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[
"What about the dinosaurs made then unable to survive the K-T extinction?"
] |
[
false
] |
What is it about dinosaurs that made them die out to the K-T extinction, while other animals survived? How did the survivors survive? Was it just by sheer luck that the dinosaurs died out and mammals etc. survived through the extinction?
|
[
"This is an excellent, but incredibly complex question. But here goes: just a few notes on the subject but not at all a comprehensive answer:",
"First off, dinosaurs weren't the only casualties - lots of groups went extinct, from many of the planktonic foraminifera, on up to many groups of mammals (yes, mammals went extinct at the KT, too), all of the marine reptiles (the ones that weren't already extinct) and many many more.",
"Dinosaurs are the most conspicuous extinction because they were the dominant tetrapods of the time. However, what often gets glossed over without any mention is that dinosaurs were struggling before KT event. Sure T. rex and Triceratops were rocking the party up until closing time, but overall dino diversity had been shrinking steadily for a couple of million years before the main event. This was also true for other groups as well (marine icthyosaurs were extinct long before the KT).",
"So a lot factors were leading up to a bad time for Earth even before the celestial body arrived. All that said, nothing over a certain size survived, eliminating all the big things. And as for the small dinosaurs, overspecialization was probably their biggest problem (highly specialized life history strategies and inability to generalize). ",
"I'm not sure what the person below meant about the smaller ones surviving. No dinosaurs survived the KT except for the true birds (which were already true birds by that time)."
] |
[
"From wiki",
"\"A lingering impact winter... made it impossible for plants and plankton to carry out photosynthesis.\"",
"\"Yet the devastation caused by the extinction also provided evolutionary opportunities. In the wake of the extinction, many groups underwent remarkable adaptive radiations — a sudden and prolific divergence into new forms and species within the disrupted and emptied ecological niches resulting from the event. Mammals in particular diversified in the Paleogene, producing new forms such as horses, whales, bats, and primates. Birds, fish and perhaps lizards also radiated.\"",
"\"K–Pg boundary mammalian species were generally small, comparable in size to rats; this small size would have helped them to find shelter in protected environments. In addition, it is postulated that some early monotremes, marsupials, and placentals were semiaquatic or burrowing, as there are multiple mammalian lineages with such habits today. Any burrowing or semiaquatic mammal would have had additional protection from K–Pg boundary environmental stresses.\""
] |
[
"Not all of the dinosaurs went extinct. The larger ones did, while many of the small species of dinosaur, mammal, reptile, etc survived. Large animals were more vulnerable because they couldn't find shelter from the impact and resulting firestorms, and would not have been able to find enough food afterward."
] |
[
"Smoking during pregnancy"
] |
[
false
] |
[deleted]
|
[
"The baby's source of oxygen and nutrients comes from the mothers blood. When the mother smokes cigarettes, all the harmful chemicals like cyanide, lead, etc enter the mothers blood stream. The two main chemicals responsible for most birth defects are nicotine and carbon monoxide. Nicotine narrows blood vessels making it harder for oxygen to get to the baby and red blood cells pick up molecules of carbon monoxide rather than oxygen, also depleting the amount of oxygen going to the baby. ",
"This article goes more in depth with this subject."
] |
[
"What I have stated is true, and though it might be oversimplified, it does not make it any less true. Sure we don't know ALL of what happens, but we do know some.",
"Edit: If you want information from something besides \"one of those poorly run internet health sites\" ",
"here is an article from the CDC basically explaining the same thing."
] |
[
"Impaired fetal oxygen delivery is the BEST studied cause of problems in pregnant women who smoke. Like other posters said here, nicotine is a major factor. It causes vasospasm and acutely decreases intervillous perfusion (decreases blood supply to the fetus). ",
"It's also been ",
"suggested",
" that nicotine impairs fetal lung development via interaction with nicotinic acetylcholine receptors.",
"Carbon monoxide from smoking gets into the blood stream and forms carboxyhemoglobin in the red blood cells (think of it as a messed up form of hemoglobin that cannot bind oxygen, because it binds carbon monoxide too tightly). This also diminishes fetal tissue oxygenation.",
"Direct damage to fetal genetic material is also a way smoking harms the fetus. This can occur through many, many mechanisms (there are thousands of harmful molecules like ammonia, polycyclic aromatic hydrocarbons, hydrogen cyanide, vinyl chloride, nitrogen oxide in cigarettes that can for example cause oxidative damage and essentially mess up fetal chromosomes)."
] |
[
"Is there anything interesting in our solar system that is outside of the ecliptic?"
] |
[
false
] | null |
[
"Pluto is probably the most well-known highly inclined object in the Solar System. Its inclination is over 17 degrees.",
"Ceres is inclined at about 10 degrees. The asteroid Pallas is inclined at almost 35 degrees, and there are a number of less-well-known asteroids of higher inclinations."
] |
[
"High-inclination objects tend to be of interest ",
" of their high inclination.",
"Retrograde asteroids are very rare, whereas retrograde long-period comets are quite common. ",
"https://en.wikipedia.org/wiki/List_of_exceptional_asteroids#Orbital_characteristics",
"Eris is the most highly inclined dwarf planet, with a 44 degree orbital inclination. Even compared to other \"scattered disc\" objects (a population that Eris is the largest known member of), Eris's inclination is high."
] |
[
"How do they stay inclined without falling? ",
"Revolving objects ",
", even ones with zero inclination. They are just falling so fast, they miss the sun entirely!",
"But seriously, inclined in comparison with what?",
"The sun's equator and the average plane of rotation of the solar system."
] |
[
"Question about Theorhetical Physics, Flatlanders, and Time."
] |
[
false
] |
Let me know if this is the wrong place for this. We understand ourselves to be perceiving three dimensions and sensing the fourth as Time. Now, lets imagine that we were flatlanders, only able to perceive two dimensions. Obviously, in this two dimensional space, we'd still be able to sense time - time would move forward, moments would progress from one to another. Would this be an instance of them "skipping" a dimension into the fourth, somehow utilizing the third dimension as their "time" dimension, or does it suggest that our assigning the fourth dimension as "time" to be relative only to our third-dimensional rationalization? (To go further: Flatlanders wouldn't understand the concept of depth., or how to move "deeper" into something. What if we call the fourth dimension Time, but there is in fact another "direction" that hypothetical fourth dimensional beings can move in, but are as alien to us as depth is to a flatlander?)
|
[
"I don't think you should consider time as a fourth dimension - and certainly not ",
" fourth dimension. ",
"If you lived in Flatland, you would have 2 dimensions, or using your line of thinking 3 with the 3rd as time. You wouldn't assume that there is a different 3rd dimension and time is #4.",
"Have you read Flatland? Imagine a 4 dimensional sphere passing through our world. It would appear as a small sphere, grow in size, then shrink until it disappears. Just like a 3 dimensional sphere travelling through a piece of paper."
] |
[
"That is precisely how I've come to understand it; yet, people often describe the new direction in the fourth dimension as time: We can go forward in time or backwards in time, so as to move through the fourth dimension, analagous to our third dimensional ability to \"go deeper\" (as compared to a flatlander).",
"This seems that a flatlander would describe it in the same terms, moving forward and backwards. They wouldn't describe it as \"deeper\" (I.e., referring to the next dimension up), right? ",
"...Am I making any sense? Maybe I need to rethink my terminology. "
] |
[
"Try reading through my ",
"type-up of space-time",
". it may not be exactly what you're talking about, but while time is a dimension ",
" space, it's not connected in exactly the same way that the space dimensions are connected to each other. There's a rich, more general expression of geometry that can describe geometries well beyond what you're familiar with on a piece of paper."
] |
[
"What is the general math behind L-points and the interplanetary transport system?"
] |
[
false
] |
I think I have a good grasp on how gravity assists work, but I've never been able to find anything but the most superficial article on the interplanetary transport system other than saying "it's complicated" and "needs a computer". Some questions include: If a probe were to do a flyby of lets say Earth-Moon L-1 what would be the ideal and realistic Delta-V gain and how is that calculated? How are the windows for L-points determined? What determines how long the probe spends in a Halo Orbit? What exactly is a Halo Orbit? How can it really be "zero" propellant for some routes? How do travel times compare to a Hohmann? Other than L-points and Gravity Assists what other landmarks are there on the interplanetary transport system? I know this is a lot but I just can't find any good mathy sources out there and I would love to crunch some rough numbers rather than just rely on iterative simulations.
|
[
"Good questions, and lots of questions; this will be long.",
"L-points, more commonly called Lagrange points, are a set of 5 locations between two large planetary bodies in which one orbits the other (although they both orbit each other, 1 of them has way more mass and only slightly moves). At these special Lagrange points, a spacecraft/object can be \"deposited\" with zero velocity and feel no net acceleration - it would stay exactly in 1 spot, relative to the two planets.",
"The Lagrange points are numbered, though the conventions change sometimes depending on who you talk to. Generally, I've heard it as the L1, L2, and L3 points lie on the line that connects the two planets (called the apse line). L4 and L5 are other points that lie +/- 60 degrees off the apse line.",
"Here's a great picture which illustrates the Lagrange point system:\n",
"http://www.ottisoft.com/Activities/Lagrangian%20points.gif",
"Stability:\nL4 and L5 are stable Lagrange points. L1, L2, and L3 are unstable Lagrange points (in the plane of orbits). This means if you're a spacecraft at L4 or L5, if you happen to get nudged a little out of the exact location, you will start oscillating about the original point, just like a pendulum swinging (stable). If you're at an unstable Lagrange point (L1, L2, or L3), and you happen to get a little too close to one planet, you'll start drifting towards it. However, there are out-of-plane orbits which can stably oscillate about the L1-L3 points. These are called the \"halo\" orbits. The orbital period (time to make 1 loop in the orbit) depends on how far away from the Lagrange point you are and how fast you're going in the out-of-plane direction.",
"For instance, you could put a spacecraft near L1, and give it some slight motion out of plane (\"up\"): the spacecraft will tend to oscillate in a big loop around the L1 point. This loop can look like a halo, hence the name. However, it's easy to do very strange looking orbits called Lissajous orbits, which are very, very loopy and silly looking. Just Google it, and you'll the silliness.",
"Although this theory is great, it's limited. In real-life (practical astrodynamics), we have more than just gravity to deal with. You have to account for solar radiation pressure (the small force created by the solar wind that pushes on your spacecraft), non-uniform gravity fields (Earth's and the Moon's gravity fields are kind of \"lumpy\").",
"There isn't a very tight launch window for the Lagrange points (if any). All of the Lagrange points hold the same relatively position between Earth and the Moon throughout the month. As a result, it's more of a matter of timing the Earth rotation with respect to the departure spacecraft orbit, not waiting for the Lagrange points to \"line up\" like we have to do for the ISS or going to other planets.",
"You don't gain Delta-V by going to the Earth-Moon L1 point. The Lagrange points are just \"empty\" points in space, except for some accumulated dust and rocks. To use a gravity assist, you have to \"steal\" momentum from a large planetary body (like Jupiter). Gravity assists work by changing the direction of the spacecraft velocity relative to the sun - this momentum is taken away from the planet, but it's effectively negligible.",
"\"Zero Propellant\" Routes:\nOnce you have enough energy, you can very easily transfer from 1 location to another inside the Earth-Moon system. A German mathematician by the name of Carl Jacobi discovered that you can calculate the regions of the Earth-Moon system that are reachable. What this means is that you can very easily travel inside the Earth-Moon system once you have developed sufficient energy.",
"Hohmann transfers are very easy to compute, which makes them great for \"back-of-the-envelope\" mission design/planning. However, they work for transferring from 1 orbit around a central body to another orbit around the same central body. This isn't the situation in a Lagrange point: Lagrange points only work because of the gravitational pull of the two planetary bodies. So they're really apples and oranges. A Hohmann transfer travel time depends on the two orbits you're transferring between. A very low thrust trajectory will generally be much slower than a Hohmann transfer for short transfers. When the transfer time starts increasing, it's very valuable to have that constant thrusting to cut down on travel time.",
"The reason everyone says you \"need a computer\" is because the laws of motion for an object in the solar system are non-linear differential equations that only have closed form (analytical solutions) for the two-body problem (the object and another object/planet) and the restricted 3-body problem (two large bodies (like Earth-Moon) and a small body (spacecraft)). The way real spacecraft mission design is done is by using numerical integrators on a computer and numerically integrating the differential equations of motion.",
"Given the number of AskScience posts about space, I should really start a YouTube series explaining this stuff (Khan Academy-style). ",
"Resources for further learning:\n",
"http://en.wikipedia.org/wiki/Lagrangian_point",
" - I was actually very surprised by the quality of the Wikipedia page on Lagrange points.",
"A good intro book on orbital mechanics is \"Orbital Mechanics for Engineering Students.\" It doesn't have much on Lagrange points or halo orbits, but you'll need to master this material before you can move onto the more \"exotic\" orbits. Entire books have been written about Halo orbits and Lissajous orbits.",
"If I haven't answered a question to your satisfaction - let me know. I can follow up in the comments."
] |
[
"If you do get around to posting a video series I would love to see it. Maybe we could start an AskScience video lecture series for the public to help understand some of the more frequently discussed concepts here."
] |
[
"The key is to do your calculations in the frame that rotates at the same rate as the large masses, and is centered on the center of mass of the system. Since this is a rotating frame, you have to consider not only gravity but also the (fictitious) centrifugal and Coriolis forces. When you consider the total force (sum of gravity, centrifugal, and coriolis) you end up with a force field where the Lagrange points are the points with no net force (and you can ignore the coriolis effect for stationary objects). Though only some of these points are stable, i.e. are a local minimum for potential. These are points 4&5.",
"The idea of \"zero propellant\" means that there are some paths, along equipotential surfaces, that do not change the potential energy of the particle. This means that the only energy needed is for pure motion, it's like pushing a ball on a flat ridge; you don't need to push it up our down the hill to change its position. ",
"Feel free to ask more questions."
] |
[
"How long is the free mean path inside an electron microscope tube?"
] |
[
false
] |
I figure it has to be at least as long as the vacuum chamber itself, from the electron gun down to the sample. But I'm wondering what the preferred value is. Twice the length of the chamber? Three times? And also, of course, why that's the answer.
|
[
"Mean free path is more important for uncharged particles than charged particles. Uncharged particles, such as photons and neutrons, travel a relatively long way before interacting, and give up a significant fraction of their energy each time. ",
"Electrons (and other charged particles) on the other hand, interact many thousands of times before they are completely stopped. They have small scattering events with atoms as they pass by. So in normal materials, the mean free path is on the order of microns or less.",
"In a perfect vacuum, the mean free path is infinite, since there is nothing to interact with. In a near vacuum, of course, there is some slowing of the electrons, but this can usually be neglected. I'm not sure of the electron energy used in an electron microscope, but I work with devices that accelerate electrons for treatment of cancer and other diseases. In these machines, electrons are accelerated to energies of 6 MeV or more, and travel roughly 50 cm in air before reaching the patient. The rule of thumb is that the electrons lose about 200 keV of their energy (< 5%) per meter of air traveled. The energy loss depends on the original energy, of course, but this is pretty constant for energies from 1 MeV to 25 MeV.",
"I know this doesn't directly answer your question, but hopefully this helps. Maybe if you explain more about why you care about the mean free path of electrons in a microscope we can tell you more."
] |
[
"I'll gladly tell you more, I'm not sure I made my point. I understand the interaction volume inside the specimen when you shoot it with an electron gun, and I understand the many scattering events that make up this interaction volume. This interaction volume is roughly 1-2 microns for a typical accelerating voltage of ~20 kV or so. That is, the electrons will scatter off of the atoms in your sample in an \"arena\" the size of 1-2 microns.",
"I also understand that in a perfect vacuum the mean free path is infinite, but you and I know electron microscope chambers aren't perfect vacuums. The vacuum that I see get pulled is on the order of 10",
" Torr, for example. I think it should be possible to calculate the mean free path in between the gas molecules knowing the pressure inside the vacuum, but I might be wrong on how easy it is to calculate. So, why do I want to know more about this?",
"You say that in a near vacuum, the slowing of the electrons colliding with the gas molecules can be neglected, but that's the very reason why I asked this question. I ask what this path length is because a professor told me that a vacuum needs to be pulled in a SEM to create a large mean free path so the electrons can reach the sample without banging into oxygen/nitrogen molecules. The microscope wouldn't operate under 1 atmosphere of pressure, and it will work better and better until a near-perfect vacuum is pulled. I just now got curious as to wonder how long that mean free path needs to be. If it won't work in standard pressure, that's because the electrons are going to bounce off of too many gas molecules and we won't create an image. At approximately what point do we reach a path length that's long enough for the far greater majority of the electrons to hit their target? Would it be the length of the tube? That doesn't seem reasonable, because that means the average distance between gas molecules would be the whole length of the apparatus, which doesn't make sense in a non-perfect vacuum. If I imagine 10 gas molecules taking up a chamber that is 1 meter long, then they'd be about 10 cm apart for an average length. But only 10 gas molecules in this chamber is totally unrealistic, there are more gas molecules than that."
] |
[
"Right after I replied, I found the answer I was looking for. The equation was on Wiki, surprise surprise.",
"It says ",
"here",
" that the mean free path in a pressure of 10",
" mbar (which is about 10",
" Torr) is about 1,000 cm, or about 10 meters. So a gas molecule is going to bounce of the wall of the chamber many, many times before hitting another gas molecule. Which I'm guessing means more the same for an electron.",
"If my intuition is correct, the fractions of electrons that hit a gas molecule inside an electron microscope is extremely small."
] |
[
"Do the harmful chemicals that are listed in anti-smoking ads come from the additives that the manufacturer adds or are they inherent to the tobacco itself?"
] |
[
false
] | null |
[
"Most of the stuff listed comes from pyrosynthesis, or incomplete combustion. Arsenic, what they call rat poison, comes from the fertilizers. Tar, is the total particulate matter caught on a filter pad, you can see it in the filter too, minus nicotine and water. Nicotine comes* from the plant as well, in addition to tobacco specific nitrosamines which are carcinogenic.",
"*I realize now that I didn't explain the process. There are three main processes by which something gets into mainstream tobacco smoke. Combustion, pyrosynthesis, and distillation.",
"Carbon dioxide and water, along with nitrogen oxides and other oxides, are formed during combustion in the ember.",
"Pyrosynthesis occurs in a narrow region directly behind the ember where it is cooler and depleted in oxygen. Different carbohydrates fragment and form radicals which can then combine or react with gases to form anything from small volatile organic compounds to large polycyclic aromatic hydrocarbons (PAHs are a major component of tar). These chemicals comprise the majority of tobacco smokes carcinogenic hazard. Many of these will be present in smoke from all burning organic matter, although different factors can affect their relative amounts.",
"Distillation occurs when semi volatile compounds transfer to the gas phase completely intact, just like boiling ethanol from wine. Nicotine and different oils are transferred to smoke through this mechanism.",
"A major additive to cigarettes is ammonia. Nicotine is protonated, and charged, at the pH of unaltered tobacco smoke. Ammonia ",
" raises the pH making nicotine an uncharged, neutral molecule and it will be more quickly taken up in the body. Ammonia can increase amounts of different nitrogen heterocycles, which can be hazardous.",
"Sugar is also a common additive, and it will behavior similarly to the innate carbohydrates in tobacco.",
"Some cigarettes have metal oxides in the paper to help keep the ember lit, and at a higher temperature. This increases combustion, and can lower pyrosynthesis, however, metals pose their own hazards."
] |
[
"Pack a day habit of most commercial brand cigarettes is equal(give or take a few either way) to 300 chest x-rays a year.",
"You're comparing apples and oranges, or in this case photons, alpha and beta particles.",
"Also worth pointing out the commonly used LNT model is pretty shoddy."
] |
[
"Very nicely explained. Only missing one item: It's the dose which makes the poison. That's a fact which is conveniently ignored by the ads."
] |
[
"Why does low gear act as a brake when going down hill?"
] |
[
false
] |
Why does low gear act as a brake when going downhill? I understand when going uphill, low gear is needed for a higher force (torque) at the wheels. But when going downhill, the work comes from gravity, and the difference between low gear and high gear is at the same speed, the gears in the engine (before the gearbox) spin faster with less force (torque). Does it just rely on the resistive force in the engine to keep the car at a constant speed? What exactly is the resistive force?
|
[
"Most of the braking effect is actually due to vacuum caused by the closed throttle plate, the energy absorbed by compressing the air is mostly returned to the engine on the following expansion stroke, the air acting much like a spring."
] |
[
"The resistive force is the engine compressing the air in the cylinders. When you use a low gear you are spinning the engine the fastest for your speed. Therefore the most compression events happen per time, and you get the most breaking. ",
"Tldr, your converting kinetic energy to hot air"
] |
[
"Thanks for pointing that out.",
"I had a nagging suspicion that I didn't know what I was talking about.",
"I actually had no idea that diesels controlled their RPM via fuel regulation as opposed to air regulation in a gasoline engine.",
"You wouldn't happen to know the reason for the differing designs would you?"
] |
[
"Do animal's limbs 'fall asleep' like human hands and legs and such do? My cat sleeps in weird positions but never seems to wake up with a leg 'asleep' but her motions."
] |
[
false
] |
What the title says. Why doesn't my cat sit there shaking her numb paw from it being in a weird position?
|
[
"This is a tough question to answer for sure since we can’t know how they’re perceiving things, and I apologize in advance that this is anecdotal and not sourced, but I believe that they do. Most mammals have roughly the same neurologic and circulatory structures as humans do so there’s no reason to suspect they wouldn’t, and in a veterinary setting if an animal is drugged, has decreased consciousness from various injuries, a bandage or other pressure point, we definitely have to be conscientious about rotating which side they’re laying on and performing PROM (“passive range of motion” stretching/massage exercises) and sometimes if they haven’t been sedated enough to call for that but have been extra deeply asleep in the hospital they can limp for a minute when they first get up or otherwise behave similarly to how you would expect for someone experiencing “my leg fell asleep.” ",
"I believe the reason you haven’t seen it in your cat is that positions that look strange and uncomfortable to you are perfectly fine for her body shape, and also that when they aren’t sedated, most animals have the good sense to switch positions before something like that happens to them. Humans are often taught from a very young age to sit still in uncomfortable chairs, and more prone than a cat to stay up too long for work/school/etc so when we finally do sleep we’re more likely to crash hard and not reposition ourselves the way we normally would even in our sleep. Hope that makes sense!"
] |
[
"They absolutly can! They just move before it get worst. I work with cows and you see them with numb leg when they slept too long on one side. Most of the time, they switch side before this happen. We even need to do it ourself when one has an injury, because their weight can litterally cut off their blood circulation."
] |
[
"Thanks for this, I enjoyed reading your answer. The conditioned to be uncomfortable, I really get that. I Akshay the time for this answer."
] |
[
"Viewing in the dark."
] |
[
false
] |
When I'm in the total dark with eyes open, are they focusing on something? Do they just act like an auto-focus camera that cannot focus on anything and keep trying? Also do eyes acts like a camera with respect of light? If I keep looking at a very little light up object in the dark, will I see it better over time?
|
[
"Your eyes aren't focusing on anything in total darkness, they will dilate to try to get as much light in as possible so you can see. No, you will not be able to see better."
] |
[
"Also do eyes acts like a camera with respect of light? If I keep looking at a very little light up object in the dark, will I see it better over time?",
"Your retina won't continue to accumulate light over time, no. For one thing, your eyes are constantly moving in ",
"saccades",
", so the image would constantly be moving around on your retina.",
"However, if you've recently been in a bright environment, your ability to make out dim objects will be dramatically better if you wait a few minutes. ",
"Dark adaptation",
" starts quickly with pupil dilation, but it takes up to half an hour for your photoreceptors to reach their full sensitivity."
] |
[
"Do you have any reference for this?"
] |
[
"Why does the colour of my eyes change?"
] |
[
false
] | null |
[
"Eyes don't change color. However, the iris may be ",
" as a different color based on lighting conditions, and even based on comparisons with surrounding colors."
] |
[
"Updated from Wikipedia source:\nThe appearance of blue, green, as well as hazel eyes results from the Rayleigh scattering of light in the stroma, a phenomenon similar to that which accounts for the blueness of the sky. Neither blue nor green pigments are ever present in the human iris or ocular fluid.[3][5] Eye color is thus an instance of structural color and varies depending on the lighting conditions, especially for lighter-colored eyes.",
"That's pretty awesome, never thought of it that way but it makes sense. I noticed when I was younger that it would change if you turned the lights off and then back on, which from this sounds like your iris reacting to change the pupil dilation is causing a structural change that results in different light scattering. Science!",
"Original: Do you have any sources that back that up? I had always been under the impression that it could change, would love to see some factual evidence behind the phenomena one way or the other!"
] |
[
"Do you have any sources that back that up?",
"The only thing I can provide this close to bedtime is Wikipedia:",
"Changes (lightening or darkening) of eye colors during puberty, early childhood, pregnancy, and sometimes after serious trauma (like heterochromia) do represent cause for plausible argument to state that some eyes can or do change, based on chemical reactions and hormonal changes within the body.",
"This indicates that, while color technically ",
" change, it's a slow-occurring, long-term alteration of pigmentation, not some short-term reaction to emotions, weather, or what color shirt you're wearing."
] |
[
"MEDICINE Could healing gels be possible?"
] |
[
false
] | null |
[
"The trick is to constrict the healing effect to the wound, otherwise it will cause intergrowth. So just recreating the effect is not the way to go, but you'll have to increase the speed of the body's own effects."
] |
[
"Hmm. Good point didn't even think about that. It's one thing to speed up healing but you have to stop it as well. "
] |
[
"Cell based \"patches\" are already available and might be similar to what you're asking. Again, as a previous post mentioned, it'd be important to constrict the healing effect to the wound. However, more importantly, it's a cost vs. benefit thing. There are already patches which are able to heal chronic ulcers/wounds (specifically for diabetics, which this is a larger problem) using a cell-based product (it's called Apligraf). There's the more traditional skin-graft as well. However, with the cost and complications of creating an autologous skin-graft or utilizing Apligraf/similar biomaterials, it's simply not worth it to treat normal cuts which heal well anyway (there are a number of complications for autologous grafts which involve the donor site, and then there's always issues with allografts utilizing cells from other donors). ",
"Regarding using stem-cells/catalysts for healing instead of a patch: your skin has a basal layer of stem cells which can regenerate and heal most cuts, and with all biology, these things take time. \"Speeding up the process\" or speeding up cell division, the immune response, etc, could cause serious problems downstream - such as, an overly robust scabbing could also cause thrombus formation in capillaries, overly robust fibroblast infiltration can cause too much scarring, overly robust epithelial migration and division could cause cancers, etc. The military has tons of money funding research towards accelerated wound-treatments, but so far the closest thing which would be safe and feasible is developing a better \"patch\" rather than a \"catalyst/wound gel\"."
] |
[
"Can color be heard?"
] |
[
false
] | null |
[
"Color is a psychological not a physical property. The human visual system gives rise to the experience of color and different experiences occur for different wavelengths or combinations of wavelengths. ",
"Pressure on the ear drum is experienced as sound and does not typically produce color experiences. ",
"Some people have a type of synesthesia called ",
"chromesthesia",
" in which sounds are experienced as (i.e. associated with) certain colors. This has nothing to do with wavelength and does not occur at the level of the eye or ear. Although we are not sure of the exact mechanism, it is generally believed that it occurs somewhere in the brain beyond our sensory organs."
] |
[
"\"Different experiences occur for different wavelengths or combinations of wavelengths\"\nAre these wavelengths different from sound waves? I know we percieve them different and they are different sizes, but is there a bigger difference between them?"
] |
[
"Yes. These are properties of photons. Sound is the result of changing air pressure. Lots of things are spatial or temporal waves. I can draw a wave (e.g. a sinusoid) on a piece of paper. That too has a wavelength. It's kind of like saying \"my table has a width and my pencil has a width so is the table the same as the pencil?\""
] |
[
"Does commercial lumber contain enough infect fragments of DNA from the tree that produced it, for genome reconstruction and analysis?"
] |
[
false
] |
[deleted]
|
[
"Depends on how it is treated. But DNA analysis has been successfully used to track illegally logged timber. It seems more common to use other techniques to identify the origin, though, like isotope ratio analysis."
] |
[
"That's a big maybe",
"That's a mostly yes with a lot of maybe, depending on how crazy you want to be. ",
"Forensic genotyping",
" of lumber to try and catch illegal timber has been around for years. Could you do this for an entire genome in every tree species? Probably not without a lot of fine-tuning. There would also be considerations like how much water is left in the wood or what secondary metabolites does X wood produce that could screw with DNA to take into consideration. But these would be mostly technical. A lot of the stuff we do to wood can potentially help to preserve DNA too. ",
"This",
" might help with using molecular genetic tools to source wood origin. There will, of course, be instances where no DNA can be recovered. But many times you can and even if it just a strand or two we can now amplify that enough to run tests."
] |
[
"That's a big maybe. DNA degrades fast. There's probably not enough intact sequences left. But pinpointing the origin with an isotope ratio analysis could still work."
] |
[
"limitations of photon frequency?"
] |
[
false
] |
If I wave a magnet back and forth once per second, have I produced a light wave of 1 hertz? Is there a lower limit as to how low the freq can be using this simple method of generating light? Also is there an upper limit to freq of light? I think with very very high frequency gamma rays, they interact with the dirac sea and force virtual particles into reality - anyone know the ballpark of this upper limit?
|
[
"A photon's frequency is equivalent to its energy - the more energetic a photon, the higher its frequency - and at a certain point, called the ",
", we don't really know what happens. It's been suggested (as below, by QuantumBuzzword) that that might turn it into a black hole, but there are plenty of issues with that idea, and in any case physics at those energies is so speculative and poorly-understood that we can't really say anything firm about what happens. So there ",
" be an upper limit, but we don't yet know enough physics to say!"
] |
[
"If you look at Maxwell's equations, there's no real lower limit on EM radiation. What you're proposing should create an ultra low frequency radio wave. ",
"For pair creation, it comes in at an energy of 1.022 MeV, which is directly proportional to the frequency by E=hf. This process is actually quite common inside stars, and puts an upper limit on mass.",
"Finally, a really hard limit to the frequency would be a point where a photon's energy is enough to collapse it into a black hole. But this is at the intersection of quantum and general relativity, so its not well understood enough to put a number on."
] |
[
"An important point worth mentioning is that pair-creation requires that the photon interact with something ",
" than the vacuum/Dirac sea. This ties in with the second important point worth mentioning: assuming relativity is correct (as most do) there is no upper-limit to the photon's frequency ",
". In other words, there is no upper-limit to a photon's energy or frequency, but if the CM energy is high enough, it may begin to interact differently than an ordinary photon, because gravitational effects become important."
] |
[
"Do planets slowly grow in size?"
] |
[
false
] |
[deleted]
|
[
"The burial of archaeological sites is an indication of erosion and deposition (i.e. mass is transferred from one area to another) as opposed to growth of mass/volume of the Earth through time. Whether we are talking about archaeological sites or fossils, we have to consider that there is significant preservation bias, meaning that the sites/material that is preserved are those that are in areas well suited to be preserved. ",
"To illustrate this, let's consider two paired examples, an artifact (or fossil) placed in the landscape (1) on a broad, largely flat floodplain of a river and (2) on the steep slope of a mountain. For case 1, it is positioned in a net depositional area meaning it likely will not move very far and it has a high chance of being buried at (or very near) the original spot it was placed the next time the river over tops its banks and deposits a layer of sediment (and subsequently buried deeper and deeper the more floods occur). For case 2, it is in a net erosional area, meaning that it will likely move (e.g. slide down hill, caught up in a landslide, make its way to a fast flowing river, etc) and it will either not be preserved where it was first placed (likely ending up in a net depositional area) or not be preserved at all as it is destroyed / damaged during significant transport."
] |
[
"It’s a redistribution of existing mass. ",
"Imagine it as a sand dune. If you place something on top of it and come back a million years later , that object will no longer be on top. Due to wind , rain, other factors. ",
"Now scale it up to an entire planet, with all of its forces acting upon it."
] |
[
"This is mostly compensated for by the loss of atmospheric hydrogen to space. We lose ~3kg/s to space. This is about 300 tons per day."
] |
[
"Why are poison dart frogs brightly colored?"
] |
[
false
] |
How did it come to be that brightly colored frogs survived the processes of natural selection? Let's say that we have two frogs, both poisonous, one camouflaged, and one brightly colored. A predator would go for the one that it can see, the brightly colored one. The predator would die in either situation, but it would seem to me that selection would always favor camouflage as opposed to vivid coloration. I know that this is not the case as there are many poisonous species that have bright coloration, but I would like to know why such coloration gets selected.
|
[
"You have made a key assumption. Many poisonous animals dont necessarily kill their predator. Many make them very sick, and most simply dont taste nice and are spit back out.",
"It is to the advantage of the frog that the predator survives. There have been studies that show that if a bird eats a brightly coloured but not toxic frog first, it will take many toxic frogs to teach it not to eat them. If it eats a toxic from first, it will rarely if ever try to eat one again.",
"Camouflage only works so well: on some backgrounds, while moving, or in certain weather conditions it fails. By teaching the predator not to eat you, and making sure they can not mistake you for something else, it makes a longterm impact.",
"In teaching predators, this can be passed on to offspring. On very long time scales, it could even be instinctual, whereby the predator is not attracted to eat bright things."
] |
[
"Many poisonous animals dont necessarily kill their predator. ",
"That's it. Right there. I didn't even think of that. Thank you. It makes much more sense now."
] |
[
"Glad to help."
] |
[
"Is the sun a black body?"
] |
[
false
] |
I know this is in an idealized context, but I've seen the sun described as a black body before. Does that mean it's in thermal equilibrium if it emits black body radiation?
|
[
"The plasma that makes up the \"surface\" of the Sun is in pretty good thermal equilibrium, so the sun's spectrum is pretty close to that of a blackbody. (I say \"pretty good\" because sunspots, for example, cause variations in temperature across the surface.) ",
"There is a bigger complication, though: at different wavelengths we see through to different layers of the plasma, which are at different temperatures. Those variations of depth as a function of wavelength modify the emission spectrum from that of a perfect blackbody. See ",
"here",
" for a nice plot comparing the actual spectrum (above the earth's atmosphere; ignore the sea-level curve for this discussion) to a blackbody spectrum."
] |
[
"Don't forget about the absorption lines in the solar spectrum. That's how we discovered helium!"
] |
[
"Absolutely! But that's a case of \"seeing to a different depth\"... at those wavelengths we are not seeing as deep into the sun, so the photons we do see come from a cooler, outer layer. (ie the cooler layer is absorbing photons at the line frequency from the hot inner layer, but is also re-emitting those in those lines, albeit less intensely)."
] |
[
"Dinosaurs in Space (as ejecta)?"
] |
[
false
] |
I read that the crater at Chicxulub is over 110 miles in diameter. I can't find estimates of the mass of ejecta sent into space at escape velocity. What would the math be to determine how much of it was dinosaur? Given current biomass per square kilometer, and assuming the volume of escape-velocity ejecta can be found, what are the chances? Additional questions: If a dinosaur did make it into space, what would the overall likelihood of it remaining in our solar system and not impacting another body for 65 million years be? Would it be recognizable or would exposure destroy it?
|
[
"I think the main issue would be the heat of the impact at ",
"the crater site",
":",
"\"The impactor had an estimated diameter of 10 km (6.2 mi) and delivered an estimated energy equivalent of 100 teratons of TNT (4.2×10",
" J). By contrast, the most powerful man-made explosive device ever detonated, the Tsar Bomba, had a yield of only 57 megatons of TNT (2.4×1017 J), making the Chicxulub impact 2 million times more powerful. Even the most energetic known volcanic eruption, which released approximately 240 gigatons of TNT (1.0×1021 J) and created the La Garita Caldera, was substantially less powerful than the Chicxulub impact.\"",
"This visualisation from Imperial College",
" shows how far out the radius of high temperature would be.",
"In summary while some of the atoms and molecules that made up the dinosaurs would have been sent out into space, it seems highly highly unlikely that a full dinosaur would have been sent at escape velocity. "
] |
[
"Ignoring the calculation to figure out what percent of the ejected matter had dino-origins, you should be aware that the ejecta gets completely fucked for a variety of reasons. I can think of 3 main sources:",
"Heat and speed of the projectile, as well as heating of the air underneath the projectile by compression during descent, transfers a lot of energy to the material that will be ejected. ",
"The impact event itself produces very high accelerations. Ejecta will experience a massive shockwave and high g-forces.",
"After accelerating, the material ejected from the surface has to pass upward through the atmosphere, being heated during its ascent in the same manner as the projectile was during its descent. ",
"You might be inclined to think, \"Well, maybe something on the ground can survive the really really high temperatures if it's only exposed to them for a split second, before it's whisked away like the kids that get abducted by Peter Pan?\" I'll put all of these scenarios aside for a second and I'm going to focus on that last point for a second. I'll take a guess that the largest meteor that can survive falling to the earth without burning up entirely is roughly the same size as the largest ejecta that can survive being chucked up. This makes sense; if something falls into the atmosphere really really fast and heats up, then something ejected really really fast is going to basically experience the same phenomena in reverse. The minimum size limit for a meteor to survive descent through the atmosphere (or equivalently, the maximum limit for almost complete burn-up), is about 25 m in length. ",
"So how big were the dinosaurs that were around during the Chicxulub impact (65 million years ago that caused the Cretaceous extinction event)? Well, TRex and Tricerotops are two examples. TRex was 5 meters tall, and 15 meters head to tail, so it's too small. Tricerotops was smaller, about 9 meters long and 3 meters tall. Okay, so they were probably too small. ",
"What was the biggest dinosaur that may have lived on the Yucatan peninsula in Mexico, the site of the Chicxulub impact? The biggest I can find (by Googling headlines for \"Largest Ever Dinosaur Discovered in Mexico\") is Alamosaurus, which was actually discovered in New Mexico (close enough) in 1922. They were common in the late Cretaceous (spot on again), and were 16 m head to tail and 6 m tall. I'm still going to bet that the mighty Alamosaurus would be incinerated before it made it out of the atmosphere. ",
"What about an aquatic dinosaur? The largest marine dinosaur in the cretaceous that I know of is of the family Pliosauroidea, but is again about the size of the Alamosaur (and looks a lot like the fabled Loch Ness Monster too, or the Pokemon Lapras, since it was based on this dinosaur). ",
"So I think it's pretty safe so say that there are probably no dinostronauts in the solar system, but that's not to say that dinosaur matter hasn't been strewed through space- at least in fragments anyway. In fact, this is one semi-plausible explanation for the origin of life on earth. If life couldn't have begun via abiogenesis on earth, perhaps it could have been seeded by biological ejecta from other planets, whose life was crushed in an impact event much like Chicxulub. It's not impossible, and this theory has a great name, which is why I want to mention it. It's called Panspermia, and its evidence includes fragments of a meteor that may have been ejected from Mars and may contain primitive Martian microbes, and science fiction novels. ",
"Bottom line- I wouldn't be surprised if there's plenty of dinosaur bits in orbit, but they were probably cooked to a crisp before they made it there. "
] |
[
"It could have ",
"tea",
"."
] |
[
"Everything is expanding from the center of the universe. Can we see more or less depending on where we look?"
] |
[
false
] | null |
[
"The universe does not actually have a center. Everything (not gravitationally bound) is expanding away from everything else. Not a 'center.' ",
"Every direction we look is ultimately moving away from us, and it would appear that way from any other location as well."
] |
[
"The ",
"cosmological principle",
" means that, when viewed over sufficiently large scales, the universe looks the same everywhere.",
"Also, there is no single \"centre of the universe\". To only slightly simplify: the big bang occurred at every point in space, and every point is moving away from every other point.",
"At the instant of the big bang, all of space was at that point, hence the big bang happened \"everywhere\".",
"You can see ",
"here",
" that as ",
" (the bun) expands, every point move away from every other point...so from any one point of view it looks like you are at the center."
] |
[
"And, might as well add a deep field image to this post: ",
"http://www.nasa.gov/images/content/690958main_p1237a1.jpg"
] |
[
"Can you see the curvature of the earth when looking at an ocean horizon?"
] |
[
false
] |
When I have gone to the beach I always thought that the horizon of the ocean looked curved, as if I were seeing the curvature of the earth. So is this true, or is there something wrong with my eyes? Also, if you can see this effect, but it is not in fact caused by the curvature of the earth, what is causing it?
|
[
"Searched",
"Relevant ",
"discussion",
"Original question by ",
"Sm3ulders",
"When looking at the horizon (at the beach, looking over at the ocean for example) you can see a distinct curve. Is this curve the curvature of the Earth, or the curve in your line of sight? Apparently you can only see things for 12km.",
"I have been having this debate with some friends and we can't find a definitive answer on Google. Please help Reddit! ",
" Sorry for the title typo, I didn't realise until it was too late.",
"Top comment courtesy ",
"tombleyboo",
"There is a limit to how far you can see and this limit (the horizon) forms a circle around you. This circle is the curve you're seeing. It is a result of the curvature of the earth, but this curve is not the curvature of the earth: the raduis of the earth is 6000km or so, far too big to be detectable in the few kilometres that you can see.",
"By the way, ",
"this",
" explains how far you can see.",
"Edit: to illustrate the difference: imagine the earth was a 1m diameter beach ball. The diameter of the horizon you can see (if you're 6' tall standing at sea level) would be like a 1mm diameter circle. If you look only at a 1mm circle on a beach ball, would you be able to detect the curvature? the 1mm diameter curve of the actual circle is much more noticeable. (Edit again: it's actually a 2m beach ball, or a 1/2 mm circle)"
] |
[
"I don't know what this statistic is supposed to refer to, but it's somewhere between wrong and useless as stated. For instance, the sun is rather more than 30 miles away, and is quite visible."
] |
[
"Thanks for that! And sorry, I know reddit's search is less than par, so used google unsuccessfully instead. This will make my trip to the beach next week more informed. "
] |
[
"AskScience AMA Series: We are Andrea Copping, Biological Oceanographer, Genevra Harker-Klimes, Physical Oceanographer, and Meg Pinza, Coastal Scientist. We study the environmental effects of marine energy at Pacific Northwest National Laboratory. Ask us anything!"
] |
[
false
] |
Hi Reddit!! Marine energy is a huge, largely untapped energy resource. So huge that more than 10% of Pacific states' electricity demand could be satisfied by developing a fraction of the wave energy available off the West coast. Imagine a future where we could harness ALL of our oceans' energy, including energy from moving water, like waves, currents, tides, and offshore winds. Renewable energy like this is not only immense, but its predictable nature allows power grid managers to offset more established, yet variable renewable resources such as wind and solar power. And on a regional scale, widespread marine energy has the potential to provide localized power sources in isolated coastal regions and areas susceptible to extreme events, such as hurricanes, flooding, and storm surge. But are there environmental costs to widespread installation of marine energy devices in our oceans? How does marine life react to these devices? And is this approach safe? At the U.S. Department of Energy's (DOE) Pacific Northwest National Laboratory, we are tackling these exact research questions . Ask us Anything! We're looking forward to this! We'll be on at 9 AM PT (12 ET, 16 UT). Ask us anything!
|
[
"Hello, thank you for taking the time to do an AMA with us! This is a really interesting topic. What sort of potential environmental impacts have you found from marine energy? Are there ways to mitigate them?"
] |
[
"The main concerns are around what could happen to animals around rotating turbine blades, either collision risk or changes in behavior. Underwater sound from devices may also be a concern as this could interfere with navigation, hunting prey, and socializing. There are other lesser concerns, but most do not indicate real risks to individual animals or populations. There is still a lot of uncertainty about the effects of marine energy devices, so additional research and monitoring is needed. If mitigation is required is needed, there are several methods that are being investigated and look promising.",
"References:",
"https://tethys.pnnl.gov/publications/state-of-the-science-2016",
"https://tethys.pnnl.gov/management-measures"
] |
[
"Wind energy, particularly offshore wind energy, has progressed a lot in the last 20 years, with the cost reduced significantly. Marine energy is expected to follow the same pattern. European studies have suggested the levelized cost of energy with be in the range EUR 0.17/kWh and EUR 0.23/kWh by 2020. As arrays are developed and the supply chain becomes more established, the costs will be reduced further. While the cost is unlikely to be lower than offshore wind energy, other benefits, such as predictability and low visual intrusion, are likely to make the value proposition for marine energy overall.",
"References:",
"https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2018/Jan/IRENA_2017_Power_Costs_2018.pdf",
"https://www.irena.org/documentdownloads/publications/tidal_energy_v4_web.pdf"
] |
[
"How do geese know which way north/south is?"
] |
[
false
] | null |
[
"Along with that, most birds have an extra sense, magnetoreception, which allows them to detect the Earth’s magnetic field, and therefor know which direction is north or south."
] |
[
"Interestingly, there is some evidence that suggests that birds primarily use there magnetoreception not as a compass but as an altimeter. "
] |
[
"It is most likely related to their ability to detect the intensity/density of the magnetic field as they fly through it. ",
"The further from the earth you get the weaker its magnetic effect."
] |
[
"Can anyone help us identify what kind of bone this is? My brother found it in northern Missouri and has no idea what animal it is from."
] |
[
false
] | null |
[
"All those pictures are thumbnails. Could you share larger pictures?"
] |
[
"Crap. Sorry, this is my first post. "
] |
[
"Fixed!"
] |
[
"How is gender evolutionarily advantageous?"
] |
[
false
] | null |
[
"No, it is advantageous to have sexual reproduction because new gene combinations lead to a process of natural selection. Genetically identical beings, such as in asexual reproduction, could all be wiped out from one external factor. The genetic differences in offspring underlying sexual reproduction allow for differential survival success. As for the question of how sexual reproduction itself evolved, that question is much better left for an evolutionary biologist.",
"EDIT: Also, gender and sex are not the same thing. Sex is the biological definition of male or female, and gender is the accompanying characteristics and how someone expresses (or doesn't) express their sex."
] |
[
"In the literature on reproductive genetics the word 'gender' is commonly applied to male/female systems. Obviously 'gender' has a distinct meaning within psychology/sociology/anthropology, but this is not the context here.",
"No, it is advantageous to have sexual reproduction because new gene combinations lead to a process of natural selection.",
"Asexual systems still produce genetically variable individuals through mutation, which is acted on by the same processes of natural selection as sexually-produced variation. The difference really is in the degree of variation produced, and that sexual reproduction allows for the combination of advantageous alleles from different parents, and also the purging of deleterious alleles.",
"Asexual reproduction also presents a proximate two-fold advantage because all of a parent's genes are passed to progeny. And there are the advantages that the OP suggests, of not have to expend energy searching or waiting for a mate. In nature, these pros and cons must be balanced to produce the observed distribution of sexual and asexual lineages.",
"The genetic differences in offspring underlying sexual reproduction allow for differential survival success.",
"Again, this is the same for asexual lineages, just to a different extent. For example, some purely clonal lineages have been shown to persist over long evolutionary timescales and to diversify into discrete genotypic/phenotypic clusters in a manner reminiscent of sexual species. Any theory which seeks to explain observed reproductive diversity with the relative advantages and disadvantages of sexual vs. asexual systems must accommodate the existence of these anciently derived, diversifying asexual lineages. This remains one of the hot topics in evolutionary biology. One insight is that many organisms are not strictly sexual or asexual but exploit a range of adaptively finely-tuned intermediate or composite strategies.",
"As for the question of how sexual reproduction itself evolved, that question is much better left for an evolutionary biologist.",
"I'll have a go if the OP shows interest."
] |
[
"Most species reproduce asexually. But the majority of life is too simple for sexual reproduction to even be a possibility. By numbers and biomass, bacteria and archaea far outnumber eukaryotes, and not all eukaryotes reproduce sexually. Horizontal gene transfer is common in prokaryotes, but shouldn't be confused with sexual reproduction. ",
"I don't know what the estimates are for the percentage of multicellular organisms that reproduce sexually vs. asexually, or even if someone's tried to estimate that."
] |
[
"Why do particular foods such as bananas' phloem bundles (strings), eggo waffles, grape seeds/skins , and even some breakfast cereals sometimes leave a dry feeling in your mouth? (a dry that can't be wet if you know what I mean)"
] |
[
false
] | null |
[
"I think the sensation you're referring to is called \"astringency\" and is caused by tannic acids, which around found in a number of fruits, teas and wines. The tannins bind salivary proteins and cause them to precipitate, leaving a rough or dry feeling in your mouth.",
"http://en.wikipedia.org/wiki/Astringent"
] |
[
"It's the buttermilk they use in their recipe.",
"Buttermilk as an oral astringent: ",
"http://www.ncbi.nlm.nih.gov/pubmed/16772560",
"Eggo ingredient list: ",
"http://www.kelloggs.com/en_US/kelloggs-eggo-buttermilk-waffles.html"
] |
[
"Awesome, thanks for the info! But eggo waffles? I wonder is that is the same acids? "
] |
[
"Have we ever detected seasonal changes in spectrum (redshift / blueshift) from nearby stars due to the Earth's rotation around the Sun?"
] |
[
false
] |
As a rough estimate, the rotation of the Earth around the Sun changes its velocity relative to nearby stars as much as 200 km/s, as compared to its velocity six months later. While large compared to the speed of space probes, this is pretty small compared to the velocities of stars or galaxies relative to the Earth. Is it possible for us to detect the change in spectrum introduced by such as a small change in velocity? Has this been done in practice?
|
[
"Correction, our motion around the sun is about 30km/s.",
"The doppler shift from this motion is indeed imprinted on all radiation we receive. It's easier to see it in spectral lines than in the whole spectrum. It's even easier to see it in pulsar timing than in optical spectra."
] |
[
"Thank you"
] |
[
"It's too small.",
"It's easier to detect the parallax shift in nearby stars."
] |
[
"Can spiders walk backwards?"
] |
[
false
] |
I know this sounds stupid, but they don't have vision behind them. Can they purposefully move backwards?
|
[
"Species that use vision to hunt like wolf or jumping spiders do have vision behind them, and yes spiders can walk backwards, trapdoor spiders do this every time they drag a still struggling victim into their lair never to be seen again."
] |
[
"Wolf spider"
] |
[
"wolf [...] do have vision behind them",
"Sorry, what?"
] |
[
"How can a cell work so accurately on the molecular level?"
] |
[
false
] |
When I think of a human cell and it's inner workings I find it hard to believe how everything can work so accurately since the inner structures actually seem rather chaotic. For example, theres protein synthesis... First you have the extremely long DNA string rolled up, in a more or less randomly / unpredictable coil. Then, some protein floating in the, compared to the tiny DNA molecule, large space of the nucleus somehow manages to correctly attach to the correct spot of the DNA. When transcription is done, the mRNA somehow manages to correctly attach to the ribosome, which seems rather unlikely given the randomness of it's position and rotation.. The amino acid transporters, which also are flowing around randomly, then also correctly attach to the ribosome one after another... Mathematically, the chance of all this happening seems infintely small. I imagine this kind of like having a large bowl of water and throwing in an amount of different, small-ish LEGO structures - then shaking it wildly and hoping for the correct connections to form... It seems all so random, unpredictable and as if it shouldn't work at all.. So in short, my main question is: How can a cell, which is in itself rather chaotic - since the working proteines and enzymes are moving and rotating unpredictably - work so well?
|
[
"It's important to remember that cellular processes are not the result of a single enzyme finding a single substrate to react with. Pretty much every process is governed by many copies of the same enzyme circulating the cell, able to bind with many copies of the same substrate. While the individual probability of enzyme #298234 binding with substrate #480534 is low, the probability that some enzyme A binds with some substrate B is sufficient to drive cell processes. To map this to another example, imagine a single person looking for a ball in a large field. That seems pretty difficult. Now, what if there were 50 people, and 50 balls? The likelihood of at least some people finding a ball is significantly higher. If the cell needs to adjust the system, it can modify either the number of people looking, or the number of balls, and thus affect the extent to which the process is activated.",
"Also keep in mind that molecular interactions can't be modeled by two legos clicking together, since that doesn't take into account the energy balance that is so important. If a bound enzyme is in a lower energy configuration than an unbound enzyme, then the energetics and kinetics of the system will drive it towards finding a substrate and binding. An example would be thinking of a box filled with magnets and iron balls. If you shake that box around, you will likely find that most of the magnets found iron to 'bind' to, because that's the most favorable state of the system.",
"TL;DR: Molecular functions are rarely on/off binary systems, but rather have a range of activity due to the large number of molecular actors. Energetics of binding and other reactions also play a large role in making reactions happen."
] |
[
"Well, it ",
" quite chaotic. It's nothing like an engineered machine, where everything occurs in a precise, well-defined and stepwise order, where the parts play well-defined purposes and functionality is neatly separated, and so on.",
"It ",
" random. But that does not mean 'unpredictable', it just means that the outcomes are ",
". You just have very very many molecules in a cell, moving about and bumping into each other very rapidly (by our scales). ",
"It's also thermodynamical - reactions occur because things tend towards lower energy, and a cell cannot function without energy to fuel all those reactions. Shaking a bag of legos, on the other hand, won't cause them to link up, because there's no significant energetic gain in them doing so. Put your legos in a basket with a hole in it, inside another container, and shake ",
" around. Now there's an energetic gain for them to be at the bottom. And while the occasional lego on the bottom might bounce back up through the hole into the basket, you'll surely find that after a bit of shaking, that all or almost all the legos are now at the bottom. You can't predict ",
" exact legos will end up on the bottom, but the overall outcome isn't very 'unpredictable' is it?"
] |
[
"How can a cell, which is in itself rather chaotic - since the working proteines and enzymes are moving and rotating unpredictably - work so well?",
"The high number of collisions guarantee the activity. Not only is ",
"what arumbar said",
" correct -that is, you're not shaking a single lego to bind with another singular lego - the number of collisions per second is in the billions to trillions range, and that increases dramatically with concentration."
] |
[
"If I have 100g of Uranium 235 for one half-life, what determines which 50g decays?"
] |
[
false
] |
As half-life is the time it takes for half of a sample to decay, what determines which half will decay? Furthermore, what determines the part that will be around after 100 half-lives?
|
[
"As far as we can tell it's a completely random process. So \"nothing\" determines it, strictly speaking. "
] |
[
"Half-life only really applies to bulk amounts of atoms, and cannot explain more than the relationship between quantities of starting materials/products vs. time (It's a bit like thermodynamics in that regard). It won't tell you which atoms will decay and when.",
"Spontaneous radioactive decay is what you want to be looking at to attempt to explain what individual atoms do. There are a number of hypotheses as to the cause of this effect but so far none are conclusive."
] |
[
"Physics is appropriate. Chemistry is the study of how different atoms interact. But if you are concerned with the nucleus of atoms decaying, that is physics.",
"Of your 100g of Uranium, the 50g that will have decayed will be interspersed among the whole amount."
] |
[
"\"Crappy beer gives me such a hangover.\" Is this true?"
] |
[
false
] |
If you drink a lower quality alcohol beverage will you get a worse hangover? And if yes, why? Thanks!
|
[
"barkeep in a beer-specialized bar here. (I never thought I'd cite my credentials on this subreddit :o)",
"'Quality' in beer is a difficult subject. There's a lot of pshychology involved but that aside lets look at the ingredients. All beer is made out of grains (mostley barley but wheat, maize and sometimes oats and rice), hops and water. ",
"The glucose from the grains is the main source of alcohol in beer when it gets transformed by the yeast strain. Some lower quality beers (but also some 'a' brands like american budweiser and the likes -note that the 'a' brand status ≠ quality-) use cheaper sources of glucose like maize or rice. Sometimes even plain sugar is added to boost alcohol content.",
"This sacrifies taste over alcohol content as the substitutes used don't have the aromatic qualities barley malt has. This creates a beer that tastes 'thin' and usually these beers are advised to be consumed 'ice cold' as your tastebuds are less perceptive in beverages of low temperature (this is why warm coke tastes awful, for instance).",
"Therefore this cheaper beer will satisfy you less in the beer taste and fill be less filling, then a well-brewn beer, while still delivering its dose of alcohol, this is adding to your hangover.",
"I must say that I think the largest contributor to the 'not my regular hootch'-hangover is psychological. Sure, cheaper materials make for inferior quality and sure some additives may have a biological effect that may increase the hangover's effects (I heard about this of sodium bisulfite in wine, but I'm not and expert in biology, so I will leave that one open).",
"Perceived quality, however, is a great aspect of the booze industry. And most likely you (as everybody else) have been subconsciously influenced by this in a way. People tend to overestimate their tastnig abilities and memory. Emotional arguments are very important in taste perception. ",
"A psychologist might fill this in further, but a fun way to find this out with friends is to have them blind-taste common brands of beer (cheap shop-owned brands aswell). Have them rate the beers from memory, beforehand, and then have them compare results. I can assure many bricks will be shat.",
"Wow, I'm getting sidetracked a bit. So I will close my argument with the following, I will try to make my main point consise.",
"Quality in alcoholic beverages is very much more emotional than a taste thing. Some additives may add to your hangover. But if you are drinking a beverage that you consider to be inferior and still manage to get drunk, then the hangover will be considerably worse. Most of that effect is emotional/phychological imho, but I'll be checking this thread to see if one of the science guys can prove me wrong.",
" Some spelling and wording. Some mistakes remain, not a native, my apologies to the OCD-prone."
] |
[
"What you would call a \"crappy\" beer will most probably contain more chemical additives than a quality beer. It is reasonable to assume that these additives will cause or aggravate some of the symptoms associated with hangover.",
"I can attest to that from personal experience. I'm Austrian but live in Australia. In Australia, 3 or 4 \"standard\" beers (VB, or similar) cause me far more grieve than double that amount in Austria, where beer is brewed according to the German \"Reinheitsgebot\": the only legally allowed ingredients in a beer are water, hops, malt and yeast."
] |
[
"Quality in alcoholic beverages is very much more emotional than a taste thing.",
"So beer is to men as cosmetics is to women."
] |
[
"Why 100 neurons per \"pattern recognizer\"?"
] |
[
false
] |
In his latest book How to Create a Mind, Ray Kurzweil argues that the neocortex consists of 300 million pattern recognizers. Each of them is capable of recognizing just one pattern, consists of, on average, 100 neurons, and takes, on average, 8 inputs (page 196). I couldn't find an explanation of where these numbers come from, other than that the number of pattern recognizers is the estimated total number of neurons in the neocortex (30 billion) divided by the average number of neurons in each pattern recognizer (100). Wouldn't it be more logical to assume that each neuron is a pattern recognizer in its own right, and each synapse is its input, and so there should be 30 billion pattern recognizers with 1000+ inputs each? Is there any neuroscience research that supports Kurzweil's claims?
|
[
"It is generally believed that there is population coding going on in neurons, most likely to counteract noise, so it's not unreasonable to suppose that each neuron is ",
" \"a pattern recognizer in its own right.\" To explain this briefly (and very very inaccurately), imagine you have 100 neurons, each of which gives the \"right answer\" 10% of the time, and one of 1000 wrong answers, chosen at random, 90% of the time. Then if you \"poll\" 100 neurons to see what the answer is, you'll get a peak at the right answer, even though each individual neuron is more likely to be wrong than right. Again, this is very simplistic -- neurons don't work ",
" like that -- but that's a very quick way to get a feel for the statistics of population coding.",
"That said, I have no idea what Ray Kurzweil is talking about, and it would not surprise me if he doesn't either. He is not know for having a rigorous understanding of biology, and he might just be making stuff up. The neocortex does have structure to it, it has different layers, it is organized into columns (maybe this is what he means?), and it has different regions responsible for different tasks. While some people believe that the neocortex is homogenous, in the sense that the anatomy of the motor cortex (for example) is similar to the visual cortex, most people don't argue that it is homogenous at the granularity of 100 neurons."
] |
[
"Is \"population coding\" a good term to search for? Are there good review papers, especially ones that address the degree of this \"redundancy\"? Is there any evidence for \"8 inputs per pattern recognizer\"?"
] |
[
"Can't think of a good review right now, but there is a wikipedia article on it that might have some useful links. Regarding \"8 inputs per pattern recognizer\" that seems a bit nonsense. I assume that when he says pattern recognizer, he means \"filter.\" For example, filters in the visual cortex are reasonably well studied, and (in the case of so-called simple cells) code for things like oriented edges. However, such filters typically have a lot more than 8 inputs. They take in a range of inputs from their receptive field, as well as additional inhibitory lateral connections from nearby filters.",
"The whole thing about \"recognizing just one pattern\" is also quite misleading (well, incorrect is probably a better word). For example, complex cells take as input the output of the simple cells (the \"edge filters\"). They typically respond to a range of oriented edges, and might code for things like \"horizontal edges in various positions\" or \"edges of varying orientations in a fixed position\". So they're not recognizing just one pattern, they are pooling similar patterns from filters lower down in the hierarchy. It's not unreasonable to extrapolate that these sort of pooling operations might take place at higher level of abstraction too, so that in fact most mechanisms don't recognize \"just one pattern\" but instead reprocess the responses of other neurons from other parts of the hierarchy, performing things like pooling operations or other more complex processes.",
"All in all, this talk of 8 inputs per pattern etc. sounds a little like describing a computer as a machine that performs logical and and or operations using gates, each of which takes on average two inputs. Correct or not, such a description is utterly unhelpful for understanding what's going on :)"
] |
[
"Is human intelligence limited?"
] |
[
false
] | null |
[
"It depends on what kind of threshold you mean. It's very unlikely that any human being will be able to keep the whole of science and mathematics in his or her mind at once, for example. ",
"But if you're talking about the kind of intelligence where we can comprehend concepts if we put our minds to a particular concept, then no, there is no limit to intelligence in that regard because complex things get broken down into manageable levels. The motion of particles, for example, is ",
" complex, so we break it down and name each and every one of the different things going on."
] |
[
"There is no way to know if such concepts exist since we can't comprehend them in the first place. There may be things out there that a higher being (if it exists of course) can comprehend and we wouldn't even be aware of it; just like your cat and calculus example. So my answer would be yes, human intelligence is indeed limited."
] |
[
"Considering that intelligence isn't very well defined, I'm not. That's why I took two alternate definitions to increase the chances that I wrote about the OP's definition of intelligence."
] |
[
"What is the speed of gravity (or a gravitational wave)?"
] |
[
false
] | null |
[
"The speed of a gravitational wave is the same as the speed of light. The best paper on this is ",
"this one",
" by Carlip."
] |
[
"This isn't a good explanation, ",
"I'll link to the wiki",
".",
"Basically, this is more easily understood classically in terms of EM fields interacting with a polarisable medium, or in condensed matter quantum field theory terms as quasiparticles created by mixing of the electron and photon fields.",
"Trying to think of the photons bouncing around the material being absorbed and re-emitted seems to be a result of trying to introduce QM photon thinking too early in the explanation."
] |
[
"The speed of light in a medium differs from c, but the paper states that the speed of gravity = c, which is constant. "
] |
[
"Is this a new theory of gravity?"
] |
[
false
] | null |
[
"Hello,",
"We don’t evaluate personal theories here.",
"Cheers."
] |
[
"It's not a full theory just an interesting train of thought. I'm not asking for evaluations just conversations with other people who might find it interesting. "
] |
[
"That is not something that we offer here."
] |
[
"How do polarised lenses block the glare from water?"
] |
[
false
] | null |
[
"Light wave energy can oscillate up and down, side to side, or any angle in between. The molecules in the lenses or lens coating allow only one angle of polarized light to pass through and block all others. If the angle is chosen to allow all vertical oscillations to pass, then any horizontal ones are blocked. Light glancing off water at a low angle are primarily horizontally polarized."
] |
[
"That's lot clarifying anything. There is absolutely no quantum physics going on here. 'Clarifying' polarisation of light by referring to the 'spin' of photons is almost always actually misleading the reader.",
"Saying a photon has spin is also technically incorrect because there are only 2 (linearly independent) polarisations of light, whereas a spin 1 particle should have 3 (linearly independent) spin states. Massless particles can't have spin, they have helicity. For the purpose of conservation laws, helicity is a form of angular momentum like spin and orbital angular momentum."
] |
[
"You did a great job of explaining that. Thanks for sharing some knowledge."
] |
[
"Would it be possible to have a planet (possibly gaseous) with an entirely flammable atmosphere?"
] |
[
false
] |
[deleted]
|
[
"You'd agree that the Hindenburg with its hydrogen was very flammable.",
"Similarly Jupiter is composed of about 90% hydrogen.",
"So, yes, Jupiter is flammable...",
"Except, since there is practically no oxygen, the hydrogen can't burn."
] |
[
"The meteor impacts and constant lightning would help with that.",
"Hydrogen and oxygen can start combining on their own seemingly at random as well."
] |
[
"Even if jupiter did have enough oxygen to burn the hydrogen I would assume that it would have caught on fire and burnt out early in its life?"
] |
[
"What makes the properties of elements?"
] |
[
false
] |
According to my gen chem teacher the number of protons makes an element itself. What makes Carbon, Carbon? How does the atomic makeup give every element such drastically different characteristics?
|
[
"Basically: electrons. How many electrons and their locations decide how an element interacts with other matter. Elements above and below any given element on the periodic table have similar electron arrangements, so they have similar properties. Strontium can substitute calcium in bones, for example. Silicon harbors similar behaviors to carbon, that's why some people suggest silicon-based life may exist on other planets, (however, that's unlikely). Reactivity and ability to combine with other elements are pretty much all decided by the outermost \"valance\" electrons. ",
"Electrons farther from the nucleus are easier to remove, or in the case of a nearly full valance, don't pull as hard to get the full outer shell. Electrons closer in are much harder to remove, and are very needy when they are close to fulfilling a noble gas configuration. These statements explain why flourine is so much more reactive than the halogens below it (7 close electrons that need just ",
"). Also why cesium is usually more reactive than lithium or sodium. ",
"As for carbon, it's a small atom with half a full valence (4) of the 8 electrons. This gives it the ability to bond with multiple atoms, ions, or molecules, sometimes with multiple bonds between them."
] |
[
"Thank you! She claimed it to be too advance for us, and I just really wanted to know."
] |
[
"Okay, but how do protons, electrons, and neutrons, imbue elements with their ",
" qualities. I'm not talking about reactivity. I mean why does adding or subtracting subatomic particles fundamentally change something from gold to radon?"
] |
[
"If you crossbred all of the modern domestic dogs together, would you end up with their common ancestor, the grey wolf? Or is it more complicated than that?"
] |
[
false
] |
Would you end up with a wolf, or a generic looking mutt? If that would work, are there other interesting things we might be able to breed back? Like a saber tooth tiger or something?
|
[
"Very good question. Short answer: You get a generic looking mutt, more or less like many of the mutts you see in animal shelters or on Caribbean beaches.",
"The reason you don't get a wolf is that all modern dogs descend from a single domestication event and share certain evolved traits. There are ",
"dozens",
" of places in the dog genome where modern dogs are identical with each other but different from wolves. If you mix modern dogs together, these regions would still be dog-like, not wolf-like."
] |
[
"Humans didn't come from Neanderthals, they were a whole different sub species that went extinct"
] |
[
"That's a pretty interesting idea, but unfortunately, it wouldn't work.",
"Dogs have ",
" (78 altogether). They get 39 from their sire and 39 from their bitc-... mom. Crossbreeding means that a dog gets 39 pairs of chromosomes from one breed, and 39 from another. This makes it impossible to crossbreed all the dogs in existence.",
"Evolution doesn't work like Power Rangers. That is, it doesn't mean that all modern dogs are merely Zords of the grey wolf common ancestor that you can piece together to create a Megazord again. The genetic information of the common ancestor has changed significantly over time, leading to the many different kinds of dogs you find today, and it's impossible to perfectly trace back the entire genome of the common ancestor even from thorough DNA analysis, let alone crossbreeding."
] |
[
"Does quantum mechanics violate causality?"
] |
[
false
] |
First, how is causality defined? Secondly, does quantum mechanics violate causality? In what theories and interpretations is causality violated and in which is it preserved? Naming theories and interpretations is okay if you don't have the time to explain anything
|
[
"No, causality is not violated by entanglement."
] |
[
"This has come up before, so I'm going to take what I think is a good guess: You're thinking of determinism, not causality. And yes, determinism is dead.",
"(There's room for a long and drawn-out discussion of the subtle differences between Laplacian determinism and unitary evolution, and knowing this place, that discussion will be had to a ",
" degree, so just stay tuned.)"
] |
[
"No information can be transferred between the entangled particles. There is no violation of causality.",
"Haven't we had this discussion before?"
] |
[
"What is the typical carbon content of hot and cold rolled steel used in industry?"
] |
[
false
] | null |
[
"http://www.onlinemetals.com/productguides/steelguide.cfm",
"That is a quick primer on steel types from a supplier. As it notes, most commercially available steels are between 0.2 and 1.7% Carbon by weight. The alloys you are interested in are ductile so they are probably nearer the end 0.02%. If you know the name of the alloy in question, its name probably references the carbon content. (1040 steel is 0.4% carbon and 1020 steel is 0.2% carbon)"
] |
[
"Depends on the industry and the application. The most common for piping carbon steels is 0.2 though."
] |
[
"Thanks a lot"
] |
[
"Is it possible for a moon around a planet to have it's own moon in orbit?"
] |
[
false
] |
Say for instance Europa had a small moon in orbit around itself? Is that kind of thing just unstable?
|
[
"The magic astronomical phrase to Google here is \"",
"Hill sphere",
"\" - that's the volume around a body where the body's gravitation dominates the gravity of whatever it's orbiting around.",
"Anyhow, ",
"here",
"'s a pretty good explanation of the situation.",
"Short answer: yup. But usually they're not very stable over long periods of time."
] |
[
"A few additional points/details:",
"The Hill Sphere is based on the circular restricted three body problem in which there are two massive bodies in circular orbits about each other and the third body is massless. So, while the idea of the Hill Sphere is a useful concept it cannot be taken too literally if the orbits of the massive bodies aren't circular, if the third body's mass is significant (in comparison with the massive bodies), or if there are other massive bodies about. So, only if something exists well inside (or well outside) the Hill Radius can one make strong statements/conclusions.",
"\"Hill sphere\" - that's the volume around a body where the body's gravitation dominates the gravity of whatever it's orbiting around.",
"To be precise (nitpicking): Imagine the line between the two massive bodies. The Hill Radius is the distance from the body being considered to the point along that line at which the radial force vanishes, that is, where the forces from the two massive bodies are of equal magnitude (i.e. the 1st Lagrangian point). The Hill Sphere is a sphere with that radius.",
"Also note, if the third body is well in the Hill Sphere but not in-plane (the plane in which the two massive bodies orbit) then the other massive body may induce fairly strong perturbations on inclination of the third body's orbit (the angle between the third body's orbit plane and the orbit plane of the two massive bodies). So while the third body's orbital distance may be fairly stable its inclination may vary substantially.",
"In the link maschnitz provided they talk about the regime in which tidal forces from the planet are important for destabilizing sub-satellites as the regime in which tidal forces from the planet will cause the host moon to synchronously rotate (be tidally locked). While these two regimes are related and perhaps equivalent to first order they are not the same. The moon does not have to be synchronously rotating for one to be in the regime where sub-satellites will be destabilized by planetary tides. Also, planetary tides is not the only process that can destabilize sub-satellites. For example, other moons could cause destabilization (especially when in resonant situations like that of the Galilean satellites).",
"Lastly, about the timescale over which these sub-satellites could exist: I think it's important to note that the survival timescale is short enough such that it would be ",
" unlikely to observe them currently around any of the Solar System's moons."
] |
[
"Technically the same process occurs, but there's a huge difference in scale.",
"Earth and the moon can be called a binary planet system because they're relatively close in mass. The moon has about 1% as much mass as Earth, which is enough to make Earth wobble significantly. But the Earth is only 0.0001% as massive as the Sun, which means the star barely notices our pull at all.",
"The Earth/moon system orbits a point 4000 km away from Earth's center. Earth's whole radius is about 6400 km, so it's a pretty significant wobble.",
"The sun/Earth system (ignoring all other planets) orbits a point only 500 km away from the sun's center. The sun is close to 700,000 km in radius, so 500 km is nothing. It barely knows we're here at all."
] |
[
"What’s the difference between anti-platelets and anticoagulants? In what circumstances do we use each of them?"
] |
[
false
] | null |
[
"This topic gets really deep, but here is a quick summary: Your body makes blood clots through a mechanism called the clotting cascade. This, very simply, begins with platelets clogging up the hole by forming a kind of mesh, and then different clotting factors reacting with each other to to finally form fibrin that fills in that mesh resulting in a stable clot. Antiplatelet meds work to decrease the “stickiness” of platelets so the mesh doesn’t form so easily, and anticoagulants work by interrupting different stages of the clotting cascade so a clot doesn’t form as easily. Depending on the diagnosis, different meds will be prescribed to elicit the desired effect. For example, someone with atrial fibrillation (and therefor prone to blood clots forming in the atria of the heart as blood stagnates a bit without a proper squeeze) will be put on an anticoagulant (such as coumadin or eliquis), and someone with a fresh stent in a coronary artery will be put on an antiplatelet such as plavix so that platelets don’t stick to the fresh stent. Again, there are physicians who dedicate an entire career to this subject and this is a very rudimentary explanation"
] |
[
"That was amazing, thank you"
] |
[
"Antiplatlets generally prevent clumping and clotting just based on contact within blood vessels. Aspirin and plavix are 2 common examples. They work well for people with a little plaque build up and preventing platelets from snagging and forming a clot. Since they don't interfere with clothing based on signalling tho, just reduce the platelets available to fix the clot it may take longer for a bleed to stop if an injury happens, but this risk of bleeding complication is much lower than anticoagulants \nAnticoagulants generally act somewhere (often the liver) to prevent the signal the body sends saying to make a clot and interfere with that process entirely and can break down already existing clots as well. Examples include warfarin and heparin. Generally these are much more effective for artificial heart valves or AFib at making sure clots don't form at all in those higher risk situations. The major downside is since the clotting process is essentially turned off throughout the entire body GI bleeds and strokes from bleeds are much more common. And injuries from falls etc can result in much more serious damage as blood doesn't clot to close the wound off"
] |
[
"Atmospheric Escape: Where would I end up?"
] |
[
false
] |
What does an atmospheric escape mean? If I were a single atom of helium, escaping Earth, where would I go? Is there a pool of Helium where it takes the least amount of energy to be, a sort of Helium suburb? Are Helium and Hydrogen the only chemicals which can escape within a human-livable period of time?
|
[
"What does an atmospheric escape mean?",
"Atmospheric Escape",
"If I were a single atom of helium, escaping Earth, where would I go?",
"Space.",
"Is there a pool of Helium where it takes the least amount of energy to be, a sort of Helium suburb?",
"The particles do not escape/collect because they have low energy, rather some particles have a higher energy than the average, and this may translate into sufficient kinetic energy for them to achieve escape velocity. ",
"Are Helium and Hydrogen the only chemicals which can escape within a human-livable period of time?",
"In our atmosphere, they are the only elements that escape to a notable quantity in a human-lifespan, but even this is relative. The quantity is minor compared to the quantity that remains in the atmosphere."
] |
[
"It achieves escape velocity, which is to say it is able to overcome the gravitational pull of the earth and shoot off into space. Essentially yes, it goes off in no particular direction. Since the gravitational pull of the planet cannot restrain it, it does not hang out in a spot near the earth."
] |
[
"I appreciate the answer! It answers only half of my question, because of my own written shortcomings!",
"My real curiosity is if there is a particular spot in Space surrounding the Earth where the H/He might end up, like in the Thermospere, or perhaps in the area surrounding the Earth's atmosphere.",
"The core of my question is: Does H/He simply float away in no particular direction? "
] |
[
"Is there any evidence that dinosaurs migrated like birds do now?"
] |
[
false
] |
Watched this video that shows the migration of a pair of Honey Buzzards from the Netherlands down to Africa. If dinosaurs migrated seasonally across vast distances, would there be any fossil evidence and does that evidence exist?
|
[
"Yes - there is rather good supporting evidence for this from stable isotopes in growth bands within teeth (a bit like tree rings). Continuous tooth growth served as a recorder of the O and C isotope signatures of feeding grounds, and cold vs warm areas have distinctly different and recognizable isotope signatures which directly affected the signatures of the growth bands. Thus we see growth bands in their teeth with alternating isotopic signatures from different areas.",
"reference 1",
"; Fricke et al., 2011, Lowland–upland migration of sauropod dinosaurs during the Late Jurassic epoch.",
"reference 2",
"; Fricke et al., 2009, Hadrosaurid migration: inferences based on stable isotope comparisons among Late Cretaceous dinosaur localities"
] |
[
"It is indeed rather neat that it resolves this way. Should have added that non migrating species don't show the variation in O and C isotopes in their own growth rings. ",
"There are indeed cool things slowly beeing resolved through new applications of research tools: dino pigmentation, the feathers thing, diet, behaviors such as flocking and social dynamics. Fascinating really, especially when one remembers how little we knew a mere 25 years ago."
] |
[
"It is indeed rather neat that it resolves this way. Should have added that non migrating species don't show the variation in O and C isotopes in their own growth rings. ",
"There are indeed cool things slowly beeing resolved through new applications of research tools: dino pigmentation, the feathers thing, diet, behaviors such as flocking and social dynamics. Fascinating really, especially when one remembers how little we knew a mere 25 years ago."
] |
[
"\"In a universe with three time dimensions and only one space dimension for example, the speed of light would be the lower limit for all motion\", why is this?"
] |
[
false
] |
This is a line from the March issue of the BBC's science and tech monthly called Focus (I recommend it to anyone by the way). I understand, I think, the ideas being discussed here, such as in our universe time only has one dimension, one way that it can flow. But I do not understand why, if the space of our universe was a single dimension or a line, the speed of light would be the lower limit. Also, if this is the lower limit, is there another upper limit?
|
[
"That's a bit of mathematical wankery, really. It doesn't mean anything except in the most abstract, unphysical sense.",
"If you start with the laws of physics that describe kinematics, then ",
" that there could exist tachyons — particles with energy that can only be quantified in comparison to ordinary particles by using imaginary numbers instead of real numbers — and ask what the laws of physics would look like to them, you find that the sign of the metric, which describes the geometric relationship between space and time, flips from –+++ to +––– (or vice versa, if you started out with the opposite sign convention). One way to interpret this is to say that to a hypothetical tachyon, the universe appears to have one spacelike dimension and three timelike dimensions instead of the other way round, but that's not really a ",
" interpretation of the maths.",
"It's analogous to constructing a problem in arithmetic in which you start with two apples, then someone takes away five. How many apples are you left with? A mathematician would say \"minus three apples.\" But any reasonable person would instead simply say \"You can't take five apples from me if I only have two to give you.\"",
"(And an economist of course would talk endlessly about the principle of ",
" and how it affects capitalisation and the free flow of wealth in an apple-based economy.)"
] |
[
"Dirac predicted the positron based on what you might call \"mathematical wankery\". His equation gave negative energy solutions, but instead of declare them non-physical, he posited that the corresponded to an undiscovered particle."
] |
[
"Didn't it often happened in the past, that mathematical wankery predicted some real things which at that time seemed absolutely surreal?"
] |
[
"Why did the matter that formed our solar system form 8 planets instead of clumping into a bigger star?"
] |
[
false
] | null |
[
"In short, because the protoplanetary disk was so large. When things are in orbit, they don’t just go straight towards the star; they can maintain that large distance. Any clumps of matter large enough would have a larger influence (gravity gradient) on their immediate environment than the sun(like how the moon pulls harder on us than the sun), and matter would be attracted to them instead."
] |
[
"While this is true, you're missing out on a few things. First, that even though single objects to tend to fall into relatively stable orbits over time, a gas cloud would eventually collapse down onto the star due to collisions over time.",
"What keeps the gas from doing so however is that at a certain point after a star begins to fuse hydrogen, the outward radiation pressure pushes the gas away, keeping it at a distance that would eventually form planets. If the gas just stayed in a stable orbit, then planets themselves wouldn't form."
] |
[
"The main point is that not all the gas in the gas cloud has a chance to collapses into the star in the center because the gas further out is gonna take a longer time to collapse than the gas near the center. The material further out is still falling inwards but once a protostar has formed it start getting really hot and will radiating heat so solar wind and radiation pressure will start to push mass away from the center to prevent more mass to join the star. ",
"From ",
"https://jupiter.geo.kyushu-u.ac.jp/machida/arxiv/sfe.pdf",
"Calculations show that typically, ∼ 30% of the initial cloud mass is converted into the protostar and ∼ 20% remains in the circumstellar disk, while ∼ 40% is ejected into the interstellar space by the protostellar outflow.",
"So for however much mass you have in your cloud only around 30% will become the star and some of the material will stick around to form planets while everything else gets blasted away into space once the star is ignited. "
] |
[
"How have tardigrades survived five mass extinctions? Also, what makes them so resilient in extreme environments?"
] |
[
false
] |
I was watching Cosmos and Neil Degrasse Tyson mentioned that tardigrades have survived five mass extinctions (meaning that they've been around for hundreds of millions of years). They can survive in the most extreme conditions, including the cosmic radiation of space, 10 years without water, and intense volcanic heat. What makes them so good at surviving?
|
[
"Well, Tardigrades have the distinct ability to enter a really intense kind of hibernation. They eliminate nearly all the water in their systems before going into \"hibernation\", replacing it with a sugar trehalose, which both protects membrane as well as serving as a retainer for the water thats left in the tardigrade. This sugar, Trehalose, is the glue that keeps this magic together. Its incredibly stable, turns into a gel, and stops cells from splitting or disrupting. And best yet, all it needs is water, and it'll return to a more liquid form, releasing the bonds it had on the cells it encapsulated, and returning it to full functioning form.",
"Turns out, being nearly completely empty on water also makes them incredibly resistant to lethal doses of radiation, mostly because less water content provides less reactants for ionizing radiation (that kills things). And to tack on to that, tardigrades only have 75-800 base pairs of DNA, but their DNA effectively repairs itself in event that the radiation does damage.",
"In freezing temperatures, the water content of the tardigrade goes down all the way to 3%, meaning when it eventually thaws, displacement is a non factor.",
"Ironically, in the end, its water that we use to measure future capacity for life, but its really the water that kills everything in extreme conditions. "
] |
[
"Wikipedia: \"Tardigrade genomes vary in size, from about 75 to 800 megabase pairs of DNA.\"",
"^ That seems much more reasonable. "
] |
[
"That's fascinating. Are tardigrades the only known organisms to use trehalose in this way?"
] |
[
"What causes this ring of fire from a Desert Eagle? *Link in description* (x-post r/woahdude)"
] |
[
false
] | null |
[
"that ring is a toroidal vortex, it happens because the jet of hot gasses leaving the muzzle shears past the stagnant air around the muzzle creating a ring of rotating air/gunpowder:",
" well illustrated here",
". ",
"I assume the flame in the ring is more visible because the hot gasses in the vortex ring barely get mixed with outside air and stay concentrated & hot while the main jet of hot gasses will extinguish quicker because it gets mixed with more outside air"
] |
[
"Short answer: The combustion products of the gunpowder (and some powder that is still combusting) mixing with ambient atmosphere. The ring itself is being pushed by the overpressure wave exiting the muzzle.",
"All firearms produce muzzle flashes. A flash hider/suppressor is sometimes used to redirect the gas into discrete jets so that the user's sight is unimpeded. In a rifle suppressor, the amount of heat and pressure produced is often so high that it ignites ambient atmosphere and as a result special materials (like the kind you see in rocket engines, such as inconel) are used.",
"So that's a lot of energy, right? Not all of it needs to be used to push the bullet, and isn't: Just beyond the chamber of of the barrel there's a tiny hole that uses some of that gas to work a piston just underneath the barrel, which in turn is what drives the action of the gun. A fundamental design that has been used in rifles and machineguns for over a century. The DE is unique in that it's one of those rare gas operated pistols; it shares more of its DNA with rifles than it does with your typical semiauto handgun; most of those use the recoil generated by the barrel instead of gas pressure to work the action.",
"The designers of the original AR15 platform of rifles, from which the M-16 was developed, realized that you don't even need a piston: You can just let some of that hot gas impinge inside of a carrier in the heart of the rifle's mechanism and it works just as well (albeit dirtier).",
"tldr #2: The same stuff that produces that ring is actually being used to operate the gun."
] |
[
"Thanks for the link to \"Physics Girl\" - that's an awesome video (and series!) She is asking questions, testing processes, looking for reasons behind results.\nShe's got the Scientific Method included: observation, question, hypothesis, experiment, conclusion!",
"When I was in school, there just weren't girls interested in physics... I'm so happy to see this example presented and perhaps it will encourage more young women to seek out courses in science."
] |
[
"How does long term, childhood trauma physically change the body? And are the effects reversible?"
] |
[
false
] | null |
[
"In many ways. For example, certain types of mental trauma can even show up on MRI scans.",
"To anyone who is interested in trauma and trauma therapy, I wholeheartedly recommend van der Kolk's book ",
"The Body Keeps the Score",
". It is brilliantly written, not very long, and well-researched. I also recommend this to anyone looking to deal with their own trauma, as understanding your body's reaction to your environment can help you cope with it.",
"Dammit, now this post is just an ad. I stand by it though, as the book answers your exact question in far greater depth than I ever could."
] |
[
"OMG ask me questions! I'm a NeuroAffective Relational Model practitioner and have been studying trauma for years. Anyway, ",
"yes long term childhood trauma can and does physically change the body, and yes it's effects are reversible to a degree. I actually started my career in trauma healing as a massage therapist, studying structural integration. ",
"To answer the question of \"how\" psychological trauma effects the body is not easy to answer as it depends on the individual, the trauma they experienced, how they relate to those experiences, and perhaps most importantly how they currently relate to themselves. It can show up in all kinds of ways though - in muscular holdings, facial expressions, even organ function and systemic things like inflammation. ",
"The thing though is if one were to focus on those things, it's not a direct path to fundamentally healing those things that are seen as \"the problem\". It can be a part of a wholistic treatment program, but the juice is in accessing the parts of self that one has been avoiding, which takes an outside person who both knows what they are doing, and can hold space with you in unconditional compassion."
] |
[
"What are you referring to? All the reviews seem to agree that it is a brilliant book. Obviously it contains case studies -- what kind of scientific work on the subject would not?",
"Edit: just clicked the link in the post I was responding to, and it seems to be some sort of self-help website. If you are interested in the scientific side of things, you probably want to stay clear of organizations like that. (Actually, if you are a victim of trauma, you ",
" want to steer clear of organizations like that. They are probably well-meaning, but so are people who treat your cancer with homeopathy.)",
"Also edit: if you are trying to cope with your own trauma, obviously get a therapist, ",
" start reading books with potential triggers in them. Not the other way around."
] |
[
"How is the speed of a spacecraft measured? Is it the rate of increasing distance from earth? From the sun? Is it the affected by the earths orbit?"
] |
[
false
] |
Question sort of popped into my head today. When a spacecraft, or probe is traveling in our solar system, they often state that its traveling at x miles/second. Is that the rate of increasing distance from the earth? If the earth was orbiting away from the probe, would the probe then have a faster velocity compared to when the earth is orbiting toward the probe? Also, in the same vein, how are speeds of orbits or planetary rotations measured? Are the always referenced to the sun? This sort of stuff bothers me, like once in physics, a teacher asked me "how fast is the earth moving right now?", I responded "With reference to what? To us? Then its not moving at all" She stated I was wrong and spat out a number, and a few classmates laughed at me. Thanks for the help guys!
|
[
"It depends. If a probe is being sent from Earth to Mars, for instance, there are three phases of flight.",
"The first phase is where the probe is under the influence of the Earth. The orbit here will actually be what's known as a hyperbolic trajectory. It's an \"orbit\" that causes the object to escape the gravity of the planet which dominates (Earth), ending up with a so-called \"hyperbolic excess velocity,\" or a velocity above and beyond that required to escape. So near Earth, our Mars-bound probe's velocity might be given relative to the Earth.",
"After leaving the influence of the Earth, the probe is orbiting the Sun. During this phase, the speed is generally given as the orbital speed of the probe around the Sun. The orbit of the object (if it was the only object in the Universe besides the Sun) would be an ellipse, and if the probe never encountered Mars, it would remain in this orbit around the Sun.",
"The third phase is the hyperbolic trajectory again, but this time at Mars. It's more-or-less the reverse of the hyperbolic trajectory the probe followed at Earth; this time, it's approaching Mars instead of leaving. In this case, the speed might be given relative to Mars.",
"(This method of modeling orbits is, incidentally, called the method of patched conics).",
"So you can see, it really depends on what phase of flight you're talking about. If the probe is not approaching any planet, the speed is almost certainly given relative to the Sun. If it is near a planet, the speed is often (but not always) given relative to the planet. It's much more unusual (but not unheard of) to give a speed relative to the Earth for precisely the reason you say - the Earth's orbit would affect the relative velocity, and it would thus change depending on time of year, oscillating between a higher and lower velocity. This isn't a useful velocity to know for distant probes, and while it can be calculated, it's not the one that's usually reported.",
"Also, in the same vein, how are speeds of orbits or planetary rotations measured?",
"The speeds of orbits are measured relative to the Sun (where we say the Sun is stationary. It isn't, but for orbital velocities of planets, we imagine it is). The rotational speed of the planets are given relative to the distant stars, which we pretend are stationary (this is the necessary reference frame because the orbit of the Earth around the Sun means one Solar day [the time from Solar noon to Solar noon] is a bit longer than the time it takes the Earth to rotate 360 degrees about its axis).",
"She stated I was wrong and spat out a number, and a few classmates laughed at me.",
"She shouldn't have done that. From your own reference frame, the Earth is stationary and the Universe is revolving around you (hence, the appropriate answer to being told, \"The Universe doesn't revolve around you!\" is, \"Yes. Yes it does.\"). While she probably wanted the Earth's orbital speed around the Sun, without giving a reference frame, it would have been entirely appropriate to give the speed of the Earth as it careens around the galaxy (~792,000 km/h, in case you're curious)."
] |
[
"Just to add, the actual speed in relation with Earth is calculated by measuring the doppler effect in the radio communications with the spacecraft. "
] |
[
"Awesome response, great information. Very interesting and not as straightforward as one might think. Thank you for your time!"
] |
[
"How do forward swept wings on an aircraft differ from a Delta wing and a straight wing?"
] |
[
false
] |
I know the basics of lift, however I was curious about how these wing types differ. Thanks!
|
[
"A straight wing is the basic configuration, it always stalls in the axis of symmetry first which is rather stable, is easy to manufacture structurally, and can hold a lot of fuel. Drawbacks are it's large lift induced drag coefficient, making it suitable for low airspeeds only. ",
"Delta wings allow big wing area with low wing span, making them structurally good, have large internal volume for fuel, and are excellent in supersonic flight. They have a very large critical angle of attack, making them good for maneuverability, but that big angle of attack makes pilots vision in front of him rather limited, requiring high approach and landing speeds. ",
"Forward swept wings eliminate some of the problems of normal swept wings, because they have inward span wise flow making the wing stall at the root first which makes ailerons effective in a stall, and reducing wingtip vortices and the drag that comes with them. Problems of this configuration include yaw and stall instability (wing root stalls first, but because it is located aft, it increases nose up moment deepening the stall), and very dominant aeroelastic phenomena, which require extremely strong materials for it's construction.",
"This is just a short version, if you wish to know more, I would recommend \"Aircraft Design: A conceptual approach\" by Daniel P. Raymer."
] |
[
"The wing designs change the aerodynamics of the aircraft. Most importantly, the wing configurations changes the stability of the aircraft under different flight profiles. Essentially, there's a trade off between speed, maneuverability and lift.",
"Each has its advantages and disadvantages, but at a high level: forward swept is neutrally unstable and allows for high maneuverability at the cost of complex controls and significant loss of lift. Delta wing is similar to forward swept, but tends to be slightly more stable. Straight wing is generally the most stable with the highest lift, but decreases maneuverability and has low top speed do to drag."
] |
[
"Straight wings are less suitable for high speed due to transonic and supersonic effects, rather than induced drag. In fact, straight wings can have much lower induced drag than swept or delta wings. Induced drag largely depends on aspect ratio, which is why gliders have these massive wingspans and straight wings.",
"Also, most GA aircraft are designed to stall from the wing root first (by twisting the wings so the root has a higher angle of attack). This results in more gentle behaviour, and prevents accidental spins."
] |
[
"If we selectively bred mice for millions of years could we increase their intelligence similar to a human's?"
] |
[
false
] |
As in; We measure a group of mice's intelligence (through mazes or other tests initially), and selectively breed only the most intelligent. Over millions of years could we eventually breed mice with intelligence similar to a human's, or at least capable of abstract thought?
|
[
"Excellent, I was rewriting my population genetics notes last night.",
"Since I'm typing on a phone, the short of it is that there are limits to artificial selection. After enough selection, you'll reach the limits of variation for the trait you originally selected for, and while they ARE smarter than before, you'll find your mice can't get any smarter without introducing a new gene to their population [edit: ie, by mutation]. There will be certain genes in humans that give us our advantage in intelligence (such as FOXP2) that mice will not possess (not that I can check for FOXP2 right now) that your starting population of mice simply won't have in their gene pool to be selected for.",
"I can say more and link to sources once I get to a computer, but here's my answer for now."
] |
[
"http://www.reddit.com/r/askscience/comments/ly72u/could_we_breed_another_species_to_our_level_of/",
"http://www.reddit.com/r/askscience/comments/kzd50/ethics_aside_how_long_would_it_take_to_breed_dogs/",
"http://www.reddit.com/r/askscience/comments/kitiq/could_you_selectively_breed_chimps_to_human_level/"
] |
[
"Mice seem to have FOXP2",
".",
"\nedit: Also, with a time period of 'millions of years' mutations that have positive effects on intelligence are very probable. I'm far from an expert, but I think that with careful selection you'd get the maximum intelligence that's possible with mice' current genes in a couple of decades. Afterwards there's little else to do except hope for better mutations."
] |
[
"How do trick candles work?"
] |
[
false
] |
What keeps them lit, or makes them able to re-light after being blown out? How does blowing them out NOT work?
|
[
"You know how when you blow out a regular candle there is still a little bit of a glowing ember at the tip of the wick? Well trick candles also contain in the wick some magnesium which ignites at the temperature that that ember is glowing at causing a flame which reignites the rest of the wick."
] |
[
"The data you are looking at is for solid block magnesium. When powdered or finely shaved it is extremely flammable at very low temperatures. ",
"an MSDS"
] |
[
"When a candle burns, it's not technically the wick that's burning, but rather the wax. Candle wax is generally made of paraffin which is the real fuel, with the wick acting as incident surface.",
"When lighting a candle, you're actually melting some wax at first, which vaporizes the paraffin fuel and causes a flame when combined with oxygen. That flame then vaporizes more fuel and the process becomes self-sustaining. You can test this by blowing out a candle, and then holding a lit match in the vapour trail just above the wick, and the candle should light again.",
"Trick candles are exactly the same as normal candles, except there is an additive in the wick (generally fine magnesium flakes) that ignite at relatively low temperatures, around 400° C. When you blow out the trick candle, these magnesium flakes ignite (seen normally as those \"sparks\") from the heat of the burning ember on the wick and it is that ignited flake that will relight the paraffin vapour (that has been vaporized by that same ember).",
"tl;dr magnesium flakes in wick reignite the paraffin"
] |
[
"Are black holes literal \"holes\" or \"rips\" in space, or are they actual objects?"
] |
[
false
] |
I've read about black holes that can "move" across space, orbit each other, and revolve. I guess I always grew up thinking black holes were literally that: holes in space; that after enough mass has accumulated, that whole "collapsing in on itself" thing makes a hole, not an object. Am I mistaken? How could a "rip" or "hole" move around like an object without leaving a "tear?"
|
[
"We don't know what a black hole is made of, or if the question even makes sense; classical gravity theory tells us that it's a singular point, not a \"rip\" in space but a point where the curvature blows up, and there's no problem with that sort of thing moving around, because curvature can change. Compounded in this is that there's no such thing as absolute position, so there's no absolute notion of where a black hole ",
" leave a \"tear\" even if it were possible.",
"But as it is we can't trust classical gravity theory at very close distances to the center of the black hole because at those short distances quantum effects become important, and we don't know how to make gravitational physics and quantum physics work nicely together. Until we have a theory which unifies the two, the nature of the black hole center - whether it's truly a singularity, or perhaps something more exotic - remains speculative."
] |
[
"A black hole consists of two things, really, a singularity and an event horizon:",
"The singularity is where all the mass in a black hole is concentrated in a single infinitely small point of space.",
"The event horizon is the sphere around the object inside of which nothing, not even light, can escape (ie where the escape velocity becomes greater than the speed of light), and inside of which nothing can therefore be observed. While it's not a physical barrier, just a point where gravitational forces exceed a certain level, it's generally considered to be the \"edge\" of a black hole as an object.",
"The use of the words \"hole\" etc are merely descriptive, and don't imply anything more than that some scientist or scientific journalists decided it would be a good word to describe them with.",
"Edit: I'm not sure why I'm being downvoted, the above is all correct. If it doesn't quite answer your question feel free to clarify in what way, but please stick to reddiquette in future."
] |
[
"Where are you? Can you answer that without answering ",
" to something else? Any answer you give (i.e. 'my house', street address, city, state, nation, continent, Earth...) can still be questioned with \"but where is ",
"?\"",
"For most day-to-day purposes it's easy to forget that positions are all relative. Most of us don't need to think about how we are constantly moving as the planet rotates on its axis while orbiting the Sun, how the Sun is orbiting the galactic center, how the galaxy is itself in motion, etc.",
"People once thought Earth was the center of the universe. Not only is that not true, but ",
", and so there is no basis for measuring any position absolutely."
] |
[
"How much time and what treatments is needed for the astronaut to fully recover after a long mission in zero gravity?"
] |
[
false
] |
Mark Vande Hei is back after almost a year on ISS. I wonder - how long will it take him to fully recover? Are there side effects of such a long mission that cannot be undone e.g. osteoporosis?
|
[
"Here's a pretty detailed document on a European astronauts reconditioning program after a 6 month mission. They tailor the things specifically to the astronauts though so the exact exercises won't necessarily be the same for each mission.",
"https://eprints.soton.ac.uk/405193/2/Postflight%2520reconditioning%2520for%2520European%2520astronauts%2520ACCEPTED%2520MANUSCRIPT.pdf",
"Basically lots of gradually increasing exercise starting off with stuff like pool exercise, and stuff like running while suspended, working up to normal workouts, and a lot of body coordination training to get used to moving/balancing in gravity again.",
"The NASA program I think runs 45 days, though they will still be collecting data for months after. For a yearlong example Scott Kelly is kindof the main case study on account of having a twin brother to compare to. While lot of researchers got involved.",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7580864/",
"But as a quick summary, the stuff that didn't return to baseline after 6 months was: \"some genes’ expression levels, increased DNA damage from chromosomal inversions, increased numbers of short telomeres, and attenuated cognitive function\"",
"Basically no health problems, but a bit of increase risk of them in the future. And while the attenuated cognitive function sounds bad its only some specific types of tests, and not a major decline. To quantify the degree it's kindof like you can have good days and bad days takin the same test, but now you're averaging around the bad days."
] |
[
"While ",
"/u/Skusci",
" has some good info, this is not true for bone and muscle. Long-duration space flight can lead to some significant bone and muscle loss, and while bone/muscle mass can be recovered to pre-flight levels, it usually isn't. Further, the quality of bone and muscle post-flight is often poor when compared to pre-flight conditions. ",
"With bone specifically, bone mineral density may return to normal values due to cortical bone remodeling, but there is some evidence that trabecular bone may never fully recover if atrophied beyond a critical value. This can lead to significant deficits in bone strength, despite having similar pre- and post-flight bone mineral density. ",
"https://asbmr.onlinelibrary.wiley.com/doi/full/10.1002/jbmr.1948",
"There is some evidence in muscle that there is a fiber type shift from slow-to-fast twitch muscle fibers in a variety of muscles following 6 months aboard the ISS. ",
"https://journals.physiology.org/doi/full/10.1152/japplphysiol.91578.2008?hits=10&HITS=10&author1=Trappe%2C+S&searchid=1&sortspe=&maxtoshow=&FIRSTINDEX=0&RESULTFORMAT=",
"This is significant because as far as anyone can tell, once these Type I (slow muscle fibers) convert to a IIa (or IIb, or a hybrid) they are not capable of switching back to a type I fiber. Personally, I think it's more likely that the type I fibers are not converted, but lost entirely. Although the apparent shift in fiber composition could be interpreted either way in this study. ",
"Finally, astronauts have absolutely zero professional incentive to participate in \"recovery\" studies beyond what NASA or other space agencies require of their astronauts. If any investigator were to uncover a potential recovery deficit in an astronaut, it ",
" disqualify them from future missions."
] |
[
"Thank you for your answer! :)"
] |
[
"how are earthquakes predicted?"
] |
[
false
] |
How exactly are earthquakes predicted? To what extent is the prediction based on past earthquakes? When people say the area is "due" for a large earthquake statistically how true is that statement.
|
[
"Earthquake prediction is in most cases an extremely difficult challenge. Almost all predictions are based almost entirely on how often the fault has ruptured in the past combined with how long it has been since it last ruptured. So it is ",
" fine to say you are \"due\" for an earthquake if it has exceeded the average recurrence interval since the last one. However, recurrence intervals often have a large spread to them (earthquakes don't occur regularly like clockwork), so it's not like an earthquake is necessarily ",
" once you become ",
" - so it can be a misleading way to talk about it.",
"Another rule of thumb is that the longer it has been since the last earthquake, the larger the next one will be, since the underlying stresses will have had more time to build up. But again, there are plenty of exceptions to the rule.",
"Improving earthquake prediction has been one of the 'holy grails' of geologic hazards for a long time, but actively monitoring what's happening deep below the surface is well beyond our current abilities - and earthquake hypocenters are usually many to ",
" many kilometers deep. There are other pieces of evidence that ",
" give us warnings of an upcoming earthquake (such as swarms of smaller earthquakes leading up to the large rupture, or possibly the release of gasses preceding an earthquake) - but they only work on a site-by-site basis, and even then often not very reliably."
] |
[
"To add to the excellent answer by ReturnToTethys, another interesting aspect of earthquake \"predictions\" form a statistical perspective is the differing way they are presented. For example, the USGS will assess seismic hazard based on the things outlined in ReturnToTethys's answer, and then assign something like \"a 10% chance of ground acceleration exceeding X threshold in 50 years.\" This is useful and about the best we can do, but at the end of the day, it's also really hard to evaluate. Basically, if we reach the end of our 50 year time window and the area in question has not experienced a ground acceleration of said threshold, is our model right and we were just in the 90% or is our model wrong? The difficulty (or impossibility) of validation is one of the biggest criticisms of most probabilistic seismic hazard assessments. That being said, there's not much of a better alternative and to a certain extent this is what the public and entities like insurance companies want."
] |
[
"In Japan there is short term \"prediction\", though \"detection\" is more accurate. A national network of sensors detects ",
"P-waves",
" kind of the first weaker part of the quake before the main S-waves hit(?) quickly analyzes them and if it looks major, sends a warning to radios and mobile phones (mandatory and default setting for all 3G phones) and many control systems that can give people a few seconds or more to take cover, trains can emergency stop, etc..",
"There are a few false alarms, but it works pretty well."
] |
[
"What's the best telescope for an ameteur astronomer?"
] |
[
false
] | null |
[
"Is this your first telescope? Have you tried (1) large binoculars (2) going to a local astronomy club and seeing through one of their telescopes? I say, try one of these 2 first or else you will be highly disappointed. Meade does not seem to offer the 8-inch Dobsonian anymore but I would always say that this or something similar will be a good starter scope."
] |
[
"Are you located in the US?",
"If so, check out craigslist. I have found incredible deals on CL on decent scopes. My first scope was an 8 inch Odyssey that I picked up for 175 bucks, a few months later I found a 10 inch for 300 that came with an OIII filter(90 bucks by itself). I sold the 8 inch later for 200 bucks after some upgrades and the 10inch I sold for 300 but kept the filter.",
"My point isn't to brag but to go second hand for your first scope. Astronomy is one of the few hobbies where there is a continual supply of well cared for, high quality used equipment.",
"Don't waste your time and money with the scope from amazon.",
"THIS",
" is a much better beginners scope if you are set on buying new.",
"As someone else mentioned, a nice pair of binoculars may also be an option, however to see a \"good\" look at saturn a pair of binocs capable of doing that are going to be more than 500 bucks.",
"All that said, the best scope is the one you use the most. If the scope you end up with is a pain in the butt to use, then you won't use it and its just going to sit inside and never get used.",
"My favorite scope was my 8inch dob. Took about 5 minutes to set up, had better than average optics, and got used the most because it was so easy to use.",
"Feel free to PM me if you have any specific questions.",
"UPDATE - ",
"Found this on my local CL",
" This is a nice deal. Depending on where you live, it may take a few weeks for a good deal to pop up, but buying used will definitely be the best bang for your buck.",
"Another",
" on CL. This is the 13.1 inch version of the 10 inch I had. I would jump on this scope if I had the cash and lived in phoenix. This scope looks like hell on the outside but if the optics are in decent shape, this is a hell of a deal. You will be able to see the cassini division in saturns rings, clouds on jupiter, the spiral arms of M51, dustlanes in andromeda, and the veil nebula without a filter. Some of the best scopes I have ever looked through looked like hell during the day, but had incredible optics...."
] |
[
"My father has his own Meade. It's about ten years old, but he's lost all of the lenses but the broadest. I've used my fair share of telescopes, and look at the moon with binoculars when I can. I'll look at Meade ad what I can afford. Thank you."
] |
[
"Does notation exist for it possible to \"write\" any real number?"
] |
[
false
] |
[deleted]
|
[
"No. In fact, almost every number cannot be described using mathematical notation. If you were to randomly pick a number between 0 and 1, then there would be a zero percent chance that it will be describable. Same for any interval [a,b].",
"See ",
"Definable Real Numbers",
"."
] |
[
"We're using math to pick it, not a computer. Math is independent of the universe, so it doesn't matter what ",
" can do in our limited existence, it matters what ",
" can do in it's existence where it doesn't have to worry about minor things like only being able to use pseudorandom algorithms. Math has true, working completely random processes, even if we don't.",
"If you want to get technical, then we have the uniform distribution on the interval [a,b], and so we also have the random variable X associated to this distribution. If S is any subset of [a,b], then we can look at the probability P(X is in S) which is the area under the uniform distribution above the points in S. It then happens that the definable elements of [a,b] are a (measurable) subset of [a,b] and the area under the uniform distribution over this set is zero. So we have P(X is definable) = 0.",
"See: ",
"https://en.wikipedia.org/wiki/Uniform_distribution_(continuous)",
" and ",
"https://en.wikipedia.org/wiki/Measure_(mathematics)"
] |
[
"See Definable Real Numbers.",
"At the top of that page:",
"This article's factual accuracy is disputed...",
"This article possibly contains original research...",
"This article needs attention from an expert on the subject...",
"This article includes a list of references, related reading or external links, but its sources remain unclear because it lacks inline citations.",
"That wikipedia page probably shouldn't be used as a reference."
] |
[
"Is it theoretically possible to harness gravity waves? More specifically with Moscovium (Element 115)?"
] |
[
false
] | null |
[
"Are you looking for sources about gravitational waves or about superheavy elements? Because these two topics have almost nothing to do with each other."
] |
[
"The longest-lived isotope of element 115 has a half-life of less than one second, so nobody is using it to propel anything, unless they can produce it on the fly. If that were possible, it doesn't seem like it would be a very efficient method of propulsion.",
"This website",
" has information about all of the known nuclides, including half-lives and decay modes."
] |
[
"I don't really even know; both? ",
"Full disclosure, and it's a bit embarrassing, but I'm a sucker for all things extraterrestrial (I know how tinfoil hat-ty this sounds). Bob Lazar, an area 51 whistle-blower, claims that he was part of the reverse engineering of certain air-crafts in the 70s. He also claimed that the aircraft was gravity propelled using a element not known at the time, or naturally found on Earth, element 115. ",
"The story is shaky, and the evidence isn't exactly solid, but nonetheless I'm intrigued beyond anything else. You can look into all you want and I'm skeptical of it myself; however, I'm wondering where do I even start to learn more about physics and chemistry? I know that it'll be no short venture to learn what I want to learn for this, but I've got a lot of free time now since I graduated and am always hungry for more knowledge. If this is possible I want to be able to know for myself and not have someone else tell me it is or it isn't. Maybe it'll take 10 years, but if I stuck with it I could maybe feel comfortable enough to try and study it extensively; but first I need to know where to start. ",
"I don't know if this makes much sense, or if I am just rambling at this point, but I do know I want to know more."
] |
[
"If I were placed into a hollow sphere with super-massive walls, would I experience time dilation but not gravity?"
] |
[
false
] | null |
[
"In Newtonian gravity, the gravitational field within a hollow, uniform sphere exactly vanishes. (This can be proven rather easily using the divergence theorem and noting that the field must be spherically symmetric.) Outside the sphere, the field is that of a point particle with mass equal to the mass of the sphere and located at the center of the sphere.",
"In general relativity, a similar result holds. Inside a hollow, non-rotating uniform sphere, the metric tensor is Minkowski, i.e., spacetime is flat. This means there is a global inertial coordinate chart for all points within the sphere, and that there is no time dilation between any two observers who are at rest with respect to each other. Outside the sphere, the metric tensor is Scwarzschild."
] |
[
"To clarify, that means someone far from the shell will observe time dilation of the people inside the shell, right?",
"So it's kinda like a plateau - flat, but at a different \"elevation\" to the rest of spacetime. The inside of the shell should also contain more space (that is, length contraction in all directions, so you can fit more than you'd expect in there)... uh... or does it?"
] |
[
"Incidentally, it's the same principle that causes charged hollow spheres to have no electric field inside."
] |
[
"How are bacteria species differentiated if they reproduce asexually?"
] |
[
false
] | null |
[
"I found a very interesting paper on species differentiation in prokaryotes:\n",
"http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1764935/",
"A method which has been used a lot is the analysis of 16s ribosomal RNA, where above 97% sequence identity is considered within the same species.\nBut because this makes some species differentiated by other means the same, it is a problem. So there is yet to be found a single means to do it."
] |
[
"So all living things except viruses (Im a fan of saying that they are alive) make ribosomes, this is made with rRNA or ribosome ribonucleic acid, there are three of them, 5s, 16s and 23s where the number refers to their relative size. Since these genes are conserved for all living organisms, they are useful for drawing family trees for all organisms. These genes also have conserved parts and parts that allow for more variation. ",
"Before genome sequencing, species in prokaryotes or other single celled organisms would have been phenotypic, basically a description of the general characteristics of the organism.",
"Basically what is or is not a species is a little arbitrary. Note that it is even a little arbitrary in sexually reproducing organisms as closely related species can reproduce and make fertile offspring which can then backcross with a parental lineage and thus transferring genes between two different species."
] |
[
"Species vary by a number of characteristics, but mostly it comes down to genetics. The difference in the genetics between bacteria allow them to produce different proteins, and through those proteins they can have different effects on their environment.",
"Now you may be asking, how did they differentiate/evolve from the same common ancestor into genetically distinct species, given their asexual nature. The simple answer is that no replication is perfect. Even though unicellular asexual replication produces pretty much an \"exact\" copy of the original cell, the process is error prone. Replicating DNA, the genetic code, is not a perfect process. Many of these errors can kill the organism, but every now in then the error is neutral or beneficial. Accumulation of these changes over times can cause different lineages of bacteria to differentiate from each other into new species.",
"Going deeper, DNA replication error isn't the only way bacteria evolve. Some can inject pieces of DNA into their fellows and some can take up free DNA from the environment. In addition there are viruses which function to insert pieces of DNA into bacteria.",
"TLDR: In short, even though they reproduce asexually, the process isn't perfect. That, combined with other methods, leads to the differentiation of bacteria into different species."
] |
[
"What would we observe if a micrometeorite traveling at relativistic velocities impacted Earth?"
] |
[
false
] |
[deleted]
|
[
"That's less energy than you might guess. A kiloton is equivalent to about four gigajoules, which is on the same order of magnitude as the energy released by a good-sized thunderstorm."
] |
[
"The K-T event is estimated to have released about 10²³ joules. That was pretty interesting."
] |
[
"It wouldn't do anything because it would be going into the atmosphere at that speed and burn up in the atmosphere due to frictional heating. It wouldn't arrive on earth in one piece."
] |
[
"Does increasing gravitational potential energy increase the mass of an object?"
] |
[
false
] |
If you add energy to an object, such as by heating it to add thermal energy, it increases very slightly in its mass. Does the same happen if increase an object's gravitational potential energy by changing its height? If this were the case, and the mass did change, how would the potential energy be affected, since mass factors into it?
|
[
"In the context of General Relativity, the answer is no. ",
"Gravitational potential energy is just a mathematical way to represent how masses behave in the presence of one another, and is a description of the local spacetime curvature around an object. "
] |
[
"Is there another model where you can increase gravitational potential without actually increasing mass?"
] |
[
"Gravitational potential increases with:\n- increasing mass\n- decreasing distance between masses ",
"And, pedantically, by mass I mean \"energy density\" which can be matter or energy...."
] |
[
"If the ice caps carrying on melting at their current rate, roughly when will Arctic shipping lanes become a major thing?"
] |
[
false
] |
This seems to be an advantage of global warming that I bet more than a few people would be willing to hop onboard with, but will it ever realistically be a thing?
|
[
"Somewhere around 2040-2060 according to a ",
"recent study",
". "
] |
[
"North pole is just ice, south pole has land under not sea "
] |
[
"that's like asking why there's a lot of land on the east side of Britain but not much on the west. There's a continent centered on the south pole called Antarctica. Since it's cold down there, Antarctica and the sea surrounding it are largely covered by glaciers and sea ice.",
"There is no such continent centered on the north pole, just the arctic ocean, a body of water more or less surrounded by the northern coasts of Europe, Asia and North America. The northern ice cap is made up almost entirely of sea ice, unless you count the glaciers on Greenland and Iceland."
] |
[
"Why Does Sublingual Metals Help Fight \"Onion Tears\""
] |
[
false
] |
I heard this on Oprah years ago, that a paper clip in your mouth, under your tongue, was the best way to fight those tears when cutting onions. When my organic chemist Grandpa (from years ago, retired now...) was over for dinner last night I asked him why it helped and he was stumped. He did explain that you teared because sulfuric acid was being produced in your tear ducts - but didn't know what any metal in the mouth would have to do with anything. Probably un-related but I used that trick for years cutting onions for a job but later had my tongue pierced - since then, and I removed it over five years ago - I can eat raw white onions without it bothering me at all. Am I still getting some weird effect? Or is this whole metal thing an old wives tale anyways?
|
[
"There is no mechanism that can remove the irritant, ",
"sulfenic acids",
" that are the breakdown products of amino acids when cells of the onions are lysed. While metals are often good for catalyzing organic reactions, even if it removes the vaporized sulfenic acids, placing it under your tongue makes it impossible for that to work."
] |
[
"So it's more likely that the paperclip is sticking out of your mouth (while under the tongue) is the reason it works?"
] |
[
"Even if the metal is catalytically active, it's highly unlikely a paper clip will work. There's a reason ",
"catalytic converters are built the way they are",
" - even if the metal catalyzes the reaction of something in the air into some harmless product, you need a high surface area in order for that to occur with any degree of success."
] |
[
"Why do scars never heal?"
] |
[
false
] |
If the body replaces all of its cells over a period of a few years why do scars stay with a person for life and never look like normal skin afterwards?
|
[
"This is my understanding. The difference in texture you notice between your regular skin and scar tissue is because of the way that the collagen is deposited by the fibroblasts that are healing the deep wound. Normally it is random, but in the case of scar tissue all of the fibres are aligned in the same direction. Even if cells are replaced they are still constrained by the extracellular matrix that has been laid down. But sometime scars do fade a bit, even collagen slowly gets altered by the various cell movements that keep epidermises intact throughout an organisms life."
] |
[
"scars occur because the layer of skin 'stem cells' was interrupted. it then has this chasm it needs to fill. Unfortunately, there is no 'base' to rebuild the skin from. Therefore the adjacent skin stem cells start by filling in the base with granulation tissue. Unfortunately this not the same as the regenerating base that's usually there and is unable to produce the normal skin you're looking for. Instead fibroblasts and collagen arrange to fill the gap above the granulation tissue base. This is what the 'scar' is, and it doesn't heal because there is no skin regeneration process in that area any more. This is called healing by secondary intention.",
"Compare that with a superficial cut where the stem cell layer is intact - it is then able to produce new skin from the base up. No scar",
"That's why big wounds are closed with stitches, glue, staples etc. It brings the base layer of skin stem cells close together so the 'chasm' is minimally large. This is called healing by primary intention."
] |
[
"Normally it is random, but in the case of scar tissue all of the fibres are aligned in the same direction.",
"This sounds wrong. Do you have a source? From what I know from muskuloskeletal injuries, tissues like ligaments and tendons are the few that have extremely aligned collagen fibers. The reason they are never the same nor as strong after injury is the scar that fills in has fibers that are very haphazardly aligned. I would be shocked if our skin could remodel itself with aligned collagen, and if it did we would be using people's scarred skin for ligament replacements and they would be near impossible to tear in one direction but not the other, but skin scars are nowhere near that strong, they are even weaker than skin. What would even be the mechanism to align the collagen fibers? In ligaments and tendons patients are instructed to purposefully mobilize the tissues in a certain manner to apply stress in the correct direction to get more of the fibers to align. I would be very surprised if skin, which doesn't even have aligned collagen, was doing this spontaneously. "
] |
[
"What is the effect of bird flu on wild populations of birds?"
] |
[
false
] |
A cursory glance on google/google scholar didn't really answer this question, so I decided to ask it here. Basically I was wondering what the effects of highly pathogenic types of bird flu is on wild bird populations. Does it have significant ecological effects? I am mainly interested in this as it seems that the HPAI variants seem to have originated from domestic bird populations (or so I have been told).
|
[
"H5N8 bird flu has varying mortality rates among different birds, from 5% in some species to 39% in others",
"The effect of the bird flu among wild populations is theoretically similar to the effect it will have in humans if it becomes transmissible which is to say it kills them by the thousands",
"Birds have fewer tools to help them fight pandemics, and humans cull them en masse to make sure it never evolves enough to spread to us",
"Even still, with fewer regulations on bird farms and fewer wild spaces for birds we may yet see a human transmissible bird flu and another human pandemic",
"https://www.cidrap.umn.edu/news-perspective/2017/11/high-wild-bird-death-rates-detailed-dutch-h5n8-outbreaks"
] |
[
"Birds with bird flu exhibit strange behavior, diahrrea, head swelling, and sometimes discharge from the eyes",
"Human flu is comparatively very tame. Some asymptomatic birds have been observed to still die spontaneously after contracting bird flu (likely stroke or blood clot)",
"https://www.petmd.com/bird/conditions/respiratory/c_bd_Avian_Influenza"
] |
[
"Birds with bird flu exhibit strange behavior, diahrrea, head swelling, and sometimes discharge from the eyes",
"Human flu is comparatively very tame. Some asymptomatic birds have been observed to still die spontaneously after contracting bird flu (likely stroke or blood clot)",
"https://www.petmd.com/bird/conditions/respiratory/c_bd_Avian_Influenza"
] |
[
"Why does our sense of humor change as we get older? Specifically why do young kids enjoy slapstick and funny faces?"
] |
[
false
] | null |
[
"Yeah also neat little tidbit a lot of users in this sub reddit have tags next to their names of what they specialize in. I like to think they are full fledged scientists in lab coat speaking to us lessers for their entertainment."
] |
[
"I still laugh at fart sounds and I am a first year medical student."
] |
[
"Do we really gotta get that specific? Especially when this is a subreddit about many different kinds of science."
] |
[
"What is the average distance between individual pieces of \"space junk\"?"
] |
[
false
] |
I've seen the graphics of how much "space junk" is out there and I've also read that space is very large and is easy to underestimate this. My question stems from someone asking when there would be so much space junk that we would not be able to put more into space. So, just how far apart (on average) is the space junk? Does this figure exist somewhere? Without anymore knowledge than seeing a graphic and knowing how large the earth is, my guess would be that on average, individual pieces of space junk are 300 miles apart. How wrong is my intuition?
|
[
"It's probably within three or four orders of magnitude. I'm far too lazy to do the maths right now, but I ",
"worked this up",
" not long ago, based on the number of ",
" in orbit. If you had a couple of numbers, you could adapt the calculations to see how close or how far you are."
] |
[
"Using his numbers I got about 1,600km, which seems about right. Keep in mind that is only how far apart they are on average, at any given moment. "
] |
[
"While your post is interesting and related, for my poor mind it does little to answering my question. My horrible math just told me that they are 3,417,541,557 miles from each other based on your ratios. I'm quite sure I've done something wrong. "
] |
[
"Is the term \"bandwidth\" a dumb term?"
] |
[
false
] |
I have an annoying friend who always says the same complaint about the term "bandwidth" when it comes up in regards to networking. "Bandwidth is a stupid term. It has nothing to do with data rate." Then he goes into a vague, not fully educated explanation in regards to its meaning as used for signal bandwidth. I am certain that he doesn't even know an EM radiation goes about 300 million m/s. He is just regurgitating something a professor told him. Any suggestions on what I could say to shut him up?
|
[
"I see where you are coming from, that is, it is not the most explicit term, but it is not a stupid term. My understanding is that it goes all the way back to Harry Nyquist, who along with Shannon pretty much wrote the book of digital signals.",
"One of Nyquists most important and fundamental discoveries, is the so called Nyquist Rate, which, to quote Wikipedia \"In 1927, Nyquist determined that the number of independent pulses that could be put through a telegraph channel per unit time is limited to twice the bandwidth of the channel\". This is digital signal processing 101. In otherwords, in a communication channel that is subject to a low-pass filter (i.e. high frequency information is removed) the maximum rate that data can flow through is at twice the cut-off frequency of the filter. Moreover, once we know the signal to noise ratio, we can figure out the real world upper bound (Thanks to Shannon). So if we have a wire cable that has a bandwidth of 100kHz, and a Signal to noise Ratio of 10, then it",
"Data rate = BW log2(1+S/N)\nDate Rate = 100e^3*log2(1+10)\nDate Rate = 350 kbit/s \n",
"So when someone says \"My internet connection has a bandwidth of X\" they are really saying \"My internet connection behaves as if it has a bandwidth of X\", because of course, it probably has a higher bandwidth, but the data rate is limited by the ISP.",
"Just in case this was unclear, wires and fibre optics all do have bandwidths. Wires always low-pass filter electrical signals, and fibre optics have bandwidths for various complex reasons.",
"But my advice is to let your friend chill, it's a well accepted term at this point, and has been for 50 years. No one is going to say you are even technically correct at this point. It is now a worth with two meanings, one of which is \"the frequency components at communication channel can sustain\" (original meaning) and the other is \"What is the actual data rate of the communication channel\""
] |
[
"This is a truly great answer. ",
"To be clear though, your friend may or may not actually be correct. It comes down to what he said ",
" The amount of information per symbol is based entirely on the noise distribution, and not changed by bandwidth. If your friend said the ",
" of the channel, instead of data rate, then yes he is correct. But if he used the exact words of ",
" then he is wrong. There is a lot going on here, so I will give you an overview.",
"There are two distinct parts that give us BW log2(1+S/N), the first being the maximum (symbols/second) which you can send symbols over a channel without incurring ISI, which is 2 BW, and the second being the channel capacity (bits/symbol) of a gaussian noise channel 1/2 log2(1+S/N). The channel capacity is not actually a function of the bandwidth. But channel capacity is something devoid of the concept of frequency.",
"The product of these two, giving us bits/second, is BWlog2 (1+S/N). This term is often confused with capacity, which it is not. This is the maximum capacity of the model given we wish to avoid ISI. Thus in practice, the actual bits/second ",
" depend on bandwidth. In fact the relationship is linear.",
"Honestly, though, entering into a debate on this subject should be approached first by jumping into the subject of communications. If you really want to converse on this subject, you will first need to learn ",
"digital signal processing",
" and ",
"information theory",
". Those are the two entry level texts in the field. Although you may be able to find them both by just google searching."
] |
[
"I already responded once, but I am going to use this as a warm up writing for the day. This will be a lot deeper and hopefully with the clarity of someone post coffee. Keep in mind that I absolutely love this stuff, so I might get off track at some points because it is just so gosh darn fun. There is also a word of caution regarding the common (fields outside of information theory) use of information.",
"I fully agree information flowing through a channel is a very interesting concept. The particular name we give that branch of Information Theory, is Shannon Theory. So yes, I share your enthusiasm.",
"The first thing we must do is discuss why you think of bits/event as that formula, later to be defined as ",
", and how to build up to information. For any event which we are interested, it would be desirable to communicate all possible outcomes. Take for instance a coin flip, for which it could land heads or tails. For each outcome heads or tails we may associate a binary string. Examples include 0 for heads and 1 for tails, or the string 01 for heads and 10 for tails. Both of these enumerations though can be used to convey the same number of outcomes, and thus both can be used to completely describe the events. Still, given no errors in the binary string, it is hard to make a case for 01 and 10 over 0 and 1, and intuitively it seems desirable to go with the shorter string for brevity. So lets go with that assumption, we want to enumerate all possible outcomes with this shortest sequence possible. ",
" it would be prudent to consider what we mean by shortest possible string. For instance, lets say I have three events, one with high probability say 15/16, and two with probability 1/32. Now if we were to try and find sequences of the same length to describe all events, we would be left with strings of length 2 (in particular 00 01 10 11). One of these would be unnecessary. Instead if we were to consider sequences of different length, the immediate thing you would do is put the shortest length sequence to the high probability event. In this particular case, I can assign 0 to the event having probability 15/16, and 00, 01 to the remaining events. I could of course, also chosen assignments of 0 and 1,01 respectively to obtain a even shorter code but this code would not be uniquely decodable for repeated outcomes (001 could either be 0 01 or 0 0 1 for instance), but the cost associated with uniquely decodable code compared with its alternative is not overly prohibitive so we shall forget this little tangent.",
"Now we have a goal, to define information as the shortest string possible. And with it enters the entropy function. The entropy of a random variable Y with events y_i, and probability of event p(y_i) is",
"H(Y) = -\\sum_{i} p(y_i) \\log_2 p(y_i)\n",
"and is actually axiomatically derived from a few choice axioms. This equation is all too commonly associated with the information of a random variable. It is not, if anything, it is actually ",
" about the random variable. Now lets go back to what we were looking for, the shortest possible expected length sequence to describe all events. We can define the expected length description as ",
"\\sum_{i} p(y_i) l_i\n",
"where i is the index of the event, and l_i the length associated with event y_i of it (so for the previous example p(y_1) = 15/16, p(y_2) = 1/32 and p(y_3) = 1/32, our lengths in turn were l_1 = 1, l_2 = 2 and l_3 = 2, and our expected length sequence was 17/16). We can now introduce the really really cool thing,",
"\\sum_{i} p(y_i) l_i > H(Y)\n",
"and there always exists a uniquely decodable code such that",
"H(Y) + 1 > \\sum_{i} p(y_i) l_i.\n",
"At this point it is prudent to step back and consider what this means. We began with a reasonable goal of enumerating all possible sequences in the shortest manor possible. We have done this using the function we have termed entropy. ",
" Similarly, lets suppose we have two random variables Y and X, and we want to consider the same question, minimum expected string length needed to describe all events, but this time we know we have already observed X. This quantity is called conditional entropy, and is written H(Y|X). One may think of this as how random an event is given a observation. Like a fisherman saying they caught a X-foot fish, the actual fish has length Y. Clearly the fishermans statement has some impact on the overall distribution of Y but does not fully tell you the actual fish size.",
"Now we can introduce information. In specific ",
". The mutual information can be thought of as how much information Y tells us about X (and vice versa how much X tells us about Y) and is specifically",
"I(X;Y) = \\sum_{i,j} p(x_i,y_j) \\logt p(x_i,y_j)/(p(x_i)p(y_j) )\n= H(Y) - H(Y|X) = H(X) - H(X|Y) = H(X) + H(Y) - H(X,Y).\n",
"Now this formula should make ",
" sense if I have done a good job with my exposition. If not, this may rectify. Prepare for some amount of handwaving. Lets consider the difference between H(Y) and H(Y|X), for this is the formula for mutual information. What do these quantities represent? Well H(Y) is representative of the expected number of sequences to describe all possible outcomes of Y. For a moment consider these outcomes to be nearly equally probable (this extends to differing probabilities as well using some clever use of exponentials and bounds). In this case, the length of all sequences will be roughly equal as well. Clearly the length of the binary sequence and the number of different sequences contained are related. In fact the total number of binary sequences possible for a n-length binary string is 2",
" Thus, because Y can best be represented as a H(Y) length binary string, you would expect there to be 2",
" ",
" sequences associated with Y. The same goes for Y when we consider X, and once again we obtain 2",
" Once again assume there is no variation over the different X=x_i, and for every possible x we now have 2",
" different sequences which may occur. Lets say our goal is to determine how many of these x_i values we can reliably differentiate (which is a reasonable definition for information). If the observations though correspond only to a single value of x_i, we can write the total number of observations as the sum of the observations given event x_i, or",
"2^H(Y) = \\sum_{i} 2^H(Y|X=x_i) = |X| 2^H(Y|X).\n",
"Thus an upper bound is immediately clear, and in particular ",
"|X| < 2^H(Y)-H(Y|X) = 2^I(X;Y).\n",
"This can also be extended to consider overlapping regions but then I have to introduce list decoders (given an observation how many possible sequences are there) and some other terms which can get quite muddy. Suffices to say, I(X;Y) can be thought of as not just a definition of information, but an extremely good definition of information. In fact, the capacity of a channel is the mutual information. "
] |
[
"Why does gunpowder need the three specific ingredients of charcoal, sulfur and saltpeter? What purpose does each ingredient serve?"
] |
[
false
] | null |
[
"Saltpeter (KNO3) is an oxidizer. Charcoal and sulfur are fuels. Together they will burn rapidly (exploding if confined)."
] |
[
"To add to this: You need a oxidizer to start the combustion reaction. In most combustions, like in a bonfire or in an engine, your oxidizer is air, specifically Oxygen. Now Oxygen is a good oxidant, but if you want a faster burn, it's not good enough. That's where nitrates come in. Nitrates are nasty good oxidants."
] |
[
"Oxygen is great, but as atmospheric gas you simply don't have enough. You need it as liquid or solid with the corresponding high density. Liquid oxygen would work, but then you have too cool your explosives."
] |
[
"[String theory] If energy is simply vibrating 1-dimensional points, what powers these vibrations?"
] |
[
false
] |
[deleted]
|
[
"Whoa, there's a lot of words in this question. Energy is energy, it's just a conserved number that doesn't have a physical realization, string theory doesn't change that in any way. But let's talk about particles first in order for you to understand what exactly string theory is about.",
"In string theory, particles are modes of vibrations of tiny strings. Think of a guitar, if you strum one of the strings you will produce a very rich spectrum of harmonics. This spectrum is characterized by a set of integers that are the multiples of the fundamental harmonic. Or in other words, once you strum a string, you can produce a \"zero mode\", which is the fundamental, or you can produce a mode that has twice the frequency, or 3 times the frequency... and so on.",
"A string in string theory is very similar. It has a spectrum, but this spectrum is what you associate with particles. Each particle carries a mass that is the frequency of its associated harmonic. If you strum this string very lightly, you will produce a \"zero mode\", in case it exists. If you strum it harder, you will produce an excitation of the first harmonic... etc etc. But in order for you to produce this first harmonic excitation, you need to give the string a minimum energy, and this threshold energy is the mass. Whatever excess energy you give, will result in moving the string around, which is kinetic energy. But notice that once you give energy for the string to produce this first harmonic, it won't lose this vibrational energy since there is no friction. It will just keep on oscillating forever or until this mode decays through some interaction. So in a sense, you just need to power the initial vibration (which is, give the energy to create the particle), and then if the particle is stable, it will vibrate forever.",
"If you're a distant observer, you won't really observe the tiny string. What you will observe is that if you collide some particles, sometimes the decay result will be a light particle, sometimes it will be slightly heavier, and even slightly heavier, so on... you can observe the \"spectrum\" of the particles and check that it matches what you calculated from the spectrum of the string."
] |
[
"Let's put it like that: once a particle is created, it can exist forever if its stable. But if you want to describe why this particle appeared in the first place, then you need interactions. A particle can't just pop out of nowhere, it needs to have been created in some collision or as a decay process of some less stable particle."
] |
[
"Interactions! Whenever you throw one particle against another (let's say you accelerated a proton at the LHC and threw it against other protons), you have this \"strumming\"."
] |
[
"With all the breakthroughs in genetically engineered plants, what's to prevent us from 'seeding' Mars?"
] |
[
false
] | null |
[
"Plants need a lot of light, water, warmth, and oxygen in addition to carbon dioxide. Mars is very limited in terms of (2), (3) and (4). The need for oxygen and water isn't really something that you can easily engineer out, and the fact that much of Mars is freezing cold makes it even worse."
] |
[
"This has been removed because the question is too broad or too vague. If you’re still curious, please conduct some basic research and resubmit a more specific question.",
"For more information regarding this and similar issues, please see the ",
"FAQ."
] |
[
"This question has been removed because highly speculative in nature. Exceedingly imaginary hypotheticals often invite non-scientific speculations.",
"For more information regarding this and similar issues, please see the ",
"FAQ."
] |
[
"What is the smallest thing we can see with an optical lens (i.e. without an electron microscope) and why is there a limit?"
] |
[
false
] | null |
[
"It depends on what you mean by \"see\". I will assume you mean optical imaging using traditional lensing. In that case, resolution is diffraction limited. Traditional lensing works on the principle of light acting like little bundles of rays that refract through lenses and can be focused. Unfortunately, light is not a little bundle of rays, but is a wave. And waves experience diffraction, meaning that a supposed parallel beam of waves actually spreads out as it travels. ",
"Traditional lensing therefore breaks down when the diffraction gets strong enough that the ray model becomes invalid and the image blurs together. Diffraction decreases as the frequency of the EM waves increases and as the size of the system's collection aperture increases. Therefore, the \"the smallest thing that we can see\" using traditional optical lensing really depends on what frequency and what aperture you are using. Visible light traditional optical lensing systems can only resolve objects that are about 200 nm in size, at best. Going to much higher frequencies, such as X-ray, gives better resolution, but I don't know if X-ray microscopes count as \"traditional\", as you can't just run an X-ray through a glass lens. The best traditional visible-light optical microscope would use incident violet light and as large of an aperture as possible.",
"There are non-traditional imaging techniques that can beat the diffraction limit, but they have their own limitations."
] |
[
"As ",
"/u/cyprezs",
" said, there's a difference between resolving and seeing. A simple way to think about resolving is a two-point system. If we're trying to image two bright points, there's a limit to the separation between them where we can actually tell they're two distinct objects. Two bright dots that are closer together than this (the diffraction limit) look like one object."
] |
[
"chrisbaird gave a great answer about what the smallest thing we can resolve with an optical lens is, but it is important to keep in mind that there is a difference between being able to see something and being able to resolve it. To just see something, all you have to do is to detect light that it scatters or emits, and to that end, there is no limit on how small of things you can optically see. Many labs image single atoms using optical lenses, for instance, despite them being hundreds of times smaller than a wavelength of visible light."
] |
[
"When pizza burns the roof of your mouth and \"skin\" dangles down, what is that? Is it actually skin? Some other type of membrane? Does it scar?"
] |
[
false
] | null |
[
"It's a layer of mucous membrane that's been killed by heat. Not skin, but similar.",
"Wounds inside the mouth tend not to scar too often or very much because most of the tissue in there regrows fast, and is kept moist while regrowing, which prevents scabs (which actually slow wound healing down a bit.)"
] |
[
"It's more susceptible to the environment. Scabs are hard and keep things out."
] |
[
"Why can't the rest of our skin function in a similar manner?"
] |
[
"How are the images on the Voyager probe kept?"
] |
[
false
] |
I've tried researching how they're kept, but all the sources say they're on the phonograph record. Are the images on film, a metal plate, etc?
|
[
"The so-called \"Golden Record\" included on the Voyager is pretty interesting in its own right. The record consisted of gold-plated copper, with a spiral array of grooves encoding all information. As such, the record was an early form of an analog video disk. The basic operation was fairly straightforward, you were supposed to put a stylus on the outer edge of the disk and to turn the disk at 16.7 rotations per minute. The signal you read out would then correspond to a series of frames, each having 512 lines each having about 500 dots. As a result, in 12 seconds you could read out a grayscale image. ",
"So far so good, but now came the tricky part. If this information was to fall into the hands of an alien species, how do you communicate how the record is supposed to work. To help with the process, the engineers who designed the disk came up with the user's manual from hell, ",
"shown here",
". You were supposed to look at ",
"this pictogram",
" and figure out that it corresponded to a unit of time corresponding to the hyper-fine transition in hydrogen. Next, by building up binary numbers in this unit system, you could figure out how quickly you should rotate the disk. Finally, the next series of images was supposed to show how the waveform you read out encoded frames of 512 lines. Easy as pie! ",
"If you want to read more, ",
"this page",
" has a more thorough explanation of the technical details of the disk and its set of instructions."
] |
[
"The signal you read out would then correspond to a series of frames, each having 512 lines each having about 500 dots. As a result, in 12 seconds you could read out a grayscale image.",
"Exactly what I was looking for. I was so confused on how they actually stored the images. Thanks for the explanation! "
] |
[
"Did they test this method using scientists who had no knowledge of what the info meant? I guess it would be impossible to truly test it since anyone capable of solving it would have a concept of record players and scan line image storage, but even so, I'm sure they would have put it through some trials."
] |
[
"Why does highway MPG decrease ~linearly with speed, when the power to overcome air drag goes up v^3?"
] |
[
false
] |
[deleted]
|
[
"The first thing to note is that miles per gallon is not a linear quantity; for example, which increase in fuel economy will give you save you more gas over a distance of 10,000 miles?",
"a) 10 to 11 mpg",
"b) 33 to 50 mpg",
"It's a trick question; they both would save you about 100 gallons over 10,000 miles.",
"Similarly, if we look at the Mercury Mountaineer's fuel economy at three different speeds: 23.8 mpg @ 55mph, 21.2 mpg @ 65 mph, and 17.8 @ 75 mph.",
"Over the course of 100 miles, the Mountaineer would burn 4.20 gal @ 55 mph, 4.71 gal @ 65 mph, and 5.62 gal @ 75 mph. If you plot these in Excel, you can see that it does not look like a very linear trend. This confusion with differences in miles per gallon is a big reason why there is a push to move towards a standard like gallons per 100 miles, but I digress.",
"The next issue is that there are only three points of data, which is the absolute minimum number of data points required to establish a trendline. Ideally, you'd want more data to firmly establish what kind of relationship you're looking at with fuel economy vs. speed.",
"Finally, cars have different efficiencies in different operating conditions. This is due to a number of factors, too many to accurately account for just by looking at this data."
] |
[
"Where are you getting that drag increases at the cube of velocity?",
"Power, not drag. Power due to drag is force times velocity, giving you another factor of v."
] |
[
"Where are you getting that drag increases at the cube of velocity?",
"Power, not drag. Power due to drag is force times velocity, giving you another factor of v."
] |
[
"What causes the chaotic rotation of celestial bodies such as Pluto's moon Nix or Saturn's moon Hyperion?"
] |
[
false
] |
is a simulation of the rotation of Pluto's moon Nix. According to wikipedia, it's rotation can only be predicted 30 days into the future before it becomes too chaotic. What causes this chaotic rotation?
|
[
"Rotation about an object's intermediate principal axis in unstable. This is known as the ",
"tennis racket theorem",
", since it can be observed by holding a tennis racket face up and throwing it into the air so that it will spin end over end once to allow it to be caught by the handle. There's a good video of the effect demonstrated on the International Space Station.",
"If the moons were isolated from other objects, we might be able to predict the rotation as long as we know enough about them to accurately model their principal axis, mass, and rotation speeds. Chaotic systems have subtle dynamics that are below the threshold of what we can measure. Over time, the effect of not modelling these dynamics causes our model to accumulate errors that get amplified as our model gets more and more off track until its predictions completely diverge from observations.",
"The gravity of nearby objects would act on the moon in subtle but haphazard ways as it constantly reverses direction and flips, affecting the rotation in ways that we just can't account for with enough accuracy. So the errors compound until the model fails, after about 30 days of simulated time."
] |
[
"It's a many-body problem. We can only fully solve 2 body problems - to approximately solve more than 2 (eg the planets) that we need assumptions like one body has essentially all of the mass (the sun).",
"When you have a dynamic system with more than 2 bodies, and the masses of more than one are non-negligible, then we simply can't \"solve\" it using mathematics, we have to simulate it instead.",
"The simulation is dependent on the initial conditions (position, velocity, acceleration, mass, moments of inertia etc) of each body, and if any are out, then the simulation will start off accurate but eventually be too inaccurate to use as small errors compound. ",
"The Pluto system has a small planet and large moons, so you can't assume one body has most of the mass like the Jovian one. Also, we simply can't measure the position/speed of the moons accurately from so far away, and we don't know what the mass distribution within each body is (ie, do they have spherical density? Is their mass lumpy beneath the surface?)",
"edit: A bit more technically, there's a feedback loop involved. The motion of the body depends on where the other bodies are, and the motion of the other bodies depends on where the first body is. With a two-body system this is solved easily. With a normal planetary system it can be mostly solved because the motion of other small moons doesn't depend on the position of any one of them, it essentially just depends on the position of the planet alone, and the motion of the planet doesn't really depend on the tiny moons (which breaks the feedback)"
] |
[
"It is not about working out the math, it is proven that you can not analytically solve the problem for more than two bodies."
] |
[
"Can optical circuits depend on when you check them?"
] |
[
false
] |
I've been absorbing information about quantum mechanics from various places, trying things out on paper, and I wanted to make sure I wasn't going off into lala land. So, consider . It's a bit like a with a cycle added to cause the photon to "decay" out of the circuit instead of exiting immediately. Note that the detectors don't contain information about when the photon was recorded, only if it was recorded. Also, suppose that it is not interacting with the outside world . The light source releases exactly one photon, we wait, then we check the detectors (at which point the system interacts with the outside world, of course, but before that it is isolated). My question is this: does the amount of time you wait before checking the detectors affect the proportion of times that the bottom detector goes off? My current understanding is that it does. If you wait a long time before checking then the result is basically equivalent to not having the loop, in which case the right detector never goes off due to destructive interference (because the detectors are not time-sensitive). But if you check early, say after three cycle periods, then your interaction creates a difference between earlier and later photon arrivals that reduce the destructive interference and so the right detector would go off a non-negligible proportion of the time. Is this understanding correct? In the idealized abstract scenario? In real experiments? Where can I find resources to answer this sort of question?
|
[
"Maybe I should go through the math of why I think they differ. Fair warning: this could be completely misguided.",
"The system starts out with a single photon being emitted, with the default amplitude of 1:",
"1 * |PhotonEmitted>\n",
"The photon travels to the first half-silvered mirror, where it is split. The part that goes through the mirror has its amplitude multiplied by sqrt(1/2) and the part that is reflected has its amplitude multiplied by sqrt(-1/2):",
"sqrt(1/2) * |PhotonHeadingRightwardTowardsCenter> + sqrt(-1/2) * |PhotonHeadingDownwardTowardsBottomLeft>\n",
"I'm going to use the shorthand that s = sqrt(1/2) and i = sqrt(-1). I'm also going to shorten the state names a bit:",
"s |RightwardToCenter> + i s |DownwardToBottomLeft>\n",
"As you can see, the photon is now in a superposition of two states. One component will hit the center half-silvered mirror, using the same rules as before, and the other will hit the bottom left mirror, multiplying its amplitude by sqrt(-1):",
"s^2 |RightwardToRight> + i s^2 |DownwardToLastMirror> + i^2 s |RightwardToLastMirror>\n",
"Two components of the superposition are heading towards the last mirror, but from different directions and with different amplitudes. Iterating again, they'll end up reaching equivalent states:",
"i s^2 |UpwardToTopRight> + (i s^3 |BottomDetector> + i^2 s^3 |RightDetector>) + (i^2 s^2 |RightDetector> + i^3 s^2 |BottomDetector>)\n",
"When the same state appears multiple times, we add up the amplitudes contributing to it (interference). The above state is equivalent to this:",
"= i s^2 |UpwardToTopRight> + (i s^3 + i^3 s^2) |BottomDetector> + (i^2 s^3 + i^2 s^2)|RightDetector>\n~= 0.5 i |UpwardToTopRight> - 0.15 i |BottomDetector> - 0.85|RightDetector>\n",
"To 'check' the system now, we would square the amplitudes of the magnitudes to get the probabilities of being in each state:",
"~25% in cycle, ~2% bottom detector went off, ~72% right detector went off [note: the extra percent was lost in the rounding]\n",
"However, let's assume we didn't mess up the system by doing that and continue iterating it's state. We were here, I believe:",
"= i s^2 |UpwardToTopRight> + (i s^3 + i^3 s^2) |BottomDetector> + (i^2 s^3 + i^2 s^2)|RightDetector>\n-> i^2 s^2 |LeftwardToTopCenter> + (i s^3 + i^3 s^2) |BottomDetector> + (i^2 s^3 + i^2 s^2)|RightDetector>\n-> i^3 s^2 |DownwardToCenter> + (i s^3 + i^3 s^2) |BottomDetector> + (i^2 s^3 + i^2 s^2)|RightDetector>\n-> i^4 s^3 |RightwardToRight> + i^3 s^3 |DownwardToLastMirror> + (i s^3 + i^3 s^2) |BottomDetector> + (i^2 s^3 + i^2 s^2)|RightDetector>\n-> i^5 s^3 |UpwardToTopRight> + i^3 s^4 |BottomDetector> + i^4 s^4 |RightDetector> + (i s^3 + i^3 s^2) |BottomDetector> + (i^2 s^3 + i^2 s^2)|RightDetector>\n= i^5 s^3 |UpwardToTopRight> + (i s^3 + i^3 s^2 + i^3 s^4) |BottomDetector> + (i^2 s^3 + i^2 s^2 + i^4 s^4)|RightDetector>\n",
"This is where the detectors not being time sensitive was important. If they marked down the arrival time of the photon, then the detector states would be distinct (|RightDetectorAtTick3>, |RightDetectorAtTick5>, ...) and not interfere.",
"At this point I can see the pattern of how the loop will decay, and can figure out that the system will approach this state:",
"...> (i s^3 + i^3 s^2 + i^3 s^4 + i^3 s^5 + i^3 s^6 + ...)|BottomDetector> + (i^2 s^3 + i^2 s^2 + i^4 s^4 + i^4 s^5 + i^4 s^6 + ...)|RightDetector>\n= i (s^3 - s^2 - (s^4 + s^5 + s^6 + ...))|BottomDetector> + (-s^3 + -s^2 + (s^4 + s^5 + s^6 + ...))|RightDetector>\n= -i |BottomDetector>\n",
"Meaning the eventual state, if you check much later, is:",
"100% Bottom detector went off\n",
"(Oh, whoops, when I asked the question I forget that the cycle flipped the amplitude and made the destructive interference occur on the right detector.)",
"As you can see, that state is different from if we checked early, and has even \"erased\" the right detector going off."
] |
[
"What do you mean by a detector that is \"not time sensitive\"? Real detectors (e.g. an avalanche photodiode) can certainly give you the photon arrival time.",
"My intuition would say that at late times only photons that circulated in the loop would contribute to the observed signal, so you would observe an equal number of counts at the bottom and right detectors."
] |
[
"A detector that transitions to the exact same state no matter when a photon is received, allowing later receives to interfere with earlier ones.",
"I think the resolution to the question is \"the detectors are impossible\", meaning no interference. They violate reversibility."
] |
[
"How is it that gravity slows the passing of time?"
] |
[
false
] |
While looking into general and special relativity I read that gravity can slow the passing of time. Is that why time is considered relative, because this happen slower in different settings? How does that disprove the Euclidean view, and why is it not simply just understood as a property of physics that things just go slower with more gravity? Or am I just all wrong on my understanding of all of this...
|
[
"The speed of light c can be derived theoretically from electromagnetism, simple experiments which can be done in any inertial frame allow you to calculate the constants epsilon_0 and mu_0. The expression for c is this, \nc= 1/sqrt(epsilon_0 * mu_0). Because the experiments you perform to find epsilon_0 and mu_0 are independent of reference frame, the speed of the electromagnetic waves must also be independent of the reference frame. Hence c = constant."
] |
[
"Hmm, well firstly you will never feel your own time to slow down regardless, you cannot change your position in a gravitational field and see your watch slow down, you will always measure time ticking at a rate of one second per second. You will observe other clocks ticking at different rates dependent on their position in a gravitational field and their velocity relative to you. There is time dilation in General Relativity due to the gravitational fields and there is time dilation in Special Relativity. In Special Relativity, the constancy of the speed of light between reference frames means that time ticks at different rates in each reference frame. ",
"To see this think of the path a light beam is observed to take if you are in a train and you shine it from the floor to the ceiling, it's a straight line right? Now imagine watching someone doing that while you stand on then platform, for each unit the light beam travels upwards you also see it travel to the right a small amount, so you will say the light beam is moving diagonally, this means that the diagonal path will be longer than the path straight up. The important point is that in these two cases the speed of light is the same, therefore changing the distance will imply a corresponding change in the time taken to travel that path (this is needed to keep the speed of light constant). ",
"I hope this isn't too unclear."
] |
[
"Gravity is the curvature of spacetime.",
"In a gravity well the photon needs to travel a longer distance than somewhere absent a gravity well. However, relativity says that we will ",
" measure the speed of light as a constant speed. The only way the photon can traverse this longer distance (which we usually cannot perceive) is to change the speed our clocks run at. If they run slower then the photon in the gravity well can go from A --> B and be measured as light speed.",
"Remember, if we take a yard stick and take it to deep space, far from any gravity well, we will measure its length as 1 yard. If we take it to just outside a black hole we will still measure its length as 1 yard. The photon",
"While the effect on earth is small it has been tested (they took two accurate clocks and placed one on the ground and one on top of a water tower and in time the two differed)."
] |
[
"Why do my bones ache when I get really sick?"
] |
[
false
] |
[deleted]
|
[
"usually when people with a flu describe \"bone pains\", its Myalgia, which is a horrible ache in the muscles, often the big groups; shoulders, back, thighs. ",
"I cant describe the exact chemistry of it, but these things are usually part of a generalized systemic response, often modulated by inflammatory mediators and probably WBC activity. "
] |
[
"Joint pain is also a common flu symptom, technically called ",
"arthralgia",
", and is a result of a viral infection.",
"If there is accompanying fever, it is more likely to be an influenza virus than a cold virus."
] |
[
"When the body is fighting an infection it's common to see a set of characteristic behaviours (sickness behaviour) and physiological responses. This is to help to body fight the infection, one of these may be hyperalgesia by the release of IL-1. This increased sensitivity to nociception may explain part of the aching feeling.\nSource: ",
"http://www.ncbi.nlm.nih.gov/pubmed/8221116"
] |
[
"Generally in sci-fi movies, when 0g is activated, objects around the actors start floating with no force pushing them \"up\", is this scientifically inaccurate?"
] |
[
false
] | null |
[
"Not scientifically inaccurate, but suspiciously convenient. In zero gee, or free-fall as on the ISS, seemingly very little force is needed to push things around. Notice in videos from the ISS how everything is tied to the walls in some way, and when they try to \"hang\" a microphone, no matter how carefully they place it, it immediately starts wandering off. Even air movement is enough to stir things up.",
"In movies, though, the fact that ",
" starts flying around is a bit annoying. People certainly would immediately take off, from the force of their feet unconsciously pressing against the deck when gravity was still \"on.\" But an object that was lying on a table, for instance, would not likely start floating away immediately, but would be obviously \"wobbly\" and would soon begin tumbling.",
"What really annoys me is when actors pretend to be weightless by moving in slow motion. Work on your sense memory, people."
] |
[
"If you're specifically referring to rocket launches where microgravity starts when the engines cut off, the way that works is this:",
"During the rocket burn, you are being accelerated forwards by some amount (let's call it a 1 G burn, 9.8 m/s acceleration.) Your body is being compressed back into your seat by that acceleration, same as if you were laying on a hammock at home.",
"The engines cut off. Your flesh, previously compressed by your mass being shoved forward, now is free to rebound; that compression can provide some small forward push assuming that you were just laying on the seat instead of strapped down. Other unsecured objects that were compressible would have similar rebound. Also, on most rockets, there is a lot of vibration during burns; those vibrations would end up leaving all unsecured items with some random remaining vector at the time of engine cutoff.",
"A contributing factor for humans or animals would also be that we tend to apply muscle force to counteract any external forces; sudden changes in those external forces take time for us to change the muscle force applied, resulting in motion immediately after a sudden change in forces.",
"If instead of that kind of end-of-burn event you're talking about cutting off an artificial gravity source, the compression and muscle tension effects I mentioned would still apply but, depending on what fictional gravity source you're using and how it failed, the vibration/random vector effect might not exist."
] |
[
"I'll assume your question takes place on a spaceship, far away from the gravitational influence of any planets or stars, with 'artificial gravity' which is then suddenly 'turned off'.",
"To understand how object will behave in this scenario, imagine you had a weight resting on a spring, such that the spring is compressed, but not completely. The weight is pulled down by the artificially gravity, compressing the spring more and more until the spring is pushing back on the object with the same force that gravity is pulling down on it. So, when the artificial gravity is turned off, there is suddenly no gravitational force countering the force of the spring and the spring will push the object upward as it decompresses.",
"The same thing will happen to any object resting on a surface, say, the floor. Though not as obvious as with a spring, the floor is ",
" deformed by the gravitational force from a mass resting on it. (This is true of everything from trampolines concrete.) So, when the gravity is 'turned off' the same thing will happen as did with the spring: the ",
"normal force",
" from the floor will suddenly lose its gravitational counter-force, and the floor will push any object resting on it away as it deforms (reforms?) back to its original shape."
] |
[
"If neanderthals and early humans mated and produced offspring, wouldn't that require that they are actually the same species"
] |
[
false
] |
Neanderthals and early humans interbred . Also, we group a species by their ability to mate and produce fertile offspring (wolves and dogs are the same species). Wouldn't that mean that these two species were actually the same species?
|
[
"Check the first couple sentences in wikipedia: ",
"http://en.wikipedia.org/wiki/Species",
"In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. ",
", the difficulty of defining species is known as the species problem. Differing measures are often used, such as similarity of DNA, morphology or ecological niche. Presence of specific locally adapted traits may further subdivide species into \"infraspecific taxa\" such as subspecies (and in botany other taxa are used, such as varieties, subvarieties, and formae)",
"So, that's not a strict definition."
] |
[
"There is more that goes into the definition then just the ability to interbreed. The line that defines one species from another is subjective and is drawn on a case by case basis. Different scientists will draw the line in different places. Many factors go into deciding where this line should be. I will give you an overview on speciation in case you are not familiar with it. Basically we can look at speciation in three stages.",
"Two populations are part of the same species, all individuals can interbreed. Through several possible mechanisms mainly: (allopatric, sympatric speciation or parapatric) these two populations begin to diverge, not necessarily in physical appearance but more importantly in behavioural and sexual compatibility.",
"You have two populations that are diverging but for a time can still interbreed. They may create hybrids, but these hybrids are less suited, or less fit to the environment. They are selected against or they become increasingly rare. If selective pressures remain the same over the course typically of many hundreds of generations (see: phyletic gradualism , for exceptions see: punctuated equilibrium) then these two populations will continue down the 'path' of speciation. ",
"At some point enough differences have accumulated between the two populations such that they can no longer interbreed or produce viable offspring.",
" This helps us decide what a 'species' should be.",
": The two populations can no longer physically meet (separated by a mountain range, inhospitable ecosystems in-between the two suitable ranges, a river), the penis cannot fit into the vagina, the sperm cannot penetrate the egg. The date, time or place of mating is different, behaviourally they are different: mating rituals differ...",
": Even though the sperm may be able to penetrate the egg, chromosomal differences are so large that the embryo aborts itself. Chromosomal differences are very large, any hybrid produced is sterile, if hybrids are fertile they die before they can reproduce because they have a large amount of defects....",
"In biology and specifically, genetics, the term hybrid has several meanings, all referring to the offspring of sexual reproduction. There are many types of hybrids but the two that refer directly to the issue of humans and neanderthals are this:",
"Hybrids between different subspecies within a species (such as between the Bengal tiger and Siberian tiger) are known as intra-specific hybrids. These are/can be very common. Subspecies are another subjective matter, and usually a set of criteria need to be met, such as two populations of a species living in two different areas where gene flow between them is very very low, or becoming non-exsistant. Or that it is obvious that sexual and behavioural barriers to reproduction are being produced. Or that hybrids between the two subspecies are have less-vigour and are dying/ not suited to their environment.",
"Hybrids between different species within the same genus (such as between lions and tigers) are sometimes known as interspecific hybrids or crosses. These are less common, but still very easy to produce in zoos if the ranges of the animals do not overlap naturally. It is possible that humans and neanderthals were capable of hybridization especially in light of the DNA evidence.",
"In our case when we are talking about neanderthals or other members of the genus homo we are talking about either hybrids between different subspecies or hybrids between different species. Just because you can hybridize does not make you the same species. Many people argue the the cultural differences between humans and neanderthals as well as their relative geographical isolation meant that any interbreeding events were relatively rare. Only a few such events could have resulted in the transfer of the DNA expressed in the study. It does not mean humans were breeding with neanderthals frequently. I argue that we are separate species that retained the ability to interbreed but because of external barriers (behavioural, cultural and geographical), reproduction events were rare.",
"Being able to breed with our ancestors or other homo species alive at the time does not take away from our 'human-ness' it only tells us that either:",
"a. we were subspecies",
"b. we were species that were on the road to divergence, but we still retained the ability to interbreed.",
"In our case, it is possible neanderthals died out before true separation took place, however that does not take away from the fact that 1. the species were diverging and 2. We are here and they are not. This likely puts us into the camp of being separate species e.g. b"
] |
[
"Again, people could argue this a number of ways. There are several things to consider. As of now, ",
"the dog",
" - (Canis lupus familiaris), is a subspecies of the gray wolf (Canis lupus). \"The domestic dog was accepted as a species in its own right until overwhelming evidence from behavior, vocalizations, morphology, and molecular biology led to the contemporary scientific understanding that a single species, the gray wolf, is the common ancestor for all breeds of domestic dogs. In recognition of this fact, the domestic dog was reclassified in 1993 as Canis lupus familiaris, a subspecies of the gray wolf Canis lupus\"",
"This is because all dog breeds can interbreed with wolves. But as you suggested some morphological problems might arise between small dog breeds and larger counterparts. First it is important to note that breeds are not a viable definition. \"Despite the centrality of the idea of \"breeds\" to animal husbandry, there is no scientifically accepted definition of the term. A ",
"breed",
" is therefore not an objective or biologically verifiable classification, but instead a term of art amongst groups of breeders who share a consensus around what qualities make some members of a given species members of a nameable subset\". ",
"This is because we artificially select for certain traits, but if dogs were left to their own devices likely no such traits would arise. i.e. dogs would be more homogenous in appearance and behaviour but perhaps certain populations would be better suited to their local environment. We just sped up the process so to speak and made it really extreme - more extreme then nature would likely allow.",
"We can see this in the extreme example of the bulldog: \"Some dog breeds have acquired traits through selective breeding that interfere with reproduction. Male French Bulldogs, for instance, are incapable of mounting the female. For many dogs of this breed, the female must be artificially inseminated in order to reproduce\". Other breeds a small female who is inseminated by a large-breed male results in pups that are too big for the female and so the female requires a c-section. In nature it is unlikely that such extremes would ever come to fruition - namely because you can't have artificial insemination in nature.",
"So perhaps humans are creating new species, from our own desire to create extreme traits. These traits are usually detrimental to the dog, cause health and reproductive problems. So many would argue that these are not considered species - but more anomalies. Time will only tell in terms of our ability to breed dogs into separate species. But so long as we continue to artificially cross breeds then they will likely remain one species as they will likely retain their ability to have pregnancies that come to term. However, if we stopped artificially cross-breeding very unlike breeds then perhaps those extremes would speciate - or they would die out (more likely this option). ",
"classified under the same species when many dogs will not mate with wolves because of selection as well as physical and geographical limitations.",
"Because we know that all dogs retain the ability to breed with each other they are classified together. And while all dogs can breed with wolves they are somewhat different in that they are domesticated so they are a 'subspecies'. The definition of a subspecies is also made on a case to case basis - in this case it is 'domestication' that separates the two. So they retain the ability to interbreed but they are different enough to warrant a subspecies classification. i.e not all classifications have to do with the ability to interbreed."
] |
[
"How bad is pure Nicotine for humans (without the tobacco/smoke)?"
] |
[
false
] |
[deleted]
|
[
"In Sweden many people (more tham a million at least) use \"snus\" pouches of tobacco under your lip which have twice the amount of nicotine of cigarettes. We have looked hard for harmful effects and found very few, it might raise your risk of mouth cancer but that risk is very small to begin with. ",
"So as long as you don't OD on it, nicotine itself is not particularly harmful. ",
"As an aside I might add that snus is banned by the EU (Sweden has special permission) and that is ridiculous and stupid."
] |
[
"Interesting. Is chewing tobacco permitted in the EU? It does increase the chance of mouth cancer quite significantly, but it sounds like the tobacco in Snus is contained and not masticated. "
] |
[
"Snus comes in these little packets(as far as I know of the brands/varieties). \nSo yes it is contained and not masticated."
] |
[
"Why is it relatively cheap and easy to make Canine Rabies Vaccines while it is very hard and expensive to get a human Rabies Vaccine?"
] |
[
false
] | null |
[
"The human rabies vaccine is typically given after a bite, not before. Post-exposure, the vaccine will need to be given with a dose of rabies immunoglobin (rabies antibodies). This is the expensive part. It is derived from human blood, which needs to be screened for any diseases beforehand, and the antibodies themselves are hard to come by in the general population because so few people have gotten the rabies vaccine.",
"Edit: just to clarify, many people who work in certain fields (e.g. vet clinics, animal shelters, wildlife rehab centers) do get the rabies vaccine as a precaution. If you live in an area with a lot of wild animals, consider getting the shot, too. If you aren't at risk or potentially exposed to it, you don't typically need it. ALSO, as a commenter below me said, make sure you seek medical attention after any potential animal bite/scratch, even if you don't see a mark, and even if you are vaccinated for rabies.",
"With that said: ",
"don't forget to sign up for the annual Michael Scott's Dunder Mifflin Scranton Meredith Palmer Memorial Celebrity Rabies Awareness Pro-Am Fun Run Race For the Cure!"
] |
[
"Does this mean if you’ve gotten the vaccine your blood can be used to help make the antibodies? I mean like as an ordinary rabies vaccinated citizen, is there a way I can help?"
] |
[
"I looked it up and it seems like certain plasma donation centers specifically seek people with recent rabies vaccines. I also noticed that I might not qualify right now due to other adventure travel (malaria risk). I’ll definitely keep it in mind for the future if I stay up to date with my boosters and stay out of the skeeter zones."
] |
[
"Ask Anything Wednesday - Biology, Chemistry, Neuroscience, Medicine, Psychology"
] |
[
false
] |
Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...". Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists. Please only answer a posted question if you are an expert in the field. . In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away!
|
[
"What species of mammal dies of starvation in the wild most frequently relative to death by other causes?"
] |
[
"Seems like sea lions maybe. I wouldn't expect it to be anything lower in a trophic pyramid (e.g. prey animals), because those are more often eaten."
] |
[
"How come sleep paralysis tends to predominately occur when laying on your back while sleeping?"
] |
[
"How much, if at all, have covid vaccines been improved since public release?"
] |
[
false
] |
This question applies to the vaccines available to the public. Are we still on version 1.0? Have formulas been improved as more variants are researched? Have we even made it to 1.0 considering that they were released under emergency release guidelines? Here in the US I only hear about Pfizer, AstraZeneca, and J&J. What are other promising vaccines and how do they stack up to the 3 I mentioned? Are other less reputable countries, like China and Russia, reporting advances in their vaccines and has anyone been able to verify the claims?
|
[
"You forgot about moderna. And from my uninformed point of view, I would think once you get a medicine approved by the FDA you can’t really modify it without having to go through the approval process again, that’s what would make sense to me at least. So id gander we’re still using the same version of the vaccines that was first released"
] |
[
"So far, none of the vaccines on the market have changed their formulations in any significant way. I assume, that minor production details may have changed to optimise yields and so on, but not to an extent that affects final product. ",
"BioNTech/Pfizer, Moderna and AstraZeneca are working on a booster against South African variant, but seeing as that has been gradualy driven down by the Delta, it's hard to say what will happen. Moderna is also working on a refrigerator-stable mRNA-1283."
] |
[
"The vaccine formulation and production process is approved, which is a lengthy process. Once approved, the production protocol and formulation cannot deviate from what has been approved. Each year, the new vaccines then undergo an accelerated approval process.",
"For completely new influenza vaccines, they need to go through the usual lengthy approval process first. For example, the FluMist had to go through its own approval process eventhough traditional influenza vaccines are already approved and on the market.",
"It's also worth noting that the way the influenza vaccine annual approval is set up is an exception to the usual process."
] |
[
"Would the sun be brighter if we could see UV rays?"
] |
[
false
] |
I'm in Physics 30 and recently have been learning about light waves. I understand that our visual spectrum is between infrared and ultraviolet, but hypothetically, if our spectrum could expand to view ultraviolet light, would the sun appear brighter due to the UV coming from it? All answers are appreciated, just started learning the basics of waves and struck some curiosity!
|
[
"Not really. UV radiation makes up ",
"less than 10% of the sun's light",
" at ground level: the majority of UV light is absorbed by the atmosphere. To give you an idea of how minor the effect would be, that's comparable to the change in brightness ",
"between July and January",
" due to Earth's elliptical orbit."
] |
[
"There is no qualitative difference between sunlight in the winter and summer. It's really hard to say for sure whether your personal experience was real or just observational bias. There are many factors which might contribute to what you describe:",
"1",
"2",
"But again, it's really impossible to say how much of what you describe is a real effect, except to say that there is no difference in the spectrum of sunlight between seasons."
] |
[
"I noticed that in the summer, colors are more vibrant on a sunny day and in winter it seems like colors have a duller look with a slightly blueish tint. Am I seeing things? "
] |
[
"Does artificially restricted breathing improve aerobic (or some other) capability like training weights would?"
] |
[
false
] |
I'm sorry, but I couldn't think of a more succinct way of putting it for the life of me! My question is this: if someone were to use, say, a gas mask while doing aerobic exercise, would it have any benefits at all? Would it be detrimental? Have no effect? By the term "training weights" I used in the title, I mean weights like the ones martial artists might use on their arms while training. I don't know if the example can even be applied to my question, but it's the closest analogue I can think of. The background to my question is practical - during service I used to go jogging with a gas mask on, and I enjoyed it. If I recall correctly, the one I was using let about 70% of air in compared to your normal breathing effort without it (because of the resistance of the filter). I've been curious about this for a long time, but I haven't really known who to ask.
|
[
"This is exactly what I was looking for. Thank you!"
] |
[
"This is exactly what I was looking for. Thank you!"
] |
[
"You could diminish oxygen, which would be like training at altitude. "
] |
[
"What's the \"lifetime\" of a water molecule?"
] |
[
false
] |
I saw on my Facebook feed just now, and it got me thinking. How long does the average water molecule last? I know that whenever hydrogen is burned, it combines with oxygen and the byproduct is water. I know that electrolysis and other water splitting processes happen all the time as well. And finally, there are nuclear processes that cause atoms to fuse and break apart happening too. So what are the chances that ANY water molecule has lasted 65 million years, intact, much less existing within my body right now?
|
[
"The chances are effectively nill. Water continually autoionizes.",
"http://onlinelibrary.wiley.com/doi/10.1002/bbpc.19550591020/abstract",
"This gives a figure of each water molecule doing that once every ten hours."
] |
[
"In nature, photosynthesis is the only (large scale) process that splits water into Hydrogen and Oxygen",
"It might be the only one splitting water in oxygen and hydrogen, but not the only one using up water. Proteins, fats and starch all hydrolyze, that is, undergo decomposition by reaction with water. ATP is continuously broken into ADP and phosphate, destroying a molecule of water in the process. While each of these processes happen in both directions, producing around the same number of molecules that they destroy, it is not the same water molecules that are produced.",
"In addition to this, the process 2 H",
"O <-> OH",
" + H",
"O ",
" goes on continuously in any liquid water, meaning that a given oxygen atom is unlikely to be attached to the same to hydrogen atoms for long.",
"Note: I can't load the picture in the original post, so please excuse me if I am missing the whole point of this discussion"
] |
[
"In nature, photosynthesis is the only (large scale) process that splits water into Hydrogen and Oxygen",
"It might be the only one splitting water in oxygen and hydrogen, but not the only one using up water. Proteins, fats and starch all hydrolyze, that is, undergo decomposition by reaction with water. ATP is continuously broken into ADP and phosphate, destroying a molecule of water in the process. While each of these processes happen in both directions, producing around the same number of molecules that they destroy, it is not the same water molecules that are produced.",
"In addition to this, the process 2 H",
"O <-> OH",
" + H",
"O ",
" goes on continuously in any liquid water, meaning that a given oxygen atom is unlikely to be attached to the same to hydrogen atoms for long.",
"Note: I can't load the picture in the original post, so please excuse me if I am missing the whole point of this discussion"
] |
[
"Realisticly, how far away are we from a robot that would be indistinguishable from a human being?"
] |
[
false
] |
I mean in terms of appearance and conversational ability. I'm not expecting this to be a specific timeframe, probably extremely vague, but I'm just very interesting to hear an expert's take on it.
|
[
"It can't be impossible. Surely we are just biological machines? We are proof that it is possible.",
"Or am I wrong?"
] |
[
"This is hundreds, if not thousands, of years of. ",
"I would have to disagree with that. One thousand years ago the height of technology was the mill. From the mill to the microchip is a bigger jump by many orders of magnitude than from already having robots that are beginning to mimic humans, to them succeeding at it. The biggest challenge would be passing the Turing test of course, but quite a few researchers feel that AGI is somewhere between 20 and 50 years away, and having looked into it myself, I am inclined to agree. "
] |
[
"Asking for a timeframe for computerized advancement is just asking for trouble. There's probably no other technology which people have predicted more incorrectly."
] |
[
"How do redox reactions actually work?"
] |
[
false
] |
[deleted]
|
[
"I don't know the mechanism there offhand, you'd have to look in the academic literature. Most likely it involves a number of pathways and intermediates. But the simplest would seem to be Mg + H2O +H",
" --> MgOH + H2, followed by MgOH + H2O + H",
" --> Mg(OH)2 + H2"
] |
[
"I didn't think of it that way. Probably why my searches for H-metal bond turned up nothing."
] |
[
"Well those (metal hydrides) exist. It's a possible intermediate too, although it seems unnecessary because if you have a proton and a water molecule, you can form the hydroxyl and H2 almost directly. Electrons move fast relative everything else."
] |
[
"Before the Riemann Sum was devised, how did people understand/visualize the integral?"
] |
[
false
] |
If differentiation and integration were practically invented/discovered together, how is it that the Newton Quotient was thought of but not the Riemann Sum? What did it even mean to integrate without the limit of the Riemann Sum?
|
[
"Mathematicians had been doing ",
" Reimann sums for centuries before Reimann came on the scene. In fact, Archimedes had found the area of a section of a parabola using an infinite series of triangles milennia before Reimann sums were invented. ",
"As far as integration goes, Newton had done something similar to Reimann sums in his calculus, but it wasn't mathematically rigorous. Reimann made it rigorous. What that meant for Newton was while his method was superbly useful and arrived at the correct results, it didn't do so in a rigorously logical fashion. "
] |
[
"You might be interested in The Historical Development of the Calculus by C H Edwards. A lot of libraries have it and it offers some really interesting insights to this kind of mathematical development."
] |
[
"\"If I have seen further it is by standing on the shoulders of giants\"",
"-Isaac Newton",
"This statement holds a lot of truth in mathematics (and thus all further abstracted sciences). Great examples of this can be Euclid's Elements which only established a rigorous and orderly arrangement of the rules which already existed. Fouriers paper on the superposition modeling of a signal took 3-4 papers before it was consider rigorous enough and we are still trying to figure out what to do with Mandelbrots grand ideas."
] |
[
"Why do mountains have peaks instead of having \"flat tops\"?"
] |
[
false
] | null |
[
"Largely because of erosion. Almost all erosional processes that are important in mountain environments (e.g. rivers, glaciers, hillslope diffusion, mass wasting) have a slope dependence, i.e. the rate at which they occur is at least partially dependent on slope and they generally proceed faster when slope angles are greater. This really ties back to them all being ultimately driven by gravity.",
"Now, if we ignore other factors that influence erosion rate and just say that erosion rate in a landscape is proportional to slope and we imagine a high elevation, flat topped region with steeper slopes surrounding it (i.e. a plateau), it quickly becomes clear that this is unstable. At the boundary between the steep part and the flat part, there is a large erosion rate contrast (i.e. high where slopes are high, low where slopes are low) which will essentially 'eat' into the flat part pushing the boundary between the steep and the flat part into the flat part (and replacing flat topography with steep topography in its wake). Now, this isn't just happening in one place, it's happening in all places around the boundary between steep and flat terrain, progressively shrinking the flat part of the terrain. This is basically the process of cliff retreat, with probably the most clear examples ",
"being what we see in areas with layered rocks",
", though this example is complicated, as there is a lot of interesting dynamics happening in these types of landscapes. However, the same general principle applies to landscapes not built in layered rocks.",
"Ultimately, the sort of equilibrium condition for a landscape are boundaries between areas with different slope directions but with roughly equivalent erosion rates (i.e. if both sides are lowering at the same rate, the boundary between them will stay approximately in the same place). This tends to form ridges and occasionally peaks (which are often manifest as the intersection of several ridges)."
] |
[
"In addition, not all mountains are peaked. Stratovolcanos like Mt. Rainier in Washington State are more like huge piles of debris, and have rounded tops. Longs Peak in Colorado is flat at the top because its top was once the bottom of the central sea in North America."
] |
[
"Cape Town, South Africa also has a mountain called Table Mountain, and the top is pretty much completely flat"
] |
[
"What's the chemical/sensory difference between the spiciness of wasabi and that of hot peppers, for example?"
] |
[
false
] |
[deleted]
|
[
"Wasabi's spiciness comes methylthioalkyl isothiocyanates. Spiciness from plants in the genus Capsicum comes from capsaicin. ",
"Both compounds play with the neurons normally used to sense heat or damage (thermoreceptors and nociceptors). They bind to and open ion channels, thus allowing depolarization leading to an action potential being propagated to the brain. ",
"As for their different effects, I have two theories. ",
"Firstly, both compounds seem to act on the TRPV1 ion channels, while methylthioalkyl isothiocyanates seem to also act on TRPA1 receptors while capsaicin may not. ",
"Also, methylthioalkyl isothiocyanates are more volatile than capsaicin, allowing them to move further up your nasopharynx. "
] |
[
"I don't know about the biological/perception side of it, but the burn from hot peppers comes from ",
"capsaicin",
", while the burn from wasabi (as well as mustard and horseradish) comes from ",
"allyl isothiocyanate",
"."
] |
[
"To follow up: while true about wasabi, most wasabi products are actually horseradish. Horseradish is prohibitively expensive (and quite rare). I think wasabi (possibly actually truffles [also commonly replaced with cheaper/more accessible products in truffle oil]) are the most expensive foodstuffs (by weight, I think).",
"Horseradish",
" stimulates the same channels, but via mustard oil. So in this case, it is just as the differences between eating peppers and mustard. "
] |
[
"When traveling at relativistic speeds, do you feel more massive?"
] |
[
false
] |
As you travel close and closer to the speed of light you mass changes with the formula m=m0/(1-(v My question is this: if you travel close to the speed of light would you "feel" heavier" than if you were standing still. I ask because if this were true, there would be a way to determine how fast you were going relative to absolute space without needing an external reference point.
|
[
"your mass doesn't change with that formula. It's an old poor way of teaching relativity. What happens is that mass ",
" to be defined to be p=mv. But relativity said: p=(1-(v/c)",
" )",
" *mv. Well someone along the way decided to smush that first term and the mass term together into a \"relativistic mass.\" But that's a terrible way of doing it because it makes people ask exactly your question. Mass is one thing and one thing only. E",
" - (pc)",
" = (mc",
" )",
" . It's the Lorentz-invariant magnitude of the energy momentum 4-vector."
] |
[
"No!",
"Think about it this way: There is a perfectly valid reference frame right now where you are travelling 99.9999999% the speed of light. Do you feel more massive?"
] |
[
"No. The key part about relativity is in the name: everything is relative :). There ",
" any absolute frame, all reference frames are equally valid.",
"In your own reference frame you aren't moving, so you don't feel any relativistic effects."
] |
[
"Is pricing a product with a price ending in 5 (e.g. 29,95) as effective as prices ending in 9?"
] |
[
false
] |
[deleted]
|
[
"In some cases it's used to denote clearance or sale items or the such, my job that uses .99 for most of our prices uses .98 or .97 to denote clearance prices and in a few cases we have used .00 for other items but less frequently"
] |
[
"When I worked in retail, prices ending with 95¢ were discontinued products, and those ending with 97¢ were final clearance items that we had to get rid of ASAP. And I think we'd set it ay 98¢ when we manually changed a price for a deal so that customer service would be aware that a deal was made if the customers tried to be smartasses and attempted to return the warranty after getting a reduction on the item that was conditional to buying the warranty."
] |
[
"I don’t know about effectiveness but in general there’s ",
"Benford’s law",
" which often shows up when you look at data."
] |
[
"Is there any way of knowing whether a proton is positive without comparing it to something negative?"
] |
[
false
] | null |
[
"Benjamin Franklin came up with the convention; he called the kind of charge from rubbing silk on a glass rod \"positive\", and the kind of charge you get from rubbing amber with fur \"negative\". As far as I know, there are no records of why he chose this convention."
] |
[
"As Amarkov said, it's just a convention. We could just as easily have defined protons as having a negative charge and electrons as being positive.",
"(Edited for mistyping)"
] |
[
"It would have made a lot more sense for modern electrical engineering. Electrons are the ones moving in electricity, but physicists tend to always consider current positive, so they often measure current in the opposite direction, leading to loads of student confusion and sign error."
] |
[
"Why don't long-distance runners have a lot of muscle in their legs?"
] |
[
false
] |
[deleted]
|
[
"Good example, ",
"here",
" the dark muscle is what the shark uses for long distance and the lighter for quick bursts. "
] |
[
"While I'm not knowledgeable of the exact anatomy, I have a friend who is doing her PhD and has been a long distance runner for her university for years. Her explanation is that increased strength doesn't help a distance runner much, and the excess weight would be more of a hindrance than a help. This is why sprinters have a lot of mass in their leg muscles as well, because the weight is a negligible hindrance for that short of a distance. I'm not sure how LDRs maintain slimmer leg muscles exactly, but I would surmise it is due to less weight training with their legs, and more focus on duration training."
] |
[
"Sprinters also need more acceleration. Long distance runners are basically repeating the same motion over and over without concern too much for power.",
"It's like asking why not use a drag racer car for a 100km race [without pit stops]."
] |
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