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[
"I added cold water to Everclear (95% Ethanol) and the bottle felt warm, why?"
] |
[
false
] |
About a 50:50 mix or 100ml:100ml.
|
[
"Here",
" you can find some values for the enthalpy of mixing water and ethanol at different ethanol concentrations. In all cases, the processes is exothermic. That is, the process produces heat and warms your solution.",
"Edit: why is this the case? It turns out that small chain alcohols are much better hydrogen bond donors and even better acceptors. This is due to the inductive affects of the carbon groups on the electron density of the oxygen. As such, they form stronger hydrogen bonds with the water molecules. This has been shown experimentally ",
"here",
" and ",
"here",
"."
] |
[
"If you wanna see something else that's pretty cool then mix X volume of water with X volume of alcohol and then notice that you get less than 2X total volume of mixture.",
"I.e, 200ml of water + 200 ml of alcohol does not equal 400ml of mixture"
] |
[
"It'll depend on the proportions, a ",
"50/50 mix by initial volumes will give a total volume of about 96%."
] |
[
"Are blood samples a good measurement for chromosome errors throughout the whole body?"
] |
[
false
] |
If it is discovered through blood samples (which I beleive is the common way to measure this), that a certain chromosome error is present in say 50% of all cells. Would it then be safe to assume that this distribution holds true for the entire body: skin, brain, liver, everything. Or might there be different concentrations in different parts of the body? By chromosome errors, I'm thinking of cases were there are 1, 3 or more chromosomes in one "pair". Bonus question: How many cells are usually measured? tens, hundreds, thousands? (I posted this in "Biology", I'm not sure if it should be there or "Medicine".)
|
[
"As you probably already know, many people with genetic abnormalities (Downs syndrome for example) are mosaics. Some of the cells have one set of chromosomes and another has a slightly different set. This is caused by a division error early in embryo formation.",
"The distribution of the cell types is often very uneven and may be ",
"highly visible",
" if the condition effects skin and hair. One child I worked with while volunteering for a school for the mentally handicapped in Costa Rica had pink and white tiger stripes following ",
"Blaschko's lines",
", although I have never been able to find the name of her condition and the (educated) Costa Ricans at the school believed her condition was caused by the mother going out during an eclipse and being exposed to lunar rays. Still, it was cool to see how some of her teeth had developed normally and how a tiger stripe crossed some teeth and made them a different shape.",
"A blood test will tell you what the patient's bone marrow looks like but it will tell you nothing about the rest of their body. "
] |
[
"My understanding is that mosaic conditions will follow patterns in embryo development. Skin is derived from the ectoderm and bone marrow forms from the mesoderm.",
"If you need to know this for medical reasons then don't trust me (or Reddit) but I could almost guarantee you that it can be that sharp a divide or sharper. Once cells are set down a path during embryo development they stick with that path very firmly."
] |
[
"Thank you, this is a very good answer. So by \"very uneven\", does that mean that e.g skin could have <10% or >90% of abnormal cells even if the blood test measures about 60% abnormal cells?"
] |
[
"How do scavenger birds locate the carcasses they want to eat while flying?"
] |
[
false
] | null |
[
"Turkey vultures have an extremely sensitive olfactory system, and they can detect a single molecule of cadaverine or other compounds given off by dead animals. Then they cast back and forth the way a tracking hound does, until they detect a gradient and can follow the gradient \"upstream\" to find the source."
] |
[
"In addition to the previous answers (smell, sight, etc) Another thing vultures do is that they glide at some distance from each other, but still close enough that they can see the closest one. So when one of them located a carcass and thus lands, the ones closest to it instantly follow, and on and on it goes. This isn't actually coordinated behaviour, it's just the most efficient method for each one of them.",
"Different vulture species also exhibit different bill shapes and specialisations in order to avoid competing with each other. In Europe, the enormous and solitary cinereous vulture comes first, because it is able to rip the hard hide and frozen meat open. It is followed by the griffon vultures (they're the stereotypical vulture, the one you think about when you image them) which are gregarious and will eat the softer flesh. After them comes the smaller Egyptian vulture, which has a long, thin bill and can worry at the little pieces of meat left on the bones, and finally the lammergeier or bearded vulture, which has a fully feathered head and eats the bones. Note that this isn't a hard rule and that most of them will be perfectly satisfied with a regular piece of meat, but it's the usual order.",
"All in all, vultures are wonderful birds which're of great use to the environment and it's great to see more people taking interest in them."
] |
[
"Another type that’s often seen with Turkey Vultures is the Black Vulture. The Black Vulture doesn’t have the sense of smell that the Turkey Vulture has. Instead they follow Turkey Vultures to the carrion"
] |
[
"Can a virtual photon be diffracted?"
] |
[
false
] |
Can a virtual photon be diffracted? If two plates are electrically charged creates a electrical field, this field can be diffracted by a small slit, since the quantum electrodynamics says that the electrical field is quantized as "virtual photons". Have these photons properties like frequency or momentum or something like that? I'm deeply thankful in advance for any answer to my question. Thank you.
|
[
"Virtual photons are not physical states. They are a label applied to some terms in integrals in an approximation framework called \"perturbation theory.\" A static electric field is not diffracted through a small slit. "
] |
[
"http://profmattstrassler.com/articles-and-posts/particle-physics-basics/virtual-particles-what-are-they/"
] |
[
"Indeed, it is what we expect the electric field to do. But despite the very fact that virtual photons are not physical states (and I would add that they are not particles at all), how do the electric field behaves if it are forced to pass a small slit? For example, if two plates electrically charged are separated by a neutral plate with a small slit on it, does the field converges geometrically to the smal hole and after had passed, it reaches the other plate, flowing in a path that is regulated by the principle of the least action. Or not?"
] |
[
"What does a medical study mean when they say \"increases risk of death?\""
] |
[
false
] |
The text that prompts this is: "There is currently a widespread belief that any degree of overweight or obesity , however our findings suggest this may not be the case." (from the Gizmodo article linked ). Isn't the risk of death 100%? How can it increase?
|
[
"In any given finite period, there is a chance that you will die. In the next 5 minutes, it is pretty small (unless you are making fun of a biker`s moustache or something) but over the course of a year, it is more likely and over decades, it is even more likely. ",
"Increases risk of death means that for some finite period, the chance of you dying goes up. "
] |
[
"Risk of death is assessed as a comparative measure between two populations. For example, let's say you have 1000 people taking a medicine vs 1000 people who are not taking the medicine. If, in the duration of the study (eg 10 years), you find that 500 of the people taking the medicine died vs 300 of the people not taking the medicine, then we would say that there seems to be a correlation between the medicine and increased risk of death. (This would have to be run through stats to ensure statistical significance.) In this simplified example, the risk of death for the no-medicine group was 300/1000 (0.3), while the risk of death for the medicine group was 500/1000 (0.5). The attributable risk in this case is 0.5-0.3 = 0.2. The relative risk is 0.5/0.3 = 1.7. In other words, the med increases your risk of death by about 20%, while making you about 70% more likely to die as compared to someone not taking the medicine. Keep in mind this is all based on population studies and really only applies to populations (I think Bayesian stats delves into this in more detail). "
] |
[
"The best way to think of this is in regards to an experiment.",
"Let's take a hypothetical experiment (which would never get ethics board approval), where ten unlucky \"volunteers\" (PhD students bribed with the promise of free Kraft Dinner and coffee) are randomly assigned to one of two groups. ",
"All ten of them are taken up in an airplane and then forced to jump out (you threw the Kraft Dinner and coffee out of the plane, and they chase it). However, group one (five students) were all given parachutes. ",
"Group two weren't.",
"It is highly likely (though not completely so), that there will be 100% survival among the 5 students with parachutes, and 0% survival among the group with no parachutes.",
"The conclusion of this study would be that not wearing a parachute increases the risk of death.",
"Same thing with a study looking at obesity. When you take two groups of people, one who is obese, and one who isn't, and compare them... the obese group will have a higher risk of death. In other words, if you followed these two groups over a period of time, less obese people would still be alive at the end of this time period, than non-obese people."
] |
[
"Can someone help me understand the connection between Poincare's Fuchsian Functions and the transformations of non-Euclidean geometry?"
] |
[
false
] |
I am studying problem solving and analogical thinking in psychology, and one frequently used example of analogical thinking is the example above. I am hoping to understand a little bit more about this relationship so I might obtain a little bit of understanding on the analogy itself. I was hoping for a relatively simple answer, though I understand that might not be possible. I have a little (college) mathematics background, if that helps.
|
[
"I don't know how in-depth I can be on the mathematical portion, but basically, Poincare comes us sometimes as a prominent example of analogical analogical, i.e applying an understanding of one concept to another to learn more about. An example sometimes brought up in science is the Wright brothers developing the airplane due to their experience making bicycles (applying concepts of balance and control).",
"One popular anecdote given by Poincare is that he was doing something completely unrelated when, to use his words:",
"\"At the moment when I put my foot on the step the idea came to me, without anything in my former thoughts seeming to have paved the way for it, that the transformations I had used to define the Fuchsian functions were identical with those of non-Euclidean geometry.\"",
"He then (apocryphally) went on to develop the Poincare conjecture. Me and my professor are doing work on analogical transfer and would like to use Poincare as an example, but we ourselves are not well versed in the subject matter and were hoping that someone could help us understand exactly what connection Poincare made. If we knew a little bit more about the similarities between those two concepts it would be a great help, we understand the other analogies we're looking into okay, but this one is a pain =D",
"Thanks for any help anyone can offer!"
] |
[
"Can you be more specific? The topic of Fuchsian groups is rather advanced and broad. Riemann surfaces, elliptic functions, fundamental polygon theorem, Mobius transforms, etc. It seems bizarre to me that fuchsian groups would be a commonly cited example of non-Euclidean geometry in a non-mathematical field like psychology. There are many more accessible and illustrious examples. Can you be explain more about how Fuchsian groups crop up in psychology?"
] |
[
"Why try to use an analogy you don't yourselves understand? Isn't that the exact opposite of what analogies are about?"
] |
[
"If a curveball was thrown in an obstacle-free, zero-gravity environment, would it follow a spiral pattern or return to the pitcher? If it's a spiral - does it curve inwards or outwards?"
] |
[
false
] |
Alternatively, in the case that a curveball somehow requires gravity to function - if it was thrown from atop a high enough place, would it loop back to its origin point (disregarding altitude), or would it spiral?
|
[
"It can't curve if there is nothing there to curve the path. It at least requires air, that will slow down the spinning and motion of the ball and it will stop eventually."
] |
[
"The curve of the ball is dependant on the resistance of the air to the spinning motion. All pitches take advantage of such resistance. A ball will even rise once it catches the air just right. A spinning ball in an space with air but without gravity would move in a curve until the air resistance stopped the spin. In a gravity free space the spin is independant of the angle of motion of the ball so spin would have no effect on trajectory. "
] |
[
"If the ball kept spinning at the same rate and flying at the same speed and stayed in clean air and probably a bunch of other assumptions it would fly in a circle.",
"The thing that makes the ball curve - air resistance - is also going to slow the ball down, and slow down the ball's spin, if you start accounting for that, it probably predicts some kind of spiral and eventual stop. To a first order approximation, the 'bend force' is proportional to both velocity and angular velocity (",
"http://en.wikipedia.org/wiki/Magnus_effect",
") so whether the spiral is in our out will depend on initial properties of the throw, the ball, and the relationship between viscous torque and viscous drag."
] |
[
"Do infalling photons contribute to a black hole's mass/momentum?"
] |
[
false
] |
[deleted]
|
[
"You've just stumbled upon one of the most interesting unsolved problems in physics, the black hole information problem. No, Hawking radiation has nothing to do with what went into the black hole. It's thermal, meaning it only depends on the black hole's temperature.",
"This is a problem because in physics you're never supposed to be able to ",
" information. If you burn a copy of Shakespeare's complete works, it might be impossible in practice to recover the contents of the book from the embers, but in principle it can be done. The information never actually goes away, even if it gets hopelessly scrambled.",
"But if you toss that Shakespeare into a black hole and then study its Hawking radiation, you won't be able to reconstruct anything about the book other than its mass and angular momentum. This seems like a paradox. Is the information gone or not? Either way, it seems we would have to give up a treasured premise of physics."
] |
[
"Yep! From the perspective of gravity, there's no functional difference between \"matter\" and \"energy\" - they all gravitate the same way. And a black hole is (as far as we know) nothing but pure gravity. From the outside, there's no way of knowing what went into it, so there's not a super well-defined sense in which it's \"made of\" photons or dark matter or gas or puppies. Once that stuff is behind the horizon, all you know is the black hole's total mass, spin, and charge."
] |
[
"Isn't there Hawking radiation coming out of black holes that can tell us what fell into the black hole?"
] |
[
"Since in nuclear fission a very small amount of matter is converted to energy, is it Theoretically possible to create matter from energy and have we done this?"
] |
[
false
] | null |
[
"Yes, creating matter from energy is perfectly doable.",
"One example would be particle accelerators such as the LHC. In the LHC, proton beams are accelerated and thereby given a very high amount of kinetic energy. These highly energetic protons collide and produce various new particles. The combination of newly produced particles often has a higher mass than the 2 protons that collided to form them.",
"Consider for example the production of a Higgs boson. The Higgs boson was found to have a mass of 125 GeV (giga-electronvolt), while a proton has a mass of 938 MeV (mega-electronvolt) or slightly less than 1 GeV. So the 2 protons that collided to create a Higgs boson have a combined mass far smaller than the mass of the particle that was created.",
"And this is possible thanks to the fact that the protons had such a high amount of (kinetic) energy going into this whole mess."
] |
[
"Uh, this is an ill-posed question. The LHC is a research instrument, so metrics like efficiency are not really defined. Furthermore, the Higgs boson is unstable and will decay very shortly after being created (potentially into two massless photons)."
] |
[
"Not in a very useful sense, no. The energy that's stored in the chemical bonds is \"matter\", in the sense that it has mass and you could theoretically weigh it on a scale (if you had a scale precise enough), but that's an even more minuscule fraction (by hundreds of thousands of times) than in a nuclear explosion."
] |
[
"Why aren't humans ever born with mirrored internal organs?"
] |
[
false
] |
Such as heart on the opposite side of the chest and all of the other innards flipped accordingly.
|
[
"But they are",
"."
] |
[
"Your heart is larger on one side because one side of the heart is only pushing blood to your lungs while the left side must push it through your whole body. With things like lungs, your left lung I believe is smaller to accommodate your heart lean. Limbs tend to be mostly symmetric until used, ie a righthanded person having more development on the right than left."
] |
[
"They actually can be. It is known at situs inversus. A total situs inversus patient has complete mirror of all internal organs. In most cases though there is only a partial mirroring, and can lead to major health problems. "
] |
[
"Does the sun pass on momentum to the earth through photons?"
] |
[
false
] |
Since photons have momentum wouldn't a collusion between a photon and the earth transfer some momentum to the earth. If that was the case wouldn't the sun gradually be pushing the earth away from it.
|
[
"Are you implying that light doesn't carry momentum?"
] |
[
"There is a ",
"radiation pressure",
". Wikipedia gives the radiation pressure on the Earth due to the Sun as 9.15 N/km",
" ."
] |
[
"Photons are actually a viable explanation of the discrete nature of light, just as with all particles."
] |
[
"Why do they seem to find a cure for every single fatal disease every week in the news and then I never hear of it again?"
] |
[
false
] |
Every time I come on reddit I see "bone marrow transplants cure cancer" or "gene therapy 100% affective at curing HIV" It seems like we have been curing every disease every week for the past 10 years and then forgetting about it
|
[
"It's overly sensationalized media attention and poor scientific journalism. Those media reports are fueled by people who read the research (or at least we hope they do) and then create headlines. As you've noticed, the headlines (and very often the popular media summaries of the research as well) are not very accurate representations of what the research really meant."
] |
[
"No. Not at all. Curing one rich person makes ",
" less money than an entire population of people. Get it out of your head that only the rich have access to cures for incurable ailments.",
"Pharmaceutical companies are global entities. Yes, you were correct to guess that the motivator is money, but you gotthe key demographic wrong. It is ",
" and not wealthy individuals. These companies can see that finding another treatment for a common disease in a rich country is a more profitable endeavor than curing/treating a disease in a poor one. This is a large reason why there is a disproportionately small amount of research into drugs for diseases such as Malaria.",
"As for your little rant about Vicodin. The ",
" it was reported to be \"crap\" was because it has Acetaminophen in it, which can be extremely toxic to the liver. The ",
" they put Acetaminophen in it was so that it would not be abused, like ",
" pain-killers are. It's a deterrent.",
"I feel like a lot of your rant is more aimed at the decisions made by the FDA because ",
" decide which drugs are available in this country."
] |
[
"It's a lot of distortion at many levels between researchers and the public. A lot of this work is being done in basic research labs. In these labs researchers use cell culture, animal models and all sorts of interesting doo-hickeys to discover new things about diseases. The problem is that it's all painfully specific and detailed. Each lab investigates one tiny teeny thing at a time.",
"For example, maybe a lab finally (after years of research) tracked down a gene that helps a certain type of cancer metastasise. They can (in their model organism) manage to manipulate the cancer cells and destroy the functioning of this particular gene/protein/enzyme. ",
"So they get very excited (because it's cool) and publish a shiny research paper that says '",
"'. ",
"Then the university publishes a press release saying '",
"'.",
"Then some lazy journalist comes along and goes '",
"'. ",
"And the public says:'",
"'",
"It's all because basic research is complicated and extremely specialised. Most researchers are at a loss if they even walk into the lab next door. It takes years of hard work to really understand what's going on in a specific research project. So it's not really suprising that everything gets simplified and distorted by the time it gets to the general public. It's a pity though, because most of these same journalists, if they put a little more leg work in, could work with scientists to provide a lay-persons explanation of the research and its implications. It's just too hard to do and to be honest not a lot of people are really that interested in reading a detailed article about the next small step in understanding cancer."
] |
[
"How big is the chance that you drunk the same water molecule twice?"
] |
[
false
] | null |
[
"Credit to the last time this exact same question was posted ",
"u/verylittle",
" provided this response:",
" For any given water molecule, the odds are basically negligible. But the odds that you've drank at least one water molecule twice are pretty much 100%. ",
" Think in terms of the numbers of water molecules on earth. In a cup of water there are about 10",
" water molecules (100 g / 18 amu ~ 10",
").",
"The total mass of water on earth is approximately 10",
" g of water, which works out to about 10",
" water molecules on earth. ",
"So if you pick 10",
" molecules out of 10",
", put them back into the 10",
" and mix them back up, and randomly choose another 10",
", what are the odds you'll pick at least one atom twice? We can approximate it in the same way we do the ",
"birthday problem:",
" P = 1-e",
" where n=10",
" and m=10",
". Turns out this number is basically equal to 1, so the odds are ",
" that any two glasses of water will have at least one atom in common. This generalizes between ",
" cup of water - in that cup of coffee you're sipping right now, the odds are good that it has shared atoms with basically every person to ever live. ",
"It's pretty cool how Big Numbers",
" work out. A tiny probability, given sufficient chances, becomes a certainty. ",
"https://www.reddit.com/r/askscience/comments/4mndsq/whats_the_chance_of_having_drunk_the_same_water/"
] |
[
"On the other hand water molecules you already drank from your breath and sweat will get in every drink that is poured in your vicinity."
] |
[
"That assumes that all the water on Earth is \"well-mixed\" on the timescale of a lifetime. It isn't. So you're not picking water molecules at random each time.",
"For example, if all your drinking water comes from an aquifer where water takes hundreds of years to get to from the surface, you'll ",
" drink the same water twice."
] |
[
"Apart from the oceans, are there any parts of the Earth which remain unexplored?"
] |
[
false
] | null |
[
"Caves dude. All sorts of caves. I forget the statistic that BBC's Planet Earth gives, but there's a huge percentage of Earth's caves that as of now are totally unexplored, or only partially explored due to their depth and there's a an almost certain chance that we haven't even discovered a large portion of them in existence. "
] |
[
"Couldn't we use some sort of sonar or something to find the big bubbles of not-rock and then dig down to them?"
] |
[
"I once personally mapped a previously undiscovered cave. It was a hellish little thing. A 500-foot-long underground stream. The cross section never exceeded 2 feet in either dimension, and it was generally around 1 foot high and a foot and a half wide, with around six inches of fifty degree running water. Wetsuit country, no question.",
"I was \"lead tape\" because I was the skinniest (at 16, I was a wiry little lad). We knew we probably wouldn't be able to turn around, so I crawled in backwards the whole way, with the measuring tape tied around my wrist and my compass and inclinometer in my upside-down helmet (which I took off and dragged along with me, because it was too tight to wear) when i wasn't shooting. We gave up when it narrowed to the point that the water line nearly reached the ceiling, and I could no longer keep my instruments above water while still making progress backwards.",
"We were exhausted. 500 feet into a hillside, and it felt like a marathon. Round trip was around 5 hours, counting the time we spent surveying.",
"It occurs to me that it is fairly likely that nobody has been inside that cave since then, either."
] |
[
"How can we tell what the function of a certain part of a brain is?"
] |
[
false
] | null |
[
"A surprisingly large amount of research in this area involves cases where certain areas of the brain have become damaged in individuals due to trauma, stroke or some other event. Behavioural studies pick up patterns of abnormalities in the behaviour of these individuals and this provides evidence that a particular part of the brain is important for a particular thing."
] |
[
"Most of our I initial ideas have come from the effects of brain damage on people's knowledge, abilities, behaviour and memory. We have then built on our initial knowledge via experiments on people undergoing brain surgery for which patients are awake as there are no pain receptors in the brain. ",
"Finally and more recently active brain scanners allow us to see what parts of the brain are electro chemically active during varied behaviours. "
] |
[
"There's an awesome book called \"The man who mistook his wife for a hat\" or something close to that. With interesting stories about brain injuries and the resulting changes noted. ",
"Edit: Here it is on .pdf. ",
"\"The man who mistook his wife for a hat\""
] |
[
"The space between atoms, that electrons fly around in: what is it made of, and what do we know about it?"
] |
[
true
] |
[deleted]
|
[
"Nothing. There doesn't have to be \"something\" throughout the entire universe (and the vast majority of the universe is so-called empty space).",
"Though, of course, electrons aren't really classical particles, but more probability waves, so it doesn't make too much sense to talk about them having positions. But the above still addresses the spirit of your question."
] |
[
"Hadrons are particles like protons and neutrons that are made up of quarks. You're probably thinking of the Higgs Boson.",
"The Higgs field might exist throughout all space, but that's really just a mathematical construct. Just like the electromagnetic field and the gravitational field also exist throughout space - they have values at every point, but that doesn't mean there's really anything there."
] |
[
"I think the double slit experiment would make you cry."
] |
[
"Can Astronomers actually see other galaxies rotating, other stars moving, and other such events in \"real-time\" or does space appear to stand still?"
] |
[
false
] |
[deleted]
|
[
"These",
" are the remnants of the supernova that exploded in 1987. ",
"These",
" are the locations of stars around a very massive, invisible object in the center of our galaxy. ",
"Barnard's Star",
" is moving pretty fast, by star standards. In all of those you'll notice that things are changing over the course of several years. If you're lucky enough to be looking at a galaxy as a supernova explodes you'll see ",
"a very bright star appear",
" and then fade over the next few weeks.",
"You won't see galaxies rotating or anything like that. That takes millions of years. If you watch Alpha Centauri for long enough, you'll see the two stars rotate around each other in 80 years."
] |
[
"Other galaxies are too distant for us to see them change in any measurable fashion from how they looked when we discovered them. The angular velocity of the stars in the galaxy is just too small from this distance, and our resolution on our telescopes isn't high enough to resolve any position changes. ",
"However, if you point the telescope at opposite ends of the galaxy spiral, you get opposing redshift and blueshift in the spectra, which tells us how fast on average the stars in that galaxy are moving."
] |
[
"It's probably different because after the supernova went off people looked back to see if there were any recent images of that galaxy, and that's what was available."
] |
[
"What causes the relative sweetness of sugars?"
] |
[
false
] |
My question started when I saw listed as an ingredient in the Junior Mints I was eating. Apparently, invertase is added to table sugar— —to make : a which apparently is sweeter and less than sucrose. However when reading the Wikipedia page for , I found of the relative sweetness of different sugars. The problem is that it says inverted sugar is half as sweet as sucrose. This directly disagrees with the Wiki page on inverted sugar. Does anyone know which information is correct? Also what properties of these sugars cause them to be sweeter? Google searches for sugar receptors only yields confusing results. (: I'm sure this has to do with taste receptor proteins and their shape so pictures would be nice. :)
|
[
"Because in di-mers like sucrose, the sugar is in pairs (glucose and fructose) hence we split the two for them to be actual pure sugars. But Inverterd sugar syrup already splits the two and we taste the pure glucose/fructose.",
"On a bigger scale, starch consists of many sugars and we dont taste the sweetness since it doesnt break down as fast. Try chewing a bread and keeping it in your mouth for half a minute and you will start tasting sweetness as the saliva breaks it down into simple sugars."
] |
[
"I understand that breaking sugars down into less complex forms makes them sweeter. That's a good point. (: I remember doing that same bread trick but with dry pasta in elementary school :) ",
"But, why is fructose sweeter than glucose? And where should invert sugar really be on this graph?"
] |
[
"I wouldnt imagine fructose being sweeter but I am guessing since Fructose is more natural sugar and since we are designed to find sugars pleasant to taste so we will eat more of it in nature, fructose would be more pleasing. \nThat is just a guess."
] |
[
"sleeping elevation level"
] |
[
false
] |
is there any difference to the body sleeping with the mattress on the floor makes to keeping the mattress on a frame?
|
[
"Keeping it on a frame makes it harder for the spiders to get you. (australian here)"
] |
[
"to expand on one of those, less mold if you live in a wet climate "
] |
[
"Fewer ",
"miasmas",
" as well."
] |
[
"Does increasing muscle mass also affect the tensile strength of tendons?"
] |
[
false
] |
Let’s take a body builder, do their tendons have a higher tensile strength than an average person?
|
[
"short answer, technically yes.",
"long answer: while they do adapt, tendons take way way longer to become stronger. that's why many people in gyms injure their joints - muscle power increases way faster than it takes a tendon to strengthen, so their joints can't cope with the new forces involved in moving ever-increasing amounts of weight. anyway, it can be done, see rock climbers who over time train their fingers and forearms to bear more load, but even then, it takes years"
] |
[
"In non-drug takers there is an upper limit on how much muscle a bone can hold once you account for bone density, height, etc, and those muscles will have a maximum tension threshold, so it would stand to reason that tendons would have a similar maximum tension threshold. For obvious reasons it would be incredibly difficult to measure what those might be."
] |
[
"Isn't there also an individual upper limit to how strong tendons can get?"
] |
[
"Question about quantum fields"
] |
[
false
] |
It is my understanding that every elementary particle exists as an excitation within a 'quantum field'. But some of the particles have nearly identical properties besides their masses (electron, muon, and tau, for example). Are these similar particles different levels of excitations in the same fields, or does each particle have its own field? And how many quantum fields are there anyway? What are they called?
|
[
"The similar particles with a different mass (like electron, muon, and tau) belong to different fields. Having multiple excitations of a single field corresponds to having multiple particles of that type.",
"As to how many quantum fields there are in the real world, that's sortof an arbitrary question which is based on how you label them. In terms of known fundamental fields, it makes enough sense to say there are 16 fields, one for each type of ",
"particle",
". However, being technical, you can subdivide these into further components, which may increase your counting; The gluon field represents all gluons, but there are actually 8 types of gluons. Mathematically we treat them as one bundle, though, so we usually refer to a single gluon field.",
"However, quantum field theory can be used to model objects which are not fundamental, for example, one can use what's called a pion field to model nuclear physics. These fields aren't fundamental, however, they can be treated as fundamental when you are looking at processes where there is not enough energy to break apart a pion into its components. The pion field corresponds to a pion particle, which really exists, but is not a fundamental object- it is made of two quarks, which we believe to be fundamental."
] |
[
"Because we don't have flavour changing neutral currents, really.",
"If the muon were just a higher energy level of the electron, it would suggest that there should be a muon -> electron + gamma decay. But that is not observed. There is some symmetry or quantum number that prevents it.",
"Now, these kinds of decays are observed in the quark sector through loop diagrams involving W bosons, accounting for the CKM matrix. But this doesn't suggest that the these are energy levels of a specific particle since it occurs through a loop."
] |
[
"Why don't we consider the three charged leptons (electron, muon, and tau) to be different energy levels of the same particle? Same for up-type quarks, down-type quarks, and neutrinos?"
] |
[
"When Archaeologists discover remains preserved in ice, what types of biohazard precautions are utilized?"
] |
[
false
] |
My question is mostly aimed towards the possibility of the reintroduction of some unforseen, ancient diseases.
|
[
"Well, none, really, apart from the care made to preserve the specimen. By the time any frozen remains are thawed enough to be discovered, the cat's already out of the bag, so to speak. Ancient pathogens are a concern, especially as the permafrost continues to thaw. Here's an article about an ",
"anthrax outbreak",
" a couple of years ago, with a strain that had been frozen for almost 80 years. And here's one about some ",
"42,000-year-old frozen nematodes",
" that were recently revived. Bacteria, fungi, and viruses are all locked away in the permafrost, glaciers, and even lake ice, and many could be pathogenic when they wake up."
] |
[
"Yes, but indirectly. The most dangerous viruses are the ones that jump from animals to humans, because we don't have defenses against them. (HIV, ebola and SARS are three that have made the jump in 'recent' history.) The more people going into the jungle to exploit it, and the more animals coming into human towns because we destroyed their habitat, the more chances there are for something to make the jump.",
"Bats in particular are bad because they're carriers for the most nasty-death sort of viruses (like ebola, and several cousins of ebola). Bats are important jungle pollinators. There is already much more bat-human contact due to deforestation. It's a matter of time before we get another hemorrhagic fever outbreak. If we're lucky it will continue to be like ebola and die if the local climate is below shirt-sleeve temperatures. If we're not..."
] |
[
"Is it possible as well for new viruses to be hidden in jungles that could spread as cut More down"
] |
[
"Is there any medium that can change the wavelength of light that runs through it?"
] |
[
false
] |
Such that when the light exits the medium, it is a different wavelength from when it was entering?
|
[
"Yep. This is how fluorescent lamps work (or those energy saving ones).",
"The mercury vapour inside the tube emits UV light which is then absorbed by the (white) phosphor (",
" phosphorus) coating on the inside of the lamp. The phosphor then re-emits photons with a range of frequencies (and so wavelengths) in the visible spectrum which merge together to make white light.",
"Black lights (those UV lamps you get in nightclubs and things) are exactly the same, but without the phosphor coating."
] |
[
"Yes. Check out ",
"Nonlinear Optics",
". ",
"Typically, whatever method you choose works only within a narrow band (for one very specific color) and is very weak, so you need a very strong source to begin with. ",
"You've probably encountered a device which uses this effect before. Almost all green laser pointers are actually infrared lasers in disguise. The infrared laser light is directed through a frequency doubling crystal (an example of second harmonic generation) which converts two 1064nm photons into one 532nm photon. "
] |
[
"There are such materials. They are materials that have a strong nonlinearity in their polarizability. ",
"Typically uses are optical frequency doubling (aka second harmonic generation) and frequency mixing (two signals in, sum and difference frequency signals out). Even with \"strongly\" nonlinear materials, the efficiency of these devices tends to be measured in single-digit percentages."
] |
[
"Why haven't we found a cure to Nodding Disease?"
] |
[
false
] |
I understand why there are so many afflictions that we can't fix, but after some preliminary research, it looks like the disease is caused by a pathogen, which to me suggests that we should be able to find a way to fix it. Is this is a social or political issue? In case it's not clear, I'm talking about the disease affecting young children in parts of africa
|
[
"Also, just because something is caused by a pathogen doesn't mean it's elementary to treat - like HIV, naegleria, necrotizing fasciitis, etc. Couple that with the fact that it affects a small number of people in countries that rich people don't care about and it's an uphill battle."
] |
[
"The situation is being framed in a rather bad light, it's all about resource allocation. I mean would you honestly advocate moving a significant amount of resources from aids and cancers to little know diseases that affect a small number of people? The cost to develop cures for a disease is not dependent upon the number of people afflicted. If it takes hundreds of billions of dollars to \"cure\" a disease it better be spent on disease that effect a large number of people. ",
"Look at it this way, If you could cure aids or nodding disease but only one, which would you choose? That's essentially the same problem policy makers face, due to a finite amount of resources.",
"That being said if you want to support more research funding and regulation that makes it less costly to get drugs and therapies through the FDA so that it becomes reasonable to spend resources on smaller lesser known diseases. I am behind you all the way."
] |
[
"Never heard of it, so looked it up:",
"Nodding disease or nodding syndrome is a recent, little-known disease which emerged in Sudan in the 1960s. It is a fatal, mentally and physically disabling disease that only affects children, typically between the ages of 5 and 15. It is currently restricted to small regions in South Sudan, Tanzania, and northern Uganda.",
"and there's your answer, it's not widespread and nobody with any money gives a fuck. While it's obvious that some research has or is being done Pfizer isn't exactly scrambling to cure it. "
] |
[
"How does temperature relate to electromagnetic waves?"
] |
[
false
] |
How does temperature cause light essentially? Like when you heat up something redhot, it emits gradually from infrared and into the visible spectrum, but how does the movement of atoms lead to photons being emitted?
|
[
"Thermal Radiation",
"Thermal energy results in kinetic energy in the random movements of atoms and molecules in matter. All matter with a temperature by definition is composed of particles which have kinetic energy, and which interact with each other. ",
"These atoms and molecules are composed of charged particles, i.e., protons and electrons, and kinetic interactions among matter particles result in charge-acceleration and dipole-oscillation. ",
"This results in the electrodynamic generation of coupled electric and magnetic fields, resulting in the emission of photons, radiating energy away from the body through its surface boundary."
] |
[
"What DrIblis said is correct, but it's not the cause of thermal radiation.",
"Nickel62 gave a good explanation.",
"If it were the atomic energy levels releasing the radiation, we'd only see discrete colors that correspond to the energy levels. But we don't we see continuous colors. ",
"In order to explain this, you need to know that accelerated charged particles radiate photons. I can't explain why, so just believe me.",
"So when the atoms (and their electrons) are in thermal motion, they're bumping into each other, exchanging momentum, and constantly accelerated in various ways. When they accelerate, they release photons. And since they can accelerate however they want, they release a continuous spectrum of light.",
"This is thermal radiation."
] |
[
"I understand atomic levels and their emission spectrum, but I know that a heated material moves up the visible spectrum, regardless of its emission spectrum."
] |
[
"Do female to male sex reassignment patients choose their penis's size? If not what defines it?"
] |
[
false
] | null |
[
"There are two types of FTM bottom surgery that people get, but I think this question is probably more in reference to phalloplasty. In that case, it depends on multiple factors like graft area, blood flow, and whether the person chooses to have implants placed for erection. In general people can make size requests up to the size allowed by those factors (i.e. could choose to be smaller if they wanted to). It's also possible that due to complications some of the new phallus can be lost which may affect size. Generally people are discouraged from choosing sizes significantly larger than 5-6\" even if it is possible based on their body type because phalluses created from these procedures don't retract and expand the way a cis penis typically does, so people sometime have difficulty managing a large penis in day to day situations, especially during the healing process when significant support is required."
] |
[
"The other type, for those wondering, is called Metoidioplasty. They're different both in surgical method, and results, though both typically involve scrotoplasty, and both require any implants to be inserted in a separate procedure after healing to lower the chances of rejection. ",
"Instead of using skin grafts to create a larger penis, 'meta' as it's nicknamed, creates a micro penis by releasing the clitoris tissue from the pubic bone, as well as using mucosal tissue to extend the urethra through it. There is no option to choose size, size is dependent on physiology, as well as growth already experienced from taking testosterone. The end result is a micro penis that's fully sensitive, able to harden with out implants, able to be urinated through (peeing standing up can still be difficult however because of lack of length), even has some foreskin, but is incapable of penetration. Scrotoplasty is typically performed as a second stage for phalloplasty, but in metoidioplasty it's completed as a single procedure. ",
"To give you an idea of the difference in complexity of the two procedures, phalloplasty takes about 8-10 hours for the first surgery, and is usually done in three stages, phalloplasty, scrotoplasty, then implants, with time for healing inbetween each. Metoidioplasty can include scrotoplasty in its main operation as one surgery performed in approximately half that time or less. ",
"You can't get metoidioplasty if you already had phalloplasty, but you ",
" still get phalloplasty after you get metoidioplasty. I personally chose, for multiple reasons, to have metoidioplasty as my first procedure and phalloplasty as my second, instead of having phalloplasty as the first procedure, and scrotoplasty as a second procedure."
] |
[
"There’s two major kinds of implants, one is an inflatable tube that fills with saline from a reservoir placed in the pelvis (my friend has this kind and the pump in in one of his balls! It’s cool) and the other kind is a rod with a series of connections that make it flexible. There’s pros and cons to both. The rod can be troublesome because you might end up looking like you have a boner, but I think it’s stiffer for penetration, so some people like that. The pump can give you a nice tactile difference between flaccid and hard, and you have the option of controlling how much it’s inflated but it might be more prone to wearing out. more research is needed, bc all studies thus far have been in cis male patients."
] |
[
"How much energy do you lose when coupling gears with a clutch?"
] |
[
false
] |
I'm not thinnking about a car specifically. Say you have a system where you want to lose as little energy as possible and you want to couple two gears with different speeds. When using a clutch, how muc energy is lost?
|
[
"Sorry for being vague.",
"Say I have a wheel on one end that is moving with a certain speed. I want to transfer as much of the wheel's energy as possible to another wheel, which starts out as sitting still. How much energy can I hope to actually transfer if I use a clutch? (I can't think of any other system to transfer the rotation from one wheel to the other)"
] |
[
"A clutch will only add rotational inertia if it is fully engaged. If it is not fully engaged, then some energy will be lost due to friction between the plates. Also, if the system is a propulsion system and is being propelled itself, the weight of the clutch will require energy to be propelled forward. Your question is very vague."
] |
[
"A clutch doesn't really transfer energy from one wheel to another. A clutch is a break in a shaft so that one side of the shaft can be disconnected from the other. So having a clutch that is engaged loses no energy as it is no different from just having a shaft."
] |
[
"If a calorie/Calorie is a measurement of energy, does hot food have more calories than a cold version of the same dish?"
] |
[
false
] | null |
[
"The scientific definition of calorie: The energy needed to raise the temperature of 1 gram of water through 1 °C (now usually defined as 4.1868 joules).",
"The 'food' definition of Calorie/kilo-calorie or 'food energy': the convention is to use the heat of the oxidation reaction, with the water substance produced being in the liquid phase.",
"So, to answer your question, A hotter dish has more calories of energy (scientific definition) while it has identical 'food energy' (food definition) since this measurement is based on a chemical reaction rather than actual energy.",
"Source: Nuclear engineer, specifically thermodynamics class from a long time ago, plus a quick google and wiki look up.",
"EDIT: This link explains things quite well. ",
"http://en.wikipedia.org/wiki/Food_energy"
] |
[
"Yes, but it ends up not making a big difference. That didn't stop some people from turning it into a diet fad, though. I saw a website that was talking about how letting a tablespoon of snow melt in your mouth burns on the order of 100 calories, and how it was a perfect diet food. Well, not really. 100 calories is only .1 Calorie, with a capital C, which is what we use for food energy. You wouldn't want to let 1000 tablespoons (4 gallons, ~15 liters) of snow melt in your mouth when you could just not drink a soda."
] |
[
"So further to this, if you drink cold orange juice direct from the fridge in the morning your body a) has to digest it, and b) warm it up to core temperature of 37°C. To warm it up the body will use energy (the whole warm-blooded thingy)"
] |
[
"What things were predicted by math before their observation?"
] |
[
false
] |
Dirac predicted antimatter. Mendeleev predicted gallium. Higgs predicted a boson. What are other examples of things whose existence was suggested before their discovery?
|
[
"I think the ",
"discovery of planet Neptune",
" is a very famous example. The position of Neptune was predicted using the unexpected changes in the orbit of Uranus by Urbain Le Verrier, and was observed shortly after that. "
] |
[
"Edmond Halley used Newton's math to predict the return of a comet in 1758",
". This was a verification of Newton's theories. The comet was named Halley's comet in honor of Halley."
] |
[
"Rutherford predicted the neutron in 1920. He was wrong about its composition, but it was nonetheless discovered in 1932 (though first generated in 1931).",
"The neutrino was predicted by Pauli in 1930, coincidentally also called the neutron in the theoretical literature. The neutrino was detected in 1956.",
"General Relativity was formaly presented by Einstein in 1915 with many predictions. Specifically, light bending consistent with GR was first observed in 1919, gravitational redshift was observed in 1954, and frame dragging was finally confirmed in 2011.",
"Richard Feynman offered a theoretical proof that gravitational waves could be detected in 1957 (this had been in debate since 1893), and they were finally directly observed in 2016."
] |
[
"A spider at the door of my new rental has killed about 7 spiders and rolled them into a big ball which it now calls home. Why? Should I be afraid of this spider?"
] |
[
false
] | null |
[
"Biology"
] |
[
"Biology"
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"/r/AskScience",
"For more information regarding this and similar issues, please see our ",
"guidelines.",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"Why don't warm and cool air masses in the atmosphere mix together?"
] |
[
false
] |
As anyone living in the American midwest recently knows, we've been having some really crazy weather that seems to switch between winter and summer on a daily basis. I believe this is due to warm air masses from the south and cold air from the north colliding and the edge between them constantly moving. Why do these air masses continue to stay separate instead of mixing together for a more stable temperature?
|
[
"This...isn't quite right, though. There's a big difference between viscous diffusion and thermal diffusion (defined as the Prandtl number).",
"The fact is that warm and cold masses of air ",
" mix - it's just that temperature differences are also steadily maintained by the vast difference in the amount of sunlight the equator receives versus the poles. Storms and vortices result as a consequence of this mixing - in essence, you can think of the global weather system as a giant heat engine, increasing entropy from temperature mixing while deriving mechanical work as wind."
] |
[
"I'll add one point to the discussion, and I'll try to keep it simple (but hopefully not diminish the accuracy too much).",
"Along the boundary where warm and cold air masses collide (a front), they do mix. But air masses are so large that they can't mix through each other entirely. The front between these air masses is also constantly on the move too, as weather systems spin up and move through. This is the epic back-and-forth battle between warm and cold that affects the American Midwest as you've described.",
"But what keeps a front's temperatures from becoming more diffuse? In a word: frontogenesis. This is what happens when air from deeper within the two air mass is transported (as wind) toward a front. So it's like a constant supply of reinforcements being brought to this battle line. ",
"This image",
" is a nice example, I think. The red lines are the wind. Warm air from the south is being transported northward, and cold air from the north is being transported southward. Where they meet is the front, the yellow dashed line, where there is a sharp difference in temperature across a short distance. In a situation like this, the front is experiencing frontogenesis: its temperature transition zone is becoming sharper and more extreme as progressively warmer/colder air from within the two air masses gets mashed up along the front. The opposite can also happen where a front can get weaker; this is called frontolysis. None of these processes last for long in any given spot (on the order of days or less) because weather systems are constantly on the move, doing their eternal dance. In different locations between two or more air masses, there are always fronts that are being created and destroyed, strengthened and weakened, depending (partly) on the winds within them."
] |
[
"In addition to the different densities of hot and cold air, the air over land, sea and ice are heated differently (since energy is emitted and reflected by those surfaces differently). Also the earth is rotating, so air is being heated as it moves into the sunlight. So the system, earth, is dynamic and there is no stationary time for the system to equilibrate to a homogenized air temperature. "
] |
[
"If North America converted to 240v electrical systems like other parts of the world, would we see dramatic energy efficiency improvements?"
] |
[
false
] | null |
[
"No. In reality, power loss is actually because of the transmittance of power from the power plant to your house/local transformer. the power lost is defined by P=RI",
" where P is the power lost, I is the current going through the wire, and R is the resistance of the wire. Now there are a few more equations that dictate the resistance of the wire and the current, but what it comes down to is that as it turns out, the power lost is inversely exponentially proportional to the voltage running through the wire. So by having the voltage of the wires be ridiculously high (about 10,000 V) you lose very little power (under 3%) over extremely long distances (think 5000km). once that power reaches your home, it gets down-converted using an inverter. The equation for an inverter is V1/N1=V2/N2, which means you are able to change that 10000V at X amps into something usable, like 120V at a much higher current. When you are talking about switching to 240V, what you are talking about is a loss of energy that is actually almost non-existent, in the order of magnitude of 10",
" This is why, when you have a converter in another country, you are able to power your device without losing any energy really.",
"Edit: yeah, so I definitely made a bunch of mistakes while writing this. I'm not really an E&M person, but I'm in the class now so I kinda knew about this. So yes, I meant transformer not inverter. The equation is still right though. And my figures are definitely an underestimation. About 5% is lost in the transmission, not 3, and there is some power lost in a real transformer (though not in an ideal one)."
] |
[
"You would have to define \"dramatic\" but the increase would not be as much as you might think. That is because most of the energy which is lost is lost between the power plant and your house, not inside your house. And the wires between the power plant and our house are already running at 100's of thousands (or even millions in some cases) of volts. "
] |
[
"I believe you meant a 'transformer' as the device used to step up or down the voltage. With AC systems, this is done with a transformer and that equation you supplied.",
"Inverters are used to convert AC to DC and DC to AC."
] |
[
"Is it possible that there is another planet in our solar system that we can't see?"
] |
[
false
] |
[deleted]
|
[
"Yes! Theres an area just outside of Pluto's orbit (\"just outside being very relative\" called the Oort cloud that used to be considered empty! Turns out theres a dwarf plant a little smaller than Pluto recently discovered there, and patterns of light diffraction suggest there may be thousands of planets from the size of our moon to bigger than the earth out there in the cloud. Unfortunately, these regions of space where little light reflection occurs, and where gravitational pull has much less affect, are very difficult to study. Heres an article published in March 2014 in Nature about what may be found in the Oort cloud: ",
"Oort Cloud"
] |
[
"Behind the sun? No. ",
"That would only work when the planet was at the exact same distance of Earth and it would be noticed in the orbits of all the planets. Also that planet would only stay behind the sun relative to Earth for a couple of tens of years because Jupiter would pull it before or after the perfect orbit. "
] |
[
"To extend a little beyond the answers so far any planet existing the in inner part of the solar system would have been noticed long ago. Beyond detection by satellites a 'hidden' planet would have given itself away by the gravitational force it exerted on the other planet's orbits. This is how we originally discovered Neptune for example, it's existence was inferred though discrepancies in Uranus' predicted orbit before it was actually seen.",
"There's also other kinks in having a second earth. Because Earth's orbit isn't entirely circular the two planets wouldn't have equal spacing at all times and this would eventually cause them to fall out of sync with each other. They would either move into different orbits, collide, or be ejected from the system altogether, see Theia as a possible example of such an object. ",
"Also as an aside, it's been hypothesized that after the initial collision with Theia Earth may have temporarily had a second moon which formed in a manner similar to what you were thinking about (see Prof. Erik Asphaug). The thought is this moon collided the one we see after a few million years contributing to the mountainous far side. Though as far as I know this is still more theoretical than anything else.",
"Expanding on the above because we know the orbits of the existing planets we can predict with a reasonable degree of certainty where other undiscovered planets may exist. There are only so many places in the solar system that another planet could remain in a stable orbit for a long enough period of time to still be around today. At this point those potential locations are basically in the Kuiper belt and beyond."
] |
[
"How are scars permanent if our skin is constantly replacing itself?"
] |
[
false
] |
[deleted]
|
[
"There are many layers of skin cells, the bottom layer is called the Stratum Basal. This layer is Alive and constantly dividing, creating new skin cells which die and rise to the surface of your skin.",
"Scars can develop it the Stratum Basal is injured, for example in a deep wound. This prevents the cells there from Dividing regularly, which can create a different skin texture which appears as a scar.",
"There are methods to repairs the Stratum Basal by skin transplants or stem cell treatment, but these are quite expensive and plastic surgery is usually a better alternative unless in the case of extremely bad burns."
] |
[
"Do you know if the formation of scar tissue is a programmed response, or just haphazard tissue formation? That is, does a scar-forming wound induce any sort of pathway that is only active as part of a scar-formation response?"
] |
[
"Yeah there's inflammatory and wound healing processes/pathways that try to repair damage to body tissue. "
] |
[
"is there a proof why nubers are dividable by 3 if sum of their digits is dividable by 3?"
] |
[
false
] |
so my question is this: i would like to see the proof how we know for certain that this rule works for every number. i dont know how to explain the rule. rule being that number 261 is dividable by 3 because 2+6+1=9 and number 9 is also dividable by 3. hope i explained it good enough. I am sorry for lacking english speaking/writing skills
|
[
"There is a proof.",
"It's important to note that something like \"261\" is really just shorthand for an actual mathematical expression: 2*10",
" + 6*10 +1. Almost anything that has to do with a digit representations of number (eg: why does multiplication algorithm we learn in 3rd grade work?) can be resolved upon realizing that decimal representations are really nothing more than convenient ways to write numbers down.",
"In our case, note that any power of 10 is exactly one more than a multiple of 9. In particular:",
"So if we have a number, like 261, then we can write it as",
"Because 9 is already divisible by 3, the only way that 261 itself can be divisible by 3 is if 2+6+1 is divisible by 3. This result is actually stronger. If N is a number, then the sum of its digits is called its \"Digital Sum\", which we'll denote by n. From the same reasoning as with 261, write all the powers of 10 as one more than some number that is just 9s repeated, we can write ",
"This means that, no matter the number, N-n will ",
" be a multiple of 9. That is, the difference between a number and its digital sum is always a multiple of 3. The only way that this can happen is if both N and n have the same remainder after division by 3. Therefore, a number and its digital sum always have the same remainder after division by 3 (or 9). So when one of these remainders is 0, it follows that the other is as well. So if the digital sum is a multiple of 3 (or 9), so is the original number."
] |
[
"thank you very much. ",
"i love how simple these proofs are if you think the right way about them. but in the same time, i couldnt come up with them in 100 years."
] |
[
"That was an unexpectedly cool question and answer. I feel I tiny bit smarter",
"Thanks!"
] |
[
"If Violet and Red are on opposite sides of the wavelength spectrum for visible color, why are they so similar (i.e on a color wheel they merge into each other)?"
] |
[
false
] | null |
[
"Hi! This is a good question, and we've covered it several times before. You may like ",
"this thread",
" and ",
"this thread",
". Let us know if you have any follow up questions!"
] |
[
"Ah! Thanks, sorry, I searched with the wrong keywords in the physics section and not in neuroscience or with different keywords in physics, thanks!"
] |
[
"No need to apologize! Reddit search isn't the best, and honestly I'm not sure which field those questions should go in. I remembered a post from a couple weeks ago so I knew it'd pop up. :) Just let us know if you need anything else!"
] |
[
"Why are household electrical sparks blue? And why is lightning white? Aren't they the same thing?"
] |
[
false
] | null |
[
"Lighting bolts are actually a bit violet. A quick google image search can confirm this.This is due to their extreme temperature, in excess of 50,000 degrees. (I forget if it's C or F).",
"The color that a lighting bolt as you see it is determined primarily by two factors. One is visual saturation, the other is atmospheric color occlusion.",
"Visual saturation is why any intense monochromatic light source appears to be white. The color that we see something to be is primarily determined by which of the cone cells in our retina are stimulated by a light source.",
"There are two things that can throw this off. One is that there is a maximum signal that a cone cell can deliver to your brain. Something can't simply look brighter subjectively than this. The second is that there is no hard and fast cut-off for color detection. The filtering drops off from a peak color response as a bell curve, more or less. Say that you have a bright blue source of light, and it is so bright that the blue cells are sending out their maximum brightness signal. Not only that, but even with far less sensitivity to this light, the red and green cone cell are firing too. Your brain is going to see red+blue+green and perceive it as white. ",
"Lighting bolts don't have to be as bright as a laser to cause this effect because they are not monochromatic light sources. There really is red and green light in there too, even if it isn't as bright.",
"The same thing applies to the filters and sensors in a camera.",
"The atmosphere affects colors by preferentially passing red light through. Violet light from distant bolts will be selectively attenuated, and they will appear reddish in the same way as a sunset, once this light is filtered out. Just the right amount of attenuation would make a bolt appear white by itself without needing to appeal to visual saturation. ",
"A small spark is cooler. The peak emission will be blue light, and there won't be enough light in total to cause visual saturation. You probably won't see it from far enough away to see any atmospheric distortion as well. "
] |
[
"Very good explanation , thank you. Is it safe to say that electrons give off photons in the blue range?"
] |
[
"Electrons give off photons of all frequencies, generally. The higher the energy of the photons, the bluer the light will appear. ",
"Air is non conductive, and you usually have to give electrons a lot of energy before they will conduct through it. (High Voltage). This means that the air and electrons will get very hot and emit primarily blue and violet light. There are ways to generate sparks of different colors, but they require different gasses than regular air."
] |
[
"Is there an empirical study that shows that diversity of culture, background, ideology, and preferences actually improve society?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"/r/AskScience",
"For more information regarding this and similar issues, please see our ",
"guidelines",
"You can find the basic answer with a google / wiki search. Please start there and come back with a more specific question."
] |
[
"I didn't ask for any of that... I simply asked if a study had been done before. I would like to read it. Please reinstate."
] |
[
"In offering peer review, it is included and implied that we won't do the necessary bibliographic review.",
"Thanks."
] |
[
"In psychology how do I know what I'm measuring is actually what I want to measure? What if eye contact has nothing to do with extraversion or introversion? But we defined it as such."
] |
[
false
] | null |
[
"In the behavioral sciences, this is an issue referred to as validity. In a general methods class, they generally teach about 5 types of validity:\nFace, Concurrent, Predictive, Convergent, and Divergent.\nThe conglomeration of these types of validity can help you determine whether or not you have a good measure of your variable (in this case extroversion).",
"Face validity is a fairly simple concept: Does your measure make sense 'on the face of it'? In other words, just thinking about it, does it make sense that the more extroverted you are, the more eye contact you make? This type of validity check only really covers obvious things though, and in this case, I think you could successfully argue either way. Thus, I'd rely more on the next types of validity.",
"Concurrent validity asks if your measure of extroversion correlates well to other, established measures of extroversion. There are several self-assessment measures of extroversion available, and if you can show that people who score highly on those measures (long established and use) also have more eye contact with other people (either through your own experiments or through other papers), then you'd have a stronger argument that eye contact is related to extroversion.",
"Predictive validity asks the same question, but in a different way. Does your definition predict the same sorts of things that extroversion would predict? For example, the more extroverted a person is, the more likely they are to spend time at parties with lots of people. So, if you can show that more eye contact in the lab ALSO predicts more time at parties with lots of people, you'd have data to support the validity of your measure.",
"Convergent validity doesn't really apply in this situation, because you're only using one measure. However, most psychology highly supports the idea of converging operations - that is, you should always be measuring variables in more than one way. When you do that, do your measures correlate with each other? If so, you have data supporting the validity of your measures.",
"Finally, Divergent validity is the idea that what you're measuring is distinct from some other concept. EG - eye contact is also considered a measure of how attracted a person is to whoever they're making eye contact with. You'd need to provide data showing that your eye contact data is NOT correlated very strongly with ratings of attractiveness, otherwise you're not measuring extroversion. At best, you're measuring extroversion AND something else. At worst, you're not measuring extroversion at all.",
"Source: Teaching research methods in college\nBook1: • Gravetter, F. J., & Forzano, L. B. (2012). Research methods for the behavioral sciences (4th ed.). Belmont, CA: Wadsworth",
"Book2: Cozby, P. (2007). Methods in Behavioral Research (8th or 9th or 10th Edition)."
] |
[
"The questions asked can not be defined any better than Koriania has just detailed. Bravo and ole for helping OP (most likely a second semester psychology student?) out."
] |
[
"What if I say how open you are or how closed you are is defined as how often you make eye contact with someone among other variables, how do i know to include this in the measure of that particular personality trait."
] |
[
"what makes water reflective on a molecular level?"
] |
[
false
] |
Hi Reddit, I was just wondering what makes water reflective on a molecular level?
|
[
"Water reflection is due to the fact that it has a different electrical ",
"permittivity",
" than air does. This causes light going through water to move more slowly than light that goes through air. As it turns out, this difference in light velocity causes refraction and reflection when light moves from air into water. The ratio of the speed of light in a vacuum to the speed of light in some medium is the media's ",
". The refractive index is related to permittivity, which I mentioned earlier.",
"So, why does water have a higher permittivity than air? The reason is that water is more polarizable than air is. Water in the absence of an electric field has a natural dipole moment caused by the relative electronegativities of oxygen and hydrogen. At the oxygen end of a water molecule, there is a relative negative charge density (a relative increase in density of electrons) when compared to the hydrogen end of the molecule. When subject to an electric field the water molecules align themselves so that the oxygen ends face the positive electrode and the hydrogen ends face the negative electrode, somewhat cancelling the electric field. This gives rise to greater permittivity, which changes the refractive index, which causes the reflectivity of water."
] |
[
"/u/Cholly",
" already answered this question: The strong intrinsic electric dipole moment of the water molecule and the lack of this in air is what makes the interface between air and water reflective to light. What part didn't you understand?"
] |
[
"I actually didn't understand that connection, so I felt like the question was unanswered. Would you mind explaining why this boundary causes a change in direction of photons?"
] |
[
"Blood iron level or the anemia test before blood donation"
] |
[
false
] | null |
[
"Every hospital I've worked in reports hemoglobin in g/dL, but if that was g/L it would be a normal value."
] |
[
"Ahhh, I saw ",
"this",
" wikipedia page, but the units were dL, personally I have never seen dL before so I skimmed over, but it meaning I assume decilitre makes perfect sense. Thanks for clearing that up."
] |
[
"Oh no confusion, just curiosity. They wouldn't have taken my blood if I was low."
] |
[
"If snow is just water, is it possible to have snow like effect with different elements/substances?"
] |
[
false
] | null |
[
"Yes. Many substances form crystals under the right conditions. Dry ice for example is CO2 in solid form, it can be crushed and looks just like snow - with finer crystals.",
"Fun example, as is often wondered at, it snows (or rains) diamonds on ",
"neptune"
] |
[
"On earth no, but other solar system bodies have the potential to produce snow from other substances. ",
"Here",
" is a NASA article about Titan and methane ice clouds at its north pole."
] |
[
"Yes, in the Earths interior there may be ",
"iron snow",
" and may be important for the geodynamo on Earth and other planets/moons (",
"Davies and Pommier 2018",
", ",
"Wong and Aubert 2020",
", ",
"Soderlund and Schubert 2014",
"). ",
"You can also get helium rain which is also thought to be important for the Jupiter and Saturn dynamos (",
"Ni 2020",
"). In particular, helium rain may be the reason why Saturns large scale magnetic field is implausibly axisymmetric (",
"Stevenson 1981",
")."
] |
[
"Is time a result of the expansion of the universe?"
] |
[
false
] |
I have been thinking a lot about time and how it . Does traveling at the speed of light stop time for the traveler? I understand that anything with mass cannot travel at c, as it would require an infinite amount of energy. In this case, lets consider a photon. As a photon travels, it does not experience time, right? So, does that mean time is an emergent property of other factors? related: I often see people asking why we cannot travel faster than the speed of light. Is this because the universe expands at the speed of light? Picture a guy running down a walkway that is materializing under is feet. He cannot run beyond the walkway, so his speed is limited. In this example, the materializing walkway is the expansion of the universe, and the guy is a photon. If time does not exist from the photon's perspective, then isn't time a function of other factors? Is this a bunch of nonsense? Is my donkey on the wrong trail?
|
[
"The universe doesn't \"expand at the speed of light.\" First, it's exceedingly likely that the universe is now and always has been infinite in size. Not at all that sphere of explosion that's so often portrayed in popular media. When we say that it expands, we mean specifically that the distance between regions of space ",
" over time, without those regions of space actually being 'in motion' in any meaningful sense of the word. To think of it as just growing less dense is slightly more accurate than \"expanding.\" So in this regard, no the universe's expansion has nothing to do with the speed of light.",
"It's also not really meaningful to ask what time means for a photon, because ",
" we pretend that we can make a frame for the photon, in addition to this 0 time bit, it also only travels 0 distance. So of course it takes no time to do it in, because it hasn't gone anywhere. You wouldn't make the claim that distance doesn't exist now would you?",
"Time just is. Just like any of the other dimensions. It has some properties and we're not really sure why it has those properties and not other properties. But its existence is just as real and fundamental as any other direction you can look in."
] |
[
"oh sorry, I was trying to be encouraging not insulting. Merely saying that without years of training in the field, you can get ideas that seem right or interesting. If you don't feel compelled to gather those years of training that's completely okay too, so long as you come here and ask us and are okay with seeing why we don't believe that particular idea. (or someone else who knows, I guess)",
"The only problem are the people who don't have the training, who get an idea they think is interesting and then refuse to hear why it's wrong or not accepted. That's something I really can't stand. Because physics is so complicated that you can gather so many sciencey words together and make it sound like you have something new and enlightening to say, but really are just telling people falsehoods. ",
"But as long as you're a reasonable person, there's no reason not to keep on dreaming up cool ideas about the world. Just fact check them before you start really believing in them. ;-)"
] |
[
"no it's worth while to always ask questions and think about science. Before I had a proper science education I was full of crazy-ass ideas much like this one. So really, don't feel bad.",
"Does the photon change states at different points in space? It takes time for it to travel the space between two things. 8 minutes from the earth to the sun. So I'd say that it both travels through space and time. The problem is that it doesn't do \"anything\" from it's own perspective because it doesn't go \"anywhere\" and doesn't take \"any time\" to not move there. But that's just a lot of nonsense, because you can't get an object with mass to go the speed of light anyways, and everything we know with charge has mass. (light only interacts with charged particles and thus only particles with mass.)"
] |
[
"How does the language in which we think change?"
] |
[
false
] |
So at one time the language my brain uses to express thought changed from one language into another and I can’t understand the process behind that. (At that time I lived in another country for some time and was not confronted a lot with my first language.) How does that happen? My brain made all these associations throughout my life doesn’t it have to “reboot” all the information? Isn’t it difficult to translate everything I remember? Why does my conscious mind do that, even though I understand my first language better? As you can tell, I have a VERY rudimentary understanding of neuroscience. Do these questions make sense? Language is so fundamental to how we think. I am just confused about how this drastic change happens.
|
[
"Languages have evolved and/or be designed to be very flexible in their ability to relate to the world and our thoughts. Our brains have evolved to be good at associating different inputs/concepts with one another.",
"When you learn your first language as a child you’re learning, for the first time, to relate spoken (later written) words with the sensations, feelings and actions that you’re also learning to deal with. Sometimes this process might take place with more than one language simultaneously in multilingual homes.",
"When you start to learn a second language later in your childhood or adult life you’re instead initially learning to associate the words and grammar of the new language with the old language you already know. Probably partly because your brain is a bit less plastic as you get older, and partly because the first language is already connected to all of the underlying concepts. You’re no longer a blank slate, it seems natural to you to connect the concept of a dog with the word for “dog” in your first language, and it takes time to start remembering that that word is the same as the equivalent word in your new language. Where a child starts with no words and is stuck with what they have at any given moment, you already ",
" words for everything, so you’re never stuck, you just sometimes won’t know/remember the ",
" word for that concept. Your first language will always be active, and then you may or may not be able to translate that easy first language word into a more difficult second language word.",
"So initially your first language acts as a kind of intermediary between your second language and the underlying concepts. But as you use the new language more and more (especially if living in the relevant community) your brain gradually forms direct associations between the new words and the underlying concepts. The second language becomes so practiced that sometimes the first word or phrase that comes to mind will be from your “second” language. At that point you’re “thinking in” your second language.",
"The key distinction here is between the network of relationships among words, and the network of relationships among concepts. We don’t store our information about the world purely in words. We have mental images of objects, memories of sounds and relational concepts etc. Language is heavily connected to all of that, or we wouldn’t be able to express it in words, but they are not one and the same. When we learn a new language we are adding a new layer of associations on top of the old, but the pattern of the non-linguistic networks that hold the underlying concepts doesn’t necessarily change much (although obviously we are constantly changing in all sorts of ways). As your second language supersedes your first language you are simply emphasising one set of language-concept associations over another."
] |
[
"Language is definitely not fundamental to how we think. It's fundamental to how we ",
". We think all the time without having a word for things, indeed we often don't have words to express an idea or feeling. I'm sure you've had an idea of some sort in your head and couldn't find the right word for it. Sometimes we can't even find the right sentence to describe an idea or feeling we have. This doesn't mean we aren't thinking or feeling, or that our thoughts or feelings are incoherent. It simply means they are incommunicable at that time.",
"You may be interested in the Sapir-Whorf hypothesis and related ideas. The 2 main ones you'll come across are strong and weak linguistic determinism. Briefly, Strong Determinism is currently seen as false, and it states that language determines and constrains thoughts. The weak form says language merely influences thoughts, and is more broadly accepted."
] |
[
"Gonna have to massively disagree with you here… while we can conceptualise something and struggle to find words to put to it, that doesn’t mean language isn’t fundamental to cognition.\nThere’s a bunch of work done on the effects of ‘Language Deprivation’, something that (sadly) often occurs in deaf children who, understandably can’t fully access spoken language, and who also aren’t given access to a sign language.\nIt has a huge negative impact on cognitive development, and if not remedied (with access to a language) before the age of 6 or 7, leaves a person with a lifelong irreversible detriment to their ability to think."
] |
[
"Would the new hydrophobic material weve been seeing online have negative impacts on water treatment plants and the environment?"
] |
[
false
] |
The stuff as seen seems amazing, but could it potentially be a dangerous pollutant when being washed away into treatment plants, rivers, general environment etc?
|
[
"Generally if it's really hydrophobic it will either sink to bottom or float to the top of the pool of water it's in, making it relatively easy to clean in a treatment plant. Think cooking oil for example. Let it aggregate on top, then scrap it off, easy-peasy.",
"If it gets out into the world that's another story. If it's not biodegradable it will eventually aggregate somewhere and sit there for nigh-on forever. Provided it isn't toxic that's not an issue. I see people touching this stuff with their bare hands so I wouldn't worry too hard about that. ",
"I would be far more concerned about the millions of gallons of oil that get spilled than this business."
] |
[
"If it's hydrophobic, it won't mix with water. If it doesn't mix, it's either more or less dense than water and will therefore sink or float. What about that is controversial to you?"
] |
[
"You say oil isn't that bad of a pollutant because it is easily biodegradable (which it isn't in relation to most substances commonly described as such) yet you have no information on this substance to support the comparison against this product.",
"While oil is not toxic itself, it still interacts with the oil that covers most animals, therefore impairing their movement as well as skin-dependend thermorregulation and gas exchange. Being both hydrophobic and oleophobhic, this product would likely not pose such dangers.",
"Finally, unlike oil, which is only useful in huge quantities, only extremely thin coatings of this substance are necessary to get the job done, so even accidents involving its transport would likely be on a scale that's much easier to handle.",
"EDIT: ",
"According to their FAQ",
" their product is translucent; assuming it's less dense than water, it would also cause less problems for photosynthetic organisms in its vicinity as it wouldn't drastically reduce the amount of sunlight that gets to them."
] |
[
"AskScience AMA Series: We are Drs. Emily Landon and Allison Barlett, infectious disease experts from UChicago Medicine, here to answer your questions about life after your COVID-19 vaccine. Ask us anything!"
] |
[
false
] |
Hello ! We are infectious disease experts from the University of Chicago Medicine. Emily Landon, MD, specializes in infectious diseases and leads the academic health system's infection control and prevention efforts. As the medical specialist for the High-Consequence Pathogen Preparedness Program, Dr. Landon has helped steer UChicago Medicine, the University of Chicago, and its affiliates through the COVID-19 pandemic. She also regularly advises businesses, industries and government officials on how to best respond to the global crisis. Allison Bartlett, MD, MS, is a pediatric infectious disease expert who specializes in the medical management of acute and chronic infectious diseases in children and the associate medical director of the pediatric infection control program, and has spoken on the unique challenges and medical issues facing kids during the COVID-19 crisis. As multiple COVID-19 vaccines are rolling out around the world, infectious disease experts and government health agencies are beginning to issue new guidance on all aspects of life, from social distancing to mask wearing. But in this nebulous state where some are vaccinated and some are not, what does that mean for day-to-day life? What can (or should) you be doing differently, or the same, once you've been vaccinated? What can you expect after getting the vaccine? We'll be on at 4:30 PM ET (20:30 UT), ask us anything! Links: Username:
|
[
"How likely is it for people who are vaccinated to still be carriers for COVID that could potentially get non-vaccinated people sick?"
] |
[
"There is conflicting media about just how effective/ineffective the new virus variants are at usurping the current vaccines. What's the real story?",
"What is your opinion on the Astra-Zeneca rumored side effects?",
"Is it likely we will be carrying around \"vaccine-passports\" for a while to participate in normal societal activities again?"
] |
[
"How soon before those who are vaccinated will need to be given a booster to protect against variants? Or will the variants become a moot point once we reach herd immunity?"
] |
[
"If a regular Nuclear reactor produces energy by heating water into steam, how is a cold fusion reactor supposed to produce energy?"
] |
[
false
] | null |
[
"'Cold' in this case just means not having to raise the material temperature so high that kinetic energy alone is sufficient to initiate fusion. The result is still fusion and the energy output should still be in large part heat."
] |
[
"Lets add a number: 15 million degrees K.",
"This is the core temperature of the sun where fusion happens. Is a few hundred degrees K of the steam generated in power plants cold? Yes."
] |
[
"Question: How does a cold fusion reactor work?",
"Answer: It doesn't.",
"http://en.wikipedia.org/wiki/Cold_fusion",
"Cold fusion is now generally called LENR (Low Energy Nuclear Reaction)",
"No-one has it working yet. There is most likely some kind of effect taking place associated with it, but there's no agreement that it's a nuclear reaction (or even that there ",
" an effect taking place).",
"Right now, LENR is basically yet another miracle wonder \"invention\" that attracts naive investors who are not scientifically literate."
] |
[
"Does the blood-brain barrier exist for all animals with brains?"
] |
[
false
] |
[deleted]
|
[
"As you move from simple animals to more complex ones, you end up seeing something like a 'brain' even before you see a circulatory system. For example, nematodes have a nerve cluster that functions as a kind of brain, but have neither heart nor blood vessels nor any separate circulating fluid we would consider analogous to blood. \nAnts have a circulatory organ that pumps fluid forward into the head, from whence it then flows back to the rear, but no network of blood vessels. Whether they (or other insects) have any kind of membrane to filter substances out of the brain, I don't know. It does not seem likely given the absence of blood vessels and the space constraints of their physiology.",
"So I believe the answer is no. But replace 'animals' with 'vertebrates' and I am much less sure ... maybe an expert on primitive fishes could weigh in..."
] |
[
"Although you are correct that CSF plays a role in circulating some nutrients and removing waste products, the blood brain barrier and the meninges are ",
" the same thing. Blood vessels do go through all layers of the meninges to supply the brain. Oxygen is supplied by blood.",
"The BBB consists of specialized cells around the capillary blood vessels that limit the diffusion of certain molecules (including antibodies), bacteria, and many drugs."
] |
[
"I thought CSF only interacted with the exterior surface of the brain and the brain tissue adjacent to ventricles (diffusion through the pia mater) and was actually a weak point in the blood/brain barrier to microbes? Isn't it the glial astrocytes wrapping around blood vessels and controlling passage from blood to neurons that serves as the blood/brain barrier? I hope I haven't been misunderstanding this :/"
] |
[
"Re: Subreddit of the year -- Let's brainstorm on how to increase/maintain the *quality* here. Also, what additional sciences would you like to see recognized by their own category?"
] |
[
false
] |
[deleted]
|
[
"it seems the majority of people want to have the FAQ act as a firewall or filter. ",
"This post",
" made a great suggestion that would work the way the reddit admins have set up their messaging system.",
"If we could develop the FAQ to be general and thorough and have good reference material and links come up when people try to submit, we have a shot at preemptively filtering out lots of already answered questions. If the post has been answered in a FAQ, then we can send people there and follow up if needed. ",
"So two things, a pop-up ",
" page and further developing the FAQ seems to solve most of the worries that panelists have about the questions.",
"As for bad answers, we must vigilantly downvote and explain why."
] |
[
"It doesn't matter whether it's for subreddit of the year or not. We should have an interest in keeping this board as high quality as possible. ",
"In this regard let me provide my observations into the discussion:",
"The strength of this board is in its civility. Ultimately everything boils down to having civil discussions about factual matters. ",
"It should remain as meme-free as possible. I joke from time to time on here, but that's usually well after the question has been well answered by someone and we've broken off into smaller tangential discussions.",
"Pseudoscience should remain forbidden. That being said, many topics like string theory or determinism are in a murky state between established science and philosophical conjecture. Philosophy may be informed by scientific knowledge, but it is not scientific itself. I sometimes tend to let my personal philosophy show, but I usually try to disclaim it as such. I'd like feedback as to whether I should just keep it out entirely (or as a community whether we should just keep it out)",
"I know that we should be able to \"answer in excruciating technical detail\" but sometimes people pose questions that just aren't often considered by scientists, or the scientific knowledge on the subject is minimal. In this case, may I suggest that we encourage ",
" speculation on the matter. Ie, I know about this piece of physics and this piece of physics and between the two I think the answer is ",
". But also disclaiming this as such speculation is ",
" important.",
"Google, Wiki, and FAQs. Please, I beg of ",
" answering, if ",
" personally feel that the question is trivially answered by one of the above sources, ",
". Don't give some snarky \"Let me google that for you\" response. Downvote the question if you'd like, I guess. But it does ",
" any favors for you to be condescending. There are plenty of times where I know of an idea, but I don't know the technical name for it, and that makes googling tough. Wikipedia is often overly technical or wrong when it's not technical enough. Old discussions as FAQs are great starting points, but this is about ",
" science to people. "
] |
[
"Should we 'reward'/recognize top contributors in some way?",
"I don't think that's a good idea. Sometimes people message me and tell me they like my shit, and that's a more meaningful reward than a Best Redditor Ever medal."
] |
[
"Is it possible that bacterial spores act as \"life pollen\" throughout the universe? Is there any compelling evidence for panspermia?"
] |
[
false
] | null |
[
"It is possible. There is no evidence though other than the general fact that life exists so it must have begun/arrived somehow, and perhaps fallaciously that there is no well supported theory of abiogensis on Earth as of yet."
] |
[
"How do posts like this get downvoted in askscience? Who does that?"
] |
[
"It's absolutely relevant. Trolls. "
] |
[
"Could the casimir effect explain gravity?"
] |
[
false
] | null |
[
"No, they're completely unrelated."
] |
[
"Could you further explain"
] |
[
"The Casimir effect is due to the electromagnetic force."
] |
[
"The Heisenberg Uncertainty Principle."
] |
[
false
] |
I've been reading a lot of physics books recently out of curiosity and interest in physics (I'm a compsci major). I was wondering if anyone could explain to me the Heisenberg Uncertainty Principle. I get what it's saying about how if one property is measured to high precision the others can't be. I'm confused as to why this is true.
|
[
"There are multiple ways to approach this. ",
"The most intuitive approach is you ask how you would simultaneously measure both for some quantum system (where this principle becomes important). E.g., if you want to measure an electron's position, how do you do it? You bounce photons off of it and measure the photons locations in a detector. Well to measure its location to a very high precision, you need photons with very short wavelengths, and those impart higher energy/momentum to the the electron (for a photon shorter wavelength means higher energy), making you uncertain of its momentum.",
"Now, the physicist approach is that the mathematical underpinnings of quantum mechanics have it as such that position and momentum are conjugate variables of each other. E.g., there's position space and its Fourier transform is momentum space. From this foundation you can derive the uncertainty principle (e.g., momentum is equal to the derivative the wavefunction in position space with respect to position (p ~ d/dx); and position is a equal to the derivative of the wavefunction in momentum space with respect to momentum x ~ d/dp; hence they don't commute and in the minimum uncertainty they can have (sigma_x sigma_px = hbar/2 is if the wavefunction is Gaussian shaped).).",
"Now that may sound nonsensical if you don't have the math background, but that's how physicists think of it (in the framework of QM which explains lots of phenomena and has been very well tested). To simplify to non-mathematical language, when we have a particle (like an electron), before measuring its position or momentum, it doesn't have a definite position or momentum. It has a continuous probability function for both that are related by a transformation (e.g., the function might tell us it has a 10% chance of having a position between x=1cm and x=1.1cm, and and 20% chance of having a momentum if measured between p=0 kg m/s and 0.1 kg m/s). These transformation will take particles with very narrow probability range for having a momentum in a small range and make it so they have a wide range of position."
] |
[
"First, note that it doesn't mean if any one property is measured precisely than no other property can. Certain properties cannot be measured simultaneously, like x position and x momentum. In QM, properties like position and momentum are not determined to be a specific value, but by a probability function that assigns certain results certain probabilities. A discrete example is that while a particle may have a 50% chance of being at position 2, it also has a 25% chance of being measured at positions 1 or 3. It turns out that when you know the position of a particle very precisely, so the position wavefunction narrows, the momentum wavefunction broadens, and you know it less well.",
"Unfortunately, any understanding of the UP that's more than skin deep really takes some math. Observables exist mathematically as operators, and in the language of linear algebra, observables cannot be measured simultaneously beyond a certain degree of accuracy if they do not share eigenstates."
] |
[
"I think a lot of confusion in understanding the Uncertainty Principle comes from descriptions that start off by using measurement example (high energy photons give better position, but impart momentum). This implies that the problem lies in the measurement and if there was a way of measuring without imparting energy, etc. it would go away.",
"Such descriptions usually go on to state that its impossible to measure both at the same time 'in principle', but by this time its too late to remove the measurement notion from the readers brain.",
"The clearest description I have seen (in a lay book I read, but I can't remember the title) is something like ",
"this one here",
"Basically, if you think of particles as waves, then for a 100% certain momentum, the wave description needs to be a perfect sine wave. But for 100% position it needs to be series of interfering waves at different wavelengths (momentums) that result in a narrowed position."
] |
[
"What is the mechanism for smell? Where can I find images of the main organic molecules we detect with our noses?"
] |
[
false
] |
I understand that the tongue tastes only salt, sour, sweet, bitter and umami, and that the nose detects several thousand different chemicals and therefore (along with mouthfeel), the nose has a great impact on the sense of taste. But what is the mechanism for an olfactory bulb cell to detect a specific organic molecule? And what do they all look like? There's a few , and I know that the chemicals in peppers and mint (capsaicin and menthol respectively) are responsible for their apparent hot and cold. But is there a more comprehensive source of images of all such chemicals humans can sense? Edit: has some information but does not fully answer my questions.
|
[
"You should note that receptor-ligand interactions are never limited to ",
" ligand per receptor, so it's not like there are only 5 molecules taste receptors respond to. Likewise, it's not like there are several thousand different receptors, each for the unique chemical your nose is sensitive to.",
"What part of the post you linked to doesn't answer your question? ",
"This comment",
" and the resultant discussion gives a good overview of the study of olfaction - not to mention that the ",
"Wikipedia article",
" lists the competing theories on how the receptors interact with the ligand.",
"So knowing all this, your question:",
"... is there a more comprehensive source of images of all such chemicals humans can sense?",
"is akin to asking if there is a comprehensive list of images of all chemicals humans can see, or touch. If such a list exists, it'll be a ",
", if not limitless, list, and there isn't much purpose in making such a list. The closest you can get is any ",
"MSDS",
" database - just look up any chemical and you'll find, under physical characteristics, whether it has an odor."
] |
[
"You should note that receptor-ligand interactions are never limited to one ligand per receptor, so it's not like there are only 5 molecules taste receptors respond to. Likewise, it's not like there are several thousand different receptors, each for the unique chemical your nose is sensitive to.",
"Exactly. A single receptor can 'sense,' if you will, many kinds of compounds, because sensing isn't a yes or no question. Different molecules can have different binding affinities for the same receptor, meaning that a receptor isn't necessarily a perfect fit for a single molecule. For example, the OP himself cites capsaicin and menthol, but the channels they activate (TRPV1 and TRPM8, respectively) are simply heat- and cold-sensitive channels. That those compounds activate those channels are likely coincidence. Indeed, as far as TRPV1 (the heat-sensitive channel) is concerned, it's also activated by allyl isothiocyanate, a compound in mustards, horseradish, and wasabi. But examination of that molecule and capsaicin reveals no superficial similarity; both are likely examples of plants we have bred for culinary purposes ",
" they happen to activate those channels, rather than us having evolved channels to specifically detect those molecules."
] |
[
"is there a more comprehensive source of images of all such chemicals humans can sense?\nis akin to asking if there is a comprehensive list of images of all chemicals humans can see",
"Yes, but the sense of taste can be represented by five basic chemicals - salt (NaCl), sugar (glucose and other sugars), sour (H+ ions in acids), bitter, and umami (monosodium glutamate). ",
"Similarly the colours we sense can be broken down into three basic primary colours, red green and blue (for nitpickers: yes I'm aware this is an oversimplification as the cone cells for any colour eg red are also able to detect a ",
"range of frequencies",
" ) We can create a photo realistic image on a computer screen using only three colours in different proportions at each pixel.",
"Is smell completely distinct from the other senses in that it cannot be broken down into a small number of key components like this? The question was prompted by ",
"this article",
" talking about the ten basic types of smell. ",
"They claim the ten basic smells ares:",
"Fragrant\nWoody/resinous\nFruity (non-citrus)\nChemical\nMinty/peppermint\nSweet\nPopcorn\nLemon\nPungent\nDecayed",
"I don't have access to the original paper, and I'm unclear what \"woody\" and \"popcorn\" smells are exactly. Minty smells would be due to menthol, Lemon smells due to limonene.",
"Actually in looking this up, I've answered some of my own question - there is a good list here of some of the basic organic molecules that produce many of the ",
"most common smells here"
] |
[
"Will Mount Everest always be the tallest mountain?"
] |
[
false
] | null |
[
"No, eventually enough physical weathering will take place that it has worn down and plate tectonics will create newer mountain ranges that are higher given enough time. We are talking about long long periods of time here of course. Possibly millions of years. "
] |
[
"It's actually relatively simple to have an approximation of the size of the biggest mountain using force balance at the surface of the earth. If I remember correctly from my Geophysics classes, it should be around 10 000 m high, so Mt Everest is actually quite close."
] |
[
"Technically there must be an upper limit of how big (in matters of base area and height) a mountain can get, because it has to support it's own weight. Also considering that the earth crust has a certain thickness and the mantle isn't quite solid underneath, a mountain will sink back in eventually, making mt. Everest smaller than newer others of comparable size some day."
] |
[
"Need Translation from Medical-ese to plain English"
] |
[
false
] |
Can anybody explain simply how the drug Vidaza works? Description from Wikipedia: Azacitidine (5-azacytidine) is a chemical analogue of the cytosine nucleoside used in DNA and RNA. Azacitidine is thought to induce antineoplastic activity via two mechanisms; inhibition of DNA methyltransferase at low doses, causing hypomethylation of DNA, and direct cytotoxicity in abnormal hematopoietic cells in the bone marrow through its incorporation into DNA and RNA at high doses, resulting in cell death. As azacitidine is a ribonucleoside, it incoporates into RNA to a larger extent than into DNA. The incorporation into RNA leads to the dissembly of polyribosomes, defective methylation and acceptor function of transfer RNA, and inhibition of the production of protein. Its incorporation into DNA leads to a covalent binding with DNA methyltransferases, which prevents DNA synthesis and subsequent cytotoxicity.
|
[
"So your DNA is like a necklace, made up of a string of beads which carry your genetic information. There are four 'beads' which we give the abbreviations A, T, C, and G (these are just carbon-ring molecules called nucleotides). ",
"Azacitidine, or Vidaza, looks a whole lot like bead C (cytosine), and can get put onto the DNA (or RNA) necklace like a nucleotide. But when DNA has Vidaza instead of a cytosine, the enzyme that builds the DNA strand gets all stopped up at that point (like throwing a wrench in the gears of a DNA machine). ",
"Since DNA synthesis is necessary for cells to grow and divide, any cell that is trying to divide will be stopped and killed by the Vidaza wrench in its gears (and especially the rapidly dividing cells in our bone marrow which make all of our blood cells, like red blood cells, white blood cells, etc.). ",
"Thus Vidaza is useful for a disease like leukemia, where the blood-cell-forming bone marrow cells, or 'hematopoietic' cells, are growing out of control and need to be killed or slowed down.",
"The methylation part is a little more in-depth, but the main thing is that it interrupts the useful functioning of DNA and RNA to kill off the rapidly dividing cells of cancerous tissue"
] |
[
"The side effects of Vidaza mostly come from its potential to colaterally kill off other dividing cells that are important and vulnerable, like the cells of our epidermal skin, our hair, the lining of our stomach and intestines, and our red blood cell producers."
] |
[
"Thanks!"
] |
[
"As a US resident I always hear about all of the invasive species we have here from other continents. Do other continents have invasive species from North America?"
] |
[
false
] |
Stink bugs, spotted lantern flies, kudzu plant, asian carp, lion fish, etc, etc. Seems like we are being taken over here in the US with all of the invasive species from other continents. What I am curious about is where other continents have to deal with any invasive species from North America? The only one I remember reading about is raccoons in Germany, but I hardly see trash pandas as invasive and displacing/threatening native species.
|
[
"Absolutely yes. For another example to add to this thread, the slider turtle (",
") is a pond turtle endemic (native) to the southern United States, where it is commonly seen basking on logs and banks of ponds and slow-moving rivers and streams in large, dense groups. Common varieties include the yellow-bellied slider and the all too familiar red-eared slider (",
" and ",
" respectively, although the genetic relevance of this division has recently been challenged), the former of which is endemic to the east coast and deep south and the latter of which is endemic to Texas and the Mississippi watershed.",
"Sliders are easy to breed and produce large numbers of tiny and adorable offspring, so they became very popular in the exotic pet trade, and are often sold very inexpensively with hardly any information about care provided to unsuspecting customers. I would go as far as to describe the industry of breeding and selling baby slider turtles as predatory, exploiting people who know very little about reptile care at the expense of the health and quality of life of the animals. I could link you to sites that will sell you baby turtles for $5.99 or less each, but I choose not to.",
"The result of this horrific market is that thousands of baby sliders are sold every year to people who have no idea how to care for them. Many will die very quickly from neglect and improper husbandry, but others will survive and grow. And grow. And grow... A baby turtle can be only an inch or two long, whereas the adults may exceed a foot. The adults and juveniles are active and voracious, and will require a large enclosure with a powerful filter, much more than most people are equipped to handle. Unfortunately, this means that many of these turtles either live their shortened lifespan in miserable conditions, or ",
", are released into the wild by well-meaning but terribly irresponsible keepers.",
"Sliders, particularly the red-eareds, have now been introduced well outside their native range. They have populations established in New England, where they compete with native endangered turtles like the spotted turtle. They encroach on the range of the endangered Blanding’s turtle in the Great Lakes, Midwest, and Ontario. They have popped up in urban environments far across the country, in the Denver, Salt Lake City, Phoenix, Spokane, and all along the Pacific coast, within the native range of the Pacific pond turtle.",
"To make matters worse, sliders are now common in Europe, where the story is much the same as in the US. Europe has a number of native freshwater turtles, including the European pond turtle and the Spanish terrapin, both of which now compete with red-eared sliders introduced into their native ranges. Unfortunately for them, sliders are large and aggressive turtles, and have been observed competing directly and violently for basking areas and food resources with native European turtles. Basking helps raise a reptile’s metabolism, allowing it to process food more rapidly, as well as providing it with the energy to forage for food more efficiently. By crowding native turtles out of basking areas, sliders simultaneously raise their fitness while lowering that of their competitors. In some cases, European turtles seemed to actually avoid bodies of water with chemical signals of sliders, indicating that sliders are capable of totally extirpating them from their natural habitat.",
"My research has focused primarily on the spread of sliders in the US and Europe, but I am aware that populations have also been established in South America, Asia, and Australia, where they are no doubt not doing the local turtles any favors. Turtles are a severely threatened group of animals worldwide, and global turtle diversity is facing rapid depletion as habitat is removed, populations are harvested for meat, and invasives like the slider are introduced into communities that cannot compete with them. I love slider turtles, and I do not blame them for their destruction. It is our fault collectively that they have become a danger to their fellow turtles, and unfortunately remedying this problem will require significant legislative efforts to stop the breeding and sale of turtles (which in my opinion is abusive to the turtles) as well as eradication efforts in the wild. Unfortunately, these are expensive long-term solutions to a problem most people, particularly legislators, don't know or care anything about at all.",
"Sources:",
"Impact of the introduction of the red-eared slider(Trachemysscriptaelegans) on survival rates of theEuropean pond turtle (Emysorbicularis)",
"Competition for basking places between theendangered European pond turtle (Emysorbicularis galloitalica) and the introduced red-eared slider (Trachemys scripta elegans)",
"Distribution and Abundance of Invasive Red-Eared Sliders (Trachemys scripta elegans) in California's Sacramento River Basin and Possible Impacts on Native Western Pond Turtles (Emys marmorata",
"Unusual population attributes of invasive red-eared slider turtles (Trachemys scripta elegans) in Japan: do they have a performance advantage?",
"The Practicalities of Eradicating Red-eared Slider Turtles(Trachemys scripta elegans)",
"And as a bonus: ",
"here's a video I made for a graduate school project on niche modeling of sliders in Europe. It's not very exciting."
] |
[
"Certainly for the U.K. is the Eastern grey squirrel native to NA, and has massively replaced our [beautiful] native red squirrels. They can transmit a virus to the red squirrels, or just generally outperform them in a survival-of-the-fittest manner. We now have active efforts to protect the remaining areas where red squirrels are found (see links below).",
"This",
" is a pretty helpful website form the Wildlife Trusts regarding the matter. ",
"One of the conservation projects also has quite a detailled site with publications regarding conservation",
".",
"I have been lucky enough to see red squirrels on Brownsea Island, but I imagine most people around my age, unless they live in Scotland, will not have seen one."
] |
[
"The American Bullfrog, native to Eastern and Midwestern regions of the US, is an invasive species in Canada, Mexico, Central and South America, Western Europe, and Southeast Asia. (",
")",
"The Tecoma stans flowering shrub which is native to the Americas (primarily from southern US and Mexico) is invasive in the Pacific Islands (Cook Islands, French Polynesia, Guam, and many more.) (",
")"
] |
[
"Is it possible to have type 1 and type 2 diabetes at once?"
] |
[
false
] |
Has anyone experienced these two conditions simultaneously? Edit: Thanks for the answer!
|
[
"Not really, and there is a lot of overlap, as there are significant genetic factors that influence metabolism, fat storage, food drives, etc. It's one of the things I've talked with a few endocrinologists and internists about as far as my own treatment courses go. ",
"There is a project at the University of Kentucky looking at the links between inflammation, obesity and diabetes, but I'm not sure if they have published anything concrete yet."
] |
[
"Yes, the two diseases have different causes and affect different parts of the body. Type 1 is the lack of insulin production in the pancreas. Type 2 is insulin resistance in muscles, fat and liver. Untreated, they have the common symptom of high blood sugar."
] |
[
"Yes. ",
"Type 1 is typically autoimmune. The body destroys the insulin-producing cells of the pancreas, sees them as foreign. Someone who has type 1, I would not expect that they would be diagnosed with type 2 later on. Because there are no insulin producing cells to speak of. ",
"Type 2 is the more interesting one - the (typically obese) body is resistant to insulin. The pancreas can't produce enough and sugar levels skyrocket. What happens is the insulin-producing cells of the pancreas begin burning out and dying off. Now that makes things even worse, because now there are even FEWER cells to make insulin, so supply/demand ratio gets even worse. As this cycle continues over a long period of time, basically a person now has Type 1 diabetes, as in, no insulin-producing cells anymore. Such a person would have both Type 1 and Type 2 diabetes."
] |
[
"What is at the bottom of deep fresh water lakes like the Great Lakes?"
] |
[
false
] | null |
[
"That depends on the lake.",
"Usually, the very bottom is bedrock, like granite or limestone or so. However, over years, this gets smoothed down by currents to form sand, which is mixed with materials that have sunk, like leaves, wood, dead animals, and human garbage, as well as various soils and sands that have washed downstream. ",
"Low spots tend to fill in more, like drifting snow, so you end up with flat areas filled with silt, with high areas of exposed rock. "
] |
[
"In the larger lakes, it varies a lot from place to place, based on currents and silt coming in from shore. For example, here's a high-level map of bottom sediments in Lake Michigan:",
"https://databasin.org/datasets/31fe67a2eef3486b9d978daf6b35323f",
"Take note that the areas marked as \"sandy\" have boulders the size of cars mixed in, so don't think of these as smooth gradations from sand to gravel to silt, but more a map of what fills in the areas that aren't rocky outcrops.",
"To get a better idea of the overall morphology, you can look at these charts, and the accompanying descriptions:",
"https://www.ngdc.noaa.gov/mgg/greatlakes/lakemich_cdrom/html/geomorph.htm",
"I couldn't find any really good pictures of what the bottom looks like away from shore (probably because nobody bothers to take them unless there's a shipwreck), but I think this gives a pretty good idea what sorts of things are down there. "
] |
[
"For some reason that description freaks me out. I just picture it all dark down there..."
] |
[
"What happens when an oil \"deposit\" runs dry??"
] |
[
false
] |
So with the various oil related issues, from the deep water well breach to the tankers spilling oil.. I thought of a question.. if these wells are tapping into large underground deposits of oil.. Are these deposits like underground lakes of oil? Are they like underground caves filled with oil? When we drain them... Are they then big open caverns? I know enough that in order to take something out of a sealed environment.. Something else has to replace it... Typically air? Water? Like the big oil deposit under the gulf of Mexico... We drain it dry... What fills the space the oil occupied? Water? If so... Couldnt something bad happen like the gulf of mexico draining into it causing a big vortex??
|
[
"Oil is usually trapped in a porous rock. The rock structure is also under an enormous amount of pressure (thousands of feet of rock sitting on top of it), so if you just dug an air-filled hole down to the reservoir, the oil would come gushing up like a geyser. It can't get out normally because there's layers of impermeable rock above it.",
"So nothing replaces it: it gets squeezed out, like the water from a sponge.",
"As time goes on, the pressure in the reservoir decreases and the wells produce less. They can increase the flow by drilling another well and injecting high pressure water into it. But eventually the amount of effort required to get the oil exceeds the value of it, so the well is exhausted. They fill the hole up with concrete and leave it.",
"I'm not a petroleum geologist, but I ",
" worked on a reservoir project a few years ago that gave me some basic background.",
"Also, this: ",
"http://www.oilandgasevaluationreport.com/2010/05/articles/oil-field-basics-1/the-2-ps-of-economic-reservoirs-porosity-and-permeability/"
] |
[
"Just to clarify from this answer: there are no big lakes or caves filled with oil that we drill into. We extract it from the tiny ",
"pore spaces",
" in between grains of a reservoir rock."
] |
[
"Laymen here. Just putting it out there that the we won't extract the oil to extinction. We will extract it only to a point where the cost of extracting it far outweighs its benefit."
] |
[
"Would it be correct (albeit a bit sloppy) to state that the observable universe is only 1/infinity-th of the total universe?"
] |
[
false
] |
And if it is, I think my head might just explode.
|
[
"Since the question's been answered adequately, let me rant for a minute.",
"And if it is, I think my head might just explode.",
" don't do this. This kind of \"woah wow man\" thinking is a ",
" among younger people these days, and it needs to stop. Have some self-respect. Stop underestimating your ability to understand the universe around you. You are not simple monkeys swinging from branches and flinging poop and being completely baffled by all the green stuff around and that big blue thing over your heads. You are ",
" with minds unlike anything else in the entire universe. You are that which ",
" You are not rough beasts who respond only to noxious stimuli. You are fully capable, armed with nothing more than time and perhaps a stick to scratch out symbols in the dust with, of ",
"So stop saying that your mind has been blown or your head is exploding. Every time you do, all you accomplish is to broadcast to the world, \"Hey, fellow human beings! Fellow cogitating badasses! I am unaccustomed to using my brain! I pass the time by digesting food and expelling carbon dioxide from my lungs! I am comparable to a water buffalo!\"",
"Just stop it. Don't sell yourselves so damn short. You're the unquestioned, unchallenged kings and queens of the universe. Fucking act like it."
] |
[
"After being chastised for not standing up for your own intelligence it seems you decided celebrity worship was the right way to go. Please try again."
] |
[
"\"Imagination ... is more important than knowledge. Knowledge is limited. Imagination encircles the world.\" ",
"A rather important physicist said these words. A sense of awe and wonder at the world around us is not something to be denigrated."
] |
[
"What would happen if a person stayed underwater continuously without drying off? Like.. for a day, a week, a year, whatever."
] |
[
false
] |
Would their skin dissolve? How would salinity of the water affect this? Edit: Words.
|
[
"Well, David Blaine was in a tank of water for a week. From Wikipedia:",
"On May 17, 2006, Blaine was submerged in an 8 feet (2.4 m) diameter, water-filled sphere (isotonic saline, 0.9% salt) in front of the Lincoln Center in New York City for a planned seven days and seven nights, using tubes for air and nutrition. During the stunt, doctors witnessed skin breakdown at the hands and feet, and liver failure."
] |
[
"It is a similar effect as weightlessness on astronauts. Circulation problems occur and the liver cannot function properly. Gastrointestinal problems and other symptoms are experienced by long-term underwater divers as well."
] |
[
"Any idea what caused the liver failure? That seems to be an odd condition from being submerged."
] |
[
"Why can't we transplant organs (like kidneys) from primates or other mammals into humans?"
] |
[
false
] | null |
[
"Short answer is we can, their are folks walking around with pig heart valve.",
"Longer answer is that we have a hard enough time overcoming rejection on human transplants. Using organs from other species would only compound it. Here is a tragic example. ",
"http://en.m.wikipedia.org/wiki/Baby_Fae"
] |
[
"Perhaps unfortunately, humans are not machines in which you can just replace a defective part with another equivalent or similar part.",
"The human body (or, really, any animal) has evolved a very successful immune system, which actively seeks out anything in your body that is not a part of you, and exterminates anything it finds. So when the immune system finds a transplanted organ, it determines that the organ is not \"you\", and attempts to destroy it. Throughout the history of humankind as a species there has never been a case when having something that is not \"you\" inside your body would actually be beneficial. The immune system isn't prepared for the possibility that the foreign bit in you is actually \"your\" heart.",
"Even with human-to-human transplants, we have to go great distances to suppress this mechanism. Transplants can only be preformed between individuals with similar genetic markers, and the immune system of the receiver has to be suppressed, often for the rest of their life (which brings its own complications). Getting the body to accept pieces of a completely different species would be almost impossible.",
"(Unrelated to the original question, but this is one of the reasons why cancers are so dangerous: cancerous cells are ",
" cells, and thus the immune system doesn't recognize them as foreign and doesn't try to fight them.)",
"(Unrelated 2: Researchers are trying to avoid problems with rejection by growing organs from your own stem cells. If this research is successful, the cultivated organs would actually bear the same markers as your own, and thus in theory your immune system wouldn't try to reject them as it identifies them as \"yours\".)"
] |
[
"Basically because our body can differentiate from \"self\" and \"Non-self\" and your immune system attacks everything that is non self. ",
"But, some people may be able to survive with animal parts if they consume immunosuppressant. "
] |
[
"What is the optimal running speed for an average human being in terms of energy?"
] |
[
false
] |
[deleted]
|
[
"8mph is not walking speed. "
] |
[
"This",
" study by Karen L. Steudel-Numbersa and Cara M. Wall-Scheffler in 2009 found that \"optimal runningspeeds averaged 2.9 ms",
" in females and 3.7 ms",
" in males\"."
] |
[
"Lets look at the marathon shall we? Quite a feat to run 26.2 miles. I know I can't do it. Hell, I know a lot of people that can't do it. In 2005, the average time for all male finishers in the US was 4 hours 32 minutes. That's a pace of 5.78mph, or 2.58m/s. ",
"source",
"Unfortunately, the standard deviation is not listed. However, world record marathon times are getting ever closer to 2 hours. Currently, the record is below 2 hours 4 minutes. Or a pace of 5.68m/s. Clearly, quite fast. Seriously, that's faster for 26.2 miles than a lot of people can sprint. Crazy fast Kenyans and Ethiopians. No doubt.",
"Now, if the most efficient speed for a human being was in fact 3.7m/s or 8.276mph, then shouldn't the average be a little closer to a 3 hour 10 minute time? Not necessarily. This is because EVERYONE HUMAN has a different predisposition for athletic ability. Ergo, 3.7 is not THE BEST. It sure as hell may be the best for a lot of people, but not everyone. "
] |
[
"How many sustained G’s can the human body take, as in how many could the human body take for days or weeks continuously?(eg on a spacecraft under constant burn)"
] |
[
false
] | null |
[
"Not much more than 1g. Probably 2g is already too much.",
"NASA has conducted several studies for human acceleration tolerance. Key findings are:",
"Most of this research was focused on designing launch and reentry vehicles that can provide a comfortable acceleration for humans. It also provided guidelines to design the position of astronaut seats during launch and reentry. Most notably during launch you get very high accelerations at the end of each stage. As most of the mass of the rocket is propellant, and each stage has an engine that was sized for pushing it at full mass, when it's almost empty the force stays nearly the same so it accelerates a lot as it has become so light. But this peak acceleration doesn't last long before they drop the stage and continue with a smaller engine.",
"Also, most of the studies focused on short durations, in the order of minutes. We know that 2g forwards while seated is tolerable up to 24h, but we don't know how much longer.",
"Now given the premise of the question of \"days or weeks continuously\", duration appears to be the main limiting factor, but position counts a lot as well, as you can't expect people to stay seated forever.",
"For details take a look at this link: ",
"https://ntrs.nasa.gov/api/citations/19930020462/downloads/19930020462.pdf"
] |
[
"Just to add a fun bit to this, forward acceleration is sometimes referred to as \"eyes in\" and backwards acceleration as \"eyes out\". You might imagine why."
] |
[
"i can't answer for days or weeks, for moments the rocket sled experiments gave huge numbers.\nI can't find my note but i think they maxed at 70 GS (based on the effect on the test subject whatever the high test was is probably past the limit you want to expose someone supposed to be functional to)"
] |
[
"Nuclear Reactor Design"
] |
[
false
] |
I'm not a nuclear engineer, but I have a fair bit of knowledge in this regard. Lately, I've been reading a lot about Hyman Rickover* and the development of nuclear power, and one question keeps bothering me, gas cooling. A lot of coolant/moderation combinations were considered in the early days of nuclear engineering. I can see why liquid metal coolant/moderation was pursued, and rejected. I can understand many of the advantages of the various types of water/graphite. What I don't understand is why no one has ever seemed very interested in gas cooled reactors, at least until . Helium can't be irradiated, which means it can drive a turbine directly without a heat exchanger. As a gas, it won't interfere with passive safety features like a melting valves. Can anyone explain why there hasn't been more interest in this kind of reactor? Edit: Decided to put up a about .
|
[
"i am a nuclear engineer (although still young so I'll try my best).",
"I think there are a few reasons why gas cooled reactors havent had too much put into them. \nFor one, the US NRC is very stringent and i think the rest of the world would need to be running gas reactors for 20 years before they would let a permit get issued.",
"Water has inherent safeties with it (when water is the also the moderator), because as its temperature increases, or it undergoes a phase change into steam, you lose moderator and reactor power decreases.\nWater provides a LARGE amount of shielding. Nuclear fuel can kill people instantly if unshielded, and water is an inherent protection if you have a breach in containment. Just a dozen feet of water keeps radiation levels not only bearable but rather low, even for freshly removed fuel. ",
"water keeps mean neutron path very short, most of the neutrons will be absorbed before they hit the vessel walls, and a large amount of neutrons will be absorbed in water in the resonance region (assuming non-fast reactor). Gas reactors have to deal with excessive neutron exposure of the reactor vessel, while also being at much higher temperatures and pressures. Right now the primary issue limiting reactor lifetime is reactor vessel embrittlement in US BWRs and PWRs, so we would need new designs of vessel to handle the increased exposure.",
"Gas reactors need to operate at up to 1600 Degrees C, and would require a different fuel cladding design for safety margin, and possibly a different type of fuel (something instead of UO2 ceramic fuel). The fuel cladding is your first barrier to release of fission products, and needs to be designed to handle the much increased temepratures and pressures in a gas reactor.",
"Gas cooled reactors are fast reactors, which mean they need no moderation. Moderation allows for some inherent safety factors such as neutron absorption in the moderator's resonance regions, as well as moderator temperature causing a reduction in reactivity. These are passive reactivity reductions, and can respond within the time frame of your core's neutron population increase, requiring no action. By not having them, you need to strictly design gas cooled reactors with large safety margins, and the consequences of violating those margins could be much greater than in water reactors.",
"Fast reactors breed plutonium, which could have proliferation impacts. Fast reactors also have a much greater response to instantaneous neutron flux changes, making it a little more difficult to manage and requiring more analysis of transients. Your only main sources of negative reactivity in this type of reactor are any control rods and the gaseous neutron poisons, both of which are not passive negative feedback responses. Again with safety being the top priority, the US doesnt like these things. Control rods can take several hundred milliseconds to respond, while adding gas would take longer.",
"Again i'm going to emphasize the fact that these reactors respond to fast neutron flux. If you have a fast flux change, the reactor will respond to that almost instantly (microseconds or less), and there are very very few passive ways to absorb excess reactivity in this setup. if you have a transient that would cause an increase in reactivity, past what the doppler effect can absorb, you could end up in a situation with increasing prompt neutron population and risk entering an unsafe level of prompt to delayed neutrons. the design, engineering, and safety analysis of these scenarios need to be extensive before there is any talk of making gas reactors a standard commercial product.",
"as for the reasons we have mostly water based reactors, they are easier, have a lot of inherent safeties, and for the most part are just like coal burners, and it just made sense to follow down that path.",
"TLDR: Mostly safety, also just easier to do."
] |
[
"A BWR runs at about 550 F and 1020 pounds pressure, and I believe a PWR is something like 620 and 2000? (i dont know the temp. i work at a BWR, but i am pretty close on the pressure).\nThe secondary loop in a PWR runs around 1000 pounds pressure as well I believe and that is the part which goes through the turbine....\nSeems like existing turbines and designs are based around that 1000 pound pressure 550 degrees temperature range...possibly.",
"as for negative feedback, the issue is mainly how do you control steady state power.\nRemember first, the moment you add reactivity to the reactor, it will continue GAINING power UNTIL enough negative reactivity is added to cancel it out.\nPWRs rely on the temperature in the core and moderator. As it goes up, moderator density and core thermal absorption increases to remove that additional reactivity, until you are at a higher power level with a net of 0 reactivity.\nBWRs rely on steam in the core. As the core increases in power, it boils more steam causing you to lose moderator (Steam is bad at moderating), until the net reactivity is 0. BWRs can also increase/decrease reactor core cooling to have fine tuned control of reactor power. (within thermal margins). PWRs use the turbine load to remove heat from the primary loop to fine control reactor power. ",
"In a gas reactor, how would you control it? You can add CO2, but how do you get it out? PWRs put boron in their primary coolant loop to control bulk reactor power, but boron is very hard to filter and primarily gets burnt off through neutron exposure. BWRs dont use boron (except during emergencies) because when it boils it sticks all over the fuel.\nHow do you remove CO2? I'm not sure...especially at those temperatures and pressures. if the primary way to remove it is by burning it off, then it can only be used for bulk power control.",
"Typically you wouldnt want to move control rods. BWRs and PWRs have limits on moving rods due to pellet cladding interaction, and have to do it in a controlled fashion and usually at lower power levels.\nThe exception to the above is the much newer plants which have fine motion control rods and have designed for it, they can have the computer move the rods milimeters in and out to control power (dont ever expect that sort of automated system to come to the US).",
"Gas plants could use fine motion control rods to manage power. Fine motion rods were not used until the mid/late 90s i believe, which may have contributed more to them not being looked at."
] |
[
"Good question. I'm sure somebody will have a detailed answer, but I think it has to do with the amount of potential energy stored in a phase transition. The transition from liquid water to steam for instance. This is related to why refrigeration and heat pumps use not just a compressible gas, but a liquefiable gas. The liquid can absorb large amounts of heat at constant temperature until evaporation is complete, and turn it into PV-work and vice versa. "
] |
[
"What is the actual risk of cardiac arrest during exercise?"
] |
[
false
] |
For example; Patrice Muamba's heart attack during an EPL match.
|
[
"Some estimates are :\nUS high-school and college athletes (age 12-24) - 0.5 per 100,000 per year.\nIn Italian competitive athletes (age 14-35) 3.6 per 100,000 per year. The rate is estimated as five times higher for men than women, and twice as high in college athletes than in their high school counterparts.",
"Source:Sudden Cardiac Death in Young Athletes; a Literature Review and Special Considerations in Asia, Asian J Sports Med Mar 2011"
] |
[
"What is the actual risk of cardiac arrest during exercise?",
"It depends...",
"Statistics can tell you how many have heart attacks during physical exercise, and from that we can make various estimates. But that is all general information with absolutely no relevance to the individual. ",
"A wide array of factors come into play if you want to figure out the chances of any one specific individual dropping dead from a heart attack while exercising. Genetics, birth defects, injuries, decease, nutrition, fitness level, etc.",
"Patrice Muamba suffered from a undiagnosed heart defect, which greatly increased his risk of having a heart attack."
] |
[
"And does anyone know if a heart rate monitor would help you know if you're pushing yourself too much increasing the risk of having one?"
] |
[
"Will anti-matter every be an economically viable energy source?"
] |
[
false
] |
I understand that antimatter is currently produced in particle accelerators, requiring a huge amount of energy attempts even to produce a very small amount. But will this always be the case? Do the laws of thermodynamics prevent us from creating anti-matter with less energy than what we'd get back from it's annihilation with regular matter? If we can find a simple way of "flipping a bit" in a proton to make it an anti-proton then it seems all of our energy problems will be solved? This, of course, is ignoring the insane difficulty of actually containing antimatter.
|
[
"I am no astrophysics, but this is what I have been told:",
"It is true that you would be able to create a perfectly working galaxy with anti-matter. However, since we know that we are made from matter, there would be a boundary between matter and antimatter. This boundary would shine in gamma rays. Even at the low densities of matter of intergalactic space. No such boundary has been seen."
] |
[
"I am no astrophysics, but this is what I have been told:",
"It is true that you would be able to create a perfectly working galaxy with anti-matter. However, since we know that we are made from matter, there would be a boundary between matter and antimatter. This boundary would shine in gamma rays. Even at the low densities of matter of intergalactic space. No such boundary has been seen."
] |
[
"As others have pointed out, antimatter is not an energy ",
" because it's not naturally occurring.",
"But ",
" are not naturally occurring, and we get energy out of them, so there must be something else applicable here. That something else is the idea of using antimatter to ",
" energy. You stuff energy into it when you make it, the same way you stuff one of those springy snakes into a can. Then when you open the can — that is, let the antimatter interact with matter — you get the energy back out.",
"Except that can't work. I don't mean it's not economical; I mean it ",
"Take a hydrocarbon of some kind and combine it with oxygen in the right way, and what do you get? You get some sort of waste product depending on your fuel, but you also get ",
" That heat is useful. You can use it to do work. It escapes into the local environment, but you can ",
" the way it escapes by putting something in its way. Something like a piston or a turbine. On its way out of your system, the heat ",
"Take an antiparticle and combine it with a particle and what do you get? Neutrinos and gamma-ray photons. Both of those escape into the local environment, but the difference is you can't put something in their way to harness their energy. Gamma-ray photons interact only reluctantly with matter, and when they do it's in an ionizing way rather than a thermal way. Neutrinos don't interact ",
" So the energy you just liberated through particle-antiparticle annihilation simply slips out of your hypothetical \"antimatter engine\" doing nothing useful for you at all.",
"In other words, particle-antiparticle annihilation releases a great deal of energy, but not in any ",
" way. You can't harness that energy to do mechanical work. Which makes the idea of an \"antimatter engine\" a losing proposition right from the start."
] |
[
"How do we know that there is an unobservable universe beyond the observable universe if we can’t see it?"
] |
[
false
] | null |
[
"Direct electromagnetic radiation from something is not the only way to learn about its existence. The matter that emitted the cosmic microwave background we see today was in contact with matter a bit farther away. There is no light from that matter that reached us directly, but it influenced things which we can see today. In addition we could see e.g. neutrinos emitted from this matter, as they could freely move around earlier than light. This leads to the concept of the ",
"particle horizon",
". Without inflation it is just a bit larger than the observable universe, with inflation it is vastly larger."
] |
[
"Based on our current understanding of spacetime there are two possibilities: either the universe is infinite or it loops back on it’s self such that going in one direction for long enough would bring you back to where you started. If the universe did loop back on it’s self like that it would be finite and could be any size, but if it were small enough we would be able to detect evidence of space curving in that way.",
"Experiments have been done and as far as anyone can tell there is no space curvature of that sort. That means one of two things: either the universe is so large that the curvature is too small to detect or the universe extends infinitely in every direction. Either way, that is a lot of room for more unobservable universe and the Big Bang as we understand it would make all of it evenly filled with galaxies. I suppose technically we can’t be 100% sure that there is more out there but there is evidence for it."
] |
[
"That's the answer, basically. One should add that it is based on the assumed validity of Einstein's field equations."
] |
[
"Large-Scale \"Finger Over the End of the Straw\" Trick?"
] |
[
false
] |
I'm sure everybody here knows when you put a straw in water, put your finger over the end, and pull it out, the water stays in the straw. What would happen if someone were to try and recreate that on a much larger scale? Would you be able to, say, swim around in the water in the tube? What if you swam to the bottom of the tube and stuck your hand out of the water?
|
[
"It wouldn't work, because of the ",
"Rayleigh-Taylor instability",
". Consider the liquid surface at the bottom of the straw. If it bends a down little bit (bulging out in a particular place), even on the few-mm scale, then the water pressure becomes slightly higher at that bulge (there is a taller column of water above it), and the higher pressure will cause the bulge to grow into a drop. Likewise, if it bulges ",
" a little bit into the water, there is a shorter column of water above the bulge and the lower pressure will cause the bulge to grow into a bubble.",
"For small items like straws, the R-T instability is damped out by ",
"surface tension",
", which imposes an energy cost for the total area of surface -- so bulges, which increase the surface area, cost energy. That imposes a restoring force: small bulges up or down get corrected out by the surface tension. ",
"A nifty experiment you can do is to do the finger-over-straw trick with normal water, and then try to do it with water that has dish soap in it. Dish soap greatly reduces the surface tension (to make it easier to wet greasy dishes). That will prevent you from being able to transfer strawfulls of water, because the R-T instability can take over when the surface tension goes away."
] |
[
"just take a drinking glass, submerge it open-end up into a full sink so it fills with water.",
"Then turn it upside down and pull it out. As soon as the rim of the glass leaves the water, all the water falls out."
] |
[
"Also a quick test with a bottle or jug would show this isn't feasible when stepping up to larger diameters."
] |
[
"If you put a giant copper coil around the Earth, would you induct a current strong enough to harness energy from?"
] |
[
false
] | null |
[
"I assume you are talking about induced current as a result of the earths magnetic field. This only happens when there is a ",
" (a change in magnetic field). This can be calculated by the relation:\n",
", where Φ is the magnetic flux and t is time. \nFlux is equivalent to the magnetic field strength times the area of the field: ",
"*.",
"Lets see ",
" the size of a current that could be produced. Note that the coil has to be moved, and lets assume** no resistance** in the coil. \nThe diameter of the earth is 12742000m, and so the area (cross sectional) is** 4x10",
" π m",
" and the circumference is** 1.3x10",
" π m",
", and so:",
"**Φ=BA",
"=45x10",
" x 4x10",
"=1.8x10",
" Wb**",
"Maximum flux occurs when the coil is perpendicular to the field, and is a minimum (0) when it is parallel, so it has to turn** 90 degrees** for that flux to be achieved. This means it has to travel ",
" Lets have the coil stationary and let the earth rotate below it, so the earth at the equator is moving at 465ms",
" . So travel this distance it will take ",
". Lets put these numbers into the formula into Faraday's law of induction: ",
", where n is the number of coils, and emf is in volts (this is similar to the proportional statement about current mentioned before). Lets see how much a single coil will get us:",
"So EMF = (1.8x10",
") / (2.15x10",
") ",
"= 7x10",
" volts.",
"So yes, a current can be induced (theoretically). The more turns you put as well, the more current you will have."
] |
[
"I dont know the magnitude of the earth's magnetic field, but either way you would need to move the coil relative to the magnetic field. The voltage is proportional to the speed that you move the coil at, perpendicular to the magnetic field. So if the coil is just sitting out there, stationary relative to the earth's magnetic field, you would not harness any power."
] |
[
"Thank you for the in depth reply! "
] |
[
"Biologists of Reddit, what is it in virtue of that photoperiodism causes thicker fur during winter in animals?"
] |
[
false
] |
Disclaimer: Apologies if this is poorly worded or inaccurate in any sense. I do not study science. This question arose from an argument (based on speculation) that I had with someone last night. Our argument regarded the cause of seasonal changes in animals. I argued that the sun is central to biological processes and blah blah. I confess I am rather ignorant about biology, I could not offer a more technical explanation, and now my interest is piqued. What process exactly does the sun set into motion that amounts to thicker fur?
|
[
"You're talking about photoperiodism, there's a little bit at this wiki article",
"http://en.wikipedia.org/wiki/Photoperiodism#In_animals",
"Essentially changes in the the dark-light balance during the year change the hormonal regulation of the animal's body. Some of these hormonal changes will have effects on the hair follicles by changing the regulation of genes in the follicles which inturn will change the way that the hair is structured or the keratin is laid down."
] |
[
"There's a theory as to the certain timing of physiological processes that is governed by what's called a \"",
"circannual rhythm",
"\". It's similar to a circadian rhythm but takes place on an annual scale.",
"Essentially there's an internal clock that takes into account photoperiods, weather conditions, and other factors like declining resources that allow the animal to say \"Winter's coming, time to start growing fur.\" This clock is part of a larger network of neurons and command centers that rely on the environmental information to let off the proper signals to start growing heavy fur. ",
"In essence, the sun is only a part of the combination of external environmental factors that work together to give off a signal to both the neuronal complexes AND the internal clock to command the growth of hair to prepare for winter. "
] |
[
"Thank you so much. It definitely seems I overlooked the complexity of conditions involved - namely the role of internal mechanisms. And at first after reading your response I wanted to ask whether internal mechanisms are only useful insofar as they are stimulated by external cues. Then I realized this can be applied to the inverse - external cues are only useful (relevant even) insofar as they are received by internal mechanisms. Thanks again for your time. Your response has spurred me to consider this more critically."
] |
[
"How do colorblind people perceive lasers at the wavelengths they cannot see?"
] |
[
false
] | null |
[
"the common forms of colorblindness (",
" and ",
") don't really reduce the range of visible wavelengths (at least, not significantly), they just reduce the discriminability of wavelength patterns. the 'missing' cone pigments (so-called Long and Medium pigments for protanopia/deuteranopia, respectively) are so similar that they mostly overlap in their spectral sensitivities.",
"a protanope might report more difficulty seeing pure very-long-wavelength light, like a red LED or laser light. but they should be able to see it if it's strong enough.",
"a rare form of colorblindness is ",
" (lack of short-wavelength pigment), in that case short-wavelength light will be relatively invisible, so the visible spectrum really is significantly reduced (the short-λ pigment covers a really different range to the L/R pigments). but tritanopia is not what we typically refer to when we say 'colorblind'."
] |
[
"The question shows a misunderstanding of what colour blindness is. It's not that there are colours the person cannot see: it's that there are colours they can't distinguish. A colourblind person can perceive the same range of wavelengths of light as someone with full colour vision."
] |
[
"More specifically, colorblind folks (at least the common red-green type) still have functioning rods, so they would be able to see the laser. And they have functioning blue and red cones, which will still fire slightly even in response to a green laser. So the laser will still be present perceptually, but it might look like a desaturated tan color ( because none of the cones are firing very heavily)."
] |
[
"Why do I sometimes hear electronic/mechanical noises in my head?"
] |
[
false
] | null |
[
"We cannot advise you about your own personal human body experiences."
] |
[
"Hi EKUSUCALIBA thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
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"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
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", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"We do not offer ",
"medical advice",
" on ",
"/r/AskScience",
". Please see our ",
"guidelines.",
" If you have concerns about your health, you need to speak to a medical professional.",
"Questions based on personal anecdotes or isolated events tend to invite speculation and more anecdotes, which are not allowed on ",
"/r/AskScience",
".",
"For more information regarding this and similar issues, please see our ",
"guidelines.",
"If you disagree with this decision, please send a message to the moderators."
] |
[
"Can an object become a black hole by moving fast enough?"
] |
[
false
] |
this week in school we have been learning about special relativity and we learnt that an objects mass increases as its speed approaches c. Does this mean there would be a point where its mass is large enough that it could become a black hole?
|
[
"No. The easiest way to see why the answer is no is to remember the laws of physics have to work the same in every inertial frame of reference (per special relativity). If the object won't act as a black whole in its stationary frame of reference, the same must be true for any other frame of reference where its speed can be arbitrarily high."
] |
[
"Here is my (well-deserved) rant against relativistic mass. (Your answer is buried in there somewhere. The answer is \"no\".)",
"I honestly do not know why many intro texts, courses, and teachers insist on telling students that an object's mass increases as its speed increases. This concept is so incredibly misleading and incorrect, that it's no wonder so many students are confused by it.",
" ",
"The concept of relativistic mass is used only in some vain attempt to keep the Newtonian formula for momentum (p = mv) true in relativity as well. That seems like a good idea, for then the formula for total energy would be rather simple also (E = mc",
"). Beyond those two very specific uses, there is no use for the concept of relativistic mass and you just end up getting a bunch of nonsense.",
" ",
"For one, you find that Newton's second law no longer has the nice formula F = ma, and you have to assign different relativistic masses to each direction of the force. That is, in SR, the force is not always parallel to the acceleration, and the \"mass\" appearing in the tangential direction is different from the \"mass\" appearing in the transverse direction. Second, we end up getting rather nonsensical implications, like that which the OP has come across. If mass increases as an object's speed increases, then eventually it should be massive enough to be within its own Schwarzschild radius and become a black hole... but in its own rest frame it's not massive enough. So what's going on? (It's not a black hole.)",
" ",
"Relativistic mass is really just another name for the energy E. So where does relativistic mass come from anyway? The formula for the momentum of a particle with \"rest mass\" ",
" and velocity ",
" in SR is ",
" = γm",
", where γ is the Lorentz factor. So to retain the formula ",
" = M",
", we define a new \"relativistic mass\" given by M = γm. But it's actually just much more natural to define a new quantity called the 4-velocity, whose spatial components are γ",
". The time-component is γc, and the whole thing is U = (γc, γ",
"). The 4-momentum is then P = mU, in analogy with Newtonian physics. The mass of a particle is then ",
". All observers agree on the value of ",
".",
" ",
"Relativistic mass is really just a desperate attempt to hang on to old formulas and concepts from Newtonian physics. An object that is accelerated ",
" appear to have increasing inertia, but only if you look at the problem from a Newtonian view. The object's speed cannot exceed ",
". If the object (in its own frame) is accelerating at some constant (proper) acceleration ",
", the outside observer will see the object slowly decelerate to zero acceleration as its speed approaches ",
". So it appears as if the inertia (the ",
" appearing in F = ma) is increasing. This is a ",
" way to analyze that problem. For one, this analysis is based on Newton's second law, yet the relativistic mass is related to the number ",
" appearing in the momentum formula p = mv. This is a subtle issue. In Newtonian physics, the \"m\" appearing in F = ma and p = mv are automatically the same number. But if you carry out the above analysis that the accelerating object's inertia is increasing, then you have to give up the notion that the \"inertial mass\" and \"momentum mass\" are actually the same. (Again, the reason is that the force is actually not parallel to the acceleration in general, and to have any hope of consistency, relativistic mass would have to be different in the transverse and parallel directions.) Today, we understand that energy plays that inertial role. The mass doesn't change, but the energy formula has changed in such a way that the object's energy approaches infinity as its speed approaches ",
".",
" ",
"Why jump though all those hoops and redefine the concept of mass in such a way that turns out to be woefully inconsistent once you start to analyze more complex problems? It's better just to realize that relativity requires that the universe has a different ",
" than that of Newtonian physics. The impossibility of an object's speed exceeding ",
" has nothing to do with increased inertia, but rather the underlying geometry of the universe. Thus it is more natural to change how we view and define position and velocity, especially once we see that time and space must be unified into spacetime. (Of course, once you go to GR, despite the difficulties in defining mass, it is very immediately obvious that you should not define it in a frame-dependent way. So relativistic mass is super incorrect in GR.)",
" ",
"Despite Einstein himself discouraging the use of relativistic mass, the concept became very popular. In the late 1980s, several physicists began a bit of a movement against relativistic mass. I was in high school in the early 2000s when I first learned physics, and I have never personally used a text or taken a course that used relativistic mass. (I didn't even realize such a concept existed until halfway through college when I came across an old text on relativity.) So I am guessing that somewhere in the 1990's or maybe even the early 2000s, the majority of physicists had gotten on board with the death to relativistic mass. So today when I read questions like that of the OP, I just cringe and wince. Who the hell is out there still teaching this terrible and outdated concept? Ugh."
] |
[
"The mass of the object doesn't actually change as it speeds up. The modern definition of mass is Lorentz-invariant, so it doesn't change with speed.",
"I really adore this sub. Until just now i was holding on to the arcane explanation that anything with mass cannot reach the speed of light because its mass would increase to infinity. Now I'm looking forward to being hopelessly confused at a slightly more technical level."
] |
[
"How does getting knocked on the head knock you out?"
] |
[
false
] |
I mean, you can get knocked out from a punch to the jaw, from a blow to the back of the head, maybe other ways. What's the physical mechanism of losing consciousness?
|
[
"I've answered this question before, but I can't find it. So I'll try to give a brief answer.",
"A great answer is, we don't really know.",
"However, a very likely guess comes from the act that neurons don't like to be \"jiggled\". I've seen first hand how most neurons will start to behave very abnormally if you poke them. It is likely that in most cases, the sharp impact causes all sorts of mechanical stress on the brain, torque, pressure, sherring etc. This causes abnormal neural activity. And this causes a loss of conciousness.",
"Now it MAY be that typical \"knockout\" style loss of consciousness may be due to abnormal neural activity in some specific population of neurons. But I am not aware if this is true. As an MMA fan, I always note that punches that cause rapid rotation of the skull (i.e. hooks to the jaw, or upper cuts) are the most likely to cause knockouts, as opposed to jabs, which can still cause huge energy transfer. Now it could be the the biomechanics of the neck means that jabs end up causing less acceleration on the brain that the aforementioned rotation causing punches. However, an alternative idea is that specific punches cause specific parts of the brain to be under more stress, and those certain parts might be more important in maintaining consciousness.",
"But as I say, impact causes mechanical stress, mechanical stress makes neuron behave strangely. Strangely behaving neurons can cause you to lose conciousness. "
] |
[
"would that be similar to the mechanism by which people are choked out or (if this is even real, I don't know) something like a karate chop to the neck? or is that a different process?"
] |
[
"Choked out is caused by a loss of blood pressure to the brain. This then causes neurons to behave strangely, though whether this is due to loss of oxygen partial pressure, or due to the loss of physical support of the brain, or even some other mechanism is unclear.",
"Chop to the neck, no idea. Is that a real thing? If it is, I guess it had more to do with a knock out than a choke out."
] |
[
"How detailed is our knowledge of our own solar system? Is there any possibility of there being a physical body large enough to be classified as a planet that we have not discovered yet?"
] |
[
false
] | null |
[
"First let me tell you the story of how Neptune was discovered. ",
"All planets prior to Neptune were discovered by astronomers looking at the sky. As some scientists were looking at the data for the positions of Uranus in the sky, they noticed that Uranus was not behaving quite as predicted by Newton's gravity. They did a few calculations and determined that another planet had to be out there, gravitationally pulling on Uranus to give it the orbit that it had. Lo and behold, when astronomers pointed their telescopes where the scientists told them, there was a planet right where it was supposed to be. ",
"So, long story short, it is unlikely that there is any planetary sized body in our solar system as we would have detected its effects on the orbits of the other planets. "
] |
[
"Here's a chart",
" showing how large a planet could be at a given distance from the Sun without WISE detecting it. Looks like a planet the size of Neptune would need to be at least 3000 AU away (100 times Neptune's distance from the Sun), one the size of Saturn more than 10,000 AU away, and one the size of Jupiter more than 40,000 AU away.",
"All of those distances are within the Oort Cloud."
] |
[
"There is a space telescope called WISE (Wide-field Infrared Survey Explorer) that scans the sky looking for things like this, and it has not found anything. It has been scanning the sky long enough that if there was something like that out there, WISE probably would have found it by now."
] |
[
"Directional sound: how do we distinguish front from back?"
] |
[
false
] |
I understand how the brain determines the left-right direction of incoming sounds based upon a time lag between the sound reaching one ear compared with the sound reaching the other ear (and also the volume drop between your ears). However, how does your brain determine front from back? If a sound is coming from 45 degrees (front-left), the time lag and volume drop would be the same as sound coming from 135 degrees (back-left). Is it a result of the shape of our ears affecting the shape of the incoming waves?
|
[
"It's mainly due to the shape of your ear--the quality of the pitch changes slightly due to the shape of your ear being non-symmetrical with respect to front and back.",
"I don't know exactly ",
" these changes manifest themselves (i.e. what the front/back filters do), but I know this is the general principle."
] |
[
"I studied this exact question for my undergraduate thesis, and again in graduate school. Let me first point out that the problem is inherently 3D, not just front-back. This is part of a complex process called auditory scene analysis, which is the general problem of figuring out what things in the environment are generating sound, where they are, and what kind of environment are you in (e.g. bathroom vs. cavern vs. forest). There are multiple replies here that address various parts of this topic, so I'm going to try to integrate all of these into something that hopefully makes sense of the whole process. Much of what I'll write is described in detail in the book ",
" by Jens Blauert - a bit dated now, but still a great resource if you can find it.",
"The first step in this process is sound localization, which the OP has summarized. We determine the ",
" of a sound based on the time lag between the arrival at the two ears (the interaural intensity difference, or ITD) and the intensity difference at the two ears (the IID). Both the ITD and IID depend on the ",
" in the distance from the sound source to each ear. Mathematically, this gives rise to a roughly conincal shaped surface for which the ITD and IID are indistinguishable (the \"cone of confusion\" that cinematicorchestra mentioned). This step helps with localization in 3D, since you've now restricted the set of possible locations to this surface. I should point out that this analysis happens early on in the brainstem, and is done on a per-frequency basis, so different sounds can be associated with different cones.",
"Second, your external ears (the pinnae, the big flappy things that most people think of as \"ears\"), along with your head and torso, filter sounds because they don't vibrate the way air does. This gives rise to a head-related transfer function (HRTF), which depends strongly on the direction from which sound is coming. This is what many people in this thread have mentioned. In combination with the cone of confusion, the HRTF can often pinpoint a sound quite well. The HRTF has its limitations, though. It works by creating a notch that prevents sound in a narrow, high-frequency range (typically ~8-12 kHz for humans) from entering your ear. This works great if your sound source is full of energy in that frequency range, but not so much if it doesn't (or if you've lost hearing in that range). I should also point out that this analysis requires integrating information across frequencies, and so happens at a higher level of processing in the brainstem.",
"Third, small head movements will resolve much remaining confusion, by dynamically changing all of these other bits of information. This analysis probably takes place in the cortex, since it requires integrating information across different sensory modalities. I actually collected evidence of this during my undergraduate work 5 years before the Wightman & Kistler paper that alexanderwales linked to, but I didn't have enough data to be publishable, and didn't have the experience to understand that I was already 99% of the way there.",
"Fourth, there's a phenomenon called the ",
" which affects how your brain interprets time-dependent changes. Specifically, for a few milliseconds after the onset of a sound source, your brain ignores changes in information about the location of that source. This is a useful adaptation because it lets you localize sounds properly even in a reverberant environment (where you will hear echoes within that time frame). I don't know offhand where this processing takes place, but my instinct tells me it's in the upper brainstem (inferior colliculus or medial geniculate body). ",
"Fifth, you can approximate the distance of a sound based on its frequency content. Low frequency sounds travel further than high-frequency ones (this is why thunder cracks when it's close and rumbles when it's far away).",
"Finally, as cubist_castle (who mentioned several of these effects) pointed out, if you hear something and you can't figure out where it is, your brain will tell you that it's behind and/or above you. The reason why this is an advantageous trait should be obvious.",
"This is sparsely referenced since my references are at work, but I'll happily add them for anyone who is interested."
] |
[
"Yes, the shape of the ear acts as a directionally sensitive filter.",
"http://en.wikipedia.org/wiki/Sound_localization"
] |
[
"how much potential energy is accrued the further a body moves away from the earth?"
] |
[
false
] |
obligatory excuse my ignorance. if an object at rest on earth is lifted to a higher altitude then the kinetic energy required to do so is converted to potential energy? so is there a limit to this? If an object is lifted higher and higher until it is only negligibly affected by the earth's gravitational field, does the amount of potential energy it gain keep increasing too? Would the voyager probe or some equivalent far off former piece of earth have enormous potential energy?
|
[
"Neatly this is how escape velocity is found. The kinetic energy of an object at escape velocity at sea level (or any other altitude you define escape velocity from) is equal to the amount of GPE it needs to gain to get out of the Earth's gravity well, basically to reach infinite distance at zero velocity.",
"Note that both KE and GPE have a mass term, which is why we talk about escape velocity which is independent of mass."
] |
[
"To lift an object at a steady speed (and therefore to not add or lose any ",
" energy between start and end of the lift) requires exactly balancing the force of gravity.",
"F = GMm / r",
"The gravitational potential energy gained is equal to the work done by the lifting force, which is force times distance moved",
"W = Fd",
"So to find the gravitational potential energy gained by lifting an object from a finite distance R to infinity, we integrate the force with respect to r",
"W = ∫ (R to ∞) (GMm / r",
" ) dr",
"(Forgive my nonstandard notation for the limits.)",
"That integral is finite,",
"W = -GMm / R",
"I have glossed over one aspect - proving that gravity is a conservative force, that is that the work done doesn't depend on the path taken. Newtonian gravity is a conservative force, although general relativity isn't, but potential energy is still finite in GR."
] |
[
"It does go up as you move away from the Earth, potential energy is a negative number, therefore the closer it is to 0 the bigger it is"
] |
[
"What are these weird white hairs that grow really fast on my body?"
] |
[
false
] |
I've noticed them on other people too. They are very fine and thin white hairs that seem to sprout overnight. I get one under my chin and I also get one in my eyelashes on my left eye. My husband has one that grows out of his eyebrow and one on the top of his ear, and my friend has one that sprouts right out of the middle of her forehead. They aren't there and then in a matter of days they are, and are at least half an inch to an inch long. Does this phenomenon have a name? What causes this to happen?
|
[
"I would remind those responding that this isnt ",
"/r/DAE",
"Guidelines regarding commenter etiquette ask us to focus on answering the question.",
"Of 31 comments I see one reasonable response ( theswedishshaft )"
] |
[
"thin white hair sounds like ",
"vellus hair",
", though you seem to describe isolated single hairs. Anyway, vellus can be influenced by hormone fluctuations in both males and females.",
"Disclaimer: I am not a scientist (not in the exact sciences anyway)."
] |
[
"Some people just bloom late."
] |
[
"If boiling (or heating to 100ºC) kills all germs, what is the component in \"gone bad\" meat that can make you sick even after it is cooked."
] |
[
false
] |
If I had to guess it would be that maybe a chemical reaction creates some sort of toxin that obviously doesn't 'die' but I'm an art student and really have no idea..
|
[
"Bacteria produce toxins, ",
"endotoxin",
", which is part of the bacterium, and released when the cell dies, and ",
"exotoxin",
", which is secreted by the cell when it is alive. Both of these can survive the boiling process. "
] |
[
"Endotoxins would be my guess as well, but I want to point out that 100°C doesn't necessarily kill all bacteria. Length of exposure and pressure affect survival rates, and some bacteria can survive in extreme environments just fine. Example: strain 121 can survive autoclaving treatment (121°C at 15 psi for 20 minutes)! ",
"http://en.wikipedia.org/wiki/Strain_121"
] |
[
"A good way to tell if it is the endotoxins that caused the sickness or the actual bacterium is the onset of symptoms after consuming the food. If it is rapid, immediate to an hour or so, then it is probably the chemicals in the food. If you wake up sick then the bacterium were probably not all dead, they were also not in the food long enough to leave the chemicals behind as well so it was probably due to the sanitation of the food preparation. It can also take up to 24 hours for a culture to reach a point in your system where it is large enough to start making you ill. This makes it hard to pin point what food caused the problem sometimes."
] |
[
"If a skydiver's parachute never opened, would their body splatter upon impact, or would they make a small crater in the ground?"
] |
[
false
] |
[deleted]
|
[
"We are mostly water. Water is pretty good at absorbing energy. People stay pretty well intact when they hit the ground fast. The gorey stuff is usually the result of other situations. Like being dragged or sliding on concrete after an MVA."
] |
[
"They would hit the ground moving at terminal velocity which is around 122 mph or 195 km/h which is fast enough to severely injure and probably kill them but not really fast enough to make a crater or a \"splatter\""
] |
[
"Humans rarely fall into pieces from a fall. They would likely just bounce a bit. I've read about parachuters bouncing into trees after a fall. There is footage of people jumping from the WTC on 9/11, they just thud."
] |
[
"How significant is the effect of spicy food on metabolism?"
] |
[
false
] |
I've been going through a lot of Sriracha sauce lately and it got me thinking. I have always read that spicy food helps with weight loss as it speeds up your metabolism. Is this caused by irritating the gastrointestinal tract, causing food to pass more quickly, giving a similar result as not eating as much? Does it mean if one is to eat a fattening dish, covering it in hot sauce negates some of the unhealthiness? Is there an upper limit to the beneficial effects of capsaicin? I found a similar question asked , thought it doesn't really answer my question. Thanks!
|
[
"Most studies i've seen on it suggest that metabolic rate may be raised by about 10% for a rather short duration. ",
"See this abstract",
" for one example. RMR was only elevated for about 30 minutes. Sorry for the only-the-abstract link.",
"There are several studies out there researching other possible benefits to ingesting capsaicin:",
"\"may be useful in ameliorating meal-induced hyperinsulinemia\"",
"anti-inflammatory",
"more anti-inflammatory mechanisms"
] |
[
"I have been told that capsaicin consumption will make my sense of smell weaker.",
"Is there any truth about this?"
] |
[
"I'm not a nutritional or biochemist of any kind, but I think it has to do with the compound ",
"capsaicin",
". Hopefully someone else with formal training can expand on this? "
] |
[
"Does therapy work?"
] |
[
false
] |
[deleted]
|
[
"The APA sure seems to think so. ",
"Here's their official statement regarding the effectiveness of psychotherapy",
".",
"Here's most relevant passage.",
"Research on Effectiveness",
"WHEREAS: the effects of psychotherapy are noted in the research as follows: The general or average effects of psychotherapy are widely accepted to be significant and large, (Chorpita et al., 2011; Smith, Glass, & Miller, 1980; Wampold, 2001). These large effects of psychotherapy are quite constant across most diagnostic conditions, with variations being more influenced by general severity than by particular diagnoses—That is, variations in outcome are more heavily influenced by patient characteristics e.g., chronicity, complexity, social support, and intensity—and by clinician and context factors than by particular diagnoses or specific treatment \"brands\" (Beutler, 2009; Beutler & Malik, 2002a, 2002b; Malik & Beutler, 2002; Wampold, 2001); "
] |
[
"Reminder: ",
"/r/askscience",
" is not the place for personal anecdotes. Please provide sources for your posts. "
] |
[
"As others have noted, there's plenty of evidence to suggest that psychotherapy is effective in the treatment of disorder. However, there's lots of variability in clinical practice and theory. It's a bit to broad to say that \"psychotherapy\" works. There's lots of practical differences between say Cognitive-Behavioral Therapy and a more Psychoanalytically-oriented (think Freud-y) therapy, which means we shouldn't lump them together when we talk about effectiveness. I think it's safe to say that most modern therapists (and members of the public) think it's important that treatments are grounded in evidence of their effectiveness and therefore only employ proven methods. The APA discusses what it means to be evidence-based and the issues surrounding the topic ",
"here"
] |
[
"if atoms and particles have \"rest mass\" or \"rest mass energy\" when they're moving is their mass different? how does the higgs field relate to rest mass?"
] |
[
false
] |
[deleted]
|
[
"People used to define masses which change based on how the object is moving, but they are ugly and generally an unnecessary concept. These days \"mass\" and \"rest mass\" mean the exact same thing. Rest energy is just rest mass times c",
".",
"The Higgs mechanism gives certain particles some of their (rest) masses in the standard model of particle physics."
] |
[
"If you define mass to be the energy of an object in its own rest frame, that's an invariant quantity. That means that no matter what frame I'm in, your mass is always defined to be the quantity that ",
" measure in your own rest frame. All observers agree on that."
] |
[
"In this instance, how is energy conserved?",
"Energy is conserved in each individual reference frame, but it's not invariant under change of reference frames."
] |
[
"Can't understand torque transfer in a LSD differential - i have a little example of locked differential, maybe someone would help to explain what would happen if we replaced locked with LSD diff?"
] |
[
false
] |
So i watched a video from youtube channel EngineeringExplained about - here's the picture of the So he explains that in that situation we have about 9000 N on the back of the wheels. Because one wheel is on the snow, the maximum force that you can apply to the wheel without spinning it would be 4500*0.3 (friction coefficient) = 1350 N of the force. When we exceed 1350 N, the wheel will "want" to spin, but because it's locked differential, it won't spin and the torque will transfer to the second wheel. So lets say we have a wheel radius of 0.4 m. To spin both wheels we'll need to exceed: 0.4*(4500+1350) = 2340 Nm. Is that right? Plus, in that situation the wheel on the snow gets 540 Nm, and the other on the pavement 1800 Nm(thus the 77/23 torque distribution that he mentions). Lets say we have the same situation but the differential is an LSD type and it has torque of an 180 Nm(i can't understand what does this number means too). Plus, the differential is not fully locking. What will happen if we send the same amount of the torque to the wheels(if we have an LSD differential with an 180 Nm torque split(?) )? How will the torque that needed to spin both wheels(2340 Nm) will be distributed? If it is not fully locking, then we don't have to "wait" to exceed the 2340 Nm point, is that right? But if the distribution is not,for example, like in locked - 77/23,and lets say it is 60/40, then it is not "enough" 2340 Nm to spin the second wheel(60/40 split means 1404/936), and we'll need more torque from engine to be able to spin that wheel.. I am completely lost.. Maybe can someone explain me a little bit?
|
[
"180Nm is what it takes for one wheel to spin differently than the other. So the the wheel in the snow gets 1350 ",
" , the other gets (1350-180). ",
"Limited slip differentials aren't designed for this."
] |
[
"Sorry, that should have been (1350+180). Also the 180Nm could be either constant, initial, or maximum torque difference between the wheels. Constant being independent of torque applied, initial being with no power applied through the drive train, and maximum being max power applied with max traction.",
"Limited Slips aren't designed for situations with high traction differences. They can be, but they cause similar drivability problems of locked diffs but ware out faster. ",
"Your right, I should have given some clear work. So lets use this example,",
"The driver side wheel is lifted into the air and isn't touching anything, the torque required to spin this wheel in an open (normal) differential is 0Nm. The passenger side wheel is on the ground and for calculation simplicity needs 5000Nm of torque to spin. BUT, It's not about making the tires spin in place, it's about acceleration.",
"If the 180Nm in your limited slip is constant, the drivers side will require 180Nm to spin independently of the passenger, and the passenger will require the same of the driver. Lets say your wheels are a total of 75cm tall and you spin your driver side wheel up to 425rpm (just over 100kph). Because the differential is providing the torque to the passenger side wheel via the limited slip, hp is figured from rpm of the driver side wheel and torque applied to the passenger side wheel from the limited slip, you are providing 14.565hp to the passenger wheel. ",
"Now if it is not a constant, but initial, we have the same because the torque required starts at 180Nm and increases in relation to the torque applied from the driveshaft so the more torque applied to the wheels increases the torque differential (wind resistance and internal friction are factors but are in practice irrelevant). The driver side wheel needs 0Nm to turn so only the initial 180Nm is supplied to the passenger passenger side. ",
"If 180Nm is maximum then it is possible that no torque is applied to the passenger wheel because the driver side wheel needs 0Nm to spin.",
"EDIT: Some words."
] |
[
"So this torque is constant? Like always there will just this difference(-180Nm) of torque? And what do you mean by that that they aren't designed for this? You can't calculate precisely how torque will be distributed in a different conditions?"
] |
[
"Why, if we get a new set of skin every 80 days or so, does skin ever become wrinkled and old?"
] |
[
false
] |
Cells replace each other, so why does skin age if they are new cells?
|
[
"Collagen and elastase degradation in the skin matrix. These proteins give skin its flexible nature. Over time the protein is no longer secreted as readily by fibroblasts and the existing matrix begin to degrade, resulting in looser skin."
] |
[
"As much as I'm flattered that so many people have remembered senescence and telomerase after cell biology class, there's a lot of misinformation in this thread due to the assumption that the skin is made entirely of cells. The collagen/elastase that ",
"/u/CarlJungBlood",
" correctly refers to are actually found in the extracellular matrix - these proteins are secreted by cells but are not maintained inside cells. The age of the cells producing these proteins will have minimal impact on their stability, rather factors which impact the rate at which they break down are key effects on skin integrity. ",
"Here's",
" a study showing how chemical damage from smoke impacts collagen in the extracellular matrix supporting skin cells."
] |
[
" ",
"Look, I also remember being a biochemistry major and learning about telomerase for the first time and thinking, \"WOW, if only we had a perfect version of telomerase and were invincible to DNA damage/errors, we could live forever!\" But that's not the way it works.",
"Telomeres are not there to make you age. They are there as an anti-cancer mechanism. If a cell becomes cancerous and begins dividing at a very fast rate, it ",
" use up its telomeres and die sooner than a normally-dividing cell would.",
"There are currently ",
"many, many",
" different theories on why we age. It's been hypothesized that cells are more or less \"programmed\" to turn off certain genes as we age, but what triggers these genetic changes or what the evolutionary point of it is is not well understood. (It is possible that short telomeres may trigger these events, but it's not \"normal\" for a cell to totally run out of them and start chopping off useful DNA.)"
] |
[
"why do most celestial bodies rotate?"
] |
[
false
] | null |
[
"It's pretty much just conservation of angular momentum. Most astronomical objects form from some large diffuse cloud and gravitationally shrink. To conserve the angular momentum, any net rotation in the large initial object (even if initially just random and very small) can end up having a large effect.",
"For example, stars start out from a cloud about a light year across. In shrinking from 1 light year to one solar radius the rotation velocity increases by 10 million times. Thus if there is ",
" net rotation at all in the cloud, just by random chance or torques from the galaxy or nearby stars or whatever, then the final object (a star) will be rotating noticeably."
] |
[
"You're right and this is nitpicky but what you're really explaining is why things rotate faster as they condense, not necessarily why they rotate in the first place. You're close with the mention of the rotation being seeded \"",
"\" net rotation, but that net rotation need not be influenced by neighboring systems and it's not random chance. The rotation is guaranteed by the fact that there's effectively zero chance that all the particles (or at least sets of particles in exactly equal proportions) that collapsed to form the body did so at the exact same moment on the exact same point. "
] |
[
"So a body rotates faster the more it shrinks in size. The rate of rotation depends on the conservation of angular momentum while the shrinking depends on the gravity of the body. Is that right?",
"So my question is, when a black hole forms, can we calculate how quickly it would end up rotating at a given mass and initial rotation?",
"What are the dimensions of the singularity? I've read that it's a point. Is this wrong?",
"If it is a point with reduced dimensions, would the increase in the rate of rotation, due to the conservation of angular momentum as the black hole collapses to a point, cause the matter inside the singularity to approach the speed of light? How is that possible? I thought that matter can't reach that speed so what happens to it?"
] |
[
"I'm confused between the calories I learnt in high school Physics and the calories associated with nutrition."
] |
[
false
] |
What is the relationship? If a piece of food has 100 calories on the backside label, what does that mean? Does it mean that it will take my body a 100 calories (418J) to burn it off? Does it mean my body has to generate that 100 calories?
|
[
"It'll take 418 ",
"joules. The food Calorie is actually a kilocalorie."
] |
[
"1 calorie is the amount of energy to raise 1g of water 1°C, in food the Calorie you see i actually a kilocalorie (hence the capital C)"
] |
[
"To add to that, this link explains somewhat well the concept of this calorie thing ",
"http://recipes.howstuffworks.com/question670.htm"
] |
[
"What exactly does it mean when something has a \"negative\" charge or a \"positive\" charge? Why do like charges repel and unlike charges attract?"
] |
[
false
] | null |
[
"Charge is an intrinic property of particles. The determination of “positive” or “negative” is purely a convention. You could easily flip what you call positive and negative and get back the same Physics. (If you did this now there would be positively charged electrons and negatively charged protons) Macro-scaled objects can be charged one way or another by having more electrons than protons (negatively) or less electrons than protons (positively). The greater the difference the greater the charge. At this scale you could imagine pairing up each proton and electron to cancel out their charges and the resulting charge is just the excess of electrons or protons. ",
"Now a simple (albeit somewhat crude) answer for the direction of the resulting force between two charges can noticed by considering the formula:",
"F=k•q1•q2/r",
"Where q1 and q2 are the charges, k is a constant, and r the distance between the charges. Now if q1 and q2 are both positive or both negative their product is positive, thus they repel. If q1 and q2 are different (one positive and one negative) their product is negative and thus attract. ",
"While this description might be too hand wavy, the only first principles derivation I know would require a dive into QED, so I hope this is satisfactory."
] |
[
"Right, CPT is the full symmetry, but that is really beyond the scope of this question. ",
"Also, you could imagine that if we originally had chosen the electron to be positively charged we would have determined all the same physics happening and things we typically think as being one way get flipped by due to CPT symmetry. Saying it is fundamentally negative is an over-exaggeration to the other degree. If history had taken that route (electrons are positive), you'd suggest that its fundamentally positive otherwise we would need to use the right hand rule instead of the correct left hand rule. ",
"At the end of the day all these things are due to a choice. Now choosing an electron to be positive means you need to rewrite certain things to make other phenomenon make sense but at the end of it all it is still just a conventional choice."
] |
[
"Thank you!"
] |
[
"Was Pangaea the only land mass at the time and how do we know that?"
] |
[
false
] |
[deleted]
|
[
"Depends on how you define 'only landmass'. A ",
"reconstruction of paleogeography for the Permian",
" during kind of the middle of the the existence of Pangea highlights that while the bulk of landmasses are semi-continuous, i.e. ",
"Laurasia",
" and ",
"Gondwana",
" are joined, there are semi-isolated portions of continents and continental fragments on the other side of the Paleo-Tethys (and as Pangea breaks up, on either side of the Tethys) ocean. There were also almost certainly smaller islands within ",
"Panthalassa",
" related to subduction zones, e.g. island arcs, for which we don't have as much direct control on. If you want a lot of detail on the assembly and breakup of Pangea, ",
"Stampfli et al, 2013",
" is a good review. Or if you want a more interactive exploration, check out the ",
"Paleomap Atlas for GPlates",
", though this requires installing GPlates (which is free).",
"To the more general aspect of your question, we know what we do about the shape of Pangea and other forms of the continents at different times through a variety of means to form ",
"paleogeographic reconstructions",
". Chief among this are ",
"plate reconstructions",
", which rely heavily on ",
"paleomagentism",
". While there are isolated areas of submerged continents, e.g. ",
"Zealandia",
", because of the density and thickness contrast between continental and oceanic crust, generally, continental crust (and the portions of plates which are made up by them) are pretty resistant, allowing us to reconstruct past plate geometries with some amount of confidence. That being said, our confidence in our reconstructions decrease as we go back in time as the record becomes increasingly incomplete."
] |
[
"Also, continental crust can’t sink! It’s much lighter/less dense than oceanic crust - continental crust is what geologists call “felsic” (for the mineral feldspar, which can contain sodium, potassium, or calcium depending on the subtype of feldspar, plus silicon!) while oceanic crust is “mafic” (contains a much higher percentage of minerals containing magnesium and iron). Oceanic crust gets recycled through a process called subduction, whereas continental crust never sinks/gets truly ‘recycled’. It gets modified through erosion, continental collisions (mountain building), etc., but never re-melted and re-erupted. Pretty much all the continental crust there ever was/ever will be has been around since if was first erupted (or, more accurately, since it first floated to the top as the lighter minerals solidified first, like ice on top of water. Google ‘Bowen’s Reaction Series’ to learn more about why the “felsic” material cooled first and rose to the top!)."
] |
[
"This is kind of the 'Geology 101' version of things, however in reality, there is a measurable (and in some sense significant) amount of continental crust recycling through the combined processes of subduction erosion, subduction of eroded sediment, and true continental subduction / foundering of crustal roots (which is restricted to large scale continent-continent collisions). Certainly it is true to say that the rates of this recycling are slow compared to the recycling of oceanic crust, but it is recycled and more recently in geologic history, it's argued that the rates of continental crust removal may be approximately equal to the rates of continental crust generation, though the exact balance is definitely an open question and one that is hard to evaluate, e.g. this review by ",
"Hawkesworth et al, 2019",
"."
] |
[
"Are the dorsal ridges on Human/Mammal vertebrae vestigial organs? [Biology]"
] |
[
false
] |
If so, what function did they serve in our common ancestors, and is there any evidence to show that they are either shrinking or growing?
|
[
"Nice question! I assume you are refferring to the ",
"spinous processes",
" of vertebrae? If so, they actually serve some important functions for muscle attachment! Some muscles that originate or insert there include: the erector spinae and interspinals. this muscles helps flex the back (arch your back! that's your erector spinae helping out!). Another one is the trapezius muscle - which originates along the spinous processes (and other bits) of the cervical and thoracic vertebrae, and inserts on scapula. this muscle helps move and support your whole arm - pull your shoulder blade back! that's the trapezius doing it's thing!",
"You also have two special vertebrae - the atlas and axis - which have a very different set of ridges. those actually attach to muscles that help move and rotate your head!",
"There's also a set of ligaments that helps keep the spinal column bones together - the interspinous ligaments. they all attach and insert on the vertebral processes. ",
"Those are a few examples - the ridges are actually pretty important to keep our body moving!"
] |
[
"Thanks for your answer!"
] |
[
"for sure! no problem :)"
] |
[
"Can you help me wrap my head around the idea that if you rotate an electron 360 degrees it's different, but if you rotate it 720 degrees it's back to the same state?"
] |
[
false
] |
Imagine that I have a magical box. Inside the box I have a bunch of suspended non-interacting electrons. I also have a magical pouch, which also has a bunch of suspended non-interacting electrons. Now I dump the electrons from the pouch into the box such that they hit head-on, and I watch which ones interfere. Imagine that instead of just dumping the electrons in the box, I walked around the box once first. Am I supposed to believe that the opposite electrons will interfere if I've walked around the box once (i.e. I see the box electrons to be 'rotated 360 degrees' with respect to the pouch electrons)? This seems silly to me.
|
[
"Searched",
"Relevant ",
"discussion",
"Original question by ",
"darksoulshaman",
"I was just reading ",
"this",
" thread, which has a lot of science-related comments, and it reminded me of something interesting my high school chemistry teacher once said.",
"He said essentially if you took a (tiny) marker and put a dot on an electron, then rotated the electron around a single axis, you would have to rotate it 1.5 times to actually see the dot again.",
"Is that true? What causes this if it is? Or if it isn't true, is there some similar property that I am mixing this up with? What (if any) are some other interesting properties of electrons that are mind-bending?",
"Top comment courtesy ",
"iorgfeflkd",
"That is sort of correct. Electrons have a spin of 1/2, meaning that you have to rotate them 720 degrees to turn them around once. To get an idea of what this means, hold a coffee cup with your right hand, but with your palm facing right on the handle (with the handle towards you). If you rotate the cup under your wrist 360 degrees, your hand will be upside down. If you rotate it another 360 degrees in the same direction, your hand will be back to where it started.",
"Appropriately named video"
] |
[
"Thanks, search bot. I have indeed seen the Dirac cup trick (or Feynman plate trick, or whatever you want to call it), but unless the electron is attached to something by, say, an arm, it doesn't really make much sense to me. I'm still looking for an answer to my question above, which essentially boils down to 'can walking around an apparatus once cause experimental differences'. If so, any intuitive explanation as to why (that doesn't involve e.g. an arm attached to a shoulder) would be very much appreciated."
] |
[
"When doing quantum mechanics you have to be careful to separate the concept of the wave function from the probability. You need to rotate the electron 720 degrees to get the wave function back to where it started. If you rotate the system 360 degrees then the wave function will be negative one times the original wave function. But since the probability of any measurement is proportional to the mod square of the wave function rotation by 360 will not change any measurement that you make just the wave function. "
] |
[
"Why do acidic foods dissolve copper pots?"
] |
[
false
] |
According to the Food and Drug Administration, acidic foods cause copper on unprotected cookware to dissolve into foods. If you use unprotected copper-lined pots and pans, research the acidity of certain foods. Excerpt out of the table of galvanic series: With more noble metals being higher up, shouldn't the H atoms of the acid be unable to oxidize copper atoms? Cu + 2H → H2 + Cu seems impossible without an external power source
|
[
"They're pretty close in the galvanic series, but it's possible to get local cathodic/anodic activity, possibly a concentration gradient at a nick in the copper.",
"Honestly, copper can corrode in plain water as well (pH 7). Edit: at elevated temperature ",
"Regarding the galvanic series, these are certainly a good guideline, but on the metal surface you can have smaller areas that are electrochemical ly active causing corrosion.",
"Edit: The intro of ",
"this article",
" suggests that small amounts of chloride in this HCl pickling solution can create copper chloride (which may be soluble?)."
] |
[
"My electrochemistry knowledge is very rusty, but I think you're right as far as where you got started. You should actually use the Cu(2+)+2e(-)->Cu(s) potential = +0.337 I think. But you will still get the same result.",
"However, let's look at Cu+2H(+) -> Cu(2+)+H2, for the sake of more understanding, even though this is an oversimplified reaction",
"Even though the reaction is non-spontaneous (gibbs free energy change is positive), there is still an equilibrium with K=e",
") = [Cu(2+)]/[H(+)] which will be a really small number. So the dissolved amount of copper will be really small, but some will still be leached. This might be the problem.",
"Iff you filled a copper pot with water, and let the equilibrium develop, the water would gain a small concentration of copper ions. If you dumped out the water, and refilled the pot with fresh water you could leach off even more copper. If you did this continuously (aka a copper pipe), you would eventually wear away a lot of the pipe. I'm thinking the oxidation mentioned in Nirvana's comment might happen faster.",
"Since iron has a negative standard electrode potential, iron pipes wear a lot faster with water. That's (probably one of the reasons) why we galvanize iron/steel pipes with zinc."
] |
[
"This is an interesting question!",
"The standard electrode potential for hydrogen is for 1 mol/L strong acid (pH = 0) against a platinum electrode with an atmosphere of H2 (1 Bar). This is an equilibrium system, where the activities of all species in the redox couple are equal. You notice the anion of the acid doesn't feature in this at all; it is electrochemically inactive.",
"Inorganic anions are often both electrochemically and chemically inactive, however organic acids, like citric acid, are more complicated. The electrochemical behaviour of citric acid solutions is affected by the stability of the metal-citrate complex (which is neglect in the galvanic series), because it can bind chemically to metals and this affects the thermodynamics of the reaction significantly.",
"In reality, the formation of Copper Citrate complexes drives the dissolution of your pots, while I'd have to read more to be certain, this effect ",
"appears to be made worse",
" by the formation of an insoluble 2xcopper 1x citrate (i.e. Cu2Citrate not Cu",
" ) salt."
] |
[
"What would I experience if I was trapped in an air bubble on a sinking battleship?"
] |
[
false
] |
After looking at this picture: And seeing this video of a man they did find in an air bubble on a sunken ship: If I was trapped in an air bubble on lets say the Bismark and the ship was sinking to the bottom of the ocean, what would I experience in the air bubble as the ship descending to its resting depth?
|
[
"If it were to sink deep enough, provided the air bubble were large enough to sustain life, eventually oxygen toxicity would kill you. See the ",
"MOD table here.",
"Oxygen toxicity",
" occurs at about ",
"1.4 atmospheres,",
" or about 187 feet of depth. Nitrogen narcosis is highly variable between individuals, but- at 80% atmospheric concentration- getting \"narked\" is common at depths over 100 feet, and \"usually incapacitating\" (ibid) at 300'.",
"Also note that as depth increases and the partial pressure of oxygen increases, things become more flammable. It is generally thought that there were some survivors on the submarine ",
"Kursk",
" that died hours or even days later when an oxygen generator came into contact with water, causing a flash fire with a film of oil and fuel that covered the surface of the water, causing pretty much everything that was combustible in the enclosed chamber to burn. Anyone who survived THAT would probably die soon after from carbon monoxide poisoning. FWIW, the bow of the Kursk was at a depth of 108 meters. The chamber in which the survivors were caught was slowly filling with water, making it impossible to escape after a relatively short period of time, due to the likelihood of death from decompression sickness due to the saturation of nitrogen under pressure.",
"It also seems likely they didn't try the escape hatch as the method to escape relies upon allowing water (at nearly freezing temperatures) into a tightly confined space until the pressures equalize, and then hoping the hatch isn't jammed from the initial explosion or the collision with the ocean floor, and then swimming upwards nearly a hundred meters without bursting your lungs. And THEN you have to hope a ship will notice you before you freeze to death in the ocean. So perhaps they can be forgiven not trying to escape."
] |
[
"The pressure inside a submarine is one atmosphere, while outside it's higher, so eventually it gets crushed. But in this scenario, the ship is not sealed, the pressure inside and outside is the same, but the air bubble gets smaller and smaller. So there is no force to crush it."
] |
[
"Good answer, something to keep in mind is that every 33 feet of salt water is equal to one atmosphere of pressure. So while the human body would be able to handle upwards of 30 atmospheres of pressure temporarily a few things would happen at those depths: first, you would likely very quickly succumb to nitrogen narcosis (feels somewhat similar to being stoned and impairs your judgement and the euphoric feeling would likely make it easier for you when you do die). Second, as the pressure increases the air pocket would be compressed. By 30 atmospheres the air pocket would shrink to 1/30th of its original volume. Third, while the air compresses you would use that air much faster.",
"Edit:ignore the third point, as ",
"/u/nonstandarddeviation",
" pointed out that wouldnt apply in this situation."
] |
[
"If shaking a carbonated beverage in a can increases the pressure, why does letting it sit for some time decrease the pressure back to normal? What happens to that pressure?"
] |
[
false
] | null |
[
"The key here is nucleation.",
"https://www.youtube.com/watch?v=l5xbgNTxApo",
" - this video explains it all. Basically, small bubbles stick to the sides of the can when you shake it. When the pressure is released/lowered, those bubbles expand. And that rapid expansion pushes the liquid out.",
"When a can \"settles\", the bubbles either float to the top or dissolve into the liquid again. This is why you should flick a can before opening it. Flicking dislodges the bubbles and stops it erupting - and it actually works."
] |
[
"CO2 is dissolved in liquid. When you agitate(shake) the can you are adding kinetic energy which drives the gas out of the liquid phase. All the molecules are moving around at an increased rate and the gas comes into contact with more gas molecules and the liquid with the liquid. Molecules of the same kind typically want to be with each other. Think how water droplets next to each other will join to form a single bigger one.",
"When you let the can rest the amount of energy (kinetic) you put into the can will dissipate and now your system has an increased pressure. To reduce the stress, the pressure will drive the gas back into the liquid. Enough so that the system comes to ",
".",
"This may not be the same amount of gas dissolved in the liquid as when you first grabbed the can. Equilibrium is not an exact amount, but a state dependent on variables. For instance, temperature; if you took the can out of the fridge and let it warm up some amount during this whole process the amount of gas dissolved would be less. As heat is another form of energy."
] |
[
"Shaking carbonated beverage increases pressure because it releases CO2 from beverage to air gap in the can. When you let it sit, CO2 slowly gets back in to the solution. That decreases the pressure back to normal. "
] |
[
"How could a topical application of medicine travel to the targeted muscle?"
] |
[
false
] |
I have had several friends recommend some kind of topical cream for my muscle cramps. They say you just massage it into the skin at the problem area. I think this must be baloney, mostly, because anything that gets through the skin would be more or less carried away by the blood and metabolized right? I see an added benefit of the massage being helpful in itself, but come on, medicine on the skin doesn't just sink in deeper and deeper through tissue and into muscle, or does it?
|
[
"Topical pain-relief solutions work by “jamming” the pain signals from the muscle/joint. Most of these ointments have menthol as the active ingredient which basically gives you a mild chemical burn over a large surface area of skin.",
"This overloads the nerves and sends the “mildly warm” signal to the brain instead of the more discreet pain signal from a pulled muscle or sprained joint.",
"Vibration can also override discreet pain signals which is what makes massagers help reduce pain."
] |
[
"I had wondered about this, too. But it seems the data from meta-analyses consistently holds out on their efficacy beyond placebo.",
"https://sciencebasedmedicine.org/topical-nsaids/"
] |
[
"Sure works for me - I have severe arthritis in my hands, and I use a cannabis infused topical cream. Without it, I’d be a walking crone with talons for hands. Feels pretty good on my old knee too. ",
"As for HOW it works, or WHY? Don’t know. Just know that it does. "
] |
[
"With two observers in two different frames of reference involving relativistic mechanics, is length dilated, or time, or both?"
] |
[
false
] |
I'm brushing up my Relativity knowledge (12+ years out of touch) but I understand the basics. In this case, say, observer1 is moving at a constant speed approaching c, and the other is stationary. Also, keeping gravitation out for this one - will get to General Relativity later.
|
[
"Both. I don't believe there's a way to get one without the other. Normally you formulate questions so you only have to consider one or the other but a full battery of questions about what each observer 'sees' and measures will definitely include both at some point."
] |
[
"One or the other.",
"Consider muons rushing from space down through the atmosphere to the ground. From our point of view they take a certain amount of time which is far more than their half life. This is possible because we see them traverse the atmosphere with dilated time.",
"From their point of view, however, their clocks run at the normal rate...but they can still reach the ground because the atmosphere is length contracted.",
"Basically, we see the \"normal\" length but slower time, and they see \"normal\" time but shorter length. These effects are exactly equivalent."
] |
[
"We would also see ",
" length contracted, and they would also see ",
" time dilated. So, it's not one or the other, it's both.",
"In your muon example, there are two reference frames. There is the \"Earth\" reference frame, and the \"muon\" reference frame. Either reference frame can be considered at rest. If so, then the other reference frame is considered to be in motion, and the other reference from exhibits both length contraction and time dilation from the perspective of the non-moving frame.",
"So, if you consider the Earth frame to be at rest, then the muons will exhibit time dilation (they will seem to last a lot longer than their half-lives would suggest is possible) ",
" they will exhibit length contraction (which is admittedly hard to observe for a batch of muons, but if the muons were extended objects like spaceships, you would see it).",
"If you consider the muons to be at rest, the Earth reference frame would exhibit length contraction (the trip from the top of the atmosphere to the bottom would seem much shorter in distance), ",
" it would exhibit time dilation (the Earth's inhabitants would seem to age slower from the perspective of the muons, albeit only for a split second because we're dealing with very short time frames here)."
] |
[
"What is the exact wind speed the average weight seagull needs passing over it's wings to 'hover'?"
] |
[
false
] |
Just walking up form the bus stop, and I saw a seagull 'hovering'. Now, presumably the wind speed was just enough to pass over it's wings to generate enough lift to offset the seagulls weight, and it got me thinking. What is the exact wind speed that the average weight seagull needs flowing over it's wings to offset it's weight?
|
[
"It's going to vary. Unlike an airplane, which can only slightly change the shape of their wings, birds have much greater control. Changing the wing shape will change the lift and drag on the wings. I don't know much about how birds flap, so I don't know if their wings are always the same shape when flapping or not.",
"Generating enough lift to counteract the bird's weight isn't enough, that alone is what normal flight is. The bird also has to be generating enough thrust to counteract the drag on their wings."
] |
[
"Purely horizontal wind won't do it as the seagull is not producing any thrust when hovering, and the drag would push it backwards. To truly hover there needs to be an updraft for the seagull to 'fall' through to keep up forward speed."
] |
[
"You'll still need a force to counteract the drag of the high-speed wind."
] |
[
"Is it possible to travel backwards in time under the current laws of physics?"
] |
[
false
] |
I understand time dilation can create a discrepancy of perceived time from those within the moving object, but are there any hypothetical way to travel in the opposite direction against the flow of time?
|
[
"The problem with time travel to the past is that it violates conservation of energy/mass. Say you time travel back three days and appear in your room. In the local reference frame, you were not there one second and then you are there the next second. Mass/energy has therefore been created out of nothing, which is not allowed. You hang out for three days and then time travel back again alongside your original self. You can see where this leads: you end up with an infinite number of you appearing out of no where, which is nonsense. This is not a psychological effect. Send back in time a rock and conservation of mass is still broken, and a runaway infinity is still possible. "
] |
[
"However, it has been shown (by Richard Feynman) that antiparticles are regular particles traveling backwards in time.",
"It was shown that you could think of them that way as they would still obey certain symmetries, but that isn't what they ",
". For instance, a box of antiparticles isn't going to disobey the second law of thermodynamics, so clearly they ",
" going backwards in time generally."
] |
[
"However, it has been shown (by Richard Feynman) that antiparticles are regular particles traveling backwards in time.",
"It was shown that you could think of them that way as they would still obey certain symmetries, but that isn't what they ",
". For instance, a box of antiparticles isn't going to disobey the second law of thermodynamics, so clearly they ",
" going backwards in time generally."
] |
[
"Is there any difference between eating vitamins from say, a vegetable or eating vitamins from a pill?"
] |
[
false
] |
Everyone who's ever had an opinion on this says that natural is better. But then they just say, because it's natural. So I want to know, is there any science behind this or is it just the naturalistic fallacy at work? Thanks.
|
[
"Doctor Stephen Novella talked about this on the Skeptics Guide. If memory serves then eating a pill gives you a very narrow benefit, lots of one specific vitamin. However eating your veg gives you a far far wider range of vitamins that pills simply cannot match. I believe that if you relied on pills, you would not be as healthy as someone who eats their veg. I'll try and find the episode, but if its not in the notes we're lost. Nope sorry, its not noted."
] |
[
"Yes, they put actual iron filings in the cereal. Because our body needs actual iron to survive. Yes, we process iron in that form."
] |
[
"Yes, they put actual iron filings in the cereal. Because our body needs actual iron to survive. Yes, we process iron in that form."
] |
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