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[
"Discoveries at the LHC besides the Higgs boson?"
] |
[
false
] |
[deleted]
|
[
"There's the entire heavy ion program which is used to study nuclear matter at high temperatures and densities, which melts into a fluid and is the state of matter that filled the universe in the first microsecond. Unlike HEP it's less focused on trying to find rare types of events and more about measuring the properties of things we already know exist. As a result it's not as likely to grab big headlines but there is a lot of science being done there."
] |
[
"Depends what you mean by discovery. ",
"Apparently mine is too narrow a definition.",
"The LHC has produced a wealth of physics results, including lots of exclusion limits on physics beyond the Standard Model and more precise measurements of many processes in particle physics. However, I believe it's quite a stretch to call those things discoveries.",
"I'll break down what I think someone could reasonably mean by asking about discoveries at the LHC. Let me know if you think there's something missing.",
"\nNo. There are some anomalies, but nothing convincing yet.",
"\nOnly the Higgs boson.",
"\nYes, there are several new charm and beauty hadrons, including a few new tetraquark candidates and the first ever pentaquark candidates.",
"\nYes, numerous."
] |
[
"We also saw some super exotic states of matter, like pentaquark states (five quarks in a bound state, rather than the two (e.g. pions) or three (e.g. protons and neutrons) quark states we see usually. We may even have seen six quark states, but my memory is fuzzy and I'm on mobile so I don't fancy the effort of googling that for you!"
] |
[
"What exactly is stopping us from cloning Mammoths?"
] |
[
false
] | null |
[
"Some of the difficulties are discussed ",
"here",
"."
] |
[
"Well, an immediately obvious problem is the lack of available mammoth wombs around. To quote Monty Python: "
] |
[
"Couldn't you use an Elephant womb?"
] |
[
"Does a person sweat when they swim?"
] |
[
false
] | null |
[
"Apparently a lot...",
"I lived with some swimmers in university. They heard of many studies where pre-post workout mass differences were 1-2Kg. Thats a fair bit of sweat. I asked them this question myself. ",
"Publication abstract:\n",
"http://journals.lww.com/acsm-msse/Citation/1994/05001/1192_Weight_Loss_and_Sweat_Loss_During_Swimming.1194.aspx",
"This was in young swimmers. Adults sweat a fair bit more."
] |
[
"\"Personal anecdotes and layman answers are not acceptable posts.\""
] |
[
"\"Personal anecdotes and layman answers are not acceptable posts.\""
] |
[
"If there are diseases we can get from animals, that are harmless to them, are there disesases that we can unconciously give to animals?"
] |
[
false
] |
Not sure if earth sciences are the correct field to ask, but it sounds correct
|
[
"Rinderpest jumped species from cattle to humans in the Middle Ages and became measles. Measles then jumped from humans to dogs in the 18",
" century, becoming Canine Distemper. More recently, Canine Distemper mutated again and infected Seals in the 1980s, becoming Phocine distemper. ",
"Refs.:",
"Furuse, Y., Suzuki, A. and Oshitani, H., 2010. Origin of measles virus: divergence from rinderpest virus between the 11 th and 12 th centuries. Virology journal, 7(1), p.52.",
"Nambulli, S., Sharp, C.R., Acciardo, A.S., Drexler, J.F. and Duprex, W.P., 2016. Mapping the evolutionary trajectories of morbilliviruses: what, where and whither. Current opinion in virology, 16, pp.95-105."
] |
[
"Did it become milder, or was the surviving population more resistant? Maybe some of both?"
] |
[
"Unconsciously? Do you mean without us knowing that we have the disease? If so, that would depend on the symptoms and the general symptom behavior of the disease. You may not know you have a disease but you still could. If not, the idea of mosquito vectored diseases involves the human transmitting the disease to mosquitoes at some point in the pathogen's life cycle, usually."
] |
[
"What's the science behind rhythm?"
] |
[
false
] |
Why, when listening to a 4/4 chord progression, does the song seem to 'peak' just as the count (or 4/4 cycle) repeats? Is rhythm purely psychological, or is there a scientific reason why we love to headbang? In a similar vein, are there numbers to show the difference between 3/4 and 4/4? They feel different to the ear, and I know it's due to the numbers of beats in a measure, but what, scientifically, is a measure? What's a beat? Why do certain groups of sounds of certain lengths 'fit,' and others don't?
|
[
"It never ceases to amaze me how diverse and complete the askscience panel is."
] |
[
"It never ceases to amaze me how diverse and complete the askscience panel is."
] |
[
"upvoted and saved - thank you very much."
] |
[
"When the universe expands and the galaxys move away from each other quite fast, how can it be that andromeda and milky way will collide anyways?"
] |
[
false
] | null |
[
"Both the Milky Way and Andromeda are part of the Local Group, a cluster of over fifty galaxies. The galaxies are close enough to be gravitationally bound together. As the galaxies orbit the center of gravity of the Local Group, some of them are moving toward each other because that's the path of their orbits. The Milky Way and Andromeda just happen to be on a collision course. The Local Group is itself part of the Virgo Supercluster, which is also gravitionally bound.",
"At greater distances, gravitational attraction between galaxies is much weaker, so it is believed that dark energy takes over. The existence of dark energy is not yet proven but the evidence is very strong. It is believed that dark energy is driving the accelerating expansion of the universe.",
"tl;dr Over large scales, dark energy is causing galaxies to move away from each other, while gravity is more dominant at smaller (but still mid-bogglingly large) scales, causing some closely neighboring galaxies to move towards each other."
] |
[
"Over large scales, dark energy is causing galaxies to move away from each other",
"They would move away from each other even without dark energy - just slower than they do."
] |
[
"The universe expansion is really quite slow, except when measured at ridiculous distances. As such it is really only meaningful between ",
" of galaxies, and really not even then but only between ",
". "
] |
[
"How does the brain calculate the passing of time independent of simple estimation? Is there a biological mechanism?"
] |
[
false
] |
The brain must use knowledge of how long thought processes take and can estimate time passing based on tasks and such, but is there a mechanism for linking to circadian rhythms or some other biological clock. I mean on a small scale. For example, I can often predict accurate to a minute or so when 5/10/15 minutes has passed, but my brain couldn't do this simply based on tasks, as time seems faster and slower based on different tasks. It also seems like such short spans of time are too short to rely on circadian rhythms. Is there some sort of feedback loop in brain neurons or is it biochemical?
|
[
"There are circuits in our brain that line neurons end to end, making small feedback loops based on the time it takes to have the signal make a full lap. Smaller loops are integral in music, rhythm, and even rhythmic movements like walking, swimming, blinking. This very strait forward process is thought to be at work in all temporally dependant activities. "
] |
[
"Great answer to a great question! thanks! I have always wondered how we perceive time but never had a definite answer."
] |
[
"Thanks. Neuroscience is a big interest of mine on account of free online courses and also I'm insane. ",
"It's crazy how a concept as abstract as time is so easily dealt with and, in a way, ",
" by the brain. "
] |
[
"This webpage claims to prove that Newtonian mechanics allows for indeterministic behavior. Can someone please tell me if it's correct?"
] |
[
false
] |
And if it isn't, what's wrong with it?
|
[
"I'm sorry, but you're wrong.",
"However, it first requires a small perturbing force (arbitrarily small, in any direction, to set it moving).",
"No, it doesn't. That's the whole point. If you assume that Newtonian mechanics is time reversable, then the fact that there exist solutions in which the ball stops at the top and remains there (however chaotic the system may be, or how sparse such solutions are) implies that there are solutions in which the ball starts at the top and spontaneously—really, really spontaneously—starts to roll down in any direction. No motive force, no perturbing effect; it ",
".",
"In fact, you don't have to assume time-reversability; the solution provided ",
". I mean, the guy works out the math. You can ",
" the math. And it's absolutely correct. The equation given ",
" a solution to Newton's equations of motion in which the ball ",
" at time T.",
"This is possible because there's no assumption of ",
" in Newtonian mechanics (provided we assume \"Newtonian mechanics\" means \"systems that obey Newton's three laws of motion\"). Notice that his solution is not four-times continuously differentiable; the fourth derivative is constant 0 for t <= T and constant 6 for t > T. If Newtonian mechanics requires ",
" solutions, then such solutions can be ruled out, but the fact is that the solution he provides is ",
" consistent with Newton's three laws."
] |
[
"I got about halfway down the page, and I'm stopping at this line:",
"Equation (3) describes a point mass sitting at rest at the apex of the dome, whereupon at an arbitrary time ",
"No, it doesn't. In classical mechanics, no motion is spontaneous. Since the apex is an equilibrium point (albeit an unstable one), it will roll away once it has been pushed. However, it first requires a small perturbing force (arbitrarily small, in any direction, to set it moving). This force can come from a variety of sources, but ",
" ",
"In reality, a system like this would be highly chaotic and it would be basically impossible to predict which side the ball would roll down (unless, of course, you knew which direction the wind was blowing), but that would not make the classical mechanics any less deterministic. ",
"Edit: I'd like to take the opportunity to point out that the author should be above such a sophomoric mistake, seeing as ",
"he has an undergraduate degree in chemical engineering, though his PhD is in the philosophy and history of science.",
"Edit 2: People seem to be downvoting the good comments in this thread, which is a shame. Truth is not a democracy, so I challenge you to prove me wrong in the comment box, rather than with the arrows. "
] |
[
"If you assume that Newtonian mechanics is time reversable, then the fact that there exist solutions in which the ball stops at the top and remains there (however chaotic the system may be, or how sparse such solutions are) implies that there are solutions in which the ball starts at the top and spontaneously—really, really spontaneously—starts to roll down in any direction. No motive force, no perturbing effect; it just starts to roll.",
"This is a good point, I missed this before.",
"Notice that his solution is not four-times continuously differentiable; the fourth derivative is constant 0 for t <= T and constant 6 for t > T. If Newtonian mechanics requires ",
" solutions, then such solutions can be ruled out, but the fact is that ",
"Actually, the problem is clearly inconsistent with the first law:",
"If an object experiences no net force, then its velocity is constant: the object is either at rest (if its velocity is zero),",
"With no net force at the top of the dome, velocity must stay zero, which would rule out the other solutions on physical grounds, albeit not mathematical ones. The second law, his equation given, is satisfied, but the first law is not. Wouldn't you agree?",
"Seems silly that the post is just that easy to disprove after all this, but there it is."
] |
[
"If you fired a gun straight down off a cliff that was arbitrarily high (i.e. 1000km high), would the bullet eventually slow down to terminal velocity? How long would that take?"
] |
[
false
] |
I assume that if an object is falling at a speed faster than its terminal velocity, and has no force acting upon it to make it sustain that speed, that it'll slow down to the terminal velocity. If this is true, how long would it take for the bullet to reach this speed?
|
[
"Yes it would slow down. Terminal velocity and how long it would take to reach that velocity would be based on the ballistic coefficient of the bullet. Some bullet manufactures publish this number, some do not. Also keep in mind air resistance SQUARES as speed doubles. So the faster the bullet is moving, the faster it slows down."
] |
[
"Thank-you. As an aside, what would make manufacturers not want to publish the ballistic coefficient number if they had it readily available?"
] |
[
"After firing, gravity pulls downward, but (more than that) air resistance would be slowing it down (accelerating up). Eventually it would slow down to the point where those two were balanced. The time would partly depend on the size, shape, and surface roughness of the bullet. It would also depend on the initial velocity that it was shot with. It's not a simple solve either, because acceleration itself is a function of time in this case.",
"Edit: clarification, per ",
"/u/Spell125",
"'s confusion."
] |
[
"Why is there a need for dark energy to explain the exponential expansion of space?"
] |
[
false
] |
[deleted]
|
[
"Dark energy, in its simplest form, is essentially what you are describing. The part you are missing is that, without dark energy, empty space won't just expand, something has to drive it."
] |
[
"I went to a talk recently where dark energy was explained like this:",
"If you have some sphere of mass that is expanding at some rate, gravity will slow down that expansion.",
"However, if you use the same model but require that the density inside the sphere remains constant while it expands, you get accelerating expansion.",
"So dark energy, whatever it is, acts like some condition that space doesn't get less dense as it expands, and thus the expansion accelerates.",
"Is this a good way to look at it? It was very interesting to me and the speaker is a cosmologist so I figure he has some credibility."
] |
[
"You can definitely think of it that way, though there are few steps to actually get from that description to the result of accelerated expansion."
] |
[
"If you place 2 glasses of water, one 50 degrees Fahrenheit and the other 90, in a room that is 70 degrees, which will reach room temperature first and why?"
] |
[
false
] | null |
[
"Heat transfer is proportional to: ",
"Temperature gradient.",
"Thermal conductivity.",
"Area of contact. ",
"Let's assume the area of the water surface in each glass is the same. Since the temperature gradients are the same initially, it comes down to the question of whether the thermal conductivity is the same for 50 degree water and 90 degree water. ",
"Turns out it isn't. This is a value that is temperature dependent for water. ",
"This pdf",
" gives standard values on page 4. ",
"At 90 F (305K), the thermal conductivity is higher than at 50 F (283 K), so the rate at which the 90 degree water will cool will be faster than the temperature that the 50 degree water will rise. "
] |
[
"Wouldn't black body radiation also play a role in cooling the warmer glass first? Or is this effect too small to matter?"
] |
[
"I did a small experiment to look into this. First I am going to put some unsupported speculation.",
"Thermal conductivity of water: by eyeballing the graph this varies by about 7% in the temperature range we're talking about. My hunch is that convection is a more important mechanism for heat transfer than direct conduction is. This especially since the water is being cooled/warmed all up and down the sides of the glass, which would tend to promote convection. I suppose the viscosity of water is relevant to the rate of convection, and this varies by quite a lot: 1.3 mPa s at 10 deg. C and 0.8 mPa s at 30 deg. C. This is going to promote cooling of the hot glass. It would be great if someone else were better able to quantify these effects and the relative importance of convection vs. conduction. ",
"Black body radiation: This is going to be the same for the hot and cold glasses as long as the radiating surfaces the glasses can see are also at 70 deg. F. The hot glass is cooled radiatively and the cold glass is warmed radiatively.",
"Evaporative cooling: a very crude experiment to put a ballpark figure on this. I put 80 mL of water in a 100 mL glass beaker and warmed it to 38.0 deg. C. I recorded its mass every minute for 7 minutes, leaving the balance doors ",
"(like this)",
" open between measurements. The measurements were reasonably consistent (loss of 28, 19, 21, 17, 17, 14 mg each minute) and after 6 minutes the total mass lost was 116 mg. The temperature at the end of the experiment was 33.9 deg. C. ",
"The heat capacity of 80 g of water is 4.2 J/g*K * 80 g = 336 J/K. A change of 4.1 K is a loss of 1400 J total. ",
"The heat of vaporization of water around room temperature is 44 kJ/mol. 116 mg of water is 6.4 mmol, so the total heat lost via evaporation was 280 J or 20% of the total.",
"These measurements were taken in a very slightly drafty lab, in a location somewhat protected from air currents, on a somewhat humid day. (44% outside.) In other words I would say the rate of evaporative cooling could be quite a bit higher than it was here--especially if you were using coffee mugs, cardboard cups, anything that would slow down the other routes of heat transfer.",
"Evaporative cooling would be much less important at 50 deg. F than at 90, but this time it will be working slightly against you.",
"In summary, the hot one will approach r.t. at least 20% faster than the cool one due to evaporative cooling. Other factors (viscosity and thermal conductivity) also favor the hot one. "
] |
[
"Dumb question: Can we use sound waves for large scale levitation?"
] |
[
false
] |
I saw footage where scientists used to speakers pointed at each other and caused droplets of medicine to levitate between them. Would it be possible to use speakers beneath a car to make it levitate?
|
[
"1: the size of the object you can levitate is limited by the half the wavelength of the frequency you're using. In ",
"this video",
", the biggest object that can be levitated is ~7mm. In order to levitate a car, you'd need a 75hz wave. Problem one: this would be audible. Problem 2: this would be ",
" audible. Air would attenuate the volume by half every 30km.",
"2: Square cubed law. The mass of the object increases with size",
" and the area of levitation increases with size",
" so the pressure required increases linearly with size. A car would require an incredibly loud sound. It would probably not survive being levitated just from the heat of the surrounding air bearing the sound passing through it, not to mention the air pressure the car would be exposed to.",
"In the end, you're essentially trying to levitate the car by surrounding it with explosions; this is not a very good idea."
] |
[
"There is no such thing as a dumb question in science; else, where would we be today?!",
"To answer your question: yes, absolutely... at least in the future.",
"In fact, researchers have already successfully been able to levitate and manipulate suspended objects using sound waves. This science is known as Acoustic Levitation. Levitating an object as heavy as a car has not yet been accomplished, but researchers are working precisely on that. Already, advancements have been made in being able to lift heavier and heavier objects.",
"In 2013, a team of researchers from Switzerland's Federal Institute of Technology (ETH Zurich) presented an acoustophoretic transducer that was able to levitate water droplets and manipulate them in air. The big advancement here was that they were able to accomplish this without splitting the droplets; this previously had not been successful. ",
"For further reading:",
"Foresti D, Nabavi M, Klingauf M, Ferrari A, and Poulikakos D. Acoustophoretic contactless transport and handling\nof matter in air. ",
" 2013; 110(31): 12549–12554."
] |
[
"It's a big leap from 10 microliter water droplets to a car. There are plenty of things that are feasible on the small scale that can't be translated up multiple orders of magnitude in terms of effect."
] |
[
"Don't planes have a GPS, if so , why can't we just look up there location when they crash, or where they were before the crashed, to see where they're at ?"
] |
[
false
] | null |
[
"If there is an accident in the sky then the signal stops being transmitted. This is reported as \"we've lost contact\". The plane may still travel a great distance after that moment and the wreckage may be dispersed. Black boxes on planes have a local copy of that information."
] |
[
"But couldn't there just be (I'm not to knowledgeable on the GPS side of things) a chip in the black box that sends out a signal showing where the plane is ? Cause the black box is hard to be destroyed , so if there was a chip that could put out a signal showing where the plane is wouldn't that work ?"
] |
[
"Send a signal how? To what? You need a mechanism for doing that. It's not just a chip. Think about radio towers for example."
] |
[
"To all doctors/surgeons, how are the organs in our body held in place?"
] |
[
false
] |
Are they just floating around??
|
[
"They are attached to the body wall through connective tissue."
] |
[
"Visceral organs are enclosed in the ",
"peritoneum",
", which is a membranous sac. It has many folds (mesentery, omenta, ligaments) which attach organs to each other and the walls of the abdominal cavity. Organs are also connected by the ",
"adventitia",
", which is a layer of connective tissue that lines most organs."
] |
[
"Amazing how we know the names of the connective tissues. Really makes me want to become a doctor but idk lol "
] |
[
"Isn´t dogbreeding a proof for evolution?"
] |
[
false
] |
[deleted]
|
[
"Honestly, I would suggest that folks not waste their time in this debate. The Pope has flatly stated that evolution is a valid theory. So given the massive amount of material about evolution online and the Catholic Church's \"endorsement\" - anyone who still embraces the parables of a two thousand year old book really isn't going to ever listen to reason. ",
"State your case, then walk away. There are better ways to spend your time. "
] |
[
"Most people still arguing this are protestants who view the pope as a heretic."
] |
[
"Creationists will tell you that it's not evolution. They'll talk about \"kinds\" rather than species. They'll say that the instructions set needed to make all those breeds have been in the dog's DNA since the first days of creation, thousands of years ago, and that you can breed dogs til kingdom come and you'll never end up with a human."
] |
[
"Is it possible to create something with data on in, completely shielded and send it to a remote region of space, where it would survive beyond the last star burning out and essentially exist forever?"
] |
[
false
] | null |
[
"If anything managed to evolve in order to survive infinitely",
"Entropy doesn't decrease in a closed system. There's no way for something to live forever or a mechanism (like a computer, robot, spaceship, etc) to operate forever.",
"In addition, the universe is expanding. Say you have an exploratory robot that can disobey the 2nd law of thermodynamics (and continue operating forever). You'd have to answer the question of if the robot could explore the universe faster than its rate of expansion."
] |
[
"So... there's truth and not-quite-truth here, because of the distinction between what an outside observer would see, and the subjective experience of the entity doing the data-processing. You can do tricks with speed of processing that lead to infinite subjective time in finite \"objective\" time."
] |
[
"You said",
"If anything managed to evolve",
"I took that to mean you just wanted something that would be capable of \"finding\", and I thought a robot would probably last longer than something else (like an animal or a person).",
"We aren't sure of the nature of dark matter, but it looks like it doesn't react to energy the same way that normal matter does. Still, it's not going to provide a magic way to provide energy to something forever. Toward the end of the universe, it's believed that matter will be spread thinly across the universe. There won't be such a thing as \"abundant material\". Some theories even predict that matter particles have a half-life, and that they'll decay eventually, leaving a universe with no matter remaining, and energy spread so thin and evenly that it won't be able to do any work in the universe."
] |
[
"In the documentary \"Gasland\" faucets and hoses connected to area wells are shown to be flammable. I heard this is a misrepresentation and it is an unrelated cause. Is that spin from gas companies?"
] |
[
false
] | null |
[
"Several of those scenes were filmed in Colorado, where subsequent analysis by the EPA and the state revealed the methane in the water is biogenic (i.e., from microbial decomposition of organic matter), not from gas wells. There was one result of contamination from gas production. ",
"If you are interested, a two page summary of the analysis, published by the state of Colorado, can be found here: ",
"http://cogcc.state.co.us/",
". It is titled \"Gasland Correction Document\"."
] |
[
"And it goes WAY back. The earliest reports surveying the region reported that methane was all over the area, and made it difficult to drill wells in. The wells caught fire. Known problem. ",
" known problem.",
"IIRC 2 out of the 3 cases they'd featured were ",
" known to be biogenic (natural surface) methane. ",
"The 1 remaining well, the gas company had a wellhead with a bad casing on it right next to the water well. This WAS thermogenic (drilling-related) methane. But it was also highly localized, the neighbors had zero contamination. The gas company just wanted to comp the landowner IIRC.",
"The problem is not specifically related to fracking at all. It's ANY drilling where the well's improperly cased, even if fracking wasn't used to activate the deposit.",
"AFAIK they can just install gas separators and there's no problem. ",
"Something of note- what's the theory here? That fracking has poisoned the entire region's water with methane? Well, it was already \"poisoned\". No, wait, nobody cared. The existing naturally occurring methane doesn't have any known environmental consequences. If it reaches the surface in a spring, it just bubbles out. Animals didn't die from drinking it. "
] |
[
"So... it's spin from anti-business eco-activitists, then?"
] |
[
"The Boeing 747 was tested up to Mach 0.99. Could it fly above Mach 1 is safety wasn't a factor? If so, what would happen?"
] |
[
false
] | null |
[
"Yes. If the aircraft were to enter a dive, it could pass mach 1 - ",
". It is suspected that this indeed occured during ",
"china airlines flight 006",
". The pressures and shockwaves involved could easily tear the wings off, rip up all the structural panels and cause explosive decompression. The engines would likely fare the best out of all the components because the fan blades already exceed supersonic speeds even before the aircraft itself reaches mach 1. "
] |
[
"They do create shock waves. That's part of the reason turbine engines are so damn noisy. It isn't expressed as the loud sonic boom you get from a fuselage in open atmosphere though."
] |
[
"If I'm going to be pedantic here, and I am. The blades themselves don't really exceed the speed of sound. Instead, it's the air travelling through the blades, which is being accelerated, because they're essentially a bunch of tiny nozzles, that is travelling greater than the speed of sound in that medium.",
"This sets up a fairly stationary shock, and the pressure wave associated with it just bounces around a lot on the solid surfaces producing that nice dulcet jet engine white noise we know and loathe.",
"A lot of the noise from a jet engine is from the exhaust jet too. Jet noise is a pretty big deal at airports and part of my PhD is trying to reduce it."
] |
[
"Would it be possible to attach a probe to an asteroid, and have it return after one orbit?"
] |
[
false
] |
Would it be possible to send a probe with cameras and stuff into space, somehow attach it to an asteroid, and get a free ride around the solar system? The next time it passes near earth it detaches and returns. We could pick an one we know the orbit of, which returns in 5-10 years or so. Imagine the timelapse photos and the value of the data it could collect "for free" in relatively short amount of time.
|
[
"Sure, but it doesn't make sense. In order for a probe to land (gracefully) on an asteroid, it must have a speed virtually identical to the asteroid. And if you can reach that speed, you might as well skip the whole asteroid part and send it in orbit by itself."
] |
[
"Yup, there's no free lunch (nor free launch)."
] |
[
"If you could get into an orbit that would rendezvous with an asteroid, you'd already be in that orbit and you wouldn't get any free benefit. "
] |
[
"Thought experiment: You have 100 coins. Flip each one: if heads remove the coin, if tails add 100 more coins. Keep flipping until you have no coins. Will this process ever terminate?"
] |
[
false
] |
It seems like it's never technically impossible, and it's an infinite process, which makes me think it must terminate eventually, but the process gets statistically more and more difficult to complete with each flip. What happens mathematically?
|
[
" There is a (very slightly greater than) 50% chance this process terminates. Indeed, no matter how many coins you add because of tails, there is always at least a 50% chance the process terminates. The process terminates with probability 1 if and only if a tails results in the addition of either 0 or 1 new coins.",
" This type of problem is called a ",
". Classically, a branching process models a population in which offspring in one generation is produced from the previous generation with some probability distribution. These models are usually simplified to make the problems much more tractable. For instance, although the analogy of reproduction is useful, we assume that the individuals can reproduce asexually and we are really only interested in the distribution of direct successors to a given individual.",
"In your particular problem, in the language of a branching process, we would say the following:",
"p",
" = probability of an individual having 0 direct successors = 1/2 (i.e., probability of the coin flipping heads)",
"p",
" = probability of an individual having 101 direct successors = 1/2 (i.e., probability of the coin flipping tails)",
"p",
" = 0 otherwise (because a coin has either 0 or 101 successors only)",
"The reason a flip of tails gives 101 successors is that the coin itself is not removed (1 sucessor) and 100 new coins are added (100 more successors). The reason a flip of heads gives 0 successors is that the coin itself is removed (i.e., the coin \"dies\").",
"If X",
" = # of individuals in generation ",
", we are primarily interested in the ",
":",
"p = lim P(X",
" = 0) as n --> infinity",
"In the context of your question, the extinction probability is the probabilty that the process terminates. You can read all of the details of how to solve this problem online. This is a standard problem in a graduate or advanced undergraduate course on probability or stochastic processes. The central object of interest is the probability generating function",
"G(z) = p",
" + p",
"z + p",
"z",
" + ... + p",
"z",
" + ...",
"In our problem, the generating function is",
"G(z) = (1/2)(1 + z",
")",
"The extinction probability is found by solving the equation G(z) = z. (The proof of this statement uses one of my favorite theorems in all of applied mathematics, the ",
". If z",
" denotes the probability of extinction of a particular genealogical line at or before generation ",
", then G(z",
") = z",
". Hence the extinction probability is given by taking the limit of z",
" as ",
" --> infinity. The contraction mapping theorem shows that this limit always exists and is must necessarily solve the equation G(z) = z.)",
"Note that since p",
"+p",
"+p",
"+... = 1, it is always the case that G(1) = 1. So there are exactly two cases:",
"(Note that if p",
" = 0, then it is always the case that G(0) = 0, in which case the extinction probability is 0. This makes sense since the equation p",
" = 0 means that every individual always has at least one successor. So extinction is not only almost surely never going to happen, it's actually impossible.)",
"Okay, so what about our case? We are in the first case: there is a root of G(z) = z between 0 and 1. The root is approximately z = 1/2 (to many decimal places). This can be seen in a handwavy manner: since 101 is very large, (1/2)",
" is extremely small. So the expression \"G(1/2) = 1/2\" reads \"1/2 + small = 1/2\". So there is a root near z = 1/2. You can use the intermediate value theorem and/or mean value theorem to prove that there is a root to G(z) = z just beyond z = 1/2.",
"So there is about a 50% chance of extinction.",
"Is that surprising to you? Maybe. Even though it's easy to see it's possible for the process to terminate, getting even 1 tails increases the number of coins so much. So it gets harder and harder to go extinct as the process continues. In fact, let's modify the problem slightly. Instead of adding 100 coins, let's say you add ",
" coins where ",
" ≥ 0. Then the generating function is",
"G(z) = (1/2)(1 + z",
")",
"With a little bit of work, you can show the following:",
"G(z) = z has no solution between 0 and 1 if N = 0 or N = 1",
"G(z) = z always has a solution between 1/2 and 1 if N ≥ 2",
"This means the following:",
"If a result of tails means you add either 0 or 1 new coin, the probability of extinction is 1.",
"If a result of tails means add at least 2 coins, there is a greater than 50% probability of extinction.",
"No matter how many new coins you add because of a tails, there is ",
" a probability of at least 50% of extinction.",
"In fact, if you study branching processes in general you will find that there are only two possibilities: either the population dies out or it survives and the population becomes arbitrarily large. That is, the population either goes to 0 or to infinity. There is no stable finite population somewhere in the middle.",
"You can also show that the probability of extinction is 1 if and only if the individuals, on average, have ",
". (The only exception is if individuals always have exactly 1 offspring, in which case G(z) = z identically.) This is equivalent to the condition G'(1) ≤ 1. Note that in our case G(z) = (1/2)(1 + z",
"), hence G'(1) = (N+1)/2. So the probability of extinction is 1 if and only if N ≤ 1, which we already found out earlier. Note, however, that if G'(1) > 1, we only know that the extinction probability is ",
" 1; we don't know whether the extinction probability is 0 or positive.",
"Again, we only start with 1 coin. If z",
" is the probability that the population is extinct at or before generation ",
", then it is true that G(z",
") = z",
". Since we start with 1 coin, clearly z",
" = 0. To get the extinction probabilities at each generation, repeatedly apply the function ",
". For sake of definiteness, suppose each tails brings in 100 new coins.",
"z",
" = 1/2",
"z",
" = 1/2 + 3.9 x 10",
"z",
" = 1/2 + something even smaller",
"So if ",
" is rather large, the greatest risk of extinction is right in the first generation. This is no surprise since there's only 1 individual. But look at how hard it becomes to go extinct in just 1 generation. The probability of going extinct in generation 2 is about 3.9 x 10",
", an extremely small number. For future generations, the extinction probabilities are even smaller.",
"What if we only added 2 new coins at each tails? We know the extinction probability solves z = (1/2)(1+z",
"), which is about z = 0.618, or a 61.8% chance of extinction. What are the extinction probabilities at each step?",
"z",
" = 0.5",
"z",
" = 0.5625",
"z",
" = 0.5890",
"z",
" = 0.6022",
"z",
" = 0.6092",
"So, again, most of the risk is in the very first generation. But notice that the chance of going extinct in generation 2 is not ",
" tiny, it's 6.25%.",
"We already know the extinction probability of a particular genealogical line, i.e., starting with 1 coin. Each genealogical line is independent and identically distributed. So if you know the chance of extinction with 1 coin is, say, 61.8%, then the chance of extinction with a starting generation of 10 coins is (0.618)",
" = 0.0081 = 0.81%. Small, but not zero.",
"Since there is always at least a 50% probability of extinction no matter how many coins you add on a tails, there is always a ",
" probability that entire population goes extinct. For instance, if you start with ",
" coins, then the probability of extinction is at least (1/2)",
". Extinction is still guaranteed (probability 1) if you add only 0 or 1 new coin on a tails (because the individuals have no more than 1 offspring on average)."
] |
[
"This is amazing. Thanks so much for your in depth response."
] |
[
"I edited my response. What I wrote originally was for starting with 1 coin. If you start with ",
" coins though, the problem is not much harder since each starting coin has an independent and identically distributed \"genealogical line\". If there is positive probability that 1 coin goes extinct, there is positive probability that any number of coins goes extinct."
] |
[
"When was the sonic boom first identified, or predicted?"
] |
[
false
] |
Though I know things like bullwhips and canon fire create small sonic booms, as far as I can gather the noise wasn't identified for what it was at the time. Historically (as far as I can tell) the first large object to break the sound barrier and create an identifiable sonic boom as the V-2 rocket developed during WWII. My question is was the science behind the sonic boom already theorised at that point, or did the sound come as a surprise? Did they know the rocket would make a sonic boom, or was the theory being the boom developed later to explain what they heard?
|
[
"For the theory bit of your question, maybe just read ",
"this",
". Shock wave theory existed well before WWII. Shock waves aren't unique to blunt bodies; a shock wave is just a pressure disturbance that propagates faster than the local speed of sound in a given medium. Basically, they figured out shock waves around the time that the rest of thermo was figured out by a bunch of the main players in the late 1800's. I can't remember the date for the actual Rankine-Hugoniot relationships."
] |
[
"I find that quite surprising consider that by the time Yeager broke Mach 1 in 1947 sonic booms were a known phenomenon and the V-2 had proven that self-propelled objects could break the sound barrier. I remember reading that hearing sonic booms was how many in London knew a V-2 was about to or had just struck, and the V-2's distinct \"double bang\" (much like the Space Shuttle's) was well known to Londoners. ",
"Perhaps Yeager was referring to it being unknown if humans could withstand supersonic speed, although again I'd be surprised as diver-bombers had reportedly broken the sound barrier before Yeager, the difference being that was gravity assisted acceleration, not self-propelled like the X-1."
] |
[
"Recommend reading Chuck Yeager’s semi autobiography by Leo Janos. He talks about the theories everyone had at the time. One theory was that as speed went up that resonance could rise to infinity making the trip impossible. ",
"Plus that book is a really good read for a non-fiction book."
] |
[
"Why does the near side of the moon look so different to the far side?"
] |
[
false
] |
I've heard some differing opinions about why the near side is much smoother than the far side. Is there a consensus on why?
|
[
"The newest and most logical theory is that when the object that became the moon (a Mars sized protoplanet) smashed into the protoearth, it turned the protoearth into a big ball of lava, and formed a ring of lava around the earth. That ring became the moon. As the moon cooled, it did so much faster than the earth due to it's much smaller size. The radiant heat from the earth still being molten rock kept the near side of the moon significantly hotter for much longer than the far side (also, keep in mind that the moon was a bit closer than it is now), which was exposed to the vacuum of space and cooled down significantly faster. This means that the moon's vulcanism was more easily able to penetrate the earth-side of it's crust, resulting in the \"seas\" we see on the near side today. It's also why the crust of the far side is significantly thicker than the crust of the near side. This can be best illustrated by comparing it to a fire on a cold night. You feel radiant heat from a fire, keeping you warm on the side exposed to the fire, while still feeling the chill of the cold night on your back. This is the same thing the moon would have experienced from a molten earth and the cold vacuum of space, just scaled up many, many orders of magnitude."
] |
[
"So it was tidally locked from the get-go? "
] |
[
"No, but the rate at which it locks is an inverse function of distance cubed. So it would have been a fast process with the moon being so close. "
] |
[
"Does the sun have a solid(like) surface?"
] |
[
false
] |
This might seem like a stupid question, perhaps it is. But, let's say that hypothetically, we create a suit that allows us to 'stand' on the sun. Would you even be able to? Would it seem like a solid surface? Would it be more like quicksand, drowning you? Would you pass through the sun, until you are at the center? Is there a point where you would encounter something hard that you as a person would consider ground, whatever material it may be?
|
[
"Before anyone goes mocking this question, it's actually very clever. Let me explain.",
"The sun is fluid, all the way through, even if that fluid is very different than any you might be used to on earth. It's a plasma, meaning that the electrons are separated from the nuclei (though the level of ionization varies with temperature and depth). This traps light, specifically photons, which bounce back and forth between charged particles. ",
"The deeper you go, the denser this plasma gets, as it gets compressed by all the weight on top of it. The outer most layers of the sun that you see, 'the photosphere', is just the part where this plasma has such a low density that photons can escape from it. But it's actually a layer about 300 km thick, because the average distance a photon can travel here before bumping into a charged particle is a few 100 km. This means they escape, shining off into the solar system. This does a good job of giving the sun an apparent 'surface,' but it is by no means solid, and the sun extends well above the photosphere.",
"So if you were invincible, impervious to the incredible heat of the sun, what would happen if you tried to stand here? Well, you'd fall like a rock. The density of plasma in the photosphere is far less than the density of earth's atmosphere- you'd fall as if there's almost no drag. It would be like freefall- very, very hot freefall.",
"So would you ever stop falling? Yes! Why? Bouyancy, from your relative density. Denser things sink, like rocks in water, but less dense things float, like helium balloons in air. And remember, the sun gets denser as you go down. The core is a hundred times denser than you, so if I tried to put you there, you'd float up. Wherever you start, you'd eventually stop when you reach the part of the sun that is just as dense as you, about 1 g/cm",
". ",
"Coincidentally, that's ",
"Needless to say, I don't know how you're planning to get yourself out of this mess, but I hope you brought some spare oxygen tanks."
] |
[
"You're welcome!",
"Since we're talking about the photosphere, I want to volunteer more information which is just way too neat not to share. ",
"The photosphere looks really cool.",
" That pattern is made of 'granules' - those are the tops of convective columns carrying hot plasma like a conveyor belt to the sun's surface. The centers are where the hottest plasma wells up, which then moves outward towards the edges where it is cooler (and thus a little bit darker), where it starts to sink back down again. The picture doesn't give you a sense of scale, ",
"but these granules are about the size of north America",
".",
"But that means they're only about 1000 km wide, which is far far smaller than the surface of the sun. Still, these convective cells extend deep into the sun, so the outer layer of the sun is made up of like a hundred thousand giant worm-like conveyor belts of hot gas all carrying heat to the surface.",
"Science!"
] |
[
"This is a really good answer. Thank you!"
] |
[
"How does the decibel system in water compare to in air? Do humans perceive things to be louder underwater?"
] |
[
false
] |
Sperm whales are known to produce sounds of over 200 dB. Is this the same thing as 200 dB in air? Would it burst my eardrums if I was close to the whale?
|
[
"Well one of the major differences is that because dB are defined in terms of a reference sound intensity level, some baseline value, that you always need to know what that baseline is. By the most common convention the reference values used in air is 20 uPa, and the most common convention used in water is 1 uPa, which means the two aren't directly comparable just in terms of that. You would have to subtract about 26 decibels to make the underwater conventional decibel give you a value for pressure equivalent to the above water decibel convention. ",
"Getting a value for the power carrier by the sound is a bit trickier still, because that depends not only on the pressure but on how fast water molecules are moving due to the sound wave and water is substantially less compressible than air, so they don't move as far through a wavelength at the same pressure, and the sound underwater will contain less energy. "
] |
[
"Probably, but without details on how it's measured it's hard to tell, dB in this context reflects the change in pressure due to the sound, but that gets measured at a point, so you need to specify a location for this sound. Usually we use 1 meter, and if we can't get to 1 meter we make adjustments based on what it should be at 1 meter. But sound isn't produced by point sources and those adjustments assume it's a point source, for very large objects, it can sometimes give you an impossible number because you're measuring the volume inside the speaker in a spot that doesn't actually have that volume.",
"With that said, yes, if you're under water and get 200dB of sound in your ears, hearing damage is going to happen, but without knowing exactly the location that the volume is speced, we don't actually know if such a spot exists."
] |
[
"Even with the energy being lower, do you think it would be enough energy damage the hearing of a person near swimming near the whale?"
] |
[
"How large can a star become?"
] |
[
false
] |
How large can a star grow (if they grow in size at all) before it collapses due to its own gravity?
|
[
"Around ",
"150 times the mass of the Sun",
" at the current age of the universe. This is based on the amount of luminosity can be transported through the star before the radiation pressure would overcome gravity (if the radiation pressure is higher than the gravitational force then the star will undergo mass loss). Stars above this mass can not form by stellar formation pathways and have to be the result of mergers.",
"In the past stars may have got to 300 or more times the mass of the Sun. This would be at a time when there were little to no elements heavier than lithium in the universe."
] |
[
"Sun will end fusion at the stage of producing carbon (and less of other similar mass elements like oxygen).",
"Stars living billion+ years don't go supernova.",
"Supernova explosion takes much longer than a second."
] |
[
"The collapse happens in seconds, the following “explosion” as the matter bounces out again takes hours."
] |
[
"What is the mechanism for energy released by a black hole merger?"
] |
[
false
] |
I've heard that when two black holes merge there is an incredible amount of energy released. And that this energy which is released is often equivalent to the mass energy of a few solar masses at least, in the case of the merger first detected by LIGO. As I understand, nothing can escape from within the Event Horizon of a black hole but somehow something must get out because there is energy released when two black holes merge together. My question is, how can energy be released by to merging black holes? Is this some form of Hawking radiation? What is the mechanism that allows for this release of energy? Bonus Q: how is it that merging black holes which are orbiting each other can have their orbits decay? I would expect, since the mass inside is a singularity, that tidal forces, which are usually the mechanism for bleeding off orbital energy, wouldn't really make sense between two point masses.
|
[
"The energy is lost as gravitational waves. That's what LIGO detects, and then using the energy measured at the detectors and the distance to the source of the gravitational waves, they can calculate how much total energy was given off by the source. The energy does not come out of the black holes themselves, but from the orbital energy of the system. As this energy is lost, the orbits decay until they merge. Every system with an accelerating mass emits gravitational waves, but they are only measurable for extreme situations like binary black holes or neutron stars. The earth-sun system loses energy to gravitational waves at a rate of about 200 Watts, but this is insignificant compared to the 10",
" Joules of energy contained in the system and won't cause the orbit to decay significantly within the lifespan of our solar system."
] |
[
"\"Analysis of the signal along with the inferred redshift suggested that it was produced by the merger of two black holes with masses of 35+5\n−3 times and 30+3\n−4times the mass of the Sun (in the source frame), resulting in a post-merger black hole of 62+4\n−3 solar masses.[1]:6 The mass–energyof the missing 3.0±0.5 solar masses was radiated away in the form of gravitational waves.\"",
"https://en.m.wikipedia.org/wiki/First_observation_of_gravitational_waves"
] |
[
"I read somewhere that the mass of the new black hole that was produced was significantly less than the two original masses combined, meaning they lost energy as gravitational waves. Was that wrong then?"
] |
[
"Is there an agreed-upon, independent measure of how strong a password is, regarding crackability? Every website thinks differently about how strong my passwords are. (Not sure if right subreddit but it's CS so I hope yes)"
] |
[
false
] | null |
[
"It depends on whether your password is ",
". ",
", then the calculation is just",
"number of characters * log base 2 (the number of possible characters that we can choose from). This gives us the workfactor for cracking a password in bits. So a 10 character long ",
" alphanumeric password would have a workfactor of:",
"10 * log base 2 (62) = 59.54 bits of entropy. Which would mean that on average, about 2",
" trials would be needed to break this. ",
"For passwords that are ",
" chosen randomly, this is harder to compute, and depends on the characteristics of the language that the password is generated from. The rule of thumb is that for English passwords, the first character has about 4 bits of entropy, the second has about 2, and each subsequent one has 1 bit or so. The amount of entropy per character in English is about 1 bit when we're looking at regular, uncompressed data. "
] |
[
"The basic question to ask is \"how many possible passwords are there\" under the rules that are required by a website. The more possible passwords, the less guessable any one password is. ",
"I know that ",
"/r/askscience",
" doesn't like comics and stuff, but the xkcd \"",
"correct horse battery staple",
"\" comic actually does a good job of explaining this. ",
"The traditional measures that websites use of \"password strength\" are pretty terrible: eight characters, use of caps, numbers, special characters, etc.. These don't add ",
" entropy to your password, whereas going from a dictionary of about 100-200 possible characters to tens of thousands of real words would increase strength immensely. ",
"The irony is that \"correct horse battery staple\" would not be allowed by most websites, but Horse12! (which is much weaker) would be. "
] |
[
"I highly recommend reading this article: ",
"http://arstechnica.com/security/2013/05/how-crackers-make-minced-meat-out-of-your-passwords/",
"That will show you exactly how crackers actually attempt to crack passwords. The strength-estimators you typically say are generally based on difficulty of brute-forcing it, but unless it's 6 characters or less, no hacker really does a pure brute force attack. Here's a paragraph towards the end talking about what they got:",
"What was remarkable about all three cracking sessions were the types of plains that got revealed. They included passcodes such as \"k1araj0hns0n,\" \"Sh1a-labe0uf,\" \"Apr!l221973,\" \"Qbesancon321,\" \"DG091101%,\" \"@Yourmom69,\" \"ilovetofunot,\" \"windermere2313,\" \"tmdmmj17,\" and \"BandGeek2014.\" Also included in the list: \"all of the lights\" (yes, spaces are allowed on many sites), \"i hate hackers,\" \"allineedislove,\" \"ilovemySister31,\" \"iloveyousomuch,\" \"Philippians4:13,\" \"Philippians4:6-7,\" and \"qeadzcwrsfxv1331.\" \"gonefishing1125\" was another password Steube saw appear on his computer screen. Seconds after it was cracked, he noted, \"You won't ever find it using brute force.\""
] |
[
"Friction and car acceleration"
] |
[
false
] |
The other day I was thinking of a test problem from high school physics from over 10 years ago. It was an acceleration/velocity/distance/time question that hinged on the fact that the force causing a car to accelerate is friction on the wheels in the direction of the acceleration, which is equal to mu*Fn. My question here is an extension of this. The sole acceleration force is friction and since the weight of the car is constant, the acceleration would simply be a function of the coefficient of friction. I always thought of the coefficient of friction to be a constant that depends on the inherent properties of the two materials (to a first order estimation, let's not get too picky here). But in this situation it seems to be variable, dependent on the acceleration as well. Therefore, mu would theoretically be able to take on any value between 0 and the max (ignoring rolling friction), for a given road surface and tire material. How do I resolve this seeming contradiction? Is there an issue of slip where only the max acceleration force occurs with no slip and any acceleration less than that involves slip? It seems weird thinking that there is always slip occurring at any acceleration less than "flooring the car" type of acceleration.
|
[
"For static friction the friction force is ",
" to mu",
" x Fn, it is always less than that. Once the friciton force passes that limit, slip begins and the friction force will be equal to mu",
" x Fn. ",
"Edit: think about pushing a big box, the lateral force is equal to your exertion but it doesn't slip. Now, when your push exceeds that limit, it begins to slip and the acceleration will be equal to [F - (mu",
" x Fn)]/m "
] |
[
"aha! yes that's it. your comment made me remember the oft-overlooked (at least for me) relationship that friction is not equal to but is <= mu*Fn.",
"Thanks"
] |
[
"The friction force is a result of the normal force on the tires, and during acceleration the centre of gravity of the vehicle shifts towards the rear of the vehicle (due to inertia) and changes the normal force on each tire. This works in your favour if you have a rear wheel drive vehicle, but if you have a front wheel drive car then this reduces the amount of torque the wheels can use to propel the car.",
"There's also the aerodynamic drag force, which assuming no wind starts at zero when the car is at rest and builds exponentially as the car increases in speed."
] |
[
"What causes this effect? Is it chromastrobic light?"
] |
[
false
] |
At the link below, you can see at the 10th normal mode of an oscillating string, you get color production if the light from a projector shines on the string. Does this have to do with how the projector creates white light, as well as the frequencies of the string and refresh rate of the projector being close? Is this the same thing that Paul Friedlander uses in his chromastrobic light sculptures? An explanation would be fantastic. :) Thank you.
|
[
"I believe it does have to do with the refresh rate on the projector. If you go frame by frame from the 8th second to the 9th second of the video, you can see that the string bounces back and forth slightly about 6 times, so its fundamental frequency is roughly 6 hz, so the 10th mode we are seeing is near to 60 hz. This is a common refresh rate for projectors, as is 120 hz (not sure which this is).",
"The projector and string are a small fraction of a hz off of eachother and we are seeing a beat phenomena. The projector probably displays its red, blue, and green right after eachother, so at different phase differences we see different colors on the center of the string. We tend to see the reds, greens, and blues alternating between the outside and inside of the string waves as each beat progresses. The patterns are symmetric so probably the projector is 120 hz.",
"The reason this all works is that the string spends a small fraction of each 60th of a second in the center area, and during that time only one color is actually being projected by the projector. Notice that the extrema of the waves (where the string spends a higher fraction of the time) tend to mostly be white or at least magenta/cyan/yellow (2 colors)"
] |
[
"Here's my best guess. I'm only a physics student: Longitudinal waves cause compression and decompression in the medium they travel through. The pressure of the air around the string will change as it oscillates. These changes in air pressure can change the light's refractive index, changing how we see it.",
"This is definitely not the case. First of all, the air flow would be turbulent near the string, so you would not get such smooth transitions or forms. Secondly, this explanation does not explain the time variance of the colors (that string is oscillating dozens of times per second, and yet the colors only appear to cycle on the order of a second or so - a very good clue that this is, indeed, a beat phenomenon related to the frequency of oscillation and of the projector). Third, there is no way that the string is causing sufficient pressure differences to cause the air to behave so visibly like a prism on such a small scale."
] |
[
"Very cool. I don't think this has to do with the refresh rate on a projector, nor do I think it's exactly the same as Paul Friedlander's chromastrobic light. Friedlander describes chromastrobic light as \"light that changes color faster than the eye can see,\" leading to his moving light sculptures to appear as though they're a collection of unique images strobing on and off.",
"Here's my best guess. I'm only a physics student: \nLongitudinal waves cause compression and decompression in the medium they travel through. The pressure of the air around the string will change as it oscillates. These changes in air pressure can change the light's refractive index, changing how we see it.",
"If anyone could confirm or deny this that would be great. It's hard to find anything about this online."
] |
[
"How is destruction of a nuclear explosion filmed?"
] |
[
false
] | null |
[
"There was a special type of film created for the intense exposures; a type of film that only the intense radiation from a nuclear test could expose. Also the ",
"Rapatronic Camera",
" was developed for ridiculously high shutter speeds."
] |
[
"There was an earlier discussion about this. Here's my response copied over:",
"I don't have a source available, but i remember reading that some cameras are shielded by huge wedged-shaped concrete blocks. The camera points sideways and a mirror allows the scene in front to be recorded. When the pressure wave reaches the camera the mirror may be obliterated but the concrete block in front of the camera protects it.",
"How did they get the cameras in those nuclear weapon demonstration videos to not be obliterated?"
] |
[
"couldn't you just place the camera in a Faraday cage?"
] |
[
"Is the speed of light the fastest anything can move, or is that just because we can't perceive anything that would move faster?"
] |
[
false
] | null |
[
"It's the fastest anything can move."
] |
[
"Do we know why?"
] |
[
"It’s a postulate of relativity, and we observe that relativity holds in every experiment we’ve done."
] |
[
"Could any planets in our solar system be extrasolar captures? How could we tell if they were?"
] |
[
false
] | null |
[
"The tricky part of extrasolar capture is that you have conservation of energy to deal with. If a planet that wasn't orbiting the sun was on a trajectory that brought it close by, it would have enough kinetic energy to escape the sun as well. You need to add a third body to make capture work. For example, a planet could graze by Jupiter and transfer some kinetic energy, leaving the planet trapped in an orbit and adding boosting Jupiter to a higher average distance from the Sun.",
"It is possible though, and ",
"this paper",
" explores the topic in more depth. They talk about clusters of stars that might have some extrasolar planets floating around. Capturing an extrasolar planet would probably leave you with a higher eccentricity and an orbit in a different plane from the other planets, so those features would be clues that capture happened. But a planet that formed around our sun could be sent into a funny orbit by interacting with another planet as well, so it would be tough to prove how a given planet was formed.",
"The 8 planets in our solar system have pretty low eccentricities and they line up in a nice plane, so they were most likely all formed from the same protoplanetary disk. An extrasolar capture would have to graze an existing planet just right to settle into one of those orbits, and even then it would have an orbit that was too close for comfort with at least one other planet."
] |
[
"Setting aside the obvious eccentricity/velocity arguments which were already well covered by ",
"/u/AugustusFink-nottle",
", one way of testing might be through rare earth abundance patterns. These tend to be relatively uniform for the bulk of materials within the solar system and are tied to the average composition of the dust cloud from whiwh our solar system accreted. This is exemplified by the relatively constant REE patterns found in météorites, notably chondrites, and in the Earths primitive mantle. ",
"Where it gets complicated is if the planet in question is ageologically active and geological processe have differentially remobilised the REES, as happens on Earth. Inasmuch as you could get a bulk view of the REE pattern of the whole planet, through sampling of a large collection of samples for instance, you might perhaps be able to test whether a given celestial body is of extra-solar derivation or not."
] |
[
"There is a hypothesis that this may be true of Uranus due to the odd tilt of its rotation. As far as I know, this is not the mainstream view of Uranus. But, it is a possibility.",
"https://www.quora.com/Is-it-possible-Uranus-used-to-be-a-rogue-planet"
] |
[
"Is there a limit to how fast an airplane could go for stable, long distance flights?"
] |
[
false
] |
Theoretically, How fast could an airplane consistently go over a long trip (thousands of miles)? The current fastest plane is a Cessna Citation X which can go a max of like 720 mph. How much faster could we safely go then that?
|
[
"The X-43 achieved a speed of Mach 9.6 (11.850 km/h) for a few seconds and remains as the fastest aircraft ever.",
"I can't tell for certain the fastest speed that could be achieved by a plane but I believe the limits to fly faster come from three main numbers: specific impulse (Isp), skin temperature and drag coefficient (Cd).",
"Isp tells you how much thrust you can produce by burning a certain amount (given in mass flow or weight flow) of fuel per second. Turbofans propelling commercial aircraft have Isp in the orders of 10000 s - as they only carry the fuel and the oxidizer is freely available in the atmosphere. Rockets on the other hand need to carry both and have Isp in the order of 100 s (350-400s for most rockets). Turbofans can't operate at speeds much higher than the speed of sound, say Mach 3. Beyond Mach 3 you need Ramjets (up to Mach 6) or Scramjets (beyond Mach 6), which don't rely on movable parts to produce thrust. The problem is that they have a smaller Isp (~1000s) and that number tends to decrease with an increase in Mach number. Some missiles are propelled by Ramjets but Scramjets are a relatively new field. So the first problem is propulsion.",
"Temperature is a straightforward number. The faster you fly the hotter you get. The Concorde speed was limited by its Al alloys which were limited to ~125 ºC. The SR-71 had to be built with Titanium alloys to withstand continuum temperatures of 300 to 400 celsius degree. The air gets hotter because it is slowed down (in the airplane frame of reference) and the increase of temperature is proportional to the mach number squared (isentropic flow). At higher mach numbers, shock waves appear and the flow is no longer isentropic. ",
"Better explained",
". A high degree of sweepback would be needed to reduce the temperatures at high Mach numbers. Overall this a problem of materials and new alloys/ceramics need to be invented to fly at high Mach numbers for so long (hours).",
"The last one is a problem of aerodynamics: the drag coefficient and the Lift to Drag ratio (L/D). Concorde had a L/D ratio of 7,5 and the Space Shuttle had a L/D of 4,5. That is why the Space Shuttle would approach the runway at such a steep angle and Concorde had a range of ~7000 km. A L/D ratio is important because of the ",
"Breguet Range Equation",
": a small L/D penalizes range albeit that could be offset by the high speed. The design would probably resemble a delta wing or a lifting body.",
"Anyway those are just the most important aspects. Other issues would need to be adressed such as handling issues, fuel, very turbulent boundary layers and reusability (I am not sure that such a vehicle would be able to fly more than a hundred hours)."
] |
[
"Turbofans propelling commercial aircraft have Isp in the orders of 10000 s - as they only carry the fuel and the oxidizer is freely available in the atmosphere.",
"Is that only because of the oxidizer, or does free reaction mass noticeably help too?"
] |
[
"Hydrogen-oxygen reaction needs 8 g of oxygen for every gram of hydrogen, while kerosene-air needs 16 g of air (21% oxygen) for every gram of kerosen. So the short answer is that turbofans greatly benefit from the free air available as compared to rockets. ",
"But the complete answer should take into account the fact that turbofans don't burn all the air that comes through the fan. The ratio of air that pass through the combustion chamber and the air that doesn't is known as bypass ratio (BPR). Most modern turbofans have BPR close to 10 so a lot of the air goes unburned. This air is propelled by a large fan driven by the turbines. So there are two sources of thrust: the air-fuel that is burned and the air that is not.\nHere are some numbers I came across:",
"This greatly increases the Isp because thrust is mass flow times the exhaust velocity and power is proportional to mass flow times the exhaust velocity squared. Turbofans move a large amount of air at small speed, consuming less power and using less fuel.",
"So I dare to say turbojets are 15 to 20 times more efficient than rockets because they don't carry oxidizers and modern turbofans are 2 to 2,5 times more efficient that turbojets because of the BPR."
] |
[
"Why do we sometimes hear the same repeating sound as alternating between a higher and lower note? (tick tock of a clock) (click clack of high heels)"
] |
[
false
] | null |
[
"Sometimes, they are not the same sounds. For example, variations in the ruling of the floor or your walking style can cause the heels of your shoes to click differently.",
"As for the familiar tick-tock of a grandfather clock, that is caused by a two-step motion of the pendulum inside it."
] |
[
"I know what you're talking about. A big part of it is that the mechanical elements that produce the sound is not 100% consistent. There will always be some dominant frequency that your brain is more likely to pick up on. That's where the psychology side comes in: \"more likely.\" ",
"You may have noticed that you can sort of get such sounds to \"play a tune\" in your head. This is simply a case of aural filtering - your brain is selecting which frequencies to focus on so it will pick them up slightly clearer and therefore more dominant. This is The Same Thing Our Brain Does When Focusing On A Conversation In A Crowded Room. \nAssuming that frequency isn't surpressed too much by the randomness of the mechanical event causing the sound, you can more or less make a melody from the clicks and ticktocks."
] |
[
"There is a possibility that the two sounds are not 100% equal given many variables with say heals hitting the ground and pavement may be different. However, hearing a tick-tock is a psychological phenomenon due to grouping and attention. Humans put in accents to sounds that don't occur in the actual stimulus. ",
"If you want to learn more below are some papers on the subject.",
"\"Accents in Equitone Sequences\" by Povel and Okkerman, 1981",
"Link: \n",
"http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.296.3719&rep=rep1&type=pdf",
"\"The Ticktock of our Internal Clock- direct brain evidence of subjective accents in isochronous sequences\" by Brochard, Abecasis, Potter, Ragot, and Drake, 2003",
"Link:\n",
"https://www.researchgate.net/profile/Renaud_Brochard/publication/10708403_The_Ticktock_of_Our_Internal_Clock_Direct_Brain_Evidence_of_Subjective_Accents_in_Isochronous_Sequences/links/0fcfd50eaab31b68e1000000.pdf"
] |
[
"Does brushing your tongue harm your taste buds?"
] |
[
false
] | null |
[
"Dentist here.",
"To answer your question about tongue brushing and potential damage to our taste receptors. Yes and No.",
"Let's start with how it would be a Yes, and work in to the final answer of No:",
"If you are using a hard bristled toothbrush, highly corrosive toothpaste (usually whitening toothpaste or something with a thick paste of baking powder mixture), then Yes, you can erode the taste buds on your tongue away.",
"But is this a permanent change to your tongue?",
"No. And to explain this, I'm going to explain the make-up of our tongue's dorsal surface (the part that contains our \"taste buds\").",
"Our tongue is a muscular instrument which is used to not only taste food, but also to recognize poisons/toxins (partially through taste), to determine the quality of food by texture, and to help you not only hold on to your food during mastication, but to also chew and swallow your food by acting as a muscular plunge. ",
"It contains specialized structures called \"papillae\" which are outcroppings of the epithelium making up the tongue and are often confused with just \"taste buds.\" There are several type of papillae, and each has their own function.",
"The most numerous type of papilla is the filiform papilla. It is shaped like a little finger that comes off the surface of your tongue and actually does not really involve itself with taste sensation. They are the the part of your tongue that allows you to hold on to food and determine texture. They are also what make your tongue feel rough when it is dry. If they grow too long or their growth is altered by certain anti-biotics, peroxide-based chemicals, or unusual chemical reactions, then they act negatively to hold on to bacteria or fungus to give you a minor case of something called \"hairy tongue.\" I can explain that more if you like, but it's a bit outside the realm of your question. Overall, if you brush too hard, you're more likely to scrape some of these guys away, so your taste won't really be affected directly. What will be affected is how well your tongue can hold on to food and water (which is absolutely necessary to \"taste\") so your taste will be indirectly involved. As a neat experiment, try completely drying your tongue off with a dry towel and then put some sugar or salt on it. If you dried it off thoroughly, you won't be able to taste either!",
"The taste buds actually involved in taste are the fungiform papillae. They are little, mushroom-shaped bumps (as their name suggests) on your tongue interspersed throughout. Their histologic structure actually shows that they're like little caverns with centralized \"bulbs\" that are connected to the cranial nerves in charge of distributing taste reception. These are very tough to brush away or damage with toothpaste or a toothbrush because of how they are formed and shaped. So brushing them will not affect taste. (This is how we overall come to the answer of \"No\").",
"The other types of taste buds are a bit more boring and are located on the sides and back of the tongue. Brushing them would be very hard to do and even if you did, nothing would happen. If you're interested in learning about them further, feel free to read about the Circumvallate Papillae and the Foliate Papillae. They are also involved with taste, but act mostly as a defensive feature where something very bitter or toxic tasting will be ejected just prior to being swallowed. I'm simplifying a bit, but it's close enough to reality to get the point :)",
"Now, let's say that you did somehow manage to rub off the top layer of your tongue and damage the papillae somewhat. Well, in a little over a week, that'll clear right up as their average turnover is 10-14 days :)",
"So, now you can see how the answer is both a Yes and No, depending on how you want to perceive it.",
"But because I really doubt you're going to grind away the top layer of your tongue, rest easy, my friend, and continue to brush your tongue, your teeth, and even the roof of your mouth! Keep your mouth clean and take care of it, because we only get one!",
"Also, mandatory dentist reminder: Floss!",
"EDIT: Thanks for the Gold! That was unexpected! :D"
] |
[
"In actuality it may improve taste perception.",
"http://onlinelibrary.wiley.com/doi/10.1111/j.0303-6979.2004.00507.x/full",
"However, it may be different for some tastes vs. others (e.g., NaCl vs. citric).",
"1",
"2"
] |
[
"Ok, that's funny. I guess I should have quoted what you said in my reply, I thought the deletes were done."
] |
[
"In the early stages of the Big Bang (Quark-lepton era) why was there slightly more matter than antimatter?"
] |
[
false
] | null |
[
"We have some hypotheses, but we don't know.",
"One thing we do know is that matter and antimatter are not perfectly symmetric -- in collider experiments we have been able to start with equal amounts and end up with unequal amounts.",
"Problem is, all of the known symmetry-violating processes combined are not able to explain the full abundance. At most they explain why a galaxy or two of matter was produced more than antimatter, not an entire observable universe's worth.",
"Typical hypotheses tend to be along the lines of \"there are other unknown processes like the known ones which existed in the early universe\" and we have some models of such hypothetical processes (generally called \"baryogenesis\" hypotheses) but we don't actually know of any such processes; there may even be multilple unknown processes responsible. It is an active area of research!",
"Hope that helps."
] |
[
"If you can definitively answer this, there's a Nobel Prize with your name on it.",
"The best hypothesis we have right now is merely \"something to do with the weak force\" because its the only one that ",
"treats matter and antimatter differently",
". However, the known asymmetry isn't large enough to explain the overabundance of matter vs antimatter.",
"Side note: that overabundance is actually rather small. If you look at the amount of matter remaining, vs the amount of light radiation (produced by annihilating matter/antimatter) there was only an excess of about one part in a billion of matter. That is for every 1,000,000,000 particles of antimatter, there were 1,000,000,001 particles of matter produced. Most of them annihilated, and the tiny excess left over accounts for all of the matter in the universe."
] |
[
"That's possible sure, but a hypothesis of \"there actually are equal amounts of matter and antimatter, it's just in an area we can't observe\" isn't falsifiable. There'd be no way to differentiate between our understanding being wrong, and our understanding being correct "
] |
[
"When an animal is eaten whole, how does it actually die? Suffocation? Digestive acid?"
] |
[
false
] | null |
[
"It varies depending on the species and what their specific eating mechanism is. But generally speaking if the animal is swallowed whole while still alive it will suffocate first and then be broken down by the digestive system. "
] |
[
"Suffocation doesn't kill you by keeping you from breathing air, it kills you by keeping you from reoxygenating your blood which starves your brain of oxygen. Fish still need oxygen, they just get it through a different process than breathing. "
] |
[
"Good thing we cleared up the whole 'eat your fish and drink its bowl' thing"
] |
[
"Are neutrinos an exception to the higgs field?"
] |
[
false
] |
I was reading this reddit topic about the higgs boson, and i didnt understand why it stated that a neutrino doesnt care about the higgs field, as far as i know in order to have a mass you must interact with the higgs field!? Is the thread wrong or theres something i dont understand? Thread:
|
[
"In order to give mass to fermions, the Higgs interaction requires there to be both right-handed and left-handed versions of a particle.",
"Neutrinos are only known to interact with the weak force. The weak force only couples to left-handed fermions and right-handed antifermions.",
"As such, right-handed neutrinos and left-handed antineutrinos have never been observed.",
"They might exist as ",
"sterile neutrinos",
", or it might be the case that neutrinos are their own antiparticle (",
"Majorana fermions",
") so a right-handed neutrino is just an antineutrino."
] |
[
"The post you quoted is telling you about the Standard Model as it was developed when people thought neutrinos were massless. In the SM, neutrinos do not couple directly to the Higgs. However, following the discovery of the neutrino masses, we now have a few proposed models for their mass, with all of the major ones involving coupling to the Higgs in some way. I don't believe there's enough experimental data to definitively say which model is correct. "
] |
[
"As mofo69extreme said, neutrino mass is an emerging field of understanding. It arises as a consequence of the various observations of neutrino oscillations, such as the most recent ",
"T2K",
" run."
] |
[
"After astronauts leave Earth’s gravity, what stops them from going towards the sun? If the sub can hold planets in orbit, would it not be able to pull in smaller objects?"
] |
[
false
] | null |
[
"Yeah they’re in free fall"
] |
[
"They don’t leave earths gravity. They can’t go directly towards the sun because they are going incredibly fast around the sun, it takes a lot of energy to decelerate to be able to fall in"
] |
[
"So when the say ZeroG there is still some gravity taking place?"
] |
[
"When and why did the English accent in early America fade away, and the American accents come about?"
] |
[
false
] | null |
[
"English as it was spoken during colonial times isn't the same as it is spoken now in either Britain or America. Both populations have had their pronunciation drift over time. So Americans never lost their British accent, because they never had what we would now call a British accent to begin with.",
"You can look up \"Original Pronunciation\" (Called OP English) to get an idea of how pronunciation has changed over time since the early 17th century. There are people who do Shakespeare productions using reconstructed OP to recreate what Shakespeare's plays would have originally sounded like.",
"P.S. I should have linked ",
"this",
" from the beginning.",
"P.P.S. ",
"Here",
" is another video talking about a modern accent that many think is close to what colonial-era English sounded like."
] |
[
"That's a common factoid, but it's not really true. The first problem is that there are many dialects in the British Isles and North America that are much more conservative than either standard British English (called Received Pronunciation) or standard American English (called General American). Both standards have conservative features and innovations. For example, General American hasn't merged ",
" and ",
"— this is usually the sole basis for the claim that it's more original—but Received Pronunciation hasn't merged ",
" and ",
" or ",
", ",
" and ",
" or ",
" and ",
"; RP also doesn't rhyme ",
" and ",
" or ",
" and ",
", which is original. Not to mention Irish and Scottish English distinguish the vowels in ",
", ",
" and ",
". GA has unrounded the o's of ",
" and ",
"; RP has broadened the a's of ",
" and ",
". GA has retained ",
" and ",
" (for ",
"); RP has retained ",
" and ",
". I'd say, if you go feature by feature, RP is more conservative than GA. While some New England and Old South dialects are more conservative than General American, various dialects throughout the British Isles are more conservative than Received Pronunciation or any American dialect.",
"Here are some sources:",
"https://en.wikipedia.org/wiki/Phonological_history_of_English",
"https://en.wikipedia.org/wiki/Phonological_history_of_English_vowels",
"https://en.wikipedia.org/wiki/Phonological_history_of_English_consonants",
"https://en.wikipedia.org/wiki/History_of_English"
] |
[
"There never was a single English accent and still isn't. America was populated firstly by various English accents and then various non-English accents which grew over time regionally depending on the mix of people. Most English accents have remained relatively similar in their respective regions but again, movement of people and the advent of TV and radio has affected all accents, some to a very small degree and some to a large degree. The 'English' accent you probably think of is called Received Pronunciation and is newer than the US is. This isn't a 'natural' accent and is onpy spoken by people of a particular schooling and isn't very common. "
] |
[
"Biologist of Reddit, I need a word."
] |
[
false
] |
[deleted]
|
[
"It's death in every microbiology text have laying around my apartment. "
] |
[
"I looked at all my textbooks and they all say death as well. I was so sure there was a different word for it."
] |
[
"Is senescence what you're looking for?"
] |
[
"In terms of physics, what is common between the same notes in different octaves?"
] |
[
false
] |
In terms of physics, notes are defined by their frequencies, right? The higher frequency is, the higher the note is. So if we're going through all notes, do re mi..., at some point they repeat. So why, for instance, the note "do" from the first and second octave sound, so-called, in unison, whilst they have different frequencies? Also, why there are excactly seven notes?
|
[
"If you look at the frequency of two notes that are an octave apart, one will be twice the other. This is significant because a note is not actually a single frequency; it has a *fundamental* frequency, which is what we think of as it's frequency, but it also has a ",
"series of overtones",
". And the first overtone is ",
"double the fundamental",
") frequency, which means that when you play a note and the octave above it, the other note sounds consonant because it's fundamental is already in the overtones of the original note.",
"",
"The decision for 8 (not 7) notes in the major scale is an arbitrary historical decision. There are scales with more notes, and scales with less notes. Even the 12 note per octave system that modern pianos use is arbitrary; there are ",
"15",
" and ",
"17",
" (and ",
"more",
"!) note scales."
] |
[
"I wouldn't say it's entirely arbitrary. 8 notes per scale is a good number to allow for the thirds and fifths for European major chord harmonics (not that it's the only number that would work, just that that puts a few restrictions on regarding what notes are expected to be available as part of a scale.)",
"Excellent explanation though."
] |
[
"Relative pitch is logarithmic. ",
"To go up by an octave, multiply by 2. To go up by a perfect fifth, multiply by 1.5. To go up by 1 semitone, multiply by 2"
] |
[
"What causes an archaeological site to become buried, are the buildings sinking over time or the land elevation increasing?"
] |
[
false
] | null |
[
"Sedimentation mostly. Wind, rain, vegetation (and its decay) causes a build up of sand and dirt that engulfs the area, so in a sense, land elevation is increasing",
"A good modern example of this is ",
"Kolmanskop",
", which is an abandoned diamond mining hub in Namibia that is being quickly buried by the desert.",
"There is probably also a certain amount of sinking, if the substructure is unstable, but it's mostly building up."
] |
[
"Not really, erosion is also at work, plus gravity compresses the layers beneath us. Sandy structures are good examples of this process happening on a human time scale, because they build up and erode quickly. For example, the Island of Nantucket is losing its northern coast to erosion, but it's gaining on its southern coast thanks to sediment build up.",
"Also keep in mind, archaeologists don't generally find whole buildings so much as foundations, except in cases like Pompeii where the whole city was buried in a cataclysmic event, usually buildings deteriorate and collapse."
] |
[
"Good answer from ",
"/u/Critical_Liz",
",",
"I'll just add a little bit to the effect that the soil underlying any given object is far from being a static environment, but rather a constantly shifting dynamic system. This was pointed out by none other than Charles Darwin himself in one of his lesser known works (",
"The Formation of Vegetable Mould through the Action of Worms",
"). Darwin documented the rate at which bioturbation shuffled the soil around, and over, historical artifacts such as fallen stones at Stonehenge and various other artifacts."
] |
[
"Why do bioluminescent organisms seem to only give off light in the yellow to green wavelength? Why are there no red or blue or violet lights produced by such organisms?"
] |
[
false
] | null |
[
"A Google image search for \"bioluminescence\" shows lots of blue and red."
] |
[
"Animals that bioluminesce usually do so for a reason. To find mates, to lure in potential prey, as a warning, and so on. Most ocean-going animals actually give off blue light. This is because, due to the properties of water, blue light is the last wavelength of light to be filtered out of water. In layman's terms, blue light travels the farthest in water, which is why deep water appears blue. So, most ocean-going animals that bioluminesce do so because they WANT to be seen. So, the most efficient color of light to use if you want to be seen is the wavelength that can be seen from the farthest away. A lot of land-living animals that glow, like fireflies, are more in the green area because those are the colors that light-adjusted eyes tend to see best. ",
"There is actually one particularly awesome species of fish that does produce red light in the deep ocean. Red light, because of it's wavelength, is the first color to be filtered out. Almost every animal with eyes in the deep that we've found does not even have the photoreceptors in their eyes to see red light. There's no point to be able to see what's not there. So, from a few hundred feet deep to the sea floor, there is absolutely no red light. So, many animals that make a living by hiding have developed a red coloration. There is no red light for them to reflect back so even animals with the best of eyes wouldn't see them since they don't have red photoreceptors. The cool animal of this story is called a ",
"loosejaw",
". You can see in the picture that the fish has red spots under its eyes that produce red light. It also has the ability to see the red light that it produces. So, it swims around in the dark with its red flashlights, looking for red animals to prey on. The kicker is that the prey animals can't see the red light the loosejaw is producing, so it's never aware of the danger.",
"I love nature!"
] |
[
"Happy to help :)"
] |
[
"What would an ant do if it was stranded from its colony?"
] |
[
false
] |
Could it potentially join a new one? Would it try to survive on its own?
|
[
"Not an entomologist or student of myrmecology but it's pretty easy to deduce. It will behave in line with it's standard functions. Ant farms are sold with stranded ants, typically no queen (for pest control reasons), and behave just as a colony normally would, but simply without a way to produce a new brood.",
"Basically, an Ant, by itself, will try to run a hive, by itself. It will dig tunnels, gather food, and ultimately die, all alone. See, ants don't like living with other ants unless they belong to the same family (not taxonomy, in terms of genetics).",
"Also, one of the rare few cases of an ant joining a new colony is the Argentine Ant, which being found in Japan, California and along the Mediterranean Sea, are all genetically identical. They think they're all part of the very same colony, and genetically and as far as the hydrocarbon smell goes, they are.",
"Again, I could be wrong on this, my understanding only comes from a lifetime of watching and reading on ants like crazy, I'm nowhere near good enough to be a proper entomologist. We'll just have to wait for one to come along."
] |
[
"thanks for the answer. thats interesting that it would still try to run a colony. it would be interesting to test how far or how long an ant would have to be away from the home colony before it decides to try and build a new one vs. trying to find its way back home"
] |
[
"Could it potentially join a new [colony]?",
"That's somewhat a linguistics issue.",
"If/when they can join, it's unclear to me if it'd be called a new/different colony or part of the same colony.",
"Some might then call it a large multi-queened colony, or a supercolony, or a megacolony - rather than a new colony.",
"http://en.wikipedia.org/wiki/Argentine_ant#Global_.22mega-colony.22",
"The three colonies in question were one in Europe, stretching 6,000 km (3,700 miles) along the Mediterranean coast, the \"Californian large\" colony, stretching 900 km (560 miles) along the coast of California, and a third on the west coast of Japan. ... individuals from one nest can mingle in a neighboring nest without being attacked. Thus, in most of their introduced range they form \"supercolonies\". ... Argentine ants in their native South America also co-exist with many other species of ants, and do not attain the high population densities that characterize introduced populations."
] |
[
"If we sent our most powerful nuke to the moon, could we see the explosion from earth with our naked eye?"
] |
[
false
] | null |
[
"During which phase of the moon?"
] |
[
"It'd be easy to see during new moon, less light to drown the flash out."
] |
[
"It'd be easy to see during new moon, less light to drown the flash out."
] |
[
"If all species of insects gone extinct, what would happen? How would Earth change over time?"
] |
[
false
] | null |
[
"Such hypothetical / speculative / open-ended questions are better suited for our sister-sub ",
"/r/asksciencediscussion",
". Please post there instead."
] |
[
"So, do I delete this post?"
] |
[
"Already removed"
] |
[
"When I drive fast, I find that the normal bumps of the road tend to disappear in the ride quality. Why is this?"
] |
[
false
] |
So today I drove at 180km/h (pretty fast for an old school lexus es300) and then realized that the highway i was traveling on suddenly got a lot smoother than it normally was. My conjecture is that air underneath the car is creating lift. Is this explanation correct?
|
[
"TL;DR The suspension \"catches\" the bumps with transferring them to the car at high speeds.",
"When you travel slowly over a (small) bump, your front wheel is lifted up and with it the front of your car. Then it goes down again and the same happens to your back wheel/back of the car.",
"At high enough speeds (and small enough bumps), your front wheel goes up and compresses your suspension. Due to the high speed, the suspension is released before your car can follow the movement and sitting in the car you do not feel the bump.",
"When you start and stop feeling bumps depends on the height and length of the bumps (the higher and longer the bump the stronger), the speed (the faster you go the less you feel them) and the hardness of your suspension (the harder the suspension the more you feel bumps)."
] |
[
"This was on an episode of ",
"MythBusters",
".",
"Essentially you drive so fast that gravity doesn't get a chance to pull you down between bumps in the road; you just skip along the tops of them. ",
"Think of shooting a bullet vs throwing a ball, both horizontally. They both actually fall towards the ground at the same rate at g = -9.8m/s",
" and will hit the ground at the same time (ignoring earth curvature). However, since the bullet is traveling so much faster, it's traveling at practically a horizontal line (in actuality it's following the path of a very very wide downwards parabola).",
"Also suspension and the vertical inertia of your car helps."
] |
[
"On the downside, the big bumps get worse."
] |
[
"If a woman got pregnant and the two choices were each other's twins then would it be possible to tell who the father is?"
] |
[
false
] |
[deleted]
|
[
"only twins that came from the same egg have the same dna, if they came from two fertilised eggs they will not be the same. Also, if they have the same dna, them being twins would not help discover who the father is, it would be the same process as analysing the dna of a single child "
] |
[
"Yeah sorry it seems I need to clear some thing up. I was rather tired when I typed this up. I meant if a woman had sex with twins and got pregnant from one of them would it be possible to tell."
] |
[
"This has actually happened.",
" and it is impossible to tell with genetic (not fraternal) twins. "
] |
[
"Evolution question"
] |
[
false
] |
[deleted]
|
[
"Many traits are not due to pressure from natural selection, but are instead due to ",
"genetic drift",
". Essentially, in traits not under selective pressure, neutral mutations might create traits that confer no advantage or disadvantage to fitness. If there's no pressure to remove the trait or increase it, it will become ",
"fixed",
" in the population at a certain probability.",
"But if a group of people sharing the trait migrate to a new area, this will create a ",
"founder effect",
", perhaps markedly increasing the frequency of the relatively rare neutral trait and decreasing other neutral traits in that population. Then the trait is much more likely to become fixed.",
"In this manner, you can have trait differences in populations that confer no selective advantages.",
"However, it should also be noted that many traits ",
" due to selective pressure, like skin color as you mentioned - though dark skin was the ancestral trait.",
"Edit: Clarified \"fixed\" terminology and added link to population genetics definition."
] |
[
"In addition to what you have said, it is possible for traits that do not increase fitness to become prevalent in a population through sexual selection. A peacocks feathers or a bird of paradises tail are examples of this. So if it just so happened that the gender that picks their mate likes some trait (whether it be beneficial, neutral, or negative) that trait will become prevalent in the population. A bird of paradises tail confers no advantage to it, actually it makes the bird easier to catch for predators. But since females select for long colorful tails, long tails are what males came to have."
] |
[
"Uh no, genetic drift ",
" that a trait will either dominate the population or be wiped out, entirely by ",
". See the Wikipedia articles ren5311 linked above."
] |
[
"How have cancer treatments actually improved?"
] |
[
false
] |
We see headlines all the time about positive results in studies with mice, but what has translated to usable treatments in humans?
|
[
"According to ",
"this",
" NIH report, the average mortality rate due to all cancers in the US has declined by about 1.2% every year for the past 24 years (1.5% annually over the last 12 up to 2014, last data reported). That means that if you were diagnosed with cancer that had a 50% survival rate at 5 years in 1991, on average, being diagnosed with the same cancer today would give you an 80% survival rate at 5 years. ",
"This is not due to treatments alone, but also due to other advances in medicine, the key ones being in early detection mechanisms and better cancer classification allowing for earlier, more accurate diagnoses which can then be treated with appropriate treatment. So overall, cancer care is improving quite a bit in terms of patient outcome. You can of course debate merits of survival vs cost/side effects of treatment, but that's another topic completely.",
"Keep in mind that when you read about a result in mice that looks promising it's still quite a ways away from the clinic or market. Typical clinical trials last 1-6 years, and there is often a lot more pre-clinical development that goes on between \"our mice don't die as much\" and getting ready to go to the clinic. There are exceptions to this for diseases and cancers that have very poor or no treatment so that those drug options can be put into the market as soon as possible. However, for the majority of products, it means that the latest recently approved cancer therapeutic for some cancer or other had that article about being a promising lead in mice about 8-10 years ago at least. In the process, good candidates are whittle down to great candidates and those furthermore whittled down to excellent candidates. Thus, if you are lucky, for every 10 things that help treat cancer in mice, maybe 1 thing helps treat cancer in humans too. Not the best accuracy rate, but significantly better than picking things at random, or testing drugs on tress for example.",
"Cancer itself is a disease state with very very vast set of possible underlying causes, thus we never truly get closer to treating \"cancer\". We just get better and better bit by bit in treating this cancer, then that cancer, then the other cancer. Over the last couple of decades we have gotten much better at understanding the molecular nature of many cancers and many of the headways in treatments have been about finding therapeutics that target those specific mechanisms. So we continue making one drug at a time helping one type of patient at a time, slowly, slowly making progress in overall cancer survival. "
] |
[
"Immuno-oncology. They have been focusing on treatments that allow your immune system to attack tumors. The first was Yervoy, an IV antibody treatment, but now there are better antibodies (the PDL1 antibodies, like Keytruda.) Also, even better seems to be CAR-T, in which they pull T cells out of your body and engineer them to fight your tumor, then put them back in. Of the two approaches, CAR-T appears to work better (so Pfizer should definitely not bother buying BMS, which only has antibodies, and should focus on a CAR-T company to purchase and lay everyone off from.)",
"Anyhoo, this Immuno-Oncology stuff is a major revolution. Many formerly untreatable cancers now have like a 20% cure rate with the antibodies, and it seems like even higher for CAR-T. Next up is combining these treatments with traditional chemotherapy drugs. By figuring out these combination treatments, we should be able to get great treatments for most cancers, possibly pushing the 5 year survival rates up and the cure rates up using the immune system. ",
"There was just a big paper on using cancer vaccines to cure certain types of tumors in mice. It's mice only, for now, but looks good. That'll take a year or so to get to the clinic. "
] |
[
"I work in software in this field. It's promising, but still a very long ways off from becoming a standard part of cancer treatment.",
"They can take tumor samples and determine what genetic events may have lead to tumor formation",
"We can ",
" do this right now.",
"and the likelihood of drug resistance in treatment.",
"As far as I've seen, we know nothing about this.",
"They can then tailor the cocktail of chemotherapeutic drugs and surgery options based on ... which genetic alterations are present.",
"Again, we're just barely starting to be able to do this. One of the big success stories that makes its way into a lot of talks is a guy who had lymphoma (IIRC), was treated by a targeted drug regimen, showed dramatic recovery almost immediately... then relapsed and died almost immediately.",
"The big problem is that cancer keeps mutating. It's not nearly as simple as just \"sequence the cancer and compare it to the normal to see what changed\". Each individual cancer cell is likely to be wildly different, and you have to sample a bunch of DNA strands to get a picture of the genome, so you end up with tremendous amounts of noise."
] |
[
"Will bacteria always find a way to become resistant in the end?"
] |
[
false
] |
I know that through heavy use of anti-biotics certain bacteria have become resistant to them since they become resistant over time. However there was this article awhile time ago that that talked about cold plasma killing bacteria. Is it scientifically possible that this method could create plasma resistant bacteria?
|
[
"So, an organism can evolve to survive something that would fundamentally kill it? Like, a bacteria could adapt to survive alcohol or boiling water?",
"Well, there's already ",
"an Archaean that can survive autoclaving",
" which is done at 121ºC (above the boiling point of water at 1 ATM). It lives in hydrothermal vents though, and as far as I'm aware, theres no concern of it being pathogenic. And alcohol is entirely ineffective against bacterial spores (not the active, reproducing cells themselves, it still kills those).",
"That said, some parts of the ",
"adaptive landscape",
" are simply inaccesible to certain organisms. Arthropods are simply not going to evolve beyond a certain size. There are physical constraints that the weight of their exoskeleton puts on them, such that if you constructed an arthropod the size of a rhinoceros, it's muscles would not be strong enough to carry its skeleton.",
"Similarly, these constraints certainly could exist in microbes. Archaea are ",
" different from bacteria. I don't recall my microbiology all that well, but many structural facets of Archaean cells are different from those of bacteria, so the ability to survive above the boiling point of water may be something that is just not possible given what bacteria have to work with.",
"Alcohol is able to kill microbes in part because it is less polar than water, so it can easily dissolve in the lipid bilayer (cellular membrane), and pass into the cell, where it just denatures all of the proteins, making the cell unable to function. It's really hard to imagine how a functioning, reproducing cell could evolve resistance to this sort of thing. In fact, it's generally considered impossible, as far as I know.",
"I guess I don't know exactly how this cold plasma treatment works, to be honest, and as such I'm not really the most qualified to talk about it. Just for fun, I did look up the most recent paper on it, published in the Journal of Medical Microbiology in January. Here is what looks like the paragraph most relevant to our questions:",
"Bacterial spores are more resistant than vegetative bacterial cells to plasma (Hong et al., 2009; Kayes et al., 2007; Lee et al., 2006; Venezia et al., 2008). When non-spore-forming Gram-positive and Gram-negative bacteria were compared, the results were controversial. In some cases, no significant differences were detected (Kayes et al., 2007; Venezia et al., 2008), whilst other researchers found that Gram-positive bacteria were more resistant than Gram-negative bacteria (Lee et al., 2006). These discrepancies can be attributed to variation in the plasma devices used, and therefore in plasma compositions, producing different effects. ",
", where most studies included a unique strain for the bacterial species (Kayes et al., 2007; Lee et al., 2006; Venezia et al., 2008). Further studies using a wider range of strains are required to determine whether the variability in resistance to plasma is characteristic only of Gram-positive pathogens and how strain-specific sensitivity depends on the plasma composition.",
"[emphasis mine]",
"If there ",
" strain to strain variation in the effectiveness of the treatment, then that seems to suggest that there are genetics underlying why some live and some die. If this is the case (which it may not be), then it's hard for me to see how at least some amount of resistance couldn't evolve. I certainly ",
" be misunderstanding something though, so if someone who knows more about this cold plasma stuff could enlighten me that would be great!",
"Now, your second question:",
"Also, since all these bacteria are rapidly evolving, how do we use taxonomy to classify something that's gained a resistance to something, like when speaking about a bacteria that is immune to penicillin and its ancestors that could still be kicking around from before, but weren't exposed to it. New species, sub-species, or something different altogether?",
"Well, I think in clinical settings what is relevant is what the particular bug in question ",
", and what treatments it responds to. I'm quite disconnected from clinical/medical work, so I don't know exactly how they do it.",
"From a more academic point of view, however:",
"There is a problem with the concept of a \"species\". That is, they are semi-arbitrary constructs we've made up in order to help us better classify and study things. In plants and animals, it works relatively well. Enough so that we don't really have to worry ",
" much about this \"",
"species problem",
"\", as it is called.",
"With microbes though, it's a whole different story. Microbes don't always pass their genes down in neat, vertical patterns that allow us to construct the nice, clean, species trees we can with many multicellular eukaryotes. Microbes do ",
" of ",
"horizontal gene transfer",
". HGT allows very distantly related microbes to trade DNA amongst themselves. In fact, this is a large part of the way that antibiotic resistance spreads. Genes for resistance wind up on plasmids inside the cells, and then these cells (either intentionally or unintentionally, there is more than one method) transfer the plasmids to other cells, which are suddenly now antibiotic resistant.",
"One of the defining characteristics of any evolutionarily relevant grouping of organisms, however, is that the members of the group should all be more genetically similar to all other members of the group than they are to any individuals who are not members of the group. How can you manage to make any sort of meaningful classification when these little things are just tossing their genetic material back and forth amongst one another, without concern for our constructed species \"boundaries\"?",
"Some have suggested that it really isn't meaningful to attempt to assign species groupings at all among bacteria, and rather that we should think of the entire domain as one giant gene pool from which different groupings of genes assemble together in cells in order to better replicate themselves. This is roughly how I feel about the matter, if you hadn't guessed."
] |
[
"It's kind of like saying will human skin ever become resistant to bullets. I don't know too much about cold plasma, but if it perforates the membrane like alcohol does, then there's not really any individual mutation (to my knowledge) that can account for slightly higher survivability among certain bacteria within a population.",
"Disclaimer: I do not have a PHD."
] |
[
"Is it scientifically possible that this method could create plasma resistant bacteria? ",
"I assume you are referring to ",
"this",
" article, or a similar one.",
"Quote from the article:",
"Importantly we have shown that plasma is able to kill bacteria growing in biofilms in wounds, ",
"So, given this statement, I might ask you: if this actually becomes a regularly used treatment, what do ",
" think will happen?",
"Also, as far as I can tell, the treatment could only be used for surface infections where you can physically get the torch in position over a localized infection. Perhaps you could go in surgically for internal infections? I'm decidedly not a medical doctor, so I really don't know.",
"If it is the case that you could only use it for infections that are easily accesible from without, then that seriously cuts down the number of applications this technology has. This could also mean that the selection pressure exerted by the treatment might be a lot smaller than that exerted by antibiotics, and thus it could take a lot longer for resistance to evolve.",
"this",
"especially** in medical contexts. I don't really know myself, but I would never count evolution out. It's absolutely unbelievable some of the adaptations living things have come up with.*"
] |
[
"Could you in theory, train someone to have pseudo-synesthesia?"
] |
[
false
] |
Could you develop a pseudo-synesthesia in a child from a young age? For example, maybe when teaching a child colors, each color would correspond to a tone or sound. Is that something that would, in theory, be possible? Or are there too many limitations? I was just curious.
|
[
"What you're describing wouldn't be pseudo-synesthesia, it would just be making word or sound associations for objects. Synesthesia is when a person actually ",
" to a stimuli in a sensory modaility where they shouldn't have a sensory experience to that stimuli. "
] |
[
"Some people describing the effects of psychedelics seem to be describing synestesia. If you used these too often would some of the effects stick?"
] |
[
"What people experience when using psychedelics is actually better classified as a sensory hallucination. Sure, these experiences have some similarities in description to ideopathic synesthesia, but as far as what is actually going on in the brain the reason for the experiences are quite different. As for your question, I am unaware of any reports of people experiencing \"permanent\" sensory hallucinations from use of psychedelics, and based on functional neuroanatomy I would think it to be pretty far fetched. "
] |
[
"How do computers and phones (et cetera) know the exact percentage of battery life they have remaining?"
] |
[
false
] |
I mean... what is being read by the hardware that tells the equipment such an exact numbers? Is the calculation purely software based or do some electronics come into play?
|
[
"Electrical engineer that does power management for cell phones here. You can relate remaining charge to open circuit voltage of the battery, but you can't rely solely on this for two reasons: the relationship is nonlinear and there are many valleys where OCV remains fairly constant but state of charge changes dramatically; and most of the time you are drawing current out of the battery (which has its own internal resistance), making it difficult to determine the true open circuit voltage. To deal with this, we estimate OCV periodically by measuring battery voltage during light loads, and combine this information with the integral of the current being drawn from the battery (typically via sense resistor). This provides a reasonable estimation for the current state of charge. ",
"The phone turns off when the voltage reaches a particular threshold. This is to protect the battery from being damaged by deep discharge. This explains why poorly designed phones can sit at 1% battery for a very long time: the estimating algorithms that combine OCV and the current counter think the battery should be almost dead, but the estimation is wrong. Or, the phone will report 10% battery life and then suddenly die because the estimation algorithm was overestimating remaining charge. As well, pulling a large amount of current from a weak battery (say, using camera flash) will cause the voltage to sag and trip the shutdown feature, even if there is still enough charge left to power the phone for a while longer."
] |
[
"Because a battery's voltage drops off as it discharges",
", by measuring the voltage of the battery, you can get a pretty good idea of what percent is left. "
] |
[
"Or it can integrate the power used over time. Dunno which, if any, devices do this, but I'm pretty sure some do."
] |
[
"Does the expansion of the universe increase the travel time between the earth and another point of the universe ?"
] |
[
false
] |
[deleted]
|
[
"Within our local \"gravitationally bound system\" that is not expanding along with the rest of the universe, no. To get from Earth to Jupiter, or another star in our galaxy, or a member of the \"Local Group\" like Andromeda... no.",
"But, to get to a galaxy far far away... yes. The expansion creates more space out there, so it takes longer to traverse it."
] |
[
"The equations that we use in General Relativity (Einstein's equations)[",
"https://en.wikipedia.org/wiki/Einstein_field_equations",
"] tells us the relationship between the curvature of spacetime and the energy-density of the stuff in it. If you put \"black hole\" in the energy density part, you get \"curved spacetime around the black hole\" as your answer for what spacetime looks like.",
"To write down something relevant to the whole universe, we put down \"homogeneous smoothly distributed stuff\" in the energy-density part, and then ask what spacetime looks like. The answer is the Robertson-Walker metric, which describes an overall expanding or contracting spacetime. ",
"We think that \"homogeneous smoothly distributed stuff\" input for the energy-density is a good description of the contents of the universe on very large scales... kind of like looking at a gas, where you can ignore the fact that it's made up of molecules. ",
"But clearly the Robertson-Walker metric is not the correct description when we examine clumped objects on small scales where things are not smoothly distributed. There, we need to start from the beginning with Einstein's equations, and we get out the curvature of spacetimes for \"cluster of galaxies\" or \"galaxy\" or \"solar system\" or \"black hole\", with no expansion over time. Because these are all gravitationally bound objects, we often (though maybe fuzzily) define a rough crossover point between places where we can or can't use the Robertson-Walker metric as being between \"for the homogenous universe\" and \"for gravitationally bound systems\"."
] |
[
"Can you explain where the expansion occurs and why it doesn't occur everywhere. I had never thought about this till your answer. "
] |
[
"For an astronaut living in a low gravity environment (like on a Mars base) would swimming be as good of an exercise to maintain muscle mass as it is on Earth or would the low gravity somehow make it less strenuous?"
] |
[
false
] | null |
[
"I believe swimming on mars would be very similar to swimming on earth if we assume that swimming is basically all happening under the surface of the water.\nWhen something is floating in water, the weight of the object is equal to the weight of the water displaced",
"mg = Mg ",
"Where m is the mass of the object and M is the mass of the water displaced, and g is the acceleration due to gravity. From this equation we can see that g cancels out, so floating would be the same regardless of the strength of gravity. ",
"Swimming is good exercise because you have to accelerate the water to get moving which means you have to apply some force to the water (f=ma). And to do work on the water you must apply that force over some distance. This work is what we feel as exercise. Since the water is itself floating in the water gravity cancels out here too. The work done moving water around, under water, is not dependent on gravity. Notice that this is different than say, lifting water weights in air. Swimming is more like lifting water weights under water. The water weights are neutrally buoyant meaning that gravity cancels out, and the work done is not going into raising the gravitational potential of the weights, but goes into increasing the kinetic energy of the water."
] |
[
"Certainly. This would not be a cost effective way to have astronauts/Mars Explorers exercise, but as far as I know, the physics checks out."
] |
[
"Yeah! I'm sure you are aware of ",
"/r/spacex",
" and what they are doing to help accomplish this. I hope to work there one day. I like your idea about measuring progress. Even without looking for specific baths/constructed water pools, progress could be measured by calculating the average distance of a population from a potable water source. Even if it doesn't signify a pool or bath, greater distance from water would necessitate faster transport, or better water storage/ transportation. "
] |
[
"Like a gravitational field, does a strong electromagnetic field also affect the flow of time?"
] |
[
false
] |
Does it also dilate time or work in the opposite way and speed it up?
|
[
"The energy in an electromagnetic field does contribute to the energy tensor which is the source of gravity. But the contribution is generally negligible, decreasing as 1/r",
" (instead of 1/r like the mass distribution) and celestial bodies being more or less electrically neutral. "
] |
[
"The problem is that for something to have a large electric charge, it has to have a large number of like charges together. Since like charges repel and unlike charges attract, the formation of such a body would be energetically unfavorable."
] |
[
"A ",
"magnetar",
" has a magnetic field of about 10",
" to 10",
" Tesla. These are objects with the strongest known magnetic fields, and they have a corresponding energy density of around 4 x 10",
" J/m",
". m = E/c",
", so the mass density corresponding to this field is 10000 times that of lead. As a rough estimate, we could multiply that density by the volume of a neutron star of radius 15 km to ",
"obtain a \"mass\"",
" of about 10",
" kg. A neutron star has mass of order 10",
" kg, so even though 10",
" is a big number, even a magnetar's magnetic field has an associated mass density that is negligible when compared to its actual mass."
] |
[
"With ICP (Inductively Coupled Plasma), how are you able to harness the energy if it reaches temps between 6000K - 10000K. Wouldn’t the exterior melt instantly?"
] |
[
false
] | null |
[
"So many plasmas are very high temperature. But it's important to think about the heat capacity and total power.",
"Plasmas are very low pressure gasses typically. When you transfer 1 Joule (for example) out of them, they can drop tremendously in temperature because there simply aren't that many atoms in the plasma.",
"It's more useful to think about the total power of the system here for heatsinking. If you drop 20W of power into the plasma, then the anode and cathode and chamber need to dissipate 20W. If you dump 300W in, you need to dissipate 300W, if you dump 5kW in then you're going to need active cooling.",
"What the high temperature does do is create the opportunity for reaction with the chamber walls. If you have an oxygen plasma, it will oxidize the walls. If you have an argon plasma, even at 10000K argon isn't going to strongly react with standard materials, but it may physically ablate them. If you have a nitrogen plasma, it may form a nitride. If you have a hydrogen plasma, it will reduce the chamber walls."
] |
[
"They use the magnetic field to contain the plasma. If you surround the exterior with a vacuum the heat (mostly) won't escape. ",
"But usually it takes energy to make the plasma, what applications are you thinking of which harness the energy?"
] |
[
"The plasma \"torch\" assembly actually consists of multiple concentric quartz tubes each with their own gas feed. The outermost feed helps cool down the inner tube that contains the plasma core / induction zone.",
"The hottest part of the plasma, where the induction happens, is also relatively small and temperature drops rapidly when you move away just a couple millimeters.",
"It's also worth remembering that it's not temperature that does damage but heat. The amount of heat energy in the plasma isn't particularly high (the RF generator being usually around 1,5 kW) and the system isn't very hard to cool sufficiently. In fact, highly concentrated samples can easily extinguish the plasma.",
"Source: I'm an analytical chemist working with ICP."
] |
[
"My mom claims that margarine is \"one molecule\" away from being plastic. True or just downright crazy?"
] |
[
false
] |
[deleted]
|
[
"Water is one atom away from bleach, and air is mostly made up of the same stuff as laughing gas...",
"There's a ",
"snopes article",
" on this.",
"Basically, the properties of chemicals depends so hugely on small differences within a molecule that even if margarine had a very similar to plastic, that doesn't mean there's anything particularly unhealthy about it."
] |
[
"H2O2 is not what someone means when they are colloquially referring to bleach. Sodium hypochlorite is."
] |
[
"Hydrogen peroxide (H2O2) is a bleach, and air is not too far off a 2:1 nitrogen:oxygen ratio (more like 3:1 or 4:1 I guess).",
"But my point is that it's silly to say those sorts of things. N2O is completely different to have molecular nitrogen and oxygen in the air, and water isn't particularly good at making your hair go blond. Similarly, saying margarine has a similar chemical structure to plastic doesn't really tell you anything in itself."
] |
[
"How do B-Cells identify viruses?"
] |
[
false
] |
It is clear that most pathogens are identified via specific membrane proteins on their surface, but since viruses do not have a distinct metabolism, they can't produce them before infesting a cell. So how exactly are they identified in the humoral response?
|
[
"This is a tricky question because B-cells actually don't identify viruses. An infected cell produces an antigen through processing and presenting it. Then CD4 of the T-helper cell will bind to that antigen presenting cell. THEN, they can either relay the message cytotoxic T cells or to B-lymphocytes (causing them to proliferate and differentiate into plasma cells - producing antibodies). When T-helper cells relay the message to the B-cells, this is called the humoral immune response."
] |
[
"Also there's a good animation of the process ",
"here",
"."
] |
[
"B-cells actually recognize viral antigens using pathogen recognition receptors (PRRs) such as toll-like receptors (TLRs) and presents the antigen on an MHCII, but most require additional signaling from a matching CD4 T-helper in order to activate. Some B-cells can activate without T-cell signaling (T-cell independent activation).",
"http://en.wikipedia.org/wiki/B_cell#Activation_of_B_cells"
] |
[
"Why do dogs not lose all of their hair when going through chemo treatments, but humans do?"
] |
[
false
] | null |
[
"Chemo preferentially kills rapidly dividing cells, cancer cells are fast growing but so are some normal body cells like those in the hair follicles so they are destroyed as well. Dogs' hair doesn't grow as fast as humans so it's less affected, but I doubt it is entirely unaffected."
] |
[
"Most breeds of dog grow their hairs to the length of their coat and then the hairs stop growing for a while before they shed. Dogs like poodles, sheepdogs, etc. that need their hair cut are susceptible to hair loss with chemo; some agents are more likely to cause hair loss than others. In all dogs undergoing chemo, shaved patches of fur will likely grow back slower."
] |
[
"Thank you. That makes a lot of sense!"
] |
[
"What genes iterate and change the fastest? Is it the simpler, shorter DNA or the more complex?"
] |
[
false
] | null |
[
"The short answer is that all DNA base pairs have an equal chance of mutation, so long genes are more likely to pick up a mutation somewhere along the line than short ones. They are larger targets.",
"The long answer is that DNA mutation rates can be affected by mutagens, heat shock proteins, and DNA methylation. The more DNA is used, the more likely it is to be damaged. ",
"In short, it's a lot more complicated than that. And it should be pointed out this is a completely different question from \"Which genes evolve the fastest\", which is also interesting."
] |
[
"No, no, no. Actually, each chromosome has several \"hot spots,\" in which DNA is mutated much more quickly than the rest. As of now, we don't know why this is, but we can regularly observe it.",
"Furthermore, a mutation in a long gene has a much greater chance of being \"silent\" than a mutation in a short gene. So, just because there are more nucleotides in a longer gene does not make it more likely for it to \"change\" more."
] |
[
"No DNA is simple or short. Any given gene that codes for a protein is thousands, or tens of thousands of base pairs long. Multiply that by 200 and change for the shortest known chromosome, 23Y, or the male chromosome, and you have a really big number. For even the shortest chromosome, which is probably 1/200th the length of your longest chromosome. (They are numbered 1 through 23 based on decreasing length). (EDIT - the 1/200th is a total educated guess based upon knowing karyotypes. I suspect that I am UNDERESTIMATING the length of the longer chromosomes/overestimating the length of the Y. Request for a genetics expert to clarify if they wish. I know DNA compacts a ridiculous amount during mitosis, I am sure I am underestimating.)",
"Resonating's answer is correct, every single base pair has an equal chance of mutation. Longer chromosomes are also more likely to \"pick up\" a mutation. But which chromosome it is on is sort of a mute point, it matters what gene it is on.",
"Which genes change the fastest gets much more complicated. How vital is that gene to life?",
"A gene(s) affecting eye color might mutate quite quickly. You can live with a different colored iris.",
"The gene(s) (2) for hemoglobin do not mutate much. If your hemoglobin is mutated in detrimental ways, you are at best a sickle cell or thalassemia sufferer, and will likely have a significantly shortened life span. Worse mutations and you live shorter or are not even born. Thus, some genes mutate very very slowly, because even minor mutations are selected against, by the fact that you don't mess with something really basic and really vital to life, when it works. It has worked so well and stayed the same for so long because it IS really good at what it does, and randomly throwing a kink into it is 99.9999% of the time going to screw it up and not make it better."
] |
[
"Can you jump between cars moving at high speed?"
] |
[
false
] |
I've had this one rolling around in my brain for a while and thought I'd reach out as a new redditor and try my luck. Anyway, let's say I'm somehow standing on the hood of a red sports car, moving at 100mph. Moving parallel to my car is another red sports car, also moving at 100mph. Can I successfully jump from the hood of my car to the other or will I jump and find the cars speeding on whilst I fall to the ground at a much slower speed? Thank you!
|
[
"No, most likely yon won't even be able to stand on the hood of a red sports car going 100mph. The wind will knock you over. It's equivalent to a category 2 hurricane. I am willing to bet you won't be able to stand up in the seat of a convertible going 100mph.",
"Next time when you are in a car going 100mph(not that I am telling you to speed), stick your hand out the window and experience the wind."
] |
[
"If we ignore air resistance, and assume that the cars' trajectories are very smooth, it would probably go pretty well.",
"In reality, though, it would be fairly similar to jumping between two cars, both stationary (but shaking a lot, I suppose) in 100mph wind.",
"I wouldn't attempt it. That wind (in the actual presented scenario, we would think of it as air resistance) would be more than enough to throw your landing off. You probably wouldn't miss the second car entirely, but you wouldn't land where you expected to."
] |
[
"This is what I thought - thank you!"
] |
[
"Could salt water be chemically desalinized?"
] |
[
false
] |
[deleted]
|
[
"sure, there is no reason ",
" that this couldn't be done. In fact, ",
" reactions are an example of this.",
"I don't know of any practical method for doing this, however. ",
"http://en.wikipedia.org/wiki/Salt_metathesis_reaction"
] |
[
"I believe what you are talking about is called a Ligand or a molecule which will come in and bind to an ion. ",
"While there is no reason to suggest they can't exist for Sodium, there is a small problem. First of all if you want a non-polar molecule you need to eliminate or neutralize the charge for both the sodium and chloride. Which in turn means you need something that is strong enough to reduce sodium yet not so strong that it reacts with water. If you can't make it non-polar then you need a compound which will cause the new complex ions to precipitate out. Both of which presents its own problems.",
"Typically the largest problem with ionic species is the fact you have to maintain charge neutrality. This is either done by eliminating charge or replacing charged species (Similar to what a ion exchange resin does). In the case of sodium it is so soluble in water that it is very hard to pull it away from water. ",
"Even if you did successfully find a compound that would do this, odds are it would take way more funds to produce it than it currently costs to distill or use other desalination methods."
] |
[
"Very few large scale evaporation facilities exist, mainly because they have to be enormous to be effective. ",
"However, when they do exist, they do not remove all the water. They fill the facility with water, evap for a while, and pump/flow out a saltier brine. The salt does not stay in the building. Then, with new tide comes less salty water, and they restart. "
] |
[
"If one would point the Hubble Telescope, or a similar powerful telescope to a close body such as the Moon, what would be seen?"
] |
[
false
] |
[deleted]
|
[
"Can Hubble Space Telescope See Flag on the Moon?",
" ",
"the smallest feature that the Hubble Space Telescope can resolve on the Moon's surface. It is just under 100 meters."
] |
[
"Thanks a lot for that, right to the point and with all the details I wanted."
] |
[
"this is a signal to noise ratio (SNR) issue",
"with long exposure, the idea is that your signal will accumulate faster than your background noise eg white gets whiter and black gets blacker.",
"the increased SNR \"increased\" the resolution in that it pushed the actual resolution closer to the limit of the telescope in the ideal case."
] |
[
"is there any proof of other dimensions?"
] |
[
false
] | null |
[
"If by \"proof\" you mean physical evidence, then, no, there is not. There's only evidence for the familiar four dimensions of spacetime."
] |
[
"The mathematics of high-dimensional spaces aren't just used for modelling spacetime. ",
"One really important class of applications for high-dimensional geometry and topology comes from big data analytics. Suppose you have a data set with two thousand pieces of information about each of some large number of people. This is a collection of points in a two-thousand-dimensional space. If you can say anything useful about the topology or geometry of that collection of points, it may give you important information about the data. (This is actually an area of very active research: for those who know what the words mean, the key idea is manifold approximation.)",
"Another important context in which large numbers of dimensions naturally arise is configuration spaces. Suppose you have a robot arm with three hinges and a rotating shoulder. There are four variables here: the angle of each hinge and the angle of the shoulder. Thus, the possible configurations of the arm can be treated as a four-dimensional space. Questions about how to move the arm efficiently can be treated as questions about length-minimizing paths in that configuration space."
] |
[
"Mathematics deals with higher dimensions but that ultimately doesn't really mean it will be good at modeling reality.",
"We have self-consistent models of the universe which use higher dimensions (string-theory or M-theory) but we don't have any reason (yet) to believe they're any better than our existing models."
] |
[
"Venus has been described as an example of \"runaway greenhouse effect.\" Would it be possible to reverse the greenhouse effect on Venus and lower the temperature on the planet?"
] |
[
false
] | null |
[
"It would be at least as easy as taking an ice moon of Saturn to Venus."
] |
[
"I think you're drastically underestimating how hard that would be. Good luck correcting the path of that moon if your math isn't completely perfect."
] |
[
"Yes, there are some interesting terraforming proposals. I read a cool one by Paul Birch, which remarkably I found on ",
"archive.org",
", where he suggests dropping one of the ice moons of Saturn on the planet to both fix the rotation problem (Venus has a very long day) and add some water. He suggests freezing the CO2 down into blocks and storing it under the ocean (the one we made from the fucking ice moon), similar to the ",
"methane clathrates",
" that we have at the bottom of our oceans."
] |
[
"What is the reason beavers build dams?"
] |
[
false
] | null |
[
"They're creating a habitat. Beavers make dams across streams and small rivers in order to create a large, still pond. They then build a lodge out in the middle of the pond. Contrary to certain media portrayals, beavers don't live in or on their dam. They may not even build a dam if they find a suitable natural pond or lake. Lacking that though, they need a relatively large body of still or slow-moving water as a territory."
] |
[
"Having water to hide in protects them from predators. They flood areas so that they can access their food sources (woody plants) from the safety of the water.",
"Of course, this is all instinctual and they will build dams even where there is already a pond. Evidence has shown that they react to the sound of running water by institutionally trying to build a dam over it, even if there is no actual water present."
] |
[
"Beavers have teeth that grow continuously so they have to gnaw on trees to file their teeth down and keep them at a practical/comfortable length, even if they don’t end up biting the tree down and using it "
] |
[
"Do we know why our DNA is shaped as a helix? Why is it a twisted and not straight line? Are there advantages to this shape?"
] |
[
false
] | null |
[
"In addition to the advantages, the double helix shape allows for the DNA to condense much more than a linear counterpart. Think of it as stretching out a slinky; there is a much longer string of metal than when coiled. The condensed shape in and of itself also had advantages. Endonucleases (enzymes that destroy DNA/RNA) are present in the cell in order to protect the cell from foreign DNA/RNA of invading viruses/bacteria. Condensing our own DNA allows for us to avoid degrading our own DNA."
] |
[
"We know that DNA is a helix (well, a double helix to be more precise) because ",
"we literally took a picture of it",
" (from above, looking down on the two intertwined helices). As for why, it's the same reason a lot of macromolecules form helices; try stacking L-shaped blocks end to end into a tower. Chances are that because they're asymmetric, your tower eventually forms a roughly helical shape of some kind - particularly if you adopt a repeating pattern. The same thing is going on with DNA; the constituents are asymmetric but stacked in a repeating pattern with the interior bases stuck to one another by hydrogen bonds. The fact that these bases are all slightly different only serves to exacerbate the already twisted form that the strand takes.",
"Are there advantages to this shape? Well for a start it's pretty stable. Way more stable than single stranded RNA which probably formed the basis for simple life in the early days. It's also pretty easy to condense so you can fit a lot of information into a small space (all your cells contain about 3 billion base pairs inside their nuclei, so the form that information is stored in needs to be easily compressible)."
] |
[
"your answer is otherwise great, but I'd like to point out that the famous \"photo 51\" is ",
" a literal picture \"from above, looking down on the two intertwined helices.\" It is a diffraction pattern produced by an xray beam that was perpendicular to a large number of parallel DNA molecules. The pattern is not a literal image of the DNA, but rather a Fourier diffraction pattern, from which the shape of the DNA can be back-calculated."
] |
[
"What is the true number of Covid infections in Switzerland and could there already be herd immunity?"
] |
[
false
] | null |
[
"Questions based on discussion, speculation, or opinion are better suited for ",
"r/asksciencediscussion"
] |
[
"r/askscience",
" is not designed to assess personal theories and models. Questions based on discussion, speculation, or opinion are better suited for ",
"r/asksciencediscussion",
"."
] |
[
"r/askscience",
" is not designed to assess personal theories and models. Questions based on discussion, speculation, or opinion are better suited for ",
"r/asksciencediscussion",
"."
] |
[
"How do they \"encrypt\" communication with satellites and rovers? What safeguards exist to keep unauthorized people from hacking their systems?"
] |
[
false
] |
Thanks in advance for any answers.
|
[
"I am currently involved in the ground segments of several exploratory deep space missions and the signals coming from/going to our probes are not encrypted in any way.\nThis is due to several factors:\n1) these missions are purely scientific and have no military component. \n2) in order to send something to the probe, you would actually need a really huge satellite dish of 35 or 70 meters in diameter and send with >50 kW of power. You can't put something like that in your backyard.\n3) adding encryption opens a whole new box of problems. E.g. when the data is unencrypted and there are transmission errors, you can generally salvage some information from the telemetry packets, which you could not so easily do if it was encrypted. \n4) processing power: the processors we fly are actually quite old and slow. You want all their resources available for stuff that matters, not encryption.\n5) often, the communication protocols and telemetry packet definitions are designed pretty badly. In one mission, we are actually happy that someone remembered that a CRC could be useful...",
"Communication on the ground is a different matter. Here, data is encrypted except for really old and long-running missions.",
"I can not speak for missions with a military missions or LEO satellites, because I am not involved in one of these. But only a few days ago, I saw a post of a guy who was able to intercept communications from the ISS and a few years ago I read an article about Brazilians who use an outdated US military communications satellite to make \"phone calls\"..."
] |
[
"Nitpick: please dont use \"encode\" when you mean \"encrypt\" (similarly \"decode\" and \"decrypt\"). They have very specific and defined meanings for two very different actions."
] |
[
"Nitpick: please dont use \"encode\" when you mean \"encrypt\" (similarly \"decode\" and \"decrypt\"). They have very specific and defined meanings for two very different actions."
] |
[
"Why spinning black holes have a ringularity instead of a zero thickness disk?"
] |
[
false
] |
If the sole reason of postulating a ring at the center of the black hole is because point mass cannot have angular momentum then why not just have disc instead? A disc is more intuitive shape that any rotating mass would tend to form, we see it with bulging of the plantets and stars. Moreover the existence of a ring would imply the singularity is orbiting something at the center of the black hole or that something is keeping the ring from collapsing back into a point mass
|
[
"... The problem is that since the singularity is, well, singular, it’s outside the domain of the theory itself to predict or describe anything about, so how can you even state that it has or doesn’t have angular momentum?",
"If we just take the schwartzchild singularity, I shouldn’t think that GR has anything to say about the properties of the point singularity (except perhaps in the limit, as r tends to 0).",
"Well, it turns out that it's probably a moot point ",
" because a couple of years ago a group of mathematicians found that the solutions to Einstein's field equations for Kerr black holes ",
"aren't actually valid beyond the Cauchy horizon",
":",
"Einstein’s equations work by quantifying how space-time changes over time. In mathematical language, it takes derivatives of an initial configuration of space-time. In order for it to be possible to take a derivative, space-time has to be sufficiently “smooth” — free of discontinuous jumps. Dafermos and Luk indicate that while space-time exists beyond the Cauchy horizon, this extended space-time isn’t smooth enough to actually satisfy Einstein’s equations. Thus, even with the strong cosmic censorship proven false, the equations are still spared the ignominy of outputting nonunique solutions.",
"“It makes sense to talk of the Cauchy horizon; however, you can’t continue beyond it as a solution of Einstein’s equations,” said Reall. “They’ve offered pretty convincing evidence that that is true, in my opinion.”",
"So a lot of the mathematics that was taken for granted as valid or at least probably valid, concerning the interior regions of black holes and especially singularities, turns out to actually not be valid at all according to their work. That being said, there's still over half a century of mathematical work published on the topic, so ... yeah.",
"It's also still not a totally settled matter either I don't think, as the paper in question was posted as a preprint to Arxiv and as far as I'm aware hasn't yet been accepted for publication in any peer-reviewed journals, so there could be a flaw. But if you read the work, it claims to be applicable to Kerr black holes specifically, so it's definitely relevant.",
"But anyway, even if we aren't actually sure what goes on in the interior of black holes because the mathematics breaks down and becomes nonpredictive (i.e. singular), we can still speak sensibly about the ",
" of black holes and how spacetime would work outside of it, and according to general relativity's ",
"no-hair theorem",
", a classical black hole can be described entirely by three parameters: its mass, charge, and angular momentum. The angular momentum has important physical consequences for exterior objects, as it has an impact on phenomena such as ",
"the Lense–Thirring effect",
", wherein an object orbiting a rotating black hole will precess in a way that an object orbiting a non-rotating black hole would not. And of course the event horizon of a black hole with angular momentum is shaped differently, and this will be important for maintaining an orbit, etc. So it definitely does matter, physically, whether a black hole has angular momentum or not.",
"As for the potential existence of a singularity (whether point or ring or otherwise) and whether the singularity can be said to possess angular momentum or not, those are murkier waters. But general relativistic calculations ",
" mathematically valid up to at least the Cauchy horizon (inner event horizon) of a black hole, and it can be shown that beyond the outer event horizon, there is no force which could prevent collapse of any infalling matter ... so, it's not exactly unreasonable to expect, at least at a naive level, something like a singularity, even if the mathematical description of such a thing is physically nonsensical.",
"For us to ",
" understand what goes on in the interior of a black hole, in all likelihood that would require a proper theory of quantum gravity, which we just don't have. Consequently, we don't actually know for certain, ... and we probably can ",
" know for certain, at least not empirically."
] |
[
"Why spinning black holes have a ringularity instead of a zero thickness disk?",
"... a ringularity ",
" a zero-thickness disc. Sort of.",
"More accurately, it is a ",
", and not a disc. A disc is a solid shape — like a frisbee — while a ring is hollow on the interior. In other words, a ring is to a disc as a ",
"sphere",
" is to a ",
"ball",
".",
"Point is, a ring singularity has zero volume (i.e. zero thickness).",
"Wikipedia: Ring singularity",
":",
"\"Since a point cannot support rotation or angular momentum in classical physics (general relativity being a classical theory), the minimal shape of the singularity that can support these properties is instead a ring with zero thickness but non-zero radius, and this is referred to as a ringularity or Kerr singularity.\"",
"A disc is more intuitive shape that any rotating mass would tend to form, we see it with bulging of the plantets and stars.",
"Not any rotating mass. Accretion \"disks\" are rings, not actual discs. So are things like asteroid belts, and the rings of planets like Saturn.",
"Moreover the existence of a ring would imply the singularity is orbiting something at the center of the black hole or that something is keeping the ring from collapsing back into a point mass",
"Something ",
" keeping the ring from collapsing into a point mass: the presence of angular momentum, which a point mass cannot have in a classical theory."
] |
[
"I believe you are just taking issue with a minor abuse of language. \"Support\" in this context doesn't mean \"physical support\" the way that, say, a steel beam might support the weight of a bridge. It just means that mathematically a zero-volume point can't have a nonzero angular momentum because there is no means by which it can have such -- in other words, it is \"not supported\" in the sense that it is \"not possible\" or \"not applicable.\" For a system to have angular momentum, a part of that system must necessarily have linear momentum in a direction tangent to the system's center-of-mass, in that system's center-of-momentum frame ... but for a perfect point, there ",
" no way to achieve that, as there is no part of the system besides the point itself and that part has zero linear momentum in the center-of-momentum frame ",
".",
"So to put it in other words, the ",
" involved do not support (admit / allow / justify) a point particle having angular momentum. Consequently, only something with strictly positive spatial extent in at least one dimension (such as a ring) can have angular momentum.",
"Hope that helps clarify."
] |
[
"Could someone explain the use of the different units utilized in radiation science?"
] |
[
false
] |
I'm so confused with all the units used for determining radiation. Can someone please explain to me what's the difference and the USE of the the units? I've been told to speak to patients in terms of BERTs... but then.... Grays, Siverts, Curies, Bequrels, Rads... etc... Is there also a difference when describing "generated" radiation (ie electron beam to a W target) vs natural? If I can't figure it out I'm going to be a completely shit clinician for my patients :( Why the hell can't we just have one set of units :(
|
[
"The reason that there are so many different units is because many of them express different things. Though some of them are simply rescaled versions of others.",
"So, here goes. Radiation comes in various forms and from various sources. Turn on a lamp and you've got radiation that you can see. Leave it off and it will still radiate, you just can't see it. So does your table. Or you, for that matter. Radiation is simply the transfer of energy in the form of waves/particles.",
"Next up is radioactivity. Something is radioactive when its atoms are unstable and randomly decay into smaller components. During this decay, radiation is emitted. This radiation is usually in the form of photons (gamma radiation), electrons (beta) or helium nuclei (alpha).",
"Finally, an important property that is relevant for medical purposes is whether radiation is ionizing or not. Ionizing radiation is energetic enough that it can knock an electron away from an atom. This changes the structure of the compound and can be a cause of damage to biological tissues. When we talk about health effects of radiation, it is almost exclusively about ionizing radiation (though the distinction is rarely ever made explicit). The worst non-ionizing radiation can do is heat up the object it hits.",
"Now, on to the units. The Curie and Becquerel units express the same thing: The activity of a sample of radioactive material. This is measured by simply counting the number of decay events taking place per second. The Curie was originally defined as the amount of decays in one gram of radium. The Becquerel is simply the number of decays per second. So if a sample has 1 radioactivity event per second, we speak of an activity of 1 Bq. 1 Curie is equal to 3.7 * 10",
" Bq.",
"Next up is the Gray. This unit is used to express how much energy is deposited by radiation in a kilogram of matter. With the restriction that it only measures ionizing (= potentially damaging) radiation while non-ionizing (= generally safe) is not counted. So the Gray unit expresses how much damaging radiation is absorbed. The definition of the Gray is 1 Joule of energy from ionizing radiation per kilogram of matter. From this point on, I'm omitting the adjective \"ionizing\" from \"ionizing radiation\", since all units that follow only apply to ionizing radiation.",
"In health applications, the Gray is often used to express what radiation dose is needed to get an effect with certainty (e.g. \"if you're exposed to X Gray of radiation, you will experience <unpleasant effect>\").",
"The Rad is a unit that expresses the same and is equal to 0.01 Gray. It is no longer being used, so avoid using it if possible.",
"Next up is the sievert. The sievert, like the Gray, is also equal to Joule per kilogram, but it expresses something slightly different. The Gray doesn't distinguish between different types of ionizing radiation or the area of the body affected by it. The sievert is used to express the \"effective dose\" that measures the health effect of a certain amount of radiation on a human body.",
"The dose in sievert is obtained by taking the true dose in Gray and multiplying it by a weight factor that expresses how damaging the radiation is, depending on the type of radiation and where it is applied. Weight factors are determined by international organizations.",
"Sievert is used when expressing the effect of radiation as a probability (\"if you are exposed to X sievert, your chance to develop <unpleasant thing> is increased by Y%\"). Whenever the radiation dose is high enough that damage is certain (for example radiation burns), Gray is used.",
"But for most medical applications, sievert is an easier unit to use, since 2 sources of radiation with the same effective dose in sievert are likely to have the same health effect, even though the true dose (in Gray) may be different. The disadvantage is that sievert is not a very exact unit, since the weight factors tend to be averaged for the population and can be hard to determine.",
"Finally, we end up with the BRET. This stands for Background Radiation Equivalent Time. Radiation can come from artificial source, such as an X-ray machine, but also from natural sources, such as cosmic radiation and naturally present radioactive substances (for example radon, which is readily present in buildings).",
"Everyone is constantly exposed to this natural background radiation. The level of background radiation tends to be several milisievert (mSv) per year, but this varies significantly with location. The unit BRET is used to express the amount of time it would take for a certain dose to be applied had it come purely from background radiation.",
"So when a certain procedure exposes the patient to a BRET of 10 days, that means that the effective dose of radiation received by the procedure is the same as 10 days worth of background radiation. This makes the BRET the easiest unit to refer to for people without background knowledge of the subject matter. Grays and sieverts don't really tell you much (is 0.1 Sv alot? Most people would say no, but it's actually more than most people would receive in a lifetime), but BRET allows you to directly link the effective dose to something that people are exposed to every day. Procedure with a BRET of 1 day? No worries whatsoever. BRET of 1 year, once a week? Might be worth reconsidering. ",
"Since the strength of the background radiation varies with location (and significantly so), the BRET is not a universal unit. In addition, the long term effects of low doses of radiation are incredibly hard to properly measure. How do you correctly estimate the effect a low radiation dose had in a 5% increase in cancer cases when there are so many other factors that can play a role? Ideally, one would keep several groups of 1000 people in separate, but identical environments with different levels of background radiation for 30+ years. But I've been told there are ethical problems with this.",
"edit: To summarize: Curie/Becquerel and Gray/rad are excellent units for physics: They express exactly and accurately what happens, but they are don't easily translate into actual effects on humans. Sievert and BRET are great units for biology and medicine: They are tailored to measure the effect a dose has on a human being and make it easy to compare the effects of different sources of radiation, but they are not rigorously defined."
] |
[
"If I remember correctly, isn't there also a time variant complication when considering biology? ",
"For instance, 0.01 Grey imposed on a given human over a week would be much less damaging than over 5 seconds. I think it has to do with the error correcting ability of our DNA repair mechanisms - errors are easier to correct with fewer mistakes if there's only a few of them, than a whole bunch of errors all at once. "
] |
[
"For the first two bullet points, we normally use the ",
"linear no-threshold model",
", which implies that 0.01 Gy given all at once, or spread in 10 sessions of 0.001 Gy over a month carry the same risk of developing a cancer.",
"There are those who believe the above model is not realistic and defend the threshold model (i.e. small doses are harmless) or the ",
"hormesis",
" hypothesis (i.e. small doses are beneficial) instead. These two hypothesis aren't as supported as the first, though, and unfortunately the evidence is inconclusive.",
"On the third point I have just a small correction:",
"acute radiation syndrome can occur",
"Actually it ",
" occur if the dose is high enough. This is why we call it deterministic effects, as opposed to cancer which is a stochastic (random) effect."
] |
[
"Why does the sun appear orange at sunset and sunrise but during the day appear white?"
] |
[
false
] | null |
[
"As photons from the Sun pass through the Earth's atmosphere, they experience Rayleigh scattering, whereby low-wavelength (bluer) light is preferentially scattered compared to redder light (Rayleigh scattering depends on 1/wavelength",
"). This is why the sky appears blue during the day- since blue sunlight is scattered every which way, we see it coming from the whole sky whereas the longer-wavelength light appears to mostly just come from the Sun. ",
"At sunrise and sunset, these photons must travel through more atmosphere to get to the observer, and thus the blue light is all but completely scattered away, leaving the Sun and the sky surrounding it to appear red."
] |
[
"Also, In the atmosphere there are particles such as dust and Sahara sand that does the refraction. The sun rays reflect off of the bottom of clouds when it is low in the sky adding to the colors seen."
] |
[
"It actually works opposite of this on Mars. The dust in its atmosphere scatters red light more, so the sky is red and sunsets are blue."
] |
[
"Why don't our animals get sick as often as we seem to?"
] |
[
false
] |
I've had a lot of pets, and never had them get a cold or flu. And yet here I am, ever year, suffering through the season's cold. So what gives with humans and getting sick?
|
[
"another way of putting it:",
"diseases like to spread between conspecifics (i.e. another dog is the most likely carrier of a dog pathogen). dogs don't tend to congregate in big groups where they come into contact with hundreds or thousands of other dogs. in that sense it's a matter of probability.",
"livestock, on the other hand.. your typical feedlot, with thousands of animals packed into small spaces, is rife with disease, and so the population is constantly being dosed with antibiotics etc to keep them from dying (before we kill and eat them :|)."
] |
[
"It comes down to exposure. On daily basis pets don't come into contact with as many carriers of pathogens as we do. They also don't deposit and pick up as many pathogens off of surfaces (such as door knobs). "
] |
[
"Yes, there more human pathogens on a door knob than there are dog pathogens on a dead bird. Why would there be a significant number of dog pathogens on a bird?"
] |
[
"How do chemists theorize whether a chemical is combustible or not?"
] |
[
false
] |
Is there something specific about the chemical formula or molecular structure that causes combustion reactions with oxygen? If so, how can one tell if a substance will ignite without igniting it? I've searched this and can't find anyone who has asked this before.
|
[
"In terms of the thermodynamics, (ignoring the kinetics or activation energy required to initiate a reaction) deciding whether a reaction will be exothermic or not is dependent on the energies of the products and the reactants. Carbon based compounds tend to be highly combustible due to the large energy gain from creating carbon dioxide and water (if hydrogen is present, as is typical with carbon based compounds). That is, the products are more stable and so the reaction is driven towards creating them. Even diamond burns under the right conditions.",
"TNT is a good example of this. Upon detonation is forms nitrogen gas (N2) as well as water and carbon dioxide. Nitrogen gas is extremely stable (let alone the water and carbon dioxide) and so the reaction is energetically driven forwards."
] |
[
"Diamonds are combustible. Sapphires are not because the aluminum is already oxidized to its lowest energy state. Carbon atoms in cellulose are not \"loose\", indeed they are much more tightly packed together in (C6H10O5)n than CO2 in air. They combust because carbondioxide and water are both lower energy states than C6H10O5."
] |
[
"Well, there are two things to look at",
"Oxidation. Atoms require a positive ionic charge to ignite with oxygen. The first step is something really wanting to grab hold of that O and not let go.",
"It's energy state. Combustion happens when a sustained chemical reaction produces energy.",
"\nA good general rule is that if the atoms in the compound are able to make a smaller compound by filling up with O2 it will be combustible. For this reason, almost anything with carbon will be combustible. An exception to this rule is metals with a positive ionic charge. These will form larger oxide compounds when they burn, but the idea of moving from high energy state to a low energy state is the same.",
"The problem with a rule like the one you're looking for is that there are lots of extenuating circumstances. The example I had of burning metal is something that can actually happen, it just needs to be really hot and have a high O2 concentration."
] |
[
"Do thermochromic leuco dyes go from transparent to translucent or transparent to opaque?"
] |
[
false
] |
[deleted]
|
[
"Leuco dye just means a pigment that changes colour based on some sort of trigger.",
"Specifically for thermochromic pigments ",
"examples can be found of almost any colour transition",
".",
"In the link above there is ",
"a clear that turns opaque blue when heated",
"an opaque blue that turns clear when heated",
"an opaque blue that turns opaque green when heated"
] |
[
"Got it.",
"Reverse thermochromic pigments",
". Colourless and heat changes to pink / green / blue / black."
] |
[
"Got it.",
"Reverse thermochromic pigments",
". Colourless and heat changes to pink / green / blue / black."
] |
[
"Question about time dilatation."
] |
[
false
] |
[deleted]
|
[
"This of course ignores the spaghettification effect of the black hole as you approach the event horizon.",
"Interestingly, if the black hole is big enough, you can safely approach the event horizon without the tidal forces being sufficient to cause you any harm. You could get well past the event horizon of the supermassive black hole at the galactic centre, for example, without significant tidal stress. The same is not true for a typical post-stellar-death black hole, however.",
"In fact, if you just threw the person at the black hole the distant observer would never see them cross the event horizon. They would seem to freeze in time just outside of it (and then fade away as the light from them got more and more red shifted).",
"It's worth noting too that you can calculate the time at which the last photon will escape from something falling into a black hole, and it's pretty quick - fractions of a second. More details ",
"here",
"."
] |
[
"You're feeling around the idea of an asymptote, here. The equations describing time dilation have a form essentially the same as 1/x, as in ",
"this graph",
". As you can see, as you approach x=0, the line gets closer to the y axis. In fact, as you get closer to x=0, the line gets arbitrarily close, but it never actually gets there.",
"Of course, the line gets close enough to the axis that it's ",
" vertical, and ",
" touches it, but neither of those things is ever ",
" the case, which is an important mathematical distinction. So, whilst you could achieve an arbitrary level of time dilation you could never actually stop time because you never actually get to the speed of light. However, you could get arbitrarily close - however precisely the observer is measuring your time passage to detect time dilation, you could in principle go fast enough that the time dilation is more than they can detect.",
"(And also, this is very hypothetical, and I'm not saying anything about what amounts of time dilation any particular real life spaceship setup might be able to achieve.)"
] |
[
"(And also, this is very hypothetical, and I'm not saying anything about what amounts of time dilation any particular real life spaceship setup might be able to achieve.)",
"There is another way to do this.",
"If you lowered someone towards the event horizon of a black hole to you (the distant observer) the person being lowered would appear to move more and more slowly (their clock would tick slower) the closer they got to the event horizon.",
"In fact, if you just threw the person at the black hole the distant observer would never see them cross the event horizon. They would seem to freeze in time just outside of it (and then fade away as the light from them got more and more red shifted). Actually they would never quite be fully \"frozen\" in time to the outside observer but their clocks would be running so slowly it would appear they were frozen in time.",
"Unfortunately for the person headed towards the black hole time does not freeze and they will pass the event horizon never to return.",
"This of course ignores the spaghettification effect of the black hole as you approach the event horizon."
] |
[
"Why do fevers cause weird, vivid dreams? What do fevers do to your brain?"
] |
[
false
] |
First, there was a question like this a year ago, but there were no satisfactory answers. I was hoping someone with new insight may be able to shed light on the phenomenon. Anyway, I've always had crazy dreams/nightmares when I had a fever. They were always extremely vivid and life-like (which meant that they usually turned into nightmares.) Also, what exactly happens to the brain? I know why (apparently) the body creates the fever, but I'm looking for the side-effects. I would assume it simply causes extraneous firing of neurons, but I'm hoping there is more. Thanks
|
[
"It's a great question that's surprisingly hard to answer! Here's my best shot. Fever can be induced by chemicals called ",
". Many ",
" (immune-signalling molecules) are pyrogens. When you get an infection, your body releases more cytokines.",
"There are ",
"well established connections between cytokines and sleep",
". Specifically, a higher concentration of some cytokines induces sleepiness, which is why you get sleepy when you have an infection. Altered sleep during infection is thought to be part of the acute-phase response to help recovery. Interestingly, when you get insufficient sleep, your immune system function is impaired -- ",
"people who habitually sleep less than 7 h per night are ~3 times more likely to contract the common cold following exposure via nasal drops than those who habitually sleep more than 8 h per night",
".",
"You might then surmise that since our most vivid dreams occur dreaming REM sleep (note that it ",
" possible to have dreams in NREM sleep too, they just tend to be more mundane) we must get more REM sleep when we are sick and have a fever. Surprisingly, however, increased ",
"cytokine concentrations",
" and ",
"fever",
" result in ",
" REM sleep! This may be partly due to the fact that during REM sleep, shivering is not possible due to muscle atonia, making it more difficult to efficiently thermoregulate.",
"So what's going on? Well, sleep is often much more fragmented when we have a fever. Body temperature generally decreases during NREM sleep. It has been proposed that frequent awakenings to raise temperature may be a mechanism to prevent undue heat loss.",
"A plausible (but by no means verified) answer to your question is that people simply remember more dreams due to sleep fragmentation associated with some fevers. People dream every night and will report dreaming about 90% of the time if awoken from REM sleep. These dreams are typically vivid and bizarre in character. However, we don't usually remember most of these dreams because short-term memory does not function normally during sleep. You only tend to remember a dream well if you are awake for some time after it."
] |
[
"I always assumed that the weird dreams were caused by the elevated body temperature leading to the brain chemistry not working quite as well as it does at normal temperature. Especially since it's so hard to think coherently when one has a temperature. It also seems like the higher your temperature, the less your brain is able to think. So it seemed reasonable that it would affect dreams as well.",
"Wouldn't the simple fact of elevated body temperature affect brain/neuron functioning?",
"Edit: typo"
] |
[
"Wouldn't the simple fact of elevated body temperature affect brain/neuron functioning?",
"All chemical reactions that I am aware of are effected by temperature. Some go faster when the temperature gets elevated, some go slower. Since at a fundamental level all biology reduces down to chemical reactions, it is reasonable to conclude this is the case."
] |
[
"Is there anything, apart from the cost of it, preventing us from accelerating Moore's Law?"
] |
[
false
] |
[deleted]
|
[
"Physical space. We reached or will reach soon the end of moore's law. You heard of 7nm CPUs, transistors in them are already very very small, small enough that it is possible to count atoms in them. Moore's law says that every two yeard density of transistors doubles. By its prediction soon we should have transistors made of only one atom, which is not possible."
] |
[
"Just to be clear, Moore's Law has to do with transistor count, not \"processing power\" directly. Transistor counts ",
" continued to increase exponentially up to the present day, and this is a big part of why we have gotten the improvements in power efficiency, cost, cache sizes, and multi-core parallelism that you talk about. But, clock speeds and processor architectures haven't improved much since 2005 or so. What this means is that the chip makers have been successful in pushing Moore's Law but they haven't been able to translate those transistor counts into sequential performance the way they used to be able to. ",
"Sequential processing performance in 2019 is moderately better than what we had in 2005, but not amazingly better. If you're lucky, maybe up to 10x better depending on what application you're trying to run. 10x sounds like a lot, but if you look at the 15 year time period between 1985 and 2000 there's about a 1000x (one thousand times) performance improvement, which in terms of processors is comparing early generation Intel 386 processors to late generation (1GHz) Pentium III processors.",
"If your application is not algorithmically parallelizable, which is the case for a lot of important applications, then you probably haven't seen many performance improvements in the last 15 years. Even if your application is parallelizable, parallelization is still challenging for many programmers, and intelligently architecting large systems with parallelism is a big challenge, especially if your application wants to make any kind of service-level guarantees. ",
"https://www.karlrupp.net/2015/06/40-years-of-microprocessor-trend-data/"
] |
[
"Perfect answer. IMHO, the R&D budgets to push Moore's Law isn't there anymore. There was great financial rewards in getting more and more power out of a chip. In 2019, research is going more towards getting the same processing power to consumers at a lower initial cost and lower power consumption. Software companies are getting better and better at using all those processor cores and threads to their advantage. Advancing Moore's law isn't as needed anymore. ",
"Those companies who are truly into pushing processor power are going away from transistors and more towards Quantum Computing."
] |
[
"IAMA recent PhD graduate in Alzheimer's Drug Discovery. Listen to my thesis inside, help me get it animated, and AMA!"
] |
[
false
] |
[deleted]
|
[
"Oxidative stressors seem to play a large role in neurodegenerative diseases such as in ",
"Parkinson's Disease",
" and possibly AD as well. AD is also characterized by a degeneration of multiple brain structures that synthesize acetylcholine and ",
"norepinepherine",
". ",
"Recently, I stumbled upon a paper about a ",
"Cystamine-Tacrine dimer",
" that mentioned neuroprotective effects against H2O2 stress in cell lines, inhibits acetylcholinesterase activity, inhibits amyloid beta aggregation, and protects against other ROS via ERK1/2 signaling pathways. It seems like if this drug makes it into clinical trials it could really make a difference in treatment of the disorder in humans (although we are a far ways away). ",
"So basically, my questions are this: ",
"1) How do you feel about oxidative stress in neurodegenerative diseases? Is it a new \"hot topic\" that will blow over, or is it the real deal that can offer a lot of therapeutic benefit? Additionally, is a drug that is focused on a cystamine-tacrine dimer practical for humans? ",
"2) We have a decent understanding of AD through cell lines, rodent models, and human fMRI / PET, (etc...), but clearly, we still have a long way to go (thanks for your effort in this quest!). How well do these findings in lower species translate to humans? And how long do you think it will be until we really start to see effective treatments that can stop or even potentially reverse the progression of the degeneration? ",
"3) Something I haven't really looked into with AD is neurotrophic factors. What is the general consensus on using VGF / BDNF / etc... on treating neurodegenerative diseases? Is it practical? ",
"4) Do you think that AD / PD is really a \"disease\" ? Or is it just normal degeneration of the brain due to aging? It seems like if a human lives long enough, there will be neurodegeneration in some form, therefore, it is really fair to call it a disease? "
] |
[
"I work in cancer drug discovery, and I'm very curious what the pipeline looks like for alzheimer's. Do you use cell lines for drug screening? What pathways/proteins do you target? What is the goal of the drug therapy (e.g. inhibition, anti-aggregation, anti-misfold, neuroprotection)?"
] |
[
"Which target(s) do you think are the best bet for a drug therapy? If it's amyloid, do you think the drug will have to be administered preventatively rather than after symptoms appear?"
] |
[
"When standing next to a radio receiving a weak signal, why does it fade out as you walk away?"
] |
[
false
] |
Is your body acting as an extra antenna?
|
[
"Your body is interacting with the radio waves in several ways, some of which boost performance and some of which impede performance.",
"First, if you stand with the antenna between you and the source, you may be reflecting energy from the source back towards the antenna. Depending on the exact configuration, this can provide a significant boost to the power of the received signal. Radio frequency EM waves bounce quite well of conductive surfaces (like the ",
"dish of a satellite dish",
").",
"Second, your body may be blocking other paths that EM waves can take from the transmitter to the receiver. Blocking these other paths can improve the effective signal-to-noise ratio (SNR), allowing the receiver to pick more useful information up from the static. Imagine you were talking to a friend over 10 telephone lines all with a slightly different delay. It would be really hard to understand. Now, drop 9 of those lines. While you are now getting less overall signal from your friend, the result is much easier to understand. Radio waves bouncing off random surfaces has exactly this 'multiple telephone lines' effect.",
"Finally, there is a bit of a confirmation bias here. Standing near a radio is nearly as likely to degrade the signal as improve it. However, you are much more likely to remain standing where you improve the signal (if you are listening to the radio). This makes you think that moving away always degrades the signal, even if that is not true."
] |
[
"We could, but it's much more predictable and effective to bounce them off a specially-made surface which is highly reflective and exactly the right shape. That's why we have ",
"dish antennas",
"."
] |
[
"We could, but it's much more predictable and effective to bounce them off a specially-made surface which is highly reflective and exactly the right shape. That's why we have ",
"dish antennas",
"."
] |
[
"What exactly does it mean for a superfluid to have phase coherence?"
] |
[
false
] |
I have heard about phase coherence in the context of quantum optics (e.g. superradiance) but was wondering what exactly the precise meaning of phase coherence in superfluids is and how it arises.
|
[
"In superfluid theory and, indeed most of many-body theory, phase coherence generally means that the wave function of an individual particle is in phase with wave functions of other particles (at least on some long-range scale). This allows one to use the whole macroscopic wave function approach. ",
"For instance, in simple lattice models, if certain assumptions are satisfied, like when the tunneling/hopping term dominates the interaction term in the Hamiltonian, then (at low temperatures) the system will have a ground state which consists of every particle in a identical state spread across the entire space. This is a phase coherent state and the quantum phase the system is in is called a superfluid. "
] |
[
"Ahh that makes sense. Thank you. How exactly does one prepare the molecules to be phase coherent at higher temperatures (it appears it occurs naturally as T goes to 0 K)?"
] |
[
"Yes, provided that the system is a superfluid at low temperatures you just need to cool it sufficiently to get the superfluid phase. "
] |
[
"How does the expansion of the universe affect the average distance between particles?"
] |
[
false
] |
I don't mean interatomic or subatomic spacing getting larger due to the expansion of the universe. I mean if you took the average distance between all particles in the universe, from the distance between two carbon atoms in a benzene ring to the distance between the benzene ring and an ion in the Sun to the distance between the ion in the Sun to a bit of matter in the Andromeda Galaxy. So if could somehow account for every particle* in the known universe, calculated the distances between each particle and every other particle, and then averaged that, would I get something closer to the distance between galaxies or the distance between atoms in a molecule? *For the purposes of this discussion, if it's feasible, limit particle size to an atom.
|
[
"Of course it does. Let's say you have two galaxies. Galaxy one contains N particles and galaxy two contains M particles. If you increase the distance between those galaxies, you're going to be increasing all of the M*N intergalactic distances, even if you don't increase the (N",
" + M",
")/2 intragalactic distances, which will definitely change the average distance.",
"Assuming they're far enough apart for the expansion to be relevant, the distance between a particle in galaxy one and a particle in galaxy two will be much larger than the distance between two particles from the same galaxy, which means that the average distance should be roughly linear in the intergalactic distance. The analysis is only slightly more complicated if you start adding galaxies, but the fact is that the average distance between any two particles definitely increases."
] |
[
"It doesn't. On the scales of galaxy clusters and smaller, there is no expansion of the universe. The higher mass density of these smaller regions means that there's gravitation on these scales rather than expansion of the universe."
] |
[
"Awesome, thanks. This sort of popped into my head randomly, this answer definitely clarified things."
] |
[
"Besides the Turing Test, is there any other checkbox that must get ticked before we can say we invented true artificial intelligence?"
] |
[
false
] | null |
[
"This is a good question, in the sense that it can be used to clarify multiple intertwined misconceptions about AI.",
"First, ",
"?",
"In computer science, the field of AI research defines itself as the study of \"intelligent agents\": any device that perceives its environment and takes actions that maximize its chance of success at some goal (Russell & Norvig, 2003). The central problems (or goals) of AI research include reasoning, knowledge, planning, learning, natural language processing (communication), perception, and the ability to move and manipulate objects. [1]",
"In colloquial use, what is implied by ",
" is what John Searle hypothesized as \"strong AI\" (Searle, 1999, \"Mind, language and society\"), which is inadequately defined. Quoting Searle: \"The appropriately programmed computer with the right inputs and outputs would thereby have a mind in exactly the same sense human beings have minds\". The field of AI initially was founded on this premise; the claim that human intelligence \"can be so precisely described that a machine can be made to simulate it\" (the Dartmouth proposal). It has become exceedingly clear this description eludes us (machines have no mind, and our emulation of organic brains has only been done at a very small-scale, see OpenWorm) that's why CS has moved gradually to a definition that excludes (mental) facilities once thought to require intelligence: optical recognition, competing at a high level in strategic games, routing, interpretation of complex data, etc. This is the reason approaches like the CM-originated \"cognitive simulation\" have been abandoned.",
"This is the first major problem with \"true artificial intelligence\": to test for it, one must first define it precisely and unambiguously.",
"Secondly, Searle's \"strong AI\" is now a ",
" goal of AI research, and not part of its definition. Creating lifelike simulations of human beings is a difficult problem on its own that does not need to be solved to achieve the basic goals of AI research. Believable human characters may be interesting in a work of art, a game, or a sophisticated user interface, but they are not part of the science of creating intelligent machines, that is, machines that solve problems using intelligence. Its creation, existence, and implications are more relevant to the philosophy of artificial intelligence (Turing, 1950, \"The Imitation Game\"), the impact of which on actual AI research has not been significant (John McCarthy, 1996, \"The Philosophy of Artificial Intelligence\", What has AI in Common with Philosophy?)",
"AI researchers have argued that passing the Turing Test is a distraction from useful research [2], and they have devoted little time to passing it (Russell & Norvig, 2003). Since current research is aimed at specific goals, such as scheduling, object recognition, logistics, etc. it is more straightforward and useful to test these approaches at the specific problems they intend to solve. To paraphrase the analogy given by Russell and Norvig: airplanes are tested by how well they perform in flight, not by how similar they are to birds - aeronautical engineering isn't the field of making machines that behave like pigeons, to fool other pigeons.",
"So, secondly, due to its irrelevance to the modern understanding of the field as well as the complexity of its imprecise definition, \"strong AI\" is not an active area of R&D.",
"[1] This list of intelligent traits is based on the topics covered by the major AI textbooks, including: Russell & Norvig 2003, Luger & Stubblefield 2004, Poole, Mackworth & Goebel 1998, Nilsson 1998",
"[2] Shieber, Stuart M. (1994), \"Lessons from a Restricted Turing Test\", Communications of the ACM, 37 (6): 70–78"
] |
[
"That line about the pigeons is great. I've been looking for something that cuts to the core of the limits of human form for AI and robotics."
] |
[
"He outlined a bit of the history and current state of the field, but he did not attribute a hard definition to artificial intelligence. If anything, he discussed more of what AI isn't than what it is. ",
"Edit: word"
] |
[
"How much damage can be caused by a single swapped pair in our DNA?"
] |
[
false
] |
Say a pair that is normally G - C, what would happen if it were swapped for A - T, or even just flipped to C - G? What amount of havoc could that wreak?
|
[
"That kind of change is called a ",
"single-nucleotide polymorphism",
", or SNP. Depending on where in the genome the change occurs, it can make quite a bit of difference in an individual.",
"Diseases caused by a SNP are Mendelian genetic disorders. ",
"Thrombophilia",
" is an example of a disease that can be caused by a SNP, in this case in the F5 gene."
] |
[
"Check out the amino acid chain code groups. (There is an actual name for the table and i cannot remmeber what it is buttt..) it will tell you what would happen to a specific part of the genome if certian thins were to be switched around. Most of the time though nothing becuase you body has several ways of detecting changes to the DNA in your body and destroying the cells it contains. If you are able to take college level genetics you would learn all about it."
] |
[
"Sickle Cell anemia is another example of a disease caused by a single nucleotide change. In this case, an A is swapped for a T, and instead of the normal valine amino acid, you end up with a glutamine, causing a sticky patch on hemoglobin that ultimately leads to sickling of the red blood cells. "
] |
[
"Are there any species in which the females compete with one another over males for sex?"
] |
[
false
] |
It seems like a lot of species in the animal kingdom have the males compete (fight, show off, etc.) with one another for "breeding rights" with the females. Is there any species that do the opposite of this? Edit: Wow, thanks for so many responses! I think the best scientific answer is "The Bachelor" though...
|
[
"Female ",
"Jacanas",
" behave much like male lions. ",
"In species where both parents need to work together to raise offspring females may compete to partner desirable males, this happens in ",
"kingfishers",
" and of course in humans."
] |
[
"The answer is you're both right",
"Its called sexual selection as opposed to natural selection, where both genders are seeking partners based on the most desirable traits.",
"Where there isn't much choice of selection, either by lack of partners or low social standing, the criteria for mate selection has to decrease, but can still lead to success of the offspring and/or group."
] |
[
"The answer is you're both right",
"Its called sexual selection as opposed to natural selection, where both genders are seeking partners based on the most desirable traits.",
"Where there isn't much choice of selection, either by lack of partners or low social standing, the criteria for mate selection has to decrease, but can still lead to success of the offspring and/or group."
] |
[
"If the Big Bang theory is correct, how can we look back in time if we were once at the center of the event?"
] |
[
false
] |
I was reading an article today about how hubble is getting close to seeing the very beginnings of our universe very close to the big bang, and it got me thinking about how that could be possible. What I don't understand is that even if space is continuing to expand, why would we be seeing light that is so old? For instance, lets say that space is expanding far slower than the speed of light, and therefore, our point of perspective is moving away from the epicenter of the big bang at that slow rate, wouldn't the light from the origins of the big bang have passed our vantage point long ago? Even light that is hundreds of millions or billions of years old should have passed us. On the other hand, lets say that the universe is expanding at the speed of light, wouldn't that mean that we should have a spot in our field of view, corresponding to the epicenter of the big bang that is complete darkness, since light would never reach our vantage point, as we are accelerating at the same rate as the light waves? I have been unable to find a satisfactory answer to this on the googles. edit: Thanks to Clever-Username789 and aescolanus for the clear explanation. I assumed there was just something I did not understand, but nothing I ever found before could explain it in simple terms. Reddit delivers again.
|
[
"The big bang did NOT happen at one point in space. This is the fault in your understanding. At the instant of the big bang the universe was infinite in density AND size. Then the big bang caused this infinite space to start expanding, hence no longer infinite in density.",
"When the universe transitioned from being opague to transparent (the time that we observe as the cosmic nicrowave background) photons were permitted to travel without being interupted. So they could travel indefinitely in every direction from every point in the infinite expanse of the universe until being absorbed by a detector of some sort. This is what we're looking for, and we see it in every direction we look. If we were in Andromeda we would also see the same CMB in every direction. If we were in a galaxy 10 billion light years from here we would see the same CMB at the same distance from us and come to the same conclusions about the universe.",
"The big bang happened everywhere at once, every point in space is the origin of the big bang. We are not in a special center point of the universe, only the center of our observable universe."
] |
[
"This is the fault in your understanding. At the instant of the big bang the universe was infinite in density AND size.",
"This is by no means certain, even if the universe is currently infinite in extent."
] |
[
"The misconception here is that the big bang occurred at a specific point, when in fact it occurred at ",
" point. The farthest we can see is the point when the universe became cool enough for electrons to bind to protons and form gas (instead of plasma), before this, the universe was opaque. This is the cosmic microwave background."
] |
[
"what creates the heat in our body?"
] |
[
false
] |
is it just the friction of moving blood and other things constantly moving or is it the digestion of food?
|
[
"The major source of heat is the release of chemical energy through cellular respiration!",
"For example, glucose breaks down into carbon dioxide and water, but it also liberates heat."
] |
[
"Additionally you might google for ",
"Thermoregulation",
" since different animals and organisms have quite an interesting variety of mechanisms to keep their body temperature. Especially in very hot/cold environments."
] |
[
"Exactly correct.",
"However, cellular respiration is a lot of stuff. Generally heat is generated in the Krebs cycle by the proton gradient created across the mitochondrial membrane. This is regulated by signaling factors received and sent by factors in the hypothalamus.",
"Our bodies heat up due to the hypothalamus controlling this activity through secretion of eicosanoids. This activity is increased when signaling from molecular recognition occurs in the serum from particular pyrogenics- such as lipopolysaccharides."
] |
[
"Looking for a material with unusual properties. Can anyone help?"
] |
[
false
] |
So I am looking for a material (preferably a plastic or a coating that can go on plastic) that will fluoresce when illuminated by a wavelength of light not produced by fluorescent light bulbs, stay luminous for a brief amount of time after the light stops shining on it, and then go back to normal. Is anyone aware of something like that? EDIT: Looking for floor tile sized pieces
|
[
"I'm sure somebody would custom-make it for you if you offered them huge amounts of money.",
"Before you do that try waving a UV laser pen around a flooring store and see what lights up. Maybe try some of the carpets. Fluorescent dyes are added to all kinds of things to make stuff look brighter."
] |
[
"You might want something like this: ",
"http://www.thorlabs.com/newgrouppage9.cfm?objectgroup_ID=296",
"They light up under only specific wavelengths"
] |
[
"try uv paint makers, they might be able to modify their paint to the wavelength you need? "
] |
[
"What's the density of this newly discovered massive black hole?"
] |
[
false
] |
It's been mentioned in the news that a 21 billion solar mass black hole has been discovered. According to the last point in the the density of a billion solar mass black hole would be the same as air. That really makes no sense to me. A little help science?
|
[
"Just because something is massive doesn't mean it's dense. ",
"Beyond that, the definition of density used in this article is the mass divided by the volume of the event horizon. There is some debate over whether this is a reasonable definition for the density of a black hole. It's turns out that this definition of density means that as a black hole gains more mass, it becomes less dense. The most dense black holes are the small ones. Here's the equation for the density using this definition:",
"density = c^6 / 6 pi G^3 M^2\n",
"You'll notice that density increases as mass M increases. ",
"If you're interested in astronomical objects that are actually dense I suggest reading about ",
"neutron stars",
". Black holes are actually pretty lame ;)."
] |
[
"To be perfectly honest, black holes don't have a density. All of the mass exists at a single point in the middle of the black hole. "
] |
[
"I think you're off by a little bit.",
"Should be \n (c",
" ) / (8 pi G",
" M",
" )"
] |
[
"Does an electric current induced through a metal change the tensile strength of that metal?"
] |
[
false
] |
I was watching a video that talked about how the strength of a metal is based on its bonds and the arrangement of those bonds. How does a flowing current through a metal affect that tensile strength? Does it make any difference (even a negligible one), or is it completely unrelated?
|
[
"The current would heat the metal, which would reduce it's strength. I suppose for a metal with a low ductility transition temperature, the heating could make it ",
", or able to absorb more energy before actually breaking. "
] |
[
"Others have already mentioned that you'lljust have joule heating in a typical metal, but there are some materials (mostly ceramics and I believe two known polymers, PVDF is the big one) that are ",
"piezoelectric",
". These materials aren't electrically conductive, but when subjected to an electric field exhibit molecular/atomic confirmation changes that change their mechanical properties. ",
"Edit: fixed the link"
] |
[
"As the others I'm not coming with a definite answer here, so I'm just adding to what has already been mentioned.",
"When you are running a current through a system you will change the behavior of the system. When the system sits still in its ground state (at T=0 K) it is in equilibrium (even when strained) but when you run a current through it you are constantly adding and removing electrons and the system is no longer in equilibrium (though it may be in a steady state). The properties of the system will thus be different and will in general also depend on the current, temperature - anything! In most cases (I guess) the effect on the strength will be negligible - but you can almost always find some system that has a particular different behavior. One can probably even engineer nanostructured materials that become stronger/weaker when a current is applied - but I don't know any. One could for instance exploit the fact that the current will generate a magnetic field and this will interact with the spins of the stationary electrons/atoms doing something to the properties of the material..."
] |
[
"Why is integration much more difficult than differentiation, despite them being just the inverse operations of each other?"
] |
[
false
] | null |
[
"First we need to clear up some terminology. I think we're okay with what differentiation is, but what we mean by \"Integration\" is a bit unclear. Technically, integration is how you define the signed area under a function over an interval using Riemann sums, ie the limit of smaller and smaller rectangles. In this sense, integration is NOT the \"inverse of differentiation\" because all it does is give a number which is the area under a curve. ",
"But what \"Integration\" means in the common vernacular is \"Anti-Differentiation\". This is the process of taking a function and finding another function whose derivative is the original function. The reason that this is called \"Integration\" is because we can use integration as a tool for doing this. And, conversely, we can use Anti-Differentiation as a way to do real Integration. This is the ",
"First Fundamental Theorem of Calculus",
" and the ",
"Second Fundamental Theorem of Calculus",
" respectively.",
"What you do in a Calculus class is ",
" actually integration. Instead, if you are computing areas, then the bulk of the work you do is anti-differentiation until the very last step when you do the F(b)-F(a) which, by the Fundamental Theorem of Calculus, gives you the integral. To do anti-differentiation in a calculus class, you need to take a function and apply derivative rules in reverse until you get a single function that is the anti-derivative - you don't need anything about integrals. In fact, pretty much every \"Integral Rule\" is actually just secretly a derivative rule written in reverse and with a (fake) integral sign in front of it.",
"With this, we can answer your question.",
"If we're thinking about ",
" integration - area under curves - then this is actually ",
" easier than differentiation. You have to work kinda hard to find functions where the notion of \"area\" does not make sense for them. The classic example is the ",
"Dirichlet Function",
" which is 1 on rational numbers and 0 on irrational numbers. It jumps between 0 and 1 so fast that we can't make sense of the area under its curve in this way. Though, there are ",
"more powerful methods of integration",
" other than with Riemann Sums where you ",
" integrate functions like this. So integration is actually really powerful and, in a sense, really \"easy\" because of this.",
"Anti-differentiation, in a sense, is both equally as hard as integration while also being harder than integration. For pretty much any function you can think of, I can find you and anti-derivative very easily. If you give me almost any function f(x) that you can think of, then I can immediately give you an antiderivative: Let F(x) be the integral of f(t)dt for t=0 to t=x, then the Fundamental Theorem of Calculus says that F(x) is an antiderivative of f(x). (You can change the starting point from t=0 to t=anything that works.) So anti-differentiation is actually pretty easy because integrals are easy, and this is often how it works in applications because computers can computer integrals very easily by just using rectangles to approximate the area.",
"But, likely, none of this is what you were talking about when you asked the question. You were, likely, referring to the experience of computing integrals in a calculus class - which is, unfortunately, vastly separated from all of this and is, unfortunately, more artificial and less reflective of what happens outside of a calculus class. In a calculus class, what you are doing is almost exclusively working exclusively with ",
"Elementary Functions",
" - which is an artificial constraint. You will want to do everything we talked about above, but with the added constraint that you must use elementary functions. And THAT is hard. ",
"You can think of this process as a purely syntactical manipulation. In fact, \"Calculus\" more formally means the manipulation of symbols using fixed rules, so you see it pop up in other places in math totally unrelated to what we typically think of as \"Calculus\" (eg, ",
"Lambda Calculus",
"). You are merely trying to use fixed rules to take symbolic sentences made from the symbols \"x\", \"sin\", \"cos\", \"exp\", \"log\", \"arcsin\", \"*\", \"+\", \"-\", \"/\", etc to get new symbolic sentences made from these things. Eg, for differentiation, you use the rules to take the symbolic sentence \"sin(cos(x))\" and turn it into the sentence \"-sin(x)*cos(cos(x))\".",
"In this sense, differentiation is the FORWARD direction. The derivative of every basic elementary function (sin(x), e",
", x",
", log(x)) is an elementary function. This is because all of these functions have a nice relationship to ADDITION. For example sin(x+y)=cos(x)sin(y)+cos(y)sin(x) - very nice. This allows for straightforward computation of derivatives using limits since the limit has the term f(x+h) in it. The reason that all these have a nice relationship with addition is a bit more complicated, but they ultimately are associated with things like circle and hyperbolas which have very simple/easy arithmetic structures associated to them. Or you can think of elementary functions as being functions you can build using these special functions that have a special relationship with addition. Furthermore, the Product Rule and the Chain Rule also preserve \"Elementary Function-ness\". So for these reasons, if you have an elementary function then its derivative will also be an elementary function. The rules are also straightforward to apply and so differentiation is the forward direction in this situation.",
"But, in terms of symbolic sentences, derivatives tend to make elementary functions more ",
". sin(cos(x)) is much more simple than -sin(x)*cos(cos(x)) - but they are complicated in ways that fit with the rules above. If you have been Chain Ruled, then you need to be of the form g'(x)f'(g(x)). So they are complicated in specific ways. This means that to do anti-derivatives, you need to be able to put complicated expressions into specific forms in order to apply the reverse-derivative rules in order to find anti-derivatives. Things like u-substitution, partial fractions, integration by parts, etc are methods to facilitate this. But if they aren't complicated in a derivative-like way, then you simply cannot find anti-derivatives in terms of elementary functions.",
"For example, the function e",
" is complicated but not in a derivative-like way. It has an anti-derivative, ",
"a really useful one for real life applications",
", but that anti-derivative is best written as the integral of e",
"dt from t=0 to t=x which is very useful even if it's not really approachable from this calculus-class mindset where everything is reduced to elementary functions. There are complicated ",
"theorems",
" and ",
"algorithms",
" to figure out when you can do this to elementary functions, which is interesting in its own right."
] |
[
"Beautiful. Yeah, every time I code up an integration, I stop and think, “…is that right, it’s really that simple?” Because it’s just a sum of lots of tiny things and that’s how it gets treated. No resemblance at all to the rigmarole of figuring out how to tackle some huge nasty antiderivative in Calc II."
] |
[
"Yeah, interesting how rapidly the sum of those areas can converge to the true anti derivative as the width of those Riemann rectangles decreases"
] |
[
"Are the number of electrons equal to the number of protons in the universe?"
] |
[
false
] | null |
[
"Given that those aren't the only charged particles by a long shot, it might be more interesting to ask whether the overall charge of the universe is neutral, or whether it's unbalanced, in the same way that matter/antimatter is unbalanced."
] |
[
"Yes, at least within our observable universe. If it were not we would need electromagnetic corrections to general relativity in order to describe the behavior of celestial objects on large scales. Since we do not, we can conclude that there is no significant contribution from an unbalanced amount of charge (even a small imbalance would be significant too, because the EM force is something like 10",
" times stronger than gravity, which is why a simple fridge magnet can overcome the gravity of the entire Earth).",
"Note that this is not definitive proof because disproving the possibility of a single unbalanced charge is effectively a black swan problem (a universal negative). All we can say is that there are stringent limits in how unbalanced it can be, that the data is consistent with exactly zero net charge, and that there are no known processes for violating it even in the early universe as far as we can determine."
] |
[
"I can believe that charge is conserved, but do we know that it's ",
"?"
] |
[
"Why are there 144hz monitor? Where did that number come from"
] |
[
false
] | null |
[
"DVI was developed when 16:10 monitors were popular, especially for digital displays that actually used DVI. Since most 16:10 monitors were 1920x1200 or lower (except for 2560x1600). Therefore, 1920x1200 @ 60hz is a logical max resolution/bandwidth for single link DVI. I don't think it was a technical limitation, it was just that 1200p@60hz was a logical maximum resolutoin at the time.",
"When dual link DVI was introduced, it doubled the bandwidth available (with 2 streams, hence dual link). While this was originally intended for 2560x1600, it also allowed for 1920x1200 @ 120hz. Again, a very round and \"normal\" refresh rate and resolution.",
"However since then, we've moved to 16:9 and 1920x1080 - since 1080p has a lower resolution than 1200p, we can push a slightly higher refresh rate (144hz) with the same bandwidth of Dual Link DVI."
] |
[
"It's the highest refresh rate Dual Link DVI (connection) can support at 1920x1080.",
"Dual Link DVI can do 1920x1200 @ 120hz or 1920x1080 @ 144hz",
"To get more bandwidth, you would have to use DisplayPort 1.2 or 1.3, which I think would allow for 1080p @ 240hz in the case of 1.2"
] |
[
"that doesn't really explain it. thatsS like saying \"thats all it can do because that all ",
" part can do\". the real question is why is it limited to 144hz. you'd probably have to look into the specification of the DVI protocol to find out. It likely has to do with being able to reliably output data to the screen without timing problems given the speed of the output and processing time."
] |
[
"used AAA 24 battery just hissed and rolled slightly on its own. What could have caused this?"
] |
[
false
] |
I had a couple of used AAA 24 batteries on my desk while browsing reddit. Suddenly, one let out a hiss, kind of like water hitting a hot frying pan. The sound lasted around .5 seconds and the battery rolled half an inch. I'm really curious as to what could have caused this...?
|
[
"Most consumer batteries have a tiny pressure fail-safe that will release in the event of a battery going bad and building up pressure. The hissing you heard was the battery releasing the pressure that had built up inside due to a chemical reaction. The rolling may have been caused by the escaping pressure. ",
"Here",
" is a video on how batteries are made."
] |
[
"Please everyone, no more comments about possession, demonic souls, magic, farting, defending territories and aliens. They're just going to get deleted. "
] |
[
"Here's a link",
" which goes straight to the time where the safety feature is explained "
] |
[
"Is Mathematica 8 worth getting?"
] |
[
false
] |
Yeah? I already have Mathematica 7. I'm a senior-level astronomy+physics major.
|
[
"There's no reason to upgrade to 8 if you already have 7. It's got some integration with Wolfram Alpha but other than that I haven't found any significant differences.",
"If you don't already have Mathematica, then what are you getting it for?"
] |
[
"There are plenty of free programming languages if what you want is to program. if you don't have any problems that don't require the specific bonuses of using mathematica, then why waste the money on a license?"
] |
[
"There are plenty of free programming languages if what you want is to program. if you don't have any problems that don't require the specific bonuses of using mathematica, then why waste the money on a license?"
] |
[
"Why is it when I focus on the source of a sound (e.g. looking directly at someone talking) I can hear and comprehend them better? Can hearing be \"focused\"?"
] |
[
false
] |
As an example, if I'm in a lecture and someone is talking while I'm not directly looking at them, this periphery noise is harder to understand than if I looked directly at them and focused my visual attention on them. Does this mean you can actually focus and pinpoint your hearing according to your visual focus? Or is this just a function of focusing your attention on them and merely digesting what they're actually saying rather than dismissing it as periphery noise? I guess if this were the case the same concept would apply to your sensation of smell? TLDR: is "aural focusing" a thing?
|
[
"For speech in particular, looking at the speaker allows you to lip-read to better parse the conversation. Many adults who suffer gradual hearing loss don't realize it until the hearing loss has progressed significantly because they are able to compensate by reading lips."
] |
[
"It is pretty simple actually. If you look at the design of the ear it is intended to catch sound coming directly at us. Peripheral noise typically won't encompass your head so information going in only one ear provides only one stream of data and nothing to cross reference it to. Compared to directly in front of you where both ears pick up on the sound the direction and origin of the sound is a lot easier to determine.",
"- Sound in both ears = focusing"
] |
[
"In addition to this, there is the ",
"cocktail party effect",
", which describes the phenomenon of suddenly \"tuning in\" to a conversation you've previously been filtering out when you hear your name spoken, for example. Someone else can probably explain this more fully, but essentially you are constantly filtering out non-essential information from your conscious attention, until something unusual or important happens, which is then elevated to your conscious attention. "
] |
[
"Since Pluto's eccentric orbit crosses that of Neptune's, will there be a point where both collide?"
] |
[
false
] |
Reading Neil Degrasse Tyson's 'Death By Black Hole' where he mentions Pluto has an orbit much like an asteroid with an eccentric orbit, to the point that it crosses the orbit of Neptune. Is it possible that Neptune and Pluto could collide in the future?
|
[
"No.",
"Pluto's orbit doesn't intersect Neptune's in three dimensions, and they don't even come close. Pluto's orbit is at a considerable angle to the ecliptic (the plane that the solar system mostly lies in).",
"Additionally, Pluto's orbit is in 3:2 resonance with Neptune's, providing further protection from a collision."
] |
[
"As the other comment states, Pluto travels around the sun 2 times for each 3 times Neptune does.",
"There's more to it than that, however - this resonance actually stabilizes the orbits somewhat. If an impactor were to perturb Pluto's orbit to 1.4999 times that of Neptune, the resonance will actually reestablish itself.",
"This stability means that Pluto and Neptune never get close. ",
"I can't find a credible source for this, but I believe they never get closer than the Earth gets to Saturn."
] |
[
"What does the 3:2 resonance mean?"
] |
[
"How did someone discover that the t-rex had vision based on movement? If it is true or not how do we know either way?"
] |
[
false
] |
Just like the title says, how do we know what kind of vision the t-rex had.
|
[
"No one has ever discovered that, except maybe for Michael Crichton and Steven Spielberg. The T-Rex likely had excellent vision. Possibly even better than a hawk's.",
"http://www.todayifoundout.com/index.php/2014/05/true-t-rex-couldnt-see-didnt-move/"
] |
[
"I don't think Crichton/Spielberg actually made it up, it's a common misconception applied to predators in general which they just extended to dinosaurs. Clearly not true though, because if predators could only see moving objects, they would just run around slamming into trees and walls and rocks and stuff, so it's very obvious that they can see stationary objects just fine.",
"It's one of those misconceptions which is very weird (at least to me) because it can be disproven with some very very basic reasoning. People just apparently don't bother to think it through like... at all, and it spreads.",
"It is true, for the record, that many (if not all) animals respond more to moving visual stimuli than stationary ones, but that doesn't at all mean that they somehow can't see stationary objects or something. "
] |
[
"In Lost world, the book, Chriton specifically says the T. rex doesn't have vision based on movement. One of the characters thinks he can hold perfectly still in front of it and gets killed."
] |
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