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[
"If we discovered and traveled to a habitable planet outside of our Solar System, finding vegetation, could we figure out if something is nontoxic/edible without eating it?"
] |
[
false
] |
What kind of tests could we run to figure out if extraterrestrial vegetation is edible? Would our "earth" toxicology tests work? If we came across compounds never before seen, how do we know if they are poisonous?
|
[
"Peruse a ",
"list of organic chemicals",
" if you're curious. Only a tiny percentage are non-poisonous, hence most successful lifeforms have far more skin than mouth.",
"As for degrading it with gastric acid... try that on ammonia, or sulfuric acid. Outside a rather small pH range, you'd be dead long before your digestive system neutralized (pun intended) the threat. Also, most organometallic compounds are poisonous no matter how you break them down."
] |
[
"I remember hearing that aboriginals in Australia would test food items for toxicity by feeding it to another animal and then following that animal to see what would happen. If that didn't work they would also rub the food on a sensitive portion of their body (inner thigh, armpit, etc.) and see if their skin reacted.",
"While these aren't chemical assays or analytical methods I think they would still be valid."
] |
[
"Am I correct in thinking that while we couldn't eat them, we could still use them for fuel? Carbohydrates + combustion reaction works regardless of what planet you're on."
] |
[
"What distinguishes time from the other 3 spatial dimensions? Couldn't time just be seen as a 4th spatial dimension?"
] |
[
false
] | null |
[
"There's a key difference between 4D space and (3+1)D spacetime. If you were to just take the usual three Cartesian coordinates and add a fourth (u), the metric for that space would be:",
"ds",
" = dx",
" + dy",
" + dz",
" + du",
".",
"You can think of this as being the Pythagorean theorem of 4D space, it's how you measure distances between two points. All of the four dimensions here contribute the same way to the metric; there's nothing special about any one. And you could mathematically come up with transformations that rotate your coordinate system leaving the metric invariant, which would just be analogous to spatial rotations in 3D space.",
"However the metric for Minkowski spacetime is (in +++- signature):",
"ds",
" = dx",
" + dy",
" + dz",
" - (c dt)",
".",
"First, the time coordinate is conventionally given as ct rather than just t, because the coordinates should all have the same units. But more importantly is that the time term comes with the opposite sign as the space terms. Now, if you want to define rotation operations which leave the metric invariant, they have a different form than before. ",
"If you make a rotation which mixes spatial coordinates, you get a transformation of the form x' = ax + by, and so on, where the coefficients a and b end up taking the form of sines and cosines of the rotation angle, for example. But transformations which mix space and time coordinates in Minkowski spacetime, like ct' = act + bx for example, instead end up with coefficients that are ",
" sine and cosine functions rather than normal sines and cosines. These hyperbolic rotations in spacetime correspond with ",
" transformations, which are changes between reference frames which are moving relative to each other. ",
"Geometrically, this metric has the form of a hyperboloid whereas the form of the 4D space metric was just a 4D sphere. And while normal sine and cosine rotations leaving the metric invariant allow you to rotate your coordinate axes however you want on that sphere, these hyperbolic rotations only allow you to \"rotate\" your coordinates along that hyperboloid. A concrete example of this is the fact that if you have one reference frame where an object is moving with a speed less than c, there does not exist any valid boost transformation which will take you into a reference frame where the object is moving faster than c. The transformation laws in Minkowski spacetime don't allow it.",
"This relative negative sign between the space and time coordinates in the metric is what ends up being responsible for much of the weird and non-intuitive things in special relativity."
] |
[
"You can plot a \"faster-than-light\" worldline on a spacetime diagram without it physically meaning anything. It will remain faster-than-light under any transformation (you can change whether it's going forwards or backwards in time, though)."
] |
[
"A universe where time is a space",
" dimension would be a very different place:",
"https://www.gregegan.net/ORTHOGONAL/ORTHOGONAL.html",
"Easy time travel, electrical fields that oscillate sign over distance, and collisions that require a third particle to spontaneously arrive at just the right time are a few of the odd things that happen."
] |
[
"How are spacesuits sealed from the vacuum of space when assembled?"
] |
[
false
] |
I understand that the space suit provides air pressure to keep the fluids in your body in a liquid state, and that the suits are assembled in different pieces for the limbs and such. But how are these separate pieces sealed from the vacuum of space when assembled? (i.e. where the separate pieces connect)
|
[
"The same way as docking. Joints lock tightly so air can't escape. It's like putting your finger over the neck of a bottle and flip it upside down. The liquid inside won't come out because your finger is in the way. ",
"Basically, a space suit is an upside-down water bottle with a finger on the neck. "
] |
[
"Thank you. I just found some information about the \"Quick Connection Rings\". If one piece of the spacesuit is compromised/punctured, will the rest of the suit be compromised? I know that there are many pieces involved. "
] |
[
"One of the things that you have to understand is that space suits aren't at that high of a pressure, otherwise the astronaut in them wouldn't have the strength to bend his fingers and the like. The PLSS backpack used during the Apollo Moonwalks maintained the suit at 4.3psi (one atmosphere is about 15psi). The suits were pressurized with pure O2, which is why there was still sufficient oxygen for the astronauts to breath.",
"Most of the joints in a space suit are made by welding the different rubber/plastic layers together, and through very careful sewing. The only joints that actually are made when donning the space suit is the joint between the torso and the legs, between the arms and the gloves, and between the torso and the helmet."
] |
[
"Does any amount of mold on food indicate that the entire thing has gone bad?"
] |
[
false
] |
I've heard that by the time you can see visible mold growth on some parts of a bit of food, the rest of it is already colonized by an unhealthy amount which has simply not yet grown to visible concentrations. Is there any merit to this?
|
[
"Depends on the food - the USDA ",
"has a neat chart",
" that explains what's safe to eat with mold."
] |
[
"Depends on the food, and the quantity you are talking about. A bit of mold on the outside of a hard cheese is nothing to worry about. Mold on bread is more likely to be present throughout the loaf. Mold on one corner of a 100kg side of beef may have penetrated a bit, but is irrelevant to what's going on at the other end."
] |
[
"Wow, that's really interesting. Thanks for sharing!"
] |
[
"I tend to focus a lot more on the way the people move and speak in tv shows and film than in the story. Is this normal?"
] |
[
false
] | null |
[
"Hello,",
"We can't offer personal evaluations or advice here."
] |
[
"Do you know any sub that could?"
] |
[
"You could try ",
"/r/answers",
"."
] |
[
"How do water softeners work?"
] |
[
false
] |
How exactly do water softeners soften water? I know that they change atoms around and have something to do with ions of some sort.
|
[
"They use ion exchange resins. The resins are designed so that it initially has sodium ions at the resin's active sites. When exposed to hard water the hard ions (Calcium and Magnesium) take the sodium's spot on the resin which releases the sodium ions back into the water. ",
"In a nut shell it just swaps out the \"Hard\" ions with \"soft\" ions.",
"If you want a more detailed description you can look up ion exchange resins. Here is the wiki link for it. ",
"http://en.wikipedia.org/wiki/Ion-exchange_resin"
] |
[
"All water softeners use ion-exchange mechanisms to take the ions responsible for hard water (usually calcium and magnesium) and replace them with another ion like sodium. As for how they do that, well... It varies.",
"Off the top of my head, I can think of two different methods used for ion exchanges. The first ones I dealt with in labs were zeolites, aluminosilicate minerals that act like negatively-charged molecular sieves. These minerals contain arrays of tiny (Angstrom-scale) pores in their structure, which contain sodium ions in them. Due to the higher ionic charge of calcium and magnesium ions (2+ as opposed to 1+), they adsorb to the zeolite more effectively than the sodium ions, effectively displacing them. Zeolites are used a lot in solid or powdered mixtures that work best in soft water, such as laundry detergents.",
"The other one that I can think of is chelating solutions, such as ethylenediaminetetraacetic acid (EDTA). These solutions contain molecules that can form coordinate bonds (similar to covalent bonds, but using either lone pairs or a negatively-charged organic ligand) with two sodium ions ",
" one calcium or magnesium ion at a time. It's the same basic principle as the zeolites mentioned above, but you can use aqueous solutions. Chelating solutions are most often used in food products (I've seen it listed on the back of some nutrition bars at work, I'll snap a picture if requested). They're also used in treating heavy-metal poisoning (you may have heard of chelation therapy?).",
"This isn't an exhaustive list, of course; ion exchange is serious business in all forms of chemistry, so I'd imagine new methods are being discovered or developed all the time.",
"Source: Underemployed Biochemistry grad losing his mind in retail.",
"EDIT: Just realized this subreddit probably appreciates actual sources as opposed to passive-aggressive snarkiness.",
"Zeolites: \nWikipedia: ",
"http://en.wikipedia.org/wiki/Zeolite",
"\nBritish Zeolite Association: ",
"http://www.bza.org/",
"Chelating solutions:\n",
", 3rd ed. by Miessler and Tarr: ",
"http://www.amazon.com/Inorganic-Chemistry-Edition-Miessler-Hardcover/dp/B009O31BQG",
"Wikipedia: ",
"http://en.wikipedia.org/wiki/Ethylenediaminetetraacetic_acid"
] |
[
"Retail isn't that bad... (lol) Thanks."
] |
[
"Will the continents shift, break apart, or change like they did with Pangea?"
] |
[
false
] | null |
[
"Will the continents shift,",
"The continents are part of ",
"tectonic plates",
", which are rigid sections of ",
"lithosphere",
" that move together. The plates are constantly moving and we can measure their motion with GPS stations, e.g. ",
"this page",
" includes a map where you can view the rate of motion of individual GPS stations (and you can change which stations you want to view and the reference frame for the velocities). ",
"break apart, ",
"The breaking apart of plates is referred to as ",
"rifting",
", and yes, some plates are in the process of rifting as we speak. A good example is the ",
"East African Rift",
", which is splitting the African plate into the ",
"Nubian and Somali plates",
".",
"or change like they did with Pangea?",
"Generally, most plates are at least partially changing their shape continually via deformation along their boundaries. New oceanic lithosphere is created at ",
"mid-ocean ridges",
" and old oceanic lithosphere is returned to the mantle at ",
"subduction zones",
". These processes, unless perfectly balanced in terms of rates (e.g. a plate with a spread ridge on one side creating lithosphere at x mm/year and a subduction zone on the other side consuming lithosphere at x mm/year), will cause the shape of a plate to change over time. When continental portions of plates collide, e.g. the ",
"ongoing of the Indian plate with the Eurasian plate",
", because continental lithosphere (generally) can't subduct, this process leads to a shape change of the plates and eventually the ",
"suturing",
" of one plate to another (essentially forming a new, single plate)."
] |
[
"Thanks for the detailed answer! I hope I'm not getting annoying here, but one thing that interests me is the local fault system in my neighbourhood - the Eger Graben. From what I know from my limited geological readings, it's a remnant of the hercynian orogenesis which built up the middle German mountain ranges that are now eroded down to pale remnants. ",
"We still get the occasional light quake from the fault, but it's really inconsequential. So, after all my blather, is that a remnant of the formation of the current plate here?"
] |
[
"As far as I know, there is no formal definition of a strict size cut off or something like that as to when you would call something a plate vs a microplate. For something to be a microplate, it needs to be 'plate-like', meaning that it needs to be a section of lithosphere whose movement can be described by a single rotation and have semi-clear boundaries. Depending on how rigorous you want to get with that though, you could end up dividing up lots of areas near plate boundaries into series of increasingly small microplates. At some point, you've basically defined a continuum, hence (at least in part) the continuing debate within the tectonics community of continuum deformation vs microplates (and maybe why some others in the tectonic community like myself try to stay out of said debates). ",
"Theoretically any major structural system (i.e. fault system) could form the boundary of a current or future microplate, it all depends on how coherent the deformation of the section of lithosphere partially bounded by that fault system is, i.e. could we reasonably consider it 'plate-like'."
] |
[
"If a nuclear weapon is made by splitting an atom, why is it only possible with uranium?"
] |
[
false
] | null |
[
"There are a few different nuclides which can be used to make fission bombs (uranium-235, plutonium-239, etc.)."
] |
[
"What about those elements make that possible?"
] |
[
"Those particular nuclides readily undergo neutron induced fission reactions."
] |
[
"Do nonpolar organic solvents denature proteins, and if so how?"
] |
[
false
] |
Today in my O. Chem lab, we were using an enzyme called Acylase I to turn an alcohol + vinyl acetate into an ester, and whatever. So anyway, we put the alcohol, the vinyl acetate and some acylase I into our reaction containers, along with some Hexane. And this one dude asked our TA how the hexane doesn't denature the Acylase. I've never taken a biochem class or a microbiology class, but my speculation was that a nonpolar solvent wouldn't really mess with anything. But the dude said hydrophobic molecules prevented Van Der Waals interactions, and were used a first step in protein denaturation. The TA himself had no idea what effect the hexane would have/wouldn't have on the enzyme. So, yeah.
|
[
"Nonpolar organic solvents certainly ",
" denature proteins, although whether they do and to what extent depends entirely on the protein. ",
"Proteins consist of amino acid residues, which can be polar or nonpolar (and charged as well). If a protein has a lot of polar/charged amino acid residues on its surface, that's no problem in a polar substance like water. But if you put it in a nonpolar solution, then it'll be energetically favorable to move those polar groups in towards the middle of the protein and try to have non-polar ones facing outwards. (How much it moves here depends of course on how tightly the chains are bound to each other)",
"Conversely, a globular protein that's 'supposed' to be in water may have its internal helices and beta-sheets and all that bound to each other with non-polar (vdw) interactions. (",
"Pi-stacking",
" phenylalanines, for instance) Since the surrounding solvent is polar, it'd be energetically unfavorable to have those non-polar groups bind to the solvent instead. This is what I believe what your TA meant by \"preventing vdw interactions\". (although you still have vdw interactions, just with the non-polar groups and the solvent, rather than with the ones they're 'supposed' to interact with)",
"In short, by changing the solution environment (polar/non-polar solvent, pH etc), you're changing the solvation energy of the protein. Since a different conformation of the protein might have a lower solvation energy in those conditions, it might denaturate. (provided that there's not too high an energy barrier to twist and move into this lower-energy conformation)"
] |
[
"Probably there would be an interaction with any amino acid side chains that are aliphatic e.g. valine, phenylalanine, leucine. This would cause a change in shape and therefore reduce the activity of the enzyme on the substrate(s). ",
"I wonder though if by removing the hexane, or other non polar solvent you could return the activity of the enzyme. As the Van der Waals forces are weak."
] |
[
"If the enzyme is normally in water, it will have polar groups on the outside (usually). This means if you put it into a non polar solvent, there won't be any sort of pressure on the enzyme to maintain its shape, and it could become denatured. It depends on the protein though."
] |
[
"How real was the risk with turning on of the higgs collider?"
] |
[
false
] | null |
[
"You are talking about the Large Hadron Collider (LHC).",
"The kind of reactions that scientist create in the LHC occur daily in our atmosphere when cosmic rays strike earth. If there was any truth to any of the doomsday scenarios associated with turning on the LHC, then these scenarios would have already be triggered by cosmic rays. The fact that the earth is still here is very strong experimental evidence that this doomsday predictions are wrong. ",
"There was zero risk. "
] |
[
"As far as I remember no scientists said there was danger. Hawking was taking about the possibility of micro-blackholes occuring during the reactions. But they were never a danger. By definition they would be unstable and ",
" disintegrate. ",
"He only mentioned it because it might mean that Hawking Radiation could have been detected by the LHC. Of course the news hears Blackholes and instantly starts grinding the doomsday axe."
] |
[
"The real danger was from catastrophic sealing failure resulting in very costly explosions. There was no real danger to our planet from the experiments performed. Just danger to the budget of the LHC and lots of wasted helium. "
] |
[
"Why don't we have ceramic engines?"
] |
[
false
] |
Ceramics can be heated to higher tempratures than common engine materials without melting. By doing so increasing the efficiency of the engine. What's stopping us?
|
[
"While ceramics are extremely heat resistant and much harder than (most) metals, they're also very brittle. I just don't think they would be able to stand up to the punishment that steel can.",
"It also isn't exactly the easiest material to work with, requiring very specialized machinery and techniques. I seriously doubt the efficiency gains would come close to offsetting the additional costs of material and manufacturing."
] |
[
"Besides brittleness, there's a bit of a problem with conductivity. Sure ceramics can have very high melting points, but combustion temperatures can get just as high pretty easily. That's a big problem if your refractory material can't get rid of its heat. Metals on the other hand have lower melting points but are really good heat conductors. That means a combustion chamber can be way above the material's melting point but its walls can be effectively cooled to keep them solid. Inside the engine you have a relatively cool boundary layer of gas against the wall as a result.",
"This is all just to say that ceramics won't let you go so dramatically hotter as you might imagine from just looking at melting points.",
"Edit: So... this is a bit embarrassing but I saw \"engines\" and thought \"rocket engines\". I imagine the above might not be as relevant for engines operating at lower temperatures."
] |
[
"There have actually been a couple ceramic engines made by researchers (in academia and industry). Lots of good info on how the properties of selected ceramics are beneficial/disadvantageous [here].(",
"http://ceramicrotaryengines.com/",
")",
"I seriously doubt the efficiency gains would come close to offsetting the additional costs of material and manufacturing",
"Most definitely speculation. Given the enormous ",
"room for efficnency increases",
" and the high volume of production ICEs, coupled with the face that ceramics' development cost is heavily tied to the initial NRE of creating molds, I think it's fair to say that there is a possibility that there could be overall reduction in cost, in the long term, associated with the development of ceramic engines."
] |
[
"Do we feel the planet moving? Does the Coriolis Effect affect the way we move?"
] |
[
false
] |
I find it odd that so many things that humans do, we do counterclockswise. NASCAR, track bicycle racing, Whirling Dervishes, circumambulating the Kaaba in Mecca... Does it have to do with the predominantly right-handedness of the population? Or is right-handedness a result of the Coriolis Effect?
|
[
"Short answer, No.",
"The coriolis effect is small and drowned out by other sources in most cases.",
"Only on large distances and long times (e.g. cyclones) does it produce noticeable effects.",
"As for right handedness, please not that the cradle of humankind is most probably africa at or below equator. There the coriolis force would work the other way round if at all."
] |
[
"Does the foucault pendulum work with the same principle of coriolis effect? "
] |
[
"Coriolis also affects very fast moving objects.. ",
"If you were to fly at mach 15 through the upper atmosphere you would have to compensate for the apparent force. "
] |
[
"What's actually happening when you age wine?"
] |
[
false
] | null |
[
"some of the other answers in here are talking about fermentation and aging in barrel, both of which happen before a wine is actually bottled and sold. ",
"here are some of the things that happen as wine ages in the bottle:",
"color: newly released red wines are often more bright red-purple, while aged wines tend toward garnet-brown. this is due to the gradual polymerization of anthocyanins (the compound responsible for the color in grapes / wine) - reaction with acids in wine cause the compounds to increase in size and eventually precipitate out of solution, forming sedimentation at the bottom of the bottle.",
"acidity: the esterification of acids result in a reduction of acidity and increase in aromatic compounds. this has the effect of softening the mouthfeel and introducing some tertiary aromas (leather, tobacco, hazelnut) that are indicative of an aged wine.",
"tannins: these are the compounds in a red wine that have a drying effect on the inside of your cheeks, and are considered an important component of more powerful red wines like cabernet sauvignon and nebbiolo. in young wines, tannins can sometimes feel overpowering in the way that the grittiness and bitterness of chewing on grape seeds may overwhelm the taste of the grape itself. over time, the tannins in wine (coming mainly from the grape skins during the fermentation process) react with acids to precipitate out of solution - this, like reduced acidity, results in a softer, smoother mouthfeel. ",
"all in all, the result of an aged wine is one of increasing complexity due to chemical reactions on the main components of the wine. the vast majority of wines nowadays are meant to be consumed immediately or within a couple years of purchase - only a small percentage are meant to be aged (high-end bordeaux, burgundy, italian, napa, etc)."
] |
[
"only a small percentage are meant to be aged (high-end bordeaux, burgundy, italian, napa, etc).",
"What wines age the best? How long can they be aged before the quality begins to decline? For consumers is it worth buying modern wine with the intent to age, or is the difference not very noticable these days?",
"Are modern wines meant to be consumed immediately because the production process has eliminated much of the need for aging? Or is it just that the industrialization and commercialization of large wine producers has made it more cost-effective to eliminate the aging process, despite producing an inferior product? Both?"
] |
[
"Sulfites is correct, however, fermentation only takes about a month to complete."
] |
[
"Is there any truth to the claim that Earth is losing it's magnetic field?"
] |
[
false
] |
I have seen a couple of internet articles, but I wanted to know the truth behind this. What timescale are we looking at? What are the effects of this going to be on society and daily life?
|
[
"Well, the magnetic field will dissipate, but this will be on the time-scale of billions of years in the future. The reason why this is, is because the magnetic field is created by the flow of current, induced inside the outer liquid core of Earth (which is comprised of Iron and Nickel). As the Earth cools off and radioactive decay ceases (which will be billions of years into the future, far after Earth is supposed to be swallowed by the Sun as it inflates into a Red Giant), the Earth's liquid core will solidify, thereby ending the flow of current, and the magnetic field in the process.",
"Magnetic reversals are changes in polarity (N/S swap. Right now, the Southern magnetic pole of Earth is located near the geographic North Pole. This is why the Northern piece of your compass lines up with the magnetic \"north pole\" even though it actually has an opposite polarity.",
"In short, yes over time Earth will lose its magnetic field, but this will be on a time scale deep into the future. Polarity changes can weaken portions of the magnetic field, but it won't have a catastrophic impact, except for on our electronics (as seen by the effects of solar flares exciting particles in the upper atmosphere, which can penetrate to the surface and potentially cause widespread blackouts). This is, of course, a very, VERY unlikely occurrence."
] |
[
"National Geographic may say it, but I would be more interested with probing the sources of their article. Keep in mind that our instrumentation back in 1845 was limited, and with that comes great err in calculations of strengths such as magnetic fields, especially when a magnetic field such as Earth's (which is not symmetrical) is involved."
] |
[
"Well....",
"On a compass, you see, the magnetic north part of the compass points in a certain direction. As you know, north is attracted to south. Therefore the north end of a compass would naturally point to a magnetic south pole. So, the \"North Pole\" as we would call it is actually closest to a magnetic south pole. We call it the North pole, but it is really a North-seeking pole."
] |
[
"What is considered to be the most destructive or powerful thing in the universe?"
] |
[
false
] | null |
[
"Well, any black hole, let alone a supermassive one, is powerful enough to destroy more or less anything that gets too close to it. On the other hand, contrary to the sci-fi depiction, they aren't like vacuum cleaners, so they don't actively suck things in to their doom. Basically things that get close enough fall in the same way something that gets close enough to earth falls to the surface. A super massive one would have a bigger 'danger zone' radius I suppose, if you wanted to look at it that way."
] |
[
"The (presumed) black hole at the center of the milky way exists in a compact astronomical radio source called Sagittarius A* (just an FYI in case you want to look up more on it on your own).",
"I don't know what the exact boundaries of it are, but the star S2 orbits it at about 17 light hours, (about 0.002 light years, or around three times the distance from the sun to pluto) without being destroyed. ",
"So in a way, it comes down to what you mean by 'most destructive.' You'd have to get closer for it to cause problems like a nearby stellar explosion, but on the other hand, if a stellar explosion engulfed a black hole, I believe the black hole would simply consume the matter that fell within range and be otherwise undisturbed. "
] |
[
"The (presumed) black hole at the center of the milky way exists in a compact astronomical radio source called Sagittarius A* (just an FYI in case you want to look up more on it on your own).",
"I don't know what the exact boundaries of it are, but the star S2 orbits it at about 17 light hours, (about 0.002 light years, or around three times the distance from the sun to pluto) without being destroyed. ",
"So in a way, it comes down to what you mean by 'most destructive.' You'd have to get closer for it to cause problems like a nearby stellar explosion, but on the other hand, if a stellar explosion engulfed a black hole, I believe the black hole would simply consume the matter that fell within range and be otherwise undisturbed. "
] |
[
"Does the neurotransmitter has to change firing rate to have real effect?"
] |
[
false
] |
Does the neurotransmitter has to change firing rate of neuron that receives it to have real effect? Are there neurotransmitters that don't change firing rates of neurons even indirectly but cause noticeable change in brain behavior?
|
[
"If a neurotransmitter never changed the firing rate of the postsynaptic neuron at any point in time, the answer would be yes. Often neurotransmitters have metabotropic (as opposed to ionotropic or ion channel based) effects that are subtle and/or do more to modulate potential for plasticity than to directly impact the firing rate. However, even metabotropic activation typically leads to changes in rate of the postsynaptic neuron, even if those changes may be subtle and/or delayed over time. "
] |
[
"The only direct effect of a neurotransmitter is to activate one or more types of synaptic receptors (by definition). So yes and no."
] |
[
"Why were you downvoted?"
] |
[
"About AC and DC in homes:"
] |
[
false
] |
This is something I've wondered for a long time. Bottom line: I hate AC/DC converter bricks. They're everywhere and every gadget you own save a few computer/gaming peripherals need them. I think it dawned on my when I my mom used a wall-charger in her car to charge her cell phone. She had to use an inverter to do it. What that means is: 1) The car puts out 12V DC power to the lighter plug 2) Her inverter converts the 12V DC to AC 3) She plugs in the brick to convert the AC back to DC so she can charge her phone!? She did this because she didn't have a car charger for it at the time. This is insanity and I realized it's only slightly less insane at home. I understand that AC can be transmitted through lines much more efficiently to our homes, but why does it have to stay AC once it gets here? Why can't I have a standardized 12V DC wall plug and eliminate a box full of these stupid AC/DC converter bricks? DC/DC converters to step the voltage up or down are much smaller and I have to believe are more efficient right? Seriously, sitting at home right now, name something that has to have AC input in your home that isn't just converting it to DC before it uses it. All I can think of is the real heavy machinery like washers/dryers which might be using AC motors. Is there a problem with power transmission (or anything else) over short distances I might encounter if all my home's plugs were DC with one or two exceptions for ubiquitous AC appliances?
|
[
"If I remember right, AC motors are usually smaller. Most DC electronics have to do with circuit boards, and AC would not work with them. But any appliance that has a pump or motor needs AC unless the ENTIRE industry were to change over. "
] |
[
"I work as an engineer at a power supply company (we make wall inverters that charge your phones and devices) ",
"the primary concern right now is that every device out there requires different voltages. You have cell phone chargers running off 5V, your radio running off 12V, your power drill charging on 24V, and etc. ",
"In order to take your supposed 12VDC power source and convert it into a voltage that your device requires, you'd still need a DC-DC converter, thus still requiring a converter brick. ",
"That, on top of what you mentioned before with efficiency. Government agencies require specific levels of efficiency, which, if you run a DC-DC converter, is much lower than an AC-AC converter. Either way, you still need a converter and circuitry."
] |
[
"they're not. Take a look at the AC-DC converter for an iphone/ipod. have you seen the size of those things?",
"There are two main types of DC-DC converters. Linear and Switching. For a linear converter, the difference in voltage is dissipated as heat, therefore requiring a fairly large heat sink to meet safety standards.",
"Switching converters also require quite some circuitry, and can take up just as much real estate.",
"The components that really take up the most space in an AC-DC converter are the transformers, heat-sinks, and capacitors. Then there's circuitry both to filter out the output signal, as well as preventative circuitry which protects the consumer in case of misuse or failure. Even with a DC-DC converter, you will still need all those components to protect the device it's powering, as well as the user. ",
"With that in mind, think about this also - Inside your standard laptop power supply, you already have a fairly good sized capacitor, capable of holding enough charge to injure you. Now, that power supply provides a couple amps of electricity at most. Think about how much amperage your whole house needs. Do you really want a capacitor storing that much charge in your house?"
] |
[
"Are sociopaths exclusive to humans?"
] |
[
false
] |
[deleted]
|
[
"Maybe. I'm currently involved in a project that is investigating some genetic polymorphism that have been linked with sociopathy in humans in a nonhuman primate. I won't say it results in animal \"sociopathy.\" The word sociopathy is frequently regarded as the ontogenetic manifestation of psychopathy, which evidence suggests is a genetic phenomenon. Really we could only say humans are sociopaths because only humans have those special sociocultural influences that result in the \"sociopathic\" syndrome (in order to flout social conventions, there first must actually be social conventions to flout). But some of the baser elements of the disorder, like aggression, risk-taking, and sexual promiscuity, might have correlates in animal models. "
] |
[
"http://www.pbfcomics.com/?cid=PBF033-Deer_Laser_Eye.jpg"
] |
[
"Very interesting, and thanks!",
"(in order to flout social conventions, there first must actually be social conventions to flout)",
"Now, forgive me if I sound ignorant or ill-informed, but don't certain animals, like chimps and dolphins have social conventions? Or am I thinking about their societies in the wrong way?"
] |
[
"Why does the strong force increase with distance whilst the residual strong force decrease with distance?"
] |
[
false
] |
[deleted]
|
[
"The residual strong force is analogous to the Van der Waals force. ",
"A system of two equal and opposite charges near each other is called an ",
"electric dipole",
". The total charge of the dipole is zero, so you might think that far away, the electric field produced by the dipole is small. And that would be correct.",
"The field of a point charge (a monopole) falls off like the ",
" of the distance while the field of a dipole falls off like the ",
" of the distance, which is faster. ",
"The Van der Waals force is essentially a combination of various dipole-dipole forces between molecules. It's a weak, short-ranged interaction between particles with no net electric charge.",
"Now take that same sentence and replace the phrase \"electric charge\" with the phrase \"color charge\", and you're basically describing the residual strong force.",
"Of course the strong force is more complicated than the electromagnetic force, and the residual strong force is more complicated than the Van der Waals force, but this analogy can help you wrap your mind around what's going on.",
"The strong force between quarks increases with distance (really the potential increases roughly linearly, so the \"force\" is constant) because quarks are confined. It's a fact of the universe that all particles found in nature (below the deconfinement temperature) are color singlets, which have a net color of \"white\". I don't know that it's understood \"why\" that's true, but I'll leave that for someone else with the appropriate expertise to explain.",
"So whatever complicated QCD dynamics is going on inside the nucleons, the nucleon as a whole always has a net color of white. If the nucleons are close enough together, they can interact strongly via short-range force which looks like a meson exchange force. Since mesons have mass, this force has a characteristic length scale inversely related to the meson masses. This is why we see that the residual strong force only has a range of a few femtometers."
] |
[
"Well \"beam\" makes sense to me, but I work around lots of charged particle beams so maybe I'm biased."
] |
[
"Sure, you could make a case for all four. But it's clear they wanted you to pick protons."
] |
[
"What determines what wavelength of light is reflected from object?"
] |
[
false
] |
If i have a green apple, shined on by light from sun. The apple appears green. Because all wavelengths of light are absorbed except for some that appear green to us. But what determines the color of the apple? Is it the size of the molecules on the apple surface?
|
[
"The transmission/reflection spectrum of a material is a function of the ",
"electronic structure",
" of the molecules composing it. You can imagine an electron as a charge on a harmonic potential; the electric field in passing light excites the electron into an oscillatory motion. When the frequency of the excitory field is much slower or much faster than the electron, it doesn't move much and transmits most of the light. Near resonance, it absorbs more of the light, and just above resonance frequency, it reflects most. The overall reflection spectrum will have features of all of the atoms and molecules in the material; for example, you can see the contributions of various gases to the ",
"atmospheric transmission spectrum",
". If you want a more quantitative treatment of this, MIT opencourseware has ",
"some good slides",
" on the topic."
] |
[
"TL;DR: it's the number of protons in most common atoms on the reflective layer of apple surface. The most outer layer is transparent wax (try to scrub apple with knife, it's fun).",
"Wavelength of any photon is determined by it's energy. wavelength = planks constant * speed of light / energy.",
"What defines energy of reflected photon? Amount of energy absorbed by electron that was \"hit\" by incoming photon.",
"Story version. A photon \"hitting\" an atom of apple may transfer its energy (excite) to atom's electron. Electron, being weird quantum fella, can only absorb energy from certain discrete list of values, too less or too much and interaction doesn't happen. Now suppose the photon was just right and excited an electron to a higher energy state. Electron doesn't like to excited and uses quantum magic to emit a photon in random direction and drops to it's stable (lower) energy state. Emitted photon's energy is precisely difference between excited and stable energy states.",
"Why different atoms have different energy levels? ",
"https://physics.stackexchange.com/questions/160548/what-enables-protons-to-give-new-properties-to-an-atom-every-time-one-is-added",
"More broad article on particle radiation from particle deceleration ",
"https://en.wikipedia.org/wiki/Bremsstrahlung"
] |
[
"This part is well known: under ideal light source that emits all frequencies evenly, an \"ideal red\" object (absorbing all frequencies except some red range) will receive more energy than same size/shape/etc \"ideal green\" object. ",
"https://depts.washington.edu/cmditr/modules/lum/600px-Emspectrum_energy.jpg",
"Now back to reality, the most important obstacle is Sun or common artificial light sources have far from even frequency distribution. After that, red/green apple actually interacts with light in far more complex ways than ideal red/green object. See NASA study how addition of green light is better for growing plants than blue+red combination previously thought as ideal \"because they reflect green\".",
"http://coffeeshopphysics.com/articles/2013-02/01_viruses_have_no_color/visible_spectrum.png",
"http://blogs.discovermagazine.com/badastronomy/2008/07/29/why-are-there-no-green-stars/",
"https://www.ingentaconnect.com/content/cog/habit/2005/00000010/00000002/art00001",
"http://hortsci.ashspublications.org/content/43/7/1951.short"
] |
[
"Why do scientists hypothesize dark matter and not some non-matter phenomenon that generates gravity? I.e. why consider it \"matter\" at all? Or is \"dark matter\" just short for \"gravity-producing phenomenon\"?"
] |
[
false
] |
For example maybe there's just an interaction we don't know about that produces gravity. Or is that an unlikely or impossible scenario? From Wikipedia I see and and , but it's unclear why these are so marginalized.
|
[
"They're marginalized for two main reasons:",
"1) They don't explain the data better than (cold) dark matter does, and lately have often had a harder time explaining several observations, and",
"2) They're ugly as sin. The equations governing a theory like TeVeS are just plain gross, and the only reason anyone even dreamed up such gross equations is because they wanted to reproduce MOND.",
"All of these theories, dark matter and modified gravity, are really \"dark matter theories,\" because all of these introduce new fundamental fields and particles. Dark matter, at least, seems to work with only one type of dark matter particle. Theories like TeVeS and STV add at least three or four new particles into the mix.",
"A mysterious new particle we can't see may sound ad hoc, but it's at least a very simple hypothesis. And we're pretty sure the ",
"Standard Model",
" isn't the last word on particle physics, so the idea that there are more particles out there and that some of them don't interact electromagnetically (i.e., are \"dark\") is not weird at all. Plenty of theories we've come up with for reasons unrelated to dark matter end up producing a dark matter particle anyway.",
"These modified gravity theories, on the other hand, have no motivation in fundamental physics - they're dreamed up solely to solve the dark matter problem. ",
" They're worth looking at. But they're not elegant, they're not well-motivated, they don't do a great job explaining the data, and there's an alternative hypothesis - dark matter - which beats them on all of those counts.",
"Oh, and nowadays these modified gravity theories need some dark matter to work, anyway."
] |
[
"I ",
"answered a similar question",
" two days ago. MoND was proposed in the 80s when the \"missing mass\" problem was really starting to make itself clear, but lots of other observations over the last three decades have really favored dark matter just being some hard to see particle (or class of particles). See, for example, the ",
"bullet cluster",
". Also, as adamsolomon said, the idea of dark matter being some new particle that's hard to see isn't really that weird. It's actually one of the simplest possible solutions."
] |
[
"the idea of dark matter being some new particle that's hard to see isn't really that weird. It's actually one of the simplest possible solutions.",
"It's also not unprecedented. The neutrino was predicted to exist decades before it was directly detected, and it's similar to the particles that are expected to make up dark matter."
] |
[
"When synthesizing new elements, how do scientists know about the number of atoms they produced and how do they measure the rate of decay?"
] |
[
false
] |
I'm very sorry if this is a noob question. I never paid attention in chemistry class. Anyway, here we go: I've been watching some videos about the synthetization of Ununoctium / Oganesson recently and got some questions: In the video I watched, they said that they synthesized x atoms of Ununoctium. How can you measure something this small? Also, how do you measure the time for it to decay, which is also a very small time?
|
[
"How can you measure something this small?",
"The decay products of these extremely heavy nuclei hit your detectors. Then you can plot histograms, apply gates, and eliminate events which did not come from the nucleus you're interested in. Once you've eliminated all extraneous events, you just count the number that remains, and that's an estimate of the number that you produced (correcting for detection efficiency, etc.).",
"Here",
" is an example of how this kind of experiment works."
] |
[
"Nice paper, let me try an ELI5 version:",
"Superheavy elements are produced in fusion reactions, where you hit a heavy nucleus (say, a californium nucleus with 98 protons and 154 neutrons) with a lighter nucleus, in this case the choice of calcium-48 (20 protons and 28 neutrons) is popular.",
"The fusion of these two nuclei is extremely improbable as the resulting object is very unstable. Think about the process as trying to ",
"build a human pyramid by jumping onto an already quite high pyramid",
": You need to get it exactly right, a bit too much momentum/energy and the whole thing collapses in a heap (watch from 0:40).",
"Those nuclei that have fused together are now flying forward into a recoil separator, where a series of electric and magnetic fields is tuned such that the expected heavy reaction products are focused onto a silicon detector, and everything else is deflected away. The cleaner this separation is, the easier it becomes to identify your wanted superheavy products.",
"To make the experiment easier one uses a position sensitive detector, e.g. by segmenting it into many pixels, each acting as a separate detector. ",
"When they hit the detector, they implant into the surface of the Si detector, which gives a signal. I record the position on the detector and the time of day and wait. Eventually that nucleus will decay mainly by alpha emission, giving me a signal in the detector at the same position. I take note of the energy and time of day and continue to wait until I have seen the full decay chain, or observe a spontaneous fission event at this position (They have much higher energies than alpha decays).",
"At the end of this I have measured one atom and its decays and I wait for the next one to come in.",
"Regarding the timing, we can measure times in the nanosecond range very easily with standard electronics (Even a PC runs at GHz frequencies, i.e. each clock cycle takes less than a nanosecond).",
"The lower limit of the halflife of the original atom comes from the time of flight through the separator, which is typically of the order of one microsecond. If it lives much shorter than this, it will decay before reaching the detector. An upper limit for the decay time is given by the time I am prepared to wait for the decay. "
] |
[
"Typical Si detectors are 300 micrometer thick. Recoil energies are of the order of 5-40 MeV (depending on the reaction, target thickness, vacuum vs gas-filled separator etc), so implantation depths are a few micrometer. ",
"Transmissions are quite high for the channel of interest: 40% and more are not difficult, but they depend a little bit on the reaction, e.g. alpha-xn channels will get a larger recoil cone from the kick of the heavy alpha, which reduces transmission over the pure xn channels. The trick is to take the sub-nanobarn cross section and transmit it almost completely, while taking the barn cross sections for the unwanted (quasi-) fission, transfer reactions, etc. and reducing their transmission to 1 in 10",
" or better. ",
"We get punch-through events from forward scattered elastic He or H when using gas-filled separators filled with low-pressure He or H gas (DGFRS, GARIS, RITU, etc), and usually put Veto detectors behind the implantation detector. ",
"We tend to use a thin gas detector (Multi-Wire Proportional Chamber or a Channel Plate) in front of the implantation detector to allow the distinction between an implant (is in coincidence between Si and MWPC) and an alpha (is in anti-coincidence between Si and MWPC). ",
"Rates are dominated by transfer products which end up at similar magnetic rigidities as the primary channel. Slits help, but one has to live with some of these. That is where the segmentation of the detectors helps, because EACH pixel can take a certain rate, having 5000 pixels means your correlation time goes up by a factor 5000.",
"Reading through this, we are in danger of drifting away from the target audience :*) Perhaps a more detailed discussion is better via PM? "
] |
[
"How do benzodiazepines cause memory impairments? Specifically spatial memory impairments?"
] |
[
false
] |
So I know the mechanism of action for the therapeutic effects of benzodiazepines is by binding to the GABA-A receptors. I was wondering what the mechanism of action for some of the side effects caused by benzo's are. More specifically what happens chemically that leads to spatial memory deficits in rats and humans?
|
[
"Alright, so the best way to explain this is probably by plasticity. As neurons fire, they become stronger. This process can occur over a long period of time, or over milliseconds. In the hippocampus, which is the section of the brain that deals with memory, this process of plasticity is directly related to the receptor. Basically, if the presynaptic cell fires multiple times, causing an action potential in the postsynaptic cell, then the synapse will be strengthened. This mechanism comes about due to Ca++ levels in the presynaptic cell and also in the postsynaptic cell. There is also another receptor in the postsynaptic cell. This is the NDMA receptor. This receptor has a Mg+ block in the channel. To remove the block, the cell must be depolarized. For this receptor to work, the ligand must bind, and there must be depolarization (it is a coincidence detector). When the channel is open, Ca++ is allowed into the postsynaptic cell. This Ca++ causes more AMPA receptors to be placed into the cell. The AMPA receptors bind to glutamate. ",
"The effect of benzodiazepines has been linked to retrieval mechanisms in the brain and also to a baseline decrease in glutamate release. This would then cause there to be less of the effect on long term memory as there is less glutamate to activate the receptors that have been placed into the cell, causing there to be no overall strengthening of the synapse. This would explain the effect of long term memory that benzodiazepines have. More information can be found at ",
"http://neurologiauruguay.org/home/images/publicacion/benzodiazepines%20and%20memory.pdf",
" and also at ",
"http://www.ncbi.nlm.nih.gov/pubmed/9483554"
] |
[
"I don't think there is 1 thing that happens, it's a system change. If you are looking for a schematic, I'm sure something exists that will show you the molecular pathway, but I can assure you that looking at that is mind numbing:) (Btw, I'm a neuroscientist and who has worked/published on opioids and spatial memory).",
"So yeah, the real answer is that we don't really know because the system is massive. Much like HypnoticHamster said, a decrease in plasticity is one of the reasons, but how that happens is super complex. \n The ultimate answer is that cells can't talk to one another. To list off a few things that cause that...\n1. Dendritic spines decrease (basically cells can't talk to one another)\n2. Neurotransmitters (many of them) either decrease/increase, screwing up how systems talk to one another.\n3. Receptors actually move or are no longer available (While this isn't directly a \"chemical\" thing, it changes how the chemicals communicate w/ the cell)\n4. Cells shrink or die (this is very common, it's also sex specific)\n5. Many different outside sources also influence everything I have listed above. (hormone level, stress, sex, age, etc).",
"If you are looking for a molecular pathway, I'm sure we can find something:)"
] |
[
"Would you be able to equate a neuron as being a switch that is either on or off? What you said made me think of something IT related."
] |
[
"Do trees grow at a constant rate?"
] |
[
false
] |
This struck me today when I was looking at some young saplings near old, established trees. Does their growth slow over time? Or does it only appear to slow because there's so much more to them and their growth remains constant?
|
[
"Material scientist here. Absolutely not. Tress grow at different rates. The evidence can be seen in unequal thickness of growth rings. During drought or tough conditions, rings are compacted, during wetter seasons rings can be quite large. Often a ring will be black from forest fires etc. So many other factors come into play such as amount of sunlight, soil nutrients etc too. Saplings tend to grow quicker as also evidenced by a large sapwood component of growth rings... I could go on but hope this helps."
] |
[
"No. They require things to grow. In order for the tree to increase its mass, it must take in matter. If the tree is not eating very well, it will grow slower. Other things like temperature affect the growth rate as well because a lack of heat can slow biochemical reactions and too much heat can denature proteins and inactivate enzymes. It’s a balance. But simple answer, no."
] |
[
"It does, thankyou!",
"\nWhat if, hypothetically, all conditions were perfect?"
] |
[
"When you put your fingers on both leads of a battery and are grounded why do you not get shocked?"
] |
[
false
] |
Title
|
[
"Ohm's law states that the voltage (V) is equal to the product of the resistance (R) and the current (I)",
"V = I × R",
"Rearranging that, the current is equal to the quotient of the voltage divided by the resistance",
"I = V ÷ R",
"NIOSH states that the resistance of an average human body is 100 000 ohms (Ω). Assuming a 9 volt (V) battery we get",
"I = 9V ÷ 100 000 Ω",
"I = 0.00009 amperes (A)",
"That's 0.09 milliamperes (mA). I think 500 mA is lethal. ",
"Here's a PDF",
" of the effects of different currents on the human body.",
"Tl;dr: not strong enough"
] |
[
"Ah this is what I assumed but I didn't think skin resistance was so high. Thank you for your detailed explanation "
] |
[
"You can get shocked if you put a 9v battery on your tongue you can feel it tingle. The reason you cant feel a 9v when you touch it to your finger is that it is not strong enough to overcome the resistance of your body."
] |
[
"If all the races of the world continuously cross-bread with each other would we eventually get one composite race?"
] |
[
false
] | null |
[
"No, because race is a sociological concept, not a scientific one. Now if you asked how skin color would turn out...I'd say there would always be variations in color, even if they are shades of brown. In which case human nature would probably take over and create \"race\" out of natural variation. "
] |
[
"um, we already can't group traits together like that. "
] |
[
"um, we already can't group traits together like that. "
] |
[
"Can you force Psychopathy?"
] |
[
false
] |
If a certain very traumatic or life changing event happens, can it force Psychopathy(turn your amygdala off) or can it speed up the rate for developing Psychopathy?
|
[
"If a certain very traumatic or life changing event happens,",
"psychopathology after traumatic stress -> cf. post-traumatic stress disorder (PTSD)",
"can it force Psychopathy(turn your amygdala off)",
"there's a lot more to it than reduced amygdala activity in certain conditions",
"can it speed up the rate for developing Psychopathy?",
"primary/idiopathic psychopaths are famously immune to stress and fear",
"example from ",
":",
"Psychopaths seem to suffer a kind of emotional poverty that limits the range and depth of their feelings. At times they appear to be cold and unemotional while nevertheless being prone to dramatic, shallow, and short-lived displays of feeling. Careful observers are left with the impression they are playacting and little is going on below the surface.",
"A psychopath in our research said that he didn't really understand what others meant by fear. \"When I rob a bank,\" he said, \"I notice that the teller shakes. One barfed all over the money. She must have been pretty messed up inside, but I don't know why. If someone pointed a gun at me I guess I'd be afraid, but I wouldn't throw up.\" When asked if he ever felt his heart pound or his stomach churn, he replied, \"Of course! I'm not a robot. I really get pumped up when I have sex or when I get into a fight.\""
] |
[
"Thanks so much! Just needed some information on this topic for a essay for psychology. "
] |
[
"I am confused by what you mean by \"psychopathy\" and defining it as \"turning the amygdala off\". Psychopathy is basically another word for mental illness.",
"Are you asking if traumatic or large events can cause emotional blunting and problems with memory consolidation? If so, then yes. But please define what you mean further."
] |
[
"Is cannibalism bad for you?"
] |
[
false
] |
I was watching the Book of Eli, and it shows people who have eaten a lot of human flesh have "the shakes" (their hands tremble). Is there any known harm caused by human cannibalism?
|
[
"I've never seen the movie, but it sounds like it is referencing ",
"kuru",
", a prion disease (think mad cow disease) that causes trembling that became transmitted in a Papua New Guinea tribe because of their cannabalistic practices."
] |
[
"I don't know specifically, but my intuition would say no. Why would human meat be that much different from beef or pork? And we won't be producing anything toxic to humans, since the original human had to live too.",
"However, I guess there might be an increased risk of transmissible prion disease from eating human meat. Human forms of prion proteins are probably more potent than say bovine forms (not sure about this- need to look it up or someone to confirm). Prion misfoldings or mutations might spontaneously develop, and eating human meat with prion proteins is going to have a high risk of transmission.",
"Apparently, if you remember the Mad cow scare from a few years ago, the epidemic of Mad cow was caused because cattle were being ",
"fed the remains of other cattle",
", thus causing the transmission of prions."
] |
[
"There's increased risk of viral infections. Cross species viral infections do happen, but it's common for virus not to cross species boundaries.",
"Edit I am not a biologist, nor do I play one on TV."
] |
[
"Did the universe really begin with a singularity?"
] |
[
false
] | null |
[
"\"Singularity\" just means some point in a field equation where the field value goes infinite. That's all it means.",
"There are cosmological models in which some term in some equation goes infinite at ",
" = 0, and models in which none do. They are all, to within the limits of our ability to make observations at present, indistinguishable.",
"So the short answer to your question is maybe, and if so it doesn't matter."
] |
[
"Since",
"there is currently no theoretical model that explains the earliest moments of the universe's existence because of a lack of a testable theory of quantum gravity [1]",
"it is difficult to answer this question with certainty (which I deduce you want, having used the word \"really\"). However, it is \"beyond reasonable doubt, [that] the universe was once a gravitational singularity\" [1][2].",
"Further reading:\n[1]",
"Wikipedia on ",
";\n[2]",
"Wikipedia on ",
"."
] |
[
"Thanks. I ask because I read an ",
"article by Victor J. Stenger",
" (page 2, line 36) where he claims that no cosmologist nowadays would tell you that the universe began with a singularity and I am puzzled."
] |
[
"Why do cysts form and why is the body unable to remove / heal / rid itself of said cysts?"
] |
[
false
] | null |
[
"Cysts are more typically seen as fluid filled growths as opposed to a granuloma or abscess which is more likely to refer to a \"walled off\" infection of typically bacteria. One reason why they form is the body does it on purpose, if the immune system \"thinks\" it can't handle the disease (best example is TB) it will wall it off, separate it, and leave it be. Essentially the reason they form is because the body is unable to beat the infection, so it settles for a draw. At that point, the difficulty in healing comes from the lack of access, so even if someone does start to receive antibiotics or if their immune system becomes stronger it's still difficult because now there is a physical barrier to the infection.\nAlso, lapses in the immune system can cause recurrence because the infection is then stronger than the immune system (ex. TB becoming active again in an HIV patient). Does that help? Short answer, they form because the immune system is overwhelmed and decides to protect the entire body by sacrificing a certain area."
] |
[
"So if someone is prone to cysts what does that usually mean?"
] |
[
"Yes. I figured it was an inability to rid what it contains. Once the barrier is formed is it periodically maintained or does the body allow it to gradually break down and \"check\" if what is contained remains. The cyst itself isn't a means to create an inhospitable environment as in the TV can sustain itself there? (Is tuberculosis a virus?)"
] |
[
"What is laughter, and why do we do it?"
] |
[
false
] | null |
[
"The behavior of laughing most likely came about as a means of communication. The general purpose would have been to inform others of false predator alarms. Danger was expected, and when nothing happened, laughter was a sign that any danger had passed or was never there. Laughter still serves its purpose as a response to the non-threathening unexpected as humor, but its not uncommon to also see people \"laugh it off\" after escaping from some dangerous situation."
] |
[
"Important distinction: Laughter is a form of communication, but not classified as a part of language. It doesn't take place in the \"language\" parts of the brain. This is why babies know how to laugh before learning any other form of communication. It's why all cultures have people that laugh even though all other forms of communication aren't universal. ",
"Here's some interesting info on the evolution of laughter."
] |
[
"Laughter seems to exist as a stress relieving mechanism. It is often a barrier to empathy ( when empathy is the sharing of someone else's pain/trouble/suffering) that's why it can be so easy to laugh at someone else's bad fortune (and why its frown upon to indulge yourself into too much mean laughter: We dont like someone who has no empathy, its frightening because its a-social). Laughter is meant to cancel an anxious state. As to why it is vocal and seems to be made to be heard by other individuals around...we'd need an expert on social behaviors to understand. "
] |
[
"Can flies detect electric currents in the air?"
] |
[
false
] |
As per title. Observation was made regarding a behavioral change.
|
[
"Usually not, but in special conditions they can, like when fatally close to an electric bugzapper. The electric field gradient spreads their legs and wings, at least in the case of mosquitos. ",
"Please provide the details of your observation: how many amperes and at what distance?"
] |
[
"More than once flies have detected this zapper from across the room. They instantly go into 2 modes of behavior: \nA.) Freak out panic mode where they will go from the \"lost circle buzz\" into a more chaotic wall bounce.\nB.) Hiding down low in places with cover.",
"I've observed it many times. Dunno the amps but it clearly is strong enough to suck them in for zapping within a range of about 2-3cm"
] |
[
"Follow up questions: Do you know if its the electrical current, is there a light going on with the zapper that might be affecting their behavior (visible or UV spectrum)? Have you tried turning the zapper on and off to see if the flies will revert to their previous behavior once you have turned it off? Then turn it back on and see what happens? Any idea what kind of fly, standard house fly, fruit fly? ",
"Edit: These are just other ways to test and see if it's the electrical current of the zapper or another cue that might be causing the behavioral change."
] |
[
"Followup from \"The Roundest Object in the World\" video... why is the material (silicon-28) to make it so expensive and how would they make it?"
] |
[
false
] |
This was recently posted on , and I'm not so interested in the shape... I was wondering about why the cost was so astronomical for the silicon (which has a market price of ~$25/kg of standard polysilicon)?
|
[
"Silicon is dirt cheap. Literally. Almost a third of the volume of the Earth's crust is silicon. There's plenty out there.",
"The kicker here is the extraordinary high purity. That sphere is one of the purest macroscopic objects, elementally and isotopically speaking, that exists on Earth, if not in the Universe."
] |
[
"That said, the industry exists to make silicon elementally pure. Isotopically pure seems to be (by the other comments) the proverbial kicker here. Obviously, their enrichment schemes are rather lab-scale at this point... what's to keep someone from making comercially viable Si-28 for, say, the electronics market?"
] |
[
"So what your saying is true, the electronics market uses silicon thats >99% pure, HOWEVER, it is not isotopically pure. Now, there are (from my understanding) no advantages, or very minimal, to having an isotopically pure silicon. That combined with the fact it is so expensive to produce is why it is not used in electronics. Now, maybe in non-consumer products (Military, a huge project like the LHC where cost isn't really an issue) one might use isotopically pure silicon because it does give a minimal gain. However, there is no use for this substance in consumer products.",
"Edit: Just to expand on the isotopes and performance; weight (of the Si) plays no part in the applications (transistors, microprocessors, etc), its all about the purity of Si (in general) due to having a uniform chemical/physical property, not molecular weight."
] |
[
"Is there a way to universally measure time that is seperate from earth and it's rotation around the sun?"
] |
[
false
] | null |
[
"yup. \"Since 1967, the second has been defined to be: the duration of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom\" en.wikipedia.org/wiki/Second"
] |
[
"A meter is defined in terms of the speed of light, so yes, we already do.",
"It should be noted that due to relativity, even though the speed of light is always the same, and a second is always the same.. two people will measure the same thing and get two different answers, and they'll both be right. "
] |
[
"Yes, you can use an ",
"atomic clock",
", which exploits ",
"electron transitions",
". The time between jumps is distributed as an exponential distribution. If you know the theoretical time between jumps (t, in (nano)seconds), counting jumps of a known, reasonably large, number of atoms (n) will allow you to estimate that t*n seconds have passed with error decreasing with n (or possibly the sqrt(n), it's bar-thirty on Friday : ).",
"FYI: The SI unit 'seconds' is defined using an atomic clock."
] |
[
"Infinite Hotel Paradox. Is this a good explanation of Infinity or does it violate the thought of infinity?"
] |
[
false
] |
I found this while on a you tube binge. I couldn't help but feel this thought experiment is... wrong. I felt I grasped infinity pretty well, but does my explanation make sense, or am I missing a fundamental part of this thought experiment? I was thinking (and posted on youtube.) "If the hotel is full though that assumes there are already infinity guest bookings. Adding another infinite amount of guests is saying you want to cram 2*infinity people into infinity rooms. I would assume since both the guests and the rooms are infinite that you are adding 2 people every time 1 room is created. This problem doesn't make sense because instead of putting the people into a room they are instead moving between rooms and not actually put up in their own room. The freeing up of 1,3,5,7,9 etc..... doesn't actually free them up. You created a wave of people moving. lets assume you instantly told, everyone they are going to move and you moved them, Because it's infinite you'll never free up enough space (the hotel is occupied at every number you get to) for another infinite amount of people. I'll explain what this has done another way. Two strings that are infinitely long, one red, one blue. Both wish to occupy the same space. Red string is already in that space, to create room for blue string you create a wave, and feed blue into the now empty space. The red wave will go on infinitely and you will infinitely fill in blue for red. You never finish putting blue string in because it's infinite, and red string is never again "at rest," because it is constantly moving for blue. I understand it's supposed to be a way to illustrate how large infinity is, but surely there has got to be a better way to explain this." Edit: The more answers I get explaining unique ways of understanding this issue I get the more fraking excited I am by the concept. You guys/gals Rock!!!
|
[
"The nature of infinity is such that adding to it doesn't make it larger. Subtracting from it doesn't make it smaller.",
"So (2 * ",
" infinity)= ",
" infinity, and ",
" infinity+ ",
" infinity= ",
" infinity. I think the problem is that you are imagining a fluid situation that isn't fluid. You aren't \"creating\" rooms (as you have stated in your explanation). All the rooms are already there, and they aren't being created, nor being destroyed.",
"Your example of the string is a problem. You see, we have been talking about ",
" infinity, not ",
" infinity, which would more accurately describe the string (a continuum, rather than something compose of individual discrete objects). The same flaw in your conception is present in that analogy. The strings aren't \"moving\". It isn't a fluid situation."
] |
[
"Infinity isn't a number, therefore if you define Infinity as a set of all possible numbers, it still wouldn't contain itself."
] |
[
"I'll explain what this has done another way. Two strings that are infinitely long, one red, one blue. Both wish to occupy the same space. Red string is already in that space, to create room for blue string you create a wave, and feed blue into the now empty space. The red wave will go on infinitely and you will infinitely fill in blue for red. You never finish putting blue string in because it's infinite, and red string is never again \"at rest,\" because it is constantly moving for blue.",
"I don't see the equivalence. ",
"I felt I grasped infinity pretty well, but does my explanation make sense, or am I missing a fundamental part of this thought experiment?",
"Because it's infinite you'll never free up enough space (the hotel is occupied at every number you get to) for another infinite amount of people.",
"Most likely, since the argument in the video seemed correct to me but you are disagreeing with the conclusion. It seems you're assuming that the process of people in the hotel moving to even numbered rooms never terminates, correct? Why do you not have the same objection when we added just a single person to the hotel? The two scenarios really aren't all that different, instead of picturing that all of the people in the hotel scrambled from room n to room 2n picture instead that the concierge took the 1st person in the bus to the 1st room. We've reduced this to the case of adding one person, except instead of being instructed to move one room over the hotel guests are instructed to double their room number. Great, we've reduced it to a solved problem and we're done with the 1st person in the bus. Next we take the 2nd person in the bus, take them to room 3, and instruct the hotel guests as above. Again, solved problem, we are done. We can continue this way and for every person in the bus we can find them a room in a way that everyone that was already in the hotel has a room, as we intended to do.",
"The point isn't to free up enough rooms, because you need to free up infinitely many rooms and infinity is finicky to deal with if you picture it as a number. So the way the problem is handled is you need to find a way that each person is assigned at most 1 room in the hotel, if you can assign them at least 1 room in the hotel you don't need to keep track of whether you've freed up enough room as every guest has a room and your job is done. As you can see the staff in the hotel are work to rule, fucking unions.",
"One issue you may be having is you're attributing too much to the physical plausibility of the scenario. This is a cute illustration, but at the end of the day what you're actually dealing with is sizes of sets, in particular you're answering the question \"how do we quantify the size of a set with infinitely many elements\". You can say they're infinitely large but how do we compare them when we have the natural numbers (1,2,3,...) and the integers (...,-1,0,1,2,...), is one bigger than the other? What do we even mean by size?",
"The answer interestingly is that there are as many natural numbers as integers, which we get when exploring for a bit what we mean by size of a set, something also known as cardinality.",
"Suppose we have a set containing 3 letters, {a,b,c}, and a set containing 3 numbers, {1,2,3}, how do we say which is bigger? Well we can count them both up and end up with 3 elements in each, which is great but that isn't going to be of much use in the infinite case. Another way to go about it is we can find a way to assign a unique letter to each number and a unique number to each letter: a corresponds to 1 and vice versa, b<->2,c<->3. We call that assignment a 'bijection'. We can also figure out when one is bigger than the other by similar means, suppose we compare {a,b,c}, and {1,2,3,4}, we can see the second set is bigger, but why? Well for every letter we can assign a unique number a->1, b->2, c->3, but we have a number (4) that can't be assigned a unique letter. It is useful with infinite sets to do the assignment one way, without checking if the reverse can even work, and say that the second set is ",
" as the first.",
"Now let's go and compare the integers with the natural numbers. Now since the integers contain the natural numbers we see the integers are at least as big as the natural numbers. What we need to show is that the natural numbers are at least as big as the integers, we do this by the assignment process above. That is to say given an integer we need to assign it a natural number and no natural number can be assigned twice. How do we do that?",
"Let's start with the largest integer that isn't a natural number, 0 (in my definition), and assign it to 1. Now let's put the natural numbers in themselves by taking a natural number and multiplying it by 2, which is the assignment 1->2, 2->4, 3->6,... ",
"Which natural number would be taken by this process? well 1 is taken and so is the even natural numbers. What's left is 3 and every odd number bigger than it. So we can assign -1 -> 3, -2 -> 5... (the algebraic rule here is whenever k<0 , assign(k)= 2* |k|+1.",
"Summary: This shows that the integers and the natural numbers are of the same size, a sort of paradox similar to Hilbert's hotel. One thing to note here is that we don't need to make an explicit mention of infinity until the last step. We can make our assignments for finite numbers, prove that the assignment never puts two integers to the same natural number, and then show that the assignment can go over all integers. The lesson from this, and Hilbert's hotel, is that dealing with infinity is usually hard and it can be sensitive, so the approach to take is to somehow reduce it to a problem with finitely sized sets and show that the properties you want carry over in the infinite case."
] |
[
"What is the slowest thing in the universe?"
] |
[
false
] |
Any object we perceive as stationary is still moving through the universe at vast speeds, but I would like to know what the slowest object in the universe is.
|
[
"Because all rest frames are equivalent, any object in its own rest frame is the slowest object in the universe."
] |
[
"So does the reference frame speed (sorry if that is the wrong term) adjust by shifting time to account for my different speed in the two cases?",
"Yup. That's exactly why time dilation and length contraction happen in special relativity.",
"Basically, you have to pick between time and distance being universal and absolute across reference frames, or you have to pick the speed of light being the same across reference frames.",
"edit: To be a little more explicit, let's say that someone on a spaceship shoots a beam of light that travels from point A to point B. Because the person in the spaceship is moving, someone on Earth will say that the distance between A and B is greater, because B \"moved away\" from A while the light was traveling.",
"So, there are two options. The first is that the light appears to travel faster to the person on Earth, which allows it to cover the greater distance in the same amount of time. The other is that light travels at the same speed, but the two observers disagree on how long it took. That's time dilation."
] |
[
"What's a rest frame?"
] |
[
"I have some questions about the big bang"
] |
[
false
] |
First one: For some reason, in my head, the big bang has always been the creation of the universe, including the 'firmament' of space throughout which all matter is dispersed. I've become to suspect my intuition may be incorrect, that 'space' as we know it has 'always been here', or at least we don't know anything about its origins, and the big bang is merely the first thing we know about all the matter in the universe, not the universe itself. Which is correct, if either? Second, if my memory serves, when we look around we see the universe expanding all around us ('ignoring' for the moment that it is also accelerating). And I can't quite intuit the answer, so I have to ask: should we be seeing different motion depending on where we look, and would this be able to tell us the direction of the center of the big bang? In other words, if you are in an explosion, does the stuff on the outside of the explosion behave in any way differently than the stuff inside the explosion ? Moving slower or accelerating differently or what have you? And third: I know that dark matter and energy are still just defined as the 'unknown force' that is moving the universe in ways we can't understand, but is there even a guess as to how this could come about? Any fringe astrophysical theories that could possibly explain it? Is this 'just' a question we don't have an answer to yet, or are we still not even sure where to start looking?
|
[
"I'm about to give the worst introductory course on modern cosmology that the world has ever seen. I apologize with all my heart in advance for how utterly inadequate this is going to be. But maybe I can add just the tiniest bit of illumination to a dense and highly complex subject.",
"There will be simplifications and approximations contained herein. I'm not going to talk about maybes or could-have-beens; I'm just going to summarize the most widely accepted cosmological model we have right now. Anyone who wants to quibble with me over the data is welcome to do so. I reserve the right to snap at you in irritation, then feel awful about it later and come running back to offer a teary-eyed apology.",
"With that out of the way, warm up your imagination muscles and come with me.",
"The universe is infinite. It just keeps going, on and on forever. If you set out in a rocketship, you could keep going in a straight line until you got bored without ever reaching a boundary, or ending up back where you started. It's ",
" … and what's more, ",
"The universe has an average density. If you studied a little physics in school, you might remember that density is what you get when you divided a quantity of mass by the volume of the space that encloses that mass. But the volume of the universe is infinite! How can you calculate the volume of an infinite universe when infinity isn't a number? In the interest of doing this without any equations, I'm going to ask you to just trust me on this one. The universe, despite being infinite, has a well-defined density. We don't know exactly what that density is, but we have a good estimate that puts it on the order of one atom of hydrogen per cubic meter of volume. There are local fluctuations, obviously! I'd say the cubic meter directly beneath my feet right now contains a hell of a lot more than just one atom of hydrogen! But if you ",
" averaging all the cubic meters that contain lots of stuff with all the cubic meters between galaxies that contain nothing at all, you come out to about one hydrogen atom per cubic meter.",
"But it has not always been this way! The density of the universe changes over time. Is that because new matter is popping into existence out of nothing? No; in fact we know that matter — or more properly, mass-energy — can't just appear out of nothing. So if the density has remained constant, then that means the ",
" of the universe must change over time.",
"But how can the volume of an infinite, endless space be said to change? If it's infinite now, isn't it always going to be infinite?",
"This is where I need you to stress that imagination muscle a bit.",
"Start by remembering your Euclidean geometry, from grammar school. In the Euclidean plane, the distance between two points is given by the Pythagorean theorem. Because I promised to do this without any equations, I'm going to skip over exactly what the Pythagorean theorem says, and instead just remind you that the ",
" between points in the Euclidean plane depends on nothing but the ",
" of those points. If you want to change the distance between two points in the plane, you have no choice but to ",
" one or both of the points.",
"But the geometry of our universe is not Euclidean. In particular, the distance between two points in our universe depends on the relative positions of those points ",
"Think of the age of the universe as a sort of ",
" To determine the distance between two points, you calculate it as you would on the Euclidean plane, and then you multiply your answer by the age of the universe. That means the distance you calculate today won't be the same as the distance you calculate tomorrow.",
"In the real universe, the relationship between the age of the universe and the distance between fixed points is a complex one, but that's the gist of it. Take two points, don't move them, and over time the distance between them will increase.",
"We understand extremely well ",
" this happens. The equation that describes it — which I won't get into here! — is actually incredibly simple, one of the simplest equations in all of modern physics. But ",
" this happens is a complete mystery. We know that something must be causing it — with a few notable exceptions that serve to prove the rule, things in our universe do not happen for no reason — but we have no idea what that cause is. Because theoretical cosmologists got really tired of saying \"that thing that causes the universe to expand that we don't know what it is\" all the time, it was given a placeholder name: dark energy. Nobody knows what dark energy is. Right now, it's just a variable in that equation I alluded to. Cosmologists hope to know more about it in the relatively near future, but for right now, it's just another one of those fundamental mysteries of life.",
"Now, let's turn our attention to the earliest history of the universe. If all distances are increasing with time, then necessarily there must have been some time in the past when those distances were minimized. After all, it makes no sense — not even in the hard-to-visualize world of modern cosmology — to describe the distance between two points with a ",
" number! Clearly there's some point in the past that we can imagine when the ",
" of the universe was as small as it can ever be. What was the value of the scale factor at that time? Was it zero? Was it just a very small positive number? We don't know. But we know for a fact that it was ",
" a thousand times smaller than it is today — by convention, we define the scale factor in the present time as being equal to one, so it was ",
" 0.001 in the distant past — and we have very good reason to believe it was much, much smaller than that.",
"Imagine just for a moment what the universe would be like if it were a thousand times more dense than it is now, if everything were a thousand times closer together. There's a lot of empty space in the universe — billions upon billions of light-years of it in every direction — but a factor of a thousand is still a factor of a thousand. In the distant past — about thirteen and a half billion years ago in fact — the universe was a thousand times hotter than it is today. Right now, the average temperature of empty space is just three degrees above absolute zero; back then, it was three ",
" degrees above absolute zero. And it was like that ",
" The ",
" was filled with a dense plasma of mostly hydrogen ions that was as hot and as bright as the sun.",
"And that was the ",
" of the Big Bang. That's after the universe had had some ",
" to expand and cool off. No wonder it took another dozen billion years for things to settle down to the point where planets could form and life could exist on one.",
"Before that period — which goes by the technical name \"the surface of last scattering,\" because it refers to the time in the distant past when the universe finally became transparent to visible light — things were even more exciting. As you imagine going back further in time, things become even more dense, and even more hot. Heat up a hydrogen plasma hot enough, and even the ",
" that make up the plasma won't be able to hold together any more. They dissociate into their component quarks and gluons, forming what's called a quark-gluon plasma, an unbelievably degenerate state of matter that we just barely understand at all.",
"Before that … nobody knows. It's a mystery. We don't know what the universe was like when it was so dense that not even quarks could exist. Maybe there's some kind of matter that's even more fundamental than quarks that can only exist at those energies. Maybe it was all just primordial energy in some form we haven't yet imagined. Nobody knows yet.",
"But eventually, if you imagine yourself back in time far enough, you get to a point where everything reaches either a minimum or a maximum. All distances in the universe? Minimized. All densities? Maximized. What was that point like? Was the scale factor of the universe so small that we can hardly imagine it? Was it ",
" Nobody knows.",
"But we do know that point existed. All our models tell us that it had to be there, about thirteen and a half billion years ago. We just have absolutely no idea — not even fringe-science guesses — what it was really like.",
"But we're working on it."
] |
[
"A delight to read. Thanks for putting this together! ",
"Oh, and just so we're clear, it turns out I was right in the first place. We are talking about the origins of space it self, and not just all the 'stuff' we find in it. Space is, in fact, changing shape, and the origins of our universe are tied in with that space and not just with things moving around inside of it. Keen!"
] |
[
"It's both, actually. Every atom that exists, ever has existed or ever will exist congealed out of that primordial quark-gluon plasma, in one way or another."
] |
[
"The human retina has three types of color receptors: Red, Green, and Blue. How would our vision differ if you added a fourth color such as Yellow?"
] |
[
false
] | null |
[
"Just a comment, the so-called \"red\" cone is actually most sensitive to 560nm, which is greenish-yellow, not red. It actually is not very sensitive to red light. (It is ",
" sensitive to red light than the other 2 cone types, but it's actually just a slightly modified version of the M cone, and its peak frequency is only slightly shifted from the M's). Most textbooks illustrate this incorrectly. (",
"ref",
" for peak sensitivity)",
"Anyway, there are a lot of other vertebrates that have 4 cone types - the ancestral vertebrate seems to have had 4 cones, and mammals have lost 2. (presumably during a phase of nocturnal evolution. At about the same time, we mammals evolved a much better ear than the other vertebrates: more sensitive and better high-frequency perception). For example fish, reptiles and birds all have four cone types. Old world primates are in the middle of re-evolving a 3rd cone and there's some evidence that a few rare women (tetrachromats) have, and might even use, a 4th. ",
"ANYway, theoretically a 4th cone would allow us to perceive a greater assortment if distinct hues in the regions of the spectrum where the new cone's sensitivity overlaps with another cone. As it stands now we actually can't distinguish blues and reds very well. There is a vast swath of short wavelengths that we perceive as just \"blue\" because only the S (blue) cone can pick them up, meaning that our brain has no way to distinguish one short wavelength from another, similar short wavelength. There's similarly a vast swath of long wavelengths that we perceive as just \"red\" because only the L cone is being stimulated. Then there's a relatively small set of wavelengths, quite a small portion of the visible spectrum actually, where we perceive quite a lot of different hues: green-yellow-orange. That's because this is the region where a small difference in wavelength causes a large difference in ",
" stimulation of the 3 cone types. So - cones with overlapping sensitivites give us the ability to perceive very similar wavelengths as very different hues. Presumably something similar would happen if we added (say) a UV cone or a true red cone.",
"tl;dr - probably we'd see a greater variety of distinguishable hues where now we see just \"blue\" or \"red\".",
"Refs: Am on phone on a flight that is about to take off, will have to add refs later. (Self ref, I wrote the color vision chapter for Freeman's \"Biological Science\".)"
] |
[
"Excellent answer. I would just like to emphasize the point you make that it's a misconception that we have \"red\" \"green\" and \"blue\" cones. Cones have sensitivities to different wavelengths. ",
"Here is a bit of an elaboration on why we need more than 1 kind of cone to see color: If you only had one kind of cone, you wouldn't be able to discriminate changes in wavelength from changes in intensity of light. For example, imagine you have a single cone that is most sensitive to 600nm light. That cone could be stimulated to an equal extent by a bright 500nm light or a dim 600nm light. In order to be able to distinguish different wavelengths of light, you need at least two cones with overlapping, but different peak sensitivities. Then, their relative stimulation could disambiguate the intensity from the wavelength."
] |
[
"Neuroscientist at Newcastle University have actually found someone with a ",
"fourth cone",
".",
"In this case I believe the cone was sensitive to wavelengths within the color spectrum - which means this individual is able to better distinguish between colors, but not see any extra colors. There is the other possibility that someone has a cone outside the color spectrum, possibly into the ultraviolet spectrum. That would give an individual to see more colors, or even see stuff normal person cannot."
] |
[
"Are some fat cells we store/burn more nutrient rich than others based on the foods we eat or are they all basically the same?"
] |
[
false
] |
To simplify the question I’m going to say we burn fat in layers like an onion, which I don’t think is true. If I eat nothing but an abundance of healthy balanced foods ( enough to gain a layer fat which we’ll call “good fat” ) then for a period eat nothing but Cheetos ( for my next layer of fat which we’ll call “bad fat”) Is the Cheeto layer less nutrient/ does it provide less energy than the fats made from healthy foods? Or is fat just fat and there is no good or bad? If we take away the layer burning idea and fat is burned more randomly, could it be we get little spurts of energy because our body randomly burned a bit of “good fat”?
|
[
"I do believe that quality of diet does change quality of fat stored (I can look up some sources), but that is different than being more \"nutritious\" fat. Fat is good or bad based on what it does hormonally. Some fat is pretty good at producing these things called inflammatory cytokines, which you don't want. ",
"The fat we store isn't bound with the nutrients it came in with. All fat is the same energy, fat is 9 k/cal per gram."
] |
[
"So fat is released from fat cells usually by endocrine signaling which is signaling through the blood stream and thus hits most of your fat cells pretty evenly. We don't do anything like burning fat in \"layers\" although some fat stores are more responsive to releasing fat to be used for energy than others.",
"",
"The other interesting bit here is that \"bad fats\" actually have more energy than \"good fats\". The difference in the names has more to do with their effect on the body. \"Good fats\" are typically referencing unsaturated fats which we're actually able to extract less energy from than saturated fats. Unsaturated fats tend to have a lot of beneficial effects. Aside from being a straight nutrition source, they also tend to suppress general immune/inflammation pathways.",
"",
"I think the disconnect here is what you're referring to as \"energy\". I'm guessing you mean the feeling of being energetic which is actually quite different than the potential energy of your fat stores. Feeling energetic is a state of mind and can often be quite disconnected from cellular energy. ",
"",
"The cheetos for example, they're full of not only saturated fat, but that fat is deep fried creating a lot of oxidized fats (basically when you heat fats for long periods of time, oxygen from the air can get stuck on them). Our body doesn't really have a good way to deal with oxidized fats so the immune system has to deal with them. When your immune system is activated in this way, it signals to the brain to chill out while it's dealing with the problem (just like when you're sick) and will make you feel tired while it mounts an immune response to clean up these foreign fat molecules."
] |
[
"The fat has the same amount of nutrition value whether it came from a healthy diet or unhealthy one. Usually the unhealthy diet has morw fat in general but as the other redditor said fat itself has the same nutritional value per gram.\nAlso the body has white fat and brown fat. White adipose tissue is the one that stores energy and the brown fat cells burn fat to create heat - termogenesis. The fat you gain from the healthy diet and the Cheetos is both white fat and will not be in any kinds of layers but it will be mixed and burned evenly. The fat below the skin by itself isn't that dangerous - it is dangerous when it is inside the vascular system, causing diseases(often they go hand in hand though).\nHope that cleared things up - have a good day!"
] |
[
"How can I test whether I can taste phenylthiocarbamide?"
] |
[
false
] |
Apparently some humans taste it as quite bitter and others taste it as nothing. What foods or things can I use to see which group I belong to?
|
[
"PTC paper strips are extremely cheap, and I would ask middle school/high school biology teachers if they have it since it's a common demonstration. Otherwise you can find a 100 strip vial (complete overkill) for a couple of dollars on ebay/amazon/etc. According to wiki, natural foods do not have PTC but they sometimes do have related molecules that affect taste, but if you want to have conclusive evidence evidence you would have to taste pure PTC."
] |
[
"I can find no reputable sources for cilantro containing PTC. The sharp division in different people's opinions of cilantro has led some people to think that there may be a genetic component to the way it tastes, and this hypothesis was inspired by the PTC gene. It seems that this has then mutated into a belief that cilantro actually contains PTC itself, but as far as I can tell, this is not the case."
] |
[
"http://www.amazon.com/PTC-TASTE-PAPER-VIAL-STRIPS/dp/B001D7FF5E/ref=sr_1_1?ie=UTF8&qid=1301242237&sr=8-1"
] |
[
"If we could intercept our first radio transmissions in space, would they still sound like they did when they left Earth?"
] |
[
false
] |
I thought about this question after watching posted on Reddit. It got me wondering if we (or aliens) could intercept our first radio transmissions in space, would they sound like they did when they left Earth. Would we be able to hear famous broadcasts like the Hindenburg disaster or Hitler's declaration of war? Or would the signals have dissipated over such long distances and time? Also does the same hold true for TV broadcasts?
|
[
"Signal-to-noise ratio is a bigger problem than the inverse square law.",
"Imagine someone is trying to whisper to you in a very crowded lunchroom. The sound is reaching you just fine, but can you tell what they're saying apart from the background? If the whispers are much, much quieter than everybody around you shouting then distinguishing them becomes mathematically impossible.",
"Making your radio receiver more powerful also makes the static louder. Even if you build a radio receiver the size of a solar system (why not if you're bored, rich and at Kardashev level 2?) then you still can't hear anything faint except from neighboring solar systems."
] |
[
"Our first radio transmissions started a bit more than 100 years ago, TV came a few decades later. That makes roughly a sphere 100 light years in radius where our signals have had enough time to travel to. This is really a very small space, not leaving the Milky Way and not reaching some of the stars we see to the naked eye (e.g. Betelgeuse will still take 500 years to receive them). The video you linked talks about hundreds of billions of Sun-like stars, but within such a small sphere that number must be a lot smaller.",
"If the receiver is moving at a moderately high speed with respect to us then the signal will be frequency-shifted due to the Doppler effect. This is not the biggest problem, though. If radio waves spread in all directions then the power per area decreases due to the inverse square law, and at 100 light years this effect will have attenuated them a lot (it's already hard enough to receive signals from Voyager and it's just a few light hours away). You'd need a HUGE parabolic antenna to receive anything that can be distinguished from background noise, and it would have to be pointed to us. For these reasons I'd say it's unlikely that anyone is hearing.",
"But... if anyone right now is receiving our first radio transmissions and replying to them, we won't know for 100 years until their signals reach us.",
"All of the above makes sense only if they can understand and decode our signals.",
"Anyway, assuming they can decode them, they have the huge parabolic antenna and can correct the frequency shifting, then they should look and sound like on Earth.",
"TV broadcast is a bit more complex than analog audio, so it'd be a bit harder to understand how to decode it. They'd have to guess at least what the hsync and vsync signals mean (end of line and end of frame, respectively). Color coding is even more complex."
] |
[
"This makes me feel like we will literally never encounter another intelligent species through transmissions alone. Am I wrong to say for example, a receiver the size of a solar system is comparable to trying to find a friend in Greater Tokyo using only morse code clicks of a pen on a table and not moving around very much?",
"I'm beginning to think of interstellar communication as mere fantasy. Something that the universe, in its sheer size, exceedingly discourages. No matter what advancements we make, we are still held behind by intrinsic properties of the universe that make it laughable impossible."
] |
[
"How do we derive results from a blood test?"
] |
[
false
] |
So I've recently had some blood tests done, and they've emailed me the results (with notes from my doctor, don't worry, I'm fine) and it got me to thinking, how do they make all these counts? Here's a couple of exerts from my full blood count: I've blacked out my results, the 'normal ranges' are the numbers in brackets, and I'm going to have to dive into Wikipedia in a moment to find out what things like HCT are, but I have a couple of questions: 1) How in the blazes do they go about counting these things? Surely it's not something as simple as a surveying square on a microscope slide? 2) How have we worked out what is considered to be within the normal range? Is this something that is frequently calibrated as time goes on? 3) When they take your blood, the phlebotomist fills a number of vials with various coloured lids and gunk already in the tube, what are these additives(?) and why do certain tests require the blood to be stored in such a way? I think that's about it, thanks for any insight!
|
[
"1) Most machines these days use ",
"Laser Flow Cytometry",
"Back before this technnology, we would make a smear of your blood on a slide and count the number of cell type per high power field and average it out - slightly more complicated than this but in essence this is the process.",
"2) Reference values (\"normal\" range) is just an average of the population and to my knowledge does get adjusted",
"3) The most commonly used tubes are EDTA, Sodium/Lithium Heparin, and Serum. EDTA and LithHep are the most common anticoagulant tubes. ",
"EDTA is the more potent one and is good for haematology tests - it binds quite strongly and so will prevent your blood cells from coagulating. Haematology pretty much is a test of your types of blood cells (this is the test that you've posted) - it's showing your levels of red blood cells and their components, white blood cells and their components, and platelets.",
"Heparin is used for biochemistry tests - so testing different enzyme levels, proteins, glucose, bile, etc in your blood. Why EDTA isn't used is because it interferes with calcium readings as well as some of the other biochemistry values.",
"Serum tubes will activate coagulation - this will use up some of the proteins and factors in the blood and is used for a lot of hormone tests.",
"There are heaps of other different types of tubes: guess a good starting place is ",
"here",
"I just feel like I did my final exams again...sorry if I was a bit vague haha not my favourite memories =P"
] |
[
"Congratulations gentlemen, you passed.",
"(I run a hospital laboratory)"
] |
[
"1). Red blood cell counts are commonly done with automated systems collectively called \"Flow cytometry\". However in the past (and in labs without big budgets) this was done manually with a fixed volume of blood spread over a slide. Not my ideal job but I've heard it can be very relaxing.",
"2). The normal range is determined by testing groups of normal healthy people. As the make up of the population changes this 'normal' range may change and as our knowledge of diseases increases this range my change so these figure is constantly being reviewed and re-considered.",
"3). Different blood tests look at different things.. For example EDTA (purple) tubes are good for tests that need whole blood samples as they prevent clotting without degrading the cells whereas Citrate (light blue) tubes prevent clotting reversibly way so the blood can be used for clot testing.",
"(HCT is commonly hematocrit which can be thought of as the amount of cells to actual liquid ratio in the blood sample, about 45% cell matter is normal and a big increase is a good indicator of dehydration."
] |
[
"Ask Anything Wednesday - Biology, Chemistry, Neuroscience, Medicine, Psychology"
] |
[
false
] |
Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...". Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists. Please only answer a posted question if you are an expert in the field. . In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away!
|
[
"One of the prevailing theories is that in youth, the brain recognizes (possibly even encodes into memory) most information as important because it does not know what is important and what isn't. As we mature, our brain figures out what is important and what isnt, so recognition and encoding of routine things (your commute, your bedtime routine, your lunch break) is less common, and saves encoding tasks for \"noteworthy things\". So due to the larger gaps of important attention, time appears to dilate.",
"I wish I had the link for the neuroscience that tested this, but maybe a neurologist knows more.",
"Source: physician, psychiatrist"
] |
[
"I'll try and add to this, since my background is in neuropharmacology.",
"One of the huge issues with understanding depression/anxiety/mood issues is because there are multiple brain areas that contribute to various feelings (happiness, fear, etc.) and it's some combination of the above that we don't really understand that forms our overall \"mood\". Each of these systems expresses several neurotransmitter systems in varying degrees (and, to make matters more complicated, some neurotransmitter systems can modify other neurotransmitter systems) so there are multiple, and complex levels of control. If ANYTHING goes wrong with any of these neurotransmitter systems, it could be a potential cause for a change in one of the basic emotions that leads to overall mood. This could either be a change in the amount of neurotransmitter released, a mutation that changes the neurotransmitter itself so it doesn't bind as well to the receptor, or the receptor changing in numbers/composition/location of expression to change the overall effect of the neurotransmitter binding to a receptor. ",
"As you may have gleaned from my previous paragraph, issues of mood and anxiety come from a variety of brain areas and therefore involve maaaaaany areas of control. This makes it really difficult for us to \"pinpoint\" what causes it (and, in reality, it's probably a different cause for each person, considering the complexity of the system and the number of ways it could go wrong.) Additionally, finding good animal models for depression and anxiety is difficult, further preventing any conclusive research on the topic. The best we can do for now is to study these neurotransmitter systems as best we can to understand how they work, in order to be able to better recognize how they go wrong. "
] |
[
"If the teeth degrade slowly enough that the early human could survive to reproductive age and have children, then it couldn't be selected against in evolutionary terms. Also, it's likely the absence of refined sugar in the prehistoric diet meant that the teeth degraded relatively slowly. One last point is that humans high intelligence and ability to manipulate things with our hands means that even if someone did lose several teeth, they would likely still be able to feed themselves sufficiently by breaking the food down manually or via cooking, and would therefore still pass on their genes.",
"The short way of saying all this is that there was no selection pressure to evolve the ability to regenerate enamel."
] |
[
"What happens when a small black hole passes through an object?"
] |
[
false
] |
[deleted]
|
[
"For a black hole say at the super smallest size possible to be around for more than a second ( about 2.5 solar masses which is still pushing it. It is probably closer to 3 solar masses ) would still have such a strong gravitational pull it would just eat everything that it passes through probably collapsing most things it passes through if not take everything with it. Also, the smaller the black hole is the hotter it is. A black hole 1 solar mass is about 60 nanokelvin and has a 2 mile event horizon, a black hole the mass of our moon is about 1.7 kelvin and only 1/10th of a millimeter across, but you get much smaller you start getting a LOT hotter. 1/2000 the size of the moon is only 1/20 millionth of a millimeter but sits at a toasty 3300 kelvin which is about 5500 Fahrenheit. So yes small enough to pass through things but also cause a massive amount of destruction at the same time. ",
"TL;DR - smallest solar mass black holes could destroy and absorb pretty much anything it touches. Super light black holes don't live long enough to do any damage but if they did it would be a very hot experience. "
] |
[
"Wow, thanks for dredging through this post from two days ago! I appreciate the insight.",
"So is it fair to say then, by implications within your post, that black holes decay faster as they get less massive / smaller event horizon?"
] |
[
"Much actually. Look up Hawking Radiation and it will explain a lot of the details of how but essentially it radiates energy out faster the smaller it gets. Also why it gets so much hotter too. There are almost no observed black holes that are less massive than 2.5 solar masses and those last for billions of years. The super tiny ones are pretty much only in the quantum size where the hawking radiation vaporizes them in microns of a second. \nAnd your welcome! I love going through to see if i have enough knowledge that I can share :)"
] |
[
"Is there a link between sub-atomic particles and consciousness?"
] |
[
false
] | null |
[
"Do you have some details that would turn this into a question which is amenable to science? Consciousness is a huge mystery and is really the realm of philosophy"
] |
[
"Where might we one day observe consciousness if it is indeed observable, Would it manifest as a sub-atomic particle, reside within one, or something else?"
] |
[
"No idea, genuinely recommend you go have a look around ",
"r/askphilosophy"
] |
[
"Could you just by knowing the chemical composition of a compound determine its properties?"
] |
[
false
] |
Like if you didn’t know what water was but knew it was h2o, could you tell it’s state change points and that it’s a clear liquid etc
|
[
"Yes and no. Understanding the thermodynamics of a material is a very very very very difficult endeavor. In principle you could start with a model for each of the component atoms, then form a model for how they form a molecule, then form a model for how those molecules interact with each other, and finally use that model to calculate the partition function for a collection of molecules and derive various free energies and thermodynamic properties that would tell you everything you need to know about phase changes, specific heat, equations of state, and just about everything you could want to know.",
"Now if you wanted to solve this problem exactly here's how far you could get:",
"1. Model the hydrogen atom.",
"\n2. That's it.",
"Turns out we can get an exact solution of the Schrodinger equation for exactly one atom, and it's hydrogen (makes sense, it's just one proton and one electron). So if you ",
" want to get anywhere, you need to start making approximations. Now this isn't exactly a bad thing, we can approximate the atomic structure of a lot of atoms pretty well! So now we have a hydrogen atom and a pretty good model for what an oxygen atom looks like.",
"Next we want to model a molecule, and once again we can't solve exactly for how two atoms bond, but we can make a pretty good model. So now we have two hydrogen atoms, a pretty good model for an oxygen atom, and a pretty good model for how they stick together to make a water molecule.",
"Here's where things get even harder. There are two routes we can take: the partition function route and the simulation route.",
"The partition function is obtained from the Boltzmann factor of each of the possible states of a collection of atoms. The Boltzmann factor is an expression that's related to the probability of a certain state in terms of its energy and the temperature, but I won't do any serious math here. This route is great because if you can exactly solve for the partition function of a system you can derive any property of the system you could ever want. This route is terrible because it's impossible to exactly solve for the partition function of any real system. But we've been making approximations so far, and we can continue now. The problem is that these approximations won't be as good. The partition function of a bunch of independent atoms isn't too bad, but when they interact (which they have to to form condensed states) it becomes a lot more difficult, even more so when you realize that each molecule isn't just a little ball but an object with internal structure and states. I can't explain much further how you would solve this because it depends a lot on what you're modeling and on what properties you're trying to find out, but basically you can try various approximations and models to calculate various things to varying degrees of success. I know that's not specific at all but I'm trying to explain the entire field of statistical mechanics and thermodynamics.",
"Simulation can be a lot better if you're trying to solve one specific problem, for example the melting point of water. What you can do is use molecular dynamics, which numerically solves for the interactions of every atom in a system over and over and over again in timesteps to simulate some behavior. As you might guess, this is very computationally expensive. You can't do this by hand, and it doesn't run very quickly on a modest computer. You're taking the models you made of your atoms earlier and telling the computer to solve for the interactions of ",
" in your simulation cell, usually containing tens of thousands of atoms, use that calculation to figure out where the atoms will move, move them just a tiny bit, and then do it all over again. Timesteps are on the order of femtoseconds to picoseconds, depending on how fast things are moving. That means you need millions of timesteps to simulate even a ",
" of time. So you can see why this isn't very practical to figure out the behavior of a material under all sorts of conditions, but can be used for specific things.",
"Final point, usually experiments are used to verify the models you make at every level of this process, otherwise you might think you've done a good job but you've made some assumption or small error that ends up throwing everything off. If you're trying to model a material from the ground up without any way to actually test it, you're in for a wild ride."
] |
[
"Hi pasthegucci thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
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", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"An excellent question but also an extremely difficult question which may be why no one else has tried to answer it yet. I'll give it a go although I'm not the best chemist so hopefully a better one will come along and correct me.",
"The chemical composition does indicate a lot about a substances properties, particularly how the molecules will bond and interact with each other. For example, molecules with lots of oxygens and hydrogens will be more likely to form hydrogen bonds and so the overall substance will be denser and more stable than it should be.",
"However, what something is made of is only half the story with the orientation of atoms and the bonds in the molecule being he other major half. This is especially important in drug development which I am involved in. For example, the classic case of thalidomide which has two different shapes of the exact same molecule (one of the bonds bends to the left in one shape and to the right in the other). One form was a very good anti-nausea drug and so was given to pregnant women who suffered from morning sickness. Unfortunately, the other shape caused fetus development to become wildly deformed and most of the babies that did get delivered lived only short lives.",
"So, in theory if you knew everything about a substance including both composition and shape then yes you probably could make a reasonable simulation as to what the reactions will be and there are a lot of simulation chemists who do try and predict molecular reactions. However, and I say this as an experimental scientist, there is still much doubt and uncertainty in present day simulations although they do serve as a reasonable starting point to direct potential experiments.",
"I hope some of this made sense and if you have any questions please feel free to ask!"
] |
[
"How does getting the flu shot work if your bodys t cells remimber the virus, why get it every year?"
] |
[
false
] |
So our body will remember a virus that has entered and been defeated . So then why is it we get the flu shot every year ? Do they just give you multiple flu virus strains ? Or is it a single virus strain every year. My guess is that they pick a strain that they think will be going around that year . Any answers are appreciated
|
[
"The flu mutates rapidly and there are many possible varieties out there. Scientists do some research and statistical guesswork about what kind of flu is likely to surge and then they make a vaccine to inure the public to it. This is also why sometimes people get massively sick despite taking their vaccine."
] |
[
"I believe they pick the four most probable strains for that year, among the many flu strains that we have identified. So, while it may end up being a booster (remind your immune system of it, kind of like exercising) for one strain, the others will be novel. In general vaccines use either severely weakend or inactive strains to help your body learn and build antibodies. Really no different from when other expose you to it the first time, except then it's the full force of the strain and your body may need some time to build up a defense. This way it has a head start. "
] |
[
"Thank you for the knowledge "
] |
[
"If a boat floats in a current, under no other power, can it be turned with the rudder?"
] |
[
false
] |
If there was no wind, or any other force applied to the boat except for the water current could it be turned with a rudder? I feel like if the boat and the water are moving together, the rudder would do nothing, but everyone I ask disagrees.
|
[
"If the boat is stationary with respect to the current, no forces would act on the boat and it would not move.",
"However, real life currents are not smooth, and their energy often varies with depth and location. Depending on the design of the boat and depth of the rudder, it may be possible to direct the boat with a deep rudder."
] |
[
"Sailor here. No wind, no movement, no rudder action. Even in a current you are at the mercy of the elements."
] |
[
"You are right, it would do nothing, provided the boat was not moving relative to the current."
] |
[
"What is the difference between time-dependent density functional theory and molecular dynamics? What are some limitations of each?"
] |
[
false
] |
What is the difference between time-dependent density functional theory (TDDFT) and molecular dynamics (MD)? What are some limitations of each? I know that TDDFT can be used to calculate excitation energies. I have heard that MD can be used to see how the atoms in a molecule move. I guess I'm just confused on the word "time" since MD depends on time as well but maybe in a different sense?
|
[
"Isn't Molecular Dynamics classical? It's just Newtonian particles interacting through some ad hoc classical potential that may or may not be quantum-INSPIRED. Conversely, DFT solves the many-body Schrödinger equation under the assumption of some approximated form for the quantum correlation/exchange physics."
] |
[
"Neither are approaches I have any familiarity with but in a purely MD simulation there are no states. It's just a bunch of classical pinballs acting under a funny classical force. Dr. Google tells me that there IS something called \"excited state MD\" but that seems to be a hybrid approach where classical nuclei are moving in an effective potential due to electrons which are treated quantum mechanically.",
"As for TDDFT, again no familiarity, but I'd assume you could pull excited state dynamics out of it. Don't much see the point of it if you couldn't calculate things like that."
] |
[
"Yes that sounds right to me. Do you know what you would use each for though? Like would you use MD for excited state lifetimes or something? And could you use TDDFT for those as well?"
] |
[
"Do blood clots stay inside of your veins/arteries forever after they form or are they eventually absorbed back into your body?"
] |
[
false
] |
[deleted]
|
[
"There are three possible courses of action after thrombus formation.",
"1) nothing. some vessels can become chronically thrombosed.",
"2) recanalisation. basically the thrombus largely stays in place but the body reorganises it to create a new canal through the middle, essentially creating a new vessel through the clot.",
"3) dissolution and resorption. enzymes and factors break down the structure of the thrombus and the vessel reopens as it dissolves."
] |
[
"Blood clots are gradually resorped by the body over time. For example, after someone gets a DVT in their leg, they are often put on blood thinners by doctors. These blood thinners don't help in resorting the clot. The body takes care of this on its own. The blood thinners are too prevent the cloud from growing further or to prevent new clots from forming."
] |
[
"The tissue plasminogen activator (t-PA) is a serine protease that gets released from damaged blood vessels, their job is to catalytically activate plasmin an enzyme that will degrade the fibrin mesh in the blood clot. The degradation results in end products that are soluble."
] |
[
"Why do we have a depression in our skin above our upper lip? Does this have any significant purpose?"
] |
[
false
] | null |
[
"It's called the 'philtrum' and is the last bit of the face to fuse together: ",
"https://www.youtube.com/watch?v=wFY_KPFS3LA",
"Horror show starts at 00:30."
] |
[
"For the record, this is exactly why some calico cats have the \"split face\" coloration, where there's a clear vertical separation of color from one side of the face to the other. "
] |
[
"Thanks for the time stamp lol"
] |
[
"Is it possible for a planet to be bigger than a star?"
] |
[
false
] |
[deleted]
|
[
"In terms of volume, yes. Neutron stars and ",
"exotic stars",
" are generally smaller than planets (but heavier). In terms of mass, no. Celestial objects over 13 Jupiter masses are called stars (brown dwarfs) and celestial objects below 13 Jupiter masses are called planets (gas giants). The cut-off is somewhat arbitrary but it's about that size where the object can sustain enough hydrogen fusion to glow in the visual spectrum.",
"The distinction between hydrogen-fusing stars and\nbrown dwarfs is well defined. But what distinguishes brown\ndwarfs from planets, given their similar sizes and atmos-\npheric properties? Astronomers vigorously debating that se-\nmantic question fall mainly in two camps. One advocates a\ndefinition based on formation—a brown dwarf condenses\nout of giant molecular clouds, whereas a planet forms via\ncore accretion in a circumstellar debris disk. The other fo-\ncuses on interior physics: A brown dwarf must be heavier\nthan the mass threshold for core fusion of any element,\nroughly 13 Jupiter masses, or 0.012 M\n. Pluto’s recent demo-\ntion has focused attention on the ambiguity of the term\n“planet” in the solar system. Brown dwarfs are forcing us to\nreexamine a related ambiguity in a galactic context",
"http://astro.berkeley.edu/~gmarcy/astro160/papers/brown_dwarfs_failed_stars.pdf"
] |
[
"IIRC, Jupiter is about as big as a planet can be. Add more hydrogen, and it'll shrink a little bit (due to the higher gravity.) Add considerably more hydrogen (at least 12 times), and it'll undergo fusion, and thus become a star.",
"Brown dwarves are about the same size.",
"\"Real\" Sun-like stars are bigger: the pressure due to the fusion increases their volume.",
"OTOH, a ",
"neutron star",
"'s radius is (probably) in the ballpark of 12 km, making them smaller than planets. I'll let you decide whether you wanna call them \"stars.\""
] |
[
"Jupiter is about as big as a planet can be",
"Almost true. The largest gas giants can be up to about twice Jupiter's diameter, especially if their atmosphere is puffed out from being close to their sun.",
"Add considerably more hydrogen (at least 12 times), and it'll undergo fusion, and thus become a star.",
"At 13 Jupiter masses it will only become a brown dwarf. A true red dwarf star needs at least 80 Jupiter masses.",
"\"Real\" Sun-like stars are bigger",
"Usually, but the smallest red dwarf stars are not much larger than Jupiter, and may even be smaller than the largest gas giant planets, though of course they are much more massive."
] |
[
"When you have a lump of decaying material, like Radium, it doesn't all decay at once, at the same rate, right? Different atoms will \"pop\" at different times? What implications does this have?"
] |
[
false
] |
So I'm just imagining a lump of Radium. It's decaying, but not every atom is in lockstep with the others, right? Some atoms will decay into other things first, and some of those will be on their way to some other thing too, and so on and so on. Yes? What practical implications does that have? Is it not really a "lump of radium" but a "lump of mostly radium and smaller amounts of other things"? How do you ever really know what you've got there?
|
[
"So I'm just imagining a lump of Radium. It's decaying, but not every atom is in lockstep with the others, right? Some atoms will decay into other things first, and some of those will be on their way to some other thing too, and so on and so on. Yes?",
"It's equally probable for any given nucleus to decay. But that's the thing -- it's a probability. Some of them will decay in the next moment and some won't.",
"What practical implications does that have?",
"Well for starters it means that unstable nuclei can exist for a certain period of time before decaying. I'm not really sure what kind of answer you're looking for.",
"Is it not really a \"lump of radium\" but a \"lump of mostly radium and smaller amounts of other things\"?",
"Sometimes. Aside from the fact that it's almost impossible to get anything to be 100% pure, your nuclei of interest could very well be decaying into other elements. However it's not necessary. There could be decays that don't transmute the nucleus (for example gamma decay) which would leave your radium as radium.",
"How do you ever really know what you've got there?",
"If you know that your particular nucleus of interest decays a certain way, you can measure the radiation coming from the object and that will tell you how much of your nucleus is left."
] |
[
"While I can't comment on the physics, I'll comment on the implications in computing. One question that comes up here often is how random numbers are generated, and the answer is that truly random number generation requires a physical process that is random. Radioactive decay being one of those processes, a suitable isotope hooked up to a Geiger counter is a valid physical source of randomness."
] |
[
"I'm gonna chime in here (not that your explanation wasn't spot on) because I think there is some misunderstanding when it comes to decay. It's not a stuttering random effect. Yes whether a particular nucleus decays is very random but there are so many (i.e.billions and billions etc.) that it is a completely predictable progression when applied to a large mass.",
"More data is more accurate, we may have no clue what an individual particle will do, but when we know what ten trillion particles will do we can generally begin to model a predictable behaviour (trillion is actually a small number but I didn't want to say quazilluion 'cause that would be weird)"
] |
[
"If viruses are non-living then how did they come to use RNA and DNA? Do they share a common \"ancestor\" with something that would be considered to be living?"
] |
[
false
] |
[deleted]
|
[
"The way you ask this kind of implies that DNA/RNA use was somehow ",
" by living things, but really, RNA came before both viruses and living cells, and each arose from there. So technically, yes, viruses have the same ancestor as all living things, if you consider random RNA tidbits an ancestor. But since RNA isn't alive either, it's not really considered an \"ancestor\" of anything in the scientific community.",
"A little more detail on what I mean, though: most hypotheses about the origin of life express some form of the following progression: small organic molecules arose first, then the specific organics necessary to create RNA eventually did coalesce into RNA, and eventually, some RNA molecules with intrinsic self-replicating properties formed and began to perpetuate themselves, somewhere along the line becoming associated with lipid membranes that would have been able to protect them from the harsh outer environment, and from there catalyzing the synthesis of some proteins, from which more functions could arise, and also switching over to DNA as the primary source of that information, etc. At each step of the way, whatever clump of molecules could replicate itself the best was \"favored\" simply because more of them would get produced. Already the basis of natural selection is obvious :)",
"So, in terms of natural selection, viruses most likely represent a divergence in self-perpetuation \"strategies\". Living organisms went the \"contain all your own machinery and just obtain nutrients from the environment\" route, and viruses went the \"contain only yourself and obtain machinery ",
" nutrients from the environment\" route. Each has significant advantages that would definitely explain how they managed to persist into the present day without one completely outcompeting the other.",
"There are several hypotheses on ",
" how and when viruses developed, but since even basic DNA loops (plasmids) can be viruses, I favor the idea that viruses probably evolved alongside primitive cell-like structures (and later, bacteria) with considerable exchange of genetic material along the way. It's also likely that more complex viruses didn't emerge until after true living cells, when all that fancy machinery was available for them to hijack. But they did always consist of RNA or DNA.",
"Hope that wasn't too much of an information overload - I tend to get a little overenthusiastic about being able to actually answer the questions here :) feel free to ask for clarification on anything!"
] |
[
"Another theory of the origin of the virus is that it was produced by bacteria as an alternate form of a plasmid (a kind of \"virus\" that bacteria deal with but are also symbiotic and form the closest thing to bacterial sexual reproduction)."
] |
[
"the answer is: We aren't sure!",
"There are a few hypotheses about the origin of viruses. The genes of many viruses seem to share things in common with genes in organisms. One hypothesis out there is that what would eventually become viruses first started out as portions of cellular DNA or RNA that then became independent or gained the ability to move from cell to cell. Another hypothesis is that these viruses emerged very early in evolution, and some of their genetic material was left behind in the cells.",
"Here are some resources for you:",
"http://www.mcb.uct.ac.za/tutorial/virorig.html",
"A Nature article with an overview of the hypotheses that I briefly mentioned"
] |
[
"Where and why are there gaps in the fossil record?"
] |
[
false
] |
The main argument I hear people use against evolution is the presence of gaps in the fossil record. I never have an argument back, though I assume not everything can be preserved, but I would like to know this. Thanks!
|
[
"From ",
"http://evolution.berkeley.edu/evosite/misconceps/IICgaps.shtml",
"Response: The fact that some transitional fossils are not preserved does not disprove evolution. Evolutionary biologists do not expect that all transitional forms will be found and realize that many species leave no fossils at all. Lots of organisms don't fossilize well and the environmental conditions for forming good fossils are not that common. So, science actually predicts that for many evolutionary changes there will be gaps in the record.",
"Also, scientists ** have** found many transitional fossils. For example, there are fossils of transitional organisms between modern birds and their theropod dinosaur ancestors, and between whales and their terrestrial mammal ancestors."
] |
[
"Some excellent answers here dealing with the fact species are continuously varying - the fact is species are a human attempt to classify things that are only as good as the data available.",
"To deal with the reason why there are gaps in the fossil record - fossilisation is an incredibly rare occurance. The animal has to die, come to rest (preferably without bits missing or being scavenged later), become buried in sediment which is of the right chemistry to not dissolve the skeleton, be buried to depth (not eroded!), have a groundwater pass through for long enough and rich enough in the right minerals that the skeletal parts get replaced by more stable minerals, then the rock has to be brought back up to the surface by erosion for us to find it.",
"Even in a marine setting where deposition is dominant and there is little erosion this can be really difficult. Particularly the getting back up to the surface at the end bit. In a terrestrial setting, where erosion dominates, fossil preservation is extremely rare indeed. There are entire ecosystem types that are literally ",
" in the fossil record. We have no idea what mountainous flora and fauna looked like at any point, because they're not depositional environments. Same with rocky desert and several others."
] |
[
"also, consider this: Scientist has 2 fossils A and C; creationist says 'aah but theres a gap'...later scientists find fossil B (which goes in the gap)....but creationist says 'aah but now you have 2 gaps'... ",
"and so it goes on: for the creationist, more evidence = more gaps. Doesnt really work as a logical argument, does it?"
] |
[
"How do the \"Miracle Berry\" tablets work?"
] |
[
false
] |
I've seen these Miracle Berry tablets that claim to turn sour things sweet, and on the they claim "The truth is, science doesn't completely know (it has something to do with the protein miraculin that bonds to your taste buds, but the exact cause is still a mystery). But the berries work, and it's a miracle." I don't believe them. How do they work?
|
[
", such as HCl, oxalic acid, lactic acid, formic acid, acetic acid and citric acid; the sweetening effect is ",
" (Kurihara and Beidler 1969). The sweetening effect of a miraculin solution reaches its ",
" (Kurihara and Beidler 1969). A ",
". The taste-modifying effect of miraculin can be ",
", although it depends on the concentration of the miraculin solution. ",
"Kurihara and Beidler (1969) suggested that the ",
"; the conformation of the protein changes under acidic conditions to induce sweetness. This speculation comes from results that show that the thresholds for salty, bitter, sweet and sour tastes remain unaffected after holding miraculin in the mouth. Furthermore, holding miraculin on the tongue does not turn sourness into sweetness when gymnemic acid, which depresses sweetness, is held in the mouth after applying the miraculin solution. ",
" Some studies have revealed that miraculin does not possess taste-modifying properties as a monomer (Ito et al. 2007; Matsuyama et al. 2009). Additionally, mutagenesis and simulation analyses have shown that two histidine residues play an important role in its taste-modifying activity (Ito et al. 2007; Paladino et al. 2010) (Fig. 2). Moreover, the three-dimensional structure of the homodimer predicts a widely open conformation at acidic pH and a closed form at neutral pH (Paladino et al. 2008); it has been suggested that the histidine residues are involved in this conformational change (Paladino et al. 2010). Neoculin, another taste-modifying protein, also exhibits an open conformation at acidic pH on the basis of crystal structure analysis and molecular dynamics simulation (Shimizu-Ibuka et al. 2006). ",
".",
"Against these backgrounds, more recently Koizumi et al. (2011) succeeded in quantitatively evaluating the acid-induced sweetness of miraculin using a cell-based assay system at the molecular level. They also clarified that ",
" and suggested that miraculin bound to hT1R2 at the N terminus region. In near future the modifying mechanism from sourness to sweetness may also be clarified by the developed cell-based assay system for miraculin activity. ",
"source",
"TL;DR: We have a decent amount of evidence suggesting a mechanism, but there are many details that have not yet been filled in."
] |
[
"Found a nice explanation \n",
"Here",
" and ",
"Here",
" that I could understand!"
] |
[
"Yeah, not only do they work but are an effective diet aid as you can satisfy a sweet tooth without so much sugar."
] |
[
"Do women have appetite changes to go with monthly cycles (excluding the obvious period cravings)?"
] |
[
false
] |
Half the month I have absolutely no appetite and barely eat. The other half of the month I am ravenously hungry. Is this related to me being a woman, or is this just a human thing?
|
[
"People are only just starting to track this stuff & figure out how diff hormones affect different people, so I don’t think anyone really knows the answer to your question.",
"but it sounds like follicular phase vs luteal phase to me!"
] |
[
"Thank you! I’ll look that up 😊"
] |
[
"one friend of mine has figured stuff out by tracking it herself. always writing down what day menstruation started (full flow), & writing down extreme moods.",
"Look up how long the luteal phase is (it’s pretty constant in everyone). One way to thin k of it is we have 2 different normal hormone balances, luteal & follicular, with little anomalies around LH surge, ovulation, & menstruation starting."
] |
[
"If we have 2 identical particles and launch them at the same time in different directions and then we measure first particle momentum and the other position wouldn't we find the exact momentum and location of any of the particles ?"
] |
[
false
] | null |
[
"No, because the particles will form an ",
"entangled system",
". The two particles are in quantum superposition and measuring the momentum of one necessarily increases the uncertainty in the position of both of them, since otherwise this kind of system would be a neat shortcut around the uncertainty principle."
] |
[
"Entanglement doesn't violate relativity because no information is exchanged in this so called speed you are referencing. Relativity limits the speed that ",
" can propagate at to c."
] |
[
"I see that this occur at least 10,000 times faster than the speed of light but general relativity theory limit it at c, how is this possible? "
] |
[
"Is the universe a perpetual motion machine?"
] |
[
false
] |
[deleted]
|
[
"I'm not clear what you mean by perpetual motion machine.",
"Yes, the universe is a closed system, so any energy that it has now won't be going anywhere.",
"The second law of thermodynamics is still in effect, however, so entropy will constantly increase until there is no longer any \"useful energy.\" This is called ",
"heat death",
"."
] |
[
"Yes, the universe is a closed system, so any energy that it has now won't be going anywhere.",
"Not really. Energy is only conserved locally. The universe can't be described in terms of a single instantaneous reference frame for more than, well, one instant. So you can't really talk about energy conservation on the scale of the whole universe. The notion doesn't apply there."
] |
[
"Hrmph. Reddit seems to have eaten my first reply.",
"Energy isn't Lorentz-invariant. Change reference frames, and the total energy of a system changes. Our universe isn't time-translation invariant. You can only ",
" that it is on small scales. Hence, energy conservation is purely a local phenomenon. It's not sensible to talk about the total energy of the universe, because it changes depending on when you measure it."
] |
[
"What would happen if you dove in a pool while covered with a hydrophobic material?"
] |
[
false
] |
As the title says. Lets say you get in a skin tight suit or something similar, sprayed yourself with a hydrophobic material (like shown in this video ) and dove into a swimming pool? Would it make you float? Would you glide through the water?
|
[
"Likely not much would be different. Let's say you wore a teflon suit, the water would still wet to the teflon suit, as a water-teflon interface is lower energy than a teflon-air interface PLUS a water-air interface. To demonstrate this at home, put a drop of water on a (unheated) teflon cooking pan. The water wets the teflon, despite \"beading up\" more than it would on a more hydrophilic (metal) pan.",
"A thin layer of entrained air surrounding your teflon suit would be metastable at best, and not persist through the agitation of swimming."
] |
[
"There would be a thin layer of air surrounding you, as shown in ",
"this video",
" of hydrophobic sand.",
"EDIT: Stop upvoting me and listen to cosmicosmo4. I don't know what I'm talking about and he does. "
] |
[
"They become very fast, and get used by all top competitive swimmers for a while and then get banned from formal competition. High end swim suits use patterns of hydrophobic and normal material (mainly the \"FastSkin\") and were banned about 2 years ago.",
"http://en.wikipedia.org/wiki/LZR_Racer"
] |
[
"Physics - Nuclear Fusion"
] |
[
false
] |
I was trying my best to explain nuclear fusion to somebody today and I came to one important question: If you perform nuclear fusion with, let's say, Deuterium and Tritium, having Helium 4 and a Neutron as a result, with incredible amounts of energy of course, where do the matter destroyed by the fusion go? Wikipedia says that the Neutron is "freed" in the reaction, but in my opinion you actually reduced some matter to an energy status. Can matter and energy be the same thing, something we would call "being" generally speaking? I understand that the sun takes hydrogen and makes helium and so on. Could we say then that the end of the universe will come when all matter have been fusionned in very heavy atoms, freeing energy but emptying the world at the same time?
|
[
"where do the matter destroyed by the fusion go?",
"What destroyed matter? You start with a Deuterium atom (p + n) and a Tritium atom (p + 2n) and end with an alpha particle (2p + 2n) and a free neutron (n): two protons and three neutrons go in; two protons and three neutrons come out.",
"Wikipedia says that the Neutron is \"freed\" in the reaction",
"That's what I just said as well.",
"but in my opinion you actually reduced some matter to an energy status.",
"I really wish I had a better way to say this, because I find myself saying it an awful lot and I think it offends people, but your opinion isn't relevant to this discussion. All that's relevant is what our theories predict and what experiments reveal, and on this they agree.",
"Can matter and energy be the same thing",
"Energy isn't a ",
", it's a quantity (of certain systems) that can be measured. Things ",
" energy."
] |
[
"Mass and energy are the same thing. Think of rest mass as energy that is \"trapped\" in one place. Some of this \"trapped\" energy is freed in the D-T fusion reaction."
] |
[
"E=mc",
"This is why nuclear fission reactions are so violent. Mass can be converted to energy and when released that conversion scales the mass by the speed of light squared. The same occurs in fusion. An interesting thing about atoms is that the mass of the whole does not equal the mass of its parts. This difference is described by the equation above and we can measure the energy put out by a reaction to prove it's true. "
] |
[
"What would happen if a human body stops producing hormones altogether?"
] |
[
false
] | null |
[
"People often forget that insulin is a hormone. Sorry to burst the bubble, but it is very simple. You would go into Diabetic Ketoacidosis, much like a type 1 diabetic, fall into a coma and die within the first 24-48 hours. ",
"You may have some competition is ADH (Anti-diuretic hormone) which prevents water from being reabsorbed in the proximal tubules. However, the ADH you had in your system when you stopped producing hormones would probably outlast the lack of insulin production."
] |
[
"All the above is true. However these hormones act slower than cathecholamines such as norepinephrine and dopamine. Without these hormones you would have no blood pressure and go into shock, then multi organ failure quickly resulting in death. "
] |
[
"There is no reuptake of acetylcholine, it's all catabolised by acetylcholinesterase. I'm quite sure death would be near-instantaneous if ",
" hormone synthesis were to suddenly halt."
] |
[
"I can't seem to understand what a virtual image is in optics. Secondly, is a rainbow an example of a virtual image?"
] |
[
false
] | null |
[
"When you look at something, your eyes see and your brain interprets rays of light diverging from individual points of the object. This is called image formation.",
"When you look through a magnifying glass at something, you still see rays of light that ",
" emanating from a common point, but those rays of light didn't actually start there. They actually started from the object and bent at the lens, then went to your eye. Because the rays you see don't actually touch each other, the image is called a ",
"."
] |
[
"So, to add to this, yes, a rainbow is a virtual image.",
"In this picture",
" the rainbow will appear to be coming from the top right."
] |
[
"Easy determinant is whether the image can be produced on a screen or not - real images will, virtual images won't. Reals are produced by light rays that actually converge to a point (which is where we perceive that point to be), whereas virtuals only appear to converge at a point, but actually originated from somewhere else entirely.",
"So for instance if you look through a magnifying class at an object, and the object is close enough to the lens to be focused on, you will see a magnified image on the object on your retina. The image produced by the magnifying glass is a virtual image - it can't be produced on a screen held up between your eye and the lens, and the object only appears bigger because the lens bends the rays so that they appear to have originated from a point much closer to the lens than they really did (the image formed on your retina is a real image, but that's because your eye has its own lens inside - for the sake of this example, just ignore what's going on inside your eye and think of it as just an observer).",
"If on the other hand you move the lens away from the object, at one point everything gets distorted and blurred and starts looking farther away - at this point the lens is generally producing a real image, and could theoretically be visible on a screen (most light sources aren't bright enough to make this perceptible though). Instead of rays diverging and appearing to be from a close point on the far side of the lens, they are converging at a real point on the near side of the lens. The point of blur inbetween is when the object is at the lens' focal distance, resulting in the rays emerging from the lens parallel to each other.",
"The best way to understand the difference is probably diagrams, and I guess I could post some from wiki here, but at that point you're probably better off just reading the wiki pages on real and virtual images.",
"Authority: I took highschool physics, not a professional Optics guy sorry :/ But I don't think there is very much scope for the advanced theory changing in the above stuff"
] |
[
"Why did old CRT TVs get some discoloration when you hold a magnet up to them?"
] |
[
false
] |
And why dont modern led tvs do that.
|
[
"The pixels of a CRT are made from a phosphorescent material that emits light when hit by electrons. To create the picture, a modulated electron beam is swept over the screen to selectively light up the pixels you want to light up. For each point, you actually have three pixels for the elementary colours. If you put a magnet up to it, you distort the electron beam, and thus it does not hit where it is intended to any more, causing colour and shape distortions. In a modern TV, the pixels are actively light emitting semiconductors which are switched on and off and do not need such an electron beam."
] |
[
"In a modern TV, the pixels are actively light emitting semiconductors",
"This is only true of OLED and Plasma displays. In LCD TVs, each pixel does not emit discrete light, rather it blocks or passes light from a single large uniform source behind a colour filter."
] |
[
"The electron beam was definitely being pushed around as others have suggested.",
"I interpret your question of 'discoloration' to include long-term changes to the picture (as opposed to just 'distortion'); colors being thrown off or \"color halos\".",
"The reason this happens is on some models of television there were also a thin metal mask between the electron gun and the phosphor inside the tube; this was used to define sharp edges and dark shadows between the 'pixels'. This metal mask could pick up some residual magnetism from the magnet you're playing with and permanently throw off the beam. TVs then had to be 'degaussed' to eliminate that residual field.",
"Source - did this as a child. Learned not to do it again ;0)"
] |
[
"What are a cat's whiskers for and how do they work?"
] |
[
false
] | null |
[
"They are used by cats to help navigate, especially in the dark. They are very sensitive to being bumped, so as a cat walks forward in darkness, any time the whiskers get bumped, the cat knows they're about to run into something.",
"The tips of their whiskers are usually about the width of their body. This helps them decide if they can get through a given space, such as a crevice or cat door. If they put their face into the hole and their whiskers get through, they know their body will fit through too. Helps prevent getting \"stuck\"."
] |
[
"Couple of questions here: ",
"If a cat were to put on a lot of weight and start to 'bulge', would the whiskers grow to compensate? ",
"Do the whiskers account for a cat being able to compress somewhat?",
"\nI.e. it's ribcage can be smushed so the cat is thinner, fat can roll around the bars or whatever it is try to fit through etc."
] |
[
"\"If a cat were to put on a lot of weight and start to 'bulge', would the whiskers grow to compensate?\"",
"No. Source: my cat Jojo, currently 22lbs and on a diet."
] |
[
"What are the issues with using tritium as fuel for a radioisotope photoelectric generator?"
] |
[
false
] | null |
[
"And many of them have ",
"CURIEs",
" of tritium in them. I have some self glowing exit signs that are only dimmly lit in the dark but were initially filled with 20 Curies of tritium!"
] |
[
"Tritium has a fairly long half-life so it doesn't emit radiation rapidly. Because it only emits beta particles rather than photons directly, it also requires a second compound to allow photons to be generated - this isn't very efficient process.",
"Have you seen a tritium light source? They aren't very bright even in complete darkness. Do you really expect it to generate a significant amount of power?"
] |
[
"I don't mean for conventional use, I thought I saw NASA used tritium for a RPG on a probe."
] |
[
"How does our brain wake itself up?"
] |
[
false
] | null |
[
"It's all a balancing act. The hypothalamus--the trapese artist of the brain--has two hubs decidated to sleep and wakefulness. The ventrolateral preoptic area (",
") promotes sleep. The lateral hypothalamic area and the posterior hypothalamus (",
") promotes wakefulness.",
"",
"",
"The LHA/PH works in concert with a group of monoamines: ",
" from the locus coeruleus (LC), ",
" from the dorsal raphe nuclei (DRN), and ",
" from the tuberomammillary nucleus (TMN). These monoamines fire rapidly during wakefulness, slow down during NREM sleep, and cease firing during REM sleep.",
"",
"Noradrenaline is also known as ",
". One way I like to think of it is as a volume knob for surprise. High levels makes the slighest inconsistencies stick out; it indicates high cognitive alertness. You're sharp as a tack. Low levels makes life dull and bland; nothing seems to make an impression on you. You're bored. A fun fact: your pupils dilate and constrict along with levels of noradrenaline, so the next time you have a hot date you might want to gaze into the windows of their souls.",
"",
"If you're old enough to remember it, people used to get really drowsy from taking antihistamines. This is because the old type of antihistamines crossed the blood-brain barrier which normally prevents potentially toxic substances to enter the brain. By preventing the wakefulness-promoting effects of histamine, old antihistamines made people fall asleep. Modern antihistamines thankfully don't cross the blood-brain barrier.",
"",
"I would say something about serotonin, but it's just too mysterious. It's older than neurons. It's about as old as life itself. And yet I haven't found a single decent review article on its role in cognition.",
"",
"These monoamines are recruited by the LHA/PH to control wakefulness.",
"",
"Orexin neurons in the LHA/PH project to the LC, the DRN, and the TMN. Neurons in the LC, the DRN, and the TMN also project to the LHA/PH; they inhibit its activity. When monoamine activity drops, orexin neurons are freed from inhibition and increase monoamine activity. When monoamine activity increases, orexin neurons are inhibited and monoamine activity drops. This is how wakefulness is stabilized.",
"",
"You might remember hearing about people developing narcolepsy after getting swine flu vaccinations in 2009. It turns out that a part of the H1N1 virus resembles a piece of an orexin receptor. In these people, their own immune system attacked the system that stabilized wakefulness.",
"",
"",
"The VLPO relies on the inhibitory neurotransmitter GABA. As well as inhibiting the LHA/PH directly, the VLPO also inhibits the TMN and the LC. In turn, the LC and the DRN inhibit the VLPO (again stabilizing the current state).",
"",
"",
"The LHA/PH is targeted by several systems. We have already discussed its interaction with monoamines. In addition, it is regulated by the gloriously-named suprachiasmatic nucleus (SCN). The SCN the internal clock of the brain, synchronized through photoreceptors that keep track of day/night cycles through the amount of light available. It is also influenced by the metabolic state of the body via ghrelin, glucose, and leptin. In other words: hunger keeps you awake. It is also targeted by the amygdala. In other words: bears keep you awake.",
"",
"There are other interesting players in this game. Adenosine is a metabolic byproduct of neuronal activity; it builds up when you think. Adenosine inhibits orexin neurons. As you now know, this makes you sleepy. Caffeine blocks adenosine receptors; this is why coffee keeps your mind vigilant.",
"",
"I could also have discussed acetylcholine, but I think this is more than enough to answer your question so I'll leave it be.",
"",
"",
"The brain wakes itself up by flipping the switch from the VLPO to the LHA/PH. Orexin neurons in the LHA/PH stabilizes sleep and wakefulness states so you don't flip and flop hazardly between the two (which would be called narcolepsy). Several players are responsible for making this switch. You might not have eaten much the previous day, in which case increasing levels of ghrelin would give the LHA/PH the nudge it needs to fend off the VLPO. Or maybe it's simply morning, in which case the SCN will prompt the LHA/PH to wake you up as scheduled. Or perhaps a sudden loud noise stings the amygdala and triggers an emergency awakening. Either way, the scale suddenly tips to the LHA/PH rather than the VLPO. Depending on circumstances, you will either wake up completely or go back to sleep. It all depends on which forces acting on the two hypothalamic systems wins out in the end.",
"",
"References:",
"",
"The sleep switch: hypothalamic control of sleep and wakefulness",
"The neural circuit of orexin (hypocretin): Maintaining sleep and wakefulness",
"Adenosine: A Mediator of the Sleep-Inducing Effects of Prolonged Wakefulness",
"",
"Sources for statements not covered by the above can be provided if desired."
] |
[
"Absolutely fascinating. Thank you for taking the time to so clearly articulate this complex system. Greatly appreciated."
] |
[
"From an external stimuli perspective I believe it is light that initiates it (naturally). However, loud noises often do the trick.",
"From a biochemical perspective I recall that adenosine is the neuromodulator responsible for regulating sleep cycles. How it does that I'm not 100% on but that gives you a starting point."
] |
[
"When was the sonic boom discovered? What was the general population's reaction?"
] |
[
false
] | null |
[
"By going faster than the speed of sound.",
"https://en.wikipedia.org/wiki/Whipcracking#Physics"
] |
[
"Lashes of whips can create sonic booms. So... very long ago? At that time there was no good explanation for it of course.",
"Edit: Wrong word."
] |
[
"I bet most people assumed the crack of a whip was from the tip hitting itself rather than breaking the sound barrier."
] |
[
"Would it be possible to make contact lenses that have the same effect as 3D glasses?"
] |
[
false
] |
Has this been done? Would it be safe? Is it possible? Would it work?
|
[
"I'm no 3D expert but my understanding is that all you need are 2 different \"filters\", one for each eye. Then you display 2 slightly different images, each one being able to be viewed by each eye's filter. ",
"So for example back in the day when you had to use those red and blue glasses, there was an image displayed that would be seen by the eye with the red filter in front of it, and a slightly different image for the other eye with the blue filter in front of it. Therefore, you could easily just use one red contact lens in one eye and a blue contact lens in the other and end up with basically the same effect. Any thoughts?"
] |
[
"Use polarized filters (one vertical, one horizontal for ex) and you have the same idea as passive modern 3d glasses."
] |
[
"Using just vertically and horizontally polarized filters leads to the problem of bleed through when you tilt your head. (It is possible to get the lenses oriented the right way in the same way that contact lenses can maintain their orientation for astigmatism.) The circular polarizations used by RealD 3D don't have that problem."
] |
[
"If hand sanitizer kills 99.99% of germs, then won't the surviving 0.01% make hand sanitizer resistant strains?"
] |
[
false
] | null |
[
"Most hand sanitizers use alcohol, which kills indiscriminately. It would kill us if we didn't have livers to filter it, and in high enough doses will kill anyway. Some germs survive due to randomly being out of contact, in nooks and crannies and such, not due to any mechanism that might be selected for."
] |
[
"Let's say you throw 1000 humans into a volcano. One of them happens to land on a ledge inside the volcano and escapes. If he has kids, they will not be volcano resistant."
] |
[
"Sanitizers almost always use alcohol, which bacterial cells don’t really have any cellular means of developing resistance against. You may as well worry about developing resistance to having a nuke dropped directly on your face. Alcohol essentially saps bacterial cells of all moisture instantaneously, and to combat that they would need to develop characteristics which would essentially make them not even bacteria anymore (like a plant-like cell wall or a eukaryote-like complex cell membrane)",
"EDIT: I got a few things wrong, thanks for pointing them out everyone! (no sarcasm intended).",
"Alcohol doesn’t work mainly by sapping moisture, it actually causes the bacterial cell membrane (and eukaryotic cell membranes also) to basically dissolve. We can put it on our hands because of our epidermal outer layer of already-dead cells which basically doesn’t give a fuck about alcohol.",
"Some bacteria actually can develop resistance to low to moderate concentrations of alcohol, by devoting more resources to a thickened cell membrane.",
"Look up bacterial endospores. These can survive highly concentrated alcohol solutions and cause surfaces to be re-colonized under the right conditions."
] |
[
"What happens to the mass of a burned object?"
] |
[
false
] |
[deleted]
|
[
"a completely isolated system will experience no loss of mass. If it is a realistic system, there will be a slight conversion of mass into energy, but the amount will be incredibly tiny. Say you release 10 kJ of heat, E=mc",
" so you take 10/(300000000)",
" g of mass lost. The heat would actually be much greater than that, but even a couple million joules produces a negligible change in mass"
] |
[
"The average heat of combustion of wood is about 15MJ/kg, So 10kg would create 150MJ of heat. By E=mc",
" , m=150,000,000/300,000,000",
" =(5/3)x10",
" kg. That'll be the loss in mass, roughly."
] |
[
"g or kg? You guys keep changing it."
] |
[
"I was musing yesterday and caused a debate I hope /r/askscience can help me with. Can Usain Bolt, out accelerate a car?"
] |
[
false
] |
[deleted]
|
[
"For Bolt to beat a car to 100 meters that car has got to be about dead. Bolt's best time to 100 meters is 9.58 seconds. That's an average speed of 23.3 MPH, which is obviously very impressive. But any car that's only managed to average 23 MPH after almost 10 seconds of acceleration is in very bad shape."
] |
[
"Based on 20m splits from ",
"Sports Scientists",
" His maximal acceleration is the first 20 meters, from 0-25km/h in 2.89 seconds. This works out to ~2.4m/s",
" ",
"Based on ",
"0-60 Times",
" the acceleration of a 1985 civic is 0-96kmh in 11.8 seconds. That works out to 2.25 m/s",
" ",
"So yes. At least for the first 20 meters.",
"As for your actual question, He would be passed before 100m was up. At 2.25 m/s",
" it takes 9.428s for the car to finish 100m. So no, the car would still win. "
] |
[
"It wouldn't have to be a competent driver. You could forget the handbrake and leave the car in first gear, a decent sports car will still win. ",
"Car: Lotus Elise 2011",
"\nSome numbers:",
"\n0-97km/h: 4.4 seconds",
"\nAverage Acceleration: 6.123 m/s",
" over the first 4.4 seconds",
"\nDistance traveled during initial 4.4 seconds: 59.277m ",
"Assuming bolt is traveling 23 mph (10.28 m/s) for the entire race, he would have only covered 45.24m during the initial 4.4s. ",
"So unless he can now catch the car, there is no way he can win."
] |
[
"Why do pathogens transmitted with a vector often cause more severe diseases than those transmitted by direct contact?"
] |
[
false
] | null |
[
"Okay nevermind I found it!\nSince vectors can transmit the disease even if the diseased is dead, it doesn't matter if the pathogen multiply quickly, hence a high death-rate. But other diseases which need to be transmitted from different carriers can't multiply as quickly because then they'll kill their first carrier and quickly become extinct."
] |
[
"I don't think that's right. Ebola, not vector-transmitted, can transmit disease up to five days after death. Myxoma virus of rabbit, transmitted by sand-fleas in Australia, wasn't transmitted after death because the vectors didn't feed on dead bodies. I don't believe that mosquitoes will bite dead bodies, either. ",
"I'm not convinced it's true that vector-borne diseases are actually more dangerous. Smallpox, not vector-borne; Ebola, not vector-borne; rabies, not vector-borne; etc etc. West Nile disease, vector-borne, very low fatality rate. Etc etc. ",
"Here's an alternate explanation, without any support but my imagination. If it's actually true that vector-borne disease are more dangerous (and as I say I'm not convinced that's true) it may be because to be successful, a vector-borne pathogen needs to replicate to very high levels in the blood, otherwise when the vector bites the victim they won't pick up any of the pathogen. And very high levels of replication might be (but aren't necessarily) associated with increased virulence."
] |
[
"I found my answer in a biology book which hopefully should be correct. They presented a chart that showed overall death-rates among vector-transmitted diseases aswell as non vector-transmitted diseases, where it was higher in vector-transmitted ones. The chart didn't have a source though, but I'll trust it.",
"The reason why there are exceptions according to my book is because diseases like smallpox for example can live with a dead host for years, and because of that it's still a pretty high chance that another suitable host will be around the body.",
"I think this solution sounds right, but as always there are exceptions."
] |
[
"What is the physiological/biological/psychological response to self harm (i.e. cutting)"
] |
[
false
] |
I am working on licensure for being a counselor. Often clients who engage in self harm, such as cutting, say that it is self-medicating. What I want to know is what causes them to feel medicated? I know that psychology plays a role in this but it cannot only be psychological. These clients also often express that the cuts or other forms of self harm do not actually cause physical pain. What is going on there? TLDR: Soon to be LPC, What is the physiological/biological.psychological response to self harm?
|
[
"Injuries trigger the release of endorphins, which in the case of normal injury is to cause an analgesic effect. In the case of cutting, they're going for the \"side effect\" of endorphin release, which is to get a sense of euphoria. In basic terms, cutting is like taking a drug, without the physical addictive properties of drugs. ",
"As to not causing physical pain, it certainly would cause physical pain (unless you have a very rare condition that causes you to be unable to feel pain, of course). It's likely that it's a psychological dissociative effect if the patient honestly believes they feel no pain. It's also entirely possible that the patient does feel pain, but doesn't want to be honest about it. Many cutters do say that they can feel the pain, and in fact the pain is what they're going for. "
] |
[
"Awesome! Thanks. Do you have any journal article references for this? I would love to read some research on it. APA or MLA citation or link is fine."
] |
[
"Alright. I've tried like hell to find you free copies of these, but failed. You'll have to get the journals:",
"Plasma B-endorphin levels in patients with self-injurious behavior and stereotypy - American Journal on Mental Retardation, v95 n1 p84-92 Jul 1990",
"Relationship between release of beta-endorphin, cortisol, and trauma severity in children with blunt torso and extremity trauma. - Journal of Trauma 2007 Feb;62(2):320-4"
] |
[
"Why is that when you get a cut (a big cut, not paper cut), and water gets poured on it, it burns?"
] |
[
false
] | null |
[
"When you have a cut, tissue is exposed that does not have the protective hydrophobic layer of skin. ",
"Water is hypotonic and when those exposed tissues are exposed the cells swell and it causes irritation. That's why 0.9% NaCl is often used to irrigate wounds because it is isotonic and does not cause the cells to swell or shrivel. "
] |
[
"So to wash a minor scrape or wound without access to saline, would it be preferable to use a mix of 9g/liter of table salt and filtered water over just using water from the tap?"
] |
[
"depends on whether 0.9% by volume or weight"
] |
[
"Dear Scientists, How hard is it to synthesis Diesel or Petrol or other fuels obtain by crude oil?"
] |
[
false
] | null |
[
"Not hard, just not worth it while there's cheap oil to burn.",
"Basically, you use a ",
"gasifier",
" to generate a mixture of H2 and CO gasses, called \"synthesis gas\". This is basically done by burning a chunk of carbon (which can come from coal or biomass) in an oxygen-starved atmosphere, and then passing hot steam over the coals. The water molecule will yield its oxygen atoms to two different carbon atoms, so the overall reaction looks like:",
"H2O(g) + C(s) -> H2(g) + CO(g)",
"This process produces other products, too, depending on the composition of your feed stock.",
"Anyways, once you have your synthesis gas, you pass it through a ",
"Fischer-Tropsch reactor",
", which uses high temperatures, high pressures, and a metal catalyst to condense the hydrogen and carbon monoxide into hydrocarbons. The length of the carbon chain can be controlled by varying the reactor parameters mentioned above in addition to the \"cooking\" time.",
"I don't know enough about chemistry to tell you how the whole catalytic process works, but hopefully somebody will come in here and enlighten both of us. Point is, the technology does exist to do what you mention and it's fairly mature; it's just not (yet) economically competitive."
] |
[
"Thanks and appreciate your reply"
] |
[
"There was a ",
"plant",
" that up to a few years ago was cranking out crude oil from turkey offal. ",
"But it ",
"shut down",
" due to financial problems."
] |
[
"What causes the two big population spikes in China's population pyramid?"
] |
[
false
] |
China's population pyramid is unique, as it has two large groups of people at the age 25-35 and 45-55. I would guess this has something to do with their one-child policy and their explosive population growth since the 1900s. but i haven't found any sources on this. Could anyone help me out?
|
[
"I believe the first \"spike\" was due to (a) the great leap forward in the early 1960s which killed a lot of people, and (b) decreased birth rates starting around 1970 due to a two-child policy and then one-child policy. Basically, starting in the mid 1960s, birth rates dropped. Consider also decreases in mortality, especially ",
"infant mortality",
", in the 1960s and 1970s, which tends to shift the spike later.",
"The second is an \"echo\" of the first spike. There were more young adults entering breeding age around 1990 compared to 1980 or 2000, due to the earlier spike."
] |
[
"Not an expert, but are you sure it's two spikes and not one dip for ages 35-45? Also what year was the population pyramid you're looking at published in?",
"Because if you're thinking about China 45 years ago, you're talking about the middle of the Cultural Revolution. If your pyramid is a few years old, the 35-to-45-year-old group could be exactly those born in the Cultural Revolution."
] |
[
"FWIW, I found a chart of birth rate in China ",
"here",
" showing birth rate peaks around 1963 and 1987. ",
"And the Chinese population pyramid for 2016 ",
"here",
"."
] |
[
"Question about specimens suspended in blocks of glass or plastic, and how they're made."
] |
[
false
] |
At my elementary school library, there were a bunch of specimens - mostly of insects, spiders, scorpions, seahorses, and coral - that were perfectly suspended in glass. At least, I'm fairly certain it was glass. My question is, how can something organic be encased in glass like that, and positioned so perfectly? Wouldn't the heat from the glass-making process utterly destroy them? Just how are specimens like this made? Even if it was acrylic or some kind of plastic, wouldn't they still have to be made at temperatures too hot for delicate specimens to remain intact?
|
[
"It is likely encased in plastic. When making plastic, you mix together chemicals to form a polymer, but not necessarily at high temperature (usually 100 degrees C). You can then place the specimen in the liquid plastic and cool it.",
"This is a common lab done in undergraduate organic chem courses."
] |
[
"Thanks. Exactly what I wanted to know. "
] |
[
"If you're interested in this kind of thing, there's a subreddit called ",
"How It's Made",
"."
] |
[
"Are terrestrials and gas giants the only two possible types of planet?"
] |
[
false
] |
According to Wikipedia, the planets in our Solar System fall into two categories: Terrestrials (Earth-like planets primarily made of rock, sometimes with an atmosphere), and gas giants. Are there any scientific theories regarding other types of planets that could exist, or does the scientific community currently believe those are the only two possible types of planet?
|
[
"There's actually an extensive list of planetary types on Wikipedia: ",
"http://en.wikipedia.org/wiki/List_of_planet_types",
" that said some like \"rogue planet\" could be a \"rogue terrestrial planet.\" However following the type theme of terrestrial and gas giant there are also ice giants, iron planets, ocean planets, coreless planets, and so on that are similar in \"kind.\"",
"Within our own solar system Pluto (not a planet, but a dwarf planet) has a surface composed of more than 98% nitrogen ice based on spectroscopic analysis. Although it is a combination rocky and ice body (estimates are 50–70% rock and 30–50% ice by mass.)"
] |
[
"That list doesn't really address the question.",
"It's just a flat collection of groups with no indication of which categories are mutually exclusive and which are not. For instance, ",
", ",
", and ",
" are all on the list. We know of ",
" of either of the latter classes, and the ",
" class doesn't exclude any of the former three classes.",
"The list also doesn't give any indication of hierarchy in taxonomy. For instance, the list is topped by the root the taxonomy: ",
", which encompasses every other class in the list. There is more depth in the hierarchy as well - ",
" are a subclass of ",
", ",
" are a subclass of ",
", and ",
" can be considered a subclass of any of those except ",
". (A gas giant leaving behind a mostly iron core is pretty unlikely.)",
"And, to answer the question, ",
"It became known in the 1990s that Uranus and Neptune were really a distinct class of giant planet, composed of about 20% hydrogen, compared to the heavier gas giant's 90%."
] |
[
"From what is known about Gliese 436b, the ocean extends so far down so as to substantiate a good percentage of the total planetary radius. From these theoretical depths, liquid water would be under such a tremendous amount of pressure that completely exotic forms of ice would form such as Ice VII. However, as far as astronomers can fathom, Gliese 436b would still have a small rocky core."
] |
[
"Can somebody explain why radio waves can go through matter (i.e. walls), but visible light -which has more energy- cant?"
] |
[
false
] |
As you may know, my physics knowledge is limited, but i've wondered this for a while. It goes hand in hand with me trying to disprove people who keep saying radio waves from cellphones can cause cancer... to which I always reply it doesn't make sense.
|
[
"Essentially yes, although I want to be sure I answer you accurately so I'm going to go a little into it, to make sure I understand your question.",
"So as I'm sure you know the eltro-magnetic spectrum, such as Radio Waves, Visible light, Ultraviolet, X-Rays and Gamma rays are all made up of photons. The reason that X-Rays don't produce any visible effects is because (if we use the same example as above) Their energy is too great. ",
"To show this I want to amend my first example a bit to get a bit more accurate and yet try to remain simple. Lets say for example that the entire EM spectrum has an energy range of +1 to +200. And the visible light spectrum, has a range of +50 to +58, with white light having all energy levels in it. This is why we get different colors, because some materials absorb different wavelengths of this energy range. Just wanted to clear that up before moving on.",
"So X-rays lets say have an energy range of +150 to +180, well the only thing we can see is energy levels of +50 to +58, and thus materials that we can see need some where between +50 to +58 to reach their excitation state. X-Rays are simply too energetic and don't match exactly what most of everyday materials need to their excitation state, meaning they pretty much overshoot the threshold. ",
"Something that you may also wonder is why do most organisms only have a propensity to things in a very narrow band of the EM spectrum, well this is because right where the visible range lies, is pretty close to the size of most individual animal/plant cells. We can see Gamma Rays because we would need to be able to develop a cell that can accurately react to an interference the size of nucleus. And just the opposite problem with radio waves. So visible light spectrum is where most organisms settle as far as sight goes. It just makes sense. ",
"I hope this helps, if not post a follow up, and I'll do my best. Remember the numbers I used to represent energy levels are completely arbitrary and only have meaning to convey the concept in a simplified fashion, not the real energies associated with what we're talking about."
] |
[
"You will still see the box because it absorbs all visible wavelengths but blue. Most ordinary materials eventually absorb or reflect all visible wavelengths. The only ones that don't, require these massive excitation energies.",
"Remember all of what we can see is a combination between absorption and reflection. So something blue absorbs everything but blue, which it reflects. Now if you illuminate the blue box with a red light, (no other light) the box will absorb the red light, and there is then nothing to reflect, so the object is black.",
"I'll try to find a video on youtube to support this, as it can be a tricky one to think about. =D"
] |
[
"I find this explanation specious. Cell phones are related to cancer formation - specifically, people who develop brain tumors are predisposed to develop them on the side of the head that they use to talk into their cell phones. ",
"http://journals.lww.com/epidem/Abstract/2004/11000/Mobile_Phone_Use_and_the_Risk_of_Acoustic_Neuroma.3.aspx",
" ",
"http://www.sciencedirect.com/science/article/pii/S0090301909001451",
" ",
"http://oem.bmj.com/content/68/9/631.short",
" ",
"Now, I am ALSO comfortable saying that the overall risk of brain cancer does not go up much, if at all, from cell phone use. Because there are plenty of studies that show that as well. What I am NOT comfortable with is someone ignoring scientific findings because his version of physics says it cannot be true. There are temperature sensitive oncogenes, and cell phones warm the ear canal, and that ALSO is a possible mechanisms for lateralizing the cancer. My personal view is that the science is consistent with people who are predisposed to developing brain cancer getting it slightly earlier in life, and getting it lateralized to the side of their cranium that is exposed to cell phone radiation. This explanation fits 1) the consensus data on lateralization of tumors 2) the consensus data on overall risk and 3) the temperature sensitivity of known oncogenes. ",
"You should, with 100% certainty, read the epidemiological literature before you dismiss something because YOUR physics says it cannot be true. "
] |
[
"Would it be possible for humans to drink seawater?"
] |
[
false
] |
I just read this article " " saying how cats can drink seawater, and my thoughts were that we humans are seeing a future water shortage. Would it not be better for us to instead of looking for a way to remove the salt from the water find a way for us to drink the seawater like cats can? Perhaps through future genetic manipulation?
|
[
"The main problem with drinking seawater is that it actually dehydrates you. Your body senses an overload of salt in the intestines and secretes water into the lumen to lower the concentration gradient. The result is actually a net water loss, rather than a water gain."
] |
[
"When I read the link that i had in the text it says that the cats kidneys I believe it was is able to process the water so its drinkable.\nWould it not be more simple to try to achoeve something like this instead of trying to find a energy efficient way of separating the salt from the water?"
] |
[
"I feel uniquely equipped to answer this question. I'm a vet student going through diseases of the kidney right now. One of the main differences between the cat and human kidney is that the cat kidney is unilobar where the human kidney is multi-lobar. Part of the physiologic differences that exist as a result of this anatomical difference is that cats can concentrate their urine to a much much higher degree than humans. Humans are much more sensitive to electrolyte imbalances caused from sodium overload. If you've ever smelled cat urine outside a littler box, you've probably noticed the very strong odor associated with it. This strong odor is caused by the high concentration of excretive products in the urine."
] |
[
"[Physics] How did physicists prove that gravitational waves do not travel faster than the speed of light?"
] |
[
false
] | null |
[
"Physicists have known for a long time that gravity \"moves\" at the speed of light. According to Einstein's theory of relativity, nothing can ever move faster than c, not even gravity.",
"Last year, physicists observed a neutron star collision that caused a gravitational wave and a burst of gamma rays to be detected at nearly the exact same time, proving that they travel at the same speed, c.",
"https://www.sciencealert.com/speed-of-gravitational-waves-and-light-same"
] |
[
"Additionally, the gravitational wave was detected at two locations with a time interval between equal to distance/c. "
] |
[
"If some signal carrying information is sent faster than light, you can choose a reference frame in which its effect precedes its cause, allowing you to affect the past. "
] |
[
"Can someone review this video showing the solar system moving through space, is this a correct approximation or false visualization and why?"
] |
[
false
] | null |
[
"Phil Plait gave a very good commentary on this video.",
"While it's an amusing attempt at depicting the motion of the solar system in the galaxy, it gets a lot of stuff pretty wrong. "
] |
[
"/u/VeryLittle",
" already answered this but I want to reinforce the point that the video, while visually appealing, is not a helpful portrayal of the solar system. At the very beginning it commits the unforgiveable offense of claiming that the Sun isn't the center of the solar system. One of the major premises of relativity is that you can pick whatever reference frame you like and you should still see the same things happening (corrected for time dilation and other relativistic effects of course). So for the video to say that a (poorly portrayed) version of the Galactic reference frame is the \"correct\" reference frame is just completely and totally wrong. ",
"All the babble about vortices is completely and totally without meaning."
] |
[
"... The ecliptic plane is inclined about 60° from the galactic plane (and not 90°) like in the video. We are moving through the galaxy basically following the galactic plane.",
"The rest of the video about life and spiral mumbo jumbo is precisely that: Mumbo jumbo pseudo-scientific woo.",
"EDIT: I did not look at the video very closely on my first look: It's utter bullshit, The sun does not lead the solar system around the galaxy, sometimes the planet precedes the sun and sometime they don't... The video is speudoscience horseshit. "
] |
[
"I live in Florida, will I be able to witness the upcoming lunar eclipse?"
] |
[
false
] |
[deleted]
|
[
"This should help",
"http://eclipsegeeks.com/images/NASA%2010%20dec%202011%20TLE%20eclipse%20geeks.jpg",
"Short answer - not really"
] |
[
"The ",
"wikipedia",
" page may give you more details. It looks like the moon will set in the eastern time zone before the partial eclipse begins, so you will not be able to view the eclipse in Florida."
] |
[
"Looks like not :("
] |
[
"What purpose do tails serve on mammals?"
] |
[
false
] |
Same with lizards and other reptiles, is there an evolutionary advantage?
|
[
"For balance and stability. Both by moving laterally to increase stability and decrease \"wobble\" while running, and in some cases to adjust the center of mass to a position where it may be more easily manipulated.",
"In addition to that, some animals (like elephants, rhinos, horses, and cows) use them to keep insects off, swatting at mosquitos or flies with their tail.",
"These are the most common functions, but others do exist: such as the ability of some reptiles to shed their still wriggling tail as a decoy, or the paddle-like tail of a beaver."
] |
[
"How would a turtles or rats tail aid in stability?"
] |
[
"Rats use them to balance, like when they run along a thin rope. If they fall right, their tail goes left, keeping them balanced. Like the long pole that tightrope walkers utilize, but evolutionarily developed rather than implemented as a deliberate tool."
] |
[
"Do kidneys adapt to whether/regions with higher temperature?"
] |
[
false
] |
It is known that after some time in a weather with much higher temperature than we are used to, we adapt by having changes in our sweating and metabolism. I do not know whether our kidneys also adapt in the long term by, for example, reabsorbing more water and producing urine with a higher concentration of solutes.
|
[
"A simple answer to your question is yes they do, but the adaptation is not as simple as x degrees increase in temperature so y amount of change in reabsorption. ",
"Our metabolism adapts to maintain body temperature at about 98 F which is what the kidneys will be exposed to, but what does change is water level in the body because of high ambient temperature (assuming the individual is not drinking more water) and therefore blood volume/pressure, which the kidneys sense and release an enzyme called renin which results in a cascade of events that lead to thirst, increased sodium absorption and water absorption.",
"So the adaptation itself is in response to changes in body water content than temperature.",
"Fun fact - there was no difference observed in the kidney mass of mice (might have been rats i read that Paper this morning... ughh..) that were given high salt diet when compared to move given normal diet for 12 months.",
"I am about to fall asleep.. will try to add the refs tomorrow"
] |
[
"Thanks so much for your response. I deal with population data of some sort and have noticed that the longer (years) some people are working at a very hot place (not born there), the more urine indicators of dehydration with no signs of kidney damage."
] |
[
"It is very interesting you mention that, we do know for a fact that isolated kidneys, slices or nephrons have a higher capacity to reabsorb salts compared to what is noticed in vivo. Which cna explain why you don't see kidney damage even though there are doing more."
] |
[
"Can you eventually die from lack of sleep?"
] |
[
false
] | null |
[
"To add to this, there is a prion disease called Fatal Insomnia which leads to total sleep depravation and death. This is the only time I’ve heard of sleep deprivation becoming fatal. I imagine that those without the disease will end up sleeping at some point whether they like it or not."
] |
[
"While no human has been attributed sleep deprivation to a cause of death, the university of Chicago did a study on rats, after 32 days of total sleep deprivation all the rats were dead. They didn't all agree of a specific reason they were dead, other then whatever the actual reason was, it's due to the lack of sleep. Brain damage was also believed to be present as a result.",
"Given how close they are to us, it's speculation that we would fare the same.",
"But we do start having a ton of other problems the longer we go without sleep, which make it very hard to stay awake, or not get injured due to them. In top of that a major way people stay awake long periods of time, by drinking lots of energy drinks, had led to numerous people dying from cardiac episodes.",
"Overall while nobody had died specificity because of sleep, many have died as a result of incidents caused by not sleeping. There are also studies that indicate a long term pattern of poor sleep time may impact your health negatively, including lowering life span."
] |
[
"I have never read of a cause of death being lack of sleep in any publication. However, sleep deprivation can cause severe impairment in the individual, leading to drastically heightened risk when , for example, driving a car.",
"Sleep deprivation, given enough time, will cause psychosis, but it will not cause direct death. Eventually an individual will be engaging in \"micro-sleep\" whether he likes it or not, if not outright loss of consciousness."
] |
[
"How do we know the age of light that we receive on Earth?"
] |
[
false
] |
Meaning, how do we know that certain objects are x distance away and certain objects are y distance away? How have we measured the furthest objects away to be 13.7 (I think) billion light-years away? I understand that all objects outside of our local cluster of galaxies are red-shifted. Is it some kind of interval measurement between the frequency of the wavelengths?
|
[
"A photon doesn't age or degrade in any way, so the age of it must be measured by figuring out the distance it's travelled. ",
"Distance of stars can be measured in a couple of ways. One uses triangulation. We know the diameter of our orbit, so if we are to measure the angle of a star when we are at the aphelion of our orbit and then measure the angle of the star again when we are at the perihelion (6 months later) we can calculate the distance of the star using trigonometry. This only works accurately for relatively close-by stars.",
"Another method is to measure the brightness of the star. Stars that emit a specific colour signature are the same temperature (dependant on class of star). If we know the temperature, we know approximately how many photons are being emitted. The photons at a given distance decrease by the inverse square law, so we can calculate how far away the star is by how many photons we are receiving from it over a given period of time."
] |
[
"I believe the triangulation method can only provide accurate distances for stars within 500 light years or so. It's been quite a few years since Astrophysics class. ",
"After some quick rough calculations using the built in calculator on windows, since I don't have another one available atm, I got something closer to 3/1000th of a degree. One of us is off by an order of magnitude, not a big deal when you're discussing distances like 500 light years in any case. And it was probably me since I was having trouble figuring out how to input values using scientific notation on said windows calculator, so I could have easily missed or punched in an extra zero.",
"Anyways, these angles obviously must be measured with extreme accuracy and precision. And anything beyond 500 light years the error becomes too great."
] |
[
"3/10,000th's of a ",
". 2pi radians = 360 degrees. Also helpful is knowing that a parsec is the distance at which 1 AU subtends 1 arcsecond (it's short for \"parallax second of arc\"). A star 3 pc away has a parallax of 1/3 of an arcsecond ~ 1/10,000th of a degree. We can now measure parallaxes of a couple tens of milliarcseconds. The GAIA spacecraft launching later this year will do even better."
] |
[
"What determines the rate at which lightning moves across the sky?"
] |
[
false
] |
There's a pretty good thunderstorm going on outside my window, and it occurs to me that I can watch lightning progress across the sky - meaning it's 'traveling' at substantially less than the speed of light. It was my understanding that electrical charges travel at something approaching c. So, given that's clearly not the case, what determines the rate of propagation of a lightning bolt?
|
[
"Here is an interest slow motion video of lightning (with time display at the bottom):",
"http://www.youtube.com/watch?v=-bvmEYxEYiA",
"You can see a lightning has two steps, first an ionized air path is created, this is the slow part, because air takes time to get ionized, you can see one took over 50 milliseconds to run across the screen in the video; second step is the main discharge, and often multiple discharges. ",
"BTW, electric charge (like electrons) does not travel at near light speed, it is the electric field that propagates at c. "
] |
[
"Very neat. I suspected it had to do with the ionization step, but I (incorrectly, I guess) assumed that the plasma would not luminesce until the discharge phase, which should be (relatively) instantaneous. I guess what I am seeing is the electric charge slowly burning it's way through the cold air in the cloud.",
"Cool stuff."
] |
[
"The speed at which light propagates through transparent materials, such as glass or air, is less than c. The ratio between c and the speed v at which light travels in a material is called the refractive index n of the material (n = c / v). For example, for visible light the refractive index of glass is typically around 1.5, meaning that light in glass travels at c / 1.5 ≈ 200,000 km/s; the refractive index of air for visible light is about 1.0003, so the speed of light in air is about 90 km/s slower than c. ~ from ",
"Wiki",
"The refractive index of air is 1.00027712, and that of water vapor is 1.000261. Air that is wet and dense with water vapor, like the air of a thunderstorm, will actually actually have a lower index of refraction than normal air. Since the speed of light increases as the index of refraction decreases (v = c / n), the speed of light would actually be faster in a thunderstorm than in normal air.",
"Regardless, a difference of 90 km/s out of 300,000 km/s will not make any difference to human perception."
] |
[
"Do we know where in the universe the big bang occured?"
] |
[
false
] | null |
[
"Everywhere"
] |
[
"When I picture a bang, it happens at a central point and matter moves outwards. How can it happen everywhere?"
] |
[
"Because the Big Bang is just a name, a purposefully derisive one. It was nothing like a chemical explosion"
] |
[
"How are sea turtles so good at holding their breath?"
] |
[
false
] |
Apparently sea turtles can hold their breath for up to seven hours while they're sleeping. How the heck can they do this??
|
[
"Here's a good post: ",
"http://www.emperordivers.com/blog/2009/07/how-air-breathing-diving-animals-hold-their-breath.html",
"TLDR: basically, air-breathing animals that dive have an extra protein that's like hemoglobin (which carries oxygen throughout your blood) called myoglobin. What happens is animals breathe a few minutes or so before they dive, and the myoglobin gets rid of the C02 in the blood and replaces it with fresh oxygen, ",
" extra oxygen for the dive. The animal goes under, uses up the oxygen already in the blood, and then the myoglobin releases its extra oxygen & takes up the C02--which is what triggers animals to take a breath. This goes on until enough CO2 builds up that the animal needs to breathe again."
] |
[
"As in diving mammals and birds, several factors influence this capacity: ",
"some sea turtles, such as leather backs, can store large quantities of oxygen in their blood and in their muscles, bound to hemoglobin and myoglobin, respectively. Shallow water species however don't show this specialisation.",
"the heart rate of diving sea turtles is massivley decreased and the blood flow to certain organs is limited during a dive",
"these areas where circulation is limited undergo anaerobic metabolism - sugars are broken up without the use of oxygen"
] |
[
"To add to the below: reptiles have much lower metabolic rates than mammals, since they're not maintaining a body temperature. This is especially true at low temperatures. Snapping turtles winter in the mud below ponds, not breathing for months."
] |
[
"Question about the Schrodinger’s Cat thought experiment"
] |
[
false
] |
From Wikipedia: Schrödinger's cat: a cat, a flask of poison, and a radioactive source are placed in a sealed box. If an internal monitor detects radioactivity (i.e. a single atom decaying), the flask is shattered, releasing the poison that kills the cat. There is a supposed 50% chance of this happening. The Copenhagen interpretation of quantum mechanics implies that after a while, the cat is simultaneously alive and dead. Yet, when one looks in the box, one sees the cat either alive or dead, not both alive and dead. This poses the question of when exactly quantum superposition ends and reality collapses into one possibility or the other. My question is this: If the only way to tie a quantum phenomenon to larger world of classical mechanics is to utilize some sort of device (in this particular iteration of the famous though experiment, a radiation monitor) to detect the quantum phenomenon, then why would any interpretation of QM (outside of the consciousness-causes-collapse interpretation) imply that the cat would be alive and dead at the same time? Even under the Copenhagen interpretation, wouldn’t the measurement of the radiation cause the quantum eigenstates to collapse into a single state? It seems to me that it would not be possible to tie a quantum phenomenon to larger world without first making a measurement, causing the wave function to collapse. Can anyone tell me what I am missing here?
|
[
"The problem is that Schrodinger's cat is a terrible way to illustrate quantum mechanics. All it's trying to demonstrate is that as long as you can not observe something, the particles exist in all possible states. You have to act on a particle in some way to observe it (shoot electrons at it or something), and when that act occurs, the particle has to choose one state.",
"Schrodinger's cat was developed to show normal people just how ridiculous quantum theory is. It was not developed for people to think long and hard about."
] |
[
"He thought it was ridiculous."
] |
[
"Schrodingers cat was meant to illustrate how unphysical that interpretation is not as an actual thought experiment.",
"It is entirely a byproduct of the probabilistic nature of QM. If you have a particle (or a cat) you must account for the all possible outcomes of the solution if you have not measured the solution. This is achieved by creating a wavefunction that is a superposition of all possible states. Until perturbed by an observer there is no way to tell exactly which state is occupied thus it has to be in all possible states.",
"Now of course we know this is unphysical and the object really is in one state or another there is just no way to tell which.",
"wouldn’t the measurement of the radiation cause the quantum eigenstates to collapse into a single state?",
"yes but as an outside observer how are you measureing this without \"opening the box\" (using an IR camera counts as opening the box etc). In fact just a photon leaving the cat and striking the box is technically a \"measurement\" but the only observer is the atom it strikes not you as an outside observer. Thus for all intents and purposes the wavefunction has not collapsed in your reference frame.",
"Its a key concept of all of science. In order to measure something it MUST undergo a state change. You cannot observe something in a stationary state and it must be perturbed to be seen/felt/heard/measured etc."
] |
[
"If you lived in a cold climate, had a heated home, but instead of walls you had lines of small stirling engines, could the difference in temperature power the heater and keep you warm?"
] |
[
false
] |
Of course i don't mean there to be , it would have to be a sealed home. I guess the way to store and convert the energy to the heater would be the harder part, but still, how viable would this be? I realize this is absurd, but i'm wondering if this could work considering one could have a large difference in temperature (IE if it's -10C outside, and inside its +20C). And of course you'd need something to start up the heater and get it going. Feel free to point out any misconceptions about stirling engines i may have made, thank you!
|
[
"Stirling heat engines (or any heat engine) will do exactly what you ",
" want: transfer the thermal energy outside. ",
"In the process, they will create a relatively small amount of energy (1-263/293 = 10% at most) through work that you could turn back into thermal energy inside, but it won't come close to the amount of thermal energy sent outside and wasted."
] |
[
"The energy from your heater is used to power the engines which in turn power the heater.",
"This sort of self-supporting energy source doesn't work, it would otherwise be free energy.",
"What you ",
" do is put a little electric motor to drive something like a sterling engine which will then be acting as a ",
".",
"A heat pump is just an air conditioner running in reverse. A heat pump generally moves more heat than the energy it takes to drive it, but thermodynamics is perfectly okay with this because energy is not being created."
] |
[
"If the inside of the house started out hot with cold outside of course the engines would run, but they would generate much less energy to run the heater than the house would lose through the engines running."
] |
[
"What's the smallest celestial body that could maintain a satellite in orbit?"
] |
[
false
] |
Could we put a satellite in orbit around, say, the moon?
|
[
"Anything in theory could have a moon around it thats smaller. \nIn ",
"universe sandbox",
" for instance they male a tennis ball orbit a bowling ball (which should work if nothing more massive is around) "
] |
[
"That's fine, we've had plenty of satellites orbiting the moon."
] |
[
"This, it depends on what else is nearby. There could be a tiny pebble orbiting a small asteroid, but as soon as it gets near another asteroid, the orbit will be perturbed."
] |
[
"Why is it that your eyes can \"pan\" smoothly back and forth when following a moving object, but are more \"stuttery\" when you try to do the same without a moving object?"
] |
[
false
] |
What I'm observing is that when I move my finger back and forth in front of my face, my eyes seem to follow it smoothly. But when I stare at the wall and move my eyes back and forth without focusing on anything in particular, I find that my gaze "jumps" at certain intervals. Sorry I can't articulate it any better than that, but I hope that makes sense to somebody.
|
[
"I don't think he is describing saccades. He means when his eyes track an object they move smoothly, but if he attempts to move his eyes smoothly ",
" following an object he can't do it. In any case, saccades movement is too small to be 'visible'. "
] |
[
"I don't think he is describing saccades. He means when his eyes track an object they move smoothly, but if he attempts to move his eyes smoothly ",
" following an object he can't do it. In any case, saccades movement is too small to be 'visible'. "
] |
[
"Not sure what the focus of your question is (no pun intended!), but this might be of interest: ",
"http://en.wikipedia.org/wiki/Smooth_pursuit#Smooth_pursuit_in_the_absence_of_a_visual_target",
"And ",
"here's a non-paywall version of the paper cited for \"Performing smooth pursuit without a moving visual stimulus is difficult\"",
" that I think speaks to your questions."
] |
[
"Why do we use the word 'volume' to refer to how loud something is, when volume is typically a measurement of physical size?"
] |
[
false
] | null |
[
"This is an etymological question and the short etymological answer is: Etymologically, they mean the same thing. ",
"Here's a link to ",
"'s etymology dictionary entry.",
" Let me sum up the history of the word:",
"The Latin word ",
" means \"to turn\" or \"to wind\" (you see this in \"-volve\" words like \"revolve\"), this led to the French using the word ",
" to describe a scroll or a bound book, which was adopted by English to mean the same. It then came to describe a book within a set, and then circa 1520, they started to use the word to describe the ",
" of a book. 100 years later, they started using the word to describe bulk, mass or quantity.",
"So how did \"Volume\" come to describe loudness? It was simply a natural application of the word. It occurred in 1784 in a ",
"review of Handel's \"Messiah\"",
" in the context \"volume of sound\". We can't be entirely sure who used it this way first or precisely when, but it simply was meant to mean the \"mass\" or \"size\" of the sound."
] |
[
"For those interested in this post and answer, I also recommend ",
"/r/etymology",
" as a fun sub."
] |
[
"I'm an acoustician and this is the correct answer. Contrary to the other answers, there's no physical reason to call the loudness \"volume\". If that knob had been named to reflect the science and engineering behind it, it would be called \"gain\" to reflect the gain of the audio amp feeding the speakers.",
"Yes, volume can be related to pressure by the ideal gas law and others, but that's irrelevant here. Pressure transients can also be carried by waves which do not involve a net volume change. (In fact, the short-term change in volume occupied by some parcel of air is negligible for sound--this is required for the acoustic approximation to the Navier-Stokes system of equations.) Speakers do not create volumes of air, nor do they cause net displacement of volumes of air. The sound waves radiate outward from the speakers, but the air particles do not (they just move back and forth as the wave passes)."
] |
[
"How close would you have to be to the Sun to be warmed by its heat without an atmosphere?"
] |
[
false
] |
As I understand it, (of course I could just be wrong) if you leave the atmosphere towards the sun the temperature would drop to absolute zero. Inside the atmosphere particles can collect the Sun's energy and therefore some amount of heat exists, even if it's very little high up where the air has very low density. So how close would you have to get to the Sun to be warmed by its rays directly, and enough to maintain a body temperature?
|
[
"The whole thing comes down to balancing the thermal radiation you radiate away with the thermal radiation you take in from the Sun. How much heat you radiate depends on your own temperature, as your temperature gets higher you radiate away more heat. The heat you take in from the Sun depends mostly on the distance from the Sun and also the material of your space suit. Some materials absorb more heat than others.",
"Let's say you're at the same distance from Sun as Earth is, that is 1 AU. And you're wearing a black space suit which absorbs practically all the energy from the sunlight. Then if you do the ",
"calculations",
" you'll find that your equilibrium temperature is pretty close to 0 degrees Celsius. Not exactly a comfortable temperature but pretty far from absolute zero or the three Kelvin (-270 C) that's often quoted as the temperature of space. You'd get to normal room temperatures at about 0.8 AU to 0.9 AU. And we didn't take into account your metabolism heating you at all."
] |
[
"it depends how warm you want to be, but as long as you can see it (even if you're out by pluto), you're being warmed by radiation. radiation travels best through a vacuum (e.g. space), whereas convection is heat flow within a flow. conduction is heat flow through a solid/liquid/gas that isn't moving.",
"in other words, all the heat we get from the sun comes from radiation."
] |
[
"Well the question you need to answer first is \"How fast does my body lose heat in space?\" If you answer that question then you find the distance where the rate your body takes in heat (in this case where you absorb enough light from the sun) matches the rate your body loses heat. ",
"In short if you want an exact distance, can't really give you one because I can't answer those questions without the corresponding information. So the answer is sort of a lack luster \"Close enough\" :/"
] |
[
"What happens when we cut plastic?"
] |
[
false
] |
Just bit one of off a shirt and wondered what was actually being done to the polymer when I bit it. My understanding of plastics is that they're composed of monomers linked together via covalent bonds. This sounds like the bonding of diamond, but obviously it is not the same. Are there weak intermolecular bonds between long chains of polymers? how did biting the plastic affect the structure of it?
|
[
"It's all a matter of scale. While you commonly associate chemical bonds with something solid and strong - like diamond - it's only the case when there are both strong bonds and ",
" of them. Individual bonds are very weak and easy to break.",
"Depending on the type of plastic, there are varying degrees of cross-linking between the polymer strands. So when you break the plastic, you're both disrupting intermolecular interactions and breaking chemical bonds."
] |
[
"A telephone directory, also known as a telephone book, telephone address book, phone book, or the white/yellow pages, is a listing of telephone subscribers in a geographical area or subscribers to services provided by the organization that publishes the directory. Its purpose is to allow the telephone number of a subscriber identified by name and address to be found."
] |
[
"http://en.wikipedia.org/wiki/Polymer",
"http://en.wikipedia.org/wiki/Fracture_in_polymers",
"In a polymer, you have long (or short) chains of lined C atoms that might have any number of groups attached to them. These chains might be cross linked. They might be ordered. They might be jumbled and knotted.",
"Polymers are REAALY diverse.",
"If you bit it and used high pressure with a really low area of contact you were probably severing actual C-C bonds, as well as tearing the chains apart from other chains.",
"If for instance you stretch a plastic grocery bag, you are more akin to untangling chains until the level of tangling is low and then the chains themselves start breaking.",
"TL;DR Polymers are diverse and fracture is a complex topic in materials science.",
"Source, BS in materials."
] |
[
"Are there any predators or parasites that feed on intestinal worms, when they're in the intestines?"
] |
[
false
] | null |
[
"There are many hyperparasitic bacteria that use nematodes and cestodes as hosts. Most forms of multicellular life on earth can serve as host for at least one species of parasite, and that includes other multicellular parasites. The term you are looking for is \"super-\" or \"hyperparasitism\"."
] |
[
"Would there be health complications with ingesting or trying to maintain a colony of the hyperparisites? Would a pill of them be an effective medicine for fighting these parisites? Or do we just not know enough about their effects?"
] |
[
"Is it any better if your parasite has a parasite?"
] |
[
"Is there a \"light-horizon\" that represents that edge of the knowable universe with respect to any practical purposes?"
] |
[
false
] |
The universe is expanding. Not from a central point (because there may be no coherent way to speak of a central point), but from all points in all directions simultaneously. This has been revealed experimentally as all astronomical bodies recede from each other at rates proportional to their distance from one another! The farther away something is from an observer, from us, the faster it recedes from us. If the two bodies get far enough away from each other, their recession approaches, reaches, and exceeds the speed of light. This forms an effective "horizon" for the observer at either point, since distant stellar bodies are receding fast enough that their light traverse the ever-increasing distance between the observer and the horizon. In other words, if I'm understanding the idea correctly, even if the universe is endless, assuming that we are never able to travel faster than the speed of light, there is a necessary boundary formed for our knowledge and exploration generated merely by the expansive properties of the universe? Is this right? If so, why doesn't this get brought up more in discussions about the universe being infinite? If there is an absolute knowledge horizon for less-than-light beings (LTLs), can't we just treat the universe as having a very distinct "edge"?
|
[
"In other words, if I'm understanding the idea correctly, even if the universe is endless, assuming that we are never able to travel faster than the speed of light, there is a necessary boundary formed for our knowledge and exploration generated merely by the expansive properties of the universe?",
"Yes, there is such a necessary boundary. It's referred to by a number of names, including \"cosmic event horizon,\" \"cosmic light horizon,\" etc. Whatever you call it, it's the limit of our ",
" universe, and it changes over time.",
"From this article on the ",
"observable universe",
":",
"\"Though in principle more galaxies will become observable in the future, in practice an increasing number of galaxies will become extremely redshifted due to ongoing expansion, so much so that they will seem to disappear from view and become invisible.[8][9][10] An additional subtlety is that a galaxy at a given comoving distance is defined to lie within the \"observable universe\" if we can receive signals emitted by the galaxy at any age in its past history (say, a signal sent from the galaxy only 500 million years after the Big Bang), but because of the universe's expansion, there may be some later age at which a signal sent from the same galaxy will never be able to reach us at any point in the infinite future (so for example we might never see what the galaxy looked like 10 billion years after the Big Bang),[11] even though it remains at the same comoving distance (comoving distance is defined to be constant with time, unlike proper distance which is used to define recession velocity due to the expansion of space) which is less than the comoving radius of the observable universe. This fact can be used to define a type of cosmic event horizon whose distance from us changes over time; for example, the current distance to this horizon is about 16 billion light years, meaning that a signal from an event happening at present would eventually be able to reach us in the future if the event was less than 16 billion light years away, but the signal would never reach us if the event was more than 16 billion light years away.\"",
"There is also something called the \"particle horizon,\" which is a bit different from the cosmic light horizon:",
"\"The particle horizon is the maximum distance from which particles could have traveled to the observer in the age of the universe. It represents the boundary between the observable and the unobservable regions of the universe, so its distance at the present epoch defines the size of the observable universe\"",
"\"The particle horizon differs from the cosmic event horizon in that the particle horizon represents the largest comoving distance from which light could have reached the observer by a specific time, while the event horizon is the largest comoving distance from which light emitted now can ever reach the observer in the future.\"",
"why doesn't this get brought up more in discussions about the universe being infinite?",
"Well, (a) it does, just not as much among laymen as much as among actual cosmologists, since it is less relevant/important to laymen, and (b) it generally doesn't have much meaning when speaking about the topology of the universe and whether or not the universe is infinite. It's not really a fundamental property or limit of the universe as much as it's a consequence of the universe's expansion.",
"If there is an absolute knowledge horizon for less-than-light beings (LTLs), can't we just treat the universe as having a very distinct \"edge\"?",
"Not really, no, because another civilization living out near the \"edge\" would observe a completely different \"edge\" than we would, so the question \"whose edge is the real edge?\" arises. Well, nobody's edge is the \"real edge,\" because it isn't a real edge. :P",
"Beyond that, things outside our observable universe can also affect things inside it. Case in point: we do already have some possible observational evidence for the existance of things outside of our observable universe: the ",
"dark flow",
" appears to be a gravitational anomaly whereby a number of galaxies in our observable universe are flowing toward an unknown gravitational source outside of our observable universe."
] |
[
"There is a 'cosmic event horizon' from beyond we will never receive any signal, however, this horizon doesn't correspond to the Hubble distance (where v=c), it is actually further away.",
"This is an excellent article about this",
", see the chapter titled \"Running to stay still\" which talks about exactly this.",
"The article is based on ",
"this paper",
" if you want a more in-depth explanation."
] |
[
"Scientifically speaking, we assume the explanation that requires the fewest additional assumptions. Sure we ",
" assume that somewhere out there beyond our horizon the universe wraps back around on itself... but that's an unscientific statement. ",
"Given all of the data we have available",
" the universe is flat and infinite."
] |
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