title
list | over_18
list | post_content
stringlengths 0
9.37k
⌀ | C1
list | C2
list | C3
list |
|---|---|---|---|---|---|
[
"Could we create a computer program with all the known laws of the universe to reverse engineer what we don't already know?"
] |
[
false
] |
Could we create what is basically a 3D CAD program that had all the known laws of the universe and then ran experiments on it - such as accelerating particles close to the speed of light a la a mass hadron collider - and observing the difference between what happens in the program and what happens IRL? Would this be plausible at all, even if using the bleeding edge of computing hardware?
|
[
"What you asked is exactly what is done in almost all of physics. ",
"If any scientist tells you that some problem is \"an active area of research.\" It generally means that a new phenomenon is happening, a phenomenon where the theory (which is now calculated using computer simulations) breaks down and didn't predict what actually happened accurately. ",
"Also, it is worth mentioning, that we are not using 3D cad programs, or anything. We are writing our own programs, our own simulations that are broken down and distilled down to the fundamentals of each question at hand. Sometimes this is hard and computers arn't good enough to calculate what we would like to learn about, and this is why fields such as computational physics exist. ",
"Currently, simulations and theories have predicted and, actually require, a Higgs Boson for instance, but it has never been observed. So your question is exactly what is happening at the LHC, we are chasing after this difference. ",
"So as a whole, we are simulating things all the time, both real events and theoretical events, and comparing them to the known universe. When things diverge, new physics is formed. Also, when a theory predicted some experimental result never seen before, it helps solidify that theory as being more likely accurate / a better representation. ",
" This is by definition the scientific method. ",
"Guess -> Compute Consequences -> Compare to Nature",
". And we can compute the consequences both with a computer and simulations, or by hand as it was done in the past. This is the history of science at its core. "
] |
[
"To some extent this already happening. In a lot of branches of science where it is not practical to perform direct experiments we design virtual ones (i.e. computer models). ",
"For instance, I work with geological models which reproduce the behaviour of rivers and coasts in response to climate and sea level fluctuations. I'd love to be able to model each grain of sand as it is transported by the river. However, I am working on scales that make this impossible, both spatially (100's of km",
" ) and temporally (millions of years). So I make huge simplifications and use emperical equations which describe how large sediment bodies behave over time. A lot of my calculations are averaged: I calcualte what is happening on average on a area of 10's to 1000's of m",
" , and only do this once for every year or so.",
"So yes, we can use models to try to reproduce reality, and see where mismatches occur and learn from those. But each model is only applicable to a very limited area of interest. It would be great to combine everything in one model but that would be computaionally impossible. ",
"One interesting result which was found using computer models (outside of my field) was the idea of dark matter. Models were created of galaxies using all the visible matter in these galaxies. However these virtual galaxies did not behave as the real ones did. Scientists found that adding a bunch of invisible matter solved that difference."
] |
[
"If any scientist tells you that some problem is \"an active area of research.\" It generally means that a new phenomenon is happening, a phenomenon where the theory (which is now calculated using computer simulations) breaks down and didn't predict what actually happened accurately.",
"I wouldn't entirely agree with this. I think active research areas are more commonly situations when people are trying to determine the implications of current and trusted theories."
] |
[
"What happens to pharmaceutical medicine when they are past their expiration date?"
] |
[
false
] |
Does the chemical composition change to make it less effective? Or maybe toxic? Are these not stable compounds? Do environmental factors have an effect? How is the expiration date calculated?
|
[
"For completeness sake, light can also break down some compounds. This is why hydrogen peroxide usually is sold in a brown bottle, for example. "
] |
[
"Most pharmaceuticals are organic compounds so they tend to react with atmospheric oxygen and water over time. The chemical degradation is accelerated at higher temperatures and upon exposure to air and humidity (breaking the seal). For example, acetylsalicylic acid (aspirin) can break down to salicylic acid and acetic acid by reacting with water and undergoing hydrolysis. salicylic acid is actually the primary ingredient in wart removal creams as it is very good at dissolving keratin. So yes the medicines can become toxic and environmental effects play a major role. "
] |
[
"Expiration date is calculated by doing stability testing. At certain intervals and storage conditions, the drugs are tested to see if 95% or so of the active compound is still detectable in the sample. This stability testing also helps determine if the label claim for the expiration date is valid for all samples going forward."
] |
[
"Is it true that small animals cannot be hurt in a fall from any height?"
] |
[
false
] |
[deleted]
|
[
"In principle, yes. (In vacuum, no. But the animal would have other problems in vacuum anyway...)",
"The key here is the concept of terminal velocity - the falling velocity at which wind resistance and gravity cancel out. It seems the larger you are, the more wind you need to balance gravity*, resulting in a higher terminal velocity.",
"So I'm not sure about mice, but think of an ant...? They will survive any fall. They simply don't get fast enough.",
"Edit: *) The surface area and the cross-section area of a body scale quadratic with its radius (read: size in one dimension), while the weight goes cubic. In short: Bigger means more area in the wind, but ",
" weight. Smaller means the opposite: Less cross-section, but disproportionately less weight to carry."
] |
[
"I figure if a mouse can survive a 2.3 meter fall, which is what? 100x it's height or so, then it can survive a higher fall too.",
"~science~"
] |
[
"Coming from personal experience when I was 5 years old. It is not true for hamsters."
] |
[
"Why do women, on average, live longer than men?"
] |
[
false
] |
For example: Of the 69 supercentenarians on that list, only 5 are men. What are the reasons for women living longer?
|
[
"Part of is is lifestyle. Men traditionally participate in warfare/engage in non-state violence for frequently than women. Men are also more likely to hold a physical labor intensive or dangerous job that results in greater wear and tear or source of accidents. I'm sure some nutritional and genetic factors play a role as well, but I can not speak on them sufficiently."
] |
[
"FYI looking at outliers like that doesn't really give you a representation of the average. There's good census data like ",
"this",
" (pdf) that shows that the average life expectancy for for American women is about 5 years longer than that of men. ",
"The reasons are varied - behavior may be a part of it, in addition to things like ",
"cardiovascular disease",
" (pdf). I'm not sure that there's a single answer - it just comes down to a combination of physiologic factors and environmental ones. "
] |
[
"Men have shorter average lifespans due almost entirely to the effects of stress. When you control for stress factors, men and women have the same life expectancy. "
] |
[
"How does Fredkin gates bring computational energy cost to a zero?"
] |
[
false
] |
Also, Here in this video, what does Phil means when he says that it requires energy to raise information? Around 6 minute mark.
|
[
"The idea is that a reversible logic interaction won't in theory require energy input, because of conservation-of-energy. In a billiard-ball conservative logic gate, for example, the balls start off with their initial velocities and, under perfect conditions, carry those velocities to the output. If they collide then directions will be reversed but nothing lost (assuming perfect restitution / alignment / lack of friction etc). In a non-conservative logic gate, though, you're required to input energy to force the output into a certain state, replacing whatever state it happened to be in beforehand.",
"Take a look at this original Fredkin/Toffoli paper on the subject, section 5 (nondissipative computation): ",
"https://cqi.inf.usi.ch/qic/82_Fredkin.pdf",
"Edit: and saying \"information\" is specifically framing computation as a war between known states you care about (like 1s and 0s) and random outside influences that would disrupt it. The non-conservative gates, by forcing their outputs into a known state, can be certain that their desired signal state is well-preserved, at the cost of having to \"dissipate randomness\" through heat (this is the same thing that happens in the maxwell's daemon situation, with the daemon having to \"reset its memory\" to overwrite previous unwanted states). In a conservative gate you just assume the output will still maintain the information you put in, rather than forcing it to. This requires no energy expense, but it also means that random outside influences (like the friction etc mentioned above) can build up over time and successive gates as signal error and eventually make your signal worthless, coming out the other end more random than known state.",
"In the paper they talk about using massive redundancy for error checking (do the same operations in 5 different circuits and hope you get the right answer from most of them), or you could introduce a bit of signal correction here and there to force things back into a known state, using energy like the destructive gates do.",
"These added issues, coupled with reversible circuits having to be more complex than non-reversible even in the ideal case, mean that we don't really use them for now except in quantum computing, where it's a requirement because quantum interactions are all necessarily reversible (conservation of quantum information)."
] |
[
"Thank you for taking time to write this reply."
] |
[
"I think that \"raise\" is a mishearing of \"erase\". The fundamental cost of computation is that of erasure. Nature did a piece on what was the fastest computer possible, which resulted in a roughly 1 kg red hot sphere, heated by the energy cost of erasure, a small sphere due to the time required to communicate. The cross sectional area of connections would feature too. This fact somewhat takes the wind out of the sails of the \"we live in a simulation\" fantasy: it would be a very hot simulation indeed. ",
"The CSWAP or hobbit-sounding Fredkin gate is a universal, meaning that, like the NAND gate, any logical function can be constructed from combinations of it. CSWAP gates can be run backwards, performing inverse logic, but te entities constructed from them of course cannot. The quantum qubit implementation of a CSWAP gate opens the way to conventional gate construction and thus - maybe - programmability."
] |
[
"How do oil based lubes break condoms down?"
] |
[
false
] |
Title
|
[
"If you don't mind, could you go into more detail on the non polar interaction? I find these kinds of things really interesting"
] |
[
"If you don't mind, could you go into more detail on the non polar interaction? I find these kinds of things really interesting"
] |
[
"A good picture of non-polar interactions is to think about instantaneous dipoles attracting one another (",
"https://en.wikipedia.org/wiki/Van_der_Waals_force",
") and the competition between the forces. ",
"The picture of dissolution is solvent-solute (oil-latex) interactions overcoming the solute-solute (latex-latex) interactions. ",
"Polar molecules attract nonpolar molecules because they can induce charges (like ",
"here",
"), but they attract other polar molecules even more strongly than the nonpolar molecules. This means polar molecules form a posse of polar molecules, preferring to attract polar molecules over nonpolar molecules. So a polar solvent like water won't dissolve latex very much since the polar solvent prefers to clump up with itself.",
"On the other hand, nonpolar molecules aren't too selective about who they interact with. So the nonpolar-nonpolar interactions (oil-oil, oil-latex, latex-latex) all compete with each other. A homogeneous solution is more disordered <=> entropically favored, so you can imagine dissolution eventually winning out in the end by a thermodynamic argument."
] |
[
"If someone were to replace their bed with a hammock, would they be at risk for any health problems?"
] |
[
false
] |
[deleted]
|
[
"There are studies done on researching how hammocks affect sleep. Without researching the details of it, it seems to be a positive effect. You would have to read or ask about the individual studies to check the integrity.",
"Here's an article based on one such study",
".",
"As far as health effects, I'm not aware of any and I'm not aware of ",
" studies that demonstrated or tested health effects.",
"The only minor ones I can think of (",
", but it's pretty much common sense):",
"There's not really anything that can happen to any organ system (neurological, cardiovascular, etc.) that would be more likely to occur in a hammock rather than a bed or floor.",
"That's about as scientific as I'm able to get on the topic of hammocks..."
] |
[
"I also thought of sailors, and then it occurred to me that this topic would be a great example of how to manipulate data to imply causation that isn't there: \"Hammock users ten times more likely to get scurvy, study shows.\""
] |
[
"Every sailor on every naval vessel prior to the 20th century slept in a hammock. It was not at all unusual for the largest class of three masted warship to have as many as 800 men aboard, all sleeping in hammocks. Even in port between voyages they slept aboard the anchored ship rather than sleeping in barracks on shore. Back then a life in the navy was literally a lifetime, with crew members joining before they were twenty and staying in service well past their forties, sleeping in hammocks all the while. I have read of many seagoing medical issues but I have never heard mention of health issues arising from hammock use."
] |
[
"Our moon orbits around the Earth, the Earth around the Sun, and our Sun orbits the Milky Way. Is there a central object that our galaxy orbits around? If so, does that object orbit around anything else?"
] |
[
false
] | null |
[
"The Milky Way is part of the Local Group of galaxies. Andromeda (aka M31) and the Milky Way are the two biggest galaxies in it and the center of mass lies in between them. We are not orbiting it per se, but are more on a collision course with Andromeda and will collide in 300,000,000 years or so. ",
"source",
" (pdf). ",
"Edit: M31 not M33",
"Edit edit: more info:",
"The Local Group is part of the Virgo Supercluster and lies on its outskirts. The majority of the mass is in the Vancetti and Virgo clusters. We are currently moving away from the center of the Supercluster, but will probably be pulled into the Virgo cluster one day. ",
"source"
] |
[
"The probability of stuff like stars, planets, etc actually colliding in this galaxy-galaxy collision is probably really low, right? I'm thinking this because I imagine that empty space makes up the overwhelming majority of the volume of a galaxy."
] |
[
"The chance of a direct collision is very low. However, there will be significant effects due to gravity. The various stars and black holes in the two galaxies will disrupt things as they pass by each other. ",
"More info here",
". Overly dramatic ",
"simulated video",
" of what crash might look like. "
] |
[
"How does methanol damage the optic nerve and cause blindness?"
] |
[
false
] | null |
[
"Methanol is metabolized by alcohol dehydrogenase to formaldehyde and formate, the latter of which causes optic neuritis and, subsequently, blindness. Formate is toxic to mitochondria via its inhibition of cytochrome oxidase, as described ",
"here",
". This is the same mechanism as with cyanide and carbon monoxide. The result is that cellular respiration fails and the cells die."
] |
[
"Do non-lethal doses of cyanide and carbon monoxide also cause blindness?"
] |
[
"Yes, in both cases. I've included some resources below.",
"Quattrocolo G, Leotta D, Appendino L, Tarenzi L, Duca S. A case of cortical blindness due to carbon monoxide poisoning. Ital J Neurol Sci 1987;8:57–8.",
"Katafuchi Y, Nishimi T, Matsuishi T, Kimura Y, Otaki E, Yamashita Y. Cortical blindness in acute carbon monoxide poisoning. Brain Dev 1985;7:516–9.",
"http://emedicine.medscape.com/article/814287-overview"
] |
[
"How do we know which strain of influenza to make the annual flu vaccine for?"
] |
[
false
] |
Viruses constantly change genetically so how do we know that the flu vaccine for 2015-2016 will protect us from the flu virus that will be circulating during flu season?
|
[
"We use a variety of heuristics, including information about strains circulating previous year in the same hemisphere, strains circulating six months prior in the opposite hemisphere and notable emergent strains."
] |
[
"This answer requires some context. Most flu vaccines now target two proteins that are on the viral capsid of the flu virons; Hemagglutinin and neuraminidase. When you see a flu named H[x]N[y], it's catagorized by the form of these two antigens. Hemagglutinin aids in the entry of a virus into a cell, and neuraminidase it's exit. They are both the target of many vaccines and other drug stratagems. ",
"Now, if the antigen in questions mutation is so minor that the folding structure of the protein is essentially the same, the body will still recognise it! (Albeit perhaps with less efficacy) But if the change is major enough (but not so much that the function of the protein is impaired enough that the virus fails anyway) we need a new vaccine to immunization against it.",
"Expanding our view, medicine tries to target vaccines with antigens thay are stable when it can-- some viral proteins are so vital that changes to them are almost certainly going to cause the virus to be in viable. We call such traits ",
". Flu unfortunately is very good at mutating and the proteins we can easily target are also able to endure a fair amount of modification while remaining functional, and has interesting interactions with flu viruses of OTHER species that are so utterly different to the original human flu that the bodY has no way to deal with it. This is why people were fairly freaked out by avian and swine flu."
] |
[
"Interesting! Thanks for responding."
] |
[
"How do we MEASURE sidereal rotation period of planets¿?"
] |
[
false
] |
The period of the rotation in its axis. How do we know the period of jupiter, Saturn.... Is it via observation or simple physics? I haven't found anything related about HOW do we measure it. So I would really appreciate a detailed answer. Thanks.
|
[
"For all planets, we measure them through observation. Take a telescope, and you will see the rotation of Jupiter ",
"quite easily",
". You need a better telescope for further planets, or probes. From the observed rotation, it is trivial math to relate the observed movement and the observer movement to measure the sidereal rotation rate.",
"The only thing is that for rocky planets the rate of rotation has a clear definition, the gas giants' rotation is not uniform. As with the sun, the equator rotates faster than the poles, as you can see in the video, and, although there are models, we are not sure how the interior behaves. "
] |
[
"So, actually there's not a \"formula\" or \"ecuation\" to calculate the rate of ration?",
"Because I'm a (soon to be) physicist and I have found a ecuation that describes with high acurracy the rotation of all planets (with rocky planets it's perfect but with gas giants deviates a little).",
"So, my question is. What I have found has already been found or not? (That ecuation doesn't need much data from the planet, and it could be used also for exoplanets)"
] |
[
", actually there's not a \"formula\" or \"ecuation\" to calculate the rate of ration?",
"Because I'm a (soon to be) physicist and I have found a ecuation that describes with high acurracy the rotation of all planets (with rocky planets it's perfect but with gas giants deviates a little).",
"So, my question is. What I have found has already been found or not? (That ecuation doesn't need much data from the planet, and it could be used also for exoplanets)",
"It is very unlikely a formula that predicts the rate of rotation without lots of input exists. To our best understanding of the formation of solar systems, the rate of rotation of planets is decided by the history of impacts of the planet.",
"If what you have found is something that describes rotational motion, for solid planets especially, it is well known. ",
"I encourage you to play with formulas as much as you can, the important question is always : what is the input, or variable, and what is the output, or the results. In this case, what does your formula predict, and what does it need as inputs?"
] |
[
"Why do we freeze for a split second when something startles us or makes us jump?"
] |
[
false
] |
I notice when I'm absorbed in something or not expecting anything unusual something to happen and a loud noise or visual stimulus comes, I jump or "freeze" for a split second. Is there any neurological reason why this happens, I can't see any advantage from the evolutionary standpoint.
|
[
"The freezing response is mediated by a circuit involving the amygdala and a part of the brainstem, the periaqueductal gray. This circuit can coordinate the typical motor output: freezing, jumping, yelping, etc.",
"Anyone can come up with plausible-sounding evolutionary \"explanations,\" but this can easily spiral into just-so storytelling. ",
" The important part is the (comparative) neuroanatomy and behavior.",
"Edit: there was a removed comment that asked whether \"why\" questions are even answerable. Here is the response I was typing before it was removed:",
"We can answer \"little\" why: the mechanics of what happens, the steps, the neural substrates, the behavior, etc. ",
"It is much harder to answer the \"big\" why: what genetic, developmental, and environmental factors triggered the appearance, prevalence, and conservation of a particular neural circuit and behavior in a mammalian ancestor millions of years ago."
] |
[
"Without going too deeply into it, the mammalian freezing response is mediated by a downregulation of the activity of the vagus nerve and the feedback loop associated with its sensory function (80% of the vagal function is afferent) via the vagal nerve centers in the brainstem. Normally the nucleus ambiguus (NA) functions to control the upregulation of heart rate, breathing rate and respiratory sinus arrythmia in order to control the increase in oxygen availability and perfusion to the brain and muscles in what is called a focusing event. However, if the stress is high enough (and also in people who have developmental malformation, which can occur for a number of reasons) then the activity of the NA will subordinate to the neighboring (evolutionarily older, i.e. reptilian) structure from which the NA developed, called the DMNX (dorsal motor nucleus of Cranial Nerve X [that is, the Vagus nerve]). This causes the massive downregulation of activity in order to conserve energy and oxgen in preparation of an attack which cannot be countered (freezing/playing dead) that can be seen in many mammals. This decrease in metabolic activity is like a massive parasympathetic response (leading to accute bradycardia and a sensory feedback loop slowing the brain activity). It is also responsible for sudden cardiac arrest (scared to death) during massive stress. The reason mammals die during this type of event is another excellent example of evolution's \"imperfections\"... Mammals have much higher basal metabolic needs than the reptiles who originally evolved the DMNX. This is reminiscent of the origination and pathway of the vagus itself... It \"wanders\" very seemingly inefficiently around the body of mammals (see Dawkins example of this giraffes). For specifics about the nature of the freezing response, read about the Polyvagal Theory. This has been well understood for over 30 years."
] |
[
"There are times you can figure things out in more detail. I mean, it's pretty simple to show that a population of bacteria in a plate evolves the trait that provides resistance to antibiotics because they were exposed to low levels of that antibiotic. You can perform replicated experiments to show that the antibiotic selects for bacteria with the trait, and that selection by the antibiotic is sufficient to increase the frequency of bacteria with the resistant trait.",
"Basically, to show that Y selects for trait X, you have to show that under context Y organisms with trait X are at an advantage and (here's the tricky part) for historical things like what we are talking about you have to show that this held true way back when the trait first originated. Because some things are selected for one reason, and the secondary benefit only shows up later. ",
"For traits with complicated effects on fitness, it can also be hard to say what particular selection pressure was more important...does a lizard run fast because it helps it escape predators, or catch prey? How do you tell if running fast is helpful for both?"
] |
[
"Why do illnesses, diseases, germs, bacteria, etc... harm their hosts to death, in turn, killing themselves?"
] |
[
false
] |
I tried to make it as short and simple as possible, otherwise Id ramble forever and sound like an idiot...
|
[
"There are millions and millions of bacteria that don't kill their hosts or cause any pathogenic effects. ",
"Some of them do, and we obviously tend to notice them more because they'e make us ill and kill family members and what not. These are said to have 'virulence factors'. Usually, death doesn't give any advantage but illness typically does. If you cough and sneeze and vomit and have diarrhoea the bacteria is spread more. Sometimes, unfortunately, this kills you. As long as the bacteria manages to replicate a lot before the host dies, the bacteria will be okay. If there's a bacteria that kills a person the second it enters them, then it won't be very successful and die out.",
"Viruses can't really help causing damage since they need to take over the host cell to make some more, which typically causes damage."
] |
[
"Well, if you think about it, organisms who reproduce are the ones who pass on their genes, so any offspring will have the genes of someone who had qualities that helped them survive in time to reproduce.",
"If it produces a toxin that makes people cough a lot, it's going to pass itself around and have multiple replication sites, so it'll be well represented. If it starts killing, say, 20% of the people it infects, it doesn't matter, since it will have potentially set up another 10 infection sites in other people. it's genes will be passed on, and it will still 'exist'. Pathogens typically don't select for these fatal effects (apart from things like the fact that tuberculosis lives inside immune cells), it's just mutations that happen, and we notice, because it kills us."
] |
[
"The Earth isn't a host. We're using stuff we find on it. Are sheep living out of a host by eating grass from a field? Are birds living out of a host by eating worms from the ground and building nests in trees? If you classify the Earth as a living thing, every single form of life is like a vius living out of a host, but they aren't because the Earth isn't a living thing. People often say we're tampering with nature, but they forget that we ",
". ",
"The planet isn't alive. It's a giant rock floating through space. You can't kill the planet. "
] |
[
"Are there any poisons/toxins which, if taken separately, are fatal, but if taken simultaneously, are not?"
] |
[
false
] | null |
[
"Atropine and physostigmine, in the right combination.",
"Physostigmine causes dangerously high levels of the neurotransmitter acetylcholine. Atropine prevents cells from sensing acetylcholine.",
"Atropine is actually used as an antidote for acetylcholinesterase inhibitors (like physostigmine and sarin), but it is poisonous in its own right."
] |
[
"Yes for example if you are dying from an opiate overdose (coedine, heroin, etc) you are given Narcan. In simple terms it goes to every receptor that has bonded with the opiate and kicks it out. It's an incredibly painful sensation apparently. "
] |
[
"It essentially throws you into full blown opiate withdrawal which is very painful by itself."
] |
[
"Who was the first person who discovered that moon has reflected light?"
] |
[
false
] |
I already searched on google but couldn't find any source. Some say that it was leonardo da vinci, and some say that it was Anaxagoras.
|
[
"Anaxagoras of Clazomenae is probably the first ",
" person to suggest this, and Anaxagoras actually understood some aspects of the sun/moon/Earth relationship ",
" than Leonardo did almost 2,000 years later.",
"Anaxagoras proposed that the sun's glow came from its intense heat, like a red-hot stone (which is mostly correct) and that the moon reflected the sun's glow (correct), that solar eclipses were caused by the moon moving between the Earth and the sun (correct) and that lunar eclipses were caused by the Earth moving between the moon and the sun (correct). The big thing he got wrong was that he thought the sun actually ",
" a red-hot stone (instead of a white-hot ball of mostly hydrogen).",
"Anaxagoras' ideas were new enough to be ",
" among Athenians, ",
"who imprisoned him in 450 BCE",
" for teaching that the moon reflected sunlight, as well as for teaching that the sun was a hot physical object itself and not a god (as was the accepted Athenian belief at that time.) Later Greek thinkers would expand on (or independently discover) Anaxagoras' teachings, including Aristarchos of Samos who developed the first (known) heliocentric model, and also understood that the moon reflected the sun's light.",
"But I bring up the severe response to Anaxogoras' \"moon reflection\" idea as evidence that he was not simply repeating ideas he'd received from earlier Athenians whose writings have been lost to time. Anaxagoras' \"moon reflecting sunlight\" idea was seen as new and dangerous to the Athenians of his day.",
"EDIT: What Leonardo figured out in 1510 was not that the moon reflects light ",
", but rather that the moon also reflects light ",
". When the moon is in, say, its crescent phase, the dark part of the moon isn't 100% black...there's still a very faint glow. Leonardo figured out that ",
"sunlight could reflect off the Earth to the \"dark\" parts of the moon and then be reflected back to us again as \"earthshine\"",
"."
] |
[
"Super interesting read. I guess a hot stone is a decent guess when you consider the fact they have no idea what the fuck plasma even is."
] |
[
"If you don't get an answer here, you can also try ",
"/r/askhistorians",
", ",
"/r/historyofideas",
", ",
"/r/historyofscience",
", or ",
"/r/philosophyofscience"
] |
[
"Question regarding light and lasers"
] |
[
false
] |
I've obtained a recent extreme interest in physics lately. I've been learning a lot of random concepts online, and doing small experiments of my own. I decided to pull out my old 532 nm 35 mW green laser pointer today and toned down its intensity in order to more safely study some effects of optics. I found a pair of 3D glasses, and noticed that the red lens seemed to attenuate something like 99% of the beam; I could only make out a very faint beam on the other side when turning out the lights, even though the original beam was very strong. Much of it appears to be reflected, and then what's left is a yellowish-orange diffusion at the spot of incidence on the surface of the lens. If the wavelength of the laser beam is highly concentrated around 532 nm, how could the diffuse scattering seem to redshift a good 40-60 nm? My best guess is that green photons are being absorbed and then remitted at a slightly larger wavelength, with the extra energy being maintained as thermal motions. Thoughts? : My first guess was that there is an appreciable distribution to the left and right of 532 nm, which isn't easily perceived in tandem with the full brunt of the beam. But I disregarded that because I assumed that the distribution may be too small. Now that I think about it, it seems like it may very well be the case! Because if red light is able to go through easily, then almost red light would have more success than the green, but not quite enough to manage itself all the way though and therefore randomly bouncing around a bit. I could be completeley wrong, but it's fun to think about! : Never mind, the distribution seems to be, indeed, too small.
|
[
"Yup, that's probably correct. "
] |
[
"Yes, dyed plastic usually fluoresces quite well. Green -> red (longer wavelength, lower energy). There shouldn't be any blue you can see with a naked eye. There are processes that can do this, but they are very weak, nonlinear effects."
] |
[
"Your fist guess was correct there too; The linewidth of a diode laser beam is larger than for many other kinds of lasers, but it's still only on the order of a few nm, AFAIK. It wouldn't be enough to appreciably change the color."
] |
[
"How hot does something have to be before touching it becomes painful?"
] |
[
false
] | null |
[
"This will depend on the object you are touching. Some materials conduct heat much better than others. Also, some have a higher ",
"heat capacity",
", that is the amount of heat it takes (in units of energy, joules for example) to heat a specific amount of the object a certain amount (measured in kelvin). So you have two things to consider, how much heat and how fast. For instance a sauna could be heated to 80ºC and be comfortable but a hot tub is uncomfortable above 45ºC. That is because water conducts heat much better than air or the cedar bench you are sitting on in the sauna."
] |
[
"At a the Ontario Science Center I saw a display that was basically a table with a surface which was a parallel series of thin closely spaced alternating warm and cold bars(about 4mm diameter, perhaps 3mm apart). When you touched this surface it felt burning hot. The lesson being that pain and our ability to sense temperature are not absolute. I can't seem to find a link with more information about this sort of trick."
] |
[
"This depends on several variables such as duration, where contact is made on the body, etc. This threshold will also vary from person to person."
] |
[
"How does one clean something that dissolves in water?"
] |
[
false
] |
[deleted]
|
[
"You clean them in something other than water.",
"For example, if you want to clean special lenses that are made of pure sodium chloride, you can wipe them down with something like hexane."
] |
[
"It's probably not a good idea to use organic solvents on something you intend to ingest. Just wipe it off with a dry cloth."
] |
[
"It's probably not a good idea to use organic solvents on something you intend to ingest. Just wipe it off with a dry cloth."
] |
[
"How do you measure air pollution?"
] |
[
false
] | null |
[
"It depends on which pollutants you're interested in, and whether you need active near real-time assessment, or only weekly/monthly averages. ",
"The most comprehensive case of course, is when you need to know everything, right away. Many urban centers around the world have networks of automated air quality monitoring stations which measure and report pollutant levels at an hourly to daily rate, depending on the jurisdiction.",
"The most commonly monitored pollutants in urban settings are ",
"NO₂ (nitrogen dioxide)",
"SO₂ (sulphur dioxide)",
"O₃ (ground level ozone)",
"CO (carbon monoxide)",
"PM₁₀ (particulate matter < 10 μm)",
"PM₂․₅ (particulate matter < 2.5 μm)",
"The measurement method used varies by the nature of the pollutant.",
"Particulate matter, such as dust, ash, smoke, and soot are widely measured using Beta Attenuation Monitoring. This technique employs the absorption of beta radiation by solid particles filtered from a known volume of air. The degree of absorption is proportional to the mass of the absorbing material, and thus can be used to determine the pollutant density in the original air sample.",
"Among the methods for measuring the concentration of gaseous components of air pollution are techniques which raise the excitation level of the target substance from its ground state, and then count the photons generated as it de-excites:",
"Chemiluminescence. In this method, the pollutant to be measured is made to undergo a chemiluminescent reaction. Reactive intermediates are formed which enter electronically excited states. Their subsequent transition back to ground state is accompanied by a release of energy in form of light. The photon count in this light is proportional to the amount of the pollutant in the sample.",
"Laser-induced Fluorescence. In this method, atoms/molecules of the target substance are excited into a high energy state by the absorption of laser light. They subsequently return to their ground state by releasing one or more photons.\nThese photons are counted to determine the concentration of the pollutant in the sample.",
"This is not nearly an exhaustive list of measurement methods. ",
"This document",
" is a good starting point for learning about passive and active methods for measuring many forms of air pollution."
] |
[
"Nitrogen Dioxide and Carbon Monxide and perhaps CO2, to a degree. The easiest way to measure it is likely by taking a sample, testing that sample via some indicators or a reaction which can tell us the exact number of molecules present in a reactant. Once we have this number, we can actually calculate the average air density and thus the exact number of molecules pollution in a given region, depending on how far from the epicenter such pollution is occurring. "
] |
[
"The \"acceptable\" limits vary from jurisdiction to jurisdiction, and usually have different values across different averaged periods (1 hour, 1 day, 1 year). The simplified figures below are set by the United States Environmental Protection Agency:",
"SO₂ - < 75 ppb, 1 hour average",
"NO₂ - < 53 ppb, annual average",
"O₃ - < 120 ppb, 1 hour average",
"CO - 35000 ppb, 1 hour average",
"PM₁₀ - 150 μg/m³, daily average",
"PM₂․₅ - 12 μg/m³, daily average"
] |
[
"Why is there so much attraction going on at the subatomic level? Strong force, weak force, electromagnetic force. Quarks forming protons, protons and neutrons forming a nucleus, electrons orbiting the nucleus. Why should it be that all this attraction happens at all?"
] |
[
false
] |
Gravity is explained as spacetime being warped by mass. I've heard it compared to a heavy ball sitting on a rubber sheet, stretching it down and causing nearby objects to roll toward it in this depression. I get this. Kind of. But what about at the subatomic level? Is there a single phenomenon that explains attraction in general? I mean, why should attraction occur at all?
|
[
"The rubber sheet analogy isn't a great one. It still relies on the notion of things rolling downhill, and thus requires some kind of gravity in the first place. I prefer this more correct, and still simple explanation.",
"If you complete a closed loop in a flat space, you end up facing the same direction you started. This is not the case ",
"if you do the same in a curved space",
". It turns out that objects taking the longest possible route through a space like this display the tidal effects of gravity (two point masses falling towards the centre of the earth/massive spherical object approach each other as they do so).",
"Regarding your other question, I would just make sure to add that there is no \"reason\" why anything happens, things just are. But that is philosophical, and you were after a single explanation for these phenomena.",
"As it happens, there is such a thing, and it's called gauge symmetry. It turns out that a large class of physical objects (which are called fields) display what we call U(1) gauge symmetry. This means we can multiply the field by an arbitrary complex number and still hope for the physics to remain unchanged (this is why it's a symmetry). If we make this leap, we end up connecting these fields to a vector field (the one we call a photon field, excitations of which are called the gauge boson). In other words, these objects are charged objects, and the interact via the electromagnetic force.",
"There are actually other gauge symmetries which give us the other forces - SU(3) (this is not a single complex number, it is a matrix of these that satisfy certain relationships) gives us the strong force (or quantum chromodynamics) and the weak/EM forces are the leftovers of a larger symmetry SU(2) x U(1). If this last symmetry was to hold, then all the gauge bosons should be massless; but the weak bosons are not (70-80 GeV). The Higgs mechanism is introduced to explain this.",
"You may also be interested in the ",
"Kaluza-Klein theory",
" from the 1920s. These guys found that EM interactions could be described by introducing a 5th dimension of spacetime."
] |
[
"I presume you mean \"how\", and not \"why\". As for why, I can't point to anything other than the anthropic principle -- if it was any other way, we wouldn't alive to observe it.",
"For \"how\", the Standard Model speaks of messenger particles and virtual particles. Virtual particles are exchanged between charge carriers, which \"communicate\" the force, in a sense."
] |
[
"The strong, weak, and electromagnetic forces are not universally attractive. You probably know enough about electromagnetism to know this already- electrons are attracted to protons, but electrons repel from electrons. The same sort of phenomenon occurs with the strong and weak forces, to.",
"The reason it seems like they are attractive is as you cut your way down from molecules to atoms to protons to quarks, you're splitting apart bound states of objects- in order for the things to clump up, they must have an attractive force. But that doesn't mean all configurations of objects are attractive. However, the pieces that you find naturally clumped up must be in an attractive configuration."
] |
[
"How can people increase their cardiovascular output capacity by training, even though lung volume essentially remains the same?"
] |
[
false
] |
During intense aerobic exercise, I believe that the supply of oxygen to the lugs is the 'rate limiting step', which results in the body spending as much energy as possible, given the amount of oxygen provided by the lungs. That being said, how can people dramatically increase their aerobic output power with training, even though the volume of their lungs essentially remains the same?
|
[
"It’s not the size of the lungs, but the ability of the body to deliver the oxygen throughout the body, and to then expel the carbon dioxide waste. That’s why endurance athletes focus on improving aerobic and anaerobic capacity as a measure of cardiovascular potential/fitness, not lung size."
] |
[
"Great question! The body works as a system, and even though you might have huge lungs, the other cooperating systems might not be able to use all that oxygen effectively. \nTo increase your long-term endurance (running or exercising for long intervals), it takes time to train you body to use that oxygen more efficiently. \nMuscles need oxygen to do their work, and long-duration training (like jogging, biking, or aerobics) will gradually increase the mitochondria in your muscle cells, and increase the amount of oxygen your muscle cells can take in. Long-duration training also builds up your body’s ability to remove the waste products from your muscles, like lactic acid, which is what causes your legs to feel like lead weights after just running a short distance. \nOne way to measure how well your body uses all that lung oxygen is to know your VO2Max (Maximum Oxygen Volume). It’s a measure of fitness, of how much oxygen your body can pass through the muscles, while under a controlled test (usually tested on a treadmill). After training for long durations, you can increase your VO2Max."
] |
[
"Thanks for the reply. Then why does an unfit person (like myself) go out of breath while exercising, even though my lung capacity is more than enough?"
] |
[
"How fast will atmospheric moisture adsorb to dry glass?"
] |
[
false
] |
I've got an argument brewing with another scientist I work with about this. Let's say I pull some glass at room temperature out of a drybox. How fast does moisture from the air start adsorbing onto it, and how long would it take to equilibrate? My thought is that significant levels of moisture will adsorb within seconds.
|
[
"I would say that it is heavily dependent on the humidity of the air outside the box. I work with air sensitive materials pretty often and we coat glass slides with novel films for various purposes. If you pull the glass out of the drybox, or better yet an oven with desiccant inside it, you can transfer the slide to a coating apparatus (sealed system) and flush with argon and avoid significant water adsorption. Flushing with an inert gas while heating in a sealed environment will further remove any adsorbed moisture from the transfer but is usually not necessary unless its very humid in the lab.",
"One way to tell is to dry it and quickly weigh it on a four decimal scale. You should note a small change in weight the longer it sits out and you can calculate a time dependence for adsorption by weighing in regular intervals."
] |
[
"This paper is really in depth and will help answer your question. I'm sure there other other relevant literature sources if you go through the citations or do your own search that might give you a more specific answer in terms of time scale. I think it depends on what you call significant. It looks like the majority of the adsorption happens on the order of minutes and not seconds, but it may depend on the relative humidity.",
"The nature of water on surfaces of laboratory systems and\nimplications for heterogeneous chemistry in the troposphere (PDF full text link)",
"From the top of page 610:",
"most surfaces came to equilibrium with water vapor\nwithin 15 minutes"
] |
[
"Pretty fast I think although it (obviously) depends on the moisture content of the air.",
"I've always learnt that to keep glass dry it needs to be either above ~130 C or stored in a dry environment. I would only trust glass to be completely dry if heated above 130 C in a vacuum and subsequently stored in a dry atmosphere."
] |
[
"Why isn't flooding considered to be a good explanation for the mounds of the Mississippian culture?"
] |
[
false
] |
Some wiki hopping brought me to a page on who apparently built quite big mounds with structures on top and at least partly lived near rivers and on floodplains. I'm no archaeologist, I actually study hydrology, and the first thought that occurred to me was that these mounds could serve an obvious purpose as a safe haven for when the river flooded. However the wiki doesn't seem to mention them serving this purpose. Wiki states the mounds were used as ceremonial and burial places, however this is also logical in the context of flood protection, because I can imagine you don't want your sacred sites to be flooded and covered in river sediments periodically. Also chiefs often lived on them and they probably also didn't want their homes to be flooded either. Look at this picture of the , they are right next to the river. In the Netherlands and other parts of Europe for floods and were already built in 500BC. Other in America didn't live in the flood plains, but maybe they just took the mound building culture developed on the floodplains to other regions. So my question then is why didn't archeologists start from the assumption that mounds were used against floods and that the other purposes for them logically follows from the fact that they survive floods.
|
[
"I can give you an anthropologist's perspective on why this theory is not prevalent. The mound builders in Mississippian culture probably did not start erecting these structures earlier than 800 CE. There simply wasn't a large civilization there earlier on. The Hopewell culture in Ohio did build smaller mounds, however, which were used for ceremonial purposes. These mounds were too small to be of any use as flood protection. The Aztecs and other Meso-American cultures were already building pyramids and mounds in the first century. So the cultural diffusion would have to go the other way around if somehow other mound building cultures inspired activities in the Midwest (this seems very unlikely to me). At Teotihuacan, there are drainage systems built into the pyramids, so it seems more likely to me that mound-building technology would have been used for drainage or aversion of water rather than a place of high ground, but that's just a guess. It is unlikely that Mississippian architecture has any connection to shelters in western Europe. ",
"I looked up some things on Academic Search Premier, but wasn't able to find any scholarly articles discussing your exact question. The only related articles I found were discussing the problems with flooding in relation to excavation and preservation, since some mound sites apparently got buried by river sediment. I did find one article on agriculture stating that \"virtually all known sites are situated along the outskirts of low sandy ridges, where they are free from danger of floods,\" but this is for field plots, not mounds. Another article suggested a city in Kansas was built under the protection of a natural levee. I would have to research this further, but my hypothesis is that mound-building cultures probably dealt with seasonal flooding through the strategic placement of structures and fields, and employed drainage ditches, levees, and other smaller adjustments to local topography rather than mounds, which are extremely labor intensive."
] |
[
"I really appreciate your input, however I'm still not totally convinced. You mention that some mound sites are currently buried under river sediments. Couldn't it be likely that earlier small mounds for small villages before 800CE have just been washed away? Or the older mounds might have been used to fertilize the soil with as has ",
"happened to actual flood shelter mounds",
" in the Netherlands.",
"As an hydrologist those \"low sandy ridges\" sound like the ",
"natural levees",
" rivers often make when they flood. i.e. not safe places in big events. The sands get deposited first when rivers overflow because they settle out when it is still flowing quite fast (and destructive), the loam and clay settle out further along the floodplain in that order when the flow is slow enough for those to settle to the bottom. I guess the low sandy ridges could also be those of historic river beds and therefore be further away from the flowing river and less in danger. However in severe floods they also are likely to get flooded or washed away.",
"If not mounds, then I do wonder how these people dealt with floods, because drainage, ditches and levees are no match against a natural river system such as the Mississippi if it's not heavily regulated and damned (or diverted for agriculture) as it currently is. Controlling the flow of a river is a much greater task than erecting some mounds, which is why early cultures in the Netherlands used these mounds as safe havens. Only when the density of artificial dwelling hills and people became large enough there was enough incentive and manpower to make dikes. Also you need a good central government to control a river because one weak point in the defense can mean disaster."
] |
[
"I just found ",
"this old paper",
" which confirms that they lived and farmed mostly on loamy flood deposited soils due to their fertility and easy tillage. No mention of the mounds though."
] |
[
"can your body get \"used\" to adrenaline?"
] |
[
false
] |
i know adrenaline can do all sorts of awesome stuff like send more blood to your lungs and heart, and cause your senses to heighten and all sorts of stuff. but if you get into situations that causes the release of adrenaline a lot will your body eventually get "used" to it and make it harder for it to do all those stuff effectively? also if it doesn't, can you just endlessly pump yourself with adrenaline to just make everything better? i assume it probably makes certain stuff harder
|
[
"Approve of this suggestion. TL;DL, stress in short bursts is good, chronic stress (which is what constant adrenaline amounts to) is the reason we have such high levels of hypertension and heart disease etc etc.",
"Chronic stress can also adversely affect childhood development ",
"http://developingchild.harvard.edu/topics/science_of_early_childhood/toxic_stress_response/"
] |
[
"Approve of this suggestion. TL;DL, stress in short bursts is good, chronic stress (which is what constant adrenaline amounts to) is the reason we have such high levels of hypertension and heart disease etc etc.",
"Chronic stress can also adversely affect childhood development ",
"http://developingchild.harvard.edu/topics/science_of_early_childhood/toxic_stress_response/"
] |
[
"A ",
"pheochromocytoma",
" is an adrenaline secreting tumor. I think it provides a good model for the situation you are describing. Pheochromocytomas are classically associated with a triad of symptoms: headache, sweating, and tachycardia. They are also a cause of persistent hypertension. ",
"Interestingly, many pheos go undiagnosed. These are termed \"subclinical pheochromocytomas.\" While the dose of adrenaline is a factor, there is also a process of adrenergic desensitization that occurs. This was described in 1984 in rats with pheochromocytomas (",
"paper",
"). ",
"The two theorized methods for decreased response were decreasing numbers of receptors and weaker interactions between adrenaline and the receptors. (More information of subclinical pheos ",
"here",
".) ",
"So, in there is probably some decrease in the body response to adrenaline with excessive exposure. There are also some obvious continued systemic effects in patients with high levels of adrenaline that is not compensated for by desensitization. ",
"The extent to which you want to correlate this with your situation is at your discretion, but I think that pheos can be a proof of concept. "
] |
[
"We are putting in two wells in remote villages in Malawi. The salt content is high in these regions. How can we make the water more drinkable?"
] |
[
false
] |
Hello All! We have a well company putting in two bore holes in a remote village in Malawi. These regions are known to have salty water. To the point where it is sometimes not okay for drinking. Does anyone have any solutions to this problem? How can we make the water drinkable? What equipment can we get here that is economical and easy to train how to use it? Is there any organic way of removing the salt? Anything we can add to the pump? Didn't know where to put this. This area has really high cholera cases, we need a solution asap! Edit: Issues: No firewood or charcoal. There is a near by water source but is VERY polluted. It is a heavily populated area. 200+ people will be using the water source so it needs to be able to produce enough water. If each person gets 10 liters a day it needs an output of AT LEAST 2000 liters daily. No electricity. Theft of equipment. Maintenance: cost/training. There is a lot of sun. There is down time in the rainy season where it is very cloudy but that only lasts about 2 months. I am not an engineer, so I need you guys that understand the above limitations and knowledge about this to upvote what will work best, if any, and then explain to me like I'm 5 how it will work. Edit: . There is lots of wind here. I didn't think about this because I have never seen it utilized for anything. Just to clarify to those that think I own a well company and have no idea what I'm doing: I do NOT own the well company. I came across this village that is in desperate need. Well companies here seem to not care so much about salt content issues and just drill the holes and go. I wanted to know more about what can be done with salt content. Please stop insulting me for it. Also: If there are any Hydrogeology experts/students that want some field experience I'd be happy to organize a trip out here and see what we can do?
|
[
"I am a water/wastewater engineer. If I understand correctly:",
"Sources: brackish groundwater, polluted (with what? assume human waste?) stream.",
"Restrictions: no electricity, fire, or charcoal.",
"Producing: 2 m",
" per day of potable water.",
"I am not a politician so I won't mince words, you are pretty much fucked. Here are my thoughts.",
"Groundwater. How deep are your wells? Do you know the geology? Can you drill deeper, or in a different area? If you invest in knowledge (geology survey) and a one time cost in equipment (deep drill) you could produce something that has low maintenance costs and can produce the volumes you require. Recommend to proceed.",
"Distillation. Solar distillation will not produce the volumes you require. It's a boy scout science project, it doesn't scale to the scenario you have. Recommend to not proceed.",
"Conventional Treatment. RO with some pretreatment is ideal here. Needs electricity. Needs trained operators. Costs a shitload of money. Long shot is getting funding for this and tieing into someone else's electrical infrastructure. Problems with long term maintenance and consumables. Recommend not to proceed unless \"angel\" is in the area (ie large mine, etc, looking for a PR boost).",
"TL;DR Your only realistic shot is drilling better wells."
] |
[
"This will not scale to the required volumes at all. You would need hundreds/thousands of small stills, or a large still that would have capital, construction, and maintenance requirements that are completely insane.",
"Best approach is a hydrogeological survey and better well design/drilling.",
"Source: I am a water/wastewater engineer who works in the desalination field."
] |
[
"Hydrogeologist here, as a general rule of thumb, water gets more saline as you go deeper. There are some exceptions to this, near mountain fronts where permeable layers outcrop, then dip steeply under the overlying rock, which may contain a separate permeable unit with salty water from a distant recharge area for example. It all has to do with how long the water has been in the rock. I'm not familiar with the geology of this area, I would consult with a geologist/hydrogeologist who is. Some places just don't have fresh groundwater, especially in dry regions that can't adequately recharge an aquifer. It may be easier to treat poopy surface water than drill wells that may not even produce, then depend on desalination."
] |
[
"Why is the human sense of smell so weak?"
] |
[
false
] |
What sort of evolutionary benefit can a weak sense of smell be? Is it just that we rely on eyes so much that it doesn't really matter how the sense of smell changes. It would seem to me that weakening it would be a bad thing in terms of evolution.
|
[
"Evolution is not free. Bodily structures cost energy, complexity, and space. Weak smell is a benefit in the sense those biological resources are better spent somewhere else.",
"It is like putting a towing hitch on a Prius. There is nothing ",
" with a towing hitch, but it is weight and space spent on something that just isn't terribly useful for that kind of car."
] |
[
"I can expound on the \"cost energy, complexity and space\" bit. Compare the relative size of our ",
"olfactory tract",
" to a mouse's ",
"olfactory bulb",
". The olfactory tract in humans is the two flat structures at the base of the brain ending in a bulbous connection, whereas in mice, the olfactory center comprises the two rather large structures to the front of the brain. Relative to brain size, the mouse's \"smell center\" is huge. In humans, it is much smaller, but the size of our ",
"visual cortex",
" relative to brain size is much, much higher than in a mouse.",
"Additionally, looking at our genome, the mouse ",
"has nearly 1300 genes for olfactory receptors (20% pseudogenes), whereas humans have a similar range of recognition but only 1/3s the number of genes/coded receptors.",
"We have indeed chosen to specialize differently."
] |
[
"In what way is it weak? I mean, compared to a dog it isn't that great, but humans have been shown to be able to ",
"scent track",
" and we are able to detect scents with a concentration of less than ",
"1ppb.",
"That 2nd link goes on to tell us how some smells aren't odours at all, but are triggering temperature or pain receptors, like Menthol."
] |
[
"Is it possible to calculate how fast we're moving through time?"
] |
[
false
] |
[deleted]
|
[
"One second per second. Which also happens to be the speed of light."
] |
[
"You're always at rest relative to yourself, remember."
] |
[
"Correct. My mistake."
] |
[
"Who is more likely to get struck or hurt by lightening first? A man under a tree, the man in the swimming pool or the one on the golf fairway holding a 5 iron?"
] |
[
false
] | null |
[
"The tree is the most dangerous since it is likely much higher in the air than the pool or the golfer. While the tree may conduct much of the electricity through it's trunk, there will no doubt be transient forks that may hit anyone standing under the tree and kill them. "
] |
[
"The \"path of least resistance\" is a clever metaphor for lay-persons but it is not an entirely accurate portrayal of how electricity works. Electricity will generally follow all viable paths, but the current is inversely proportional to resistance. Lighting going through air works a little differently but you are not safe under a tree that gets struck by lightning. If the tree gets struck there is a good chance you will get electrocuted. ",
"According to some weather sites being under trees is apparently the leading cause of injury from lightning, but that statistic may just reflect the fact that people run under trees for safety more during lightning storms. This is all speculation but i would bet that everything else being equal, you would get directly struck more often in the golf scenario."
] |
[
"I've always thought that the main danger of someone standing under a tree is shrapnel when water inside a tree boils after it was struck."
] |
[
"Is there a \"due north\" for determining x,y,z coordinates in space?"
] |
[
false
] |
This had me puzzled when reading about distances of objects from the sun, earth, etc...
|
[
"Celestial Coordinate systems is how you would orient yourself with one other object in space. With the use of Right Ascension and Declination.",
"Be careful here - there are actually many different coordinate systems used in space. Right ascension and declination are only useful if you're talking about where you'll see an object relative to the Earth, since it's based on Earth's axial tilt.",
"A spacecraft would be more likely to use the ecliptic coordinate system (relative to Earth's orbit), while studies of nearby star clusters would likely use the galactic coordinate system (relative to the plane of the Milky Way), and so on."
] |
[
"In short, no. Everything in space is based on a relative coordinate system (called the Celestial Coordinate System). Basically, if you want to know where you are, you use other objects (planets, stars, other spacecraft, etc.) as a reference point, and determine where you are based on that. ",
"Very similar to how orienteering and pioneering people use a topographical map to determine where they are based on where they are in relation to nearby geographical points(mountains, rivers, oceans, etc.).",
"Edit: \n",
"http://en.wikipedia.org/wiki/Celestial_coordinate_system",
"\n",
"http://csep10.phys.utk.edu/astr161/lect/time/coordinates.html",
"Celestial Coordinate systems is how you would orient yourself with one other object in space. With the use of Right Ascension and Declination."
] |
[
"Here is a long but thorough read on the development and implementation of the International Celestial Reference System, which is the current standard reference system as designated by the IAU (International Astronomical Union). Its origin is the solar system barycenter and its axes are determined with very accurate measurements of quasars.",
"http://aa.usno.navy.mil/faq/docs/ICRS_doc.php"
] |
[
"Why does food get cold much faster after heating it in a microwave as opposed to on the stove etc.?"
] |
[
false
] | null |
[
"As long as you heat both to the same temperature and then treat them the same after heating then they will behave exactly the same. There should be no chemical or physical changes upon heating, so all that matters is how hot it gets and the conditions around it during cooling.",
"The only difference between the two heating methods is that the microwave heating is much more focused than stovetop heating. The microwave primarily heats the water, with some small amount going into the container. The stove will heat the burner and the container primarily, with the heat then conducting through those into the liquid. Once you stop the microwave the heating completely stops, however if you stop the stovetop you could still heat the liquid as the burner and container will still be hot. If you remove the liquid from the heat source immediately after the heating is finished then there is no difference between the two cases."
] |
[
"It could come from a variety of factors. Once you stop the active heating there is a lot more latent heat in the stovetop, so if you let the food sit for a little after cooking there will be a noticeable difference. Microwave heating can also be deceptively uneven (ever try to microwave a hot pocket, especially without the sleeve?). Since the microwave generally doesn't allow time for much heat convection you can have super hot zones while the majority of the food is still cold, either due to hot spots in the microwave or distribution of stuff in the food. Stovetop heating takes longer and uses convection to more evenly distribute the heat.",
"There could also be differences in moisture retention between the two methods. I don't have any data to work with but if one method dries out the food more than the other it could cool faster. Water has a very large heat capacity and so losing a significant amount of water during cooking could lower the foods ability to retain the heat.",
"The arguments above mostly only apply to mostly solid food though. If you heat a liquid to boiling it will be essentially the same temp throughout, and heat transfer within the liquid should probably prevent significant hotspots in the microwave (if you don't get all the way to boiling)."
] |
[
"Thank you for your answer!",
"I heard this so many times though that it makes me wonder: did this myth come to be because people tend to heat their food less in a microwave so that it is significantly warmer when prepared normally? It's just their impression that it cools faster after microwave but in reality it was on a lower temperature to begin with."
] |
[
"How \"efficient\" is a supernova?"
] |
[
false
] |
[deleted]
|
[
"You are on track but your terminology is a bit off. Roughly 0.1% of the mass is converted to energy. The rest remains as mass - these are the two fission products that are created. So the \"potential energy\" - the difference in binding energy between the uranium nucleus and the two daughter products, is entirely released in the reaction. You are using \"potential energy\" to refer to \"mass energy\" (ie E=mc",
" ).",
"So your question would better be stated \"what percentage of the mass of a star is converted to energy in a supernova explosion?\""
] |
[
"You are on track but your terminology is a bit off. Roughly 0.1% of the mass is converted to energy. The rest remains as mass - these are the two fission products that are created. So the \"potential energy\" - the difference in binding energy between the uranium nucleus and the two daughter products, is entirely released in the reaction. You are using \"potential energy\" to refer to \"mass energy\" (ie E=mc",
" ).",
"So your question would better be stated \"what percentage of the mass of a star is converted to energy in a supernova explosion?\""
] |
[
"Your typical type II supernova sends out 99% of its energy via neutrinos. About 0.01% comes out as light.\nFun fact: The star's atmosphere is ejected at around 10,000 km/s"
] |
[
"Will we be beaming information through the earth (as opposed to around) in the future?"
] |
[
false
] | null |
[
"Since most of the Earth is not transparent, the fastest data transfers would occur at the speed of sound through the Earth which is approximately 10km/s ",
"(order of magnitude estimate)",
". Satellites communicate at the speed of light, which is about 300,000km/s (30,000 times as fast as the speed of sound through the earth).",
"So communicating directly is not worthwhile. What if we drilled a hole? That would make the path much more direct. Lets assume an ideal situation - we want to talk to someone directly on the other side of the world. Lets say there's a tunnel through the center of the earth with a fiber-optic cable running through it, and that heat and gravity are negligible. The earth is about 12,000km in diameter (rounding down), so light would take ",
" to get to the other side of the planet.",
"Lets use an inefficient network of three ",
"geostationary satellites",
" and see how much slower that network is. In ",
"this diagram",
", each satellite is about 35,000km above the earth (x). That means that the signal must travel 35,000km to get up, then sqrt(35,000",
" = ~50,000km twice, then back down 35,000km. That makes for a total distance traveled. Total distance traveled is 170,000km or so. That's about a half a light-second (",
"), or about 10x as long as going through the center of the earth. ",
"When you include the fact that the deepest we've ever drilled was about ",
"12km",
", and that took a national-level effort, it's clear why we use satellites."
] |
[
"Thanks for the reply! I am a little unclear on what \"transparent\" means in this context. ",
"Why would the speed of sound through the earth be the deciding factor? Is there no speed of light through earth? I mean radio waves penetrate concrete and other stuff (and they are at least EM radiation if not actual light), why not the entire earth with sensitive enough detectors?",
"Edit: Also, neutrinos? From what I've heard they interact very weakly with matter, what if we had a neutrino detector and generator that isn't huge and very sensitive"
] |
[
"Sure, radio waves could penetrate a couple feet of concrete. But the earth? No way. 12000 miles of rock stops just about anything. MAYBE not neutrinos. But if a neutrino doesn't interact with 12000 miles of rock, how would it interact with anything we build? There's really no other way to catch a neutrino than \"Fill a giant tank with water and hope something hits it\". The same property that allows them to travel great distances also keeps them from being suitable to transmit information."
] |
[
"How can you permanently flatten a PTFE sheet?"
] |
[
false
] | null |
[
"Not the right sub. Maybe try ",
"/r/askengineers"
] |
[
"Thank you. Should I delete the post? "
] |
[
"Already removed"
] |
[
"Why don't we see any main sequence Red Giants or Blue Dwarfs?"
] |
[
false
] |
Pretty simple question, probably with a pretty simple answer. Blue Dwarfs are a theoretical stage of life for Red Dwarfs, that much I know, but why don't we see any small main sequence Blue stars? Is it just not possible to get that hot and that small? And the same goes for Red Giants - all the big stars seem to be Blue. Why are none of them Red? Why is that only the dying stage of a larger star?
|
[
"A star's evolution is mostly driven by just two numbers: its initial mass, and its age. Almost all stars of the same mass will go through the same evolutionary stages at the same ages. We see a diversity of stars because stars were formed at different times and with different masses. There are other effects, but they are secondary effects, and you can understand most of what's going on by just looking at mass and age.",
"In the \"main sequence\", a star burns hydrogen in the core through nuclear fusion. This process is ",
" sensitive to temperature: doubling the temperature can produce 100x as much power (and consume Hydrogen 100x faster). A more massive star has a higher pressure and temperature in the centre, and produces a ",
" more heat than a less massive star. This sets the colour of the star. A cool star is red. A warmer star is orange or yellow. The hottest stars are white, then blue. This also sets the age of the star. A massive star will burn its fuel ",
" faster than a low mass star - so fast that it completely overwhelms the fact that it has more fuel to start with. Our Sun has a life-time of maybe 10 billion years. A star 8x the mass of our Sun will only live for ",
" of years - thousands of times shorter. A star 10% of the mass of our Sun will live for ",
" of years - no red dwarf star has died \"of old age\" in the history of the universe.",
"This is a tight and very strong relation. You have long-lived low-mass cool red stars, short-lived high-mass hot blue stars, and everything in the middle. You don't get small bright blue stars (on the main sequence) because small stars don't have enough gravity to produce enough pressure to get that hot.",
"Late in life, things get more complicated, and this tight relation breaks down. Stars will run out of hydrogen fuel in the core, and go through stages of burning helium and heavier elements, and/or burning fuel in a shell ",
" the core. These tend to puff up the star through increased pressure, and you end up with bright burning core or shell, surrounded by very large but low density \"atmosphere\", which is somewhat cool just because it's so spread out that each chunk of gas isn't getting that much heat going through it. Because they are large in size (although note they haven't gained any mass), and are cool, they are \"red giants\".",
"Once a star completely runs out of fuel, it will run out of pressure and collapse. This can be accompanied by a dramatic explosion as new reactions occur at the extreme densities you get from stuff collapsing without support. That's where you get supernovae and so on. The compression also generates a lot of heat, so you're left with an extremely hot and dense remnant. These are neutron stars and white dwarfs and so on.",
"Just to sum up: during the \"main sequence\", stars have a very simple evolution that depends almost entirely on the starting mass, which sets the pressure and temperature, and therefore reaction rate, at the core of the star. Massive stars are hot and blue and short-lived, low mass stars are cool and red and long-lived. But once the hydrogen in the core is used up, the simple relationship is broken, and all sorts of interesting things happen."
] |
[
"we do see blue dwarfs",
"Yeah, but the term \"blue dwarf\" isn't used in astronomy that much, typically because it causes confusion. Usually when I've heard it used, someone asks for clarification whether they meant an O- or B-type main sequence star, a blue dwarf galaxy, or even a ",
"hypothetical star that doesn't exist yet",
". It can be useful shorthand when you want to distinguish blue main sequence stars from blue supergiants, but it's not really common parlance the way \"red dwarf\" is.",
"Sirius, is one of them",
"Sirius is an A-type star, which is really more white than blue. If you're going to stay true to the uncommon parlance then that's problematic, because now you'd be calling it a \"white dwarf\" - a white main sequence star - which is quite different than a ",
"white dwarf",
"."
] |
[
"The red giant is one of the last stages of stellar evolution. This means that the star does not have enough fuel to continue resisting gravitational collapse, after the star begins to swell to prevent collapse (this is an attempt to balance the forces of gravitational collapse and internal pressure), so the star becomes larger and turns red."
] |
[
"What makes molecules stable?"
] |
[
false
] |
I'm in Biology, and I'm having some trouble grasping these concepts. I was wondering if anyone could help. Is a molecule most stable when it has an equal number of protons and electrons? (no charge)
|
[
"The presence or absence of a charge does not necessarily make any difference. ",
"Stability is actually really relative - there is no absolute measurement for stability. A molecule can only be more stable than another molecule. A more accurate word is \"persistent.\"",
"The short answer is: A molecule is stable when there is not an energetically-accessible mechanism (or pathway) available that allows it to react and form a more stable molecule or molecules. More stable molecules have less energetic bonds but you always have to consider these in ensemble with any other molecules/atoms that in the system which they can react with. If an ensemble of molecules can react to produce a new ensemble of molecules in which their net bond energy is lower, they will. Again, to do that, they need pathway that's accessible with the amount of energy available. If there's less energy available, the reaction proceeds more slowly. If it's slow enough, the molecules can be said to be stable. I'm sorry that's not much of an answer. I feel like all I said was \"A molecule is stable when it doesn't react.\" :(",
"The long answer is: Most of Chemistry. "
] |
[
"In molecules, there are several kinds of bonding that may occur, each of them having differing strengths. Van der Waals forces inside a molecule (it also works on intra-molecular and larger levels) which is the weakest, and then covalent (which is deemed the strongest by bonding energy, but in reality there are no such borders) and ionic bonding. VDW works between molecules because of polarities of atoms in that single molecule attracting or repulsing other molecules' atoms. (I do not know nor could I find how this works on single-atom level, I'd love to hear why) Covalent bonding is sharing of electrons between two atoms, and they tend to be pretty stable. (diamond) ionic bonding is basically trying to juggle electrons between a molecule's atoms to get a global optimal for the molecule. It doesn't always reach neutral, and a molecule being neutral doesn't really mean much in terms of stability because even when an atom is inside the molecule there might be an another molecule or atom that wants it more strongly, therefore tearing it apart from the last molecule. (in other way of saying, reacting to that molecule) But also there are very few rules without exceptions in chemistry; and I am saying very few not for because I know a rule that doesn't have exceptions, but for that there might be one I don't know of. "
] |
[
" has it down, but I just wanted to add my $0.02.",
"It's true that the entire field of chemistry is devoted to understanding the reactivity of molecules, and (in the 20th century) the underlying quantum mechanics that really describes why. Still, there are a few basic trends that apply maybe 95% of the time that can help you get a firmer hold on reactivity:",
"The electrons of an atom are arranged in valence shells. Atoms are most stable when they have completely filled shells (or sub-shells), and they tend to form molecules based on a give-and-take of electrons that allow them to do so. The main block elements (boron, carbon, nitrogen, etc. on the right of the periodic table) tend to want an outer shell with 8 electrons in total to be stable, and will either donate or accept electrons to reach that point. The transition metals (in the middle) tend to want 18 electrons in their outermost shell to be stable.",
"Atoms have ",
"electronegativity",
", which is basically a qualitative description of how much they like electrons. If a molecule has more electron density on more electronegative elements, it's typically more stable.",
"Nature tends to like symmetry at a microscopic level. Thus molecules tend to be more stable when in the most symmetrical shape possible. (There are MANY exceptions to this, but it's a good general principle.)",
"Just remember what ",
" says: molecules are only stable "
] |
[
"What are carbon nanotubes?"
] |
[
false
] |
Can anyone please explain what carbon nanotubes are in the most non-scientifical way possible please? I understand that they are sheets of graphene and there are SWNT, DWNT, and MWNT. BUT i dont understand why they are soooo much better than normal graphene and the difference between the types of nanotubes. as in electrical properties and why (for example the electron flows or mechanism when funtionalized.) thank you soo much
|
[
"Just pretend it's just like chicken wire rolled up into a tube -- except the wires are made of very stable carbon-carbon chemical bonds. They are so tiny that around one billion of them will fit onto a meter stick. ",
"However, you don't have to roll up the wire lengthwise. You can do it at an angle. You can make the tube diameter larger, or smaller. You can put tubes within tubes. You can make them capped or uncapped. You can decorate some parts of the tubes with chemical groups. You can wrap the tubes with other molecules. The possibilities are virtually endless, but also very nontrivial to accomplish!",
"Each of these structural motifs potentially allow someone to tinker with some important property of these nanotubes -- whether it's tweaking their optical, electrical, thermal, mechanical, chemical properties, or whatever that is of interest for the application at hand. In a sense, it is as if there are more interesting ways to tinker with nanotubes than with a single flat sheet of graphene. Just from a non-scientific point of view, a flat sheet of graphene seems so boring compared to these nanotubes! But I should emphasize that it does not mean that graphene is not interesting at all. Graphene is interesting in its own right and there is plenty to learn and discover just from studying flat sheets of carbon atoms.",
"So let me go back to rolling the nanotubes. Depending on how the tube is rolled up, it can behave either as a metal, or a semiconductor. If you do a search for the \"band structure of nanotubes\" all the nitty-gritty details can be found."
] |
[
"are there any ways to explain its electronic properties without being VERY technical?"
] |
[
"Like what coniform said, the rolling plays a very important part in determining the electronic properties. So, depending on how you roll it, you can have one of three electronic behaviours:",
"1) Metallic conduction:\nThe nanotube acts like a metal and conducts electricity very well. In fact, it exhibits \"ballistic conduction\", which means that it has negligible resistance.",
"2) Small bandgap semiconductor: \nIt's similar to silicon, which is also a semiconductor. This means that it can conduct electricity fairly well with the help of an energy source (usually heat or sunlight).",
"3) Large bandgap semiconductor:\nThe nanotube is now essentially an electronic insulator and can hardly conduct electricity.",
"What I love about this is that the fundamental material (a single sheet of graphene, or the chicken wire in coniform's analogy) is the same for all 3 cases. The only thing different is how it is rolled, and you can get such a wide range of electronic behaviours. "
] |
[
"How do the Starlink satellites in very low orbit overcome drag?"
] |
[
false
] |
The more closely orbiting satellites have an altitude of 340km/210mi. Does atmospheric drag play a major role there? I know satellites often have a small engine to maintain orbit, but wouldn't it burn through the fuel relatively quickly? How long of a lifespan can be expected?
|
[
"The Starlink sats are only below 400 km for a few weeks immediately after launch. They are gradually raised to their mission orbits of about 550 km (where atmospheric drag is considerably less) using Krypton ion thrusters. These electricly powered thrusters are also used for station keeping and the eventual deorbitting of the satellites. The sats' expected operational lifespan is on the order of 5 years."
] |
[
"It's temporary for the current satellites (they raise their orbit to 550 km), but later they'll deploy satellites that will stay at ~350 km. They will need to use their ion thrusters a lot, otherwise their orbit decays within months.",
"Wikipedia has a table",
"."
] |
[
"TBF, 550 km is still a very low orbit (as it relates to atmospheric drag), so the question is still valid, and answered, IMO, very concisely."
] |
[
"I noticed that a strong disc magnet will refuse to flip over in my hand, always landing the same side up. Can anyone explain this behavior? Video inside."
] |
[
false
] |
Thanks! *Edit I'm disappointed that I'm being downvoted here. I have a real mystery on my hands and I've documented it as best I can. I would have expected people to be much more curious about this phenomenon, but everyone seems to be dismissing my evidence. I've even made an additional video here on request:
|
[
"Have you tried asking someone else to do this without telling them the purpose of the experiment (a blind test)? You may be inadvertently influencing the way you're tossing the magnet because of your expected outcome, though it's also possible that it's being influenced by magnetic fields that are keeping it oriented since its relatively light and small. "
] |
[
"Pretty sure it's just how you're throwing it. Notice in the slo-mo of your video that you're throwing it straight up so it doesn't really flip. There is a point in the video when it gets a good flip and does land on the other side. Try actually flipping it so it spins several times in the air. My guess is the results will be more even."
] |
[
"There is no way this would happen outside of a magnetic field (the earth's field just isn't strong enough to cause this). It must be the way you are flipping it. "
] |
[
"How exactly do non-Newtonian fluids work, and what determines the force at which they 'activate'?"
] |
[
false
] |
So I've been trawling the internet for a while, and I'm struggling to find a high quality and reliable explanation for why the fluids posses their unique properties. A friend suggested that I try my luck with the good people of Reddit's AskScience, so I'm hoping you can help me on this one. What I'm somewhat more interested in though, is what exactly determines the necessary conditions for different non-Newtonian fluids to solidify. For example, I doubt that a cornstarch and water mix could stop a bullet, but I understand that it's very much possible for polyethylene in a glycol gel to do just that. What makes the two so different? Many thanks in advance.
|
[
"I am gonna restrict my answer to shear thickening fluids, as that is what your question seems aimed at.",
"These fluids usually suspensions of a solid particles in a liquid, such as corn starch in water. At rest the corn starch particles are completely surrounded by water molecules, which is their preferred state. If you introduce a low shear rate (aka, move it around slowly) the particles move around a bit but maintain their protective layer of water molecules. At higher shear rates the particles are pushed together. These larger particles obstruct the flow of the fluid, giving it an increased viscosity. If you make the shear rate high enough the viscosity becomes so high the fluid is essentially solid. Once you lower the shear rate the particles will return to their original state and the fluid will be able to flow freely again."
] |
[
"Thank you for the answer! As a bit of a follow up, is there any chance you could tell me why that is the preferred state of the molecules? Some specific intermolecular force, or something else entirely maybe?"
] |
[
"In addition to what yoenit said, I'll point out for yourself or anyone else who is reading and curious that a fluid is not the same as a liquid. A fluid is merely a substance that when under shear force will deform to a depth of 0."
] |
[
"At what point, specifically referencing Earth, does Euclidean geometry turn into non-Euclidean geometry?"
] |
[
false
] |
I'm thinking about how, for example, pilots can make three 90degree turns and end up at the same spot they started. However, if I'm rowing a boat in the ocean and row 50ft, make three 90degree turns and go 50ft each way, I would not end up in the same point as where I started; I would need to make four 90degree turns. What are the parameters that need to be in place so that three 90degree turns end up in the same start and end points?
|
[
"The answer to the title question is \"always\". The Earth is spherical. Period. Whether the spherical shape of Earth matters to you is dependent on the what you're measuring and your threshold for error.",
"As to your more specific question...",
"On a sphere, the area of a triangle formed by three geodesics (arcs of a great circle) is given by",
"A = R",
"(a + b + c - π)",
"where ",
", ",
", and ",
" are the interior angles of the triangle and ",
" is the radius of the sphere.",
"If you want your triangle to have three right angles, then this formula reads:",
"A = πR",
"/2",
"and, as a ratio of the total surface area of the sphere,",
"r = A/(4πR",
") = 1/8",
"So if you want to make some sort of journey on the surface of Earth and get back to where you started by traveling along great circles and turning 90 degrees exactly ",
" two times, then the surface area enclosed by your path must be 1/8 the total surface area of Earth. (That's about 3.7 times the land area of Russia.)",
"Of course, there's no reason you ",
" travel along great circles. In that case, your triangle can have three right angles and enclose an arbitrary small area. But then the sides of your triangle would not be the proper analog of \"straight line\" for spherical geometry."
] |
[
"A good way to visualize this is to cut the earth into 8ths. Cut it in half at the equator, then cut the northern and southern hemispheres in half, then cut each quarter in half again. The surface area of each of those 8 pieces will be 1/8 the surface area of earth, and each one will have three 90* angles on the surface. You could trace that piece out by leaving the north pole, making a 90* turn when you hit the equator, flying 1/4 the circumference of the the earth then making another 90* turn back to the north pole. When you arrive at the north pole you will make a 90* angle from your departing line."
] |
[
"Okay this is a baller example for anyone who was having trouble visualizing it, hadn’t even though about a physical object having three corners that explain it so easily"
] |
[
"On a cellular level, what causes a sore throat?"
] |
[
false
] |
I am very curious as so what is happening to yor cells when you have a cold and a resulting sore throat. Responses are much appreciated.
|
[
"First read about ",
"pharyngitis",
".",
"Then read about this ",
"inflammation",
".",
"Then ask any questions you have.",
"I don't mean to sound condescending but watching the episode of The Magic School Bus where they go inside Ralphie when he is sick will really help visualize everything. ",
"link"
] |
[
"I agree with luckypenne, but to briefly write something here: sore throats as either viral/bacterial pharyngitis/laryngitis/tonsilitis are manifestations of pathogens colonizing and destroying actual cells that they are using to replicate. Both the destruction of cells and the presence of pathogens stimulate chemical messaging to your immune system to react and infiltrate the site. Some of these chemical messages directly contribute to the pain felt, and inflammation occurs. Inflammation itself has many effects that can contribute to the pain including a sudden influx of many immune cells to a site (causing swelling), increased blood flow by dilatation of blood vessels (causing redness and heat), and the white spots you sometimes see during a sore throat are often the pathogens and dead cells being cleared away by neutrophils and macrophages.",
"Tonsilitis is interesting as well since the tonsils are lymph nodes, which generally are sites for lymphocytes (a broad categorization of immune cells) to be recruited and to be \"taught\" what pathogens to recognize.",
"Hope this was helpful and accessible, this is always an interesting topic and I love thinking about this stuff!"
] |
[
"I have to agree with the Magic School Bus episode. I watched it with my kids, and I really don't think I could do a better job of explaining it simply. "
] |
[
"If the environmental conditions were favourable, would it make a positive difference to launch rockets from areas with high elevation such as Colorado?"
] |
[
false
] |
[deleted]
|
[
"Would it be beneficial to launch at high elevation?\nYes. You start off closer to space, which means you need a little less fuel or can carry a bit bigger payload.",
"But Colorado? No. The best places to launch rockets into space are locations near the equator. This is because the rockets more or less piggy-back the rotational kinetic energy of the earth, reducing the energy needed to achieve orbit. Points along the equator have the highest rotational kinetic energy, because they are the furthest from the axis of rotation- further, I would bet, than the Colorado mountains."
] |
[
"For low Earth orbit, most of your energy is spent accelerating sideways rather than lifting the rocket up. Consider that the ISS orbits the Earth every 90 minutes, so it is moving very fast. Because of this, being close to the equator is more helpful than being high up.",
"Not that being high up doesn't have some advantages - there is a little less potential energy cost and the atmosphere is thinner so there is less drag, allowing you to save some fuel costs. But construction of and shipping materials to a launch facility on a mountain costs much more too. The total costs don't end up being a big advantage. And for safety reasons, it is a good idea to build your launch site with an uninhabited area to the east in case your rocket explodes and crashes, which adds another constraint.",
"The most used launch facilities for large rockets (Cape Canaveral, Guiana Space Centre, Baikonur Cosmodrome) tend to be about as close to the equator as the relevant space agency has access to with a large uninhabited area to the east. None of them are very high up in altitude."
] |
[
"Theoretically, yes. The higher you start, the easier it will be. ",
"However, there are quite a lot of variables in play besides elevation. First, the closer to the equator the better, as you get a boost from the rotation of the earth.",
"Second, you need the infrastructure available to support a space program. Roads, personnel, large enough area, etc.",
"And third, you need to have a clear 'downwind' path for safety. You wouldn't want your rocket blowing up over a city. ",
"All these reasons is why the US built it's space program in Florida. Tons of flat land, major metropolitan area relatively close by, ocean downwind. "
] |
[
"Do things that have similar scents/smells have similar chemical makeup? Or can two distinctly different things with distinctly different chemical makeups smell the same?"
] |
[
false
] | null |
[
"Actually, they just have similar ",
" but may have completely different compositions. Certain molecular bits (functional groups as they are called) have shapes that cause certain molecules to fit in certain receptors, but molecular bits that are similar in shape and size can also fit in those receptors.",
"The other half of it is your interpretation. The scent of pine needles and lemons is pretty distinct, and not something most people would confuse, even though the molecules (pinene and limonene) are pretty similar in shape and composition."
] |
[
"A bit of trivia:\nStereoisomers can also have different smells.\nAn example is R-carvone (spearmint) and S-carvone (caraway seeds)."
] |
[
"\"An alternative to the widely accepted theory of shape olfaction\"",
"Eh, the shape theory is more testable and makes more sense."
] |
[
"How do we know which river merges into which and continues being that river?"
] |
[
false
] |
I.E. How do we know the Missouri River flows into the Mississippi instead of the other way around?
|
[
"The bigger river is the main one. Look at the convergence between the Mississippi and Missouri rivers ",
"here",
". The Mississippi river is the bigger one.",
"It's worth noting that you are sort of working backwards here. The Misssissippi was named downstream, at the mouth, and then mapped backward to the source. This is simplified but... it's less a matter of following the Mississippi down to the spot where it joins with the Missouri and then figuring out what to name the resulting river, and more a matter of following the Mississippi upward, coming to a fork in the river, saying \"ok, the larger side is the Mississippi, so we need a new name for the smaller branch leading in\""
] |
[
"Just wanted to add, sometimes things are named and then we just go with it even though it should change when more is discovered. Where the Ohio meets the Mississippi, the Ohio is the larger, so it should be the Ohio to the gulf. "
] |
[
"Also true"
] |
[
"Ask Anything Wednesday - Biology, Chemistry, Neuroscience, Medicine, Psychology"
] |
[
false
] |
Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...". Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists. Please only answer a posted question if you are an expert in the field. . In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away!
|
[
"You still produce respiratory droplets just through normal breathing, you just don't produce as many of them. And most people cough or sneeze occasionally for reasons unrelated to having a virus (like dust, or stepping out into the sun, etc). Asymptomatic spreading is probably much less effective than symptomatic spreading for most viruses. Just because it happens sometimes doesn't mean it's necessarily common."
] |
[
"How does asymptomatic viral shedding cause new infection, if a virus is typically spread by respiratory droplets?"
] |
[
"What’s the process of making a vaccine? Can you elaborate on vaccines with dead or alive viruses?"
] |
[
"Why does the hair on the average human head continue to grow while all other primates have hair that stops naturally at a relatively short length?"
] |
[
false
] | null |
[
"It's theorized that long human hair came about much in the same way.",
"Citation?",
"If this was a Fisherian runaway process, then that would mean that many individuals should have a strong ",
" predisposition to be attracted to individuals with long hair. I'm rather skeptical of that. I did a really brief search, and I've been able to find lots of places that say \"long hair could be the result of a Fisherian runaway selection\", but no where have I been able to find any evidence. ",
"Fisherian runaway selection is one of those things that is really freaking cool, invoked as an explanation for damn near everything people can't explain in evolutionary biology, but damn near impossible to demonstrate in humans, and thus probably accounts for a lot less than it gets invoked for.",
"I think \"It's theorized...\" is a little bit too strong of a statement. \"Some people have speculated...\" seems more apt, although I'll happily eat my words if there's evidence out there that I haven't been able to dig up."
] |
[
"It wouldn't, since by the time most men go bald, historically they already would have passed on their genes. Aka Doesn't Matter, Had Kids."
] |
[
"Think Peacocks.",
"Peacock feathers likely evolved because Peahens saw brilliant plumage as a sign of health. So, Peahens who liked brilliant plumage mated with Peacocks who had brilliant plumage.",
"The male children of these Peacocks and Peahens likely had more brilliant plumage, while the female children likely had a preference for brilliant plumage. So, they mated.",
"Their male children likely even had ",
" brilliant plumage, and their female children likely had ",
" of a preference for brilliant plumage. And so on and so forth, until you get the ridiculous Peacock feathers of today.",
"This process is called Fisherian runaway sexual selection.",
"It's ",
" ",
" that long human hair came about much in the same way. After early humans lost much of their body hair, longer head hair became a sign of good health. So humans who had long hair and a preference for long hair mated, producing children who had longer hair and a bigger preference for longer hair. And so on, and so forth."
] |
[
"Does the salinity of ocean water increase as depth increases?"
] |
[
false
] |
Or do currents/other factors make the difference negligible at best?
|
[
"As the name suggests this circulation is driven almost entirely by changes in temperature and salinity",
"This is one of these 'facts' that are often repeated, but are actually false, and it's simple to explain why. Aside from mixing within the ocean interior, all processes that affect the density of water (e.g. evaporation, precipitation, and sea-ice formation) occur at the surface. As a result, whilst it's possible to form dense waters at the surface of the ocean (which can sink), there is no process that can reduce the density of the resulting deep waters, and thereby bring them back to the surface. In other words, it is ",
" for the 'thermohaline circulation' to be driven by changes in temperature and salinity.",
"In actual fact, the more-accurately-named meridional overturning circulation is chiefly driven by a combination of winds in the Southern Ocean, and interior mixing (e.g. ",
"Gnanadesikan (1999)",
", ",
"Johnson ",
" (2007)",
"). The formation of dense water masses is a necessary condition to have strong overturning, but it isn't the driver."
] |
[
"As the name suggests this circulation is driven almost entirely by changes in temperature and salinity",
"This is one of these 'facts' that are often repeated, but are actually false, and it's simple to explain why. Aside from mixing within the ocean interior, all processes that affect the density of water (e.g. evaporation, precipitation, and sea-ice formation) occur at the surface. As a result, whilst it's possible to form dense waters at the surface of the ocean (which can sink), there is no process that can reduce the density of the resulting deep waters, and thereby bring them back to the surface. In other words, it is ",
" for the 'thermohaline circulation' to be driven by changes in temperature and salinity.",
"In actual fact, the more-accurately-named meridional overturning circulation is chiefly driven by a combination of winds in the Southern Ocean, and interior mixing (e.g. ",
"Gnanadesikan (1999)",
", ",
"Johnson ",
" (2007)",
"). The formation of dense water masses is a necessary condition to have strong overturning, but it isn't the driver."
] |
[
"Cooled water from the poles sinks as a result of both its salinity and temperature profile. Cooler water is denser than warmer water. Cooler water with high amounts of salt is even more dense. So it sinks and is replaced by less dense and less saline (fresher) water. So yes, the salinity of water increases with depth. See ",
"this",
"."
] |
[
"Alcubierre metric and T^00 energy density: how is the \"total energy\" calculated and what does this \"mean\" on a practical level?"
] |
[
false
] |
I realize that people have asked about , but reading the various warp drive papers and trying to understand the physics behind them motivated this question; the question itself is only tangentially related to Alcubierre. The specific question stems from (warning: PDF) and the third equation in that paper: T = -(c /(8 G))(v ρ /(4r c ))(df/dr) Where: If I am not mistaken (and I probably am!), this equation's units come out to be Newtons (kg m/s ) rather than anything I understand as "energy density" (e.g. Joules / m ). That aside, it's often said that a warp drive using these principles would require tremendous amounts of energy (negative energy at that, but let's table that particular aspect for this conversation) -- What's the next mathematical step? Further, , such that the warped spacetime is established and then remains, or is it something that must be expended continuously (representing, perhaps, the per-second energy expenditure)? Appreciate any insight into understanding the math here anyone can offer!
|
[
"The stress energy tensor represents a lot of things together. T",
" represents something ",
" how the P",
" value changes with respect to the X",
" direction (where P and X are 4-momentum and 4-space vectors respectively). {specifically, it's the P",
" flux through a surface of constant X",
" } ",
"Traditionally, we use 0 as a time-like component, so the 0 components are like a time-like slice of space-time (thus just 3-space, so densities of things in this case). And the time-like component of momentum is energy. So, for any time-like slice of space, we expect an energy density of T",
" . That's how I'd interpret the term.",
"I'm not sure about the dimensional analysis you've done, but IIRC, you won't find a \"density\" per se, you'll find that T",
" calculates some energy content given some location (in the coordinate system used by the equations). ",
"So you input something like r = blah, and what the df/dr value is at that point, and what value of rho you are calculating for at that point and what speed the warp is moving with, and then you get an energy for that point. Moreover, you'd probably like to integrate over all 3 dimensions to find a total amount of energy."
] |
[
"I'm having a hard time understanding how units of Force can be used to describe energy density (or even energy content).",
"Recall our first definition of energy in physics. We define work to be Force (dot) displacement. A force applied along some displacement is work. Work is energy. ",
"I was really confused about that dimensional analysis, and looks like I was wrong. I don't have my relativity texts off hand to double check or go into more detail myself, but from some dimensional analysis from the electromagnetic stress energy tensor, I'm pretty sure that wiki is right in that the correct answer is mass density. Or (Joules/c",
")/m",
" if you'd like. How to get from the provided component to that... is not clear to me. I agree with the steps you've taken along the way.",
"Anyway, this is a one-time thing ",
" You'd only need to get a bunch of negative mass density put together once, and you'd have a warped space around it. Just the same as having positive mass density makes a warped space around it permanently that creates gravitation effects.",
"However, because it's negative in energy density there's a trick I think we're trying to use. If we make the space surrounding some area have ",
" energy, then the area has a negative energy with respect to its surroundings. I think there are some experiments that try to manipulate some quantum effects like the casimir effect to create a laboratory experiment we could use to test the effect. (seeing as how we don't know if negative mass can exist at all)"
] |
[
"The final quantity is the squared derivative of a dimensionless function, so will also be dimensionless.",
"This is your mistake! The derivative of a dimensionless function with respect to a dimension-full parameter is ",
" dimensionless. All of the rest of your dimensional analysis is correct, but you should find (df/dr)",
" has units 1/m",
" since the derivative w.r.t. length carries the units of inverse length with it. So following your calculation, you should get:",
"((kg * m)/s",
")*(1/m",
") = (kg*(m/s)",
")/m",
" = J/m",
", energy density, since the definition of a joule is J = kg*(m/s)",
"."
] |
[
"The moon is able to redirect the sun's illumination onto the earth. Does the earth also illuminate the moon the same way? With less, or more intensity?"
] |
[
false
] | null |
[
"Yes it does. If you can find a place with low enough light pollution, (mostly places away from cities) look at the moon when it is in the crescent phase. You will see the bright crescent illuminated by the sun and you will see the rest of the moon's disc illuminated by reflected earth light. It's faint but unmistakeable."
] |
[
"Yes. Think of when the moon is a thin crescent. It is often possible to see the entire moon, because the part not illuminated directly by the sun is receiving reflected illumination from the earth.",
"Also, as bright as a full moon appears, the moon's surface has an albedo of .12, which means that only 12% of the incident light is reflected. By contrast, the earth's albedo is very high when there is extensive cloud cover. This means that the illuminate on the moon resulting from reflection from the earth is much higher that reflection from the moon to the earth."
] |
[
"Sun->Earth->Moon->your eyes on Earth"
] |
[
"Is there hard data on the number of potentially catastrophic issues fixed before Y2K?"
] |
[
false
] |
Most of what I've seen in the 18 years since has been along the lines of "nothing really happened, so the panic was silly." But do we have any data on the number of fixes that prevented disasters the scramble to prepare for it? I guess it might be hard to count the number of times somebody said "well could have been disastrous, I'm glad we caught it", but has anyone put together that type of estimate?
|
[
"As Y2K passed with a low number of computer failures due to the Y2K bug, post-analysis is less of a Computer Science issue, and more something better discussed in terms of business and governance, as your question is less about the science of computing, and more about the human response to the bug. But I'll try to answer your question the best I can anyway.",
"Y2K: The Bug that Failed to Bite",
" has a good overview of some of the issues surrounding Y2K reporting. I'll be referring to it in several places in the following discussion.",
" It details some of the history and efforts of the Global 2000 Coordinating Group, which provides some illuminating information for the topic at hand.",
"There are some significant challenges in gathering data on possible Y2K catastrophes. Firstly, we effectively had two different classes of organizations around the world when it came to Y2K reporting: those that were legally required to report because they were part of an industry involved in significant infrastructure, and those who weren't. Of those who weren't, reporting on Y2K readiness was generally optional. Your local power plant being Y2K compliant is significant; your local McDonalds not so much.",
" Because of this, we only really have good data on regulated industries that were forced to report; even then, who was forced to report and the level of reporting often different between countries.",
"Even within regulated industries, there was often a reticence to openly report any shortcomings. This was especially true in the banking sector; according to George Douglas of the Royal Bank of Canada ([CRAW01], pp.273):",
"\"Banks don’t normally fess up to their shortcomings; if they did, their customers and bank regulators could lose confidence in them and then they would risk losing business.\"",
"Indeed, ",
"this became a problem for Global 2000",
" -- initially the group had intended to release global readiness reports to the public, however many became concerned that there may be a significant flow of capital out of countries and organizations behind on their Y2K readiness, further hampering their ability to prepare for Y2K. In the end, Global 2000 decided to only make the report available to participating organizations, who were permitted to make it available to major investors under an NDA. The reports were never leaked to the press ([CRAW01], pp. 277), however you can see a copy in [CRAW01] on pp. 282.",
"Because of all of this, I'm not sure you'd ever be able to get a really good snapshot of how many disasters were prevented by Y2K fixes. It was in many industries best interests to fix the issues they found as quietly as possible. Companies didn't want to spook investors, and countries didn't want to see an outflow of foreign capital or social panic. Because of all of this, focus was more on ",
" as opposed to ",
".",
"As [CRAW01] reports on pp 279 (",
"):",
"In the run up to Y2K, participants in Global 2000 could reflect on their efforts to fix the bug and maintain public confidence. Paradoxically, if the bug failed to bite, the whole exercise would be open to criticism as a “nonevent.” None-the- less, they felt reassured by member organizations’ claims to have ",
". No doubt failures would occur, such as exchange-rate display panels refusing to function, but their reduction would make them more manageable.",
"However, also in [CRAW01] on pp. 279:",
"Toward the end of 1999, as firms in the group began final preparations for the event, a number of accepted practices gradually eroded. Not only did openness begin to disappear, but collective activities that many Global 2000 members had pushed were not adopted or carried through by the group.",
"I suspect we'll never truly know the totality of the crises averted, due to both the success of Y2K mitigation efforts, the secrecy involved in many efforts, the focus on readiness as opposed to specific disaster scenarios, and the late erosion of best practices as the date itself came closer.",
"I hope this helps!",
" -- [CRAW01]: Crawford, R. J., & Story, J. (2001). Y2K: The bug that failed to bite Berkeley Electronic Press.",
"\n",
" -- I couldn't find a freely accessible copy anywhere; that shouldn't be necessary for the following discussion.",
"\n",
" -- your local McDonalds being Y2K complaint would be important to shareholders and customers, but doesn't really constitute significant infrastructure.",
"\n",
" -- [FEDE99]: Feder, Barnaby J. (1999). Group Rethinks Ratings on Year 2000 Readiness. New York Times, Jan 27 1999."
] |
[
"This makes me think of movies like Deep Impact or Armageddon. In Deep Impact, an asteroid threatens to wipe out humanity, but the government initially keeps it quiet to avoid panic. This story makes me think that’s a very plausible scenario IRL. Before, I would have thought, “how could so many people stay quiet?” I suppose if only a handful of people know the truth, and no worker bee knows the whole story, then indeed a major event can be kept secret.",
"Thanks for the thoughtful morning."
] |
[
"Thank you. That definitely helps. Without more precise numbers, would it be irresponsible to say Y2K could be labeled one of these two options?",
"-A crisis averted because of widespread preparation.",
"-A less serious situation that didn't call for the degree of concern it received."
] |
[
"Why is it that cutting an artery often leads to immediate blood loss and death, but amputating an entire limb carries a high survival rate?"
] |
[
false
] |
Or at least that's the way it's often portrayed in the media.
|
[
"Please don't do this-you're better off putting pressure on the wound and getting immediate emergency help"
] |
[
"Please don't do this-you're better off putting pressure on the wound and getting immediate emergency help"
] |
[
"When a limb is completely amputated, and an artery is completed transected, this allows the artery to spasm, close up, and retract back into the wound. This is why even complete traumatic amputations may not bleed as much as one would expect from such a severe injury."
] |
[
"Which one of the two isomers formed by connecting a benzene ring with the isostructural borazine would be more stable, the one with a carbon-boron bond or the one with a carbon-nitrogen one?"
] |
[
false
] |
If one of the benzene rings in biphenyl was substituted by a borazine one which of the two isomers would prove more stable? Does the fact that the carbon-boron bond is stronger than the carbon-nitrogen one tell the whole story?
|
[
"It doesn't tell the whole story, because you also have to consider the relative strengths of the B-H and N-H bonds. I believe that the N-H bond is stronger, so that should help the case of the rings being connected through the boron.",
"I wish I had time to run a calculation on this molecule so I could say something more concrete."
] |
[
"No, if you make the bridge between the boron and carbon, that's one less B-H bond that can be in the molecule. Same deal for nitrogen. You have to consider it all for an accurate estimate of relative energies."
] |
[
"A quick search on wolframalpha indicates that the B-H bond is slightly stronger than the N-H one, 389 kJ/mol vs 386 kJ/mol."
] |
[
"Is there a way to generate, and subsequently visualize, a tagged protein in vivo?"
] |
[
false
] |
The question is a bit vague. Is there a way to give an animal something (food, injection, etc.) such that it begins to produce the tagged version of a protein? Has this been done? For example, lets say you want to visualize dopamine production in the brain. Can you change the production of the protein such that they begin to incorporate some sort of reporter that can be visualized in vivo? Or maybe...is it possible to transfect a cell with some vector with DNA for the tagged protein (in an in vivo model) such that it starts producing the tagged protein? Or will this be detrimental to the organism? The purpose of asking this question is because I'm just thinking that it might be a way to visualize processes as they happen in a living organism, so we wouldn't have to sacrifice and do histology or something.
|
[
"Not my branch of biology, but this sort of thing definitely does happen. However I don't think it's very practical in adult animals. In cell/microbiology you can generally transfect or transform the cell with either an altered version of that same protein fused with a ",
"GFP",
" reporter or simply GFP with the same promotor/operator as the gene of interest. These can both serve as reporters for gene expression, with the GFP fusion tag allowing you to visualize mRNA or protein localization in the cell at the cost of possibly interfering with function. I don't think the GFP by itself is harmful, however. To get the genes into an animal, you need to perform some kind of gene therapy. This is certainly possible, but I'm not sure too easy on animals that have already developed. However I think it is done quite frequently on the zygote so the organism can be studied later in the life cycle. It is especially used to study gene expression during",
" embryogenesis",
". Injecting some kind of vector into an adult organism would be much harder. And for humans, probably not an ethical line of research. Another obvious limitation is that you have to more or less be able to see inside the organism you're researching, so visualizing the ",
"nervous system of ",
" is easy but for something like a mouse you're only going to be able to see it in the skin or ",
"eyes",
". Of course you can just go ahead and ",
"slice it up",
" afterwards."
] |
[
"I don't know about production, but you can do ",
" imaging using transfection in a variety of models. One example is ",
" tadpoles, which are transparent enough to visualize while still alive; you can transfect a marker for whatever you're interested and visualize it many times in a living organism."
] |
[
"Absolutely! We do this a lot in my line of work, often by transfection (as you suggest) which causes the cell to express the a fluorescent version of a protein, or introducing some kind of fluorescent molecular probe that selectively binds to the protein in question.",
"Generally, these sorts of probes emit in the visible range. The trouble with in vivo studies is that visible light is highly scattered and absorbed by the tissue. You can just about get away with it in small animals, but it's a lot tougher in humans. If you want to image in vivo on a very small scale, one could use an intravital fluorescence microscope - it's invasive but it circumvents some of the issues with signal attenuation."
] |
[
"How long can a virus’s incubation period truly be?"
] |
[
false
] |
[deleted]
|
[
"HIV can take years to manifest symptoms, or even show up in tests. It's part of why they recommend testing regularly, even if you haven't been sexually active in a while, or your last test came back clean and you've been monogamous since then."
] |
[
"I know that ",
"rabies",
" is known to have a possible incubation period of up to 7 years. If I recall correctly, HIV and one of the herpes viruses can have incubation periods on the scale of decades as well. ",
"Again, if I recall correctly (and there is no guarantee that I do), it has something to do with viral propagation through the nerve cells. A rabid bat takes a chunk out of your leg one day and the rabies virus infects the nerve cells in your leg. Those nerve cells infect the ones nearby, etc, all the way up until it reaches your brain. That's when symptoms begin."
] |
[
"Just a quick correction, the median and mean incubation period for Covid-19 is about 5 days. 14 days represent the upper end of the incubation period and is the exception, not the rule.",
"Sources: ",
"https://www.rki.de/DE/Content/InfAZ/N/Neuartiges_Coronavirus/Steckbrief.html#doc13776792bodyText4",
" (in german)",
"https://www.who.int/news-room/q-a-detail/q-a-coronaviruses",
"https://www.medscape.com/answers/2500114-197431/what-is-the-incubation-period-for-coronavirus-disease-2019-covid-19"
] |
[
"If there used to be a lot of water on Mars, what happened to it? Did it leave the planet and atmosphere?"
] |
[
false
] |
^
|
[
"Mars almost certainly had an ocean worth of water early in the life of the Solar System. However, the planet's low mass means it also has a relatively low escape velocity, and all sorts of escape processes can cause atmosphere to leak out to space. ",
"Water vapor on its own is just a bit too heavy to easily escape Mars (heavier molecules have slower speeds, and thus a harder time reaching escaping velocity). However, Mars has no form of ultraviolet shielding the way that Earth has an ozone layer. Gaseous water vapor that evaporated from the oceans could push high into the atmosphere and be exposed to ultraviolet photons. These are energetic enough to split water into its constituent hydrogen and oxygen atoms.",
"Hydrogen is a very light atom, and can very readily escape Mars out to space. On an early Mars, this would primarily occur through two processes:",
"Just being warm enough, the fastest moving hydrogen atoms can reach escape velocity.",
"Early in the Solar System's there were a lot more impacts from asteroids, and Mars happens to be located very close to the asteroid belt. From our estimates of impact frequency at that time and location, there were more than enough to blow off most of the Martian atmosphere in just the first 100 million years.",
"(A lot of folks might mention the fact that Mars currently doesn't have a magnetic field and thus exposes it to the full force of the solar wind. While that's an important process now, it's likely Mars did have a magnetic field early in its history.)",
"So that's what happened to the hydrogen that was in all that water...but what about the oxygen? Well, an oxygen atom is 16 times heavier than a hydrogen atom, so it's considerably more difficult for it to reach escape velocity. ",
"However, free oxygen is also very reactive, so most of it likely reacted with surface minerals before it had a chance to escape. After all, the Martian surface was originally black like lava rock; only by getting massively oxidized did it turn red.",
"If you want to know more about atmospheric escape processes on all the planets, I'd highly recommend ",
"this PDF",
" - great layman-level reading material.",
": Water vapor in the atmosphere was split up by ultraviolet light. The hydrogen was light enough to escape into space, while the oxygen got locked up in rocks on the surface."
] |
[
"That's actually an incredibly cool tidbit about why mars is red. Is this the only/biggest reason for the colour?"
] |
[
"If we look far enough back at the history of mars would there be an explanation as to how it built up an ocean in the first place, before it all started disappearing? When I see water on mars being explained it always starts half way through the story where mars already has a ton of water and it all starts disappearing from there. "
] |
[
"How do the antibodies in mother's milk get into baby's blood stream?"
] |
[
false
] |
Don't they get destroyed in the baby's stomach?
|
[
"Great question. I didn't know either, so I looked it up a little and found this: ",
"The capacity of the digestive tract to absorb intact proteins must not last beyond one or two weeks, since once foods other than milk are ingested the proteins and other antigens in them would also be absorbed intact and could act as immunogens to which the growing animal would become allergic. IgA in milk is, however, rather resistant to digestion and can function within the gut even after intact absorption into the bloodstream has ended. Human colostrum is also rich in IgA, with the concentration highest immediately after birth.",
"From: ",
"http://www.britannica.com/nobelprize/article-215587"
] |
[
"Antibodies are not tiny! They are ~150 kDa! Just as a clue, the average molecular weight of an amino acid is 110 Da. Hence, a 150kDa protein would have around 1360 amino acids! ",
"Tiny structure doesn't really have relevance as far as enzymatic processes go either. "
] |
[
"My knowledge is in non-human domestic animals, but we are all mammals, so I hope you will still find it relevant.",
"No, they do not get destroyed in the stomach. During the first day, the PH is quite a bit higher due to residual amniotic fluid in the GI, and the epithelial cells lining the digestive tract have different properties which allow them to take in whole protein, including immunoglobulins. At this time the digestive tract is said to be 'open' (although an open GI means other things too, depending on the context). ",
"The ingestion of immunoglobulins is aided by FcRn (neonatal Fc receptor) which moves the immunoglobulins and transports them from the lumen to the basolateral side of the cell. As the cells undergo turnover in the GI (which occurs fairly quickly) they lose the FcRn, the pH becomes lower, and the digestive system becomes 'closed'. The combination of immunoglobulins available in the colostrum varies by both species and time lactating. Most of the time for domestic animals it will be IgG and IgA, but sometimes it is IgE, and rarely it is IgM. ",
"After they get into the system, they have a variable half life based on their particular physical properties. Once the maternal antibodies are gone they are gone forever, but by that time the neonate's immune system should be able to respond on its own. The neonate does not inherit the immunity of the parent, but is rather able to form its own immunity from that point forward.",
"Piglet article!",
"EDIT: for comprehension"
] |
[
"Electrolysis of water yields proportionally small amount of gaseous Oxygen. Where does the Oxygen go?"
] |
[
false
] | null |
[
"Some of it might turn into carbon dioxide, but then you should just be collecting carbon dioxide instead.",
"You have nothing listed that can form a solid precipitate and didn't report one. Did the electrode have a metal core? Is it possible that there was a leak on the oxygen side?",
"You probably want to use electrodes made of good stainless steel or platinum or something else relentlessly nonreactive. Carbon electrodes are more for sparks and melting things. If it is leaking then it will probably still leak with a new electrode, and if it is chemical then changing the electrode will prevent oxygen from disappearing."
] |
[
"Something like this is more suited for ",
"/r/chemhelp",
" or ",
"/r/homeworkhelp",
"."
] |
[
"Perhaps, I will try. Thank you :)"
] |
[
"Can you use a regular compass on Mars?"
] |
[
false
] | null |
[
"Thank you so much for the thorough answer!"
] |
[
"Thank you so much for the thorough answer!"
] |
[
"I've seen some more recent studies that point towards Earth having a large moon that is in a relatively stable orbit being the reason that our planet still has a molten spinning core after billions of years. It's an alternative theory to the old \"radioactive materials are the reason Earth still has a molten crust and hot spinning core\"... one that makes more sense because the tidal forces from the Earth and Moon interacting with each other does create serious measurable stresses on the Earth. It also explains why planets in our solar system without large moons are cold and dead below their surface but the more Earth sized moons of Jupiter are still very much warm and seismically active.",
"https://www.sciencedirect.com/science/article/pii/S0012821X16301078",
"https://cosmosmagazine.com/geoscience/no-moon-no-magnetic-field-no-life-earth-study",
"Btw. Earth's moon also has a molten core as a result of the ebb and flow of the gravity pulling on the two bodies. As a result of this lunar dynamo, once-upon-a-time the moon generated it's own strong magnetic field.",
"https://www.nasa.gov/topics/moonmars/features/lunar_core.html",
"http://advances.sciencemag.org/content/3/8/e1700207"
] |
[
"Could you carbon date something from the future?"
] |
[
false
] |
I was watching Terminator guys! And I started wondering whether you'd be able to date something from the future
|
[
"In principle yes, but it won't be of much use.",
"Carbon dating doesn't determine the age of an object, but rather how long it (or the organic materials it was made of) has been dead.",
"Carbon comes in multiple forms (isotopes). The most common one, carbon-12 is stable. However, a heavier form, carbon-14 is radioactive and will automatically decay after some time (half life of about 5700 years). Carbon-14 is created in the atmosphere due to an interaction between atmospheric nitrogen and cosmic radiation. ",
"Plants then absorb carbon of all forms through photosynthesis. This is a continuous process, so even though some of the carbon-14 will decay, more will be absorbed and ultimately, the level of carbon-14 in the plant will be equal to the level of carbon-14 in the atmosphere. When animals eat the plant, it will absorb the carbon in the plant and the body of the animal will also maintain a level of carbon-14 equal to that in the atmosphere.",
"When the plant or animal dies, this process stops. The carbon-14 present in the plant will slowly decay, and won't be replaced. So the carbon-14 level in the plant or animal will decrease with time. By measuring the level of carbon-14 in the material and comparing it with the atmospheric level, we can estimate how much time has passed since the organism stopped processing new carbon.",
"There are a number of additional considerations to take into account. For one, the burning of fossil fuels changed the picture. Fossil fuels are created from organic remains in a very slow process. By the time the remains have turned into oil, almost all the carbon-14 will be gone. So when we burn fossil fuels, we're dumping a lot of stable carbon into the atmosphere, but very little carbon-14. This has changed the ratio between stable carbon and carbon-14 in the atmosphere in the last 200 years. And this has to be taken into account when performng carbon-dating.",
"On the other hand, nuclear explosions provide a good source of carbon-14 and nuclear tests in the '50s and '60s caused an increase in the atmospheric carbon-14 levels. An archaeologist that tries to carbon-date objects from our era millenia from now has to be aware of this.",
"Now, if an object from the future is transported back to our time somehow (lets ignore the issues surrounding time travel). What would we measure when we'd try to date it?",
"If it's still alive, then we'd measure the carbon-14 level of the atmosphere from the future time that the visitor came from. This gives us very little information, since atmospheric C-14 levels will depend on how badly we managed to mess up our atmosphere between now and that point in the future. Massive nuclear war just before the time traveler departs? Spike in C-14 levels. Still burning tons of fossil fuels? Lower C-14 levels. In any case, we won't be able to get any time-measurement out of it.",
"If the visitor has been dead for some time (preferably hundreds of years), we can perform carbon-dating to get an estimate as to how long it has been dead. But this will be a very rough estimate, since we'll have no idea what the atmospheric C-14 levels were in the lifetime of the time traveler. In addition, we'd only be able to make a rough estimate of how long the visitor has been dead, not from which point in the future he came."
] |
[
"Holy shit. I didn't know how bad I wanted to know this until finding this post! Thank you for your comprehensive answer. "
] |
[
"You hinted at a possible answer without striking it. The so called 'bomb pulse' ",
"https://en.m.wikipedia.org/wiki/Bomb_pulse",
"Basically because of the atomic bomb tests the ratio of C14 is elevated as compared to C12. The rate that this ratio falls has been tracked and it is not unreasonable to think it could be extrapolated. ",
"This however relies on some assumptions.",
"1) there will be no major changes to the C14/C12 ratio (i.e. No more bombs, no real changes to fossil fuel burning) in the future and therefore our extrapolations would remain valid. \n- This is not very likely due to global warming, peak production, technological advance and sadly North Korea.",
"2) the future biological object is not from so distant in the future that the increase in C14 levels due to the bomb pulse would no longer be present in the atmosphere it lived in or was created in so they are no longer present.",
"So the answer is a pretty safe yes for things in the very near future, a maybe with big error bars but probably no for 10 to 100 years in the future window and a definite no too much beyond that."
] |
[
"Is it possible for a large moon have a satellite of its own?"
] |
[
false
] |
I was watching and it mentioned that the Galilean moons were the size of planets.
|
[
"Due to the tidal effects from the host planet, orbits around a moon would not be stable in the long-term. In the short term, you can orbit a moon just like any other body, but we don't expect to find natural satellites of moons due to how brief the arrangement would be."
] |
[
"I don't think they left anything in orbit. There are currently two craft that I know of in orbit around the Moon, the ",
"Lunar Reconnaissance Orbiter",
" which has been orbiting for nearly 5 years, and the ",
"Lunar Atmosphere and Dust Environment Explorer",
" which has been orbiting for about six months."
] |
[
"Hi, did the Apollo projects leave something in orbit around the moon? Is\nit still there?"
] |
[
"Chemically, what differentiates a good shampoo from a bad one?"
] |
[
false
] |
Like chemically what ingredients should I be looking for and which ones should I avoid? I've been having a hard time finding correct information about this since sites are terrible. So which ones SHOULD I look for/get? What are the good ingredients? I've been googling and I can't find credible sites for this. It's bothering me. In before someone recommends drbronner, what's so special about them? Seems like reddit really likes their marketing.
|
[
"As an expert, I'm going to disagree with everyone except ",
"thisaccountisbs",
". My background: I worked for one of the world's largest producers of shampoo in R&D.",
"Shampoos are not slightly acidic, their pH isn't that important.",
"The surfactant is really important in making the stuff work.",
"There are additives to make them smell good etc etc but mostly they are affecting your perception of how well it works. Some of the anti-frizz and moisturizing stuff isn't complete bull, though.",
"A great piece of data that floated around the company: They did a comparative test of two shampoos to see which one consumers preferred. One was white, the other had a small amount of dye in it to add a pale yellow color. Otherwise, they were completely identical. Consumers preferred the yellow one because people associated the off-yellow color with a higher chemical content, ie it \"cleans better.\"",
"Also, NO, the lather is NOT necessary.",
" There are literally thousands of surfactants that work even better than the common ones (sodium lauryl/laureth ether sulfate) but most of them never make it out of the research lab. There are specific cases where people want soap that doesn't lather (mostly industrial) but for home use, non-lathering soap doesn't sell because consumers have become conditioned to believe that if soap doesn't lather, than it doesn't work."
] |
[
"This is going to sound glib, but you should use whatever shampoo makes you happy. They all more or less work the same, but shampoo companies are really good at manipulating human psychology. Even knowing all this, when I go to buy my next bottle of shampoo I can't help but think about how dumb I am for springing for the more expensive stuff since its exactly the same, but that I can't help but feel like maybe it works a little better or at least is more pleasant to use. ",
"If you're literate in gibberish (ie, chemical naming systems) you can read the back of most shampoo bottles and you'll find that they all more or less have the same ingredients, and what really matters is the relative amounts. There was some hubabaloo in the industry a couple years ago about guar or some such, but seriously. Its all the same. ",
"Which is the reason that I can't make a specific recommendation. There is no single shampoo that is the \"best.\" I have ones that I know that I enjoy using, but one of the things that frustrated the R&D people at the shampoo company I used to work for is that there is simply no accounting for personal preference.",
"The purpose of conditioner is to restore the protective layer that shampoo strips from your hair. The oil in your hair is really important for protecting it from damage from the environment, but its also where a lot of unpleasant smells and sometimes dirt can get trapped which is why shampoo is designed to remove it. Conditioner replaces it with a polymer (ie, plastic) that will protect the hair until it is washed out and makes it feel smooth and silky again. The lubrication also helps prevent knots and tangling.",
"The thing about sulfates is silly. Some people are allergic to sulfates, 99.999% people aren't. If you've eaten a frozen pizza without having an adverse reaction, you're not allergic to sulfates. There may be something about the environment when it comes to sulfates, but I'm not familiar with that."
] |
[
"I seem to recall it was at least a decade old. ",
"As for organic and green...trust me, the marketers manipulate those too. For example: Ever notice how recycled paper products are usually brown? This is to make you think, \"Oh, they didn't want to waste money/resources dying/bleaching this paper and so they just left it its natural color. I feel so good about myself for using this environmentally friendly product, even if it is a kind of ugly color.\"",
"Most recycled paper products come from office paper, which is white. The brown is a dye."
] |
[
"Why don't cats and dogs get brain whiplash when they shake their head?"
] |
[
false
] |
You know those shakes dogs do when they try to get rid of water? Seems quite high speed. Cats do it just to straighten their hair. Yet they are fine with it. Is it because their brains are small compare to humans?
|
[
"This research on ",
"wet dog shaking",
" suggests that they shake at a frequency of 4Hz. The high speed video on the site seem to show that the dogs actually only shake their head by a fairly small amount, maybe only 40 degrees of arc in total.",
"I just tried to shake my head at the same speed and arc, it's not too difficult to do."
] |
[
"But if you look at ",
"this plot",
" it clearly shows that all the dogs they have data for (circles) are shaking at less than 10 Hz, with larger breeds shaking slower.",
"I will concede about the video however, I only watched the first 2 or 3 shakes. The amplitude does get bigger with time."
] |
[
"It says dog shakes up to 30Hz.",
"This video, from your link",
" show the dog shaking his head almost 180 degrees from side to side.",
"I am sorry, you are obviously wrong."
] |
[
"Could you trap light in a fibre optical cable, if you sent a short beam through and spliced the ends together before it reached the other end?"
] |
[
false
] |
And if yes, how long would it continue to travel, assuming the cable is a couple of light seconds in length? Edit: Thanks for you answers.
|
[
"No need for such an elaborate procedure. ",
"Getting light to travel in a circular path isn't anything super exciting and is done routinely. These structures are called ",
"optical ring resonators",
" and they have widespread applications in fiber optics, especially telecommunication.",
"Here's what they look like",
"and an animation",
" and ",
"another",
"a lecture on youtube"
] |
[
"You can trap light in a small glass sphere such that it ",
"races around the inside edge of the sphere",
" many times before leaking out."
] |
[
"Even if you could splice it quickly enough there is still attenuation in the fibre that gradually reduces the energy of the propagating light. In the best optical fibre the attention is about 0.2 dB/km at 1550nm, which is actually very close to the theoretical minimum for silica. Even if we assume the splice is perfect and contributes nothing to the overall loss of the fibre the amount of light energy in the fibre will halve every 15km. So after 30km we have 1/4 of what we put in, after 45km we have 1/8 and so on. ",
"This is why we use fibre amplifiers in long haul telecommunications links. Without which fibre optic communications in between the continents is impossible, or at least completely impractical. "
] |
[
"Where do lichen get their phosphorus?"
] |
[
false
] |
All life on Earth has DNA, and DNA is made of Carbon, Hydrogen, Oxygen, Nitrogen, and Phosphorus. Therefore, all life needs access to these 5 atoms in order to grow. Lichen seem to be able to grow almost anywhere. I understand that they get their carbon from CO2 in the air (via photosynthesis), and hydrogen/oxygen are present in water. Wikipedia says some lichen have cyanobacteria, which is capable of nitrogen fixation (i.e. extracting nitrogen from the air into usable form). This explains nitrogen. But there is no phosphorus in the atmosphere. Where do lichen get their phosphorus?
|
[
"It is thought that they derive most of their phosphorus directly from the rocks they grow on with* some likely minor contributions of P in rain water. ",
"This paper suggests that they enhance weathering of rocks to increase P availability",
"edit: with instead of without"
] |
[
"As far as I know all rocks have some amount of phosphorus, but the concentration can vary ",
"by a factor of 30",
". Lichen productively would certainly be limited on very low P rocks but I don't know the threshold at which it would become more limiting than other factors. "
] |
[
"Interesting! So does that mean lichen cannot grow on rocks that have no phosphorus? If my roof tiles had no phosphorus, would that prevent lichen from growing on my roof? (Or can they use phosphorus from dust/pollen when in an urban environment?)"
] |
[
"Is there an online resource where one would be able to find info on the relative safety of certain substances to humans?"
] |
[
false
] |
This is regarding a number of substances/chemicals. I've tried using google scholar, but the papers that come up are rarely relavent. Any help for a layman here?
|
[
"MSDS"
] |
[
"You can search for the MSDS for the particular product and get all the necessary information, though I will warn that things will often sound much more dangerous than they are (even water can be deadly, when misused!). If you want strictly toxicological information, the MSDS is probably sufficient. If you're wondering if it's really okay to use something in the open air or to touch it with or without gloves, sometimes it's hard to tell."
] |
[
"erowid.org"
] |
[
"E-Coli in your body."
] |
[
false
] |
Okay, so I understand that there is E-Coli in the body naturally. So why does the body respond so badly to E-Coli from an outside source? Also, Does anyone know how much E-Coli it takes to actually cause the body to respond adversely?
|
[
"What you are talking about is the difference between colonisation and infection. Colonisation is basically the 'natural' populations of bacteria in and on your skin, mucus membranes, and gastrointestinal system. Infection occurs when the virulence factors of colony of bacteria outcompete the host immune system. This happens for a variety of reasons and depends of a huge number of factors. We'll look at food poisoning as an example. E. coli are present in large numbers all around the body, just living their lives, without causing any great harm because the body can control them. Usually, the E. coli that cause food poisoning will be a different strain from the colonies that live in your body, strains that have greater virulence. But they don't have to be. If a colony strain alters their virulence factor expression, or come in contract with another bacteria that can increase their virulence by changing the environment or providing certain nutrients, etc, they can change from colonising to pathogenic, and cause disease. ",
"Technically, infection occurs when the number of microorganisms reaches 100 000 per gram of tissue, or per mm3. This isn't a hard and fast number and depending on what paper you're reading this will threshold will change a bit. It's also more applicable to wounds than to gastro, but you get the point. "
] |
[
"different strains",
"http://www.cdc.gov/ecoli/general/"
] |
[
"I'm pretty sure the most common pathogenic strain of E. coli is the 0157:H7 strain that produces a shiga like toxin that causes diarrhea."
] |
[
"When sending things to other planets, why do we choose not to use the moon as a mini gravity-assist? Surely it would just reduce fuel (even slightly) and thus reduce the mass of spacecraft?"
] |
[
false
] | null |
[
"We can and do! The STEREO probes used the Moon for instance.",
"One thing that makes it tricky is that the Moon moves so fast in ",
". The Moon is orbiting the Earth at 1 km/s, compared with other planets that are moving at 10s of km/s, but the Moon is much closer, so its angular speed is much higher. The Moon moves around the Earth at about 12 degrees a day. Venus at its most rapid moves across the sky at about 1 degree a day.",
"This means that if you have to delay your launch by a couple of days due to weather, the Moon is in a completely different location in its orbit, and a gravity assist might not work so well. The Moon is also so close that you can't fix this with small adjustments along the way. You can wait until the next month, but by that point the other planets will have moved, and you're probably in an even worse situation.",
"With Venus or Jupiter or whatever, delaying by a few days only makes a small difference in the orbital configuration of the solar system. And because your probe is travelling for months, you can make small adjustments to somewhat make up the difference.",
"So yeah, we can use the Moon, and we do use it fairly often, but it's a little tricky, so we don't use it every time."
] |
[
"Lightning around the time of launch is a big no-no. Also wind shear can affect stability/control of a vehicle during launch. Flying into clouds with ice particles (e.g. hail) could be bad for the structural integrity of the vehicle. Remember that a breakaway piece of foam ended up dooming the shuttle Columbia.",
"Here's a sample list of launch criteria:\n",
"https://en.wikipedia.org/wiki/Launch_commit_criteria"
] |
[
"Lightning around the time of launch is a big no-no. Also wind shear can affect stability/control of a vehicle during launch. Flying into clouds with ice particles (e.g. hail) could be bad for the structural integrity of the vehicle. Remember that a breakaway piece of foam ended up dooming the shuttle Columbia.",
"Here's a sample list of launch criteria:\n",
"https://en.wikipedia.org/wiki/Launch_commit_criteria"
] |
[
"Why is Neoprene more resistant against ozone?"
] |
[
false
] |
Why is Neoprene more resistant against ozone than regular rubber (latex)? Regularly, I think that the dubble bonds in the rubber polymers burst when they react with ozone, so that the whole rubber eventually ruptures. This doesn't occur to the same extent with Neoprene (polychloroprene). Why? Does it have something to do with the chlorine in the rubber, that the chlorine reacts with the ozone instead of the dubble bonds? Please explain!
|
[
"Thank you!!!"
] |
[
"Is it so that the more crosslinks there are in rubber - the more oil resistant the rubber is?"
] |
[
"Yes, ozone deteriorates rubber by reacting with the double bonds to cause breaks in the rubber polymer. ",
"Ozonolysis is an electrophilic reaction",
", meaning the ozone attacks electron rich double bonds. Natural latex rubber has ",
"methyl group substituents on the double bonds",
" remaining after polymerization, and alkyl groups are electron donating, so its double bonds are electron rich, and readily attacked.",
"Neoprene rubber has a ",
"chlorine on the double bond",
" instead, and being electronegative, chlorine is electron withdrawing, which leaves the double bond electron poor. So ozone does not attack it as readily. ",
"Butyl rubber",
" has fewer double bonds remaining than natural rubber (polyisoprene), so it is ",
"somewhat resistant to deterioration by ozone",
" for that reason. But neoprene (polychloroprene) has just as many bonds as natural rubber (polyisoprene), and is resistant to attack by ozone because the double bonds are electron poor."
] |
[
"Why don’t wild animals get ill from drinking dirty outside water whilst we do?"
] |
[
false
] |
Dirty water (found outside) is portrayed as having all sorts of bacteria, viruses and fungi etc meaning that we can’t drink it without getting very sick. How is it we’ve evolved to have very little tolerance for this meanwhile other animals can drink almost any water found outside and be fine?
|
[
"Well, we haven't, really. For the vast majority of our existence on this planet we drank the same water as other animals. Over a billion people make do without a source of clean water even today. You rarely get \"very sick\" from drinking water from a river or a lake, unless it's obviously contaminated in which case other animals tend to avoid it as well."
] |
[
"Most wild animals have parasites precisely becaue they drink dirty water and eat raw food. The thing is most parasites don't outright kill their hosts so there is a certain managable parasitic load.",
"Heres a pretty great and easy to read article",
" from the University of California about how mammals generally deal with parasites and pathogens in the wild."
] |
[
"People have been drinking outside water since water has existed. Unless it has been exposed to pollutants (especially human fecal matter) it isnt dangerous. If water is infected animals as well as humans can get sick but often have partial immunity to common local bacteria. So would feral humans living in the same conditions. Like animals, we can often tell if something smells or tastes \"bad\""
] |
[
"Do lucid dreamers have a better chance of waking up from a coma?"
] |
[
false
] | null |
[
"Sleeping and Coma are two completely different things. In a full coma there is no sleep-wake cycle. The brain is turned off just enough so that the body doesn't respond to anything, but not so much that the heart stops. Sleep, on the other hand, is a very active brain process full of signals and semi-random nerve firings, most of which we don't fully understand. So a man in a coma, does not dream, and since he does not dream, he cannot lucid dream and attempt to wake himself."
] |
[
"He is talking about a tv episode coma i.e. The patient is 'fine' but just in a 'coma' yeah it is kind of hard to understand but i get it"
] |
[
"Being physically completely fine and being in a coma are mutually exclusive states, I'm sure."
] |
[
"How close to a perfect sphere is a black hole?"
] |
[
false
] |
Is there much variation in the surface of a black hole? I'd imagine because of its relatively small size and huge mass black holes would be very close to a perfect sphere.
|
[
"A black hole with zero angular momentum has perfect spherical symmetry. But any realistic black hole will likely have ",
" angular momentum. In that case, it's not longer spherically symmetric but rather axially symmetric about the axis of rotation."
] |
[
"A better visualization of that, for me at least, is if you blow up a billiards ball to the size of the earth, it would have higher mountains and deeper valleys"
] |
[
"I don't think anyone takes the time to identify and name mountains on billiard balls. "
] |
[
"Does muscle repair faster when asleep, rather than lying completely motionless?"
] |
[
false
] |
Let's say you go to the gym and do some lifting, for example bench press. Will your pectorals repair faster if you're sleeping or will it repair at the same rate as if you were lying still? Thanks
|
[
"Your answer is a combination of pseudoscience and myth. Lactic acid isn't the boogeyman it is purported to be, and stretching has had scant support in scientific studies for reducing injury or soreness, see: ",
"http://www.ncbi.nlm.nih.gov/pmc/articles/pmc1250267/"
] |
[
"Your answer is a combination of pseudoscience and myth. Lactic acid isn't the boogeyman it is purported to be, and stretching has had scant support in scientific studies for reducing injury or soreness, see: ",
"http://www.ncbi.nlm.nih.gov/pmc/articles/pmc1250267/"
] |
[
"Sleep involves increased secretion of growth hormone, which does stimulate increased protein synthesis in skeletal muscle.",
"http://science.education.nih.gov/supplements/nih3/sleep/guide/info-sleep.htm"
] |
[
"If time is relative, and we traveled in space a distance that is light years away at light speed, would we age, or would there be a time delay?"
] |
[
false
] |
I'm curious as to whether or not traveling at higher speed towards distances light years away would affect the aging process? I know that we cannot achieve actual light speed, but can come close. To what extent is time dialated if we could, in fact, travel at such great distance at such high speed? How far of a distance would it take for a human to biologically age, if at all? I apologize in advance for any holes in my question. Answers explained in common tongue would be greatly appreciated, as I'm not as science savvy as some. I could post this in /rELI5 but I'd like to get some deep insight from you fine folks here. Please let me know if this post belongs elsewhere.
|
[
"It depends on the speed you're moving. If you were to move at slightly more than .7c (square root of 1/2, to be exact), then your subjective time would pass half as quickly as time \"outside\". That is to say, a second in your ship would take 2 seconds to pass. If you were in that ship for 50 subjective years, a century would pass \"outside\".",
"Time is dilated according to this function: t = t_0*(1 - v",
"/c",
")",
", where v is your speed, c is the speed of light, and t_0 is the length of time you perceive to pass. As v approaches c, (1 - v",
"/c",
")",
" approaches infinity; the faster you go, the slower time passes. While you can't move at the speed of light, if you were to go, say, .9999999999c, 1 second in your ship would take 19 hours, 38 minutes, and 31 seconds (70711 seconds) to pass to a stationary observer (and by the time that happened, you'd have been able to cross the orbits of every planet in the solar system)."
] |
[
"\"Outside\" means \"relative to a stationary observer.\" Which is complicated to explain in depth because, relative to you, the observer is the one moving at close to the speed of light, and so you'll see time moving more slowly for him. And even more complicated because time dilation by relative velocities isn't the only type of time dilation.",
"It's really complicated to explain time dilation in depth, but the equation I showed is derived from a thought experiment: Imagine a photon bouncing between two parallel plates",
"(1)",
". The plates are separated so that every nanosecond, the photon goes from one plate to the other and back again (about 15 cm), and every time it bounces it hits the same spot on each plate. If the plates were to start moving perpendicular to the way the photon was bouncing, to an observer the photon wouldn't be bouncing straight up and down. It would be moving in a diagonal path that was longer than 15 cm",
"(2)",
". This additional length can be reconciled using the Pythagorean theorem, and the ratio of the distance between the plates and the distance the photon appears to travel is directly proportional to the amount that time gets dilated.",
"Of course that only explains the equation. It doesn't really explain ",
" time gets dilated, and unfortunately that takes a much more rigorous understanding of general relativity."
] |
[
"Well, regardless of the speed, the pilot will age. This is the realm of relativity, so the ",
" is what is important.",
"Let's say you are on the ship, and I am sitting there with you. We're traveling pretty quickly, how fast exactly isn't totally relevant for the thought experiment. If we travel for 30 years, I'll see you age 30 years, and you'll see me age 30 years. In the reference frame of our ship, time is moving normally (one second per ship second, if you care to think about it that way). The problem arises when we look back at Earth and see that it has aged considerably less than we have, maybe 15 years because we were traveling so fast (0.5 seconds per ship second).",
"The bottom line is, time does not change inside any particular reference frame, but instead there is a discrepancy between reference frames when one is moving with respect to the other. Everybody we considered is aging, just on their own time.",
"Edit for idiocy."
] |
[
"Red/blue shift in a contracting universe."
] |
[
false
] |
[deleted]
|
[
"That would be true only for galaxies on your own side of the center of the universe. Galaxies on the other side of that center would be blue-shifted no matter the acceleration factor. And if you're at the center of this universe, everything would be blueshifted.",
"Also, you're assuming that such a universe would have a center that was somehow causing all other matter to fall into it. When we talk of our own universe expanding, it is not expanding out from some point, but rather space itself is getting larger, distances are getting longer, etc.. The reverse of this, distances all getting smaller in a universe without a definable center, would mean that any vantage point in the universe would appear to the in the center from there, and so all galaxies would be moving towards it, those further away much more quickly than those nearby."
] |
[
"The short answer to your first question is yes.\nThe question of the expanding universe actually belongs to the domain of general relativity. Within this theory you can construct solutions where the scale of space varies at different times, however, you can convert this to a point of view where the scale is not changing but the speed of light is. Thus, general relativity does not discriminate between the points of view, to my knowledge.",
"A bit of relevant wikipedia on the ",
"expanding universe."
] |
[
"Since there is lorentz contraction as you approach c",
"This is not true with respect to space expanding. The rules about masses approaching the speed of light do not apply to space.",
"I guess the question is what is more fundamental, distance, or c?",
"Definitely ",
". But remember that the speed with which space expands is not limited by the speed of light, and it doesn't experience Lorentz contraction or time dilation."
] |
[
"What are some factors that determined the size of Earth's dominant species?"
] |
[
false
] |
Many species of dinosaurs were very large. Why did they evolve to be larger than many of our current land animals? I assume the force of gravity played a part in determining the size and strength of humans as well as other forms of life on this planet. If humans evolved on a planet with higher gravity is it likely that we would on average be relatively stronger and larger? If a copy of Earth existed but was scaled up say 10 times in size, would all forms of life be 10 times larger than they are on a normal sized Earth?
|
[
"Dinosaurs were among the most varied vertebrate family on earth. It is unsurprising then that they had vast differences in size, some being as small as pigeons and some being quite massive: size allowed species to fill a niche and they filled it.",
"As for why large size was abundant, it is hypothesized that a fair amount of that has to do with atmospheric O2 content. Up until the late cretaceous the atmosphere pushed like 35 percent o2 content, and if dinosaur respiratory systems were anything like as efficient as the respiratory systems of their ",
"modern descendents",
" then they easily could fuel some serious metabolism.",
"As for the last question: on a planet 10 times as large as earth I'd imagine life would actually be much smaller. The largest animal on earth (ever!) is the blue whale, and it must live in water: unsupported by water their massive bulk would crush them. A lower gravitational pull would make it much easier for large life to function.",
": What i just wrote there is pretty vertebrate-specific actually. There are some plants out there that absolutely dwarf blue whales. Low gravity would make it easy for MOBILE life to function and be mobile, but whose to say thats universal: on another planet the dominant species might be some sort of sentient purple sludge pool that covers kilometers of area and is untroubled by notions of up or down."
] |
[
"First of all, please define \"dominant\" species, in some ways, we're walking hotels for bacteria ;)",
"Secondly the size of organisms is the result of evolution (no duh), which is a complex interplay of the organism within a food web/chain. Whale that feed on planktons need to be relatively large in order to efficiently swim around and filter feed itself. Same idea applies to many herbivorous species that feed on nutrient poor food sources. Take an example of bovines, they need a large enough stomach for bacterial fermentation to occur to supplement them with additional nutrients. Some trees are very large and tall, because they have to compete for sunlight in its environment. Most predators need to be at least the size of its prey."
] |
[
"Many species of dinosaurs were very large. Why did they evolve to be larger than many of our current land animals?",
"Straight Dope to the rescue.",
"All of your other questions seem to assume that evolution is following a predictable pattern. It is at its very heart random. The path that evolution takes will select a set of organisms well suited to the environment, but the number of possible solutions to \"well suited\" is incredibly large. ",
"It could have been possible, even on this planet, to have \"humans\" relatively stronger and larger; in fact, if Neanderthals had been more successful, that might have been the case. It could also very well be possible that all forms of life could be ten times bigger (given many other adjustments).",
"To speculate on how evolution works on other planets is interesting, but no one is going to be able to give you an honest answer. However, I'd say all of your hypotheses seem reasonable."
] |
[
"What did Cambrian land look like?"
] |
[
false
] |
[deleted]
|
[
"Just some algae covered rocks near the oceans edge - the land would have many geological features (mountains, valleys, rivers (it still rained back then), sand (rain and wind erosion) but there would be no soil. No plants, no algae growing far away from a water source.",
"Here is an older picture of what it looked like under water",
"http://www.search4dinosaurs.com/Cambrian-Burgess-Shale.jpg",
"http://universe-review.ca/I10-27-Cambrian.jpg",
"Land would have looked like this (minus the weeds you see...oops):",
"http://mw2.google.com/mw-panoramio/photos/medium/10569816.jpg",
"or this",
"http://albert.rierol.net/viewer.html?img/MangroveBay2007/6319_Martian_landscape.jpg&Martian%20landscape",
"or this",
"http://www.dailygalaxy.com/my_weblog/images/gusev_crater_with_water_1.jpg",
"In the Ordovician: Green algae were common in the Late Cambrian (perhaps earlier) and in the Ordovician. Terrestrial plants probably evolved from green algae, first appearing in the form of tiny non-vascular mosses resembling liverworts. Fossil spores from land plants have been identified in uppermost Ordovician sediments. The green algae was similar to today's sea moss.Colonization of land would have been limited to shorelines. Among the first land fungi may have been arbuscular mycorrhiza fungi playing a crucial role in facilitating the colonization of land by plants through mycorrhizal symbiosis, which makes mineral nutrients available to plant cells; such fossilized fungal hyphae and spores from the Ordovician of Wisconsin have been found with an age of about 460 million years ago, a time when the land flora most likely only consisted of plants similar to non-vascular bryophytes.\"",
"http://en.wikipedia.org/wiki/Ordovician#Fauna",
"In the Silurian (443 - 416 MYA), moss (non-vascular plants) covered wet areas near streams, lakes and ocean. Vascular plants started to form, here is an example.",
"http://upload.wikimedia.org/wikipedia/commons/thumb/e/ee/Cooksonia.png/220px-Cooksonia.png",
"But only by the Denovian did land plants really make an appearance. Here is an image of the Denovian (416 - 359 MYA):",
"http://www.creationism.ws/devonian_land_scape_501a.jpg"
] |
[
"EDIT - ",
"this is so cool - representation of soil accumulation during denovian",
"Soil is the accumulation of dead plant organic matter it takes a long time to make. Soils would likely have been thin in early Devonian especially as you move away from water. The Devonian saw a flourish in the colonization of land by plants, but it still took a long time. ",
"In the early Devonian (416 to 397.5 mya) plants were very simple, not vascularized, did not have roots, were likely only a few centimetres tall - something more akin to a moss like plant. On the surface, excessive runoff would have been prevented by ground plants - like the (bryophytes)[",
"http://en.wikipedia.org/wiki/Bryophyte",
"] - commonly represented by mosses which can make thick spongy mats. But little would have stood in the way of mass weathering events - floods, windstorms...As time went on the plants became more complex and dead plant material could begin to accumulate, thicker soils begin to form.",
"Only by the middle denovian (397 - 385 mya) do we begin to see the development of complex plants standing several meters tall. Roots also help stabilize soil - but roots did not exists in early denovian (if you try and pull a moss from the ground you will find its quiet easy - same principle, they also lack roots). The rudimentary root systems developed later (middle to late D), but even these early plant's roots would not have been like what we see today. They would be shallow and simple in structure. Not great at preventing soil erosion, or even protecting plants from being uprooted. Obviously it was good enough to keep plants alive/protected from erosion events. During this time there was nothing as large as our trees today, most would have been shrub like and low to the ground. ",
"this is a better picture of the middle to late Denovian landscape",
". Plants here might be max 10 meters tall. At this point only ferns, horsetails and mosses exists (as well as many extinct species of similar structure and type). True leaves and roots begin to develop - which means stronger support structures but also more organic matter to create/regenerate soils.",
"By the end of the Denovian we see the development of lignin, which means wood - and this means bigger, taller plants with deeper complex root systems. The worlds first forests appear, but these still would have been dominated by ferns, horsetails and lycophytes. Soils would have been thicker, whole stretches of land covered by plants.",
"Soil erosion would have been a problem, but soil in early Devonian would have been thin and almost non-exsistant because soil is made up primarily of organic matter. The first colonizing plants would be directly affixed to rock/weathered rock. Into the middle and late Devonian we see the development of root systems, leaves and larger stronger plants (represented today by ferns, mosses and horsetails) these would have stabilized existing soils and would have helped facilitate the accumulation of new soils. As plants became more complex in structure they would have slowed the rate of erosion."
] |
[
"Very informative, thank you! Would the land have been that red like mars because there was no soil? I guess I hadn't thought of that part. "
] |
[
"Is there a significant difference in harm done between sleeping 1-2 hours and not sleeping at all? Are they equally bad or not?"
] |
[
false
] |
Is there a 'healthier' choice between getting 1-2 hours of sleep and not sleeping at all (ie. trying to avoid drowsiness in the morning)? Assuming someone who had to make this choice one time per week, which one is better for his mental/physical health?
|
[
"In general, naps are beneficial in reducing the effects of sleep deprivation. 1-2 hours of sleep is certainly not healthy, but it is better than nothing (although see the caveat below).",
"For example, ",
"this study",
" kept participants awake for 88 hours. One group had to stay awake the whole time, while the other group were allowed a 2-hour nap every 12 hours. The nap group performed vastly better in terms of cognitive performance and reaction times.",
"Another study",
" kept all participants awake for 39 hours. After 14 hours awake (at 9pm), some participants were given a 2-hour nap. Those who were allowed to nap performed significantly better in terms of mood, alertness, and performance.",
"The other important thing to consider with naps is ",
"sleep inertia",
", which is the groggy feeling upon first waking up. Sleep inertia is due to the time it takes for the brain to transition from sleep to wakfulness. It is therefore most severe when awakening from a deeper stage of sleep.",
"Within the first few minutes of awakening from deep sleep, performance is considerably worse than after 24 hours of continuous wakefulness. Any nap ",
"longer than about 10 minutes",
" results in sleep inertia. ",
"The effects of sleep inertia dissipate over ~1-2 h",
". So, if a task has to be performed within this critical window, a long nap will actually result in worse performance. Beyond that, the nap is beneficial."
] |
[
"This'll serve. Thank you for the dedication to source every statement, I expected much less."
] |
[
"A friend had a class at 8:30am, and asked me at 5:00am if he should go to sleep a bit or skip it completely.",
"He finally decided to sleep until 7:00am :)"
] |
[
"Why does music sound so much faster to me when I first wake up?"
] |
[
false
] |
I know one of my friends has experienced this as well, although I have heard people have this happen late at night as well.
|
[
"Your mind has a rhythmic expectation that affects how fast or slow it perceives reality. If you play a computer game, try this cool trick to observe a similar effect:",
"Watch a replay in that game at 2x speed for about 20 minutes and then play a game at normal speed. The game will feel like it is in slow-motion because your mind's \"clock\" has been set to a higher speed.",
"You get the opposite effect if you do the game in slow motion and then play at normal speed. Suddenly everything is going much faster than you keep up with even though you previously played at that speed just fine.",
"The effect wears off after only a few minutes, though. I suspect that something similar is happening to you while you are asleep where your mind is being clocked slower while asleep and still readjusting when you first wake up."
] |
[
"Watch a replay in that game at 2x speed for about 20 minutes and then play a game at normal speed. The game will feel like it is in slow-motion because your mind's \"clock\" has been set to a higher speed.",
"Exactly. I used this method for a short skill-boost in some online tournaments I've attended. And let me tell you, it works noticeably well."
] |
[
"Is it the same thing we experience when driving? I always find that driving at 30mph feels unbearably slow after pulling off the motorway."
] |
[
"When is a rock considered to be “born”?"
] |
[
false
] |
You often hear that a rock is 1 billion years old or 300 million years old or whatever age it may be. What is the starting point for a rock’s age? I assume it might vary based on the type of rock, like maybe volcanic rocks are “born” when they emerge from a volcano, or sedimentary rocks are “born” when they harden from whatever swampy material they were before, but I’m not sure, and Googling mainly tells me that Dwayne Johnson was born in 1972, which is interesting but not helpful. Since just about every rock is made of material that has been around since the Big Bang, it’s confusing to know what science considers the start of a rock’s existence. What defines a rock’s birthday?
|
[
"Your assumption is largely correct. At the simplest level : 1) For igneous rocks, the age generally reflects when the rock crystallized from a melt (i.e., when it solidified). 2) For sedimentary rocks, the age reflects when the sediment that forms the rock was deposited. And 3) for metamorphic rocks, the age represents the age of the metamorphic event that transformed the prior rock (i.e., the protolith) into the metamorphic rock in question.",
"Now, for all of these, there is nuance and complication. First and foremost, very often (especially for igneous and metamorphic rocks) we are estimating the age of the rock by dating minerals within that rock via some ",
"geochronologic method",
" and as described in one of our ",
"FAQs",
", what these ages reflect with respect to the \"age\" of the rock depends a lot on the mineral and method in question and the context of the mineral within the rock. ",
"Thinking about the details of the different types of rocks, extrusive igenous rocks (i.e., volcanic rocks) are probably the least problematic as they solidify relatively quickly so the age of the rock (and the minerals within them) ",
" are all pretty consistent and tend to represent a single event. For intrusive igneous rocks (i.e., igneous rocks that crystallize in the subsurface), many of these can be very large and represent many intrusive events. So, a large body of igenous rock like a ",
"batholith",
" may in fact have a wide range of ages reflecting discrete events that progressively built the large body of rock. E.g., something like the Sierra Nevada batholith (that forms the bulk of the Sierra Nevada mountains in California) does not have a single age but rather a range of ages, but individual rocks within that batholith will have a single age within that range. ",
"Sedimentary rocks are a bit more complicated still as of course they represent pieces of older rocks that have been eroded, transported, and deposited (generally, at least when talking about clastic sedimentary rocks, like sandstones, etc) so the individual bits, i.e., the detrital grains that make up the sedimentary rock, will have a range of ages that all predate the depositional age of the rock. By convention though, if we talk about the age of a sedimentary rock, we mean the approximate time in the past when the sediment was deposited, not the the age of the pieces that were deposited (in some cases, we do care about the ages of the bits as this can tell us about the source of the sediment, but we would generally not describe these ages as the age of the sedimentary rock, though there are ways to estimate the depositional age of the rock from the ages its constituents sometimes, e.g., ",
"Coutts et al., 2019",
"). For chemical sedimentary rocks (e.g., evaporites, carbonates), the age would reflect the time of their precipitation or deposition.",
"Metamorphic rocks can also be quite complicated as they tend to represent not a single event (though some can), but rather a progressive history of metamorphism so choosing a single age might not be very representative. In these cases, it's very context dependent. If we have indications of the timing of different metamorphic events preserved in a single rock (from different ages from different minerals within the rock, etc), we might just describe the age of the rock as a range, or pick some point within the history, e.g., the timing of peak metamorphism. In some cases, we might really only have constraint on the timing of that last event as this has \"overprinted\" all the previous events. Some other times, we might be more interested in the age of the protolith, i.e., the rock before it was metamorphosed, so might describe the rock in terms of that age."
] |
[
"What an amazing response! Thank you!"
] |
[
"This isn't really a direct answer to your question, but as a sidenote:",
"Since just about every rock is made of material that has been around since the Big Bang,",
"The exact opposite is true. The Big Bang only created Hydrogen, Helium, and Lithium, every element heavier than that was created either in fusion in a star core or in a supernova explosion. The rest of the stuff on Earth came from whatever supernova left the gas cloud that formed the Solar System."
] |
[
"I have a weird question about micro-gravity."
] |
[
false
] |
Testicles use gravity to regulate their temperature by hanging closer or further from the body. So what happens in space? does it cause discomfort to astronauts? Also does micro-gravity increases the risk of testicular torsion? Are 'private' problems caused by space travel documented by space agencies?
|
[
"I'll attempt to answer part of this question seriously. I wouldn't know anything about the first two questions, but in terms of the third question you may be interested in ",
"this nice Slate piece",
" which has quite a bit of information.",
"In addition, you have several problems with radiation. Cosmic rays can damage male sperm -- not to the point of infertility, as many astronauts have conceived after sometimes extended stays in space -- but more importantly can seriously harm human fetuses. ",
"Link.",
"Finally, female rats in microgravity have rather difficult labours. ",
"Link, behind paywall.",
" This doesn't bode well for humans, who have rather difficult labour already."
] |
[
"So what happens in space? does it cause discomfort to astronauts?",
"The testicles may ride higher in microgravity. I don't think that it would cause discomfort. Think of it this way: when lying down, gravity is not pulling the testicles downward. Is it uncomfortable to lie down?",
"Also does micro-gravity increases the risk of testicular torsion?",
"It's feasible. There is ",
"some evidence",
" to link torsion to colder weather. One explanation for this is that a sudden exposure of cold causes tension in the cremaster muscle, potentially pulling a loose torsion tighter. This could apply to microgravity."
] |
[
"Well, that makes sense, it also reduces the payload of the spacecraft.",
"Thanks"
] |
[
"At what temperature does moving water freeze?"
] |
[
false
] |
I was thinking about this as it get colder out. Small ponds will freeze at 32 but does it need to be even colder to freeze a stream since the water is in motion? If so how cold?
|
[
"Water always freezes at the same temperature. The stream and the pond just have different ways of distributing the heat and ice that allows the pond to freeze over first. ",
"In a pond, as you get close to freezing, the warmer water sinks to the bottom. This is because the ",
"density of water peaks at about 4 C",
". The water at the surface is exchanging heat with the air, so once the air gets below 0 C and the surface water is at 0 C, ice will form. Without strong currents, the ice forms a smooth sheet on the top with liquid water below.",
"In a stream, the flow ensures the water is mixed and the temperature is more uniform from top to bottom. So you need to cool the entire volume to 0 C, not just the surface layer. And you need to cool it before it flows out of the stream. Once the water gets down to 0 C, ice can begin to form. But any ice will be pulled along with the current, so the stream deposits the ice at its edges first."
] |
[
"There are two main types of energy which are thermal and kinetic.",
"I have no idea what you are trying to say here. Thermal energy is a catch all term for many kinds of energy stored internally in a system, including kinetic energy."
] |
[
"There are two main types of energy which are thermal and kinetic.",
"I have no idea what you are trying to say here. Thermal energy is a catch all term for many kinds of energy stored internally in a system, including kinetic energy."
] |
[
"Do processors work with radio frequencies?"
] |
[
false
] |
Is it rf, electron movement or something else? I thought electron movement was slow.
|
[
"Do you mean a computer processor? It's just simple electricity, which travels very fast (",
"https://en.m.wikipedia.org/wiki/Speed_of_electricity",
"). Remember it is not a single electron that flows, but a propogation of charge (like an ocean wave). "
] |
[
"Thanks but I don't think it's so simple. In fact your article does talk about the question.",
"The speed at which energy or signals travel down a cable is actually the speed of the electromagnetic wave, not the movement of electrons.",
"An electromagnetic wave is radio frequency as far as I know.",
"Edit: You may be exactly correct but I don't understand precisely what is happening so I'm trying to get some clarification. Thanks for your answer."
] |
[
"What you appear to be asking about is the electric field. The drag speed of electrons is very slow (actually it's very fast, but since they move here and there and everywhere, they have a ",
" defined on their average movement, which is very slow). But the electric field propagates along the wire at almost the speed of light. As soon as it reaches the far end of the wire, the electrons that were already there start moving, so the effects of electricity are almost instant.",
"Frequency doesn't have anything to do with speed, though. The frequency of a processor means how many times per second the clock signal changes between 1 and 0 (i.e. some voltage or zero voltage at the wire level), but increasing the clock frequency won't make the signal propagate any faster."
] |
[
"Would the Higgs Field reaching true vacuum state be catastrophic for us no matter when/where it occurred, or are there distances at which it could happen and its effects never reach us, due to propagating too slowly to overcome the rate of universal expansion?"
] |
[
false
] |
[deleted]
|
[
"It's really a bad time to talk about this. The Lambda-CDM model which is about the expansion of the universe from the big bang and dark energy is arguably the biggest debate in cosmology right now.",
"The Lambda-CDM model includes a Hubble constant which is a parameter of the expansion rate of the universe. There are many ways to measure the rate of expansion and the Planck spacecraft launched specifically to measure this constant in the cosmic microwave background found in 2018-07-18 that the constant that things are moving away from each other is 67.66±0.42 km/s for every megaparsec or 3.26 million light years of distance they are separated. ",
"Other method that have measured the expansion rate from very distant quasars with the Hubble space telescope found that the expansion is 73.52±1.62 (km/s)Mpc. Both of these observations are very precise measurements with less than 1% uncertainty and the numbers don't agree. The result should be the same but another study in 2018-11-06 found the number to be 67.77±1.30 (km/s)Mpc and 2018-09-05 they found 72.5 ±2.3(km/s)Mpc. It seems to be either around 68 or 73 (km/s)Mpc depending on what method you use to measure and with more precise measurements being done it only starting to look worse and worse.",
"There was another study published just two months ago which used yet another method to measure the constant and their constant value also agrees with currently best accepted value of 67.74±0.46 (km/s)/Mpc but their data also showed a statistical significance of 94% that dark energy density and the Hubble constant increase with time. ",
"https://www.nature.com/articles/s41550-018-0657-z",
"If dark energy is getting more powerful like this most recent result shows then the universe will end with a Big Rip where all stars, planets, atoms will be torn apart by the expansion of the universe. In that case even nearby objects like the (would be) moon will eventually be moving away from earth faster than the speed of light so a vacuum state catastrophe occurring at the distance of the moon would never be able to reach the Earth if you ignore the fact that both the Earth and the moon would have been ripped apart billions of years earlier due to the expansion. ",
"With the concordance model then everything outside our local group will be accelerating away from us faster and faster with time and we get a slow heat death of the universe. With a expansion rate of 67.74km/s per Mpc then at 4426 Mpc then the expansion would be 299,817 km/s and faster than the speed of light at 299,792 km/s. A true vacuum state propagating from a point separated by 4426 Mpc or 14.43 billion lights, 1/6 × diameter of the observable universe would never reach us. "
] |
[
"The distance between two objects grows at a rate proportional to the distance between two objects. Even with a constant Hubble constant, there is a horizon to how far light can travel due to universal expansion. Everything in this horizon is called the “observable universe.”",
"To put this another way, suppose light can travel distance 1 (in some unit) in time 1 (in some unit), but in that time the distance 1 has doubled to 2. Now light travels another distance 1 in time 1, but the remaining distance has once again doubled to 2. You can see that light will never reach the point B which was 2 unit was away at the start.",
"Final note, this is different from Zeno’s paradox because the time for each step is 1. In Zeno’s paradox you travel 1 unit distance in 1 unit time, then 0.5 unit distance in 0.5 units time, then 0.25 and so on. The ancient Greeks found this difficult to resolve because most of them refused to add infinite sums, even if they converge.",
"In the expanding universe, light travels distance 1 in 1 time unit, then distance 0.5 (expanded to 1) in time 1 unit, then distance 0.25 (expanded to 1) in time 1 unit, and so on. This sum does not converge."
] |
[
"Thank you for such an informative comment! You are awesome. :) "
] |
[
"Can you count algae in a non-pure culture with a hemocytometer?"
] |
[
false
] |
I would like to get a quantitative count of algae in an IBC tote full of nutrient rich water(used for hydroponics). We've noticed biofilm in the tank and would like to get a baseline algal count before we start treating it. I've used a hemocytometer to count algae before but only in pure cultures. I was just wondering if it would work in a non-pure culture. Thanks!
|
[
"My advice to you is to stop looking for a perfect solution. What you need is a close enough estimation, as even a modest amount of error will likely not be significant for your results. Here is an arbitrary example for you to get the gist : ",
"Initial Measurement : 5.0e5 cells / mL",
"Post-Treatment Measurement : 5e2 cells / mL",
"Percentage of Algae Cleared:",
"Assuming No Error = 99.900%",
"Assuming 10% error = 99.888%",
"Assuming 20% error = 99.875%",
"Assuming 30% Error = 99.857%",
"But I will throw out there... why not use a spectrophotometer to measure OD at 750nm instead? Just another option if you decide to forgo the hemocytometer, and could be a good way of avoiding the problem with filamentous algae."
] |
[
"That's an interesting idea as well. We have a recirculating system right now and the filters aren't perfect, my worry with the spectrophotometer (as well as the current hand held ATP monitor that were using) would be the non living particles would potentially cause us to get improper results. ",
"I could be totally wrong here, I don't know enough about it."
] |
[
"If your tank has a problem with Particulates, then yes, this could change OD readings. And I would agree with you that the field widely accepts this method as inaccurate due to this problem. In this case, OD readings will likely overestimate algae content. In contrast, using a hemocytometer will likely underestimate true algae content, because of limitations of accurately counting filamentous algae. Recognizing that both methods have their limitations is important, but this does not render their measurements as useless.",
"This is one of those scenarios where you need to evaluate your time vs accuracy of results. If you need more precise and accurate measurements for your experiments, then neither of these methods will work for you, and you should instead consider measuring total biomass. But spectrophotometric analysis of cultures is valued because it is so quick and easy."
] |
[
"How do cell phone and laptop batteries wear down?"
] |
[
false
] |
Why do cell phone and laptop batteries lose maximum capacity with substantial use?
|
[
"Over time a lithium polymer battery develops internal resistance and loss of charge acceptance due to frequent charging and discharging. This is because of cell oxidation, the cells of the battery loosing electrons, that occurs resulting in lower charge acceptance. Cell oxidation also causes the high internal resistance which causes less amperage to be available to the device.",
"Source"
] |
[
"So I'm not too knowledgeable with computers and laptops. What would be the best method of charging my laptop in order to maintain its health and functionality?",
"At the moment it is on charge the vast majority of time, but if it's not then the battery will drain down really low, sometimes all the way until I plug the charger in. Is is bad to keep it on charge most the time? is it bad to let the battery run really low/die? I'd appreciate the help :)"
] |
[
"The smaller the depth of discharge the better. So a battery that is frequently discharged only 10% will last a great deal longer than a battery frequently discharged to 50% capacity. Lithium batteries don't have the dreaded \"battery memory\" associated with Nickel batteries, so a full discharge is not necessary for a healthy battery. Lithium batteries also have a voltage cut off built in because of fire danger so leaving them plugged in is not harmful, they will not overcharge. "
] |
[
"What causes us to feel heartache? Are there any evolutionary advantages to the pain we go through?"
] |
[
false
] | null |
[
"Was anyone under the impression that \"heartache\" involves the cardiac muscle? Do you have any evidence that emotional distress and/or physical symptoms (such as tightness in the chest) upon the severing of romantic relations is cultural? Certainly the term \"heartache\" is cultural, but again I don't think anyone was under the impression it involves the cardiac muscle. The association of romantic love with the heart almost certainly derives at least partly from the physical symptoms of longing and loss (fullness, weight, or tightening in the chest) rather than vice versa. "
] |
[
"Was anyone under the impression that \"heartache\" involves the cardiac muscle? Do you have any evidence that emotional distress and/or physical symptoms (such as tightness in the chest) upon the severing of romantic relations is cultural? Certainly the term \"heartache\" is cultural, but again I don't think anyone was under the impression it involves the cardiac muscle. The association of romantic love with the heart almost certainly derives at least partly from the physical symptoms of longing and loss (fullness, weight, or tightening in the chest) rather than vice versa. "
] |
[
"I don't really have an answer to OPs question as it is outside my field; however as my comment is slightly off-topic, I'll keep them brief. Hopefully it is interesting, if nothing else.",
"There is a condition called 'Takotsubo cardiomyopathy' which is also known as 'Broken Heart Syndrome'. It is characterised by left-ventricle dysfunction following extreme psychological stress. To be clear, this condition is a world away from the 'heartache' that OP was talking about."
] |
[
"What is happening when you \"get the wind knocked out of you\"?"
] |
[
false
] | null |
[
"Getting the wind knocked out of you is often referred to \"being hit in the solar plexus\". That's actually a misnomer, it has nothing to do with the solar plexus, which is also known as the ",
"celiac plexus",
".",
"Blunt trauma to that region can ",
"cause the diaphragm to spasm",
", making it difficult to take normal breaths."
] |
[
"Getting \"hit in the solar plexus\" has nothing to do with the solar plexus (",
"source",
"). Motor and most sensory innervation to the diaphragm is via the phrenic nerve at spinal cord levels C3-C5. The celiac plexus is T5-T9 and providing innervation to the viscera of the abdomen, not the diaphragm."
] |
[
"Getting \"hit in the solar plexus\" has nothing to do with the solar plexus (",
"source",
"). Motor and most sensory innervation to the diaphragm is via the phrenic nerve at spinal cord levels C3-C5. The celiac plexus is T5-T9 and providing innervation to the viscera of the abdomen, not the diaphragm."
] |
[
"Growing fruit trees from seed, what triggers fruiting?"
] |
[
false
] |
When growing fruit trees from seed (apple, pear, citrus, etc.), there is a wide variation of time when the seedling will mature and grow fruit. Some apple seedlings will produce fruit in a little as 3 years, some 10 years, some many years past 10 years. What causes this difference? Is fruiting genetically determined, size of the tree, size of roots, number of branches, etc? Or is it a combination of many factors?
|
[
"With respect to apples the biggest influence would be the type of rootstock used. As another poster mentioned, commercial apple trees are propogated from small segments of branches (scions) from the desired cultivar which are then grafted onto the roots of another apple tree cultivar (the rootstock). The rootstock of the tree influences the mature size of the tree, and rootstocks selected for dwarfing characteristics generally produce a tree that fruits earlier than a full-size, \"standard\" tree.",
"In the plant kingdom in general plants usually don't flower until they start approaching their mature size. In that respect it makes sense that a dwarf tree will fruit earlier in its life than a taller tree."
] |
[
"Apples are done this way because they are not true to seed, meaning you won't get the same type of apple as the parents were. Doesn't really answer the question, but growing an apple by seed could get you one of something like 40,000 different apples, most of which are not good to eat. If not familiar, look up Johnny Appleseed for an interesting story."
] |
[
"Hmmm well in practice fruit trees are propagated from cuttings and thus are clones and are not grown from seeds. Propagation ensures the consistency. Keep in mind that fruit trees are highly altered and manipulated from their wild ancestral form. Many tree varietals found in nurseries cannot be grown from seeds at all. But that’s about as much as I know. Hope this helps and I look forward to more detailed answers. Great question!"
] |
[
"How does antimatter (potentially) improve space travel?"
] |
[
false
] |
[deleted]
|
[
"Assuming you have some mechanism to get mass amounts of antimatter and sufficient technical know-how to safely handle it, you could use it to provide thrust for a spacecraft that's orders of magnitude better than anything we can dream of doing today. Speculative designs (sci-fi locked to hard numbers, basically) have fantastic predictions such as being able to travel to Mars using only a few grams of antimatter.",
"It's basically the holy grail of propulsion.",
"A note on the 'few grams' thing: it's noted in ",
"this presentation",
" (pdf warning) linked to by the ",
"wikipedia article on the subject",
" but I can't find other references to it. Nevertheless it demonstrates the great promise the technology could have."
] |
[
"This is assuming we will never improve the current accelerators and stuff like that."
] |
[
"naturally, though 8 orders of magnitude increase in intensity, much less storage, of anti-matter will not be the easiest thing. "
] |
[
"If the type of element is directly correlated with its number or protons/neutrons/electrons, why aren't there infinite elements and why is 'discovering' a new one a big deal?"
] |
[
false
] | null |
[
"Because you can't put an arbitrary number of protons and neutrons in the nucleus.",
"A proton by itself is stable while a neutron is unstable. Happily, the proton is slightly more stable than the neutron is unstable, so the two together are stable. Thus, you cannot add too many neutrons without adding more protons to compensate.",
"Protons are attracted to protons and neutrons that are close nearby, but repelled by protons that are far away. Unfortunately, if you start packing a bunch of protons and neutrons, there will be more and more protons that are far away from any given proton than protons and neutrons that are close nearby. So you cannot add too many protons either.",
"If you cannot add more and more neutrons without adding protons, and you cannot just keep adding protons willy-nilly, then you don't really have that much freedom. There are only 253 combinations of number of protons and neutrons that have been observed to be stable."
] |
[
"There are not necessarily infinitely many elements that can exist, because eventually there will be a point where the system is so heavy that it won’t be able to sustain bound states if you add anymore nucleons.",
"Discovering a new one is a big deal because we’ve already discovered all the ones that aren’t extremely difficult to produce."
] |
[
"Their explanation doesn't rule out the island of stability because they didn't specify ",
" exactly the number of protons becomes too high for the nucleus to remain bound. Nobody knows the answer to this question.",
"\"Superheavy element\" typically refers refers to elements with Z > 100, so we've already discovered 17 of them (Z = 101 - 118).",
"There is another class, called \"hyperheavy\", which refers to Z > 126. None of these have been observed yet.",
"Also, we have a bunch of FAQ entries on superheavy nuclides that you may be interested in, in our nuclear physics and chemistry FAQs."
] |
[
"Why is time measured in with 60 seconds/minutes and not 100?"
] |
[
false
] | null |
[
"It is based on the Sumerian number system that had a base of sixty instead of 10 and sixty is a superior highly composite number meaning it has many divisors. What this means in practice is that you can divide an 60 minute hour evenly with twelve different factors, many more than a ten based system would allow.\n The Babylonians adopted the 60 based number system and divided the circle into 360 degrees and the degrees into 60 minutes and 60 minute seconds. These became our minutes and seconds.",
"\n",
"https://en.wikipedia.org/wiki/Sexagesimal"
] |
[
"Because 360 can be divided by : ",
"1,2,3,4,5,6,8,9,10,12,15,18,20,24,30,36,40,45,60,72,90,120,\n180,360",
"100 can only be divided by:",
"1, 2, 4, 5, 10, 20, 25, 50, 100.",
"Or 24 factors against 9. Now it may not matter, but historically easy division was important."
] |
[
"Shortly after the French revolution, when they were converting to decimal units (metres, litres, grams etc) they also decimalised time. Each day consisted of 10 hours, each with 100 minutes, each with 100 seconds, giving 100,000 seconds in a day (our system has 86,400 seconds per day). It never caught on though, presumably because 100 has fewer factors than 60 and thus doesn't divide up as neatly. After a couple of years they switched back to the old system."
] |
[
"How would you determine the molecular identity of the ion that is being transported through a receptor activated channel? Have there been any experiments that were designed to accomplish this?"
] |
[
false
] | null |
[
"There have been LOTS of experiments designed to accomplish this.",
"It's usually pretty simple. The first step it to make a guess. In order to do this, you need to know the \"reversal potential\" of the current through the ion channel. You do this by the following, you stick a small glass electrode inside a cell that has the ion channel your interested in, and activate the channel. Using relatively simple electronics, you hold the voltage over the membrane at a certain voltage (e.g. -100 mV). If the ions flowing through the ion channel are negative charged, they will be repelled by the negative potential, and hence you will get a current flow equivalent to positive charge flowing into the cell (i.e. inward current). You do this at various voltages (say from -100 to +50 mV), and at some point the direction of the current will flip (e.g. in our case, the negatively charged ions will flow into the cell because they are attracted to the positive membrane voltage). The exactly reversal potential depends not only on the charge of the ion, but on the concentration of the ion inside and outside the cell (this is because if there is a high concentration of the ion inside the cell, relative to outside, then the concentration gradient will drive ions out of the cell, even against an electric field). Because of this, ",
". This allows us to make a very good guess. Potassium should have a reversal potential of about -90 mV, Sodium should have a reversal potential of about +40 mV, Calcium should have a reversal potential of about +80 mV, Chloride: - 50 mV, mix of Sodium and Potassium, 0 mV.",
"We can then bath the cell in solutions that contain altered levels of these ions: If we add lots of potassium to the outside of a cell, the reversal potential of a current that is being mediated by potassium should change, but if it is a chloride ion channel, changing the potassium wont do anything.",
"Also, certain drugs/other ions are known to block most ion channels that depend on a particular ion: Cesium or TEA blocks most Potassium channels, Cadmium or Cobalt blocks most Calcium channels. (But these aren't great bits of evidence by themselves, they just add weight to the argument)."
] |
[
"Thanks a bunch!! Are there other known techniques aside from the one you outlined? Also, are there any notable experiments that you could list that have used that technique? "
] |
[
"Those are the main ones.",
"Notable experiments? Well probably the most famous is",
"Currents carried by sodium and potassium ions through the membrane of the giant axon of Loligo",
"A. L. Hodgkin and A. F. Huxley",
"But that might be a bit difficult to understand because it is so old."
] |
[
"When a marathon runner hits a wall, what happens physiologically? And what's happening when they push through it?"
] |
[
false
] | null |
[
"I can't say. The reason we can say that marathon runners' walls are caused by glycogen depletion is because it's so extreme, and that analytical models (such as the one I linked you) can produce results that more or less match observed results. ",
"On the other hand, given a random person in the gym, or out running, there are so many factors at play that it is difficult to point specifically at glycogen depletion. As a guess, I would wager that it likely isn't the case. The amount of glycogen an average person keeps in their liver (which gets released into the blood stream for use) should be enough for well over an hour of moderate intensity exercise.",
"And now for more speculation. There are a variety of things at work. One is that people often underestimate exactly how much time and work it takes to really 'warm up'. Personally, I find that the first 5-10 minutes of my runs feel absolutely terrible compared to the rest. Another is that you may simply be working at too high of an intensity for your aerobic energy system to keep up. At some point in, you've reached enough of a deficit, and 'hit the mini-wall', and then, YOU SLOW DOWN and/or PAUSE. Either one would give you the time needed for your aerobic energy systems to catch up. And this is ignoring psychological factors.",
"In other words, given an average person in the gym, it would be difficult to tell without hooking them up to measure VO2 and heart rate. "
] |
[
"Your body has a limited store of carbohydrates (in the form of glycogen). This is usually your body's primary fuel when engaging in exercise. Hitting the wall occurs when you've depleted your store of glycogen. Pushing through it is the processing of forcing your body to start using fat stores, which is a process that takes more energy. Here's a nice study where the author attempts to create a model to estimate a specific runner's point of 'hitting the wall'.",
"http://www.ploscompbiol.org/article/info%3Adoi%2F10.1371%2Fjournal.pcbi.1000960"
] |
[
"Very cool, thanks! Would it be fair to say that when someone is working out and doing cardio, after they hit their \"mini-wall\" and keep going, they're starting to burn off fat?"
] |
[
"What would the effects of negative-mass (if real) be in space-time?"
] |
[
false
] |
effects/properties/uses/etc.
|
[
"Well, you could stabilize wormholes with negative energy density aswell as create an ",
"Alcubierre drive",
" (Warp drive). But ",
"negative mass",
" would show weird phenomena. For example, it would always repel \"positive\" matter (runaway motion).",
": Also imagine exerting a force on a negative mass. If you were to push it away, it would move closer to you."
] |
[
"No. E",
" is the sum of squares and is always positive. E can still be negative."
] |
[
"\"Negative mass\" is a moot concept. The fundamental quantity is not mass, but mass squared (E",
" - p",
" c",
" = m",
" c",
" Since m",
" = (-m)",
" \"negative mass\" is exactly the same thing as positive mass.",
"If mass ",
" would be negative, you would get tachyons. However, tachyons cannot exist as physical particles. If they exist in a theory, that indicates a flaw in the calculation, namely a false vacuum."
] |
[
"Animals other than humans can laugh- are there animals that can cry?"
] |
[
false
] |
If not, what's so special about crying? How is it different from laughter?
|
[
"are we assuming here that animals laugh for the same reasons humans do? I'd like some references for that for a start. ",
"Crocodile tears? It's a hard life when everyone's afraid of you. "
] |
[
"This article is a good start:",
"http://www.nytimes.com/2007/03/13/science/13tier.html?ex=1174536000&en=9e64514e5d308a59&ei=5070&emc=eta1"
] |
[
"It's not quite the same though is it? In the examples of animal 'laughter' it's a social tool. Human laughter can be this, but humans also laugh when they're completely alone because they find something funny. Animals playing might be having 'fun' but that's not the same as finding something funny. "
] |
[
"Is it possible to mathematically determine the wavelength of light being reflected off of a particular kind of molecule?"
] |
[
false
] | null |
[
"Yes, this is done by calculating the energy levels of the electrons in the molecule using quantum mechanics. The light that is absorbed and re-emitted (reflection on a microscopic scale) depends on the difference between these levels."
] |
[
"The simplest way to take the following into account: ",
"The nucleus acts on the electrons with a force of 16ke",
" /r",
" where k is Coulomb's constant, e is the fundamental charge, and r is the radius of each electron.",
"The electrons experience a centrifugal force mv",
" /r that is equal and opposite to the electric force.",
"Electrons at each energy level have an angular momentum mvr=nh/2pi where n is the number of the orbit and h is Planck's constant.",
"From this you can figure out that the nth level has an energy of (-13.6 electron volts)x(16",
" )/(n",
" ). Electron volts are a unit of energy. To figure out the energy difference between levels (m and n), you multiply the ground state energy 16",
" x13.6 eV by (1/n",
" -1/m",
" ) and that tells you the energy of the photon absorbed or emitted as an electron jumps between them. You can convert energy to frequency with Planck's constant.",
"It gets a bit more complicated then this, you have to use a full quantum mechanical description of the atom rather than this semi-classical version that works best for hydrogen."
] |
[
"Wavelength = speed of light / frequency.",
"Wavelength = color, in normal practice."
] |
[
"How would a bleeding wound react in space?"
] |
[
false
] |
Hello, I've been wondering this lately. Assuming it's not zero gravity (i read somewhere that the current ISS is under something called instead), and for the sake of it there is a doctor and medical equipment available. If someone gets a deep wound, caused by stabbing, would it be possible to treat it the way we treat them on earth, if at all? how would the body react under micro gravity environment, in terms of bleeding and healing? would it form just a huge blob of blood? would it be any risk for the blood to stay inside the body? (instead of it pouring outside the body). PS: My apologies if something seems unclear to you, English is not my native language so i had a bit of trouble making my questions clear enough. Feel free to point out anything seems unclear. Also, i'm not sure if it should go under Medicine or Physics.
|
[
"They have actually ",
"done experiments",
" on this, including performing ",
"small surgeries",
" during parabolic flight. The gist seems to be that surface tension of blood does cause it to form a dome above the wound but that normal surgical techniques like suction and sponges are still effective. "
] |
[
"Once again, they injured a bunch of rats on Endeavor to answer this question;) ",
"Turns out that",
" wounds are likely to to have a poor healing response in micro-gravity. ",
"They are looking at ways",
" to overcome this, perhaps with stem cells. "
] |
[
"If left open, yes, it would be a big blob of blood, and interestingly enough, it would stay a big blob, attached to your body similar to how tears do in space (Chris Hadfield demonstrated this recently, IIRC), until some force moved it away. ",
"Other than that, the wound should be able to be treated as it would on Earth - pressure, sterile dressing, all that. Depending on the wounds location and severity, the affected astronaut may have to take special precautions when exercising, which is pretty important in space."
] |
[
"Why would a spinning ring in space create artificial gravity?"
] |
[
false
] | null |
[
"First of all, the centripetal force would throw you ",
", not inward. So you would be standing with your feet on the inside of the outer surface, and your head pointing back toward the center. ",
"Technically, if you were floating in the middle of the ring before it started spinning, then yes it would just spin around you. But assuming you started on the inside of the outer surface and started moving with the ring, it would tend to throw you outward. This force keeps you pressed against the wall and acts like an artificial gravity."
] |
[
"So what your saying is that objects on the inside of the ring would have to be made to rotate around the ring at a rate equal to the ring?"
] |
[
"But wouldnt it would only throw you outward if there is something tethering you to the center or to the ring itself. Wouldn't only work if the ring were divided into sections who were at an angle of 90º to the center of the ring? that way the astronauts in each section would feel the constant acceleration of the floor beneath them similar to how elevators make you feel more heavy. My only issue is that if individuals were on a floor that ran 90º to the center of the circle- THEN there would be a force holding them in place and they would begin to move outwards. At what angle would the floors have to be at so that this is countered?"
] |
[
"Do the FAA, Air Force, or any other flight monitoring/traveling agency go to any kind of special \"alert status\" during events such as tonight meteor shower? Are we at an increased risk of flying tonight?"
] |
[
false
] |
Bonus question: odds of satellites and planes being taken out by a meteor?
|
[
"No. Not in the least.",
"It depends heavily on composition, size, and the angle at which it enters the atmosphere, but most of the pretty meteors people are seeing tonight are well above surface of the Earth, probably greater than 60 miles. For reference, a commercial jet typically flies at an altitude of 6 or 7 miles. ",
"Here's some background info if you're interested.",
"Enjoy the show if it's clear where you live! There are a few places streaming online, including a nice one from some friends over at ",
"NASA's Marshall Space Flight Center",
", and you can find tons more links on ",
"SpaceWeather.com",
" right now as well.",
"Edit: There are some articles online from back in the mid 90's speculating that TWA's Flight 800 was struck by a meteorite, which some consideration about it's likelihood from the ",
"Cosmic Variance Blog",
" as well as ",
"Scientific American",
", but both conclude that it's potentially plausible considering the number of flights for the entirety of powered commercial flight (not a fair comparison, since planes in the last 30 years fly higher than in the previous 50), but ultimately very very unlikely given that planes are slender, fast moving targets. ",
"It's also very important to note that both of those articles were written well before the official accident report for that flight was released, which ultimately concluded that a short circuit ignited fuel vapors and caused the crash."
] |
[
"Are we at an increased risk of flying tonight?",
"Meteors fall through the atmosphere at all times. It's not like space particles only wait until you're facing away from the sun to hit earth."
] |
[
"I've been freezing my ass off looking East since 9. Damn Columbus Ohio for light pollution. I haven't seen any yet."
] |
[
"Why do different vaccines last different amounts of time?"
] |
[
false
] |
I know different types of vaccine preparations have different effectiveness at stimulating immune cell recognition, but why do some wear off before others? Thanks!
|
[
"This has to do with the course of illness of a given disease -- slow vs. fast.",
"Vaccines are meant to induce a high antibody response against a given pathogen. Being vaccinated usually results in high antibody counts in an individual that persist for certain amount of time (usually fairly long). These antibodies fight the infection very quickly if they are maintained at high levels. ",
"In addition, your body has certain immune cells called memory cells that serve as very long term keepers of the knowledge of how to fight the infection. But if you have little antibody circulating, these memory cells take longer to ramp up your immune system to fight whatever infects you. They have to multiply and build antibody levels up.",
"Now, for some vaccines, antibody levels will decline over time to levels that are no longer suitable for fighting off infection rapidly. If the disease is something that can hit you very quick, it is essential to maintain constantly high levels of antibody. No time to wait for slow memory cells. Hence booster shots, which keep antibody levels higher so that you can be ready to fight when you need it.",
"Some diseases (like measles and polio) take a much longer time to go from infection to symptoms. In this case, your body has enough time to wait for you memory cells to kick in and fight off the infection that way. So even if you antibody levels against them are low, you can afford to wait. ",
"Quick source here. Plenty to read if you want to search more"
] |
[
"Appropriate reply. It also helps the OP to know that different serum concentrations of antibody are determined to be acceptable \"normal\" levels based on the the type of antigen for which they're specific. Hep B concentrations that are considered effective would be far different than concentrations considered effective for MMR. ",
"Not to mention that the individual reacts differently immunologically to the protein structure of the antigen in each vaccine. If you and I both received the same vaccine it is not abnormal a few years down the road for each of us to have vastly different antibody titers and one need a booster while the other doesn't. The immune system can vary in effectiveness to the same degree that other traits in humans can vary. You may be able have a 40 inch vertical leap without much training however I could never get there due to my genetics. The same stands for immune system response and effectiveness. ",
"It also is important to note that the protein structure of certain antigens are more obvious to the body as non-self therefore illicit a stronger immune response than others."
] |
[
"Thanks a lot for posting, very helpful and 100% answered my question."
] |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.