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[
"If you could take a representative section of the sun and instantly move it off by itself, what would happen to it?"
] |
[
false
] |
Say you could snatch away say, 5% of the sun by mass that was proportionately identical to the sun; then plop it down in an area of space that's minimally affected by any external gravitational forces. Would it just become a tiny star just like the sun? Supernova or collapse on itself?
|
[
"If its small enough, the outward forces would blow it apart and you'd get a fairly impressive explosion, though most of the matter involved would simply be scattered across space instead of being converted into energy, so it wouldn't be on the scale of a supernova or anything. If the section is large enough that the gravitational forces overcome the outward nuclear forces, you'll have a small star. The smallest stars have about 10% the mass of our Sun, so I'd guess your scenario would cause the explosion. "
] |
[
"Not when it's just 5% the mass of our Sun. The gravity would be too weak."
] |
[
"If what OP is saying is that this would be a copy of the sun with all the properties kept the same but just 5% of the mass/size, then this object would be at MUCH higher temperatures and pressures than any object of it's size would every naturally be at. That means it will definitely \"explode\". How spectacular and permanent this explosion is would depend on the actual numbers. It might just puff out slightly, it might explode into a large cloud then re-collapse, or it might explode out and never reform. It all depends on the energy stored inside it as heat/pressure versus the energy it would take to pull each particle out to infinity (energy required to give each particle escape velocity). If there is enough energy, the object will disperse, if not it will blow out then stop/collapse. "
] |
[
"Why is it that, in any other country, extremely heavy rain is frequently accompanied by lightning, but here in Ireland, we get, max, 2 or 3 storms a year?"
] |
[
false
] |
I love lightening. I live in Ireland. We get torrential downpours of rain, daily. Frequently they are epic, wind-driven, biblical sideways rain (at least where I live, in a very exposed rural location). Yet we almost never get so much as a thunder storm. Actual fork lightening, you know, the exciting kind, comes only a handful of times a decade. I was in Germany recently, and there were 8 lightening storms, with real forkers, in 5 days. As a lightening fan, I feel hard-done-by. Ireland's weather sucks. So, AskScience, WHAT GIVES?!
|
[
"You need warm, humid air to be pushed into extremely high altitudes, so that the moisture can turn into ice and start building a charge. Ireland doesn't have warm humid air."
] |
[
"Not just turn to ice; you need the droplets to become supercooled (remain liquid at temperatures below freezing) so that they can form an ice crystal/water mix that collides with other ice crystals.",
"This is also why you very rarely see lightning behind snow. The moist, but cold, air masses which cause snow never go through this state, just straight to crystal form."
] |
[
"Your weather and that of the UK and a lot of western Europe is mostly controlled by the Gulf Stream, the effect of which is so broad, that you don't get the sharp temp. gradients that we get here in the States. The fronts that we get here in Texas are sometimes very powerful and can spawn tornados, hail, snow, very high winds, huge dust storms, and massive displays of lighting. The cold fronts are called blue northers and the temp. drop across them can be 50+ degrees F. We don't get as many as we used to in the 50s and 60s but to stand out and see one of these fronts come through is truly a moving event. To smell the ozone and feel the south wind rush past you, then comes the calm for about 10 minutes and then the front hits like a train. The windows and doors rattle, the leaves come off the trees, the temp starts to drop. It is really a very exciting experience. ",
"These same cold fronts are also what cause the horrendous tornados like we had a few months ago. Not something you want to go through.\nI have read that the US has the most widely varied weather in the world because we have 3 large bodies of water around the country. ",
"If you want lightening go to Florida. It has the most and worst in the world. There is a place in Venezuela that has a spectacular show but it is mostly cloud to cloud lightening, but it is still very impressive. "
] |
[
"Why is the human lifespan almost twice as long as average fertility rate?"
] |
[
false
] |
What is the evolutionary reason that we live for so much longer than the amount of time we are able to reproduce?
|
[
"I read that that's because the infant mortality rate was like 30% and, if you lived to be older than five, life expectancy was about 60."
] |
[
"I read that that's because the infant mortality rate was like 30% and, if you lived to be older than five, life expectancy was about 60."
] |
[
"to take care of offspring while able bodied parents were busy?"
] |
[
"Can it be so cold that clouds would freeze in the air and fall down as one massive unit?"
] |
[
false
] |
Or would it be too cold at that point to form clouds? But at that critical point of freezing temperature, what would happen to the clouds that are still in the air? Titanic clouds falling down like WHOMP.. shiiit..
|
[
"In theory nothing is impossible, but even if this did happen it would just be an extremely rapid snowfall, and not a huge single block of ice. The amount of water in a cloud can be quite large (many tons) but it is quite diffuse. In an 'ordinary' cloud in a mass of air above freezing temperatures, the water particles exist as tiny droplets coalesced on microscopic solid particles in the atmosphere known as condensation nuclei. When the temperature within the cloud is below the freezing point, the clouds still exist but may exist as tiny ice particles. Clouds made of ice tend to have a wispy appearance and are quite common in the high altitude range, where it is very cold. This is why cirrus clouds (the high, wispy clouds) often appear the way that they do. For large masses of ice to form, an ice particle needs to be blown around and 'collect' more water to freeze onto it, before it finally becomes too heavy and falls as hail. Even the largest hail stones recorded take a very long time being blown around inside a cloud before they fall, so for a whole cloud to fall as a solid piece of ice would be practically impossible. Even if a shock-cooled cloud were to freeze and fall instantly, it would simply fall as very fine icy mist that would either melt or accumulate as powdery snow."
] |
[
"No problem! There's actually a very good book called ",
" that explains the science and nature of clouds and other atmospheric phenomena really well. It's really interesting and a great read, highly recommended. "
] |
[
"Well that settles that.\nThanks for taking your time to answer!"
] |
[
"I know that long term use of steroids suppress the immune system but how? I would really appreciate if someone told me how it does that to our body?"
] |
[
false
] |
I know that long term use of steroids suppress the immune system but how? I would really appreciate if someone told me how it does that to our body?
|
[
"Steroids are really a subgroup of signalling molecules called hormones. Hormones can deliver chemical messages around the body, influencing a myriad of different functions, often through their effects on gene expression.",
"Strictly speaking, we should be calling these compounds corticosteroids, a subgroup of glucocorticoids, so as not to confuse them with the anabolic steroids which are related to testosterone ans some athletes use them to improve their performance. ",
"A major component of their function is the disruption of cytokines. Like hormones, cytokines are messaging molecules and cells of the immune system constantly use different types of them to talk to one another and to mediate immune responses. Immune cells can release cytokines as a call-to-arms to other immune cells. This is the essence of the inflammatory process - cells sending and receiving chemical messages and responding accordingly.",
"Inflammation gets a lot of bad press, but really, inflammation is a beneficial process crucial for restoring disrupted tissues back into homeostasis. The problems arise when inflammation becomes chronic. ",
"While cells of the innate immune system are the mediators of acute immune response (the kind that comes and goes when needed), the adaptive immune system can cause long-term (chronic) inflammation when set off. For example, in autoimmune disease, the adaptive immune system mounts an adaptive response against the body's own cells, causing long-lasting inflammation as the enemy (our own cells) is always present.",
"And here is where our corticosteroids step in. As noted above, hormones often act by altering gene expression in cells. Corticosteroids in particular alter gene expression in white blood cells, controlling differentiation, cytokine production and other activities. They disrupt the machinery which controls inflammation.",
"Hope this answers your question!",
"\"The anti-inflammatory and immunosuppressive effects of glucocorticoids, recent developments and mechanistic insights\" ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3047790/"
] |
[
"Yes. At high doses of glucocorticoids during which you may see significant lymphopenia (T-cells mostly, but B-cells to some degree as well), it is estimated that lymphopenia appears within 2 hours, peaks at 6 hours, and resolves within 24-48 hours. Note that these kinetics are with respect to a pulse dose - I'm not aware of what the recovery kinetics would be if one were on high-dose steroids for an extended period of time.",
"Also note that some of the most feared effects of steroids are in a semi-binary nature. For example, profound immunosuppression from extended exposure to steroids can result in ",
" pneumonia (PCP). One can stop the steroids in order to let the immune system recover more to fight the infection, but that still doesn't change the fact that one developed the pneumonia in the first place.",
"P.T. Fan et al. (1978) Effect of corticosteroids on the human immune response: comparison of one and three daily 1 gm intravenous pulses of methylprednisolone. ",
" 91(4):625"
] |
[
"so is the effect on immune system reversible"
] |
[
"Why is lithium-7 hydroxide monohydrate used as a power systems coolant? Is it considered a salt? Why it is used as a PH regulator on nuclear reactors?"
] |
[
false
] | null |
[
"I've been a nuclear reactor operator for 6 years. I don't know too many specifics as we didn't use this on the plant that I worked on. We used to use trisodium phosphate dodecahydrate and disodium phosphate in order maintain ph in the 10 to 11 range. You want to maintain a basic pH in order to minimize general and pitting corrosion in metals used in the plant. Im not sure if this answers part of your question let me know if it does."
] |
[
"LIOH is used in solution, generally in water which is used as a coolant and moderator in pressurised water reactors PWRs.",
"LiOH can be used in nuclear reactors to increase the pH in the coolant. This change in pH ends up decreasing the corrosion rate in your system which leads to lower output of deposits being released into the coolant. These deposits can affect the plants hydraulic performance, change heat transfer properties of certain components and also can lead to a build up of radioactive material in the coolant created from the neutron activation of the corroded material in the reactor core. "
] |
[
"Generally it's used to help offset boric acid addition in pressurizer water reactors. Boiling reactors which use no boron don't inject lithium. "
] |
[
"If everybody had an electric car tomorrow, could the NA power grid support it?"
] |
[
false
] |
[deleted]
|
[
"According to ",
"this study",
", in the U.S., as of 2006, 84 percent of the additional electricity demand created by 220 million electric vehicles charging overnight could be met by idle generation capacity.",
"That estimate doesn't include any additional capacity of hydro, renewables, or nuclear plants, or of peaker units. It also neglects the amount of grid electricity that would no longer need to be consumed during the production of gasoline.",
"Some have suggested",
" that with just the energy used to produce a gallon of gasoline an electric car can actually drive farther than an average car would by burning that gallon. In fairness, the 8kwh/gallon figure refers to the total energy used in gasoline production: some of that is obtained from natural gas, and some electricity is produced on-site by refineries.",
"So in short, probably. But since the adoption of electric cars will obviously be more gradual than you propose it's clear that there will be plenty of time to prepare the grid for any additional strain."
] |
[
"Yes, because the majority of rechargers would be during off-peak hours."
] |
[
"Citation?"
] |
[
"Is time dilation observed with particle accelerators?"
] |
[
false
] |
I'm familiar with the twin paradox - though I'm still rough on where and why the frames of reference shift for the twins - but what happens when we accelerate particles to near light speed? Do they "age"? Is this an absurd question? -edit- Actually, I think I just don't understand time dilation in general. I understand it has to to with relativity, but I don't understand what "relative" is actually anchored in, like with the twin paradox.
|
[
"This is a great question. The time dilation of the muons created by cosmic rays hitting the atmosphere is an example of this. As measured at rest the decay rate of the muon is fast enough that a muon created in the atmosphere should decay before it reaches the earth's surface. But we see just as many muons at the surface as we do high in the atmosphere. ",
"The reason for this is that time dilation stretches the decay time. In the muon's frame of reference the decay takes the same amount of time as it would at rest. But we on earth observe the muon's 'clock' to be running slower than it is, and thus the decay time is stretched out long enough for the muon to reach the surface.",
"The particles accelerated in a particle accelerator are similarly dilated, but we don't really notice these effects. The thing is we only really shoot charged particles that a fairly stable. For example at CERN they're shooting protons and at RHIC they're shooting gold, which are both stable. An experimentalist might be able to give you a specific example of an accelerator where time dilation is critical to the experiment."
] |
[
"Yes."
] |
[
"Yes.",
"This is a problem every physics undergrad solves in their special relativity course ",
" :",
"Muons have a lifetime of XXX seconds in an inertial reference frame. How long would it take a Muon to decay when it is moving at YYY speed ? (lifetime = time taken for it to decay into something stable, because muons themselves are unstable)",
"Its like saying that if you lived for 100 years standing still , it would look like you lived for 100+ years to someone moving really fast.",
"Random stuff shows up on searching : ",
"http://iopscience.iop.org/0954-3899/29/8/392",
"Its been observed in the case of cosmic ray Muons which enter earth's atmosphere though."
] |
[
"Apparently piranha can detect blood from 2 miles away, how?"
] |
[
false
] |
What is the mechanism they use to do this? And would it not take a lot of time for the pheromones to reach them?
|
[
"They can't. Neither can sharks. They can, however, detect very low concentrations. The blood still has to diffuse through the water and physically reach them, though. It's not like someone cuts themselves and instantly a fish 2 miles away can smell it. That's not how it works."
] |
[
"I think the word is usually used more narrowly than that",
"Unless it is shark blood, it is. A pheromone affects the same species, an allelochemical affects other species. Both are examples of semiochemicals (or so says my masters thesis, at least. There seems to be differing opinions on the exact definitions)."
] |
[
"A lot of plants inhibit germination or growth of all plants near them. My thesis was an investigation of specific compounds from clover that could be responsible for this effect, both against other plants, which could be helpful in weed control, and against clover itself (clover soil sickness), which is a problem for (particularly organic) cattle farmers. The first case is allelochemical, the second is pheromonic.",
"Other than that, the smell of certain plants being wounded (think the smell of freshly cut grass) attracts predators of their typical pests. ",
"For animals, especially the insects go wild in semiochemicals. The larvae of the butterfly ",
"large blue",
" is adopted by a particular species of ants, where it eats their eggs and larvae. This must include mimicking the ant's pheromones, which I guess would be allelochemicals in this case, as it affects another species."
] |
[
"How much does the liquid magma of the Earth affect it's surface temperature?"
] |
[
false
] |
So, say, if we were on just a solid rock of a planet, instead of one with a heated core, would it be a very different place to live?
|
[
"Very little. It depends of course on local geology, but is generally well below 1W/m2 compared to sunlight being 1000W/m2",
"You can of course see the effect on poles, there is magma under Antarctica just the same, but it's still covered with couple km thick ice.",
"So in terms of temperature it makes no difference directly. But indirectly tectonic activity makes a very large difference. With a solid core we wouldn't have mountains left, it would have all eroded flat over billions of years. Without volcanic emissions we wouldn't have enough carbon for lush foliage, because it has a tendency to form sediments. Earth would be an iceball without enough CO2 to keep the heat in."
] |
[
"This is not correct though. Good counterpoints are Venus, which has no intrinsic magnetic field, only a relatively weak induced one, and yet still has a thick atmosphere or Mercury, which has an intrinsic magnetic field and effectively no atmosphere. This comes up ",
" on AskScience and there are numerous threads considering the relative role of gravity, active volcanism, and magnetospheres for keeping planetary atmospheres, e.g., ",
"this thread",
" where various posters lay out the details and highlight that gravity / escape velocity is the dominant factor in whether a planetary atmosphere is maintained, this ",
"specific comment by one of our panelists",
" addresses this misconception directly."
] |
[
"Deflects solar winds which would otherwise strip the atmosphere.",
"Wikipedia has a good overview of how it works ",
"https://en.wikipedia.org/wiki/Magnetosphere"
] |
[
"Is it possible for a falling object's terminal velocity in a given atmosphere to exceed the speed of sound within that atmosphere?"
] |
[
false
] |
It's my understanding that, as the fluid the object is falling through increases in density, the terminal velocity of the object will decrease while the speed of sound through that fluid increases, and vice versa as the fluid decreases in density. Is there a set of conditions under which the object's terminal velocity exceeds the speed of sound under those same conditions? Is it feasible that conditions like these could be met here, on earth? What kinds of extreme terminal velocities could be reached on earth, feasibly? I'm interested in better understanding the factors at play in determining terminal velocity, and in the extremes able to be achieved.
|
[
"Sure. ",
"This guy",
" broke the speed of sound in freefall about a week ago. All you need is a large, non-lifting, not too draggy body.",
"FYI, speed of sound for air at the conditions found anywhere in the atmosphere is a mostly a function of just composition (as in how much water vapor, etc.) and temperature. It is only a very weak function of density.",
"Speed of sound for dry air is ",
"c = sqrt(gamma_air*R_air*T)",
"where ",
"gamma_air is the ratio of specific heats for air, roughly 1.4",
"R_air is the specific gas constant for air, roughly 287J/kg/K",
"and T is the temperature, in K. ",
"For example, the speed of sound at 20°C (293K) is ",
"343m/s",
".",
"Terminal velocity of an object is the speed at which the force of drag exactly counteracts the force of gravity so that the object no longer accelerates. The force of gravity for an object of mass m is ",
"m*g",
"where g is the acceleration of gravity (9.8m/s on earth).",
"and the force of drag at terminal velocity is ",
"(1/2)*C_D*density_air*v_terminal",
" *A",
"where A is the object's cross-sectional area and",
"C_D is the drag coefficient, which can vary a lot with velocity and geometry, but you can set it to 0.5 for an okay approximation for non-streamlined objects.",
"Equating those two expressions and solving for terminal velocity gives ",
"v_terminal = sqrt(2*m*g/density_air*C_D*A). ",
"For example, an iron ball with radius 1 meter has a mass of ",
"33500kg",
" and a cross-sectional area of ",
"3.14 m",
". With a C_D of about .5 and air density at sea level of about 1kg/m",
" that gives a terminal velocity of ",
"2030m/s",
". You can play around with the formulas I gave to see what exactly it takes for terminal velocity to break the speed of sound."
] |
[
"It absolutely boggles my mind that he couldn't hear or feel the sonic boom. I know ",
", but it's just so unintuitive."
] |
[
"In the atmosphere (and any gas in general), it would seem that the speed of sound is strongly dependent upon temperature as opposed to any other variable (pressure, density, water vapor). In the atmosphere, a speed of sound profile would roughly correlate with a temperature profile in terms of its shape. Wikipedia article (sorry): wikipedia.org/wiki/Speed_of_sound"
] |
[
"Why are SpaceX trying to land their booster on a barge rather than land?"
] |
[
false
] | null |
[
"Rockets sending a payload up to orbit are launched over oceans. If anything were to go wrong with the launch, it is much better for the rocket to land in the ocean. Depending on how early any issues happen, the rocket could have a lot of fuel on board. If that exploded over land or worse exploded on impact and there were any people or infrastructure around, it would be devastating.",
"The barge is placed in a location not too far off the natural trajectory of the first booster stage. The amount of fuel on board for the controlled descent is kept to a minimum, so the majority of the time that the booster is falling toward the ocean, it's in free fall. The rockets for controlled landing only fire very close to before it lands.",
"It would require far too much fuel to manouevre the booster anywhere else. "
] |
[
"Several points:"
] |
[
"I believe their initial tests were over land. They sent the rocket up, hovered for a few moments and landed it back on land.",
"Being over the ocean is mostly due to the massive amount of fuel on board for orbital insertion. There are likely regulations requiring this, of course, but also common sense. So, to condense this reply down to a single word: yes."
] |
[
"Why does the human body check the CO2 amount instead of O2 to determine if you got enough oxygen?"
] |
[
false
] | null |
[
"CO2 forms a buffer system in your blood , it actually exists as several different components depending on how much of it there is (CO2 +H20 => H2CO3 <-> HCO3",
" <-> CO3",
"). If CO2 builds up in your blood it causes a pH shift. The nifty thing about this is that it's (normally) easy to regulate by controlling breathing patterns (if your blood is too acidic, you have too much CO2, you breath more, and it is expelled. Too basic and you breathe less letting CO2 accumulate). Shifts in pH are pretty easy ways to trigger effects in the body. Oxygen on the other hand is (for the most part) bound to hemoglobin and not just floating around free. Also dissolved oxygen won't participate in the same type of buffering system as CO2 - so it is \"more difficult\" to develop a system around measuring it. "
] |
[
"The pH of your blood would drop, causing a condition known as ",
"acidosis",
". If it's from lack of breathing, it is specifically ",
"respiratory acidosis",
"."
] |
[
"no, your saturation stays the same unless you are at altitude or a hypoxic environment in the absence of disease. SaO2 is what you're referring to"
] |
[
"How does space debris impact earth's environment and atmosphere?"
] |
[
false
] |
I know that it affects our space travel and satellites but does it have any affect on our environment on earth?
|
[
"Most space debris is dissolved by the atmosphere far before it reaches the earths surface. This is because of the massive amount of friction that the object must endure on its journey from space to our surface. Because of this, space debris does not affect the earth’s environment and atmosphere much at all. If a larger piece of space debris, say a large asteroid were to enter our atmosphere, a series of events close to what happened with the dinosaurs would occur."
] |
[
"It could. This is why in most cases fuel is dumped before re-entry, especially in case of hypergolic hydrazine-related fuels, which are toxic."
] |
[
"Just wanted to mention that it's less about the friction that the object experiences and more about the heat generated by extreme air compression in front of the object as it slams into the atmosphere. Kind of the same sort of concept that a \"fire piston\" camping tool uses to provide embers to start campfires."
] |
[
"How do scientists know that we evolved from single-celled organisms?"
] |
[
false
] | null |
[
"Imagine a book by Shakespeare. Now imagine a book as complex but a lot longer.. Our genome might be that big. ",
"A bacteria's genome is considerably smaller (several fold) but from everything we know we find that their genome is basically made up of a large number of chapters that resemble very closely (70-80% of the words and sentences) to chapters that are found in the human genome. And most of them kind of tell the same story too. ",
"If our genomes were indeed books, no sane person would ever doubt that they all are modifications of a single master book written a long time ago: the similarities are so obvious. And if you trace the lineage of modifications back it becomes very convincing that we did indeed come from single-celled organisms.",
"Also there really is no plausible possibility we can think of for life having originated without via a single-celled precursor."
] |
[
"Single celled animals came before multicellular animals."
] |
[
"Really if you think about it it took billions of years, because before that 500 million years we had billions of years of just single-celled life evolving on its own. ",
"The fossil record aside, the fact is that all multicellular life is made up of unicellular organisms and that the cells are mostly made up of the same fundamental parts as unicellular life. This leads to the conclusion that the one was likely made up of the other and therefore the other likely came first."
] |
[
"What is super-symmetry?"
] |
[
false
] |
I recently watched the documentary Particle Fever and this word was used often. Can someone explain to me what it is and why Super-symmetry would be supported by the Higgs Boson having a mass of 115 Gev. And since it has been found that that the Higgs Boson has a mass of 125 Gev what could that mean?
|
[
"Basically it's the idea that for each particle with a given spin (electrons have a half, photons have one, etc), there is another particle with a spin that differs by one half. Some processes might occur differently if, for example, these particles were being created, but there hasn't been any evidence of that thus far in the LHC experiments."
] |
[
"I answered a similar question ",
"here",
" a while back."
] |
[
"Well supersymmetry is an extension of particle physics beyond the standard model, so the idea that the standard model is the end-all-be-all of particle physics (nobody really thinks that, but it's a strong null hypothesis) is at odds with it. Supersymmetry also doesn't take gravitation into account, and we live in a universe with gravity, so there needs to be an additional reconciliation there."
] |
[
"How was 20 seconds determined to be the appropriate time to wash your hands?"
] |
[
false
] |
If you wash your hands for only 10 seconds, does that kill only. half the germs? If you wash for 30 seconds, are you able to kill off even more viruses? What research was done to establish the current time frame of hand washing?
|
[
"It takes a detailed 4 or 5 minute scrub, to get practically all the germs and viruses. I don't know of any studies about 20 seconds specifically. ",
"https://www.ncbi.nlm.nih.gov/pubmed/16553905",
" Seems that \"normal\" hand washing gets rid of about 92% of bacteria; I have little idea how effective it is for viruses. One might expect that a good 20-second wash would be 99% effective, and adding another 20 seconds would raise that to 99.99%.",
"But even if you could wash & kill 100% of the germs and virus, as soon as you touch a contaminated surface (such as your dress or pants), or come closer that a meter to another person without protection ... then zham! you're unclean again."
] |
[
"our outermost surface of our skin isnt alive, its a layer of dead cells and keratin so it doest really effect our living tissues"
] |
[
"If they disrupt DNA bonds for viruses/bacteria does that mean they disrupt DNA bonds for humans as well?"
] |
[
"Will it ever be physically possible to have low latency (100ms and lower) for people in South Africa connecting to Europe?"
] |
[
false
] |
As somebody that lives in SA, we often have to connect to overseas servers and play with 180+/- ping, which is impossible if you want to play competitively. So with all of the talk of 5G, and other new technological advances, will low latency ever be possible, because those signals still have to physically travel to Europe and back?
|
[
"The main limitations for network latency are:",
"For the first, physics gives us an upper bound: the speed of light",
" which is 299 792 458 meters per second. That's the fastest anything can go, so it gives us a hard limit. At this speed, a round trip time of a bean of light between Johannesburg and Frankfurt, Germany",
" (a distance of approximately 8700km as the bird flies) would take 52ms.",
"Unfortunately, it's difficult to attain this full speed here on Earth -- the fastest fibre optic cable is capable of about 204 000 000 m/s",
" Assuming a direct path, that's a 84ms round trip time for light to reach one end, and bounce back.",
"That gives us a hard limit to the maximum speed you'll ",
" achieve between Johannesburg and Frankfurt, and a ",
" maximum speed you could ever achieve. However, real-world speeds are always going to be slower, as transmitting a bit of data isn't an instantaneous event -- there is a minimum signalling time required to define a \"bit\" of data",
" This adds very slightly to the overall latency -- you can't process the data in any manner until you have some data to decode.",
"On top of this is the time taken to decode and process the data itself. This is highly variable, and there can be a ",
" of segments on the network where processing takes place. Optical amplifiers add a tiny bit of latency. Optical-Electrical components (used to convert the optical data to a form usable by a computer) add a further 5 - 10 microseconds each time the signal passes through one. Each network hop, where data is decoded and routed will add time. And the destination server still needs to be able to receive the data, decode it, process it, and then transmit a response -- which will have all the same transmission delays as the initial one-way leg of the trip.",
"None of this accounts for one of the biggest sources of network latency delays in the world today: buffer bloat. Routers are designed to have buffers big enough to hold roughly 250ms of data. Busy routers that are receiving data fast enough can thus each add up to 250ms of extra latency, as they simply hold onto the packet while it transmits other packets in front of it in the queue. It's like entering a busy subway station -- sure, the station can handle a lot of people at once, but if it's jam packeted you may have to wait for a few trains before you can get on. The same goes for network packets -- they enter the router, but may have to wait while other packets are transmitted.",
"In an absolutely best case scenario, you'd have a single hop between you and your destination (that is, you'd be wired directly into your destination), and wouldn't be sharing bandwidth with any other systems (that is, you wouldn't have to pass through any routing equipment). In such cases, you should ",
" be able to get down to around 85ms RTT",
" But actually getting this speed in the real-world is likely going to require significant advances in technology to get the signalling speed up faster, and would require you to have your own dedicated line that runs directly in a great circle",
" between South Africa and the target European city, with no routers in between and a minimal number of optical amplifiers to get your signal from A to B. None of that is likely realistic, hence why it's very difficult (and may be unlikely to ever) to get the latency down to 100ms. HTH!",
" -- in a vacuum.",
"\n",
" -- I picked Frankfurt because it's a major city somewhat central in Europe.",
"\n",
" -- ",
"Source",
".",
"\n",
" -- Due to Quadrature Amplitude Modulation you don't generally transmit in individual bits, but instead send a signal that represents several bits at once. But the time required to transmit a QAM symbol is analogous to transmitting a bit, so I'll just use \"bit\" as shorthand for what is really a QAM symbol.",
"\n",
" -- Round Trip Time.",
"\n",
" -- the shortest distance between two points on a sphere."
] |
[
"Given neutrinos' low interaction with other particles, wouldn't you have to generate a ",
" of them to send a signal that can be detected at that distance? Doesn't that place an unacceptably high lower bound on the size and energy requirements of such a transmitter?"
] |
[
"See \"not practical\". It might be good enough for high speed trading, sending individual bits faster than everyone else, if the monetary incentive is large enough."
] |
[
"Why is there a correlation between positivity and geographical height in the English language?"
] |
[
false
] |
For example saying things such as " " vs " ", or " " vs " ". It seems so arbitrary. Did one of the first civilizations just decide this is how it's going to be? Or is there an actual scientific explanation?
|
[
"Why wold 'high' being better be a recent development? 'High' has meant 'great' and 'illustrious' since Old English ",
". For instance a 'highway' isn't called that because it is/was a road that's higher up, but rather it's the more important, main road. ",
"That's true of other Germanic languages too, like the North Germanic words for 'right' (direction) are all cognates of 'higher' because the right hand was the 'higher' one. So that's also meant in a figurative way as 'better'."
] |
[
"Actually, there is a proposed reason for it based in cognitive linguistics. As you pointed out, we tend to associate up with positivity and good and down with negativity and evil. The reason for this likely lies in posture. When we're healthy, we stand up straight. When we're sick, we're forced to lie down. Fear and shame prompt one to hide oneself while standing tall invites attention and curiosity, things that are only welcome to those with pride. Over time, we develop neurological associations between feeling good and being physically up and between feeling bad and being physically low. Those associations are so strong that it's hard to bring one to mind without the other, and they take the form of metaphors in language. George Lakoff has several excellent books related to the matter that go into way more detail than I could possibly provide here."
] |
[
"There's a reasonably large amount of work exploring metaphors like this by George Lakoff and Mark Johnson, and while your point that ",
" that instantiate the general metaphor are fairly young has some merit, I think your overall point that \"TALL IS GOOD\" is a recent thing is pretty off-the-mark. First off, the two metaphors \"TALL IS GOOD\" and \"LOW IS BAD\" aren't unrelated. Second, whatever the date of particular expressions that have currency today, there's etymological families like English ",
", Russian ",
" 'small', Latin ",
" 'bad', like OCS ",
" 'great', Russian ",
" 'great, big', like English ",
" and Greek ",
" 'under', or like OCS ",
" 'bad' and Lithuanian ",
" 'to bow'. These associations are common, varied, and old enough that I think it's quite unreasonable to claim that these metaphors are new.",
"Edit: It's also not true that ",
" has no historical connection with verticality. The oldest citation the OED has for ",
" is from ca. 1300, where it's used with the meaning \"to cast or fling down\"."
] |
[
"If someone was about to be shot in the chest/torso, would it be beneficial to tense the body, relax the body, or no difference?"
] |
[
false
] |
Would tensing somehow minutely limit the impact at all?
|
[
"Theoretically, yes. Practically, probably not but maybe.",
"When muscles contract, the sarcomeres pull over each other like a million little games of tug-of-war. The final result is that the muscle becomes shorter, but denser. ",
"See animation here",
".",
"At some point (far enough distance from shooter to victim) this difference in muscle density could possibly affect how far into the victim the bullet travels. In the case of penetrating injuries, a distance of a few millimeters can mean the difference between life and death ",
"as this kid found out",
"! (NSFW!)"
] |
[
"If we look here",
" it seems that density of fibers increases by 25% when contracted in rats. ",
"Here",
" we have a density measurement of 1.06kg/liter in a mouse.",
"Kevlar has a relative density of 1.44, so if we work from it's capabilities and extrapolate the muscle out to now 1.325 we can see there's a good increase in the density of muscle fibers, but the problem is that kevlar works because it's layered, and because of it's tensile strength, not it's density.",
"Maybe someone else can do the math, but I doubt there's going to be enough of a benefit for it to matter."
] |
[
"Thanks! And sorry for posting multiple times, Alien Blue was acting up."
] |
[
"If I fell asleep in an airtight room filled with only enough oxygen to keep me alive for a few hours, would I wake up before dying?"
] |
[
false
] | null |
[
"You would probably wake up gasping for air before dying slowly. The partial pressure of oxygen in air is 21kPa. And in blood about 13 kPa. It gets diluted as it makes it's way through the lungs. ",
"If some one was in a room with fixed amount of oxygen the concentration of oxygen in that room would fall in an exponential fashion. You would get a similar mirroring in your arterial concentration. Your body has chemoreceptors which predominantly sense carbon dioxide levels (that's why you get breathless when holding your breath, your carbon dioxide levels rise) but they do sense oxygen levels but only when they drop to a significant level. ",
"Once the partial pressure of oxygen in blood falls below 8kPa, which in normal life happens at altitude you will start increasing your respiratory rate and depth of breathing. And this will increase massively for every drop in kPa. ",
"As in OP's situation it would be an insidious onset there would be a considerable amount of time before one dies. Arterial blood samples have been taken from people near the top of everest and people have been alive with arterial oxygen pressure of around 4kPa (I can't remember the exact number)",
"There are a host of other acute physiological changes that occur to keep you alive longer. ",
"Edit: spelling"
] |
[
"You would wake up after your blood oxygen levels dropped below a certain point, which is what happens to people with sleep apnoea. The level required for you to lose consciousness is lower than the level which would wake you up with a start, so you would wake up, and then probably pass out quite a bit later. "
] |
[
"Then why do people dying of nitrogen asphyxiation die peacefully? They're breathing a gas with absolutely no oxygen yet they pass out and die without struggling. Same goes for people breathing helium. CO which eliminates the bloods ability to carry oxygen kills people in their sleep all the time. People only seem to panic when they breathe air with elevated co2. "
] |
[
"If Robert Hooke discovered individual cells in \"micrographia\" in 1665, why is the first working microscope atributed to leeuwenhoek?"
] |
[
false
] |
[deleted]
|
[
"Honestly, I don't think it's true that van Leeuwenhoek is credited strictly with the invention of the first microscope; certainly he's credited as the father of microbiology and ",
". There were microscopes built decades before van Leeuwenhoek entered the discipline (including by such luminaries as Galileo). Van Leeuwenhoek became well-known among his contemporaries as a lens and microscope-maker of uncommon skill and he was the first to observe independent microorganisms (\"animalcules\"), rather than cells of macroorganisms, so ultimately his is the name that became associated with microscopy even though Hooke was also a pioneer. Hooke in general has not been popularly credited with as much as he probably deserves, much of which has been recently attributed to his feud with Newton (who, as the later President of the Royal Society had a ",
" of power to decide who got credit/became prominent). "
] |
[
"So who actually invented the first microscope?",
"According to Smithsonian Magazine, a Dutch father-son team named Hans and Zacharias Janssen in the late 1500s.",
" They invented a compound microscope with magnification between 3x and 9x. Of course, single-lens magnifying glasses predated this compound microscope by centuries.",
"Also, werent most of leeuwenhoek`s findings more or less ignored in the sense that no one else made effort in furthering microscopy till around the 1700 hundreds?",
"It's true that van Leeuwenhoek was the most advanced microscopist during most, if not all of his lifetime (for the reason that he could build superior microscopes to everyone else) but I'm not sure what you're talking about, as he was active into the early 1700s. It is worth mentioning, though, that microscopy benefited greatly from bright artificial lighting, including spermaceti candles, paraffin lamps, gas lamps, and eventually electric lighting."
] |
[
"So who actually invented the first microscope?\nAlso, werent most of leeuwenhoek`s findings more or less ignored in the sense that no one else made effort in furthering microscopy till around the 1700 hundreds?"
] |
[
"So exactly what IS energy?"
] |
[
false
] | null |
[
"Well to ",
"put",
" it as Richard Feynman did:",
"\"There is a fact, or if you wish, a law governing all natural phenomena that are known to date. There is no known exception to this law – it is exact so far as we know. The law is called the conservation of energy.\nIt states that there is a certain quantity, which we call “energy,” that does not change in the manifold changes that nature undergoes. That is a most abstract idea, because it is a mathematical principle; it says there is a numerical quantity which does not change when something happens.\nIt is not a description of a mechanism, or anything concrete; it is a strange fact that when we calculate some number and when we finish watching nature go through her tricks and calculate the number again, it is the same.\nIt is important to realize that in physics today, we have no knowledge of what energy “is.” We do not have a picture that energy comes in little blobs of a definite amount. It is not that way. It is an abstract thing in that it does not tell us the mechanism or the reason for the various formulas.\"",
"For everyday use however, I'd refer you to the textbook definition of energy: the ability to do work. I know it's a vague and unfulfilling answer but that's because energy comes in so many forms it's hard to put one definition on it, and this works the best. If you want to give an object kinetic energy, you got to get it moving, and to get it moving, you expend work. If you want to give an object gravitational potential energy, you expend work to change it's height about of the surface of the earth. But you can't get energy out of anywhere. Whenever you give or take energy, that energy comes at an expense from some other place. "
] |
[
"In general relativity, energy conservation can be violated. Since spacetime is time-translational-variant Noether's theoerem doesn't really apply.",
"You don't need GR to violate conservation of energy. Noether's theorem ",
" applies. It applies in classical mechanics, relativistic mechanics, quantum mechanics, relativistic quantum mechanics, etc.",
"If your system is not invariant under translations in time, the Hamiltonian is not conserved.",
"Cosmological expansion is one particular example, and it just happens to be a case where you use GR to describe it."
] |
[
"What is it as a \"thing\"?",
"I believe the takeaway here -- what Feynman and ",
"/u/imthedogtor",
" are driving at -- is that there ",
" a \"thing\" that corresponds to what energy is. Energy is not tangible, not ",
" -- it is a purely mathematical property that can be used to ",
" an object or system: it is part of a ",
" of a thing, but is not a thing in and of itself. Much in the same way that momentum is not a thing, and frequency is not a thing, and so on. Those concepts ",
" things, but ",
" things in and of themselves.",
"This is further reinforced by the fact that energy is relative -- two observers in different reference frames can see the same object/system as having different amounts of energy. So energy is not, categorically, something that is a definitive part of an object or system, or something with a physical form. It's just a number that we can use to describe systems, and per Noether's theorem, whenever that number doesn't change, it means that your system possesses a certain symmetry (symmetry under time coordinate translations). To a certain extent, you can see differences in energy (of the same object in the same reference frame) as being a measure of the degree to which that symmetry is held or violated. If the energy remains unchanged after some transformation or process is applied, the symmetry is held perfectly. If it changes, then the symmetry is broken or otherwise not possessed by the system.",
"Hope that helps!"
] |
[
"Is plate tectonics really necessary for preventing continents from sinking into the sea (through erosion)?"
] |
[
false
] |
Numerous books (like Brownlee's "Rare Earths" say that). But on the other hand, a fairly recent discovery showed this: ScienceDaily (June 25, 2007) — A University of Utah study shows how various regions of North America are kept afloat by heat within Earth's rocky crust, and how much of the continent would sink beneath sea level if not for heat that makes rock buoyant. "If you subtracted the heat that keeps North American elevations high, most of the continent would be below sea level, except the high Rocky Mountains, the Sierra Nevada and the Pacific Northwest west of the Cascade Range," says study co-author Derrick Hasterok, a University of Utah doctoral student in geology and geophysics. "We have shown for the first time that temperature differences within the Earth's crust and upper mantle explain about half of the elevation of any given place in North America," with most of the rest due to differences in what the rocks are made of, says the other co-author, David Chapman, a professor of geology and geophysics, and dean of the University of Utah Graduate School. Were plate tectonics required to uplift the Eastern half of the U.S? Even though it probably hasn't been uplifted by plate tectonic processes for millions of years?
|
[
"Huh, it's nice to see news from my Alma mater, and I've worked with both of these people. But, to answer your question, if there were no plate tectonics to begin with, this would mean that the fundamental view of our Earth would have to change. There probably wouldn't be any convection currents in the mantle, which means that the outer core wouldn't be producing heat, which means that we would be on a dead floating rock, not much unlike the moon. ",
"To get to the point of the section that you linked, they are saying that the buoyancy produced by the addition of heat can cause an area to be 'artificially' higher in topography. However most of the isostatic conditions on continental crust is due to the type of crust, not just the heat flow. ",
"The information in the linked text is nothing new, and I'm not quite sure why they are making a large deal out of it, as it is something that has been known of and studied for about 20-30 years. However, it might just be the scope of the effect, rather than the mechanisms. ",
"*edit : Sorry, didn't even answer the last part of your question: There were mountain building events called the Laramide and the Sevier orogenies which were due to the pushing of the oceanic plates onto the North American Plate. After that, there was extension between the mid portion of Utah to California. This extension thinned out the continental crust and with it brought hot asthenospheric material nearer to the surface, which is the main portion of where the heat came from that they are speaking about in that article. Again, this is stuff that has been known for quite a while, so the importance of this article seems. . . artificial"
] |
[
"depends on if there is active sedimentation or erosion, but on a whole, yes it will erode until it gets to point that it becomes low enough to have standing water, and then it will most likely experience sedimentation and filling.",
"Take a look at ",
"this map",
" of the elevation of the mid-U.S. Note how it steadily decreases to almost 0 from the west and the east. The west has active tectonics, and the East has passive tectonics (however it was a mountain building event rather than a basin event such as in the center of the U.S.). "
] |
[
"The local temperature gradients can be determined by a number of factors, namely: ",
"When you have continental extension, and especially the wide-rift style type of extension in the Basin and Range, the temperature gradients are basically determined by the depth to moho, and the amount of stretching (which is also linked to the depth to moho). The convection currents really only come into play if you unroof the mantle, thus producing proto-oceanic crust, and then oceanic crust. Before that stage, the convection currents may help the extension, but it is the fact that the extension was there to begin with that the currents may help. . If that makes sense. "
] |
[
"What portion of a person's calories are absorbed in the stomach as opposed to the intestines?"
] |
[
false
] | null |
[
"It depends on the food, only glucose can be absorbed directly into the stomach, because it does not require any digestion. Disaccharides and polysaccharides need digestion prior to absorption. "
] |
[
"Also, alcohol is the only other thing to be absorbed in the stomachs itself"
] |
[
"I always thought it was possible to absorb a small amount of carbohydrates in the form of glucose in the oral mucosa and stomach. (Medical personnel sometimes give orange juice or glucose paste to treat insulin shock in people with low blood sugar. It works so quickly that I always thought it didn't have time to get to the intestines.) But glucose is already a form of broken down sugar (I don't know how well you could absorb polysacharides this way) and absorption by mouth and stomach certainly isn't a route that you could use for lipids and proteins. (The stomach is more acid then a car battery. I think it can absorb acid things well but it can't absorb oils because oils aren't soluble in the hydrochloric acid that's in the stomach. You need bile from the liver-which acts a bit like bleach-to make fats soluble for absorption.) Plus there are people alive today who have had their stomachs removed because of stomach cancer risk and they do fine without them...",
"...Almost forgot. The stomach can absorb aspirin and alcohol (both of which are slightly acid.) Alcohol has seven calories per gram so if you're like me and you consume a great deal of both each day then you could theoretically get a significant amount of calories from stomach absorption alone. But that's the only way you could get a significant amount of calories from your stomach."
] |
[
"Can you refract light in a circle with the right materials?"
] |
[
false
] | null |
[
"Actually, you can: you make a ",
" big one, fire off the beam of light, then take the light source out and replace it with a mirror/refraction setup before the light finishes making the circuit. "
] |
[
"No.",
"One way to see this is because the equations that describe the motion light can be reversed in time. If you have a setup that somehow causes light to travel in an un-ending cycle, you should be able to reverse time and watch the light going in an un-ending backwards cycle. And that right there is the conflict: \"un-ending cycle\". If you have a perfect loop such that light can never get ",
" when the system is run backwards in time, it means that light will never be able to get ",
" to a perfect loop when the system is run forwards in time.",
"It can't be done.",
"You can build a perfect loop (use mirrors, it's easier), but you can't insert any light into it."
] |
[
"You can make loops and insert light in them. But it's cheating and not what OP had in mind. For example lasers are sometimes built in a loop. The insertion of the light is called \"pumping\" which is in big systems nothing more than shining light on a lasing crystal.\n",
"https://www.rp-photonics.com/ring_lasers.html",
"Also, more specific for a circle, there exist something called \"Optical Ring Resonators\". ",
"https://en.wikipedia.org/wiki/Optical_ring_resonators",
"\nBut that isn't simply refracting anymore as OP specified, it's a wave guide in which the light sort of resonates with a nearby light wave."
] |
[
"What species is this bird? seen in Florida"
] |
[
false
] | null |
[
"Hi! We generally don't do ID questions. You'll do much better in ",
"/r/whatsthisbird",
", which is full of people who want to identify birds. I'm a birder and I'm not sure what this is...was this really a wild bird from Florida? It looks like a tanager of some kind, but not anything native to the state!"
] |
[
"oops! sorry was looking for a sub like that and couldn't find it! thanks for the re direction :) it was around the disney animal kingdom park, so i suppose very likely it could have been from around there"
] |
[
"Good luck! I'm curious now, too. "
] |
[
"When your car windows fogs up on the inside during cold weather, is it better to use hot hair or cold air to clear it up?"
] |
[
false
] | null |
[
"This is what happens:",
" you'll eliminate condensation by having both sides of the window at the same temperature. Corollary: keep the aircon on, otherwise the window will fog up again because of the temperature difference.",
" you'll add capacity to the air to absorb moisture (warm air has a larger capacity, think humid summer days vs. dry winter days), thus removing it from the window. This process will take a bit longer between heating up the air and transferring all the vapour away from the window, but it will be more sustainable, and, more imporatantly, more comfortable."
] |
[
"I was told to use warm air + turn on AC so the warm air would be drier, does that make sense? But it works!"
] |
[
"BOTH: Turn on the AC and turn up the heat. Assuming the ambient humidity is at all high (which is probably is if your windows are fogging up) AC coils will collect condensation, drawing some moisture out of the air before it enters the cabin. If you then heat that air up, you further reduce it's relative humidity allowing it to pull the moisture off the window quicker. The exception to this is if the outside air is VERY cold (significantly below freezing) where the air can't be holding much water to begin with. In these cases turning on the AC just makes the air colder, not dryer. In many cars (Hondas at least) you don't have a choice though, as switching the airflow director to the defrost setting automatically turns on the AC.",
"Also, TURN OFF RECIRCULATE. If your windows are fogging up, the air outside the cabin almost certainly has less moisture in it than the air inside the cabin.",
"One weird case: If you're in a hot, extremely humid environment (e.g. south-eastern US during summer) and you turn up the AC too far, you can start getting condensation on the OUTSIDE of the windows. In these cases just turn down/off the AC.",
"Whenever you're running the AC, before you turn off your car TURN OFF THE AC AND LEAVE THE FAN ON FOR A FEW MINUTES. Otherwise the moisture will sit on the AC coils and grow mold. Turning off the AC lets the coils warm up to ambient and shed their moisture (assuming the ambient RH isn't ",
" high)."
] |
[
"When my fork or spoon scratches against a bowl or plate, does it scratch off tiny, perhaps microscopic, pieces of the bowl? If so, are these bad to digest?"
] |
[
false
] | null |
[
"In all likelihood, yes. However, unless you actually make visible chips, we're talking really, really microscopic here, and really small amounts. They would certainly not be big enough to cause any physical damage (cut up your intestine, for example) and most would probably pass straight through undigested. Some materials (some clays or ceramics, for example) might have some elements which could be absorbed by the body and used for something or other. Again, though, we're talking really minute amounts, so the effects would be tiny.",
"The exception could be some particular materials (lead, for example) that could be absorbed by your body and over (a long) time, accumulate and cause you harm, which is why we don't often use some materials as food containers or cutlery (again, lead springs to mind).",
"In any case, if the (really, really) minute amount of material belonging to our cutlery and plates that we consumed while eating was bad for us, we probably would have stopped using plates and cutlery long ago."
] |
[
"Just adding here: Ceramics are made by mixing compounds and baking them at really really high temperatures. This causes the atoms to relax to really stable configurations - if they could react with anything, they most likely already did that. So ceramics are quite chemically inert which means you can often use them to store reactive agents without they react with the container and also doesn't give off atoms from their structure. So most likely they will also not react with anything in your body and just pass through. Of course they can still contain certain elements that can be extracted/dissolved in the right environment, but they are of course avoided in products for food use."
] |
[
"Thanks for the reply!"
] |
[
"What causes 'suicidal thoughts'?"
] |
[
false
] |
I'm a little bit curious after reading about the side effects of drugs such as Accutane, where a Redditor described being tempted to drive into a tree because of taking Accutane? What happens physiologically in our body that causes those thoughts? At a stretch, I understand depression, because it's...simply a disinterest in life. But actively wanting to perform an act to kill yourself...? I don't get how a drug an incite you to have those thoughts. As in, is there a 'suicide' trigger in your brain? A thousand apologies for the non-medical, unclear language I'm using.
|
[
"\"Suicidal thoughts\" could be defined in 2 ways: ",
"I think number 2 is more relevant to your question. This is ",
"an article",
" about ",
"this study",
" on the phenomenon, experienced by a third of the sample at some point in their lives. The researchers reach a conclusion (people misinterpret the instinctual safety signal) which they admit is speculative. I have read about this before, and remember another theory which speculates that the urge to jump encourages people to move away from dangerous places, and so increases their chances of survival (cannot find source). ",
"As to the effects of drugs on this phenomenon, I can't find any research, and shouldn't speculate as this is askscience."
] |
[
"Originally l'appel du vide in French. It has a lot to do with existentialism and the understanding of our \"radical freedom\" in an absurd existence."
] |
[
"Originally l'appel du vide in French. It has a lot to do with existentialism and the understanding of our \"radical freedom\" in an absurd existence."
] |
[
"Can a decimal be even or odd? Is there a classification for decimals like even and odd for whole numbers?"
] |
[
false
] |
If I have the number 2.2, which looks even at first glance, and divide it by 2, I get 1.1. To determine if a number is even, it must be divisible by 2 and produce a whole number. Obviously this isn't the case, so therefore 2.2 isn't even. But does that necessarily mean it's odd? Is there a different type of classification for decimals like we have for whole numbers?
|
[
"\"Even\" and \"Odd\" apply only to integers."
] |
[
"You can talk about evenness of rational numbers. Take a fraction A/B, where A and B are integers, and factor out all the 2's from them. If there is a positive power for the 2's then the rational number is even, if there are no 2's, then it is odd. If there is a negative power for the 2, then they are like, super-odd or something.",
"For example, 20/27 = 2",
"*5/27, so 20/27 is even. There are no 2s at all in 37/35, so it is \"odd\". There are only 2s in the denominator of 15/14=2",
"*15/7, so 15/14 is \"super odd\" since multiplying by 2 still results in an odd. ",
"This doesn't work with arbitrary real numbers. Also, don't look towards decimals to try and learn anything about a number, it can lead you astray. Decimals tell us how the number interacts with 10, and not much else."
] |
[
"It can help us identify p-adic integers. If |x|",
"<=1, which happens exactly when x is not \"super-odd\", then x is a 2-adic integer. This is pretty handy in number theory and p-adic analysis in general. Though, we don't call things \"super odd\". "
] |
[
"Theoretically, could we selectively breed out or drastically reduce the need for sleep?"
] |
[
false
] |
Let's say we have animal 'X' which reaches reproductive maturity in say, 1 week. Is there some sort of chemical indicator that we can identify that correlates with a decreased need for sleep which can subsequently be enhance with focused breeding? Edit: I guess I should note that animal 'X' has no qualities that are outside of normal bounds. It can be any animal you choose provided it exists (cat, rat, sloth etc)
|
[
"Coincidentally I recently came across ",
"this article in the Wall Street Journal reporting on the 1-3% of the population that need less than 6 hours of sleep",
"Dr. Fu was part of a research team that discovered a gene variation, hDEC2, in a pair of short sleepers in 2009. They were studying extreme early birds when they noticed that two of their subjects, a mother and daughter, got up naturally about 4 a.m. but also went to bed past midnight.",
"Genetic analyses spotted one gene variation common to them both. The scientists were able to replicate the gene variation in a strain of mice and found that the mice needed less sleep than usual, too. ",
"Is 4 hours short enough for you?",
"To date, Dr. Jones says he has identified only about 20 true short sleepers, and he says they share some fascinating characteristics. Not only are their circadian rhythms different from most people, so are their moods (very upbeat) and their metabolism (they're thinner than average, even though sleep deprivation usually raises the risk of obesity). They also seem to have a high tolerance for physical pain and psychological setbacks. ",
"Not only do they need less sleep, they are upbeat, energetic and thinner than normal. ",
"I hate them already"
] |
[
"They might be mistaking the cause and the symptom. It could be possible that the gene causes them to be more healthy/upbeat/resilient and that in turn causes them to need less sleep."
] |
[
"Either way, I'm jealous. "
] |
[
"What's so special about beef that humans can basically eat it raw and not get sick?"
] |
[
false
] | null |
[
"Most harmful bacteria that will contaminate beef requires oxygen so it's only alive on the outside of your steak. Searing the outside and leaving the inside raw kills the baddies on the outside while the inside was already fine.",
"Also that's why you're supposed to cook hamburger more because once ground up the bacteria is spread throughout the patty not just the outside like a steak."
] |
[
"Your oxygen point isn't quite right. It has to do with the poreousness of the beef itself. Beef is not very poreous and as such the bacteria isn't able to get down past the surface like it is with chicken, which on the flip side is very poreous as compared to beef."
] |
[
"what adaptations do predatory animals have to avoid becoming ill from consistently eating raw meats?",
"Animals that eat raw or rotten foods have a stomach that provides a much harsher environment to ingested microbes. The extreme example are the carrion eaters such as vultures that can eat dead and rotting flesh on a regular basis. They have gut flora that is very hostile to ingested bacteria (in addition to the acidic environment).",
"Ref Nature"
] |
[
"Why can’t fish get rabies?"
] |
[
false
] |
Hi all, Aquarium enthusiast and 2x rabies shots recipient. I have lived dangerously so to speak, and lived! But I have a question for you all. I was at my local fish store joking with the owner who got gouged by one of his big fish (I think a cichlid). I made a joke about rabies and he panicked for a brief moment, until I told him it’s common knowledge that fish don’t get rabies. I was walking home (and feeling bad about stressing him out!) when I started to wonder why. For instance, the CDC says only mammals get rabies. But there’s a case of fowl in India getting rabies. I saw a previous post on here that has to do with a particular receptor that means birds are pretty much asymptomatic and clear it if exposed. Birds have been able to get it injected in lab experiments over a hundred years ago. I also know rabies has adapted to be able to grow in cold-blooded vertebrates. So, what about fish? Why don’t fish get it? Have there been attempts to inject fish in a lab and give them rabies? Or could they theoretically get it, but the water where they bite you essentially dissipates the virus? Or is there a mechanism (e.g. feline HIV —> humans) by which the disease can’t jump to fish? Thanks for any insight. I will be watching Roger Corman’s “Piranha” while I wait on your answers.
|
[
"Rabies basically enters via the muscles and is transported into the motor neurons preferentially (though I believe sensory neurons are also affected- someone else can jump in here).",
"The cells themselves at the point of infection, and cell membranes probably aren’t any less susceptible (this is an in vitro study, but you get the idea. ",
"https://pubmed.ncbi.nlm.nih.gov/1975976/",
") but the transport and and crossing the neuromuscular junctions requires a bunch of things (myotubules, probably nicotine receptors and colchiine binding sites. All of which are analogous but really different in fish. So basically, the proteins and structures in fish are doing the same things but the structure is different enough for the rabies virus not to be transported. As doors are all recognizably doors, but your key will only open some of them."
] |
[
"Good metaphor, thanks!"
] |
[
" binds to the p75 neurotrophin receptor which is highly conserved in mammals. Other vertebrates also have it but it's structured differently; rabies has adapted to infect reptiles, and we've artificially infected birds and even insect cell cultures. There's no reason it ",
" infect fish though temperature might be an issue - it would have to adapt to their variant of that receptor (or another receptor).",
"However, you can get lots of other nasty infections from open wounds in aquariums, including Mycobacterial or Erysipelothrix infections, which can spread to the bone and result in amputations."
] |
[
"Do the \"Smart Alarm Clock\" smartphone apps really wake you up at the ideal time by monitoring your sleep cycles?"
] |
[
false
] |
I know there is legitimate science that explains sleep cycles & rhythms but is the simple app plus gyro-meter in a handheld smartphone really adequate to wake you up at the ideal time? I've heard many anecdotal success stories but my suspicion is they may be placebo induced.
|
[
"It CAN work for some people, but is by no means perfect. It is certainly based on some scientific principles (i.e., movement can be a marker of transitional sleep stages). The problem is that movement is not a reliable marker of transitional sleep stages in everyone, and there can even be significant individual variations from night to night. So, basically it's based on science, and can work for some people some times. There are some more advanced apps coming out, including a very basic (3 channel I think) EEG headband that connects to your phone. If we can advance ",
" technology, I'll be pretty impressed."
] |
[
"polysomnographer here. I doubt it but maybe. Understanding what sleep level people are in takes eeg monitoring (brain waves which are different in every stage) eog monitoring (eye movement which will show rapid eye movement in REM) and emg (muscle activity, and in REM the body paralyzes from the next down as to not act out dreams). What I've gathered from these apps is that it measures movement/sound and lack of those 2 is considered \"deep sleep\". Of course there are various factors that can skew these stats ie someone else in bed moving, phone ringing in the middle of the night etc. However if you have no movement or sound and have a \"normal\" sleep cycle (4-6 REM cycles in roughly 8 hours) I suppose this thing can assume you've been through all that is needed and wake you up but in no way is it reliable."
] |
[
"I researched these in college.",
"The apps are a huge problem if you sleep with a partner, a pet, or get up throughout the night to urinate or acquire water. These can all produce false positives that will throw off the phone's interpretation of your \"rhythm\". ",
"It certainly works for some people (the popularity can attest to that), but some walk away disappointed."
] |
[
"Do we have any idea what prevents the massive force of repulsion between the protons in the nucleus of the atom?"
] |
[
false
] |
Are there any interesting theories out there? Or are we completely clueless? Also, I would love to see some interesting articles linked here!
|
[
"The \"strong nuclear force\" is a completely different thing, much stronger than the electric force at short ranges, and it doesn't care about electric charge."
] |
[
"Nothing prevents it; they ",
" feel electrostatic repulsion due to each others' charge.",
"However there's a much stronger, usually attractive force between nucleons. It's the residual strong force. This is why nucleons bind together and form nuclei."
] |
[
"Ah ok that makes more sense. Still find it odd that there is a large attractive force between subatomic particles of the same charge..."
] |
[
"How dense were dinosaur populations (e.g., t-Rex, velociraptor, brontosaurus) at the height of their respective time periods?"
] |
[
false
] |
[deleted]
|
[
"I would think sauropods, being massive herd animals, required quite a bit of room to graze. Realistically how many animals could one herd of creatures that size consist of?"
] |
[
"I would think sauropods, being massive herd animals, required quite a bit of room to graze. Realistically how many animals could one herd of creatures that size consist of?"
] |
[
"Its not so much about how many is in a herd but how big of a area does that herd range. You could have hundreds of individuals in a herd but only a herd for every hundred miles or it could be two to a herd but a herd every few miles."
] |
[
"Biology: When you wake up in the morning and your covers aren't all bunched up(meaning you didn't move much in your sleep) does that really mean you got a \"deeper\" nights rest?"
] |
[
false
] |
I don't know much about sleep or sleep patterns, but I'm curious to know a little more about this topic.
|
[
"All I really know is from what I learned in my AP psychology class this year, which isn't much :/. I just remember my mom always saying that if I didn't move around much in my sleep, I mustve slept \"really good\". Just curious to see if there's any truth in what she's saying. "
] |
[
"If that is all yes there is some truth to it. Your mom did not lie to you."
] |
[
"Well if your covers are not disturbed, you may or may not have moved much during the night. But if the covers are all at the foot of the bed, or hanging off the ceiling fan, then you certainly HAVE done some moving around...."
] |
[
"How important are the expiration dates on food really? Obviously it's certainly an issue for perishable food, but do the expectation dates really matter for dry goods and canned food?"
] |
[
false
] | null |
[
"Canned food, which has been completely sterilized, is preserved for infinity - as long as the container is intact and keeps the contents sterile. No microbial processes will spoil the food, however if acidic substances are stored in tin cans (like vegetables), the acids might interact with the tin coating, thereby spoiling the food. But this seems to be a rare event. ",
"But preserving food always leads to a trade-off in the quality of the food. I´ve once eaten a canned, 20 year old army ration - it was an edible, more or less grey pulp. Therefore not all canned food is completely sterilized, otherwise nobody would want to eat it. ",
"Also, ",
"here is a (german) article",
" about canned bread from WWII, that was still edible 50 years later. ",
"/edit:",
"Here is a picture of the canned bread",
"/edit2:",
"As for you Muffin Mix: It depends on how much you trust the packaging and the initial preservation. ;)",
"If its a dry powder, then only few microbial processes can take place - but still some xerophilic funghi might be able to grow there. \nSo the answer to the question if it´s still safe to eat it is a clear: \"Maybe.\""
] |
[
"Obviously it's certainly an issue for perishable food, but do the expectation dates really matter for dry goods and canned food?",
"Even here it's less an issue than most people believe. Even with highly perishable foods such as yogurt and all-natural cream cheese the expiration dates don't mean to much. It is MUCH more important whether or not the ",
"cold chain",
" has been interrupted and if yes, for how long (among other things. Even if the cold chain was interrupted for a significant amount of time, the fridge temp at your house makes a huge difference - colder meaning longer eatable, of course).",
"Most expiration dates on those products assume an interrupted cold chain and a somewhat high fridge temperature.",
"Personally, I have conducted... involuntary experiments on the matter. I eat tons of milk products, often forget about them in the fridge, and they will keep weeks beyond their expiration dates. If it doesn't look bad and/or smell bad, taste it. If it doesn't taste bad, it isn't.",
"There currently is research being done on a chemical label ",
" [EDIT: the manufacturer] can glue on products, that color codes how \"well preserved\" the cold chain has been for the product and that also considers the age of the product as well. As long as the label is anything but a solid blue, you can eat the product. The research group hopes to save millions of tons of milk products from unnecessarily being thrown away. Can't find their work right now, unfortunately, I just remember the problem being difficult."
] |
[
"I guess it comes down to having your brand name associated with product quality.",
"Selling electronics/cars/ect. that break every year makes a lot of sense if you want to boost sales, it doesn't mean it's a good economic choice for your company. (It also doesn't mean it's necessarily bad - e.g. Apple. The product is not expected to outlive the 1000-2000 charge cycles). It just means there is room for a competitor that focuses on quality. "
] |
[
"How would the images on the Golden Record (on Voyager 1) be displayed?"
] |
[
false
] |
Is there like some sort of projector that lights up or something? I have no idea how the images will appear. I guess I understand how to start it, however what happens after?
|
[
"Nope. There’s a stylus to read the record just like a vinyl record and some instructions on the back to interpret the analog signal and a “You got it right”-welcoming screen that will show a perfect circle if everything is calibrated correctly. ",
"So other than the record and stylus it’s BYO when it comes to showing the picture and hearing the sound. ",
"It’s not that much of a stretch that an alien civilization that can intercept an interstellar space craft the size of a minivan can probably stitch together a few electronics to read and display the signal. Since we give information on timing and distance via universal units of measurements - think bananas and elephants but for physicists - then it shouldn’t be too hard. ",
"The Wikipedia article on its playback is a good start. ",
"https://upload.wikimedia.org/wikipedia/commons/thumb/e/ed/Voyager_Golden_Record_Cover_Explanation.svg/800px-Voyager_Golden_Record_Cover_Explanation.svg.png"
] |
[
"an alien civilization that can intercept an interstellar space craft",
"That's a really important point. The chance that Voyager hits something is tiny, and even if it would hit a planet it would burn up or get destroyed by the hard impact. It won't be studied by people who just discover how sound waves work. To even have a chance to decode something an alien civilization needs to detect the tiny inert spacecraft over astronomical distances and needs to launch some sort of recovery mission."
] |
[
"Each image is encoded in binary on the disc in three channels: Red, Green, and Blue. The first image is a white circle so if they decode any one of the channels correctly, this will be the first clue.",
"There are also instructions that show each image is constructed from 512 vertical lines, with 8ms between each pass and then interlaced like an old CRT television. A space-familiar race should be able to put that together, and then adjust the aspect ratio to make sure the image they pull out then matches the circle shape."
] |
[
"Can I save myself from \"nerve gas\" poisoning by ingesting tomato leaves?"
] |
[
false
] |
Looking at how atropine is used as first-line treatment for poisoning by organophosphate nerve agents like Sarin, Soman, Tabun, VX etc. (i.e. anything that acts by inhibiting acetylcholinesterase enzyme), would naturally occurring tropane alkaloids administered orally have the chance to save my life, or reduce the damage, if administered soon after exposure? Would oral administration by anywhere near fast enough, what kind of dosage would be appropriate, and how likely am I to accidentally give myself a fatal dose of atropine? What effect would the other alkaloids have, i.e. scopolamine, etc? Thanks guys, as always. EDIT: Spelling
|
[
"As a graduate from the US Army's Nuclear, Biological and Chemical school, I'd say no.",
"We were taught that even the atropine auto-injectors that the military issued would likely be useless if you got a good dose of Sarin or VX. The atropine was just issued as a \"hope for the best/better than nothing\" type of thing."
] |
[
"Right. I was guessing that perhaps there was some amount of hope because when I was reading about the Tokyo Subway Sarin Attack, when the victims were being treated in hospitals hours later, some doctor who recognised the symptoms of nerve agent poisoning faxed information about the antidote to the city's hospitals, was said to have saved many lives, and prevented serious nerve damage in others. Though it has to be noted that the dosage that most of the people affected received was quite low in that particular case."
] |
[
"If tomato leaves contained any kinds of alkaloids which were useful I suspect they would be in far far too lower concentration. Most natural products are. You'd have to eat tonnes of leaves. Also the time for the leaves to be digested and make their way into the bloodstream would be orders of magnitude slower than the amount of time the nerve agent took to kill you.",
"tl;dr: no."
] |
[
"Is unplugging an electronic device that is fully charged, then plugging it back in so it charges more bad for the device?"
] |
[
false
] |
I've noticed that every rechargeable battery, if unplugged then plugged back in, keeps charging. Is this increasing the charge? Does it hurt the battery or cause it to wear out faster?
|
[
"When your battery reaches ~95% charge most devices will 'trickle charge' i.e. they will add small amounts of charge compared to the normal charging. They do this because it isn't good for the battery to be fully charge for long periods of time, they can lose their capacity over time if you do this a lot.",
"By unplugging the charger and plugging it back in you are probably starting the normal charging up again so that you go from ~95% to 100% charge. ",
"If your device is smart in anyway (smart phones) then you will most likely not do anything to harm the device itself but you may lose capacity in the battery over time.",
"(note this applies to lithium ion batteries, other kind of batteries behave differently)",
"http://arstechnica.com/gadgets/news/2011/02/ask-ars-what-is-the-best-way-to-use-an-li-ion-battery.ars"
] |
[
"It depends on the type of battery used in the device and the battery-specific term is called \"short cycling\" if you wish to look into it more.",
"The short answer is there's no harm, at least with respect to the ubiqutious Lithium-ion batteries or Nickel Metal-hydride. Its an idea left over from rechargeable Nickel-Cadmium batteries which would develop a \"memory effect\" unique to their chemistry. In NiCd batteries this \"memory\" can be reset by fully discharging the cell before recharging it.",
"If you have further questions on battery chemistry just reply to this comment."
] |
[
"Thanks for the response and the source!"
] |
[
"If humans survived for 100 thousand years, wouldn't the evolution of some species be obvious to see?"
] |
[
false
] | null |
[
"Biology"
] |
[
"Biology"
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"A good home for this question is our sister subreddit ",
"/r/AskScienceDiscussion",
" because of its open-ended or speculative nature. Please feel free to repost there!",
"Please see our ",
"guidelines",
".",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"What, physically, happens when I get the wind knocked out of me?"
] |
[
false
] |
When I was younger I thought it was my lungs fully emptied, but that doesn't make sense. Is the diaphragm going too far one way? Is it a by-product of evolution?
|
[
"Unfortunately this is a common misconception. The celiac plexus is located deep to the diaphragm and actually has no contribution to diaphragm activity (it functions to help regulate your foregut). It is correct that having the wind knocked out of you is due to a diaphragmatic spasm, but this is directly due to the trauma of the blow. This is why it is more likely to get the wind knocked out of you with a full breath in your lungs, since when you exhale your diaphragm is protected by your ribcage."
] |
[
"Getting the wind knocked out of you is often a response to a hard blow near your solar/celiac plexus. ",
" The force of the impact causes your diaphragm to spasm, causing it to not work as intended.",
"Until the spasm goes away, your diaphragm will have trouble working properly.",
"Source: ",
"http://en.wikipedia.org/wiki/Celiac_plexus",
"Edit: Corrected as per the reply."
] |
[
"Whoops, you're totally right. My bad, thanks for the correction."
] |
[
"Do vinyls really have a better audio quality than CDs?"
] |
[
false
] |
I think everyone knows a person, which loves vinyls and often states how much better the sound is. The theoretical background behind this assertion is, that a digital saved audio file can only have a finite accurateness, while this is not true for analag stored audio (until the effects of quantum physics occur etc.). But my question is: Do vinyls have a better sound than CDs? CDs have a samling rate of 44.1 kHz, so as per the sampling theorem one can represent frequencies up to 22 kHz, which is enough for humans (afaik). The samples have 16 bit, I do not know whether humans could hear a difference if they had 24 or 32 bit. On vinyls, a major drawback is in my opinion the loss that occurs when pressing the vinyl and when reading the information (I think noise when reading the information is unavoidable). I also heard, that the rotational velocity of vinyls is too low and that with a higher speed one could achieve a more exact representation of the original audio. I have searched the web, but I only found biased discussions between "digital" and "analog" lovers, are there any studies on that topic etc?. Edit: Thanks for the answers. I did not think that there are so many factors which play a role in representing the audio signal.
|
[
"I have searched the web, but I only found biased discussions between \"digital\" and \"analog\" lovers, are there any studies on that topic etc?.",
"When it comes to high-end audio and music listening gear, the placebo effect plays a huge role in people's perceptions. More importantly, when people make qualitative judgments about audio gear, they aren't necessarily judging the audio ",
". Instead, they are rating their ",
" of the particular audio experience, but projecting that into terms of audio quality. The ritual of carefully loading a vinyl on to your favorite record player and delicately placing your expensive, high-end needle into the track you're about to listen to is bound to induce some sort of anticipatory pleasure, which will color the user's perception of the track. Furthermore, the subtle crackle of dust and imperfections on the record signals to the listener that this is, indeed, a vinyl record and conjures up all of the associated pre-conceived perceptions about what vinyl should sound like.",
"Often, you'll find self-proclaimed audiophiles declaring that one CD player has better PRAT (pace rhythm and timing) than another, despite the fact that the timing drift for the clocking systems in even the worst CD players are well below what humans could perceive, let alone the amount of variation it would require to alter the pace, rhythm, and timing of replayed audio. In fact, this is one area in which vinyl would arguably have much worse performance than CD, due to the mechanical rotation of the disc and all of the timing variations that come with it.",
"As for quantitative audio quality differences between the two mediums, the CD is superior. CDs operate at a sampling rate of 44.1kHz. These are discrete points, versus the continuous signal produced by a physical vinyl groove. However, the Nyquist-Shannon sampling theorem explains why a 44.1kHz sampling rate is sufficient for completely reproducing frequencies up to 44.1 / 2 or 22.05 kHz (See ",
"http://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampling_theorem",
" ). True response will actually be lower than 22.05 kHz due to the various anti-aliasing filters involved in the analog-to-digital and digital-to-analog conversion process to prevent frequencies above 22.05 kHz from aliasing down into the audible range (See ",
"http://en.wikipedia.org/wiki/Aliasing#Folding",
" ).",
"Furthermore, the CD is recorded with 16 bits of resolution, results in an output with 65,536 discrete voltage 'steps' on the output. This does introduce some quantization noise, because the real signal is 'rounded' up or down to the nearest of the 65,536 steps. This is another area where some people claim vinyl is superior due to the lack of quantization of the output. But in practice, vinyl only has 9-10 bits of resolution (IIRC) due to manufacturing tolerances. To achieve around 16 bits of resolution, the tolerance of production for the groove would have to be on the order of 1/65,536 or ~0.001%. That's not going to happen on those tiny grooves. Also, you have to consider the non-zero inertia of the physical pick-up moving across those tracks, which will introduce a separate set of distortions as it moves around.",
"Side note: CDs are often mastered internally at 24-bits, but this isn't because humans can hear the difference between 16-bit and 24-bits. Instead, 24-bits gives the producers more bit overhead to use in the mixing process. Various operations will lose bits and introduce more noise, so starting with 24-bits gives the audio a much better chance of still having 16-bits of good information by the time the mixing process is complete. True 24-bit sources are actually very difficult to implement properly, as various voltage noises in the circuit start becoming significantly large relative to the signal voltage. 24-bit sources are pure marketing.",
"There is one more complication in this comparison. Not all distortions are actually perceived as negative by listeners. Jean Hiraga introduced the concept of ",
" many years ago (See ",
"http://www.stereophile.com/reference/406howard",
" , I can't find the original right now). The idea is that certain harmonic distortions are actually perceived as enjoyable or superior by listeners. It's counter-intuitive at first, but explains why many speak of preferring the 'warmth' of tube amplifiers, despite their obviously higher distortion characteristics relative to truly linear amplifiers. This is just another example of how perceived audio 'quality' is only loosely correlated with how accurately the audio signal recreates the original signal.",
"So to answer your original question: Vinyls do not have better ",
" audio quality than CDs. However, it's entirely possible that listeners would ",
" vinyls to have a higher ",
" audio quality due to a combination of psychological factors."
] |
[
"This is a fantastic video that explains the digital side of things from the guys who make the Ogg Vorbis encoder and a lot of other good stuff.",
"http://xiph.org/video/vid2.shtml",
"In general, 44.1 KHz is enough for anyone and is capable of perfect fidelity (more can sometimes introduce noise if the speakers cannot precisely reproduce sounds at that frequency) . 16 bits of amplitude is not quite capped for humans, an attentive listener can theoretically tell the difference between 15 and 16 bits (after a lot of money spent on equipment), but 24 is far more than enough and 32 would be ridiculous. There is some debate at where Vinyl falls in terms of bit depth, but common consensus has it under 16, typically 12-14 depending on specific production details and how often the record has been played."
] |
[
"I will not attempt to answer the entire question, but I will add this to the discussion. A vinyl record decreases quite drastically in quality as the needle moves from the outside edge, to the center. This is because rotational speed is constant, while the radius of the circular groove gradually decreases while the record plays. So the songs near the outside of the record sound noticeably better.",
"\nAnother issue with most players is that as the tonearm sweeps across its arc, the side to side angle at which it meets the groove changes. At only one point on the record does it align with the grooves. There are ways of solving this problem, but they tend to be very expensive. "
] |
[
"How do we detect what colours an organism can perceive?"
] |
[
false
] |
I understand colour blindness tests in humans, but they can verbally communicate. How do we know that dogs are colour blind or that the mantis shrimp can perceive more colours than we can?
|
[
"the main way to understand animal color vision is to see what photopigments are expressed in their retinas (or whatever they have). in vertebrate vision, each photopigment serves as one dimension in the visible color space, so the more pigments you express, the larger the space of colors you can experience. humans and most old world primates have three daytime pigments, so we're all \"trichromats\", with a three-dimensional color space; most other mammals just have two pigments (like a 'colorblind' human), so they're all \"dichromats\", with a two-dimensional color space.",
"many (most?) birds are ",
", with four functioning daylight photopigments; so we assume they experience more colors than we do.",
"as far as i know, most invertebrates have at least trichromatic vision; bees are trichromats, like us.",
"the famous mantis shrimp is an odd example; it has like a dozen pigments, but ",
"it seems unlikely that it uses them to set up a color space",
" (it would be amazingly complicated if it did; ); it's more likely that those pigments are used to create a sort of linear wavelength domain, which is very rare in the animal kingdom.",
"you can also do behavioral testing with just about any animal, by using a standard sort of 'T-maze' design. basically, you put the animal in a chamber with two exits, each of which is marked by a different stimulus, one of which has been associated with a reward (food or water usually). if the animal can get the right answer consistently, this implies that it can distinguish the stimuli, and these behavioral distinctions can be used to estimate the animal's subjective color space.",
"these behavioral tests generally bear out the basics of color theory, i.e. that if you have X expressed photopigments in your photoreceptors, you have X-chromatic vision (with some exceptions exemplified by the mantis shrimp)."
] |
[
"You are very kind. Thank you very much for you detailed explanation! "
] |
[
"Good explanation. One thing I'd like to add: just because an animal has more photopigments, or photopigments that cover a larger range on the spectrum, doesn't automatically mean that it perceives more colors. Color discrimination ability is an important factor that can be revealed by those behavioral tests. Show an animal two increasingly similar spectral colors and sooner or later they won't be able to tell the difference between them. Humans can tell apart spectral colors as close as 1 to 4 nm. Mantis shrimp only to about 25 nm (source: the paper you linked). I read a paper about pigeon vision once and they had a discrimination ability of around 10-20nm, if I remember correctly.",
"In addition to mantis shrimp, butterflies are another example where the amount of photopigments does not match the dimensionality of their perceived color space. Some species have 6 to 8 pigments, but ",
"appear to be just tetrachromats",
"."
] |
[
"Does all baryonic matter decay?"
] |
[
false
] |
Does the Universe have a unique “ground state” where entropy dictates matter inevitably go?
|
[
"The lightest baryon is the proton. So if baryon number is really always conserved, the best we can do is have all baryons decay into protons.",
"Well we \"know\" that baryon number is not conserved at high energies due to the Adler-Bell-Jackiw anomaly of the standard model such that only B-L is conserved.",
"Also cosmological history already tells us that B should not be conserved."
] |
[
"The lightest baryon is the proton. So if baryon number is really always conserved, the best we can do is have all baryons decay into protons.",
"Well we \"know\" that baryon number is not conserved at high energies due to the Adler-Bell-Jackiw anomaly of the standard model such that only B-L is conserved.",
"Also cosmological history already tells us that B should not be conserved."
] |
[
"Do ",
" elements decay? To what?"
] |
[
"AskScience Cosmos Q&A thread. Episode 8: Sisters of the Sun"
] |
[
false
] |
Welcome to AskScience! If you are outside of the US or Canada, you may only now be seeing the seventh episode aired on television. If so, This week is the eighth episode, "Sisters of the Sun". The show is airing in the US and Canada on Fox at Sunday 9pm ET, and Monday at 10pm ET on National Geographic. Anyone can ask a question, but Popular science shows, books, and news articles are a great way to causally learn about your universe, but they often contain a lot of simplifications and approximations, so don't assume that because you've heard an answer before that it is the right one. If you are interested in general discussion please visit one of the threads elsewhere on reddit that are more appropriate for that, such as , , and . Please and . We'll be removing comments that break our rules and some questions that have been answered elsewhere in the thread so that we can answer as many questions as possible!
|
[
"A bit of a correction to the science in the show: Not all supernovae are actually nuclear explosions. ",
"The show portrayed the death of the star Rigel in a ",
"core collapse supernova",
", which is indeed the expected fate, but Tyson incorrectly referred to it as a nuclear explosion. In fact a core-collapse supernova gets its energy from the gravitational potential energy of the star's core, which is released as it collapses into a proto-neutron star. Many nuclear reactions take place in the extreme environment of the supernova, but on the whole they actually ",
" energy rather than release it. ",
"I explain some more details in the last section of this comment.",
"Some supernovae are indeed nuclear explosions, including ",
"explosions of white dwarfs (type 1a supernovae)",
" and the ",
"explosions of the incredibly large stars that existed in the early universe (pair instability supernovae)",
". There are also the ",
"classical novae",
" that he described taking place on the surfaces of accreting white dwarfs."
] |
[
"With a show as broad as Cosmos you're going to see a lot of generalities and some innacuracies to appeal to a brlad audience. Sagan had the same problem when he started talking about the Library at Alexandria for example."
] |
[
"It is tightly bound by its own gravity, so it does not disperse. It will be a small dark ball of mostly carbon and oxygen. This phase could be called a ",
"black dwarf",
". There are not expected to currently be any black dwarfs in the universe, because the universe is not old enough for a white dwarf to have sufficiently cooled."
] |
[
"If I moved a lake (includes plants, fish etc.) from here to mars, would the inhabitants survive?"
] |
[
false
] | null |
[
"Think about what sort of things fish, other marine life, and plants need to survive on earth. Then think about the environment of the earth is different than the environment on mars, and if the life in the lake could handle that kind of change. ",
"I'll start you off with one. Earth is the 3rd planet from the sun, while Mars is the 4th. Depending on the time of year, Mars is like 40-200 million miles away from Earth, so it's that much farther from the sun. The sun is like a big camp fire, and the closer you are to it, the hotter you feel. So mars is farther away from the camp fire, and as a result its quite a bit colder there. In fact its thought to be about -17 C- -250 C depending on the time and season. The coldest ever recorded temperature on earth is about -75 C. So basically, the lake would be pretty frozen, but depending on how deep it was it might not be frozen all the way through, so maybe some of the more hardy life could survive",
"Can you think of another difference like that between earth and mars?"
] |
[
"There is a rare atmosphere on Mars. It exists, but pressures are so low that water would boil away. "
] |
[
"Except that the ice is going to sublimate from the top down on warm days (depending on latitude), progressively exposing more water to freezing. "
] |
[
"True Zero G"
] |
[
false
] |
[deleted]
|
[
"It depends what you mean by \"zero g\". One of the fundamental tenets of general relativity is that acceleration and a gravitational force are fundamentally indistinguishable. If you're stood inside a sealed box, there is no experiment you can perform which will tell you whether you're stationary in a gravitational field (sat on the surface of a planet, for example) or whether you're being accelerated and experiencing no gravitational field (or indeed some combination of the two).",
"Therefore, a point mass in a stable orbit is experiencing zero gravity. (The specification of a point mass is important here, because anything with spatial extent in orbit feels tidal forces.)",
"There may also be points in the universe where the net gravitational field is 0 (or at least unmeasurably small) - that is, the gravitational field from all the objects in the universe balances out.",
"If you're asking whether we can somehow block gravity, the answer is no."
] |
[
"I did specify a point mass because of this, but I should have been clearer about the simplification made. Apologies."
] |
[
"One of the fundamental tenets of general relativity is that acceleration and a gravitational force are fundamentally indistinguishable.",
"That's not true - if it was, then there would be no such thing as gravity, since GR is a diffeomorphism-invariant theory (i.e. it works in ",
" reference frame). You cannot transform away the tidal aspects of gravitation.",
"Quick explanation: imagine a free-falling box around a large mass (say, the Earth) with two equal-mass objects inside. As the box approaches the centre of the earth, the two masses inside will approach each other. This is the tidal aspect of gravity that can be described by a curved spacetime."
] |
[
"Do we get heat from other stars?"
] |
[
false
] |
So we are heated by our sun but do others starts also heat us or are they just too far? If we do get heat, how much do we get?
|
[
"Your answer to this question is very good. There are a few interesting exceptions though. If for example Alpha Centauri were to go supernova things would change a bit, a bright supernova can be more than 10",
" brighter than Alpha Centauri. Meaning it would heat up Earth to a significant degree. Only for a short while thou. You probably do not have to worry about it though, it does not appear like Alpha Centauri will ever go supernova. ",
"Another interesting calculation is what would have happened if the sun was in the middle of a ",
"globular cluster",
". One star alone would still not enough to heat up Earth. But since there are so many stars around it would add up to a significant heating. It was some time ago I did the calculations, but as I remember it you don't get a proper night inside a globular cluster. The globular cluster produces to much light for that, and it is the same all day."
] |
[
"All forms of radiation, including heat, have the relative intensity of 1 over R squared. Put another way, if you increase the distance that you are from a star by a factor of 2, you receive a quarter of the energy. The Earth is approximately 93,000,000 miles away from the sun, a distance that can be represented by approximately 8 light-minutes. Other than our sun, the nearest star is at Alpha Centauri, a distance of approximately 4.3 light years away. Using round numbers, Alpha Centauri is 100,000 times farther away from us than the sun. Holding all things equal, the nearest star provides us with 1/10",
" times as much energy as the sun does. Certainly all of the energy from all the stars that is emitted in heat and other forms of radiation is less than twice this number. As such, it is needless to say that this amount is negligible, and is not worthy of mention in day to day calculations."
] |
[
"Whenever I think of this, I can't help but be amazed at the sensitivity of the human eye. True that there are many stars JUST under our visual acuity, but a starry, clear night away from any city is pretty shocking. The eye can pick up a tiny, tiny amount of energy.",
"I've noticed that dark nights on the beach are very different in the presence of the moon light. It's much easier to see when the moon is shining. Any idea on a calculation of the radiative intensity of the full moon's reflection vs the sun? How about the heat transfer?"
] |
[
"If a lack of sunlight has the propensity to make us depressed, why did humans migrate to the Arctic Circle?"
] |
[
false
] |
.
|
[
"Because lack of food has a tendency to make us dead"
] |
[
"Depression isn't something that is going to take immediate hold or even necessarily have a detrimental effect that would effect reproduction. There's resources up there, and we can live up there and breed successfully. So we went, and the reduced competition doesn't hurt either. "
] |
[
"Were central (laterally speaking) Europeans forced Northwards due to a lack of food?",
"(Sorry, my knowledge of ancient human migration is poor.)"
] |
[
"When you're running and you get a stitch, what is actually happening? And what causes it?"
] |
[
false
] |
[deleted]
|
[
"This phenomenon is known as '",
"exercise-related transient abdominal pain",
"' (ETAP), and unfortunately while a number of theories exist we don't know definitively what its cause is. The ",
"leading hypotheses",
" include 1) diaphragmatic ischemia, 2) peritoneal irritation, and 3) stress on ligaments supporting subdiaphragmatic viscera (notably, a ",
"muscle cramp of the abdomen/diaphragm is not considered likely",
" to be related). Each of these theories has some evidence for and against it. It is thought that ",
"drinking fluids prior to exercising",
" is related because it leads to extra weight on the supporting ligaments, but again much of this is still up in the air."
] |
[
"It is important to be a bit careful here. ",
"It is easy to show it causes extra weight.",
"\nIt is easy to show it results in more stitches. ",
"Not so easy to show the extra weight is what is causing the stitch, and eliminating all other causes. "
] |
[
"I'd imagine the difference is being ",
" versus having a stomach full of water."
] |
[
"Is it possible for human clones to evolve?"
] |
[
false
] |
For example, if you were to make a clone of yourself and that clone were to make a clone of itself, is it possible for it to evolve over time?
|
[
"It should be noted that individuals don't evolve. Populations, however, do."
] |
[
"Thank you for that. So depending on the time of cloning it could evolve... I've been wondering that ever since watching that DQ commercial. "
] |
[
"Short answer is yes. Cloning would mean that the clone has the same DNA as the donor at a single specific time. From birth the clone would then grow up developing random mutations as any normal person would, these would then be passed on to a future clone. ",
"Edit: You would probably see a little less evolution over time compared to normal humans, due to the removal of certain processes that occur in normal reproduction that produce genetic changes, but this is being pedantic. "
] |
[
"Is terraforming of Ganymede feasible?"
] |
[
false
] | null |
[
"NOTE: Speaking off-flair here as someone with a laymans interest in this sort of thing.",
"It depends on what you mean by \"terraform\". First off, the thick atmosphere of Titan is due to the fact that it is extremely cold. Atmosphere retention is a function of planet mass and temperature (and sources of gas, but more on that later). Bigger or colder and you can hold more. Warm things up, and you can hold less.",
"That said, Ganymede might still keep an atmosphere if you could somehow warm it up to room temperature, but the reason for this is why terraforming it would be difficult. The moon is basically half rock, half ice. If you warm it up, the surface (which is ice) will simply melt. Eventually you'd wind up in a moon covered 100% with a hundreds-of-kilometers deep ocean. Constant outgassing of this ocean might give you a water-vapor and ammonia atmosphere. So you'd wind up with a world ocean (probably quite unstable, as bits of ice melt off the seafloor and bob to the surface unpredictably) and an unbreathable atmosphere of unknown thickness. Makes building any sort of structure problematic. Not to mention being in Jupiter's radiation belts, though presumably an atmosphere would reduce that hazard."
] |
[
"For further reference on why temperature is important at Ganymede, have a look at ",
"this graphic. ",
" The surface temperature would need to be drastically increased before the atmosphere was breathable. ",
"Further, ",
"the total solar irradiance at Jupiter is ~27 times less than at Earth",
", meaning that even a powerful greenhouse gas effect would not have as much energy to turn into heat.",
"Mars would be an easier place to learn to terraform. "
] |
[
"I learned awhile ago that any question requiring speculation, particularly those related to science fiction, are absolute karma graveyards for anyone actually giving scientific responses. People really, really don't want to learn that they will never travel the stars in faster-than-light space ships. I personally think these kinds of questions should be deleted."
] |
[
"Why is cycle detection the key to integer factorization?"
] |
[
false
] |
I have been spending a lot of time lately with Pollard's Rho algorithm for integer factorization. While I have managed to implement it and I've tried both Floyd's and Brent's cycle detection algorithm I don't really understand why we're looking for a cycle to find a non-trivial factor of n? What does the sequence generated by g(x) = (x + 1) mod n represent? I understand the cycle detection algorithm itself (letting a function work its way through the sequence faster than the other function (i.e. the hare and the tortoise)) but I do not understand how this translates to finding a non-trivial factor to n?
|
[
"A short summary:",
"Cycle detection is not the key.",
" are the key.",
"The sequence (x",
" + 1) represents nothing; it is pseudo-random.",
"Let's say we have a pseudo-random sequence (a_i) of integers mod n, where n=pq with p and q unknown. If, by chance, we find i and j such that a_i ≡ a_j (mod p) but a_i ≢ a_j (mod q), then we know that the value (a_i - a_j) is divisible by p but not by q and thus GCD (a_i-a_j, n) = p, which gives the required factor.",
"Since the sequence of values (a_i) (mod p) is pseudo-random, we expect that such a collision will happen after we draw about O(√p) values, which is also O(n",
"). But the stupid algorithm would be as follow:",
"compute value a_i\nlook for value a_i in the list\n if the value a_i is found: return the collision\n else: insert the value in the list\n",
"We immediately see that such an algorithm has a time complexity of O~(n",
") (The O~ means that I am neglecting logarithmic factors, which cover the cost of computing a_i and doing list look-up and insertion). But it also has a ",
" of the same magnitude, since we need to store a list of all previously found values.",
"While time complexity is a relatively minor hindrance (... you just have to wait a bit), memory complexity is a big no-no (you really need all that memory at once). But luckily, the cycle-detection algorithms allow us to trade off that memory complexity, at the price of slightly increased time complexity. Namely, we replace the list of previously computed values (a_i) by a second instance of the algorithm running twice as slow as the first one, and know (by the \"rho\" drawing) that we will eventually be able to find a cycle and thus a collision.",
"Finally, (x",
" +1) is a very weak pseudo-random sequence (do not use this to generate your private keys...), but it is enough for us since basically all we need is to be unable to predict its dynamic behavior (and in particular cycle length): we see that any affine function (x -> ax + b) would have cycles of length n (unless we are extremely lucky in our choice of a) so that the next simplest, fastest choice is (x",
" +1). But I have also seen Pollard rho implemented with other sequences (for instance involving bit-level manipulation)."
] |
[
"What are you even talking about? Are you sure you wrote this in the intended place?"
] |
[
"Yeah, well, simply stated there is nothing in the universe that is random, what you have are equations, nothing more, nothing less.",
"so all this talk about random had far more to do with things like wishful thinking than anything else."
] |
[
"Using VOIP, is there a maximum bandwidth of data that can be transmitted?"
] |
[
false
] |
Consider this thought experiment: I initiate a perfectly stable VOIP call to a machine which can translate verbal english into a file. I spend 1 hour reading the contents of which is 4,749 KB, resulting in me transferring 1.350 KB of "real" data per second, with the VOIP call (using G.729 and 8kb\s), in reality consuming 28.1 MB to transmit the file. Now say perhaps I verbalize the file in 9 min 53 seconds instead of 1 hour. Rather than 1.35KB\s, I've transmitted at almost exactly 8kb\s, the same rate that the VOIP connection itself requires. What happens if I were to verbalize the file in 9 minutes then? Does the 8kbps that the VOIP call maintains act as a maximum bandwidth that can be transmitted? At 9 minutes, I'd be transferring data at 8.79 kbps, which is higher than the VOIP connection itself. Would this data simply be lost? In my example above, I the maximum bandwidth that the system could handle. If I wanted to initiate a new and different connection without knowing the maximum bandwidth, is there any way I can be sure that my message gets delivered without data loss?
|
[
"VoIP typically uses ",
"audio compression",
" for audio data transmission. While there are a pretty wide variety of algorithms currently in use (depending on the provider), most of the compression algorithms used fall into one of the following categories:",
"In all three situations, data is lost. There really isn't a situation where your message isn't delivered without data loss. Fortunately voice communications contains a lot of redundancy; you can lose a good amount of data and still be understandable. You can easily experiment with this yourself: record a sample of your voice, and then compress it at various rates with any audio compression codec (i.e.: MP3), and see how low you can go before you can't understand what you said anymore.",
"Perhaps a slightly better thought experiment is that instead of voice, think about using an old-style modem on a VoIP line. A 28.8k modem gets pretty close to the theoretical limit of a traditional POTS line",
" So the question becomes: what is the fastest theoretical modem speed that my VoIP can support?",
"There isn't a single answer, as there are a number of VoIP implementations out there that use different compression algorithms, and different bandwidth allowances. A traditional G.711 VoIP connection however can handle up to 64Kb/s (8KB/s) -- that's going to be the maximum rate you can transmit bits across the line, without data loss.",
" - 56K modems took advantage of having the ISP end being purely digital; due to this you can't get a 56K connection between two residential 56K modems, and the 56K when you did connect to a suitable ISP was only in one direction.",
"\n",
" -- as this is just a thought experiment, we can ignore the fact that modems don't tend to work all that well over VoIP without some special handling (like V.MoIP) due to packet jitter in the VoIP layer that isn't present in a POTS implementation. "
] |
[
"Per your answer, perhaps I use narrow-band compression, and attempt to transmit at a higher bitrate than the VOIP connection actually supports. ",
"That's really not possible. The best you can do is saturate the link. It isn't as if an application ",
" a certain amount of bandwidth. VoIP systems just send a near-constant stream of packets. The packet rate is determined by the bit rate of the audio compressor. For many VoIP applications this is fixed (such that you get a constant number of bits for a given amount of time, regardless of content). ",
"That itself suggests loss, but is there any way to determine what data is affected?",
"No. The data is completely lost. You might consider using a linear error-correcting code to try to rebuild the lost data on the receiving end, but for this to work you need to add even more bits.",
"If your application needs more bits than a given VoIP codec can supply then chances are very good transmission over VoIP isn't the right solution. The only \"solution\" to your problem is to define and implement your own codec with a higher bitrate (at which point it would seem to be meaningless to use VoIP at all -- you could just use a raw TCP socket if you're defining your own protocol, and use nearly as much available bandwidth as you'd like)."
] |
[
"but is there any way to determine what data is affected?",
"You're up against two things, one is the theoretical maximum data transmission rate. Followed by limits to the encoding used by the VOIP system. The latter point is important because the compression used by VOIP will be optimized for voice and will probably under perform when fed a rich broadband audio input. (Think of the difference between someone signing and modem noises)"
] |
[
"Every once in a while my toothpaste tube spontaneously explodes. Why?"
] |
[
false
] |
It has a hinge cap and sometimes it opens itself and oozes out all over the counter. I assume it has something to do with pressure. Is the toothpaste evolving gas?
|
[
"Your ",
" leaked? How is that possible?"
] |
[
"The tube probably somehow got hotter, so the toothpaste expanded."
] |
[
"I'm looking at this on my phone, so I can't read the small print - does this toothpaste contain bicarbonate of soda, by any chance?"
] |
[
"What type of genetic mutation causes Phenylketonuria (PKU)?"
] |
[
false
] |
I've searched through the internet and I can't seem to find any conclusive discussion or explanation about what type of genetic mutation causes PKU - does anyone, in this field, know what it is?
|
[
"In addition to the above answers; there are around 5 tipes of PKU with clinical significance. Each is caused by a different mutation in a different enzyme. Most (I do not dare say all) enzymatic reactions in the body are just parts in a greater machine; Glucose to glycogeen takes many steps. Just so, many steps are requierd for phenylalanine metabolism. In each of these enzymes a defect can arise. Suppose that there are 8 steps, than in each of the genes coding for the enzyme (or part of it that enzyme) that are requierd for producing it, a mutation could arise. This mutation could be random, or you could already have been bron with it. For that some testing needs to be done. Since there are many steps and enzymes involved there is no conclusive answer to what causes PKU. Any facotr that could lead to gene mutation (mutation of a single enzyme will not be enough) could be a cause. ",
"As bonus; Types of PKU:\nPKU 1- enzyme defect; phenylalanine dehydrogenase\nPKU 2- dihydropteridine reductase \nPKU 3- 6-Pyruvoyl-tetrahydropterin synthase\nGTP cyclohydrolase 1 defeciency- GTP cyclohydrolase 1\nCarbinolamino dehydratase deficiency- Pterin-4alpha-carbinolamine dehydratase ",
"All of the above types are autosomal recessive. ",
"EDIT: Source; Fauci AS et all. Harrison's Principles of Internal Medicine 17th edition. Inherited Disorders of amino acid metabolism in adults. 2470-2471p"
] |
[
"PKU is caused by mutations to the gene Phenylalanine hydroxylase. A quick wiki search tells me that there are ~300-400 distinct mutations that have been identified as causing this disease. Most are missense mutations, and most (as expected) occur in the catalytic domain of the enzyme. "
] |
[
"PKU is defective phenylalanine metabolism. The metabolism of phenylalanine to tyrosine is dependent on an enzyme called phenylalanine hydroxylase. So any mutation that causes a change in the enzyme's amino acid structure (and hence shape and function) [missense mutations and even frameshift mutations] or prematurely stop protein synthesis [nonsense mutations] would render the enzyme dysfunctional, causing PKU."
] |
[
"Do mosquitoes do anything for the ecosystem?"
] |
[
false
] |
[deleted]
|
[
"It's been estimated that in Alaska alone, mosquitos weigh ",
"96 million pounds",
" [1]. ",
"Taking 50,000 tons of nutrition out of an ecosystem seems like it's going to lead to serious consequences."
] |
[
"I'm glad you clarified. I was terrified of Alaskan mosquitos for a minute."
] |
[
"Yeah, I mean that would be at least ten."
] |
[
"why do most of the planets revolve around the same plane?"
] |
[
false
] | null |
[
"Source: I'm an astrophysicist.",
"The reason is the physical principle known as conservation of angular momentum.",
"Before the planets formed, the solar system was just a giant cloud of dust and gas. Initially, the cloud had some net spin. As it collapsed, it began spinning faster and faster (just like an ice skater who brings in his/her arms). Also, the cloud began to flatten, due to gravity and some centrifugal forces.",
"That is why everything orbits in the same plane, and it is also why most planets and moons spin in the same direction!"
] |
[
"Yep, the same goes for galaxy evolution too, but not really for galaxy clusters. Clusters don't really flatten out at all, but they do cluster into filaments because of gravity."
] |
[
"I also notice that our galaxy is also pretty flat. Does this extrapolate further out to clusters of galaxies?"
] |
[
"Could a \"flash freeze microwave\" be made to flash freeze food?"
] |
[
false
] |
So, I know that microwaves head up the water molecules, in turn heating up the food very quickly. But could it be possible to do the opposite, to freeze water molecules very quickly to intern freeze the food?
|
[
"No. Its vastly easier to add energy to a system than to remove it."
] |
[
"The closest thing I can think of is ",
"Doppler cooling",
", but its capabilities are nowhere near what you're describing."
] |
[
"Setting aside methods like Doppler Cooling, which can only be used to cool very small amounts, on the order of individual atoms, there isn't a way to do what you're suggesting.",
"To add heat to a system, you need to add energy. Microwaves do this by emitting light, the magnetic field of which causes some of the molecules inside the food to start wiggling around. Those wiggling molecules will hit the other molecules, passing off some energy to them. Think of it sort of like hitting one ball with another, the second ball is put into motion by some of the energy from the first one. The net result is that all of the molecules in the food start moving around quicker, which is the same thing as getting \"hotter\".",
"To cool something down, you have to get that energy out somehow. To do so, you need to have it bounce into something that is moving slower, causing the second molecule to pick up a bit of motion, and the first molecule to lose some.",
"Restaurants often need to cool soups down quickly, so that they can get it into refrigeration quickly and allow less time for harmful bacteria to grow.To do so, they use a cooling paddle, which is basically just a container full of ice that is stirred around inside the soup. When the soup bumps into the cold paddle, it loses some molecular motion, and the paddle gains some.",
"There are certain techniques which can be used to do something similar by using light, but they have to be very precisely tuned to the particular atom involved, and are only practical for small sample sizes. It's definitely not something which could ever be made practical for objects as large as food."
] |
[
"physicists say to laymen \"observing a quantum particle causes the wave function to collapse\" but what does this mean mathematically? what does a collapsed function look like compared to the original?"
] |
[
false
] | null |
[
"Here is an example",
", where the quantity being measured is the position of the particle. Initially it has a wavefunction which is a superposition of many locations in space. After the measurement, the particle is localized at a single point in space, and its wavefunction becomes like a Dirac delta function at that point."
] |
[
"Well the original function can be arbitrary wavefunction, and the final function is a Dirac delta function. I can make up a function for the example in the picture, it looks like a Gaussian function.",
"So the original wavefunction would be something like",
"f(x) = N*exp[-k((x-x",
")",
"+(y-y",
")",
")],",
"and the final would be",
"f(x) = N'*δ(x-x",
")δ(y-y",
")."
] |
[
"The most important thing to know about that statement is that \"an observer\" doesn't mean a guy looking at it. To be \"observed\" just means anything of any type interacting with it an iron atom can \"observe\" another atom if it interacts with it in any way. People put a lot of spiritual significance on a choice of words that implies a person looking. "
] |
[
"Why is it so hard for women to get pregnant?"
] |
[
false
] |
Or am I just misinformed? In my personal experience it took me years before I got pregnant, and I've heard so many people say it just takes time. You know the classic scene of a woman telling her husband she's ovulating - such care goes into trying to get pregnant, why is it so hard? What is it about us that prevents trying couples from getting pregnant within the first, I dunno, month of trying? Has it always been this way?
|
[
"Well the fertility rate in men has been dropping significantly across the board. One study associates it to ",
"pollution",
" but there is much speculation over ",
"other factors",
".",
"\"The latest scientific studies have also shown that the average sperm count has fallen by up to 50% from 380 million sperm to about 180 million sperm per ejaculate. This means that men are now ejaculating half the number of sperm than they were 50 years ago. All blamed on environmental estrogens, known as ‘Endocrine Disruptors’(87000 chemicals found in food & our water from pesticides, detergents, preservatives, plastics, and the pill).\"",
"http://www.usatoday.com/news/health/2003-06-17-pesticide-usat_x.htm",
"Interesting Documentary:\n",
"http://www.cbc.ca/documentaries/doczone/2008/disappearingmale/infertility.html"
] |
[
"It's not necessarily that hard. 85% of couples having regular unprotected sex will conceive within a year, 95% within 2. ",
"Source"
] |
[
"Also conjecture, but I wanted to point out that due to women seeking careers before having a family more often nowadays, many women are having children later in life. This has an affect on both parent's lowered fertility due to age. ",
"Whereas in the recent past it was not uncommon for a woman to become pregnant as young as 16-19, many women are waiting until their 30's or even 40's. ",
" No longer conjecture, references cited below."
] |
[
"Can a larger black hole pull out objects within the event horizon of a smaller black hole?"
] |
[
false
] | null |
[
"No. ",
"In addition, if their event horizons touched, the two black holed would merge to form one larger black hole."
] |
[
"It's not quite as simple as that. One feature of the equations of General Relativity is that they are non linear, which means if you know two different individual solutions, their sum is not necessarily going to be one. Classical gravity and all other forces are, however, which is why we intuitively assume it as a generic feature of nature."
] |
[
"Layman here, ",
"Wouldn't the gravity of a second black hole reduce the net force on an object between them, even deforming the actual event horizon of the first? Wouldn't there be some kind of Lagrangian point between them that could even lie inside the original event horizon? "
] |
[
"Why does metal spark in the microwave?"
] |
[
false
] | null |
[
"Microwaves are electromagnetic waves, meaning that they (like light, radio waves, and other forms of electromagnetic radiation) can potentially induce a current into a conductor. ",
"This is how radios work. You generage an oscillating (think sine wave) electrical signal in a long metal rod (transmitting antenna) which sends out radio waves that via magnetism's role in electromagnetic waves (think waving a magnet past a coil to generate current really fast, only instead of waving that magnet, your transmitting antenna is creating that fluctuating magnetic field that induces an electric current) induce a detectable voltage/current shift in the recieving antenna (which plays music). ",
"So, microwave cookers (700 watts or 1000watts or higher) focus all of this electromagnetic energy into a little box. Think about this, think about how much apparent energy a 100 watt bulb puts out (including heat and light), now multiply it by 7, 10, or 12 depending on your make and model and focus that onto a little piece of metal. But microwaves aren't light bulbs, they're similar to FM or AM radio waves and induce an electric current in the metal. ",
"BUT! here's why it sparks, the microwaves oscillate, so they charge up one side of the metal positively and the other negatively. This charge builds up on the edges (Specifically small peaks and ridges on the edge of the metal) which ionize the air around it (Fancy term for charging the atoms so that the electrons jump to higher energy levels, which makes them more mobile as well) and sparks fly (excited atoms glow because electrons that drop levels emit light, making the atoms less excited).",
"Oscillating waves though, remember that? So, because the electricity (and microwave peak/trough) \"sloshes\" back, what was once positive is now negative and vice versa. This keeps the voltage from building and building to the point that you get arcs and not just sparks. Also, just like a light bulb, passing current through metal heats it up, now a spoon doesn't get hot enough to glow, but it will spark.",
" It's not a bad analogy to think of a piece of metal in the microwave as a bowl full of water (the water is the electric field). The microwaves simulate a paddle pushing the water back and forth and the sparks are what happen when the water sloshes over. "
] |
[
"conducted on the surface of the metal; it does not get absorbed by the conductor. This is why most thick cable is strands of smaller wires braided together, like a rope.",
"There is not a significant decrease in resistance for stranded wire vs solid because all the wire strands are shorted together. Further the skin effect only comes into play for AC and the degree is a function of frequency. The choice of stranded vs solid is almost always a tradeoff between cost and mechanical properties. Most thick cables are stranded because they'd be extremely difficult to bend or work with if they were solid (e.g. using rebar for wiring)."
] |
[
"conducted on the surface of the metal; it does not get absorbed by the conductor. This is why most thick cable is strands of smaller wires braided together, like a rope.",
"There is not a significant decrease in resistance for stranded wire vs solid because all the wire strands are shorted together. Further the skin effect only comes into play for AC and the degree is a function of frequency. The choice of stranded vs solid is almost always a tradeoff between cost and mechanical properties. Most thick cables are stranded because they'd be extremely difficult to bend or work with if they were solid (e.g. using rebar for wiring)."
] |
[
"Does an hourglass flow at a constant rate? If so why?"
] |
[
false
] |
I feel as if it would slow down slightly as there was less pressure from the sand above it. Can you explain some of the fluid dynamics or relevant physics for why it behaves the way it does?
|
[
"Sand granules are too large and static to follow the physics of fluid dynamics, at least at the scale of an hourglass, so there isn't really a \"pressure\" to speak of. Instead, contact forces distribute weight downwards unevenly. (Uneven force distribution is present in fluids as well, but the constant particle motion and sheer number of particles per unit of volume averages that out into what we know as pressure in our scale.) In an hourglass, most of the weight of the sand in the top chamber is transferred to the sides. The sides help to maintain the structure with normal forces and frictional forces. A good way to visualize the arrangement of forces is to picture the sand as a set of Roman arches loosely stretched over the aperture. Picture the sand not as a liquid, but as a static structure forced to resettle as the lower extremity vacates.",
"With all that in mind, how quickly sand vacates the top chamber is dependent on the aperture's size and the local acceleration due to gravity. Both of these are (usually) constant, and this yields constant flow."
] |
[
"This is just a guess.",
"please avoid speculation in this subreddit."
] |
[
"This is just a guess.",
"please avoid speculation in this subreddit."
] |
[
"This may be the wrong sub, but do you think this could make a pina colada without a blender?"
] |
[
false
] | null |
[
"It completely depends on the ratios of ingredients. A large enough amount of sugar, milk fat, and vodka in there will make it slushier. Any alcohol especially lowers the freezing point and makes things slushier. You'll have to experiment. "
] |
[
"...but as far as you're aware this would work?"
] |
[
"There exists some ratio of those ingredients for which you will get a slushy-like substance, but I cannot guarantee it will be a worthy substitute for using a blender."
] |
[
"What is the speed of a bubble rising in water a function of? And is there an absolute limit on that speed?"
] |
[
false
] | null |
[
"/u/Asinus",
" is correct that the rising force is due to the principle of buoyancy, and ",
"/u/perso_nel_mondo",
" is correct that Stoke's Law can be used to calculate the terminal velocity for a rising bubble - however only for small bubbles where the viscous drag dominates and the droplet is still spherical.",
"To directly answer your question though, yes, there is an absolute speed the droplet can rise at. This is called the terminal velocity, the same term we use when an object is falling through the air and reaches a maximum velocity.",
"This",
" paper by Yersel is a senior project where the student very simply derives the terminal velocity for a rising droplet in the Stokes regime. The equation is:",
"v = (2*(rho_l - rho_g )*g*r",
" )/(9*mu)",
"Where rho_l is the density of the liquid, rho_g is the density of the gas, g is acceleration of gravity, r is the radius of the droplet, and mu is the viscosity of the liquid.",
"However this equation is only valid when the bubble is small, spherical, and moves relatively slowly. As the droplet gets bigger other physics come into play.",
"This",
" paper by Tomiyama is a more thorough look at bubble terminal velocities. In the Stokes regime there are really just two forces to account for: buoyancy force and viscous drag. As the droplet gets bigger two other forces can come into play: surface tension and inertia.",
"Depending on which forces are small or large, the terminal velocity can fall into 1 of 3 different regimes: the Stokes or viscous force dominant regime, the surface tension dominant regime, and the inertia dominant regime. The other equations are a bit too complex to put here without MathJax support or something, so you can just read the paper.",
"If you read through the paper, you'll see that the bubble undergoes different shapes from spherical to oblate spheroid to other more complex shapes, and instead of rising straight up it will start to move in zig-zag or helical motion as well. It turns out that you can predict what shape the droplet will be based on a dimensionless number called the Eötvös number:",
"Eo = (g*(rho_l - rho_g)*d",
" )/gamma",
"Where g, rho_l, and rho_g are the same as above, d is the diameter of the bubble, and gamma is the surface tension of the gas/liquid interface. If Eo<4 then the bubble will be spherical, as it gets larger then it starts to take on other shapes and behave more chaotically as it rises."
] |
[
"The go-to piece of information here is Stokes' Law which relates fluid viscosity, drag, size (bubble size, in this case) and velocity. ",
"To interpret in the context of a rising bubble, the absolute limit on speed occurs when the buoyant force equals the drag force. So, from Stokes, as velocity increases, drag increases. ",
"Buoyant force is a function of the difference in density between the bubble and the surrounding fluid.",
"Clearly, it gets far more complex than this: Bubble shape, rise motion impact on shape, hydrostatic pressure, turbulent shear, etc... But is all reduces to these aspects."
] |
[
"As others pointed out, this is not an easy subject. Yet it has been extensively treated in literature, beacuse of the many industrial fields where you need to know the behaviour of gas-liquid interface.",
"Most discussed is probably the flow of bubbles in tubes, or the formation of bubbles on a surface liquid-solid and the way it affects the flow of the liquid. But there are also results for bubble rising in water, as you can find in this paper: ",
"Hua, Jinsong, and Jing Lou. \"Numerical simulation of bubble rising in viscous liquid.\" Journal of Computational Physics 222.2 (2007): 769-795.",
". See fig. 7 for data on terminal velocity.",
"As you can see, the physics behind it is quite complex. I'll try to mention the effects at play.",
"First there is buoyancy. Your bubble is less dense than the surrounding fluid and therefore starts rising. ",
"Now, an object moving in a fluid is subject to a ",
"drag force",
". The combined effect of drag force and buoyancy brings the system to an equilibrium where the two forces are equal in value and opposite in direction, thus determining a terminal velocity. So, to answer your last question, there is a limit to the speed.",
"Unfortunately things do not end here.",
"The drag coefficient that enters the drag equation and so determines the drag force is a function of velocity, shape and size of the object, density and viscosity of the fluid (there are other parameters of interest but I'm assuming the velocity is slow enough to ingore them - Mach number becomes relevant when it is no longer small). In fluidodynamics these parameters are usually put together in a dimensionless one called ",
"Reynolds number",
". The reason for this choice is the fact that systems with different shape, size, velocity, viscosity and density will often behave very similarly if they have the same Reynolds number.",
"Specifically our bubble would have a drag coefficient that only depends on its Reynold number (and so would be quite stable once at equilibrium) if it could keep constant its shape. Unfortunately the shape changes, due to viscous stress (big bubbles can fracture or assume almost torus-like shapes) as you can see in ",
"fig. 2",
".",
"Furthermore the trajectory is not a straight line but it is more of an oscillating path (fig. 8 in Hua Jinsong et al.) thus impacting on the drag coefficient.",
"So far I have ignored the variation of pressure but, for a long rise in the fluid, the change in pressure might become relevant and determine an expansion of the bubble, changing again the value of parameters."
] |
[
"What happens if primordial black hole evaporates in the Earth's atmosphere ?"
] |
[
false
] |
I read that small black holes could have formed in the early universe and that there is a possibility that they move through space and actually could hit the Earth. Depending on their mass they actually could pass through the planet without doing measurable damage, since they are so small and don't influence many particles with their event horizon. But I am more interested in what happens, when a black hole evaporates through Hawking radiation. It is often stated that since the rate of this radiation would become increasingly stronger when the black hole becomes smaller, it will eventually end in "burst of energy". But how massive would such a burst be? I read somewhere a 1000 ton black hole would evaporate in just over a minute. What would happen if it was flying through our atmosphere during his last breath? Would it cause destruction?
|
[
"I found a calculator for the intensity of Hawking radiation on a ",
"website",
". I am not exactly sure how to interpret the numbers though. The luminosity seems pretty high but I don't know what effect it would have if it came from an event horizon that is way smaller than a proton.",
"According to this calculator it would release an energy which starts at ~3*10",
" watt per second and would become even stronger in the following 84 seconds. So it already begins over 1000x stronger than the biggest nuke ever (Tsar Bomb), somewhere close to the annual energy comsuption of the whole world (again: per second!)",
"Maybe I made a mistake but that sounds like global extinction to me or am i getting something totally wrong ?"
] |
[
"We don't know exactly what goes on as the black hole shrinks to nothing, as far as I know.",
"You can just quickly look at ",
"the Hawking radiation equations",
" and see that Hawking radiation temperature as well as instantaneous power outflow are inversely proportional to black hole mass, which means the power output is going to spike towards infinity as the mass goes to zero.",
"The problem is that Hawking radiation comes from GR, which fails at the quantum level. So we need a theory of quantum gravity to really know for sure."
] |
[
"Safe to say, it would not look good. According to some science in an answer ",
"here",
", the explosion from a black hole with a mass of 5 grams would be three times stronger than the Nagasaki and Hiroshima atomic bombs combined, and I seriously doubt anything would get better if you increased the mass, it would just get far worse."
] |
[
"Are the benefits of fish oil (omega-3) pills proven?"
] |
[
false
] |
As the title asks, am I benefitting from this substance, or am I wasting my time and money consuming fish oil tablets. Note: I also eat fish at least once a week.
|
[
"The Omega-3 ester extract of fish oil has been proven stringently enough to reduce triglycerides to be ",
"approved by the FDA as a pharmaceutical."
] |
[
"Related: Can people with Fish allergies take them? "
] |
[
"I can't answer whether they'll aggravate your allergies but I can say this. There exist plant versions of the omega 3's. They're found in flax seeds (as well as other plants). Your body will convert the omega 3's in them into the animal forms (EPA/DHA). The conversion rate is awful though, something like 10%, but it might be the only way to get your efa's if you're allergic."
] |
[
"How valid are the claims that fluctuations in solar activity can account for a significant portion of our global warming woes?"
] |
[
false
] |
I know that it is pretty well understood that humans are contributing to global warming but I was trying research the validity of some of the claims that it may not be as bad as the hype. What role does solar activity play in climate models? How much do we really understand? Is there a consensus in the scientific community about it's role?
|
[
"Sallie Balliunas tried desperately to connect solar fluctuations and flares to climate change (research paid by Carbon Fuels think tanks) and failed miserably. Only one of her papers was accepted by an accredited publication, and the review process was so flawed and the findings so incorrect that other scientists and editors rebelled until they retracted.\n",
"http://en.wikipedia.org/wiki/Sallie_Baliunas"
] |
[
"A plot from the IPCC comparing the various components of changes in radiative forcing: ",
"http://www.ipcc.ch/publications_and_data/ar4/wg1/en/figure-ts-5.html",
"If you really want to dig down, the best recent publication is the 2010 review article by Gray et al. ",
"http://onlinelibrary.wiley.com/doi/10.1029/2009RG000282/abstract",
"Bottom Line: In terms of the earth's climate, observed variations in solar output are real but small compared to the effects of the anthropogenic changes in the earth's atmosphere. ",
"edit: added link to Gray et al paper"
] |
[
"Your source is hardly unbiased, they are skeptical of anything that doesn't support AGW unquestioningly. ",
"\"Unbiased\" =/= \"Unwilling to call something out as false\". Just because the vast majority of garbage is on the denier side doesn't mean that any source that recognizes that fact is biased. Do you take issue with the fully cited figures?"
] |
[
"Why are Uranus's moons equatorial?"
] |
[
false
] |
Assuming a protoplanet (or more) collided with Uranus, why would the moons change their orbital plane to match Uranus's equator? If they were there before the collision, how were they affected by the collision so that they moved so much? And if they were captured after the collision, why is it that they didn't stay in the ecliptic like pretty much every other moon or planet? I thought that maybe it had to do with a similar mechanism as that which causes tidal locking, but even that seems too extreme. I've been searching for a few hours, with no results.
|
[
"So first, let's get this out of the way: The idea that Uranus got knocked on its side by a severe impact early on is an old theory, and in the past 20 years this idea has strongly fallen out of favor. It turns out it's almost impossible to have an impact large enough to turn Uranus on its side that doesn't completely obliterate the planet.",
"The working theories now are that either there was a near miss (simulation show that it's quite likely Uranus and Neptune changed places early in the history of our Solar System, with some near passes in the process), or that Uranus lost a moon and the planet was tidally disrupted in the process, or ",
"possibly both",
".",
"Whether it was a near miss or a moon loss, though, the immediate situation afterwards leaves Uranus orbiting on its side with the moons still in the equatorial plane - and that's not going to be a stable configuration over billions of years. Those moons will raise tidal bulges on the planet, which in turn get dragged over the planet as it rotates. These off-center bulges then create a source of non-centered gravitational attraction, pumping up their inclination until they eventually fall in line with the equator."
] |
[
"the moons' orbits would have been brought into line by the gravitational attraction of the slight equatorial bulge caused by Uranus' rotation.",
"That's not really how equatorial bulges work on inclined orbits. They cause a ",
"regression of the nodes",
" (causing the orbit to wobble) as well as ",
"precession of pericenter",
", but it won't change the magnitude of inclination, just its direction."
] |
[
"Currently, how widely accepted is the Nice model? What, if any, are the most likely competing hypothesis?",
"Venus is the only terrestrial planet that lacks a moon. Could a moon loss scenario also apply there?"
] |
[
"Why is there a Voronoi diagram on my giant Reese's peanut butter cup?"
] |
[
false
] |
I just finished a class in computational geometry, and I bought a giant Reese's peanut butter cup at the grocery store and when I opened it up, I saw a familiar sight. There was what looked like a on the top of it. I took a picture and put in the coordinates of the pixels where the sites approximately would be into and the results matched almost perfectly. Here are the images of the peanut butter cup, the generated Voronoi diagram and them overlaid: Why would this be there? Do they use this in the manufacturing process?
|
[
"I think this math question has an engineering-flavored answer: the melted chocolate that they use to cover the peanut butter probably has a somewhat high viscosity. If all of the chocolate were applied in the center of the cup, it would take a while for all of it to spread evenly over the surface (and it would likely require an external heat source to keep it from cooling too fast and making a mound of chocolate in the middle). A more efficient technique would be to apply melted chocolate at several points on the surface. Each Voronoi cell corresponds to a different chocolate-application point. ",
"\nEdit: coloring is likely due to flow patterns, not temperature gradients (thank you, ",
"/u/Sergris",
") "
] |
[
"The reason is fairly simple. What is a Voronoi diagram? It's a diagram created by taking pairs of points that are close together and drawing a line that is equidistant between them and perpendicular to the line connecting them. That is, all points on the lines in the diagram are equidistant to the nearest two (or more) source points.",
"Well, whatever those nozzles were, and whatever was coming out of them, chocolate or air, it was coming out at the same speed: where did the two (or more) fronts of chocolate/air/whatever meet and cancel? At a point roughly equidistant from the source nozzles, where there is a clear transition point on the surface of the chocolate."
] |
[
"I would agree, except that the difference in color is from the variation in surface shear flow direction, not temperature gradient. Chocolate doesn't turn different colors depending on how fast it cools, but variation in the orientation of chocolate particles would definitely do it. Rheoscopic fluid would be an excellent example of this effect. "
] |
[
"How is it proven that entangled particles don't have a well defined spin?"
] |
[
false
] |
In video Veritasium tries to explain this at 2:13 but I don't get it. He states that if entangled particles have a well defined spin (vertical and opposite) and are measured in a horizontal direction (perpendicular to the spin) there is a 50/50 change for each particle being spin up. And that this would give a 50% chance that both particles would have the same spin violating the law of conservation of angular momentum. I am totally missing the point here. Why would entangled particles having a well defined spin have a 50% change of both having the same spin and particles with undefined spin not?
|
[
"If the two particles had a well defined spin in the vertical axis, one being up and one being down, if they were measured in the horizontal axis they would each have a 50% chance of being measured spin up or spin down, independent of each other. For instance, if particles A and B had well defined spin in the vertical axis (say A was spin up and B was spin down), if you then measure particle A in the horizontal axis, it will have a 50% chance of being measured as spin up and a 50% chance of being measured as spin down - that is how particles of well defined spin behave. Similarly if you measure particle B in the horizontal axis, it will have a 50% chance of being measured as spin up and and 50% chance of being measured as spin down. So 25% of the time both particles will be measured spin up, and 25% of the time both particles will be measured spin down, so in total 50% of the time they will have the same spin.",
"However, with entangled particles, they will always be measured to have opposite spins, no matter which axis they are measured in, as long as it is the same axis for both particles. So if you perform the same experiment as above, but with two particles that have their spins entangled, (rather than being well defined in the vertical axis), when you measure their spins on the horizontal axis (or any axis for that matter), they will each have a 50% chance of being spin up or down, but the result will always have the spins opposite."
] |
[
"Particles with well defined spin cannot be entangled, for the reasons above. Entangled means they always give the opposite result no matter which axis they are measured on. If the two particles are not entangled but are simply opposite, you get the results I described in the first paragraph. As soon as you measure the spins of entangled particles, the entanglement is broken and you now have particles of well defined spin which behave as such from then on.",
"As for the video, he doesn't talk about particles being both entangled and having well defined spin, he just says they are created with well defined spin in opposite directions."
] |
[
"Thanks for your answer. I understand what you say but the bit in the video about entangled particles with a well defined spin is still confusing to me. Are there any experiments done with entangled particles with a well defined spin like the experiments done with entangled particles with an undefined spin? Or is Veritasium talking about imaginary entangled particles with a well defined spin and a thought experiment why these particles don't exist? And if he is talking about a thought experiment why does this not apply to entangled particles with an undefined spin?"
] |
[
"Is it possible to control which direction heat flows on the atomic of molecular levels?"
] |
[
false
] |
Is there a material that can transfer heat in desired directions rather than just march towards equalizing temperatures between two objects? I don't have a background in physics or chemistry, I just had a curious thought after thinking about how well my Yeti cup keeps things cold. I'd love to learn more about our understanding of heat flow, and any cool efforts ongoing on the subject.
|
[
"Thermal conduction is the transfer of heat by collisions between particles and movement of electrons within a body. Heat likes to flow from higher energy places (hotter) to lower energy places (colder), and electrons and other stuff like to go where the ",
"free-energy (combination of energy and entropy) is lower",
".",
"The flow of heat also favors the path of least resistance, with higher flow rates when thermal conductivity is higher, just like an electric current favors branches with smaller resistance in electrical circuits.",
"So if you want to direct heat you must create highly conductive paths between the things (or spaces) that you want the heat to flow to and from, but you always need a free-energy difference between them to make the energy flow.",
"There are various ways of doing this, the most obvious is by connecting your object of interest to a colder or hotter object/ambient according to your need. The other is artificially inducing a low free-energy state in one end of your thermal circuit, this is like ",
"thermoelectric devices",
" such as ",
"Peltier coolers",
" work.",
"A good example of very efficient heat flow directing by employing highly conductive materials is the use of ",
"heat pipes",
" to redirect heat from your notebook’s cpu/gpu to the coolers.",
"There are other exotic ways of cooling down stuff, like ",
"using lasers get particles or molecules temperature down to the millikelvin range",
".",
"About your Yeti cup, it keeps things cold/hot by keeping the thermal conductivity very low. You have 3 ways of conducting heat: conductive transfer, convective transfer and radiative transfer. Conduction and convection require a physical medium, one way to prevent that is by creating a vacuum between the double walls of your cup. You can reduce radiative transfer by using mirrored surfaces (probably on the inner side of the cup walls) that bounce back the heat.",
"This basically sums it up. Unfortunately, I can't give you a better answer regarding controlling it precisely at an atomic/molecular scale."
] |
[
"Very informative thank you! "
] |
[
"So could it be possible to make a structure at the atomic scale \"locking\" the atoms to only move in a two dimensional sense?"
] |
[
"If a pregnant mother drank enough to get drunk, would the baby as well be drunk?"
] |
[
false
] |
If the baby did not die, would it technically be drunk?
|
[
"The Alcohol enters the Mother through the stomach/intestines and is absorbed into the blood. The mother's circulatory system is ",
"not directly connected",
" to the fetus's circulatory system, as it is routed through the placenta and then through the umbilical cord. However, ",
"alcohol can permeate the placenta",
" and enter the fetal circulatory system. A normal BAC reading wouldn't ",
"really be helpful",
" in this case, but the fact is that the baby would have alcohol in ver circulatory system.",
"Of course, I don't know the rate at which the fetal circulatory system's BAC would rise in correlation with the mother's circulatory system (i.e. how quickly/much the alcohol diffuses through the placenta) so it's possible that, if the mother drank the bare minimum to have a BAC which was just barely over the legal limit, that the fetus's BAC would not be high enough for ver to be considered legally drunk.",
"Disclaimer: I'm not a health professional, I'm just a college kid. My answer is based off of my understanding of the human body as taught in high school and off of the websites I linked. I hope this answer is satisfactory and doesn't count as 'layman speculation'."
] |
[
"The placenta is about as permeable to alcohol in the blood as the blood brain barrier in the mother. The baby would have the same BAC as the mother, except the baby is much smaller, so the effects would be way more pronounced. On the other hand, it depends when in the pregnancy this happens, and I don't know how we could measure what a fetus is experiencing before its brain is fully developed."
] |
[
"What?"
] |
[
"Is It True Helium Is a Liquid At 0 Kelvin?"
] |
[
false
] | null |
[
"Solid helium is quite cool. It's probably the solid with the least density, if you exclude aerogels and other composite stuff. It's density at 1.15K and 66atm is 0.2 g/cm",
" That's a fifth of water. And it's highly compressible, almost five times as much as water. The reason is that the zero point energy is so high that the atoms tend to be very far apart and so it's quite easy to put them closer by applying pressure.",
"And some recent experiments seem to indicate the existence of a brand new phase of matter called the ",
"supersolid",
" phase. It's like a 'solid' with zero 'viscosity'. While it's not well understood yet and there are controversies regarding the experimental data, everyone agrees there's something there.",
"But in other ways it's a solid like any other solid."
] |
[
"It freezes at higher pressures."
] |
[
"What properties would solid helium have? This concept is hard to wrap my head around."
] |
[
"Do the points where a curve function and its derivative intersect hold some significance?"
] |
[
false
] |
We're doing calculus in school now. And I was wondering whether the points where y = y' are used in science, engineering or some field? Are they called something? I was wondering when I graphed a cube function and its derivative .
|
[
"Exactly. The function y=e",
" is its own derivative: the function's graph and its derivatives graph are the same, over the whole length of the graph from minus to plus infinity. And it is the ",
" function with this property.",
"BTW, if you want to get your jargon right: You wrote \"y=e",
" \", which describes the graph as the line formed by the points (x,y). Mathematicians like to think about such an expression as a \"function\" f, i.e., a machine into which you can put a value x and it spits out the value y at the other end. They say that the function f \"transforms\" x into, say, e",
" and write: f(x) = e",
" They call x the \"argument\" to the function (you called it \"value\") and y=f(x) the \"value\" of the function at x (you called it \"answer\")."
] |
[
"Thanks! That makes perfect sense. I just have a question here:",
"If some function y fulfills the differential equation y' = y, then we have that y = Ce",
" is the exponential function. This is used rather widely in applications.",
"So for the graph y = (c)e",
" , the answer of y for any value of x on the graph will also be the answer of its derivative (y') for that value of x? (pardon if wrong jargon)."
] |
[
"Thanks! That makes perfect sense. I just have a question here:",
"If some function y fulfills the differential equation y' = y, then we have that y = Ce",
" is the exponential function. This is used rather widely in applications.",
"So for the graph y = (c)e",
" , the answer of y for any value of x on the graph will also be the answer of its derivative (y') for that value of x? (pardon if wrong jargon)."
] |
[
"how do molecules in cells know what to do?"
] |
[
false
] |
ive been reading a lot of biology and ect chemistry stuff recently, and in normal chemistry its like, ok, we've got a couple molecules in a jar, there's only a couple things they can do. and they do that. but in biology it seems like there's this infinite possibility for things to go wrong. oh, ok there's this DNA in this nucleus and there's this other thing that's gonna copy it, but how does it get there, and why doesn't it react with some other random molecule along the way? (not specifically that case, but as a general rule)
|
[
"It's because biological molecules fit together geometrically. The molecules in a cell are all careening around at random, but if they don't fit together, they just bounce off of each other. This continues until they find a match, and then some reaction occurs. Actually there are some molecules that fit into a lot of other molecules, but they fit in a way that only does one thing that affects how two or more other molecules might interact. ADP is one of these. It fits into a lot of molecules, and sometimes into complexes of molecules, then it gives a little bump of energy that pushes a reaction over the hump.",
"Ubiquitin is another molecule that fits with a lot of molecules. Its presence provides a means of regulating many cellular processes.",
"Some molecules fit where they shouldn't, and then you have trouble. These are generally known as poisons. They don't reside in the cells, but can be introduced from the outside. Carbon monoxide fits into the same spot as oxygen in hemoglobin, and it's fairly stable that way, so it causes suffocation by preventing hemoglobin from carrying and releasing oxygen to the cells. "
] |
[
"The cellular molecules that I am going to address are proteins, specifically enzymes (proteins that are able to catalyze a reaction, i.e. they increase the efficiency of the reaction without being consumed by the reaction itself).",
"The short answer is that they do not actually \"know\" what to do. You have thousands of enzymes in your cells, and each of them is extremely specific to a single catabolic/metabolic reaction, or a small group of very similar reactions. Take for example lactase, which breaks down lactose into glucose and galactose (one big sugar into two smaller sugars). Lactase is not traveling around your cells looking for lactose because it \"knows\" it is supposed to break it down. Rather, both lactase and lactose will move freely within the cell and the reaction will only occur when the enzyme and its substrate randomly encounter each other. The enzyme does not actively pursue lactose (although it is possible other cellular mechanisms could help localize lactose and lactase within the same area to encourage the reaction). ",
"Summarily, enzymes do not \"know\" what to do. Initiation of a reaction is a matter of serendipitous interactions between enzyme and substrate (e.g. lactase and lactose), and completion of the reaction is a matter of thermodynamic equilibrium. There are many intricacies that I did not address, but I think this may at least partially answer your question."
] |
[
"I feel ",
"Brownian motion",
" should be mentioned. It's tempting to anthropomorphise molecules as the combination of Brownian motion and varying levels of interactivity makes it seem like molecules seek each other out, but really, most molecules have bumped into most other molecules in the cell and some of them stick and others don't. "
] |
[
"Is it possible to breen pedigree calves with non-pedigree calves?"
] |
[
false
] |
I got this question for school (it's rufly translated from dutch) and to be clear it's not about it being possible for pedigree cows and non-pedigree cows to have a child; it's about if it would be possible for a non-pedigree cow to have a pedigree cow/calve as child. If not as some sort of surrogate... Might this be possible in any way?
|
[
"I'm not sure about cows, but with cats, dogs and horses, the animal has to have pedigree ('pure') parents and grandparents in order to be called pedigree. The word 'pedigree' basically means 'family tree', and in terms of animals it's used to show that this animal has pure parents and pure grandparents, with no other breed mixed in. ",
"So, for example if I had a pedigree Labrador dog and mated him with a Labrador-looking dog which didn't have a pedigree, the puppies would look like Labradors, but they would not qualify for pedigree certification, because not all of its family tree are certified Labradors. "
] |
[
"All \"cows\" are the same species. They can have fertile offspring together. A \"pedigree\" cow (or any animal) is just one that has a record of lineage."
] |
[
"to be clear it's not about it being possible for pedigree cows and non-pedigree cows to have a child"
] |
[
"Why do my feet feel like they're burning if I put them in warm water when they're cold?"
] |
[
false
] |
[deleted]
|
[
"I'm surprised no one has answered this already, as this question is fairly easy to answer. Your feet feel like they're burning because of the difference in temperature. The rest of your body doesn't feel that way since it is not as cold as your feet, as the difference in temperature between your body parts and the water is less than that between your feet and the water.",
"\nTo help illustrate this: if you immerse yourself in a tub of water that is roughly heated to body-temperature, while your own body is at body temperature, then you'll barely feel a thing. Conversely, if you're super cold and shivering and step into the same tub of water (heated to body temperature), then the water will feel much hotter. The sensation of \"hot\" and \"cold\" is all relative, really."
] |
[
"I've thought this effect related to the involvement of \"cold\" thermoreceptors in burning sensations and that it was essentially a variant of the ",
"Thermal Grill Illusion",
".",
"Perhaps someone can elaborate or dismiss this."
] |
[
"Found this on page 5 of ",
"Craig and Sorkin, 2001",
":",
"[...] there is a cross-modal interaction between\ninnocuous thermosensory (cool–warm) activity and C\nfibre-evoked pain. Therapeutic cold or warmth has a\nperipheral palliative effect on inflammation and on\nsensitized nociceptors; in addition, there is a central\ninhibitory effect on pain that occurs in the forebrain. The\nthermal grill illusion of pain, in which a painful ice-like\nburning sensation is elicited by spatially interlaced\ninnocuous warm and cool stimuli, demonstrates this\ninteraction by showing that the reduction of cooling-\ninduced thermosensory activity (by the simultaneous\nwarming) can unmask the noxious (burning) sensation\nnormally caused by noxious cold. This disinhibition, or\nreduction of the normal inhibition of pain by cooling, is\nassociated with lamina I spinothalamic activation of the\nanterior cingulate cortex (Craig et al., 1996). A conduction\nblock of peripheral nerve A fibres (by maintained pressure)\nthat eliminates cooling sensibility (conveyed by Ad fibres)\nenables an innocuous cool stimulus to produce the same\nburning sensation (via C-fibre nociceptors). The intense\nburning sensation caused by putting warm water on feet\nthat are numbed by cold, an unmistakable thermoregula-\ntory distress signal, is probably based on the same\nmechanism."
] |
[
"If I remember a song in my head, lyrics and all, does the brain use the equivalent amount of memory to store this as it would need in a device?"
] |
[
false
] |
[deleted]
|
[
"This is a difficult question to answer. And it's even quite difficult to explain why it is difficult.",
"Let me put this question to you. Pick up whatever is to closest to your right hand, say, it's a pen. How many megabytes is that pen? Is that a reasonable question to even ask? Plainly, it currently is not represented in a digital form, but perhaps you mean, \"How many megabytes would it take to store that pen in digital form?\" Well then the question is, to what resolution? If you just say the pen is basically a cylinder, it will only take a few bytes to store it. However, if you wanted to store it absolutely perfectly, down to every atom, well, by my very very rough calculations (assuming each atom needs 3 64bit numbers for its position/state), it would take on the order of 1 yottabytes, which is about 3000 times the total amount of digital storage in world. Just for a pen.",
"I point this out for two reasons, firstly, when it comes to things that exist first in the \"real world\" (non-digital world) talking about how many bytes it is, is pretty weird. If I ask you how many bytes a pen, or a piece of paper or a car takes up in the real world, it kinda doesn't make too much sense when you think about it at first. Secondly, it shows you how something that exists in the non-digital world can take up completely different amounts of space, depending on how you store it. So your 50mb for a song is actually 50mb for some estimation of a song. It does not contain all of the sonic information of the original song, just some approximation of it, that happens to sound similar when you listen.",
"HOWEVER, people do try to figure out information content. Information content can be measured in bits. In this way, the outcome of a fair coin contains one bit of information*. Also, if you took an bitmap image, and compressed it with a lossless algorithm, so that it took up less space on your hard drive, but when reconstructed you got the exact same picture, then the information content is the same. This way we can think about our \"how much storage space does a \"pen\" take\" now can be addressed in a slightly more meaningful way; if our \"stored pen\" could be reconstructed into an exact replica of our original pen, then the \"stored pen\" (irrespective of how many gigabytes it took on the computer) would have the exact same information content as the real pen.",
"So, now we can ask, how \"good\" is your memory of the 50mb song? If, after listening, you could in some manner recreate it (with a guitar, synth program, just by singing it, however...), and recreate it perfectly, then your brain had all the information content as the original 50mb song. However, every mistake, would count against you.",
"TL;DR. Talking about how many digital bits your brain stores is as silly as asking how many digital bits is a pen. However, you can compare information content. If two representations of the same content can produce an identical output, then they have the same information content.",
"*An aside, to explain the coin flip. I say a fair coin flip contains one bit of information. This is because before hand, you cannot guess it's outcome. Thus, the result is completely new information. However an unfair coin flip contains less information. This can be explained (roughly) like this: For instance, if the coin came up heads 75% of the time, then it only contains 1/4 of a bit. This is because beforehand, you \"kinda knew\" the outcome. If you guessed heads, you would get it right 3 times out of 4. Thus out of 4 coin flips, you would only have been wrong once, hence you only got new bit of information once, so for 4 flips, you got one bit of information, so each coin flip contains 1/4 of a bit."
] |
[
"There is at least one man who is able to imagine complex pieces of music with an accuracy level that was thought to be theoretically impossible until it was shown that he does it. He's an American Rag-Time concert pianist called Bob Milne. ",
"It's not just that he can 'hear' symphonies by imagining them, he's demonstrated the ability, under controlled conditions, to imagine FOUR symphonies simultaneously, so that when the neuroscientists studying him would ask at certain points questions like 'what are the trumpets in the Beethoven piece doing now and what are the violins in the Mozart piece doing?' he was able to answer correctly. ",
"I can understand how a person could imagine one orchestral sympathy fairly accurately, I can't do it on demand but I have experienced auditory hallucinations which made me think someone had put on a record in the next room because I can hear Holsts' 'The Planets suite' or whatever it might be and it sounds too real to just be a product of my mind. But to be able to 'hear' four at the same time as he does and to be able to control it, that's insane. ",
"Radiolab did a feature on Milne in 2011, about his ability and the investigation in to by Penn State neuroscientist Kerstin Bettermann.",
"http://www.radiolab.org/story/148670-4-track-mind/",
" "
] |
[
"There is at least one man who is able to imagine complex pieces of music with an accuracy level that was thought to be theoretically impossible until it was shown that he does it. He's an American Rag-Time concert pianist called Bob Milne. ",
"It's not just that he can 'hear' symphonies by imagining them, he's demonstrated the ability, under controlled conditions, to imagine FOUR symphonies simultaneously, so that when the neuroscientists studying him would ask at certain points questions like 'what are the trumpets in the Beethoven piece doing now and what are the violins in the Mozart piece doing?' he was able to answer correctly. ",
"I can understand how a person could imagine one orchestral sympathy fairly accurately, I can't do it on demand but I have experienced auditory hallucinations which made me think someone had put on a record in the next room because I can hear Holsts' 'The Planets suite' or whatever it might be and it sounds too real to just be a product of my mind. But to be able to 'hear' four at the same time as he does and to be able to control it, that's insane. ",
"Radiolab did a feature on Milne in 2011, about his ability and the investigation in to by Penn State neuroscientist Kerstin Bettermann.",
"http://www.radiolab.org/story/148670-4-track-mind/",
" "
] |
[
"If a bird is inside a box, but it's flying, does the box weigh the same as it would if the bird was standing on the bottom."
] |
[
false
] |
I was staying with one of my buddies at his grandmothers house for a few days, and somehow we got onto this question. To me and my buddy, it seemed simple. If the bird is flying the box would weigh less because the weight of the bird is being supported by the bird itself so it's not combined with the weight of the box.
|
[
"If the box is closed (no air coming in or out) then the box will weigh the same on average regardless of whether the bird is flying. Over a long period of time, the average acceleration (averaged over time) of all the mass in the box (bird, air, and box) is zero, which means that the forces sum to zero (averaged over time). The forces are the supporting force from your hand and the force of gravity on all the mass in the box. Therefore, the force you're applying to the box is equal in magnitude (averaged over time) to the force of gravity on everything in the box (including the bird).",
"One way to make sense of this is to remember that birds (and airplanes and helicopters) fly by pushing air down. If the air can't go down through the floor of the box, then the floor of the box must stop that air. On average, this force applied to the air by the box is the same magnitude as the force applied from the bird to the air (which is the weight of the bird)."
] |
[
"You are correct. This is one of the reasons why beaverjacket's answer has \"averaged over time\" everywhere in his answer. The lift birds create is rather variable, and what will likely be turbulent airflow inside the box only makes this worse."
] |
[
"Let's say you have a tall box with a bird in it... if the bird is increasing its height, does the box begin to weigh more during it's climb?",
"I imagine: bird hovering = static downforce = opposite of weight of bird. So equilibrium.",
"But if the bird is climbing, they're exerting a downforce more than they're weight until they reach equilibrium. ",
"Am I wrong here? Just curious."
] |
[
"Is there such a thing as negative water pressure? has it been studied?"
] |
[
false
] |
I got this question by pondering Luke Skywalker suspended in some kind of water tank while convalescing ( ). You know when you're in the tub with a cup, and you completely submerge the cup, filling it with water (no air) and then turn it upside down and raise the bottom of the cup above water level? It would seem to me that there would be some kind of negative water pressure in the cup. Imagine doing that on a massive scale, in a large swimming pool. When I dive down 10+ feet in a swimming pool, my ears start to hurt from the pressure. If, in such a pool, there were a similar inverted, giant glass - sealed at the top - filled with water (that is, the water is in the glass only because of vacuum, like the bathtub cup) that rose 10+ feet above the surface of the rest of the water, what would it feel like to swim up in it? Would my ears hurt just as much, except in the opposite direction? Are there any possible therapies or treatments or scientific phenomenon that occur, or occur more readily, in such a vacuum like, negative water-pressure environment? Have there ever been studies or research conducted in this direction?
|
[
"It would seem to me that there would be some kind of negative water pressure in the cup.",
"No, the pressure just goes below the atmospheric pressure.",
"Would my ears hurt just as much, except in the opposite direction?",
"It would feel a bit like in an airplane that rises rapidly. Yes, the ears could hurt a bit. ",
"Here is a very small version",
". ",
"And one for fish",
".",
"Are there any possible therapies or treatments or scientific phenomenon that occur, or occur more readily, in such a vacuum like, negative water-pressure environment? Have there ever been studies or research conducted in this direction?",
"Go into a swimming pool on a mountain and you have the same result: Nothing special. The effects of lower air pressure in general are well-studied.",
"If you try to make the column of water too high, you reach (nearly) zero pressure at about 10 meters (if your pool is at sea level). That's how mercury barometers measure air pressure - by the height of this column. Mercury is used because it has a high density, so the column is shorter."
] |
[
"If you try to make the column of water too high, you reach (nearly) zero pressure at about 10 meters",
"Presumably swimming upwards into a sealed tube 10 meters high with a vacuum at the top would have nearly the same effect as jumping out of the airlock of a space ship. Except that the void at the top would be filled with water vapor at 4kPa (at 30°C) instead of a vacuum, so the water on your tongue would not boil.",
"This could be called a negative gauge pressure i.e -96kPA, relative to normal atmosphere."
] |
[
"Remember that you can't really have negative pressure. You can have a negative relative pressure, where something is at a lower pressure than some other arbitrary zero point, but you can't have the absolute pressure be less than zero, it's just not possible. ",
"EDIT: You can have negative pressure! In liquids and solids, at least. It happens when the material in question is under tension. If you think of pressure as coming from a measurement of the force pushing in on an object's surface, then if you put that object in a liquid under tension then the force on the object's surface would be pushing away from the object. My analogy in regards to the original question left out a relevant distinction. Shame upon me. "
] |
[
"Why is the moon not spinning?"
] |
[
false
] | null |
[
"An orbiting object not spinning like that is called \"tidally locked\". If you search this subreddit for this keyword you should find a lot of explanations on how it works. This is not unique to the moon."
] |
[
"tidally locked",
"Thanks for the explanation. I just read about tidal locking, I didn't know it is called that. ",
"Wow, this theory makes zero sense. It seems another one of those weird explanations that humans come up with when they have no explanation (pyramids, evolution, gravity, supernatural etc.). It says \"the tidal locking is almost certainly mutual.\" only that it is not in earth's case. Which makes the whole theory invalid. Also it says \"close binary stars throughout the universe are expected to be tidally locked with each other, and extrasolar planets that have been found to orbit their primaries extremely closely are also thought to be tidally locked to them.\" which means it is all a theory. ",
"If the moon was affected by earth's gravity it would be getting closer to earth at geometrical speed which means it should have crashed with earth long time ago. It can't be affected by earth's gravity and then stay in the same place while being locked by it because of its gravitational force (imagine a simple magnets experiment). This all makes zero sense.",
"Is there a logical explanation for this? Is there a theory that checks out rather than contradicts itself? Why that particular side of the moon is locked? Why is the earth not locked to the sun's gravitational pull? How can moon be locked if it is too far to be affected by earth's gravity? Satellites are not affected by it so why is the moon?"
] |
[
"There is a lot of missconceptions in your comment. The moon is definitively affected by Earth gravity (as well as the opposite). Tidal locking is a fairly straightforward consequence of Newtonian gravity on non-symetrical bodies. ",
"Satellites are definitely affected by earth gravity, this is why they orbits the earth and don't fly out.",
"If the moon was affected by earth's gravity it would be getting closer to earth at geometrical speed which means it should have crashed with earth long time ago. It can't be affected by earth's gravity and then stay in the same place while being locked by it because of its gravitational force (imagine a simple magnets experiment). This all makes zero sense.",
"No I would advise you to look up how orbits work. If you have a bit of calculus under your belt you can derive the equilibrium positions of tidal locking relatively easily. "
] |
[
"Does electricity slow down as it moves along a wire (or other conductor)?"
] |
[
false
] |
If you use a generator and have a wire running from it, would there be a point at which the wire was too long to be useful? Could you run a generator in New York and power a lamp in LA? Does it slow down, peter out, and if yes to either, why?
|
[
"The main issue with long distance power transmission is that you don't get 100% transmission. A lot of electricity is lost to heat (and other energy) as the electricity moves down the wire.",
"Our grid isn't very efficient, and this is one of its big problems."
] |
[
"It seems that by \"slow down\" you mean \"get weaker\", is this correct?",
"The main issue affecting long-distance electrical power transmission is voltage drop due to the resistance of the wire. If this voltage drop is too large it will affect the equipment trying to draw power from the line. "
] |
[
"can you expand on (and other energy)?",
"I understand loss of energy through heat (non-perfectly insulated wires, transistors, etc)"
] |
[
"How exactly do physicists interpret line integrals of vector fields?"
] |
[
false
] |
First of all, please forgive my poor physics-knowledge. I was told that physicists use line integrals quite often, and when I searched for examples, I found the following several times: "For example, the work done on a particle traveling on a curve C inside a force field represented as a vector field F is the line integral of F on C." (From Wikipedia) This, however, I don't quite get. For example, let V be a vector field and C a curve parametrised by a function r in such a way that V(r(x)) is orthogonal to r'(x) for all x. Then the line integral of V on C is equal to 0 - but speaking from a physical perspective, I'd still have to apply a force to a particle to move it along its path C through V, wouldn't I? Please show me my mistake!
|
[
"I'd still have to apply a force to a particle to move it along its path C through V, wouldn't I?",
"Nope! Or, at least, an arbitrarily small force would suffice. The point is that the vector field would not be doing to work to stop you. This is analogous to pushing a box along a horizontal, frictionless surface. Gravity acts perpendicularly to the motion, so you do no work. Technically, you had to supply some force to accelerate the block in the first place, but once you've done that the ball will move unimpeded the rest of the way.",
"Edit: For a general curve, you'd have to supply a force to change the direction of the particle as it moved along the curve, but again, if you're willing to wait an arbitrarily long time for the particle to traverse the curve you can make the force arbitrarily small."
] |
[
"The integral along C doesn't tell you the force needed to move the particle along C, but rather how much work the field V does on the particle as it moves along C. If the field and the path are always orthogonal the field does no work on the particle as it moves, which tells you that as you move the particle around, you don't need to do any extra work to counteract the field. For example, moving a weight parallel to earths surface, there is no work done to counteract gravity, but you still need to do work to accelerate the object. ",
"If you just place a particle in a field that exerts some force on it, like a gravitational or electric field, then the particle will move along some curve determined by its equation of motion (i.e. Newtons second law, F=ma), and then you can calculate the work done by the field by integrating along this curve. "
] |
[
"Gravity is a conservative vector field - consider the Earth's orbit around the sun. It keeps going around and around the sun and coming back to the same place every year. No work has been done on the Earth at all during this time."
] |
[
"Why was Bismuth, Antimony, and Arsenic discovered so early in the history of Chemistry?"
] |
[
false
] |
I read the other day that they were all discovered before the 14th century, and I'd just like to know why. Chemistry at that time wasn't very advanced, it was just beginning thanks to Alchemy. Even phosphorus and Nitrogen were discovered really early, compared to the rest of the elements on their respective period. So why was that group's elements discovered so soon, and how?
|
[
"The scientists at that time looked at a bunch of minerals and heated them up or reacted them and eventually some interesting things came out. Arsenic can be isolated by heating the mineral arsenopyrite. The arsenic is driven off in gas form and can then be captured.",
"Antimony sulfide was well known and ",
"\"the roasting of crude antimony could be done in a current of air under moderate heat until it burnt, and that if it were heated more strongly it would melt like lead. This statement might suggest the idea that he was acquainted with the metal itself.\"",
"Bismuth, which has been known since ancient times, was often confused with lead and tin. By the 1400s, people had begun to suspect that bismuth was a distinct chemical element, but it was not isolated until 1753. I suspect it was made the same way, by heating minerals."
] |
[
"Thank you!"
] |
[
"If you don't get an answer here, you can try ",
"/r/askhistorians",
", ",
"/r/historyofscience",
", or ",
"/r/philosophyofscience"
] |
[
"Global Warming: Sea Level Rise of 50cm. What is the big deal?"
] |
[
false
] |
First off, I want to make it clear that I am not a global warming skeptic. I know that 97% of scientists agree with AGW. I understand the issues with temperature increase and how it affects ecosystems. I understand the issues with ocean acidification. But I simply do not understand why a sea level rise of 50cm by the end of the century is a big deal. I live next to the coast and I have been to the beach many times. There is usually a couple of meters high worth of sand from the point where I park my car to the water level. If the water level rose by 50 cm over the course of a century, I probably would not even notice it.
|
[
"It causes damage to lots of areas close to the ocean and damages freshwater habitats near to the shore.",
"The temperature rise is perhaps more significant, as are the effects on weather."
] |
[
"This is exactly it. Both parts of the concern.",
"Assuming the water is coming from melting polar ice caps, you're going to see some serious fluctuation of ocean currents, which is large responsible for governing weather, particularly on areas near the coast."
] |
[
"Half a meter is a very big deal if your regions's altitude is close to sea level. Half of the Netherlands, for example, is only one meter above the current sea level. Hurricane Katrina shows you what can happen to areas like Louisiana. Many pacific islands are equally close to the sea level and many, many people live very close to the sea level especially in the developing world.",
"It's not that they will suddenly all be under water permanently, but that phenomena such as for example storm tides will have a much bigger effect, by penetrating further inland and fouling land and water supplies. There's also faster erosion of coastlines to consider.",
"Finally, that half meter is at the very lowest end of the range for predicted sea level rise until 2100. The current sea level rise follows the upper end of the most recent IPCC AR4 predictions (59 cm) and those were far too conservative as we know now. On the current path, we're more likey moving towards 70-80 cms and according to the more dire predictions, the sea level rise till 2100 could even reach up to 2 meters. This is summarized ",
"here",
"."
] |
[
"If someone receives a donated organ, can that organ be donated again when they pass?"
] |
[
false
] | null |
[
"Not an expert here, just a doc.",
"I have never heard of that thing happening so I guess there are reasons for it not being practical.",
"One I can think of is that once you operate in a person, his/hers organism, trying to put things back, makes a lot of connecting tissue where you disturbed it, so taking this thing out without damaging it is much harder than taking the previous out and putting that in.",
"When you operate for a second time in the same area things can really be a mess, even in relatively simple surgical procedures.",
"Still hope a more qualified person can answer it. It is a good question."
] |
[
"I heard that donated organs only last so long because of damage to the organ builds up over time due to slow chronic immune rejection of the organ, so maybe that's why. I wonder if someone who recieved a transplant and died in a car crash a week later could still donate though."
] |
[
"I work with a few doctors and nurses in a kidney and liver transplant team. Never heard of a liver being replanted however it is possible to reuse kidneys. \nThat being said, it would only be taken if the patient receiving the kidney had almost immediately passed away, before any long-term use occured. \nTake this answer with a grain of salt though."
] |
[
"The past never ceases to exist? If so, this means that, in someway, we never cease to exist too, am i right?"
] |
[
false
] |
(pardon my english, not a native speaker)
|
[
"This thread is oddly void of meaningful information."
] |
[
"This is one of those questions that — deliberately or not — takes advantage of subtle ambiguities of language to give the impression of meaning where no meaning exists. A Buddhist would say that the only possible meaningful answer to the question is \"mu.\"",
"That said, I have this big, empty box in front of me and a few free minutes, so I think I'll type for a little while. There will be nothing of importance below this point; feel free to stop reading if you like.",
"Consider the phase space of the universe. The phase space of a system is an abstraction. As the name implies, it's a space; the space has one dimension for each degree of freedom of the system, and every point in the space represents a unique possible configuration of that system.",
"At the first instant of time, the universe existed in a particular state, represented by one point in the phase space of the universe. As the universe evolved, it followed a smoothly continuous trajectory through phase space, like the path a bumblebee follows through the air. That trajectory traces out a curve through infinite-dimensional phase space; the length of the curve, if you were able to measure it as you would measure a piece of string, is equal to the age of the universe at any given moment.",
"The phase space of the universe, then, can be divided neatly into three clearly defined regions. There are all the points that do not lie along the phase-space trajectory of the universe; there are the points that do lie along the trajectory excepting the last one; and there's that one last point on the curve, the endpoint that represents the state of the universe right now.",
"We have names for these three regions.",
"The first region — the set of all possible states of the universe that do not lie along the universe's trajectory through phase space — we call \"the future.\"",
"The second region — all the points along the trajectory excepting the last one — we call \"the past.\"",
"The third region, that one single point, we call \"the present.\"",
"\"The past,\" then, is nothing more than a name for a set of states. It's the set of all states the universe has been in ",
" the state the universe is in right this very instant. That word \"except\" there is a very important one; the state the universe is in ",
" is not \"the past.\" It's \"the present.\" \"The past\" is the set of all states the universe ",
" but ",
"From this, we can see that, logically, \"the past\" is ",
" a set of states that do not exist.",
"To say, then, that \"the past never ceases to exist\" is demonstrably false. It's not a question of interpretation or of philosophy; it's simple logic. By definition, \"the past\" consists of all the states the universe has been in but ",
" the one, single state that the universe is in right now. The one point in phase space that can meaningfully be said to \"exist\" — that is, the ",
" in infinite-dimensional phase space that corresponds to something physically real — is ",
" excluded from \"the past\" by simple definition.",
"Ergo, \"the past\" does not exist. If it existed, we would have to call it \"the present.\""
] |
[
"I suggest you try asking the people in ",
"/r/Philosophy",
". Scientists are reluctant to answer this type of question because there is no clear answer and no real way to test whatever answers you can come up with. ",
"/r/Philosophy",
" is quite a good subreddit. ",
"Good luck!"
] |
[
"Imagine 2 spheres weighing 1g each, 1cm in diameter, and placed 1m apart in space..."
] |
[
false
] |
Assuming no other outside forces, how much time would it take for gravitational force to cause them to eventually touch? I am sure there is probably very simple math for this. Please help a dumb artist! I've posted this question several times and don't get any responses...
|
[
"Unfortunately the maths isn't very simple; you get a nonlinear second-order differential equation as follows:",
"F = Gmm/r(t)",
"F = 2ma = 2mr''(t) (the 2 comes in because the force is applied to each sphere, so the relative acceleration is doubled)",
"-> r''(t) = Gm / (2r(t)",
" )",
"with the boundary conditions that r(0) = 1 and r''(0) = 0, and you want to solve r(t) = 0.01.",
"This is solvable, and there are various approaches to doing so (Wolfram Alpha will do it, but not with boundary conditions), but it's not particularly friendly.",
"I put together a ",
"quick program",
" to do this naïvely numerically, and got a little over 3 million seconds, or about 35 days. This is subject to floating point errors etc, and I'd be interested in the result if someone solves this analytically (or with a better numerical algorithm), but it should be about right.",
"(edit: typo--)"
] |
[
"If we use them as point particles instead of 1 cm spheres, you can use the ",
"free fall equation",
" to calculate it, and get 3.04 million seconds, or 35 days, 4.5 hours."
] |
[
"This is not an exact calculation, but they would exert an initial force of 6.7x10",
" N. Which means the acceleration would be something like 6.7×10",
" This is where I get fuzzy. That acceleration will change as they get closer to each other, but for a ballpark, it would take about 3x10",
" to accelerate to the average velocity needed to go 1m in 3x10",
" seconds. 3 million seconds is about a month.",
"I hope that's within an couple orders of magnitude of the correct answer. Someone who can do two-body calculations should answer this for real."
] |
[
"Why is Helium not commonly used for inert atmospheric reactions?"
] |
[
false
] | null |
[
"heavier than air gasses are preferred as they can be contained, utilized, and reclaimed far easier than lighter than air gasses....",
"\nThe expense is negligible for most operations. My kid brother goes through a tank of argon every month or two welding.. Id have to say Argons MORE readily available than helium in my area at least. "
] |
[
"Argon is like 1% of air, it's massively more available on earth and essentially renewable. Helium floats high and awat."
] |
[
"Weight and cost. Helium is much lighter than air, so in the atmosphere, you’ll lose most of it before it reacts. Nitrogen is commonly used for preservation because it about weighs the same as air. With that it is much more commonly produced "
] |
[
"What actually are the 'impurities' that allow flux tubes to penetrate superconductors, achieving Flux Pinning?"
] |
[
false
] |
I was curious about the process of Flux Pinning, and found that thin flux tubes from a magnetic field actually the superconductor itself, locking it in place, almost. However, I couldn't find any information on how or what these impurities are or come to be. Are they just small holes? I'm not sure if this is too mundane a question to answer, but I find the whole subject of Flux Pinning fascinating. I'm a Physics (British definition of) college student, so I'm essentially a layman, haha. Thanks a lot.
|
[
"According to the ",
", ed. Walter Benenson, John W. Harris, Horst Stöcker, Holger Lutz, ",
", places at which the magnetic flux tubes in type-II superconductors may be fixed. Such pinning centers may be dislocations, grain boundaries, or segregations, i.e., defects in the crystal lattice."
] |
[
"Hm, didn't know about Google Books! Ah, so it could really be anything that flux tubes could penetrate? Even grain boundaries ",
"? That's quite interesting. Thanks a lot, I might pick up the book, so thank you also for linking it."
] |
[
"Even grain boundaries (presumably in wood?)?",
"Wood isn't superconducting :).",
"The individual crystals that make up your typical multicrystalline sample of metal or ceramic are called \"grains\". That's what it means by grain boundaries."
] |
[
"How \"bright\" is WiFi?"
] |
[
false
] |
Assuming you could convert 100% of the amount of energy that the signal contains and convert it entirely to a certain wavelength of visible light how would that compare to a common bulb or led? Please consider a home series wireless N variety access point, and if possible give us a comparison to a lightbulb, christmas light, etc.
|
[
"FCC regulation is that output power be less than 1 Watt. Typically it is less, about 100 mW. For comparison, a typical ",
"LED",
" is about half that, around 50 mW, and a standard 60 W incandescent puts out about 1 W of visible light. So a standard WiFi router would look like a low-wattage incandescent or a bright LED. "
] |
[
"Great answer! Another interesting point is that a wifi photon has about 100,000 times less energy than a visible photon, so while a power meter will show less power than a typical lightbulb, if you had a microwave photon counter, it would show dramatically more photons being emitted than from a lightbulb."
] |
[
"It's really not, though. When you build a laser, you don't say \"this one's going to shoot 10 photons per second, better make them high-energy photons!\". You say \"I'm going to put in 1 kW, better make sure as much of this power as possible makes it to the target!\"",
"High-energy photons get absorbed more easily - gamma-ray lasers would be useless because it gets absorbed by the atmosphere, so you'd just have an expensive space heater. On the other hand, radio-lasers would be useless because they'd pass through the target, leaving it more or less unharmed. So you want something that passes through the atmosphere but is absorbed (not reflected!) by whatever your target is. ",
"That's not the only loss, though. Generating the laser - for some wavelengths we can make lasers more easily than others. You don't want to waste 100 kW in heat and produce just a 10kW laser beam, if you can avoid it! Optics - you'll want to collimate (focus) the beam, and maybe aim it; diffraction gratings, lenses, and mirrors all work differently at different wavelengths, so that needs to be accounted for.",
"I'm sure I'm missing something."
] |
[
"Benzene is a known carcinogen. Why is it that by adding just a methyl group, toluene is not carcinogenic?"
] |
[
false
] |
[deleted]
|
[
"The big difference is metabolism. Benzene is metabolized, to a small extent, to a reactive epoxide that can alkylate DNA (likely via the sort of intercalation mentioned by ",
"u/croutonicus",
"). Toluene, though, is very easily oxidized on its methyl group to benzoic acid, which is excreted harmlessly through several routes."
] |
[
"Toluene has the same basic shape as benzene, the methyl group is not big enough to prevent van der waals interactions with aromatic DNA bases."
] |
[
"Neither benzene nor toluene are stable enough in vivo to interact directly with DNA, it is their metabolites that show differences in DNA intercalation."
] |
[
"How do physicists separate neutrinos from particle collisions from neutrinos coming from the sun?"
] |
[
false
] |
How are neutrinos from high energy particle collisions separated from the thousands of neutrinos that would pass by from the sun? I know that neutrinos are detected using conservation of momentum, but wouldn't neutrinos that pass by from the sun alter the momentum of the collision?
|
[
"Well, most neutrinos that are detected do come from the sun. If you're referring to experiments that use man-made neutrinos (so to speak), then they employ highly anisotropic detectors, meaning only neutrinos coming from a specific direction can trigger the detector. It's also necessary to measure the background flux, the amount of neutrinos detected when the source is off, so you can account for that in your measurements."
] |
[
"Most of the neutrinos created in collider experiments have a much higher energy than those emitted by the Sun. The Sun emits neutrinos of energy 10 MeV or less. Also, detectors have directionality. They can detect which direction the neutrinos are coming from. As far as the collider experiments are concerned, neutrinos are detected on account of their interactions with nucleons. This causes decay products to be sprayed in a particular direction. This direction is same as the neutrino direction. The energy of the particles in spray can me measured and sum is a measure of neutrino energy."
] |
[
"How do you design an anisotropic detector for neutrinos? I'm only familiar with the \"put a giant tub of water deep underground\" sort of detector."
] |
[
"Why are the air intakes of fighter jets so often on the bottom of the plane?"
] |
[
false
] |
Just as an example, the F-16 is like a vacuum cleaner, and will suck up ANYTHING off the ground nearby. That's a problem when rocks, tools, and bolts, get sucked up into the air intake, so I'm wondering why they continue to be below wing level. As I'm not an aeronautical engineer, the only good reason I can think of so far is to have the cockpit out from in front of the intake. Is there more to it?
|
[
"For fighters, having the intakes above the wings would create a visual obstruction for the pilots, a definite disadvantage in a dogfight. Generally, the top of the wing is more aerodynamically sensitive than the bottom and stalls are caused by flow separation between the air stream and the top of the wing, so you want to avoid anything that might disrupt the airflow over the top of the wing. Similarly, you don't want anything to disrupt the airflow into the intake itself and, intuitively, it seems like having the canopy bumped out would generate a trickier flow pattern to feed into the engines. You could certainly design around it, but it's easier to stick them under the wing where the nose of the plane can smoothly guide air straight into the intake.",
"For reference, the only two aircraft I can think of with intakes above the wing are the stealth fighter (F-117) and stealth bomber (B-2). The fact that they're both stealth leads me to believe the intakes were moved above the wing to reduce the effective cross-section from ground-based radar, but this is speculation on my part."
] |
[
"I'd like to add to this answer. ",
"Most of the American (well most of the planes) have intakes below the plane. But good ole Russian planes (MIG 29) have 2 intakes. ",
"One above the plane one below",
". These help in taking off on runways with debris on them as the intakes won't suck up anything on the ground unlike a F15 "
] |
[
"On a serious note though I imagine it would be quite useful to save time having to sweep debris from a warzone runway that's been attacked, or be able to use a dirt/gravel improvised runway."
] |
[
"[Physics] How does the the Beta function describe the strong nuclear force?"
] |
[
false
] |
I've always wondered what were the mathematical laws that describe the strong and weak nuclear forces. I was watching the Elegant Universe and it said the Beta function describes the strong nuclear force. Can someone explain the physics of how the describes the strong nuclear force?
|
[
"The other two commenters saying that you are confusing it with the Callan-Symanzik beta function are mistaken; the ",
"Veneziano amplitude",
" really ",
" the Euler Beta function.",
"In particle physics we are interested in calculating scattering amplitudes. These are functions which, given a set of incoming and outgoing particles and their momenta, tell us the property of some scattering process or another occurring.",
"If you've seen a ",
"Feynman diagram",
", that's a useful picture of what happens in a scattering process. The key idea is that the incoming particles combine into internal \"virtual particles\" which carry on combining with each other or splitting off according to the Feynman rules until eventually you get the outgoing states.",
"The internal virtual particles are different from real particles because they don't have to have the correct mass-energy m",
" = E",
" - p",
"; their momenta are determined by momentum conservation at the vertices and we can have E",
" - p",
" = anything.",
"But when the momenta of the incoming particles are just right to make an internal virtual particle have a mass-energy which is nearly the same as that of the corresponding real particle, the amplitude gets really, really big. It's basically the same as if the incoming particles coalesced into a real physical particle which then decays, which quantum fields prefer to do if possible.",
"We see this behaviour in scattering amplitudes because they contain factors like 1/(",
"-",
") where ",
" is the mass of an internal virtual particle and ",
" is a function of the momenta of the external particles called a ",
"Mandelstam variable",
". You can see that when the external momenta are such that ",
" is about the same as ",
", the amplitude diverges to infinity; this is called a \"pole\". In particular, this is a pole in the \"",
" channel\"; if we used the Mandelstam variable ",
" then this would be a pole in the ",
" channel.",
"This is exactly how the Higgs boson was discovered in 2012, by the way; the LHC experiments found that the scattering amplitudes had a peak when combinations of the momenta of outgoing particles squared to give 126 GeV.",
"In the 1960s, quantum field theory - the theory which we now know to underpin all of particle physics - was reasonably well understood as applied to electrodynamics and the weak force, but no-one understood how it could be used for the strong force. The data that they had were that they could see peaks in the amplitudes. People were trying to guess the form of the amplitudes, knowing where the poles should be, using certain symmetry constraints that were hard to implement.",
"Veneziano wrote down the first amplitude with the right properties in 1968, it has infinitely many poles in both the \"",
" channel\" and the \"",
" channel\". It is given precisely by the Euler Beta function ",
" = ",
"(-1-",
" ' ",
",-1-",
" ' ",
"). ",
"We now understand that the amplitude describes the scattering of the lowest-energy states in string theory. The fact that there are infinitely many poles in both channels corresponds to the fact that there will be a pole at each harmonic of the string which is mediating the interaction.",
"You may find this paper interesting: ",
"The Birth of String Theory",
" by Paolo Di Vecchia.",
"Edit: by the way, Veneziano's amplitude is only approximately right; the approach that it was part of, ",
"S-matrix theory",
", was abandoned in favour of QCD as a theory of the strong interaction in the early 70s, though a small number of people kept working on what became string theory.",
"Edit 2: Why are the incorrect answers the most upvoted ones? This is so irritating."
] |
[
"I think you're confusing it with a different kind of beta function: ",
"http://en.wikipedia.org/wiki/Beta_function_(physics)"
] |
[
"As iorgefeflkd pointed out, the beta function you've linked to is not the same beta function as is referred to in particle physics. In fact, every quantum field theory has a beta function, even quantum electrodynamics, but it is particularly relevant for understand the strong nuclear force, or more specifically quantum chromodynamics (QCD), which is the quantum field theory that gives rise to the strong nuclear force.",
"The problem is that QCD is hard to calculate with at low energies (or, equivalently, at large distances), which is related to the fact that when we look at nuclei we see protons and neutrons, which look very different from quarks, which are supposed to be the fundamental particles of QCD. By calculating the beta function of QCD, you can learn something about how it's behaviour changes at small distances compared to large distances, and in fact you can see that QCD ",
" easy to calculate with on very small distance scales, which explains why when you probe the inside of protons with high-energy electrons (deep inelastic scattering), you can start to see three quarks floating around in there, which isn't apparent at all when protons and other hardrons interact on nuclear scales."
] |
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