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[
"Why is the inner core of the earth a solid whereas it's adjacent layer is a liquid?"
] |
[
false
] | null |
[
"The temperature within the inner core is too low to melt the Iron-Nickel alloy under the pressure which exists at that depth (> 5100 km below the surface of the Earth).",
"However, at shallower depths (2900-5100 km underground) the decreased ambient pressure lowers their melting points so the iron and nickel liquefy. ",
"Near the top of the liquid outer core, pressure is just over 100 GPa, or about 10",
" atmospheres. 2200 km below, at the outer/inner core boundary, the pressure has increased to over 300 GPa."
] |
[
"As time passes the liquid stratum solidifies, meaning that in the future the Earth will no longer have a magnetic field, right?"
] |
[
"Well, before that happens, the Sun is going to be stressing the biosphere. It's luminosity increases by something like 1% every 100 Myr. So that'll cause changes long before the magnetic field becomes a problem."
] |
[
"There are two 1-mile loops. One is totally flat. The other is uphill/downhill, but the net elevation is 0. Does the hilly one take more energy to run?"
] |
[
false
] |
If so, why?
|
[
"of course, the hilly one requires more energy to run.",
"when you run, you expend more energy going up hill, for all the reasons you would imagine--overcoming gravity to elevate your mass uphill. On the downhill side, too, your body is actually now also maintaining balance to keep you upright, using different muscles in different proportions and controlling your speed. ",
"lots of science published in popular running forums on the topic\n",
"http://www.runnersworld.co.uk/general/everything-you-need-to-know-about-hill-training/159.html"
] |
[
"No, you're not a machine that coasts downhill. You expend more energy up and down than running flat. "
] |
[
"If your body was a sphere, and our world were friction-less and loss-less, both would require zero net-work to complete. To calculate the work needed, we would take a line integral of the product of force and the infinitesimal distance vector. Integrating this over the loop would yield zero. "
] |
[
"How does the thermodynamic arrow of time imply the psychological arrow of time?"
] |
[
false
] |
Hawking, and others, have said that the second law of thermodynamics creates an arrow of time. And that the arrow of time we perceive is determined by this law. How is that the case? Why can't we use the reversibility of physical laws to send a message into the past? I know that everybody agrees we can't, but I don't see how this is implied from the second law of thermodynamics. As entropy increases, information decreases. Therefore there is more information in the past than in the future. This should mean that all the information from the future is also in the past. Wouldn't that make it easier to send a message back than forward? I'm missing something here...
|
[
"Making any sort of record, whether it's a memory or an external one like a note, is a thermodynamically irreversible process. That is, it involves an increase in entropy.",
"Therefore there is more information in the past than in the future.",
"There is more information ",
" in the past. The second law of thermodynamics (as applied to information theory) says that ",
", the information about ",
" decreases over time. This is known as ",
"Shannon entropy",
"). "
] |
[
"The statement of the second law of thermodynamics (as applied to information theory) is that if you start with some piece of information (eg. a written message), then transmit that information through some method with some noise, the amount of information contained in that message will decrease over time. (Stated that way it seems pretty obvious.)",
"Entropy (in this context) is simply a measure of that information loss, so information entropy is only defined in terms of some initial set of information."
] |
[
"Whenever we do theoretical physics, we necessarily always discuss the physics of some closed system (it's just not possible to define most physical quantities in a meaningful way otherwise). The information we're talking about losing here is the information about the previous state of that system. So if we're going to talk about reversing time for that system, we either have to know or make assumptions about the previous states of that system. But that's exactly the information we're talking about losing as entropy increases.",
"For example, consider a lukewarm cup of coffee with cream spilled on a table. Was the coffee hot when it was first put in the cup? When was the cream added? Was the cream stirred in or simply poured? Was it spilled before or after it cooled (if it was ever hot)? How long ago was it spilled? There's hundreds of previous states that this could have been in (and that's just counting the more probable ones). We don't know the answers to most of these questions, and for many of them, there's no way to ever find out. ",
" is the kind of information that's lost as the entropy of a system increases. "
] |
[
"Why is BICEP2 located at the South Pole?"
] |
[
false
] | null |
[
"This is addressed in the experiment's ",
"FAQ",
":",
"Why the South Pole?",
"Water vapor in the atmosphere absorbs microwaves, making detailed studies of the CMB impossible from most places on earth. The South Pole is near the middle of the Antarctic plateau, the driest environment on the planet. At an effective altitude of over 10,000 feet (~3000 meters), stable weather patterns and winter temperatures averaging -72F (-58C), the South Pole is the closest a ground-based telescope can get to being in space. The patch of sky we study is visible from the South Pole continuously, 24h each day for the whole year. The National Science Foundation’s US Antarctic Program, which operates the South Pole Station, provides excellent infrastructure, communications, and support for the small team needed to run our telescopes, including our winterover scientists Steffen Richter and Robert Schwarz."
] |
[
"Oh that one is a pretty simple answer. Not only is the south pole largely uninhabited which allows for less interference, but being in the south pole is actually the closest that we can get to space while being at ground level on earth.",
"I'm sure there are more reasons, but that is the gist of it."
] |
[
"thank you!"
] |
[
"What happens to the body/brain when someone is under hypnosis? Is it a real state of mind, or is it power of influence?"
] |
[
false
] |
I have wondered about this since I was a university student. I've taken many psychology classes and different courses studying the human mind and hypnosis has always interested me but I also think it could be just the 'power of influence' or something similar. I have even tried to let myself be hypnotized on 2 separate occasions, but, I was told I might not be susceptible to hypnosis. So that has made me skeptical whenever I further read or observed someone being "hypnotized" for an intensive psychology session, or even on stage in a hypnotist/mentalist show. Is it real and what happens to the mind/body if someone can be successfully hypnotized? Edit spelling
|
[
"So...it's all fake then. If you're just following instructions then clearly you know you are in control and the hypnotist can't make you do anything."
] |
[
"So...it's all fake then. If you're just following instructions then clearly you know you are in control and the hypnotist can't make you do anything."
] |
[
"According to Derren Brown (see the JRE podcast with him), there are a mix of experiences. Some people just go along with it, some people manage to convince themselves to go along with it to the point they're certain they had no choice, and others seem convinced that it must have been real as they don't remember it.",
"In terms of the mentalism thing, one of his big points was that being in such a strange situation as being called up on stage in front of an audience puts people in a position where they are suggestible because they are so anxious and out of their depth. So it's more like being lead by someone confident and competent the first time you do something, you're less likely to have questions if you have no idea what you should be doing.",
"There is some research into it. Genuinely hypnotised people have had their brains imaged.",
"https://digest.bps.org.uk/2013/08/01/neuroscience-gets-serious-about-hypnosis/"
] |
[
"Poincaré recurrence puzzles me greatly, could someone elucidate it?"
] |
[
false
] |
I have read some about the Poincaré recurrence theorem, and it left me very much confused, especially the examples given. If you have all particles that make up a gas in one corner of the room, in a matter of seconds the pressure will reach an equilibrium. Due to Poincaré recurrence, in an almost arbitrarily long time, the room will return to the state with all particles in one corner of the room. But how? Why would the particles do that? If the volume of the room is constant, and the amount of "stuff" in the room is constant, pressure should also be constant. I don't see where time comes in as a factor in this at all. Also, how would such an event look like? Would particles all of a sudden "decide" to not obey Boyle's law (among others), and spontaneously rush into the corner of the room? Would they be driven by some force against the pressure of the gas already in the corner? Could anyone clear it up for me? Sorry if I misinterpreted the whole concept, my understanding in this field is poor.
|
[
"Due to Poincaré recurrence, in an almost arbitrarily long time, the room will return to the state with all particles in one corner of the room.",
"But how?",
"Complete chance combined with a near-infinite amount of time. It's a little bit like the \"an infinite number of monkies on an infinite number of typewriters\" thought experiment, except that unlike in the case of the monkies, there is a limited amount of possible things they can type (a finite amount of configurations of gas in the room), so ",
" they will type the literary work of your choice (be in the configuration you want). This isn't actually true of the monkies/typewriter because there is no limit to the number of characters that can be in a piece of work",
"Why would the particles do that?",
"Why? There is no why -- they just do, out of necessary consequence of random change. Because they are moving; it's a gas. A gas in a room like you are imagining is always changing, the molecules are always moving. Consequently, it will change through every possible random change it can make, given enough time. One of those random changes will eventually be one where all the particles are in the corner of the room.",
"If the volume of the room is constant, and the amount of \"stuff\" in the room is constant, pressure should also be constant.",
"Pressure is ",
" constant. Remember, this is a gas. Sometimes there will be sizable deviations from the approximately-constant pressure in different areas, because the density in any given region is going to be slightly different from the average.",
"The longer you let the gas bump around in the box, the more large deviations you will see from the average pressure. But they will be fleeting deviations. ",
" one will be a large deviation like the kind you are looking for. But like the rest, it will be fleeting, and after it reaches that configuration it will bounce off that corner and go back to a near-average-like state.",
"I don't see where time comes in as a factor in this at all.",
"The system changes over time, going from one \"microstate\" (configuration of gas molecules) to the next. All microstates are energetically accessible, and the next microstate is basically random. So, given a landscape of accessible microstates for the system, and given the fact that it will progress through all of these microstates, ",
" it will reach a microstate that is extremely rare and deviant from the highly-probable near-average microstates.",
"Also, how would such an event look like? Would particles all of a sudden \"decide\" to not obey Boyle's law (among others), and spontaneously rush into the corner of the room?",
"Basically yes. It would look like the exact ",
" of if you started with all the particles in a corner, and then let them go to fill the rest of the room. So it would look like all the particles move spontaneously into a corner of the room.",
"The particles don't \"decide\" this, and the fact this happens does not violate Boyle's law, and it does not violate the modern formulation of the second law of thermodynamics (which is statistical/probabilistic in nature, not absolute like was believed in classical thermodynamics).",
"Would they be driven by some force against the pressure of the gas already in the corner?",
"Basically yes. Ideally, there should be equal pressure in all directions, approximately anyway, due to molecules bouncing off of eachother. But in this type of situation the various gas particles would all end up on trajectories into the corner of the room (out of chance), and would not collide with eachother until they were in the corner, so suddenly there would be no pressure on one side (where that corner is), and all of the molecules would bounce their way into the corner.",
"Hope that helps."
] |
[
"Basically, the movement of particles in a gas is (under certain assumptions) entirely random. Each individual particle just cruises around doing his own thing until he hits someone else. The fact that gases expand to fill their containers is just a consequence of the fact that if there's \"a lot\" of gas in one region and \"a little\" gas in another region, the gas particles in the denser region will basically be driven into the rarer region because there's less stuff to throw them off track in the rarer region.",
"Now, if you have particles in a box, there's a limited number of configurations they can be in - titanically huge, but limited. And if you include configurations that are \"close enough\" to a given configuration - like, you just want most of the particles in one end of the box, but you don't really care about the position ",
" in that region, just their bulk behavior - the chance of that configuration or one close enough to it reoccurring as the particles do their thing goes from infinitesimal (note: not actually infinitesimal, but just extraordinarily small) to an actual possibility - still rare if you have a lot of particles, but definitely possible. And since it's possible, it ",
" happen given enough time. You can predict how long it will take depending on the size of the system and how close you want to get to your given state.",
"Please note that this is not intended to be mathematically rigorous, but that's the basic concept."
] |
[
"Also: these particles could violate Boyle's law because Boyle's law is an approximation made under the assumption that particles are approximately uniformly distributed. "
] |
[
"Is there any evidence to show that people with blue eyes are more sensitive to light than those with brown eyes?"
] |
[
false
] |
Any scientific studies on the subject of light sensitivity and eye color?
|
[
"The eye sensitivity to light is dictated by the density of the rods/cones and by the density of macular pigment. Macular pigment provides \"sunglasses for your retina.\" It absorbs light before it can pass into the rods/cones. There are studies that show blue/green eyed persons have lower macular pigment than those with brown eyes. For instance:",
"http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1298217/?tool=pmcentrez",
"But the color of the iris does not have a direct effect on macular pigment density. All this means is that iris color and pigment density are correlated, but only light entering the pupil can reach the retina. It's not like the blue iris reflects more light into the eye or anything like that."
] |
[
"Are we asking if there is an optical sensitivity or an overall sensitivity such as to if one burns their skin more quickly or slowly?"
] |
[
"i dont know, but i have green eyes and i cant go outside on a sunny day unless im wearing polarized lenses."
] |
[
"Why is enthalpy interchanged with heat?"
] |
[
false
] |
I.e heat of fusion = enthalpy of fusion
|
[
"In thermodynamics heat is defined as dQ = TdS, i.e., the temperature times the change in entropy of the system. Enthalpy is defined as dH = TdS + VdP, the heat plus the volume times the change in pressure, and it is often referred to as the heat function. If the system's pressure is constant, then dP = 0, so enthalpy is equivalent to heat. Hence why they are often used to describe the same scenario."
] |
[
"Thanks, it's nice to see the difference mathematically!"
] |
[
"Enthalpy and heat are both ways to describe energy. Enthalpy is a specific type of heat related to the breaking/formation of chemical bonds. The main difference between the two is that enthalpy is a state function. Heat and enthalpy can be equal in certain cases (e.g. reversible isobaric processes)."
] |
[
"Is it possible to cold weld the repelling ends of magnets together? If so, would their magnetic fields align?"
] |
[
false
] | null |
[
"It doesn't. A dipole magnet is already aligned. Like this: <<<<<<<<<<<",
"Now I break it: <<<<<< / <<<<<",
"And each of those is an identically aligned dipole magnet, without having to change the spin."
] |
[
"Magnetic fields are due to the spin of electrons within the magnet. Placing two magnets together would not change the spin of the electrons, so the magnetic fields would not align.",
"However, over a long enough period of time, if you keep magnets near each other, the magnetic fields from one will affect the spin of the electrons in the other, so eventually the magnetic fields will align. This can take several weeks/months or even years if the magnets are weak. "
] |
[
"But doesn't snapping a dipole magnet in half result in two dipole magnets? How does that change the spin of the electrons, if what you say is true?",
"Edit: Thanks for the responses! I think I understand."
] |
[
"i don't understand how fast quantum computers are?"
] |
[
false
] |
Quantum computers use qubits instead bits for computation. it says on wikipedia that a quantum computer with n qubits is equal to a classical computer that has 2 bits. one of the fastest quantum computers we have right now is a 512 qubits. but that means it can do 2 calculations or about 1.3E154. That is more than the number of atoms in our universe. How is that even possible, in the coming years it say we will have quantum computers with a million qubits. that is 2 calculations per second. That can not be possible. i don't understand or is that quantum computers are only that fast at solving problems like that for specific problems in math and science.
|
[
"No no no no. Quantum computers do not let you check an exponential number of states in a single operation. A quantum computer can be in a ",
" of an exponential number of states, but they cannot just tell you which of these states is correct in a single op. If this was true then BQP would trivially be a superset of NP, but their relation remains an open question in CS. ",
"Unfortunately, I am not expert enough in the field to provide a great top level answer in this thread but I do know enough to say that this answer is wrong. "
] |
[
"No no no no. Quantum computers do not let you check an exponential number of states in a single operation. A quantum computer can be in a ",
" of an exponential number of states, but they cannot just tell you which of these states is correct in a single op. If this was true then BQP would trivially be a superset of NP, but their relation remains an open question in CS. ",
"Unfortunately, I am not expert enough in the field to provide a great top level answer in this thread but I do know enough to say that this answer is wrong. "
] |
[
"it says on wikipedia that a quantum computer with n qubits is equal to a classical computer that has 2n bits.",
"This is a misreading of the article. Its not at all the case that they're in any way \"equal\". Its true that in general in order to ",
" n qubits, you would need 2",
" classical bits. This makes it very inefficient to ",
" a quantum computer with a classical computer, but really says nothing about their relative power or capabilities.",
"In terms of most understandings of \"speed\", classical computers are and almost certainly will continue to be ",
" faster than quantum computers. Quantum operations are way slower, and are also very error prone. However, it happens that there are some very interesting and powerful things that quantum computers can do that make them capable of outperforming classical computers for very specific use cases, some of which happen to be super super important (such as factoring).",
"But in general, I think its a huge (but common) mistake to claim that quantum computers are \"faster\" than classical ones."
] |
[
"What determines how many chromosomes a child will have if the parents do not have the same amount?"
] |
[
false
] |
[deleted]
|
[
"This happens and is quite interesting. As an example, think of a chromosome with 6 genes, ABCoDEF (the o is the centromere). You are aware that chromosomes can duplicate, but what happens if only the centromere is duplicated? In that case you'd get a situation like ",
"this",
". Now, when this cell begins to line up chromosomes a few things can happen. Since they haven't lost information, they can still line up effectively, and everything is good...unless the cells undergo meiosis. In that case there would be a lot of errors due to there being an odd number of centromeres. For all the majesty of the cell, it's actually pretty dumb. It's going to just randomly choose which centromeres go where, so most times you'll get something like one cell getting ABCo while the other gets ABCoDEF and oDEF. Neither of those cells are likely to produce viable offspring. However sometimes, one cell will get ABCoDEF and the other will get ABCo and oDEF. Both of the daughter cells in this instance should be able to undergo meiosis successfully. So while fecundity is reduced, the two-chromosome variant can still spread in a population. It likely would die out, but could by chance propagate substantially until it beats out the one chromosome version."
] |
[
"Starting back when nothing resembling humans existed, I'm curious as to how we came to have 23x2 chromosomes.",
"We know some details about this. Chimpanzees have 24x2 chromosomes, but humans have 23x2, even though our DNA is very similar overall. The missing chromosome is ",
"because of a telomere-telomere fusion event in chromosome 2",
". ",
"As far as how two parents with a different number of chromosomes make viable offspring, I don't know. But even though hybrid species are usually sterile, you can sometimes get ",
"fertile mules and hinnies",
", so the mismatched chromosomes don't always prevent reproduction. Probably the fused chromosome human ancestor had lower fertility at first, but they somehow managed to reproduce enough that humans overcame the bottleneck."
] |
[
"It's likely, way back in the primordial ooze, that chromosomes used to be circular, resembling bacterial plasmids that we see today, and that reproduction was asexual rather than sexual. In this case, large mutations are passed on more easily. By the time linear chromosomes and sexual reproduction develop, single chromosome duplications probably happen less, however whole genome duplications might occur. In fact, when you look at plants, chromosomes in closely related species often show this kind of pattern (4 chromosomes in ancestor, then 8, 16, etc.). Chromosomal duplications in animals are less common. \nA fused or broken chromosome is less problematic. During meiosis and mitosis, chromosomes pair up along spindles, which guide half of each pair to new cells. As long as a chromosome is there, the content doesn't necessarily matter (as in, if it has an extra piece, the process won't be hindered). It's when an extra chromosome is present, or one is missing, that the resulting cell can be harmed through gene dosage effects, where too many copies of a gene are transcribed. These kind of mutations are often lethal, which is why we don't see many single chromosome duplications. "
] |
[
"Is fusion power still on track, 20 years later?"
] |
[
false
] |
In discussions like , this graph is often referenced, which shows the progress that's been made in fusion power, measured as triple product vs time: But the last point on that graph is around 1998, 20 years ago. When I , this decades-old graph is the only one I see. Is the triple product still doubling every 1.8 years? What would this graph look like if updated to today?
|
[
"I fear the graph is still up to date - no new records since them. JT-60U still has the highest triple product. ITER should beat it, but not before 2027. It should release 10 times more fusion power than necessary input power when run with DT plasma (2035+), a huge milestone. After that it is \"just\" making a viable commercial reactor out of the technology. The successor, DEMO, is planned to demonstrate reactor-like conditions. Once that runs we'll know how viable fusion power plants are."
] |
[
"To add to this: DEMO is intended to be the first reactor to demonstrate that nuclear fusion reactors can operate comperially and it's planned for the 2040s or 2050s - that is if all goes well with ITER and then DEMO, which should operate in the range of 2 to 5 GW with a net gain of some 1 to 2 GW that can go into the power grid. Real plants then possibly will require an even higher power output than DEMO. ",
"All this means that ",
" fusion power is actually viable - shown by ITER - and then it turns out it alsi is ",
" viable - shown by DEMO - we'll see actual, even larger fusion power plants pop up during the 2060s or 2070s. So if you're 40 or younger today you have a chance of seeing it happen. ",
"I just hope we do get honestly serious about researching fusion and put some real effort into it instead of mucking around (relative to the economic power of the large industrial nations that benefit from working fusion power and scientific research) like we have done for the last decades. "
] |
[
"Why is it so expensive? What are those $100 billion getting spent on?",
"When you speak of \"costs to construct\", do you mean as in following a known design, or as in doing some research in the middle and perhaps testing out multiple approaches?"
] |
[
"Are toes really necessary or just an evolutionary hang-up?"
] |
[
false
] |
I realise that we use them for balance, but people can have toes amputated and regain full mobility. Lets face it, toes are gross, a pain in the ass to keep clean/manicured, and they don't seem that useful. Clearly early ancestors used them for climbing trees, grasping objects etc., but we just keep them in our shoes. This has puzzled me for while, do you think we could evolve sort of hinged end at the end of the foot, or get rid of them altogether?
|
[
"I realise that we use them for balance, but people can have toes amputated and regain full mobility",
"This is just not true. Sure they can ambulate -- which I am guessing you are calling mobility -- but without toes their foot structure is completely compromised compared to that of a normal healthy individual. Sure they are small and, according to you, are gross but their importance in each stage of gait is paramount to the function of our feet. ",
"Many of what you would call the leg muscles actually insert onto the toes (ie. flexor digitorum longus, flexor hallucis longus, extensor digitorum longus, tibialis posterior...to name most of them) and function to stabilize and support the arches of the feet, provide strength as a lever to propel the body forward, adapt to uneven surfaces and absorb and distribute pounding forces with each step. There are also many 'intrinsic' muscles which work intimately with the toes to provide a solid base for each phase of gait. The toes also play a role as the touch-down points of several of the different arches of the foot which help absorb and distribute weight with the help of static ligamentous structures and dynamic muscular support. ",
"Toes are one of those things that might seem like vestigial structures but you really don't fully appreciate their purpose until they are gone. ",
"EDIT: Not to mention their role in proprioception. "
] |
[
"Do you foresee a future where people with toes either die young or never get laid? Because that's the only way toes are getting \"evolved out.\"",
"Interestingly, there is a group in Africa, the Wadomo, where it is common to have ",
"two toes",
". "
] |
[
"Can you explain the part where you say people who have toes amputated regain \"full mobility\"? I'm sure they will not be able to climb trees as fast as someone with toes. Or even run as fast (I'm just guessing though).",
"I personally don't think ANYTHING in our body is there without purpose. Even the frigging appendix. My personal opinion is not fully unfounded though."
] |
[
"Are insect cells smaller than the cells of larger mammals?"
] |
[
false
] |
Say you have a gnat or mosquito. Are the cells that make up the insect smaller in size compared to something like a human or rhino or are there just less cells that make up the insect?
|
[
"As a general rule, animals that are smaller tend to have lower cell counts, rather than having smaller cells. There's a size limit on how small things can be before they get too small to be useful.",
"Anyway, even within one organism there's a huge range in sizes.",
"So generally, fewer cells, rather than smaller. I can't give exact details though."
] |
[
"To add to the first reply with an example. Between wax worms, mice, and humans, the size of the immune cells that protect these animals are quite similar even though the animals have drastically different sizes."
] |
[
"Mostly, just less cells. Small animals lack the really long nerve cells you find in large animals (because the nerves don't go as far) but on the other hand may have other large cells. For example, ",
"some flies",
" have sperm cells that are 5.8 cm long. Yes, longer than the fly. Yes, that is crazy."
] |
[
"Do inertial reference frames really exist, are are they just a useful approximation? Related to orbits."
] |
[
false
] |
This might be a bit of a mess, since it's not something that I really know a lot about, other than accepting what I've been taught about the laws of physics being constant in all inertial reference frames. It may seem a little stream-of-consciousnessy. So discussions come up from time to time about Earth orbiting the Sun, and whether it really is objectively wrong to say that the Sun orbits the Earth. Even if you take the centre of mass instead of the surface, an argument that commonly comes up is that Earth is a non-inertial reference point, because we are accelerating around the Sun. Seems reasonable enough. But then my thoughts meander a little. The Sun experiences acceleration as it orbits the centre of the galaxy, and the galaxy experiences acceleration as it is drawn towards Andromeda, and their combined system experiences acceleration as they are drawn towards other galaxies in the Local Group, and the Local Group experiences acceleration as it is drawn towards other clusters, and so on and so forth. Doesn't this mean that no reference frame is inertial, because every possible point you can choose will always be accelerating relative to something? And how does the expansion of the universe play into things? So then I search and come across , where the top rated comments talks about reference frames that are inertial. And then my brain goes back to the beginning, thinking that if if we're only concerned with locally inertial frames, then if Earth is orbiting the Sun, does it not automatically follow that it's no less accurate to state that the Sun orbits Earth, if we're only only considering the two bodies as a system, and if we treat the centre of mass of Earth as our reference frame? Do we even need to change our reference frame if we move out to looking at the whole solar system, or the galaxy? Is it scientifically to keep using Earth as our reference frame, or is it just less computationally convenient? I'm becoming thoroughly confused, and less and less certain that I've even barely understood what I thought I knew. given gravitational attraction between all matter in the universe, is there really such a thing as a universally inertial reference frame? And in the context of the answer to that question, is it really 'wrong' to say that the Sun orbits Earth, or is it just a convention that makes things easier to conceptualise and calculate?
|
[
"So discussions come up from time to time about Earth orbiting the Sun, and whether it really is objectively wrong to say that the Sun orbits the Earth. Even if you take the centre of mass instead of the surface, an argument that commonly comes up is that Earth is a non-inertial reference point, because we are accelerating around the Sun. Seems reasonable enough.",
"I think this may be where you're getting caught up. When you make the argument \"you are accelerating around the Sun,\" you are assuming that the Earth is in what is called an \"accelerating reference frame,\" as opposed to an inertial one. However, reference frames which are under a gravitational influence do ",
" experience proper acceleration, as measured by an accelerometer. This surprising fact lead Einstein to conclude that a body \"in free-fall\" was actually in an inertial reference frame, not an accelerating one, and that is the idea that ultimately gave birth to his theory of general relativity.",
"So, although it does \"sound reasonable enough,\" it actually isn't!",
"This seems to resolve your question -- since all of those frames you mention (that of the sun orbiting the galaxy, that of the Earth orbiting the sun, etc.) ",
" all actually inertial, because there is no proper acceleration occurring. The apparent acceleration is due to the inertial motion of bodies ",
", which is the equivalent of a straight line in a curved spacetime. Proper acceleration, then, changes the geodesic along which the body travels. However a body like Earth is on a geodesic that circles around endlessly -- an orbit. Therefore even though it circles around, it cannot be said to properly accelerate."
] |
[
"You have to be very careful here. The Earth's orbit around the Sun is only locally inertial, but it is not inertial in a global sense. That is to say, there is not experiment you can do on the Earth, involving only things on the Earth, to see that you are accelerating around the Sun. But there certainty are experiments you can do (looking how the position of the stars change throughout the year, for instance). ",
"Locally inertial and globally inertial are both well defined concepts and not all locally inertial frames are globally so. "
] |
[
"The apparent acceleration is due to the inertial motion of bodies along a \"geodesic\", which is the equivalent of a straight line in a curved spacetime. Proper acceleration, then, changes the geodesic along which the body travels.",
"Thanks a lot. That part especially makes a lot of sense."
] |
[
"How does the human brain keep time?"
] |
[
false
] |
I understand circadian rhythms, but I want to know how our brains keep time in a more immediate sense. For instance, how can I count the seconds at a fairly consistent pace? How do I a specific interval of time has passed? Digital computers rely on quartz clocks for timing calculations, so is there a similar feature in our brains?
|
[
"As far as I can tell from a literature search, I don't think the molecular mechanism underlying the perception of time is known at all. It is linked to different neurotransmitters (.e.g.), since a lot of psychoactive substances have dramatic effects on the perception of time. It is probably even harder to study in other model organisms since we don't know if they perceive time the same way we do, especially since our time perception depends on consciousness. A ultradian cycle that would represent one second for us may be represented by 10 cycles in another organism that is easier to study. Interesting question... "
] |
[
"There is current research on \"time cells\" in psychology labs, specifically Howard Eichenbaum at Boston University and Gyorgy Buzsaki at NYU. Basically, they found cells in the hippocampus (a major component in memory acquisition and consolidation) in the limbic system. Although their research doesn't specifically demonstrate a \"sense of time\", they show that there is an inherent system in the hippocampus that is able to have a sense of time between two events. Here are two papers that might be helpful:",
"http://www.cell.com/neuron/abstract/S0896-6273(11)00609-X",
"http://www.sciencemag.org/content/321/5894/1322"
] |
[
"a lot of psychoactive substances have dramatic effects on the perception of time",
"This. Psychedelics such as LSD and other substances that bind to the 5-HT2 receptors can have a dramatic effect on the perception of time.",
"It seems that time is counted by the entire brain and not by a single organ in the brain like what happens with digital computers."
] |
[
"What examples are there of evolutionary traits that originally helped individuals of a species, but were bad for the species as a whole?"
] |
[
false
] |
I was inspired to ask by u\atomfullerene 's comment in a recent thread.
|
[
"Now alcohol is slowing civilization rise. ",
"What does that even mean, how was it measured? ",
"Even better, alcohol had destroyed native americans.",
"What? I'm pretty sure that was genocide at the hands of an oppressive & expansionist government. Sure rampant alcoholism prevails on the reservations, but that's a symptom of a problem, not the actual problem. "
] |
[
"Now alcohol is slowing civilization rise. ",
"What does that even mean, how was it measured? ",
"Even better, alcohol had destroyed native americans.",
"What? I'm pretty sure that was genocide at the hands of an oppressive & expansionist government. Sure rampant alcoholism prevails on the reservations, but that's a symptom of a problem, not the actual problem. "
] |
[
"Humans evolved digestion of alcohol many thousands years ago. This allowed us to eat fermented fruit from underneath trees that have fallen down and still be able to run from a predator.",
"There is absolutely no evidence for this. Please cite a source"
] |
[
"With all the discussions about planets and their moons, I was wondering, Is it possible for a Super Earth, or even bigger than that but has the ability to support life, have a moon that can also support life?"
] |
[
false
] |
What I mean is that is it possible to have a very large life supporting planet, like our own, to have a moon that is also supporting life. I just think it would be awsome to be able to sit down and look up at night and see a moon that looks kind of like your own planet.
|
[
"Yes, in theory you could have two planet sized objects orbiting a common center of mass, both within the habitable zone. A much smaller object like Earth's moon would have difficulty supporting a stable atmosphere for a long period of time."
] |
[
"Depends on the chemical makeup of the atmosphere you want. Heavier, colder gases are easy to retain, but typically less useful. A warm, light atmosphere like Earth would need a planet of similar size, but a cold, hydrocarbon atmosphere like that of Titan can exist on a much smaller body."
] |
[
"Here is a size comparison of Europa to our moon",
"There is speculation that there may be life on Europa although I doubt it's anything large."
] |
[
"Do people change or are they merely re-conditioned?"
] |
[
false
] | null |
[
"I don't understand the difference between the two things you are describing.",
"Also, there is no nature/nurture debate, really. It's almost always a mix of both"
] |
[
"I can see my vagueness. Let me try giving an example.",
"The proverb, \"Once a cheater, always a cheater\" or for example a drug addict or alcoholic or a career criminal.",
"If they cease cheating, using, drinking, and stealing, is there really a fundamental change or are they just the product of behavioural re-conditioning. Conditioned not to engage in those behaviours. "
] |
[
"It seems like you are asking \"did they change as a person or did they just change their behavior\", that is, do they not ",
" to do X or did they just learn not to do it / that they shouldn't. Something like that? "
] |
[
"Suppose you had a very rigid ruler and you placed it along the equator at a very smooth site. How long would the ruler need to be before you would see space appear between the ruler and the ground because of the curvature of the Earth?"
] |
[
false
] |
And could it potentially expand into outer space if it was long enough? And if it was long enough and wide enough could we use it to escape Earth's atmosphere in space travel?
|
[
"Math.",
"You're doing it wrong."
] |
[
"Math.",
"You're doing it wrong."
] |
[
"Ok. Since we want a soccer ball of 71 cm fit underneath the ruler, we must take the radius of the earth and subtract .71 m from it. That gives us a 'vertical' (assuming for the problem that we think of the earth as its circular profile) length of 6378099.29 m. So treating that length as the 'opposite' side of a right triangle formed by it, the 'horizontal' distance or 'adjacent' side we're looking for, and the radius of the earth as the hypotenuse, we can use good 'ol soh cah toa, to get the answer. Sin(theta) = opposite/radius of the earth. We solve for theta, which is 89.97 degrees. Then, cos(89.97) = adjacent/radius of the earth. Solving for the adjacent side, which is one half of the length of the ruler required to get a soccer ball underneath, we get 3.008 km. For a total length of 6.016 km.",
"\nI was a bit off before. See image. ",
"http://imgur.com/a/wZvBf",
" Before, I assumed the opposite side, Oe, plus the ball height was the right way to do it, but iorgfeflkd below started it right by using the radius of the earth (hypotenuse) plus the ball height instead. So we have Sin(theta) = Oe/(Radius + .71m). Gives us an angle of 89.97 degrees (slightly different than before if you carried it out further). Then it is simply radius + .71m multiplied by Cos(89.97), which equals 3.009 km. And once again we need twice that amount otherwise the ruler would be completely cantilevered. So 6.018 km long ruler.",
" 3.943 km is the correct answer. I was using a circumference of .71m of a soccer ball, because I didn't realize that it is common practice to measure soccer balls by their circumference. Using soccer ball diameter of .31m and using the same process as in my first edit, we get 3.943 km."
] |
[
"If I get half of my DNA from my mother and half from my father, why is my phenotype so different than either of theirs?"
] |
[
false
] |
[deleted]
|
[
"It's also possible that OP is adopted and doesn't know it. "
] |
[
"Because each of your parents carries an unexpressed allele for those recessive traits, and you rolled a proverbial \"snake eyes\" when it came time to getting an eye color. It's the same concept behind ",
"Punnet Squares."
] |
[
"Hey, improbable things happen! Somebody has to win the lottery, even when the odds are 20 million to one! And not ALL of your genetic traits are snake eyes, just a few of them that you can see. Remember that you can't make assumptions about genotype from looking at the phenotype."
] |
[
"Can we see Action Potentials as they happen?"
] |
[
false
] |
I can't seem to find anything on the subject. Has anyone every tried to observe them? Is it possible?
|
[
"We can indirectly observe the firing of neurons by measuring the voltage change caused by ion channels opening. ",
"This technique can be done fairly simply - it is called ",
"electrophysiology",
" - and it forms the foundation of modern neuroscience."
] |
[
"I myself have never done any techniques to measure action potentials but have discussed them in paper discussions.",
"See this wiki article for more info:\n",
"http://en.wikipedia.org/wiki/Patch_clamp",
"Essentially you can measure electrical changes in the membrane using different techniques all with advantages and disadvantages. For example killing the cell after use or being able to test multiple times etc.",
"Hope that points you in the right direction atleast."
] |
[
"Patch clamps can be used to measure the electrical signal. This is a well-established technique. ",
"There are fluorescent probes that can be used to observe the change in redox potential inside the cells, too. "
] |
[
"Why people don't get sunburnt in +50°C, but get in +30°C"
] |
[
false
] | null |
[
"Temperature has nothing to do with sunburn. I got horrifically sunburnt on the bottom of my chin when I was snow-skiing in sub-zero temperatures because I forgot to put sunscreen there.",
"You'll get just as burnt in 50 as you will in 30 - but someone else may not get as burnt, or may get more burnt. It depends upon many things, including their skin type, how much melanin they have and the behaviour of their melanocytes. Also, behaviour. He may have kept more covered up or worn more sunscreen when in Bahrain resulting in just a tan."
] |
[
"Nope. He never uses that stuff and says that it's intended for metros only.",
"In Bahrain as mercenary he wore overall with top side off (tied it around waist) and in Latvia he just wore shorts. I thought it was because moisture! "
] |
[
"Sunburn is not heat related. It's ultraviolet radiation damage. It has nothing to do with moisture at all - at times, the worst you can get sunburnt is if you're in a pool on a sunny day."
] |
[
"What is the difference between freezing specimens in a \"regular\" freezer vs a -80?"
] |
[
false
] |
My department is going to be moving, and I have a small number of samples I have processed for serum, homocistine, and antiphospholipids that are currently housed in borrowed freezer space, and I am extremely nervous (despite my clear labeling) they may get lost in the fray. So I was wondering whether taking them home and storing them in a "regular" freezer would cause them to degrade in any way? I can't imagine it would hurt serum much since it's thawed and refrozen for tests on fairly regularly, but I don't know much about the other two. TL/DR: Is -80 some how more frozen?
|
[
"not necessarily more frozen, but the difference between a house freezer and a -80 freezer is that, at -80, theres is much less enzymatic activity than there would be in a regular freezer (-20 ish?). Believe it or not, there is still activity in your samples even while frozen.\nThat said, certain samples might be ok at -20, but the shelf-life wouldnt be as great. This is why you cant store meat in your freezer for 2 years and expect it to taste as well as it would have if you froze it for a few days."
] |
[
"Don't EVER use your home Freezer!\nHome freezers are \"frost free\" which means that although they are nominally at -20, they actually alternate freeze/thaw cycles every two or so hours to keep melting and eliminating the frost (which I'm sure you're familiar with from those -80's and lab freezers) that would otherwise build up.",
"Most proteins can't survive more than two cycles. imagine cycling all night! Keeping them at home would totally ruin your samples. "
] |
[
"Two things, one, aliquot your samples, repeated freeze-thaws will cause all number of problems, from volume loss, to aggregation of proteins, loss of enzymatic activity, plus, every time you that you're risking microbial growth. ",
"As for your home freezer, that is \"frost-free\" which means that it warms and cools over a few hour cycle, continuously, to prevent frost buildup. That will degrade your samples too, and that's why frost builds up in lab freezers, they are constant temp, or as close to it as possible. "
] |
[
"There are many cases of species evolving to lose limbs for a snake-like bodyplan or losing other organs, is there any occasion where a species regains the use of a vestigial body part?"
] |
[
false
] | null |
[
"I don't know if it qualifies as a body part but primates did regain color vision, a trait that all early mammals had lost in favor of better night vision.",
"The commonly accepted theory is that it was an evolutionary trait the benefited primates in determining what fruits were ripe to eat as well as differentiating different fruits by color."
] |
[
"It’s actually super amazing. The red-green color differentiating opsin genes are right next to each other on the X chromosome (so females have two pairs and males only a single pair). This is thought to be because the red-sensing version gene was duplicated (in a human/chimp/gorilla ancestor) and then evolved into a green-sensing.",
"Studies in new world monkeys (in South America generally - they branched off from African monkeys long long ago) show that this is probably true because they only have one copy of this gene. ",
" The selective pressure to maintain both alleles in the population comes down to the female apes.",
"Some females would have the same two versions of gene (i.e. red-red which would make them colorblind) however if the females have two different versions (i.e. red-green) then they can see that extra bit of color. As most people know, being color blind isn’t exactly the most challenging disability to live with in our society - but that slight edge they gain from being able to identify when fruit are ripest through better color recognition is thought to give the female apes a fitness benefit. It is even thought to allow them to gauge distances better and distinguish colors faster.",
"Edit: also note I’m using “sensing” in the terms of your brain's manifestation of color rather than the physical sense"
] |
[
"Dewclaw. Wolves don’t have them (unless they are wolf dog hybrids). Probably wolves lost them as their ancestors did less climbing over jungle branches and more running through grass where it would add extra drag. Dogs have them again because they are useful in many things"
] |
[
"Does gravity have a speed?"
] |
[
false
] | null |
[
"Check out ",
"these past threads",
".",
"A star thousands of lightyears away from the galactic center of gravity would be orbiting around where the point was thousands of years earlier if gravity can only operate at the speed of light.",
"Keep in mind ",
"this thread",
" though, to answer that question. Even though changes in gravitational field propagates at c, one would ",
" orbit where the star ",
", but rather where it ",
"."
] |
[
"Is it possible that gravity operates in some way independent of c? Relativity says nothing can move relative to something else beyond c. But does this apply to an ",
"?",
"I've heard about certain quantum effects that seem to operate this way, perhaps gravity does as well?"
] |
[
"The lack of aberration in gravity is explained by general relativity, so while it is entirely ",
" that a new mechanism exists, there isn't a present need to explore that possibility."
] |
[
"Is it possible mitochondria used to be parasites before becoming part of the cell?"
] |
[
false
] | null |
[
"Yes, it is known as the ",
"endosymbiosis theory",
". While there are some very compelling evidence, it is still an active subject of research."
] |
[
"Chloroplasts, too, are considered possible endosymbionts. It's really a rather cool idea!"
] |
[
"Unlikely that they were parasites, but mutualistic or commensalistic endosymbionts. The cell provided metabolism and/or photosynthetic capabilities to the host cell. This relationship eventually coevolved to the point where mitochondrial DNA has relocated into the host genome, rendering the mitochondria (possibly?) incapable of surviving on its own."
] |
[
"What would a habitable tidally-locked planet be like?"
] |
[
false
] |
A tidally locked planet is a planet with the same side always facing the Sun, just like the Moon is tidally locked to us and we only ever see one side of it. This is something I've been interested in for a long time, so you can imagine my excitement when we actually in 2010. Gliese 581 g got a lot of press coverage for being in the center of its star's habitable zone, but articles really only mentioned in passing that it was tidally locked. I've tried to do a bit of research here and there on my own, but I haven't been able to find much reading on tidally locked planets (if you have any, let me know!) so my only option is to cross-apply what I already know and have learned on my own - which I can put any confidence in. If, for the sake of answering the question it's easier for to assume the tidally locked planet is exactly like Earth, feel free to do so. Here's what I'm confident about. From the perspective of a tidally locked planet, the sun doesn't move in the sky at all. Because of this, one half of the planet is always day, one side is always night, with a ring in between them that is always at twilight, effectively making times of day like noon and midnight geographic locations. Tidally locked planets also don't have any axial tilt, so there would be no perception of seasons throughout a year. The night side is always "winter" and the day side is always "summer", which a sort of Spring/Autumn in between where plants neither bloom or wilt, it's just a stagnant in-between of summer and winter without any of the transitionary events we associate with those seasons. I don't want to assume any more past that, so here are some of the things I don't know. How viable is life on a planet like this, given the dark side receives no light and the day side is interminably hot? Is this environment too stagnant to expedite evolution like we've had on Earth? What will the climate be like if cold-zones and hot-zones are constant? Would cold and warm fronts always coming from the same place and with the same intensity cause geographic areas to constantly have the same weather? Would the lingering heat of the atmosphere be enough to make any of the night-side habitable? Anything you know or could share your ideas on would be hugely appreciated, and if you have any creative questions about tidally locked planets that I've totally overlooked, be sure to ask.
|
[
"Tapio Schneider’s Vimeo page has a bunch of videos of simulations of a tidally locked earth like this one:",
"http://vimeo.com/19458103",
"Here's a paper: ",
"http://arxiv.org/abs/1001.5117/"
] |
[
"My first intuition is that there would not be a water cycle as we know it, because this needs permanent bodies of water experiencing temperature differences. So, no weather, no wind, no rain. Climates exactly aligned with latitudes and only involving temperature.",
"In that case, the sunny side could be land or sea. Oceans wouldn't have currents or waves. Land area would be barren or, if evolution would have created plants that can live on water vapour from the atmosphere, filled with huge forests.\nThe dark side would be a lot like our moon, I guess, with the exception of possible ice patches."
] |
[
"Note that if the planet has even a slightly eccentric orbit, the planet will still slowly rotate. This is because when the planet is at periapsis the tidal forces are stronger and its angular orbital speed is higher than when the planet is at apoapsis. The planet's rotation is locked to the angular orbital speed when tidal forces are strongest; that is, at periapsis. This is why Venus and Mercury rotate. The Moon has a similar effect; it wiggles somewhat, meaning that the Earth is not always in the same location in the Moon's sky.",
"I've read (not just in this thread) both the viewpoint that there would be spectacularly strong winds at all times in the twilight ring area and zero winds, at all, anywhere, ever, as the planet reaches equilibrium. I'd like to see more clarification on that matter."
] |
[
"How are satellites electronically grounded?"
] |
[
false
] | null |
[
"Everyone else is absolutely missing the point. Nearly all circuits in a satellite ",
" grounded, just not to the earth. The fact that you are not on earth makes grounding ",
" important, not less. Within ",
" in an space environment you can build up large charges between different circuits just based on the electrical isolation of extremally high vacuum, and the surrounding plasma and high energy particles of space. This is coupled to the problem that the breakdown voltage of the vacuum is ",
" than air. So a potential that would not be dangerous on my lab bench would be very dangerous in space!",
"A ground is a reference 0 Volt Potential. Note that it is a reference, not an absolute! Within electrial circuits it is ",
" that any part that talks to another has a common refrence, or is electrically isolated via optical isolators. ( Using LED/Photorecptors to send information )",
"There is absolutely a reference ground between circuits external to the circuit, and they are not allowed to float. Otherwise you would have a nearly impossible task of having circuits talk to each other. Everything would have to be opto-isolated from each other. You could never have any high frequency signals without every circuit turning into a antenna. ",
"What this reference is is different between different satellites. However be far the simplest ground is the conductive frame of the circuity itself. ( Large complex satellites will use multiple grounds isolated from each other )",
"Space induces a ton of problems into circuit design. As it is not a complete vacuum you also have to deal with the plasma of high energy particles around you. Your craft can develop high static charges in the frame, or even relative to itself! ",
"NASA has an excellent introduction",
" to the problems of charge in space. As the ISS is ENORMAS compared to everything else in space it has the largest problems as well. It has multiple grounding planes, and they can generate massive potentials relative to each other. ( The Solar cells are the main concern )",
"Dr. Robert Frost at NASA has some excellent pictures ",
"here",
" showing DC arcing damage to the solar array, and discusses how the ISS deals with reducing the potential between different sections of the ISS."
] |
[
"They're not.",
"Electronics are likely using the frame itself as the common, which may be at a different potential than the surface of the earth, or not.",
"If there was no net charge on the ship to begin with, it won't \"build up charge\" because it's isolated in space. Where would the charge come from? I supposed rare ionized gasses in space? Solar flares? Maybe?",
"If you wore socks and dragged them across carpet inside a satellite, you pulled charge from the floor of the satellite into your socks, then to your body. If you touched the metal frame, you'd feel a shock as you give the charge back. The total charge was always constant. It just moved around inside the satellite.",
"What grounds the earth?? It's just a bigger satellite."
] |
[
"I get what you're saying but the earth is huge, so it can obviously absorb a lot of charge.",
"Regarding where the charge would come from on a satellite, there is energy coming in all the time from solar radiation, that is where the satellite gets its power from. This is obviously then going to be converted to an electric charge right?"
] |
[
"What is up with the Gardasil vaccine? Is it safe, effective, etc?"
] |
[
false
] |
Not asking for individual experiences or medical advice. I don't want to hear what the company has to say about it nor the anti-vaccine crowd, thus why I came here to ask. I have noticed that news sources have reported that this vaccine has larger than usual adverse side effects (seizure, coma, death) and only treats 4 out of 100 strains of HPV. I was wondering what the current reliable reports are saying about its safety and effectiveness. For others: Obviously, this does not replace medical advice from your doctor!
|
[
"The main purpose of the vaccine is not to prevent HPV infection itself but to prevent the resultant increased risk of cervical cancer caused by HPV. HVP subtypes 16 and 18 (which are both covered by this vaccine) are the subtypes most commonly found to lead to cervical cancer."
] |
[
"There is no reputable source that there are higher than usual incidents of adverse side effects of this vaccine as far as I am aware of presently."
] |
[
"To begin: I am not a medical professional or a biochemist, as my flair indicates.",
"You should look at the National Institutes of Health ",
"page",
" on the HPV vaccine. This has information on side effects, etc. You can also see ",
"this link",
" from the CDC, plus the links it includes, to see reports on the safety.",
"Of the 100 strains of HPV, the NIH reports that ",
"most are harmless",
". The strains included in the vaccine are responsible for 70% of cervical cancers and 90% of genital wart cases, according to the National Cancer Institute, as indicated ",
"here",
". The above links also indicate these strains also cause other cancers (including certain cancers of the oropharynx, anus, vulva and penis).",
"Can you source your claim that there are \"larger than usual adverse side effects\"?"
] |
[
"Why does curing raw fish make it safe to eat in sushi? Alternatively, why can you not just do this with other meat like chicken?"
] |
[
false
] | null |
[
"Sushi (actually, sashimi - “sushi” is rice) isn’t cured. Sashimi is relatively safe because it’s high-grade fish, carefully processed. Even so, occasional parasite eggs slip through and cause health problems. Chicken, on the other hand, is processed in much larger-scale operations in which slaughterhouse bacteria are endemic. You can pretty much be guaranteed you’ll be exposed to salmonella when dealing with raw chicken. Other meats are similarly relatively safe: you can, for example, eat good beef raw (steak tartare, anyone?) with relatively little risk."
] |
[
"Dont forget the chickens live highly stressed lives, which would normally cause them to succumb to diseases, except for the over administration of antibiotics."
] |
[
"Dont forget the chickens live highly stressed lives, which would normally cause them to succumb to diseases, except for the over administration of antibiotics."
] |
[
"Could you pull a boat while on it?"
] |
[
false
] |
In a hypothetical situation, if you were on a wooden boat and tied some rope to one end and stood on the other side, jumped as high as you could while pulling the rope, would the boat move towards the way you pulled it?
|
[
"Yes. You and the tie point of the boat would move towards each other. If you were in a boat that weighs as much as you do and you pulled the rope one meter, you'd go backwards half a meter, and the boat would go forwards half a meter, not accounting for friction."
] |
[
"And don't think about running to the other side and repeating the steps. As you run to the other end of the boat, the boat will be pulled back to the location it started at. You won't be able to achieve any net distance this way."
] |
[
"I know we are talking about ideal systems and such like, but in reality the boat would experience more friction than the crewman and you would slowly progress."
] |
[
"Who has the advantage in a quiz where two people have to guess a number (e.g. an amount or a prize). The first guesser or the second?"
] |
[
false
] |
I am a radio host and sometimes conduct radio quizzes. As a tiebreaker between two contestants, I use a "guess how many"-question, like "How much money did the local government spend on traffic in 2015?" The first contestant gives an answer. The second one then answers. What is most fair? A: That the first one guess a number, and the second guess a number? B: The first one guess a number, and the second says higher og lower? My thinking is: In scenario B, number 2 has a 50/50 chance, but I am not sure if number 1 has the same 50/50 chance, because the success of his opponent is down to 50/50? Another question: Is the fairness affected by the nature of the question, i.e. the difference between a random number and an actual number that might be, but unlikely is known by one of the contestants?
|
[
"If both players are rational, then there should be no difference between your two modes of play (second player guesses or second player says higher/lower). Suppose player A says 50, and player B believes the answer is 60. It will always be strictly better for him to guess the minimal increment higher than the answer of A, say 51, rather than his actual guess. This way, if the true answer turns out to be 53, he would still win where this wouldn't have been the case had he answered his actual guess of 60.",
"So if your aim is to benefit the smarter player, you should keep the second guess. If your aim is to equalize the field, then go for higher/lower.",
"As for the second part of the quesiton: Even though the precise answer (the amount of money spent by the local gov't on traffic, for example) is likely to be unknown to players, smart players may be able to come up with a reasonably good order-of-magnitude estimate. This means that if a weak player is to guess first, there is a good chance for the smarter second player to score a nearly guaranteed win. For example if the first player guesses $100, the second player should immediately recognize this as far too low and guess \"higher\" (or $101). In reverse, if the smarter player goes first and produces a reasonable guess, then the second player might as well flip a coin to determine his guess of higher or lower.",
"When using random numbers, a similar effect is present, with the difference that there is a clear optimal strategy for both players. The first player should guess the average between the lower and upper limit of the random number (assuming symmetric distribution) and the second player can guess either higher or lower, it makes no difference. If the smarter player goes first, both players will always have a 50% chance of winning (assuming the higher/lower system is used), since the first player will guess the middle value. If the weaker player goes first, he may not guess the middle value, which would give an immediate advantage to the second player.",
"So to conclude: The best solution depends on what you want. Should it effectively boil down to a coinflip? Or should there be an advantage for smarter players? Using a random number has the best chance of ending up with 50/50 odds for both players since the optimal strategy is relatively easy to see, but it may become boring when the first player always guesses the middle value and the second player has no influence once this is done. Using an actual question is definitely more interesting, but the player with more knowledge / better estimation skills will benefit in this case, but primarily if he can play second."
] |
[
"One way to minimize a second player just choosing a number either 1 above or 1 below the first player is to incentivize guesses within some amount. So \"anything within 5 wins extra prize.\" This way if the first player guesses 50, and the second player thinks its 70, the second player would not just guess 51, but rather 65 (depending on what the incentive is). Or, alternatively, you could say something like \"Any guesses not within 10 means we have to reguess.\" Of course this adds complexity, and I assume the whole idea of the radio show is to find a winner very quickly."
] |
[
"Suppose player A says 50, and player B believes the answer is 60. It will always be strictly better for him to guess the minimal increment higher than the answer of A, say 51, rather than his actual guess. This way, if the true answer turns out to be 53, he would still win where this wouldn't have been the case had he answered his actual guess of 60.",
"You constantly see this in The Price Right. Sometimes the last contestant will pick $1 since any answer above the price of the product is wrong."
] |
[
"If electromagnetic radiation all travels at the same speed, then how are we able to physically observe the visible spectrum of light from a supernova without simultaneously being harmed by the dangerous radiation emitted such as UV-rays, X-rays, and Gamma-rays?"
] |
[
false
] | null |
[
"Because the intensity of the light drops off as roughly 1/r",
". The light intensity is too weak to do serious damage, but you could still detect it."
] |
[
"While ",
"/u/Mr_iLikeEverything",
"'s answer is technically correct, it's a bunch of jargon as far as I'm concerned. ",
"The simple explanation is that the radiation spreads out. Just imagine your torchlight. It starts from a 'point', ie a lightbulb, and spreads out to cast a wide beam. If you place a piece of paper a small distance away from the torch the energy the paper receives, per unit of area (eg a square), may be some amount X. If you move the piece of paper twice the distance away, this same energy is now spread out twice as width and twice as high - so the same area of paper now receives 1/4 X, or 1/r",
" X amount of energy. The total sum of energy is still there, it's just spread out over 4 times the area. This is where the inverse square law comes in - it's simply a result of the geometry of our universe.",
"The final part to tie this together is to think of something like a supernova as a point source with no mirror like in a torch. The energy gets emitted roughly equally in all directions. You can kind of visualise it like an expanding sphere of energy. Every time the radius of this sphere doubles, a little portion on the surface of this sphere gets 4 times as big but must 'contain' the same amount of energy. By the time this gets to Earth it's so spread out that the intensity is at a safe but still detectable level.",
"Here is the ",
"Wikipedia article on the inverse square law",
" with a nice picture to visualise this spreading out, and ",
"another one for good measure",
"."
] |
[
"I actually just did some searching and I apparently exaggerated: ",
"there are a handful",
" of stars that have been resolved beyond a pixel (but never as more than a fuzzy ball).",
"It shouldn't be a big surprise, though! Most stars are about 1 million kilometers across or less. The biggest stars aren't much more than a few billion kilometers in diameter. Those sound like ridiculously huge sizes, and they are! But even more huge is the sheer distance they are from us! The closest star to us besides the sun is Proxima Centauri, and it's ",
", and it is only 200,000 km across. It's 200 million times farther away than it is big. Trying to take a picture of it as more than a point is like trying to resolve the width of a human hair in a photograph - ",
"!",
"And that's the closest star, only about 4 lightyears away. There are only ",
"about 2000",
" stars within 50 lightyears of us, most of them small and dim. The Milky Way is 100,000 lightyears across and 10,000 lightyears thick. Most stars are so far away that, even though some of them are unimaginably huge, they take up an almost immeasurably small portion of the sky. The distances between stars are mind bogglingly huger than the sizes of even the largest stars.",
"But the fact that they are static vs. the changing noise helps explain how we can confirm what they are.",
"I'd also like to clarify that for supernovae, it is not just that they are static. Supernovae within the milky way are so bright that they can outshine the moon. Unfortunately, it's been hundreds of years since there's been one so no one alive has been able to experience that, but there are historical records of it. Even supernovae other galaxies can be bright enough to be seen by the naked eye, though (they look like stars; again, much too far away to resolve). While supernovae are occurring, they tend to outshine their entire host galaxy! Noise or not, it's very easy to detect such bright phenomena as long as you're looking in the right place. Only if we're looking near the edge of our tools' ability to make anything out is noise going to be much of an issue when looking at such energetic events like supernovae."
] |
[
"Is the big red spot stationary?"
] |
[
false
] |
Is the big red spot a relative stationary storm? Or does it move across jupiter like a hurricane on earth? Do we know what has kept it going for long? And what would take for a storm like that to happen on earth? One that rages for years and doesnt move from one spot too much?
|
[
"It's a tough to define \"stationary\" when the whole planet is a big gas ball. Three different coordinate systems are commonly used for Jupiter: System I is based on the rotation rate of stuff near the equator, System II is based on the rotation rate of features near the poles, and System III is based on the planet's magnetic field -- which is presumably tied to the rotation rate of its deep interior.",
"The Great Red Spot is most commonly measured in System II, and yes, it does drift slowly over the course of years in that frame of reference (and in the others).",
"http://jupos.privat.t-online.de/rGrs.htm",
"In short, Jupiter is a fluid planet, and nothing on it is stationary with respect to anything else."
] |
[
"Jupiter is a fluid planet, and nothing on it is stationary",
"Just to add to this: The equator of Jupiter rotates once every 9h50m. Mid-latitudes rotate once every 9h55m. You can do that when you're not a solid."
] |
[
"The current available theories as to why this high-powered anticyclone continues to rage for hundreds of years is pretty simple.",
"There is no land to create friction in order to slow down the storm.",
"Just like on Earth, the Pacific storms tend to be stronger than Atlantic storms because there is larger expanses of open sea available.",
"The spot does circulate around the band it was formed inside, but does not vary much in it's latitude. It has lapped the planet numerous times since it's discovery and observation.",
"Edit: anticyclone, not cyclone. I just meant it was a strong windstorm, anyway."
] |
[
"The evolution of birdsong?"
] |
[
false
] | null |
[
"Things created through sexual selection (which I'm speculating created most birdsong) generally gain complexity and ornamentation as they involve, so just imagine a less interesting version of what you heard today. How much less interesting? Well, that's where it gets unknowable."
] |
[
"Well it depends really. There is a period where birds undergo a process called crystallization. Basically it's a point in maturity where they begin fine tuning their song as they mature. Now studies have shown birds do not inherit song from their parents but rater the frequency and rate they sing the song. So birds must hear a song to learn a song. What birds do is in their pre crystallization phase they babble like babies producing numerous notes and songs that are choppy and poor quality. this is where they learn the base of what their song will become. There are some birds which recrystillize their song seasonally. So they fix it every year when they hear more appealing notes to use. The only real evolution which takes place in bird song would be in the frequency and speed of the song. There is also the selection of song which female birds prefer so the birds who sing those songs mate. Thus other birds try to sing these songs in order to become more successful at breeding. ",
"Sorry for formatting I posted from alien blue. I hope this answered your question if not I can try and expand and clarify. "
] |
[
"A good home for this question would be ",
"/r/AskScienceDiscussion",
"."
] |
[
"Is a lightning bolt heat making light or is it light?"
] |
[
false
] |
[deleted]
|
[
"it is electricity making heat AND light..."
] |
[
"First you'd have to explain in detail what \"Electricity\" really is. It can't be done, since reference books disagree over the correct definition of the word \"Electricity.\" So just avoid it. If you mean \"electrical energy,\" then say electrical energy. Same with flows of charge, etc.",
"Lightning is a self-organized plasma structure: thin plasma filaments. In other gasses and other pressures you wouldn't see such filaments, instead you'd get glow-discharge patterns (Aurora sheets, etc.)",
"Where does the light come from in lightning? Same place as with neon signs, ",
"HID streetlights",
", and xenon camera flash: high voltage applied across a conductive plasma will cause the gas to fluoresce. It's similar to an LED: electrons get pulled farther away from atoms (which pumps up their energy,) then they emit photons when they fall back down again."
] |
[
"the light comes from heat as the electricity heats the air to ~50,000 degrees. ",
"http://en.wikipedia.org/wiki/Lightning"
] |
[
"Is there any/could there be any two elements that could undergo both synthesis and decomposition in the same environment?"
] |
[
false
] |
I'm asking if you could have elements X and Y you could have both X + Y --> XY and XY --> X + Y but not have to change the surroundings, and would therefore spontaneously switch between XY and X + Y
|
[
"In principle, literally every chemical reaction does this. Every reaction is reversible, and will follow the same pathway in both directions according to what chemists call the principle of microscopic reversibility. A great many reactions so heavily favor one side that the rate of the opposite reaction is negligible, but it is still possible."
] |
[
"You got your answer, OP, not much to add. Maybe just keep in mind that ",
" or ",
" are only valid at the molecular level, but at the level of a solution, the two occur. Not at the same molecules at the same time, of course, but one X will undergo successively the two reactions, all the time.",
"XY is not the equilibrium state of the ",
" equation.\nIf you found more XY than X or Y, then it simply means than the reaction is going faster in one way than on the other.",
"So the answer was already provided by @uberhobo : yes, there are elements undergoing both equation, and in fact it is \"almost all of them\", the exception is the contrary. And to keep that in mind, remember not to mix-up the scales (single molecule undergoing a reaction, solution coming to an equilibrium).",
"Hope I'm clear :)"
] |
[
"Literally all reactions are basically in an equilibrium, however skewed towards one side or not. ",
"Given enough pressure, heat or proper catalysts, I would dare say that all reactions are reversible, because of the fact that all reactions are basically equilibriums. ",
"Although we usually classify chemical reactions as mostly spontaneous-oneway, or nonspontaneous or equilibrium, the reality is that those ratios of going to one side or the other are determined purely by temperature, pressure and/or catalysts present. ",
"I mean, even water is technically an equilibrium of H+ and OH- molecules constantly adding to form H2O and subtracting to form H+ and OH- particles. ",
"A good thing to read up on is the 'Boltzmann Distribution', which explains that the energies of individual molecules are variable, and hence, allows for some molecules to remain lower energy (hence not bonding) or higher energy (bonds way quicker than any other identical molecules). ",
"This means that each individual molecule are different in energy, and there WILL be outliers for all chemical reactions, allowing for a sort of equilibrium to exist (even if it takes millions of years for one molecule to somehow bump into another molecule to bond, it is still technically an equilibrium) ",
"Chemical bonding relies on three main things: "
] |
[
"A physics puzzle"
] |
[
false
] |
On the floor of an elevator/lift are a blob of mercury and a lit candle in a holder. The cable snaps. What happens? (Assuming the the lift shaft to be very long or infinite.)
|
[
"Blob of mercury: The blob of mercury will, to minimize surface energy, become a sphere. The motion from changing shape will impart momentum to the sphere, and it will drift upwards from the floor.",
"Candle: The flame will die. Since the air is accelerating with the candle, convection cannot occur (wherein hot, oxygen-depleted air rises and is replaced by cold, oxygen-rich air to feed the flame)."
] |
[
"The elevator is in freefall. It's impossible for anything inside to distinguish between that and zero gravity. Anything that happens in zero gravity will also happen here.",
"No natural convection will happen. There's no direction that air can rise.",
"There may still be enough diffusion for some oxygen to reach the flame and keep it lit, but the flame will be far weaker."
] |
[
"Candle in space",
"A candle is capable of burning in free fall, but the sudden shift from stable to plummeting might make enough turbulence in the air to put out the significantly weaker flame anyway."
] |
[
"Does the gravity of everything have an infinite range?"
] |
[
false
] |
This may seem like a dumb question but I'll go for it. I was taught a while ago that gravity is kind of like dropping a rock on a trampoline and creating a curvature in space (with the trampoline net being space). So, if I place a black hole in the middle of the universe, is the fabric of space effected on the edges of the universe even if it is unnoticeable/incredibly minuscule? EDIT: Okay what if I put a Hydrogen atom in an empty universe? Does it still have an infinite range?
|
[
"In theory, yes. Gravity has an infinite range. However, it also takes some time to propagate - information about local changes in the gravitational field will propagate at the speed of light. So if a supernova goes off and creates a black hole, we won't feel the gravitational disturbance until we see the light from the supernova. ",
"Additionally, since the universe is expanding there are distances such that we will never receive information from. Anything that happens beyond that horizon will not be able to effect us. "
] |
[
"Lots of mass accelerating really hard makes gravitational waves. While the gravity of a star and similarly massed black hole will be practically indistinguishable, there will be a blip associated with the transition."
] |
[
"if a supernova goes off and creates a black hole, we won't feel the gravitational disturbance until we see the light from the supernova. ",
"Would there be any difference in the gravitational effect? Doesn't the supernova star have the same or more mass than the black hole?"
] |
[
"If you are trapped underwater and need to make it to a breathing hole, what should you do (to survive) - swim slowly and limit CO2 production? Or swim quickly and reach the hole faster?"
] |
[
false
] | null |
[
"As a freediver, the second one you said. EDIT: the most efficient way to swim is ",
"this one",
", but can be psychologically challanging to wait in such a situation. But just look at the movement. The hands are kept near the body, and all movements are slow and gentle, to reduce turbulence."
] |
[
"Well, disregarding any physiological effects, drag is proportional to the square of the velocity, so your required energy expenditure will be exponential with an increase in velocity. So super fast would not be good. That being said, there will be some optimum point as going super slow will most definitely not be an advantage either."
] |
[
"Even the weakest exponential growth rate will eventually overtake a function raised to some constant exponent (2, in the case of quadratic functions). In the long run, exponential functions break systems.",
"Like, for example, financial systems."
] |
[
"Whats the difference between moving a muscle through electrical stimulation and moving a muscle normally?"
] |
[
false
] |
I just bought a electrotherapy device about a week ago and am very curious about some of the strange things I see when I crank it up. Basically, does a stimulated muscle do all the normal stuff like burn up ATP? What differences are there if any? Fun follow up: Could we wire someone up for a life sized game of QWOP?
|
[
"When you decide to extend your arm, you send an impulse down your nerves to an effector nerve (sometimes called motor nerves), this then stimulates the muscle to contract, extending your arm. ",
"This electrical device is also sending an impulse down these same nerves stimulating a response.",
"The muscle itself knows no difference and functions identically in both cases. It will continue to use ATP, calcium will continue to potentiate contractile strength.",
"One potential difference is that under high electrical charge, the muscle can be stimulated dangerously causing too large a contraction and resulting in muscle damage. Under normal use the entire muscle does not contract. I would expect that your machine is incapable of such charges though.",
"This is used very often in pharmacology. Muscle twitch tests are where a muscle is removed from an animal (usually hamsters or other small rodents) and then given a new drug and twitch strength measured via a tension device.",
"As for QWOP, I Googled this and saw a running game. If this is to which you refer, yes. Conceivably possible. One would require an anaesthetist to administer a block on the subject's spinal cord so that the brain could pass no stimuli, then electrodes could be attached to allow stimulation of the limbs. It would not be possible (to my knowledge) to safely remove the subject's reflex arcs as these do not include the brain and unwanted nerve action is a near certainty. Furthermore, given my previous experience with ethics committee I do not see such an experiment being granted approval. ",
"I'm on mobile just now so no further reading links. If you'd like further clarification or a more on depth explanation of anything please ask."
] |
[
"given my previous experience with ethics committee I do not see such an experiment being granted approval",
"What would they think about an experiment where you lock a committee inside of a burning building?",
"Jokes aside, good info!",
"What would happen if a weight lifter kept lifting until all the ATP was used up and they could no long lift the weight and you tried to contract the muscle with e-stim? This is of course assuming that you could activate most of the muscle as opposed to the reality."
] |
[
"So ATP is made by aerobic or anaerobic respiration. In the presence of oxygen glucose is converted to a net gain of 36 ATP. For anaerobic or no oxygen, it is made in 4 ATP and acid builds up giving an oxygen debt that must be repaid.",
"For us to run out of ATP we must run out of Glucose and also fats as one eventually burns fat and protein.",
"But to run would be fatal as the muscles and also a lot of other stuff in the body would die.",
"The impulse would do nothing without ATP as there would be no energy sources for the muscles. The electricity here is only a message to say \"contract\" it provides no energy."
] |
[
"If a peice of metal was lodged in a brain, could neurons use it as a \"wire\" for permanent communication?"
] |
[
false
] |
Has this ever been observed or experimented with?
|
[
"Not quite true actually. The vast majority of neurons communicate through chemical means, where neurotransmitters in various forms trigger postsynaptic events.",
"However, there are ",
"electrical synapses",
" as well. Granted, electrical synapses are not as common as chemical synapses, but they exist and are very important for a number of functions, such as synchronizing electrical activity among populations of neurons.",
"I actually do research on implanting electrodes into rat brains, and there are a couple of ways that this works. First of all, the electrodes are generally recording electrodes - they get inserted into the brain so we can 'listen' to what the neurons are doing. Depending on the research being done, the electrode can either pick up the membrane potential of a single cell, called single cell recording, or of a group of local cells, called local field potential recording. ",
"Basically, electrodes are picking up the changes in electrical membrane potential across a cell or group of cells that can be a result of either chemical or electrical transmission. "
] |
[
"That's fascinating. I've never heard of electrical synapses before."
] |
[
"How do they connect probes into the brain to read neuronal signals? I've read something about scientists interfacing a rat brain to an integrated circuit before."
] |
[
"Does the order of different insulators affect their total insulating capability?"
] |
[
false
] |
Real world example: I have a sheet, a comforter, and a random fuzzy blanket. Does the order of the blankets matter to keeping me warm? My first guess is "theoretically, no, but with real-world conditions: ..."
|
[
"In a super crazy simple world where every variable was controlled other than energy in + energy out, then no, it would not matter, same overall result. In the real world, it matters a lot. Try putting your down jacket over your raincoat on a wet day. There are 100s of examples like this one where order and other factors matter."
] |
[
"Relative weights would factor in for some blankets, if a lightweight fabric relies on relatively large air pockets for an insulating effect, a denser blanket on top would compress those pockets and make them less insulating. "
] |
[
"Put the most easily compressed layer on top. That way the total thickness including trapped air is more, which is warmer. Some layers might be better at removing sweat, or they're easier to wash. Those reasons justify sheet below blanket below comforter."
] |
[
"Why do humans enjoy carbonation?"
] |
[
false
] | null |
[
"I hate them"
] |
[
"The bubbles that 'sting' your mouth makes your brain release dopamine. Dopamine is the chemical that makes you feel happy and can lead to addiction to multiple things such as food, drink, or drugs.\nEdit: Grammar."
] |
[
"i agree, but then why carbonate? sodas would still be sweet if uncarbonated ..and what about beer? "
] |
[
"Has anything ever broken the speed of sound underwater? What would happen / does happen?"
] |
[
false
] |
The speed of sound in water is around 5 times the speed of sound in air, or around 1500 m/s.
|
[
"The article says the missile can go 230 mph. The ",
"speed of sound in water",
" is around 3,347 mph. ",
"Cavitation",
" is the result of water vaporizing in the low pressure regions resulting from ",
"Bernoulli's Principle",
". We have a hard time getting things to 1497 m/s in air, let alone water. "
] |
[
"You must not have read the second article which says \"He succeeded in making a super-cavitation-projectile, which could be used to detonate underwater mines in the future, accelerate in water to a record speed of 5400 km/h: \"Unfortunately I am not allowed to explain very much, because a lot of what we are working on is top secret\"\n I do not know of the validity of these claims however please in future at least attempt to read links before correcting others on their content."
] |
[
"Sorry, I saw a continuous stream of blue and thought there was only one link. It's good practice to use line breaks.",
"The 5400 km/h claim seems suspicious in comparison to the other values, as well as when compared to speeds of projectiles fired through the air. I wonder if it should be 540 km/h. I'm not finding any references to that value in association with his name that aren't that article or direct translations of it."
] |
[
"Why do worms come out of the ground onto the footpath when it's raining?"
] |
[
false
] |
Whenever it rains, the footpaths in my neighbourhood are covered with of worms. Why do they come out of the dirt to lay on these hard wet surfaces?
|
[
"Worms actually breathe through their skin and they have to stay wet or moist so oxygen can be absorbed. When it rains and the normally dry surfaces are covered in water, it gives them opportunity to go where they otherwise can't. "
] |
[
"Can you, likewise, source that fact? I don't know who to believe!!"
] |
[
"Can you, likewise, source that fact? I don't know who to believe!!"
] |
[
"I'm making a scientific Christmas present concerning DNA and I was hoping somebody could help me?"
] |
[
false
] | null |
[
"You will want the DNA coding strand to match the mRNA strand: the 5'-3' strand of DNA will have the same sequence as your mRNA strand. In real life this can sometimes vary: some genes are transcribed from the coding strand (5'-3') rather than the template strand(3'-5'), but for your project no worries! Also the start codon encodes methionine so you don't have to repeat that codon.",
"So your DNA 5' strand will be ATG-GAG-AGG-AGG-TAC-etc. ",
"Cute gift ;)"
] |
[
"I'll send you a picture when it's done! :D",
"I got all the materials yesterday. I got thin popsicle sticks, gold (colored) wire, and some hot glue. I'm breaking the popsicle sticks in half and using the halves to make base pairs. So one stick can make a TA and a CG. Right now I'm color coding, and when I have enough free time I'll start gluing!"
] |
[
"Thank you :)",
"So about the methionine one, what will I do for the beginning of Christmas? I've been using \"-stop-start-\" as the space. Should I just smush it all together to MERRYCHRISTMAS?"
] |
[
"Why don't Christmas lights get dimmer as you go down the string? Does each light not suck up some of the energy?"
] |
[
false
] | null |
[
"For series lights\nThe same amount of current goes through each light, meaning each light uses the same amount of energy.\nAs you go down the strand energy decreases, but at a constant amount for each light (assuming same resistance).",
"For parallel lights\nAll the lights are wired independently and there is no first light."
] |
[
"The pressure is the same at each spout",
"The pressure ",
"."
] |
[
"Because that’s not how electric potential works. ",
"Think of the wire like a pipe of water. Each light is a spout along the pipe. The pressure is the same at each spout, rather than one end having all the pressure and the other end having none",
"Edit: in this analogy the pipe is horizontal. With a vertical pipe, the pressure is inversely proportional to height"
] |
[
"Why does the US launch rockets in Alaska?"
] |
[
false
] |
I get that they could launch over the Pacific so they don't fly over people, but doesn't the equator have an easier time due to the faster rotation of earth? Is it for longitudinal orbits? Thanks.
|
[
"Launching from the equator is mostly beneficial for equatorial orbits. In the case of polar (ie orbits that go over the north and south pole) or sun-synchronous orbits you do not get much advantage from lunching at low latitudes. ",
"It can also sometime be interesting to launch sounding rockets at high latitudes to perform measurements and experiments in the ionosphere. Due to the proximity with the magnetic poles of the earth it is an interesting area. ",
"If you look at the ",
"list of launches",
" from this spaceport you will notice that there is a lot of military weapon testing, principally the Ground-Based Midcourse Defense system. From my understanding (I cannot find reliable sources on this), the pad is also the result of the strategic location of Alaska in the missile defense strategy of the US. As such there has been some lobbying to get contracts from the Missile Defense Agency. ",
"The spaceport public funding has however been questioned as it has not be very successful commercially so far."
] |
[
"The local gravity DOES change a little based on where you are, due to the oblateness of the earth (the poles are squished together a tad bit). The distance you have to travel to get off the earth also changes due to the oblateness. But the overall local gravity difference is only about 0.35%. That's 100 pounds versus 99.65 pounds.",
"However, the spin of the earth reduces your escape velocity by a full 4.33% compared to the poles. That's +4.33% vs -0.35%."
] |
[
"There's no difference in escape velocity depending on where you launch from, but there is a different in initial kinetic energy.",
"From ",
"/u/DaKing97",
"'s ",
"second source",
":",
"\"The energy per kg [launched into LEO] at the equator is 3.25 x 107 J/kg compared to 3.26 x 107 J/kg at the North Pole. \" From Cape Canaveral in Florida, the energy per kg is 3.252 x 107 J/kg. This is a 0.3% savings over the North Pole."
] |
[
"How are we able to imitate pitch so well?"
] |
[
false
] |
If someone were to sing a song right now, most people could imitate the pitch (the notes) very easily. However, if I was asked to do the same on piano I would have trouble and fumble while doing so (despite years of playing). Is the ability to match natural pitch in the voice solely due to extensive practice by talking and if so by what age do people get good at this skill?
|
[
"The imitation of pitch in infants",
" suggests that babies from 3 to 6 months can vocally match pitches that they hear. This is before speech has fully developed, which suggests that this skill is either innate or develops even earlier in the child's life.",
"As for piano playing, unless you started before preschool age, it is unlikely that you have Absolute Pitch (also known as a perfect pitch). You probably, however, have a strongly developed relative pitch, and would be able to reproduce whatever you heard if you were told the starting note and possibly the key. ",
"This paper",
" talks more about pitch memory in adults, and the introduction talks a bit about relative and perfect pitch at different ages and levels of musical training."
] |
[
"An additional difference between piano and voice: when you are singing, you get instantaneous feedback on the pitch you are producing and you can correct that pitch almost instantaneously as well. Your voice is a little flat? Increase the pitch until everything sounds right.",
"You can sorta do this on piano, but your increases would have to happen in semitone steps (you can't play notes that are in between keys), one problem with this is that you don't get the beat effect that you do when two notes are ALMOST identical (as in their frequencies differ by a few hertz), when this happens, you get an extra feedback mechanism: you just adjust your pitch until the beats stop."
] |
[
"This is before the onset of language, which suggests that this skill is either innate or develops even earlier in the child's life.",
"I would be careful with this statement. Certainly 3-6 months is before the onset of speech, and probably before the onset of understanding of speech, but \"language\" writ large is often considered to be acquired very early, even prenatally. See for example ",
"http://crl.ucsd.edu/bates/papers/pdf/rapin1999.pdf",
" which contains a summary of early childhood linguistic development. Quote:",
"\"After many years of experience with these procedures, it now seems clear that human infants are capable of perceiving virtually all of the speech contrasts used in natural language, at birth and/or within the first few weeks of life. There is even a certain amount of (controversial) evidence suggesting that infants may acquire a reference for the speech sounds of their native language during the last few weeks ",
" (DeCasper & Fifer, 1980; Jusczyk, Friederici, Wessels, Svenkerud, & Jusczyk, 1993; Mehler et al., 1988).\" (pp 9-10)"
] |
[
"What is the eukaryotic revolution"
] |
[
false
] | null |
[
"This sounds like a high school assignment...and assuming you're in high school, your comment history..."
] |
[
"You know these accounts are free, right? You could just make another one right now. You don't even need an email address."
] |
[
"Lol im in bio150 also. Eu cells are far more compartmentalized, which i stated earlier allow for specialization. Unlike Pro, that are just one giant compartment."
] |
[
"Why does the half life not correspond with the time you can feel the effects of a drug?"
] |
[
false
] |
Caffeine half life: 6 hours, but you can only feel the effects for about two hours. Although you can feel some physical effects(anxiety, tremors, not able to sleep) you cannot feel the mental effects anymore. Same thing with Benzos, like Valium, with a half life of 200 hours, but you can only feel the effects a couple of hours. What causes this? does your body start to increase neurotransmitters that do the opposite effect of a drug? Also, why are some drugs like alcohol eliminated at a constant rate regardless of the dose(one drink per hour) but almost all other drugs are eliminated according to their half life, which Im assuming means that even with a larger dose, more is eliminated, unlike alcohol.
|
[
"Actually, alcohol is indeed eliminated faster when blood concentration is higher, because of higher concentration of alcohol eliminated in urine/breath and metabolized.",
"But alcohol is eliminated via pseudo-zeroth order kinetics - the rate of elimination is the same for most blood alcohol concentrations. It's only when you get to very low concentrations (far below that achieved by one drink) when you get first-order effects.",
"I highly doubt that the faster clearance of alcohol from drinking in a quick burst would yield a faster return to sobriety because the higher the immediate dose of alcohol to the body the greater the psychological dysfunction ('drunken stupor')...",
"I can't comment on the drunken stupor, but all the BAC vs time curves I've come across all show that bolus ingestion of alcohol is the fastest to be eliminated - and that is what forensic toxicologists use when examining drunk drivers. They give the driver the ",
" - that is, assuming all the drinks are consumed at one go, so the body has the maximum time to eliminate the alcohol. If at the time of infringement the BAC is still above legal limit, it is beyond doubt that given ",
" drinking patterns, the BAC would be above the limit as well."
] |
[
"An extreme example: the case of nicotine's effects on heart rate. A peripheral injection of nicotine is given. It takes a few minutes for most of this nicotine to even get into circulation, let alone be metabolized. The maximal effect of nicotine to stimulate heart rate increase occurs before the peak blood concentration and declines thereafter, disappearing long before it has been metabolized. Why? Many types of nicotinic receptors habituate to the drug, and thus tolerance is acquired in a matter of minutes. The half life of physiological effects can thus be much shorter than the half life of drug concentration in the body. Different body systems habituate to the drug at different speeds, so with nicotine, the metabolic effects revert to normal very quickly while the blood pressure effects are much slower, sometimes because of different receptor mechanisms, other times because of secondary drug effects (imagine if nicotine induces release of adrenal hormones which keep affecting blood pressure for a while, perhaps even longer than the drug's half life). For more information, google scholar search for acute drug tolerance. ",
"Actually, alcohol is indeed eliminated faster when blood concentration is higher, because of higher concentration of alcohol eliminated in urine/breath and metabolized. But 1 hour per drink is still a good rule of thumb for achievement of a sobriety end point. I highly doubt that the faster clearance of alcohol from drinking in a quick burst would yield a faster return to sobriety because the higher the immediate dose of alcohol to the body the greater the psychological dysfunction ('drunken stupor'), which might take more time to recover from than tipsy-ness for other reasons (damage/dysregulation of brain functions that might require sleep to recover from). "
] |
[
"There is a whole mess of processes going on that control response to a drug or compound put into our system. Biological half-life is only one of many factors contributing. ",
"Like you allude to, we have to consider a compound's biological half-life, receptors being up- or downregulated in response and tolerance mechanisms controlled by the cell's response, but also...",
"This stuff is actually pretty well studied (pharmacokinetics) and there is math behind most of it. Other things are directly measured. Rest assured if a drug is being used, this stuff has been well studied for it."
] |
[
"Can someone validate/bust the scientific claims in this post? [X-post r/trees]"
] |
[
false
] |
Here's the link Thanks
|
[
"Mostly true, often oversimplified. 220Kps is only correct for a very specific frame of reference, saying that microbial DNA which you got from your mother ",
" is 'not you' is somewhat facile, 'empty space' as used here is not necessarily a meaningful concept in quantum physics, and the physical phenomenon responsible for a rainbow exists independently of you, you are just responsible for the personal conscious percept which represents it (just like every other perception you ever have).",
"But yeah, mostly fine. However, I don't see how any of this has anything to do with epistemology or judging people."
] |
[
"All true (with some assumed definitions and limits in some cases, but perfectly reasonably assumptions)."
] |
[
"2500 is right, but I think what the 90% microbial DNA statement means is that you do have a lot of eukaryotic 'you' cells, but you also carry a vast amount of bacteria in your gut and on your skin that you rely upon for a great many things, so in that respect the statement is true. "
] |
[
"Why are avocados and kiwis green on the inside?"
] |
[
false
] |
Most fruits are either the same colour on the outside as the inside or a duller, whitish colour on the inside. In my mind I associate green parts of plants with photosynthesis and there isn't any of that going on inside of an avocado
|
[
"I can at least answer the chemistry part of the question. The fact that you are associating the color with compounds related to photosynthesis is spot on. The green color in the skin and the first layers of the flesh comes from chlorophylls and carotenoids. (",
"source",
") For the same reason avocado oil happens to have a ",
"greenish appearance",
". However, I have no idea why these compounds end up in the flesh of the avocado, hopefully a biologist can chime in."
] |
[
"This is something I've always been curious about as well, so you got me to look it up finally. I've always suspected that the chloroplasts in avocado had something to do with the production of the fats that make avocados so delicious. Chloroplasts are involved in of the physiology of plants beyond just photosynthesis. Many non-photosynthetic plants (and algae) continue to have plastid bodies derived from chloroplasts that play roles in lipid and hydrogen metabolism.",
"This paper",
" confirms the suspicion. The authors fractionated avocado flesh into a chloroplast-containing fraction and a mitochondria-containing fraction and found that the isolated chloroplasts were able to synthesize fatty acids from acetate and glucose precursors while the mitochondria and cytosol fractions did not.",
"This paper",
" suggests a reason why the chloroplasts in avocado flesh are green rather than being etiolated plastid bodies, which would still be capable of lipid synthesis, but would not be green. They found that enough light actually penetrates the outer rind and fleshy layers of the avocado to trigger the development of true chloroplasts. Light does not penetrate more than a few mm into the flesh, though, which is why there's a gradient from darker green close to the skin through lighter green to yellow close the seed. There's plastid bodies throughout the flesh, but only the outer ones have developed into true chloroplasts with chlorophyll. I would imagine that the tiny amount of light that comes through is not enough to cause significant photosynthesis, but it's apparently enough to trigger the production of chlorophyll.",
"Pretty cool. This doesn't really help with the kiwi part of your question, though, since they don't have a significant lipid content. It may be a similar explanation, but involving some other metabolic function of chloroplasts. If no one else comes up with an answer, I may try to look into that one tomorrow if I get a chance."
] |
[
"Pigments in avocado tissue and oil.",
"Ashton OB1, Wong M, McGhie TK, Vather R, Wang Y, Requejo-Jackman C, Ramankutty P, Woolf AB.",
"Abstract\nPigments are important contributors to the appearance and healthful properties of both avocado fruits and the oils extracted from these fruits. This study determined carotenoid and chlorophyll pigment concentrations in the skin and three sections of the flesh (outer dark green, middle pale green, and inner yellow flesh-nearest the seed) and anthocyanin concentrations in the skin of Hass avocado during ripening at 20 degrees C. Pigments were extracted from frozen tissue with acetone and measured using high-performance liquid chromatography. Pigments were also measured in the oil extracted from freeze-dried tissue sections by an accelerated solvent extraction system using hexane. Carotenoids and chlorophylls identified in the skin, flesh, and oil were lutein, alpha-carotene, beta-carotene, neoxanthin, violaxanthin, zeaxanthin, antheraxanthin, chlorophylls a and b, and pheophytins a and b with the highest concentrations of all pigments in the skin. Chlorophyllides a and b were identified in the skin and flesh tissues only. As the fruit ripened and softened, the skin changed from green to purple/black, corresponding to changes in skin hue angle, and a concomitant increase in cyanidin 3-O-glucoside and the loss of chlorophyllide a. In flesh tissue, chroma and lightness values decreased with ripening, with no changes in hue angle. The levels of carotenoids and chlorophylls did not change significantly during ripening. As fruit ripened, the total chlorophyll level in the oil from the flesh sections remained constant but declined in the oil extracted from the skin.",
"https://www.ncbi.nlm.nih.gov/pubmed/17177553"
] |
[
"If earthquakes happen along faults why do we define the center as a point (epicenter) instead of a line (epiline?)"
] |
[
false
] |
Is there a point on the fault where the earthquake 'happened more'? I understand how they determine the epicenter if that matters... With the whole find three places that detected the seismic activity and determine how far away it was from each one.(or at least that's how they taught it back in high school)
|
[
"The epicentre is the point above the focus, which is where the fault ",
" to rupture. The rupture itself will travel up and/or down the fault to a certain degree."
] |
[
"I don't think it's that cut and dried. There are many factors to take into account when it comes to earthquake damage - more damage was caused by fire in the 1906 San Francisco earthquake than the quake itself. Other factors like the type of ground have to be taken into account as well."
] |
[
"I must confess ignorance."
] |
[
"Can you get a stroke from breaking your neck?"
] |
[
false
] |
A friend showed me article (which is probably BS) about a guy who had a stroke after breaking his neck that turned him gay. Leaving aside for a minute whether the story is true, is it even possible for a stroke to result from someone breaking their neck?
|
[
"My uninformed opinion is:",
"A stroke is essentially a blood clot in the brain and therefore you could assume that an injury would give a higher chance of blood clotting, so it's plausible.",
"Strokes are known to affect brain function, so if the stroke affected a part of his brain that controlled sexual desire, it perhaps is possible it changed his sexuality.",
"Although it is an article in The Daily Mail, I mean, come on..."
] |
[
"I can provide a pretty good rationalization of what PROBABLY took place here. This person most likely had a some sort of pretty significant trauma that cause him to break his neck, or as they call it in emergency medicine Mechanism of Injury. Given the the mechanism was significant enough to cause a broken neck, he most likely had a significant enough injury where a stroke would be a good possibility as a result of head trauma. ",
"There are two types of strokes. One is cause by a blood clot and the other is caused by a burst vessel. Most likely a vessel was burst in his brain. ",
"Picture if you punched a concrete wall as hard as you could and broke you hand. Most likely the surrounding area will be bruised, not necessarily because your hand is broke but because of the impact. This in analagous to the bleeding that could take place in the brain as a result of an impact, that could ALSO cause a broken neck. "
] |
[
"http://www.bupa.co.uk/individuals/health-information/directory/i/ischaemic-stroke",
"There is a kind of stroke than can happen if damage occurs to those large arteries in the neck because the brain won't get enough blood. Perhaps a broken neck could involve such damage. ",
"The injury might also be associated with other brain trauma of course."
] |
[
"When a Li-ion battery is first manufactured, is it already charged? If so, how much and why that amount?"
] |
[
false
] |
[deleted]
|
[
"It actually depends on the chemical composition of cathode and anode during production of the battery (the plus and minus of the battery). I don't know what is common practice in Industry. Discharging / charging is nothing more than moving Lithium from the cathode to the anode or back by a chemical reaction.",
"After testing, manufacturers usually ship batteries at about 40% battery, at this percentage the battery shows the least degradation. This can be lower when you recieve the product with the battery due to self-discharge."
] |
[
"IIRC the batteries are actually charged/discharged in the factory for quality control - different manufacturers, capacities, testing practices result in varying degrees of remaining charge. Since these batteries are actually extremely efficient, they do not discharge much while in the packaging, hence a phone with some varying degree of battery life out of the box.",
"Tip: no, you don’t need to fully charge and discharge your new phones battery the first time using it."
] |
[
"The main reason that this used to be suggested, and not so much anymore, was due to how Nickel-Cadmium (and other Nickel based) batteries worked. If you partially charged or discharged them it would significantly decrease the life-span of the battery through the 'memory effect.' Lithium-Ion batteries don't suffer from this problem AFAIK, and if they do it is extremely insignificant compared to Nickel batteries."
] |
[
"What is the maximum temperature you can achieve simply by focusing sunlight using mirrors and lenses?"
] |
[
false
] |
My friend claims that since the temperature of the Sun's surface is around 6000 degrees Celsius, then that is also the maximum temperature you can conceivably achieve on Earth by focusing the Sun's energy on a single spot, using any number of mirrors and lenses of any kind. This seems wrong to me. Surely the temperature of the Sun is irrelevant, right? P.S: We've got a beer riding on this.
|
[
"I'm just going to leave ",
"this",
" here."
] |
[
"Your friend is correct. To heat an object more than 6000 C means you are using a cooler object to heat up a hotter one. It's a direct violation of the 2nd law of thermodynamics."
] |
[
"There is an extremely fundamental problem with most of the arguments saying it is easy to surpass 6000 K, and it's ",
" just that they violate the Second Law of Thermodynamics. (Reminder: Clausius's formulation of the Second Law is \"No process is possible whose sole result is the transfer of heat from a body of lower temperature to a body of higher temperature.\")",
"The temperature of an object is ",
" by how hot it can make other things.",
"I'll let that sink in for a minute.",
"It's not actually got anything to do with the internal energy of the stuff in question (in some sense, though if you take a statistical mechanics course you'll learn how they are related). One of the main reasons temperature is a useful quantity to talk about is precisely that it lets you make statements like this."
] |
[
"Why did the Earth originally have a super-continent, Pangea?"
] |
[
false
] |
So I get that there was a single giant landmass that spread apart due to tectonic activity, but WHY was it a single landmass to begin with? Is there a force that makes this happen or could it just as likely have begun with multiple continents from the get-go?
|
[
"Pangea was only the latest of a series of supercontinents that have been forming every few hundred million years for the last few billion years. We still don't totally understand some of the cyclical processes that form these supercontinents, but the short version is that ocean basins tend to keep spreading and continents tend to stick once they hit each other, so eventually they'll all clump together in one big landmass. Once they do, they'll tend to trap heat under them until a plume of magma bursts up through the crust and splits them apart."
] |
[
"This is called the Wilson Super Cycle and it happens every 200 million years or so. No one really knows why this happens though.",
"As a fun factoid, plate tectonics has only been an accepted scientific theory for less than a hundred years, so they haven't been working on it long."
] |
[
"A quick Google search tells me that pangea was formed by older continents and land masses joining together.",
"So pangea wasn't the original continent.",
"It is believed that several mega continents have formed and broken apart during earth's history with Pangea being the most recent. "
] |
[
"How dangerous are the Chinese fake eggs?"
] |
[
false
] |
For those who don't know what I'm talking about, . Out of curiosity, how dangerous would it be to eat those? (I heard it could lead to dementia but without much scientific explanation) The real reason behind this question: I have this great idea for a prank - and it involves making a fake egg and then replacing the yolk with a fake eye. When people crack it open, BOOM! an eye in an egg. I have absolutely no intention of feeding these to anyone. So, in light of that, here's a couple follow up questions: Anyone knows what chemicals they use and whether or not they easy to get legally and safe to handle? Other than the previous question, is there any reason not to do this. EDIT: Fixed link format
|
[
"This could be relevant:\n",
"http://www.hoax-slayer.com/fake-eggs-china.shtml"
] |
[
"Just an FYI, you've got your reddit linking backwards. You typed:",
"[http://www.youtube.com/watch?v=0US7JEfhsrA](check this out)\n",
"when what you should type to get your desired effect is",
"[check this out](http://www.youtube.com/watch?v=0US7JEfhsrA)\n",
"which yields",
"check this out"
] |
[
"Well, the ",
"recipe here",
" lists the following items as ingredients: Sodium Alginate, Gelatin, Baifan, Sodium Benzoate, Lactone, Carboxymethyl Cellulose, Calcium Carbide, Lysine, Food Coloring, Calcium Chloride--this is for the white and yolk.",
"The shell is made of paraffin wax and Gypsum powder.",
"Almost all of those compounds are actually used in foods as stabilizers or preservatives--the one exception is \"Baifan\" which apparently is a Chinese term for ",
"Alum",
". Alum contains aluminum, and aluminum has been linked to dementia and Alzheimers. However, Alum has a variety of cosmetic and medicinal uses, and it's not inherently toxic on its own.",
"Most of those compounds are readily available without legal issues. Finding the right lactone might be an issue, and you could probably do this \"synthesis\" without using it. I would search for food additives and such to find what you're looking for--I know offhand that Sodium Alginate and Calcium Chloride are currently used in molecular gastronomy as part of making different flavored gels.",
"And as for not doing it... well, I wouldn't recommend eating this, and it might be a bit work-intensive as you have to make molds and such, but all in all it might be pretty damn funny."
] |
[
"If we could look far enough into the universe, will light be red-shifted to the point of having an infinitely long wavelength?"
] |
[
false
] |
Supposedly if we move far enough away from something, the expansion of the universe means that even if we travel at the speed of light we can never reach that thing again. So does that mean the light on the cosmic horizon would be red-shifted to be an infinitely long wavelength?
|
[
"The highest redshift photons we can observe are those from the cosmic microwave background. Higher redshift photons cannot be observed because before the last scattering event -- when the CMB photons were able to freely propagate -- the universe was \"opaque\" to photons, i.e. photons were not able to travel without scattering. There were no stars and galaxies to emit photons, so we can't observe light from those objects with a redshift greater than the CMB.",
"However, in principle, as the universe ages, objects which cross the cosmic horizon will appear to us to emit light which is asymptotically approaching z=infinity. Rather than disappearing, they will become dimmer and dimmer, not unlike infalling observers for a Schwarzschild black hole."
] |
[
"I have a terrible problem with making things accessible, so if I fail miserably, feel free to let me know.",
"The CMB is different from stars and galaxies. Whereas stars and galaxies are essentially \"point source\" objects that emit light from a particular part of space, the CMB is ",
" in space. This means that CMB photons are crossing ",
" cosmic horizon all the time, and they have been since the CMB formed. However, there are CMB photons inside the cosmic horizon as well. Some will cross the cosmic horizon, while others will eventually reach us. Those photons that reach us will gradually redshift as the universe expands until they become undetectable."
] |
[
"are we saying that at any one moment in time, the CMB we see IS the current cosmic horizon",
"It's wrong to call the CMB the cosmic horizon. They're two different things. The CMB is isotropic radiation; it's everywhere in space. The cosmic horizon is a horizon associated with objects which have ever been in causal contact with an observer.",
"as time goes by, this horizon is moving back, and the CMB is red-shifting as this process happens due to the universal expansion?",
"It's true that the horizon is evolving, but it's more complicated than you might imagine. Eventually the horizon will reach a finite maximum comoving volume (though an infinite proper volume), and we'll never see anything beyond it. But those are details that aren't necessarily related specifically to the CMB and the cosmic horizon.",
"My point was that the CMB is everywhere, coming at us from all directions. There are CMB photons at our cosmic horizon which we will never see. There are also CMB photons inside our cosmic horizon which will move outside of our cosmic horizon; we'll never see them either. The CMB photons we will see are sufficiently close to us that they'll overcome the expansion of space and eventually reach us. However, as the universe expands, these observable photons -- that is, the photons that will reach us -- will become redshifted until they become undetectable.",
"I hope I didn't overcomplicate things. Let me know if this helps."
] |
[
"A sincere request"
] |
[
false
] | null |
[
"Thanks for the feedback! I agree that this is a problem, especially with our status as a default subreddit. We'll be addressing this in our next meta-post. I've removed this one, because we try to limit the number of meta-posts (posts about AskScience itself)."
] |
[
"Unfortunately this thread was deleted before I got here - I have a feeling this has to do with his objection with my involvement in multiple threads today. He repeatedly questioned my science, even going through my comment history to drop his own comment replies, culminating in ",
"this gem here",
".",
"I'd like to see what he had to say here in this thread before it was removed. I mean, if it's constructive criticism, sure, I'll listen - especially if I've been wrong."
] |
[
"Here's the text",
"Please please stick to your own area of expertise while answering questions or at best, areas where you are a 101% confident you won't slip-up. People come here to genuinely clear up their doubts, and it doesn't help giving them patently false answers."
] |
[
"is space-time discrete?"
] |
[
false
] |
This based on my understanding of the Planck second as the required for a change in the position of a photon. does this also mean there is minimum distance traveled per Planck second? Does this not mean space time is discrete and not continuous?
|
[
"The answer is we don't know. All theories that deal with this are in the super spectulative realm. Quantum loop gravity, for instance, deals explicitly with discrete space-times but we have no strong tests of this in the foreseeable future (for what can be done, see the reply comments). Historically, discrete space-time is one of the ways physics has hoped to unite relativity and quantum mechanics but as yet all theories aiming to do this have no real scientific standing."
] |
[
"This paper",
" discusses a few possible schemes by which one might test whether or not spacetime is discrete. Note that this is written for experts, but I thought I would mention it here just so that everyone is aware that there are some ideas out there of how this could be tested in the not so distant future."
] |
[
"Okay worth clarifying here: there are no ways (in the near future) of testing discreteness in a way that discreteness could fail. If such an experiment failed to find discreteness it will only tell us that, if space-time is discrete, it is discrete at smaller scales than we have measured. So it's a nice link but my point stands, unless we get lucky and find discreteness then we get only neutral results from these experiments."
] |
[
"Would it be possible to oxidise Gold using Chlorine Trifluoride ?"
] |
[
false
] |
Just asking, to be honest. I'm not really a chemistry guy but things that go ''Boom'' are always interesting, and Chlorine Trifluoride being a super-dangerous chemical that can set fire to Asbestos, would it be possible to oxidise Gold using it ? Ib haven't found a single article, paper or anything on the matter. I'd really like to see if Gold could potientially oxidise. Thanks !
|
[
"No, it's a verb used to say an atom \"lost\" or gave his electrons to another atom. "
] |
[
"I don't know about chlorine trifluoride in particular, but for your general question: yes, gold can be oxidised. You can \"dissolve\" (it's not really dissolving but reacting) gold in ",
"aqua regia",
" (\"royal water\"), where it forms [AuCl",
"]",
". Here gold has a formal +3 charge. Funnily enough aqua regia does nothing to silver and some other metals. Just goes to show how particular these reactions can be.",
"Apparently gold also reacts with elemental fluorine to form AuF",
", again with gold (III)."
] |
[
"The term \"oxidation\" is mostly an archaic term from the now proven false assumption that such reactions would require oxygen. We eventually discovered the underlying mechanics though, but we didn't update the terminology."
] |
[
"Are there any planets that an average human, theoretically, could lift on Earth?"
] |
[
false
] | null |
[
"No. Objects that small are not classified as planets"
] |
[
"By small you mean small in mass right? So even a planet made up of pure gas, it would be too heavy (with respect to gravity on Earth)?"
] |
[
"See ",
"here"
] |
[
"Do antibodies get constantly gobbled up by the immune system or does it only get gobbled it up if it binds to something? if so why."
] |
[
false
] | null |
[
"Okay so there are many kind of antibodies - IgG, IgM, IgA and IgE. ",
"IgA are only functional outside of the body (in your intestines and in your respiratory tract). IgE are only functional once bound to a very specific type of cell - they cause allergies. IgG and IgM, on the other hand, have many purposes. Which…are complicated. You have something floating around in your blood called complement. When Complement lands on something, it tells your immune system to kill whatever it lands on. So your body only wants complement to land on diseases. One of the ways it gets it to do this is by haveing antibodies (IgG and IgM antibodies) make complement settle onto diseases. In this case it isn’t really gobbled up - it makes proteins form that literally punch holes in pathogens (and ramp up your immune system so any survivors can get gobbled up).",
"The other thing it can do it make you immune cells gobble up whatever it binds too so it can kinda do both!"
] |
[
"Interesting thank you"
] |
[
"Antibodies are made by the immune system, specifically B-cells. They are used as targeting proteins so that your body can respond to diseases/pathogens. If they are expressed on the surface of the B-cell, then when they find and bind to something 'foreign', they can then cause the B-cell to proliferate (divide and multiply), meaning that your body can fight off the disease. They can also be secreted from other types of B-cells (plasma cells) which flat around to monitor your body, and then bind to foreign pathogens and act as a flag/beacon for other immune cells to come and investigate and attack (T-cells/NK cells). ",
"In terms of what happens when they're not needed, the cell surface expressed antibodies will stay around as long as the individual cell lives (the cell probably recycles and makes more to put on the surface over it's lifespan) and the secreted antibodies will degrade over time or be processed and degraded by other immune cells. The plasma cells will tick over and are there to make more if the disease invades again."
] |
[
"How high (or at what speed) would a person have to fall from to \"burn up\" in the atmosphere?"
] |
[
false
] |
Got into a bar argument and the person was of the opinion that the shuttle only gets hot because it comes in at an angle and that a person could never free fall to the earth at a high enough rate of speed to burn up.
|
[
"The \"burning\" (not really burning at all) is indeed completely due to the speed at which the shuttle enters the atmosphere. Angle isn't really the reason, it's just that the shuttle is going really fast while in orbit and the easiest way to get it back is to alter the angle just slightly which results in it coming down at a shallow angle and very fast.",
"But a person could definitely free fall fast enough to go even faster than the shuttle re-enters the atmosphere, they just need to fall from a pretty extreme height. I don't know what speed exactly you'd need to get for it to qualify as \"burning\" but if you fall from the altitude of about 5000 km, you'll enter the atmosphere at roughly the same speed as the shuttle did."
] |
[
"I don't have the know-how to do the maths, however I think that you could work it out using the resources linked in ",
"this \"xkcd what-if\" entry",
". "
] |
[
"This is a very loaded question...",
"The \"burn up\" is a result of speed, obviously. But height is not the most significant factor here. The important factor is speed relative to the terminal velocity. For example:",
"One problem with sustained supersonic flight is the generation of heat in flight. At high speeds aerodynamic heating can occur, so an aircraft must be designed to operate and function under very high temperatures. Duralumin, the traditional aircraft material, starts to lose strength and go into plastic deformation at relatively low temperatures, and is unsuitable for continuous use at speeds above Mach 2.2 to 2.4. Materials such as titanium and stainless steel allow operations at much higher temperatures. For example, the SR-71 Blackbird jet could fly continuously at Mach 3.1 while some parts were above 315°C (600°F).",
"So to ask how high a person much jump from, you must first ask how they got to that height. If they are orbiting, then that is a much more significant factor than the height. If they are geostationary, then you simply need to integrate the expression for gravitational acceleration in order to find the height at which they will be going about Mach 2-3 when they hit the atmosphere (which is a good approximation). But they would have to start outside the atmosphere, I would think."
] |
[
"would the mass of a helium balloon be positive or negative and is there such a negative mass"
] |
[
false
] |
[deleted]
|
[
"The mass of a helium balloon is positive. The weight is negative. There might be such a thing as negative mass, but we haven't encountered such a thing yet."
] |
[
"That depends on your definition of weight. I though about adding a disclaimer for this, but decided not to. Pitty.",
"Anyway, you know how you are \"weightless\" in water? Or a sub is \"weightless\"? That's the definition I used - i.e. taking into account the buoyancy. My weight is how much force I exert on things that keep me in place (or alternatively, how much force needs to be applied on me to keep me in place).",
"Whether or not you count the \"air\" is a matter of definition. Most people don't - and by that definition the helium balloon has a negative weight.",
"Yes, I know wikipedia uses your definition, but it also gives something called \"apparent weight\" which is my definition. You just use the one that's most appropriate - I think that in this case, mine is."
] |
[
"That depends on your definition of weight. I though about adding a disclaimer for this, but decided not to. Pitty.",
"Anyway, you know how you are \"weightless\" in water? Or a sub is \"weightless\"? That's the definition I used - i.e. taking into account the buoyancy. My weight is how much force I exert on things that keep me in place (or alternatively, how much force needs to be applied on me to keep me in place).",
"Whether or not you count the \"air\" is a matter of definition. Most people don't - and by that definition the helium balloon has a negative weight.",
"Yes, I know wikipedia uses your definition, but it also gives something called \"apparent weight\" which is my definition. You just use the one that's most appropriate - I think that in this case, mine is."
] |
[
"How long do landmines remain active?"
] |
[
false
] |
How long does it take for the explosives to become inert? Does the process by which the mines become unable to explode speed or slow depending on climate and soil composition?
|
[
"According to the wikipedia article for ",
"Anti-personnel mines",
" the most common primer/detonator charge used is an explosive called ",
"RDX",
" which seems to be able to maintain its capacity to explode for a very long time (extremely stable). ",
"Commonly used things for main charge seem to be TNT, Composition B, and a form of treated RDX. The US used Tetryl as its main charge. I can't find anything about how long they last, but it seems that they all pose some sort of toxicity to soil and climate depending on the environment they're in. If they're in a landmine though, it's probably sealed, so there isn't any leakage. ",
"So you'd probably have to wait for the fuze/detonator to stop functioning. Most mines use Lead Azide in this, but when protected from humidity, it's completely stable, so it wouldn't set off secondary explosives. ",
"So you'd have to wait for the spring in the detonator to degrade. Yeah....",
"Landmines stay around a loooooong time. There's a reason they were made illegal. You know, besides the immediate civilian casualties. "
] |
[
"Depends on when and who manufactured it. Many of them now have features where they will self destruct after a preset time. Many are now made of plastic and are extremely difficult to detect - even by those who laid them. Not much point in denying the enemy use of territory if you can't use it yourself. Older mines are often active for decades after being laid. The explosive is very stable, the detonation mechanism not so much."
] |
[
"Every now and then here in Virginia they find ordinance from the Civil War that is still dangerous, although landmines weren't really invented yet."
] |
[
"What size would an object orbiting the Moon need to be to be visible with the naked eye from Earth?"
] |
[
false
] |
I'd assume it would be a range of sizes depending on what it was made from, man-made or naturally occurring, and how reflective it was but what that range is, I'm curious to know and can't math well enough to figure out. I've always kind of wished there was a little twinkle in the sky you could literally see travelling round and round old Luna.
|
[
"The apparent magnitude of the full moon is −12.74. An apparent magnitude of 6.5 seems to be about the minimum visible. This means that the moon is about 305 times brighter than a magnitude 6.5 object. The object would have to have a linear size about 17.5 times smaller, which comes out to a radius of about 100 km.",
"The moon has an albedo of about 0.12. By making the object perfectly white, we could shrink it to a minimum size of 34.5 km radius.",
"If you want to see the twinkle travelling around the moon, that implies you have to be able to see the moon, so it can't just be visible during a new moon. I don't know how much bigger it would need to be, but it would be significant.",
"Edit: I messed up a sign. Let's try this again.",
"The moon is 45628445 times brighter than a magnitude 6.5 object. The magnitude 6.5 object would need a 90 meter radius if it's perfectly white. Also, if it's a new moon you won't be able to see the object either. It would only be visible during a lunar eclipse, and even then the moon would probably be too bright.",
"A glowing object would need about 46 megawatts to be visible during a new moon."
] |
[
"Now let's say the thing emitted light could you have a very powerful yet very small light be seen from far away. Basically even if a light is small is being bright enough to be noticed by our wyes"
] |
[
"Could it be smaller if the object was perfectly black? We'd only see it over the surface but we'd see it blocking the moon's light. "
] |
[
"Is Water wet? If so, why?"
] |
[
false
] | null |
[
"Hi unoriginalgarbage 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 ",
"/r/AskScience",
", 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.",
" ",
" "
] |
[
"Chemistry"
] |
[
"Planetary Sci"
] |
[
"I can't seem to find an answer that makes sense: Can matter/energy come from nowhere after universal heat death?"
] |
[
false
] |
I keep hearing that Quantum Theory allows for quantum objects to appear out of nowhere and, just as easily, disappear. I also know that this causes vacuum fluctuation. Now, my question is: Is there a chance (may it be ever-so-slight) for vacuum fluctuation to actually create an amount of mass that doesn't disappear? Basically, quantum objects appearing out of thin nothing and staying? the idea is that after universal heat death (if it occurs, it might not in an "open" universe), there would be an infinite amount of time for such impropable stuff to happen, therefore, time would lose its meaning and if one electron or quark can appear, then, at some point, they might just appear in a way to form a solar system or an Andy Warhol picture. In any normal time frame, that would be nonsense, but if your time frame is infinite... Basically, can it happen?
|
[
"virtual particles don't \"appear out of nowhere\" though that is the popular presentation of them. What really happens is that ",
" particles move ",
" they spontaneously decay and interact with all sorts of other particles between measurements. But those particles never \"really\" come into existence in a meaningful sense."
] |
[
"no, there will be particles moving about, but there won't be any way of extracting additional energy from them. They can't be used to perform work, and the system will be in the highest entropy state."
] |
[
"not in the sense you're talking about. The big bang is an allowable exception."
] |
[
"Is there any animal that doesn't get startled?"
] |
[
false
] | null |
[
"That depends on how you define \"started\". It's not really a scientific or specific term. I'm going to define it as a sudden, short-term, and quickly reversed movement to a stimuli such as light or touch.",
"You will never startle a sponge. Other animals that may not react much or very quickly to a non-harmful stimuli include shell fish, star fish, sea slugs, sea anemones, and chitons. Animals whose best defense is camoflage may not \"jump\", but may stay still or move away slowly, like stick bugs."
] |
[
"For the sake of the question, I'll define startled as a retreat from something out of fear. Things like like sponges obviously can't however, Im wondering if there is an animal that doesn't retreat or hide."
] |
[
"Than I'll repeat my answer.",
"Sponges are animals that are incapable of retreat.\nSea anemones react when touched but are incapable of retreat, as are many shellfish like muscles and giant clams.",
"Slow animals like sea slugs and star fish also will not rely on retreat as a defense as their retreat is typically too slow to do much good."
] |
[
"Do spiders ever steal another spider's web?"
] |
[
false
] |
I just rescued a spider from my bath and blew it out the window and it happened to land next to another spider's web, which caused me to wonder if it might overpower the spider that actually made the web and use the web for itself.
|
[
"Most spiders are territorial, although ",
"social species exist where multiple spiders share a web",
". Some spiders intentionally ",
"steal prey from other spiders' webs",
"--some even ",
"eat the webs themselves",
". Anecdotally, I see spiders (cellar spiders) using pre-existing webs all the time--trying to find sources to back that up, I'll update if I can find anything. Probably depends on the species, I don't know if web stealing/recycling is a universal trait."
] |
[
"The Argyrodes takes over other spider's webs and steals their food",
"This study found that some species of spiders will eat others' webs themselves if there is a low food supply",
"This Wikipedia article says that some spider families will take food from another's web, but it has no verifiable sources."
] |
[
"Your link to kleptoparasitism is a good one.\nThe dewdrop spider is another example I know of. Though they have the ability to spin their own web, they will often live in the webs of other host spiders and steal their prey. ",
"http://www.americanarachnology.org/joa_free/joa_v33_n1/arac-033-01-0001.pdf"
] |
[
"What is the data on medical marijuana messing with REM sleep?"
] |
[
false
] |
I saw a bunch of studies and assertions that it ruins REM sleep. But I also saw stuff that says it's a miracle for sleep and anxiety and nightmares. These things don't seem to coalesce into one pattern; if it helps with anxiety, then it can't also not let you get real rest, becuase over time you would get worse anxiety from not being able to sleep. Bad sleep=more anxiety. Ditto nightmares, if you can't get real rest, then you get more nightmares. So what's going on? Is the data conflicting, does it matter who's being studied and why they're taking the drug, does it matter what particular type of thing they're taking, what ingestion method?
|
[
"I can't answer all of it, but one of the main reasons cannabis is looked at as a possible treatment for things like PTSD/nightmares/night terrors/REM sleep behavior disorders is specifically ",
" it inhibits REM sleep - no REM sleep means no nightmares/acting out dreams in real life/etc. It's not that the data is conflicted there, but instead that these studies haven't been looking at cannabis as the solution in the same way you think they are (improving sleep to reduce nightmares) and instead are taking a different route that takes advantage of a normal effect of cannabis (using it to suppress REM sleep and dreaming altogether to reduce nightmares) with the side-effect of somewhat lower-quality sleep."
] |
[
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7388834/",
"A survey of available data regarding sleep and cannabinoids shows pretty much what you've said:",
"\"While indeed several studies indicate chronic exposure to THC and other CB1-activating compounds appears to produce modest sleep improvement, the quality of these current data were judged to be low in a recent Cochrane-based metanalysis (Mucke et al., 2018)\"",
"It's doing something and we need to collect more data to figure out exactly what and how. ",
"Notably, REM sleep suppression as a treatment for PTSD related night terrors/sleep disturbance is mentioned."
] |
[
"Haven't had dreams in about a decade and i prefer it that way. I use cannabis for sleep, and it has improved my condition. The dreams i saw made me really depressed in real life, not having them has stopped me of thinking just the past, now i rarely do that anymore and it is more controlled, less emotional and upsetting."
] |
[
"Why can't you smell a burning candle wick?"
] |
[
false
] |
Why is it you can smell the smoke from burning wood and charcoal as it burns, but the smoke smell from a candle wick only appears after it's flame has been put out? Is it the mass of the fuel? The size of the flame?
|
[
"When a candle is burning cleanly, melted wax is brought sucked into the wick, where the heat of the flame vaporizes it, and it then burns when mixed with the surrounding oxygen. A little bit of the wick burns, but only if the wick becomes too tall for the flow of liquid wax to reach it.",
"When you blow out the flame, you're left with a hot wick, and hot wax. It's still hot enough to emit many of the same gases it was when burning, but now there's no flame to burn them cleanly, and its actually emitting different gases and particles than it does while burning."
] |
[
"Good enough for me!"
] |
[
"This is anecdotal but I can smell candles usually."
] |
[
"How is HF so corrosive?"
] |
[
false
] |
[deleted]
|
[
"It's a good example of why \"weak\" and \"strong\" don't tell you all you need to know about an acid. It's true that hydrofluoric acid doesn't totally dissociate into H+ and F-, and is therefore a \"weak\" acid. \"Strong\" acids need a stable conjugate base for equilibrium to favor dissociation, and fluoride (F-) is incredibly electronegative and unstable. For the same reason, however, once you manage to liberate a fluoride ion, that bad boy will react with next to anything.",
"As a life tip, though, KOH and NaOH (lye) are more widely available for dissolving roadkill, and by extension, recently-deceased drug dealers. It's actually been done as an alternative to cremation that doesn't cause air pollution."
] |
[
"Electron affinity is important, but isn't the whole story, as the electron affinity of fluorine is approximately that of bromine and iodine. The H-F bond enthalpy is also much higher than that of the other halogens, and H-F also forms very strong hydrogen bonds (as well as ",
"bifluoride ions",
") with itself, which stabilizes the non-dissociated state."
] |
[
"Electron affinity is important, but isn't the whole story, as the electron affinity of fluorine is approximately that of bromine and iodine. The H-F bond enthalpy is also much higher than that of the other halogens, and H-F also forms very strong hydrogen bonds (as well as ",
"bifluoride ions",
") with itself, which stabilizes the non-dissociated state."
] |
[
"Is the human genome identical in all of us, and individual differences solely due to epigenetics?"
] |
[
false
] | null |
[
"When the human genome was originally mapped it was one version of the genome and did not account for variation. At the time it would have been too expensive and taken too long to sequence more than one human genome. Now that it's much cheaper and faster, variation is being identified by projects like the ",
"1000 Genomes Project",
".",
"There is not an infinite ways to code for a gene because a gene has finite length and there are only so many permutations available (also many or most of those permutations won't make a functional protein and will be selected against).",
"The only way to complete all variations of the genome will be to sequence the genome of every single person because new changes are still happening. By strategically sequencing from diverse groups of people we can identify the vast majority of variation. This is what the 1000 Genomes Project is doing."
] |
[
"If only one version of the genome was mapped, did it come from one person?",
"http://en.wikipedia.org/wiki/Human_Genome_Project#Genome_donors",
"Does this mean that if given enough time (say tens of millions of years) humans will start to repeat genomes that have been present in other humans before",
"Unlikely, we'll probably evolve before that happens, ie. some genes will disappear and new ones will form, and we may not even technically be ",
" anymore."
] |
[
"The genome between all individuals differs to various extents (except in the case of identical twins). While we share the same general layout in terms of what genes we have, and where they go (a generalization, as people can be born with genetic abnormalities such as ",
"Turner syndrome",
", ",
"Down syndrome",
", etc...), we differ in the exact nucleotide makeup of each gene. Different versions of the same gene are known as ",
"alleles",
".",
"Our genetic diversity is further increased because we are ",
"diploid",
" organisms, meaning we have two copies of each ",
"chromosome",
". Because half of our chromosomes come from our mother, and half from our father, you have a good chance of inheriting different alleles on each chromosome (ie. different versions of the same gene on each chromosome). It's also possible that you could inherit the same allele. The difference (or lack thereof) between alleles on each chromosome is known as ",
"zygosity",
", where homozygous = same alleles, and heterozygous = different alleles.",
"So, while epigenetics can certainly play a role in determining ",
"phenotypic",
" differences between individuals, differences between our actual nucleotide sequences are also very important."
] |
[
"Why did NASA send Rovers (spirit, curiosity, Opportunity) to Mars but destroy Cassini?"
] |
[
false
] |
[deleted]
|
[
"The environments of Mars vs Titan/Enceladus are very different in conditions and composition. The highest classification of planetary protection goes to areas that contain liquid water or ice decided by the Committee on Space Research (COSPAR)",
"[1]",
".. As a result, any mission going to these areas or looking at life detection must be sterilised to the highest degree to reduce chance of contamination of the area and of the samples. Also, just to be clear, when scientists talk about habitability they are talking about microbes and finding extraterrestrial life and not about human habitability. So planetary protection is about making sure we don't contaminate planets with Earth life so when we go to do life detection experiments in the future we can be 100% certain that if we find life, it does not originate from Earth.",
"On Mars we know the surface is a very hostile environment (its dry and blasted by UV radiation). If the rovers were contaminated then the contamination would be very localised, and likely destroyed by UV radiation ",
"[2]",
". Mars missions are also classified based on their purpose and the areas they explore and missions to those areas have the highest standards of cleanliness to make sure the area and scientific samples are not contaminated ",
"[1]",
".",
"The Cassini-Huygens mission was not expecting to find the Saturn system to be as habitable as it is, so COSPAR classifications of Enceladus and Titan were only upgraded as a result of the mission ",
"[3]",
". On Enceladus its covered in ice and potentially has liquid water beneath the surface. This means if Cassini were to accidentally land and contaminate the surface the availability of liquid water makes it a fairly habitable place. Liquid water could also transport microbes, and the potential liquid water ocean that exists below could become contaminated. We also understand the surface of Enceladus much less than Mars so its better to be safe than sorry in this case.",
"The mission team also had to take into account the best method of retiring Cassini, taking into account: science objectives, left over fuel, timescales etc. So crashing into Saturn was the best option as it didn't require much fuel, could be done quickly, didnt contaminate the icy moons, and also allowed them to get vital data on the upper atmosphere ",
"[4]",
",",
"[5]",
".",
"TLDR: Enceladus is covered in water ice, that makes it potentially more habitable than the surface of mars."
] |
[
"I think they did it to make certain any life on the craft did not contaminate a place that possibly has life on/in it. ",
"They have the planetary protection policies in place for this. Each surface that spores can get into the atmosphere has to be under 300,000 bacterial spores. At least for the rovers. There are filters for the hardware inside that are designed to keep whatever spores are in there, secure.",
"Now I can't for certain claim this but, with Cassini I think there is more of a chance of life on the moons, as opposed to Mars. Curiosity has the technology to test for bacteria against itself anytime. They sent 3 empty clean sealed containers to calibrate the sensors, and see if the life came from it or is foreign. ",
"With Cassini I think the thing is we don't have the ability to test right now, so if spores leaked and got on the moons, there would be no way of figuring out if it was natural or from us when we do end up being able to test there."
] |
[
"It was destroyed at the end of its lifespan, there was a limited amount of further exploration it could do. And its final Saturn-grazing orbit allowed it to make some observations it would not have otherwise been able to make."
] |
[
"Trig Expression Confusion"
] |
[
false
] | null |
[
"You have a right triangle. You know the hypotenuse and one angle. How do you find the lengths of the two legs? Using the rules for cosine and sine:",
"cos(θ) = (adjacent length) / (hypotenuse length)",
"sin(θ) = (opposite length) / (hypotenuse length)",
"So if you want to find the length of the side adjacent to your angle, you use",
"(adjacent length) = (hypotenuse length) * cos(θ)",
"while for the side opposite your angle you use",
"(opposite length) = (hypotenuse length) * sin(θ)",
"Here's a picture",
".",
"So now, you have this force pointing in some direction, and you want to decompose it into a horizontal and vertical components. If you know the magnitude of the force and the angle it makes with the horizontal (or vertical) axis, you can use those rules to find the horizontal and vertical bits."
] |
[
"Thank you! Great explanation, never realised it was that simple!"
] |
[
"If you are on a sloped surface, gravity doesn't point directly normal to the surface. Some portion is directed normal to the surface, while some portion is directed along the surface (hence why a ball on an inclined plane will accelerate down the plane, it is being acted on by the portion of gravity projecting along the sloped surface). In the diagram you are providing, gravity is represented by an arrow pointing straight down, at an angle (theta) with the sloped surface. If the surface had a slope of zero, the component of gravity normal to the surface would be 100% of the gravity while the component along the surface would be 0%; conversely if the slope were entirely vertical gravity would project 100% along the surface and 0% normal to it. For anything in-between, the portion projecting along the surface is sin(theta), and the portion projecting normal to the surface is cos(theta). Hopefully you can work out the rest of the example yourself."
] |
[
"[meta] Can we add a simple new rule to the subreddit? (\"Do a quick search on Google first to see that the answer isn't readily apparent\")"
] |
[
false
] | null |
[
"We (the moderators) don't allow meta posts unless we're the ones to post them (yeah, we have control issues like that). That said, what you're proposing isn't a ",
" rule, it's ",
"always been part of our guidelines.",
" Feel free to ",
"message the mods",
" if you have suggestions on how we could better encourage people to google questions first. All the best!"
] |
[
"Oh, sorry about that, I had no idea. On either point, actually. Well, I willcertainly delete this thread, but I would like to suggest that you move that part of the guidelines to a place that will be more visible (i.e. the sidebar, and perhaps on the submission page)."
] |
[
"I would recommend you not delete the thread. I already removed it and deleting things brings you to the attention of the spam filter. ",
"I thought we already had it on the sidebar, but apparently I was wrong. I'll let our CSS experts know to add that in, and see if we can't add something to the submission page. Thanks for the heads up!"
] |
[
"How close can someone get to being a natural clone of their mother or father?"
] |
[
false
] |
I've read that when genes mix, they shuffle like playing cards rather than get mixed like paint. In theory, you should get 50% of your father's genes and 50% of your mother's genes. Being that there are 7 billion people in this world, there must be some people who have a majority of their genes from one parent. Using statistical analysis, what is the maximum % that someone has of their mother or father's genes, considering there are 7 billion combinations? Sorry if this question makes no sense - I'm trying to explain it as best I. Here's where I'm getting at: If you roll dice 7 billion times, there are going to be instances where you roll several sixes in a row. Perhaps there will be times when you roll 20 sixes in a row. When you have 7 billion tries, you can get some weird results. So I'm wondering if there is someone out there who is like 80% clone of their mother or father. See where I'm getting at?
|
[
"What? This isn't probabilistic. You get half of your genes from your mom. You get half your genes from your dad (well, unless your a guy, and then you get slightly less than half from your dad). It's not like on average, a person gets 50% from mom and 50% from dad, but some people get 40% from mom and others get 60%.",
"I suppose the closest you can get naturally is if your mother and father were siblings. In which case you would something like 75% your mother and 75% father (siblings share 50% of the same alleles)."
] |
[
"It still will be 50% mom and 50% dad unless mom and dad share the same genes.",
"Sure they recombine, and each one of mom or dad's two copies has a 50% of being passed on, but in the genetic relationship between parents and offspring, you will always have the offspring be 50% identical to each parent. You do not have more than 50% of your genes from one parent by chance, so you can't be 80% a close of your mother and 20% a clone of your father.",
"If the parents are related though, you will be more genetically identical to your parents than if they were unrelated."
] |
[
"I think what he means is that the genes recombine in such a way during meiosis that they're very similar to the parents' genes' configuration."
] |
[
"Will listening to music through earphones really make me deaf?"
] |
[
false
] | null |
[
"SPL?"
] |
[
"Wait, hold on. What is this referring to, the volume of the sound?"
] |
[
"Wait, hold on. What is this referring to, the volume of the sound?"
] |
[
"would we be able to feel gravitational waves if our planet orbited two colliding black holes?"
] |
[
false
] |
gravitational waves gets weaker as they travel across space with the two colliding black holes only measuring a movement of 1/1000th of a proton, so i'm wondering if we would actually feel it if we were close to the epicenter? or would relativity get in the way?
|
[
"If you are so close that it would be notable you are already dead from tidal gravitational forces."
] |
[
"gravitational waves gets weaker as they travel across space with the two colliding black holes only measuring a movement of 1/1000th of a proton, so i'm wondering if we would actually feel it if we were close to the epicenter? or would relativity get in the way?",
"If you can measure it many light years away you can certainly measure it when you're very close by. Are you asking if a human can feel it (rather than needing sophisticated equipment)? If you are close enough you will notice the effect, though you may have other problems originating in strong gravity."
] |
[
"Ok, so I did some back of the envelope calculations that I'm definitely not qualified to perform (I really want to understand this though). Sticking with converting 8 stellar masses to energy, I get 1.4 X 10 ^ 48 joules. Lets say you're orbiting at a radius equivalent to the radius of our solar system, 5.9 x 10 ^15 meters. The surface area of a sphere with that radius is 4.4 x 10 ^ 26 m^2. Therefore the amount of gravitational energy that passes through a typical square meter at that distance is 3.2 x 10 ^ 21 joules. (Caveat: I'm imagining that gravitational energy of this kind dissipates as an inverse square b/c I can't imagine anything else.) So, unless I've made a serious order of magnitude error, it seems like that amount of energy passing through your body would have noticeable consequences. What am I missing?"
] |
[
"Do we actually know what protons and neutrons look like? I know they are always depicted like spheres, but is that what they actually are?"
] |
[
false
] | null |
[
"When we talk about the shape and the size of a composite particle, there are a few ways to quantify them. Of course quantum mechanics says that they're not just points, they're \"clouds\" of probability density. But probability densities ",
"? ",
"Where you'd find a particle (in this case a quark) if you made a measurement, or the distribution of mass, or charge. Charge densities are convenient, because they're easy to measure.",
"You just send in some probe that feels the electromagnetic force, but ideally doesn't feel the strong force (and the weak force is weak enough anyway at the relevant energies). The electron meets those requirements.",
"So you scatter electrons off of the target, whether it be a proton, or some heavier nucleus, and look at the probability of the electron scattering into different angles. And it turns out that that quantity is easily related to the Fourier transform of the electric charge distribution.",
"So it's a pretty easy experiment to run and interpret, and it directly tells you how electric charge is distributed inside the target particle.",
"Because of all this, when we talk about the \"shape\" and \"size\" of a nucleus, we're almost always talking about various moments of its electric charge distribution.",
"For the proton and neutron, they're very close to spherical, and we know that because we can estimate their ",
"electric quadrupole moments",
".",
"We know what their ",
"charge densities look like",
" (even if you can't access the paper, you can see the figures showing the charge distributions of the proton and neutron).",
"So they're mostly-spherical \"bags\" of quarks with an RMS radius on the order of 1 fm."
] |
[
"Their electric charge distributions are close to spherical, but with a small quadrupole moment (and maybe some higher moments).",
"So we know that they're ",
" quite spheres, but the leading-order deviation is pretty small."
] |
[
"It's when particles are stuck together. Like a hydrogen atom is a bound state of a proton with an electron."
] |
[
"Can you tell the race of a person by looking at their skull x-ray?"
] |
[
false
] |
So this was on the front page today. This has to be bogus right? I mean, I'm sure there are some indicators which could be useful, but there's no way to determine from that picture what race those people really are...is there?
|
[
"These are old classifications based on work that was done in the 19th century and early 20th century. The were based on the simplest of measurements, such as the cranial index (mesocephalic, brachycephalic, dolichocephalic), or the \"facial angle\", which 19th century people used as a measure of \"intelligence\" to prove that white people were smarter.",
"Most of these ideas have long since fallen by the wayside and are no longer considered useful.",
"In modern forensics, you CAN often identify the origin of a person by his or her skull, but a much more sophisticated analysis is needed. Typically, about 90 measurements are made of different features of the skull, and with these measurements, you can assign about 80% of skulls with a fair degree of confidence as to origin. The other 20% have too many mixed features to be assignable.",
"Basically, the idea is that climate affects body form, including the form of the skull. People from hot climates are generally smaller, more slender, with longer limbs. People from colder climates are bigger, bulkier, and have shorter/stubbier limbs. Due to a relatively low level of gene flow between different parts of the world in ancient times, many of these features are statistically more or less prevalent in certain populations.",
"So you can use craniometry to broadly assign people to continent of origin, such as sub-Saharan Africans, east Asians, south Asians, Europeans, etc. However, there has been a lot of mixing, specially in recent centuries. Among white Europeans, generally considered \"Caucasoid\", you will find the whole range of skull shapes, from brachycephalic through mesocephalic to dolichocephalic, depending on what part of Europe you sample from. In the US, at least a 3rd of white Americans have genetic markers showing partial descent from African populations. The end result is pretty mixed.",
"For these reasons, simple classifications of skull shape are not much used anymore. You need a detailed set of measurements, and then you can sort skulls into a few clusters based on geographic origin, but many skulls defy such analysis."
] |
[
"Yes actually you can. I took a medical forensics class and it was part of our requirements to know racial skull differences. There are 4 basic shapes of skulls: Caucasoid, Mongoloid, Negroid, and Australoid. ",
"Here's a link to the Wikipedia article."
] |
[
"True, though perhaps it would be better to say you can infer something about their ethnic heritage. We sometimes use the word \"race\" to mean \"ethnicity,\" but we also use it in other contexts where it doesn't fit as well (consider people of mixed ethnicity).",
"But yes, there are noticeable differences in the bone structure of people who come from the human populations that lived separated from each other on different continents (Europe, Asia, Africa, Australia, and the Americas). "
] |
[
"Is there an upper limit for temperature? Like how absolute zero is the lower limit."
] |
[
false
] |
In my science class my teacher was talking to us about temperature, and how absolute zero is the lowest temperature possible. He also said that there is no upper limit. That doesn't seem quite right, because temperature is a measurement of the average velocities of the molecules in the substance. Furthermore according to Einstein the fastest speed something can travel at is the speed of light, so to me it seems like there should be a limit to how hot something can get. Any information on this would be greatly appreciated.
|
[
"I remember thinking the same thing when I was in school. Then I went to university and learned relativity and was disabused of the notion. But you're asking the right questions.",
"The answer to your question is this: temperature is defined not in terms of the average speed of the particles but in terms of the average kinetic energy. ",
"Now, under sensible conditions, kinetic energy is just proportional to the square of the speed:",
"KE = 1/2",
"v",
"so you might think this tops out eventually. But it doesn't, because the above equation is just a low-speed approximation to the actual relativistic formula:",
"KE = mc",
" / (sqrt(1 - v",
" / c",
" )) - mc",
"which actually goes off to infinity as v gets closer to c.",
"So if you keep on making a system hotter and hotter, the particles' velocity approaches the speed of light asymptotically, while the kinetic energy and hence the temperature go off to infinity.",
"Thus, no maximum temperature."
] |
[
"Well, let's see. The LHC currently operates at 4 TeV so all we need to do is go to Wolfram Alpha, type in \"4 TeV / boltzmann's constant\" and we get the answer. It's about 10",
" K.",
"That's hot!"
] |
[
"The Planck temperature is not necessarily anything special. If you look at the ",
"article",
" that the Planck temperature wiki page links to as a citation for a statement tantamount to \"the Planck temperature is special\", you'll see that it presents ",
" candidates for an upper temperature limit, one of which is the Planck temperature. The other candidates range from 0.01 Planck temperatures, right down to less than a thousand-trillionth of the Plack temperature (10",
" K), further down to absolute zero (don't understand that myself) right across to \"no limit at all\".",
"It's also worth noting that that article is a pop-sci piece that goes with a TV show. This means that wikipedia article has mis-cited a source which itself isn't that reliable. ",
"In summary, don't believe everything you read on Wikipedia."
] |
[
"Is it possible to be so far away from a light source as to exist \"in between\" the light rays?"
] |
[
false
] |
This is hard to explain without visuals but think of an exploding grenade. The farther away from it, the greater chance of not being hit by shrapnel because you are "in between" the path of the projectiles.
|
[
"If it's a continuously shining, isotropic (emitting evenly in every direction) light source, then the farther away you go, the less frequently a photon will hit you. You're basically on the right track, the intensity of radiation (and thus the surface density of photons hitting a surface) decreases with the square of the distance from the source. "
] |
[
"To expand on this point, while the intensity does decrease (think number of photons hitting a 1 cm radius plate), quantom mechanics tells that the probabilty wave function of the light gives you some nonzero chance of a discrete interaction on the plate. So on a fundamental level, it is not that photons are rays or lines that are getting farther apart, but rather wave packets with probability of hitting our plate decreasing with the square of the distance."
] |
[
"No, stars emit light isotropically (equally in all directions), and even if they didn't, stars rotate so the \"dead zone\" would move. "
] |
[
"What happens to a mammal after injection of proteolytic enzyme?"
] |
[
false
] |
I've concluded brief search before asking and found only a few (seemingly) controversial reports about intravenous injection. In some cases it promotes blood clotting. In other, on contrary, their properties are described as fibrinolytic. Does that mean that blood clotting cascade is their main (only) target in bloodstream? Would the result of intramuscular injection be similar?
|
[
"Not sure what you're getting at with this question, but it would depend on which proteolytic enzyme you're talking about. Any enzyme has a characteristic set of substrates that it accepts, while other molecules can't be effectively cut by that enzyme. This is why you are seeing that some proteases are thrombogenic and others are fibrinolytic, depending on which proteins the enzyme cuts, you'll get different effects. Also, these effects are likely most discussed because it's the most common effects of proteolysis in the bloodstream. (with macroscopic results).",
"No matter what, your results would probably be bad. Introducing large amounts of any material into the bloodstream can upset the delicate checks and balances that are there. Intramuscularly would also be bad, but harder to predict as there's a lot more stuff to interact with. "
] |
[
"My question is purely hypothetical, I'm not going to conclude any experiments. ",
"From one side, it arises from of eating pineapples and specific feeling associated with it -- when your mouth internal surface is kind of partially digested with its juice. Few culinary recipes also use pineapple juice as meat tenderizer, I assume, this application is based on its same (proteolytic) property.",
"On the other side, I've read that one of aspects of endogenous intoxications such as peritonitis is \"proteases in bloodstream\" thing and subsequential intoxication with smaller non-functional proteins \"produced\" by them from whatever they meet in bloodstream . The book I've read about it doesn't seem like a terrific source of reliable information so I'm looking for additional clarification. ",
"I'm quite sure results will be bad, but what i'm interested in is the detailed sequence of actions. Like \"yes, proteases in bloodstream will slowly digest other proteins, their debris will pollute the bloodstream, liver and kidneys will face the consequences\". Or \"first thing is clotting, cardiac system will fail\". Or \"nothing will happen, you already have protease inhibitors in bloodstream to prevent such dangerous situations\". ",
"Your \"all proteases are different\" point is good and that's what I've missed. I meant digestive proteases like trypsin, was thinking about them as \"powerful non-specific peptide bond cleavers\", and considered other proteases to have generally same properties."
] |
[
"Well, introducing large amounts of most enzymes probably won't do much. Injecting proteins (enzymes are proteins) into the blood is how we can get animals to make antibodies against those proteins that we can then purify. The enzyme would get denatured fairly quickly and degraded in the bloodstream. The enzymes that might do something are ones that are supposed to be found free-floating in blood itself, which is probably why you are reading about enzymes affecting blood clotting."
] |
[
"Why does the voltage matter in powered devices?"
] |
[
false
] | null |
[
"A simple way to look at it is using ohms law which is V = I*R",
"This means that if I have some device with 110 ohms of resistance then a 110 V circuit will draw 1 Amp of current. But if you plug the same device into a 240V plug it will draw 240/110 = I = 2.18 Amps. This is a very simplified view but can be used to understand the basic reason."
] |
[
"As an analogy, think of a water faucet instead of a battery. Even if two faucets can deliver the same flow rate (ie current), if you connect a sprinkler to a faucet that has a higher or lower pressure (ie voltage) than the sprinkler was designed for, it will not work correctly. If the pressure is too low, water will simply drip out of the sprinkler instead of being sprayed around (ie lamp too dim). If the pressure is too high, it may burst the sprinkler (ie lamp will burn out)."
] |
[
"Supplying an insufficient voltage (eg. 240 V device into a 110 V outlet) will almost certainly not work and may or may not damage the circuit. It depends on the circuit. As an example, if you have some diodes or transistors in there, decreasing the input voltage might change the biasing and send current to places it isn't meant to go. "
] |
[
"Would the electromagnetic field diverge into its component fields at a low enough temperature or some conditions?"
] |
[
false
] | null |
[
"no. any changing electric field will generate a corresponding magnetic field (and vice versa). this is valid at 0K in absolute vacuum and a fundamental property of electromagnetism."
] |
[
"Electric and magnetic fields are manifestations of the same force. They are inseparable - it's the relativistic speed of the observer that makes them seem different."
] |
[
"it's the relativistic speed of the observer that makes them seem different.",
"That's only completely accurate for classical electromagnetism. It isn't true for the magnetic moments of fundamental particles."
] |
[
"Does the dark energy make it possible to have a closed universe that doesn't re-collapse?"
] |
[
false
] |
Dark energy, matter and radiation determine the total energy, which in turn determines the geometry. But since the dark energy has an opposite gravitational effect it seems that this would make it possible to have a closed geometry without a big crunch.
|
[
"yeah but it can make you have a big freeze. i.e everything expands until there is universal heat death."
] |
[
"Wouldn't it make it inevitable? If things continue to spread out forever and all stellar fuel is eventually exausted, and all black holes evaporate won't there no longer be any sources of heat?"
] |
[
"Why is a big freeze called a heat death? Shouldn't it be a cold death?"
] |
[
"What causes the iconic mushroom cloud shape?"
] |
[
false
] |
Why don't nuclear bombs just have a larger version of normal explosions?
|
[
"d4m1ty's response",
"A large enough conventional explosion also results in a mushroom cloud. You've got a mass of super-heated air that rises, carrying ash and dust skyward, resulting in a mushroom shape if the plume is large/hot enough."
] |
[
"d4m1try's explanation is wrong. But yours above is correct. The mushroom is not a wave effect, instead it's caused by rising hot air.",
"If there is no large volume of heated air in the explosion, then there may be smoke and debris, but there will be no mushroom shape. Compare IED explosions versus burning fuel explosions (gasoline, propane tanks, \"bleve\" explosions)",
"DIY:",
"If you have some dry-ice fog (or halloween ultrasonic mist maker,) you can demonstrate the mushroom stem. Hold a thin circular disk such as a paper plate or a record album a few cm above the layer of fog. Suddenly lift it vertically. You'll see a thin \"spear\" of fog which leaps upwards faster than your disk it moving. It's part of the entrained flow pattern surrounding the disk, basically a vortex-ring."
] |
[
"Intense heat. Buoyancy forces carry the smoke upwards, but as the temperature of the atmosphere decreases with height, the smoke at the edge of the rising column slows down and spreads out. Hot smoke from the centre continues to rise and sucks up surrounding air and smoke. This creates the stem of the mushroom. "
] |
[
"Why does water continue to steam below 100 celcius?"
] |
[
false
] |
So I was making a cup of coffee today. To my knowledge, you cannot boil water above 100 degrees in a kettle because energy will be taken away by steam as quickly as you can put energy in. So I assume the water I poured was 100 degrees, probably slightly less. By the time I had mixed in a bit of chilled milk, it certainly had to be less than 100 degrees. But for the new few minutes, it continues to steam. Surely this means the water is changing from liquid to gas at below 100 celcius, so why does it happen?
|
[
"Steam is virtually invisible. What you see coming off hot water is water vapor."
] |
[
"The water molecules are always moving, and every so often one of them will have enough energy to break away and become a gas. This is constantly happening, and we call it evaporation. When you add heat to the water, you increase the motion of these molecules, and, as a side effect, increase the rate at which some of these molecules break their liquid-phase intermolecular forces. If this happens at a high enough rate, you begin to see some this water leaving as steam. "
] |
[
"Because if a collection of particles has a certain global temperature, that doesn't mean that they are all going exactly the same speed. Some are going much faster than average and some much slower. So even at lower temperatures, you can still find hot fluctuations of particles that have enough energy to leave the collection entirely. Even drops of lukewarm water on a counter top eventually evaporate away. The exact same thing is happening there, it's just that if the water is hot enough then you can ",
" heaps of them leaving because there's statistically many more unusually fast ones."
] |
[
"Why does my Stainless Steel flask say \"Alcohol based liquids should not be stored longer than 12 hours\"?"
] |
[
false
] |
I'm just curious what reaction occurs and how bad it is to leave the liquid in long term. It also says "Do not store acidic or alkaline-based juices or citrus fluid". Anyone know the reason for that? Edit 1: Just wanted to thank this community. I'm quite happy about the responses I've received.
|
[
"If it is indeed stainless steel, the ability to form a passive layer has been shown to be strongly influenced by the presence of hydroxylic organic solvents (ie it's not as 'stainless' when you put ethanol in it) [1]. Since stainless steel contains both iron and chromium, and chromium is particularly adept at ripping your insides apart [2], leeching of such metals into your drink is probably not a great idea. Liquors which are acidic due to the presence of citrus would accelerate these processes.",
"[1] P.L. de Anna, Corrosion Science 25 (1985) 43",
"[2] S.J. Stohs et al, Journal of Environmental Toxicology, Pathology and Oncology 20 (2001) 77"
] |
[
"I know some people who could. I'll ask them if they can spare some time on the instrument. Seriously."
] |
[
"Perhaps it is made of aluminum with a thin stainless steel coating on the outside? I would assume this would allow them to call it stainless steel and it would be cheaper for the company than making them entirely stainless steel."
] |
[
"Help a guy battling OCD get rid of his fears of germs/bacteria"
] |
[
false
] | null |
[
"I approve of most of what you've said, but:",
"your body is absolutely infested with bacteria",
"I would say ",
" rather than ",
". Your body is inhabited by a host of bacteria called the ",
"Normal Flora",
". One of the ways these bacteria help you is by benignly occupying space that might otherwise be ",
" by harmful bacteria. As long as the normal flora are there, other bacteria have a hard time setting up shop.",
"Every time you get sick, that's your body waging bloody war on bacteria",
"Most of the time when you're sick, your body is waging a war against viruses, not bacteria. Sometimes you can get a secondary infection of bacteria when a virus causes inflammation which makes an inviting habitat for bacteria. And sometimes those bacteria are part of the normal flora. For example, when your eustachian tube gets inflamed from a viral infection, the small numbers of anerobic bacteria normally living there will experience a sudden population boom because there's no oxygen to kill them or to feed the aerobic bacteria that would keep them at bay.",
"Other times your body ",
" waging a war against bacteria, as when you leave food out for a long time and the bacteria which were already living there have a chance to grow to a large enough population to cause harm, or your leave food out and flies transfer bacteria to it, ",
" it has time to grow. You don't have to worry about small numbers of bacteria, there are always small numbers. It's just when they have a chance to grow their population that they become harmful.",
"Otherwise, god job!"
] |
[
"I approve of most of what you've said, but:",
"your body is absolutely infested with bacteria",
"I would say ",
" rather than ",
". Your body is inhabited by a host of bacteria called the ",
"Normal Flora",
". One of the ways these bacteria help you is by benignly occupying space that might otherwise be ",
" by harmful bacteria. As long as the normal flora are there, other bacteria have a hard time setting up shop.",
"Every time you get sick, that's your body waging bloody war on bacteria",
"Most of the time when you're sick, your body is waging a war against viruses, not bacteria. Sometimes you can get a secondary infection of bacteria when a virus causes inflammation which makes an inviting habitat for bacteria. And sometimes those bacteria are part of the normal flora. For example, when your eustachian tube gets inflamed from a viral infection, the small numbers of anerobic bacteria normally living there will experience a sudden population boom because there's no oxygen to kill them or to feed the aerobic bacteria that would keep them at bay.",
"Other times your body ",
" waging a war against bacteria, as when you leave food out for a long time and the bacteria which were already living there have a chance to grow to a large enough population to cause harm, or your leave food out and flies transfer bacteria to it, ",
" it has time to grow. You don't have to worry about small numbers of bacteria, there are always small numbers. It's just when they have a chance to grow their population that they become harmful.",
"Otherwise, god job!"
] |
[
"I feel for you SpamKing, my ex was mildly OCD so I understand the frustrations that go hand in hand with that.",
"So with this in mind, I would like to cover some of the 'other information on why I shouldn't be so overly concerned about bacteria all the damn time'.",
" Every day, new uses are being found for ",
"GOOD bacteria that is present",
" in the world around us, and within our bodies. And in fact, the reason that we thrive as human beings is because ",
"we are in symbiosis with dozens of different kinds of bacteria",
". So don't always think negative when you hear the word. ",
"Probiotics are everywhere",
" In the middle and high income countries, ",
"bacteria aren't the cause of the vast majority of deaths",
". The top three are heart attack, stroke, and lung disease... in other words, vastly ",
". Studies attribute these numbers to smoking, drinking, and not keeping in shape.",
" It's not just a saying. The CDC has been teling people for years: ",
"It's OK to get sick!",
" They don't want you taking weird measures to avoid it, they don't want you to chug down antibiotics. It's simply healthier to live your life, take reasonable measures but not paranoid ones, don't demand antibiotics all of the time, and keep your stress levels down.",
"I hope these points help you out, in addition to the others answering your other questions.",
"Edit 1: Made ",
" things, bold is cool."
] |
[
"How does the EM Drive break Newton's Third Law?"
] |
[
false
] | null |
[
"To be propelled forward, you need to shoot something backward. Any \"reactionless\" drive violates this principle ",
"."
] |
[
"But doesn't it send microwaves out the back? Aren't they the propellant?"
] |
[
"If it does, then it's not reactionless."
] |
[
"Is most space debris traveling the same direction? And could we take advantage by shielding only one side of our spacecraft?"
] |
[
false
] | null |
[
"No.",
"In low orbits, most of space debris came from two major events: the Kosmos-Iridium collision and the takedown of the Fengyun-1C satellite.",
"https://wattsupwiththat.files.wordpress.com/2010/06/space-debris-charts.gif",
"The Kosmos-2251 satellite was already defunct. Iridium 33 was still working. In 2009 they collided and both turned into pieces. Their orbits were radically different, almost perpendicular to each other, so their fragments remain in orbit as two clearly distinguishable \"clouds\" of debris.",
"https://en.wikipedia.org/wiki/2009_satellite_collision",
"Since they are almost polar orbits, they can cross the orbit of virtually any other satellite at a similar altitude.",
"Fengyun-1C was a Chinese weather satellite. In 2007 they intentionally destroyed it with a missile to test their antisatellite capabilities. This event alone generated more debris than any other country in its entire space history (caveat: Kosmos and Iridium were from different countries). Also this one was in an almost polar orbit, so its fragments can intersect almost any orbit.",
"https://en.wikipedia.org/wiki/2007_Chinese_anti-satellite_missile_test",
"Want to stay safe? Just stay at a low altitude. This is not only because the two major collisions happened very high, but also because at a lower altitude there's greater drag from residual atmosphere, which has a \"cleaning\" effect against debris.",
"https://upload.wikimedia.org/wikipedia/commons/b/be/Spacedebris_upd_2011.jpg",
"The ISS is at 400 km, almost on the left end of that graph. They don't dare to go any higher.",
"There's a caveat on the above: it's about ",
" debris, i.e. objects larger than 10cm that can be observed from Earth. The pentagon is tracking them and issues warnings when they are about to get closer than 5km to a functioning satellite. From time to time the ISS performs collision avoidance manoeuvres.",
"But smaller fragments that cannot be traced are much more abundant. Every time they hit a satellite, even if it's shielded and it can resist, they release many more fragments. These will be in a similar orbit to the satellite that they came from, not necessarily to the object that caused the collision, but since satellites have very different inclinations, so have their fragments.",
"All that said, we can still take advantage and shield one side more heavily than the other. Not the direction that debris moves in, but the direction that the spacecraft moves in. The ISS is shielded more heavily in the front and sides because of debris, and in the top because of meteors.",
"https://www.nasa.gov/externalflash/ISSRG/pdfs/mmod.pdf",
"In the geosynchronous orbit things are different. High inclinations make no sense here, most satellites are close to the equatorial plane, so most debris does move in the same direction."
] |
[
"If you are talking about orbital debris, which can strike satellites and break them, then yes it is mostly going in the same direction. That is because we mostly launch satellites in the same direction as the rotation of the earth (it costs a little less fuel in that direction to get something into orbit). But not every satellite is orbits right over the equator, so there is some spread in the velocities of the debris.",
"And could we take advantage by shielding only one side of our spacecraft?",
"Generally not, because we launch spacecraft in mostly the same direction as the debris. The relative velocity of the debris and the spacecraft will be spread out over a range of angles. Most of the debris will be coming from the same plane, so the side of the spacecraft facing the earth and the side facing away from the earth will be less likely to be hit."
] |
[
"They call it \"Dark Flow\", the possibility that galaxy clusters are all flowing in a common direction. There have been studies done to prove and disprove it. Though some claim that they have evidence, or at least some grounds to support the idea."
] |
[
"Why have I had hiccups on and off for four hours?"
] |
[
false
] | null |
[
"Please consult with a doctor regarding diagnosis issues."
] |
[
"this is not a diagnosis tho, i am just wondering about the biology. "
] |
[
"oh, it just sounded like a personal diagnosis is all. In that case we've had a recent hiccup thread ",
"here"
] |
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