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[
"Could a black hole that's big enough, cause a \"Big Bang\" large enough to create a new universe?"
] |
[
false
] |
I don't know much about black holes, but I'm wondering if they can get so big and heavy, that they explode in some way to create what we would perceive as a big bang. I like the idea of there being multiple universes, and that the universe can be born again and again infinitely, so I thought about what it might look like if a person zoomed out far enough to see what the universe looked like, with other universes around it. I tried to think about patterns we see on small scales and large scales, and came up with this sketch I made Since the big bang comes from one point, I thought it might look like a bubble of some sort, and if it came from an exploding black hole (White hole?), maybe there could be others too. The image I made would try to show a cross section of entire universes created by big bangs. Other universes would collide with eachother, forming big concentrations of galaxies and matter of all kinds, making huge black holes that we have not even seen yet. At these super concentrations of galaxies and stars, there would be a lot of black holes, all converging and eating eachother until there was one big enough to get too big to exist, and explode. That is, if black holes ever explode. I'm using the word 'universe' in a way that makes it sort of just an area in space created by it's own big bang. Like how we call a swirling group of stars orbiting a super-massive black hole a galaxy. I'm not very educated on the matter, just been to high school, so forgive me if this idea and question sounds silly!
|
[
"Black holes do explode, or die violently, but sadly only small ones do. In fact very massive black holes are incredibly stable and emit very, very little energy. I'm talking less then the power of a small LED. Also it's best not to think of space as nothingness, even empty space is something and the Big Bang was the beginning of space itself. As for your sketch it looks a lot like the dark matter distribution maps, take a look if your interested.\n",
"http://scienceblogs.com/startswithabang/files/2011/08/dark_matter_millenium_simulation.jpeg"
] |
[
"Thank you for your info, it's very interesting. :) I have seen that map before, it's what inspired me to make these images I make. My image would be on a much larger scale than that map shown, the jpeg you linked would make up a tiny rectangle in one universe on my image.",
"Thanks again!"
] |
[
"Very interesting! Thank you for your insightful reply. :)"
] |
[
"Physics Question: Fourier's Law, heat dissipation from one material to another?"
] |
[
false
] |
Fourier's law states that the heat flux of a material is equal to the the product of the temperature gradient in the material and the thermal conductivity of the material. But, when calculating heat dissipation using Fourier's law, shouldn't there be a variable describing an additional material, to which the original material is transferring the heat? There is no variable to take into account the thermal conductivity of the surrounding material. A red-hot steel cannonball's rate of heat dissipation would be much higher in 10°C water than in 10°C air. Conversely, a steaming hot cup of coffee would cool down much slower in a ceramic mug than in a metal cup. In such a case, shouldn't there be two different thermal conductivity coefficients in Fourier's law? Or is it that I'm approaching the calculation of heat dissipation erroneously?
|
[
"Depends on the approximations you can make. Is the solid highly conductive compared to its heat loss to the gas? Then you can use the lumped capacitance model and just use Newton's law of cooling to find the heat transfer, since the entire body is at approximately the same temperature. If not, you have to directly account for the heat transfer inside the body as well as the transfer from the body to the surroundings, which is more challenging.",
"Heat transfer problems are challenging. There are analytical solutions for some relatively simple boundary conditions and geometries, which can be applied to real-world situations only with a certain degree of error, but if accuracy is important, and your situation is complex, you're probably going to need to go with FEA."
] |
[
"You're approaching the problem erroneously. ",
"Fourier's Law describes the flow of heat in a ",
" material. For example, you can use Fourier's Law to calculate the heat flow through a solid material suspended between two heat sinks (",
"example",
"). It assumes that the material does not interact with anything around it -- and also that its internal structure is fixed. For example, as you noticed, Fourier's law disregards loss of heat to surroundings. It also would not be correct for heat flowing through a trough of water -- that water would probably have convection currents."
] |
[
"Thank you. If that is the case, how would I go about calculating the rate of dissipation of an object's heat into its surroundings? What formula exists for this?"
] |
[
"What's the difference between a cancerous and a non-cancerous tumour?"
] |
[
false
] |
[deleted]
|
[
"I haven't had an oncology course in a while, so this may or may not be entirely correct, but I hope I remember enough so that the general concept is true even if all the details are not.",
"Im guessing your question refers to the difference between a benign and a malignant (cancerous) tumour. This isn't really a black and white scenario, but should be seen as more of a spectrum.",
"Benign tumors form when cell cultures exhibit hyperplasia, an excess of cells. Basically something in the cell cycle has gone wrong and they're dividing excessively. Malignant tumors on the other hand are what we call tumors composed of cells with altered morpholigies. Basically these cells are so far mutated that they no longer resemble the culture they originally came from. As well, they display invasiveness, breaking through the basal lamina, and display potential to spread to other areas of the body.",
"Basically, a benign tumor has acquired some mutations, but nothing harmful and cells are simply dividing a lot. Malignant tumors are further mutated (there's some name for this spectrum that escapes me, and it defines a few more stages than these two, but oh well), and display altered cell characteristics.",
"EDIT: Just realized I only partially answered your question haha. They know the difference by taking samples of the tumors (a biopsy), and looking at the cells under a microscope to see if the cells are malignant or not. As well, further non-invasive methods exist to see if a tumor is potentially harmful. Looking for unique or out of place characteristics in a certain tissue type, seeing if the tumor is consuming an excess amount of glucose, seeing if angiogenesis has occurred, as well as other fMRI techniques. (Angiogenesis is the process by which tumors 'recruit' blood vessels to supply themselves with oxygen) etc. etc.",
"From what I understand (again not actually an oncologist), benign tumors are left alone if they're not causing any issues, but still kept an eye on incase further complications arise. If they're in the spinal cord or brain or something and exhibiting pressure on the nerves, or blocking major ducts etc etc. obviously they're gonna be removed though (if possible)."
] |
[
"Benign tumors form when cell cultures exhibit hyperplasia, an excess of cells. Basically something in the cell cycle has gone wrong and they're dividing excessively. Malignant tumors on the other hand are what we call tumors composed of cells with altered morpholigies. Basically these cells are so far mutated that they no longer resemble the culture they originally came from.",
"This is called ",
". Such that a well-differentiated neoplasm will resemble its tissue of origin when looked at under a microscope (skin looks like skin, esophagus looks like esophagus) and a poorly-differentiated neoplasm will look like a mess. Benign tumors generally look like the tissue they came from. Malignant ones can look like the parent tissue (good prognostically) or they can look like a mess (bad prognostically).",
"As well, they display invasiveness, breaking through the basal lamina, and display potential to spread to other areas of the body.",
"Invasiveness is an important point though it is worth noting that ",
" can bridge this requirement since its not necessarily invasive but still generally referred to as cancer (though this nomenclature has come under fire by the USPSTF). The spread to the other part of the body part is called metastasis. Almost all cancers can be metastatic though some generally don't i.e. gliomas and basal cells carcinomas. I've heard/read varying things about the potential in rare rare cases for benign tumors to spread to distant parts of the body. In general, metastasis = cancer.",
"Malignant tumors are further mutated (there's some name for this spectrum that escapes me, and it defines a few more stages than these two, but oh well), and display altered cell characteristics.",
"I think you may be talking about differentiation still. There are a variety of cellular characteristics associated with poorly differentiated tumors such as changes in the nucleus and different looking cells within the same tumor. ",
"seeing if the tumor is consuming an excess amount of glucose",
"PET/CT is what looks at this directly ",
"seeing if angiogenesis has occurred",
"This is involved in the idea of \"contrast enhancement\" or an increased uptake of contrast in CT scans which is generally associated with cancer.",
"From what I understand (again not actually an oncologist), benign tumors are left alone if they're not causing any issues, but still kept an eye on incase further complications arise.",
"There are a lot of things that go into this. Not the least of which is that we don't always know what something is until we take it out and biopsy isn't always an option. Also, even if a biopsy shows a tumor to be benign, certain tumors can harbor malignant cells that could have been missed. Also, many tumors (as you mentioned) can take up space where you don't want them taking up space and lead to problems. Even something as benign as a fibroid (leiomyoma) will be surgically removed if it is associated with increased bleeding during menstruation, problems with fertility, etc."
] |
[
"Thanks, that clarifies things :)"
] |
[
"How can space be cold?"
] |
[
false
] |
It is my understanding that if you go to space without a space-suit, you will freeze. But how can that be? If heat is 'stored' in the vibrations of the atoms involved, and there's no atoms around you to transfer those vibrations to, how can the heat leave your body, so to speak? And on top of that, why doesn't the sun keep you warm? I mean, there's nothing like atmosphere to remove energy from the sun's rays before they hit you, so shouldn't it be really hot? Sure, the rays only hit you, and doesn't warm up your surrounding air and the ground beneath you, but still. Can somebody explain this?
|
[
" Thermal energy can take a lot of forms. In matter, it's the kinetic energy of the particles. In space, the temperature is determined by the energy density of photons. If photons didn't carry energy, how else would the sun warm the earth?",
" If you were dropped in space without a space suit, the first thing that would happen to you to cause you to lose heat is rapid evaporative cooling. The water on the outer layers of your skin and exposed orifices will boil without the air pressure provided by the atmosphere, carrying away considerable heat ",
"On a related note, experiments studying the effects of decompression on dogs found that loss of pressure induced simultaneous projectile vomiting and defecation, due to the rapid expansion of internal fluids. ",
"Source",
" :D",
"As you continue to die you will be radiating photons like a black body. This would be your main cooling mechanism in deep space, but whether or not you are cooling is dependent on your proximity to a heat source like the sun. ",
"If you are in direct sunlight at earth's orbit, your front side will likely be gaining more energy from sunlight than it will be losing from black body radiation, causing your surface temperature to increase on your 'day' side. Case in point, the day time surface temperatures of the moon are in excess of 100 C, while night time temperatures are less than -200 C. ",
"You aren't as big as the moon, I hope, so your evolution will probably be somewhat similar to a small icy comet. The sunlight may cause some outgassing from the front of you, while the rest of you ends up freezing solid, until eventually the sunlight has ablated enough of your matter you and you disintegrate. "
] |
[
"If find the placement of that one smiley very disturbing.",
"Otherwise, great explanation."
] |
[
"We are actually. Everything gives off photon radiation. This is known as ",
"Blackbody Radiation",
"."
] |
[
"Can you measure pain?"
] |
[
false
] |
[deleted]
|
[
"Yes! Tell me, ",
"how much does it hurt on a scale of 1-10?",
"As crude as self-report of pain seems to be, that has been the gold standard of measuring pain for as long as medicine, and is still what is most commonly used clinically today because it is easy to collect and useful.",
"Of course, this isn't what you're asking, but doing any better than \"just ask\" is actually really hard!",
"For example, a lot of work have gone on behind the scenes of ",
" exactly to ask to get an accurate measurement of pain. ",
"How many levels should there be?",
" 5? 10? 11? 20? 100? ",
"Should it show faces or numbers",
", especially for kids? ",
"Should it be a linear scale or should it be nonlinear?",
" When all is said and done, the simple 1-10 scale performs well enough for its simplicity.",
"But pain isn't on an absolute scale, because itself is both a physiological and psychological phenomenon. You will have no doubt heard of the placebo effect. Usually, this carries a negative connotation, especially in drug trials, where we are trying to outperform the placebo. In the field of chronic pain relief, however, the placebo effect is strong enough, and pain relief difficult enough, that the placebo effect is considered by some as a method of pain relief. The most extreme example of this is ",
"controlled trials of \"sham\" surgeries",
", where under consent the study participant may be randomly assigned to \"fake\" rotator cuff, knee, and hip orthopedic surgeries (where the joint is opened and closed back up with no other surgical procedure). The kicker is? For patients in these studies, sham surgery has with similar levels of pain relief compared to actual surgery.",
"An amazing recent paper in ",
"Nature Medicine",
" sheds some light on the varied nature of placebo effects. In the study, the researchers suspected that the placebo effect had something to do with both the opioid (morphine, heroin) and the endocannabinoid (marijuana) systems, and wanted to find out how. He gave cannabinoid-blocking drug to subjects, as well as giving the subjects morphine, placebo morphine, an NSAID (similar to ibuprofen), and placebo NSAID. The blocking drug did nothing about the placebo morphine, but it could ",
" for people taking placebo NSAID. This is amazingly interesting and suggests that there are different placebo systems at work and that placebo effects can be blocked by drugs.",
"A related but opposite concept is the nocebo effect, where ideas can cause pain rather than relieve it.",
"Of course, this is about immediate pain. What about memory of pain? This poses a further problem because as it turns out, ",
"remembered pain does not behave the same way as does current pain",
". The memory pain of childbirth, for example, can change a lot depending on the individual with time, to the extent that the ",
"reported memory of the pain months later can be much less or greater than the pain reported at the time of childbirth",
", depending on factors such as the quality of care, caretakers, family circumstances, or ",
"traumatic and stressful events",
".",
"On the cutting edge of quantifying pain is ",
"Tor Wager",
". In 2013, he published ",
"a paper detailing a way of classifying pain from functional MRI scans, especially of the insula, anterior cingulate, thalamus, and S2 (somatosensory) areas of the brain.",
" According to the paper it has a very high sensitivity and specificity (doesn't mistake pain for non-pain and vice-versa very often), ",
"and could even tell physical pain from other mental pain such as the pain of rejection, or from other sensations such as the sensation of heat",
".",
"I've met Tor in person and he does fantastic work at CU Boulder. Of course, this cutting-edge research is not making its way to your local clinic any time soon; MRIs are a lot more expensive than asking you 1-10. What it does is let us understand a bit more about how pain is perceived in the brain.",
"...",
"I think I've given you enough at this point to show that not only are objective measures of pain difficult, it brings into question the level of objectiveness of pain itself. Certainly we can improve on the way we measure it, but just because it can be measured doesn't mean it's invariant or consistent, between people, or even between yourself and your own memories.",
"tl;dr: Pain is super complicated, and asking for pain on a scale of 1-10 works ok."
] |
[
"This is a fantastic overview! I feel like this is why a lot of people steer clear of pain research, because it's just as much psychology and philosophy as neuroscience.",
"I also want to add that for quantifying pain in patients, the gold standard at least here in Canada is the ",
"McGill Pain Questionnaire",
".",
"I also want to clarify that pain is our overall subjective experience, containing all of our emotional, and memory context as well as the actual noxious insult as well. This differs from nociception, which is the act of nociceptors in the periphery being activated due to a noxious insult. ",
"Nociception can be measured and quantified quite easily as information travels from the periphery to the central nervous system via electrical currents that can be measured",
"."
] |
[
"As a researcher in a neurobiology lab studying pain, we use many models to study acute and chronic pain conditions. The comments below address the obvious complications associated with the self-assessment of pain, although we avoid this discrepancy from our molecular approach, being that we limit our research to non-human subjects. So to address your question directly, one of the ways we can quantify pain is by analyzing biochemical responses that occur as the result of noxious stimuli. Several cells, especially sensory/spinal neurons, express signature biochemicals due to pain. For example, one of the most popular experiments follows the expression of c-Fos (",
"http://www.ncbi.nlm.nih.gov/pubmed/9434195",
") in the dorsal horn of the SC. This model has many obvious limitations, but still serves an important role!"
] |
[
"How does mixing magmas of different types cause large explosive volcanic eruptions?"
] |
[
false
] |
I've read from several different sources that when a fresh injection of basaltic magma intrudes into a more silica-rich magma chamber under a volcano, some sort of reaction happens that ultimately leads to a large explosive eruption. I've specifically heard this implicated for the 19th century Krakatoa eruption, where people point to volcanic rock of varying color bands indicating partially mixed magmas that cooled preserving the different rock types. However, these sources don't mention a mechanism for this. Is there some sort of chemical reaction between the different magmas? Is it a physical reaction relating to different temperature/density/viscosity/gas content/something else? What leads two bodies of relatively stable magma to generate immense pressure and explode when mixed together?
|
[
"Temperature difference. The lighter felsic magma in the primary chamber had been cooling down for some time. This theory around the magma mixing, involved a darker body of much hotter and more mafic magma intruding into the chamber. This caused a pressure spike, followed by the very large kaboom.",
"The other theory is a phreatic eruption, where a collapse in the base of the volcano wall resulted in seawater flooding the chamber - and steam from this contact with the magma resulting in the eruption.",
"Evidence of both theories exist, but either way it doesn't involve any fancy chemical reactions."
] |
[
"The added heat from the mafic magma induces convection and vesiculation (i.e., bubbles) which has long been argued to be the trigger (e.g., ",
"Sparks et al., 1977",
"). There are definitely chemical changes as a result of the mixing (e.g., the chapter on magma mixing as an eruption trigger by ",
"Morgavi et al.",
"), but I don't think these are typically considered important in the triggering process itself, but someone like ",
"/u/orbitalpete",
" who specializes in volcanology could definitely provide a more complete answer."
] |
[
"It is not so much about the mixing of two different magma leading to explosive eruptions although that can happen. There are other factors that help explain the reasons...",
" The ",
" of the magma is an important factor. ",
"i) Magmas that contain more Silica tend to be more viscous and sticky. A magma deep below is under considerable pressure and can contain a large amount of dissolved gas/volatiles. ",
"As the magma ascends to shallower depths as in a volcano it experiences a considerable reduction of pressure. This leads to the gas coming out of solution just like the fizzing of a soda bottle when uncorked. In a viscous magma these gas bubbles cannot easily escape and are trapped in the sticky melt. ",
"The expansion of these numerous gas bubbles causes enormous pressure that can shatter the rock and create explosive types of eruptions with deadly ",
" of hot ash and dust that make them particularly lethal. ",
" many volcanoes of the Andes chain and at Japan and some ancient supervolcano eruptions such as the one that formed Yellowstone are some examples of this sort of volcanism that forms silica - rich rocks such as Andesite and Dacite. ",
" ejected from Mt. Vesuvius and similar volcanoes is lighter than water simply because it consists mostly of hollow gas bubble pockets trapped in a viscous Silica rich rock. ",
"",
" contain ",
" Silica but more ",
" and Iron. The presence of Calcium and especially Magnesium (together with lesser Silica) tends to make the magma a ",
" ",
"Gas/volatiles that come out of solution from such erupting magmas can escape more easily just like the fizzing from an opened Coke bottle. ",
"This type of Basaltic Volcanism seen at Hawaii and at Iceland is generally less explosive. The fluid lava can easily flow many Kilometers engulfing anything in it's path.",
"",
" It is the ",
" that caused the stupendous 19th century eruption of Krakatoa as well as the recent eruption of Tonga. ",
"In both cases, an initial episode of volcanic activity ruptured the volcano allowing sea water to come in contact with magma. This caused ",
" to quickly vaporize into super heated steam. ",
"The explosive power of both Krakatoa and Tonga was great enough to blow up both mountains to ash, create destructive tsunamis that were recorded worldwide. The atmospheric pressure (shock) waves traveled around the world several times.",
"Such eruptions provide a glimpse of the enormous power that can be released in a single outburst of volcanism."
] |
[
"Are plants as efficient as solar panels?"
] |
[
false
] |
If I plant grass on 1km and burn it in 100% efficient engine after month, would it give me more energy than 1 km of solar panels in the same time?
|
[
"Not really, from what I have read solar panels have around a 15% efficiency (average). Plants have a ",
"theoretical maximum efficiency",
" of around 13%. Plants have an ",
" efficiency",
" of around ",
"1% to 7%",
" "
] |
[
"Not really if you look at their biochemistry. They take water, carbon dioxide, and oxygen to work along with nutrients in the soil. Then we should remember some of that energy is used to keep the plant alive.",
"Think about humans. We eat a couple of pounds of food per day, yet we dont gain a couple pounds every day. This is because we are using the energy to stay alive so the amount that goes into stored energy and growth is pretty small. ",
"Solar panels dont need to stay alive and do not need as many inputs once constructed. "
] |
[
"Not really if you look at their biochemistry. They take water, carbon dioxide, and oxygen to work along with nutrients in the soil. Then we should remember some of that energy is used to keep the plant alive.",
"Think about humans. We eat a couple of pounds of food per day, yet we dont gain a couple pounds every day. This is because we are using the energy to stay alive so the amount that goes into stored energy and growth is pretty small. ",
"Solar panels dont need to stay alive and do not need as many inputs once constructed. "
] |
[
"Will vacuum decay happen? Is there strong evidence supporting its existence?"
] |
[
false
] |
[deleted]
|
[
"Will vacuum decay happen?",
"No, it's incredibly unlikely—and that assumes our vacuum is actually metastable (lives for a long time) which is also an \"if\".",
"Is there strong evidence supporting its existence?",
"The decay of the false vacuum isn't nonsense, but a real thing depending on the physical laws. Spontaneous state changes aren't too crazy esoteric either. For example, using just you freezer or microwave, you can drop or raise water below 0 or above 100 Celsius without freezing or boiling. The water is then considered to be supercooled or superheated... and the water will remain that way until something bumps it. The water will then flash freeze or boil. You can easily find videos of folks doing this online. The only complication quantum mechanics adds is that you don't need to bump the system... eventually it will happen spontaneously. The radioactive decay is an example of this.",
"And now for some of the technical details: The Higgs field (Note: I said field, not particle) directly generates the masses of the Z and W",
" bosons and the vacuum expectation value of the Higgs field is currently understood to be,",
"This means the Higgs field fills all space with a nonzero amplitude (think height of water in a bathtub) equal to <v>. This in contrast to say the electromagnetic field whose <v_EM>=0 is zero because all of space is not filled a nonzero electromagnetic field. The Higgs field is also responsible for the rest masses of at least the quarks and charged fermions (electrons, muons, taus). The neutrinos are their own can of worms, and the Higgs field also presumably gives the Higgs particle mass—at least in the simplest Higgs model. Here is a set of 4 digestible articles for a more complete describe of what <v> means and why it gives some elementary particles mass,",
"https://profmattstrassler.com/articles-and-posts/particle-physics-basics/how-the-higgs-field-works-with-math/",
"Anyway, I am belaboring this point because it's about what vacuum decay actually does. If you change the Higgs vacuum value <v>, you change the delicate balance of how how the fundamental particles behave because their masses are tied to the <v> value. That is what vacuum decay means: You have a region of space that doesn't have the same physics because the various quantum fields are in an entirely new configuration. Vacuum decay in the simplest Higgs model is extra catastrophic because not only does the <v> change... it is unbounded and simply runs away like a ball rolling down an infinite hill.",
"The Higgs potential (Think potential energy, like a ball on a funny shaped hill) in its simplest incarnation is a ",
"\"Mexican hat\"",
" with the mathematical form,",
"Where x is complex and is the strength of the Higgs field. The equilibrium points of this potential are then given by",
"The first value is unstable, any small bump will knock the ball rolling it down the hill. The second is stable if you bump it, it will merely oscillate at the bottom of the hill. The vacuum expectation value is then, you guessed it, ",
"Now here comes our \"false vacuum\" problem: Quantum field theory is inherently nonlinear which cannot be ignored at higher energies. One way to understand this non-linearity is to repackage the coupling constants as running constants which change depending on the energy scale involved. A good example of this is the fine structure constant α. At low energies,",
"However at the energy scale ~90 GeV, the \"constant\" has increased to become,",
"The Higgs field's coupling constants do the same thing (µ",
" and λ",
") and how those constants change depends primarily on what the <v> value is (which tells us the low energy behavior of the constants and we know what <v> is because of the Z and W",
" masses) and the mass of the top-quark which is the only other particle to strongly couple to the Higgs field, besides the Higgs itself and the Z and W",
". The mass of the top-quark is around 173 GeV which is given by,",
"Finally we need the mass of the Higgs particle as well. The problem arises that if the Higgs mass is significantly less than the top quark's mass the coupling constant λ",
" flips sign and becomes negative at large energy scales. See Figure 1. of this paper,",
"https://arxiv.org/abs/hep-ph/0104016",
"The above paper assumes a Higgs mass of 115 GeV, since it's from before the 2012 discovery of m_H=125 GeV, but the principle is unchanged. For our 125 GeV Higgs this happens around the 10",
" GeV scale. If the coupling constant flips sign, you essentially flip the Mexican hat at high \"x\" value which means the local minimum <v> is not the true lowest energy state. Classically this is not a big deal, unless something catastrophic happens giving the Higgs field enough juice to jump the hill. Quantum mechanically the problem is tunneling. There is a very tiny probability that we could tunnel into the \"true vacuum,\" which would then become a bubble growing at the speed of light destroying everything in its path.",
"While this is an incredibly high energy, it is still magnitudes smaller than the Planck scale where we expect quantum gravity to play an important role. This means that unless new physics shows up somewhere before the 10",
" GeV scale... our universe is metastable. The definition of metastable is rather simple, it means the predicted lifetime of the vacuum is longer than the current age of the universe. It's metastable because we're not dead yet!",
"Couple little final thoughts,",
"We are somewhat shielded from vacuum decay because the universe is expanding. A bubble could form somewhere in the universe, but never reach us, because it started in a region of space expanding away from us at faster than the speed of light.",
"If my memory serves me right the Standard Model Higgs true vacuum isn't actually unbounded, but still is very very faraway from <v> though the details escape me, I believe they have to do with higher order behavior. I'd love it if someone could refresh my memory on this.",
"The ultimate fate of the vacuum strongly relies on the shape of the Higgs potential. Any new physics can easily change it. Alternate ideas may have multiple vacuum to tunnel into or a single \"true vacuum\" which is some distance away from <v> or new physics might cause the Higgs potential to always be stable."
] |
[
"Just want to say an undercooled liquid will still eventually nucleate a solid phase even without agitation or an outside force. Classically, the nucleation rate is severely hindered by the very small successful attempt rate. The exception to this is if you can cool it through a glass transition since then it's actually stuck in a local potential energy minima. Non-classical nucleation theory nobody has a good answer because we're still arguing about how things actually nucleate and grow. "
] |
[
"I don't have the prerequisites to understand math above, but I like the way you presented your answer. "
] |
[
"Why do my eyelids/general eye area hurt if I haven't slept enough?"
] |
[
false
] | null |
[
"Wow, and this is why we can't have nice things. Class it up in askscience please. Not the OP, but the responders."
] |
[
"Agreed. If you're not qualified to answer by virtue of having studied this particular topic for many years, there better be a link showing us where you got your information. ",
"For example, to the person that posted \"well we spend the majority of our time in REM sleep\" below, he should read this article, which says that scientists believe only 20% of sleep is REM:",
"http://www.ninds.nih.gov/disorders/brain_basics/understanding_sleep.htm"
] |
[
"Optometrist here. In general tired/fatigue causes eye discomfort for two reasons. (1)Most common is dry eye, as any others have pointed out. In general the longer we're awake and the more fatigue/tired we are the surface dries out. In addition, we blink less, causing more drying/desiccation by evaporative action. As the surface dries the body sets off inflammation/pain as a way to cause you to pay more attention close your eyes/blink to re-wet the surface.\n(2)The second most-likely cause is muscle fatigue--your eyes have muscles like every other part of your body, and they get tired, too. Focusing on things (ciliary body) and keeping them open (orbicularis oculi, levator palpebrae) takes effort."
] |
[
"What goes on in our brain when we become confused?"
] |
[
false
] |
I was trying to understand something that my friend told me the other day and it made me wonder what exactly was going on in my brain when I was so confused. Is there a change in how the neurotransmitters/neurons travel? (To be honest I'm actually not sure what happens when we're thinking normally) Or is there no change in our brain activity?
|
[
"{ Joke: Please Ignore }",
"Complex ",
" and ",
" is still too ",
" to ",
"?"
] |
[
"What do you mean confused? You mean a loss of orientation, ie not understanding date/time/place/event/identity/etc?",
"Confusion, delirium, and even dementia are the results of your brain attempting to do very normal things and being unable to adequately accomplish the task. Thought seems to be the process of many different parts of your brain coming together, tossing in their 2 cents, and some guy eventually goes, \"ALRIGHT WE GOT IT!\" And out comes whatever cognitive process you were attempting.",
"It is typically not neurotransmitter dependent, though it may involve their misregulation. The neurons don't \"talk\" to one another quite correctly for sure, but why that is varies depending on what is going on. In fever it is the heat causing a change in conduction properties. In the case of sepsis and infection, confusion can be the result of toxins altering neuronal activity.",
"Cheers!"
] |
[
"Okay well we have basically no idea how \"understanding\" works. At all. We get how learning works in principle, but what separates basic learning from complex abstraction and understanding is WAYYY beyond us.",
"The theories I am familiar with of how it works is that when you are unable to create strong enough parallels to what you already know/understand, you learn to understand the new phenomenon. But that is largely a guess based on how people report thinking."
] |
[
"If everyone was required to stay at home for 2 months with zero contact with other people could we wipe out the cold/flu forever?"
] |
[
false
] |
[deleted]
|
[
"Not a chance, the biological world consists of a lot more than just humans, influenza in this case infects a wide variety of animals, hence the \"swine\" or \"bird\" flu you hear about. Also a lot of diseases can have incubation times or even be dormant for decades like in the case of TB."
] |
[
"The ",
"xkcd-book",
" has a section about this, and the answer comes down to: Almost, but not really.",
"The common cold is usually caused by some variant of the rhinovirus, which is eradicated from the human body by a healthy immune system after about a week. And since this virus doesn't cross species, and can't infect anyone due to the isolation, it should die out.",
"The problem is that not everyone has a healthy immune system, and therefore a few strains of the virus will survive beyond the quarantine. And so they can spread across the population again, and the 2 months of isolation would have been for nothing..."
] |
[
"To further this and clarify, the flus don't infect the animals, so to speak, there is typically no disease or illness. They treat the host species as a vector, mutate for one or several generations, and then we catch this new, evolved version.",
"\"Zoonotic vectors\" are what we're talking about."
] |
[
"Is it possible for two truly simultaneous events to occur?"
] |
[
false
] |
[deleted]
|
[
"In principle nothing prohibits two events from taking place at the same time--and essentially you're bringing up a notion from Zeno's paradoxes, the notion of divisibility. Ultimately, there is nothing special that two events occupy the same parcel of time versus being offset slightly and practically, our measurement tools will break down eventually and our ability to resolve any differences will be impossible.",
"Now simultaneity actually has a much deeper problem when you consider relativity. Because both lengths and times are variable and perspective based, different observers will argue over the order of two unrelated events, say two beacons flashing on opposite sides of the city. You can see this phenomenon in this ",
"animation",
" here. So, if I'm disturbed by the \"offset\" in time between two events (spatially separated!), I can engineer my reference frame to synchronize them to put my mind at ease."
] |
[
"Define \"truly simultaneous.\" In classical physics or in the same reference frame yes. One event could happen at exactly the same time to way more than any measurable amount of time, even absolute. HOWEVER, if you then move that reference frame, you now have two events that occur at different times.",
"An \"event\" in relativity is defined at a location and a time. So to have two simultaneous events in every reference frame they would have to occupy the same location at the same time, therefore making them the same event (if you have heard anything about relativity you know the two strobes at arms length and a nose model, or something similar). ",
"Basically, no you can't in spacetime, but you can in one reference frame."
] |
[
"Did I not also read somewhere that there is no such thing as \"At this very moment in a far away galaxy...."
] |
[
"Why does it appear most craters on the moon are fairly true circles?"
] |
[
false
] |
I was looking at a video of the moon and noticed that all the craters I could make out appeared to be nearly perfect circles. I would think that an object striking the moon at an angle would form a less perfectly circular crater than a direct hit. If the moon's gravitational pull isn't very large, and it has no atmosphere to slow objects down, why does it appear that most impacts come at a very high angle?
|
[
"It doesn't have to be at a high angle to create a circular crater. If the object is moving fast enough (and it will be, since it's falling at interplanetary speeds), it will create a massive explosion when it hits. The shock wave is circular, and will be much much larger than the object itself. That's what creates the crater, not the actual path of the meteorite."
] |
[
"The impactor is completely vaporized due to the energy involved, and the shock wave is through the solid mass of the surface."
] |
[
"Yeah, when things start moving kilometers per second, not much is left after impact. "
] |
[
"Can someone harmonize these seemingly conflicting lung cancer studies?"
] |
[
false
] |
Can you harmonize these seemingly conflicting results? Our study (Moghaddam et al) and Dance-Barnes’s are similar in that carcinogenesis was initiated in both by an activated allele of K-ras (G12D in ours and G12C in Dance-Barnes’s), expressed in airway secretory cells under control of the CCSP promoter, and the concentrations of dietary curcumin were similar (1% in our study and 0.4% in Dance-Barnes’s). However, the studies differ markedly in their mechanisms of transgene expression. We used a hit-and-run strategy in which the Cre recombinase is expressed in airway secretory cells by the CCSP promoter prior to the 6th week of postnatal life to induce rearrangement and activation of a conditional K-ras allele, with permanent subsequent expression under control of the endogenous K-ras promoter in an inflammatory model (20). This strategy was adopted because we had found that the CCSP promoter is downregulated by inflammation, resulting in reduced carcinogenesis when the oncogene remains under control of the CCSP promoter (20). Dance-Barnes et al. (39) used a bitransgenic strategy with the reverse tetracycline transactivator under control of the CCSP promoter and an activated K-ras allele under control of a tetracycline-inducible promoter. Either or both of these promoters could be influenced by curcumin, resulting in upregulation of the expression of the K-ras transgene. Since tumor progression was mild in this model, occurring late in life and at a low grade, carcinogenesis should be sensitive to small changes in oncogene expression. While these differences in the genetic models could explain the discrepant findings between our studies, further experiments will be required to provide evidential support. Abstract: In the current study, we demonstrate that curcumin unexpectedly promoted the progression of lung lesions from benign hyperplasias to ADs and carcinomas, similar to the known lung tumor promoter butylated hydroxytoluene (BHT) (34–36). Furthermore, we provide evidence that after 1 week of curcumin administration in the diet, lung tissue demonstrated enhanced levels of oxidative damage. This early pro-oxidant effect may account for the tumor-promoting effects of curcumin in lung tissue. Abstract: We conclude that curcumin suppresses the progression of K-ras-induced lung cancer in mice by inhibiting intrinsic and extrinsic inflammation and by direct anti-tumoral effects. These findings suggest that curcumin could be used to protract the premalignant phase and inhibit lung cancer progression in high-risk COPD patients. "In summary, the results presented here support further the effectiveness of curcumin as a therapeutic agent, alone or in combination with current therapy against lung cancer. It could also be considered for use by current smokers or ex-smokers with or without COPD as a chemopreventive agent. Further understanding of the molecular mechanisms affected by curcumin treatment will provide a basis for rationally directed clinical testing of the efficacy of this agent and other selective anti-inflammatory/anti-tumoral agents in preventing COPD progression and lung carcinogenesis." Here is some background on Curcumin.
|
[
"One of the really cool things about scientific literature is that it's all a huge, ongoing conversation. Most of the time, when you have two papers with conflicting (or seemingly conflicting) results, the authors of the later paper will talk about the conflict, and try to give some explanations for it. In this case, the Moghaddam paper was published second, and if you look in the Discussion section, sure enough, they acknowledge that their results seem to conflict with Dance-Barnes, and talk about why that might be.",
"Another strategy might be to see if anyone's talked about this since 2009, when these papers were published. Google Scholar has a really neat \"Cited by\" feature where, given a particular paper, they'll give you a list of every other paper that cites it. If you want to move past these two papers, and see what other people have said, you can use this feature; it may be that someone figured out what the difference was, or has some other hypotheses about it."
] |
[
"thanks for the reply. in the legal services industry we have a similar organizational framework where judicial opinions are essentially having a similar conversation with each other. Published materials (cases, journals, briefs, statutes, etc.) are often citing to previous materials for reference. having said that even after reading cited studies it might be beneficial hearing a \"professional synthesis\" of the research from someone with professional training, and familiarity with the material. its one thing to read the paper, but quite another to read it as a researcher or physician studying lung cancer. because presumably they would be able to understand the background, and where it fits in"
] |
[
"The short answer is given by the paper as Jetamors pointed out. One group used a mouse that had the K-ras mutation from 6 weeks post birth whereas the other used an inducible mutation that they turned on right before the experiment. Their explanation is that while their model uses a slow and steady tumor induction, the other studied used a rapid and sudden tumor development model. You basically have to study the way they induced the tumors to see if curcumin interferes with either of their transgenic models. "
] |
[
"If human bodies reject organ transplants because of foreign DNA, why can we receive blood transfusions from other people with no problem?"
] |
[
false
] | null |
[
"Blood and organs are rejected for slightly different reasons. Organ rejection is largely dependent on ",
"MHC I/HLA",
" proteins which are expressed on all nucleated cells. These are encoded by your DNA but DNA plays no direct role in organ rejection. ",
"Red blood cells are not nucleated cells and they do not express MHC. However they do still have other surface antigens that the immune system can recognize which is why ABO and Rhesus blood type (as well as others) are determined before transfusion. But these are far easier to match than MHC which is never going to be an exact match (unless you have an identical twin). ",
"Interestingly mature RBCs not only lack a nucleus but also lack DNA and are short lived cells that do not proliferate and are destroyed within a month or so. New RBCs must always be produced by stem cells in the bone marrow."
] |
[
"It’s not the foreign DNA, it is the markers on the outside of the cells. Those are typically glycoproteins or lipids with carbohydrate chains. In a simple way of explaining, If your organ of transplant has similar markers as the recipient , rejection will be minimal. The purpose of compatibility testing and biomarkers. We can receive blood transfusion because the markers on the foreign blood is either similar or because they don’t have markers to worry about( such as O blood)."
] |
[
"So it’s rather fortunate for us, that red blood cells aren’t nucleated, and don’t produce MHC I/HLA? Otherwise we’d need immunosuppressants for any blood transfusion?"
] |
[
"What is the most toxic chemical element?"
] |
[
false
] |
I know that elements like plutonium or polonium are lethal at very low doses but they owe their toxicity primarily to their radioactivity so I'm wondering which is the most toxic element when only chemical interactions are taken into account.
|
[
"Actually it is so unstable that you can't have a sizable, pure amount of it -all of its physical properties have been calculated by theoretical calculations rather than actually measured. "
] |
[
"Surely a banana doesn't contain potassium in elemental form? The question was what is the most toxic ",
".",
"Also, \"Toxicity is the degree to which a substance can damage a living or non-living organisms\" (Wikipedia), so an explosion in your gut would qualify. :)"
] |
[
"He said toxic elements. A nuclear weapon is not an element."
] |
[
"How does the SARS-CoV-2 replicative machinery differentiate viral RNA from host RNA?"
] |
[
false
] |
How do the nonstructural proteins of SARS-CoV-2 avoid replicating human RNA while they are replicating the SARS-CoV-2 genome?
|
[
"Coronaviruses use a protein, NSP1 (non structural protein 1) to shut down host protein synthesis. Then coronaviruses utilize double membrane vesicles to separate the viral processes from the cellular ones (which are being shut down to divert all resources towards viral reproduction). The double membrane vesicles can also help avoid innate immunity/interferon response."
] |
[
"This is really interesting. Is it more correct to say that the virus is moderating the host's replicative machinery rather than providing it's own though?"
] |
[
"This is correct. Viruses hijack the host machinery to perform many of its functions. Instead of encoding the machinery it may encode a protein to hijack it. Viruses do also encode a number of other protein to aid in immune invasion. This includes proteins which bind to host proteins which seek out the virus."
] |
[
"Is it more efficient to set my home's thermostat to vary between 65F when I'm not home, and 70F when I am home... or just leave it at a constant 69F all winter long?"
] |
[
false
] |
I live in a 2 story condo/apartment in New England and I have a fancy thermostat that I can program in all kinds of various ways. I used to set it to be 70F in the morning, 65F while at work, 70F when I get home, and back to 65F about the time I went to bed. Then I got to thinking, is this actually more efficient? Is my boiler actually doing more work by having to heat up the house those extra 5 degrees 2x per day? Would it not be easier and more efficient to just set it to a constant 69F throughout the entire winter? (For reasons I dont wanna get into here, lets just assume 65F is the lowest setting). Thanks for any information you may provide.
|
[
"Most home thermostats work by turning on the heater when the temperature falls below a certain level, then turning it off when the temperature goes above a certain level. It will be cheaper to leave your house at a colder temperature."
] |
[
"\"You can easily save energy in the winter by setting the thermostat to 68°F while you're awake and setting it lower while you're asleep or away from home. By turning your thermostat back 10°–15° for 8 hours, you can save about 5%–15% a year on your heating bill—a savings of as much as 1% for each degree if the setback period is eight hours long. The percentage of savings from setback is greater for buildings in milder climates than for those in more severe climates.\"",
"Read ",
"http://www.energysavers.gov/your_home/space_heating_cooling/index.cfm/mytopic=12720",
"If you typically sleep and work around 8 hours then yes, you will save more or less depending on many factors including insulation, windows, sunlight etc."
] |
[
"It's always more efficient to have the heater or A/C off rather than working, even if you want to have it at a different temperature in the future. Keeping your house at a constant temperature uses more energy than letting it cool down when you're not there or asleep and heating it back up when you're around. "
] |
[
"If a cup of water saturated with NaCl and a cup of Ice were both brought to 0 degrees F, and then left in a room at 70F would they reach room temperature at the same time?"
] |
[
false
] |
I am trying to learn which is more efficient at keeping things cool; frozen water, or non-frozen water-salt mix. Basically, if I loaded a cooler with drinks, would ice keep it colder for longer, or would cold salt water? Thank you!
|
[
"A cup of ice will require more energy to heat up to room temperature than a cup of saturated NaCl solution at zero degrees. This is because ice requires extra energy, equal to the energy of fusion, to turn into liquid water, before any energy goes into raising temperature.",
"The reason many recommend you to use a salt water and ice mixture to cool drinks isn't because of some high heat capacity of the sodium chloride solution - but rather, salt decreases the melting point, thus the solution with ice will be colder than zero degrees. If you want to cool a can of beer quickly, it's better to submerge it in -10 C NaCl solution than in ice/water mixture at 0 C."
] |
[
"A cup of salt water and a cup of ice would not reach steady-state at the same time, because they have different heat transfer coefficients with air, and because some of the heat transferred to the ice cup would go towards the heat of fusion (to melt the ice).",
"Ice is better because of this fact - it absorbs heat which goes towards melting the ice, rather than raising the temperature.",
"Regarding the cooler, you can actually use ice and dry ice. The dry ice melts before the water ice (because it has a lower freezing point), keeping your regular ice frozen, and your goods stay dry."
] |
[
"Yes. Also, the colder you can get your ice, the more heat it will absorb before melting. Basically, you want as much thermal mass, at as low a temperature as possible. Phase changes (melting ice) helps, too."
] |
[
"If we were standing on Mars, what color would Earth be?"
] |
[
false
] |
When we're looking at Mars, it's a faint red. So what color would Earth be if we were standing on Mars?
|
[
"Here's a picture",
". It's a kind of pale gray, but that's likely due to the Martian atmosphere. ",
"Here's a picture",
" from (I presume) a satellite orbiting Mars, and it's blue."
] |
[
"No, it was taken by HiRISE: ",
"http://www.nasa.gov/mission_pages/MRO/multimedia/mro20080303earth.html",
"EDIT: To clarify, the removed comment stated that the second photo was taken from the Juno probe. The parent comment is correct. "
] |
[
"No, it was taken by HiRISE: ",
"http://www.nasa.gov/mission_pages/MRO/multimedia/mro20080303earth.html",
"EDIT: To clarify, the removed comment stated that the second photo was taken from the Juno probe. The parent comment is correct. "
] |
[
"How do meteorologist forecast the path of a cyclone so accurately?"
] |
[
false
] | null |
[
"One thing they do is throw ",
" of computing power at the problem, re-running many simulations from the same initial conditions with small perturbations. This builds up a probabilistic picture of how the path of the system is likely to evolve, given the currently available information.",
"If you watch e.g. predictions on the place where a hurricane will make landfall on the weather reports, they tend to show this probabilistic prediction visually. As the hurricane nears the coast, the corridor where landfall is predicted to happen with high probability will get smaller and smaller as time progresses."
] |
[
"And they collect tons of real world data (wind speeds, rain fall, water temperatures, etc) to feed into those models. Here is a link to the ",
"Hurricane Forecast Improvement Project",
" which talks about this kind of thing in way more detail."
] |
[
"Via Data Assimilation that blends data and model output to produce the best estimates. Some of the data is collected using adaptive sampling, they fly a plane to collect local information in and near the cyclone guided by thee forecasts"
] |
[
"What's the difference between your skin being burned by fire, UV-rays, and ionizing radiation?"
] |
[
false
] |
At a certain level of severity are they all the same or are they each radically different at every scale?
|
[
"Chemist here. On a physicochemical level they damage tissues in different ways. Heat increases the rate of otherwise negligibly slow reactions, UV excites electrons causing bonds to break, and ionising radiation kicks electrons out of molecules. But I would presume that with a high enough exposure to and intensity of either, the apparent (or ”macroscopic”) damage would be the same, at least locally."
] |
[
"A lot of the practical damage caused by UV radiation results from ",
"thymine dimers",
", and their repair mechanisms recent won a ",
"nobel prize",
"."
] |
[
"Is UV radiation considered non-ionizing? Why/why not?"
] |
[
"Quick very simple electrical circuit question"
] |
[
false
] |
When you discharge a charged capacitor, does the current go in the opposite direction that it did to charge the capacitor? And if so, how is the battery factored in? Do we then kind of consider the capacitor as the emf and the battery as a wire? (This is all in terms of basic circuits, not trying to get technical here) Thanks a bunch
|
[
"When you discharge a charged capacitor, does the current go in the opposite direction that it did to charge the capacitor?",
"Yes.",
"And if so, how is the battery factored in?",
"The capacitor discharges when the battery is no longer maintaining the voltage across the capacitor. Generally this happens when you take the battery out of the circuit (eg, with a switch).",
"Do we then kind of consider the capacitor as the emf and the battery as a wire?",
"The capacitor provides the emf yes, although it decreases exponentially as it discharges. You don't generally run current backward through a battery unless you are trying to charge it - I'm not sure of the exact behaviour of batteries as a circuit element in this case."
] |
[
"There are three states a battery can be in in this circuit.",
"Where Vbat>Vcap, the cap charges.",
"Where Vbat=Vcap, there is equilibrium, and no (or negligible) current flow in wither direction.",
"Where Vbat<Vcap, the current flows back to charge the battery, and the energy is stored. From the point of view of the capacitor, the battery's internal resistance (see the spec sheet for your battery) controls the speed with which current flows. This condition will persist until Vbat and Vcap equilibriate again."
] |
[
"When you connect the plates of a charged capacitor, excess electrons go from the negative plate to the positive plate.(Thus, charge flows from +ve to negative)"
] |
[
"Why can we develop a vaccine for COVID in 8 months, but still don't have a vaccine for other viruses that are decades old?"
] |
[
false
] |
Not anti vaccine or anything and I plan on getting the covid one, but just wondering how a vaccine for COVID was made so quickly, and we still don't have a vaccine for HIV, respiratory syncytial virus, Epstein-Barr, etc.
|
[
"HIV is a highly mutagenic virus - there are a handful of different COVID strains circulating around the world, but in HIV the virus continues to mutate readily after infection, leading to the presence of multiple strains per individual ",
"(source)",
". This makes it a much more difficult task to come up with an effective vaccine for HIV.",
"As for the others, its more of an economic reason than a biological one. The scale of the COVID pandemic has caused governments and industry worldwide to pour money into the development of a vaccine -- and that level of demand just isn't there for RSV/EBV/etc. Would love for someone with more of a background in healthcare economics to chime in here."
] |
[
"\nShort answer: Many many reasons",
"\nSlightly longer answer: "
] |
[
"I also want to throw out that the COVID vaccine is not simply the product of 8 months of work... tons of work on other similar virii, like SARS, had already been done, and we'd been working on the mechanics/production of mRNA based vaccines for a long while too. To a degree, we got lucky with COVID in that it behaved similar to things we already understood, and that we'd been working on mRNA-based vaccines for such a long time already."
] |
[
"How much of our bodies do we (humans) need to live?"
] |
[
false
] |
I searched this question up and couldn't really find a definitive answer. For example, if we lose a leg or arm, we can still very well live. How far does that go? Is it possible, like in some sci-fi movies, that we can "live" with just a brain and machine-fed nutrients? I know "live" is somewhat subjective, but let's say enough to think and perhaps communicate?
|
[
"You can lose:",
"and be more or less OK. Now, there are other things that can be compensated for. They are:",
"And there are some things which really can't be replaced in an effective way:",
"There are ways to compensate for some of these (ECMO for heart/lung, total parenteral nutrition for GI tract), but they are not long-term solutions."
] |
[
"Why would you say that, it makes sense, there is nothing strange about it."
] |
[
"Why would you say that, it makes sense, there is nothing strange about it."
] |
[
"Is mathematics universal? By this, I mean if an alien species were to develop their own system of mathematics, would it resemble our own? Would it share the same concepts?"
] |
[
false
] | null |
[
"Quite possibly not a base 10 system, but certainly any technically evolved civilization would have mathematical concepts of counting, arithmetic operations, etc."
] |
[
"Whenever I see a question like this I like to remind people that for a very long time mathematical developments were primarily geometric. Algebraic interpretations of what's going on in physical systems is, necessarily, an abstraction. Geometrically though you're not that far removed from the actual thing you are describing mathematically. ",
"In Geometry it's much easier to think of certain things as more universal. The sum of angles in a triangle for example will always be consistent in Euclidean space as half the ratio of the radius of a circle to the circumference of the circle.",
"In addition to a lot of Geometry keep in mind that a lot of math, calculus especially, was developed to help explain Physics. The notion of the instantaneous rate of change in position (velocity) as something important to know about is probably universal. This instantaneous rate of change is what we call a derivative. For Relativity to hold, the laws of Physics need to be universal, and in that sense if you had the math to do Physics, your derivative and integral (calculus) would have to look the same conceptually. "
] |
[
"A math friend once joked that all number systems are base 10, because what we call base 8 would still be written as 10. They would call our system base 12. Hm, maybe i suck at math jokes, but it was funny and thought provoking to me when I heard that."
] |
[
"Can scientist compare corona virus in the wild to what was being studied in the wuhan lab genetically to see if it matches?"
] |
[
false
] | null |
[
"Unclear what you’re asking. The wuhan lab was studying wild viruses. There are many wild matches for them. Easily googled, many recent papers."
] |
[
"I thought dna sequences were very precise. Your saying the wuhan lab had virus the genetically matched with what has been found in the wild?"
] |
[
"The wuhan viruses ",
" wild viruses. You seem to have some conspiracy theory misunderstanding here."
] |
[
"Does a Patina affect the Thermal Conductivity of Copper?"
] |
[
false
] |
I have seen a few different answers to this, from Water cooling blogs saying, "The Patina is nothing to worry about, it won't affect performance" to people using the Patina to justify why Aluminium Radiators are now preferred. So lets ask Reddit. If a Patina forms on a Copper Radiator, will that Radiator preform worse then a brand new, perfectly clean Radiator? Does it depend on the type of Patina (brown vs black vs Green) as they are different chemicals? For that matter if this is true of a Copper Patina, would it hold true for all Patinas (say for example, Silver Tarnish)? And even if it does make a difference, is this difference as significant as the decrease performance that would be caused by Paints or Powder Coats that are often used to protect the Radiator? Or for that matter is the drop in thermal performance enough to justify, say, an Aluminium Radiator? Or a Nickel coated radiator? (Something I have never seen) ((We are assuming Galvanic Corrosion does not exist for this question. Obviously that will play a bigger role in whether you will be able to use Aluminium in most cases.))
|
[
"copper oxide is what forms copper carbonate, thats true. more specifically it is i believe hydrous carbonate of malachite or hydroxide and that turns the copper green during the oxidizing reaction process."
] |
[
"the word patina is not a specific enough term, its like saying \"is food good or bad\"? a 'green' *patina (*which is a generic term for any surface coloration resulting from a chemical reaction on a surface) , is specifically called 'vertigris'. the general name for copper oxide. copper oxide will conduct heat , or electricity ,at a markedly different rate than pure copper. it has an insulating value that is greater than copper's is. it will accrue heat faster, but will also become cooled by convection , so it will certainly affect the overall efficiency of any system, but not by enough to usually matter. Obviously if the amount of oxide becomes saturated then it will physically hinder airflow through a radiator which will significantly lower its efficiency. otherwise it's probably an insignificant amount."
] |
[
"A fair point.",
"A Brown Patina, in this context, is typically the intermittent stage between raw copper and the Green Patina. The Brown Patina is Copper Oxide where as when it becomes Green it has become either Basic Copper Carbonate, or Basic Copper Chloride.",
"A Black Copper Patina usually forms in the presence of Sulfur, often artificially using \"Liver of Sulfur\" initially it is similar in appearance to a Brown Patina, but overtime will go almost completely black."
] |
[
"Can dark matter collapse and form black holes?"
] |
[
false
] |
So, the only way we can detect dark matter is through gravitational effects. Could dark matter theoretically clump so dense that it forms black holes just like baryonic matter? If so, would these black hole be any different to the ones that formed from "normal" matter?
|
[
"If you had a bunch of dark matter at low enough energy and high enough density, it could collapse into a black hole. Black holes have no identity beyond mass, spin, and charge, so it would be like any other black hole of similar charge. However, this is extremely unlikely to happen because dark matter particles have sufficient velocity to escape each others' gravitational pull, and don't lose velocity through collisions (because collisions almost never occur) the way condensing gas does."
] |
[
"Well after it becomes a black hole it's not dark matter anymore."
] |
[
"The point is that dark matter only can have very weak interactions, which makes it impossible to lose enough angular momentum to clump together. ",
"It is very unlikely that enough dark matter moves head on to the same point to form a black hole."
] |
[
"Why does color see so different from pitch?"
] |
[
false
] |
edit: that should read "seem," not "see" in the title. Color and pitch are the way our brains interpret the frequency of light and sound waves, respectively, but they seem like very different kinds of interpretation to me. While pitch has a pretty straight-forward low-to-high thing going on, color doesn't have a clear high/low interpretation. Red seems just as similar to purple as it does to orange. Color also has odd groupings of colors (we generally recognize six kinds on the red-violet spectrum) which pitch doesn't seem to mimic, while pitch has this repeating pattern every time frequency doubles which color doesn't seem to mimic. Brightness and loudness do seem pretty similar to me, and much simpler in both cases, so I'm wondering why color and brightness don't also.
|
[
"We have 3 types of color receptors in our eye, for red green and blue, so every color we see is a permutation of those three. Meanwhile, our ear has 20,000-30,000 fibers with different resonant frequencies, to tell us which pitch we're listening to. ",
"So they're quite a bit different. A large continuum of sensors for the ear, with just 3 different types for the eye that are then blended to give us a continuum of colors. "
] |
[
"Actually, they are very similar, and the color of visible light changes with wavelength in a very linear gradient from red to violet - the key is that there is no such thing as the color \"magenta.\"",
"Our minds interpret certain combinations of red and violet light into a \"color\" we call \"magenta\" but there is actually no such thing as a magenta-colored photon."
] |
[
"Also pink. There exist no pink photons."
] |
[
"When you put a spray nozzle on a hose, why doesn't pressure build up until it bursts?"
] |
[
false
] |
You attach a spray nozzle to a garden hose and turn the water on. Nothing comes out of the nozzle until you squeeze the trigger. All the while, water is still flowing into the hose. It seems like lots of pressure is being built up here. If that's true, why doesn't it burst?
|
[
"The water company is only supplying so much pressure to the water feed. Hoses are designed to be able to contain that pressure. Consider that when the spicket for your hose is turned off, the pipes within your house are holding the water without bursting, and they are only thin copper; under your sink they are a flexible rubber and steel strand tubing.",
"In the US, the water company's pressure is around 75psi I believe.",
"If you wanted to burst a hose in this way, you'd have to supply a higher pressure than what the water company gives, such as with your own pump."
] |
[
"Water pressure varies wildly, but 75psi is slightly above normal. Ultimately water pressure comes from the height of the water tower that serves your house. Each foot of height makes 0.43 psi, so a 165 ft water tower has a water pressure of about 71 psi at the base. But if your house is a quarter of a mile away, and sits 30 feet lower, then the water pressure of the water main serving your house is closer to 84 psi. If it's 30 feet higher than the base of the water tower, your pressure will only be 58 psi. Anything over 70-75 can damage the valves in your appliances and is generally hard on your plumbing. If this is the case, you can install a PRV (pressure reducing valve) right next to your water meter to get your water pressure into the 50-60 psi range, which is more normal. A plumber will do it for a couple hundred dollars usually.",
"But if your house is served by an old pump station instead of a water tower, and you only get 40 psi, like I do, then you're stuck with unsatisfying (but conservational) showers, and it takes much longer to water your lawn. They don't make pressure increasing valves, sadly."
] |
[
"If you want a more detailed explanation why water doesn't keep pushing into the hose from the water company:",
"The water company supplies water ",
", which is like how hard the water pushes against something like the sides of the pipes or your hand if you block the flow. In the narrow pipes in your house, or the larger underground pipes that bring water to your neighborhood, the water is all pretty much at the same pressure, regardless of the pipe size. (There are some pressure changes as pipes go up and down, but we'll skip that part as it doesn't change this discussion)",
"Now consider the opening of the hose, where it attaches to the spicket. Inside, imagine that bit of water that is just inside the hose. Kind of like if you put a coin in the opening in the hose, this piece of water is a disk, the same diameter as the hose, and very thin. In order for more water to come into the hose, the water in the pipe has to push that \"coin\" of water into the hose so there's room for more water to come in.",
"The water in the pipe is pushing on that coin of water on one side with the pressure of the water company, and the water that's filling the rest of the hose is pushing ",
" on that coin of water with the pressure in the hose. If that coin of water were to move further into the hose, the rest of the water in the hose would have no where to go (you haven't pulled the nozzle trigger) so it increases in pressure. The pressure from the water company is always the same, so now the water in the hose will push that coin of water ",
" so it would push it back to where it was. ",
"The pressure in the hose will therefore balance to match that of the water company's feed, and the feed can't force more into the hose, because the hose will push it right back. "
] |
[
"If a chromosome is made from two chromatids, and a chromatid is made from one DNA molecule, why do we have different chromosomes? Are all DNA molecules in our body the same?"
] |
[
false
] |
[deleted]
|
[
"Each chromosome has different genes (ie different DNA). The overall genome (composite DNA content) of each cell is identical however. "
] |
[
"Have included a TL;DR. It's not that DNA is packaged differently in chromosomes. All DNA is super coiled in the same way. It is in fact the sequence of the DNA that is different. For clarity I shall give a brief over view of the DNA structure.",
"Each DNA molecule is made up of two strands of complimentary sequences of molecules called bases. These are (for simplicity I shall use their first letter as is usual) A, T, C and G. A being complimentary to T and G being complimentary to C. It is the sequence that these bases are alined within the DNA that makes them different. For example bases 1-5 of chromosome one may be GTACA whilst the bases 1-5 of chromosome 6 may be CCGTG. ",
"These differences in sequence will result in different proteins being produced from different strands of DNA. Each of these sequences within DNA is what is referred to as a Gene. And each gene will have a different base sequence. And each chromosome contains many different genes. ",
"TL;DR No they do not pack differently. It's the DNA base sequence that differs. "
] |
[
"A chromatid is ",
" copy of a single chromosome. A chromatid occurs when cell division happens. Before the cell can split, all chromosomes get replicated and neatly organised into chromatid(s). For a brief amount of time the original (a chromatid) and its copy (a chromatid) are held together (as sister chromatids, note the plural). ",
"During the cell separation, the two chromatids will be separated and one of each will be pulled into each daughter cell, at which point we start calling each individual chromatid (note singular) by the name chromosome again. ",
"Yes, it does seem a little redundant, but, shrug. Basically, when you wrap up one of your chromosome nicely, in preparation for cell duplication, it gets called a chromatid. ",
"A chromosome (most of the time) / chromatid (single copy of a chromosome during cell separation) is indeed a single DNA molecule. ",
"why do we have different chromosomes",
"We evolved this way? Having 46 chromosomes is how evolution packed humans genetic code in our cell nucleus. Note that the duplication of chromosome (we have 23 pairs) is a form of error encoding, and therefore has a clear evolutionary advantage.",
"Are all DNA molecules in our body the same? ",
"You only have one genetic code. So for the most part, ",
" , the DNA in each of your cell's nucleus is a copy of the same genetic code. ",
"Now for the fine prints, there can be small differences cell to cell due to mutations. In some cases, the mutations can become dangerous and turn into cancerous cells. Continuing, some rare individuals are true ",
"genetic mosaic",
" . Also, in mammals, the female will also exhibit a certain form of expression in the genetic code where one of the two x-chromosome is randomly suppressed. So while all cells of the females have all the same DNA, not all cell use the same DNA in their functionning. ",
"Finally, you are host to many parasitic species, viruses, bacterias, etc...all of those also have their own DNA, and, in the broadest sense, their genomes does counts as \"a DNA molecule that is in your body\". "
] |
[
"Why does excessive/tumultuous motion people to become nauseous, and why does this happen to only some?"
] |
[
false
] | null |
[
"In short, the brain uses feedback from your inner ear, eyes, and the position of your body to figure out how to balance and remain upright. This nausea occurs when two or more of those senses contradict each other (I.e. when you're in a car, starting at something inside the car and your inner ear is saying that you are turning sharply, but your eyes are saying that you are not turning relative to the object you are starting at) and your brain becomes confused. The variation in the strength of this effect between individuals is difficult to pin down though. It's also not entirely certain why this conflict produces nausea but that's how it happens at least."
] |
[
"But why does this cause nausea?"
] |
[
"There are several theories as to why this happens, as discussed on ",
"this Wikipedia page",
" but nobody knows for certain."
] |
[
"Because the JWST will be orbiting way out at the L2 point and out of suborbit what are the backup plans if by chance JWST turns into a Hubble fiasco?"
] |
[
false
] | null |
[
"My instinct is no but it is a difficult question to answer. The L2 position is about 5 times higher than the moon, it is more complicated than that though as we do not orbit the earth at it so we not only have to gain altitude but shed our velocity of our earth orbit. ",
"We can reach L2 with significantly smaller rockets than a saturn for our probes (WMAP launched on a delta II) . A manned mission is much more complex, the additional time for both the out trip and return means more supplies but there is no lunar lander so a save of payload there. This is further complicated by the fact that the spacecraft orbits the moon (which orbits the earth) , maintaining a lot of it's velocity that it will use to return to earth but forcing it to fight the moons gravity on it's return. This is unlike in our L2 case which would likely require a much larger delta-v (change in velocity) on the way out but less to return to earth.",
"I can't say for sure and a quick google doesn't really help me but it is likely that a saturn V rocket did not have enough lifting ability to lift a spacecraft into orbit that had enough fuel onboard for the delta-v necessary to perform a return trip to L2. That said, I am absolutely open to being wrong, the lack of a moon landing and perhaps the lack of having to escape the orbit around the moon may actually mean the delta v required for the return burn to be a lot less than that from the moon possibly meaning that the total delta-v (there and back) is actually easily doable with the payload of the Saturn V.",
"TL;DR maybe, maybe not. It certainly hasn't been attempted but, of course, there was no reason to try it before.",
"I will however stand by my original statement that no past spacecraft could make it; a space mission is more than just it's launch vehicle and the apollo craft certainly could not make it to L2 and back."
] |
[
"You are right that the location of the JWST makes a service mission incredibly difficult. It is impossible for any current (or past) manned spacecraft to reach the L2 point and thus carry out any repairs to a broken design.",
"Nevertheless, the design for the JWST does include the ability to dock with other spacecraft so perhaps it would be possible for a robotic spacecraft or a future, longer range, manned spacecraft could reach and repair it. The technology to do so does not currently exist though. Cost might be prohibitive especially for a manned mission."
] |
[
"Not even a Saturn V could go there?"
] |
[
"Why is it that some people get eaten up by bugs while others seem to remain untouched?"
] |
[
false
] | null |
[
"Specifically in regards to mosquitoes, they have a preference for certain blood types and other blood characteristics which they can actually smell. First off, mosquitoes find their way to humans by following CO2 gradients in the air, simply the way you breathe and how much CO2 you exhale might make it easier for mosquitoes to make their way to you. Additionally, various factors like type-O blood, pregnancy, and even beer drinking have been shown to attract mosquitoes. Another is the presence of lactic acid in sweat, which would occur with recent exercise. Other added scents from the soap, shampoo, deodorant, and perfumes used as well as clothing, recent food smells, the particular makeup and activity of our microbiome, etc. might attract or deter mosquitoes preferentially."
] |
[
"I have a blood disorder that causes too much iron in my blood - apparently most bugs (especially moquitoes) really really hate high iron content for some reason. So most bloodsucking bugs tend to avoid me - to the point that if someone is sitting/sleeping next to me, the side of their body that is closest to mine, will be untouched - it's my superpower :)"
] |
[
"they enjoy sweet things, so they're more attracted to people with a high carb diet.",
"But... how do they know? As far as I'm aware of glucose isn't a volatile we might leak into the air through our skin.",
"Does a high carb diet cause us to release a chemical that is somehow related to \"sweet blood\"?"
] |
[
"Why don't our bodies become immune to certain diseases and illnesses once we recover from them?"
] |
[
false
] | null |
[
"It has to do with the way our immune system responds: it starts making antibodies that binds to the microbes that caused the illness; antibodies bind to specific features on the surface of these Antigens. If the virus/bacteria later evolves and that evolution changes its surface features, the existing antibodies become useless and you get sick if you catch it again.",
"In other cases, one illness can be caused by plenty of different viruses (like the common cold), so if you get one you actually get no protection against the others."
] |
[
"Is there a limit to the number of different antibodies that the immune system \"remembers\" it needs to fight illnesses?"
] |
[
"Yes, there is. But don't think about of it, it's a pretty high number of different antibodies. ",
"If you ask why, it's due to the ageing process. As you get older your body would have \"spend\" more and more of your B cells (Lymphocytes B) which are the responsable of making those Antibodies. But, as I said, don't worry about it, it would be really strange if you get to that point."
] |
[
"Bacon - Fridge required? Questions on bacterial growth..."
] |
[
false
] |
Hey Reddit, So, I was thinking about shipping some meat, however the logical refrigeration part is a bit of a bitch. Now, I mentioned this to my SO, who stated that bacon doesn't require a fridge. He stated that it is vacuum sealed and that it really shouldn't matter. His key points: no air = no decomposition. it's refrigerated because of perception and nobody would buy bacon off a shelf. Mine: Why would stores pay tonnes of money to keep it refrigerated? Why would the packaging say to keep it in the fridge? If vacuum sealed meat was all it took, why don't they seal ALL meat? I understand the concepts of bacteria requiring material (said bacon), air, and moisture, and that if one of the three doesn't exist, then it shouldn't spread, but then why do we require a fridge?
|
[
"There are plenty of ",
"anaerobic bacteria."
] |
[
"The bacteria may die, but the toxins they produce are easily left behind."
] |
[
"Staph and E. Coli are both facultative aerobes, meaning that they can survive in the presence of oxygen as well as without it, there are many bacteria that fall into this category.",
"Most bacteria cannot reproduce at a rate sufficient to create a problem below the temperatures at which we typically store food. There will be bacteria in everything you eat unless you sterilize it first (and even then there may be some. The concern is how many of them there are, and what types of/how much toxin they've been able to produce."
] |
[
"This may be a stupid question, but what is the universe?"
] |
[
false
] | null |
[
"Depends which physicist you ask, really. \nThere is ",
"string theory",
", some other scientists believe everything is a wave, maybe there are some other theories. "
] |
[
"There are no stupid questions.",
"\nYou need to focus your question a bit more if you want to get an understandable answer. I'd say Universe is the whole observable space we see and theoretically know about (i.e. the edge of universe) and all matter/anti-matter enclosed in it, whether we know about it or not."
] |
[
"What I meant that what is is fundamentally? Is is just a spontaneous energy in various forms interacting through fields?"
] |
[
"Ice and salt."
] |
[
false
] |
I was wondering, why does it burn if you put salt on your skin then put ice on it? These kids at work have been doing it, and have ridiculous burn looking injuries from it.
|
[
"\n- Richard"
] |
[
"That makes sense, thank you for the answer."
] |
[
"Also those burn looking injuries are frostbite. Very bad for you.",
"Edit: Just realize the other person mentioned frostbite in the answer. Doh!"
] |
[
"Was most of the matter in the early universe created by massive hadronization during the initial inflationary epoch?"
] |
[
false
] |
I've always wondered whether the process of hadronization was the mechanism by which most of the matter in the early universe was created. Were the earliest quark pairs/triplets/groups or the quark gluon plasma stretched incredibly quickly by inflation causing hadronization to occur on a massive scale once the initial phase of inflation ceased? I'm imagining (as a simplified thought experiment), for example, a lone quark-antiquark pair suddenly being separated by a huge distance in an incredibly short amount of time and then the new space between becoming rapidly populated by a massive amount of new mesons and hadrons (formed from the energy of the inflation due to confinement). Is this picture totally wrong or is it a decently accurate description of what happened in the early universe? Was confinement even "in place" or rather, operating, at that time, or did the initial inflation occur before confinement started to govern the earliest quarks and gluons? Thanks for reading, and I apologize if any of this doesn't make sense, I'm just an interested layman.
|
[
"It's a smart idea you've had and a reasonable question to ask, but no, we don't think it happened via that mechanism.",
"The ",
"leading theory",
" or collection of related theories has a universe that's cold and empty or mostly empty of matter but that has a great deal of vacuum energy in the form of an inflaton field. This inflaton field is a sort of ",
"unstable exotic vacuum state",
" with repulsive gravity that makes the universe expand very fast, but this field rolls down a potential slope just like a ball rolling down a hill. When the field reaches the bottom of the potential, it couples to matter fields and the inflatons decay into a hot soup of relativistic particles, converting the enormous negative vacuum energy into positive mass-energy and motion-energy in the form of matter and radiation as space reconfigures itself into the stable or ",
"meta-stable",
" low-energy state we observe today with a very low cosmological constant instead of a massive cosmological constant that blows everything apart.",
"In a sense, inflation never qualitatively ended, the vacuum just decayed from a high-energy state in which there was a tremendous anti-gravity effect from the large vacuum energy to a low-energy state in which there was a much smaller but still non-zero anti-gravity effect from the much lower vacuum energy of the new configuration, which we measure today as dark energy and the accelerating expansion of the universe, which can only be measured over vast distances because it's so weak in the current universe, and it was this decay in the vacuum state which produced all the matter in the universe.",
"Something like this ",
"could potentially happen again",
" if the vacuum were to nucleate into an even lower energy state, and this is one possible doomsday scenario in which the higgs field quantum-tunnels into a new stable configuration with a lower energy state than the current configuration; this would cause more energy to be released in the form of energetic particles in a second big-bang-type event and the resultant universe would have different physics from those we observe today, and would unfortunately most likely be uninhabitable due to the new massive higgs that would cause anything larger than a bacterium to collapse into a black hole, but this is all interesting-but-highly-speculative territory, so take it all with a grain of salt."
] |
[
"Inflaton field energy loses energy until it hits a stable level and couples with (presumably less energetic) matter fields and then it's energy is transformed into matter via some decay process.",
"More or less, and I'll elaborate a bit on that below. ",
"If this is the case, and considering that, as you say, inflation never really ended, and thus the universe is expanding (and at an accelerating rate), does this mean that the energy level at which the inflaton field coupled with the matter fields is just one of perhaps many metastable states for the field? ",
"The inflaton field is not a known field, we don't know what it is or if it's one field or multiple fields, but the simplest models treat it as a single scalar field. As it rolls down the potential, it has different behaviours depending on the steepness of the potential slope; where the potential is relatively flat, it doesn't couple strongly to matter fields and instead drives the exponential expansion of the universe, but once the field reaches the steep part of the potential slope there's a phase transition and the field experiences dynamical friction as it couples to matter fields. Without any coupling, there would be no friction and the field would roll back up the other side of the potential well and oscillate back and forth like that indefinitely, but because it couples to other fields there's a damping effect and quite a strong one, so there are only a relatively small number of oscillations near the bottom of the potential before the field settles into it's ground state, having transferred it's remaining energy into the creation of particles and the motion energy of those particles.",
"Because it's a quantum field, it has quanta called inflatons and these inflatons decay probabilistically with a characteristic energy set by the mass of the inflaton, and this energy sets the energy scale for reheating at the end of inflation and the temperature of the hot big bang, which is estimated to be ",
"somewhere in the region of 10",
" GeV",
", but could be several orders of magnitude above or below that. The inflatons are unstable precisely because they're massive and ",
"massive particles always decay",
" into lighter particles until there's ",
"nothing remaining that they're permitted to decay into",
", and the rate at which they decay depends on how strongly they couple to the other fields, which in turn depends on the state of the inflaton field, since the coupling constant depends on the field potential, so where the slope of the potential is shallow and coupling is very weak, the inflatons are ",
"stable and don't decay",
". Most of the energy (not including the energy that goes into forming dark matter) is transferred to the quark and gluon fields, forming quarks and gluons with the non-thermal characteristic energy of the inflaton decay products which then rapidly thermalise via scattering collisions in a quark-gluon plasma with a thermal distribution of energies, which later hadronizes into colour-neutral bound states, with a period where newly formed hadrons are repeatedly broken up by high-energy collisions with other particles until the universe cools enough and the inflatons have finished decaying. During the time where the inflatons are decaying, the ongoing decays continually reheat the cooling quark-gluon plasma and break up newly formed hadrons with their high-energy decay products. ",
"This is certainly not the whole story, since it's around this time that dark matter is thought to ",
"be formed",
" and the inflaton may first decay into massive supersymmetric particles which then decay in progressively lighter particles, but not much is known about those, or if they even exist.",
"Is the inflaton field currently in the process of rolling down a very shallow hill (hence the generally low energy of the vacuum) which is becoming steeper over time (the rate of expansion is increasing)?",
"No, the inflaton field, whatever it actually is, is no longer rolling down any potential slope and is in it's ground state or at least a metastable state. It's not the decay of the inflaton field that causes the universe to expand, but the ",
"vacuum energy",
" of fields in general. Because fields are quantum mechanical, even a field in it's ground state has a non-zero energy because it probabilistically fluctuates around the bottom of it's potential, so when you measure it, it's never exactly zero. This is ",
"zero-point energy",
". It's the same idea as why you can never cool something to absolute zero; there's always some quantum mechanical jitter to the particles that gives them a non-zero temperature. This energy causes space to expand, but when we try to calculate the magnitude of this energy, we get an enormous value that should result in a universe that would still be rapidly inflating, so something's going wrong with our calculations somewhere and this is known as the ",
"cosmological constant problem",
", which is one of the great ",
"unsolved problems in physics",
", though recently Unruh and others published a ",
"paper",
" that attempts to solve that problem.",
"Is there other fields with which the inflaton field could potentially couple",
"Yes, it may couple to whatever fields are responsible for dark matter. We really don't know though, since we don't know what dark matter is or what the inflaton field is.",
"I'm familiar with the false vacuum / metastable vacuum scenario in regards to the higgs field, but is there any such scenario which involves changes of state of the inflaton field, or is it simply a matter of inflaton metastability or stability resulting in no expansion, and sudden tunneling out of a metastable state resulting in expansion starting up again?",
"The accelerating expansion of the universe is due to the different manner in which different forms of energy dilute as space expands; matter and radiation slow the expansion by gravitating and vacuum energy drives expansion by anti-gravitating, but as space expands, matter and radiation dilute away asymptopically towards zero energy density while the vacuum energy stays at a constant energy density; ",
"radiation dilutes at a rate of r",
" matter and dark matter dilute at a rate of r",
" and the vacuum energy remains constant",
", so the expansion doesn't accelerate without limit, it accelerates up to a constant rate that's higher than what we observe currently but not up to inflationary rates, which require a higher vacuum energy than the small vacuum energy in our current vacuum.",
"There's no particular reason to think that the inflaton field is in a metastable state and not it's true ground state, though it's perfectly possible to construct theories in which this is the case, just as it's possible to construct theories in which there's more than one inflaton field. However, it's possible for the inflaton field to quantum-tunnel back up to a higher energy state, just immensely improbable, but if you take a really, really big picture look at things, this ability to quantum tunnel back up to higher energy states means that long, long after the heat death of the universe, when timescales are immensely long but before they're so long that you start worrying about ",
"Botlzmann brains",
" and ",
"Poincaire recurrence",
", quantum fluctuations can result in the formation of a new bubble of vacuum with a large value for the inflaton field and then it starts inflating and spawning new big bangs and new universes as some regions of the new vacuum decay while the exponential expansion causes the remaining inflating regions to constantly outpace the decayed non-inflating regions that nucleate within it, thus kicking off the same process of ",
"eternal inflation",
" that gave birth to our own universe and probably a vast number of sibling universes from some predecessor vacuum. ",
"This doesn't actually require immense timescales to happen; immense vastnesses of space work too, since it's probabilistic and with enough space for it to happen in, it'll happen sooner rather than later in some regions, but almost certainly so far away from us that the relatively sluggish expansion rate of our low-energy vacuum will still be fast enough that these distant events will never reach us until one happens locally, within 10 billion light years or so where the light-speed expansion of the bubble would eventually traverse the space between us. Of course, it only expands at the speed of light from our perspective as external observers; the new inflationary vacuum expands into itself internally at a tremendous and exponential rate. Or so I think, anyway; I've not seen a paper dealing in detail with the scenario in which an inflating vacuum nucleates inside an expanding vacuum; there are papers dealing with ",
"bubble collisions",
", but that's what goes on inside an inflating space and the expanding spaces that it decays into, not outside of it.",
"I hope that helps; some of this stuff, well, all of it really, is rather on the speculative bleeding edge of physics and subject to change as our understanding develops."
] |
[
"What happened to the quark fields during inflation, though? Was the expansion too slow to drive hadronization by tearing apart any baryons present at the time?"
] |
[
"If we are able to use to use fairly simple catalysts in labs and in industries, why do organisms utilise mindbogglingly complex catalysts- enzymes?"
] |
[
false
] |
I've read about metals and their oxides, which are simple molecules, being used as catalysts, and some simple organic molecules too. Why do all living beings have such complicated catalysts, huge molecules with intricate structures?
|
[
"There are numerous ways to go about answering this, so I'll just highlight a few that I subjectively think are the most important.",
"edit: typo"
] |
[
"M.S. in Biotechnologies here :)",
"\nSimply because inorganic catalysis can be very hard to control for a living being (think especially at bacterias, very similar to the first living forms known to have existed). A metallic catalyst will \"blindly\" catalyse any possible reaction, with no specificity. This would mean that if there are three types of molecules that can be converted into something else in a cell, and you would add the right metallic catalyst, that would just convert most part of those molecules into their respective products.",
"\nEnzymes instead have many key features useful to this purpose:",
"\nFirst (specificity), a given enzyme is going to bind only one given substrate (or a small set of them), so you can have some enzymes handling ATP, some handling ADP, some AMP, some cAMP and so on. With inorganic catalysts, you would most likely just have one metal being able to break (or join) P-P or Adenine-P groups, quickly converting all of these different molecules into Adenines and phosphate groups.",
"\nSecond (binding affinity), an enzyme doesn't always work: they generally work only if there is a given concentration of substrate present. If, for example, there is too few substrate the enzyme won't use it, preventing it from consuming all of the substrate in the cell/cellular compartment. This is crucial to allow the cell to regulate many different pathways.",
"\nThird, an enzyme can be actively and extremely quickly switched on/off with a simple modification (operated by another enzyme). This is crucial to pass signals, to switch on one pathway/mechanism or switching it off.",
"\nFourth, enzymes can pair their catalytic function with structural function, for example moving something when they catalyse a reaction (or vice versa, just take the ATP synthase example, which exploits a proton gradient letting protons pass from one side to the other of a membrane as an energy source to synthesize ATP, no metallic catalyst could do such a thing). ",
"We can use those super-simple catalysers in the industry because a factory is not just a huge sack with catalysers and some reagents inside. There are different containers and steps and there are machines/humans to move stuff from one reactor to another, so we can afford to use \"stupid\", straight-forward catalysers. A cell is not different in principle: often the catalytic core of an enzyme exploit the features of a metal molecule, but this is not kept floating around as it's not kept floating around in a factory: it is trapped inside an enzyme and only exposed to its reagent (thanks to the highly specific pocket of the enzyme). Not too different from having a tank with a catalyser where specialised workers poor the reagents in."
] |
[
"There are different containers and steps and there are machines/humans to move stuff from one reactor to another, so we can afford to use \"stupid\", straight-forward catalysers.",
"I tangentially addressed this in my comment (i.e. the process of boiling off a volatile product to drive the desired reaction), but the way you put it here made me realize that this is, in a way, exactly how a lot of enzymes work. There are enzymes that use arcane mechanisms that shuttle electrons around between residues in an elaborately choreographed process (the enzyme that deoxygenates RNA with a tyrosine radical comes to mind), but a lot of them use simple acid-base catalysis. In those cases, the enhanced reactivity afforded by the enzyme doesn't come from the catalytic residue that actually do chemistry, but from the very specific arrangement of the active site, i.e. the residues that coordinate the substrate. A general catalyst thereby becomes a specific one because the only species that will actually find its way close enough to the catalytic residues to actually react is the \"proper\" substrate."
] |
[
"Can we spin molecules using electromagnetic waves?"
] |
[
false
] |
Hello, I have been learning about radio, and now my understanding of a microwave oven is that water is polar, so changing electromagnetic fields can cause a torque(?)... Which reminds me of how an electric motor works. Surely if that's the case, we can spin molecules with electromagnetic waves. If we can, is there applications? Does anything interesting happen if molecules spin quickly?
|
[
"One of the most interesting things we can do by spinning molecules in my opinion, is identifying what that molecule is based off the way it spins. ",
"https://chem.libretexts.org/Bookshelves/Organic\\_Chemistry/Supplemental\\_Modules\\_(Organic\\_Chemistry)/Spectroscopy/Nuclear\\_Magnetic\\_Resonance\\_Spectroscopy",
"Not quite. In NMR spectroscopy, what is \"spinning\" is a particular quantum property of the nucleus, which leads to a tiny magnetic field. No actual molecular motion is involved."
] |
[
"One of the most interesting things we can do by spinning molecules in my opinion, is identifying what that molecule is based off the way it spins. ",
"https://chem.libretexts.org/Bookshelves/Organic\\_Chemistry/Supplemental\\_Modules\\_(Organic\\_Chemistry)/Spectroscopy/Nuclear\\_Magnetic\\_Resonance\\_Spectroscopy",
"Not quite. In NMR spectroscopy, what is \"spinning\" is a particular quantum property of the nucleus, which leads to a tiny magnetic field. No actual molecular motion is involved."
] |
[
"For molecules in the gas phase, unequivocally yes. For liquids, it gets complicated. For solids, (usually) not.",
"In the gas phase, molecules are mostly isolated from one another. As with all things on these scales, rotation is quantized. This means that you have only discrete allowed rotational energy and angular momentum states. And as with other things quantum mechanical, the positions and velocities are not really classically describable. But it does have angular momentum, so it is rotating.",
"The energy levels for a molecular rotation fall in the microwave regime (which will relate back to your microwave oven question). For gases, these look like a ",
"series of spikes",
": this is because gases at room temperature have enough thermal energy that many molecules are already rotating some amount already (in an excited state). When a molecule absorbs a microwave photon, it can either gain or lose one unit of angular momentum and go up or down one energy level. Since there are many starting states, you end up with many transitions evenly spaced due to the particular symmetries of quantized rotations.",
"The exact values these levels absorb at depend a lot on the structure of the molecule, including how much it is vibrating. The rotational spectra is one of the tools used to identify molecules in deep space, for example.",
"In liquids it gets more complicated, since now molecules are packed right next to each other and interact constantly. This turns our nice sharp microwave spectrum from the gas phase into a giant blob. While rotations are certainly still involved when a liquid absorbs microwave radiation, there are now a ton of molecule-molecule interactions which are also contributing to the absorption, many of which are not true rotations, but are more translational or vibrational in nature. So your microwave oven is rotating water, but not at all exclusively.",
"In solids it becomes even less of a pure rotation, since in many simple solids the molecules are stuck in a crystal lattice which dictates the position and orientation of the molecules. The excited states are essentially only the collective motions in this case.",
"One other interesting thing I'll mention is the optical kerr effect, which (at least for liquids) is closer to the electric-field-applying-torque model than the quantum mechanical stuff. If you hit a liquid with a high-intensity laser pulse (off-resonance, so no quantum transitions), the electric fields in the laser can apply a minute torque on molecules in a liquid which will create a small net alignment of the molecules to the laser field. This turns out to be enough to change the index of refraction minutely in the direction of alignment, and the effect then goes away after the laser pulse leaves as the molecules start randomly bumping into each other again. By tracking how quickly the effect goes away (less than a nanosecond typically) you can track how molecules move in a liquid. This was one of the first ultrafast (sub nanosecond) measurements of liquid dynamics developed - way back in the '60s."
] |
[
"What magnitude would the earthquake in “The Land Before Time” be?"
] |
[
false
] | null |
[
"Ok, so this is definitely on the edge (and maybe beyond the edge) of what's sort of an appropriate question for AskScience, but it's fun and it provides a useful context to understand how we discuss earthquakes and the damage associated with them, so let's go with it. For those unfamiliar, I assume this ",
"YouTube clip",
" is covering the event in question, specifically starting at 3:20 minutes into this clip (do I need a spoiler tag for a nearly 40 year old childrens movie?).",
"The first thing to be aware of is the difference between scales of earthquake ",
"magnitude",
" and earthquake ",
"intensity",
". The magnitude of an earthquake is an intrinsic property of a particular event and, at least for the most common earthquake magnitude scale, i.e., ",
"moment magnitude",
", is related to the energy released by the earthquake (technically, the scale is based on the ",
"seismic moment release",
", but we can develop an approximate equivalence between seismic moment and energy, so to simplify things, we can say this scale is based on the energy released by the earthquake). This means that the earthquake magnitude is the same regardless of your proximity to the source of the earthquake. In contrast, earthquake intensity is a measure of the experienced intensity of shaking/damage in a particular place at the surface. In detail, earthquake magnitude will be one component of determining intensity, but other things like the depth and hypocentral distance (i.e., how far away is the location from the earthquake source) along with the type of rock in the location and other local details (e.g., ",
"seismic site effects",
") will all contribute to the intensity. This implies for a single event (which has one magnitude) it will have different intensities depending on the location in question. Earthquake magnitude is a quantitative measure and is primarily determined through analysis of seismograms recorded by seismometers where as earthquake intensity measures may come from both quantitative measurements (like seismograms) but also from qualitative observations.",
"Now, with this in mind, and returning to our clip, in someways this question is similar to dealing with \"historical seismicity,\" i.e., a scenario where we have a historical account of an earthquake and we want to say something about this past earthquake, but we have no formal measurements (i.e., no seismometers). For these types of purposes, what is more readily ascertained is the intensity, not the magnitude. As with magnitude, there are a few different intensity scales, but lets consider the ",
"Modified Mercalli scale",
", which is a common one used for historical seismicity. If you look through the wiki page, you'll see that the different intensities are classified by observed effects. All of the details for built structures are not super helpful for a cartoon focused on dinosaurs, but there is enough going on in the clip for us to recognize some things described in the intensity scale, e.g., the formation of pervasive and large ground fissures and various objects (rocks, dinosaurs) thrown in the air. Looking through the intensity scale, that would definitely put this in the \"Extreme\" category, probably a XI or XII (the max on the scale). For the reasons described previously, there is not a direct equivalence between intensity and magnitude, but generally, high intensity earthquake shaking implies a large magnitude event, so we would have to assume this was earthquake was probably at least a Mw7, but more likely a Mw8+.",
"Another way to go about this estimation would be based on the duration of shaking. There is a decent amount of interest in developing relationships between duration of shaking and magnitude as the duration of shaking is a key component of earthquake engineering, so getting some approximate estimate on max duration of shaking is useful. If we look through papers considering these types of relationships (e.g., ",
"Castello et al., 2007",
", ",
"Yaghmaei-Sabegh et al., 2014",
"), we'll find a similar necessity of a lot of local (e.g., the various constants are calibrated for a set of records in a particular region) and event (e.g., magnitude, but also distance from the earthquake hypocenter) details to really say anything substantial. However, in the clip, the shaking appears to last about 2 minutes, which if we consider some of the relationships discussed in these (and other) papers, would again probably suggest a relatively large magnitude (>7) event. However, without knowing a lot more details, we can't say much more than that, and this is generally the case for things like real videos of earthquakes. Using things like the recorded duration of shaking and types of damage observed (linking to an intensity scale) we can estimate intensity, but directly estimating magnitude is always going to leave us with a very approximate value.",
"Finally, it's worth pointing out that obviously this is not a real event and in reality, the amount of land disruption shown in this is not realistic, even for extremely large events. Earthquake definitely can cause surface deformation like ",
"moletracks",
", ",
"fissures",
", or ",
"scarps",
" and similarly can cause significant landslides (e.g., ",
"Murphy, 2015",
"), but the amount and type of ground deformation in the cartoon clip is not reasonable. The scale of surface deformation will somewhat scale with the magnitude, but even for ",
", like the what was seen after the ",
"1964 Alaska quake",
", what is in the clip is not reasonable. That being said, it's not unreasonable to think about groups of animals being separated by earthquake deformation necessarily (even if we scale down that deformation to more a realistic size). The closest thing I'm aware of that sort of resembles what happens in this clip is the semi-famous (at least among geologists) pictures of a group of cows stranded after the Kaikora earthquake in New Zealand (e.g., ",
"this image",
"), but again, not anywhere near as intense as in the cartoon example."
] |
[
"r/AskScienceDiscussion",
" is like the lite version of this sub, much more casual."
] |
[
"Just for curiosity's sake, does anyone know of a better place for questions like this?"
] |
[
"Does being born blind have any effect on learning to speak?"
] |
[
false
] |
After 3 years this is my first submission anywhere, go easy on me. Watching a new Netflix movie "I am mother" ... girl being raised by a robot who has learned to speak from listening to a robot. This got me thinking if that would actually work. Obviously blind people learn to speak but I am wondering if not being able to see other's lip/tongue/mouth makes it more difficult to learn to speak.
|
[
"Possibly, although it may be related more to social interaction rather than just seeing the person form the words.",
"http://faculty.washington.edu/losterho/kuhl_nature_neuroscience_reviews_2004.pdf",
"A study that compared live social interaction with televised foreign-language material showed the impact of social interaction on language learning in infants31. The study was designed to test whether infants can learn from short-term exposure to a natural foreign language.",
"Nine-month-old American infants listened to four native speakers of Mandarin during 12 sessions in which the speakers read books to the infants and talked about toys that they showed to the infants (FIG. 4a). After the sessions, infants were tested with a Mandarin pho- netic contrast that does not occur in English to see whether exposure to the foreign language had reversed the usual decline in infants’ foreign-language speech perception (FIG. 4b). The results showed that infants learned during the live sessions, compared with a control group that heard only English (FIG. 4c)31.",
"To test whether such learning depends on live human interaction, a new group of infants saw the same Mandarin speakers on a television screen or heard them over loudspeakers (FIG. 4a). The auditory statistical cues available to the infants were identical in the televised and live settings, as was the use of ‘motherese’78,79 (BOX 4). If simple auditory exposure to language prompts learning, the presence of a live human being would not be essen- tial. However, the infants’ Mandarin discrimination scores after exposure to televised or audiotaped speakers were no greater than those of the control infants; both groups differed significantly from the live-exposure group (FIG. 4c). "
] |
[
"I would say that blind people get clues from other senses than vision. In that case probably the air blowing out of the mother's mouth (while talking close to the baby's face) would be detected by the baby's sense of \"touch\". Also the sounds you make while talking (lip contact, tongue noises, \"moisture noise\" etc) are really detectable when you pay attention to it, our brain just learned to filter it out since it is not needed when you already know how to talk.",
"Our brain learns to take the biggest hints and focalizes on them to learn tasks. Since they don't have functioning eyes other hints would be used for learning.",
"Also most so-called blind people aren't actually blind on the sense we tend to think about. Most do see, just differently enough for it to be called a disability.",
"Don't quote me on any of these infos without looking for viable sources tho, I am definitely not an expert and lack citations, these are just thoughts and memories I have from interacting with blind people."
] |
[
"Thank you!"
] |
[
"Why do foxes have slitted pupils when other members of canidae have round?"
] |
[
false
] |
I'm not sure if all others do, and I've been having a hard time finding information on it. Resorted to just looking up google images and squinting, trying to see. I got a close-up look at a fox for the first time recently at the zoo where I work, and was surprised to see its eyes were slitted. I'd just assumed they would be round, based on dogs, wolves, etc. Foxes seem to have similar hunting habits to other canidae species, as far as moving around in the day as well as the night, so why do they get the slitted pupils and others don't?
|
[
"Animal eyes that are primarily used under low-light conditions usually have optical systems of short depth of focus, such that chromatic defocus may lead to considerable blurring of the images. In some vertebrates, the problem is solved by multifocal lenses having concentric zones of different focal lengths, each of which focuses a different relevant spectral range onto the retina. A partially constricted circular pupil would shade the peripheral zones of the lens, leading to the loss of well-focused images at relevant wavelengths. The slit pupil, however, allows for use of the full diameter of the lens even in bright light. We studied species of terrestrial vertebrates from a variety of phylogenetic groups to establish how widespread multifocal lenses are and how pupil shapes are adapted to the optical systems. We found that multifocal lenses are common from amphibians to mammals, including primates. Slit pupils were only present in animals having multifocal optical systems. Among the felids, small species have multifocal lenses and slit pupils, while large species have monofocal lenses and round pupils. ",
"The red fox (Vulpes vulpes) has vertical slit pupils and multifocal optical systems (A,B). Grey wolves and dogs (Canis lupus lupus and Canis lupus familiaris, respectively) have circular pupils (D). The status of their optical systems is unclear, because some dogs have smooth photorefractive reflexes (dachshund; C), while others have clear ring-like structures (giant schnauzer; E). All members of a group of four closely related tame wolves had a central region of irregularity in photorefractive images (F). Scale bars are 5mm",
"See more ",
"here"
] |
[
"A question about pupil shape",
"In the paper linked there they mention that smaller felines tend to have slit eyes, and that this trend is present to some extent in canids too."
] |
[
"Foxes are crepuscular (feeding at dawn and dusk) and a bit more nocturnal that wolves and wild dogs. So in order to deal with poor light conditions their pupils are more slit than a dog or a wolf. Dogs and wolfs have average night vision, where a fox would have above average but not amazing night vision."
] |
[
"How do spacecraft measure their velocity?"
] |
[
false
] |
As an accomplished Kerbal Space Program spaceship pilot, I've come to understand how critical accurate understanding of velocity is with respect to orbital bodies. When spacecraft change their orbit by adding or subtracting from their velocity vector, how is this measured? I know of many physical sensors that measure acceleration (since force and acceleration are directly linked) but to get back to velocity, you need to integrate over a time period and eventually end up with an unmanageable error term for most applications. Direct measurements of velocity usually use the distance/time relationship - sending out a pulse and measuring the return time. But without a "reference" object to ping something like sonar, radar, etc off of, how does an object in the vacuum of space know how fast it's going?
|
[
"Unless we're going intergalactic (which I'm unfamiliar with how they do that), speed is always calculated based on the objects orbit, or by radar sites on the ground (when trying to determine the objects orbit). Orbits are really what determines an objects speed, so when changing orbit you burn a set amount of fuel to get a very specific velocity change which puts you in the new orbit that you want. Since it's impossible to change speed w/o changing orbit, it's easier to calculate speed from the orbit, not the other way around.",
"I suppose you could also calculate the speed using the object's positioning system (they frequently determine position very accurately using the sun, earth, stars, and/or GPS signals), but I've never worked on a project where they needed that much accuracy. ",
"As for intergalactic, I'm speculating, but it might be the only time where an accelerometer can effectively determine speed, because without friction, it could much more accurately determine your speed with an integral.\nHope I helped, unfortunately my background is entirely in satellites orbiting earth and a few simplified calculations for inter-planetary."
] |
[
"You can't measure a spacecraft's orbital elements. You can only get them from knowing the spacecraft's position and velocity vectors at a certain time. If you know the spacecraft's position very accurately (from GPS), then you can calculate its gravitational acceleration, and the accelerometer on board will tell you the deviation from that to get inertial acceleration. The IMU constantly measures acceleration, and you can integrate that to get velocity. This doesn't create that much error or noise; its differentiating that amplifies noise (i.e. differentiating position to get velocity - that makes the noise blow up and doesn't really work). We can also use position data along the entire orbit and measure its orbital period to estimate orbital elements, and from that get velocity. Also, you can use doppler shift measurements from GPS signals to estimate velocity. We use all of these things together to get an accurate estimate of velocity."
] |
[
"Imagine the possible position you calculate like a sphere for every pulsar.\nWith 2 pulsars they intersect into a circle.\n3 gives you two possible positions on this circle.\nAnd 4 signals finally give you a accurate 3D-position.",
"graphic"
] |
[
"Can mRNA technology be used to create the antibody itself, for example to replace rabies immunoglobulin?"
] |
[
false
] | null |
[
"Yes, this has been done, though not for rabies immunoglobulin (kind of pointless since that works well already). For example, from 2018, ",
"Engineered mRNA-expressed antibodies prevent respiratory syncytial virus infection",
". ",
"As with most mRNA deliveries, it’s essentially identical in concept to DNA-mediated delivery, but with the advantages and disadvantages of mRNA. DNA delivery of antibodies to animals is over a decade old, e.g. ",
"Vector-mediated gene transfer engenders long-lived neutralizing activity and protection against SIV infection in monkeys",
". A recent example is ",
"In vivo delivery of synthetic DNA–encoded antibodies induces broad HIV-1–neutralizing activity",
".",
"All of these are experimental, not in general use."
] |
[
"Sure, antibodies are just proteins and any cell knows how to make proteins. ",
"In practice, these are mainly targeting fibroblasts and epithelial cells, which are abundant, structural, and generally turn over rapidly."
] |
[
"It's not uncommon to see single monoclonal antibody therapy leading to immune escape variants, if that's what you mean. It's common to use a cocktail of multiple monoclonal antibodies as antiviral therapy for that reason.",
"Expressing mAb through mRNA or DNA could lead to the same issues, but the goal there is to provide continuous, high-level expression of an appropriate antibody (often a broadly cross-reactive mAb that doesn't easily allow immune escape) in the appropriate organ. It's also conceivable that you could express cocktails this way too."
] |
[
"Why can most people cross their eyes, but not move their eyes independently in any other way?"
] |
[
false
] |
Most people can cross their eyes but other than that cannot move their eyes independently of each other. What is so special about crossing your eyes that your eyes can move that way, but not independently in any other way?
|
[
"Our eyes are supposed to converge, which is what we all do naturally when we read. So crossing eyes is over converging, also called esophoria (or esotropia) when our eyes do it without us trying.",
"\nBut we don't have a normal situation for exophoria/tropia, which is the condition when the eyes point outwards. That's why it's easier for people to go in than out. Also, esophoria/tropia is more common since our eye muscles that control the inward motion is naturally stronger than the muscle that controls the outwards motion, and is too strong in people with the inability to keep their eyes straight. (I'm an optician student in NJ, where we have to take a ton of classes, including eye anatomy) "
] |
[
"We are able to converge our eyes (point them both towards our noses) because that is how the each retina focuses when something is moving closer to you to maintain single binocular vision",
"The body has no other need for your eyes to go in different directions. There is a fibre on each side of the brainstem called the medial longitudinal fasciculus that makes sure you move your eyes in the same direction (left/right). When there are defects or lesions affecting this fibre, it is possible to have your eyes looking in two different directions."
] |
[
"A slight correction: esotropia is not crossing our eyes. Its a condition when one eye is turned in. Crossing our eyes is called excessive convergence."
] |
[
"How large would an asteroid need to be to incinerate the entire surface of Earth after impact?"
] |
[
false
] | null |
[
"To incinerate the surface of Earth, you need a lot of energy - around 10",
" Joules.",
"The XKCD comic is fun, but in reality, most asteroids hit Earth around 12 - 20 km/s. If we assume the asteroid is traveling at 16 km/s, then it's diameter must be around 8 km to produce 10",
" Joules energy (because kinetic energy = .5mv",
" ). This assumes the density of the asteroid is 3,000 kg/m",
" .",
"This is the same amount of energy released in the ",
"Chicxulub impact",
" and it's effects are thought to be as you described.",
"For a \"slower\" asteroid, only 12 km/s, the diameter needs to be around 10 km, and for a \"faster\" asteroid, 20 km/s, the diameter would have to be about 7 km."
] |
[
"Well it depends on velocity too.",
"Here's ",
"a fun XKCD what-if",
" on the subject with fixed size and varying velocity."
] |
[
"45 Degree impact. Average speed for an asteroid impact."
] |
[
"Is it possible to discover a new element that is stable?"
] |
[
false
] |
I've been watching a lot of science fiction movies lately and in a lot of them they "discover" a new metal with super cool properties. So is it possible, or have we reached the point where there are just too many electrons around the nucleus to be stable?
|
[
"As the nucleus gets larger, the electrostatic repulsion of protons starts to outweigh the attractive strong force. So for elements heavier than bismuth, the result is that everything tends to decay by shedding protons in some way - either alpha decay or spontaneous fission.",
"All our data suggests that there isn't anything stable at masses heavier than what we already see. There is a predicted \"island of stability\" at large masses, but the term is a bit misleading. They aren't predicted to be ",
", they are predicted to be more stable than trends would suggest. In other words, they would have half-lives on the order of hours or days instead of on the order of microseconds.",
"The reason that the island of stability is predicted is because the nucleus follows a similar \"shell model\" as electrons. For instance, helium, neon, and argon are non-reactive because their electron shells are full. Similarly, iron is stable because its ",
" shells are filled. The island of stability is predicted to exist at masses where both the proton and neutron shells are full. But again, these atoms wouldn't be stable... just less unstable."
] |
[
"The reason that the island of stability is predicted is because the nucleus follows a similar \"shell model\" as electrons.",
"Well, the \"shell model\" analogy does give the general idea (some nuclei are more stable than others), and serves as a starting point, it doesn't work nearly as well for nuclear structure as for electronic structure. I've seen nuclear physics textbooks go out of their way to underline that no simple shell-filling model can actually explain all nuclear 'magic numbers'. ",
"(If you want to get technical, this is not just because the nuclear force/Yukawa potential is different, but also because the effects of \"correlation\" - the instantaneous interaction between particles - is much larger and more significant when it comes to heavy nucleons than with the lighter electrons. Uncorrelated models such as the Hartree-Fock method are enough to qualitatively describe most chemistry, and the same goes for the simpler, generalized models that derive from it. The same doesn't hold true for nuclei. Modeling nuclei is generally much more difficult than what the electrons are doing, and much less accurate. There are some similarities though)",
"To the poster: As you can tell, the main issue is the question is the stability of the nuclei. That said, there are some \"new\" effects that also come into account with the electrons at high atomic numbers (Z > 140-150 or so), because some of the electrons will start to have such high kinetic energy that you have to take into account the effects of quantum electrodynamics (specifically the creation and annihilation of positron/electron pairs). It's beyond our current abilities to calculate exactly what that'd mean for their chemistry and material properties, should such elements exist. (neglecting such concerns, we've still gone ahead and ",
"calculated the ground states",
" of atoms up to Z = 172 though) In general, relatively little is known even about the chemistry of the extant heaviest elements. They're difficult to deal with experimentally, being short lived and radioactive. But also theoretically, as the effects of special relativity on the electrons (which gets larger as the atomic number increases) has to be taken into account, making the properties much more complicated to theoretically predict accurately.",
"But it's unlikely that there will be any more elements discovered that are stable enough to be of chemical relevance, so to speak. That said, there's plenty of chemistry left to discover with the existing ones! I think \"new elements\" are a bit of a sci-fi trope because it makes for a simple and easily-understandable explanation for whatever magical material the plot requires. "
] |
[
"Island of Stability",
"The island of stability in nuclear physics describes a set of as-yet undiscovered isotopes of transuranium elements which are theorized to be much more stable than others. Specifically, they are expected to have radioactive decay half-lives of at least minutes or days as compared to seconds, with some expecting half-lives of millions of years."
] |
[
"Do mitochondria get cancer?"
] |
[
false
] |
[deleted]
|
[
"Not exactly, since we don't consider mitochondria to be separate organisms, however ",
"they do have their own DNA, and mutations in mtDNA have been linked to cancer in humans"
] |
[
"As in uncontrolled mitochondrial division inside the cell? I'm not sure if there are cancer forms where the cells start to generate excess amounts of mitochondria, but the cancer never lies in the mitochondrion per se.",
"The mitochondrial DNA only encodes 14 proteins, 13 of which are proteins of the electron transport chain (the 14th seems to be a regulatory protein of some sort, not my field). Notably missing from this list is a DNA polymerase, an RNA polymerase and a bunch of other proteins necessary for autonomous division and maintenance. These proteins and enzymes are encoded by nuclear DNA, and therefore if the mitochondrion is to divide (or even live), the DNA damage has to be in the nucleus."
] |
[
"Disclaimer: The 'as far as I know' here is implied.",
"There is still some aerobic oxidation going on in there, and, obviously, every cancer will be different due to their very nature. But glucose also needs to be delivered to the cells in some manner, which is why angiogenesis is so important for the survival of large tumours. Also, since glycolysis is terribly inefficient, they consume much higher amounts of glucose.",
"Additionally, with solid tumours, there's a sort of gradient. The surface of the tumour is well perfused and supplied with nutrients and actively proliferating, while the core tends to be either quiescent or performing its metabolic activities much slower. This is because it's really hard for a bulk of cells that sprang out of nothing, with a chaotic structure, to build itself an adequate blood supply. Often the tumour will grow faster than the blood vessels it needs contributing to this. ",
"The above can be observed by measuring the pH of different parts of a tumour. The highly acidic environment of the cores, and moderately acidic environment of the surfaces of tumours have been attributed to the higher than normal production of lactate (a byproduct of metabolism when it stops with glycolysis).",
"Two major problems of traditional cytotoxic chemotherapeutic drugs are getting the drug to the middle of tumours and the inefficiency of it on cells which are not proliferating."
] |
[
"If anything having mass has an equivalent amount of energy and vice versa, does heating up an object change its mass? How?"
] |
[
false
] |
The mass-energy equivalence states that anything having mass has an equivalent amount of energy and vice versa. If we have a mass of metal and we heat it by some x decrees Celsius then it's potential (correct definition?) energy increases. This is what I recall from my Physics classes. But how does heating up an object increase that object's mass? How does it lose mass as it cools?
|
[
"Not all energy has a mass equivalence. E = mc",
" only applies in a frame of reference where the total momentum of your system is zero. But if you consider some object in its rest frame, and increase its internal energy by an amount U, you’ve increased its mass by U/c",
"."
] |
[
"The mass increases if you heat something and take care no atoms escape, although the increase is too small to measure with current scales (getting close - might be possible in 10-20 years). The volume can change if you heat something but that is an independent topic."
] |
[
"Its mass will increase, yes, since the mass of a system at rest is equivalent to its energy."
] |
[
"How much would the sea level drop by if all the fish etc were removed?"
] |
[
false
] |
[deleted]
|
[
"I answered this ",
"on askscience",
" about a year ago and I've since expanded on it ",
"on my blog.",
" - I'll just copy paste what I wrote last time: ",
" A few microns. ",
" Let's talk about ",
"biomass.",
"\nDifferent people give different estimates, but we can probably get this to an order of magnitude. ",
"For reference, humans (all seven billion of us) put together have about 100 million tons of dry biomass, which is basically a measure of our weight without water, or approximately our carbon content. ",
"Global estimates say there is about 560 billion tons of dry biomass on earth, but only about 1-2% of that is the oceans. That's crazy considering that oceans occupy twice as much of the earth as land. ",
"The most successful species on earth, in biomass alone, is probably the antarctic krill, pushing 400 million tons of wet biomass. ",
"You ever wondered how the largest whales on earth can survive off eating crustaceans smaller than your finger?",
" It's because there's lots of them. ",
"Anyway, ",
"this paper estimates there is about 1 to 2 billion tons in fish, so let's go with that.",
" Assuming the fish has an average density of 1 ton/m",
" (which is approximately the density of water (1000 kg/m",
") and a good estimate for nearly every biological material), then the total volume of fish is: ",
" V = (1 billion tons)/(1 ton/m^3) = 1 billion m^3 \n",
"If the oceans cover 70% of the earth, then area of the oceans is: ",
" A = 4 pi (earth radius)^2 x (0.70)\n",
"so 3.5x10",
" m",
" is the surface area of the oceans on earth.",
"Dividing the above volume by this area gives us the change in sea level, and is about ",
"2.8 microns.",
" Helpfully, Wolfram informs us that this is close to the radius of an average bacteria. ",
"I had a long tangent here about interpreting this result, but it was pretty speculative so I won't include it here. "
] |
[
"Was that your plan to save the Maldives ?"
] |
[
"So not enough to save the Maldives then, thanks"
] |
[
"Do all mammals experience nausea, and how can scientists determine this?"
] |
[
false
] |
For example, dogs experience nausea and it is often indicated by drooling and excessive swallowing, and anti-emetic medications work for dogs. But outside of observed behaviors, do scientists have other ways of knowing whether nausea is something that all mammals experience? Could it be determined by studying mammalian brains?
|
[
"Nausea is a subjective experience of a physiological phenomenon. It's qualia rather than an objective, measurable state. We can definitely say that animals experience the physiological indicators of nausea but whether they experience nausea as a subjective, conscious thing is an extremely difficult and perhaps impossible question to answer.",
"It's like pain vs nociception."
] |
[
"Goats are not capable of vomiting (they usually reach a life threatened state by the time they’d need to vomit), so they are one of the mammals I had in mind.",
"I also just read that squirrels, mice, beavers, and gophers cannot vomit.",
"I still wonder whether such animals might experience nausea even if they are physiologically not capable of vomiting. I suppose it depends when nausea evolved - for example, if nausea evolved to protect us from eating things we shouldn’t eat, wouldn’t that have been long before mice diverged from other mammals in the family tree? Even if it doesn’t lead to the potentially lifesaving solution of vomiting, could it serve some other purpose that was naturally selected for, like teaching the animal to avoid the nausea inducing food in the future?"
] |
[
"Goats are not capable of vomiting (they usually reach a life threatened state by the time they’d need to vomit), so they are one of the mammals I had in mind.",
"I also just read that squirrels, mice, beavers, and gophers cannot vomit.",
"I still wonder whether such animals might experience nausea even if they are physiologically not capable of vomiting. I suppose it depends when nausea evolved - for example, if nausea evolved to protect us from eating things we shouldn’t eat, wouldn’t that have been long before mice diverged from other mammals in the family tree? Even if it doesn’t lead to the potentially lifesaving solution of vomiting, could it serve some other purpose that was naturally selected for, like teaching the animal to avoid the nausea inducing food in the future?"
] |
[
"[physics] Why does the texture of icecream change when melted and refrozen?"
] |
[
false
] |
I was eating some sorbet (not icecream I know but the same thing happens to icecream), and I made the mistake of taking a post-sorbet nap without putting it back. It melted, I refroze it, and now i'm eating it again to find that the texture is no longer soft, it's like a frozen slushie now, full of hard icy flakes. Why is that?
|
[
"its probably not a very safe idea to eat refrozen ice cream.",
"Why is this?"
] |
[
"When you refroze the sorbet, it cooled quite slowly. This allowed the growth of large (up to a few centimeters) crystals. This is the main reason your sorbet is not as good, and why chefs try to get the sorbet to freeze as fast as possible, by stirring, or by using liquid N2 (for fancy chefs). \nA second reason, is that industrial ice cream contain a shocking amount of air bubbles(up to 40%), which increases the softness (and decrease the cost), and that of course are not introduced again when you refreeze the ice cream.\nLast thing : its probably not a very safe idea to eat refrozen ice cream."
] |
[
"From what I found, the lower temperatures along with the sugar and fat in the ice cream makes it a perfect host for bacteria like listeria. "
] |
[
"How do magnetic fields work/interact?"
] |
[
false
] |
I just read most of the wiki article and another short Q&A about this and am still a little confused. I understand the electromagnetic carrier is the photon and that "virtual photons" exist in a magnetic field but I'm not sure what that all means. If I hold a compass level in my hand, the needle will align along the earth's magnetic poles. What causes the needle to move? Where are these photons coming from and what frequency (ies) are they at? This was prompted by someone suggesting animals could "see" a magnetic field. Is the earth's magnetic field just a stream of moving photons from magnetic N to S?
|
[
"When you want to talk about macroscopic magnetic ",
" it's much better to just think of it in terms of the classical field, imo. Otherwise you're talking about ",
" photon interactions with each charge, which I think is difficult to do. And each of those is an excitation of the electromagnetic interaction that on the whole appear to be a classical magnetic field anyway.",
"If we want to talk about interactions with that magnetic field, then we can talk about two things in general. Charges in motion will be accelerated in a direction mutually perpendicular to both the magnetic field and the particle's own motion. Otherwise, (most?) elementary particles, like electrons, have an intrinsic magnetic moment; ie, an electron is a very tiny little magnet. And that magnetic moment wants to align itself along the direction of the magnetic field. That's going to be the source of magnetic effects on ferromagnetic materials. Electrons that aren't partnered with an \"opposite pointing\" electron will feel the 'pull' of the magnetic field."
] |
[
"It's best not to get bogged down in quantum electrodynamics. Just remember that a field is anything that's defined over all of space.",
"In this case, we're talking about every point in space having a direction and a magnitude associated with it — a \"which way\" and a \"how much,\" basically. This value represents an acceleration. Any particle with \"magnetic charge\" (there's really no such thing, but we're simplifying) will accelerate according to the value of the magnetic field wherever it happens to be.",
"The needle on a compass is magnetic; it has \"magnetic charge,\" so to speak. So it experiences an acceleration the direction and magnitude of which are determined by the value of the magnetic field at that point. The needle's very light, and it's free to pivot in its housing, so a tiny acceleration on it will cause it to snap into alignment with the field at that point, showing you which way the field points. The magnetic field around the Earth generally points toward the poles, so we can use compasses to keep ourselves oriented when wandering unadvisedly after dark on, oh just to pick an example, Culloden Moor. Also? Ghosts. Totally."
] |
[
"Also? Ghosts. Totally.",
"So either you were reading the same thread or somehow happened upon a coincidence that the discussion was about additional sensing ability of animals versus humans and in some respects, ghosts. Creepy."
] |
[
"How does catnip get cats high?"
] |
[
false
] |
It's not smoked, injected or ingested yet they get all fucky. Why?
|
[
"Catnip (Nepeta cataria) releases a chemical nepetalactone, which binds to olfactory (smell) receptors at the epithelium tissue in a cat's nose. Here, the nepetalactone triggers a faux pheromone response. Pheromones are used for cat communication (e.g. marking places and objects) and are typically produced in a cat's facial glands (distributed by rubbing their faces against surfaces) and urine.",
"It should be noted that a cat's response to nepetalactone is hereditary and a third of cats are not affected.",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1480656/"
] |
[
"I once saw a documentary (i think it's just called \"Life\" and is narrated by David Attenborough) in which a tiger in a jungle actively seeks out a plant or fungus and starts eating it. It's a plant/fungus with a psycho active substance that triggers hallucinations in a tiger and it's assumed that the tiger knows this. After eating it, the tiger lays down and starts tripping.",
"Edit: couldn't find a clip of said tripping tiger, so here's a law breaking Jaguar instead! ",
"https://youtu.be/OqGDv0KCJl8"
] |
[
"So even cats have psycho-active plants in their evolution too. This world is awesome."
] |
[
"If all mosquitoes vanished form the face of the earth, how badly would the world food chains collapse?"
] |
[
false
] | null |
[
"Actually, mosquitos have been targeted for forced extinction by a number of groups. The ",
" thinking of some entomologists is that their threat to human life is fairly great due to malaria, and they wouldn't be that missed if they were wiped out. The ecological niche they fill would quickly be filled by other, non-malarial carrying creatures.",
"Here's",
" an article in ",
" that discusses the topic.",
"EDIT: Phrasing"
] |
[
"This sums it up pretty well",
", we can do without mosquitoes to be honest.",
"There is nothing mosquitoes do better than any other insect that might take their place except one thing, the transfer blood diseases, fewer mosquitoes means fewer people getting sick and dying.",
"The food chain would be quite all right without them."
] |
[
"There are mosquitoes in quite cold places such as Lapland as well. "
] |
[
"If the cyanobacteria that became chloroplasts were unable to sexually reproduce after endosymbiosis, how did they lose so many traits over time? Shouldn't mitosis have kept them more or less identical to their free-living ancestors?"
] |
[
false
] | null |
[
"NoDiceChicago, if you're interested, what polistes described is known as Muller's Ratchet, and it's a fascinating part of the explanation for why sexual reproduction is widespread."
] |
[
"Producing asexually and through mitosis does not mean that the genetic code can never change. When duplication of the genome takes place, sometimes mistakes are made in copying the genetic code, possibly leading to malfunctioning of the gene. If these mistakes are in nonessential genes, this has no consequences for the functionality of the chloroplast and the mistakes are maintained in the genome. When more and more mistakes and deletions take place, eventually these genes (or at least their functionality) disappear. Because chloroplasts are living within a plant cell that provides many of the essential cell processes already, there would have been a lot of genes within the chloroplasts genome that were no longer important for their survival. These genes have deteriorated over a long, long time and have been lost. There was simply no selection to maintain these genes. "
] |
[
"Mutations occur frequently in bacterial genomes -- perhaps one base change in every 10**9 replicated bases. This mutation rate is very important, and is carefully controlled. Too high a rate produces poor survival. But too low a rate is also bad. Recall that Darwin postulated the importance of descent WITH VARIATION as the key mechanism. Organisms that perfectly reproduced would not survive environmental changes, because they would no longer be well adapted. So, mutation is essential, but not too much of it. Polistes gives a very reasonable account of why (in the intracellular plant cell environment) the cyanobacteria lost much of their coding capacity.\nOther mechanisms such as horizontal gene transfer and viral infection are also very important sources of variation."
] |
[
"Can an individual's blood carry a cure for a virus outbreak like the movies?"
] |
[
false
] |
I've read there are some experiments suggesting plasma from covid survivor's could help fight the spread. Though it got me wondering how much truth is in the possibility of one persons blood being the key to a widespread virus like many movies.
|
[
"Isn't there a dude that has donated blood 1000's of times due to some unique property of his blood that is able to help others that are deficient in it? So going from that, I wouldn't be surprised if that is the case.",
"Edit: not thousands but over a 1000. His name is ",
"James Harrison",
")"
] |
[
"Yes, you can carry antibodies to the virus. A good example of this was plasma from healthcare workers who recovered from the Ebola virus being used as an emergency treatment. There's a great Crash Course video that explains this particular this case, as well as the broader discussion of the immune system defenses over 3 ~20 minute episodes: ",
"https://www.youtube.com/watch?v=I7orwMgTQ5I&list=PL8dPuuaLjXtOAKed_MxxWBNaPno5h3Zs8&index=45",
" My favorite part in that series is the analogy of antigen presenting cells to Mad Max characters! Fun and informative videos."
] |
[
"Not necessarily. If you’re a frequent enough donor they might phenotype you or if you’re found to have a rare blood type. Rare blood types are usually discovered when you have a reaction and they do a work up. Basically, there’s ABO/Rh then it gets broken down into like forty other blood groups of varying seriousness and those break down into over a hundred or so different specific antigens and each antigen has an opposite phenotype or lack thereof (most of the time). What makes a blood type rare and valuable is always a lack of a frequently seen antigen. If 99.99% of the population has a certain antigen then it’s VERY hard to find blood that doesn’t. A person lacking the antigen is prone to making the antibody if they’re given blood that has it in a transfusion, which is called a transfusion reaction. So valuable rare blood always is missing an antigen, never possessing it."
] |
[
"solar panels + bicycle + flywheel + electric generator"
] |
[
false
] |
I have a 3 member household. We use about 12 KWH per day but we could definitely reduce this number by conserving better. Let's say I am a strong bicyclist that can ride at moderate intensity for 2 hours per day. The other two members ride bicycles but not as intensely. For the purposes of this question, let's say that combined we can expect 1 hour of moderate intensity per day for a grand total of I live in sunny southern California a little north of Los Angeles. Installing solar panels on the roof should be feasible. Question 1: Assuming I could charge it up, how much battery capacity would I need to deliver steady electricity to my home? 5 KWH? 10? 20? More?! Question 2: How massive of a flywheel would that be? Would a flywheel leak too much energy to ever be practical? Question 3: How many square feet of solar panels would I need on the roof? Bonus Question: What I need to reduce my energy usage to in order to make the idea work? EDIT: other storage options like chemical batteries would be fine too. I just think flywheels are so awesome. Maybe a flywheel connected to the bicycle and a chemical battery connected to the solar panels?
|
[
"i best advice is to try to keep a 100W lightbulp on for an hour by riding a bicycle. trust me, it is already difficult enough. it gives a very concrete idea of what 1000Wh are. here is more:\n",
"http://www.manicore.com/anglais/documentation_a/slaves.html",
"site's not mine, i invite you to look around.",
"anyway, good luck"
] |
[
"You would be lucky to be able to sustain 200 W of cycling output for an hour, so for your three riders each doing an hour you're looking at 0.6 KWH of power, minus the conversion inefficiency of an inverter (~75-90% efficiency). In other words, your cycling wouldn't even make a dent in your power requirements. And using a flywheel is even more insane when cheap lead-acid batteries are superior.",
"As to how many panels, it depends on the insolation at your latitude and climate. Panels themselves are around $2 per Watt these days, but that is just a fraction of the total. You also need to pay for installation which is not trivial -- you need a qualified electrician to connect them to your home's electrical service, as well as a qualified roofer/carpenter. You also need the inverter and batteries. In all expect to spend $10k-$15k minimum."
] |
[
"10 kWh per day for 3 people sounds really low to me. Is your heat and hot water part of this? I have an electric hot water heater and I observe that a 15 minute hot shower costs me about 6 kWh, which I think sounds reasonable if you do the math.",
"My wife and I are only two people and aside from my long showers (which are not every day) we are very frugal with the power. We can't get down to 10/day average even in the spring or fall when heating and cooling are not used."
] |
[
"Why does the jaw bone shrink when teeth are removed but no other bones in the body act the same way?"
] |
[
false
] |
[deleted]
|
[
"Bones respond to mechanical loads. If the load on a bone increases, it strengthens. If it decreases, the bone is weakened and absorbed. The jaw bone is just reacting to a decrease in mechanical load by absorbing bone that was previously there. The same thing occurs in other bones in the body. For example, there is remodeling and resorption after a hip implant due to changes in the way force is distributed. ",
"Wolff's law",
" is the theory that describes these changes."
] |
[
"Stress at the attachments of muscle also causes changes in bone density and structure, as stated in Wolff's Law. ",
"There are several places on the skull that bear a large amount of stress from muscles, such as the jaw and cheekbones, which are the attachment sites for the muscles involved in mastication. "
] |
[
"Stress at the attachments of muscle also causes changes in bone density and structure, as stated in Wolff's Law. ",
"There are several places on the skull that bear a large amount of stress from muscles, such as the jaw and cheekbones, which are the attachment sites for the muscles involved in mastication. "
] |
[
"Do 3D glasses work for everyone?"
] |
[
false
] |
I've seen several 3D movies in my life, and I've never understood the attraction. At best, the glasses make everything focus better (but no 3D effect that I can see), at worst I end up with a headache. I am not color blind, but I do have presbyopia. So is there something that I'm missing? Or it it nothing more than a case of the Emperor's New Clothes?
|
[
"No. 3d does not work for everyone. Up to 5% of people cannot \"see\" the 3d effect provided by current 3d technology (which uses physics tricks with light polarity that I really can't explain well). A smaller percentage of people actually experience adverse effects from the 3d images, such as headaches, nausea, or vertigo. The most common reason would be fairly common visual problems, like ambylopia or strabismus (essentially lazy eye). In these conditions, since visual input isn't delivered to the brain the \"normal\" way, the brain figures out a different way to represent depth using the information it has. Since this method doesn't jive with the 3d tricks provided by polarized light and glasses, it can not only fail to give a 3d illusion, but can also cause an unpleasant experience."
] |
[
"Thanks for the feedback. Looks like being in the 5% isn't a good thing in this case."
] |
[
"It's polarization, and there's a pretty reasonable explanation ",
"here",
". Essentially, two different images (similar to what you'd see using your two eyes to look at an object with depth) are transmitted using \"opposite\" (orthogonal is more correct, but paints less of an intuitive picture) polarizations. The glasses are just two polarizers designed to block one of the signals (different one for each eye).",
"This effect can be seen if you have an LCD monitor and a pair of polarized sunglasses. Observe the monitor through the sunglasses and rotate them. There is an orientation that blocks all of the light, and an orientation that is the brightest. This is with linear polarization, which is orientation-dependent, as opposed to circular polarization, which is not. Unfortunately, circular polarization requires an extra element in the glasses and is therefore more expensive."
] |
[
"Why do things \"glow\" under a black light?"
] |
[
false
] |
And is there a difference between different things glowing ie; stains, white shirts, teeth, bugs.
|
[
"When you point a UV source at a material, it starts absorbing photons. The material loses most of that energy by re-emitting longer-wavelength (and therefore lower-energy) photons. Under intense UV, often you'll see pairs of photons absorbed, allowing emission of higher-energy photons than the original source.",
"The chemistry of what you're irradiating dictates what color it will fluoresce."
] |
[
"Exactly. Although the blacklights at Spencer Gifts use glass to shield the dangerious tanning rays and only let through the tail end of violet. Tanning beds use the same bulbs, but instead of glass they're made of quartz which doesn't block the carcinogenic UV.",
"Also, visible violet light will make things glow. Get an \"ultra violet\" LED flashlight. Their light is perfectly visible to human eyes at 400nM wavelength, and the \"UV\" label is just sales hype. Genuine UV is much shorter than 400 and is actually invisible and not purple. Also try a blue LED flashlight: there are a few dyes which light up yellow or orange when hit by normal blue light."
] |
[
"so you're saying black lights are just really intense UV lights? as in, I could get a tan from one? Do they use essentially uber-blacklights in tanning beds?"
] |
[
"Is analytic continuation of the Riemann-Zeta function more than just a reflection over a vertical line?"
] |
[
false
] |
Watching video of an animation showing how to think about the Riemann-Zeta function geometrically, I am left with the impression that the Analytic Continuation of the function is just a reflection. Please tell me how I am wrong.
|
[
"It's almost a reflection about the line Re(s)=1/2 (the critical line), but not exactly. If it were a reflection, then if s were a point to the left of this line, its value there would be equal to the value of the point exactly opposite on the right side of the line, and this point is 1-s. That is, we would have Z(s) = Z(1-s). But this isn't exactly what happens. In reality we have",
"So there is an extra scaling factor in there, and this scaling factor can make it totally look not like a reflection (see ",
"this",
") However, this extra scaling factor is in there because the Riemann Zeta Function is actually \"incomplete\". We can construct the Riemann Zeta Function for Re(s)>1 either by the sum of 1/n",
" for n=1 to infinity, or we an do it as the product of (1-p",
")",
" over all primes p. This is the ",
"Euler Factorization",
" of the Riemann Zeta Function. When viewed this way, the product in the Euler Factorization is actually missing a contribution from a prime. The \"Prime at Infinity\".",
"In their natural state, the Rational Numbers do not live on a line, they're just a pile of fractions that we can add/multiply together. But, if we put them on a line ordered by their absolute value, then we find that there are holes in this line, tons of holes. By filling in these holes, we are able to construct the Real Numbers. So we get the real number system by 1.) Applying a geometry to the rational numbers and then 2.) Filling in the holes left by this geometry. It might then be natural to ask \"Are there ",
" geometries we could apply to the rational numbers that result in a ",
" number system in a similar way?\"",
"It turns out that the answer is \"Yes!\" If p is a prime number, then I can say that N is ",
" smaller than M if p divides M more than it divides N, and write this as |M|",
" < |N|",
". For example, |50|",
" < |49|",
" and |16|",
"<|8|",
". This can also be extended to fractions, where if the denominator has a p in it, then that takes away from the count. So |5/16|",
"> |5/8|",
" since 2 divides the bottom more in 5/16. This gives us an alternate geometry to arrange the rational numbers, and this geometry will be nicely behaved and have holes in it, just like when we put it on the line. If we fill in these holes, then we'll get a new number system that was constructed in the same way as the real numbers were constructed, just with a different geometry. These are the ",
"p-adic Numbers",
", and there's a different one for every prime p.",
"So using the same method, we can make the real numbers and the p-adic numbers (for each prime p). These should be thought of as siblings in a big family, where the reals are the odd one of the bunch. It then turns out that the reals+p-adics are the ",
" number systems that can be made in this way. It then seems like the \"Reals\" should be included as a \"prime\" since it kinda behaves similarly to the primes in this way. We then say that the reals are the \"Prime at Infinity\" (which is a term we borrow from geometry). This \"Prime at Infinity\" doesn't have a number associated to it, but it behaves like primes in pretty much all other ways. ",
"So, back to the Riemann Zeta Function. With this in mind, the Euler Product for the Riemann Zeta Function takes into account all the primes, except the reals. It seems like the reals are then a missing from the Riemann Zeta Function. In fact, we can view the term (1-p",
")",
" that appears for the prime p in the Euler Factorization as a specific kind of integral over the p-adic numbers and we can actually construct an analogous integral over the reals. The value of this integral will be 2",
"pi",
"s(s-1)Gamma(s/2) and if we append this to the Euler Factorization we get what is called the \"Completed Zeta Function\", Xi(s). The analytic continuation of ",
" function is just a simple reflection:",
"This follows from the above expression + properties of the Gamma function.",
"Note: This isn't how the Completed Zeta Function was originally made. Originally, we just used a trick involving a change of variables in an integral to recover the Zeta Function from the integral expression for the Gamma Function, and it is this that allowed us to get the analytic continuation in the first place. This transformation hinted at what Xi(s) should be, so we used that. The whole \"prime at infinity\" concept is a relatively modern idea."
] |
[
"You can use power series to talk about it and really formalize it, but it really boils down to the rigidity of differentiable functions on the complex plane. If f(z) and g(z) are any two functions on some domain of the complex numbers, and there is an open set, of any size, so that f(z)=g(z) for all z in this open set, then f(z)=g(z) on the entire domain. Any equality of analytic function on some meaningful set means that they are equal everywhere. This is the ",
"Identity Theorem",
" for complex differentiable functions, and follows from Differentiable <=> Analytic property of complex functions.",
"To prove that the Riemann Zeta Function has an analytic continuation, we find an analytic function on the entire complex plane (except s=1) that equals the zeta function when Re(s)>1. By the property I stated about analytic functions, this is the ",
" such function, so it is the unique extension of the zeta function to the complex plane."
] |
[
"I don't typically pay attention to the usernames of people who write comments; I just skip over them and read the text. So whenever I see an explanation which answers the question so well and then proceeds to blow my mind with some weird math concept, I think to myself \"that's gotta be ",
"/u/functor7",
"\". I've never been wrong so far. Keep doing what you do!"
] |
[
"How does the immune system fight off viruses?"
] |
[
false
] | null |
[
"Firstly, the virus will invade a cell, a virus is essentially just packaged genetic material, when in the cell the virus will uncoat and release its genetic material (DNA or RNA) into the cell cytoplasm/nucleus, where transcription and/or translation will occur. The cell is now producing viral proteins which are packaged and released to infect more cells.",
"A couple of things happen when a cell is infected by a virus, firstly, it down regulates the production of some endogenous cellular proteins, importantly, MHCs (Major compatibility complexes) which are used to \"present\" antigens (foreign substances that can be recognised by the immune system) to cells of the immune system. An immune cell (natural killer cell) recognises the lack of MHC, and triggers the cell to die via apoptosis. Note that this type of cell is inefficient in itself at removing a virus infection. There are also immune cells (gamma-delta T cells), which notice production of proteins associated with cellular stress.",
"Also when cells are infected by a virus, they begin to produce foreign (viral) substances, these are detected by intracellular receptors. The detection of a foreign antigen in the cell causes the production of type 1 inteferon, this affects nearby cells, causing them to increase the breakdown of viral mRNA, inhibits viral protein synthesis, and increases the presentation of viral antigen on cellular MHC. This is the innate defence against viruses, to give a full adaptive immune response, lymphocytes must be incorporated. ",
"The remnants of the virus are presented on MHC, this is recognised by a type of T lymphocyte (CD8+ T cell) which recognise MHC (produced by all nucleated cells). The T cell which is now activated, proliferates in secondary lymphoid tissues (lymph nodes and lymphoid tissue associated with mucosal surfaces). CD8+ T cells are produced which have a receptor for the viral protein (they are clones of the original activated cell) which now leave the secondary lymphoid tissue and search for signs of inflammation (indicative of infection), these T cells destroy viral infected cells via apoptosis. ",
"There is also another type of adaptive immune cell (B cell) which produces antibody, antibodies are essentially small proteins that seek out a specific foreign antigen (in this case, viral) and bind to it. Antibodies will bind to virus which is free (ie not already in a cell) and neutralise it by preventing the virus from entering a cell. ",
"With the double attack of destroying cells infected by a virus, and also binding up virus before it can enter a cell. The virus is killed. A small population of T cells remain (memory T cells) which are able to kick into action should that exact same virus strain be encountered again, giving a much faster response. "
] |
[
"I believe phagocytes can pick up viruses, but remember viruses are intracellular parasites, so want to be inside a cell. Some can evade the phagocytes killing mechanism and live in the cytoplasm for a long time. Take HIV as an example. "
] |
[
"Yes toll-like receptors are transmembrane receptors for PAMPs (Pathogen associated molecular patterns) and is one of the mechanisms a cell has for detecting viral antigen, such as viral envelope proteins, before it enters the cell. ",
"As for your first question, the activation of a receptor (such as a toll-like receptor) leads to series of steps that causes production of a transcription factor, which can enter the nucleus and cause expression of the IFN-1 (inteferon-1) gene. As for the specific action of interferon i think you'd need someone with more of a biochemistry background (Im more medical, so have less detail). "
] |
[
"Why do we need to sleep?"
] |
[
false
] |
I know the question sounds a bit silly, but for real: Is it a biochemical necessity? Wouldn't there also be an evolutionary advantage with being able to hunt 24/7? And, consequently, are there any species that do not sleep? Thank you all for your input so far! Very intriguing, indeed, and certainly a hard nut for science to crack. I've Google-Scholar'ed around a bit and found publications from 1901 to 2005, all saying "while we don't know we need to sleep..." - unfortunately all paywalled so I can't check them out more closely before I get back to work tomorrow...
|
[
"Animal species with atypical sleep: whales and dophins can rest their brains one hemisphere at a time. Fishes can swim in their sleep. Common swifts can sleep in four-second intervals while in flight (studied by Emile Weitnauer).",
"Muscles must rest to restore ATP, brains need energy and oxygen, food needs to be digested… It makes sense to align these cycles and have one state where the entire body is resting, and another where it is entirely available."
] |
[
"Not an expert on this, but I recommend checking out an ",
"episode",
" on the topic of the excellent Radiolab for a layman-friendly discussion.",
"tl;dlisten: we don't know; maybe, but there are advantages to sleep (the dreams part goes into this); not that we know of."
] |
[
"As far as I know, brain moves information from short term memory to long term memory during sleep. I am guessing it helps that during this process, there is almost no external input to the brain.",
"Also, dreams prepare us to certain situations. It's not uncommon that people dream of being naked in front of people when then have a presentation coming up, or they dream of falling to death after you climb a tree for the first time in your life, on dream of being late to your finals during when they are approaching. You can do somethings in your dreams that you would rather not have to do irl and that might aid you in coping with the situation, should it happen irl."
] |
[
"Is vitamin C the same the world around?"
] |
[
false
] |
My parents are convinced that the vitamins in an orange (or anything natural) can not be provided in the same way by those in a multivitamin. Is there any merit to this? Aren't they just the same compounds no matter how you get them?
|
[
"Well, technically they are wrong, but in some regards they are right.",
"Vitamin C, any B Vitamin, mineral, etc., is the EXACT same where ever it comes from. At a base level these are just chemicals--your body doesn't have a clue where they come from, just that without them carrying out thousands of different reactions becomes MUCH harder. The biggest concern would be taking a fat soluble vitamin without any fat--then your body may have a harder time absorbing it.",
"However, from a strictly nutritional standpoint, it typically is better to eat the whole food. For example, take lycopene. As you may have seen on multivitamin commercials, intake of this molecule has been reported to inversely correlate with cancer risk. From the literature I've read this is definitely a possibility. However, I heard a fascinating talk last semester from a researcher discussing how these effects were greatly improved by supplementing with lycopene+its natural derivatives in approximately natural proportions. (e.g. instead of extracting lycopene from tomatoes or whatever it would be like just concentrating the tomato.) Now most of these derivatives were still synthetic, but having them in proper proportion seemed to increase their effectiveness. ",
"One last thought too--unless your diet is complete and total trash, you live in a third world country, or are extremely physically active chances are you don't need a multivitamin. "
] |
[
"The molecular structure of synthetic vitamin C is identical to that of the vitamin C found naturally in foods. The only difference between multivitamins and food is that the other chemicals in food can and do modify how well your body absorbs it. However, this doesn't prove your parents correct; some foods increase your ability to absorb vitamin C, and some decrease it. For all intents and purposes, though, there is no significant difference in absorption between natural and synthetic vitamin C.",
"EDIT: I did some further research on this point, and found that citrus can significantly increase the absorption of vitamin C, by a surprising 35%. If you're taking a multivitamin with 500% of your daily dose of vitamin C, though, this doesn't really affect you, since you're already absorbing more vitamin C than you \"technically\" need. ",
"All that being said, you should not rely on multivitamins alone. Continue to eat your oranges and other healthy foods, and supplement your dietary intake with a daily multivitamin. It is possible to get all of your essential vitamins and minerals from diet alone, but taking a multivitamin helps you maintain proper levels of the vitamins you may miss in your daily food intake. Taking a multivitamin alone is no substitution for proper diet, however. Think of it as a buffer that protects you from accidentally depleting your body's vitamin reserves. ",
"I hope this helps. You can tell your parents that a medical student told you this, so it's probably OK to believe it."
] |
[
"A lot of vitamins can have stereoisomers if produced synthetically. Usually only one isomer in a racemic mixture is biologically active. This is why vitamins are either extracted from biological sources or produced using fermentation."
] |
[
"Is it possible for an object to be travelling so fast it would bounce off the atmosphere?"
] |
[
false
] |
Basically the title, but is there theoretically a speed/shape that if it were to collide with Earth's atmosphere at a certain angle it would bounce off the atmosphere like a rock skipping on water?
|
[
"\"Bounce\" is a bad word for it. Bouncing implies that the kinetic energy of the incoming object gets converted into some sort of spring potential and subsequently converted back into kinetic energy in a different direction. That doesn't happen.",
"However, there are two things that could happen. One option is for an object to be going so fast that the atmosphere doesn't slow it down enough for capture. That can occur for any object traveling above escape velocity (as any object coming form outside Earth's sphere of influence would be) and only passing through the uppermost atmosphere. It's essentially a failed aerocapture--often interplanetary probes will be designed to use the destination planet's atmosphere to burn off interplanetary speed so that they can get into an orbit of that planet. If a probe planning for aerocapture goes too deep into the atmosphere then it can wind up losing too much speed and crashing into the surface (or just burning up or breaking up due to the increased heating and forces); too high and it'll continue on out of the atmosphere with too much speed and will leave the planet's sphere of influence.",
"The other option is similar but relies on the object having significantly un-uniform aerodynamic properties. If you imagine something like the space shuttle entering the atmosphere then it is flying like a conventional glider and can change its direction by using its wings and control surfaces. This can be used to alter the direction enough that the craft winds up re-exiting the atmosphere when a non-lifting shape would have been unable to. That's really just an edge case of the previous scenario.",
"What you don't see is an object coming towards earth, compressing a cushion of air beneath it, then being pushed back into space as that air cushion re-expands. "
] |
[
"Absolutely. The ballistic entry angle ",
"has to be just right",
" to keep that from happening. In fact, skipping off the atmosphere was a big fear during Apollo 13. ",
"There is also the more deliberate atmospheric braking, which is still kinda skipping off the atmosphere. "
] |
[
"Oh wow. So its never \"skipping\" like skipping a pebble across a pond, but its always just aerobraking right?"
] |
[
"If the circumference of the Earth is 25,000 miles at the equator, but 0 miles at the pole, why don't we feel the difference in speed at different parts of the Earth?"
] |
[
false
] | null |
[
"Because what you feel is relative to the Earth and its atmosphere, and by your exact logic, they are also moving faster at the equator and slower at the poles."
] |
[
"Hmm, that makes a certain amount of sense. But why isn't there a difference in atmosphere etc?"
] |
[
"Because from the atmosphere's point of view, it also cares most about things relative to the Earth. There isn't anything in space to keep if from spinning at the same speed as the Earth. The whole planet spins together (excluding weather effects, tides, etc.) because there isn't anything slowing any of if down."
] |
[
"What is happening during a panic attack?"
] |
[
false
] |
What is happening in the brain/body physiologically? Is it usually triggered by something or do they just happen out of the blue?
|
[
"Yes, relaying what you heard from an expert is hearsay and definitely doesn't qualify yourself as an expert, and describing your personal case is most definitely anecdotal.",
"Please ",
"consult the /r/askscience guidelines on answering questions",
"."
] |
[
"Yes, relaying what you heard from an expert is hearsay and definitely doesn't qualify yourself as an expert, and describing your personal case is most definitely anecdotal.",
"Please ",
"consult the /r/askscience guidelines on answering questions",
"."
] |
[
"Please ",
"consult the /r/askscience guidelines on answering questions",
"."
] |
[
"Why do humans \"need\" sleep?"
] |
[
false
] |
Could there ever be an animal that could just stay awake and conscious all the time?
|
[
"I can answer this question. The answer was found very recently by neuroscientists. You see, neurons in the brain use a lot of energy, and they don't have enough space to store excess chemical energy (in the form of glucose or lactate). So neurons get excess energy from ",
"astrocytes",
". Astrocytes store chemical energy, and during the day, when our neurons are energy-starved, molecules of lactate will transfer to the neurons, providing them metabolic energy. The energy reserves of the Astrocytes become depleted during a day's mental activity. ",
"When we sleep, the chemical energy reserves of astrocytes are replenished. This has been hinted at by experiment. Example: two groups (plus control groups) undergo intense physical exercise and intense mental exercise, respectively. Then they sleep. The group who exercised physically subsequently needs a normal amount of sleep (equivalent to the control group), while the group who underwent mental exercise needed more sleep. Thus we can conclude that neural activity (specifically heightened metabolic activity) is related to sleep. ",
"How does this happen? When astrocytes run low on energy, they release ",
"adenosine",
", a neuromodulator. Adenosine is an inhibitory neuromodulator. It stops neurons from firing, presumably stopping them from using more energy than is available. As the day wears on, adenosine levels rise in the brain. After sleep, adenosine levels are back to where they were. It is hypothesizes that adenosine causes most of the physical effects we collectively call \"sleepiness\": difficulty moving, clouded thoughts, laziness, etc.",
"Keep in mind that everything I've said above is just a physical explanation. And everything I've said is somewhat speculative. It's form the textbook ",
"Physiology of Behavior",
" by Carlson. Highly recommended.",
"One can also discuss evolutionary reasons for sleep. Sleep lets us conserve energy, which is very important in evolutionary terms. ",
"During sleep, our explicit and implicit memories are strengthened.",
" ",
"And to answer someone else's question, YES, you can die of lack of sleep. Ther have been reported cases as well as studies with rats on the subject."
] |
[
"From the worlds absolute leading expert, the (co)discoverer of REM sleep, who has devoted over 50 years to research on the subject:",
"\"As far as I know, the only reason we need to sleep that is really, really solid is because we get sleepy.\""
] |
[
"Just a note, but caffeine works by bonding to adenosine receptors without activating them, which makes you less tired."
] |
[
"What percentage of people are carriers for limb girdle muscular dystrophy in the UK ?"
] |
[
true
] |
[deleted]
|
[
"from the merck manual : \"On average, 1 of 3,000 boys born has Duchenne muscular dystrophy, whereas on average 1 of 30,000 boys born has Becker muscular dystrophy.\"",
"You can infer the rest from that. You can get tested if you are really paranoid but be aware that only the mother being a carrier matters because the father won't donate his X chromosome to the child."
] |
[
"Also be aware that because it is a recessive disorder even if the parent is a carrier still only 50% chance of it being passed along."
] |
[
"Er -- limb girdle muscular dystrophy is a group of similar problems with different dominant/recessive inheritance patterns. And the 50% inheritance pattern of some faulty genes is more complicated than simply dominant/recessive. "
] |
[
"What holds a cloud together?"
] |
[
false
] |
When i smoke and breath out a cloud it gets dispersed fairly quickly, even inside where there is no wind. Now I know that they are always changing but sometimes you can watch a cloud move all the way across the sky looking like the same cloud. Why dont they constantly disperse and form into new clouds due to winds/other forces?
|
[
"The key to understanding this is realizing that clouds are not a single object; they are simply a \"blob\" of air which has cooled to the point where water vapor can condense into cloud droplets. ",
"When the \"blob\" is small, like the cloud coming out of your mouth on a cold day (yes, it is technically a cloud), turbulence and diffusion quickly mix the blob with the drier surrounding air, causing the quick dissipation you see. When the blob is large, hundreds of feet or even miles across, the edge of the blob is still mixing and dispersing, but this area of mixing is very small compared to the overall size of the cloud. ",
"You can see this clearly if you watch ",
"a time-lapse video",
" of clouds moving across the sky. Different clouds form and dissipate constantly as they move with the general prevailing wind direction, even though there are little swirls of turbulence all over the place moving in other directions. Watch the smaller disappearing clouds closely, I bet that pattern looks awfully close the the \"smoke dispersion\" process you see in your own experience! It's just a difference of scales in time and space."
] |
[
"Wait, does this mean their is some dynamic of the cloud which is governed by the square-cube law? So, more massive clouds are less likely to \"disperse\"? I'm not sure what this implies, but it's still cool. "
] |
[
"Yes, there's definitely a \"square-cube\"-type effect going on here. Diffusion (both true diffusion and ",
"turbulent diffusion",
") is proportional to the surface area of the cloud on a large scale, so the larger the cloud the slower diffusion will act to disperse it significantly."
] |
[
"Why is desalination/purification/etc. of water so difficult? Why can't we just purify ocean water?"
] |
[
false
] |
Clean water has always seemed to be a pretty pervasive issue around the world. The necessity is there, so why is water purification not a bigger industry? I know there are real hurdles with it, I just don't know what they are and am wondering if the need for water will one day force us to overcome them.
|
[
"Energy. It takes an enormous amount to desalinate water."
] |
[
"If you had a dam to work with, you would have fresh water from a river or lake, and won't need desalination. Most desalination plants are needed around coastal areas where water is at sea level."
] |
[
"If you had a dam to work with, you would have fresh water from a river or lake, and won't need desalination. Most desalination plants are needed around coastal areas where water is at sea level."
] |
[
"When net gravitational force exerted on the object is zero, would gravity still affect time?"
] |
[
false
] |
Let's say there is an object which is middle of the two identical blackholes where net gravitational force exerted on the object is zero. In such a case, would gravity still affect time?
|
[
"Good question--and to answer this, let's move away from necessarily describing the net force, or acceleration, acting on that object. Instead, consider where that objects sits in terms of a gravitational well. If we think about the depression in a rubber sheet analogy of spacetime caused by a massive object, we can also think about the \"two lobe\" depression caused by the presence of two massive objects:",
"\n",
"https://upload.wikimedia.org/wikipedia/commons/4/44/RochePotential.jpg",
" ",
"Two things to note this image:",
"\n1. This is only the Newtonian picture.",
"\n2. It's an effective potential with centrifugal considerations. If you're skeptical, check out just the pure potential ",
"here.",
"Now, with that said, you can see that the L1 lagrangian point in the middle which represents the \"balance\" of forces, you can see that the overall gravitational potential energy of a particle here is still depressed. This means than when we consider the fully general relativistic situation, we're going to find that this location still exhibits gravitational redshift and dilation effects when compared with the surround free space sufficiently distant from the two massive objects.",
"In short, yes gravity will still effect time here despite no Newtonian forces--though we can't rule out GR corrections without solving for the \"double Schwarzschild\" metric to be sure."
] |
[
"What I think this means in practice is that two black holes could be circling close in the center of a galaxy with a planet at their mutual orbit point and,.. well it wouldn't be stable because Lagranian points are a semi-static solution, but the planet's time would be dilated even though it might sit in the comoving frame, for a while before it destabilized and got spagettified into oblivion.",
"If my 30 year memories suffice the Einstein metric is a mess to joust with using Christofel functions, so yeah- calculating exactly what the clocks might do could be a battle."
] |
[
"IIRC there is ",
" no solution to GR with two black holes, yes?"
] |
[
"Even and Odd Functions"
] |
[
false
] |
I'm directing this question to all walks of scientists and engineers, which is why I posted to this subreddit. Today in pre-calc, we learned about even and odd functions. I understand the definition of even and odd functions. ( f(-x)=f(x) and f(-x)=-f(x), respectively.) So, understanding this concept, my question is why do we care whether a function is odd or even? Will there be something further down the mathematics pipeline that will utilize this concept?
|
[
"You'll learn later that the integral of an odd function over a periodic interval is zero, and the integral of an even function over a periodic interval is equal to twice the integral over half the interval.",
"You can visualize this by looking at something like the sine and cosine functions. The integral can be thought of as the area under a curve (or above, if the values are negative). The sine function between -pi/2 and pi/2 is full oscillation of the function, and you can see that it has just as much area above as below the x-axis, so the integral is 0. You can do the same with the cosine function and see it will have twice the value of the integral on the interval from 0 to pi/2."
] |
[
"Because every time you instantly cross out some gnarly looking integral as equal to zero because it's odd you'll feel like a badass."
] |
[
"It's not a super-important concept in and of itself. Symmetries, of which this is a simple example, ",
" super-important in mathematics, though, and this gets you thinking about such things--the answer to your question about its utilization down the mathematics pipeline is an emphatic ",
". It is a huge and wide-ranging topic."
] |
[
"Will the recent freeze in the United States somehow result in less bugs this Spring / Summer?"
] |
[
false
] |
I'm hoping for yes.
|
[
"That depends on the species and where you are. The expansion of some species is limited due to their ability to overwinter in cold temperatures. Those that are on the northernmost temperature limit will most likely suffer from reduced populations, some becoming locally extinct. They'll recolonise, but it'll take a few years."
] |
[
"There's some speculation that the cold temperatures will have a negative impact on some invasive insect (namely emerald ash borer, wooly adeldig, pine beetle) populations, but we won't know the true extent until the spring. "
] |
[
"It might destroy some insect eggs. However, last time we had a bug free summer was when there was an intensely warm period (think 60s) in March, when all eggs hatched, followed by a snowstorm in early April, killing all larvae. I hope the freeze this time was sufficient to kill most of the bugs, but if not, let's pray for a backup. "
] |
[
"Why do Quasar's burn out?"
] |
[
false
] | null |
[
"The supermassive black holes (SMBHs) that power quasars are 'fed' via the accretion of gas. The accreting gas forms a disk around the black hole due to the conservation of angular momentum, and the disk heats up due to friction because different radii of the accretion disk orbit at different speeds. Because of the massive gravitational potential involved with SMBHs, the accretion disk heats up all the way into the far ultraviolet, and the size of the heated material combined with its temperature makes the quasar outshine its entire host galaxy.",
"Quasars \"turn off\" when there is no longer material available for accretion. The energy lost via heating and radiation is subtracted from the kinetic energy of the material in the accretion disk, causing it to spiral into the black hole.",
"As an aside, an accreting black hole is the most energy efficient engine in the Universe, converting matter to energy at a rate of ~ 10%-50%, depending on the spin of the black hole."
] |
[
"From a video on the brightest things in the universe i saw on ",
"r/videos",
" yesterday, a quasar is a ring of matter spinning around a black hole very fast fueled by stars being torn apart. They \"turn off\" when the black hole becomes so massive stars are no longer torn apart but instead \"swallowed whole\" maybe someone with more space smarts than me can elaborate "
] |
[
"As an aside, an accreting black hole is the most energy efficient engine in the Universe, converting matter to energy at a rate of ~ 10%-50%",
"For comparison, fusing Hydrogen to Helium-4 is about 0.7% efficient."
] |
[
"What happens if you were to heat water in a sealed container for a really long time with a very high temperature source."
] |
[
false
] |
I always wondered about this when I was younger: Suppose you had a 1 kg of water completely filling an indestructible container. You heat the water inside the container using something that can exceed 10,000C (container can also withstand this temperature). What happends to the water inside the container as it passes beyond being superheated and supercritical? Can the water absorb energy indefinetley and actually reach 10,000C? What would the pressure be? What would the properties of water be at this point, or whatever point the water can reach before it stops absorbing energy? What would happen if the container were to rupture after the maximum amount of energy has been absorbed from the heat source?
|
[
"Liquid water in a sealed container would, as you've described, become superheated and eventually become a supercritical fluid. At this point, you can think of it as a very, very dense gas. It would lack properties like viscosity that we normally associate with liquid water.",
"Eventually, if you pumped the energy up high enough, the energy would overcome the energy necessary to keep the molecules together, and you would see larger amounts of H+ and OH- in your supercritical fluid. If you pushed the temperature even higher, electrons would no longer be limited to localizing around a single nucleus (or molecule) and you'd develop a plasma."
] |
[
"The plasma collapses into radiation. ",
"here's a story of tungsten and steel being heated up to emit 2 billion kelvin x-rays",
"edit: after further reading and understanding, i guess the plasma only collapses until energy is radiated away. but with a constant heat source, and no energy escaping? it doesn't seem like that article sufficiently covers the hypothesis.",
"it may be of note that they've made ",
"quark-gluon plasma",
" at tens of trillions of degrees celsius in the LHC."
] |
[
"What would happen if the container were to rupture after the maximum amount of energy has been absorbed from the heat source?). ",
"Something like ",
"this",
". You do not want to be near it."
] |
[
"What is this?? http://i.imgur.com/y6fm3.jpg"
] |
[
false
] | null |
[
"You will have to re-submit to change the title, it can not be edited. But beyond that, this question can be answered by doing a google search or searching previous topics in AskScience."
] |
[
"Your link is broken. Also, please conduct a google search, you should be able to find it that way."
] |
[
"Does the link in my post work? I don't know how to edit my post title cuz that one doesn't work :-/"
] |
[
"Does roadkill select for wildlife that is more wary of humans?"
] |
[
false
] |
[deleted]
|
[
"There are not a whole lot of studies which looked into the selective effects of roadkill. The best one I know of is Brown, C. R., & Brown, M. B. (2013). Where has all the road kill gone?. Current Biology, 23(6), R233-R234. see: ",
"http://www.cell.com/current-biology/pdf/S0960-9822(13)00194-2.pdf",
"What they did was note that the amount of roadkill among cliff swallows in colonies along highway overpasses in Nebraska seemed to be diminishing over time. So they went back and took measurements of roadkill from those populations from specimens and observations gathered over 30 years, and noted that the birds killed tended to be longer-winged, while wing length in the population as a whole was decreasing, & population size was increasing (see their figure 1, A through D). From 1984 to 2014, the number of birds killed annually went from 20 to 4-ish, while the number of nests exploded from about 8000 to 25000! Brown & Brown take this to indicate that there was selective pressure exerted on the population for increased maneuverability. ",
"Coming back to your initial question, while it does appear that roadkill did indeed induce selective pressure on these populations, the trait which was selected was not so much wariness as it was agility, using reduced wing length as a proxy."
] |
[
"There is data on inventories of roadkill for assorted mammals (and other groups) in various locations, and on sites more likely to generate roadkill. It'd just that those data sets look at which critters are hit more than others, or the effect on species preservation. As I said, there is very little data which measures the effect of roadkill in terms of natural selection and selective pressure. Of species changing in response to road proximity.",
"I know of a study on salamanders (",
"Brady, S. P. (2012). Road to evolution? Local adaptation to road adjacency in an amphibian (Ambystoma maculatum). Scientific reports, 2",
"), but in that case all they were noting were differential survival rates for salamanders from roadside vs woodland populations, without going into the exploration of what mechanisms might account for the observed differences (or at least they could not find one - there were plenty of differences in clutch & egg size, but nothing which obviously indicated a specific adaptive mechanism).",
"The most comprehensive review on the topic that I know of is another paper by Brady (",
"Brady, S. P., & Richardson, J. L. (2017). Road ecology: shifting gears toward evolutionary perspectives. Frontiers in Ecology and the Environment, 15(2), 91-98.",
". He mentions studies with observed adaptive or maladaptive effects for 4 species: Fescue grass, wood frogs, and the previously mentioned salamanders and swallows. Nothing specific on emergent adaptation or selective pressures on larger vertebrates, such as raccoons or deer."
] |
[
"There is data on inventories of roadkill for assorted mammals (and other groups) in various locations, and on sites more likely to generate roadkill. It'd just that those data sets look at which critters are hit more than others, or the effect on species preservation. As I said, there is very little data which measures the effect of roadkill in terms of natural selection and selective pressure. Of species changing in response to road proximity.",
"I know of a study on salamanders (",
"Brady, S. P. (2012). Road to evolution? Local adaptation to road adjacency in an amphibian (Ambystoma maculatum). Scientific reports, 2",
"), but in that case all they were noting were differential survival rates for salamanders from roadside vs woodland populations, without going into the exploration of what mechanisms might account for the observed differences (or at least they could not find one - there were plenty of differences in clutch & egg size, but nothing which obviously indicated a specific adaptive mechanism).",
"The most comprehensive review on the topic that I know of is another paper by Brady (",
"Brady, S. P., & Richardson, J. L. (2017). Road ecology: shifting gears toward evolutionary perspectives. Frontiers in Ecology and the Environment, 15(2), 91-98.",
". He mentions studies with observed adaptive or maladaptive effects for 4 species: Fescue grass, wood frogs, and the previously mentioned salamanders and swallows. Nothing specific on emergent adaptation or selective pressures on larger vertebrates, such as raccoons or deer."
] |
[
"Why do trees have rings? And how accurate are they to the calendar years?"
] |
[
false
] | null |
[
"This is the result of alternating rapid and slow growth phases that correspond to summer and winter respectively. They are highly accurate if you are good at reading them and it's the right kind of tree growing in temperate climates."
] |
[
"This is askscience. We don't assume!"
] |
[
"So would it be reasonable to assume trees near the equator don't have rings?"
] |
[
"What is the minimum % of oxygen we could have in the atmosphere and still breathe fine?"
] |
[
false
] |
I saw a BBC documentary (The modern alchemist) where they were in a chamber with 15 % oxygen, and they couldnt light a lighter there, and a match wouldnt burn. Yet they could breathe fine there. Made me wonder how low we can go!
|
[
"this is an interesting question, and the answer will probably surprise you.",
"at this very second, we're living in an environment that's about 21% oxygen. the bulk of the atmosphere is actually nitrogen, clocking in at 78%. the 1% of air that's left over is mainly composed of argon and carbon dioxide.",
"i'm gonna go into something called \"partial pressures\" in this explanation, because it's a huge player in how we breathe and take in oxygen/expel carbon dioxide. assuming we're at sea level, the atmospheric pressure is at 760 mmHg. that means the partial pressure of oxygen (the amount of pressure that the oxygen contributes to the total) is 160 mmHg. (21% of 760 is approximately 160.)",
"if you were a diver and had to breathe from a tank, the minimum partial pressure that they recommend you keep in your tank is ",
"120 mmHg",
", or 15.7% oxygen. depending on how long/how deep you'll be diving, the composition of your tank changes.",
"so, we know how low we can survive. but why? in your arteries, your body tries to keep the partial pressure of oxygen somewhere around 95mmHg. as the oxygen content of your environment decreases, this makes it more and more difficult. as i said earlier, the air around you has a pO2(partial pressure of oxygen) of 160mmHg. by the time it gets into your lungs, this number drops to 150mmHg due to your airway moistening the air. by the time it reaches your alveoli(the last stop before it enters your arteries), it goes further down to about 105mmHg. this is due to the gas exchange that happens between your arteries and your alveoli.",
"the pO2 difference between your alveoli and arteries is ",
". in order for oxygen to diffuse into your arteries, it must be travelling from an area of high O2 concentration to low O2 concentration. so in your healthy human body, this is 105mmHg alveolar to 95mmHg arterial. that's a difference of 10mmHg, which is normal and seems like an incredibly small number.",
"as the pO2 of your environment drops, this difference becomes smaller and smaller until there is, essentially, no movement of oxygen into your blood.",
"based on what i've explained so far, i would guess that the people in the chamber didn't spend very long in there. we can survive for a while in low-oxygen environments (as mountain climbers do), but unless we're very acclimated then we run the risk of hypoxia.",
"source: ",
"wikipedia",
" it appears the answer is more like 7% oxygen at sea level."
] |
[
"I can't speak to the actual medical parts of it, but according to OSHA anything under 19.5% is considered oxygen deficient and anything under 16% is considered Immediately Dangerous to Life and Health (IDLH).",
"edit: ",
"Here's some info:"
] |
[
"Also, when mouth to mouth is preformed, about 14% of the gas pushed into the lungs of the person is oxygen. ",
"Just a cool fact..."
] |
[
"Problem with a gravity simulation: Every planet needs the same orbital velocity in order to achieve a circular orbit. How is this even possible?"
] |
[
false
] |
[deleted]
|
[
"It looks like you (or someone else!) rearranged ",
"Kepler's Third Law",
" incorrectly and are missing the dependence on distance (a) - it should be sqrt(GM/a)."
] |
[
"Lol. Well, yea. Of course I rearranged it, that's the whole point. It still worked, which it shouldn't have. Hence my problem. ",
"The good news is, I slept on it. And it took me 2 minutes of clear headed thinking to figure out the problem in the morning. Which is a lot better than spending 8 hours thinking about it without a working solution in the end...",
"Anyway, the problem was, as it usually is, that I'm an idiot. It turns out in all this time I never realized that I forgot to normalize a vector in my force calculation. Which is something you'd usually spot immediately, but in this special case the math worked out such that nothing really obvious broke. Other than Kepler's third that is... but other than that everything was fine, which apparently confused me to no end. ",
"So I guess the lesson here is, when it comes to math, programming and operating machinery, TAKE BREAKS... :/"
] |
[
"Solid science."
] |
[
"Could there be more unknown elements that exist in the universe?"
] |
[
false
] |
[deleted]
|
[
"Not really. Every element has a whole number of protons, so there can't be sneaky elements hiding inbetween the elements we know. The only unknown elements are ones with very large numbers of protons, and these are known to be unstable. There may be \"islands of stability\", where specific combinations of large numbers of protons and neutrons may turn out to be somewhat stable. But \"stable\" here means \"around long enough to be detected in a lab with specialised equipment\", and not that these elements could be sitting around in asteroids for ages."
] |
[
"Even if they have short lifetimes, are superheavy elements expected to be formed in events like supernovae or neutron star collisions? They're such massive events with loads of energy and neutrons about that to me it would seem strange if they ",
" create at least a trace of superheavy elements but we can create them in a lab on Earth."
] |
[
"\"Quickly\" ... as in seconds or minutes, long before the on-going supernova cools down enough for the superheavy elements to acquire a few electrons, and give off a detectable spectrum. I don't know how we could see anything from a few totally ionized atoms deep inside a supernova."
] |
[
"Can someone explain in layman's terms why cancer is so hard to cure?"
] |
[
false
] |
From what I've heard, there are a lot of different types of cancer and each type is different. But isn't the fundamental problem being that the cells divide uncontrollably? The and is different for each type, and that's mainly what I'm curious about. For example, how is the (pathology?) of lung cancer different than say, colon cancer? How do cancers differ at the cellular level which makes it so we have to find a cure for each one individually? Hopefully it's possible to answer this in layman's terms.
|
[
"Cancer isn't quite as simple as a cell dividing uncontrollably. There is an episode of the excellent Radiolab about tumors that gives a good layman explanation of how tumors evolve and why it is so difficult to cure.",
"http://www.radiolab.org/2010/may/17/",
" the segment in question starts at about 12:40 but feel free to listen to the whole thing (or the entire series!)"
] |
[
"Cancer is disease of the cell cycle.",
"Like how there are 1000 different diseases of skin, there are 1000 ways to break the cell cycle and develop cancer. Cancer is simply a catch all for breaking the cycle. \n",
"http://en.wikipedia.org/wiki/Cell_cycle",
"There are \"checkpoints\" in the cycle that allow the cell to divide and grow. If these checkpoints break, the cell divides like crazy. ",
"The cell cycle also overlaps with DNA repair and the \"programmed\" cell death mechanisms. Both of these are natural defenses against cancer, but when they break you loose that protection.",
"http://www.sapphirebioscience.com/images/wallcharts/abcam_cyclins_and_cell_cycle_regulation_detail.jpg",
"All three of these are extremely complex and very sensitive to changes in the amount and placement of certain proteins.",
"The end result is a disease (cancer) that can be caused by changes in any one of many many places where things can go wrong."
] |
[
"Cancer is hard to treat because \"cancer\" is thousands of different diseases, each with its own cause.",
"As we unlock the genetic basis for individual cancers, we'll get a better understanding of what makes cancers tick. We can talk in generalities about tumor suppressor genes (loss of these can give you a cancer) or oncogenes (gain of these by, say, somatic translocations can give you cancer). Understanding these concepts will give you a framework by which to understand cancers. To understand a specific cancer, you'll have to look at its genetic basis. ",
"Cancers are more different than they are similar, except insofar as they share the phenotype of \"undesirable tissue expansion.\" Am not an oncologist; they may well disagree with this perspective."
] |
[
"What do the data storage properties of nucleic acids mean for trans-binary computing?"
] |
[
false
] |
[deleted]
|
[
"There are lots of non binary computing investigations. This sort of quaternary system was a curiosity decades ago. The nucleotides can store data with high density but they are fragile (susceptible to ionization damage from chemicals and radiation) and storage and retrieval are very slow. And they are not computers, just memory. So, a realized curiosity, but just a curiosity."
] |
[
"Before computer architecture eventually settled on binary, Russians did have base-3 computer which according to wikipedia was way faster than binary alternatives of the time, and this was somehow tied to base 3 and advantages of it.",
"They eventually switched to binary computer butI've always wondered, why was base-3 such an advantage?"
] |
[
"You get more information out of it per computational cycle, and likely a higher density of information into a given number of memory components (3",
" vs 2",
"), but possibly at the cost of smaller noise margins (I don't know what the Russians were using for memory) meaning you'd need to have error-correcting logic and extra storage for error bits all over the place.",
"Some mathematical computations (anything with negative numbers) are simpler in trinary, but when it comes down to if-then, 1-0 questions much of the decision space (all the -1's) simply gets wasted and things devolve to binary anyway unless you teach your compiler to compress those things but then bug hunting becomes a nightmare."
] |
[
"Other than the Croatian Lizards, which evolved within 30 generations, what other documented cases of natural evolution are there that have occurred within recorded history?"
] |
[
false
] |
[deleted]
|
[
"No, it is still evolution. Antibiotics are a natural pressure for bacteria, they can \"evolve\" and \"reverse evolve\" antibiotic resistance. "
] |
[
"No, it is still evolution. Antibiotics are a natural pressure for bacteria, they can \"evolve\" and \"reverse evolve\" antibiotic resistance. "
] |
[
"TalkOrigins has some good stuff on this. ",
"From memory:",
"London subway mosquitoes (really)",
"Cichlid fish in African lakes",
"Speciation of ",
" introduced to the island of Mauritius"
] |
[
"If one intentionally ignores the urge to urinate, why do the bladder muscle weaken, but other muscles (eg heart) get stronger when actively engaged?"
] |
[
false
] |
I hope that makes sense. I hear that it’s bad to hold in your urine, it weakens your bladder muscles. If resisting the urge to pee is done by voluntary muscle engagement, isn’t this the opposite to other muscles that strengthen with use?
|
[
"The short-term answer: Muscles work best at their ideal length; if they are too short or too long, they won’t have maximum strength. So, if you ignore the urge to urinate, the muscles get overly stretched and do not work effectively. \nLong-term answer: actually, we see this in older men who develop prostatic hypertrophy; they are always urinating against increased resistance. Looking in their bladders with a cystoscope shows thickened muscle with ridges. But this isn’t a good thing.\nEdit: after rereading your question, I think that I need to clarify: I’m describing the detrussor muscle, which actively empties the bladder. The muscle that actively resists emptying the bladder is a different one, the urinary sphincter muscle."
] |
[
"People with any kind of blockage for urination have thicker bladder walls. ",
"Also, if you hold it too much, the bladder muscles distend too much, and that makes it weak. And you can’t empty it after. ",
"Usually combined with a blockage, the weakened muscles can’t overcome that blockage and result in retention. Then you need a probe to empty it."
] |
[
"So basically the same reason that you “weightlift” a pregnancy belly 24/7 for months and still end up with abs that are weaker than when you started."
] |
[
"If matter cannot be created or destroyed, does it follow that there is a finite amount of matter in the universe?"
] |
[
false
] |
If so, doesn't that mean the universe can only be infinite in the sense that it is infinitely expanding, and the space between matter infinitely growing larger, while the number of stars and other celestial bodies remain the same and finite? What would happen, then, if I were to pass the last star (the most farthest one, after which there is no more matter)? Could that star mark the "edge" of the universe? Edit: Also, I realize I'm thinking of the universe as being flat, which I know may or may not be true, but my uneducated mind doesn't know of any other way to imagine it.
|
[
"Not if the Universe is infinite. What should be conserved is the amount of matter in an expanding volume. Since the Universe is bigger than we can see, due to the finite speed of light, asking how much matter there is in the ",
" Universe is not a particularly scientific question!",
"It bears saying, by the way, that while normal matter (that is, matter like stars and galaxies and so forth - matter with negligible pressure, technically) is conserved like that, not all kinds of matter and energy are. This is because conservation of energy is only guaranteed to be true when physics is time-independent, but an expanding Universe clearly does depend on time. A simple example is light: if I keep track of the matter inside an expanding volume (dust, galaxies, dark matter, etc.), the total mass stays the same (assuming nothing decays away to radiation), but if I keep track of all the photons in that volume, the total energy actually goes down. This is because while the number of photons is conserved, each photon is redshifted as the Universe expands, and redshifting corresponds to lower energy."
] |
[
"Matter is not conserved; mass-energy is conserved.",
"The total amount of mass and energy is constant within the universe."
] |
[
"Actually, the total energy content of the universe is not conserved. It only would be if the universe were not expanding. ",
"http://blogs.discovermagazine.com/cosmicvariance/2010/02/22/energy-is-not-conserved/"
] |
[
"Why does an electron have the same amount of charge as a proton, even though a proton is much bigger?"
] |
[
false
] |
An example of this size could be a negatively charged cat trying to discharge a positively charged building.
|
[
"They both have a the minimum amount of charge that can exist freely in this universe. This is independent of the size of the particle. The W boson is 80 times as massive as the proton and has the same charge."
] |
[
"Quarks probably don't exist freely."
] |
[
"Binding energy",
"Not really. Binding energy is actually negative: a carbon atom has ",
" mass than the three helium atoms that made it. Binding energy is the energy you have to add to something to unbind it.",
"It turns out a proton isn't just 3 quarks. The 3 quarks usually referred to are called the \"valence quarks\", but there are constantly quark-antiquark pairs and lots and lots of gluons being created due to the strong and other forces. It is the energy of these particles that give the proton its mass.",
"This",
" is the nice clean model of a proton usually shown, but in reality ",
"this is more accurate"
] |
[
"Why are white and silver different colours?"
] |
[
false
] |
If a white object is reflecting all frequencies and a silver object is reflecting all frequencies then why do they look different? Most of the explanations I have found so far talk about specular and diffuse reflection but that doesn't seem to tell the whole story. Specifically, what about shiny white objects (like a whiteboard) or matt silver objects (like the dull side of kitchen foil)? The most satisfying explanation so far is that it's "something to do with electrons".
|
[
"Most of the explanations I have found so far talk about specular and diffuse reflection but that doesn't seem to tell the whole story.",
"Are you sure that explanation is insufficient? The range of possible roughness explains the range of possible appearances.",
" Imagine shooting a grid of photons at a perfectly flat metallic surface by collimating the light coming out of a computer screen (making sure all photons are traveling parallel). The albedo is 1 so you know they're all going to reflect. The surface is perfectly flat so you also know precisely which direction each photon is going to reflect in. They will remain in the same relative positions after bouncing off the surface. The grid (image) might be stretched or possibly reflected but it won't be \"scrambled\". You could capture the photons and use the photoshop free transform tool to get the original image back (in principle).",
" Now imagine shooting a grid of collimated photons at a slightly bumpy metallic surface. Again the albedo is 1 so they're all going to reflect. The bumps are much wider than they are tall so most surface normals still point roughly perpendicular to the surface but a few of them deviate slightly from the perpendicular. After the grid of photons has bounced off the surface it will no longer be a perfect grid. It'll still travel in roughly the same direction that it would have had the surface been perfectly flat (because it ",
" almost perfectly flat, just not exactly perfectly flat) but now some pixels will be out of place. If you had a red circle on a blue background on the computer screen you might expect to see a red haze superimposed on a blue haze after the photons had bounced off the bumpy surface.",
" Now imagine shooting a grid of collimated light at a very rough surface. The surface normals do not tend towards the perpendicular. They're all over the place. There are hills, valleys, verticals, and all sorts of nasty features. The albedo is 1 so the photons are all going to reflect but that's where our predictive powers end: there's no telling which direction they will bounce off in. After they've bounced, all traces of the original image are destroyed. There isn't even a \"scrambled reflected image\" like there was for the dull shiny surface. Just a homogeneous mix of red and blue light (homogeneous after averaging over enough photons to get rid of the shot noise, of course)."
] |
[
"And to add, shiny white is typically due to a flat but reasonably transparent film on top of a bumpy white substrate - there is partial specular reflection from the shiny film, but most of the light will come back from the bumpy surface, so you have a combination of the two. ",
"Beyond that you can have layered surfaces that reflect different wavelengths different amounts at different interfaces, or the partially reflect the same wavelengths at different depths giving interference effects, or diffract the light and so on, leading to all sorts of interesting applications like dichroic filters or anti-reflective coatings"
] |
[
"I would note that a shiny white surface like a whiteboard has a rough white surface underneath a smooth transparent plastic or glass. There is partial reflectivity from the plastic/glass, which isn't the quite same as a polished metal surface.",
"Polished aluminum is \"white.\" It has very good reflectivity across the visible, IR and UV. Silver on the other hand doesn't reflect as well in the near UV. Rough metal surfaces typically have oxidation or dirt in its crevices that give it that \"metal\" look. ",
"Here",
" is a graph of the reflectivities of some shiny metals.",
"This doesn't really address your fundamental question about how electrons play into it, but its something to consider."
] |
[
"Why are the wavelength intervals in some radio tuning interfaces not spaced in a consistent fashion?"
] |
[
false
] |
I see AM-FM radios with tuning interfaces like this all the time: Usually at least one of the broadcasting bands (FM or AM) have their numbers in irregular intervals, not linear, or not even apparently logarithmic in progression. Sometimes the FM band may have the intervals evenly spaced but the AM spacing is more "erratic" (especially the spacing between 540hz and 600khz, then a 100khz change across the same distance). What establishes the reason for the irregular spacing and granularity? Are some wavelengths naturally more difficult in certain regions to broadcast signals without interference? Are the less granular areas mostly allotted for other, non-public and non-commercial purposes?
|
[
"Radios like that use a variable capacitor to tune the stations. When you turn the dial, you are turning a set of plates which intermesh with, but don't touch, another set of plates. The capacitor forms part of an oscillator and the frequency is dependent on the square root of the capacitance. Since the square root is not a linear function, the frequency does not change linearly. It is more pronounced on the AM dial because the frequency change from high to low is almost 3:1. The FM change is closer to 1.2:1. ",
"I don't know how manufacturers choose which frequencies to label. "
] |
[
"I'm building a radio. Is there a formula I could use to accurately space out tick marks on the AM and FM radio dial? Is it x"
] |
[
"It depends on the tuning capacitor and the circuit. An accurate simulation should be able to do it, but I would just build it and graph the tuning knob angle vs received frequency. Then find the points you want to mark on the graph and read the angle off the other axis. No estimation or guesswork involved. "
] |
[
"How is LIGO different (besides scale) from the Michelson-Morely experiment, and how are they similar?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"You question is either commonly occurring or has been recently posted on ",
"/r/AskScience",
". It may also be answerable using a Google or Wikipedia search.",
"To check for previous similar posts, please use the subreddit search on the right, or Google site:reddit.com",
"/r/askscience",
" ",
"Also consider looking at ",
"our FAQ",
".",
"For more information regarding this and similar issues, please see our ",
"guidelines",
".",
"/r/AskScience",
" is not the correct forum for users to look for help on their homework, craft or personal projects, research projects, essays, etc. A more suitable subreddit would be ",
"/r/HomeworkHelp",
". Please see our ",
"guidelines.",
" Depending on the exact subject, there may be more suitable subreddits like ",
"/r/AskMath",
", ",
"/r/AskPhysics",
", ",
"/r/PhysicsHelp",
", or ",
"/r/chemhelp",
".",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"It's not a recent post here and I can't find a satisfactory answer online, you must have a good answer to block the question right?"
] |
[
"If you google \"ligo michelson morley\", you can find lots of information on the similarities and differences. If you have a more specific question, feel free to post that!"
] |
[
"What is actually happening when a jet breaks the sound barrier?"
] |
[
false
] |
Why is there a physical cloud you see, how does one actually do this and what is the effect?
|
[
"This ",
"link",
" explains it well, but I will attempt it as well.",
"\nImagine a jet as a point; as the jet moves it gives off soundwaves that are faster than it. As it passes the speed of sound it catches up to the soundwaves it already gave off while still producing soundwaves. These waves now pile up creating the loud booming noise that we hear when we \"break the sound barrier\"",
"\nEDIT: I neglected to mention that once this overlap occurs, you now move faster than your soundwaves and they no longer pile up, instead they trail you. The reason you can't reverse sonic boom (slow down so that the sound waves catch up to you) is because it would require rapid deceleration to a speed slower than the sound barrier, something planes don't have as far as I know."
] |
[
"Sound travels at some speed. The plane is not a sound wave, so it can travel faster than that. The way the sound waves it generates pile up because it is moving so quickly creates the shock wave, which has the characteristic conical form (this is where the condensation cloud gets its shape)."
] |
[
"The shock wave, and the boom, travel along behind the aircraft, ",
"as depicted in the animation on this page",
"."
] |
[
"If a bottle is completely filled with water and I shake it. Does the water still move inside?"
] |
[
false
] | null |
[
"submerge the whole bottle then close it"
] |
[
"submerge the whole bottle then close it"
] |
[
"Could we test this by putting drops of dye in the bottle and shaking it? "
] |
[
"Can a popped out eyeball still see?"
] |
[
false
] | null |
[
"Sure, if you don't damage the optic nerve.",
"It's a pretty tough cord with slack built in so the eyes can turn in their socket. ",
"There's an article in JAMA about it from 1932.. sorry for the paywall..",
"https://jamanetwork.com/journals/jama/article-abstract/1153806"
] |
[
"This is called globe luxation (i.e. dislocation) and usually results in vision loss because of avulsion (tearing/pulling out) of the optic nerve. Generally, the orbital socket and muscles around the eyeball also help hold it in place. Usually, this will present as a bulging eyeball. The optic nerve isn't long enough that your eye will still be able to see if it is dangling and flopping around; in that condition, the optic nerve is almost assuredly damaged. Below are a couple cases of vision still being present despite the eyeball being dislocated. ",
"Image warning:",
"Luxation of eyeball following trauma",
" is a case study on a woman who recovered vision to 20/60 afterwards. During the incident she could essentially see hand motion and moving light.",
"Globe luxation in histiocytosis X",
" is a case study of a child who recovered full visual acuity. During the incident, acuity could still count fingers.",
"Presuming the optic nerve is intact, you won't be making much use of that eye without closing the other eye and you won't have proper muscle control to focus the eye. The brain has good plasticity for adapting to new visual stimuli (see ",
"Erismann and Kohler: Inversion goggles",
" from the 1950s, or a bunch of youtubers), but that takes time -- days not minutes."
] |
[
"https://12ft.io/proxy?q=https%3A%2F%2Fjamanetwork.com%2Fjournals%2Fjama%2Farticle-abstract%2F1153806",
" no paywall"
] |
[
"When something gets \"sun bleached\", where does the color go?"
] |
[
false
] |
I had an old grill cover that was red, and after a few years it turned white/pink. Where did the original color pigment go and how does the sun cause that?
|
[
"Bleaching is an umbrella term that refers to (in this case) the degradation of the organic dyes that give rise to the apparent color of the material by sunlight. Such changes occur because the energy of the photons making up the light can oftentimes activate a large host of chemical reactions, particularly in the presence of oxygen (where this process is called photooxidation). \nInitially the molecule (or polymer) had a certain structure that caused it to have a specific absorption/reflection spectrum that caused it to give off the appearance of being red. After bleaching, the structure changed in such a way that the molecules no longer absorbs visible light to an appreciable extent. The material then looks white for the same reason that say white paper looks white, simply because most incoming light is reflected via ",
"diffuse reflection",
"."
] |
[
"It's because we perceive sunlight as white. If there is no absorption, then the object will reflect all incoming light with effectively no wavelength selection and so the color of the object will just be the color of the incident light, in this case- white."
] |
[
"Yep, it's destroying the melanin in the strands, and since your hair is dead there's nothing that can \"heal\" it. When sun hits your skin, it's also destroying melanin, but your skin is alive so it can heal that damage and responds by making more (hence tanning). ",
"Of course all that being said, put on sunscreen! Too much skin damage over time, and you put yourself at risk for cancer.",
"http://genetics.thetech.org/ask/ask180"
] |
[
"What do \"degrees of freedom\" really mean in research?"
] |
[
false
] |
[deleted]
|
[
"It entirely depends on context, but it generally it means \"how many variables are we in control of?\"",
"The term obviously comes from the notion of movement in 3D space: six degrees of freedom means that you can move in any of the six cardinal directions along an orthonormal basis in three-dimensional space--up/down, left/right, forward/back, roll, pitch, and yaw.",
"In a more abstract sense, it means being able to move not along physical axes (as in through space), but along some other parameter space--concentration, size, dosage, time, etc."
] |
[
"Right, the other three degrees of freedom are orientation."
] |
[
"Up, down, left, right, forward, back are only three degrees of freedom, since we \"control\" only three coordinates. A point in 3D always has three DOF, that's why it's 3D: Either x,y,z in cartesian coordinates, or r, phi, theta in spherical, or something else entirely."
] |
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