering problems”.",
"So you can get a sense of how many fissile nuclides exist, and why many of them are ruled out for use in weapons and reactors."
] |
[
"If you want to use fissile nuclides for a fission bomb, this limits you to a handful of heavy species. Engineering/practical constraints further limit you down to uranium-233, uranium-235, plutonium-239, and plutonium-241.",
"Since we are talking about an hypothetical situation, can we relax those constraints?",
"\nSuppose I could magically obtain a sizeable supply of some heavy elements like the ones with atomic number from 95 to 103, do isotopes of those elements that could be used in a bomb exist?"
] |
[
"I'm curious about the evolution of viruses. There are DNA and RNA viruses, but what are the advantages of having one on the other nucleic acid? Did the DNA viruses evolve from the RNA viruses or did they both evolve separately? Are DNA viruses more stable outside a host?"
] |
[
false
] | null |
[
"Simply said, RNA is more reactive and suitable for being used as a catalytically active entity. But a cost for this inherent excitedness is instability (though stable compounds are not necessarily non-reactive, e.g. ketones). This means that RNA is prone to errors, therefore mutations, which alter its function.",
"\"In RNA viruses, high error rates have led to the quasispecies concept in which collective populations are the basis of evolution. These populations provide viruses with high capacities for adaptation.\" (",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7149781/",
")",
"But this is not a rule, as the next sentence is: \"Yet some RNA viruses show remarkable evolutionary stability.\" This can be achieved by, for example, correcting mechanisms that slow down the rate of mutations such as the ones SARS-CoV-2 has.",
"Other viruses embrace their high rate of mutation and recombination (influenza).",
"The double helical structure of DNA gives the molecule remarkable stability, but strips it off its catalytic abilities. DNA viruses therefore tend to be more stable.",
"As for the question of the origin of viruses, they may have actually evolved several times. Some say they existed before cellular life, while others think they may have originated from cells stripping down their genomes and assuming a parasitic lifestyle. Since RNA most likely existed before DNA, RNA viruses may have evolved first, before true cellular life. DNA viruses then may have originated from bacterial or other cells, in the several origins model. (",
"https://www.nature.com/scitable/topicpage/the-origins-of-viruses-14398218/#:~:text=Viruses%20may%20have%20arisen%20from,the%20evolution%20of%2C%20cellular%20life.",
")",
"Hope this answers your question!",
"EDIT: typos"
] |
[
"To expand on why the replication error rate is lower than expected for an RNA virus...",
"SARS-CoV2 has an RNA polymerase with 3'->5' exonuclease activity which provides a rudimentary proofreading function during RNA genome replication. ",
"This is one of the reasons despite having a ssRNA genome which typically would lead a virus to have a relatively high mutation rate, SARS-CoV2 has a more stable genome with a more moderate mutation rate akin to some of the less meta-stable DNA viruses."
] |
[
"To what he said, it is likely viruses evolved in both ways, some from the ground up, while others were stripped down."
] |
[
"What factors contribute to the sex of a baby?"
] |
[
false
] |
There is so much anecdotal shit if you Google this, and there's only one previous post in AskScience that I can find (with only one comment). It seems that the main gist is that X-carrying sperm differ from Y-carrying sperm cells. This is the crux of the issue: are they different, and if so, how are they different? I understand the chromosomal thing. The question is motivated by whether or not the parents can influence the sex of their baby.
|
[
"The short answer is no. The long answer is that we have discovered several factors that influence sex on a population-wide scale. For example, during and after wartime, male babies are slightly more likely. ",
"Source",
" Also, women who are chronically stressed or in poor health are slightly more likely to give birth to girls. ",
"Source",
"."
] |
[
"I'd like to know if there are statistically significant steps you can take to influence the gender that you conceive? "
] |
[
"It could be possible, but not through anything like \"eat more cabbage\".",
"If you isolate the x or y chromosome from a male sperm cell. Female cells are always XX while male cells are XY, re-productive cells are half cells, so in a woman's case it's either X1 or X2 and in a man's case X1 or Y1. But isolating a chromosome within a sperm cell is incredibly difficult if not impossible. For clarification: an egg-cell is roughly 1000x the size of a sperm-cell.",
"Statistically you cannot improve the odds of getting one over the other. It all comes down to randomness. Which is good for the human nature as a whole."
] |
[
"I just heard that if you are near a nuclear explosion but outside of the hotzone where everything is destroyed the best thing to do is to get to a basement or garage and stay there for 7 hours-2 days. I understand the basement, but what is it that makes a garage any safer than inside a house?"
] |
[
false
] |
Aren't the walls just as thin? Many garages have windows, and it is not unheard of for someone to need to go outside to get from the house to the garage.
|
[
"You don't want a ventilation system bringing in outside air."
] |
[
"Are you certain they weren't specifically talking about ",
" garages? That would seem much more reasonable."
] |
[
"I don't think a ventilation system would be a factor in most cases. Most likely there would be massive power outages in the surrounding areas."
] |
[
"Do atoms or any other minor particle have a unique \"fingerprint\" or unique measure of information that makes them distinguishable from their similar others?"
] |
[
false
] |
[deleted]
|
[
"So to start at the largest scale, we can tell atoms from different elements / isotopes apart because they have different number of protons and neutrons in the nucleus. ",
"Fundamental particles are indistinguishable from other particles of the same flavour. (I can tell the difference between an 'up' quark and a 'down' quark because they have different charges). If I have a box full of electrons, I can't distinguish between them.",
"A really important consequence is ",
"Pauli's Exclusion Principle",
", which states that two identical fermions (particles with 1/2 integer spin - e.g electrons) can't occupy the same state within a system. This means electrons have to fill up different orbitals, sub-shells, shells in the atom and leads to all of the complexity of chemistry.",
"Pauli's exclusion principle can also be stated that if I swap two fermions, the resulting wavefunction must be anti-symmetric (this means it's the same with a negative sign in front).",
"In this case, the electrons can be in different states - so I can talk about the electron in the '1s state' for example - but the electrons themselves are indistinguishable."
] |
[
"No - unless they belong to a different element, have a different number of electrons or similar things. And, surprisingly, we can test this exactly.",
"Particles are either fermions or bosons, and follow the Fermi-Dirac or Bose-Einstein statistics, respectively. These statistics tell us how likely it is to find particles in different energy levels. If you have particles that differ in any way, then every particle type will \"follow its own statistics\". If all particles are ",
" the same, then they will follow the statistics together.",
"All tests so far confirm that multiple electrons, multiple atoms, multiple photons, and all the other stuff tested, follow the statistics together. For fermions, this means you'll never find two fermions in the same state, for example. For bosons, it means you are more likely to find many bosons in the same state than you would expect from the behavior of individual bosons.",
"We know there is no fingerprint. No matter how precisely we will be able to look in the future: There cannot be any fingerprint."
] |
[
"Great explanation thank you for your time and your answer"
] |
[
"If curlier hair retains heat better than straight hair, how come Africans tend to have curly hair, while most Europeans have straight hair?"
] |
[
false
] |
My only guess is that curly hair not only helps retain body heat, but it also helps deflect heat from the sun, while straight hair helps to absorb heat from the sun.
|
[
"People with darker skin have coarser hair because of the higher amount of ",
"melanin",
" in their hair. It isn't retaining the heat - the melanin is protecting the body from the UV rays of the sun. Also check out ",
"this",
" link from wikipedia."
] |
[
"Curly hair also retains moisture really well."
] |
[
"Curly hair and more air space. air is the only insulator. \nall that crap in your roof is just little pockets of air.\nwhy is wool so warm? little pockets of air.",
"Curly hair doesn't just retain heat it keeps it out too. ",
"In Africa the climate is kept away from the scalp via curly hair.\nIn Europe the warmth of the sun is allowed to penetrate "
] |
[
"Why do proteins misfold?"
] |
[
false
] | null |
[
"Proteins are dynamic structures which are jiggling all the time. Most proteins execute some sort of dynamic function as well, such as enzymes that require them to be able to change shape in response to some stimulus. This means that the energy landscape around a \"native\" conformation is not too steep and the protein is able to move from one conformation to another in response to some energy change such as substrate binding, pH change, presence of electric field, etc. This combined means that any functional protein is usually not in the lowest possible energy state.",
"So most structures are somewhat kinetically trapped. That is, some of the domains will fold into relatively stable structures first, and then the rest of the protein will take a shape. If you were to completely unfold and allow the protein to fold again, it would probably take a different structure, what we would call misfolding, but the activation energy for this is too high so the protein remains in a stable but not lowest energy state. Of course, statistically, high energy events happen, and some proteins will unfold spontaneously. The rate will depend on the actual energy landscape and the environment. For things like prions, the misfolded, lowest energy state actually acts like a nucleation site and provides an environment that allows for the natively folded protein to misfold easier, thus creating a feedback loop."
] |
[
"There is roughly a continuous distribution of energies within a system. Some protein will have higher internal energy at some point from a random collision or an errant chemical reaction, or temporary destabilization of water structure due to crowding... just random disturbances. The misfolding can be irreversible or could even be in equilibrium with a native state. A good analogy (although not exactly the same) is a phase change between liquid and gas, so just like water can evaporate at different rates depending on temperature and pressure, so will proteins unfold and refold at certain rates depending on chemical potential."
] |
[
"Can you elaborate on what a “high energy event” is?"
] |
[
"How does carbon-dating date the age of a man-made object?"
] |
[
false
] |
[deleted]
|
[
"As other posters have mentioned you can only carbon date organic matter (or matter that was formerly living). It can not be used to date marble. ",
"It relies on the basic assumption that the ratio of radioactive carbon (C14) to normal carbon (C12) in the atmosphere has been relatively constant in the past. ",
"When a plant grows it incorporates C14 (radioactive) and C12 (normal) at the same ratio that they exist in the atmosphere. For instance if there is 1 C14 for every 1,000 C12 (a gross overestimate) we would expect to find 1 C14 for every 1000 C12 in a living plant. (The actual ratio is 1 per 1 trillion)",
"Now, the thing about C14 is that it decays and has a specific half-life of 5,730 years. So that means if we found a dead rat in a cave and found that it had 1 C14 for every 2,000 C12, we could approximate the age of the rat to be about 5,730 years. ",
"Basically, every 5,730 years we expect the ratio of C14/C12 to halve. ",
"60,000 years represents the upper limit at which there will usually still be enough C14 present in a sample to give us an accurate date. At dates older than this, too much C14 has decayed to allow us to say with any certainity. The 1950s is considered the upper limit because the testing of nuclear and atomic bombs in the 1950s, 60s, and 70s massively increased the amounts of C14 in the air and spread it around causing local hot spots of C14, making it difficult to get a reliable trace of what is going on because of the sudden upswing.",
"Carbon 14 is produced when electromagnetic waves from the sun collide with nitrogen atoms causing them to give off a proton and become C14 atoms. This production is relatively constant and exists in a steady state with the elimination of C14 by radioactive decay. ",
"There are fluctuations in the rates of C14 production and it does vary by area, but these are usually taken into account using calibration curves. ",
"Carbon-14 acts just like regularly carbon and importantly can form carbon dioxide. This is taken up by plants during photosynthesis where it is converted into glucose and potentially other sugars and used to help build the plant. ",
"Animals get their carbon by eating these plants and incorporate carbon 14 into their muscles, bones, etc. to help them grow. ",
"Medically, this information has been used to demonstrate that most parts of the brain do not form new cells. Most people who were born during the early 1950s have a high level of radioactive carbon-14 in their brain cells, because of the nuclear testing. When these people die and donate their brains to science we can take slices of their brain and check and see whether or not there are any cells which do not have a high level of C14. The short answer is there aren't. ",
"(Arguably neurogenesis does occur in the thalamus, olfactory bulb, and select regions of neuroepithelium, but that's a different question). "
] |
[
"You can't carbon-date a marble pillar; you use it to date formerly living things.",
"And yeah, if you took a piece of wood 40,000 years old, and during its history at age 20,000 years it was carved into a spoon, carbon-dating would tell you it was 40,000 years old not 20,000. But who goes around using 20,000 year old wood (at the time) to make spoons? Usually you kill a tree and use it pretty quickly. ",
"But, could someone have taken an old piece of wood and made a flute? Yeah, but if it's the flute I'm thinking about, it was a mammoth ivory flute found in a pile of Aurignacian shit, right? If all the shit around it is Aurignacian, and if the mammoth ivory dates to whatever age it is, then it's probably an old flute, not a forgery.",
"Especially if you look at the flute itself (though it was all cracked, iirc) and they can check whether the carving grooves match those that we see in butchered Aurignacian mammoths. "
] |
[
"Carbon dating requires knowledge of how much of the carbon isotope had to have been present at the time you wish to date. ",
"As for the pillar example, suppose ",
" a historian can confirm that the marble was always mined from a certain place just a year or so before the pillar is carved. ",
"Anywho, you need the information of the initial content of carbon-14. If that information exists, you're in business."
] |
[
"What is the difference between internet streams and television broadcasting? engineering/computing"
] |
[
false
] |
[deleted]
|
[
"Internet streams are unicast/multicast while television is broadcast",
"Thats one difference",
"Also, when you have cable TV, ALL the channels are being sent on that particular cable from your cable operator. Your TV just decodes the one you want to watch",
"In case of internet streams, an individual stream of data is flowing from the server to your device.",
"This stream of data is passing through many devices, and may face congestion,etc at any of them leading to stuttering,and other issues",
"why don't televisions get their programming through the internet?",
"Mainly because the infrastructure to deliver the amounts of data doesnt exist yet. However, IPTV is catching on which is not exactly the same but similar"
] |
[
"Cable is broadcast, not multicast"
] |
[
"Cable is broadcast, not multicast"
] |
[
"If stars in a galaxy increase in velocity the further they are from the center, why do galaxies have spirals? Wouldn't spiral arms indicate slower speeds as you approach the edges of a galaxy?"
] |
[
false
] |
I understand dark matter plays a role here, keeping the galaxy spinning as one like a dinner plate. Does this indicate the spirals form before enough dark matter appears?
|
[
"Despite normal intuition when looking at a face on picture of a spiral galaxy, the spirals aren't exactly what they would seem. They are not concentrations of stars as you might assume and they have little to do with the motion of the stars. They are in fact density waves with in the material of the galaxy, namely gas and and dust. The slightly higher concentrations of particulate matter lead to the formation of larger, brighter stars. This leads to the characteristic spiral, not the motion/velocity of the stars."
] |
[
"Clear and concise answer. Thank you for that.",
"I watched a few videos covering the density waves and it makes perfect sense to me now."
] |
[
"A side note: the galaxy does not spin as one. All stars in the outer disk have approximately the same rotational speed (this is a consequence of dark matter) but the outermost stars travel further. This means the inner stars of the galaxy have a shorter orbital period."
] |
[
"How close was the moon 2.5 billion years ago? What effect did it have?"
] |
[
false
] |
From what I gather, there was a small supercontinent called Ur during this time, and everything else was ocean. If I'm a human (with an oxygen tank, since this is just before the Great Oxygenation Event) standing on Ur, overlooking the ocean, what do I see? How big does the moon look? How large are the ocean's waves? (Assuming no snowball Earth, or after first snowball Earth) covers day length pretty well, but didn't get into lunar distance. mentions that the initial day length might have been 6 hours, with an orbit of only 25,000km. Would wave height be a cube factor of the distance? (2x closer = 8x higher waves?) If so, those numbers get big fast. Thanks for the help!
|
[
"Wave height is mostly determined by the winds. Tides are determined by the moon. There may be some secondary effects of tides on waves, but the most noticeable difference would be the tides.",
"Apart from that, the tidal influence also affects the not-quite-solid (especially back then) mantle of the Earth, causing more movement, friction, and geologic activity than there is now. "
] |
[
"Okay, thanks for clarifying tide vs waves. If the days are much shorter, the Earth is spinning much faster (since the moon is much closer). Would this rotation affect the Coriolis effect and increase average wind speed?",
"Great tidbit about the geologic activity, that makes sense. Thanks!"
] |
[
"This",
" is not quite what you are looking for but has a fascinating treatment some very strange stuff that was going on millions of years ago. There is a bonus speculation about how fast Usain Bolt would need to run across a planet to live in a perpetual sunrise. Hope this helps."
] |
[
"Why and how do spiral bands form in a hurricane?"
] |
[
false
] |
I understand that, as warm air rises and creates a low pressure zone, high pressure winds rush in, warm, begin to rise in a spinning motion (due to the fictitious Coriolis force and around a region called the eye), and then condense into clouds as they cool higher up in the sky. This cool air then sinks to repeat the process. But why and how do the spiral bands form? Why isn’t a hurricane just a big, uniform mass of clouds - why are there “gaps” (spiral bands) where cool air sinks down? Is it because this sinking air forces a gap between clouds, creating the bands?
|
[
"The clouds bands are found where there are bands of potential vorticity. Potential voritcity is an dynamical variable based on angular momentum and mass conservation that is used for studying atmospheric and ocean dynamics. The bands of potential vorticity spiral because of nonlinear Rossby wave propagation that results from instabilities in the hurricane. From the ground, we can see clouds converge due to inertia-gravity waves. At a much larger scales the rain is converging in the Rossby waves."
] |
[
"Yes, I understand that. But I’m asking about the formation of the spiral bands - the areas where cloud formation is the densest and rainfall is the heaviest"
] |
[
"Because the air and earth are revolving around the the axis of the earth, so angular momentum at a scale of a hurricane twists into the spiral shape you see, clockwise for Southern Hemisphere, counterclockwise for northern"
] |
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