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[
"How was the total amount of matter in the universe calculated?"
] |
[
false
] |
I've often heard that the matter that makes up planets, galaxies, and us, is only a small amount of the amount of true matter in the universe. And that there's also something called Dark Matter, but I've always wondered how they got the percentages that they use with regard to dark energy, dark matter, matter, etc. If we don't know how far the universe extends, how were we able to calculate those percentages? Isn't the universe also constantly expanding?
|
[
"Based on a number of different methods of indirectly observing dark matter, the most famous being differences in the ",
"rotation curves of galaxies",
" between the luminous matter we see and what you need to then account for that difference, we can then estimate how much total matter there is in galaxies and galaxy clusters. Then we also can do statistics about how many galaxies there are and what the number density of them is in the local and non-local universe, i.e., how many we see in a given volume. We then know the ",
"current size of the Observable Universe",
" based on cosmological models and observations of the ",
"Cosmic Microwave Background",
". Thus, we know what the density of matter is and the total volume, so we can estimate the total amount of matter.",
"You are correct though that the Universe is expanding, which will change the density but to first order shouldn't really change the total matter. "
] |
[
"I see, but how precise do you think those calculations are to the actual composition of the universe? Since we don't know everything, they can't possibly be 100% or even 90% certain that their percentages are correct. As you said, they estimate the amount of total matter there is in galaxies and galaxy clusters, and statistics are also based on number densities and observations in a given volume. "
] |
[
"All measurements in science have errors, so I don't see a problem with this. Of course there's going to be uncertainties. We can only run through the calculations while taking into account or uncertainties and biases, and provide an estimate the total matter in the observable universe. Nobody is proclaiming this is the exact known value."
] |
[
"Why can't we simply transplant the required healthy bacteria instead of Fecal Microbiota Transplant?"
] |
[
false
] |
Just figured we would have come far enough in our medical advances where we could isolate and grow whatever probiotic we so desired. Is it a matter of it just being easier to transplant the poo itself?
|
[
"Is it a matter of it just being easier to transplant the poo itself?",
"Yes. The gut microbiome is extremely personalized and complex.",
"We still don't know enough about how the gut microbiome effects many aspects of a person's health to assume we can recreate an ideal population or define an ideal one."
] |
[
"For a long time in the future it Will probably be cheaper to just transplant fecal matter. Getting pure cultures of Every kind of gut bacteria needed may prove difficult on Its own, But mixing them in the correct ratio Will take many years to perfect."
] |
[
"There is at least one proprietary mix of gut bacteria meant to be administered after a course of antibiotics in patients with recurrent C. difficile infection. It's called ",
"SER-109",
"."
] |
[
"Jewel of Quantum Field Theory"
] |
[
false
] |
Is this an implication of a physical simplicity previously undiscovered or a useful mathematical technique for solving equations? (Or is it a subgroup of E-8 theory)
|
[
"It's too early to say. So far, it's a new mathematical technique. It will need to be confirmed thoroughly before it will see widespread use in that function. If it turns out to make correct universal predictions, it might well hint at some underlying new (and more elegant) physics."
] |
[
"here's a quote from the lecture, speaking about the mathematics: \"literally as you approach the boundary of the aplituhedron, on the boundary you see that it breaks up into lower amplituhedrons that are glued together in exactly the way that amplitudes are supposed to be. there's no gluons propagating in space-time. there is no space-time picture of any sort. this is a simple consequence of positivity.\"",
"here is another: \"the ideas are extremely simple. they generalize the notion of a triangle which generalizes the positive grassmanian and the polygon itself that generalizes to the amplituhedron, together with the idea of hiding particles is the origin of quantum loop corrections.\"",
"\"this simple mathematical structure gives a complete autonomous definition of all scattering amplitudes in planar N=4 SYM, totally free of usual QFT language: no Feynman diagrams, not even on-shell diagrams, recursion relations, etc.\"",
"apparently a mathematician figured it out at the same time, but didn't know it had real-life application. i think it's just a new mathematical representation that is dramatically simplified. he does say that there must be similar structure for gravity and pertervative string amplitudes. he also says that he thinks QM and space time will merge soon and that his work can be extended.",
"the math involved is way over my head. i hope this helps answer your question. "
] |
[
"Here's another post about the topic. Only three comments. Purpose of link is to give this very interesting and new topic some momentum.",
"http://www.reddit.com/r/askscience/comments/1nampi/what_does_it_mean_for_a_physics_property_to_be/"
] |
[
"How were the weird elements named?"
] |
[
false
] |
I'm talking about potassium, and lead. Why are they K, and Pb? Shouldn't it be P, and L (Le)? I was looking at the banner for this subreddit and wondered why some are named funky. My best guess is because they were discovered by scientists who speak a different language, ie. in X language, potassium starts with a K.
|
[
"All of these I believe are Latin.",
"The symbol for tungsten is W and comes from wolfram. I don't remember the etymology of this. Antimony (Sb), I'm not sure. Mercury (Hg) is from hydrargyrum, which I think is Greek. Might have missed some other names."
] |
[
"Some of them are Latin by way of Arabic."
] |
[
"Wow. First response pretty much takes the cake! Thanks man, and now that I see it, I do remember a few of those. I remember ferrum and aurum, but never made the connection between those and the rest of the ones which I now know to be latin-based. Thanks coniform!"
] |
[
"The focus seems to be on fossil fuels, but what other minerals and rare elements are in danger of depletion? What will the effects be?"
] |
[
false
] |
And when will it become a problem we talk about more? I imagine significantly and fiscally harvesting from landfills and space is a long ways off?
|
[
"Phosphorous"
] |
[
"There are many numbers of economically important elements with supply problems. Among them: the rare-earth elements (REE = La through Lu), platiinum group elements (PGE = Ru, Rh, Pd, Os, Ir, Pt, Au), Ta, Hf, Ag, Cu, Zn, Sn, Ni, Co, Cr, Sb, Ge, Ga, In, and even Pb.",
"Here is an excellent ",
"summary figure",
" from ",
"this article",
"."
] |
[
"This is incredibly shocking and informative, thank you.",
"Too bad uranium deposits are apparently estimated to run out in about 85 years, or else nuclear transmutation and reprocessing would make me feel a little bit better about the situation.",
"I guess we have thorium and other radioactive elements but... They'll also deplete, and you have to wonder what will happen as costs rise as it becomes more scarce, and the cost of refitting everything.",
"That helium is becoming more scarce (thanks snooptray!) is similarly frightening. I'll think twice about buying helium balloons again.",
"We like to criticize the older generations for wastefulness but... I don't think we'll be remembered very kindly either :("
] |
[
"Can we understand the Planck time and Planck length as the space-time minimal \"grid\" of the universe ?"
] |
[
false
] |
Hello, If the universe is a simulation (i'm not saying it is) or if we want to create a simulation of the universe at the most precise level, could the Planck time and Planck length be used as a grid where every object has a quantified position ? -> Are the dimensions "analogical" or "numerical". Is there a space time grid ? Thanks
|
[
"No, that is a common misconception about what the units represent. See here for a discussion of this: ",
"https://www.physicsforums.com/insights/hand-wavy-discussion-planck-length/",
"There are also some good comments by John Baez at the bottom of that article."
] |
[
"The concept of some sort of orthogonal grid doesn't really make sense for spacetime. Imagine you are looking at a photon or other massless particle. By definition it travels one Planck length per Planck time.",
"So if we map this on a grid, each tick (i.e. Planck time), it moves one pixel (i.e. Planck length).",
"Now imagine a slightly slower particle. In one Planck time, it travels, say, .9 Planck lengths. Well, now we have an issue. If it must be located on a discrete grid, it would either have to travel zero pixels (and would be motionless), or 1 pixel (traveling at c). And this applies for literally any speed other than 0 or c. So either the Planck length or Planck time can't be the fundamental pixel size of the universe. But speeds are not discrete--we can pick any speed we want for a particle, so no fixed set of measures will ever avoid this aliasing problem. Especially when you consider something moving \"diagonally\" to the grid. At a 45 degree angle to the grid, even a photon must travel 1/sqrt(2) Planck lengths along each dimension for each Planck time. That's an irrational number, which pretty much immediately explodes the idea of a fixed orthogonal grid of spacetime, as people imagine it in a simulation.",
"But wait, we know the concept of absolute speed is wrong--there are no privileged reference frames. Lorentz contraction demonstrates that for ",
" velocity we pick, it's equivalent to a different velocity in a different reference frame. This completely destroys the concept of a fixed voxel grid for the universe, at any size scale, even if you allow for continuous time. No matter how you set it up, an object moving one unit in one reference frame is moving a fractional unit in another."
] |
[
"You can't really prove a negative."
] |
[
"Recommendations for a book on history of math and/or physics?"
] |
[
false
] |
I want to start out by saying that I have developed a deep love of . A fellow Redditor turned me onto this subreddit last week and I've been glued to it ever since. Thanks guys, and keep being awesome. On to the topic: I'm doing some thinking on a question and I realized I needed to understand how math and physics evolved. Specifically, the question is "Why does the universe obey mathematical laws?" I have my theories, but I'd like to flesh them out and see if they still hold true after I have a better understanding of the history of math/physics. As far as I know, this is a philosophical question that has not been adequately answered yet, and I wanted to do some research. If anyone has any recommendations (or, hell, even any insight into this problem), it'd be greatly appreciated.
|
[
"The Discoverers by Daniel Boorstin for science. Fermat's Enigma by Simon Singh for math. If you want to read more about the history of modern physics, read the first half of The Trouble with Physics by Lee Smolin.",
"Math is just an internally consistent logic (mathematicians please don't gank me). If the universe is internally consistent and logical (cause precedes effect) then it can be described in the language of logic. Because some of the things we're describing are so precise, we use math rather than formal logical notation.",
"NB: I don't actually know anything about formal logic, or that much about math beyond the stuff I need for physics."
] |
[
"For a real \"history\" history, there's ",
", in several volumes. It sounds like what you're interested in is really closer to the philosophy of science. I'd look at something like Thomas Kuhn's ",
", or Godfrey-Smith's ",
". You may also be interested in Sagan's ",
" or even ",
"/r/PhilosophyofScience",
"."
] |
[
"I posted a link in ",
"/r/philofsci",
", and the link was appreciated, but based on the comments there it seems a lot of them don't really know much about science."
] |
[
"How long would an Ethernet cable have to be to give perceptible amount of latency?"
] |
[
false
] | null |
[
"An ethernet cable would not work well over distances that large, you would most likely need to use fiber optic cables (which have roughly the same latency). To reach 80ms in a one-way trip you would have to run a cable half way across the world or to another continent. 300ms would take a cable roughly twice the circumference of the planet.",
"\nAlternatively, if you passed a portion of the fiber optic laser beam through a near absolute zero Bose-Eistein condensate, a few feet would do the trick. "
] |
[
"To further elaborate on this. Most ethernet cables are rated for around 100 meters. Ethernet cables are usually UTP (Unshielded Twisted Pair) cables, and above those lengths, the interference starts to affect the quality of the signal."
] |
[
"You need to watch this.",
"Grace Hopper - Nanoseconds",
" ",
"ETA: After watching, you'll probably want to read this:\n",
"http://en.wikipedia.org/wiki/Grace_Hopper"
] |
[
"Is it possible for a planet in a binary system to have a figure 8 orbit that encircles both stars?"
] |
[
false
] | null |
[
"The orbit exists, but it is unstable. This means if you give the planet a small kick, it will either orbit one of the stars or be ejected from the system. More info here, ",
"http://physics.stackexchange.com/a/67260"
] |
[
"It's theoretically possible but due to it being very unstable it's extremely dependent on initial conditions and lack of external influence. If the system forms with the planet being jsut slightly off the needed CoG or any passing object causes perturbations, the system will eventually break.",
"You can simulate it in games/programs and it looks neat but that's pretty much it."
] |
[
"Also keep in mnd that \"small kick\" can be extremely small. Realistically the orbit's stability would be destroyed by one of the following sources, none of which are usually important to orbital stability:",
"All of these effects would normally be far to small to significantly affect a planet's orbit. However, a figure 8 orbit is unstable, so even the smallest change would grow larger and larger until the orbit fell apart. "
] |
[
"When someone receives a donated organ, do the cells of the new organ change their DNA to that of the host? What becomes of the DNA in the cells of the donated organ?"
] |
[
false
] | null |
[
"No, the DNA stays the same as it always was. That's why it's so important to find as close a genetic match as possible to limit the need for anti-rejection drugs. If the immune system of the new host finds the new DNA it will try to destroy the organ."
] |
[
"Wow man... my knowledge of organ transplantation was never great, but this is like a harsh, harsh reality check for me. I thought once the surgery had healed up you were kind of cooking with gas. Immuno suppression drugs are basically like AIDS-lite, aren't they? So that's your option if you need an organ transplant? Jesus."
] |
[
"and even then, the organ gets worn down over the years and a transplant patient can expect to require replacement organs sooner or later."
] |
[
"Sometimes computers get stuck processing or \"hang.\" Assuming an infinite amount of time, electricity, and a stable environment, would the computer eventually finish processing?"
] |
[
false
] |
I work in film and animation. We use often processor intensive software like Maya, Blender and After Effects. Once in a while a machine will seem to take forever to do a task. Often the assessment is "this is taking too long, just restart and rerun the operation." Now I'm no computer scientist and I imagine there's a million reasons why a computer would be stuck in a loop or hang, but assuming it could just sit there forever... would it actually solve the problem it's trying to solve?
|
[
"It depends.",
"If it is just taking a long time to render something, then eventually it will finish.",
"if it's hung because it's stuck in a loop, or expecting a response from something that will never respond, it will hang forever and do nothing.",
"Well written programs detect these situations and time out stuck resources to avoid these problems, and poor ones don't bother checking for endless loop or handing conditions. Well written ones give used feedback, a progress bar, a timer, something so you know things are happening. Bad ones just sit at an hourglass so you have no idea what's going on."
] |
[
"Oh certainly any program of any complexity has bugs that you can't completely account for, but the point I was making was about user feedback. An hourglass tells no one anything other than some process is occuring. A progress bar can show acitivity occurring (such as a download) which if it stops moving, then you know it is stuck and could cancel the operation, retry it, etc. I was meaning a UI with useful status information when a long running process is happening."
] |
[
"http://en.wikipedia.org/wiki/Halting_problem",
"Basically, there's no way to prove that any given algorithm will complete for any given input. The only way to determine it is by running it; if it finishes, it will return, if it gets stuck it will go forever, which doesn't help you know if it will ever finish.",
"Operating systems generally try to use timing methods to guess at a process being stuck or not, which works well enough for practical use.",
"Human analysis of a particular algorithm/input combo can determine if it will complete, depending on the complexity of the algorithm and programmer skill, but that's not an algorithmic approach and therefore outside the realm of computing currently."
] |
[
"The science of distance healing & aura reading?"
] |
[
false
] | null |
[
"We don't allow the posting of personal theories and intuitions here. You could try ",
"/r/asksciencediscussion",
". There is no empirical evidence supporting distance healing or aura reading."
] |
[
"Ok, would you or anyone know whether there is empirical evidence that dismisses it, or if there's currently no evidence linked to this subject at all?"
] |
[
"Sorry, I was a little hasty in my response. I wasn't able to find any empirical studies on aura reading in reputable journals.",
"The literature on distance healing is a bit more mixed, but leaning heavily toward there being no evidence for it. ",
"Here",
" is a review of several studies that found no evidence across them for distance healing. A ",
"recent study",
" in ",
" also found no evidence. ",
"This",
" is an older review which finds no conclusive evidence (some studies favor some don't), but they criticize virtually all studies for having poor methodology. The newer studies cited and reviewed above are purportedly better.",
"When searching for these things, be careful of what journals the studies are coming from."
] |
[
"How come you can literally feel a \"heart break\" in your chest?"
] |
[
false
] |
[deleted]
|
[
"I think he's referring to adrenaline release from stress. I know that I've had that same feeling during a break-up, or when something triggers jealousy, there is a burning feeling in my chest. I don't know why it is felt in the chest area, and Google doesn't seem to know either. But, my guess would be something related to adrenaline."
] |
[
"I think he's referring to adrenaline release from stress. I know that I've had that same feeling during a break-up, or when something triggers jealousy, there is a burning feeling in my chest. I don't know why it is felt in the chest area, and Google doesn't seem to know either. But, my guess would be something related to adrenaline."
] |
[
"Angina can be precipitated by emotional duress or anxiety as it is a typical response to stress",
".",
"Stress is the key factor in the situation of the ending of a relationship or other similar hardship; ",
"stress causes a host of problems",
", and may induce an endlessly vicious cycle of painful side effects."
] |
[
"Why do meteorites have a crystalline looking structure?"
] |
[
false
] |
I've been looking at meteorite rings lately, and I've noticed they all seem to have a lined, sort of crystalline structure, such as . I began wondering if that was just the finish of the ring, or if the metal actually looked that way. I did some googling, and found picture, and thought maybe it was just the way they cut it or the saw they use. That is, until I find picture, and realize it can't just be the way it's cut. So, my question is, why does the meteorite look this way?
|
[
"Not all meteorites have those crystalline structures. The pictures you linked are all Octahedrites, and when cut they exhibit ",
"Widmanstätten patterns",
". I believe the second picture is of a fragment of Muonionalusta, recovered from northern Scandinavia, and the third, the sphere, is of Gibeon, recovered from Namibia. ",
"The crystals you're seeing are nickel-iron formations, and the precise shape that forms depends on the nickel concentration. Interestingly, those crystals can only grow when the meteor cools very slowly, between 100°C and 10,000°C / Myr. To accentuate the crystals, the meteors are cut, polished, and acid etched."
] |
[
"So the rings I'm looking at, are they legitimately meteorite rings? Seems like a bit of a rare substance to get your hands on and make a ring out of, so are they actually real meteorite? Thanks for the information on the nickel iron crystals, that's very interesting."
] |
[
"I don't know much about jewelry, but they certainly look like real meteorites."
] |
[
"What would we hear if we played a sound with a frequency of 10000 Hz 200 times a second?"
] |
[
false
] |
By 200 times a second I mean a situation when the sound would be played for 2,5 ms, followed by 2,5 ms of silence. Would we hear a sound with a frequency of 10000 Hz, 200 Hz, or something entirely different?
|
[
"This"
] |
[
"https://soundcloud.com/librans/10khz",
"I made this using a frequency modulation synth. the last tone is a 200hz square wave being modulated by a 10khz sine wave."
] |
[
"It would sound a lot like 200hz. Any type of sound repeated evenly 200 times a second would sound like 200hz - the shape of the sample affects different aspects of the sound, but not the pitch. ",
"The brain's capability of interpreting soundwaves as a pitch, depending on the shape of the wave, starts at 10-20Hz. So any sample you repeat more than this threshold is going to be interpreted as a sound with that pitch. ",
"How about, say, a 10000hz frequency 2 times a second, then? Well, the brain isn't capable of interpreting something that repeats itself 2 times a second (=2Hz) as a pitch in itself, so you would just hear an unpleasant 10000hz sound 2 times a second. As the frequency it's repeated goes up from 2 and reaches the threshold you would be able to 'hear' that low frequency, but still be able to make out the 10000Hz tone. "
] |
[
"What are some ways to block pain transmission in nerves? What physiology background should I know first?"
] |
[
false
] | null |
[
"You'd need to have a good understanding of how sensory nerves transmit impulses. Basically, once a nerve is activated, it sends an electrical signal along the length of its long body (the 'axon') to the brain. Often, but not always, many nerves are involved in a chain to transmit the signal. ",
"To understand how this signal is transmitted, you'd need to know about the structure and properties of cell membranes (a phospholipid bilayer), how a potential difference is generated across the membrane, and how the membrane is depolarised and re-polarised during signal transmission. ",
"It would also be useful to know about propagating signal from nerve to nerve (junctions between nerves are called synapses) using specialised biochemicals called neurotransmitters. If you wanted, you could also look into how pain is processed by the brain, but you did mention specifically transmission through nerves, so that might be going off-topic a little. ",
"I can expand on any of these areas if you'd like to know more. Essentially you need to be thinking of electricity in terms of concentrations of ions in different compartments, so stop thinking of electicity as an electrician and start thinking of it as a biologist!"
] |
[
"Thanks a lot for your information.",
"I was just thinking if I wanted to localize targeting to remove joint pain in the knees or armwrist for instance and I wanted to create an external device to stimulate the nerves.... Does it have to be attached to the spinal cord or the brain region? Or can I just hook a device to that area of joint pain? Essentially, do I always have to start with the brain? "
] |
[
"If you want to stop pain being perceived you could either interfere with the transmission of the signal, or change how the brain perceives it. To be honest, I'm not sure how the brain processes sensory/pain signals so my instinct would be to avoid the brain (though hopefully someone with better neuroscience than me can help you there!).",
"I think your idea of stimulating the nerves is probably the opposite of what you want to be doing. Instead, you should be blocking nerve stimulation, to stop the transmission of pain. Alternatively, I suppose you could use the mechanism of a TENS machine, which uses electricity to give low-level stimulation to the area (feels like tickling/buzzing) which 'drowns out' the pain signals. ",
"Sensory nerves deliver touch/heat/pressure information as well as pain, so blocking the transmission of all signal will make the area numb. The spinal cord is probably the most accessible, but it's also very very difficult (impossible? not sure) to pick out the specific nerve you want to work with from the huge thick bundle that forms the spinal cord. ",
"You may have better luck in working with the spinal ganglia (also called 'dorsal root ganglion') as these are areas where nerve cells transmit signal from one cell to the next, and they're arranged just off the spinal cord, so may be reasonably accessible, but will serve a smaller area of the body, so your therapy will be a bit more targeted. ",
"Referring back to your original post, I may be wrong, but I can't think of a way magnetism will affect nerve signal transmission effectively in the way you want. Yes, nerves use electricity, but it's not a flowing current, it's concentrations of different ions in different compartments and I don't think these would be very influenced by magnetism. "
] |
[
"Is the wave function of a particle only a mathematical description or is it actually some sort of wave. Is there any difference between something being a wave function and being a wave?"
] |
[
false
] |
In particle physics, particles are said to behave like a wave when they are not observed. Does this mean it's actually some sort of wave or is it just best described by a wave function? Or does a wave function only describe a wave?
|
[
"There will be some people with strong opinions replying to you, but the truth is that we cannot answer this from our current state of knowledge.",
"Interpretations that think the wave-function is a real physical object are called ",
", while interpretations that think the wavefunction only describes our knowledge of the system are called ",
".",
"Neither notion could be ruled out by experiment so far."
] |
[
"The wavefunction is the true nature of matter, and phenomena such as waves and particles are just emergent phenomena we see on a larger scale, not the other way around. Simple wawefunctions are just mathematically similar to classical wave equations you'd use to describe waves in a medium such as in water or air, or on a string.",
"But yes, it is meant quite literally, as there is observable interference between phases of wavefunctions, analogous to large-scale waves interfering with each other, that makes a huge difference in how objects interact."
] |
[
"It's a \"wave\" (I explain the quotes below). Far too much emphasis is placed on thought experiments of measurements of a single particle. If one simply switches focus to the behavior of many many particles then the question is pretty clear. From that perspective, the (square of the) wave function is just the charge density, i.e. the amount of charge at that position. So the question is then \"how does charge density behave\" and the answer is like a \"wave\". It tunnels, like a \"wave\", (evanescence), it diffracts, it interferes. You can even directly image it. Wanna see what the surface of gold looks like to atomic precision? Here ya go:",
"https://en.wikipedia.org/wiki/Scanning_tunneling_microscope#/media/File:Atomic_resolution_Au100.JPG",
"Or this famous image from IBM in the 1989 (those are individual xenon atoms on a nickel substrate):",
"https://en.wikipedia.org/wiki/IBM_(atoms)#/media/File:IBM_in_atoms.gif",
"The famous Heisenberg' Uncertainty Principle is basically just a property of all waves (ocean, sound, whatever). When you want to calculate how particles scatter, it's as a \"wave\". When you trap it in a potential, it's as a \"wave\" (b-f in that illustration, it's not like a, which is the point):",
"https://en.wikipedia.org/wiki/Particle_in_a_box#/media/File:InfiniteSquareWellAnimation.gif",
"and so on.",
"NOTE: Under the strict terminology of math a wave is the name for a specific type of oscillating phenomena that results from a specific class of differential equations. Specifically a \"wave equation\". The Schroedinger equation, which governs the behaviour of non-relativistic quantum \"particles\", isn't actually a wave equation (technically it's a \"heat diffusion equation\", which is the math name for the class of equation, not a claim that it's a model of heat). So particles are \"oscillatory phenomena\" would be the more correct statement as their governing equation is one time derivative short of being a true \"wave equation\"."
] |
[
"If you were born and raised in space, would you have a greater resistance and management of UV/IR radiation?"
] |
[
false
] | null |
[
"Like others have said, probably not. From what we know of human development going from Africa to Europe skin changes did occur but the time estimates between small landmark changes are spaced by several thousand years, and that wasn't entirely due to changes in UV exposure but also dietary deficiencies. To have a chance of seeing significant adaptations you would likely need a significant population growing in space over many many generations. In all reality the best results I'd expect within the < ~10,000 year timeframe is a shift to darker skin pigmentation. Over a longer timeframe different more novel adaptations might happen but that's anyone's guess.",
"Edit: Just wanted to add that in the short term there may be changes that occur pretty much immediately as the result of some unknown or poorly understood pathways or increased expression of certain genes to help cope as well as epigenetic changes that carry on to successive generations. This all assumes that the lack of gravity still permits human reproduction and that offspring would then live long enough and be capable of reproduction. I don't know much about the state of research on animal reproduction in space so I can' t give much more than an educated guess on that side of things. ",
"Suffice to say I think it is likely that the UV exposure would be the least of a humans concerns developing in 0g (how do you make a baby develop muscle mass when it takes little effort to lift their head or move?)"
] |
[
"The ethics of performing those kinds of experiments are difficult, to say the least."
] |
[
"No, for a couple of reasons.",
"1) Lamarck got it wrong and Darwin got it right. Being born in X doesn't make you better at X. However, if 1M people are born in X then most will die, but after generations the survivors will be better at X. So it's no benefit to you directly.",
"2) Physicists have a joke that all chemistry is just 13.4eV physics. What they means is that to cause a chemical reaction you have to change electron potentials, so if you put more than 13.4eV into a Hydrogen electron, you give it so much energy that it doesn't change the electron level - it kicks the electron out all together and forms plasma. No molecule containing Hydrogen can withstand a hit of > 13.4eV and survive (actually the real number for organic chemical bonds is ",
" lower, like ~1eV). Space radiation is usually in the millions to billions of eV. Whatever you do, DNA will be damaged in that environment."
] |
[
"Why does a ceiling fan seem to rotate slower when viewed in a mirror?"
] |
[
false
] |
Perhaps slower isn't quite the correct term. I've noticed that when one looks at a ceiling fan, moving at a high rate of rpm, it's impossible to distinguish the individual blades, but if one looks at a reflection of the same fan in a mirror, the blades become somewhat visible, and the rotation itself seems to break up a bit. What's the science behind that?
|
[
"It's going to be hard for anyone to answer your question, and all answers are going to be plausible guesses that may or may not be correct.",
"That said, I do know a bit about the human vision system, and it maybe due to the fact that the fan appears further away in the mirror. So it looks smaller, and you can focus on a larger area of the fan at one time. This would make it easier for you to track the blades individually.",
"You can test this: stand further away from the fan (i.e. between as far and twice as far away as the mirror), and see if you can see the individual blades when you look directly at the fan."
] |
[
"So I just did a bit of observation, and it supports what you say.",
"It is, indeed, easier to distinguish individual blades when I am further away from the fan (however, I am near-sighted, and have no corrective lenses to test with, so this may bear some weight on my observations), and they seem to be easiest to distinguish when I have a much larger frame of reference around the fan. (IE. close up, I mainly see just the fan, and the ceiling directly above it, so there is little distance in my frame of vision, but further away, there are more objects, at different distances, which provide more depth to what I'm looking at)",
"I wonder if this may have something to do with the way our brain interprets the signal? (in the same way that the brain will 'see' a pattern, such as a face, and sort of 'fill in' the rest, so that its something recognisable) ...perhaps the slight imperfections in the mirror cause this... or the fact that we're looking at a relatively flat surface which reflects the depth of something we can directly observe, since we're in the same room.",
"I really don't know. I'm just curious as to the science behind it."
] |
[
"I'm not sure if this is the cause, but perceived speed is dependent on contrast. If the mirror were reducing the contrast (compressing the brightness level) it could reduce perceived speed of the fan.",
"I'm not sure about DoorsofPerceptron's answer. I would say the foveal eccentricity (distance to the center of your visual field) might be a better explanation than simple \"distance\". Try looking just to the side of the fan vs. the reflection. See if you can find a side distance that makes them look the same (or that changes the appearance)."
] |
[
"Is there a noticeable difference in the eye muscles between cultures that read left to right and cultures that read right to left?"
] |
[
false
] | null |
[
"I work with computer vision researchers who have explained this to me a few times, so secondhand citation syndrome in effect.",
"Your eye movement patterns are vastly predominated not by conscious, voluntary things like reading, but involuntary ones—so-called ",
"saccadic eye movements",
" are happening all the time.",
"http://www.scholarpedia.org/article/Human_saccadic_eye_movements",
"Even when your brain is completely convinced that it's doing a very plain, predictable pattern scanning left-to-right or right-to-left, your eyes are actually bouncing all over the place with these involuntary movements, some very small and some pretty significant. This is true even when you're just looking at a single point.",
"One consequence of this is that relating observed eye movement (e g. via a computer) to perception is very hard. Gaze tracking can very quickly know more about what you're looking at than you do in a conscious sense.",
"Another consequence to this that's more applicable to your question is that reading directionality isn't going to significantly change the overall usage pattern of your eye muscles, as everyone's usage pattern is still predominated by \"little darting movements all over the place.\""
] |
[
"Muscles, no.",
"But there may be some interaction..",
"We don't have \"eye dominance\" the same as handedness. Instead, the entire right field from both eyes may be \"dominant\" (like handedness) and \"dominant eye\" is a different process than dominant hand.",
"Half the visual field always crosses over at the optic chiasm so that everything seen to the right of center goes to the LEFT brain from BOTH eyes, and both LEFT visual fields feed to the RIGHT brain.",
"Also, most people pick up words tachistoscopically in the RIGHT visual field considerably better than in the LEFT visual field. That's thought due to Wernicke's area for receptive language being located asymmetrically in the left hemisphere, where visual information from the right hemisphere (left field) has a longer path to cross the corpus callosum.",
"These findings have led many to suspect it's the reason most languages are written/read left-to-right, and only a few (ie Hebrew) are right-to-left."
] |
[
"Thanks kind stranger"
] |
[
"Geologists of reddit, how is a mesa formed?"
] |
[
false
] |
A friend and I were have a bit of a question about how the Utah Mesas are formed as opposed to the steeply peaked hills in China ( ) as far as how much hydrological and pneumatic activity vs glaciation played into their formation. If some one could explain it like we were five, we'd really appreciate it, thanks!
|
[
"The difference between the Utah Mesas and the steeply peaked hills in China that you have provided a picture of is related to both the geological composition of the formations and the weathering environment of both locations. ",
"Mesas are formed by a process called differential erosion, where two rocks of differing resistance erode at different rates. Generally with mesas some sort of tectonic activity pushes rock upwards. Then, different weathering processes act upon that rock to cause erosion. These formations are most common in arid (desert-like) environments where the primary weathering processes are aeolian (wind) and hydrological (water). The flat top, known as the caprock, is typically a very hard rock of volcanic or metamorphic composition that is part of a horizontal layer of rocks. Essentially, ",
", while areas without the caprock to protect them erode away into valleys, creating the mesa. The reason mesas are very steep (normally almost vertical) and not gently sloped is because they undergo a process known as parallel retreat. Essentially, water flowing around the mesa erodes away the softer rock under the harder caprock, weakening the base of the mesa. When the base gets weak enough, a big section of the mesa all collapses at once in a vertical column, leaving straight steep walls. The Imgur link below illustrates the resultant shape created from these aforementioned processes, as well as the related landforms of smaller size (pinnacles and buttes) and larger size (plateaus). These related landforms were created by the same process, and are only named differently because of their size.",
"http://imgur.com/Xyegow1",
"The Guilin Hills in China are examples of karst formations. Karst formations happen in places where there are huge deposits of carbonate rock. Carbonate rock is fairly easily dissolved in water over long periods of time. The Guilin area was at one point a gulf filled with salt water with large deposits of carbonate rock, mainly limestone and dolomite formations. ",
" Eventually, through some sort of tectonic activity, these rocks were brought above the water surface. Since these formations are all mainly composed of similar material, they do not undergo differential erosion to the degree that mesas do. This is a large contributing factor to why they do not have flat tops. "
] |
[
"Thank you. That was very informative."
] |
[
"Those are called ",
" and you are correct. They are formed in a similar fashion to mesas, buttes, pinnacles and plateaus."
] |
[
"Is there a maximum possible acceleration?"
] |
[
false
] | null |
[
"Not by any physical law. There are practical limits, such as what a human could survive if you are talking about rockets. There are also practical limits in terms of “it would take more energy than exists in the universe”. But you could accelerate at any rate, as long as velocity stays below c. "
] |
[
"Our current laws of physics don't work for accelerations larger than the Planck acceleration, defined as the speed of light divided by the Planck time. We simply can't meaningfully describe processes faster than a Planck time.",
"10",
" m/s",
" is far beyond any acceleration we can reach in experiments (or in nature)."
] |
[
"You can have an acceleration of C/s for any duration you like, in your frame."
] |
[
"Did we know the temperature of space before we went there? How?"
] |
[
false
] |
I just learned that space is 2.7 Kelvin (-255 degrees Fahrenheit). If this is true, did we know this before we visited it? How? If we didn’t know, how did we survive that temperature?
|
[
"2.7 Kelvin is the temperature of the cosmic microwave background (CMB). If you are far away from any galaxies or other stuff then that's the temperature of the radiation around you. The temperature of gas or other stuff in galaxies or elsewhere can be very different from that. For the temperature of objects in the Solar System the CMB is irrelevant - sunlight is far more important. Temperature design is an important part of every spacecraft. Absorb too much sunlight and your spacecraft overheats, absorb too little and it freezes.",
"The temperature of radiation corresponds to a specific spectrum - basically the question how the intensity depends on the wavelength. The CMB was discovered in 1964, and measuring that spectrum told them the temperature. The first estimate wasn't very precise, of course, but it was clear that this is negligible for temperature management in spaceflight. Not surprising: At that time we had sent stuff to space for over 20 years already and the Apollo program was preparing to launch people to the Moon. If the CMB would have been relevant it would have been discovered earlier."
] |
[
"Short-term: Not a strong feeling in either direction. You only have radiation as mechanism, that's relatively slow compared to heat transfer with the atmosphere. Long-term you freeze to death or overheat depending on the amount of sunlight, infrared radiation from Earth or other objects (if nearby), and the surface properties of your space suit. You need the space suit to breathe, otherwise temperature won't be a concern."
] |
[
"What does temperature mean? This question isn't as easy and obvious as it might seem. ",
"The deepest answer in physics would most likely be, that temperature is the inverse of the derivative of entropy with respect to energy. ",
"This is called thermodynamic beta.",
"But this answer isn't very useful for everyday situations. So there are many other ways to think about temperature. Two other answers that are often used, especially in the context of space science. ",
"Using the kinetic energy of particles can be used with ",
" measurements. If there is a space probe that can measure the kinetic energy of particles in space, e.g. in the tail of a comet, then the distribution of kinetic energy can be measured and the temperature can be derived from that. But if there are no in-situ measurements possible, then we have to use ",
". For that we can use the second answer. Every object emits thermal radiation. The spectrum of this radiation is given by ",
"Planck's law",
". So in order to determine the temperature of an object all we have to do is measure the amount of thermal radiation. This is how we measure the temperature of the sun, this is how satellites measure the temperature of Earth, this is how ",
"infrared thermometers",
" work and this is how we determine the temperature of space. The cosmic microwave background is everywhere in space and it is pretty much the same everywhere. So if we measure the cosmic microwave background spectrum we can determine what temperature space has to have to emit this radiation. Of course it is a bit more complicated, the cosmic microwave background was emitted in the early universe before even the first stars were formed. Note that the temperature we feel when we touch something depends on the thermal conductivity. So, even though space has a temperature of 2.7K it wouldn't necessarily feel very cold if you were directly exposed to it. ",
"TL;DR \nWe measure the microwave spectrum in space called the cosmic microwave background and assign a temperature to it, based on Planck's Law."
] |
[
"Does the placebo effect still occur if you understand it?"
] |
[
false
] | null |
[
"\"Maybe it's not a placebo and they're telling me this to compare against placebo\"."
] |
[
"According to an IBS medical trial recently, the placebo effect does work, even when patients are told they are on placebos.",
"Link to article",
"Link to the study"
] |
[
"The old double-placebo. It's like reverse-reverse psychology."
] |
[
"What is humanity's best chance to get to another solar system, aka travel space/time"
] |
[
false
] |
Is there any hope the we will be able travel faster than light and thus get to another solar system within our lifetimes?
|
[
"Is there any hope the we will be able travel faster than light and thus get to another solar system within our lifetimes?",
"The answer to your question is a simple ",
". According to modern physics, faster-than-light is absolutely impossible. But that won't stop a horde of starry-eyed scifi fans from raving about wild impossible fantasies in which we disregard the laws of physics. "
] |
[
"No, we cannot travel faster than ",
" - we will probably never be able to travel near ",
" either, as they energy required becomes exponential. ",
"As BubbleBobble-007 alluded to, the shortest way to get from A to B is always a straight line, but if we can curve spacetime, and make a bridge, then this can be a shortcut making that straight line much much shorter, often referred to as a wormhole. However, current understanding is that we could not create a wormhole large enough or sustained for a time long enough, for anything to pass through it. ",
"There are other theoretical ideas of getting a spacecraft up close to ",
" such as inducing a gravitational field, and riding a gravitational wave if you will, called the ",
"Alcubierre drive"
] |
[
"There are other theoretical ideas of getting a spacecraft up close to c such as inducing a gravitational field, and riding a gravitational wave if you will, called the Alcubierre drive",
"The Alcubierre metric isn't a theoretical idea. The author never ever proposed this was possible. It is positively ",
". Its just a neat \"what if.\""
] |
[
"In a tilt gear wand, specifically the ones used to open and close blinds by turning, is there more leverage or torque grabbing and twisting near the top or near the bottom of the stick?"
] |
[
false
] |
I have really big heavy blinds and my wife has trouble turning them. Would there be any difference in her turning them by grabbing the top middle or bottom of the stick? If there is why is that?
|
[
"She would get more from twisting it near the top.",
"The rod has a certain amount lf elasticity, and that is going to absorb some of the \"twist\" before transfering it to the mechanism.",
"This could be a realy tiny effect, or a decently sized one mostly dependant on the rod. ",
"But either way she will get more force in the mechanism by twisiting near the top"
] |
[
"In torsion, angle twisted of ROD is a function of both torque and length so you are absolutely right. ",
"Tl/JG = angle of Twist \nT - torque \nl - length over which moment applied and resisted \nJ - polar moment of inertia \nG - shear stress modulus",
"We want angle of twist to be minimum and angular displacement to be maximum for more of the work being done on mechanism rather than being used up to deform the rod. ",
"For most rods used in blinds, this is very negligible so it won't make too much of a difference. "
] |
[
"Since the diameter of the rod is constant there is no mechanical advantage for turning the rod at the top or bottom, the only advantage is ergonomic. For me it's much easier to to turn the rod with my arm bent 90° at the elbow to adjust the slats, and to grab the rod at the highest point comfortable to slide the mechanism open or closed. I've found it's easier to slide open /close the when the slats are partially open. "
] |
[
"Why is the pericardium shiny and slippery?"
] |
[
false
] |
Pericardium being the membrane that surrounds the heart.
|
[
"The short answer is that the smooth surface of the pericardium and the serous fluid it secretes allows for a low friction cushion that surrounds the heart. "
] |
[
"To reduce friction wear and irritation on the heart as well as act a shock absorber for impact. "
] |
[
"It is shiny and slippery because it's thin, \"The parietal pericardium is a fibrous structure that is <2 mm thick and is composed primarily of collagen and a lesser amount of elastin.\"1 In terms of function, one of the things the pericardium does is prevent the heart from over-expanding and provides an extra level of elasticity when blood volume increases. When the pericardium is removed, the atria and to some extent the ventricles expand beyond normal and their efficiency decreases. The heart is still viable and functional though.",
"There is a great review on the pericardium here:\n1 ",
"http://circ.ahajournals.org/content/113/12/1622.full"
] |
[
"Analytical chem question: how to interpret mass spectra for an unknown compound?"
] |
[
false
] |
I'm currently trying to get some preliminary IDs on a number of hydrocarbons; mainly just trying to get an idea of if they're double-bonded, if they have functional groups like aldehydes, carboxylic acids, etc. I realize determining exact structure is not possible. I've attempted calculating retention indices (with an external standard of alkanes) for some of the compounds, but didn't know how to utilize the numbers without some kind of comprehensive database. I then began trying to tease out info by utilizing the mass spectra ions, but soon came to realize that the diagnostic ions don't seem to match up with functional group molecular weights (for instance, why do many aldehydes have 82 as a diagnostic ion? the aldehyde group is 29, so my impression would be that any diagnostic ions would be odd-numbered). If anybody has any pointers or advice, or perhaps a good reference to get a better grasp on utilizing mass spectra for ID, I would be greatly appreciative. Cheers.
|
[
"Let's start with that. "
] |
[
"Yeah, GC-MSD, using a DB-1, that helps me understand what type of artifacts that can come in with it.",
"What software are you using to control the GC-MSD and do integration/quantitation?",
"And your matrix is essentially whatever your analytes in question are mixed in. Are they soil samples in your dichloromethane? Plant samples in hexane? Was this based off of a synthesis, so your matrix is essentially your solvent? All these things matter and can affect your analysis.",
"What's your target concentration of these hydrocarbons? How much did you inject for your references? How did you try calculating retention index?",
"For the case of 82, I would imagine that given a hydrocarbon aldehyde of sufficient length, you can essentially cleave off a water molecule which would leave you with a m/z of 82, such as that of Hexanal.",
"Do you have an example spectra to look at?"
] |
[
"Insect cuticle? That seems very small. Are you saying nanograms total or nanograms per milliliter (ppb range?)",
"If it's nanograms total, how much solvent did you use to prepare your sample?"
] |
[
"Why aren't computer motherboards componentized?"
] |
[
false
] |
Recently, I've been out shopping for a new mobo since my old one was on the fritz. After comparing specs of different motherboards, I got to wondering why the different parts of the board aren't separate components that you can just plug together. So for example, you'd have your base CPU component that accepts a component for DIMMs, a component for expansion slots, a component for motherboard connectors, components for drive connectors, etc etc. This way, when you decide you need 4 SATA slots instead of 2, or decide that you only need 2 DIMM slots to suit your budget, you don't have to buy a whole. new. board. every time you want to make changes to your system's internals. Is this actually something workable, or a complete dream? I'd throw my money at the company that does this sort of thing!
|
[
"To some extent it is. Remember that a DIMM goes into a slot that can accept various sizes of memory. Most motherboards have more than one port of various types (PCIe, PCI, SATA, etc.). ",
"But it sounds like what you are saying is allowing for an ",
" number of, say, DIMM sockets. Those sockets need to be somehow physically connected to the CPU or Northbridge. This is done via traces on/in the motherboard PCB, and requires things like impedance matching, trace length matching, and other electrical requirements that are moderately tough. Moving signals that are fluctuating at rates of millions of cycles per second is not trivial. ",
"Could you do some of those things with cables rather than PCB traces? To some extent, although you'd usually have to sacrifice performance, and the physical layout of everything might get tricky. Is it possible? Somewhat. But it would probably make the overall cost higher, and the PC industry has thrived on aggressively pursuing lower costs. ",
"This might be more do-able if all of the busses that currently run on the mobo were done optically. It would still be tricky, but some things would get easier. "
] |
[
"To add to what ",
"/u/afcagroo",
" stated, keep in mind the level of reliability that computers are held to. In enterprise class machines you can see computers running with 99% uptime and substantial loads for months or years, performing quadrillions of operations and pretty much never making a mistake. That level of reliability becomes ",
" more difficult to maintain when you open up more and more choices to the end-user. Just look at the reliability that Apple achieves with their systems--they offer virtually no choice of hardware, but the package you get winds up having been tested far more completely as a system than a typical PC.",
"Another point is price: pick and place machines can assemble motherboard components at blinding speeds, and surface mounted chips are likely to be cheaper than a chip and a socket. For preassembled computers (which still dominate the market) it doesn't make sense to add extra human assembly steps to the process.",
"Finally, there's the point of choice paralysis. Someone building/buying a computer is already bombarded with countless options. Adding in options like what you've suggested would push even more people out of the market. "
] |
[
"The biggest lie about your computer is that it's just one computer; it's really dozens of independent processors and environments lashed together. Often these parts are pretty cheap and are unlikely to be swapped out. These parts stay on the motherboard. A few parts, like hard drives and video cards, are indeed the sort of things people wish to customize. So entire busses are engineered with sockets to allow integration.",
"That integration isn't free, and it's literally a specialty in and of itself to make expansion busses and devices that work well with them."
] |
[
"Help in Identifying a little bug"
] |
[
false
] |
As I was taking out something of my mother's car, I've found a strange bug on one of its doors. I immediately took some pictures and thought of asking here if someone knows what bug this is. Here's a link to the album with some photos: I've included a picture of my finger beside the bug to help have a reference to its size. I don't know if the location helps, but I live in Portugal. Thanks a lot.
|
[
"/r/whatsthisbug",
" is that way <<"
] |
[
"Btw it's a Plume Moth."
] |
[
"Ha! I didn't even know there was such a subreddit. I'll post it there. Thanks."
] |
[
"How is the anatomy or structure of an organism encoded in its genes?"
] |
[
false
] |
[deleted]
|
[
"Life begins with a small blob of cells. Cells comunicate with one another by direct contact and by emitting transmitters. When this blow reaches a certain size, based on the orientation of the blob towards the future placenta (or alternative), different regions on the blob determine the orientation of the whole new organism. Areas like \"front\", \"back\", dorsal and ventral are determinated by small groups of cells in these areas emitting these transmitters. Cells close by get a high concentration of these molecules, those further away get a lower concentration and also transmitters from other centers emitting different transmitters.",
"This way there are gadients of different transmitters created on the whole blob. The different concentrations of different molecules, trigger the expression of different genes, whose products (RNA and proteins) direct the formation of basic tissues. Within these tissues, the same thing happens. Local centers of cells determine the orientation of these regions, like upper and lower back, and influence the cells with the transmitter gradient to form different tissues or make them move around and building 3-dimensional structures like tubes or curvatures.",
"This \"simple\" mechanism causes a long chain reaction, becoming more complex in every step by creating new way to orient and segment the developping body. I had on year of embryology, and it´s surprisingly simple once you get the general idea. It all comes down to the interaction of transmitters in different concentrations and mixtures.",
"If you want to learn more, sea urchins are often used as a showcase organism in embryology. Terms like GASTRULATION and NEURULATION might help you find more. Even just pictures will help you a lot."
] |
[
"just a small correction: The one gene one protein hypothesis was shown to be wrong for eukaryotes. Because of mechanisms like splicing, one single gene can result in different functional proteins and RNA."
] |
[
"just a small correction: The one gene one protein hypothesis was shown to be wrong for eukaryotes. Because of mechanisms like splicing, one single gene can result in different functional proteins and RNA."
] |
[
"There are people in prison who are later exonerated. Have there been any scientific studies comparing how these people behave in prison compared to the rest of the people in prison?"
] |
[
false
] | null |
[
"Well, it is difficult to identify those inmates who are wrongfully convicted while they are incarcerated. Many of the people in prison claim that they did not do the crime for which they are imprisoned. However, most accounts relate that those inmates who are wrongfully convicted are treated differently than other inmates because they maintain their innocence throughout their incarceration period. Some people argue that maintaining innocence while incarcerated leads to disparate treatment by prison guards and other officials, who see the inmates' refusal to admit to the crime and sheer stubbornness. ",
"There have been a few studies done to determine the effects of wrongful conviction versus the effects of incarceration for someone who did actually commit the crime they serve time for. It is a very new field, sociologically, as DNA exonerations themselves are quite new (the first occurred in 1989). ",
"I analyzed data from a study that was completed in attempt to identify the incidence of PTSD, depression and anxiety among exonerees (people who are exonerated). It turns out that they do suffer from all three disorders, but it is very difficult to say if they suffer more because they were wrongly convicted or if it is comparable to the general population of ex-inmates. What we DO know is that this population of exonerees is extremely underserved when they are released. They do not get access to the same type of governmental aid as do parolees or probationers, because they in fact did not commit the crime they served time for. They are typically given nothing upon release and must depend on family/friends/attorneys for everything (at least initially). In addition, the wrongly convicted sometimes must agree to not sue the state/county government prior to being released or getting certain items of evidence tested against their own DNA (I'm not saying this is always true, but it has happened). These people are released and find that they are now in a completely different world. The average amount of time that exonerees spent incarcerated in the study I analyzed was over 10 years. The other day a man was released after being imprisoned for 30 YEARS! Think about how much has changed in the past 30 years! He has no idea how to use an ATM, a debit card, a computer, etc. Exonerees report feeling embarrassed about asking for help with these things.\nFrom accounts of those who have been wrongly incarcerated, it seems that what they go through is much more traumatic than it is for someone who did actually commit the crime they serve time for. But as of now, I don't know of any studies that have actually studied the behavior while they are in prison. ",
"edit: spelling"
] |
[
"[Masters in Clinical Psychology (Forensics Emphasis), working towards Doctorate]",
"Prison culture is pretty uniform. There are flavors and variations depending on the correctional philosophy of the administrators, geographic location, racial makeup, security level, and offense type, but they all tend to overlap quite a bit. This culture is pervasive and assimilating. It involves not only the offenders, but COs, administrators, and staff in dynamic power struggles and hierarchical structures. ",
"If you are an offender in incarceration, this culture becomes ingrained in you. There is no getting around it. Some offenders imagine that they will be able to resist the power struggles and internal politics. Sadly, not everyone can be Andy Dufresne and remain isolated and free of the victimization and acculturation. Prisons are often conceptualized as \"criminal apprenticeships,\" wherein affiliation and contact with other offenders hardens inmates and increases recidivism in the future.",
"Why is this? Because the two largest contributing factors (criminogenic needs) to criminal behavior are antisocial peers and antisocial attitudes. Even if you were able to find two or three other inmates who were willing to be your friends and help keep each other safe and occupied, you are still saturated in an environment filled with these two factors. Ordinary, vanilla people, those people who might commit only a single significant crime in their lifetime, increase the likelihood of recidivism simply through contact with this culture.",
"So your hypothetical inmate, regardless of their innocence, temperament, or personality, are going to adapt to prison life. That, or they will be victimized by anyone willing to victimize them (which is the majority). Once they adapt, they internalize antisocial attitudes and spend all of their time with antisocial peers. ",
"As for scientific studies, I have never run across any that examined incarcerated behavior compliance with wrongfully convicted offenders. I'm guessing you would be hard-pressed to find such a study, since (a) despite media portrayals, the wrongfully-convicted population is very small, and (b) those who are wrongfully convicted (and offenders in general) tend to be reluctant to participate in research after their release. Participation while incarcerated is easy to get, since they get privileges in exchange. But once they are free, they typically do not wish to participate. "
] |
[
"I think it would be very interesting to see if any studies had been done comparing their behavior after getting out too."
] |
[
"Where are fruit flies hanging out when there is no fruit? The minute you have day old fruit they seem to come out of nowhere from some dormant sleep."
] |
[
false
] | null |
[
"Actually, as a yeast geneticist, I wanted to clear up a common misconception about fruit flies. While they may eat some of the rotting fruit, their real target is the ",
"naturally-occurring yeast",
" that grows on the outside of fruit and causes the fermentation/rotting to occur.",
"I can't begin to tell you the woes of working down the hall from a lab that works with drosophila. How aggravating it is to come in to find little lines of bacteria looping all around across your yeast plates and a punchdrunk fly still nomming on your experiment.",
"Also, in drosophila labs, the main food given to flies is a thick paste of yeast on a bed of molasses-containing agar.",
"If you ever find that you have a persistent cloud of flies hanging around your kitchen, take a glass and splash a little wine vinegar in it and add some dish detergent, then tape to the top of the glass a cone of paper that has a small hole at the bottom to let the flies in. As long as the cone sits firmly on the glass and there is no gap at the side to allow the flies out, they will be attracted to the smell of the wine vinegar and come in the hole, but not be able to find the hole again to leave, and so fall in the liquid and drown because of the lack of surface tension (from the soap). These little guys were the only things that allowed us to function as a yeast lab when we were down the hall from a fly lab."
] |
[
"you are right, found this: (I had no freakin clue they layed their eggs directly in the fruit)",
"\"The fruit fly life cycle begins when a fertilized female locates a piece of fermenting fruit or other source of fermenting sugar in which to lay her eggs. She can lie up to 400 eggs at a time and male and female fruit flies are capable of reproducing as soon as eight hours after emerging as adults. The mating practices of the fruit fly allow for rapid population growth and infestation.",
" Cleaning your home of all organic debris can deprive fruit fly populations of food sources, causing them to die quickly.",
"Also, if you wish to deter fruit fly infestations, routinely check your yard. Any fruiting plants can quickly become breeding sites for fruit flies, whether the fruit is still hanging or rotting on the ground. Lastly, check any soft tissue plants like cacti or succulents. Open bulbs can also host fruit flies. If you notice swarms of fruit flies in your house or on your property, contact a local pest control company to evaluate the risk.\" ",
"source",
" ",
"In terms of how they get in I'm thinking they are so small they might be able to sneal in past door seals, etc. "
] |
[
"If for some reason you do not have plastic to cut up, any vessel containing vinegar and dish soap will attract the buggers and drown them."
] |
[
"From a quantum physics standpoint, how exactly do LEDs produce photons, and how efficient are they?"
] |
[
false
] | null |
[
"WARNING: Long post ahead",
"Alright, the key thing you have to understand is how electron behave in a solid.",
"Electrons in a solid can only have certain discrete states and, as is the nature of all fermions due to the Pauli exclusion principle, there can only be one electron in each state. So if we imagine the simple case of absolute zero where everything just wants to sit in its lowest possible energy state, things are dramatically different between bosons and fermions. All the bosons can just sit in the ground-state, but only one electron gets that spot for fermions, the next gets the second highest, the third the third highest and so on until the last electron finds a \"seat on the bus\" and that last, highest energy, filled state is called the Fermi energy and it is way, way higher than the ground-state. At a finite temperature things are very similar except particles now have a tiny bit of \"spending money\" to not sit at the absolute lowest energy \"seat\" on the bus but can explore some of the nearby seats. However, at room temperature, this \"spending money\" is only about 0.025 electronvolts (a measure of energy), where the Fermi energy is typically 100-1000 times higher. ",
"A very convenient and central quantity to understand is the \"density of states\", which gives basically the number of states available for electrons who have a given energy E\". An example of the density of states of a real material might look something like this:",
"https://i.stack.imgur.com/zX8Gv.png",
"The thing you'll notice is that there are some ranges of energy where there are NO electron states. Electrons with those energy don't exist in that solid. These are called BAND GAPS (they are called this because separated energy ranges where there ARE lots of states are called \"bands\").",
"The definition of a metal vs. an insulator/semiconductor is whether the Fermi energy, the \"last filled seat on the bus\" falls within a band gap or not. This obviously has huge implications, as insulators and metals are obviously very different. The reason is because it makes a huge difference in what an electron can do if you give it a small amount of energy. In an insulator at absolute zero (absolute zero just means I'm ignoring that tiny bit of \"spending money\" things have at non-absolute zero) the very last electron state before a band gap is fill and the first state above it is open. That means that if you give an electron any amount of energy LESS than the band gap, it won't take it. It needs to take that energy to move up and end up in an open seat, but there is no seat. By \"give energy\" we mean, usually, absorb a photon of light (though there are other ways). So at absolute zero, an insulator will absorb 0 light if it the photons in that light have less energy than the band gap. At room temperature it can still absorb a tiny amount because some tiny, tiny fraction of electrons have gotten a very large amount of spending money (since the 0.025 eV values is only an AVERAGE, some tiny fraction have more) and moved on up and thus behave in a more metallic way. Thus an insulator will only very weakly absorb light below the bandgap at finite temperature. This btw, is what makes things transparent or opaque: do they have a bandgap and is it greater than the energy associated with photons in the visible spectrum?",
"So, the real last piece is that things can run in reverse. If electrons are in a state above the bandgap and there is an open state below the bandgap, they can spontaneously fall back down in energy and release a photon whose energy is basically that of the bandgap. In thermal equilibrium this \"spontaneous jumping up\" and \"spontaneous jumping down\" are in balance and you get no net emission of light. What makes an LED is a specially designed scenario that manipulates the distribution of electrons so that there are more electrons above the bandgap then there should be at thermal equilibrium. Thus, the \"falling down\" transition happens a lot more frequently and the result is a constant emission of light whose energy is approximately that of the bandgap.",
"So you basically need to find a material whose bandgap corresponds to the color of light you want it to emit. You can see the options listed here:",
"https://en.wikipedia.org/wiki/Light-emitting_diode#Colors_and_materials"
] |
[
"What happens if an electron absorbs a photon with an energy ",
" than that of the band gap, as opposed to the exact amount?"
] |
[
"An \"excited\" electron with energy more than thermal equilibrium will shed this excess energy by scattering off other degrees of freedom. Usually the most important is phonons (i.e. atomic nuclei). On average such an electron will travel/\"make it\" a distance called the \"thermalization length\" before it's basically thermalized through such scattering back to equilibrium.",
"The thermalization length of, for example, silicon is about 10 nanometers (~100 atomic widths). So unless your device is incredibly short (an example here is, for example, a \"hot carrier cells\" which is a type of solar cells specifically designed to extract carriers BEFORE thermalization) any excess energy can be assumed to be shed. This is why the maximum efficiency of a (non-tandem) PERFECT silicon solar cell is still only about ~28%; the bandgap means it absorbs most light (maybe 80% or something but it doesn't absorb infrared light with energy below 1.1 eV, the bandgap of silicon) but, crucially, any EXCESS energy a light has abovem1.1 eV is not harvested because it is assumed lost to thermalization. ",
"Thus the paradox of solar efficiencies: large bandgaps absorb less light but that light that is collected sees less thermal loss. Put another way, solar cells absorb light most efficiently light whose energy is exactly its bandgap (i.e. such light suffers no thermalization loss). The optimal bandgap for the spectrum we receive from our sun is ~1 eV, thus why we use silicon."
] |
[
"Can there be a planet with hot poles and cold equator?"
] |
[
false
] |
If yes, what condition have to occur to make it possible? I know that axial tilt equal ~90 won't do it, because it makes both poles and equator the hottest places.
|
[
"Yes, there definitely should be.",
"I know that axial tilt equal ~90 won't do it, because it makes both poles and equator the hottest places.",
"That's actually not true. If a planet's axial tilt is greater than ~54 degrees then, ",
", it will receive more sunlight at the poles than the equator. So, if you go deep enough in a planet's atmosphere or surface where daily and even seasonal variations have a minimal effect - for example, going into a cave where it's the same temperature year-round - then this unusual annual sunlight pattern should also result in hotter temperatures at the poles than the equator.",
"This is actually the exact case for Uranus - it's tilted 83 degrees (or 97 degrees, depending on your definition of North), and our models predict you don't need to go very deep in the atmosphere before the thermal inertia timescale is longer than one Uranian year, i.e. where daily and seasonal variations in sunlight shouldn't have an effect on yearly temperatures. ",
"However...this inverted temperature structure isn't what we see on Uranus, and it still remains a mystery exactly why its poles ",
" hotter than its equator. When the Voyager 2 spacecraft flew by in 1986 during the planet's solstice, the temperature across the entire planet was shockingly similar everywhere. There are a few hypotheses floating around about why this might be (e.g. maybe it has a very efficient north-south circulation that redistributes heat particularly well), but we're nowhere near an answer just yet."
] |
[
"Well, it's exactly what I laid out above, namely:",
"Have a planet with an axial tilt greater than 54 degrees",
"Be at a depth in the atmosphere or surface where the thermal inertia is large enough that you're not affected by daily or seasonal variations."
] |
[
"Right, for even larger axial tilts, the equator would be the coldest place on the planet. I made ",
"this diagram",
" that shows the insolation (incoming solar radiation) averaged over the year vs. latitude for a variety of different obliquities (axial tilts). ",
"You can see the transition from poles-colder-than-equator to poles-warmer-than-equator happens between 50 and 60 degree obliquities. Right at 60 degrees obliquity, though, there's a little temperature bump over the equator, so it's not quite the coldest place on the planet (that's closer to 30 degrees latitude). Increasing the obliquity to 70 degrees, though, and the equator does become the coldest place on the planet."
] |
[
"Guy takes a picture of a completely dark room - What is showing up in the picture?"
] |
[
false
] |
It isn't completely black, so what's the picture showing?
|
[
"Depends on what medium he used. ",
"If it's a digital camera, as others here have already noted this will be thermal noise from the CCD or CMOS chip, and from the amplifier and the analog-digital-converter units after it.",
"If he used chemical photographic film, it's either a slight accidental pre- or postexposure during film production or development, again thermal noise, this time in the reaction kinetics of the halogenides or dyes on the film, or, maybe most surprisingly, cosmic rays or beta or gamma radiation. Alpha radiation wouldn't make it through a camera lens or case.",
"And of course it can always be a combination of any of these."
] |
[
"If he used chemical photographic film, then he also scanned it. A lot of the noise could be thermal noise from the scanner.",
"But it's most likely shot with a digital camera. "
] |
[
"This is indeed thermal noise from a digital camera. When doing astronomy photography, I take a picture of the inside of a lens cover to get an image of JUST the thermal noise, and use that template to subtract the noise out of my actual pictures. My black pictures look exactly like the post."
] |
[
"Why did the radiation from Hiroshima not last as long as the chernobyl disaster?"
] |
[
false
] |
Was it the power of the explosion blowing the radiation away or was the bomb designed in such a way as to avoid long lasting fallout?
|
[
"in chernobyl you have 180 tons of radioactive material in the core. A nuke contains 0.05 tons of radioactive material.",
"There are of course differences: a very violent explosion that absolutely vaporized the bomb and a violent explosion that desintegrated the core and vaporized some. One burst in the air, the other on the ground.",
"Hiroshima was much smaller and the material was much more dispersed. The main factor is just the vastly greater amount of material that you deal with in a reactor."
] |
[
"The Chernobyl disaster happened on the ground while the bombing of Hiroshima was up in the air. The radiation levels of Hiroshima are identical to any other place on Earth; this is because the explosion was in the air and all radioactive material was blown away by wind elsewhere.",
"The Chernobyl disaster spread radiation on the ground; this is why the radiation is still there."
] |
[
"Another thing to consider is that nuclear power plants and nuclear bombs don't produce exactly the same type of radioactive materials, and the radioactive material released in either case is a heterogeneous mixture of many different radioisotopes; this is important in assessing long term behavior. ",
"As delete_this_post says, neutron activation can produce a wide variety of radioactive material, since the energetic neutrons react with generally heavier atomic nuclei to produce different nuclei, often unstable (and hence radioactive.) In a power reactor, the neutron flux is generally controlled and exposure is limited. In a bomb, the neutron flux is extremely high; especially in a ground burst, but even at altitude, this produces a large amount of neutron-activated radioactive material that is also carried high in the atmosphere by the blast. In addition, the large amount of dust carried upwards when a nuclear bomb explodes provides a convenient place for radioactive fission products (different from the neutron-activated material) to adhere. ",
"Nuclear fission, as you might expect, is not a deterministic process; when a uranium atom splits, it produce lighter nuclei (the fission fragments), as well as neutrons and other particles. A power reactor operates at near criticality, in some cases sustaining it for years; a bomb, on the other hand, is in a state known as prompt supercriticality, which results in extremely rapid energy release. These unstable products decay at different rates, and when they decay, can produce longer lived radioisotopes or might be stable. In a power reactor, these products can be neutron activated, producing a more diverse array of new radioisotopes. In a bomb, the length of criticality is too short for this to occur. ",
"In general, a radioisotope that is more radioactive will have a shorter half life. A nuclear bomb will produce much more intensely radioactive fallout, but the period of time when it is intensely radioactive will be relatively short. On the other hand, power reactors produce lower activity products, which last correspondingly longer. Combined with bunky_bunk's observation that there is a lot more material in a power reactor than a bomb, you have a recipe for much longer lived radioactivity in a reactor, but at a level far lower than produced by a bomb. "
] |
[
"Can angle of window blinds affect room temperature?"
] |
[
false
] |
Given the recent heat wave, I was wondering if there is an optimal blind angle to reduce heat. Since heat rises, would angling the blinds downwards force the rising hot air to exit your room? (crappy drawing: ). And vice versa, if I pointed them up would it catch rising hot air from outside and bring it inside?
|
[
"Are the blinds leading to outside? Or to a window?"
] |
[
"Mesh window"
] |
[
"Yeah I would imagine during the day sunlight would have a larger effect. What about at night when it is still hot in you room?"
] |
[
"AskScience AMA Series: We're from the Pacific Northwest National Laboratory and we research pumped-storage hydropower: an energy storage technology that moves water to and from an elevated reservoir to store and generate electricity. Ask Us Anything!"
] |
[
false
] |
We are Dhruv Bhatnagar, Research Engineer, Patrick Balducci, Economist, and Bo Saulsbury, Project Manager for Environmental Assessment and Engineering, and we're here to talk about pumped-storage hydropower. "Just-in-time" electricity service defines the U.S. power grid. That's thanks to energy storage which provides a buffer between electric loads and electric generators on the grid. This is even more important as variable renewable resources, like wind and solar power, become more dominant. The wind does not always blow and the sun does not always shine, but we're always using electricity. Pumped storage hydropower is an energy storage solution that offers efficiency, reliability, and resiliency benefits. Currently, over 40 facilities are sited in the U.S., with a capacity of nearly 22 GW. The technology is conceptually simple - pump water up to an elevated reservoir and generate electricity as water moves downhill - and very powerful. The largest pumped storage plant has a capacity of 3 GW, which is equivalent to 1,000 large wind turbines, 12 million solar panels, or the electricity used by 2.5 million homes! This is why the value proposition for pumped storage is greater than ever. We'll be back here at 1:00 PST (4 ET, 20 UT) to answer your questions. Ask us anything!
|
[
"Let's say you get 1 GWHr from the grid to pump water uphill. How much energy would you be able to return to the grid when the same volume you pumped uphill comes through the turbines? What's the round trip efficiency?"
] |
[
"Great question. Round-trip efficiency (RTE) is an important part of the overall value equation. If, for example, you charge the PSH system during low-price hours, store the energy for several hours, and then discharge onto the grid, higher RTE losses means the price differentials must be greater to make up for the lost energy, which come at a cost.",
"As part of the cost and performance characterization study PNNL just completed for the US DOE (Kendall Mongird was the primary author), we researched this question by reviewing extensive literature, holding discussions with industry stakeholders, and collecting surveys from manufacturers and developers. We evaluated the RTE for six battery technologies and four non-battery technologies. Here are the results: PSH (80%), lithium-ion battery systems (86%), sodium-sulfur batteries (75%), redox flow batteries (67.5%), compressed air energy storage (52%), flywheel (86%), ultracapacitors (92%), lead-acid (72%), sodium metal halide (83%), and zinc-hybrid cathode (72%).",
"You have probably heard much higher RTEs for batteries. We have completed extensive testing on several battery technologies. When you include losses during rest, auxiliary loads, temperature fluctuations and other factors, real-world RTEs are lower than those commonly reported."
] |
[
"Thanks for doing this! I just watched ",
"this excellent talk",
" by Jesse Jenkins at the University of Pennsylvania which talked about how \"flexible base load\" is the missing piece of our future energy grid and how pumped hydro is one of the few technically feasible options we have. "
] |
[
"Why are airplane seatbelt buckles different from the ones in cars?"
] |
[
false
] |
Do the different designs make one better for a certain application than the other? Is it different safety standards?
|
[
"The 3-point belt you where in a car is meant to keep you from shooting out forward when you come to a sudden stop. The belt on an airplane is meant to strap you down to the plane so that if it suddenly drops in turbulence, you don't hit your head on the ceiling.",
"A sudden stop on an airplane would kill everyone on board from deceleration, so there is no need address this with a belt."
] |
[
"What about the latching mechanism? Why is that different?"
] |
[
"I have a vague recollection that the first \"safety belts\" installed in cars back in the late '50s/early '60s used the same kind of latching mechanism as in aircraft. Why the design changed, I have no idea."
] |
[
"Could we feasibly build a particle accelerator to probe physics at the GUT scale?"
] |
[
false
] |
[deleted]
|
[
"The GUT is scale is ~ 10",
" GeV. The current collision energy of protons at LHC is 1.3 x 10",
" GeV. It'd be quite some time before we can overcome the energy barrier of 12 orders of magnitude."
] |
[
"More like \"given that we can make a ship that is 500 meters long, can we also make a ship that is 500,000,000,000 km long?\""
] |
[
"The question makes sense but the scale required is just so flantzabishly larger than what current exists that it's sort of like saying \"given that we can make a ship that is 500 meters long, can we also make a ship that is 5000 miles long?\""
] |
[
"Why do poured liquids look like braids?"
] |
[
false
] | null |
[
"Heckuva loaded question, because there are a whole lot of factors as to why this happens, spout geometry, surface energy, viscosity, and density.",
"However, the main reason is because of the surface tension on the liquid. If water is coming out of a nominally flat spout similar to that coffee pot, the surface tension is pulling itself together (trying to make it ball up into droplets essentially) that it as it goes down the cross section of the stream goes from ovular, to circular. However, it has momentum still as it gets to this circular shape, so it is like two half of the droplet colliding with each other, so it becomes ovular again as it is squeezed (but this time deforming in the other direction). Because it is a continuous stream, it won't actually separate out into individual droplets until it has fallen some distance. Try spilling water, you will see it become droplets after some distance of falling.",
"Anyway, because momentum is conserved, you will see this happen several times before the stream breaks up. If you look at the coffee, you see it go from flat (paralell to the spout), to momentarially circular, to flat (perp to spout), to flat parallell to the spout again before entering the coffee.",
"Sorry I cannot explain it more simply than that.",
"Edit: Minor clarifications"
] |
[
"The liquid starts out in a flat shape. Surface tension tends to pull it together (circles have the lowest surface to volume ratio)",
"Surface tension pulls the sides inward, where they crash into eachother and widen out perpendicularly. (The cross section doesn't stay circular because the liquid still has some kinetic energy left over from being in the higher energy widened state)",
"The widening again gets pulled together, and spreads out again in the original direction (the picture actually stops before this point)",
"This oscillation continues until friction slows it or it hits something (like the cup). Also the liquid is thinner further down because it's moving faster but has the same volume (because speed times cross sectional area at each level is equal to the flow rate which is constant)"
] |
[
"Conservation of momentum and energy both apply here (obviously, laws of physics here). But yes, it is basically a harmonic oscillation, and the latter is probably the more apt choice for getting the point across. As the stream geometry goes from circular to ovular again, the water once again has increasingly large tensile forces applied to it trying to pull it back into that circular geometry. This decelerates the water from becoming increasingly ovular, and will eventually accelerate it back to the circular geometry, and so on.."
] |
[
"What does black body radiation emission have to do with quantum theory?"
] |
[
false
] |
I am a mathematician and I am familiar with the formalism of quantum mechanics. In virtually any quantum mechanics course I would run into this remark that the idea that electromagnetic energy is emitted in portions --- quanta --- was introduced by Max Planck in connection with the problem of black body radiation. Without this idea, they say, the black body would have to emit energy at infinite power. Could you explain in layman's terms why one arrives at this contradiction in the classical setting and how quantum mechanics resolves the issue?
|
[
"It's called the \"ultraviolet catastrophe\".",
"The Rayleigh-Jeans law, ",
"which explains spectral radiance classically",
", only agrees with experimental results at high wavelengths. Because it contains a (wavelength)",
" term in the denominator, it blows up at even moderate wavelength and diverges to infinity rapidly for small wavelengths - meaning that the total power of a radiator should be infinite.",
"When Planck assumed that energy was not continuous but could only be emitted in quanta, he eventually derived the correct spectral distribution functions.",
"Interestingly, in 1896, four years before Planck found the correct function, ",
"Wilhelm Wien independently derived an approximation that correctly describes the energy emitted at high frequencies.",
" You can see on the Wien approximation page that a roughly linear interpolation over a particular range of frequencies between the Wien approximation and the Rayleigh-Jeans law would have come close to giving the accurate spectral radiance distribution even without Planck."
] |
[
"In classical electromagnetism, we can calculate what equilibrium at a temperature looks like based on standing waves in a cavity. This yields the Rayleigh–Jeans law,",
"\n",
"http://hyperphysics.phy-astr.gsu.edu/hbase/mod6.html#c6",
" ",
"The issue is that if you poke a hole in this cavity, at equilibrium, the power coming out blows up as the wavelength goes to zero. There is no restriction on the available modes. This is called the ultraviolet catastrophe. The main issue is that the equipartition theorem fails to describe situations where k",
"T < associated energy. Take a look at Figure 10 here,",
"\n",
"https://en.wikipedia.org/wiki/Equipartition_theorem#Failure_due_to_quantum_effects",
" ",
"You can clearly see how at related by a constant, the two curves diverge. The classical partition function fails and Planck considered a modified distribution. Oddly enough it was Planck's wrestling with statistical physics and not radiation that led to this, only in hindsight was the ultraviolet catastrophe touted as a victory, it wasn't a motivation at the time."
] |
[
"In the classical setting there is a theorem called the equipartition theorem that says each harmonic oscillator (wave) mode will have the same average energy (of kT/2). If you treat light as a wave inside a resonating cavity, then the number of allowed wave modes approaches infinity as the frequency goes to infinity (this is just a result of the wave equation + requiring the wave to go to 0 at the boundaries of the box). Since each state has the same amount of energy, one can immediately conclude that this system has infinite energy density at high frequency (which is a problem). ",
"What QM says is that each mode must have an integer number of quanta of energy. Since E=hf for photons, this means very high frequency modes simply cannot be excited for long periods of time because they would have more average energy than the entire system's average energy. This introduces a natural upper limit to the frequency of the photons in the cavity and prevents the average energy density going to infinity. (If you want a rigorous description of where exactly this 'upper limit' occurs then you have to use Bose-Einstein statistics for the excited modes.)",
"You will notice that the problem essentially comes from the classical assumption of the equipartition theorem which, as it turns out, does not hold for energy modes that have energy much larger than the average thermal energy of the system. (In this case the high energy modes are said to get 'frozen out')."
] |
[
"Can humans see an atom through a microscope? Is it visible? How does it look like?"
] |
[
false
] |
I do believe I've read somewhere that the technology have yet to find away to see an atom, or something that is really small, an electron maybe. But I'm pretty sure there was something that was not visible, and were being taught to us in the most convenient shape scientists think it looks like. Sorry for being vague.
|
[
"sorta...",
"electron microscopes and other processes make it possible",
"heres a picture of \"atoms\"\n",
"https://qph.is.quoracdn.net/main-qimg-b1c72b2f8dbbdf0da3be7961662edf50?convert_to_webp=true",
"heres a picture of \"an atom\"\n",
"https://qph.is.quoracdn.net/main-qimg-9ef061f0d7878bff548edf095103d9c1?convert_to_webp=true",
"You can see the nucleus, but you should never be able to see individual electrons, only the \"halo\" that they exist in."
] |
[
"In second picture what are the colours signify? mass? temperature? charge?"
] |
[
"We have \"microscopes\" that can make out individual atoms, but they don't use light. Visible light has a wavelength orders of magnitude higher than the size of an atom, so it won't be noticeably disrupted by a single atom."
] |
[
"Are we just lucky that covid does not have a higher mortality rate or is this because more deadly infectious diseases are less common?"
] |
[
false
] |
[deleted]
|
[
"Higher mortality diseases get quarantined more aggressively.",
"If COVID had a 15% case fatality rate and most survivors were left permanently disabled, Wuhan would have been in hard lockdown four weeks earlier. Similar actions were taken when Africa had an ebola outbreak.",
"Because the disease is 80% 'less deadly' than that, it was able to slip out of the origin region and into nearly every country on Earth.",
"It's also an evolutionary advantage for diseases not to kill their host. It simply makes them better at spreading, and this creates a tendency for viruses to mutate to become less lethal. This is why the 2018 flu virus was much less deadly than the 1918 one, despite the 1918 one being an evolutionary ancestor of the 2018."
] |
[
"What if it’s 100% deadly and has very long incubation period around 3 months or longer like rabies\nbut airborne and very infectious while asymptomatic?",
"If this virus were to exists, it would be the end of humanity, no?"
] |
[
"While a super high lethality rate would have caused the virus to quickly burn out, something in the 10-20% range easily could have spread out of control. What every commenter I have seen here is forgetting is that COVID-19 can be transmitted asymptomatically for up to 12 days. SARS, which had a lethality rate of around 10%, was contained because only symptomatic individuals were contagious. If SARS could have spread through asymptomatic carriers, it is unlikely it could have been stopped before spreading globally. ",
"So yes, we are lucky COVID is not more lethal."
] |
[
"Where does the explosive energy of an airbust meteor come from?"
] |
[
false
] |
So I've been reading a little bit about the and the , both of which have been attributed to a meteoroid exploding in "airburst" event, with the object blowing up in midair after entering the atmosphere. I am wondering where the explosive energy (enough to generate a powerful shockwave) comes from in this sort of phenomenon. Intuitively, it's easy to understand the massive explosive energy release when a meteor strikes the ground. But when it's burning up in the air, there is no obvious point at which I'd intuitively expect an explosion-- no moment of impact where the entire system must release its energy violently. In fact, I'd expect the meteor to more "dissolve" under the stress, vs. cause a massive explosion. So my question is, where does the explosive energy in an airbust meteor come from? Why does it blow up instead of fall apart? (edited for spelling/grammar)
|
[
"The explosive energy comes mainly from the meteor's kinetic energy. Specifically, the meteor compresses the atmosphere in front of it. When the high-pressure air in front of the meteor seeps in to the cracks and pores of the meteor's surface, eventually the pressure inside the meteor will be enough to overcome it's structural integrity, and the meteor will explode. The rapid disintegration of the meteor releases all that kinetic energy quickly as well as causing rapid burning of the meteor's composition."
] |
[
"Think about it this way: a meteor has a certain amount of kinetic energy (generally a LOT because kinetic energy is mv^2 and typical speed is like 20 km/sec), but is relatively aerodynamic.",
"When the meteor suddenly disintegrates, its mass doesn't change, but it suddenly slows down due to air resistance. OP's \"air pressure inside\" is what caused the meteor to disintegrate, not what causes the airblast. ",
"Tunguska event has been estimated to be a 65m diameter meteor. If we assume 20 km/sec and a chondrite at 3g/cm^3 density, that rock weighs around 4x10^8 kg.",
"If we assume it had decelerated some amount, so like 10 km/sec when it disintegrated, the total kinetic energy available when it disintegrated is 4 x 10^16 J or 9 megatons of TNT. ",
"While not all 9MT is going to be emitted instantly (the bits of meteor don't just stop, but they do rapidly decelerate), you can see there's a LOT of energy available to be suddenly dumped into the atmosphere. ",
"This is a thumbnail sketch of the event-- more detailed modelling would give you a better range of values."
] |
[
"I think \"pressure inside the meteor\" in this case means the kind of pressure that's inside a marble as you're squeezing it with a hydraulic press, or, less destructively the kind of pressure that's inside a compressed spring and not the kind of pressure that's inside a balloon that's about to pop. I'm not sure about this but intuitively the air pressure inside hypothesis doesn't ring true to me."
] |
[
"The mitochondria and chloroplast are examples of endosymbiotic relationships, but are there any other examples of eukaryotic cells forming an endosymbiotic relationship with another organism?"
] |
[
false
] |
If there aren't, then what stops cells from forming such relationships? If there are, what is the nature of the symbiotic relationship, and are they able to pass on these endosymbionts to subsequent generations?
|
[
"Corals have a symbiotic relationship with Zooxanthellae. The symbiont performs photosynthesis and helps feed the coral. The coral aids the symbiont with waste removal, safety, and a supply of carbon dioxide. Corals are not born with symbionts, they acquire them from the environment. In times of stress, the coral may eject their symbiont. That's called coral bleaching because the photosynthetic symbionts are the primary source of coral's color."
] |
[
"There is still research and debates being conducted on this topic, but there is some evidence to suggest flagella, cilia, and/or the nucleus were once prokaryotic cells which were engulfed. The issue with tracing back the origins of these organelles (those that are not mitochondria or chlorplasts) is that they do not have the same evidence of localized DNA (like mitochondria and chloroplasts have -- mDNA and cDNA). The evidence for mitochondria and chloroplasts is stacked more in their favor due to this DNA as well as their structure (having multiple membranes) and replication through binary fission. As these phenomena are not seen in flagella, cilia, or the nucleus to the same degree, it is difficult to point them out directly as (once) prokaryotic organisms, as they may have undergone much more specialization than mitochondria and chloroplasts in their assimilation to the host cell, causing differing structures and means of replication than a prokaryotic cell.",
"All this being said, endosymbiosis is a difficult process to create as we see it today. The first mitochondria and chloroplasts in eukaryotic cells acted moreso like parasites to the host cell than as mutually beneficial. It would not be until the perfect interaction between host and parasite (by evolution, mutation, like, etc.) occured in which the two cells could live in a mutually beneficial until endosymbiosis could occur. From there, further specialization of the engulfed prokaryotic cell would occur to better assimilate to the environment of the new eukaryotic cell until the two would seem inseparable.",
"This difficulty in specializing the organelles through endosymbiosis is why eukaryotes are believed to only have evolved one time (and then radiated from there). The perfect interaction needed between parasite and host which does not cause the other a loss of energy or death is required, and then, many events of mutation and adaptation to the new cell environment need to be perfected so that both can coexist mutually."
] |
[
"Interesting. I hadn't considered that this relationship was the result of endosymbiosis."
] |
[
"Theoretical Fiction with Anti-Gravity materials"
] |
[
false
] | null |
[
"Wait, so that means if you hold Anti-matter in your hand, your hand will blow up?"
] |
[
"Wait, so that means if you hold Anti-matter in your hand, your hand will blow up?"
] |
[
"Not only electrical charge. Lepton and baryon numbers are also reversed, and in the case of quarks and gluons antiparticles have opposite color charge as well. If you want to turn a particle into an antiparticle (on paper, obviously) you have to hit it with the charge conjugation, parity refection ",
" time reversal operators. Charge conjugation alone doesn't get it done."
] |
[
"Why do we feel emotion from music?"
] |
[
false
] |
Apart from the lyrics, what makes music so expressive if it's just a bunch of soundwaves? Why do we associate emotions with certain pieces of music?
|
[
"Neuroscientist here. ",
"\nA combination of cultural (learned) experience and resulting anticipation. When our brains recognize a musical pattern, our experiences provide us with expectations for what happens next. For instance, horror movies tend to take advantage of our past (cultural) experiences of what \"scary\" sounds like. Additionally, whether our expectations are fulfilled or not (suspension & resolution) plays a role in our emotional response and neurological pathways of reward. ",
"\"…and so our neurons search for the undulating order, trying to make sense of this flurry of pitches…\"",
" ",
"\nPossibly, but some scholars say no. Pythagoras was one of the first to realize that math and music were related, and music theory has greatly developed since then. While physics and math do help us to understand what patterns we recognize, we don't necessarily like sounds because they are \"mathematically pure\". Rather, it is generally accepted that we like music because of its ",
"familiarity",
", and - conversely - because of its ability to defy our expectations. ",
"\n",
"Infants",
" have been found to be surprisingly adept at distinguishing musical patterns, and their perceptual ability changes with exposure to more music. ",
"\nThis is also the subject of some controversy. One issue is that studies have been performed which investigate how animals are affected by ",
" music. David Schwartz (author of source featured in #2) has argued that, if animals are affected by music, it is likely their response is related to their own environmental experiences (e.g., their species-specific communication patterns). Regardless, animals have been shown to recognize patterns just as we do (e.g., ",
"pigeons",
", ",
"starlings",
", and ",
"dolphins",
"). ",
"Fireflies",
" are the closest non-human example of animals which adhere to music synchronization. ",
"\nYou are emotionally sensitive to some stimuli, which triggers the release of adrenaline. In some people, this effect can be produced at will. Related, but scientifically hard to study at the moment: ",
"ASMR",
". ",
"\nAs atalkingfish reported, synesthesia is more of a link between perceptual systems, which may be simultaneously awesome and frustrating. I have a friend who is unable to drive while the radio is playing because \"colors and shapes obscure the field of vision\".",
" Wow, this thread really exploded! Please be patient with me; I'm running on ~4 hrs of sleep and have a few hurdles to get through in work today, but I will do my best to address your questions when I can and as best I can. [ Never stop asking questions! :) ] ",
" Added a few citation examples for animals mentioned in #4, in case people are curious. ",
" ",
"Here",
" is another excellent paper that provides a fairly thorough investigation of music and emotion. "
] |
[
"Imagine music to be a stimulus for the brain - similar to other physical stimuli such as images (in the form of cinema, perhaps), food, and drugs. Music just chooses our sense of hearing to be its medium. These sound waves that we perceive can be imagined if we see the analogy of a cinema - perhaps each frame of the movie is similar to a certain \"wave\" or \"beat\" of the music. Some people can actually \"see\" music (as colors or images) through a certain neurological condition called ",
"synesthesia",
".You can see where this analogy somewhat falls apart but I hope it gives you the idea that music, down to its core, is a series of cognitive senses that evoke a response by the brain.",
"As far as music creating this immense emotion in a human brain, some studies have been done to show that listening to music that gives you \"goosebumps\" or \"chills\" increases the blood flow, measured through PET, to areas like the amygdala, ventral striatum, midbrain, orbitofrontal cortex, and nucleus accumbens. ",
"source",
". The nucleus accumbens specifically, but also other areas, are known for their role in reward and pleasure responses - this in turn can perhaps create an emotional response from the brain. It's really cool to imagine that simple air pressure differences around us, when coordinated into rhythms and frequencies, can actually create a chemical response in our brain!",
"As for emotions relating to certain pieces of music - this can be subjective to what a person experiences that connects to the evoked emotion. But generally, humans will naturally associate certain types of music to physical phenomena. Perhaps a \"steady\" and \"even\" rhythm matches the average person's resting heartbeat and we therefore have a comfortable feeling towards it. Likewise, maybe we listen to fast and upbeat songs when we exercise to find the music to match our pacing movements and fast heart rate. It's subjective, still, but the brain will tend to organize this sense with other senses and emotions."
] |
[
"Excellent question! Science doesn't yet have a perfect answer that is completely guaranteed to eliminate unwanted associations, but perhaps the following will help:",
"Don't try to forcefully block out the person from your mind. Attempting to cover up an association may make it even stronger. Instead, accept its existence with grace.",
"Make new, happy associations. Go out and play that music as you experience a rich, stimulating life. Old memories will blend with new, and you hopefully will be able to enjoy the song fully again. ",
"Different methods work for different people. If someone here tries the above and find it's not working, please feel free to let me know and maybe we can find a solution together. I'm happy to help as much as I can. "
] |
[
"What is the ratio of food that you eat to what comes out? If you eat a one pound sandwich, what percentage is eliminated?"
] |
[
false
] | null |
[
"Also, how fast is poop made. If I ate a meal, when will it come out?"
] |
[
"Depends on your body. Quickest way to find out: EAT A LOT OF CORN in one meal.",
"The husks of corn does not digest well in our bodies. You can pretty much time it by eating it and seeing when it will appear in your fecal matter.",
"But! Stuff like chewing can get your intestines moving the fecal matter along more (via hormones) so it's not really consistent in terms of time."
] |
[
"You absorb ~90%+ of the carbohydrates and fat, and ~70-80% of the protein (depends on the source). Water is absorbed based on the level of your hydration. More fibres means less absrobed (most are insoluble). Your sandwitch is mostly carbohydrates (and water) so you'd absorb most of it. And while on the subject of poo, only a third of it is undigested food."
] |
[
"Is there any truth to this tale about Andre the Giant helping provide a \"medical breakthrough\" in the field of anesthesiology?"
] |
[
false
] |
I came across about wrestler Andre the Giant's legendary drinking abilities and found one part in particular quite interesting: (For context, this incident probably would've taken place between 1986 and 1987.) Andre was in France visiting his ailing father when the call came. He thanked Vince Jr. but said there was no way he could get back in a ring, even though he very much wanted to. Not willing to give up, Vince Jr. flew to France to speak with Andre in person. He took Andre to see doctors specializing in back and knee maladies. Radical back surgery was proposed. If successful, the procedure would lessen Andre’s pain and perhaps make it possible for him to get in the ring for Wrestlemania. If Andre was game, Vince Jr. agreed to pay for the entire cost of the surgery. The time arrived, and the anesthesiologist was frantic. He had never put a person of Andre’s size under the gas before and had no idea how much to use. Various experts were brought in but no solution presented itself until one of the doctors asked Andre if he was a drinker. Andre responded that, yes, he’d been known to tip a glass from time to time. The doctor then wanted to know how much Andre drank and how much it took to get him drunk. “Well,” rumbled the Giant, “It usually takes two liters of vodka just to make me feel warm inside.” And thus was a solution found. The gas-passer was able to extrapolate a correct mixture for Andre by analyzing his alcohol intake. On one hand, that's fascinating stuff. On the other hand, that Drunkard article appears to be the origin of that story. There are other websites that mention the story, but they either cite that article as a source or don't cite anything. Furthermore, the closest thing I found to a legitimate source corroborating this tale is a a brief mention on , and all that says is that the anesthesiologist was really nervous because he wasn't sure how much it would take to knock Andre out, and that's really all the two stories have in common. (To be fair though, there are a good deal of missing pages in that online version.) Hope that wasn't too wordy. I appreciate any help.
|
[
"Sorry, I have been in the practice of anesthesia for 20+ years and this is a new one on me. Use of ethanol does affect and/ or correlate with anesthesia action to some extent, but only very roughly. Induction doses are based mostly on ideal body weight; inhaled doses are based on partial pressure and are (largely) independent of weight. ",
"I can't discount the possibility that I have missed a major scientific breakthrough, but I doubt this is the one I missed."
] |
[
"So out of curiosity, how would you go about determining the dosage for an Andre-sized patient?"
] |
[
"According to Wikipedia, he was 2.24 m tall (7 feet 4 inches) and weighed 240 kg (at his heaviest) when he was wrestling. That puts his body mass index at 47.8, which is in the \"morbidly obese\" category. BMI is weight in kg divided by the square of the height (in meters). Less than 18 is underweight, 25 is \"ideal,\" 28 is \"overweight,\" 30 and over is \"obese.\" If you play with the numbers, we can drop Andre to a BMI of 30 (a very common figure in US) by dropping his weight to 150 kg. So he was at least 90 kg overweight (198 lbs). BMI of 30 is still kind of big, but I'd probably dose off that type of figure (150 kg=330 lean lbs). Propofol induction dose is 2-3 mg/kg, so Andre's initial dose is 300-450 mg. It's a big dose, but not horrific.",
"In actual practice I'd more likely do what we call \"titrate to effect\"- give some, watch, give some more, etc, until I gave \"enough.\" Or even more roughly, \"he looks like 300 mg,\" give that, then see if I need to give some more. I rarelly go to the trouble of a lean body mass estimation any more.",
"Not neglecting the fact that for many reasons he'd be extremely challenging to anesthetize, and I personally would be happy never having to do something like that.",
"Simplified things a bit, the physiology of obesity and anesthesia is fascinating, but only to an anesthesiologist I think."
] |
[
"If I have two round magnets stuck to eachother, with a surface between them (like a pane of glass), and I rotate one of them, will the other one rotate with it?"
] |
[
false
] |
Thank you very much for all the responses, everyone! This have me exactly the information I was looking for.
|
[
"Can confirm: it works. I've been doing this since I was a kid. More below as to ",
" and ",
" this works.",
"The question should be, more appropriately: would two perfectly crystalline, perfectly round ",
"ferromagnets",
" rotate with respect to each other (",
" magnetism) through a surface? And the short answer is ",
".",
"Long answer: It has to do with a microstructural feature within the magnet called a ",
"magnetic domain",
". Each of these magnetic domains have their own net magnetization (strength) and directions. When a ferromagnetic material is magnetized, the net sum of all of these domains is in the direction of magnetization. However, they need not be perfectly aligned. The truth would be that the two magnets wouldn't be identical, and that there would be vectorial components perpendicular to the field. These components cause disruptions in the field, and there are local environments in which the magnets will find a spot of minimum potential.",
"It is also important to consider the material properties and the width of the surface between them. Your example is perfect because it uses glass, which is a ",
"dielectric",
" and therefore a polarizable material. If the surface was thicker, the magnets would be further apart, and friction would keep one of the magnets from sliding. If the coefficient of friction was small or zero, then they would rotate to stay lined up with their local minimum potential."
] |
[
"I'd say yes. Get two magnets and try. I think a cheap disk magnet has to be at least a bit off-axis."
] |
[
"I just tried it with 2 small, neodymium disc magnets (this one), and the second magnet did NOT rotate. I tried it once with a file folder and once with an 1/8\" thick piece of polycarbonate. Nothing.",
"Neodymium magnets are far too powerful for that length scale. The friction force is directly proportional to the normal force (F",
" = µ*F",
")",
"Try it again at 1/2\" or more, or try lubricating the surface."
] |
[
"Just bought a USB rapid charger. How does a rapid charger work? And why aren't all chargers rapid chargers?"
] |
[
false
] | null |
[
"So, how quickly your phone is charged is essentially based on the amount of power that it receives from the charger. The current standard is roughly 5V, 2.1A (at least in America, I don't know if it's different in Europe). Most devices have regulators that prevent any more power from getting to the battery for safety reasons.",
"The way a quick charger works is that it just sends more power to the battery, around 9V and 2.1A. The regulators on the battery are still in effect, their threshold is just raised. It is most helpful when the battery is lowest and it can absorb the extra power that a normal charger wouldn't give. There is also usually a chip in both the adapter and the phone that communicate how much power to send to the battery given the amount of charge that it has.",
"The most common quick charger in use on phones is QualComm's Quick Charge 2.0, but there are others. As for why they're not more widespread, I couldn't really answer that question. One of the major drawbacks to them is that they generate more heat which kills electronic components faster, but leaving your phone plugged in over night is just as detrimental to the lifespan of your device as the heat, so it's kind of a wash.",
"Some people also say that the benefits basically stop after about 60%, but in my experience with my Note 4, I can charge 90% of my battery in about 1.5 hours with my quick charger, while a regular charger takes about 3-4 hours."
] |
[
"Not exactly right. The usb 2.0 standard is 0.5A, which computers usually limit to. The charger sets a voltage (like 5v) and de phone decides how much current it takes. Cell phone chargers have a resistor that tells the phone it can deliver more current, some phones use 1A, and some 2A.\nTo deliver more power means you have to make the cable thicker because the standard cable is made for max 2A. And supplying 9v instead of 5v can have bad effects on your phone (fried chips etc.) So what they did with the quick charger is that the charger actually communicates with the phone and together with the phone decides on switching to 9v. 9v x 2A is about 18W while 5v x 2A is 10W. Over the same cable.",
"The reason quick charging has become relevant is:\n1 phone batteries have gotten larger\n2 the batteries are manufactured following certain standards for faster charging\n3 monitoring battery charge rate and temperature gives more control over safe charging, so that means that as long as the temperature of the battery is in a safe range. It can be charged faster."
] |
[
"It is the same everywhere, at least for USB chargers, but USB specifies 5V 0.5A . with more power hungry devices more current has become common though"
] |
[
"Would you be able to measure your speed relative to the rest of the universe with the speed of light?"
] |
[
false
] |
What I am saying is, would you be able to measure your speed and the direction you are travelling in relative to the while universe? E.g. If you had a laser and flashed it at a detecter and calculated the speed to be the speed of light plus 100km/h, would that mean relative to the rest of the universe, the set-up is travelling 100km/h in the direction opposite that of the laser beam? Sorry if this is ridiculous, just a thought I had.
|
[
"The speed of light is constant in every reference frame. So no matter what you're doing, you'll always measure the speed of light at 299,792,458 m/s.",
"Related to that is the fact that there is no universal rest frame. That means, there's no \"relative to the universe\" when it comes to motion. Motion is always relative to something else."
] |
[
"To further illustrate this:",
"The universe has no \"center\" - there ",
" no fixed point - or even \"average point\" to call the \"base\" for the whole universe.",
"You can see this within our own solar system. We say that the Voyager and Pioneer probes are \"leaving the solar system\" and mention a specific speed at which they are leaving. But what is the reference for that speed? They were launched from Earth - yet if we use the Earth as the reference point, then they actually have a ",
" outbound velocity for a significant portion of each year! (As the Earth's orbital velocity around the sun is higher than the outbound velocity of the spacecraft - when measured relative to the Sun.)",
"When the Apollo spacecraft headed to the Moon, how did you measure their motion? Compared to the surface of the Earth or compared to the surface of the Moon?",
"As Rannasha said - the speed of light is CONSTANT. It is, in fact ",
" constant - ",
".",
"If you had two spacecraft, leaving from spaceports at the Earth-Sun L4 and L5 Lagrange points - flying toward each other, each one traveling at 0.9c, (90% the speed of light,) and shined a laser from each spacecraft toward the other, each one would see the laser pass by ",
". Likewise, if they each shined a light to the \"stationary\" (compared to each other) Lagrange spaceports, each spaceport would see both lasers (one from each spacecraft) arrive at the full speed of light.",
"Note that the lasers would be SERIOUSLY red-shifted or blue-shifted based on which spacecraft sent it. That's what happens - the speed doesn't change, the wavelength does, based on Doppler effect."
] |
[
"One thing that helped me understand it was that 'speed of light' is a bit of a misnomer. Yes, it is the speed that light travels at, but that is not a property only of light.",
"c is the definite speed limit in the universe, and nothing with mass can ever reach it -- conversely, things without mass must always travel at c. This includes light, which was the first known example and thus gave c its more common name 'speed of light', but it also includes gravitational waves, for instance.",
"So it's not a special property of light that it behaves like this; instead it is a special property of the universe that forces light (and other things) to behave in a certain way."
] |
[
"Energy generation: is our sun the ultimate source? If not, when and why would another source be preferred?"
] |
[
false
] |
As a layman, it seems that despite current technological limitations, solar energy would be the most fruitful to develop. Is that true? What barriers are present for this technology? What do you see for the future of solar?
|
[
"A lot of things are meant by solar. But I'll just say that the sun is the only energy ",
" to our planet. Fossil fuels are stored solar energy. Fission and fusion is technically a limited source of energy, even if not in practice. "
] |
[
"Ah hah! What about ",
"tidal power?"
] |
[
"Stolen from the rotational kinetic energy of the earth?"
] |
[
"Why are always purines being used for energy delivery?"
] |
[
false
] |
I always see cascades where there are G-proteins involved which obviously interferes with GTP and ATP is involved in so many reactions for instance muscle movement and what not. But why is it always the purines and never the pyrimidines? Might it be because of the little extension of the aromatic ring of the purines?
|
[
"This is a question I wrestle with a bit, I work on a protein that binds GTP, while its closest relatives use ATP.",
"I'm not certain this is known why certain purines have specific roles. It's possible we might run evolution again and find out that CTP was the central energy carrier while UTP was used for regulatory systems like GTP is now. ",
"Something to know though is that cytidine and uridine nucleosides are still used as carriers in the cell, just not phosphate/energy carriers but instead carriers of ",
"lipid precursors",
" and ",
"sugars",
". In all four cases the nucleoside is a \"handle\" that allows an enzyme to gain better binding specificity than it would be able to have with just triphosphate or diphospho-glucose.",
"I don't know quite how well established it is for ATP/GTP, but ",
"NADH/NADPH",
" are chemically almost identical based on their role, the difference between the molecules allows the cell to have mutually exclusive pools of oxidant and reductant ready - there's a good chance ATP/GTP are segregated in the same way to compartmentalize energetic versus regulatory functions."
] |
[
"Almost certainly yes. ",
"/u/superhelical",
" was hinting at this when they pointed out that if we ran evolution again we might end up with a CTP/UTP system instead. That is once one energy carrier (ATP) was fixed on early in evolution it has indeed been kept ever since by everything else. You see these kind of 'winner stays on' effects a lot in early or critical evolution, something gets established as working early on and all things today use that same system.",
"It's clear that ATP/GTP are very, very primitive as all living things use these in the same way and for very critical energy and signalling uses. Living things today are not free to evolve away from using these and most likely any mutations in critical ATP metabolising proteins will be cell lethal."
] |
[
"This might end up being a silly question but... could this not also be a case of a somewhat primitive system being vital enough to be conserved without much deviation?"
] |
[
"How much does it really help wearing white clothes versus black clothes in the sun?"
] |
[
false
] | null |
[
"Which color keeps you cooler depends a lot on whether the clothing is tight or loose. If you're wearing, say, white spandex, then the light from the sun will be reflected most efficiently, and you will stay cooler than if you were wearing black spandex.",
"On the other hand, what you see people wearing in hot, arid climates is layers of loose fitting dark clothing. The reasoning behind this is not to facilitate the reflection of light from the sun, but to carry heat away from the person wearing it. Black material is better at absorbing heat from either side (through radiation or maybe conduction) so the heat will concentrate on the surface where it can be dissipated through contact with the air. This really only works well if it's windy, though.",
"Reference: ",
"http://www.straightdope.com/columns/read/1886/does-black-clothing-keep-you-cooler"
] |
[
"This, plus darker clothing has a slightly higher spf than lighter clothing. That can make a big difference when you're outside all day. ",
"I grew up in a desert and in the summer, I would wear a loose tank top with a loose t-shirt over that. Jeans are alright, but the denim can get damp when it gets too hot, leading to some uncomfortable squeakiness and chaffing. Loose, dark, cotton clothes are the best, in my opinion. Gotta let the wind filter in there to cool you off, especially under your arms, around the stomach and between the legs. Basically, any part you try to keep warmest during the winter. You want the opposite. "
] |
[
"As someone who knows nothing about this subject, I don't understand why this was downvoted. Can someone explain?"
] |
[
"Does the ionisation of an atom via the decay of a radioactive element result in an atom of a separate element becoming unstable or radioactive itself?"
] |
[
false
] |
As above: For example- Would a gamma ray released from decaying radium result in a nearby carbon atom becoming radioactive itself due to it's ionisation?
|
[
"Ionization of an atom doesn't induce radioactivity (although it can result in the emission of secondary x-rays).",
"For example- Would a gamma ray released from decaying radium result in a nearby carbon atom becoming radioactive itself due to it's ionisation?",
"It's possible, but rare. Radiation transmuting a nearby nucleus into something radioactive is called ",
", and activation is primarily a concern with neutron radiation."
] |
[
"There are many possibilities. If it's carbon-12 in the initial state, there are many possible photon-induced reactions. For example, the photon could knock out a proton, it could knock out a neutron, it could dissociate ",
"C into three ",
"He nuclei, etc."
] |
[
"Thanks very much!",
"May I ask, in my example what would the carbon atom become then?"
] |
[
"Why does placing a cone infront of your mouth amplify the sound of speech?"
] |
[
false
] |
If you don't change the intensity of your voice, the sound still comes out louder when placing something like a traffic cone infront of your mouth. I would understand it if it's only louder in one direction, ie the cone is directing the sound infront of you, but it seems to be louder everywhere.
|
[
"It amplifies sound in the direction the cone is pointing. Ordinarily, the sound waves coming out of your mouth will spread out in a spherical pattern from the source. By placing a cone over the source, you redirect the waves into a much more focused area, thus increasing the intensity in that area at the expense of the intensity elsewhere.",
"I'm not sure why you think it's louder everywhere. That's simply not the case."
] |
[
"This relates to the answer I gave ",
"here",
".",
"The easy answer is that the cone makes the transfer of the sound waves from your mouth to the surrounding air more efficient. It would be even more efficient with an exponentially shaped horn, like a bullhorn, or with a larger cone. For lower frequencies, a larger cone is needed to reach the same effect size.",
"The harder answer is that the sonic impedance of the surrounding air is more closely matched to the sonic impedance of your mouth with the cone than to the sonic impedance of your mouth without the cone. The sonic impedance is basically how hard it is to move the air. If it is equally hard to move the air in two systems, it is easier to transfer energy from one to the other."
] |
[
"Well then why isn't it even louder when you talk through, say, a cardboard tube? Interference?"
] |
[
"How we define bacteria's species?"
] |
[
false
] |
By the definition I googled, you define a species as a group of organisms capable of interbreeding. So how do we define the species of bacterias, that just divide into two new organisms, instead of mating?
|
[
"In the olden days we defined bacterial species by their phenotypes, or how they looked and how they behaved. ",
"In the less olden days we sequenced the DNA of bacteria and clustered them based on similarity and called close enough clusters the same and different enough clusters, different species. ",
"In modern times we sequence specific parts of the genome, usually the gene encoding for a subunit on the ribosome (16s sequencing) and cluster based on differences and similarities here.",
"More info here : ",
"https://academic.oup.com/sysbio/article/50/4/513/1637149"
] |
[
"If I remember correctly, that part of the genome is highly conserved, and so it's good at showing relationships between different genomes by the differences between them because the mutation rate is consistent.",
"Other parts of the genome can under go huge amounts of genetic change by normal mutation or by horizontal gene transfer and as such, closely related species may seem very separate if the whole genome is considered.",
"",
"Feel free to correct me if I'm wrong"
] |
[
"Thank you for the answer but... why?",
"Why focus on subpart of the genome, rather then the entire thing, and why that specific subpart?"
] |
[
"What determines the lifespan of a species? Why do humans have such a long lifespan compared to say a housecat?"
] |
[
false
] | null |
[
"Here is a paper that suggests epigenetics plays a large role. ",
"https://www.nature.com/articles/s41598-019-54447-w",
"It is true that mammal size is correlated to heart rate, and both are correlated to lifespan. Most mammals get about 1 billion heart beats. Humans have managed to beat this by being more social (supporting our elders in pre-medicine societies) and then using medical technology to really overcome natural entropy."
] |
[
"Similarly, here is a new paper from Sinclair Lab also suggesting this (more specifically loss of epigenetic info). Came out a few days ago and people are still dissecting it.",
"https://www.cell.com/cell/pdf/S0092-8674(22)01570-7.pdf",
"01570-7.pdf)"
] |
[
"The lifespan of a species is determined by a combination of genetic and environmental factors. Genetic factors include the presence or absence of certain genes that are associated with aging and disease, while environmental factors include access to food and water, exposure to toxins and pollutants, and susceptibility to predators and disease.",
"Humans have a relatively long lifespan compared to many other species, including housecats, due in part to genetic factors such as the presence of telomerase, an enzyme that helps to maintain the integrity of chromosomes and therefore the longevity of cells. Additionally, humans have a relatively low rate of predation and access to medical care and other forms of protection from disease, which also contribute to our longer lifespan.",
"Early human life expectancy was ably about only 20 years too."
] |
[
"What is the smallest scale that gravity has been measured?"
] |
[
false
] |
I have read that there have been some experimental setups for measuring gravity ant the submillimeter range. What is the motivation for these experiments? How does one prevent interference from things like electromagnetism, etc?
|
[
"Roughly 100 microns.",
"One of the motivations of these experiments is to see if Newton's law breaks down at very short distances, which may be a sign of ",
"extra dimensions",
"."
] |
[
"Really? 100 microns? That seems... Big. Maybe if I had liked my MEMS class better, I'd know where to get my Nobel. ",
"Edit: I suppose you are starting to deal with ludicrously small forces at that scale, though. Much smaller compared to everyday, relatable forces than 100 microns is compared to everyday relatable lengths. "
] |
[
"Gravity is pretty weak."
] |
[
"Why specifically do these bottle lights in the Phillipines need bleach? Could they use another substance or does it have to be bleach?"
] |
[
false
] |
Here is a link to a photo of what I'm talking about. I am curious as to what the bleach specifically does to create this effect. Based on my limited knowledge, it seems to me like it just clouds the water and disperses the light better. If that is the case, could something else be used to disperse the light? On the atomic/chemical level, what is the bleach doing to the light?
|
[
"Isn't the bleach is used to inhibit algae or mold growth (in the water that's in the bottle)?"
] |
[
"Exactly. "
] |
[
"A question, based on my understanding. Mismatched punctuation. Apologies."
] |
[
"Does Heisenberg's uncertainty principle suggest that you can determine velocity and position to good precision if you don't know the particle's mass? Is there even any situation where that could come up?"
] |
[
false
] |
[deleted]
|
[
"Not in nonrelativistic quantum mechanics, in which mass is not an operator but just a constant, so that \"velocity\" can be associated with the momentum operator divided by the mass, i.e. all the uncertainty in v is due to the uncertainty in p. In quantum field theory the situation is a bit more complicated, because we get into the slippery business of how to interpret off-mass-shell states and the \"sort of\" time-energy uncertainty relation (\"sort of\" because time is not an operator), so I'm hoping someone else jumps in to cover that part. "
] |
[
"Neat, thanks."
] |
[
"Don’t neutrinos exist in a superposition of mass states (neutrino oscillations)? Is it really not an operator?"
] |
[
"How are gamma rays artificially produced?"
] |
[
false
] | null |
[
"With laboratory gamma sources, or very high-energy gammas are produced using accelerators. For example HIγS, which uses inverse Compton scattering."
] |
[
"Yes, a gamma knife uses a bunch of cobalt-60, and collimates the gamma rays emitted from its decays."
] |
[
"Thanks for the reply, could that also be what is used in a gamma knife"
] |
[
"Would a helium balloon rise or fall on the moon?"
] |
[
false
] | null |
[
"Assuming it magically doesn't burst It would fall down."
] |
[
"Yes, let’s assume is was inflated for a vacuum and would not be in direct sunlight."
] |
[
"Helium balloons only float because they are less dense than the air surrounding them. With no air they would fall like anything else."
] |
[
"Could there be a computer powerful enough to run a simulation of itself?"
] |
[
false
] |
If we had a computer that could accurately model physical reality, would you be able to build a simulated version of a computer that could run programs, do calculations etc? Would it work? And if you could do that, it then follows that you could build a simulated version of the computer actually running the simulation... Does this idea even make sense?
|
[
"It really has nothing to do with Godel's Incompleteness theorem, other than they're both arguments where we have a technique for producing a flaw in any putative example. You might as well compare it with \nthe proofs by contradiction of that the square root of two is irrational, or that there are infinitely many prime numbers.",
"Goder's result is about ",
" reachability and the structure of proofs. Here a simple argument about memory size works -- the computer simulating itself uses up all its memory -- it can't simulate both itself and the universe around it."
] |
[
"It's not a question of power, it's a question of logic.",
"To be able to simulate itself, the computer would have to be more complex than it is. And if this were to be remedied by making the computer more complex, the result would be the same -- not complex enough to simulate itself. Did that make sense?",
"This question is only properly resolved through an understanding of ",
"Gödel's Incompleteness Theorems",
".",
"The shortest explanation is to say that a there are questions that a computer of a given complexity cannot answer, and an accurate self-description is on the list."
] |
[
"Any computer can model itself if it has enough memory.. Its just a question of how quickly it can do it. Basically, all computers can be modeled as turing machines, and all turing machines can be made to run other turing machines if given their instructions."
] |
[
"How long does it take a voltage source to \"realize\" how much resistance that is opposing it."
] |
[
false
] |
In an electrical circuit, how long after the voltage source is connected does it "realize" how much current to produce based on the resistance it sees?
|
[
"The answer is \"it varies\". Do you remember Kirchoff's Laws and the Kirchoff Equivalent Circuit? Every non-perfect voltage source has a series resistance that represents voltage droop as you pull current from the voltage source. Similarly, every component and wire in your circuit has a parallel capacitance to ground that represents the electric field changing in the vicinity of the components voltage source and its components. Those two circuit-equivalent components yield a time scale (remember, a resistance times a capacitance is a time). That's the time scale you care about."
] |
[
"Why did you neglect inductance? "
] |
[
"I would respectfully disagree for certain values of \"circuit\". While shortness shrinks inductance, smaller diameters increase it. And while having thinner dielectrics grows capacitance, area decrease reduces it. When considering the current inrush to an IC during power transitions, inductance is just as important as capacitance and resistance; sometimes it is the dominating effect in power delivery. "
] |
[
"How long could DNA last in space at absolute zero? Would it decay or is panspermia really possible?"
] |
[
false
] |
A friend mentioned that he read an article about the half-life of DNA in new zealand birds being around 500 years. It got me thinking.. would panspermia be possible if the DNA was near absolute zero given that none of the molecules are moving much and thus there would be almost nothing to cause the decay of the DNA... Thoughts? Source:
|
[
"Low temperature (or no temperature) is great for preserving DNA, like most things. There is some mechanical shearing when it thaws, but at least in practical lab terms that's mostly just a function of how many times it's been frozen and thawed, not what temperature it got down to (at least assuming it doesn't go to any other states of matter after the solid phase).",
"But before the freezing or after the thawing, a lot depends on what it's dissolved with. Even assuming the solvent is water, other solutes can cause chemical damage, including just the wrong pH. Not to mention enzymes that naturally occur where you find DNA; a lot of enzymes whose main purpose is something else also have exonuclease activity. And an organic compound like alcohol might cause the DNA to precipitate out to a solid and become exposed to a lot more flavors of mechanical damage.",
"One major source of possible damage is radiation. There's a lot of it in outer space that our atmosphere (and skin) protects us from. Common DNA damage occurs when ultraviolet radiation induces chemical changes, but I guess that won't happen at absolute zero (though I don't know how much radiation it would take to heat it up to where that could happen). I'm less sure that it can't physically break, though that seems like it might be plausibly safe.",
"would panspermia be possible",
"Well, that would take a lot more than just naked DNA flying around; you'd probably need a whole live cell, and it would have to beat the literally astronomical odds to land safely on a habitable planet instead of a star or just the void. DNA's definitely not the biggest problem here."
] |
[
"Space is not at absolute zero. That temperature would imply zero molecular movement and thus DNA would last indefinitely while at absolute zero. However, that temperature or lack thereof is not currently known to exist anywhere in the universe. This doesn't mean that DNA or its chemical makeup couldn't survive in space or that panspermia isn't possible. Its an interesting hypothesis and while its still in the early stage of debate, I look forward to seeing evidence for and against this hypothesis in the future. "
] |
[
"Inside a comet?"
] |
[
"When an ISS astronaut goes out for EVA, do the airlocks conserve air, or vent it? What about airlocks on other space vehicles?"
] |
[
false
] |
I have read the layman articles on the Joint Airlock Module, but if this is answered in any I missed it. I am curious if the atmosphere in the intermediate chamber is pumped back into the station or vented out into space as the astronaut goes through.
|
[
"The Quest Joint Airlock works like this: an astronaut from either the U.S. or Russia enters the chamber, and the vacuum pump lowers the presure to 3 psi, and then to zero psi. After the air has been evacuated, the external door opens. There's also an equipment airlock that's used for overnight campouts to remove Nitrogen from the crew's bodies to prevent them from getting the bends when they depressurize.",
"It would be wasteful to let their limited air into space.",
"Edit: depressurize"
] |
[
"The lower pressure is only used because they're going into a high oxygen environment (the suit). If the station was kept at a lower pressure, they'd need a high oxygen concentration which poses an obvious fire hazard (Apollo 1)."
] |
[
"The problem with Apollo 1 was that when it was on the ground, it would have pure oxygen at full atmospheric pressure.",
"Worse, it was actually higher than full atmospheric pressure.",
"Apollo I was pressurized at 16.7psi to simulate the positive pressure environment during the plugs-out test.",
"In pure O2 at 16.7psi things don't burn, they practically explode."
] |
[
"Why does butter last for weeks whilst refrigerated but milk spoils in a far shorter amount of time?"
] |
[
false
] | null |
[
"This is less a chemistry question and more a biology question. Regardless, the spoilage of milk and many foodstuffs depends heavily on bacteria rather than inherent chemical stability. Milk is extremely rich in nutrients like sugars, fats, and protein. This provides a fairly welcoming environment for bacteria to grow and reproduce. ",
"On the contrary, butter is the fat which has been separated out of milk. While it is at the top of the list of the most calorie dense foods we know of, it is not as easily spoiled. This is due to a number of factors. One, the bacteria like fuel, but they need other things like protein to survive. They also don't proliferate very quickly in fatty environments. They tend to like carbohydrates. Butter tends to degrade chemically over time due to a number of slow reaction pathways which are aided by heat, light, and the presence of oxygen.",
"Bacteria, like us, are mostly made up of water. That means for one cell to become two cells, it needs to collect enough water for a second cell. In milk this is easy, since milk is mostly water. Butter is oily, and hydrophobic (if you get butter on your hand, your hand repels water). So even though we perceive butter as kind of slimy to the touch, it is actually dry in the sense that there is little water in it. This results in butter being naturally resistant to overwhelming bacterial infection. In fact, many people will keep butter at room temperature on the counter. It is actually more common for butter to chemically degrade (ransid butter) than it is for butter to be propagated with bacteria.",
"Butter breaks down chemically due to heat, light, and air exposure; and milk spoils by culturing bacteria. The cold refrigerator slows down bacterial metabolism, but it doesn't stop them from growing, so after a couple of weeks milk spoils. Bacteria replicate exponentially, so once they start growing they grow faster and faster. The degradation of butter is not self-accelerating, so it doesn't get faster over time. This makes the process slower. And keeping it in the refrigerator where it is cold and usually dark helps prevent its degradation."
] |
[
"Wow. That was an incredibly thorough and easily understood answer. Thank you. "
] |
[
"Also... Out of interest... Is there any reason why you know this other than good education? "
] |
[
"Proving infinity?"
] |
[
false
] | null |
[
"What do you mean by \"prove infinity\"? As it stands, this is quite meaningless."
] |
[
"Isn't infinity just a concept? An idea? Instead of a fact?"
] |
[
"So what do you mean by \"prove\" here? Generally, one writes down a ",
" about something, and then a proof of the claim consists of a series of logical deductions from our assumptions. There's no claim to prove here."
] |
[
"Is there a way to force yourself to dream about a specific something?"
] |
[
false
] | null |
[
"Oh I see. I'm not familiar with recent research on the topic and hopefully someone else with more expertise can chime in. I know there was older work that wasn't able to find any evidence for \"dream control\" methods (",
"Griffin & Foulkes, 1977",
"), but that's from a long time ago. Some more recent work has found that you can influence dream content by suggesting topics that are emotionally salient and important to the dreamer (\"current concerns\" -- not just something arbitrary) right before they fall asleep (",
"Nikles et al. 1998",
" <- pdf!). ",
"But yes, hopefully someone else can pitch in with more info."
] |
[
"Like ",
"lucid dreaming",
"?"
] |
[
"Kinda, but before you can even go to sleep you ate able to kinda control where the dream is going."
] |
[
"Why does the math of physics (and science in general) work so well?"
] |
[
false
] |
It may seem nice that the laws of physics have integer exponents (especially for calculations), but why are they integers? Is there anything special about their being integers, or is it all just a lucky coincidence? As far as I know, the math behind science is just an approximation of the truth (although a good one), but yet the math works beautifully. And then that doesn't even begin to touch the fact that a lot of physics concepts' equations match the derivative/integral relation spot-on, and I'm certain nature cannot do calculus. It'd be great to get some insight on why the equations are so elegantly simple. Thanks!
|
[
"Nature cannot \"do\" calculus, no. Nature doesn't have to.",
"Calculus was invented by humans in order to quantify values already present in nature."
] |
[
"There is a great essay about this called ",
"The Unreasonable Effectiveness of Mathematics in the Natural Sciences",
"It might be interesting for you."
] |
[
"Something to consider: a lot of equations wouldn't make sense without integer exponents, because the units wouldn't work out. See ",
"http://en.wikipedia.org/wiki/Dimensional_analysis",
"Furthermore, a lot of the exponents in physics (for instance, the 1/r",
" in gravity and electromagnetism) are determined by the fact that we have three spatial dimensions."
] |
[
"Why is sodium flouride lethal but sodium cholride (salt) isn't?"
] |
[
false
] |
[deleted]
|
[
"Since any answer is better than no answer at all: Na is soluable in water, so it detaches from F and that leaves a bunch of F ions floating around in water. Now we know that F is very very reactive and so that amount of reactivity is harmful to our bodies."
] |
[
"Because it can help strengthen teeth. Water is fluoridated at a very low level... so low that the tissue damage is negligible."
] |
[
"Most treatment plants use ozone and/or chlorine. Fluoride would absolutely wreck their infrastructure and would carry significant safety risk... ",
"Fluorine is added specifically for tooth protection. It does not replace chloride in the teeth... it replaces they hydroxy group in hydroxyapetite."
] |
[
"Probability Question"
] |
[
false
] |
[deleted]
|
[
"First, you should check to see if your question has been asked before. In this case, it has, and frequently.",
"www.reddit.com/r/askscience/comments/mafn7/if_i_toss_a_coin_10_times_and_get_heads_each_time/",
"www.reddit.com/r/askscience/comments/maayw/alright_smart_people_of_reddit_help_me_finally/",
"But in short, if you are only looking at one flip, the odds are 50/50, assuming a perfect coin, as probabilities for single events are independent.",
"Also, your question is a perfect example of the ",
"gambler's fallacy",
", assuming that your chances will mature over time."
] |
[
"The odds of picking up a coin and flipping heads 100 times in a row are astronomically low. But if you have already flipped the coin 99 times and it came up heads every time, the odds of the 100th flip being heads is exactly 50/50. ",
"tl;dr - The previous 99 flips have no affect on the outcome of the 100th flip."
] |
[
"It all depends on the question you are asking.",
"\"Bob has flipped a coin 100 times. All 100 times, it landed on heads. What is the chance Bob's next flip will land on heads?\" (50/50)",
"\"Bob has a coin. What are the odds he will flip it and land on heads 101 times in a row?\" (.5",
"Those are the two different questions you're asking."
] |
[
"Why is the iris coloured?"
] |
[
false
] |
So the question popped into my head - 'What does the iris do?' After a quick bit of research, I discover it's to control the size of the pupil - but that left me with another question - Why are they coloured? I understand they are pigmented, but WHY? Surely there is some reason? Thanks!
|
[
"It's melanin to protect the muscle from UV damage. More melanin (browner eyes) equals more UV protection. This is why people with heritage from high latitudes have lighter eyes and vice versa. "
] |
[
"just to add on:\nblack and brown eye comes from melanin in the fronter iris epithelia, \nblue and gray is due to collagen in the stoma with little melanin in the fronter iris, \ngreen and amber a combination of collagen in the stoma and melanin in iris,\nred - little melanin in fronter and back epithelia\nviolet - little melanin in fronter and back epithelia and collagen structure in stoma"
] |
[
"Wow, fascinating! :) Thanks, have an upvote!"
] |
[
"Is it possible to build a double-slit experiment at home?"
] |
[
false
] |
I really want to see this quantum effect for myself. I have a graduate degree is electro-mechanical engineering so I think I have the background to understand what I'm doing. I just want to know if and how it could be done on a budget with semi-commonly-available materials/equipment. If this is not feasible, are there experiments that demonstrate quantum mechanical concepts that can be done at home?
|
[
"Get a small piece of glass, like a microscope slide and a candle, put the candle under the slide to get it nice and black, but be careful as the heat can break the slide. Get two razor or scalpel blades, hold them together against each other and drag across the soot. You should now have two slits with width apart approximately that of the thickness of one of the blades, assuming they are symmetrical. "
] |
[
"You're an engineer, aren't you?"
] |
[
"You need two things: A diffraction grating and a laser. Point and shoot. The double slit is a very specialized version of the diffraction grating because there are only two lines instead of an infinite number."
] |
[
"Is there a minimum mass required for something to have gravity?"
] |
[
false
] |
To put it another way, why don't we see particles of dust orbiting bowling balls?
|
[
"In space, these types of things can happen. But it would be possible to calculate the velocity for orbiting such an object. ",
"Here you go"
] |
[
"No, but if we consider the force provided by a bowling ball (10 kg, approx) about 10 cm in radius, we can calculate the gravitational acceleration to be about 10",
" m/s",
" . For a 1 mg mass orbiting around it, it must have a tangential velocity less than about .1mm/sec. So considering that most things move faster than that, orbits are very difficult to maintain (also this is a universe with just a bowling ball and a mg mass), or at least somewhere sufficiently distant from other stars and planets and such."
] |
[
"Before I start I think it's important to point out that all atoms in the universe are attracted to each other, but the force attracting the two masses is directly to proportional to the product of the masses (i.e. mass of bowling ball * mass of dust particle and inversely proportional to the square of their separation. There is an equation to work out the gravitational force between two objects and it reads : F=(GMm)/r",
"\nThis means that the force is equal to the Newtonian gravitational constant multiplied by the two masses all then divided by their separation squared. say the mass of the bowling ball is 10kg and the mass of the dust is 7x10",
" and the distance between them is 0.1m, or 10cm if you prefer. The Newtonian gravitational constant is 6.67x10",
" this means the force is now:\n10(6.67x10",
" )(7x10",
" )/0.1",
" = 4.7x10",
" N\nWhich if you don't know already is ",
" as at a guess I would say the average human weighs about 700N. So going back to my very first statement the dust is attracted to the bowling ball but the force is soooooo tiny that it has a negligible effect. That is why gravity is only noticeable on big things ... like planets. Hope that answered your question! "
] |
[
"Is the metabolic rate of a person who is doing \"hard\" mental work (ie, challenging math problems, reading novel in a second language, etc) measurably different from the metabolic rate of someone who is doing \"light\" mental work (ie, watching TV)?"
] |
[
false
] |
I'm not thinking "mental work = tons of calories burned," but it does seem that things that are mentally tiring would use more energy.
|
[
"Effectively, either no or a very little change, due to the high metabolic rate (20% of the body's total energy use) being from the brain already. This means that the extra work doing, maths, a crossword, writing etc doesn't shift the actual amount of work the brain does significantly upwards. In actual fact many researchers believe that often things we expect to be difficult - exams etc do so precisely because that is our attitude towards them.",
"Scientific American",
" has a much better description of all this than I can give, so I would recommend that."
] |
[
"In Robert Sapolsky's book, Why Zebras Don't Get Ulcers, he does claim that chess grandmasters expend more calories. Digging around the google machine a bit I found this:",
"The definitive study on chess players was carried out by the physiologist Leroy DuBeck and his graduate student Charlotte Leedy. They wired up chess players in order to measure their breathing rates, blood pressure, muscle contractions, and so on, and monitored the players before, during, and after major tournaments. They found tripling of breathing rates, muscle contractions, systolic blood pressures that soared to over 200—exactly the sort of thing seen in athletes during physical competition.",
"See the original report, Leedy’s thesis, “The effects of tournament chess playing on selected physiological responses in players of varying aspirations and abilities” (Temple University, 1975) or their brief report (Leedy, C, and DuBeck, L., “Physiological changes during tournament chess,” Chess Life and Review [1971]: 708).",
"It's an old source and doesn't seem to have used indirect calorimetry or any other means to try and measure energy expenditure besides a few proxy measures.",
"Here's a study that suggests an increase in many of the same parameters during video game play: ",
"http://www.ncbi.nlm.nih.gov/pubmed/16585487",
"And finally, the resting metabolic rate during TV watching has been measured to be lower than normal.",
"http://www.ncbi.nlm.nih.gov/pubmed/8424001",
"That one is suggested to be the result of zoning out and using pretty much less than general minimums for energy expenditure. ",
"None of this says for sure that the changes in metabolic measures are specifically due to increased/decreased brain activity, and it could be as someone else suggested more of a result of our attitude (i.e., stress/anxiety) surrounding certain mental tasks."
] |
[
"I have another question: when we do heavy manual labor or exhausting athletic exercise, does the brain burn significantly more calories?",
"Another question: have we detected any specific zones of the brain with increased energy consumption during specific tasks? I once had to do some maths for a few hours non stop and my forehead went hot, could it be due to extra energy consumed locally?"
] |
[
"What propels light?"
] |
[
false
] |
Just curious, I was thinkin about it on the car ride home while passing under a stop light.
|
[
"Space is permeated by an electric field and a magnetic field, which - and bear in mind this is a gross oversimplification - describe how electrical and magnetic the Universe is acting at any point in space.",
"In the case of light, a change in the electric field causes a change in the magnetic field just ahead of it. This causes a change in the electric field just ahead of that, and so on and so on. This self-propagating change in the electric and magnetic fields takes the form of a wave, or if you look at it from another perspective, a ",
"photon.",
" So essentially, light propels itself.",
"It works a bit like ",
"this.",
" extra clarity, changed my link as per image-fixer bot."
] |
[
"I would like to clarify things regarding the statement 'light propels itself'. This makes it sound as if light is completely independent and can move at free will.",
"The energy for light to begin its motion has to come from somewhere. In the case of the stop light for example, the energy is provided from the electricity. Light is then able to continue this motion due to conservation of energy and momentum, that is, it doesn't lose its energy until it strikes something and thus is able to travel what seems to be perpetually. "
] |
[
"I could try, but for both our sakes I'd rather link to ",
"this legendary explanation."
] |
[
"So can anyone explain this p≠np? thing or why its so important?"
] |
[
false
] |
Just a college student who heard about it a few days ago. I don't know the first thing.
|
[
"I'll try to give as quick and readable an explanation as possible (without getting into deterministic and nondeterministic finite automata).",
"Basically P versus NP is asking the question are some problems fundamentally harder than other problems, or are we just bad at coming up with clever ways to solve them? Factoring is a decent example (I know factoring isn't thought to be NP-complete, but the example makes sense).",
"If I give you two numbers and tell you to multiply them, this is a very easy task. Additionally, the task doesn't get that much harder if I give you larger and larger numbers. 123 x 321 is only slightly harder to calculate than 12 x 21. Likewise, getting the product of two very large prime numbers isn't that hard. If I said give me the product of 1500450271 and 5754853343, this is something you could calculate very easily (8634871258069605953).",
"However, if I were to give you 8634871258069605953 and ask you to give me the factors, that would be a ",
" hard problem (In fact, public key cryptography relies on the fact that this is really hard). Moreover, unlike multiplication, which scales linearly in difficulty as the inputs increase in size, factoring increases exponentially in difficulty (multiplying 100 digit numbers together isn't really any harder than multiplying 3 digit numbers together, but factoring 100+ digit numbers is really hard compared to factoring something like 143).",
"P versus NP asks, is factoring fundamentally more difficult than multiplying, or are we just all really dumb and can't think of a really smart way to factor? It definitely seems like P!=NP since factoring is almost certainly harder than multiplying, but proving it has turned out to be really freaking hard.",
"If I had to put my money on it, I'd bet the proof won't come from an expert in only the field of information theory, but from someone who has a strong understanding of both theoretical physics and information theory, as I think the proof will include things like the Holographic Principle, and the idea that there is a maximum possible information density a region can have. Anyway, hope that was readable; it was definitely a touch longer than I intended for it to be. Sorry!"
] |
[
"The problem of P=NP is not to create a non deterministic turing machine (which really is a purely theoretical construct), but to create an algorithm on a normal turing machine to solve the problems in polynomial time. Once you have that, you have your pick of the litter of turing complete computers and languages to implement it on.",
"I totally agree about how quantum computing is going to shake up information theory by introducing a lot of new problems, but P=NP is a problem about traditional turing machines. Quantum computing theory introduces a new universal computer, the quantum turing machine. I am not well versed in it, but I know factoring can be done in polynomial time on a quantum computer, which is undoubtedly kickass."
] |
[
"Intuitively, it seems almost obvious that P != NP. Something a motivated college student should be able to prove in a page or two.",
"But, alas, it cannot, and despite the effort of some of the finest minds in computer science, it has eluded proof for decades. So it is interesting for that reason alone.",
"What's more, it comes up a ",
". Travel itineraries, packing a knapsack, multiprocessor scheduling, building logic circuits...finding the most efficient algorithms in all of these fields simplifies down to the same question...does P = NP?",
"Finding that P = NP would mean significantly better algorithms across all these fields and more.",
"Proving that P != NP means we have a firm lower bound on how fast these algorithms can be."
] |
[
"Are swimming pools breeding chlorine-resistant organisms?"
] |
[
false
] |
Like the overuse of antibiotics. Are we breeding super microbes through the use of pool chlorine?
|
[
"If you think of microbial resistance in human terms, it makes more sense. If you send out a plague that kills a lot of people, some will survive and will likely be more resistant. The plague is a very specific, complicated way of killing an individual. Now if instead, you threw every human in lava, nobody would survive to develop resistance. Lava is simple and direct, and you can't have a \"lava doesn't kill me\" gene.",
"Think of antibiotics (specific, complicated, potentially survivable) as the plague, and the chlorine as lava (non-specific, simple, very difficult to survive)."
] |
[
"They probably evolved gradually. Like flying, it didn't evolve by everyone jumping from the cliff (into the lava). The point is, if you apply extreme measures there is no time for anybody to evolve because everybody dies. Evolution can only happen if there are survivors who can still reproduce. ",
"Even with antibiotics, the common problem is people halfass their usage leaving too many bacteria survivors. I am not sure how exactly chlorine works, it may be possible for organisms to evolve to withstand it if they are exposed to non-lethal but still damaging doses (i.e. way less than they put into the pools). Don't quote me on this though"
] |
[
"What about extremophiles? Didn't ",
" evolve to survive extreme environments? Why can't this be possible with something like chlorine?"
] |
[
"Why and how do neutrons affect nuclear reactions?"
] |
[
false
] | null |
[
"sorry if I was a little vague. How does different isotopes affect nuclear reactions differently? Why do they have different effects?"
] |
[
"What do you mean?"
] |
[
"For chemical reactions, it's all the electrons that matter. And the number of electrons is determined by the number of protons. The neutrons are comparatively less important in chemistry.",
"However in nuclear physics, protons and neutrons are equally important to the structure and reactions of nuclei.",
"The fact that protons are charged and neutrons are not is overshadowed by the fact that they both interact via the residual strong force, which is typically much stronger than the electromagnetic force within nuclei."
] |
[
"By what mechanism is HIV transmitted from Mother to Child?"
] |
[
false
] |
[deleted]
|
[
"There is little known about why the placenta does not transmit the disease. It's not necessarily that it blocks the entrance of HIV, as NLM endorses the fact that the fetus is exposed, but the fetus does not become infected.",
"\"However, the protective effect of cesarean section (25) coupled with the presence of both HIV in infant gastric aspirates (26) and CD4+CCR5+ T cells in the neonatal gut (15) suggest most intrapartum transmission is likely mucosal.\" Yes you are right. ",
"Here's an article. -",
"http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3737605/"
] |
[
"The mother donates the WBC's with HIV inside it's genetic complex, as HIV is a endogenous virus. All WBC's with HIV don't have a antigen complex that is able to be recognized by the human body, because it is a virus capable of mutation at a fast rate. The mother donates her T-cells to the child with the unrecognized anti-gen complex, thus the child has the virus. Once these cells are inside the system, the virus will infect other fetal cells through the same pathways as any other human. "
] |
[
"So mother to child transmission occurs in three ways... \nDuring pregnancy – the foetus is infected by HIV crossing the placenta.\nDuring childbirth – the baby is infected by HIV in the mother's cervical secretions or blood. (this is the most common method and that is why if the mother is not on medicines she is advised a c section as there are more chances of secretions being mixed in the normally more traumatic vaginal delivery. Any instrumentation during delivery also makes it more likely that the child gets it.\nDuring breastfeeding – the baby is infected by HIV in the mother's breast milk (or blood).",
"The chances of MTCT are 15-45 percent. However with regular anti retro viral treatment, the rates fall down to less than 0.1%",
"When the viral count becomes extremely high, and the CD4 count of the mother becomes extremely low, the placenta may be bypassed, which leads to the fetus being affected. However this occurs in a minority and the most common mode of MTCT is intrapartum"
] |
[
"Does improving certain mental abilities limit others similar to how physical abilities do?"
] |
[
false
] |
A professional marathon runner is never going to be the weightlifting world champion, but is a professional chess player limited at language learning for example? I hope the flair fits.
|
[
"So, basically, yes. But youre not thinking broad enough. ",
"You can teach your brain HOW to look at things. If your always looking for a fact based solution, or if you only ever learn about 1 specific subject etc....then your brain is going to learn that there is only 1 way to do everything, but its going to be AMAZING at remembering how to do things that one way.",
"If you think in terms of your \"end-goal\" or you decide to become a jack-of-all-trades in your information gathering you are likely to be a much better general problem solver, and will be able to gather a bunch of information really quickly even if you dont understand it all completely. HOWEVER, youre way is never going to be the BEST way to do something, its just going to work when you need it too. ",
"So in reality a chess player would probably be really great at learning a new language because its the same type of learning.",
"NOTE: I am a cardiology person, not neurology. Its a side interest for me. This is just a general overview of how I understand it."
] |
[
"No limits of that sort. There are practical limits in number of hours per day for a person to dedicate to practicing or memorizing something, but there aren't limits or cross-conflicts to neural development.",
"Knowledge can be broadly classed as:",
"\"Declarative knowledge\": something that lends itself to being written out such as \"2 + 2 = 4\"",
"\"Procedural knowledge\": some task such as tying your shoes, that often leads to confusing explanations even from skilled people.",
"Higher-order \"Metacognitive knowledge\": applying knowledge and strategies to things such as effective study habits, ",
"Research has shown that metacognitive knowledge ",
" between subjects. So for example, learning a piece of music can teach transferable knowledge about effective use of time, self-tests, perception of small differences, awareness of the specific points causing difficulty, and strategies for overcoming those difficulties.",
" was written in the 1600s about swordsmanship. But it anticipated our modern understanding of metacognitive knowledge. For example, it recommends unrelated tasks such as farming and carpentry to build insight & perspective in ways of approaching & solving a problem, and building better discernment.",
"There are also behavioral habits that can transfer between subjects, such as organizing a day around free study time."
] |
[
"It also would depend on how mentally flexible the individual is in applying their knowledge or adapting their mental models to another discipline. For example, a classical musician may be extremely proficient at sight-reading (performing a piece of sheet music without practicing), but experience difficulty improvising over ",
"."
] |
[
"What are the risks of introducing backdoors into a cryptographic function? Can you secure said backdoor with another unique function?"
] |
[
false
] |
Politics aside, I am curious why even put backdoors into a standard function if it allows an adversarial system to have an attack vector. Rather than attacking the function, why not just attack the backdoor? I could see securing the backdoor cryptographically, but would that allow the adversary to see any unique about the given hash? Meaning, will they see that there is a part of the function that is unique to the rest of the hashed string? What risk does a state posses when they introduce a backdoor into their encryption standards/functions?
|
[
"What are the risks of introducing backdoors into a cryptographic function?",
"As you point out, the backdoors could be used by adversaries. If the adversary knows what the state knows, then it is trivial. Sometimes, a state (or a specific branch thereof) could BE the adversary.",
"Can you secure said backdoor with another unique function?",
"Yes, this is the idea. However, whatever measures you use to secure it, the state must be able to open it; therefore any adversary with the same (or more) knowledge as the state can also open it.",
"Take disk encryption. The key that is used to encrypt the disk must itself now be encrypted in such a way that the state can obtain your key (e.g. using asymmetric encryption, where the state provides a (hopefully unique) public key to you). Now, it suffices for the adversary to either solve the original problem (cracking your disk) or to solve a new problem (cracking the state's key). [Why hopefully unique? Because if the state has a small set of key-pairs, then an adversary that cracks one pair has a rich tool to open massive amounts of people's encrypted data.]",
"Rather than attacking the function, why not just attack the backdoor?",
"Hopefully, it would be harder to attack. But even if a minuscule chance that it's not would weaken the security.",
"I could see securing the backdoor cryptographically, but would that allow the adversary to see any unique about the given hash? ",
"Not sure why you're talking about hashing specifically now. But if the backdoor is implemented correctly, the actual hashing is no weaker than it was.",
"Meaning, will they see that there is a part of the function that is unique to the rest of the hashed string?",
"What risk does a state posses when they introduce a backdoor into their encryption standards/functions?",
"I'm not sure I understand these questions. Can you elaborate?"
] |
[
"Meaning, will they see that there is a part of the function that is unique to the rest of the hashed string?\nWhat risk does a state posses when they introduce a backdoor into their encryption standards/functions?",
"I think I understand it. The risks are simple: if the backdoor leaks, it's going to come to massive security breaches. \nHow? Here's an example (and keep in mind, something similar has happened in the States before): ",
"You're a CEO of your company and have digital assets. You decide to encrypt (for example) your emails with the government standard encryption algorithm (say ",
"DES",
"). Without getting into the technicalities about the key length or cypher design (",
"a good article here",
", lets assume the cypher is safe (as it was in the seventies). \nNow comes the fun part - the government, for your own \"safety\" (couldn't resist a bit of sarcasm), has implemented a backdoor which allowes them to ",
" and read them in ",
". Now comes the whistle-blower, offended by the actions of the government and leaks the backdoor to the public. Voila, your company has just suffered a major security leak and your business is endangered. ",
"If I may just add the following: no cypher is perfect (has flaws which can be explointed) and can be cracked, ",
". By adding these so-called backdoors, you are adding to the aforementioned flaws, making it more likely to be cracked in a smaller time frame. ",
"Can you secure said backdoor with another unique function?",
"Although the answer provided is technically correct, I would like to add something rather important: cryptographic security relies more on the algorithm environment than on the algorithm itself. Your cryptographic function may be mathematically flawless, but there are ways to compromise it in practice (",
"k-ary malware",
" for example). ",
"Cryptography is a fascinating topic, and I do have some sources lying around (I've done a few papers about it) if you are interested. ",
" various formatting fixes.",
" ",
"really good, fun (free) book to read",
". I highly recommend it."
] |
[
"To address your last question: The major risk of introducing any security backdoor, cryptographic or otherwise, is that you have added an additional security reliance: Security through Obscurity.",
"Someone, somewhere has access to this backdoor. The method of utilizing it must be replicable and reliable, otherwise it's a fairly useless backdoor. So in addition to any other attack vector, a backdoor introduces all of the frailties of human insecurity into the mix.",
"So now we're talking about a wetware attack. Social engineering, incompetence, betrayal, and improper disaster recovery and business continuity standards are all in play. Because some human being somewhere has a secret, and has power, and the only thing standing between you and that secret/power is human obfuscation. That's a frailty I would never want in my product."
] |
[
"What's the evidence that water vapor is gaseous?"
] |
[
false
] |
I had a discussion recently with someone who claimed that water vapor below boiling point was impossible, and that evaporated water is really tiny, tiny droplets of water, not single molecules. Can someone provide some experimental ways we know that it is single molecules and not droplets?
|
[
"that water vapor below boiling point was impossible",
"This is patently false and said by someone who obviously doesn't understand thermodynamics nor the process of evaporation. Now water vapor ",
" condense into little droplets, this is for instance what happens over a pot of boiling water and why you can ",
" steam. You're not actually seeing the steam, steam is invisible like air, but you ",
" see the water droplets which are quite small--micron scale sizes which is about as small as droplets can get before surface physics make it unfavorable.",
"You can tell because light scattering ",
" much depends on size. If water did not become gaseous from evaporation, the light scattering properties of water would be ",
" different.",
"One simple test would be to have a jar of water sealed with a water molecule sized membrane, the water would slowly escape the jar without an obvious way for drops to get through.",
"But really, you don't even need that, the thermodynamics and energy balances simply don't make sense if you disallow gas production and there's no obvious \"boundary\" that boiling point makes, in fact you can ",
" change the boiling point by altering the pressure, so there's nothing sacred about the boiling point."
] |
[
"Investigating the thermodynamic energies of single molecule escaping from the surface of a liquid vs. an entire droplet of water would generally disprove the idea that evaporated water is actually tiny droplets--tiny droplets of lots of molecules escaping coherently from a solution is not energy-favorable. Tiny droplets being emitted is essentially aerosolization. This takes a non-insignificant amount of energy to accomplish, more than ambient energy of a solution of water sitting on a counter.",
"AsAChemicalEngineer said it well in terms of light scattering. If you had the tools, you could set up a light-scattering measurement apparatus--basically a laser with a detector; if you don't detect any light scattering (assuming the correct wavelength is used vs. the size of these theoretical water droplets), then there are no particles--and hence must be gaseous water. If you really did have particulates (tiny droplets), light would scatter (and look like a haze--like the steam cloud above a pot of boiling water). But we know that's not the case based on how light does not scatter over a solution of water sitting at room temperature on the counter. ",
"Or you could just tell your friend that they are wrong and entirely uneducated on thermodynamics and solution-boundary physics."
] |
[
"Yeah, of course he's wrong and uneducated. He was just claiming that there is no real documented evidence of single-molecule water vapor below boiling point. ",
"I also offered to him measured diffusion rates, which are highly mass-dependent; measured chemical reaction rates, which would be different if water is monomolecular or bound in droplets; and observed condensation in droplets with adiabatic expansion."
] |
[
"Why does hot water clean better than cold?"
] |
[
false
] | null |
[
"Take a look over ",
"here",
" and ",
"here",
"."
] |
[
"Simply put (trying to remember from chemistry in high school so someone please correct me if I'm wrong) it's because of how atoms react to temperature. When atoms are cold they move very little but when theyre heated they get agitated and vibrate, shift, etc. This makes stuff like crusted food on dishes easier to fall off because the atoms are looser. It also applies to when you run a jar thats cold/been in the fridge under hot water and it opens easier, it loosens the atoms and therefore is easier to move the lid.",
"To make an analogy, imagine if you had a group of people (they represent the atoms) tight together (that represents cold) and you tried pushing your way through, it would be really hard to. But if the people were all about arms length apart and swinging their arms or moving (to represent heat) it would be really easy to push through, just like pushing through crusted food on dishes.",
"Hope that helps! "
] |
[
"Thanks."
] |
[
"Can you tell a right eye from a left eye like you can with bones?"
] |
[
false
] |
I know that with bones, you can tell which side of the body it came from due to its morphology, but an eye is ovoid. If someone were to find just an eye, could they be able to figure out which side the eye came from? If so, what indicates the difference? Or is it too difficult to tell because of its specific shape?
|
[
"The six extraocular muscles have a left/right pattern, especially the inferior oblique muscle with comes from the side of the nose and runs down and around the bottom. So, you can deduce left/right from the muscle attachment points in the eyeball."
] |
[
"Not to mention that the optic disc is not central, so you should be able to orientate the eye appropriately."
] |
[
"Oh yeah. No idea why I remembered the muscles and forgot that."
] |
[
"Determining the spin of a electron."
] |
[
false
] |
[deleted]
|
[
"A few more things: the 2P level does have 3 orbitals, and they are: ",
"; remember that there are 2 quantum numbers that start with m:",
", I believe that you are referring to the Ml quantum number and those for the 2p orbitals are: -1,0,1. Yes, you are correct when stating that Hund's rule required you to put all the electrons with a positive spin first for each orbital; with this rule the the Ml for B, C and N would respectively by -1, 0, and +1. Then when we add the negative spin electrons, O would be placed with B in -1; F would be placed with C at 0 and Ne would be places with N at -1. The elements we placed first (B, C ,N) would have a Ms number of +0.5, spinning positively for their last electron; and the elements that were placed later (O, F, Ne) would have a Ms of -0.5, spinning negatively for their last electron. ",
" ,"
] |
[
"Those elements are not in the d orbital so that right there could be your problem. They are in the 2p orbital. "
] |
[
"Those elements are not in the d orbital so that right there could be your problem. They are in the 2p orbital. "
] |
[
"What is actually expected to be discovered in Lake Vostok?"
] |
[
false
] |
I recently read a couple articles on Lake Vostok and was just wondering, what scientific discoveries are actually expected to be found? Like are scientists looking for earlier life forms, studying the water quality from earlier times? or is it just a mixture of a lot of different things? Edit: Thanks to everyone for your responses
|
[
"They are hoping to find life down there. Life which has been isolated from the surface for ~20 million years and has had all that time to figure out interesting new strategies for survival. "
] |
[
"Most (almost all) food webs depend on photosynthesis to begin the cycle. The classic idea of the grass gaining energy from the sun, the deer eating the grass, the wolf eating the deer yada yada.",
"There is a thing called chemosynthesis, where autrotrophs (organisms who basically begin a food cycle) gain their energy from chemical sources. (The technical explanation is that chemosynthetic bacteria oxidize sulfides or elemental sulfur to gain energy.) The most prominent example are deep sea vents which spew out tons of sulfur. You've probably seen something like this:",
"http://media.treehugger.com/assets/images/2011/10/deep-sea20hydrothermal20vent-jj-001.jpg",
"http://life.bio.sunysb.edu/marinebio/ds_03.jpg",
"Those are tube worms with a blind crab in the center of the picture.",
"Scientists expect to find this kind of biological community within Lake Vostok. Most likely not ones based around hydrothermal vents, but ecosystems that are built around chemical sources (methane clathrates, whale falls)."
] |
[
"They were hoping to find organisms that showed proof that life could sustain in situations LIKE those found at Lake Vostok. It's more important to realize that the operations that happened at Lake Vostok were testing the possibility of drilling through deep ice in order to study the liquid water below. ",
"That being said, the drilling at Lake Vostok can be seen as somewhat of a field test for Jupiter's moon Europa. There has been long speculation that life can exist below Europa's icy top-layer. If they find life in Lake Vostok, it can give insight into what kind of life may exist inside Europa.",
"Did a quick google search to find a relevant article. There's a bunch of info out there about both Lake Vostok and Europa.\nEdit: Lol, forgot to include said article. ",
"http://www.space.com/14552-antarctica-lake-vostok-europa-life-jupiter.html"
] |
[
"Could an entire pool table be potted in one shot?"
] |
[
false
] |
[deleted]
|
[
"The fact that there are infinite inputs does not imply that all outputs are possible. It may be possible to find an angle and power which would theoretically result in all of the balls ending up in a pocket, but it's possible (though I would be surprised) that there's no angle you can hit it from that will give that result."
] |
[
"Arguing this in a purely idealised/mathematical way is a bit difficult I believe. For example in an idealised 9ball setup and break, the central ball (9) would not move at all from the initial impact of the cue ball. It could only be moved from balls ricocheting off the cushions.",
"Just looking at actual 9ball breaks like ",
"this one",
" or ",
"this one",
", it seems certainly possible to get enough power into a break to have every single ball move far enough to go into a pocket.",
"So I do not see any reason why it should be theoretically impossible to pocket all balls in one break. Practically very very unlikely though.",
"I would like to see the distribution of \"number of balls sunk per break\" for professional 9ball games though. There must be some super-afficionados gathering these kinds of statistics? Maybe one could try to extrapolate from that... "
] |
[
"If we are disregarding all kinds of friction this makes sense, yes."
] |
[
"The new Orion spacecraft seems remarkably similar to the Apollo spacecraft in design and function. However, a return to lunar orbit isn't planned until after 2020. Why will it take so long to test and implement the new spacecraft if it is based on technology that was functional 50 years ago?"
] |
[
false
] |
Originally posted this to AskReddit. Sounds like it belongs here. I recently got back into space exploration history, and started reading up on the planned Orion spacecraft. The design seems remarkably similar to the Apollo spacecraft. One thing I don't understand is why will it take 10 years to develop a new craft that seems to serve the same function as something that was very functional 50 years ago. I assume all the specifications and expertise from the time were captured and preserved. Shouldn't we be able to quickly rebuild the equipment from the Apollo program, add updated computer technology, and be on the moon in a year or two? The design and testing should be the difficult part, but that has already been done. Is it simply a money issue at this point? I assume the Chinese have access to all this information as well. Why haven't they simply duplicated the technology and sent their own crew to the moon? I understand the process is incredibly complex, but if the information exists, why is it so hard to duplicate?
|
[
"One of the issues is that it's not just the equipment that needs to be rebuilt, but the equipment to build the equipment (and sometimes the equipment to build the equipment to build the equipment etc). There is also the issue of money: NASA in the 60s had up to eight times the relative budget that it does today."
] |
[
"In addition, a space program is more than the launch vehicle and spacecraft. The infrastructure required to support this equipment and the training to operate it isn't something that can be replicated overnight."
] |
[
"We could re-create the Apollo program, but it's not likely that we'd want to. The Orion spacecraft bears a strong resemblance to Apollo because the shape of the Apollo spacecraft was very ideal for expendable launch missions, and this is exactly what Orion is intended to do. It is not, however, a carbon copy of the Apollo spacecraft. It is designed as a more modern, general purpose vehicle that can be launched from many different launch systems."
] |
[
"Would wires made of anti-matter have the same electrical properties?"
] |
[
false
] |
Would the right hand rule still apply or would it be the left hand rule? Would electricity be propagated with positrons and would this change how the magnetic fields would be generated? Is it the same, but opposite or the same in general?
|
[
"All the same rules and formulas would still apply; with the definitions we use, a current going in a given direction can be the flow of positive charges in that same direction, or a flow of negative charges in the opposite direction. Or both! Magnetic fields are the same for the flow of a positively charged antiparticle (like a positron) as for a positively charged particle (like a proton). But, like you suggested, in an antimatter wire the moving charge carriers would be the positively-charged positrons, with the anti-nucleons forming the fixed \"lattice\" of the solid wire.",
"Slight aside: there are a variety of sign and handedness conventions baked in to our laws of E&M. The sign of charges, the direction of current, the direction of magnetic field, and whether to use the left or right hand rule are some of those. The choices that we use are largely due to choices made by people muddling in the dark trying to figure things out as they went along (like Ben Franklin assigning positive and negative charge). The physical observables of course don't care what choices for those we make, as long as we're consistent.",
"Note that we do have experience with \"antimatter currents\" in the proton-antiproton and electron-positron beams at various particle accelerators. We also have experience with the flow of positive and negative charges in electrolyte solutions and plasmas. We of course don't have experience building solid antimatter wires; connecting those to our instruments (or even suspending them magically in a pretty good vacuum) would be... a bit too exciting."
] |
[
"Dirac was working on relativistic quantum mechanics, combining quantum mechanics with special relativity. Considering the energy equivalence relation, he realized that there should be infinite negative energy levels, so electrons with positive energy states should fall towards negative infinity. They obviously don't and stop at the ground state. He postulated that there was something called a Dirac Sea, which essentially says that all these negative energy states were already populated by particles. One of these particles should be free to gain energy, rising to a positive energy state. Once this happens there's a hole in the sea, which should have the same mass as an electron, but a positive charge. In 1931 Dirac suggested this was an anti-electron, and that its interaction with an electron would annihilate both of them, releasing energy.",
"A year later, Carl Anderson, while observing cosmic rays, found a particle that had the same mass of an electron, but a positive charge. The year after that Dirac suggested this was a universal phenomena, and every particle has its oppositely charged counterpart. The antiproton was discovered a couple decades later."
] |
[
"One could argue that all of quantum physics fall in that bucket of \"experimental results explained mathematically\". The ",
"ultra-violet catastrophe",
" was an issue in the late 19th century physics, where established theories predicted dark body radiation to approach infinity as the wavelenght decreased, which contradicted experimental results."
] |
[
"Do we keep our atoms as we age?(more questions inside)"
] |
[
false
] |
[deleted]
|
[
"Is saying that tissue doesn't regenerate really the same as saying individual atoms aren't ever replaced, though?"
] |
[
"You are correct in assuming you gain atoms through ingestion, but also through respiration.",
"There are likely atoms that stay with you for life, or close to it.",
"An example would be ova (egg cells in women's ovaries) which go into suspended animation in a fetus. Some of them stay in that state for decades, until menopause after 50 or so (average).",
"It is imposible to know this for sure, without tagging every single atom in your body with a unique tag of some sort, an impossibility."
] |
[
"1) Yes, for instance those in the corneas of your eyes, which is one bit of tissue which isn't regenerated. ",
"2) The molecules making up your body are continually broken down and reconstructed in cells. "
] |
[
"Have a couple of questions after watching a Lawrence Krauss talk"
] |
[
false
] |
Link to original talk: 1) Is that flat universe model widely accepted? 2) Does that necessarily mean that the universe started out of a quantum event as opposed to the big bang?
|
[
"I'm just guessing here, but I'd be willing to wager that you're imagining a \"quantum event\" as something very small, and the \"Big Bang\" as something very, well, ",
"It's not that simple."
] |
[
"So I'm making an unnecessary distinction? "
] |
[
"I don't know how to answer that in this context.",
"What I mean to say is that the phrases \"quantum event\" and \"Big Bang\" carry with them entire ",
" worth of context. People literally dedicate their whole lives to trying to understand those two ideas."
] |
[
"Why do some vaccines like rabies or tetanus \"wear off\" after a few years?"
] |
[
false
] |
[deleted]
|
[
"Most of the replies so far have been useful but they fail to accurately answer your question.",
"Tetanus vaccine is a toxoid vaccine, which means you're inoculated with an inactivated toxin from the bacteria Clostriudium tetani. Inactivation of the toxin is usually accomplished via formalin washes. Due to the weak stimulatory effect of toxoid vaccines on your adaptive immune system, there isn't a strong memory effect created and you therefore loose resistance after some time (4-5 years on average). This is why you need a 'booster' shot.",
"The MMR vaccine, on the other hand, is a LIVE attenuated vaccine that produces an incredibly strong immune memory effect (both T & B cells). This strong response is mostly due to the fact that the virus has a chance to replicate intracellularly, which stimulates the release of the inflammatory cytokines that attract CD4/CD8 T-Cells, and some innate immunity cells.",
"Obviously the immune response is far more complicated than it may appear and there are various other factors involved in determining the effectiveness of a vaccine challenge to a host.",
"Source: BIO 420- Vaccines"
] |
[
"If you don't run into a version of that disease, your body decides that it is no longer a threat, and it stops producing antibodies for it. ",
"Most (if not all) of the \"lifetime\" immunizations work for one of two reasons:",
"You are constantly exposed to it (chickenpox and its ilk)",
"You are never exposed to it, and have nothing to test (ie, smallpox)"
] |
[
"That's rather over-simplified. It's not so much that Plasma B-cells stop producing antibodies as they become less proliferative (i.e., less likely to reproduce) without a cell-cycle signal due to antigen presentation. Recent findings have suggested that these Plasma cells never entirely go extinct either; long term studies looking at tetanus vaccinations have indicated that titers can be generated even after many decades since a tetanus vaccination. The initial 10-year rule came out of the inability to detect low levels and titers and the knowledge that titers fade over time without constant inocculation."
] |
[
"If two people held a string stretching from one side of the universe to the other, would it snap due to the expansion of the universe?"
] |
[
false
] | null |
[
"Yes. There is a real tension on the string from the expansion."
] |
[
"This question must come up in String Theory all the time, hey?"
] |
[
"Tension from expansion is important for cosmic strings, which are treated with a similar formalism to fundamental strings in string theory.",
"Same thing also appears when formulating string theory on a de Sitter (exponentially expanding) background."
] |
[
"What is the \"Earth-light\" that illuminates the dark side of the moon?"
] |
[
false
] |
Is it artificial light from the surface of earth or is it naturally occurring? From where I am right now (Peterborough, Ontario at 9:45pm) I can clearly see the dim sphere of the dark side of the moon, wrapped in a waxing crescent. My understanding is that the earth is lighting up its own shadow on the moon. Is this correct? If not, what is causing the illumination?
|
[
"It's reflected sunlight. Artificial light isn't nearly bright enough to noticeably illuminate the Moon.",
"My understanding is that the earth is lighting up its own shadow on the moon.",
"You're not seeing the Earth's shadow on the Moon. The Moon is partially dark because the half that faces the Sun isn't necessarily the same as the half that faces the Earth - with the Moon between the Earth and Sun, the Sun lights the opposite side from the Earth and we see a new Moon. With the Moon on the far side of Earth from the Sun, the whole side visible from Earth is lit, and partial moons are various stages in between."
] |
[
"The \"dark side\" of the moon isn't really \"dark\" it's just the side we never see because the moon is tidally locked and one face always points towards the earth. "
] |
[
"I see, thank you. I was I was confusing the phases of the moon with a lunar eclipse it seems. ",
"I think part of my question still stands though- how exactly does sunlight get to the side of the moon ",
" facing the sun?"
] |
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