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[
"Do heavier objects actually fall a TINY bit faster?"
] |
[
false
] |
If F=G(m1*m2)/r then the force between the earth an object will be greater the more massive the object. My interpretation of this is that the will accelerate towards the object faster than it would towards a less massive object, resulting in the heavier object falling quicker. Am I missing something or is the difference so tiny we could never even measure it? Edit: I am seeing a lot of people bring up drag and also say that the mass of the object cancels out when solving for the acceleration of the object. Let me add some assumptions to this question to get to what I’m really asking:
|
[
"You are correct, heavier things will accelerate the earth more than light things. The acceleration of earth is equal to G*m2/r",
" For a 1000 kg mass on the earth's surface (~6 x 10",
" m), this translates into an acceleration of about 2 x 10",
" meters per second",
" .",
"The very best accelerometers can measure things on the order of 10",
" m/s",
" , so you're also right in that we cannot measure this."
] |
[
"Yes, but you have to remember that since F=ma, a=F/m=(GMm))(r²m)=(GM)/r², the mass of the accelerated object is irrelevant; only the ",
" acceleration would be higher because the earth would accelerate towards the object at (Gm)/r², so the relative acceleration would be (G(M+m))/r²"
] |
[
"However, in terms of the question posed, if you drop the two objects together next to each other then as the Earth gets uniformly accelerated towards them (can assume a barycenter of two smaller masses) they would fall at the same rate or at least an even smaller difference"
] |
[
"How could the universe really be infinite?"
] |
[
false
] |
Wouldn't the fact that the universe isn't still the same density and temperature suggest that we didn't exactly start with energy? Maybe I'm mistaken and the universe started from a point of finite energy but infinite If this is the case then how could we ever say that the universe is infinitely large? Wouldn't there be nothing left? It seems to me that either way, you are dividing infinity by something and not getting infinity, or dividing something by infinity and not getting zero.
|
[
"Yes, if it's infinite in size, then it has infinite total energy. We don't know just how close the universe got to infinite energy density in the early universe. Our physics breaks down before we can get back to those early times. It seems to approach an arbitrarily large energy density, but it's unknown whether that goes all the way to \"infinite\" density. ",
"Anyways the finite energy, infinite density often comes from a common misconception of our local ",
" portion of the universe occupying some small point and then expanding rapidly through inflation and then more slowly expanding over the eons since. But it seems very likely that our observable universe is just a small portion of a much larger, and likely infinite volume of space. Thus that early point or maybe very small volume was but one point or volume within an infinite volume then as well. A tiny portion of the total thing"
] |
[
"and the big bang originated from one point",
"It didn't. It happened everywhere. The entire universe began expanding, \"creating\" space within itself. If the universe was ever a single point, that single point turned into a thing with 3 dimensions of space and one of time. But more likely it was just a volume with extremely high energy density. And throughout that volume, the big bang happened to expand the space between things in the volume, creating space and diminishing density. It isn't an \"explosion\" away from some central point. It's a (more-or-less) uniform \"stretching\" of the whole thing."
] |
[
"Wait, can you elaborate on the last part? Do you mean space was always infinite and the big bang started at some arbitrary point in the middle of it? I thought that \"space\" was the stuff that expanded from the big bang, which had nothing outside of it."
] |
[
"Is a black hole really a hole? Or more of a ball?"
] |
[
false
] |
As I understand it, black holes are just collections of matter so incredibly dense that the force of gravity is greater than the speed of light. So, why is there this idea of a hole? As if it somewhere? I imagine it more as a big ball of matter pulling everything around it inwards, am I wrong?
|
[
"The main reason why it's called a \"hole\" is that once something falls in, it never comes out again. It is, to all intents and purposes, a hole in the universe. In fact, it's more specifically a 4-dimensional hole, which appears as a ",
" in 3-dimensional space. The same goes with hypothetical wormholes. The movie Interstellar probably produced the most ",
"accurate depiction of a wormhole",
" thus far seen in cinema."
] |
[
"Time is indeed the fourth dimension, but the catch is that time is actually equivalent to space. In relativity, there are four dimensions, and only one velocity: ",
", or the speed of light in a vacuum. In other words, ",
", including you, me, and the photons entering your eyes right now, is moving at exactly the speed of light ",
". This speed is the speed through four-dimensional ",
". When we are sitting \"still\" relative to our three-dimensional surroundings, we are actually moving at the speed of light ",
". Conversely, a photon, which always moves at the speed of light ",
", does not experience time. Everything that ever happens to a photon happens instantaneously, in a time-independent manner. In between these two extremes, you can exchange the speed at which time is moving for speed through space such that your total speed through spacetime remains exactly ",
". This is where ",
"time dilation",
" comes from: as you go faster through space, you go slower through time, because your speed through spacetime is always exactly the same. "
] |
[
"And you're right, it ",
" a ball, in three-dimensions. But in ",
" dimensions, it's a hole, or a place where you can travel a potentially infinite distance in an ",
" dimension, a dimension that exists ",
" to the three dimensions that we are familiar with. Here, let ",
"my favorite person",
" explain it. That is why we don't use the term \"black ball\". A black hole is a ",
" four-dimensional object."
] |
[
"[Biology] How do antibodies work and why has there never been a case of bacterial resistance to such antibodies?"
] |
[
false
] | null |
[
"Antibodies, also called Immunoglobulins, are proteins that are secreted in response to an antigen, which is most commonly a protein of the pathogen, but can also be against a toxin.\nAfter an immune cell of the Innate Immune System (the first responders), a Macrophage for example, engulfs and destroys the invader, it then presents a piece of it on the cell-surface via a molecule called the Major Histocompatibility Complex (MHC). \nIn the case of Antibody production this is then presented to a B-Cell which turns into a Plasma Cell to produce antibodies specific to this antigen.",
"\nAntibodies can then work in two ways; They can neutralize the target directly by blocking important proteins on the surface, or they can prime the target for easier attack by the immune cells - The latter is called Opsonization.\nBacteria does not become directly \"resistant\" to antibodies, but there are several ways to avoid it:\n",
", causative agent of tuberculosis, can survive and even replicate inside phagocytes like macrophages, by disrupting the fusion of the Phagosome with the Lysosome, which is a \"digestive\" mechanism of the cell. The Lysosome contains various hydrolytic enzymes to break down the pathogen.",
"Sometimes members of the same bacterial species have different serotypes, which means that 2 strains cause 2 different antibody responses and are not affected by the response to the other.\nOther pathogens, like the parasites that cause Malaria, can change their surface proteins when they replicate to avoid circulating antibodies."
] |
[
"Antibodies help kill microbial pathogens through several mechanisms, which are outlined well ",
"here",
". Through the process called neutralization, antibodies can physically block outside components of pathogens. For example, antibodies against outer viral proteins can prevent the virus from binding to and entering host cells. ",
"Antibodies bound to pathogens (or almost any small particle) act as a tag which directs phagocytic cells like neutrophils to engulf and destroy these through a process called opsonisation.",
"Additionally, antibodies can activate something called the complement pathway. Activating this pathway recruits other proteins found in your blood. These proteins can further attract phagocyte, or can even form lethal pores in the cell's membrane.",
"Pathogenic bacteria absolutely have mechanisms to counteract antibodies. Some bacteria produce capsules, which are essentially sugary coats that prevent antibodies from binding to their targets on the bacterium's surface. Some bacteria, such as ",
" produce virulence factors such as ",
"protein A",
", which bind antibodies in an upside-down orientation and prevents their ability to activate immune pathways."
] |
[
"Great answer, said everything I might have and more, much better than I could have."
] |
[
"Do animals that develop thicker coats for winter depend on the temperature for it to occur?"
] |
[
false
] |
For example, I live in the northern hemisphere and my cat grows a thick coat during winter. If I were to move to Australia, how would my cat be affected? What if I had an indoor cat where the temperature remained constant?
|
[
"Not necessarily. If you have an indoor cat in a perfectly climate controlled house, you would still expect it's coat to change despite the temperature of the house not changing. Most animals that experience this change (among many other physical processes!) do it via light cues. Less day length results inane animals undergoing a change in the thickness of their coat.",
"This is why many animals have a specific mating season as well!"
] |
[
"On a related note, seasonal changes among organisms (including plants like trees who leave their foliage in the winter) are generally most commonly a function of the more periodical and reliable day length, not the greatly varying temperature."
] |
[
"On a related note, seasonal changes among organisms (including plants like trees who leave their foliage in the winter) are generally most commonly a function of the more periodical and reliable day length, not the greatly varying temperature."
] |
[
"A hotel in Hong Kong will be serving wine salvaged from the Titanic wreck. Many questions present themselves."
] |
[
false
] |
is serving a bottle of 1907 Heidsieck & Co. Monopole Gout Americain wine, salvaged from the wreck of the Titanic. Aside from this being rather macabre, many questions present themselves: How can a bottle of liquid survive at that depth? Assuming a completely full, spherical glass bottle, would there be a pressure differential between the liquid inside and the liquid outside? For a bottle of wine, wouldn't the pressure have forced salt water through the cork long ago? Assuming the bottle has survived unbroken and uncontaminated, what might the wine taste like after 90-odd years of freezing darkness?
|
[
"1) Because water, like many liquids, is very incompressible. Meaning its density changes very little with pressure. At the pressures at the wreck of the titanic, you're only talking about a few percent increase in density (and thus decrease in volume). So even if the pressure difference was maintained (see below), it wouldn't necessarily be enough to shatter the glass bottles.",
"2) It could have, in which case the wine would be undrinkable. It's happened with salvaged bottles. But in other cases, I suspect the cork just gets pushed in until the pressure equalizes. ",
"3) Like aged wine? Cold and dark is how you usually store it. The temperatures on the ocean floor are typically a few degrees above freezing. Colder than the optimal temperature for storing wine, but it'd only slow down the aging process rather than 'hurt' the wine."
] |
[
"Could the cork really hold up that long? It's difficult to imagine the contents being completely undisturbed."
] |
[
"I'm very curious about the provenance of that champagne. I didn't think RMST had sold any of the artifacts to private interests. There ",
" some of that champagne salvaged from the Baltic, found at a much shallower depth. I wonder if they actually have the Baltic shipwreck champagne instead of Titanic champagne.",
"Here's a picture of an intact champagne bottle, with cork, on the seafloor next to Titanic. So we know they survived: ",
"http://www.bbc.co.uk/manchester/arts/2004/06/10/gallery_08.shtml",
"As for taste, one would need to find an oenologist!"
] |
[
"How can 2D CMB radiation images tell us about the structure of our 3D universe?"
] |
[
false
] |
[deleted]
|
[
"The data you see in most CMB pictures already has radiation from stars and dust clouds removed (the raw data looks more like ",
"this",
", processed data looks like ",
"this",
"). Techniques for doing that are... a lot of work, but pretty good overall.",
"The we can get data from the structure of the 3D universe because although the CMB data is 2D, it shows us a \"slice\" of what the universe looked like a very long time ago. It shows us where on a giant sphere around us the universe was hotter or colder, and we know (from physics) how hot and cold regions of the universe will evolve over time. That tells us how those spots that we are seeing 13.6 billion years ago will have developed over time.",
"Let me give an analogy: imagine I take a thermal image of a pie in the oven (a few minutes after it's been inserted). It's a 2D picture, but it tells me how the heat in the pie is distributed. I know the properties of the oven (temperature and convection rates), so knowing the heat at that moment in various sections of the pie tells me how long it will take for the middle to get hot. If I also know how long it takes the pie to cook once it reaches the peak temperature, from that picture, some physics, and knowledge of the oven, I can predict how long the pie will take to cook.",
"Similarly, by looking at the 2D picture of the WMAP data, and knowing a few bits of other stuff about the universe, I can tell how the parts of the universe that produced that radiation billions of years ago will have evolved over time. That doesn't tell me about the whole universe, but I can extrapolate from those parts, and since a basic assumption in cosmology is that the universe is more or less the same on very large scales, I can then guess what the structure of the whole universe is on average, right now or at any arbitrary time in the future or past."
] |
[
"There are a few ways.",
"First, it's a snapshot of the Universe at a particular time, and as with any snapshot, we can use it to learn about the conditions at that time. That time, by the way, was about 380,000 years after the Big Bang, when protons and electrons combined to form neutral atoms, and light was freed to stream unfettered through the Universe (until they smacked into Planck, of course).",
"Second, the CMB ",
" affected, at a small level, by the Universe along the way to our telescopes, and we can learn something about the structure along that line of sight as a result. For example, Planck was able to use gravitational lensing to obtain some absolutely lovely maps of the distribution of mass (mostly dark matter) in the Universe. They also were able to discover about 1000 galaxy clusters - including, almost certainly, the most massive object in the observable Universe - using the ",
", in which CMB photons are scattered off hot electrons in clusters in a very distinctive way. That said, it's difficult to get a 3D map from these as these effects tend not to depend on how far away from us these objects are - so really you won't expect to learn much about 3D structure from the CMB. The point is that there are lots of other interesting things one can do regardless.",
"Finally, the statistics of this 2D image - how big typical hot and cold spots are for various sizes, and so forth - tells you about the processes which created those hot and cold spots, and that in turn comes mostly from physics in the extremely early Universe, a mere 10",
" seconds or so after the Big Bang. The physics of this incredibly early phase in cosmic history, physics taking place at energies ",
" of times higher than those produced at CERN, is now very tightly constrained due to Planck.",
"It's pretty cool."
] |
[
"I laugh on the inside when I hear a physicist talk about how the CMB is isotropic. A general audience doesn't know what isotropy is!",
"ie:\n",
"https://www.youtube.com/watch?v=uGbWIVzjays"
] |
[
"What would the void between galaxies look like?"
] |
[
false
] |
I am a writer and have an interesting idea for a story I would like to pursue. However, I found myself asking a question while developing the idea farther. In the story a man finds himself lost in the void of space while traveling from one galaxy to another. My question is simple; what would the man see? Would the void be full of pin pricks of light much like the night sky of earth, or would the galaxies be too far apart for the light to reach him, leaving the void utterly without light? This void is the primary setting for the story, so I would like to present it as accurately as possible. Thanks for the help.
|
[
"It would indeed be utterly blackness for the most part, but you'll be able to make out a few smears of light from nearby galaxies (if they're within a few million light years). On a dark night on earth, you can make out the smudge of the Andromeda galaxy 2.5 million light years away with the naked eye."
] |
[
"True, but I was thinking that the start and end of the journey would be quite stunning."
] |
[
"God damn, that is so fucking creepy."
] |
[
"Something that has always bothered me about crepuscular rays... The light source appears to be a couple ten's of thousands of feet above the clouds when it is obviously the sun. Is the light bouncing off the upper atmosphere or something?"
] |
[
false
] |
With photos like this it always appears to me that the light source is very close as if sitting right behind the clouds. Why does it appear to be so close when the earth is so far away from the sun. Shouldn't the light theoretically hit the earth at pretty much a 90 degree angle? Or is this just because it isn't high noon and based on my orientation the light comes from an angle? I really can't figure this one out on my own. This image makes me think that the light rays from the sun should be going straight down.
|
[
"It's exactly the same thing that's happening in ",
"this image",
". The crepuscular rays are parallel, just like the rails. In this example, if you were to lower your viewpoint closer to the ground, the apparent angle between the images of the rails would approach 180 degrees.",
"As an aside: that \"pale blue dot\" photo has nothing to do with crepuscular rays. There's no atmosphere in space to scatter light; what you're seeing is a lens flare that happens to line up with the image of the earth. Carl Sagan's \"suspended in a sunbeam\" line is just poetic license."
] |
[
"The light rays are not coming straight down, because the Sun is not above clouds. If you were standing at the point where you now think that the Sun is at 90 degree angle, you would see the exactly the same situation as in the point where you are standing now. The Sun would still be 30 degrees or something like this above horizon. The rays you see have the same length. ",
"Now imagine a stick. If you look at it perpendicular to its length, you see it in its full length. If you put it more parallel to you, meaning looking at it from the front or behind, it will seem shorter. This is the case with light rays. The rays between you and the Sun look shorter, because you are looking them from the front side (they are pointing at you), more distant rays look long, because you are looking at them from the side (they are pointing at some other dude 20 miles away). It turns out that the only case where this exact proportions come into existence is when looking into a bunch of perpendicular rays. If you still cant imagine it, take a couple of sticks and arrange them in this order. The other case where this geometry is possible are anticrepuscular rays. "
] |
[
"The idea of the stick losing length makes sense to me. But in my mind i still don't understand how two seperate crepuscular rays could ever create a more than 90 degree angle.",
"Say conditions provided me a chance to observe a set of crepuscular rays for 5 or 6 hours. I wouldn't be able to watch them move as time progressed correct? I still don't understand how the light source appears to be closer. (sorry maybe i should have posted this is in ",
"/r/explainitlikeimfive"
] |
[
"How does darkness affect us?"
] |
[
false
] |
I'm really starting to wonder how darkness is affecting my behavior, state of mind, and habits. For example, when I am at work, there is tons of fluorescent lighting, I work hard, I am productive, I constantly read and write. When I get home, my blinds are closed because by the time I get home at 5:30 or so, it's dark out anyway. So I cook dinner with lots of great lighting. However, when I am eating dinner, I turn off lights to watch movies / TV shows etc. Even when I am on the computer, the lights are dark. I get incredibly lazy. I want to lie on the couch. I don't want to do tasks I've mentally assigned myself for that day, just out of laziness; even though I know I want to. I've even begun taking naps after dinner in front of the TV sometimes. In essence, on a weeknight, unless I go out somewhere, nothing gets done. This must be due to my reluctance to turn on lights (due to the habit of watching movies/TV in darkness), because in days when I have all my lights on, I am more productive. Anyone studying light and artificial light and its effects on the body/mind? I don't have sleep problems though, except I do stay up late at night and am reluctant to go to bed.
|
[
"So what you're saying is that you're confused about needing a nap after working all day and then eating a big meal?",
"\nSure the lights help you stay awake, but I suspect its mostly because we normally only sleep when its dark."
] |
[
"Increased melatonin production."
] |
[
"I don't eat big meals, but I do get a slight insulin from meals even though they are small, so I do take a nap after, the darkness does help of course. If it was light, I doubt I would take the nap.",
"My confusion is whether the darkness is affecting everything about me. I don't want to do tasks or work on stuff when I am at home, compared to when I am in the office or something."
] |
[
"From the first Hydrogen-Hydrogen fusion event to reaching thermonuclear stability, how long does it take a proto-star to 'turn on' and become a real star?"
] |
[
false
] | null |
[
"No. In fact, the star gets less rowdy as fusion turns on. Proto-stars use convective heat transfer which is messy and unstable, leading to lots of big eruptions and flare ups. Fusioning stars use radiative heat transfer which leads to a more orderly internal layering of conditions that reduces the number of large flares. Meanwhile the star's surface heats up a little (from 4600 K to 5800 K for a star like our Sun, less so for red dwarf stars) in a slow ramp up over a very long period of time (over a billion years for the very smallest stars). Keep in mind that while fusion is a very energetic process stars are also very large, the overall density of heat generated to mass for our own sun is comparable to that of a garden variety compost pile."
] |
[
"It's complicated, and depends on the mass of the protostar. Massive stars can reach the main sequence in a million years or less, while the smallest possible stars (.08 solar mass) may take billions to reach the main sequence proper.",
"https://lco.global/spacebook/protostar/"
] |
[
"The process of transitioning from proto-star to proton burning star is a gradual one. Proto-stars begin very hot and bright due to the energy from gravitational collapse (this heat, concentrated in the core, is what initiates fusion reactions, after all). It takes several million years for a newborn star to transition from convective heat transport in its interior to radiative heat transport and to reach an equilibrium surface temperature."
] |
[
"i ask this of /r/AskScience because I feel it to be a subreddit of more credibility than /r/Scifi"
] |
[
false
] |
Is there a good book/story about a group of beings Trying to create a preserve of life to survive the heat death of the universe? I've often wondered how some (Clarkian "magically advanced") group might attempt to forestall the inevitable. EDIT: I'm horrifyingly drunk right now and this question came up during discussion. Please forgive the misspellings
|
[
"There's an Asimov short called \"The Last Question\" that kind of deals with this.",
"http://www.multivax.com/last_question.html"
] |
[
"The last question?",
"Edit: derp."
] |
[
"Many thanks."
] |
[
"Blood pressure and oxygen delivery"
] |
[
false
] |
I'm having a little trouble conceptualizing the effect that blood pressure has on oxygen delivery. Generally oxygen delivery (DO2) is said to be a function of oxygen saturation, cardiac output, and hemoglobin (with a small contribution from PaO2). But if the blood pressure is very low, it seems obvious that tissue hypoxia will occur. Is there some way to fit BP into this equation or combine BP and DO2 to describe tissue perfusion? And a more general question - obviously blood pressure matters, but does it matter? Thanks for your responses.
|
[
"Hi there, an interesting question indeed.",
"You are right, O2 delivery depends on oxygen saturation, Hb concentration, and Cardiac Output (CO).",
"You may know that CO = Heart Rate x Stroke Volume.\nIt is also equal to Pressure / Total Peripheral Resistance. \nThis last formula should help answer your question, especially if we rearrange it to: BP = CO x TPR.",
"We can see that blood pressure is equal to the CO (force/pressure being applied on the system) as well as the resistance of that system. Should CO fall then pressure falls too. Similarly with a fall in TPR.",
"CO (equal to HR x SV) can fall due to a number of things. Each of these effect either the HR, the SV or both. For example a heart attach with effect both. Heart rate may fall due to injury to the electrical system of the heart, Stroke volume may fall due to loss of muscle and consequently uncoordinated muscle contraction. In the case of blood loss, stroke volume is effected. There is physically a decrease in blood volume and therefore less blood to pump with each beat.",
"What I've tried to establish is that CO and BP are closely related and consequently so are BP and O2 delivery. I do not however know of any formulas which connect the two."
] |
[
"DO2 = (SaO2-SvO2) x Hb x 1,34ml/g x CO\nCO = BP / TPR\n\nDO2 = (SaO2-SvO2) x Hb x 1,34ml/g x BP / TPR\n",
"But this is not a helpful way of looking at it. If BP goes down, it can be because of:",
"If BP stays low, you have the following scenarios:"
] |
[
"You can consider mean arterial pressure (MAP) in that equation, something of a perfusion pressure, if you will. In order for tissue/organs to get perfused, the MAP should be above 60. ",
"This actually gives a pretty good run-down on perfusion pressures and hemodynamic monitoring."
] |
[
"How are body cell-count and cancer likelihood related?"
] |
[
false
] |
Is someone with 20% more fat cells 20% more likely to get fat cell cancer?
|
[
"So of I'm tall, I want to be even thinner to keep the cancer risk down, right?"
] |
[
"So of I'm tall, I want to be even thinner to keep the cancer risk down, right?"
] |
[
"To add an interesting point: while what ",
"/u/turbo_speedwagon",
" said is true within a certain species, this does not hold true between species. Some larger mammals, like elephants for example, rarely get cancer due to upregulation of certain tumor-suppressors. ",
"https://jamanetwork.com/journals/jama/article-abstract/2456041"
] |
[
"Is there a system of geographical coordinates in space?"
] |
[
false
] |
Let's say I want to tell someone exactly where was the earth 6 month ago in space. Is there some kind of system like on earth to tell a specific position in the universe? Given that earth is moving around a sun moving in a galaxy in an expending universe, I struggle to imagine a system of coordinate that could allow to give the specific location of a point in the universe if everything is moving. If that exists, how is it 'expressed'? Like what will be earth 'location' in the universe in 6 month from now?
|
[
"There is, and it's called the ICRS (International Celestial Reference System). It is an idealized set of coordinates, the current realization of which is called the ICRF (International Celestial Reference Frame) version 3.",
"Astronomical reference systems are based on the celestial sphere, which is the backdrop of very remote galaxies and other radio sources that are for all practical purposes so distant as to be effectively motionless. If you can fix a set of three orthogonal axes with respect to this sphere, and define its center, then you're done.",
"The center of the ICRS is the barycenter (center of mass) of the solar system. This is quite close to, but not exactly at, the center of the Sun.",
"The two biggest features on the celestial sphere for Earth astronomers are the ecliptic and the equator. The ecliptic is the circle on the celestial sphere that the Sun traces out over one year. It is the projection of the orbit of the Earth onto the 'universe'. Likewise the equator is the projection of the plane of rotation of the Earth. If you label their intersection (the vernal equinox, which is where the Sun is around March 20th) as the positive x-axis, and define that positive z is in the direction of angular momentum of Earth, you've basically captured the idea. This is called equatorial coordinates.",
"Now this is tied to the rotation of the Earth, which is not as stable as first thought, which means this coordinate system moves. That's not good. The ICRS directions we use today are more or less 'frozen in time' on January 1, 2000, with a slight offset to account for the fact that we have better measurements since then.",
"The ICRF itself is defined as a list of coordinates of some very distant radio sources which can be pinpointed to very high accuracy:",
"https://hpiers.obspm.fr/icrs-pc/newwww/icrf/icrf3sx.txt",
"Other reading:",
"https://en.wikipedia.org/wiki/International_Celestial_Reference_System",
"\n",
"https://en.wikipedia.org/wiki/International_Celestial_Reference_Frame",
"\n",
"https://en.wikipedia.org/wiki/Equatorial_coordinate_system",
"Actual astronomers feel free to arrest me on inaccuracies."
] |
[
"That's all that could be said about that coordinate system. Unfortunately it can't really tell where we are \"in the universe\". But that's really hard and for observational purposes that your reference point is quite random and moves a bit doesn't really matter. So astronomers often stick to this\nBut if you want to know more there is also a coordinate system which is based on the galactical plane and center of it. This is useful to understand the dynamics of the milky way and where we are regarding to that. If one can go even further the best thing we have as a rest frame is the microwave background. From the dipole momentum one can get the relative velocity to that which you can see as our overall velocity in the universe. But when it comes to the reference point, the most general option we have is the center of the obeserval universe and that's where we are."
] |
[
"There is no unambiguous \"this place but 6 months ago\". Such a description would need an unambiguous definition of \"at rest\" (staying at the same place), which does not exist. Something that's at rest for one observer will move for another observer and vice versa. Both views are equally valid.",
"All the coordinate systems we can introduce are arbitrary. The ICRS discussed by ",
"/u/TheBB",
" uses the barycenter of the Solar System as reference. In that case Earth is ~300 million km away from the place where it was 6 months ago (twice the Earth/Sun distance). Similarly, you could use the barycenter of our galaxy as reference. Then Earth would be ~3 billion km away from where it was 6 months ago (largely from the Sun's orbit in the galaxy). You could also use the barycenter of the Andromeda galaxy, or any other reference you like, and you'll get a different answer every time."
] |
[
"Spilled battery acid"
] |
[
false
] | null |
[
"Baking soda and water.",
"Get it wet, and then add baking soda to it. As long as it's acidic, it'll keep fizzing. When it stops, add more soda. Repeat until new soda doesn't fizz."
] |
[
"Wouldn't recommend it. Baking powder is baking soda with acid added, so it's not going to neutralize a lot of other acid."
] |
[
"Will baking powder work?"
] |
[
"Why don't we feel pain during dreams?"
] |
[
false
] | null |
[
"What? I've felt pain in my dreams many times. Having a chronic illness will do that to ya.",
"It's interesting dreaming your in a car crash with a metal rod speared through your abdomen, then to wake and realize it's just some really bad stomach pains. Sucks waking up thinking your dying and then realize you practically are. "
] |
[
"We do, just not very often.",
"Here",
" is a paper that surveyed 185 people and found that about half of them had experienced pain in a dream before. They also had them keep dream journals for a while and had 18 reports of pain dreams out of some 3000 or so total dreams. Only one was from someone who was actually in physical pain at the time, which suggests that it's at least possible to dream pain out of nowhere. (And to be totally anecdotal, I've personally felt pain in dreams at least twice and woken up pain free.)"
] |
[
"Considering the types of dreams I sometimes have, I'm glad I don't feel pain in them. I already can feel chunks of skull in my mouth, or my body slumping to the ground, that's horrific enough."
] |
[
"What's the best evidence that suggests that climate change is caused by humanity instead of something else?"
] |
[
false
] | null |
[
"Climate change is very complex issue, but I think the most straight forward argument is:"
] |
[
"Well my layman's interpretation of things has been that, essentially Earth's climate has been fueled predominantly by two factors, energy from the sun and CO2 emissions. That throughout our history, ice ages have been caused by one or the other, or both, a drop in output from the sun, or a drop in CO2 in our atmosphere leading to a cooler environment.",
"And that, the energy output of the sun if anything has been decreasing lately, and that despite that the global temperature is rising. And this is because greenhouse gas emissions have risen, and what are we doing? Pumping tons of CO2 into the atmosphere.",
"But my friend remains unconvinced that humanity is the cause, and all I have is the above layman's interpretation, I don't have any hard evidence."
] |
[
"Give this a shot"
] |
[
"What is the chemical process by which ADD drugs help normal college students concentrate for longer?"
] |
[
false
] |
Just curious about the effect on the brain
|
[
"With regard to the actual chemical process of ADD drugs, ADD drugs are typically drugs that are stimulants with similar action to cocaine or amphetamine (or in the case of Adderall, actually is amphetamine). These drugs mainly work at the dopamine transporter, (as well as the norepineprhine and serotonin reuptake transporters), which is a protein that is responsible for reuptake of dopamine from the synapses after it has been released. They either inhibit the transporter, preventing it from clearing dopamine from the synapse, or they actually cause \"leakiness\" of dopamine and cause release of dopamine into the synapse, both mechanisms with the end goal of increasing dopamine levels in the brain. "
] |
[
"That was interesting, thank you"
] |
[
"One theory is that the prefontal cortex, the bit that helps the concious mind focus, stay on task, and filter out extraneous sensory input and thoughts is underaroused ( sleepy ) in individuals with ADD",
"The prefontal cortex acts as a censor and switchboard for your concious mind. Its a gatekeeper, filtering sensory input, and all the crap your subconcious is constantly coming up with. If it is 'sleepy', it gets sloppy, and more crap gets through, causing you to become distracted.",
"Most ADD meds work to 'wake' the prefontal cortex back to 'normal' levels so it can do its job. The fact that sports and exercise can work as well may be the reason why that goofy kid you knew in HS liked to skateboard or climb all the time, it helps calm his mind down because it wakes up his cortex. Sucked in school, rocks on the dirtbike. IE, adrenaline junkies may be self-medicating undiagnosed ADD."
] |
[
"Physics question: For K=(1/2)mv^2, how is K in Joules (a unit of energy) if the unit m*kg/sec is in Watts (a unit of power)?"
] |
[
false
] |
[deleted]
|
[
"m [kg] and v [m/s], therefore K = (1/2)[kg][m/s]",
" = [kg m",
" / s",
" ] = [J]"
] |
[
"Also, you have your Watts wrong.",
"Power = Energy / time",
"Watts = J/s = kg m",
" / s"
] |
[
"Also, you have your Watts wrong.",
"Power = Energy / time",
"Watts = J/s = kg m",
" / s"
] |
[
"Will leaving the bathroom light and fan on slow the growth of mildew?"
] |
[
false
] | null |
[
"Leaving the bath fan on will take humid air out of the room. This is a proven method to prevent mildew growth. It only grows where there is moisture."
] |
[
"Does light have no effect on growth? "
] |
[
"Not sure about that one. I know that UV light can help control mildew and that fluorescent lighting does emit UV radiation, but I am unsure as to the amounts and if it would affect growth."
] |
[
"Why would my son's doctor tell hm that he in fact \"broke every bone in his foot\" when he had broken 5 metatarsals?"
] |
[
false
] | null |
[
"We can't comment on personal anecdotes / isolated incidents without resorting to speculation which we try to avoid."
] |
[
"Not sure I follow. It's rather like Question: My teacher said the tomato is not a vegetable; why would she tell me that? Answer: The tomato is a fruit. ",
"I suspect if there was an explanation like that made sense, I would have received it, so my take away is that she was in error. Thank you for your time."
] |
[
"We can't say why someone said something. That's not a science question."
] |
[
"How does your body know your old enough for puberty?"
] |
[
false
] |
I know that environmental chemicals and hormones can affect the timing by a few months or years, but I'm looking for the mechanisms for the biological "clock" of the development of your sexual organs.
|
[
"No the second \"your\". Like this:\nHow does your body know ",
" old enough for puberty"
] |
[
"No the second \"your\". Like this:\nHow does your body know ",
" old enough for puberty"
] |
[
"You're* "
] |
[
"Dangers of a penny on train track?"
] |
[
false
] |
When I was going through drivers e.d. I remember one story that stuck with me that begs the question of "is this for real?” During a drivers safety class they dedicated an entire hour to trains. For that hour we heard every way a person could be killed by a train. One story was of a child who put a penny on the train track so as the penny would be crushed as an entertaining little thing to show to the friends. The story takes a turn when it's claimed that instead of being crushed the coin shot out from between the track and the wheels of the train. Not only in a direct course towards the child's head but actually fast enough the makes its way through the skull and killing the kid. My question is to if this is possible or even probable or is it simply a urban legend put for to discourage children from playing with the train tracks?
|
[
"The same article also claims that ",
"Pennying the tracks can result in a further danger — sometimes those coins shoot out from under the train's wheels at incredible speeds, turning them into potentially deadly little projectiles",
"but doesn't cite any sources or incidents. I myself find it highly unlikely, thinking of the very shallow angle at which the penny, the rail and the rolling surface of the wheel meet. Also, when you flick pennies, there's always something acting as a spring (usually your hand, against which pressure is applied), and I can't see that happening in the \"train on coin\" scenario.",
"That being said, I'm still keeping my distance. Like, if I took a small pebble instead of a coin, I could understand how fragments of the stone would start flying around. But coins?"
] |
[
"A penny is very small and light and a train is extremely heavy and moving at speed. It's theoretically possible for the train to flick the coin off at high speed given the right conditions, but I'm not convinced it could ever reach a high enough velocity from that situation to penetrate a skull, and unless the child was standing very close to the tracks then the coin spinning/fluttering in the air would rob a lot of energy from it.",
"I could maybe believe it took his eye out if he was standing very close and got unlucky with the angles. But it seems almost impossibly unlikely it would kill him."
] |
[
"http://www.snopes.com/science/train.asp",
"Plenty of kids seem to have died trying it, at least. "
] |
[
"What determines handedness, and why is there such an imbalance of left and right?"
] |
[
false
] | null |
[
"Handedness is not binary, but is actually a spectrum. You can find out where you lie on that spectrum using this:",
"http://www.brainmapping.org/shared/Edinburgh.php",
".",
"Here's the paper if you care to read further into it:",
"http://web.psy.ku.dk/Anders_Gade/Readings/Oldfield1971.pdf"
] |
[
"Handedness is not binary, but is actually a spectrum. You can find out where you lie on that spectrum using this:",
"http://www.brainmapping.org/shared/Edinburgh.php",
".",
"Here's the paper if you care to read further into it:",
"http://web.psy.ku.dk/Anders_Gade/Readings/Oldfield1971.pdf"
] |
[
"This question was ",
"recently answered on AskScience",
", so you may find relevant discussion there. ",
"And I'd like to remind folks that comments containing anecdotes and personal speculation will be removed. Please base answers on peer-reviewed scientific literature."
] |
[
"What pattern would I draw on a map if I followed the suns direction for all the hours of daylight and stay put at night?"
] |
[
false
] |
Does the pattern change from winter to summer solstice? Does the pattern change from latitude and longitude changes?
|
[
"You mean, if you walked towards the sun all day at a speed negligible compared to Earth rotation? ",
"On small scales it would be something that looks very roughly like a rectified sine wave where the x axis goes towards the sun latitude, the y axis going east. The closer you get to the sun latitude, the more it would shrink on the x axis and stretch on the y axis. The sun latitude is what changes between winter and summer solstice, so that also answers this part of the question."
] |
[
"I assume you are asking how your path would look on a 2D map?",
"I think it would be a series of half ellipses that gradually flatten out to a straight line as you reach the sun’s latitude. When you are at that latitude, you would basically walk due East in the morning, slow down until the sun is directly overhead, and then retrace your path due West in the evening.",
"From there, depending on how fast you walk, the day-to-day changes might not be significant enough to bring back the “half ellipse” pattern. I think it would make a sawtooth pattern- you would head out Eastward in the morning, walking a few degrees off due East, until you caught up with the Sun’s latitude. Then you would be walking straight, and finish up heading due West."
] |
[
"xkcd (I think) studied this a few years ago, but I don't find it any more. If you are slow you should just oscillate back and forth close to the equator if I remember correctly."
] |
[
"How can anything be more than 13.7 billion light years away?"
] |
[
false
] | null |
[
"The expansion of the universe has caused objects to move away from us at a rate greater than the speed of light. As a result, their distance from us now is greater than the age of the universe times the speed of light."
] |
[
"Two things:",
"First, for the most part, they've been emitting light continuously since they were much closer to us and thereby receding at a lower rate. We're seeing the light that was emitted at that time.",
"Second, we can even see some objects that have ",
" been receding from us faster than the speed of light (or, at the very least, that have been doing so since before light could travel freely through the universe). This is because the distance away at which an object must be in order for the expansion to cause it to be moving away at the speed of light (called the Hubble distance) is ",
". So an object starts out some distance from us moving at faster than the speed of light. It's emitting light constantly. The light that was emitted when it was closer to us is being carried away by the expansion, but how fast it's being carried away depends on how far away the source was when that light was emitted. Over time, our \"Hubble sphere\" (the spherical shell centered on Earth with a radius given by the Hubble distance) expands and can eventually \"catch\" some of that light, at which point that light begins moving ",
" us."
] |
[
"Things that were 13 billion lightyears away from us 13 billion years ago, whose light is just reaching us now, are now farther away because the intervening space has expanded sine then."
] |
[
"If ozone has a higher molecular weight than oxygen, then why does the main body of ozone exist higher up in the atmosphere?"
] |
[
false
] |
I was under the impression that higher MW -> higher density.
|
[
"why doesn't it all sink to ground level?",
"Because the kinetic energy of O3 (at its temperature) is larger than the potential energy differences due to gravity. You might compare to a set of tennis balls and ping-pong balls in a box. If you shake the box around sufficiently violently, you're not going to get any separation with the heavier tennis balls at the bottom.",
"Gravity would have to be much much more powerful to separate it to any significant extent. (see e.g. the extreme speeds in gas centrifuges used for nuclear isotope enrichment)"
] |
[
"I know that O2 + UV light = ozone, but why doesn't it all sink to ground level?"
] |
[
"I know that O2 + UV light = ozone, but why doesn't it all sink to ground level?"
] |
[
"How did this man travel through time?"
] |
[
false
] |
I am familiar (though I don't understand) the concept of moving so fast that the rate of time-if traveling through space- changes then if you were on Earth. Would this be the scientific reasoning behind "time travel"?
|
[
"The article is somewhat misleading. Due to the speed of his spaceflight, he experienced ",
"time dilation",
", and he has suffered through 20 milliseconds less time than us plebs back on earth.",
"Edit: Didn't read your post properly. So now my answer is \"yes\"."
] |
[
"In the same way that I have time traveled here from the late 1980s."
] |
[
"Honestly, I've never seen why this ",
" seen as time travel. If you had a super fast vehicle and did laps around the solar system for a bit to come back to an earth hundreds of years in the future, that sure seems like time travel to me. Just because time dilation is explained by science, doesn't mean that it isn't still the travel through time at a slower or faster rate relative to to the bulk of humanity, ie time travel."
] |
[
"About what percentage of current American Citizens are descendants of colonial Americans?"
] |
[
false
] |
I am referring to the U.S.A and Britain's 13 colonies for clarification. Alternatively: How many American Citizens have ancestors who immigrated to the country? I realize that this could be a difficult figure to come up with, if so what is the best estimate we have/can make?
|
[
"I feel like the intent of the question was \"What % of modern Americans have ancestors that were here when the country became an independent nation?\""
] |
[
"From the OP:",
"About what percentage of current American Citizens are descendants of colonial Americans?",
"Did you even read the title of the post?",
"Edit:",
"Even if you choose to answer the \"alternative\" question, from context you should realize s/he meant ancestors who immigrated to the country after independence. (or if we must be pedantic, when they said \"the country\" they meant the United States of America, which didn't exist to be immigrated to before independence)."
] |
[
"Just because I and a colonial-era American have a common ancestor in Africa, doesn't mean I have an ancestor in colonial America."
] |
[
"How many stars are contained within our radio bubble, and how fast is that number increasing?"
] |
[
false
] |
Just as the title asks, I have been unable to find and use a complete list of stars with their distances to calculate this. I suppose I could work it out based on the average density of stars in our galaxy, but I would love to see a realistic number.
|
[
"Assuming you take the date of radio discovery, and ignore the problem of signal strength, then you're looking at however many stars lie within about 130 light years.",
"It's a lot. ",
"This map shows all the stars within just 50 light years",
", and even then only the ones visible to the naked eye. There's 133 of them, and that is estimated to be 10% of the total number. So, lets say there's 13,300 within 50 light years. Scaling that up to a sphere with a radius of 130 light years (assuming the same average frequency) gets you a number in the region of 234,000 stars.",
"EDIT - if 133 is 10%, the total should be 1,330, not 13,300."
] |
[
"133 is 10% of 1,330, not 13,300."
] |
[
"It has nothing to do with decoding. It has to do with detection. Radio signals are just light of a kind we can't see with our eyes, and like all light, they fall off in intensity with the square of the distance (because light propagates as a sphere, and the surface area of a sphere goes by the square of the radius of the sphere). Eventually radio light is so dim that you'd need an antenna bigger than a solar system to detect it at all.",
"So if you define the \"radio bubble\" as the sphere within which it'd be possible to detect radio signals coming from Earth, then the number of stars within it is one: our sun. There aren't any other stars within that sphere."
] |
[
"What is the tone of a sound?"
] |
[
false
] |
Like, I understand pitch and changes in frequency, but what is the tone difference? For example, a trombone sounds different from a trumpet. Two people singing the same notes can have radically different tones. What, scientifically, is that tone? Why doesn't it just produce the frequency of the sound?
|
[
"When a piano or a violin plays an A 440, what that means is that the note has a fundamental tone with a frequency of 440 Hertz, but it also has a set of additional frequencies in conjunction with that. What makes an oboe sound different from a clarinet, and both of them sound different from a violin, is that for any given note, even though the fundamental frequencies are the same, the additional frequencies are different for the different instruments."
] |
[
"The additional frequencies can be expressed as a combination of harmonics of the fundamental. The Fourier transform can take any periodic waveform from any instrument and convert it into a series of harmonics."
] |
[
"I believe this is called ",
"Timbre"
] |
[
"Was the sky different colors through its history?"
] |
[
false
] |
I know the sky is the color it is because the current gases and their density absorb some colors and reflect mostly blue. However, the gases and composition of the atmosphere have changed over billions of years some number of times, so has the color changes as well? Was it ever more green or red?
|
[
"The ancient Earth had a methane rich atmosphere. Due to sunlight, some of the methane formed complex hydrocarbons that condensed into particles. The particles resulted in a pinkish-orange haze, according to ",
"this article",
"."
] |
[
"The wavelengths of light involved in ",
"Rayleigh scattering",
" (the process that makes the sky appear blue) are independent of the composition of the atmosphere. The Rayleigh scattering factor is inversely proportional to the wavelength; in other words, shorter wavelengths (blue and violet) are preferentially scattered no matter what the composition of the atmosphere. In fact, if Mars did not have so much dust in its atmosphere, it would have a blue sky as well (though much darker since it's atmospheric pressure is much lower).",
"The only way the sky could have been a different color is if something was suspended in it, like smoke or dust (as in the Martian atmosphere) or clouds of some sort (as in the Venusian atmosphere). Since I assume your question is referring to a \"clear sky\", then the answer is no, the earth's sky has always been blue."
] |
[
"I'm going to upvote this as a better answer than mine. A permanent haze (similar to ",
"Titan's atmosphere",
") would certainly qualify as a \"different color sky\"."
] |
[
"Are we all descendants of a single human being?"
] |
[
false
] | null |
[
"Wow, lots of half-right answers here. In short - we are descendants of a single pair of human beings: Commonly called (rather journalistically) Mitochondrial Eve and Y-Chromosome Adam. However, these were not necessarily a mother and father pair, nor were they necessarily alive at the same time. ",
"This is what geneticists call ",
"coalescent theory",
". In a population there will be some organisms that breed and some that don't. Some will make more offspring than others. Some of these offspring will survive, some won't. Because of this, some lineages will spread through the population due to natural selection or ",
"genetic drift",
". ",
"The process looks ",
"something like this",
". Each dot is a person, each row of dots is a generation starting at the top. So, for example, the person in the top left corner has two children, who have 1 and 2 children respectively. At generation 4 we see a new haplotype arising - the green dot - and this quickly sweeps through the population. All the dots on the bottom row - the current generation - are descended from this one. So, we can roll back this process and work out that there is a single ancestor. However, this is ",
" the same as the first \"human\".",
"There's a good article on ",
"this topic here",
"."
] |
[
"All women are descended from ME…",
"It took me two solid minutes of thinking to figure out that you weren't just emphatically asserting your virility here."
] |
[
"No, speciation is something that happens to a population, not an individual."
] |
[
"Are all atoms or particles of a particular type precisely identical?"
] |
[
false
] |
I know any two hydrogen atoms or protons or what have you are identical, but are they all precisely identical? Is there any reason to think that the mass of two protons would vary slightly, or is it fixed in some fundamental way?
|
[
"Protons etc are truly identical. The evidence for that is that it gives rise to the particular weird properties of quantum mechanical systems of bosons and fermions.",
"Atoms are also truly identical ",
" they're of the same isotope."
] |
[
"Some atoms are bosons, some are fermions. Everything with an integer spin is a boson, everything with a half-integer spin is a fermion.",
"EDIT: Some effects that this implies? If you take some bosonic ions (charged atoms) you can put them into an ion trap and have them undergo Bose-Einstein condensation. ",
"EDIT: It's integers and half-integers, not even and odd. Corrected that. Confusion comes because obviously integers are even multiples of 1/2, half-integers are odd multiples of 1/2."
] |
[
"Of course, yeah. Atoms have internal structure and thus two atoms of the same kind can be in different states. But that doesn't change the fact that they'll have the exact same internal structure, same energy levels, etc."
] |
[
"What's something that was incurable 10 years ago which is curable now?"
] |
[
false
] |
people actually like if their condition is incurable now, it's going to be that way for the rest of their life. How hopeless is it really? I know cancer has not been cured what about other things. Is there any decent chance that neuropathy will be cured soon? What has been cured in the last decade?
|
[
"They invented ",
"sofosbuvir",
" and basically cured hepatitis C virus. Has been very controversial over the cost... a 12-week course of treatment costs about $84,000. But this gives a 95% success rate, so they are basically selling a product that is putting itself out of business. And they would argue they have to recoup the research costs. ",
"It is a great topic of discussion for examining the subject of drug development costs and pharmaceutical prices."
] |
[
"I know cancer has not been cured ",
"Lots of cancers have been effectively cured. Especially childhood cancers, some of which have gone from survival rates of less than 10% to greater than 90% (see ",
"Twenty years of follow-up among survivors of childhood and young adult acute myeloid leukemia: a report from the Childhood Cancer Survivor Study.",
" and ",
"Childhood and Adolescent Cancer Survival in the U.S. by Race and Ethnicity ",
"). Admittedly, that's not on the 10-year scale asked about here."
] |
[
"Yes, that's something charlatans frequently use to explain why their miracle berry/mineral/widget will cure your disease, but it's not common knowledge because the \"big drug companies\" don't want you to know.",
"In reality, there are many reasons why companies are motivated to cure diseases. ",
"The first is that they are in competition with other companies. Company P may make a lot of money on dialysis, but they sure don't want company E to beat them to the next great treatment for kidney failure.",
"The second is that there are many humans that work in medical research, from academic researchers, to phama workers, to doctors. These are PEOPLE and care about other people. Really.",
"There are plenty of examples of when companies do prioritize profits over patients, but in general, progress toward disease treatments/cures/prevention is the goal."
] |
[
"Is there a genuine scientific reason why you shouldn't refill bottled water bottles with tap water, as some companies seem to claim on their labels?"
] |
[
false
] | null |
[
"I have honestly never seen that claim before, but I could guess that in some regions the tap water could be considered unsafe due to bacterial contamination. You wouldn't want that in your bottle.",
"I also had a funny discussion with one of my organic chem teachers a long time ago when she saw us drinking bottled water out of plastic bottles. She told us that she'd never do that due to all the unhealthy plasticizers that would be dissolved in the water... and then went outside for having a smoke."
] |
[
"nah, ",
"Phthalates",
" are still widely used, in fact they are so widespread that you can basically find them anywhere in our environment nowadays. If I remember the number correctly the global production of ",
"plasticisers",
" in 2014/2015 was like 8-9 million tons (I think it's stated somewhere in the Wikipedia article). Some of the unhealthy ones like ",
"Bisphenol A",
" are being phased out, but I'm sure you can still find them in cheap PC plastic bottles (I think in China it's still used, but don't quote me on that).",
"EDIT: regarding the teacher... well, she really was a good org. chem professor, but you kind of have to live in your own little world to be concerned about plasticisers from small plastic bottles and at the same time be ok with smoking cigarettes. What she inhaled (rather frequently) is way worse than what we got from the drinks."
] |
[
"I know of two reasons that this might be the case, although only one is scientific.",
"First, the non-scientific reason is that the company has certified the quality of the water in the bottle, and put their label on it. If you re-fill it, the quality will not be the same. (Arguably, it may be as good or better - your tap water may well have more rigorous specifications than the bottling company, who, by the way, fills it with their tap water) And if the label is intact, then you are creating a product that is not theirs, but has their label on it. A manufacturer would definitely not want you putting something into their bottle and possibly, although inadvertently, passing it off as theirs.",
"However, the second reason is the real driver, although the company will deny it. It's a scientific reason - economics. The economics of you re-filling their bottle with tap water means that they will have less money and you will have more. And they don't like that."
] |
[
"What is an electriic double layer capacitor and how are they different from a standard capacitor?"
] |
[
false
] | null |
[
"Result: a capacitor charged with low voltage over a long time can kill you because it discharges at high voltage in a short time",
"The only way for a capacitor to get a higher voltage than that which charged it, is by pulling the electrodes apart. That action does work against the charge, which results in a higher voltage. Many electrostatic generators work on that principle. Like the Van de Graff generator."
] |
[
"They are formed by the ",
"electrolytic double layer",
"/) that forms at the negative electrode. It is a layer of typically two ions thick of hydrogen atoms on the surface of the electrode. This polarization represents a stored charge. It is extremely larger charge than what occurs in a conventional capacitor, but has a limitation of being limited to only a few volts. Where as conventional capacitors can store at mega-volts."
] |
[
"Technically, capacitors store energy which is converted to volt-amps when discharged depending on the resistance of the discharging circuit and the internal resistance of the capacitor. Result: a capacitor charged with low voltage over a long time can kill you because it discharges at high voltage in a short time. "
] |
[
"Will missile defense technologies ultimately tame ICBMs?"
] |
[
false
] | null |
[
"Hello,",
"This would be more appropriate for ",
"/r/AskScienceDiscussion",
".",
"Best."
] |
[
"Ok thank you!"
] |
[
"And in a more general sense, do you believe that defense technologies will out pace attack technologies, helping to reduce the possibility of mutual destruction in the longer term."
] |
[
"In a future where fossil fuels no longer existed what building materials would be used to replace steel and concrete?"
] |
[
false
] |
If fossils fuels were no longer abundant and therefore could not be used to produce energy for the production of steel and concrete what materials would be use instead? Assuming some other energy source is able to power machines to mine the required materials but not enough energy to power the equivalent of the production of steel or concrete.
|
[
"No, he is saying that steel and concrete require energy, not fossil fuels. If fossil fuels run out today those industries would instantly switch to renewables, it's not an issue at all for them. Both steel and concrete require heat to produce, and if suddenly an electric furnace was 10 times cheaper than a gas furnace, they would switch immediately. Nobody would switch building materials, because there is nothing out there with the same strength. You can't really build a 100 floor wood building. Your damn made out of wood isn't really going to last.",
"If fossil fuels went away today, energy costs would spike, and more energy intensive building materials would become more expensive. That would change how we pick building materials (wood would be somewhat more common). For buildings we would stop building up, because building out (and taking more land) would suddenly become cheaper. You also have to understand that when the prices spike like that we switch fuel sources. Before your packages were shipped using diesel powered trucks, if fossil fuel was gone then biodiesel, which is now about $5/gal would suddenly be the fuel of choice.",
"We have ways of getting steel and concrete without fossile fuels, it just costs more right now. They wouldn't go away simply because you couldn't buy fossil fuels, their prices would just jump, and people would deal with it."
] |
[
"Mostly, if all you need is heat, it's more efficient to go straight to the heat. Electricity generation systems have inefficiencies in turning whatever their energy source is into electricity, e.g. fossil fuel combustion or nuclear reactions produce heat, heat engine turns some heat into work (~30-40% efficiency because thermodynamics), generators turns work into electricity (~95% efficiency?), electric furnace turns electricity back into heat (~100% efficiency), or solar panels turn photons into electricity (~20% efficiency? ~40% with state-of-the-art multijunction cells), and in both cases all the rest of the energy is just vented to the environment as \"waste\" low-temperature heat. You could instead just burn the fossil fuels or focus the photons into a thermal absorber and get ~100% of the energy as heat where you want it. ",
"The one case I can think of where you would do that is using nuclear electricity if your required process temperature is above the acceptable temperature for the nuclear fuel elements (or if people don't like the idea of having a miniature nuclear reactor in the factory to provide process heat). In that case it's impossible to directly take the heat from the reactor, so you take electricity instead, despite the inefficiencies. If we ever get them running, fusion plants might have similar problems. ",
"Note that this is at the industrial scale ... the furnaces in the labs at my university are electric furnaces, because they do work perfectly well, and it's easier to pipe in electricity than deal with fuels or solar concentrators. It's just less efficient, thermodynamically, but at small scales that doesn't amount to all that much, especially with cheap fossil-fuel based electricity. "
] |
[
"If the energy use in production were a concern, I'm not sure it'd ever just get to a point where, suddenly, we can mine but can't do any production at all. Why should we assume that production and not mining would necessarily even be the bottleneck here? Anyway, surely it'd just get more expensive, and projects that required it would be scaled back as the price rose. There would always be some niche uses that would pay a high price for it. And with such a huge energy deficit, obviously, there would be a lot more problems in our economy than just steel and concrete production. That's not even the most critical energy user in our economy, surely the lack of electricity and transportation would hit us sooner. It doesn't even matter if we can produce steel and concrete or any replacement or not if it can't be moved anywhere. It's not safe to assume under such circumstances, that something would just emerge to replace those two wholly and in all capacities, except just requiring much less energy consumption. ",
"If we are to assume that fossil fuels are not replaced in anything near an equal measure by some other source, well, what did we do before we had an abundance of energy? Wood? Thatch roofs? Stone? The situation your describing would be pretty grim."
] |
[
"Why do airplane windows need to have that hole?"
] |
[
false
] | null |
[
"\nForemost. ",
"It has the function of demisting the outer window as well.",
"The structure is as follows. Outer pane and middle pane form a unit. Middle pane has a small breathing hole. On the inside of this unit is a quite large air gap and then the inner pane.",
"The outer and middle panes are load bearing. Where the outer is meant to be the primary and middle is a spare. Inner pane takes daily wear and tear like brushing, scratches and such away from the load bearing unit.",
"So if the outer pane fails the middle pane keeps the pressure? But what about that hole?\nCorrect, the ecs (air compressor) is vastly overpowering the loss of air through that hole thus keeping cabin pressurized. ",
"Why is it important?\nIf the outer pane fails, it is important that it looks like it fails. The pressure supplied by the small hole makes sure of that, since it pressure equalizes and transfers the load from the middle pane to the outer.\nWithout it, the middle pane would be taking all of the pressure. ",
"Source: 747-400 MAINTENANCE MANUAL 56-00-00 on wards til end of chapter"
] |
[
"Its a safety procedure, so if something happens during landing/takeoff, crew and passengers can easily see outside and rescue crews can easily see inside. "
] |
[
"There are two windows: the first one is to separate the plane and the outside, the second one prevents you from touching the first window since it is very cold when in flight.",
"\nBecause there are 2 windows, we have a space between them which should be at the same pressure as the inside of the plane (otherwise, there would be an undesired effort on the inner window), hence the hole."
] |
[
"What causes sunscreen to lose potency over time after application?"
] |
[
false
] |
Why is it that sunscreen only lasts a limited amount of time after application? Is it that it wears away, or that more sunlight is able to break through it over time, or what?
|
[
"It has always been my understanding that over time it is washed off or worn away by water/sweat/rubbing (like wiping your eyes to get water off takes a little sunscreen with it).\nMy dad (the protective doctor) has always recommended re application every 3-4 hours if you are just outdoors and every 2 hours when swimming. Also allow 15 minutes for sunscreen to dry before swimming (duh). "
] |
[
"On ",
"/r/skincareaddiction",
", I read that the skin absorbs some of the sunscreen over time, so it's no longer a barrier on the surface of the skin. Apparently that's why some powder SPFs are recommended instead."
] |
[
"So if I put sunscreen on and just stand there, then I could not get burn for hours?"
] |
[
"Is there any evidence that time is dimensional?"
] |
[
false
] |
By dimensional time i mean like a film strip where the past and future exists or is it more like motion in the sense that there is just a present that is always changing?
|
[
"Think of a 2D plot with space as one axis and time as another. Events all have a time and space coordinate. Einstein showed that when you change your velocity, the time and space coordinates \"mix\" together and rotate/twist around eachother.",
"For example, let's say you had two events, one at (0,0) and the other at (5,0) (that is, they happen at the same time, but different places). Einstein showed that if you were in a different frame of reference, to ",
", the events would happen ",
". They would no longer be simultaneous to you.",
"So two events at the same instant in time but at different spots in space, to some people are actually at different instants in time and different spots in space as well.",
"This means that \"now\" is really a relative term. What you consider \"now\" -- all the events you consider happening at a given instant in time -- actually is not \"now\" for someone else moving at a different velocity -- their collection of \"now\" events are different from your collection of \"now\" events. Some of their \"now\" is in the future for you, and some of their \"now\" is in the past for you."
] |
[
"Well...I'm not sure this is evidence enough for you, but we can \"rotate\" time (that is, two events separated only by space and not time can be rotated so that they are separated by both, and two events separated by time but not space can be rotated so that they are separated by both), mixing time and space together in that sense. The idea of \"now\" doesn't make any real physical sense, because two events separated by space only and not time (that is, that happen at the same \"time\" at different places) can be made to happen at different times as well in a different frame of reference."
] |
[
"Sorry im not sure i understand, how can we rotate time?"
] |
[
"Why does beer/soda carbonate better when cold?"
] |
[
false
] |
So there is a discussion going on in regarding carbonating beer. My mother-in-law, a long time homebrewer that under forced carbonation in a keg, beer will carbonate faster cold than if you carbonate it at room temperature. I've seen this occur myself. The absorption rate is very slow when warm, but the solvent will take the CO2 overnight if the keg is left in ice and chilled. It seems counterintuitive from a high level, as I would assume the water molecules would be more open and around faster when warm, and would be more will to mix with CO2. Best I can find however, is that it is related to the molecular polarity of water (polar) and CO2 (non-polar, I think). So why does the polarity cause water/beer/soda to carbonate better/faster at lower temperatures than warmer ones? Thanks.
|
[
"Carbon dioxide ",
"dissolves better in cold water.",
"Also note that carbon dioxide dissolved in water forms carbonic acid:",
"H2O + CO2 <--> H2CO3",
"The reaction is reversible, of course.",
"Things start to get complex from here, but this reaction also explains why you get \"sand\" in your hot water heater. Calcium carbonate (CaCO3) has limited solubility in water; it is less soluble in ",
" water, which is kind of unusual in that solids are almost always more soluble in hot water. A complete explanation ",
"may be found here."
] |
[
"It's not so much a function of polarity as a function of the temperature ",
"What you are describing is a function of [Henry's Law].(",
"http://en.wikipedia.org/wiki/Henry%27s_law",
")",
"\"At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.\"",
"Now in this case, the type and volume of liquid is constant, but what you have changed is the temperature. When the temperature is decreased, the amount of gas that will dissolve in the liquid is increased. So, by cooling the keg, more CO2 will be \"trapped\"/soluble in the beer. ",
"If you would like a more thorough explanation I would highly reccomend the solubility video at Khanacademy. It starts with salts, which relates more to your polarity observation, and ends with gases, which starts around the 9:30 mark. Cheers.",
"http://www.khanacademy.org/science/chemistry/v/solubility"
] |
[
"It seems counterintuitive from a high level, as I would assume the water molecules would be more open and swimming around faster when warm, and would be more will to mix with CO2.",
"And it is intuitive that if you shook a beer or other carbonated beverage that the gas would become more entrenched or more likely to escape?",
"Dissolving gas into water is governed by the balance of intermolecular forces. The higher the temperature the greater chance that a gas molecule can be knocked out of the solution."
] |
[
"Zero-calorie sweeteners: What are these substances? What exactly am I putting into my body? Why is there a choice, and which is doing the least damage to my health? [pic inside]"
] |
[
false
] |
This always bothered me. Why is there a choice of FOUR different sweeteners, if they all taste EXACTLY the same and all they do is sweeten my coffee?
|
[
"So let's look at the four you've posted:",
"Apart from the business concerns of competitive sweetener manufacturers, the variety exists to meet other needs as well. Consumers concerned with 'natural' foods will gravitate towards the erythritol/stevia blend, and aspartame will be avoided by phenylketonurics, those who do not taste it properly, and people who get their health information from the internet. Saccharin has the advantage of age and familiarity for anyone who became accustomed to it before the 1980s when aspartame was introduced."
] |
[
"Well, why do you have more than one brand of ketchup or whatever? That's the free market.",
"What you're putting into your body is simply chemical compounds which activate the same molecular sensors as sugar, but which don't have the same metabolic content. The ones you linked to also contain sugar (dextrose, maltodextrin). To name a few artificial sweeteners there's, ",
"sucralose",
", ",
"aspartame",
" and ",
"saccharin",
". They all have various pros and cons, in terms of taste, cost, heat-stability and other side-effects. (e.g. aspartame contains the amino acid phenylalanine, which people with the rare genetic disorder phenylketonuria need to avoid)",
"There's a huge amount of scares and misinformation about these things. They've also been subject to more scientific scrutiny than almost anything else you put in your mouth, and been found to be ",
". -That's the scientific consensus. (Why would we allow them otherwise?) You might want to compare that to coffee itself, which is far from as well-investigated, but known to contain ",
"PAHs",
" and ",
"acrylamide",
". (Both carcinogens. Also present in a lot of fried and grilled food)"
] |
[
"Aspartame is a protein. It has the same number of calories per gram as sugar. However, it is 200 times sweeter than sugar, so you can use 1/200th as much to achieve the same level of sweetness and end up with a 0 or 1 calorie drink. ",
"I believe other artificial sweeteners work on the same principle. "
] |
[
"Is it true that the human brain is the least developed brain of all mammals at birth?"
] |
[
false
] |
I was watching a documentary and a psychologist made the claim. I looked online but I couldn't find anything.
|
[
"I believe the reason for this claim is that the ratio of birth size/weight to brain size/weight in human infants is unusually large and consequently takes much longer to develop. Some animals can even walk after being born. However, with humans, that would be crazy. ",
"Humans take a huge amount of time to develop and I think that is some evidence to support the claim that we are born with underdeveloped brains."
] |
[
"It's not true, marsupial babies are born at a less developed stage than any placental mammal. And lots of mammals have small, helpless babies...mice and rats and bears, to name a few. At least humans have their eyes open! ",
"But humans do have relatively undeveloped brains especially when compared to other primates. This is because adult humans have enormous brains, and if we were born with more mature brains they'd never fit out the birth canal. So human offspring do a lot of brain growth ",
" birth compared to, eg, chimps. "
] |
[
"Hey, thank you for the answer.",
"I'm wondering if you have any sources? I want to debate the point but I don't want to seem ignorant "
] |
[
"If atoms only emit light with specific (discrete) values for wavelengths, why do bodies emit a continuous spectrum of radiation?"
] |
[
false
] |
[deleted]
|
[
"A black body is an idealized model, like a perfect vacuum or a frictionless surface. It is an approximation which holds up well in many cases, but actual things deviate from the black-body model.",
"The hypothetical black body is a substance that absorbs all light perfectly, and emits light in a well-defined spectrum depending on its temperature, ie. blackbody radiation. A single hydrogen atom is therefore a poor candidate for applying the black-body model, because it only absorbs some wavelengths of light and generally does not behave much like a black body on its own.",
"But if you took a huge ball of hydrogen, like the sun for example, and heated the whole thing up to 6000 kelvin, it follows the black-body model quite well. At this temperature, we happen to get the spectrum we are familiar with from the sun.",
"It is still the case that photons are emitted from electrons changing energy states. But energies of electrons are not limited only to their quantum numbers. There are also vibrational energy states, so if you have a gas of really hot hydrogen atoms bouncing around, there will be a lot of kinetic energy that will result in electrons being bounced around, emitting light accordingly. This is somewhat independent of what particular material it is, and then you have blackbody radiation :)"
] |
[
"But if you took a huge ball of hydrogen, like the sun for example, and heated the whole thing up to 6000 kelvin, it follows the black-body model quite well. At this temperature, we happen to get the spectrum we are familiar with from the sun.",
"Even in this case, there are still some pretty strong peaks, but aside from these it's pretty well described by the black body model. Black line is idealized black body, yellow is what the sun actually produces: ",
"http://bouman.chem.georgetown.edu/S02/lect23/Solar_Spectrum.png"
] |
[
"For my answer I'm relying on \"Optical Coherence and Quantum Optics\" by Mandel and Wolf as well as Yariv's \"Quantum Electronics,\" both bibles in their respective fields.",
"Although the previous answers are good, they are far from telling the complete story and in my opinion carry a few misconceptions.",
"Although apocryphite is right in claiming that a single hydrogen atom is a poor candidate for the black-body model, it is not because hydrogen only absorbs some wavelengths, but rather because a single hydrogen atom is not a statistical ensemble i.e. you can't speak of it as having a temperature. Conversely, this is why the sun is in fact a great black body, and, as Mandel states and indeed the graph Davecasa links to suggests, any deviations are due to the effects of filters, generally defined.",
"Now, we have have realized our first important assumption - we are working with a statistical ensemble of atoms at some temperature. What else is in equilibrium with this ensemble? The light field, of course. We can write the Hamiltonian for the light field quickly, and using our knowledge of photon statistics can derive how many photons we can expect in each mode. I think you're already familiar this part, and the important question you're now asking is exactly ",
" the ensemble you're studying couples with the light field.",
"Now, say we have the simplest two-level system, for instance a hydrogen atom with a ground state and only one excited state. If we wanted to write out the energy contribution of such a system and the light around it, we must formally include all wavelengths of light and in doing so realize that transitions between the excited and ground state may still be mediated by creation/annihilation of photons at different frequencies than the excitation frequency.\nOnce you accept that even two-level systems can interact with quantized modes other than their natural frequency, it should make sense that many-level discrete systems can, once in equilibrium, result in a black body spectrum. The caveat \"equilibrium\" is perhaps the most important here. If the pretend box our light is in is supposed to be at 3000 C, then whenever it doesn't follow the black body distribution, it is out of equilibrium. At this point it's probably best to point to what ultimately is driving the thermal equilibration process: maximization of entropy. This is a convenient goal for our physical processes and the most fundamental one."
] |
[
"What happens to the electricity generated from a solar panel if nothing is using it?"
] |
[
false
] |
If you have a solar panel sitting in the sun, but no load is connected to it and nothing is using that power, what happens to the energy? Does it get dissipated elsewhere? Will the solar panel overheat?
|
[
"There will be potential energy but until there is a path for current to flow no actual energy will be produced. ",
"Sort of like a battery it has tons of energy stored but there is no heating until there is a pathway for it to move. The release of energy is where the heat comes from."
] |
[
"There will be electric potential generated by the cell, and it will behave almost like an open circuit. In all of these devices, there are second-order leakage effects. While most of the energy you generate is getting stored electric potential, some of it is burned inside the semiconductor solar cell itself. This leakage current always exists, it just happens to have a much bigger effect here. As the voltage on the solar cell rises, it becomes harder and harder for the cell to produce more energy, so eventually the cell will reach a point where the leakage current (which tends to increase as the voltage across the cell rises) of the device consumes all the excess power generated. The point where the leakage current is equal to the current generated is the maximum open-circuit voltage of the cell. "
] |
[
"1) There is no \"electricity\" being generated if the circuit is open. The voltage between the two leads on the module can be measured, and is known as Voc, or Open Circuit Voltage. ",
"2) \"What happens to the energy?\" The modules rise in temperature just a little due to the solar energy not being converted to electricity and being conducted away. "
] |
[
"Is it possible for us to properly assume what's further beyond the observable universe? (Other minor questions inside)"
] |
[
false
] | null |
[
"Is it possible for us to properly assume what's further beyond the observable universe? (Other minor questions inside)",
"Well, cosmologists largely operate under the assumption of homogeneity; i.e., that the universe is largely the same everywhere. Our observable universe appears to be largely homogeneous (modulo local variations in the form of galaxy clusters and voids), so this is at least a reasonable assumption. But we can't really ",
" anything about the nature of the universe outside of our observable universe.",
"The reason that we cannot see past the observable universe is because light from objects farther has not had enough time to reach us, correct?",
"Correct.",
"Would this not mean that as time goes on, more and more is visible to us, because light from those further objects finally reaches us?",
"Yes for now, but possibly no in the future. It depends on just how the rate of expansion changes in time.",
"Is the process above counteracted by the increasing rate of spacetime expansion?",
"Quite possibly, but we haven't nailed down the relevant parameters to say for certain."
] |
[
"Thank you very much!"
] |
[
"I think the possibility of cosmic isolation is both fascinating and terrifying at the same time. I just wish i'd be around to see how things pan out. :/"
] |
[
"How effective is mouthwash? How close to \"sterile\" does it make your mouth and for how long? (Both non-alcohol and alcohol versions)"
] |
[
false
] |
It seems pointless to me to try and sterilize your mouth for about 20 minutes (or however long it takes for the bacteria to get back to a normal population). I still use it though (non-alcoholic one) after using a tongue scraper because it makes my breath fresher and mouth feel cleaner. How effective is the best tongue scraper? I think the tongue is like a sponge so I'm guessing a lot of the bacteria are underneath the surface?
|
[
"Mouthwashes in a nutshell:\nThe only effective mouthwashes are Listerine, Crest ProHealth, and ACT (fluoride mouthwash). Everything else is like a breath mint in liquid form. Your mouth will never be sterile, no matter how long you swish. Additionally, it's bad to swish for longer than recommended because it will burn your tissues (consistently damaging your tissues makes your cells turnover rapidly. When cells turnover rapidly, they make mistakes, which leads dysplasia, and can eventually lead to oral cancer). It takes a small amount of time for the bacteria to repopulate, I don't remember exactly how long. The only time I recommend that someone start using mouthwash is: 1) when they have very small cavities that have not extended past the enamel/dentin junction (in that case, I recommend ACT); or 2) when they don't have the dexterity to brush/floss (use Listerine or ProHealth).",
"Things that are known to cause bad breath: gum disease, decay, dry mouth, acid reflux, weight loss (aka, \"acetone breath\")...",
"Tongue scraping/brushing is great for reducing bad breath. I still use a toothbrush. But if your gag reflex prevents you from doing that, then use the loop type of tongue scraper. You've done a good job when your tongue is pink, it should not be white, yellow, or brown.",
"-DDS, 2008"
] |
[
"Should one rinse their mouth with water after using a mouthwash or not?"
] |
[
"The process is the same as a chemical burn from overuse of mouthwash. The trauma causes the need for rapid cell turnover, which leads to dysplasia. I have fitted a few people for nightguards because they would tear their cheeks up at night."
] |
[
"If it is a common misconception that your heart is on the left side of your body (and it's very much in the centre), why do you feel pain in your left arm first when a heart attack starts?"
] |
[
false
] | null |
[
"It's a misconception that heart pain starts jn the left arm. That is largely a Hollywood invention. When pain is present, the most common location for it is in the center of the chest, and it may radiate in a variety of directions-- for instance to either arm, the jaw, or the back of the shoulders. ",
"(A large fraction of heart attacks, perhaps as many as 45%, do not cause pain at all. This appears to be particularly common in women.)",
"That said, left-sided arm or jaw pain is somewhat more common than right-sided. This is probably due simply to location. Though the heart is basically centrally located, it sits at an angle such that the apex and the hardest-working parts are to the left side of the midline. "
] |
[
"It is more to the left than you think.",
"\nFrom what I've studied, internal organs do not have nerve endings responsible for pain perception, therefore during organ failure or distress, nearby surfaces will react to the problem (as in the case of the shooting pain associated with appendicitis). This can be in both arms, the pectoral muscles, even the jaw or abdominal region. The fact that the left arm is the most common occurrence seems to be simply a proximity reaction. Also it is interesting to note that for some reason, these pains are more common in women, though I do not know why this is."
] |
[
"Good question, what you said makes sense. It's possible there was never a need for pain receptors since these organs are usually protected by body parts that do have pain receptors. One would think it would be useful for some organs to have pain receptors such as the heart or brain, but as we know, brain surgery is performed while the patient is wide awake with no anesthetic used on the brain and the patient cannot feel a thing."
] |
[
"What is the fastest we've been able to accelerate a heavy element? For example, how fast have we gotten really heavy metals to accelerate in a particle accelerator, nuclear blast, etc.?"
] |
[
false
] | null |
[
"The LHC accelerates lead nuclei to roughly 99.99994% the speed of light. The RHIC does similar but with gold."
] |
[
"I don't know if this is along the lines of what you were talking about, but it's very interesting nonetheless; during the nuclear tests in the 1950's a steel manhole cover was accelerated out of a test shaft by a nuclear blast. Scientists had a high speed camera trained on the manhole cover, which only appeared in one frame of the footage. ",
"Calculations estimate the 2,000 lb cover was travelling at approximately 41 miles per second, or 147,600 miles per hour. Almost four times faster than Voyager 2.",
"To date, it's the fastest man-made object in human history, by a substantial margin over any of its competitors. Even the Juno spacecraft currently slingshotting around Earth towards Jupiter will reach a maximum velocity of only 25 miles per second, which is still quite a fair bit slower than the nuclear manhole cover.",
"http://en.wikipedia.org/w/index.php?title=Operation_Plumbbob#Propulsion_of_steel_plate_cap"
] |
[
"If we'd accelerate a radioactive nucleus to those speeds would decay slow down from our point of view?"
] |
[
"Why are toddlers and infants always putting things in their mouth?"
] |
[
false
] |
Is it to build immunity to bacteria? To explore their surroundings? Or is it simply just a quirk that they seem to exhibit?
|
[
"Exploring. Infants don't actually put things entirely inside their mouths very often, instead they bring them to their lips. This is because their lips are more sensitive and have better motor control and sensory feedback than their hands and fingers at that age, so they're better at exploring textures and shapes."
] |
[
"depending upon age, it is mostly to do with teething. (",
"http://en.wikipedia.org/wiki/Teething",
")",
"If you had sharp teeth emerging from your jaw, penetrating your skin, you'd be chewing sticks too.",
"(and remember, we're just apes, dealing with all sorts of plastic stuff lying around)"
] |
[
"I also want to comment that younger babies have an awful sense of vision (its blurry shadows and colors for months), so tactile information would be the easiest to get"
] |
[
"For this last flu season: \"Hospitalization rates in children 0-4 years old and adults 18-49 years old are the highest on record according to the CDC, surpassing the rate reported during the 2009 H1N1 pandemic.\" How is this possible with a quarantine during part of this last season?"
] |
[
false
] | null |
[
"Flu season ended before the lockdown could really have any effect. The page that you posted says that the flu season ended on april 4th, shortly after the lockdown started. The peak of the flu season was much earlier and should have been largely unaffected by the lockdown."
] |
[
"Check out this link for the ",
"Weekly US Influenza numbers",
". You'll see that the majority of the cases peaked in January. In fact, after March, which is when most states implemented their quarantines, the cases drop sharply.",
"This last flu season started earlier than usual."
] |
[
"Got it. ",
"I thought the flu season went until June when I posted this."
] |
[
"Why does our skin itch?"
] |
[
false
] | null |
[
"This has been discussed a few times before, best to ",
"search",
" first."
] |
[
"I don't know."
] |
[
"Mine doesn't itch. You should go see a doctor."
] |
[
"How do microbes in the human body survive our immune systems?"
] |
[
false
] |
Is there a constant struggle between the non-human organisms and our immune systems or do they operate without issue?
|
[
"It's not clear what \"microbes in the human body\" you're asking about. In general, there are very few microbes in the human body, and most of those that do get there are rapidly eliminated by the immune system.",
"But what about the enormous numbers of bacteria, etc, in the digestive system? Strictly speaking, those are ",
" in the human body. The inside of the gut is ",
" the body. Humans are basically long hollow tubes of meat, and the esophagus, stomach, and intestines are connected directly to the outside, not the inside. (To get food inside your body, it has to be broken down into tiny pieces and transported across the membranes that separate inside and outside.)",
"Of course, the gut is a special kind of \"outside\". The immune system does keep track of it, but is exceedingly tolerant of microbes in there. The immune system that contacts the outside world is highly specialized to not overreact. In the absence of damage to the tissues there, there's little immune response. This isn't just passively ignoring the area, either; there's a lot of very active suppression of immunity, where one part of the immune response identifies microbes and specifically says, Hey guys, these bugs are OK, they're cool, calm yourself down -- actively turning down immunity in the areas.",
"This is a huge topic, with literally many thousands of articles about it, and it's hard to summarize. Wikipedia on ",
"mucosal immunology",
" and ",
"immune tolerance",
" has some information, searching PubMed for ",
"\"Mucosal tolerance\"",
" is a start, ",
"Immunity and Tolerance Induced by Intestinal Mucosal Dendritic Cells",
" is a recent review of one specific aspect."
] |
[
"The immune system performs surveillance within the body looking for antigens. Antigens are proteins recognized as foreign. This is done via toll-like receptors (TLRs), circulating antibodies, and major and minor histocompatibility complexes (MHCs). The immune system will immediately and vigorously attack and attempt to destroy anything detected as foreign. Some microbes get around this by hiding inside cells (intracellular pathogens) and producing enzymes that breakdown the digestive enzymes used to destroy said microbes. Other microbes, such as some viruses, can lay dormant for years before becoming active and causing an immune response (shingles is an example). ",
"You're probably asking about the gut flora. The gut is technically outside your body, making you a highly convoluted tube. The bacteria in the gut is generally quite happy living in the lumen since it is a controlled environment and nutrient rich. The lining of the gut is equipped with specialized immune tissue called mucosal associated lymphoid tissue (MALT). The MALT is specifically designed to prevent intraluminal bacteria from escaping the gut and causing problems. ",
"When the gut bacteria has a port of entry, such as in a bowel perforation, a person can become very ill quick quickly. Without immediate intervention bacterial peritonitis can be lethal. Even with treatment, survival is intermediate. Even without performation, some people with ascites (fluid build up in the abdomen), get whats called spontaneous bacterial peritonitis (SBP). This is when the gut bacteria, sensing more nutrient rich ascitic fluid, will translocate through the mucosa to the peritoneal cavity and take up residence there. ",
"In short, bacteria truly IN your body are quickly dealt with or there are serious problems. The bacteria in you gut and on your skin are just there and our bodies have a sort of live and let live attitude toward them.",
"If you have specific questions on how the immune system works, ",
"this",
" is a pretty good introduction. If you need further details, feel free to message me and I'll answer what I can."
] |
[
"To add to the other comments, I want to emphasize that bacteria and other microbes like viruses and fungi also have defense mechanisms against the host immune system (they can block phagocytosis, the oxidative burst response, NETs, etc). Similar to the Red Queen hypothesis, bacteria have evolved alongside their hosts to become better at surviving the immune system (except they can do it faster). Interestingly enough, this actually adds to the problem of antibiotic resistance because antibiotics work basically the same way as the immune system. If bacteria are already getting good at surviving the immune system, then there's a chance that they'll have the same mutations that would allow it to survive an antibiotic treatment. "
] |
[
"Does the conditional expression of a transgene in a mouse model ever trigger an immune response?"
] |
[
false
] |
As an undergrad I worked with a few mouse models in which we got the mice to express the human form of a few signaling molecules and a receptor protein, but expression was delayed until adulthood. In a model like that, what is to stop the new protein from being recognized and acted upon as a foreign antigen?
|
[
"Not all transgenic mice are SCID. I think the responses here are due to variations from field to field....it would have been very hard for me to study allergic airway disease using inducible transgenes in SCID mice! So yes, they were quite immunocompetent...too much, sometimes. ",
"Typically, it's because no inducible promoter is perfect. They all leak, and you get a low level of expression no matter what. This issue does come into play with gene therapy, though, and there are whole fields of design on how to avoid it.",
"According to the gene medicine group down the hall, the TL;DR is \"when in doubt, make it express in the liver.\""
] |
[
"Interesting question. I don't know how a normal mouse would react, but most of the time you make transgenic mice that you use a model that has SCID (Severe combined Immunodeficiency) so it wouldn't matter anyway."
] |
[
"Like Bored says, if there is nothing stopping the immune response, a immune response will be mounted against the protein.",
"The same is true when the transgene encodes a hairpin sequence, such as used in RNA interference studies. Long double stranded RNAs will induce the interferon pathway, leading to cell death."
] |
[
"Why don't electrons traveling in the orbitals of atoms lose energy, although they are a mass traveling a narrow space which should require some kind of acceleration to stay close to the atom?"
] |
[
false
] |
As I learned in physics the acceleration of a mass (and the change of direction is an acceleration) results in a change of kinetic energy, so traveling in a narrow space like an electron around an atom requires acceleration to change the direction of the electron to stay around the atom, so then why are atoms stable at all and why don't electrons bounded to atoms lose energy all the time? Edit: I meant acceleration of charge, not mass, thanks for pointig this out.
|
[
"This is a good question, and one of the questions that led us away from the classical model of the atom and towards the quantum model. You are correct that the classical way we think of an atom (positively charged nucleus, negative particle in a circular orbit around it) would emit radiation, causing the electron to decay into the nucleus. The fact that this doesn't happen means this must not be the correct model.",
"We now know that the electron is not a point mass orbiting the nucleus at all, but a \"density cloud\" which constantly surrounds it. You've likely heard of the \"wave particle duality\" of light- well it's not just light which has this duality, all particles do (it's just most pronounced with light, since the less mass a particle has the more \"wave like\" it acts). So, the electron is in a wave around the nucleus (and actually, when it is in its ground state it is in a standing wave) so it doesn't radiate (in fact, when it is in an excited state it is no longer a standing wave, which is why it does radiate and then fall down to the ground state). "
] |
[
"when it is in an excited state it is no longer a standing wave ",
"I understand that an excited state is not a ",
"stationary state",
" and that stationary states are always ",
"standing waves",
" but does not-in-a-stationary-state necessarily also mean not a standing wave (a travelling wave)?",
"\nI would expect the confines of the wave in its excited state would still require the wave to be standing (or if not require, at least allow)."
] |
[
"Good Question. A stationary state is just a state that is time independent in all \"variables\". (So solutions to the time independent Schrödinger equation, more specifically eigenstates with eigenvalues). So a non-stationary state doesn't have to be a \"completely\" non-standing wave, it can be a standing wave that \"decays\". That is still a non-standing wave, but it doesn't really travel away from it's expectation value."
] |
[
"Why is the distribution of precious metals concentrated in \"veins\" instead of evenly distributed throughout the planet?"
] |
[
false
] |
I am rewatching "Deadwood" (which is a great show) and had this thought. Why did the Black Hills have gold and other places don't? It seems like everything being random, you would expect an even distribution of gold across the planet.
|
[
"Oh man, one could go into a ",
" of depth with this question. I would love to, but I'm short on time so I'll just point out a few things.",
"First, not every part of the planet has the same sorts of rocks. Some places have sedimentary rocks (sandstones for example), while others have volcanic rocks (basalt and granite for example). Obviously, the processes that are occurring around a volcano are inherently different than the processes occurring in a river, so you would expect at least ",
" variation in the distribution of elements around the planet, yes?",
"Next, even within those rock types, there are many sub-systems. Sandstone is only one of many sedimentary rocks. Same with basalt and granite being only some of the volcanic rocks. There is a whole other classification of rocks, metamorphic. If you look at a single mountain, there is not going to be one single classification of rock that it is composed of (well, very rarely so). You may have igneous and sedimentary rocks, but the ages, sources, and depositional histories of these rocks can vary in many ways from rocks of the exact same name somewhere else (or even close by). So you would ",
" some variation in element distribution even within very similar rock units (at least ",
"). ",
"Now to get to the meat of the question - one of the key processes that leads to things like mineral veins is fractional crystallization. Imagine a body of magma beneath the surface of the earth somewhere. This magma body will have a whole range of elements in it, correct? Keep hold of that thought.",
"Different minerals have different elemental structure. So here is a question - would you expect ",
" mineral to 'cool' into a solid phase at the exact same temperature and pressure? Or would you expect ",
" minerals to crystallize at different times than others?",
"I think the answer is pretty intuitive, but if you are unsure just think of ice. Ice is a mineral that moves from solid to liquid at 0 degrees (32 F). The rocks under your feet, however, are quite perfectly solid even on a very hot day. So it should be understandable that different minerals/elements change from liquids to solids under different conditions.",
"OK - so back to the body of magma beneath the surface. Let's say the magma got there from the mantle, having risen up through the crust due to its relatively low density. So it came from the mantle where things are very, very hot, and rose up through the crust to a magma chamber where things are relatively cool. Now you would expect it to slowly cool over time (assuming it doesn't erupt of course!). As it cools, what will happen? Well, we just decided that every mineral will ",
" crystallize out at the exact same time, right? So logically, some minerals will crystallize out of the magma before others!",
"This is indeed what happens - and when it does, the elements that make up those minerals are removed from the magma. So for example, Olivine is a mineral that crystallizes at relatively hot temperatures compared to most other common minerals. Olivine has the chemical formula \"(Mg,Fe)2SiO4\". So that means that as the magma cools enough to form Olivine crystals, the liquid magma loses some of its Magnesium, Iron, Silica, and Oxygen. Conversely, it becomes a little more concentrated in other elements. That isn't to say ",
" Mg/Fe/Si/O will be lost when Olivine crystallizes, just that their ",
" drop. The crystals that are formed will often sink to the bottom of the magma chamber, or get smeared onto the edges of the magma chamber. In this way, they are removed from the system and left behind (which is one place you can get concentrations of some minerals, like Garnets).",
"So now we have a magma body that is slightly cooled and it has lost some of its elements due to the formation of some early-solidifying minerals. As it continues to cool, this process naturally repeats itself - but with different minerals, each one solidifying once the magma chamber reaches the correct temperature.",
"What you will eventually be left with is an assortment of elements that don't contribute to any easily-formed mineral that cools out early. In a sense, these are elements that have a hard time becoming solid. However, given time, the magma chamber will cool enough that even these will become solid. This is another way you can get \"veins\" of very pure elements in very localized areas.",
"Sorry if this was confusing to follow, I don't have much time to proofread and re-word it. Also be aware that this is only a very, very broad overview of how ore deposits are formed, and just one of many processes at work. Really, it depends on what ore you are looking at, and some ores can form in multiple ways. I just hope it gives you an intuitive sense for why elements aren't evenly distributed across all rocks in the planet. Most importantly...",
"It seems like everything being random,",
"Very little is actually random in geology. Every rock you pick up has a history, and a reason for why it is where it is. The study of geology is learning just how ",
" the planet is."
] |
[
"If I'm understanding your explanation correctly, it seems like you'd very often find certain minerals close to each other, which in turn could tell you that you're close to hitting paydirt.",
"For example, Element X has a crystallization temperature just a few degrees cooler than Element Y. As the temperature drops, Element Y crystallizes out first as the magma chamber cools, and falls to the bottom of the chamber. As the temperature continues to cool, Element X crystallizes next, and is deposited directly on top of Element Y. As the magma chamber is eroded or mined away, these two elements should then often be found one right on top of the other.",
"Are there \"sister minerals\" that are often found near each other in this manner? Is there some mineral that can tell you that a gold seam might be nearby?"
] |
[
"Yep, good thinking, this absolutely occurs. For something like gold, there is no absolute identifier that I know of (though this is rapidly deviating from my study area), but it is definitely correlated with many minerals. What minerals will depend on how your gold in the region is being concentrated, which can be through more ways than how I mention. For instance, gold is often associated with hydrothermal regions where groundwater-rich magmas propagate through fractures in rock, concentrated gold in the process before cooling. In cases like this, it may just take physically finding a vein exposure to know there is gold there, since it may not have modified the rock in any noticeable way even a few inches away. ",
"I actually don't know of any instances where gold forms by crystallizing out of the magma chamber quite as simply as I described in my previous post - it was only to give a broad overview on why minerals may separate into distinct locations.",
"Back to gold, there are some minerals it is correlated with. One such mineral is Chlorite (In Arizona at least). Another mineral is quartz. The catch is, there is an absolutely huge amount of quartz and Chlorite that ",
" associated with gold. Nonetheless, finding these minerals can at least increase the chance you'll find gold in a location (update your priors so to speak). When gold is associated with Hematite, it is often found in greater quantities, as another example. Pyrite is another common mineral found near gold. So finding all of these minerals in one location, in a region known for hydrothermal activity in the past, might spark one's interest to prospect it more closely.",
"Interestingly, what you describe is one way mining locations are often identified. Simply by walking along the surface, seeing what minerals you find there, and reconstructing the geologic history (and geothermal history) of the location. There are a huge number of minerals in the earth, and each one tells you something about where it formed, so if you work hard enough at it you can develop a fairly reliable estimate for what minerals you may find preserved beneath the surface.",
"Moving away from gold and more into general geology, this ",
"diagram I grabbed from Wikipedia",
" basically depicts exactly what you envision. In theory, you would find these minerals stacked according to ",
"Bowen's Reaction Series",
", which is one of those things all geologists are forced to memorize over and over. In reality, the world is always more complicated than simple diagrams can depict, but it's a place to start."
] |
[
"What is the actual effective lifespan of motor oil in a car engine?"
] |
[
false
] |
I understand that the average mechanic will tell you to change your oil every ~2500-3000 miles (which we all know is far too soon anyway, right?). My main question, instead, concerns the lifespan of motor oil in a car's engine in terms of time. If I barely use my car--let's say I drive it roughly 1000 miles per year, how long is the engine oil good for? How often should it actually be replaced? Bonus question: What is a good mileage for when oil should probably be changed assuming regular, urban/suburban driving?
|
[
"Bonus question: What is a good actual mileage for when oil should probably be changed assuming regular, urban/suburban driving?",
"Read the owner's manual for your car. The manufacturer's recommended number is based on their knowledge of the engine and the type of oil that the manufacturer and dealerships buy. For most Subaru engines, the manual recommends changing oil every 7500 or 15,000 miles. I've heard of other manufacturers going as low as four or five thousand miles, or as high as 40,000."
] |
[
"If the manual says your engine can go 15k with any oil that meets some specified industry standard (e.g. American Petroleum Institute Service SN), feel free to take that at face value."
] |
[
"I agree, but just a clarification that \"7.5k or 15k\" depends on different oil types that can be used on the engine. Don't go 15k on a 7.5k oil.",
"But next time you change your oils, you can ask your repairman for a higher mileage oil perhaps."
] |
[
"Is gravity a fundamental force like the other three? [physics]"
] |
[
false
] |
I thought that matter just by being matter curved spacetime and that all gravitational interactions were just the results of objects traveling through the curved space. So, it seems more like just a property of matter and not an actual force, but I'm sure this is probably just a semantics issue and that, also, I may be mistaken or have misinterpreted something I read. Someone help?
|
[
"Gravity is a force because it accelerates mass. It's a fundamental force because it acts at a fundamentally different scale and strength than the other forces. ",
"Your question seems to be more related to unification. Right now gravity is described by a classical theory involving curved space and whatnot. The other three forces are described using quantum field theory. ",
"It seems tempting to say that gravity is just fundamentally different than the others in that it can't be described by a quantum theory; it's a purely classical phenomenon. There's a compelling argument that gravity at some level must be a quantum theory that arises from the classic debates between Bohr and Einstein. Simply put, Einstein would show that Bohr's interpretation of quantum mechanics was wrong by saying, \"hey if I measure this property there's a contradiction\", to which Bohr would invariably respond \"yeah, but that thing your measuring with is quantum too, so the contradiction doesn't exist\". The point is that if something in the world obeys quantum mechanics, then everything must obey quantum mechanics. If not you might be able to construct a theory that uses the classical theory to measure all the properties of a quantum theory exactly. ",
"Einstein insisted that reality was deterministic and set out to show it by proving that quantum mechanics was incomplete. To do this he and friends constructed the EPR paradox. They laid out three conditions for reality, one which I forget, but the other two being that reality is must be local and that it is described by some hidden deterministic underlying theory. They used the paradox to prove that quantum mechanics was incomplete. Years later John Bell used the quantum mechanics theory from the EPR paper to prove some identities that were violated by experiments. This meant that the assumptions used to derive the EPR quantum mechanics were wrong: either reality is non-local or the description of quantum mechanics is complete and contains no underlying deterministic classical theory (or both). ",
"So this is why we think there can be no purely classical (deterministic) theories in the universe. "
] |
[
"Gravity is indeed considered a ",
"fundamental force",
". It differs from the others, however, in some ways: it is always an attractive force (at least so far), and moreover has not yet been successfully united with the others. Also, gravity is described by ",
"General Relativity",
" (GR), while the other forces are described by ",
"Quantum Mechanics",
".",
"According to GR, gravity is more than just a property of matter - it's built into the very fabric of spacetime. Matter tells spacetime how to bend, and spacetime tells matter how to move.",
"The reason that gravity appears \"different\" and stands out from the other forces is that GR and Quantum mechanics seem to be fundamentally incompatible and are applied at different scales - in situations where GR (and gravity) start breaking down, quantum effects seem to rule the roost, and vice-versa.",
"It is, however, mathematically possible to unite gravity and the other forces if you invoke symmetry groups that involve a higher number of dimensions - which is what ",
"string theory",
" (and it's super-theory, ",
"M-theory",
" ) is attempting. There is another candidate for unification, called ",
"Loop Quantum Gravity",
" which does not require these higher dimensions.",
"Attempts to unite gravity with the other forces in a theory of quantum gravity that make it compatible with the ",
"Standard Model",
" posit that the force of gravitation would be mediated by force-carrying particles (bosons) called \"",
"gravitons",
"\", just as the other forces are mediated by bosons like the photon, the W & Z, and the gluon.",
" As pointed out by nonreligious, ",
"Verlinde's theory",
" seems to relegate gravity to a non-fundamental force, arising as a side-effect of holographic degrees of freedom. It's a bit esoteric, but the original paper by Verlinde can be found ",
"here",
"."
] |
[
"What does it mean that reality must be local?"
] |
[
"Can a bird track down a moved nest w/ eggs?"
] |
[
false
] |
The other day in my apartment building, a neighbor on the 9th floor found a pigeon had built a nest and laid eggs on her balcony. The maintenance guy came and moved it down along the building and put it up in a tree. I've been worried sick since she told me that this pidgeon mother has been flying around frantically looking. Would she be able to sense the eggs or could they very well of been taken/eaten by another species? I'm too upset at the thought to follow up. Ideally in similar situations where birds nest in unwanted places, what's the best process to get the nest to a place the mother can keep track of it?
|
[
"If a nest is moved there is a very good chance the bird will abandon it/not find it. Sorry to be the bearer of bad news. It is still early in the season so she will hopefully start a new nest somewhere else. \nSorry :(",
"Source: Cornell Lab of Ornithology FAQ",
"Edit: Pigeons (rock doves) nest on ledges (such as cliffs or human-made ledges) not in trees. So moving the nest is bad idea, moving the nest into a tree is even worse."
] |
[
"As a follow up, would OP be able to put bird feed to attract the bird? Would the bird be able to know its their offspring?"
] |
[
"If one would put the nest back on the balcony, would the bird then be able to find it? Or is it too late for that?"
] |
[
"Can we detect relative high ground-levels of radiation from Orbit? Would an Astronaut on the ISS holding a geiger-counter into the general direction of Earth when passing over Tschernobyl or Fukushima get a heightened response compared to the Amazon rainforest?"
] |
[
false
] | null |
[
"Alpha radiation only travels a few centimeters in air. Beta radiation will travel a few meters. Gamma radiation will travel about a kilometer. Even if you could detect the extremely low signal from the effects of the inverse square law (which would be almost certainly be lower than the natural background radiation of the Earth at that frequency), basically all of the source radiation would have been absorbed by the atmosphere anyway before it gets to your detector in orbit. The event would have to be on the scale of a nuclear weapon going off to even have a chance of being detected from orbit. ",
"Source: I pretend I know what I'm talking about because I have a degree in Physics 👍 I'm not a Nuclear Physicist, however. ",
"Edit: Here is the problem ",
" relative to Gamma radiation: ",
"http://teacherlink.ed.usu.edu/tlnasa/reference/imaginedvd/files/imagine/docs/science/how_l2/cerenkov.html",
".",
"Edit the Second: The Vela satellites, as pointed-out below, could detect the nuclear Gamma and X-ray radiation from nuclear detonations on Earth's surface. Moderate nuclear detonations would produce about 10",
" Watts/m",
" on the Vela detectors. (See ",
"http://scienceandglobalsecurity.org/archive/sgs25wright.pdf",
" for an example analysis of this.)"
] |
[
"Have a PhD in experimental high energy physics….can confirm. No way you are going to detect these in any quantity on the space station…..maybe with a very long probe? Lol"
] |
[
"Unlikely.\nYou would need quite sensitive instrumentation in the first place as the intensity of radiation drops to a quarter of its value every time you double the distance (known as the inverse square rule).",
"There is quite a bit of electromagnetic radiation kicking about up there so you would need to further shield your instrument and collimate it so that it was look at a very small field of view at any one time."
] |
[
"Where will the moon go when it eventually leaves orbit?"
] |
[
false
] |
We know that it moves x cm away every year, but are there any simulations that show where it will go? Into the Sun? Intersteller space? Possibly disrupt or orbit of or impact nearby planets?
|
[
"You know the moon moves to a higher orbit, but you are only seeing one side of the equation. The energy to move to a higher orbit has to come from somewhere. It his stolen from the Earth's rotation:",
"http://en.wikipedia.org/wiki/Day#Introduction",
"The Earth's rotation is slowed a bit over time. The Earth's day has dramatically slowed over geologic time.",
"If this exchange where allowed to continue indefinitely, eventually it would continue until the Earth was tidally worked with the Moon. Just as the same face of the Moon always faces the Earth, the same face of the Earth would always face the moon. ",
"Now I'm not sure how long this process would take. It's a good chance that the sun will go red giant before this happens."
] |
[
"tidally ",
"locked"
] |
[
"The sun will engulf the Moon and the Earth long before it leaves Earth's orbit."
] |
[
"Is there a delay in which the brain detects/perceives motion?"
] |
[
false
] |
I have noticed a slightly odd 'phenomenon' when trying to detect motion of small objects. Specifically when I had a quartz watch and I glanced to look at the time I always felt like the first second took an unusually long time (relative to a second) before the hand ticked and the watch then seemed to continue about its normal per second tick. Having recently purchased an automatic watch I now notice a similar effect. The second hand is continually sweeping - however for a very short period of time, upon initial glance it appears totally stationary (perhaps for 1/4 to 1/2 of a second) This effect can be re-seen by looking away from the watch / rotating wrist away so that clock face isn't visible and then bringing it back in to view. It's subtle but noticeable. My question therefore is what is the mechanism in which the brain detects motion of small moving/rotating objects, and is it plausible that there is a delay in doing so leading to the effect I am seeing (second hand appearing stationary for 1/4 to 1/2 a second upon first glance) Is this a known phenomenon / 'illusion' or should I get my eyes tested? :)
|
[
"What you're describing is ",
"chronostasis",
", more commonly known as the stopped-clock illusion."
] |
[
"Not only is this a thing, it has a name and is described by the very example I gave. How fascinating!",
"I could not find any references to this online! Thank you so much for the reply!"
] |
[
"Its called the stoped clock illusion,",
"When you move your eyes, your brain overwrites the period where you see a blur with the first thing that you see clearly. So if you look at a clock the first second will appear longer because your brain added the time that your eyes were moving to the 1 second.",
"You can test this yourself, you wont be able to see your eyes move in a mirror, but you will see them move if you use your phone camera as a mirror.",
"Also try to close your eyes while moving them, and think about the last thing you saw before darkness, sometimes you remember a blur, sometimes you wont remember anythubf"
] |
[
"Human Genome Data Question"
] |
[
false
] |
The human genome contains roughly 725mb of data . Of this, only about 1% of humans genetic material differs. As wikipedia states, this difference can be expressed in roughly 4mb of data. 8 bits to a byte, 1024bytes to a kb, 1024kb to a mb, and 4mb worth of difference. That's (roughly) 34,000,000 genes (bits) that differ between people. Granted, that's a rather large number of different combinations you can have (upper bound would be 34M! and the lower bound would probably be much smaller due to the fact that even among genes that can vary, there will be some that will be similar among groups of people - susceptibility to anemia, etc. but in the interest of completeness let's work with the upper bound.) Let's say we had a universal human population of 10 - WolframAlpha's answer for 34M!. Due to pigeonholing, does that mean you would be guaranteed a doppleganger somewhere in the universe? Would you be guaranteed to be a valid organ donor for that person? To take it in a slightly different direction: we model physical environments all the time - how much computational power would be needed to "run" the genome in a simulation? We already have instruction sets that are larger than 1gb, so is this feasible? As an addendum, would a virtual environment set to model chemical/biological reactions produce a viable virtual embryo, or would the virtual embryo need a virtual mother as well? TLDR: A lot of weird nature vs nurture questions.
|
[
"WolframAlpha's answer for 34M!",
"Assuming you have 34M base pairs, you don't want 34M factorial, but 4",
" which is a somewhat smaller astronomical number."
] |
[
"No, you would not be guaranteed a doppelganger, because human genetic variation is not fixed. The error rate of DNA polymerase is very low, but high enough that every individual has dozens of novel, ",
" mutations that are private to them. You would need a much, much larger population to have a reasonable expectation of a true genetic doppelganger.",
"This is also assuming no large-scale rearrangements, changes in copy number, expansions, etc... So yeah, my expectation is that you would never actually find a true \"by chance\" (as opposed to \"by birth/twin\") doppelganger, regardless of population size."
] |
[
"It seems that they're drawing their figures from encoding a single base pair as two bits (I'd assume something like 00 = A, 01 = T, 10 = G, 11 = C). But I'm not sure whether that's taking into account the fact that these base pairs are arranged in codons, which code for 20 amino acids, which you could encode with only five bits (rather than the six which DNA uses).",
"So my question is; does DNA get read in such a way that it wouldn't be possible to do this? Does the same strip of DNA get read in different ways such that it codes for multiple different things?"
] |
[
"Bacteria are able to harvest many compounds for energy. But are there bacteria that can live from electrical energy?"
] |
[
false
] |
Right now, I am studying citric acid cycle, oxidative phosphorylation and other energy related cell mechanisms. Googling about, I realized that bacteria have evolved to harvest almost all conceivable energy sources. Furthermore, scientists have been able to modify some strands to "eat" some compounds they were not able before. Because the final step to all those processes is making local electrical potential difference that is then used to make ATP, I wonder if direct voltage, induced by a couple of electrodes, could be used by bacteria for their energy needs? Of course, I guess some nutrients like amino-acids and iron ions would be included in the substrate, but not glucose or fatty acids, except in very small quantities for cell membrane production etc.
|
[
"Yes. Well, ",
"sort of",
".",
" are forming living wires that connect electron-rich upper sediment with the electron-poor deeper sediment. It is taking advantage of a natural electrochemical potential - in other words, a living wire that's feeding off a battery. Tell me that's not cool. ",
"Study",
"Injecting synthetic ATP into your arm is probably a bad idea. There is never much free ATP in the body except after a major injury. This may cause several body systems to freak out, ",
"including your heart",
"."
] |
[
"Woah! Thank you! That's more than I bargained for :D ",
"And yeah, I know about that. ATP is considered sort of a hormone when in interstitium or circulation. Fun fact: when erythrocytes go through capillaries, if the diameter is too small for them to pass, they burst and spill all their ATP, causing capillaries to dilate. One more thing: ATP in extracellular fluid is also a sign for immune system, a Damage Associated Molecular Pattern (DAMP), indicating that something's wrong. ",
"Source: med student, will look up if interested, but I think it's in Guyton. ",
"EDIT: that paper is behind a paywall *sob*"
] |
[
"I can think of no theoretical reason why such a bacteria couldn't exist. The practical reason for why one doesn't exist already is that free charge differentials aren't very common in the natural world, don't tend to last terribly long, and don't occur over distances that would allow a bacteria to travel from one to another when their first electrical source evens out."
] |
[
"Is it actually possible for the human mind to \"multi-task\" in the truest sense of the word?"
] |
[
false
] |
Is it possible for the human mind to simultaneously be consciously thinking of two things at once? Yes, I realize it's possible to be thinking two separate things while quickly switching between the two, but I don't believe we're conscious of both thought processes at the same time. For example, if I gave someone 3 separate mathematical equations to solve, would it be possible to solve all three simultaneously instead of just doing them one at a time, even if done quickly. I think there's a major difference between the two.
|
[
"No, we always switch between things quickly, and there seems to be a \"bottleneck\" of cognitive processing somewhere that restricts us to this strategy. Hal Pashler has several (e.g. ",
"1",
", ",
"2",
", ",
"3",
") papers on this phenomenon."
] |
[
"Thank you for the great answer, I'll have to look over these studies when I get a chance."
] |
[
"Well, i think you are asking a psychological question. You can't be dual cognitive. You are either aware or you're not. ",
"The brain with it's circuitry is truly a parallel processing machine. Natural functions while still being cognitive. "
] |
[
"Why does fabric and paper become so hard and rigid after being wet and left to dry?"
] |
[
false
] |
Ever left a wet paper towel on the counter? or a wet tshirt outside on a rail? When it eventually dries, its so hard that it can retain its shape. Why is this?
|
[
"This was asked before. I think the answer was that it allows/facilitates the fibers to become disordered. "
] |
[
"Here it is:",
"http://www.reddit.com/r/askscience/comments/no35z/why_does_my_washcloth_go_into_the_shower_very/"
] |
[
"Some paper has starch added to it for strength. I know copier paper and envelope paper do, and it is possible that paper towels have a small amount of starch. That can make the paper stiffer when it dries. "
] |
[
"How can it be that after 30 seconds of washing with warm soapy water, I can be reasonably sure the salmonella and e. coli are dead/gone, but my hands still reek of garlic and lemon juice?"
] |
[
false
] |
After I cut up some chicken and make a marinade?
|
[
"This is actually more of a chemistry question and has to do with polarity. ",
"All substances are either polar or nonpolar. We use the phrase \"like dissolves like\" when trying to determine what to use to dissolve something. Water is very polar, which means it is great for dissolving other polar things. The problem is that may things are nonpolar. All oils are polar. Your hands even have many oils on them already, which means other oils from the outside are going to love to stick to them. ",
"When we wash our hands, we want to get rid of all these oils and nonpolar junk that dirty our hands. We also want to get rid of the bacteria. Whole water alone can sometimes work to an extent, what you really need is a nonpolar solvent that can stick to them. Bacteria for example have polar and nonpolar parts. Many things have a combination of both. This is where soap comes in. Soap has polar ends, and it has nonpolar ends, meaning it can function to pretty much pull anything off of your skin that isn't attached.",
"Soap alone however isn't always strong enough. Some things are more polar than others, or nonpolar. Think of it as a spectrum, like a pH scale. While some things are weak enough to be quickly dissolved by soap, other things simply need a more nonpolar solvent to get the job done quickly. When I get back to my computer, I'll double check this, but I would guess that the molecule binding to your skin is VERY nonpolar and would require a more nonpolar solvent to quickly remove, such as hexanes.",
"Edit: Found the active ",
"molecule",
" for the smell! As expected, it's very nonpolar. It's the same story for the ",
"lemon",
" juice as well. Just look at that sucker. That's about as nonpolar as it gets right there."
] |
[
"It's the same story for the lemon juice as well. Just look at that sucker. That's about as nonpolar as it gets right there.",
"Interesting thing about limonene it's chiral and only the r-enantiomer smells of lemons. The l-enantiomer smells of pine trees. "
] |
[
"While this might be one point, I'd more lean towards our sense of smell being much more sensitive to even a tiny amount of molecules in the air, whereas a considerable amount of bacteria is needed to overpower our immune system, stomach acid, etc."
] |
[
"Would the pressure at the center of the earth be zero?"
] |
[
false
] |
I've always assumed that the deeper you go into the earth, the greater the pressure. And anything I've ever read about the suggests tremendous pressure. But when you think about it, this is the of the entire earth. It's that point where there is equal amounts of mass pulling in all directions. If the earth were hypothetically hollow, an object ought to float weightlessly if placed at the very center. So if this is the case, how could the very center have pressure at all? Or doesn't it?
|
[
"Pressure and gravity are not the same force. While it's true that an object near the center of the Earth would experience nearly no gravitation, the pressure from the matter surrounding it would be immense. Remember, gravity isn't just pulling you towards the center of the Earth, it's also pulling the Earth towards the center of the Earth. This massive pressure is a consequence of that."
] |
[
"This is fundamentally wrong. The gravitational force at the centre of a uniform sphere is zero. This is quite easy to show mathematically; Newton knew about it. What you're saying is only true if you're outside the spherical mass.",
"The earth is close enough to uniform for the purposes of this discussion.",
"Pressure is high at the centre because the parts above you DO feel gravitation, and as a result every is trying to move towards the centre. You're getting crushed by all the material above you, and above you means from every direction if you're at the centre."
] |
[
"You are conflating gravity and pressure. One is dependent on the other but they affect things differently. ",
"Pressure: the pressure increase as you approach the center. Pressure, in a fluid (or at least semi-fluid) presses on you in ",
" directions.",
"Gravity: while Newton's formula would indicate gavity would be infinite at the center, that's not how gravity works. Every particle, and I'm talking protons and neutrons, attracts every other. So, at the center you get a balanced state, where the earth's mass is attracting ",
" mass in all directions.",
"Is this clear?"
] |
[
"Will GSM/CDMA be completely phased out in the lifetime of LTE?"
] |
[
false
] |
Will 2G be phased out in the next ten or so years? My biggest gripe with CDMA over GSM is being forced to use Verizon/Sprint/US Cellular/etc phones. In the event that GSM/CDMA is done away with and LTE takes hold as the primary wireless phone technology, will I be able to use non-carrier specific phones on any LTE carrier? Sorry if this isn't the right place to ask this, but none of the phone/android/etc subreddits seemed any better.
|
[
"Well this gets off science a little bit, but I'll answer anyways. It's hard to predict business plans of course. However, since LTE can support more users (much larger bandwidth allotment and far better spectrum utilization) more per dollar spent (thanks to licensing and tech improvements) I will predict that it will. ",
"Now to get a little more technical, but i'll try to keep it somewhat simple. With the old technologies channels are split between data and voice. While data networks are pretty good at filling the space between users, voice is not. If a voice line isn't being used, that bandwidth is lost and only one call per voice line can be made at one time (circuit-switched). Note that early data services were also data switched, to be put simply as far as line utilization, they worked much like a pc modem. Technologies (CDMA-2000[1xRTT,EV-DO], GPRS, EDGE) which popped up around 2000 which switched data to packet switched data. Packet switched data sends a small chunk at a time effectively allowing the network to be shared more efficiently as network traffic tends to be \"bursty\". The proposed future LTE networks will bring voice traffic into the packet switched world (at least from phone to the edge of the public telephone network). Essentially, this will allow data traffic to utilize what was voice when voice calls aren't being made. Voice will still be provided with a higher priority so that low latency full duplex communication remains possible. The voice on LTE protocol is known as VoLTE, I don't have an estimate as to when that will roll out as that is up for debate from a technology and business standpoint. The two main issues technologically with VoLTE is hand-offs between towers and quality of service (ensuring that voice packets will arrive on time). Economically, a new voice network needs to be rolled out, so until then 2G/3G will still be around.",
"As another point, how do you define phased out? Frequently, old equipment from Europe, NA, and East Asia ends up in developing areas such as South America and Africa.",
"Hopefully that wasn't too long, I sort of get going with it and don't shut up. I tried to leave out to many excruciating details, feel free to reply if you have more questions."
] |
[
"Oh sorry, I didn't even answer the inner question. Most likely we will reach a point with everyone roaming to anyone. There will be issues with which bands different phones can tune to, but the tech is there, it'll be up to the businesses to allow it. ",
"One of the nice things about LTE is that the name is true (Long Term Evolution). It will be the tech for a long time. While it will be improved (and the future goal is >1 Gbps networks, time frame tbd), old devices and networks remain compatible with newer devices and networks (there may be some point where issues arise though). So once we're on the same page, we will stay on the same page (or at least the right chapter which is good enough).",
"What that means is that the issue is getting businesses to offer seamless roaming rather than the technologies (say putting a gsm and a cdma radio in a phone).",
"Are there any other limitations you were wondering about? I could probably answer a little more targeted if so."
] |
[
"Thanks for the reply. My primary concern is the limitations on phones imposed by cdma carriers and I was hoping the science of what LTE does would help me understand if that would ever go away. Odds are Verizon and the like will never get rid of their iron fist management."
] |
[
"Can you explain what happens on a cellular level what happens to bacteria/viruses when hand-sanitizer (ie alcohol) touches them?"
] |
[
false
] |
Just interested to see the chemical reason as to why it's meant to kill "99.9%" of germs.
|
[
"Ethanol - the main alcohol found in hand sanitizers is bactericidal, meaning it kills bacterial and viral cells.\nIt affects the lipids in bacterial cell walls - which are composed of a phospholipid bilayer. It makes them more soluble to water, so the cell begins to lose it's structural integrity and causes the outer membrane to disintegrate, allowing the alcohol to penetrate the insides of the cell.",
"\nThe alcohol is then able to break bonds between amino acids which make up key proteins inside the cell. Denaturing of proteins means the bacteria is unable to function. \nCell functions such as swimming movement, DNA synthesis, protection from engulfing by phagocytes (e.g. white blood cells), and reproduction are unable to occur, resulting in killing of the bacterial cell and inhibiting reproduction. "
] |
[
"Thanks Jess! I can consider this mystery solved. "
] |
[
"Why does ethanol have this effect so strongly on bacterial cell walls but not on the cell walls of our skin cells? And what effect does it have on muscle cell walls exposed in a wound? Is the \"sting\" of alcohol on a wound the sign that human cells are being damaged?"
] |
[
"What is the ideal liquid to fall into from a great height? How big of a fall could you survive?"
] |
[
false
] |
Obviously, falling into water is much safer than falling onto a solid surface but there's a limit to how far you can fall before you've built up too much speed to survive the deceleration. Most people (barring extremely rare occurrences) die after jumping off the Golden Gate (220 ft / 67 m). Cliff divers on the other hand sometimes jump off heights of ~30 meters / 100 feet safely. This made me wonder, would it possible to survive much larger falls if one fell into a liquid other than water, assuming ideal diving position of a man weighing 80kg / 180 lbs with the liquid at STP? What would this ideal liquid be? Exactly how great of a fall into this liquid would match the max force associated with falling from 100 feet into just water (which is survivable)? The same for 200 feet (which is not)? My guess is that the most important factor affecting survivability is just density of the liquid. In that case, I'm guessing isopentane (0.62 g/cm vs ~1 g/cm water) would be the ideal liquid to fall into. I'm at a loss to estimate how great of a fall you can survive though. Maybe I'm wrong; could surface tension or viscosity play a larger role in this?
|
[
"I think a better question would be: Is there a liquid that will allow you to survive a terminal velocity impact? "
] |
[
"and if so, would you be able to get out?"
] |
[
"I agree, low density is the important thing here. If you could find a very compressible liquid that would also help, but I don't know any liquids offhand that aren't basically incompressible. The pressure you'd experience hitting the surface would depend on how quickly the liquid could accelerate away from the impact point, which in turn would be goverened by the Navier-Stokes equations. This would be really hard to calculate analytically. It'd probably be hard to calculate numerically, even."
] |
[
"If the amount of CO2 in the atmosphere was instantly cut in half, (we don't want to kill the plants) how immediately would the effects on global warming been noticed?"
] |
[
false
] | null |
[
"It could actually take a very long time for temperatures to drop to pre-industrial levels, and this is the most worrisome part of global warming. The reason is that the temperature rise driven by increased CO",
" levels is not just limited to the stronger retention of thermal radiation by the greenhouse effect. Indeed, if that were the case, then you would expect global temperatures to rapidly readjust to reflect the current CO",
" levels. However, the problem is that theCO",
" levels and the temperature increase that they cause are strongly coupled to the rest of the atmosphere through a series of interrelated \"feedback mechanisms\" such as water evaporating, ice melting, etc. As a result, the temperate tracks changes in CO",
" levels quite slowly. For example, if we were for example to reduce carbon emissions to the point that the CO",
" concentration would remain constant, temperatures would actually continue to rise for years, as shown in the bottom curve of ",
"this graph",
". ",
"So now let's say we allowed the CO",
" concentration to rapidly fall, would this rapidly reverse climate change? Again the answer is no, ",
"as you can see from these two graphs",
". Even if the CO",
" levels would fall rapidly, it could take a ",
" long time for temperatures to drop significantly. It is this lag that has led people to call global warming potentially irreversible on a timescale of centuries. In other words, if we allow climate change to get away from us within the next decades, the changes could continue to be felt for tens of generations. These results are discussed in greater detail in ",
"in this great paper",
"."
] |
[
"its what climate does and has been doing for billions of years.",
"This makes it sound like the last 100 years of warming are not caused by humans, which is certainly not the case.",
"our best climate models are based on, typically, four variables for which static numbers are used to simulate.",
"Really? Which climate model are you talking about here? Have you ever actually run a climate model? Because I've run several, and never seen one this simplistic."
] |
[
"its what climate does and has been doing for billions of years.",
"This makes it sound like the last 100 years of warming are not caused by humans, which is certainly not the case.",
"our best climate models are based on, typically, four variables for which static numbers are used to simulate.",
"Really? Which climate model are you talking about here? Have you ever actually run a climate model? Because I've run several, and never seen one this simplistic."
] |
[
"Are there other animals with any form of \"agriculture\", \"livestock\", or generally tending to what will eventually be their food before eating it?"
] |
[
false
] |
I'm not expecting "Babe the Farmer-Pig" or anything, but I could imagine, say, a fox that exists which permits a few scavenging rodents to finish his scraps until the day he eventually eats them, too. Perhaps some sort of fish or turtle or crab that maintains a "garden" of algae on it's body to be eaten? Anything that might be considered even a rudimentary form of actively "growing" or maintaining resources which it will eventually eat at some future time.
|
[
"http://www.bbc.com/earth/story/20150105-animals-that-grow-their-own-food"
] |
[
"Some species of ",
"Ants herd aphids",
"."
] |
[
"Leaf-cutter ants maintain underground fungus farms fed on the leaf fragments that they collect. Other ant species guard and 'farm' aphids and collect their sugar-rich exudates."
] |
[
"[Physics] Why are we so 100% sure that the speed of light is the fastest any object can travel?"
] |
[
false
] |
I mean, we're more willing to say that time itself speeds up or slows down instead of having light move faster than 300 million m/s.
|
[
"Three lines of arguments:"
] |
[
"No, it isn't specific of QFT. You can get the idea by looking at a pendulum. Its oscillation period doesn't depend on the amplitude of the oscillation: if you release a pendulum from its maximum height, its period will be the same as if you release it half that height. The period depends only of its mass and length. ",
"Now, a wave is the propagation of a perturbation in a field. We can, roughly speaking, imagine a field as a series of pendulums interconnected, so no pendulum can be in a state too different from its neighbors. Then, we can easily understand why a wave has to have a limit speed. Each \"pendulum\" has a limit speed itself that depends on that particular field.",
"Interestingly, the wave equation accept solutions where the wave speed is less that the speed limit. That's how QFT explains why certain particles can move at the speed of the light and others not."
] |
[
"Can you explain the concept of a propagation limit? This is the first I've heard of it.",
"Is it something specific to QFT?"
] |
[
"If we have commensal bacteria in our guts that make a living by digesting our food, and whose composition can change based on our diets, doesn't this mean that the calorie in, calorie out model of nutrition is necessarily wrong?"
] |
[
false
] |
[deleted]
|
[
"The bacteria in your stomach ",
" you extract more calories out of your food. So yes in essence the calorie in, calorie out model is not entirely accurate. But then again you can't easily calculate the exact number of calories in a given food (the number listed on the box is likely just an average). Also, you can't calculate exactly how many calories you burn during certain exercises because that will vary from person to person too and likely varies within an individual. The calorie in, calorie out model is what it is... a model. The more calories you take in, the more you need to burn. In terms of specific values, its extremely difficult to make any \"exact\" calculations, for the most part you just ballpark it."
] |
[
"Calorie-in/calorie-out is a good, but over-simplistic rule of thumb. Regardless of the utility of the model, the presence of gut bacteria doesn't affect the calculus because your gut isn't considered \"in\" you. The entirety of the alimentary tract is considered outside of the body, so whatever the gut bacteria are doing isn't affecting the calorie-in/calorie-out model."
] |
[
"Just because a model is wrong doesn't mean it isn't useful. Most models are wrong, really. The goal when creating a model is to decide which variables in the system you are studying are important and which ones aren't and then leave out all the factors that can be safely ignored for your desired degree of precision.",
"There have been some ",
"promising headlines",
" in the science press lately about how gut bacteria influence the absorption of calories and people trying to come up with treatments that control weight by controlling the bacteria. ",
"However, will that pan out? How much does weight follow bacteria and how much do bacteria follow diet? Miracle weight loss cures in the science press don't always pan out. We've known that microbes are important for a while - mice raised in completely sterile environments have a lot of trouble gaining weight - but are differences in intestinal flora really a significant variable or can it be pretty much ignored? Ask again in six months."
] |
[
"What happens to metal compounds when they are heat-treated (tempered)?"
] |
[
false
] |
The chemical composition doesn't change, I'm assuming. So what makes the metal "stronger"? I saw a video of someone making a knife and they tempered it in a kiln, then alternated cold and hot cycles.
|
[
"Metals deform through the movement of ",
"dislocations",
" through the crystal structure. The atoms are packed tightly together as if they were hard spheres; attractive forces hold them together. If you wanted to move an entire plane of atoms in the crystal structure past the adjacent plane all at once, this would require a lot of energy- you would be moving many atoms out of their equilibrium position simultaneously. The theoretical strength calculated from this is far higher than the observed strength. Dislocation movement provides the explanation for this lower strength; only a few atoms move simultaneously, allowing atomic movement with far lower applied force. The sum of many dislocations moving results in net movement of many atoms relative to one another. This means that if we want to make metals stronger, we need to make it more difficult for dislocations to move. There are various methods of accomplishing this. ",
"Steel at room temperature is in a phase called \"ferrite\", which has its iron atoms arranged in a ",
"body-centered cubic crystal structure",
". The carbon atoms are part of an \"interstitial solid solution\"; they exist in gaps between the iron atoms. The carbon atoms are actually slightly larger than the gaps between the iron atoms, so their presence causes strain on the crystal structure in the region immediately surrounding the carbon atom. It is energetically favorable for carbon atoms to move to dislocations, as there are larger gaps present, reducing the amount of strain necessary to accomodate the carbon atoms. Pulling the dislocations away from their associated carbon atoms involves increasing the strain on the crystal structure, so the presence of even a tiny amount of carbon makes dislocation movement more difficult (the carbon atoms \"pin\" the dislocations). This is one reason why steel is stronger than highly purified iron. ",
"A second reason is that ferrite can only dissolve a negligibly small amount of carbon this way at room temperature, and only a tiny bit more at elevated temperatures (the absolute maximum amount at any temperature is 0.22% carbon by weight). Instead, room temperature steel (typically between 0.2% and 1% carbon by weight) is a mixture of ferrite and ",
"cementite",
", Fe",
"C, a hard ceramic. Unlike in steel or other metals, the atoms in cementite cannot move past each other without simply breaking the crystal. This means that if a dislocation is moving through ferrite and encounters a cementite particle, it has to divert around the particle instead of traveling through it (unless the stress is high enough to simply cut through the particle). This makes dislocation movement even more difficult, and increases the strength of steel even further. A dense network of tiny hard particles spread throughout a ductile matrix is a very common means of increasing the strength of a metal, used both in steel and other \"precipitation-hardened\" alloys. ",
"Now we get to the very specific behavior that causes steel to respond to heat treatment in general, and quenching and tempering in particular. ",
"Here",
" is the phase diagram of the iron-carbon alloy system, detailing the crystal structure changes that occur based on composition and temperature. When you heat steel above 723 °C, it undergoes a phase change into ",
"austenite",
". This form of iron has a different crystal structure that can dissolve far more carbon than ferrite (up to ~2% at the optimum temperature). For any steel in the typical composition range of 0.2%-1% carbon by weight, heating it to sufficient temperature will cause it to entirely transform into austenite. Upon cooling, other phase transformations occur. You will note that the phase diagram there talks about ",
"pearlite",
", a structure consisting of very thin, alternating layers of ferrite and cementite (named for its resemblance to mother-of-pearl). Structures like this are formed during ",
"eutectic",
" phase transformation, where one phase transforms into two other phases (in cases such as this where the initial phase is solid, it is referred to as a \"eutectoid\" transformation). The thin layers are because this minimizes the distance that components of the alloy must diffuse in order to change the composition of the regions from the initial composition of the original phase into the two different compositions of the two resulting phases. Steel with an overall percentage of carbon less than the eutectoid composition will have alternating regions of ferrite and pearlite, while steel with more carbon will have alternating regions of pearlite and cementite. Pearlite is harder but less ductile than ferrite, and cementite is even harder and even more brittle. Increasing the carbon content of steel thus makes it harder and stronger but more brittle.",
"Now we ",
" get to quenching and tempering. The pearlite structure can only form from austenite if cooling occurs slowly enough that there is time for diffusion to occur before low temperatures lock the atoms into place. If instead you cool the steel very rapidly from austenizing temperatures (say by plunging it into a bucket of water), a different phase transformation occurs that requires no diffusion, producing ",
"martensite",
". The crystal structure of this material is different from all previous phases, and it is extremely hard and strong but extremely brittle. Tempering involves heating the metal to a moderate temperature (well below the austenizing temperature) and holding it there for a specified amount of time. This allows diffusion to occur, causing some of the martensite to transform into ferrite, pearlite, and/or cementite. ",
"If tempering was continued indefinitely, eventually the steel would reach a state equivalent to if it had been cooled from austenite without quenching. Careful control of the time and temperature of the heat treatment allows control of the fraction of martensite that transforms into the more ductile phases, allowing for the production of a steel with the desired mix of strength/hardness and ductility. The fact that martensite is harder and stronger than even cementite means that the properties of a quenched and tempered steel will be superior to a slow-cooled steel of similar composition. ",
"There are a variety of other variables surrounding this process. For example, the cooling rate required for formation of martensite is strongly dependent on the composition of the steel. Plain carbon steels of lower than ~0.3wt% carbon content do not really respond to quenching and tempering, and higher carbon content decreases the cooling rate required. Also, for thick parts, plunging the part into a cooling bath will cool the surface very quickly, but the interior will be cooled much more slowly. This can be dealt with by adding alloying elements that decrease the cooling rate required for martensite formation (e.g. ",
"AISI 4340 steel",
", with minor additions of chromium, nickel, and molybdenum), or it can be deliberately exploited to create a part with a hard surface but a tough, ductile core. ",
"Source: my education in Materials Science and Engineering and the textbook ",
" (authors: R. Abbaschian, L. Abbaschian, R. E. Reed-Hill). Wikipedia links used for convenience. "
] |
[
"Great post. ",
"I would only add here that martensite in steels actually has the same crystal structure as ferrite- a BCC structure. Extra carbon distorts the crystal lattice tetragonally, to give a Body Centered Tetragonal BCT structure. When fully tempered, the carbon diffuses out of the structure, so that the martensite has an identical BCC structure to that of ferrite. The microstructure of ferrite and tempered martensite is still different, however, so the tempered martensite will still have different properties."
] |
[
"Metallurgy is close to black magic.",
"One thing that changes is the crystal or micro structure of the metal.",
"http://en.wikipedia.org/wiki/Tempering_%28metallurgy%29#Quenched-steel",
"Another popular process is case hardening where stuff gets added at the surface of the metal.",
"http://en.wikipedia.org/wiki/Case_hardening"
] |
[
"How come some people faint from seeing blood?"
] |
[
false
] | null |
[
"Welcome to ",
"r/AskScience",
"! Check out our ",
"new",
" posts.",
" Please consider the following guidelines to help us maintain this goal.",
"read our updated and expanded guidelines"
] |
[
"I suppose you can identify this blood-fainting gene? I'd settle for any published scientific evidence that corroborates your theory."
] |
[
"Just found this article that may shine some light on the subject.",
"http://bodyodd.msnbc.msn.com/_news/2010/09/01/5022344-why-some-people-faint-at-the-sight-of-blood"
] |
[
"How does chloroform penetrate blood-brain barrier when it's hydrophilic ?"
] |
[
false
] | null |
[
"Even heptane can be 'mixed with water to some extent'. You've answered your own question. It isn't hydrophilic to the point that it can't pass through membranes. Lipids easily dissolve in chloroform."
] |
[
"Chloroform is not hydrophilic. It isn't miscible with water."
] |
[
"It's actually partially hydrophilic. It's true it isn't miscible with water but it can be mixed with water to some extent. "
] |
[
"If the universe ia expanding what is it expanding into?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"You question is either commonly occurring or has been recently posted on ",
"/r/AskScience",
". It may also be answerable using a Google or Wikipedia search.",
"To check for previous similar posts, please use the subreddit search on the right, or Google site:reddit.com",
"/r/askscience",
" ",
"Also consider looking at ",
"our FAQ",
".",
"For more information regarding this and similar issues, please see our ",
"guidelines",
"."
] |
[
"Pleas send link to where this has been asked before. Thank you :) "
] |
[
"The FAQ can be found in the sidebar."
] |
[
"Is there any air in-between our internal organs and skin, or some sort of fluid?"
] |
[
false
] |
And what happens to any air that's introduced during surgery?
|
[
"There is a fluid that exists inside of your body cavity (",
"coelom",
") but mostly there is fat, muscles, bones and peritoneum membrane that holds your organs together."
] |
[
"There is no air in the abdomen outside the intestines. If there is air in the abdomen it's usually due to a surgical emergency like perforated bowel or trauma. Air in the abdomen after surgery is absorbed into the surrounding tissues."
] |
[
"This. We're pretty much vacuum packed."
] |
[
"Why do micro-interactions between qubits not \"collapse\" the wave functions (under Copenhagen interpretation) when things like heat and sound can?"
] |
[
false
] |
I've been trying to find what it means to be an "observer" or something that "collapses" a wave function (those things currently mean the same thing to me). Why do small things like applying a Hadamard gate not collapse the superposition but exposing it to light or sound do? Where is the cutoff? Why is the cutoff? Thanks
|
[
"What you want from a quantum computer is coherence. Whenever a quantum state interacts with the environment (i.e. becomes entangled with it), it decoheres. A fully isolated system would never decohere, but you could also never measure anything. So what you want to have in reality, is a system that is isolated as much as possible but still interacts with the environment. That way you can apply things like Hadamard transformations (which essentially only rotate a vector in Hilbert space) and keep the quantum state \"alive\" as long as possible. Note that the gate does not collapse anything - it is not a measurement. In the same way an electron flying through a magnetic field will see it's quantum state change, but it won't collapse until you measure it in a detector. After all transfromations are done, you do the measurement that collapses the state at the very end."
] |
[
"Oh, I see. I assumed you had some prior knowledge in the field since you asked about Hadamard gates specifically. Let's start with a single qubit. An electron in a trap, for example. Let's say you prepare it in a state where it is equally probably spin up and spin down along the z direction. Unless you measure it, you won't know what its spin is. Now when you move it through a magnetic field, you can rotate its quantum state to assume different probabilities for spin up and down. That's the equivalent of a Hadamard gate. Afterwards, the state is still alive, you did not measure anything. The entire \"system\" (qubit+gates) as a whole is still isolated. But you will now get different probabilities if you do measure it. By carefully designing many of these transformations with many qubits, you can achieve destructive intefererence on the outcomes that are incorrect or unwanted. So when you finally do a measurement in the end, you will (most likely) only see the correct answer. But if your quantum system is not well isolated (e.g. because there are many other electrons flying around), you risk that your nice qubit state is perturbed (i.e. it gets rotated in ways you did not want). Then the measurement at the end is worthless."
] |
[
"Oh, I see. I assumed you had some prior knowledge in the field since you asked about Hadamard gates specifically. Let's start with a single qubit. An electron in a trap, for example. Let's say you prepare it in a state where it is equally probably spin up and spin down along the z direction. Unless you measure it, you won't know what its spin is. Now when you move it through a magnetic field, you can rotate its quantum state to assume different probabilities for spin up and down. That's the equivalent of a Hadamard gate. Afterwards, the state is still alive, you did not measure anything. The entire \"system\" (qubit+gates) as a whole is still isolated. But you will now get different probabilities if you do measure it. By carefully designing many of these transformations with many qubits, you can achieve destructive intefererence on the outcomes that are incorrect or unwanted. So when you finally do a measurement in the end, you will (most likely) only see the correct answer. But if your quantum system is not well isolated (e.g. because there are many other electrons flying around), you risk that your nice qubit state is perturbed (i.e. it gets rotated in ways you did not want). Then the measurement at the end is worthless."
] |
[
"Why does most (if not all) life use phosphoanhydride bonds (ATP) as energy storage/currency when Phosphorous is limited in the environment?"
] |
[
false
] |
Is there any advantage to ATP and other phosphoanhydride bonds that seem to do most of the heavy lifting in the cells that other molecules just cannot do at all? It would seem that other kind of energy currency would compete at all if there were comparable efficiencies and traits.
|
[
"Given that nucleoside triphosphates are the building blocks of DNA and RNA, they are positively ancient and have been around pretty much since the beginning of life. The whole system kinda got locked in in that early stage. Phosphorus might have been more abundant back then and it never became so scarce so as to pose a problem."
] |
[
"It absolutely does pose a problem for many plants and algeae. But as you say, they're locked in to using RNA/DNA now."
] |
[
"In certain locations, sure. But looking at it globally, the total amount of plant biomass doesn't exactly suggest a severe problem."
] |
[
"Could there be an object that casts shadow but is not visible ?"
] |
[
false
] | null |
[
"Technically, a shadow is an area where direct light from a light source cannot reach due to obstruction by an object. So, anything that blocks visible light and creates a shadow would also have to be visible.",
"However, in the spirit of your question, it is possible to use a lens (while not completely invisible) to create a \"shadow\". If you've ever used an incandescent flashlight, you've experienced this type of \"shadowing\". ",
"Here's a picture to illustrate my point.",
" I don't know if there's a name for this type of dark spot, but it isn't technically a shadow since the light is being refracted and not obstructed. "
] |
[
"A similar example comes from schlieren. ",
"http://en.wikipedia.org/wiki/Schlieren",
"Have you ever seen waves of heat cast a shadow? This is because the hot air has a different density and index of refraction than cooler air, bending the light on the way through. It can be possible to have the heat waves (or pressure waves) cast a shadow, but not be visible to people due to their subtlety. Of course, these waves are not invisible, but they are hard to see."
] |
[
"It is similar. Air near road is hotter than air above it so air near road has higher index of refraction allowing you to see reflection of sky when looking at it from low angle.",
"http://en.wikipedia.org/wiki/Total_internal_reflection"
] |
[
"If we have 100% solar power production at home is there a point to using AC other than appliances being made for AC?"
] |
[
false
] | null |
[
"Pretty sure Edison was promoting DC and started a smear campaign against Tesla's AC - and lost."
] |
[
"Nowadays the transformation of arbitrary electrical energy sources into an arbitrary other isn't an issue anymore due to high power electronics like IGBTs. Basically any source can be rectified and smoothened to a nearly perfect DC, which in return gets chopped, upscaled and shaped to any wanted form.",
"Therefore it is easier to design a single transforming device rather than engineering a whole branch of devices made for DC use."
] |
[
"Firstly, no it's not. AC and DC pose pretty much the same danger, they will both kill a human around identical voltage in the grand scheme of things. AC is slightly more harmful to the heart, however DC is a lot more dangerous for starting fires and more troublesome for breakers as low voltage DC arcs self sustain better. ",
"Secondly, you have that completely backwards. Edison promoted DC. Ha said AC was dangerous on the basis that the high voltage produced by transformers for transmission was more dangerous, which is absolutely true, but that leads to the third issues with your comment. ",
"Lastly, the choice of AC over DC had absolutely nothing to do with who's campaign was better, and everything to do with the fact transformers work with AC and don't work with DC. Back then, DC either had to always be at low voltage (a waste of energy and a masisve cost in wiring and required small generators everywhere), be at high voltage all the time (a masisve safety risk and a problem for making insulation on devices), or have two rotating machines to convert (a masisve cost and a lot of maintenance). AC just needed a cheap transformer to solve every single one of those problems. "
] |
[
"Gambling question here... How does \"The Gamblers Fallacy\" relate to the saying \"Always walk away when you're ahead\"? Doesn't it not matter when you walk away since the overall slope of winnings/time a negative?"
] |
[
false
] |
I used to live in Lake Tahoe and I would play video poker (Jacks or Better) all the time. I read a book on it and learned basic strategy which keeps the player around a 97% return. In Nevada casinos (I'm in California now) they can give you free drinks and "comps" like show tickets, free rooms, and meal vouchers, if you play enough hands. I used to just hang out and drink beer in my downtime with my friends which made the whole casino thing kinda fun. I'm in California now and they don't have any comps but I still like to play video poker sometimes. I recently got into an argument with someone who was a regular gambler and he would repeat the old phrase "walk away while you're ahead", and explained it like this: "If you plot your money vs time you will see that you have highs and lows, but the slope is always negative. So if you cash out on the highs everytime you can have an overall positive slope" My question is, isn't this a gambler's fallacy? I mean, isn't every bet just a point in a long string of bets and it never matters when you walk away? I've been noodling this for a while and I'm confused.
|
[
"The Gambler's Fallacy refers to the belief that (for example) a long string of winning will make it more likely that the next result is a loss. This is incorrect if the games are independent.",
"Another effect, which is real and often confused with the above, is regression toward the mean. This refers to the tendency for extreme outcomes to be followed by more normal ones. ",
"So let's say you've sat down gambling and find yourself up some number of dollars. Should you keep playing? You are not ",
" likely to lose the next game than you were to lose the first one just because you've won a lot (that would be the gambler's fallacy), but you ",
" still likely you lose your winnings over time, because the game is ever so slightly rigged against you (regression toward the mean).",
"So, if you always cash out when you're ahead, aren't you beating the game? Not really. Your friend has to take into account that it's not guaranteed that you will ",
" be ahead. If the game works like a ",
"one-dimensional random walk",
", you will always end up ahead at some point, with probability one, but only if you have an infinite amount of credit to gamble with. Which, I daresay, you don't have."
] |
[
"If the game works like a one-dimensional random walk, you will always end up ahead at some point, with probability one, but only if you have an infinite amount of credit to gamble with. Which, I daresay, you don't have.",
"I'd like to add that, for a ",
" random walk you are not guaranteed to end up ahead at some time. If the game is biased in the Casino's favor (which they typically are), then there is a positive probability that you'd never be ahead even if you had an infinite pool of money to gamble with."
] |
[
"If the game is rigged against you, which casino games are, then you are always better off quitting, whether you are ahead or not. In either case you are expected to simply lose more. If you have a loss and want to wait until you are ahead, then you run the risk of going broke.",
"Gambling in a casino is generally something you do for entertainment value, not money, so all these considerations may not apply. Poker is different."
] |
[
"Would it be possible for a black hole to approach our solar system undetected?"
] |
[
false
] |
Could the first sign of it be it's effects on the planet's orbits, or is there no way it could get that close undetected?
|
[
"Is there any mechanism for creation of small black holes? Is there any reason to believe they even exist?"
] |
[
"[I'm not an expert]",
"I believe we would be able to see a ",
"gravitational lensing effect",
", as the black hole's gravity bends light around it, distorting our view of the stars behind it."
] |
[
"A black hole that size would take significantly longer than the age of the universe to evaporate, and so a primordial black hole could be this size (theoretically any size, in fact)."
] |
[
"Crosspost from askreddit: Say you have some sort of speed-of-sound reflexes. Is it possible to slap a bullet fired at you out of the way without harm?"
] |
[
false
] |
[deleted]
|
[
"I assume you'd try to hit the side of the bullet instead of the pointy. According to google, bullets rotate at 3000 rotations/second. With a diameter of 1 cm, that's about 54 km/h, which I don't think is enough to give your skin a friction burn (you could totally touch the side of a car going that fast).",
"According to google bullets are about 267 degrees celcius, which is hot, but not instant burn hot.",
"So given you could do this (which I doubt you could), I'd go with yes. "
] |
[
"It all depends on the bullet. If you were shot with a supersonic bullet, then no, you'd get shot."
] |
[
"umm given the speed of sound ~1125 fps and the muzzle velocity of most guns, you would be shot before you heard the sound of the gunfire. If someone fired a weapon from say 100 feet away the sound would reach you in .08 seconds where the bullet reaches you in .03 seconds. Given human reaction times of 200 ms or so (.2 seconds) even if you used the muzzle flash rather than sound you are not going to kung fu any bullets."
] |
[
"What happens to our brain when we find something funny? Why do we laugh? And why is it that minor mishaps like slipping off the floor, falling off a slide, etc. considered funny to a lot of people?"
] |
[
false
] | null |
[
"Here is a fairly good overview of current thinking",
"Many think we laugh at minor mishaps as a signal to others in the group that the person is okay and we don't need to take emergency action. It also helps the person who just experienced the mishap, as they get the outside signal that it wasn't a big deal or crisis, helping calm back down. "
] |
[
"You should read the fiction novel \" Stranger in a Strange Land \" by Robert Heinlein.",
"It has some interesting philosophical ideas about why we laugh. :)"
] |
[
"Because the football hit the man right in the groin LOL!"
] |
[
"Would cooking in a tall stock pot increase the boiling point (and thus cooking temperature) at the bottom of the pot due to the water pressure?"
] |
[
false
] |
I do realize that the cooking temperature at the bottom of a stock pot would also be hotter due to the fact that it gets heated from the bottom (especially if what you are cooking is thick).
|
[
"Yea, the effect will be weak, but it will be there. The hydrostatic pressure in a column of fluid on Earth can be estimates as pgh, where p is the density, g is Earth's gravity, and h is the height. So let's take a slightly exaggerated example and say the stock pot is 1m in height. Then plugging in the numbers for water, we get a pressure increase equal to 1/10 of an atm. Actually a good rule of thumb is that one atm = 10m of water, which gives the answer even more quickly. Now if we look at ",
"how the boiling point of water varies with the pressure",
", we see that at a pressure of 1.1atm, the boiling point goes up by to degrees Celclius to 102",
"C."
] |
[
"You aren't going to have one of those in your typical home kitchen.",
"Also, you want to not let the temperature of a beer mash get above 170F to prevent bad tasting compounds in the grain husk from leeching into the wort, so the not so insignificant boiling point elevation simply isn't realized."
] |
[
"What about huge vats they cook mash for beer in? Those can be 10s of meters tall."
] |
[
"Will cooling a piece of plastic increase its rigidity?"
] |
[
false
] |
Since getting it hot has the opposite effect (melting), if I stick a piece of plastic in the freezer will this make it more rigid?
|
[
"Yes it does. If you have access to a suitable piece of plastic, why don't you stick it in the freezer for a while and see for yourself? You will have to be fast though, plastics tend to warm up quickly (low heat capacity) so if you wait too long you'll feel it return to room-temperature elasticity quickly.",
"The most extreme example is a staple of any Liquit Nitrogen based presentation: drop a balloon in Liquid Nitrogen and shatter it on the table when it's frozen."
] |
[
"Yes. Every polymer (all plastics are polymers iirc) has a T_g (glass temperature), which is the point at which the polymeric chains in ths amorphous regions (more responsible for the rubber, flimsy nature of some polymers) gain a lot of rotational mobility. Every plastic that is very rubber/bendable at room temperature has T _g below room temperature. Ocnversely, every plastic which is highly rigid and brittle at room temperature has a Tg above room temperature.",
"Some background info: polymers are extremely large molecules made up of base units called \"mers\". The long chains of mers that make up these polymers are generally made of mostly carbon. When a polymer is heated above it's T_g, these carbon chain backbones gain a lot of segmental mobility, allowing the molecules to move more freely (hence they become more rubbery and malleable)"
] |
[
"I even had a piece of Tygon tubing explode, like tempered glass, when I rapped it on the table. The rapid cooling caused the same stresses in the plastic as occurs in glass that is rapidly cooled."
] |
[
"What is happening physiologically (in the lungs, alveoli, and general airway) when we cough?"
] |
[
false
] | null |
[
"Coughing is a response to the body detecting solids or liquids in the lower respiratory tract (trachea and below). While we can cough voluntarily, and to some extent suppress an urge to cough, a sufficiently strong stimulus will cause reflexive coughing that is impossible to suppress voluntarily. ",
"When coughing, you close your vocal cords, then contract your intercostal muscles to build up pressure in your airways. You then open your vocal cords suddenly to quickly exhale, relying on the force of the moving air to blow out the offending agent.",
"Coughing is neccessary in roughly two scenarios: if food or drink accidentally gets into the airways and if there is excess mucus in the airways, e.g. during an infection. Normal mucus production is continually carried upwards by the cilia (microscopic \"hairs\") of the cells lining the airways until it reaches the larynx and is passed to the esophagus. Smokers cough regularly due to a combination of dysfunctional cilia and excess mucus production due to the airway irritation of smoking."
] |
[
"Diaphragm, abdominal muscles, and intercostal muscles. The basic description above is correct, however the coughing reflex is stimulated by activation of J fibers in the lining of the airways, rather than detection of solids or liquids. Anything that irritates those nerves will cause cough."
] |
[
"“When coughing, you close your vocal cords, then contract your intercostal muscles to build up pressure in your airways. You then open your vocal cords suddenly to quickly exhale, relying on the force of the moving air to blow out the offending agent.”",
"This is what I was looking for! So just to clarify, the positive pressure that shoots the air up is caused by muscles like the diaphragm right? Are there any other muscles involved?"
] |
[
"Why do those with Down syndrome have similarly shaped faces?"
] |
[
false
] |
While most faces are still unique in some way, those with Down Syndrome can be recognizable due to smaller ears, flatter face, almond-shaped eyes, and flatter nose. With all of the variations of facial features, why does Down Syndrome give even those who have a different cultural background very similar facial features?
|
[
"The best answer anybody can give is that some gene (or most likely genes) on chromosome 21 is responsible. We don't have a specific answer to the question yet.",
"One known factor, however, that almost certainly plays a role is the ",
"overexpression of a gene associated with collagen.",
" Collagen plays a major role in the development of many different structures in the body such as bone, muscle, tendons, and cartilage. Needless to say, anything that affects these is going to have a drastic affect on one's appearance. It's also likely that this is responsible for many of the other issues associated with Down's such as muscular deficiency, weak joints, and cardiovascular problems. There are many more factors involved but to my knowledge, this seems to be the one that's most responsible for many of Down's most identifiable traits.",
"It's also worth looking at the genetics behind the disorder. First off, there is very little variation across typical humans: roughly 99.5% of genes will be the same when comparing one person to another. Down's syndrome, however, is the addition of an entire chromosome. Humans have 46 chromosomes so an additional chromosome equates to roughly a 2% difference from the norm. This means somebody with Down's is effectively 4x more different from you or me than we are from each other. Furthermore, since 99.5% of genetic material will be the same, virtually all of the differences due to Down's syndrome that are present in one person will also be present in the next. In short, instead of just having a few random individual variations from person to person you have a large set of common variations from a normal person to a person with Down's. Of course, this is a gross simplification but it illustrates the principles at hand.",
"As you can see, it's really 3 different questions:",
"That's the best I can do to explain it, hopefully it tells you what you wanted to know. And of course, please correct me if I'm wrong on anything or add on if you see something important is missing."
] |
[
"This is the correct response. Trisomy-21 reduces sensitivity of neural crest to the mitotic effects of hedgehog signaling. Trisomy-21 reduced the amount of proliferation of neural crest cells, which leads to the characteristic facial phenotype. It also tends to be associated with other neurocristopathies, such as Hirschsprung's disease."
] |
[
"Humans have 46 chromosomes so an additional chromosome equates to roughly a 2% difference from the norm.",
"Tiny nitpick: chromosome 21 is the smallest human chromosome so one copy of it only accounts for about 0.7% of the human genome."
] |
[
"Can someone in mid Indiana, go outside, look up, take a picture of the giant ring around the moon. What the hell is that?"
] |
[
false
] |
[deleted]
|
[
"Perhaps you are looking at a ",
"22-degree halo",
" around the moon? They are formed by ",
"randomly oriented ice crystals",
" in thin clouds (usually high up in the sky) refracting light from the moon at approximately a 22-degree angle. ",
"They often form around the sun too",
"."
] |
[
"This is a very common misconception. A 22-degree halo is ",
" the same as a \"sun dog\". A sun dog (also known as a parhelion, meaning \"next to the sun\") is a bright spot (sometimes rainbow colored) 22 degrees to the right and/or left of the sun. A 22-degree halo is a circle around the sun. These two phenomena often appear together, but can occur separately as well (",
"sun dogs",
", ",
"22-degree halo",
")",
"Here's a diagram pointing out the difference"
] |
[
"that's it, thanks."
] |
[
"Could we detect strong force waves and weak force waves just like we detect gravity waves and electromagnetic waves?"
] |
[
false
] | null |
[
"There can't be \"strong waves\" or \"weak waves\". Just like EM waves are coherent states of photons, and gravitational waves are coherent states of gravitons, your strong waves or weak waves would be coherent states of gluons or W/Z bosons.",
"However, gluons don't really exist. That is, there is a gluon field, but it cannot have waves, and you really cannot create a state with a gluon. This has to do with a property of Yang-Mills theories (of which quantum chromodynamics is an example), namely that they have a negative beta function - rougly, the higher the energy scale, the smaller the strength of the force. (EM does exactly the opposite).",
"This means two obvious things: 1) in the limit of very high energies, the colour force becomes weak. This is asymptotic freedom. 2) in the limit of very low energies (such as room temperature) the colour force is extremely strong. This is confinement.",
"Confinement is what is important to us. This effect makes sure the force between coloured states is so large that they cannot ever be seen. Taking a meson and trying to pull the quark and antiquark apart does not allow you to see the bare colour of the quarks - you just get more mesons.",
"So confinement is commonly formulated at: there exist only colourless, or white, states. Indeed hadronic physics has a very rich spectrum of thousands of states bound by the strong force, baryons and mesons (and more exotic beasts apparently), all rigorously white.",
"Now in Yang-Mills theory (and so also in QCD) the gauge bosons themselves (the carrier particles) are also charged under the interaction they mediate. (Precisely, they're in the adjoint representation). So if there was such a thing as an actual gluon, which is coloured, you could change reference frame to get it to an arbitrarily low energy (you can do this only because the gluon is massless). As the energy is very low, confinement applies and you get a contradiction.",
"More practically gluons interact with other virtual gluons constantly, in such a strong way that a clean state with a single gluon does not simply exist, let alone coherent states of gluons in macroscopic waves. It just cannot be created. If you give energy to the vacuum, all you'll be able to do is create colourless states. No gluons, and no quarks either. The lightest particle possible in QCD (the mass gap) is the pion.",
"People often say the colour force is short-ranged, and so this would be a very easy argument against colour waves. This is incorrect, since the range of the strong force is infinite as the gluon is massless. Instead, the actual reason is QCD is confining, and all of the above.",
"For the weak force, the mediating bosons are very massive and very unstable. W bosons decay to quark-antiquark or lepton-antineutrino, and they do so in the general order of 10",
" seconds. So that immediately kills the idea of a \"weak wave\"."
] |
[
"So if there was such a thing as an actual gluon, which is coloured, you could change reference frame to get it to an arbitrarily low energy (you can do this only because the gluon is massless). As the energy is very low, confinement applies and you get a contradiction.",
"It took me a minute to figure out what you meant by this - it's analogous to redshift, right?"
] |
[
"Yep. Any massive particle would have a rest energy associated with it, which would stop you from reducing the energy arbitrarily. With a massless particle, whose energy is related only to its frequency, you can theoretically redshift it down as far as you want."
] |
[
"How do we know photons have no mass? They can exert force, their trajectory is bent by massive objects, and they fail to travel at an infinitely fast (or slow) pace from our perspective."
] |
[
false
] | null |
[
"You can always be skeptical about whether a photon has mass or not, and look at what experiments show. You can set up an experiment to measure a photon's mass (for example by looking for deviations from Coulomb's law) and ask the question \"given that we didn't detect any mass for the photon and we know how sensitive our experiment is, what is the maximum mass a photon can have?\" And based on experiments that have been performed, that upper bound is about 10",
" kg. So if photons do have mass, it must be at most 10",
" times that of the electron. For comparison, the mass of neutrinos is not known, but the sum of the masses of the three kinds is about 1/100000 (10",
" ) that of the electron.",
"They can exert force, their trajectory is bent by massive objects, and they fail to travel at an infinitely fast (or slow) pace from our perspective.",
"None of those things are inconsistent with masslessness."
] |
[
"None of those things are inconsistent with masslessness.",
"Just to elaborate on that:",
"In fact if they were moving infinitely fast that would require Lorentz violations. Photons moving at the speed of light is absolutely a required consequence of them being massless in a lorentz invariant universe.",
"Gravity is a geometrical effect and massless things live in the same universe as we do. That is why they are also deflected by gravitational effects.",
"Massless objects absolute have momentum (which is all that is required to \"exert a force\") which is proportional to their energy."
] |
[
"No. Light does not have \"zero energy\" because its mass is zero. Light does have momentum, and no, the equation p = mv isn't applicable to light.",
"Please refer to the ",
"/r/askscience guidelines for answering questions",
". It seems you are unfamiliar with a number of topics you've commented on - or at the very least, not familiar enough to understand the finer nuances of the topic to provide a correct answer."
] |
[
"In oil/gas drilling, how is torque applied effectively to the drill bit a mile or more below the surface? Is there a significant spring effect on the shank?"
] |
[
false
] |
It seems to me that it might take many rotations at the surface to start the bit spinning against the rock, and that the extremely long shank of the drill gets twisted up somewhat. I probably have some bad assumptions.
|
[
"Your assumptions are correct- the amount of twist in the shaft is proportional to it's length and the torque input. For oil drilling shafts that are many miles long the number of turns in the shaft is quite high, can be in the tens to hundreds of turns depending on how long the shaft is. Crazy to think about- but that is reality."
] |
[
"The diameter (girth) of the shaft experiences a shear stress of Sst at its outer surface according to the equation Sst=(T*r/J) where T is the torque applied, r is the radius, and J is the shaft's polar moment of inertia. As long as the material of the shaft can sustain the applied stress it will hold up. So the amount of twist that a shaft can take is according the shear stress limit of the material it is made of and how long the shaft is. A long shaft is basically a spring, which can be wound up with a torque between the input and the output. Aircraft Carrier prop-shafts are a perfect example- they can have more than 360 degrees of twist along their length when at full steam, those are solid steel shafts more than 3 feet in diameter and over 500 feet long."
] |
[
"You are correct, however unlike in drilling through wood, the weight on bit (wob) is very carefully controlled to prevent it digging into the rock too hard, which can cause torque effects (stick slip) on the drill pipe.",
"Where the drill bit meets the rock it's more like a chipping away rather than a drilling process."
] |
[
"If the center of the earth were to suddenly explode for some reason, would the surface be obliterated as it went through the atmosphere, or would it just be shoved out into space?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"guidelines.",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"Wow, that's a fucking stupid rule. Speculation and fun not allowed, huh? "
] |
[
"We try to guaranty some level of scientific accuracy. We have found that overly speculative posts promote answers that are at best educated guesses or more often than not complete non-sense. "
] |
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