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[
"[Physics] Is it possible to have a photon so energetic that it doesn't interact with any material we know?"
] |
[
false
] |
I know that gamma rays do not interact and go through most materials, except lead for instance. That's my silly question, thx.
|
[
"More energetic photons are actually more likely to interact with materials (above a certain threshold), because it increases the likelihood of pair production.",
"This is essentially a graph of how likely a photon is to interact, vs energy",
"."
] |
[
"Equal parts pair production and incoherent scattering."
] |
[
"What band is the well near 10"
] |
[
"Higgs Boson, and inertial vs gravitational mass"
] |
[
false
] | null |
[
"No - intrinsically, the Higgs has absolutely nothing to do with gravity.",
"To understand this, pretend for a moment that there is absolutely no such thing as gravity. This is an approximation that is generally made in all of particle physics [1]. The \"Standard Model\" of particle physics does not in any way explain gravity, nor does it provide any explanation of how two particles such as protons might gravitationally interact.",
"Even without gravity, mass is very important. Massless particles, such as photons, move around at the speed of light. Without the interaction with the Higgs field, electrons would move around at the speed of light, no matter what their momentum was. When a particle has a mass, it moves at a velocity that is roughly proportional to its momentum [2].\nIntertial mass is the quantity that determines how much velocity a particle with a given momentum has.",
"Gravitational mass is the quantity that determines how much gravity affects the momentum of the particle. Originally, it was viewed as an amazing coincidence that the gravitational mass is the same as the intertial mass.",
"In the theory of General Relativity, it is actually energy density, not mass, that generates a gravitational field. A massive particle has an intrinsic \"rest energy\" of E = mc",
" where m is the mass and c is the speed of light. It is this rest energy that generates a gravitational field.",
"In the Standard Model of particle physics, the mathematics does not work out for particles to intrinsically have a mass. Instead, the only way for them to have a mass is through interacting with some field. Because an electron interacts with the Higgs field, it is slowed down. It does not move at the speed of light, instead its velocity is proportional to its momentum. Effectively, it can be considered to have a mass.",
"[1] There is a branch of particle physics that takes account of strong gravitational fields, this is where the prediction of Hawking radiation comes from.",
"[2] Near the speed of light, the velocity is no longer proportional to momentum, but gets closer and closer to the speed of light as the momentum increases without bound."
] |
[
"Thanks for the detailed yet comprehensible explanation!",
"Does anyone know why inertial mass equals gravitational mass, then? (I.e., why everything falls at the same speed, in case I'm using the terms wrong.) Or is that still an unexplained coincidence? :-)"
] |
[
"Thanks, I am glad that it makes some sense!",
"The equivalence of the two masses was one of the key facts that led Einstein to the theory of General Relativity. General Relativity (GR) starts with the implicit assumption that the two must be equal.",
"In GR, gravity is not really a force - nothing is really accelerated. Instead, spacetime is curved. When one is in free-fall, one is not really accelerating - just moving along the equivalent of a straight line in the warped space. ",
"If you think about it, one doesn't actually feel gravity. Astronauts in the shuttle are getting slingshotted around the Earth, but they don't feel any force. You only think that you feel gravity when something prevents you from falling. You feel the ground pushing against you.",
"Being in free-fall is just like moving in a straight line at a constant velocity. There are no actual forces. Forces only come into play when something prevents you from falling.",
"GR is mathematically a terrible mess to work with, so for most things people use Newtonian gravity, which is an approximation of GR at low speed and a reasonably small gravitational field (i.e. not near a black hole!). In the Newtonian approximation, gravity is treated as a force, proportional to an object's \"gravitational mass\", which is just its inertial mass. If you don't know about GR, this seems like a complete coincidence."
] |
[
"how does a cell know what it's \"body parts\" do? I mean how does the golgi apparatus know its function/what to do?"
] |
[
false
] | null |
[
"Putting it ",
" simplistic: it is all about (physical) chemistry. Molecule X binds to a receptor, which changes its form, which triggers another reaction, etc. ",
"It’s a huge chain reaction with some probability distribution (depending on binding strength, temperature, etc.)"
] |
[
"So a protein is a very big molecule. It’s so big that parts of it are attracted to other parts and cling together, think of a balloon you’ve rubbed on your hair and stuck to a wall.",
"These self-stickiness gives proteins a folded shape. There’s still some charge, but since the protein is folded a specific way, most other molecules don’t fit to bind to those charged areas.",
"However, most proteins have at least one other protein that ",
" fit. So when a protein “meets its match” the two can bind together. When they do that, their charges mingle and change and the proteins change shape.",
"This act, proteins changing shape as a result of things binding to them, is how your cell “does” stuff. ",
"So in your Golgi apparatus example, the proteins don’t know what they’re doing at all. But they have a specific shape and charge and so attract and bind specific other proteins. When they do so, they change shape and that results in the golgi doing something."
] |
[
"That's a little like asking how does a taco truck know that its a taco truck. The truck itself doesn't know what it does, but inside it has the ingredients for tacos, a taco chef, and all the signage on the outside of the truck indicating its a taco truck.",
"The same works in cells. The golgi apparatus is essentially just a collection of membranes but its the proteins within the membranes that give it the function. And if you took out all those proteins and swapped in endoplasmic reticulum proteins, then it'd be the ER (just like if you swapped out taco ingredients for ice cream in your food truck). The proteins within organelles gather together through inter-molecular interactions. There are multiple proteins whose role it is to gather all the golgi components and keep them together (NSF and p97 for example).",
"Something else to consider is how do we define organelles? While in textbooks the organelles look quite distinct from one another, they actually exist on a spectrum. For example, it was thought each cell had a single golgi apparatus housed within the cell body. Recent research has shown that there are actually other golgi-like organelles (\"golgi outposts\") positioned far from the cell body (like in axons of neurons) that perform some functions of the golgi but not others.",
"Another example would be lysosomes (a round, acidic compartment used in autophagy). The lysosomal associated membrane protein 1 (LAMP1) was considered ",
" marker for lysosomes for a long time. However, there have been multiple studies showing that there vesicles with LAMP1 on them that are not acidified which calls into question their identity. Another marker that researchers use is a protein called ",
" which, in muscle cells, localizes to a tubular network rather than vesicles. Are these networks lysosomes? Are non-acidified LAMP1 compartments lysosomes? These questions are still being debated.",
"Going back to the original question, how does an organelle define its function? By the proteins associated with it. And these proteins assemble using a large assortment of chaperones that collect the protein components, bring them to their destination, and assist in forming complexes. And while we talk about organelles as distinct parts that have distinct functions, they exist on a spectrum.",
"Assembly of the golgi: ",
"www.ncbi.nlm.nih.gov/pmc/articles/PMC5710388",
"Golgi outposts: ",
"www.cell.com/trends/cell-biology/fulltext/S0962-8924(20)30145-8",
"30145-8)",
"Heterogeneity of LAMP1 vesicles: ",
"https://pubmed.ncbi.nlm.nih.gov/29940787/",
", ",
"www.ncbi.nlm.nih.gov/pmc/articles/PMC6123004/",
"Tubular lysosomes: ",
"https://pubmed.ncbi.nlm.nih.gov/35646899/"
] |
[
"What kind of mold might this be? (image included) Is there any way to save my stuff?"
] |
[
false
] |
Went to get the holiday decorations out of the basement and some how the container (which was ~3ft (-1m)off the floor) was wet inside. I cant seem to find any mold on Google that looks quite like it. Could just be the power of suggestion but I started feeling sick within minutes of exposure. Also, is there any way to kill it without destroying all of the 40+ year collection of decorations?
|
[
"I did mould assessments for a couple years-First of all, the colour doesn't really matter, any mould is mould.",
"Anything paper based is pretty much gone, there is no saving it.",
"Anything inorganic (light strings, anything plastic or metal) give it a good scrub with some steel wool, soap, and bleach, and it should come right off-on these surfaces the mould is not growing on the material, it is growing on something on the material and should come off no problem.",
"It gets difficult when talking about things like wood- It really is a case by case basis. Most of it can be cleaned, it just takes a while. ",
"Other notes-Take it all outside, do the cleaning outside, you don't want to be kicking up spores . Until you get the chance to do that cover it all with a tarp.\nThis mould indicates a wet environment, which is okay if its a back shed, but if its inside fix it immediately. There's a leak, or a hole somewhere and you need to fix it. same way that any mouldy drywall, etc. has to be taken care of immediately or it will get worse faster than you cold believe",
"edit: I just saw that it was in the basement, which means that it is likely on more things than just your christmas decorations. I recommend having some sort of consultant (a good one) take a look with a moisturemeter if there's any dryall, etc. around. If you were in Canada, i could tell you about companies and regulations, but judging by your spelling of mould (mold) you're in the US of A.",
"And as to the health concerns, minor. There is mould everywhere, and in your case, it would almost certainly do nothing but exasperate asthma symptoms, or cause mild headaches or fatigue...those types of symptoms. When/If you do clean it though, you may want to pick up a dust mask or something of the sort- It can cause problems when you're banging on the stuff, stirring the spores into the air"
] |
[
"Almost certainly. Is it dangerous? Almost certainly not. Should they do something about it? Yes, because if somebody spends long times in their, they may get the mild symptoms i described above, but more importantly because it has a huge effect on the value of the building, and if they don't, costs will spiral out of control if they ever want to sell the building"
] |
[
"Almost certainly. Is it dangerous? Almost certainly not. Should they do something about it? Yes, because if somebody spends long times in their, they may get the mild symptoms i described above, but more importantly because it has a huge effect on the value of the building, and if they don't, costs will spiral out of control if they ever want to sell the building"
] |
[
"Can lowering the temperature of molecules and reducing their excited state allow us to pack them in tightly and create superdense matter?"
] |
[
false
] |
Perhaps my concept of it is flawed but I remember reading that as matter moves through states, condensing as they get colder, molecules take up less space due to reduced excitement. If we now have the ability to cool things down so greatly that we can actually trap particles of light, could we keep feeding something that cold with more matter? If we did could we not press more and more matter into smaller and smaller spaces to create superdense matter?
|
[
"Yes. But not for the reason you think. Read up on ",
"Bose Einstein Condensates",
"."
] |
[
"Hi, that seems flawed to me. basically PV=mRT, so for a given mass at a given pressure, if you decrease the temperature, then R is a constant so V reduces, i.e. it crams into a smaller space.\nthe same mass in a smaller space = higher density\nyou can't trap light with temperature, because the light would hit the mass you have coole and warm it up to then be released again as another form of radiation. remember that heat is just the most low-grade form of energy, everything ends up as heat eventually, including light radiation.\nif you had a given mass that was very cold and tried feeding more matter into it, then in the formula PV=mRT, you would be adding mass, keeping the temperature the same so the volume or pressure would increase. if the volume increases you haven't got more matter into a smaller space because the space is now bigger, and if the pressure increases then that will in turn increase the temperature (due to the particles interacting.\nyou would also have to define 'superdense'"
] |
[
"I'd been explaining some of the dangers of space to my daughter, and described some of the affects I'd heard of weightlessness.",
"That lead me to think about the big difference between space flight in fiction and science fiction. Gravity. They mention artificial gravity all the time, and you watch them all walking to and fro on their star ships.",
"So I started thinking, what could possible create a sense of gravity on spaceships to prevent organ damage, etc...",
"So at first I was thinking of the whole centrifugal thing, but i'd recalled descriptions of neutron stars. How they were immensely small compared to their density. I'd read an article somewhere that mentioned a neutron star being the size of Brooklyn having the same density equivalent gravitational pull of 500,000 Earths due to it's super dense nature.",
"Scaled down I assumed something that was 1/500,000 the volume of Brooklyn would be relatively small in diameter, but if it was likewise dense could have the gravitational weight of Earth. ",
"So that lead to my thinking about how to artificially create super dense matter short of collapsing a star. Remembering that Bose Einstein Condensate video I'd seen, it lead to the question I'd posed.",
"The question with it's alterior motive attached was, could we create super dense matter by slowing atomic movement, packing molecules in tighter, and thus approximate artificial gravity."
] |
[
"How does the black hole at the center of our galaxy affect our solar system?"
] |
[
false
] | null |
[
"The mass of the central black hole is about 4,000,000 times our Sun. The mass of the entire Milky Way is about 1,000,000,000,000 times our Sun. So the black hole is one 250,000th of the entire galaxy. If you magically removed it, nothing at all would change for the vast majority of the galaxy, including us.",
"There are some stars very close to the black hole which could be said to orbit the black hole itself. For these stars the gravity of the black hole itself is significant. But for most of the galaxy it isn't. ",
"Compare this to the Solar System where the mass of the Sun is 99.86% of everything in the Solar System. So practically all the mass of the Solar System is in the Sun but hardly any of the mass of the Milky Way is in the black hole. "
] |
[
"Basically no, while there is a TINY bit of gravity exerted on use by it it would about same as the amount of gravity of a single molecule on the moon (But even that is likely a far bigger effect).",
"The gravitational pull of an object does effect everything else in space, but when you double the distance between the object you weaken the gravitational pull between by four. So objects close together can be pulled into each other, but when you dealing with something like our solar system and the black hole at the centre of the universe the pull is so infinitesimally small that other stars around us completely over power it. "
] |
[
"Thank you so much. That explains it very well."
] |
[
"Found this \"rock\" 15 years ago, finally trying to figure out what it is."
] |
[
false
] |
I found this about 15 years ago (the 33 sticker is because this was the 33'rd unknown specimen from my collection). It was located on the shore of Lake Ontario near Selkirk Shores (Pulaski, NY). The object itself weighs about 1.5lbs, is cloudy mostly but somewhat clear. It is full of air bubbles and one bubble shown even has liquid and air in it which act as a bubble as a level would. It has chips and rough edges but nothing sharp. The green spots on the one side were as I found it, I cannot tell if paint or algae stains. It may be glass, but I can’t figure out why such a piece would exist full of air pockets. What is it? Why would it be on a rocky beach? How did it get there? And finally, what should I do with it (clean it up and polish it maybe?). Thanks!
|
[
"It's glass. GIS for Conchoidal fracture or slag glass rock. Possibly from a glass factory (slag)."
] |
[
"This is most likely a glass slag sample that was dropped in water and cooled very quickly. This would explain the fluid inclusions (most fluid inclusions in quartz are not visible to the naked eye, thus leading me to believe these inclusions are not natural in origin), and the conchoidal fractures. "
] |
[
"This is certainly not calcite. Calcite has a cleavage plane when fractured, this is conchoidal. "
] |
[
"Is it possible we’ve permanently eliminated some strains of colds and flu with the year long quarantine?"
] |
[
false
] | null |
[
"Yes, maybe. There are a couple of strains that there have been zero reported cases of and scientists think they may have gone extinct. Which is good news for flu shot makers because they just hope they are right about which strains they develop vaccines for months in advance of flu season. Fewer types of flu strains means they will have higher likelihood of picking the correct strains to vaccinate against."
] |
[
"There's a good explanation of this at ",
"StatNews",
". ",
"it appears that one of the H3N2 clades may have disappeared — gone extinct. The same phenomenon may also have occurred with one of the two lineages of influenza B viruses, known as B/Yamagata.",
"Neither has been spotted in over a year. In fact, March of 2020 was the last time viral sequences from B/Yamagata or the H3N2 clade known as 3c3.A were uploaded into the international databases used to monitor flu virus evolution ...",
"--",
"A pandemic upside: The flu virus became less diverse, simplifying the task of making flu shots",
"This isn't saying, by any means, that influenza, or human influenza, or even human influenza subtypes have gone extinct. The \"strains\" being discussed here are quite narrow lineages. However, it's significant because they represent antigenic subsets. In the case of the B/Yamagata lineage, it's one of two major influenza B lineages that are included in the standard (quadrivalent) seasonal vaccines. If this lineage is genuinely extinct, then it might be possibly to go back to the trivalent vaccines and still get good coverage of the B subtypes, which would be a pretty big win. ",
"The H3N2 lineage isn't as big a deal, but if it's extinct it would simplify choosing which H3N2 group to include in vaccines. H3N2 is a very complicated collection of distinct lineages, and removing one of these major groups would make strain selection for vaccines easier and hopefully more accurate.",
"If the global pool of flu viruses has truly shrunk to this degree, it would be a welcome outcome, flu experts say, making the twice-a-year selection of viruses to be included in flu vaccines for the Northern and Southern hemispheres much easier work.",
"--",
"A pandemic upside: The flu virus became less diverse, simplifying the task of making flu shots",
"How confident can we be that these lineages are gone? On the one hand, it's been difficult to get a lot of influenza viruses to analyze, because there haven't been many cases. But the flip side is that the cases that did happen, got assessed more deeply than usual -- the whole influenza analysis conveyer belt, that's geared up to deal with hundreds of millions of cases each year, now focused down on a mere few thousand. So it's certainly possible that these missing lineages are hiding out somewhere, but it's not as if experienced, careful people haven't been looking for them.",
"(Why were there so few cases of influenza? Probably the social distancing and masking used to suppress COVID. Why did it work so well on influenza? Because human influenza is much less transmissible than SARS-CoV-2. The R0 [or at least the contemporary Rt] for influenzas are around 1.5 or less; for SARS-CoV-2, probably around 4-5, considering the variants. That means even a small reduction in transmissibility -- say, dropping it by 0.5 -- would have a major impact on influenza, dropping it below the sustainable level, while having a much smaller effect on COVID.)"
] |
[
"The flu viruses generally have animal reservoirs. Things like bird flu and swine flu are named as such because those are the animals they cross over to humans from. For this reason they will come back once people stop with the various protection measures we are currently using."
] |
[
"Colonization of Venus"
] |
[
false
] |
On the Venus wiki page there is a small note about colonization of Venus. "Landis also makes a case for Venus as a target for human colonization. At 50 km above the surface, the temperature range is 0-50°C, the air pressure drops to 1 atmosphere, the gravity is 0.9 that of Earth, and the resources for life are plentiful.". I have looked at some of Landis papers but none of the ones on venus are free. My question is how would we survive? If we could design an aerial vehicle that would maintain a stable flight at approx 50km above the surface how would it be fueled? Is there enough sunlight for solar power at that level? So many questions that lead to more questions.
|
[
"This",
" article?"
] |
[
"As I recall, the theory was to use balloons of some sort to keep one aloft amongst the clouds. The big problem was corrosion, something that I have yet to read a solution for. I'm actually curious about what one would do for food, colonial expansion, the initial costs to doing this, and harvesting resources from Venus so as not to rely on sending supplies from Earth.",
"I would put the colonization of Venus as possible, but not probable."
] |
[
"A chemical atmosphere! Oh no!"
] |
[
"What do you know that nobody knew 10 years ago?"
] |
[
false
] |
How far has your field advanced in 10 years?
|
[
"Strict control of blood sugar kills critically ill patients.\nCooling patients after cardiac arrest saves lives.\nIt doesn't matter which inotrope you use as long as its not dopamine.\nIt doesn't matter whether you use saline or albumin to resuscitate critically ill patients unless they have a head injury.\nSteroids probably don't work in septic shock (an advance from probably do).\nActivated Protein C possibly doesn't work in septic shock (up from likely does).\nSmall tidal volume ventilation in ARDS saves lives"
] |
[
"Optical stimulation barely existed 10 years ago...now you have awesome stuff like ",
"this."
] |
[
"More like 13 years, but before 1998 people didn't know that the expansion of the universe was accelerating. Since then, WMAP has placed impressive constraints on the composition and history of the universe."
] |
[
"Would a star that’s about to supernova release an excess of gamma rays?"
] |
[
false
] | null |
[
"A star will show little activity as its death begins- there will be a whole lot of business going on with gamma rays and such when it goes off bang, but for a few hours before the actual event there is one marker we can detect of the coming supernova: neutrinos.",
"Since they pretty much ignore matter altogether, when the star's core starts to collapse in the cascade that will lead to the big explosion, the neutrinos will have already escaped the star and gone zooming off into the Universe. These days we can use our neutrino detectors to pick up the sudden cascades of the things, allowing us to predict were a supernova will be going off a short time before any other hint of the event reaches us."
] |
[
"We'll get a few ",
" of warning time if the supernova is in our galaxy or very close, maybe a few hours more for a few selected stars nearby. We expect a supernova with advance warning time every few decades or so. Maybe every 10-20 years now with improved detectors, I don't know, but certainly not something frequent.",
"You can sign up for alerts from ",
"SNEWS",
"."
] |
[
"Are there any upcoming supernovas that we could see?"
] |
[
"Is Corn Syrup really worse for you than natural sugar? If so, why?"
] |
[
false
] |
[deleted]
|
[
"TL;DR - It's not resolved, and if it's real it has to do with HFCS making you feel \"not as full\" as sucrose does.",
"In vitro studies show that fructose doesn't stimulate the production of insulin like glucose does ",
"1",
" Therefore, consumption of fructose is going to give rise to a different metabolic profile than consumption of glucose. ",
"Basically, this makes you eat more. This may be due to a direct CNS effect ",
"2",
" or mediated through the stimulation of leptin production by insulin on an hours-long time delay ",
"3",
" Leptin is thought to be a satiety signal; it makes you feel full. Basically, the insulin your body produces after a meal should make it so hours later you are still making signals that say \"We don't need to eat now\".",
"The trouble with this reasoning is that putting HFCS instead of cane sugar in your diet is not the same thing as replacing glucose with fructose. In fact, you never really eat glucose. You generally eat sucrose, and sucrose is what is called a disaccharide...it's a molecule of glucose chemically bound to a molecule of fructose. One glucose to one fructose...very close to the 45/55 ratio of glucose to sucrose you find in HFCS ",
"4",
"By this reasoning, ",
" sucrose with HFCS could have some negative effect, but not much, and probably not even measureable. ",
"So one camp says is should have an effect....and they have had their predictions confirmed:",
"HFCS is more likely to cause acute adverse effects than sucrose.",
"source",
". ",
"The other camp says it should have no effect....and they have had their predictions confirmed as well:",
"Sucrose and HFCS do not have substantially different short-term endocrine/metabolic effects.",
"source",
"Sorry....there's not a great answer here. "
] |
[
"You might be thinking of high-fructose corn syrup (HFCS), which is generally as bad as ordinary sugar, however has a higher amount of fructose as compared to sucrose. HFCS-55 is comprised of 55% of fructose and is used in beverages.",
"Fructose is the main issue here. Excessive fructose has been linked to; obesity ",
"[1]",
" hypertriglyceridemia (high levels of triglycerides/fats) due to its metabolic pathway ",
"[2]",
" , gout due to the rate at which fructose is metabolised, resulting in phosphate depletion which in turn produces adenosine and inosine monophosphate (IMP) ",
"[3]",
"This being said, sucrose is one part glucose: one part fructose, and excessive amounts of sucrose can cause result in similar conditions presented above, HFCS just contains more fructose which is the key element here."
] |
[
"Agree - not fully resolved. What is pretty clear is most of us eat too much sugar of all kinds and that sugar in drinks is especially bad for us. Particulalrly from a weight gain perspective as many people don't process this sugar (mentally) as calories and thus our juices and cola contribute to overeating"
] |
[
"Why doesn't normal wet sand at the beach turn into (or gives the effects of) quicksand?"
] |
[
false
] |
[deleted]
|
[
"That's not really true; quicksand ",
" exist, it just doesn't behave the way that it does in the movies. So it's possible to sink into quicksand, but you wouldn't sink far enough to drown, and would be able to escape fairly easily. ",
"Sand grains tend to lock together fairly easily, so something has to cause them to be suspended in the water in order to become liquid; as you point out earthquakes could do that, as can upwelling water from a spring. I believe that to get quicksand in still water you'd need something else in the mix (like clays or organic matter) to lubricate the grains and keep them from locking together; beach sands are quick homogeneous in size and thus lock together tightly. You can cause liquifaction in a localized area on a beach, though, by wiggling your feet in saturated sands - this is quicksand, just not very deep. "
] |
[
"Quicksand doesn't really exist. It's made up for movies. You're more buoyant than the sand and therefore don't sink. The sand is full of friction and holds itself together even under your weight. ",
"If for example something like a building was laying on some sediment with a bunch of sand and water underneath and an earthquake occurred. it is possible for the foundation to sink into the earth causing the building to collapse. That's a much more likely scenario than a human actually getting their head sucked under by quicksand."
] |
[
"When I was young, quick sand was my biggest fear. I thought it was very common and people died from it all the time."
] |
[
"How many trees would each person have to plant for our civilization to become carbon neutral?"
] |
[
false
] | null |
[
"You could possibly substitute the question with: \"how many hectares of land would be need to grow biomass to replace our fossil fuel use\".",
"Global fuel use is somewhere around 160,000 Twh.",
"Miscanthus grass can ideally produce 17 t/Ha (more like 10 in reality) per year, each tonne delivering 3.6Mwh.",
"So we would need at least 24 million square km of biomass to replace our fossil fuel use.",
"For comparison, grazing land worldwide is about 33 million square km.",
"https://en.wikipedia.org/wiki/Agricultural_land#Area"
] |
[
"So... like 3?"
] |
[
"Yes, they decompose but only after a long lifetime of drawing carbon from the air and building carbon structures. And after they do die, the carbon released is not automatically put back into the air. It fuels growth on top of them and can also go into the ground."
] |
[
"Is it possible to reach LEO by balloon?"
] |
[
false
] |
[deleted]
|
[
"He highest altitude free fall jump was ~19.5 miles (~102,000 feet, or 2.5 times the cruising altitude of commercial planes), I believe although I'm not certain, that this is also the highest manned balloon. LEO is ~1200 miles. ",
"While its theoretically possible to build a buoyant object to reach closer to those heights, we haven't discovered a light enough material to build a rigid frame lighter than air vehicle out of that could make it happen. ",
"Even if you could get somewhere closer to the 1200 miles needed to reach LEO, you'd have to build a large enough balloon/lighter than air vehicle to carry the fuel for the rocket and launch apparatus (if there is one) as well. ",
"You'd save on part of the launch platform, but increase the expense and difficulty significantly on your alternative. You also have to overcome massive material sciences problems, which may very well be insurmountable, to even consider this a viable option. "
] |
[
"The important thing to understand here is that orbit isn't really about altitude at all—the important part is velocity. If you took a balloon up to ~225mi (where the ISS orbits) and jumped, you'd just fall the long, long way back to the ground. If the ISS came near you, it would whiz past at about 27000mph."
] |
[
"Just read that the gravity pull on the ISS is 90% of the earth. Guess you still would need a big rocket to get the same speed though."
] |
[
"If gravity bends space towards objects, why does light bend around the sun?"
] |
[
false
] |
What am I misunderstanding? I think I'm getting caught up in semantics..
|
[
"Nothing is pulled or pushed. Light travels in a perfectly straight line at all times, it's just that in the presence of a gravitational field (such as due to the Sun), \"straight\" turns out to mean what happens in the picture. ",
"Basically what I'm trying to stress is that light reacts to gravity because gravity ",
" the distortion of spacetime, and light travels through spacetime. In the distance scales we commonly deal with, gravity can be thought of as a force that pulls massive objects around in proportion to their mass, but this is only a working approximation. "
] |
[
"http://www.astro-photography.net/images/figure%202%20relativity_light_bending.jpg",
"Light that would hit the sun if you ignore gravity, still hits the sun. Light that is going around the sun and wouldn't hit the earth (ignoring gravity) will actually curve in a bit when you consider gravity.",
"It is not curving away and then curving back. I apologize if I completely misunderstood your question."
] |
[
"No, I think that's exactly what I mean. So light from a star that we would not be able to see behind the sun (ignoring gravity), that would be traveling into space is \"pulled towards\" by the sun by gravity to hit Earth?"
] |
[
"Is the expression \"a hole in the space-time continuum\" meaningful in any way, or is it \"not even wrong\"?"
] |
[
false
] |
I've occasionally heard this expression in various movies or television shows. Does it refer to something that is theoretically possible, or is it just nonsensical jargon? Thanks!
|
[
"It's a pretty decent way of describing ",
"black holes",
" in non-technical terms.",
"Einstein found, while developing his theory of special relativity, that space and time are intimately related to each other. If I'm sitting on Earth and you're in a rocketship moving past the Earth, then we'll measure distances and times in different ways, and won't agree on the results. This tells us that space and time need to be considered together, as a single entity we call \"spacetime.\" (Adding \"continuum\" at the end is a thing sci-fi writers usually do. It's not incorrect, but it also doesn't add any content.)",
"Spacetime can be thought of as a four-dimensional surface, kind of like how a flat piece of paper is a two-dimensional surface (only spacetime has an extra spatial direction and also includes the time direction). Einstein's theory of general relativity tells us that spacetime doesn't have to be flat like that paper; it can also be curved, like the surface of a sphere. One way you can tell that the surface of a sphere is curved is that two parallel lines ",
" intersect, contrary to what you'd learn in geometry class, where you learned rules that apply to flat surfaces.",
"The fact that spacetime can curve has a dramatic consequence: it's responsible for the gravitational force! So a massive object will bend spacetime such that particles travelling on the straightest possible paths will inevitably fall towards it, in exactly the way that we see gravity behaving. This is because spacetime is curved like the sphere I mentioned; if you drop particles from all around a massive object, they'll follow parallel paths that intersect at the center of that object.",
"Einstein's theory of general relativity doesn't just explain ",
" gravity happens, but tells us a few new things about what gravity can do in extreme situations. It turns out there's an unusual consequence to general relativity when you have a really, really dense object. The logic is like this: nothing can travel faster than light, so if an object is dense enough that you can get so close to it that light can't escape, that means ",
" can escape its gravitational pull from that point inward. (This point is often called the ",
".) That means that if you have a star that dense, the forces keeping its molecules apart aren't strong enough to counteract gravity, and it will collapse inward and inward until it's nothing but an infinitely small, infinitely dense point.",
"But physics doesn't like infinities, and so when this happens, the mathematics of general relativity kind of breaks down. We interpret this infinitely dense point - the ",
" of the black hole - as a place where spacetime itself is no longer well-defined. A slightly more poetic way of saying it is to call it a hole in spacetime, because it's a single point where spacetime effectively doesn't exist.",
"It's worth taking a minute to connect this mathematical picture with what we know about the real world. General relativity has passed all the tests we've thrown at it with flying colors (except for maybe one or two exceptions, which likely don't have much to do with black holes). So it seems to be, if not completely right (which it isn't), an extremely good fit to experiments in almost all cases. One of the cases where we ",
" it can't be right is at the singularity of a black hole! This is because in that tiny region, we need to use the physics of the very small, a theory called quantum mechanics. Unfortunately, quantum mechanics and general relativity don't mix well, and don't yield sensible answers. We need a theory of ",
" to describe what happens near the singularity. We don't really know what the right theory will say. Maybe it will turn out that, due to unforeseen quantum effects, the singularity isn't really a singularity, and there's no hole in spacetime after all."
] |
[
"Nice explanation. You should also mention that singularities have not been shown to exist. There is no evidence that black holes have singularities. All we know about black holes is essentially that they are very dense and non-luminous.",
"Edit: I guess you kinda said that towards the end. Anyway, good post."
] |
[
"I touched on that but didn't make it explicit. Actually, I did mean to (and then forgot to) write a bit about what we do know about black holes, which is what you say: we've seen the gravitational effects of objects which are so dense that they probably can't be anything else."
] |
[
"how much force would it take to alter the orbit of a planet like earth or mars?"
] |
[
false
] |
So I was watching Futurama why not and in two episodes, Crimes of the Hot and A Farewell to Arms, Earth and Mars are pushed out of their orbits. Now obviously it's a cartoon, complete with disembodied heads and various other future-y crap but it got me thinking, what would it take to push or pull a planet in a stable orbit into an eccentric one in terms of total force? Would the planet somehow self-correct? feel free to answer with the aid of futurama memes.
|
[
"The big question here is \"how much do you want to alter its orbit?\" Any amount of force will technically alter a planet's orbit, but unless it's a very large force, it won't be detectable.",
"That said, I saw the Futurama episodes, too...let's say we're trying to alter Mars' orbit to one that will be very elliptical, having its apogee (furthest point) at the current Mars-Sun distance, and perigee (closest point) at the Earth-Sun distance. ",
"To do this, we'd have to slow down Mars' tangential orbital speed by a certain amount. If we did this just right, it would fall inward towards the Sun as it also orbited, reaching the Earth-Sun distance on the opposite side of its orbit, then loop back out again to return to the point where we did the Mars course correction.",
"First, lets get some numbers we'll need:",
"The Mars-Sun distance is, on average, 228 million kilometers",
"The Earth-Sun distance is 150 million kilometers.",
"Mars' mass is 6.42 x 10",
" kilograms",
"The Sun's mass is 1.99 x 10",
" kilograms",
"The gravitational constant is 6.67 x 10",
" in mks units",
"We'll be using the vis-viva equation for this calculation, which is:",
"V = [G*M_sun * (2/r - 1/a)]",
"...where V is the velocity of the planet in its orbit, G is the gravitational constant, M_sun is the Sun's mass, r is the current Sun-planet distance, and a is the average Sun-planet distance over the entire orbit. For circular orbits, r=a and this equation simplifies to:",
"V = [GM/r]",
"If we assume Mars is currently in a circular orbit (which it's not exactly, but hey, close enough for government work), then it's currently moving with a velocity of:",
"V = [(6.67e-11)(1.99e30 kg) / (2.28e11 m)]",
"\n = 24100 m/s",
"...or about 54,000 mph. Now, we want to slow it down to get it to an orbit with the current Mars-Sun distance at apogee and the current Earth-Sun distance at perigee...which means the average distance over that entire orbit will be the average of the Earth-Sun and Mars-Sun distance = (228 million km + 150 million km)/2 = 189 kilometers.",
"Moreover, we're going to exert our force to slow it down when it's still in its current orbit, so when it's still at the Mars-Sun distance. The vis-viva equations works out to be:",
"V = [(6.67e-11)(1.99e30 kg) * (2/2.28e11 m - 1/1.89e11 m)]",
"= 21500 m/s",
"...or about 48,000 mph. Now, to get to your original question, how much force do we need to exert to change Mars' velocity from 24100 m/s to 21500 m/s? Using the term \"force\" is a bit ambiguous for this question since you could exert a weak force and decelerate the planet over a long time, or exert a strong force and decelerate the planet quickly.",
"What doesn't change is the amount of energy required to do this - whether you decelerate the planet over a long period of time, or decelerate it quickly, you'll end up using the same amount of energy. The equation for kinetic energy is:",
"KE = 1/2 m*v",
"...where m is the mass of the planet, and v are the velocities we've previously computed. The orbital kinetic energy the planet currently has is:",
"KE = 1/2 (6.42 x 10",
" kg)(24100 m/s)",
" = 1.86 x 10",
" Joules.",
"The orbital kinetic energy that Mars will have in its new orbit will be:",
"KE = 1/2 (6.42 x 10",
" kg)(21500 m/s)",
" = 1.48 x 10",
" Joules.",
"The difference between these two - 3.8 x 10",
" Joules - is how much energy you'll need to put into the system to put Mars onto its new Earth-glancing orbit. ",
"To give you some idea of just how much energy this is, the world generation of electricity per year is only 6.8 x 10",
" Joules, about half a trillion times less than the energy you'd need to move Mars. In other words, still way, way less than humanity is currently capable of generating. On the other hand, the total output of energy from the Sun in a single day is about 3.3 x 10",
" Joules, not far off from what you'd need.",
": You'd need about half a trillion (500 billion) times the amount of energy generated by the entire world each year to put Mars into an Earth-glancing orbit."
] |
[
"Your last parenthetical addition has a typo. e=1 is parabolic, you typed e=0 twice =P"
] |
[
"Intrigued, a bit of googling got me ",
"this",
". The earth's orbit doesn't change, just that the redistribution of mass affects the earth's spin around it's axis. It's negligible, kind of like the nanoseconds of time dilation one would experience from traveling in airplanes."
] |
[
"Dear askscience: Developing a nuclear fusion reactor so we can ... heat water to generate steam to spin a magnet inside a copper coil seems like caveman overkill. Is there really no better way to generate electricity?"
] |
[
false
] |
[deleted]
|
[
"Turbines are easily the most cost efficient means of converting heat into electricity that we have. A supercritical water turbine can reach an efficiency of 50%. In comparison, even the most efficient high-tech solar cells we have only get about 40%, with your typical solar panel at 10%. In principle Stirling engines can get a higher efficiency, but it's expensive to build Stirling engines rated for a large power output. ",
"What makes turbines so useful is that they scale extremely well, allowing you to relatively cheaply build a large device with a high efficiency. It is also relatively straight forward to optimise the turbine's properties to make it as efficient as possible for a given power plant. ",
"As a bonus, the turbines can be made to spin at a rate which matches the AC current used in most electric transmission lines. This frequency is important because it determines how much energy is wasted through capacitive losses during transmission. Changing the frequency of an AC current is difficult to do efficiently, so if your generation scheme can create the right frequency to begin with, it simplifies things considerably. "
] |
[
"I see a massive ammont of heat-energy being lost during these processes?",
"Yes. This is unavoidable due to the laws of thermodynamics. What happens in practice is that whereas you get a large quantity of waste heat, the temperature it is discharged at is quite low, and hence it cannot be efficiently converted into electricity. This is not a technological limitation, it's a fundamental principle of physics. ",
"The only way to mitigate this problem is by increasing the temperature of your reactor/burner/fusion plasma or whatever. Material constraints limits how high a temperature you can reach, and thus the conversion efficiency. ",
"It is possible to collect the heat and use it to keep buildings warm, but efficiently turning the waste heat into electricity is not going to happen. "
] |
[
"There are plenty of ways to generate electricity. A steam turbine works because a voltage is generated when a magnetic field and a current carrying conductor are in close proximity to each other with relative motion. ",
"Several other ways to generate voltage are: ",
"piezoelectric ",
"http://en.wikipedia.org/wiki/Piezoelectricity",
", ",
"thermal ",
"http://en.wikipedia.org/wiki/Thermoelectric_effect",
", ",
"magnetic field (what I've already described), ",
"photovoltaics (",
"http://en.wikipedia.org/wiki/Photovoltaics",
"), ",
"chemical ",
"http://en.wikipedia.org/wiki/Electrochemical_cell",
", ",
"and friction (",
"http://en.wikipedia.org/wiki/Static_electricity",
"). ",
" and betavoltaics (",
"http://en.wikipedia.org/wiki/Betavoltaics",
") Thanks, Silpion!",
"Of these six methods, obtaining electricity from a spinning magnetic field in close proximity to a current carrying conductor is the most cost effective way to produce electricity on a large scale. The best way we currently have to do this is by forcing steam to spin a turbine, although wind and wave turbines are starting to show promise (",
" I forgot about hydroelectric power. That uses gravity to make water spin a turbine.).",
"The idea now is to figure out cheaper and more efficient ways to make steam, which is where fusion comes in. ",
"Source: I was a Nuclear Technician with an Electronics specialty for the Navy, and currently work in the energy sector.",
" For readability.",
" Thanks, IlovePopcorn"
] |
[
"What happens to a photon when it collides with solid matter?"
] |
[
false
] |
Do all photons reflect off the surface of dense objects, or do some of them "vanish" on impact? How does light interact with matter to heat up a surface?
|
[
"Yes, photons cease to exist when absorbed."
] |
[
"No object has perfect reflectance, so some photons will be absorbed. If the energy absorbed is transformed into molecular motion, this will manifest as an increase in temperature."
] |
[
"What properties of matter is it interacting with at tiny scales? Is it the electromagnetic force of the matter, its mass or something else?"
] |
[
"Abnormally Long Arm hair, Can Anyone Explain This?"
] |
[
false
] |
Hi everyone, ever since I was a kid I noticed this 1 hair on my arm that lacked pigment and seemed to grow without any limit and it grew relatively quickly. I used to pull it out, but as I got older I realized I needed to observe its true potential and see how long I could really grow it. I researched the world record for the longest arm hair which turned out to be about 5.3 inches. I set my goals on the world record and monitored the growth. Over about the course of a year the arm hair grew to about 4 and 1/2 inches. A couple weeks later I realized it was gone and my dreams shattered. This is where it gets weird though, the arm hair never showed up again for over 1 and 1/2 years. I checked it everyday for those 1 and 1/2 years and all of a sudden it finally popped up again. Over the past few months it has grown to almost 3 inches. All of this leaves me with questions. Why is only 1 of my arm hairs capable of growing like this? Why did it take so long for the arm hair to grow back? Why does this arm hair grow so quickly? Why does it lack pigment? Is there a way to increase its lifespan? EDIT: is a picture of it in December 2009
|
[
"C'mon guys, the rules are right over there ---->",
"Keep discussion on topic and focused on answering questions scientifically.\nPersonal anecdotes and layman answers are not acceptable posts.",
"I don't want to have to downvote any more of you."
] |
[
"Thanks! but any ideas on why this hair grows significantly longer than any other hair on my arm? Also it feels different, I'm not sure why."
] |
[
"Thanks! but any ideas on why this hair grows significantly longer than any other hair on my arm? Also it feels different, I'm not sure why."
] |
[
"Are there any materials we know of that absorb visible light while letting through infrared light?"
] |
[
false
] | null |
[
"Germanium is opaque to visible light but transparent in the mid-IR range. It's often used in IR optics.",
"See for example this commercial supplier of germanium lenses: ",
"http://www.tydexoptics.com/materials1/for_transmission_optics/germanium/",
"In general, in order to absorb light there has to be an electronic (or vibrational, for IR) excitation with an energy corresponding to the energy of the frequency absorbed. Elemental germanium has a band gap of 0.67 eV, meaning photons with less than this energy cannot be absorbed by electronic excitations. This corresponds to a wavelength of longer than 1.8 µm, which is in the mid IR. Shorter wavelength photons are absorbed, making germanium opaque to visible light. Germanium crystals also don't have vibrational modes that strongly absorb IR.",
"Some other semiconductors (for example, cadmium telluride or silicon) also block visible light but not IR. The principle is the same as what I explained above for germanium."
] |
[
"We often take advantage of silicon's transparency to IR light to align multiple layers of features in microprocessor fabrication between the front and back sides of the wafer.",
"Our own vision falls off with light around 0.7 microns in wavelength, and to see through silicon you need light of 1.1 micron wavelength, so you have to use a camera that picks up infrared light in addition to an infrared light source. With germanium you need to go a bit deeper like you said, to 1.8 micron photons.",
"But in this case it isn't too hard to pick up the infrared light, because this is still very \"near infrared\"; very close to our visible range, so the photons each have quite a bit of energy and we don't get too worried about needing to have a super-sensitive and noise-free detector like we do for thermal infrared (very \"far\" infrared, quite distant from visible spectrum, around 8 - 15 microns in wavelength, this is what FLIR sensors see)."
] |
[
"Yes! Germanium is commonly used for lenses on infrared cameras and is opaque to the visible spectrum but transparent in infrared. This link has some good information about some other materials which exhibit similar properties: ",
"https://www.rp-photonics.com/infrared_optics.html"
] |
[
"How can I tell if a bond will be ionic or covalent?"
] |
[
false
] |
I understand the difference between ionic and covalent bonds: With ionic bonds, an atom which pulls strongly on electrons (usually something from the right side of the table) steals an electron or electrons from an atom which pulls less strongly on electrons (usually on the left side of the table). Because the atoms (now ions) are opposite charges they attract. Covalent bonds occur when both atoms pull on electrons with relatively equal strength. Since neither atom is strong enough to take electrons from the other, they fill their valance shells by sharing electrons on molecular orbitals. The problem I have is that right now it's a matter of memorization for me which bonds are ionic and which are covalent. I know, for example that in table salt, the Na and the Cl are bonded ionically, while in methane the C and the Hs are bonded covalently. What I don't understand is how to tell whether an arbitrarily-chosen bond is ionic or covalent. Let's say, for example, I want to know which bonds are ionic and which are covalent in Cu2SO4. I can guess that the SO4 bonds are all covalent and the bond with the Cu is ionic based on the fact that the covalent bonds stay intact in most reactions involving copper sulfate, but I don't have any way of verifying this. My guess is that there's some way to calculate the pull which each atom exerts on its electrons, and that at some difference in pull the stronger atom would bond ionically rather than covalently, but I don't know how to do that.
|
[
"Simple answer: Ionic bonds require a metal. Sodium, Magnesium, something like that.",
"Longer answer: Bonds don't fall into two categories, it's more like a spectrum. Ionic bonds are on the extreme end of one side, and covalent bonds (in all their myriad forms) occupy the other 80%.",
"Think of it like this:",
"An atom's pull on electrons is called ELECTRONEGATIVITY",
" and can be calculated pretty easily. Unfortunately, this is more to memorize. (Quick and fast rule: Fluorine Oxygen Chlorine Bromine. These guys are the bullies on the playground, taking everyone's electrons.)",
"Studying up on metals and nonmetals will help a lot.",
" Memorizing your polyatomic ions and learning your periodic table will be a big help. Keep referring back to your periodic table and eventually you'll notice the trends. Talk to your teacher if you're fuzzy on the subject, a face-to-face conversation will always help more than somebody on Reddit."
] |
[
"A general rule of thumb is that if the electronegativity difference between two bonding atoms is 2.0 or greater, then the bond is considered to be an ionic bond."
] |
[
"Cool, the longer answer was what I was looking for. However, I have one more question:",
"Let's say we've got Mg, which has two electrons. Let's say an F atom comes along and ionically bonds with the Mg, making Mg+ and F-. Now, my guess is that the Mg+ ion's electronegativity is higher. Is that the case?"
] |
[
"If I put a pair of telescopes in parallel, will the effect be multiplicative or additive?"
] |
[
false
] |
Suppose I have a pair of 15x zoom telescopes (for example, I separated a pair of 15x zoom binoculars) and laid them end-to-end. Naturally there'd be some loss of field-of-vision when looking through them both. But would the resulting zoom level be 15 (i.e. 225x)? Or 15*2 (i.e. 30x)? Or something else entirely? Or am I oversimplifying? clearly I mean in , not in . With .
|
[
"I think you mean in series..."
] |
[
"Just bear in mind that the fundamental operation of a telescope is not zooming or magnification; it is light-gathering. One can only obtain so much usable magnification without enough light. So telescopes with larger apertures are used to gather more light.",
"So in fact there are now telescopes that are more like your post's title: they are in parallel, and share their light in a process called \"aperture synthesis.\" (See ",
"Wikipedia article",
". Also ",
"the Very Large Telescope",
" article talks about its use as an astronomical interferometer—ie, using aperture synthesis.) Using multiple separate scopes allows you to simulate an aperture as wide as they are separated, giving you better angular resolution (maximum zoomability) than any one telescope singly."
] |
[
"Yes! Thanks, sorry."
] |
[
"What does Alzheimer’s actually do to the brain?"
] |
[
false
] |
Why is it slow acting in some cases and fast acting in others?
|
[
"The presence of neurofibrillary tangles and beta amyloid plaques (which recently have sparked controversy). Lead to the degradation of the cortex of the brain. Dementia is the term used to describe impaired cognitive status. The severity of the disease is typically generally attributed to the amount of neurofibrillary tangles. A decrease in the neurotransmitter acetylcholine is present as well. Drugs that increase this neurotransmitter help with symptomatic management but do not slow the profession of the disease."
] |
[
"There's some new research that looked into how sleep protects against Alzheimer's. \"A study published in the journal Science revealed that cerebrospinal fluid carries these waste products away from the brain during deep sleep, acting as a guard to cognitive function . . . There’s also mounting research to suggest that getting too little—or even too much—sleep could increase your risk for Alzheimer’s disease.\"",
"\"",
"https://sleepeducation.org/nightly-brain-wash-protects-against-alzheimers-disease-during-sleep/",
"https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3001233"
] |
[
"I was taught something similar in uni maybe 3 years ago, sleep and quality of sleep is huuuuge. It's been found that in people with lack of sleep, that there's an abnormally high level of specific plaques and more related to dementia etc.",
"Shift workers are getting funked over big time, can't imagine how bad 30 years of those shifts are on the brain."
] |
[
"Is there any study on wheter the increase of depression rate in the last decades is an actual increase or an increase on diagnosis only?"
] |
[
false
] | null |
[
"This article might be a good starting point for you:",
"Hidaka, B. H. (2012). Depression as a disease of modernity: explanations for increasing prevalence. ",
" 140(3), 205-214.",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3330161/",
"I think a fair summary is that as countries develop, we notice and diagnose a lot more depression. This could be due to changes in other factors like less exercise, poorer diet, obesity, changing social interaction etc. Or perhaps as your physical needs become met, your psychological needs become central."
] |
[
"They also loosened the definition of depression so mild sufferers can also seek medical assistance. Which is good. They’ve made it far more “mainstream” so obviously there would be an uptick. A decent study would take into account the times that the definition changed and show accordingly on their stats and would or at least should mark them out. Always remember the source of any “study”. Is it funded or aka bias in some way. People who want funding to combat the uptick in community depression would try to minimize that particular information where their detractors would focus on it. Any study that doesn’t show and mark out those divinations isn’t a study worthy of note"
] |
[
"I think people would be interested if a psychologist could speak to how the publication of DSM-5 in 2013 changed the diagnosis of depression."
] |
[
"How do different kinds of objects cool in a vaccum?"
] |
[
false
] |
I have seen heated discussions in more than one thread about how, and how quickly, different things would cool in a vacuum. So, how fast would a human body, a solid metal object, or a large amount of liquid cool down in a vacuum, assuming there's no siginificant radiaition heating it up?
|
[
"A large solid object in a vacuum will cool via radiative cooling. Assuming it is hotter than the surrounding environment, it will emit more radiation than it absorbs until it comes to an equilibrium with the radiation in the environment.",
"A large amount of liquid in a vacuum will cool via radiative cooling as well as by evaporative cooling. The radiative cooling is the same as above. The evaporative cooling is where the more energetic molecules of the liquid are expelled from the surface due to the zero partial pressure in the environment (the vacuum). The liquid will continue to evaporate until it is completely dissipated or until it freezes.",
"The human body would be considered a mix of the two. It has fluid, but has a large amount of solid as well."
] |
[
"Statistical thing. All objects radiate energy via black body radiation. Relatively warm objects will radiate more than they absorb."
] |
[
"Good answer. I ",
"dug up",
" a ",
"couple videos",
" of low pressure water freezing for the skeptical."
] |
[
"Why don't true white light lasers exist? Or will they ever possible? I know we can make mock ones by combining a few elements, but it's not the real thing. Will we ever be able to combine many gasses to produce a whiter light?"
] |
[
false
] |
I read that you can combine Kr with Ar to produce a "white light laser", but it's not near true white light. Kr emits 11 different wavelengths, which is a lot but I was wondering how much more you could create. If you can combine Kr and Ar, can you combine large combinations of elements to produce even more wavelengths of light? What's the limit?
|
[
"It is possible to do this if you can find a gain medium that has a wide enough spectral width. So this would be essentially possible to do with a gas laser.",
"However, femtosecond pulsed lasers do exist with solid state gain media (Ti:Sapphire, as one example) and these do have quite large spectral widths. According to ",
"this source",
", a 1-fs pulse would have roughly the same spectral width as the visible spectrum. I think pulses of that length have been achieved, but not in the visible wavelength range. 100-fs is I think fairly routine, there are commercial companies that sell them. These would have spectral width of order 10 nm.",
"So at least in principle, you could have a handheld white laser, if you found the right gain medium. Just a simple \"engineering\" problem =)"
] |
[
"A ",
"krypton laser",
" can produce 11 wavelengths of light. It's a step function instead of all possible wavelengths, but I quoted \"white light laser\" for a reason.",
"My question is can you create a tiny, powerful beam of light, similar to that of a regular ol' laser you can pick up almost anywhere these days, but have it be seemingly \"white\". I never see these in stores, I only see red, blue and green lasers.",
"If they can combine Kr and Ar to produce something that is close in appearance to white light, why aren't these more popular and is it possible to combine even more gasses to get an even whiter light?",
"I really don't think your answer attempted to address my post. Even Wiki page for ",
"laser",
" states:",
"And although temporal coherence implies monochromaticity, there are even lasers that emit a broad spectrum of light, or emit different wavelengths of light simultaneously.",
"The Wiki page for 'ion laser' is short, and it leads me to believe the only limitation is cooling power, but it doesn't expand at all on that. Why do they need great cooling power? Why is it so much harder to excite an ion? Etc."
] |
[
"With the right gain medium how would you propose spacing the reflective surfaces such that all wavelengths add constructively? "
] |
[
"Does the airflow behave differently after Mach 1? If so, how?"
] |
[
false
] |
Hello there. Well, the question basically sums it up. I went to a technical school and kind of know how the air molecules behave or "flow" under certain circumstances, but I have no idea nor I was able to find any information about if it behaves in a particular manner after it surpasses the speed of sound
|
[
"yes it does, you usually split flows into subsonic (> Mach 0.8), transitional (0.8-1.2), supersonic (>1.2) and hypersonic (> 5). Search for gasdynamics, there you can find informations about it. You for example get heat effects and shock waves over mach 1.2. Under mach >0.3 you can even see most flows as incompressible."
] |
[
"The shockwave starts to behave differently at these speeds. My knowledge is limited to supersonic propulsion, but Ramjets are most efficient at transonic and supersonic velocities, and rely on slowing the airflow down to subsonic speeds before combustion and producing a supersonic exhaust and a ton of thrust. As we get to mach 3-7ish, we enter Scramjet territory, which does supersonic combustion. It has a different intake shape to manage the shockwave produced and to effectively mix the fuel into the supersonic flow. Once you get even faster, at mach 8-11, we hit Schramjet territory. At these speeds, the shockwave directly causes the combustion, and there is a continuously burning shockwave in the engine. Geometrically, schramjets and scramjets are very similar, but an extra bump near the rear of the engine helps control this shockwave. ",
"The reason this all matters is that detonations are way more efficient than deflagrations (~25%, according to wikipedia), and at hypersonic speeds, we can actually design air breathing engines which can detonate the fuel/air mixture. In your normal jet engines (and even in afterburning jet engines), the fuel/air mixture deflagrates, which is less efficient."
] |
[
"Is there a qualitative change around mach 5, or is it just a more extreme version of supersonic flow?"
] |
[
"AskScience AMA Series: We're Heather Job, Corinne Drennan, Jonathan Male, and Yangang Liang from the Pacific Northwest National Laboratory. We use robots to advance energy storage and bioenergy, helping to speed up discoveries. National Robotics Week is April 3-11, help us celebrate. AUA!"
] |
[
false
] |
Domo arigato, Mr. Roboto! Hey Reddit, happy National Robotics Week! These days, robots are not just fodder for 1980s Styx songs. Nor are they always famously featured in TV shows or movies, like Rosie from The Jetsons. At the Pacific Northwest National Laboratory, robots are the workhorses that help our scientists advance energy storage and bioenergy research. For example, robotic platforms are integral to helping us investigate and develop materials for energy storage applications to bolster modernization of the nation's grid. These robotic partners help our scientists do more experiments with significantly lower labor and material costs than if conducted manually. They also allow us to effectively test formulations - literally thousands of them - for the most optimal materials conditions. In the bioenergy realm, robots housed in our handle routine and repetitive tasks and empower our researchers to investigate materials while accelerating understanding and production of biofuels and bioproducts. With the robots' help, multiple experiments can run in parallel, helping us perform hundreds more experiments than with manual methods. One catalyst testing instrument can reduce four months of research to just two weeks. Additionally, one sample preparation robot can produce more than 200 formulations in a single day, something that would take a researcher a full week to do - not to mention keeping track of it all, often with greater accuracy and precision, while avoiding repetitive strain injury. Our research in grid energy storage and bioenergy is typically supported by the U.S. Department of Energy's and , respectively. We "bot" you think all this robot talk is cool! We sure do. Come ask us questions about our cool energy storage and bioenergy breakthroughs and how our robots are helping. We will be back at noon PDT (3 PM ET, 19 UT) to answer your questions! Username:
|
[
"Probably too basic a question for this AMA, but i wonder where do you see energy storage, and bioenergy in 10 to 20 years? And what is your goal for those 10-20 years! ",
"On a side question I guess for anyone that would like to answer, how realistically is it for a battery in the \"near\" future, for example that of a phone, to last more than a couple of days at best?"
] |
[
"For energy storage, it has been identified as a key to climate change mitigation. Globally, only 3% of power capacity is being stored. The energy storage capacity needs to be doubled or tripled in 10-20 years. To realize this, we need low-cost and high-efficiency energy storage technologies. With the cost decreasing and energy density increasing, lithium-ion batteries should still dominate the energy storage sector in the future. ",
"I think for biomass, it is necessary to broaden the response to carbon, where will you find your carbon in 10-20 years? Initially, you will see waste carbon play a key role as a source of carbon because it solves another problem—our landfills and too much carbon left in forests and fields. Later, you may see bioenergy purpose grown sustainable resources. At 20 years and beyond, you will see utilization of carbon dioxide . ",
"It is very optimistic for lasting for a few days more by increasing energy density of batteries and decreasing the energy consuming of the electronic devices."
] |
[
"If you had an ideal realization of your goals, what would it look like? How would you like to see the power grid advanced?"
] |
[
"How do muscles gain mass when you exercise?"
] |
[
false
] |
First post here and I have no idea whether I sound stupid or not, but how exactly do muscles gain mass when you exercise? Basically if I am to lift weights on a daily basis anyone would know that I'd eventually became stronger and my muscles will increase in mass but how exactly does it increase in mass?
|
[
"Muscles are filled with actin and myosin filaments that do the actual work of contraction. After exercise, the muscle cell releases signals that promote the synthesis of new actin and myosin filaments. This may partially be stimulated by breakage of existing filaments. Either way, the muscle cell ends up with more filaments than before, and grows to accommodate them. This is known as hypertrophy.",
"In some cases you might also get hyperplasia, in which muscle cells divide to produce new cells. But most of the time, increased bulk is primarily due to hypertrophy."
] |
[
"Skeletal muscle stem cells reside under the basil lamina of each myofiber. Damage due to increased metabolism when pumping iron cause these stem cells to form myoblasts, which divide and fuse to existing fibers. You don't make new fibers, you just add more nuclei to make more contractile proteins."
] |
[
"So you can tell when a muscle cell has been recently repaired due to the peripheral nuclei.",
"Actually recently/newly regenerated muscle cells have central nuclei. Peripheral nuclei are only in mature myofibers. "
] |
[
"How does this \"real\" invisibility cloak work?"
] |
[
false
] |
According to a camouflage company, they've created an . They've put up mockups of the design that apparently bend light around the material? But wouldn't that just make a sheet of that material invisible rather than the thing behind it? Can someone explain the physics/optics behind how this purported invisibility material?
|
[
"Roughly speaking, you can make light \"stick\" to tiny periodic conducting structures and bend this sticky light around a surface and release it behind it in a way that removes all information of the surface as the light travels past the surface. I think such a device could actually be constructed for selected wavelength above the visible spectrum, but at the visible spectrum and below it will be technically challenging to create all of these very specific tiny structures (the structures have to be as tiny as the wavelength, which is very tiny for the light you see, not to mention that you'll need different structures for all the possible wavelengths).",
"edit: That's not what these guys are doing. They are propably selling LED fabrics."
] |
[
"How? It can't. This company normally manufactures ",
": ",
"http://www.hyperstealth.com",
"This is just a marketing ploy. Noone honestly things this company somehow secretly financed a massive high-tech research program to develop what amounts to an invisibility cloak like their pictures portray. It's all photoshop and PR, until they show some verified videos or demo it in person to the press or something."
] |
[
"They did demo it in person to the press. One reporter verified that the mockups are accurate.",
"\nEdit: I will admit that it could be a conspiracy/pyramid scheme though."
] |
[
"Could we heat up Mars?"
] |
[
false
] |
I keep on hearing talk of human exploration, and eventually possible terra formation of Mars. This got me thinking, is there anything we could do to heat up the atmosphere of the planet to above zero and free up the ice? It seems if you want to live on another planet have the temperature averaging -50C is going to be a problem. Sorry for spelling/grammar drunk
|
[
"Thicken up the atmosphere, which would make the greenhouse effect start a positive feedback effect with the CO2 caps, gradually making the planet warming.",
"A load of different ways have been proposed to achieve this, but they all require technology we don't really have yet - smash some comets/asteroids into the polar caps, skip some comets off the atmosphere so that they progressively lose their water into the atmosphere, blow up some nukes in the polar caps, etc. More long term methods could be just to add slight amounts of warming (e.g. Sax's windmills in the ",
"Mars trilogy",
"."
] |
[
"The northern region of Mars has has water deposits. Very pure water. ",
"Source"
] |
[
"The surface radiation environment is about the same as LEO, measured by Curiosity. A bit of shielding shouldn't be a problem."
] |
[
"Is the incidence of genetically-related disease lower in those who would be considered 'two or more races' as compared to those who would be considered one race?"
] |
[
false
] |
I ask because I remember learning about how cross-breeding between two inbred types of corn created a more durable, disease-resistant type of corn. Can the same be said of humans? I.e., is someone who is, say, half-Chinese half-African more likely to be immune to certain diseases or have greater immunological resistance than those who are mostly one race?
|
[
"1) Race is rather arbitrary, irrelevant, and somewhat silly. There are no hard lines between human \"races\" everything very much exists along a continuum. With some populations (which again will have muddled borders) with higher levels of homogeny (people are more genetically similar) you may see elevated levels of some genetic disease. This is particularly common with founder populations where a small group of people are the genetic ancestors of a large group (example 8 million people in Quebec are largely the progeny of 3,000 people). ",
"2) With respect to immunological diseases the answer may cut more ways. Higher levels of diversity may allow the MHC molecules of the individuals to respond to a higher diversity of antigens. Conversely infectious disease have a tendency to have reduced virulence in the populations they are derived from. Because of this it is possible that some individuals of a mix race background could loose the benefit of this attenuated virulence. With respect to this attenuation I believe that TB is a good example with Africans for example having reduced outcomes when infected with Asian derived TB. "
] |
[
"The idea of race is predicated on the idea of firm racial genetic boundaries that do not exist. "
] |
[
"I realize this. You need to drop the notion of race as focus on the notion of population which is much closer to the genetic reality. The notion of population also prevents the arbitrary aggregation of divergent populations into a single 'race' based upon idiotic and arbitrary assumptions. "
] |
[
"Why do so many animals happen to have 5 fingers/toes on each hand/foot (or paw)?"
] |
[
false
] |
Why not 4? Or 6?
|
[
"Actually it started as eight. The fishes that were living in the shallows were working with a fin that had more bones. There are a couple of ideas about why they eventually ended up with five, but there's a ",
"gap",
" in the fossil record during this time and we're not quite sure yet. We need more fossils. One idea is that as that fin was turning into feet and the bones connecting it to the rest of the skeleton were turning into legs, the earliest ancestors that would become tetrapods gradually lost \"superfluous\" digits, eventually settling on five as the number that would suit its locomotion. This idea is entirely plausible. The other idea is that during the gap in the fossil record there were some number of ",
"bottle-neck events",
". They killed off the relatives of the pentadactyls that had other numbers of toes, so that by the time the fossil record resumes the only species left were the ones with five toes -- not because it's better than six, just because all of the species that had six happened to have died. That argues that it's a random process. That idea is also entirely plausible.",
"\nSomeday we'll better fill in the fossil record and get a greater understanding of what happened during the early tetrapods' transition to land. But for now, we're not quite sure.",
"\n(Edit: Wording)"
] |
[
"Actually it started as eight. The fishes that were living in the shallows were working with a fin that had more bones. There are a couple of ideas about why they eventually ended up with five, but there's a ",
"gap",
" in the fossil record during this time and we're not quite sure yet. We need more fossils. One idea is that as that fin was turning into feet and the bones connecting it to the rest of the skeleton were turning into legs, the earliest ancestors that would become tetrapods gradually lost \"superfluous\" digits, eventually settling on five as the number that would suit its locomotion. This idea is entirely plausible. The other idea is that during the gap in the fossil record there were some number of ",
"bottle-neck events",
". They killed off the relatives of the pentadactyls that had other numbers of toes, so that by the time the fossil record resumes the only species left were the ones with five toes -- not because it's better than six, just because all of the species that had six happened to have died. That argues that it's a random process. That idea is also entirely plausible.",
"\nSomeday we'll better fill in the fossil record and get a greater understanding of what happened during the early tetrapods' transition to land. But for now, we're not quite sure.",
"\n(Edit: Wording)"
] |
[
"This is actually just an historical artifact. It's called ",
"pentadactyly",
" (meaning five fingers). The first ",
"tetrapods",
" (meaning four legs) had five fingers, and the rest of us came from there. Some tetrapods have since evolved new traits like hooves, large columnar feet (like elephants), fins (whales and dolpihns) and even wings (birds and bats). But all of the tetrapods started out with five fingers and many living tetrapods have found very diverse uses for their five fingers. Bears use them to swat at prey, lizards use them to climb, racoons use them to grab, and I am using them to type. "
] |
[
"Optical Fibre and light transmission"
] |
[
false
] |
Hi everyone Stupid doubt really. Is it possible for a light particle to shatter the optical fibre when it is passing through? I remember reading about Total Internal Reflection, but at that speed, wouldn't it be like a bullet piercing a bullet proof glass at a high enough speed?
|
[
"well it's beyond stupid to downvote because of something that dumb. ",
". we can argue whether that accounts for 95%..90%..97% of losses. Whatever it's a biggy. ",
"You can argue that the precise mechanism that causes TIR to fail is scattering. But fuck man. I could argue that Rayleigh scattering is the result of ____ which is the result of ____. It's a stupid argument. The loss is failing to meet TIR. Plus that's something OP can relate too. I don't think he wants a dissertation about atomic structure.",
"where did you get you PhD from?",
"and i know why we choose 1550nm dude. i've done laser classes"
] |
[
"What do you mean shatter? Light can definitely escape an optical fiber.. light is re-amplified many times during communications... But, in that case, light leaves because TIR is not always satisfied.** ",
"I also think some energy maybe lost to coupling (if the evanescent fields get too close to something...)...but don't take my word for that. I haven't done laser stuff in school for awhile ",
"wouldn't it be like a bullet piercing a bullet proof glass at a high enough speed?",
"don't think of light as a bullet. let's use e&m cause we don't need quantum for this. Maxwell's equations govern electromagnetic fields. Through Maxwell's equations one can deduce the reflection and transmission coefficients for light in a medium. In certain circumstances when deriving the wave equations we see that no wave can penetrate the medium. ",
"...If you want to get more technical, there is a solution but it is purely imaginary and decreasing in amplitude exponentially. (imagine a exponentially decaying sine-wave). Since this solution decays to 0 amplitude, it is not transmitting any energy. Why doesn't a exponentially decreasing wave carry energy? If it did where would the energy go? If it decayed to zero in 1nm you'd imagine that it's dissipating a lot of energy in 1nm. Over time we'd have some little bomb or something. Obv doesn't happen.",
" So, ill be more precise for rndom42. Scattering and Absorption cause fiber losses. However, at optical commucations most losses are ",
"due",
" to scattering. Scattering causes losses because most scattered waves ",
". So, instead of TIR being the culpit, the culpit is microscopic variations in silicon that cause Rayleigh scattering which in turn causes waves to scatter which, because some waves fail to meet the criteria for TIR, causes power loss. :)"
] |
[
" I mean it could go backwards and still meet TIR but that is highly unlikely. ",
"anyways this accounts for >95% of the losses. so yea it is due largely to TIR losses. ",
"and i may have not taken a laser class in awhile... but by awhile i mean 6 months. it's just absurd getting down-voted in askscience because some kid read wikipedia and disagreed. "
] |
[
"Can Maillard reaction happen by boiling food in conditions that raises water's boiling point (e.g. salted water or high atmospheric pressure)?"
] |
[
false
] | null |
[
"While it is straightforward in a chemical lab to raise the temperature of steam to 140-165 C, the equipment to properly do so does not exist in a standard kitchen. Attempting to heat steam in a pressure cooker is the kind of thing that makes them explode."
] |
[
"Maillard reaction occurs from 140-165 C. A high pressure cooker raises the temperature to 120 -ish C. So using current equipment the answer would be no. You could try using steam at high temperatures to see if you can create the Maillard reaction on food."
] |
[
"As I understand you can achieve Maillard reactions in a pressure cooker by adding baking soda to change the ph value. The topic is discussed in an older reddit thread ",
"https://www.reddit.com/r/instantpot/comments/8n9v65/maillard_reaction_inside_a_pressure_cooker/?utm_medium=android_app&utm_source=share"
] |
[
"Are there weapons that have been studied that are more powerful than nuclear weapons?"
] |
[
false
] |
I know it's a scary question, but with today's technology are nuclear weapons the most powerful weapons we can produce? Or are there others that could be theoretically produced that would be even more powerful? By power I guess I am referring to sheer destruction potential.
|
[
"Teller-Ulam-style nuclear bombs can get extremely powerful, much larger than any that have ever been built. (Super-huge bombs are less useful, militarily, than a larger number of mere city-destroying bombs. So after satisfying themselves that absurdly large bombs were possible, back in the '50s, both the US and USSR turned their attention towards smaller-yield bombs.)",
"An antimatter bomb could be made smaller, but would have basically the same destructive effect as a nuke: big intense fireball, shockwave, fallout, etc. ",
"I think to get qualitatively more destructive than a large nuke, you'd have to go into some speculative physics, like runaway strangelets or supernova-like neutrino pulses generated by some unknown process."
] |
[
"In the very distant past, in the Universe's very early life, it underwent a period called inflation, in which its scale increased by dozens of orders of magnitude in a trillionth of a trillionth of a trillionth of a second.",
"I guess you intentionally didn't use the accursed term \"Big Bang\", but for clarification: That ",
" what the scientists, who knew what they were talking about, once christened \"the Big Bang\", right?",
"I know the term does not refer to the beginning of time itself. Just want to be sure if what it really refers to is what you're describing."
] |
[
"In the very distant past, in the Universe's very early life, it underwent a period called inflation, in which its scale increased by dozens of orders of magnitude in a trillionth of a trillionth of a trillionth of a second.",
"I guess you intentionally didn't use the accursed term \"Big Bang\", but for clarification: That ",
" what the scientists, who knew what they were talking about, once christened \"the Big Bang\", right?",
"I know the term does not refer to the beginning of time itself. Just want to be sure if what it really refers to is what you're describing."
] |
[
"Can we listen to the CMB?"
] |
[
false
] |
As I understand it, the CMB used to be higher energy radiation and has decayed over time. Is it possible to turn that data back into radio waves and then listen to it?
|
[
"You don't have to turn it back into radio waves. The CMB is currently peaked at a wavelength of around 2 mm, with the highest intensities between about 1 mm and 1 cm in wavelength. These are radio waves.",
"In fact, in an analog TV set, if you tune to a spot where there is no broadcast station, a fraction (if I recall correctly, around a percent) of the static you see is the CMB. And the way the CMB was first discovered was that Penzias and Wilson found that there was unexplained \"noise\" in their radiotelescope that they couldn't remove; it turned out that this was because their radiotelescope was picking up the CMB."
] |
[
"You could, but there's not much to hear."
] |
[
"Yes."
] |
[
"Is solar power viable in the U.S.?"
] |
[
false
] | null |
[
"You roommate is making a blanket black and white statement. They are almost never correct. :) The truth is usually in the gray area. We don't have to only choose solar for the sole energy source of the USA. We can implement it where it will work and where it doesn't have to be transmitted too incredibly far and do other energy sources in other places."
] |
[
"Given that most power is generated locally, and the viability of solar is mostly dependent on the amount of sunshine a place gets I'd have to say your friend's reasons are bs.",
"http://sunfarmvt.com/wp-content/uploads/2012/08/photovotaic-solar-map.jpg"
] |
[
"It'll become more and more competitive as scale increases. Mass production will drive down mfg. costs and technology advances will allow for improved efficiency. I believe these factors will make it more viable in the long-term than oil. Of course it is sustainable so big oil would rather you not invest so they can keep selling you their commodities. "
] |
[
"Why does the earth's spin about it's axis effect the shape of the earth?"
] |
[
false
] |
[deleted]
|
[
"Take a bowl full of water. Spin it. The surface of the water changes shape and the water flies out. The spinning motion sends things away from the centre and this is what happens to the earth. As it spins, the force pushes the mass outwards and this is more obvious at the equator and the planet bulges slightly.",
"\nI really don't know where you're coming from with relative speeds affecting the shape so I can't answer that part of your question as it doesn't appear to make sense "
] |
[
"Ah, I see what you're getting at. That only happens due to acceleration and inertia. When something is moving at a constant speed with no thrust, there are no forces acting on it that could change its shape. The spin of the Earth is a constant thrust against its mass, it's motion through space isn't. ",
"Think of those videos you've seen from the space station where the astronaut is messing about with a blob of water. It forms a nearly perfect sphere but it is in a tin can whizzing round the Earth at several thousand miles per hour. The ISS isn't accelerating or being pushed by anything so there are no forces to push that blob of water out of shape. "
] |
[
"Well, sure if you spin it it flings out of the bowl, but then if you throw the bowl across the room as well the water will also get pushed out of the bowl. The earth is moving through the galaxy at a tremendous speed, why does that not effect the earth while spin does?"
] |
[
"Is there a particle that is the opposite of a photon?"
] |
[
false
] |
It seems as if there is always an opposite for everything. Positrons and electrons, matter and anti-matter. So is there an opposite of a photon? If so what is it?
|
[
"Photons are their own antiparticles. ",
"Not all particles have a 'distinct' antiparticle, another example of a particle being its own antiparticle is the [; \\pi_0 ;] pion."
] |
[
"I don't think two photons can be made to interact with each other since waves just pass through each other, right?",
"In fact, they can if they have enough energy. This gives rise to things like ",
"two-photon physics",
". The most obvious way for two photons to interact is in the time-reversed pair-annihilation: instead of a positron and electron annihilating into a pair of photons, two photons \"annihilate\" into a positron-electron pair."
] |
[
"I don't think two photons can be made to interact with each other since waves just pass through each other, right?",
"In fact, they can if they have enough energy. This gives rise to things like ",
"two-photon physics",
". The most obvious way for two photons to interact is in the time-reversed pair-annihilation: instead of a positron and electron annihilating into a pair of photons, two photons \"annihilate\" into a positron-electron pair."
] |
[
"How does the collapse of a star decay the protons and electrons into neutrons?"
] |
[
false
] |
So the basic idea of the birth of a neutron star is that the incredibly massive ball of H, He, and other material implode to become a supernova after millions of years in fusion reaction as it consumed and fused the light fusion material into heavier matter. In this 10 seconds the protons and electrons are transmutated into neutrons. But how? What happens to the particles in the supernova from a particle physics standpoint? Electrons by themselves cannot be made into neutrons since they are leptons, right? And also why is it that it are specifically neutrons that are favored in this event? Thank you for reading, and thank you in advance. Cheers!
|
[
"Protons and electrons can be converted to neutrons through ",
"electron capture",
". This reaction, ",
", conserves lepton number since an electron neutrino is released in the process. This process is not unique to supernovae and happens in normal stellar activity in the ",
"second step of a proton-proton chain reaction",
", as well as in ",
"some types of nuclear decay",
".",
"A collapsing stellar core provides immense amounts of energy and pressure, which allow for (generally) endothermic interactions to occur, such as fusion of elements past iron, and photodisintegration of iron nuclei into alpha particles. ",
"This immense pressure makes it energetically favorable for electron capture to occur, since neutrons can be packed much more tightly than a proton-electron plasma. In the case of a formation of a neutron star, the neutron degeneracy pressure halts the core collapse, but if the initial star is large enough, gravity overcomes this degeneracy pressure and a black hole forms."
] |
[
"So that's why supernovae give off neutrinos that are detected in observatories. Brilliant, thank you.",
"Would there be any chance for the creation of exotic matter in similar events?"
] |
[
"\"Exotic matter\" is a pretty broad term, so I'm not sure exactly what you're asking, but as with any ultra-high energy event, you'll see interesting interactions."
] |
[
"Could someone create sound on the moon."
] |
[
false
] |
The moon doesn't have an atmosphere so that for instance you couldn't hear your fart if you were on the moon. However, there is lots of moon dust which if stirred up would remain for some time above the surface until the moon's gravity pulled it back to the surface. During that time could one hear because of the dust?
|
[
"Yes and no. ",
"However. And this is #2. Sound is relative to the range that the human ear can hear. There are gasses in space, and there are gasses surrounding the moon. But the density of gas is so small it can not carry/transfer vibrations that we can hear with our human ears. But you certainly could with specialized equipment pick up \"sound\" vibrations much like a antenna picks up radio waves. "
] |
[
"Could someone create sound on the moon.",
"Yes. Sound can travel through solids. (But no to the dust thing.)",
"It actually travels ",
" through solids, if you're not too fussed about which frequencies are attenuated how much.",
"Put your ear to the wall and cover your other ear. You'll hear whatever's in the room. Or in an extreme case, have a friend tap on a spot a few meters away from where you're listening.",
"Heck, you can hear stuff from other rooms all the time. Solid, air gap, solid. Whole point of soundproofing.",
"You're just not going to transmit sound through the atmosphere, because there's not one, and the Moon doesn't have the gravity to keep one, and any stray particulates aren't going to be at meaningful pressure."
] |
[
"An astronaut could \"hear\" a rocket land and takeoff with his helmet in contact with the ground, for some distance.",
"Or two astronauts could talk to each other by touching helmets and yelling. "
] |
[
"What happens to routers that they need reset all the time?"
] |
[
false
] | null |
[
"There's no one answer here, there are many things that can cause a router to lose connectivity in a way that ca be fixed by a reset. ",
"Off the top of my head:",
"Other reasons may exist. Ask if you want more detail on any of those. "
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"The only decent consumer grade router I have owned that shipped with stable firmware was the Billion router I owned. I don't recall ever having to reboot it due to a software/hardware fault. However after 7 years of near constant use it overheated and died. I miss that router. "
] |
[
"How can evolutionary development occur among species which reproduce via parthenogenesis?"
] |
[
false
] |
[deleted]
|
[
"Occasional mutations still occur."
] |
[
"Parthenogenesis is genetically equivalent to asexual reproduction as seen in all prokaryotes. Many biologists would be very surprised to hear that bacteria and other prokaryotes don't evolve."
] |
[
"It ",
" work fine for multicellular animals, too. Natural Selection is still in effect and mutations are possible. However, change is slower per generation than by sexual reproduction.",
"You also can't say \"If X trait were better all organisms would have it.\" Species do not necessarily have the ability to evolve a specific trait. For example, humans are not currently in a biological/environmental position to evolve unassisted flight by natural selection, even if that were an optimal trait for us to have."
] |
[
"Is it possible to view surfaces of distant planets?"
] |
[
false
] |
What I mean is would it be possible for us to actually get a surface view of a distant planet without having rovers or other objects physically on the surface of that planet? With the distance we can see in the galaxy, what is restricting us from viewing the very surface of other planets from Earth?
|
[
"Extrasolar planets are small and dim and really far away and their light is swamped by the light from their nearby stars. Existing telescopes for the most part don't even have the ability to distinguish the light from a planet direcdtly as a dot, much less map the planet.",
"There is a proposal to devise a system to image an exoplanet directly by using a starshade (a large at a level at which we could distinguish the properties of the surface. The ",
"New Worlds Imager",
". A pretty clear description of the project is found ",
"here",
".",
"The idea is to build a ",
" -- an opaque sheet over half a mile in diameter with a 10 meter hole in the center, positioned in space, with a telescope something like 200,000 km from the star shade, the whole thing acting like a giant pinhole camera feeding into a telescope. Designs include having two such systems separated by 1500 km (see ",
"this PDF",
"), combining their data."
] |
[
"So this idea they have still hasn't been approved to this date? Could the reason be because of what was listed in the article",
"After a quick google search I came across ",
"http://planetquest.jpl.nasa.gov/video/15",
"It seems that they still have several engineering hurdles to overcome. Thanks for the information on this."
] |
[
"I don't know where it stands in the internal NASA processes, but this mission is mentioned in the ",
"NASA 2011 strategic plan",
", so it seems still under active consideration. "
] |
[
"What are some recent changes in science we may have missed out on from taking courses 10,20 etc. years ago?"
] |
[
false
] | null |
[
"One of the fields that have advanced the most in the last 20 years is ",
"COBE was early 90's and wmap was early 00's. These first proper looks at the cmbr gave leaps forwards in the understanding of the early universe the anisotropies in the cmbr were amazing new science. ",
"Although a bit before 20 years, 20 years ago it would have been unlikely you'd have been taught about dark matter as it was only in the 80's that dark matter was formulated as a possible explanation of galactic rotation curves.",
"Supernova studies (1998) gave us the startling discovery of the expansion of the universe. This forced the idea of dark energy upon cosmology.",
"The hubble deep field and ultra deep field surprised cosmologists with the huge number of galaxies at high redshift in tiny portions of the sky. This really improved the understanding of the universe and they were only taken in 95 and 04.",
"Really, in general, cosmology was not a science 20-30 years ago and now it has exploded into a huge deal. You'd have missed the entire subject taught today if you went to college 20 years ago.",
"Quasars (AGN) were misunderstood before the 80's. Other compact objects neutron stars in particular were much less understood.",
"These things may not feel as fundamental as physics but if you take a class on any of these subjects the brunt of what you would be taught was discovered by these missions.",
"Solar physics is, of course, close to my heart. The fact that solar, as with a huge amount of astronomy, relies on satellites to take the largest share of data gathering means that a huge amount has been learned in the last 20 years.",
"Skylab was the first time we had ever looked at the sun properly with x-ray and it was in the late 70's. As a result most of what we know about the corona and chromosphere has come since then. Rhessi, stereo, ace, yosokoh, hinode, Ulysses GOES, TRACE, soho, sorce, coronas, sdo... All of these solar satellites launched in the last 20-25 years and each one told us huge amounts about flares, internal sun structure, the solar wind, the corona, the chromosphere, the magnetic structure, the solar cycle, space weather...",
"Beyond the sun we have learnt so much about our neighbouring planets (and their moons) than you would have been taught 20 years ago. Mars was the most visited before then and even then basically consisted of some poor quality soviet probes, the mariner and the viking probes. Mars surveyor, pathfinder, odyssey, express, all the rovers... came in the last 20 years. The majority of what we know about mars came from these.",
"The same is true about the rest of the planets, even more so normally. Most planets hadn't been visited, pioneer probes and voyager did some flybys of the outer planets but it wasn't till the likes of cassini-huygens (for saturn/titan) and galileo (for jupiter), both late 90's, that we got a proper look at those planets.",
"Away from space missions the increase in computing power of recent times has helped astronomy research. Simulations have allowed a deeper understanding of galaxy/star formation that although the principles were known was less well studied 20+ years ago.",
"Gamma ray bursts are incredible events that, although first detected in the 60's, were not even CLOSE to being explained until the last decade.",
"When we get to these kind of things we are drifting from what I am expert on. What I can say about particle physics is that: It hasn't changed much.",
"Although new particle colliders in the last 20-30 years have given great results and discoveries the majority of our understanding of the fundamental forces was laid down in the standard model in the mid 70's and it was really (Aside from some important predictions) a combination of QCD/electroweak/etc theories that were an additional 10-20 years old by that point.",
"That being said, it is not unlikely if you did particle physics in the 80's then you wouldn't be taught it the same as you are now. Education is notorious for lagging behind research.",
"The same kind of thing goes for relativity/more general QM, these theories were already 50+ years old 20 years ago and would likely be taught the same theoretically.",
"Practically though the big advance in GR is gravitational waves as well as the combination with cosmology to study the big bang. The only evidence for gravitational waves wasn't around until the 80's and would be unlikely to be taught. Nowadays it is an important field.",
"Quantum Mechanics has seen the rise of quantum computing as a real field along with science such as entanglement, encryption being areas that would have seen no teaching 20+ years ago.",
"When you go to things like solid state/material sciences. Youa re too far out of my wheelhouse but things like carbon nanotubes, quantum dots, BEC, superconductors, superfluids all this cool stuff is has seen amazing understanding and demonstration in the last 20-30 years that you wouldn't have seen before.",
"I also stuck very strongly to astronomy with some physics but I can guarantee there have been huge advances in other fields, genetics, computing, immunology, climate science, oceanology...every field will have so much more to teach people at school now than just 20 years ago.",
"The bad thing is that teaching seems to change so so slowly. Universities keep up but schools teach the same old stuff even when we are faced with new discoveries however...",
"...the good thing is that schools tend to mostly teach the basics. We have known the basics of physics for around about 100 years and although it would be nice for schools to brush on this cool, new stuff the science you have to learn for exams will have changed by very little. ",
"Perhaps what has changed the most is the teaching itself, the way it's taught rather than what's taught."
] |
[
"alot of stuff has always been a myth, until the internet came to the rescue. ",
"see list of common misconceptions in wiki. "
] |
[
"the pluto thing is just a definition, is does not give new insight. ",
"I suppose new scientific discoveries are almost always very specific, so that most people outside that specific field dont know or care about it. "
] |
[
"People built a \"Z machine\" on Earth that creates a temperature of 2 Billion Kelvin. How can this temperature be generated and why does this temperature not melt the entire facility that creates it?"
] |
[
false
] |
For scale, this is approximately 100x hotter than the center of the sun. Given that the sun only has an outside temperature of 5,500K and easily heats up Earth to 300K+ over a distance of 150 million kilometers, shouldn't a temperature of 2,000,000,000K on Earth itself cause severe damage of some kind?
|
[
"It's a VERY tiny amount of matter heated to that extreme. It's a point temperature, they aren't making the whole earth 2B Kelvin.",
"Think of it like a welding torch. The spot of the weld is hit enough to melt the metal, but the rest of the object being welded stays solid."
] |
[
"amount of heat",
"that's not an \"amount of heat\". it's just a high temperature and the point is that the total energy in the system isn't very big (certainly not enormous). heat is a way of transfering energy and since there's not much energy in the system, you'd find it hard to transfer much heat to the facility to the point where its temperature would rise significantly.",
"i mean put a drop of water on an oven surface and see how much its temperature decreases while the drop evaporates. also drop a hot needle into a glas of water and notice that the water doesn't boil.",
"\"what do you need high temperatures for?\"",
"for instance we would want to be doing nuclear fusion, for that we would want to heat a plasma so that the conditions are such that fusion reactions are likely to occur within the plasma. again you then just have a small quantity of matter at that temperature and when it touches the surroundings of the reactor it cools down immediately, while not melting the reactor (because it's not a significant amount of energy)."
] |
[
"The point you are missing is the fact that the smallness is a central part of the claim. The point here is not \"look at how hot we got something!\" It is \"Look at how small we made the collection of energy!\" If they made something so hot it ignited everything, that energy would still need to come from somewhere. And since there aren't 20 powerstations supplying the lab, logic tells us that they just squeezed a ",
" amount of energy into a tiny space. That's it. "
] |
[
"How do electromagnetic waves propagate through outer space and Earth's atmosphere?"
] |
[
false
] |
As I understand it, the force carrier for the electromagnetic force is the photon. Which leads me to ask if an emf wave is the result of photons being absorbed and emitted by the particles in the medium the wave is traveling through? And if not, can you tell us what the mechanism is that allows emf waves to travel through space and the atmosphere?
|
[
"Forget that first part. It just adds confusion.",
"Changing electric fields generate a magnetic field. Changing magnetic fields generate an electric field. These two phenomena lead to a self-propagating wave of oscillating electric and magnetic fields, originating from an initial perturbation in (let's say) charge distribution."
] |
[
"It's true that photons are the force carrier for Coulomb interactions, but those are virtual photons (virtual particles and force carriers are another topic), and it is not directly related to your question.",
"For photons there is no necessary medium or mediating particles through which they propagate in the classical wave sense (a luminiferous aether) - that was first proven by the Michelson-Morley experiments, and the later refinements.\n",
"http://en.wikipedia.org/wiki/Luminiferous_aether",
"\n",
"http://en.wikipedia.org/wiki/Michelson-Morley_experiment",
"Basically, if there were a medium through which light traveled, then it should be possible to have a velocity relative to that medium. However, these experiments showed that light has the same relative velocity no matter which direction you face relative to the Earth's motion around the Sun.",
"Photons are better thought of as quantized excitations of the electromagnetic field. The electromagnetic field can be excited (requiring energy), and these excitations can travel through space. Those excitations are called photons.\n",
"http://en.wikipedia.org/wiki/Quantization_of_the_electromagnetic_field",
"My actual field is condensed matter, so I'm starting to get out of my depth. "
] |
[
"Why does this propagating wave move at c and not just stay in the same place?"
] |
[
"Spherical mirror and light."
] |
[
false
] |
So I've been wondering about this for years. If you have a Sphere that is made out of "one way" mirror so you can see into it and you had a light like flashlight or whatever and shined it into this sphere would the light escape? Would it become too bright to look at? If you turned the light source off would the light in the sphere remain and continue bouncing around inside? I guess we need to assume that there's no seal on the sphere for light absorption. Originally I'd thought about this with a cubic mirror but deduced that the edges and corners inside would be detrimental to keeping the light in. I'm aware that "one way" mirrors are not exactly 100% reflective, but if we had a material that would operate in the way I'm imagining would it be possible?
|
[
"No such glass exists, or can exist. Let me explain.",
"One-way glass actually isn't what you think it is. Glass reflects about 4% of the light that hits it. That means that if you have a much brighter light on one side of the glass than on the other, then most of the light coming from the direction of the mirror is reflected light, rather than transmitted light from the other side, hence there is a reflection. You can see this effect when you're inside a well lit room at night and there are windows to the dark outside. The ones in police stations are better than your home's window because they add a layer of silver to the back of the window in order to make it even more reflective- this is actually what mirrors are, layers of glass with highly reflective silver spread out on the back of the pane.",
"So to answer your question... Such a one-way sphere of glass would violate thermodynamics by decreasing entropy, and would require an optical \"Maxwell's Demon\" in order to operate. I won't go into detail about the Demon here, as ",
"Wikipedia has a very good discussion of the thought experiment.",
" Basically, the glass means you would be able to sort a system that is in thermal equilibrium into hot part and a cold part. In simpler terms, it means you could take ambient heat and use it to do work, which is a big no-no in thermodynamics.",
"Also, such a one-way sphere would accumulate energy indefinitely, and as the energy density gets huge, it would eventually collapse into a black hole, in the same way that having too much mass in one place does."
] |
[
"One way mirrors are never \"one way\". They are partially reflective on both sides, and purposefully kept darker on one side that then other. This way, the light reflected from the lighted side is much brighter than the little bit passing through from the darker side, and it becomes very difficult to see anything on that side. If you are on the unlit side, your dark adapted eye makes it seems as though all of the light is getting through. This could not be because if all the light had been reflected, none would have passed through to your eye. ",
"There are things called optical resonators where it is possible to trap light. It will either bounce back and forth between mirror or go round in circles many thousands of times. ",
"Since for light, the direction of travel (with very few exceptions) doesn't really matter, the resonator must be \"leaky\" to get in the first place, unless it is created already inside. ",
"If there was such a thing as a \"perfect\" light trap, it would never get too bright to look at as there would be no light getting out."
] |
[
"If it's made out of a one-way mirror and you can see into it, then that means that the light waves can come out from inside, but the one-way-ness of it means that no light waves will be able to get into it to be reflected!",
"In any event, by conservation of energy, the sphere would never emit more light than was shone on it, so you wouldn't have to worry about it becoming too bright to look at, unless your light source is, too.",
"It sounds like what you're thinking of is an abstraction of the ",
"greenhouse effect",
"."
] |
[
"What happens if you eat a \"do not eat\" silica bag?"
] |
[
false
] | null |
[
"Haha I didn't actually eat one, was just curious. Thanks!"
] |
[
"Haha I didn't actually eat one, was just curious. Thanks!"
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"medical advice",
"/r/AskScience",
"guidelines.",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"How would I experience the world around me if I were able to run at near the speed of light?"
] |
[
false
] | null |
[
"Time dilation works both ways, so while you're travelling at relativistic speeds, you will notice that the clocks of your surrounding running slower than yours."
] |
[
"Your world would red-shift and everything would age faster around you.\n",
"http://www.youtube.com/watch?v=lPoGVP-wZv8",
"\nThis video is a really neat example, with Carl Sagan as the narrator. Visual effects are included."
] |
[
"I'm pretty sure it'd hurt a lot (if you even had time to hurt before you vaporized) :D"
] |
[
"Does the \"time\" part in \"the curvature of spacetime\" refer to time dilation due to gravity? How is spacetime being curved different from just space being curved?"
] |
[
false
] |
Also, is there any fundamental difference between the overall curvature of the universe, and the local curvatures that we call gravity? It seems like I hear the overall curvature referred to as the "curvature of space," and gravity referred to as the "curvature of space ." What's the difference (if there is one)?
|
[
"In two dimensions, positive curvature is just a basketball. What this means is that any two lines - like the lines on a basketball - meet exactly twice. It also means that your surface is finite in size.",
"Bumping this up to three dimensions, does this imply that if you have two lines (say two laser beams) that start out exactly parallel, they will intersect each other exactly twice as well? Or does it even matter how they are oriented when they start out with respect to one another? Will ",
" two straight lines in positively-curved 3-dimensional space intersect exactly twice? I'm guessing that every straight line would also always reconnect with itself (forming a closed \"loop\"), much as it does on the basketball in 2 dimensions?",
"As an important side-note, knowing the curvature of space tells us the mass density, which is why we know that there has to be a lot of \"invisible\" matter out there - which is given the (overly dramatic) name of dark matter (and/or dark energy, same damn thing I know.)",
"When you say \"the curvature of space,\" are you talking about the overall curvature of the universe? If this is the case, does that mean that the overall curvature of the universe is a function of mass/energy, and not just some intrinsic property of the universe?"
] |
[
"When you say \"the curvature of space,\" are you talking about the overall curvature of the universe? If this is the case, does that mean that the overall curvature of the universe is a function of mass/energy, and not just some intrinsic property of the universe?",
"When I wrote \"the curvature of space\" there I did mean the intrinsic curvature of the universe. And that means that the overall curvature of the universe is a function of mass/energy ",
". (As the universe is almost certainly infinite, we can't talk about the total mass/energy of the universe, but we can talk about the average mass/energy density.)",
"As for your first set of questions, I'm not confident enough in my spherical geometry to answer them. If I had to guess, my answers would be probably, definitely yes, definitely no, and yes. (For the definitely yes/definitely no, consider the equivalent of skew lines in 3D Euclidean space.)"
] |
[
"There are a lot of people who can craft beautiful and explanatory analogies around here, so I'll try and answer your questions in a short and to the point fashion.",
"There are two concepts that you seem to have not quite fully separated yet, and that is fine. Those two concepts are the local geometry of the universe (near a massive body) and the large-scale geometry of the universe.",
"The local geometry of the universe is passably explained by the horrendously misleading picture of the Earth as a bowling ball on a rubbery trampoline. Now there are better pictures out there that demonstrate what is really happening, and you should also understand that just as the mass of the Earth influences the near-Earth geometry of space, it also influences the passage of time for observers near Earth. If you want more detailed explanations of how exactly this works you should reply and somebody who can tell you more will do so.",
"However, there is a second idea at work here, and that is the large-scale structure of the universe. This is essentially a measure of how the geometry of our universe differs from the Euclidean model at large scales. Right now the data say that our universe has either a very small negative curvature (I'll provide toy models in a moment) or zero curvature - but it almost certainly doesn't have positive curvature.",
"Now what on earth does positive curvature, for example, look like? We'll work in two dimensions - understand that, if you want to abstract up to our universe, you've got to bump it up to three dimensions. (All this talk about nine or ten dimensions is a bunch of nice tricks string theorists enjoy, and they may in fact be right. But for large-scale structure we have three dimensions.)",
"In two dimensions, positive curvature is just a basketball. What this means is that any two lines - like the lines on a basketball - meet exactly twice. It also means that your surface is finite in size.",
"In two dimensions, zero curvature is just an (infinite) sheet. (It has to be infinite because there's absolutely no reason to suppose that the universe has a boundary.) So the universe could be completely flat at large scales. In a universe with zero curvature, given a line and a point not on that line, there is exactly one other line parallel to the first passing through that point. (This is Euclid's famous fifth postulate, which is why the zero-curvature case is called Euclidean.)",
"In two dimensions, negative curvature is a bitch. Not literally, but sort of. A lot of people use a Pringles chip as an example of negative curvature, which is somewhat accurate. But the important facts about a universe with negative curvature are that given a line and a point not on that line, there exist ",
" lines \"parallel\" to the first passing through the point. Negative curvature also implies that the universe is infinite (again, there can't be a boundary). If you want to look into visualizing a 2D hyperbolic universe, I would recommend looking at the ",
"Poincare disk model",
".",
"So, just to sum up, what are these two types of structure? Well, you can think about the local distortions due to mass as being a bunch of tiny dimples in the large-scale structure of the universe, and you'll be fairly accurate.",
"As an important side-note, knowing the curvature of space tells us the mass density, which is why we know that there has to be a lot of \"invisible\" matter out there - which is given the (overly dramatic) name of dark matter (and/or dark energy, same damn thing I know.)"
] |
[
"Do cities stop rivers from changing course?"
] |
[
false
] |
[deleted]
|
[
"Not sure if this is the question you're asking, but the Mississippi River has been trying to abandon its current channel and drain through the Atchafalaya River instead, and there's ",
"a system of floodgates",
" in place to prevent that."
] |
[
"Shoreline stabilization is a typical component of urbanization along rivers. Bulkheads, rip-rap, and other engineered surfaces ensure that the river stays the course, often with certain predictable consequences. Without stabilization, this probably wouldn't happen; soil could erode from under buildings and topple them."
] |
[
"This is actually a major contributor to coastal erosion in South Louisiana. Instead of depositing silt to build coastline the river is scouring it away. "
] |
[
"If I were able to stand next to Voyager I where it is now in interstellar space, would I be able to see it?"
] |
[
false
] |
I was wondering if there would be enough light (photons) out there to bounce off the spacecraft and hit our retina or if it would appear to be a silhouette against a starry sky? Or dimly lit. I got to thinking about this after watching Star Trek recently and wondering if there was enough light in deep space to make the ships look so shiny.
|
[
"You can easily estimate how well is voyeger 1 illuminated. Direct sunlight is about 50,000 lux. Illuminance falls with distace squared. Voyeger is 125 AU far. So illuminance is roughly 50,000/125**2 = 3.2 lux. So Voyager is better lit than open terain in the light of the full moon, which is about 0.5 lux. Even in the deep interstellar space lets say 1 ly away Voyager would be still visible, thou just barely."
] |
[
"Wait you realize Maku is saying you ",
" be able to see it right?"
] |
[
"To expand on this question wouldn't the background luminance from the milky way and other stars be enough? I'm pretty sure on a moonless night the ability to still see is primarily from starlight not an atmospheric reflectance of sunlight, but would love to know for sure. If it is starlight then you would be able to see voyager without regard for its distance from Sol."
] |
[
"On a nice day, black objects will heat faster than white objects, but do certain colors behave the same way?"
] |
[
false
] |
I'm on a beach on a sunny day, will my blue shirt heat up faster than my red shorts if they are the same material? Is there a significant difference?
|
[
"and on top of this, remember that there remain a lot more light outside of our visible spectrum. Particularly things that may be more or less opaque in Infrared. Like Sand can get very hot even though it's a very light color. "
] |
[
"True, to do a good experiment, you would have to test ONE material in several different colors, assuming that the material involved in pigmentation is negligible compared to the energy absorption due solely to color. Maybe different colored plastics or ceramics? Measure the surface temperature with an IR thermometer? I might just put this together and try it with my kids. This sounds like a fun experiment."
] |
[
"The simple answer to your question is that lighter colors reflect more energy Darker colors absorb more energy. Since light is energy, an absorption would increase a materials temperature. An object appears white if it reflects all colors, black if it absorbs all colors. Naturally there are gradients of color and therefore gradients of absorption. If one of these days you are bored and feel like doing some good ol' fashioned science, you can easily try an experiment at home to test the results"
] |
[
"Whatever happened to the hole in the ozone layer?"
] |
[
false
] |
When I was a kid that was all I ever heard about. "Beware of CFC's!" they said. Is this still an issue or has science proven otherwise and the concern now more focused on climate change?
|
[
"CFC's are no longer really manufactured, due to the ",
"Montreal Protocall.",
"Ozone depletion",
" is still an issue, but we no longer massively produce most of the chemicals that were making it worse. Now that we've stopped, there's nothing more to do."
] |
[
"Antarctic ozone layer bouncing back after the phase-out of chlorofluorocarbons",
"Ozone data from 1955 to 2012"
] |
[
"CFCs are ",
" effective at destroying ozone. As in, a single CFC molecule can destroy hundreds of thousands of ozone molecules. ",
"Back in the day, we were using CFCs all over the place, and pumping them into the atmosphere without regard for their impacts (largely through ignorance). ",
"The reason you don't hear much about it anymore is because of massive global regulation of CFCs, which has largely stopped the problem from getting worse (and allowing the ozone layer to - hopefully - steadily recover).",
"As Quarkster pointed out, things may not be all happy and shiny though."
] |
[
"How do the arms of galaxy’s persist?"
] |
[
false
] |
Shouldn’t the nearest part of the arm rotate around the center of the galaxy faster than the furthest part of the arm- similar to planets all having different rotational periods around our sun?
|
[
"Yeah good catch! This is actually called the winding problem in cosmology. A commonly accepted explanation to solve this problem is density wave theory, though I believe it is yet to be confirmed. Definitely check it out it’s pretty cool",
"https://en.m.wikipedia.org/wiki/Density_wave_theory"
] |
[
"Now I imagine the pattern you'd see if you recorded the galaxy from birth to today and played in within a few minutes"
] |
[
"This lady (below) was one of the first to really dig into this phenomenon. There were others before her, but she got a break with a new technology that allowed a much higher precision in measurement of velocities.",
"https://en.wikipedia.org/wiki/Vera_Rubin"
] |
[
"What type of tissue is this?"
] |
[
false
] |
I thought it was simple squamous epithelium based on its structure and nucleus location. What is the tissue in the dotted area? And what traits did you use to determine this? Thanks in advance.
|
[
"My personal favorite, Adipose (or fat) tissue. The large white area is accumulated triglyceride and the surrounding tissue has blood vessels and what appears to be some fascia. The large uniocular lipid droplet with the nucleus pressed up against the edge of the cell is very telling of the adipocyte. Only in very extreme circumstances do you find adipocytes in other tissues or lipid droplets for that matter. "
] |
[
"That very well may be the case, I'm not particularly familiar with the effects of H&E staining on the contents of the lipid droplet, but it certainly makes sense.",
"I've always found nutrition and metabolism absolutely fascinating, so during my undergraduate, I joined a nutrition lab, which happened to be devoted to the study of adipose. Here I was introduced to the tissue and how it regulated whole body lipid flux and acts as a major regulator of hunger and provision of energy to the body. The multiple levels of regulation through insulin, glucagon, and other body hormones to regulate lipolysis and lipogenisis left me wanting to learn more about the tissue. So now I'm pursuing my PhD in the study of adipose. Plus they're so darn cute. "
] |
[
"I'm no expert in histology, but I believe the nucleus of simple squamous epithelium represents a much larger portion of the cell volume compared to the adipocyte. Adipocytes are significantly larger and have very little cytosol compared to the simple squamous epithelial cell type. If memory serves, simple squamous epithelial cells are in a monolayer and have the squamous shape. I can try to expand upon that but I'll have to refer to my old text. "
] |
[
"Why is playing games fun?"
] |
[
false
] |
I understand why eating food, or having sex can gives us pleasure, since it makes sense biologically, we need to do those things to survive and procreate, but why does playing games gives us "pleasure"? And to be a bit more general, why are some things satisfying and others aren't? Like watching a good movie and watching a bad movie. Is our brain capable of training itself to feel pleasure from activities that would otherwise not cause any pleasure?
|
[
"TL;DR: Games ",
" necessary for survival and procreation.",
"Games are essentially play acting at doing something more complex (usually). Consider playing house, a child is essentially emulating their parents or other role models into \"trying out\" tasks before they get older and do it for themselves.",
"Evolutionarily, this is most likely because if you want to \"try out\" a task in the past, messing up on that task will get you or other people killed / starved / messed up in a non-specific way.",
"Also adroit game playing is a mark of intelligence, which is a primary factor in mate selection.",
"Your question also implies why we like games ",
" in modern times, where we don't need to play at hunting to train ourselves to make sure we don't starve. Given the intelligence argument as above, let me show an additional aspect of game playing: complexity breeds complexity.",
"Let me break that down: When you play a game, you're practicing (as above), which is intrinsically bound up with learning. You learn a game by establishing simple rules first, practicing, then attempting more complex play (if there is more complex play and it holds your attention, etc). This cyclical behavior creates more complex and specialized structures within the mind, which leads to mastery (as mentioned previously) and ",
"transference",
"; Where you can use some skills developed while playing a game in another context.",
"Thus the skills used in game playing enrich the mind, increasing its complexity and your ability to grasp and understand slightly more complex things. This is an oversimplification, but essentially this process of simpler tasks leading to more complex is how you learn and grow through development from a baby to an adult and beyond.",
"So game playing now and in the past has increased individual intelligence; as intelligence is a survival strategy and a selector for breeding fitness, you can see why the brain may be hard wired to enjoy gaming (e.g. increasing its own intelligence / complexity).",
"As to your question about training itself for pleasure: yes, see also ",
"addiction",
". There exists a feedback loop mechanism within the mind that produces pleasure inducing neurotransmitters that train the brain through pleasure to enjoy arbitrary stimuli; I may not have the precisely correct name, but it appears to be the ",
"Reward System",
"; I.e. liking pain (masochism).",
"PS: As to game playing above and why we would want practice at seemingly arbitrary things that have little or no value on the face of them (e.g. getting really good at Gears of War); It has been really difficult to predict - in our past as a species - which behaviors / instincts / skills would be helpful for survival; So gaming has seemingly evolved to be very general and arbitrary, a \"see what sticks\" approach, e.g. which skills are rewarded and reinforced within the social unit / society / culture is essentially an evolutionary process and ",
"collective learning",
".\nE.g. if Billy likes to play at burying plants, but no else thinks it's a good idea, they might as well let him since there's not a lot of cost in letting him play at something seemingly meaningless, then when the plants start to sprout they can learn from his \"play\" and make it better (agriculture).\n(That's a really silly example and has no basis in fact, but it illustrates that letting people \"play\" at different tasks, helps the group as a whole, since others can learn from the mistakes or successes made)",
"Source: First year graduate student in Learning Science in the Fall & undergraduate research into Games in learning Science"
] |
[
"Johan Huizinga's ",
" (",
") is considered to be the first seminal research on human \"play\" behavior. I would suggest reading this. ",
"You may also be interested in Jane McGonigal's \"Reality is Broken: Why Games Make Us Better and How They Can Change the World.\" I think it will probably not answer your question, but offers some history of human game-playing and explores the social elements of gaming. James Gee, I think, also has some interesting research on game studies, gamification, and so on. You can probably then trace their sources to peer-reviewed research that explores this in other fields: evolutionary biology, etc. ",
"I remember hearing that some non-human species use games to teach. I don't have a citation for this. We have also observed other species doing silly things for no obvious conjectured reason. ",
"This question is often addressed psychologically and socio-culturally in terms of escapism. It is related to circumstances that lead to addiction, for example. Read about John Calhoun's Universe 25 mouse society experiment and recent experiments on addiction and opiates in mice related to their environment. This section of my response is more relevant to the question \"Why do humans play games in our current world and even get addicted to them?\" In short, we have unsatisfying environments and this is a way to escape.",
"But, throughout history, there are anecdotes of humans playing games to ward off hunger, pass difficult times.",
"OP and others may be interested in Ian Bogost's work on \"serious games\" and the \"design of fun.\" Here's a short video of ",
"Bogost",
" speaking to the matter. ",
"Perhaps someone can offer a literature review on play behavior from a neuroscience perspective, though? I believe that is what OP is looking for. "
] |
[
"This is an adaptive explanation for why we are motivated to play games. It could very well be right, but it's not a mechanistic explanation of why a human playing a game ",
" enjoys it. That kind of explanation would have to appeal to an understanding of reward centers in the mind/brain, probably how reward depends on learning, etc.",
"As for OP's interest in why some things are satisfying and others aren't (e.g., why good movies feel 'good', and bad movies 'bad'), OP should look into aesthetics:",
"https://en.wikipedia.org/wiki/Aesthetics"
] |
[
"How come when viruses cross species they often become deadly (e. g. Ebola, H1N1,rabies, malaria, etc) to human, while relatively safer for the animal hosts?"
] |
[
false
] | null |
[
"I'm not sure if there's any one answer to this, but there are a few contributing factors.",
" If a pathogen is extremely deadly it can actually hurt it's ability to spread; ebola for example can become symptomatic in days and kill soon after. Because this is so fast the host often doesn't have many opportunities to spread it. Therefore, there is an evolutionary advantage to \"tempering\" the severity of infection; a microbe that has recently made the jump from one species to another has yet to undergo this selective pressure.",
" Our immune system has evolved to be adept at quickly identifying when an infection has occurred and creating a specific response to it. If we become infected by a very novel organism, it could be so different that our immune system cannot handle it as well as it could an organism that it has been in contact with for millennia, such as herpes. ",
" If a microbe makes the jump but doesn't cause severe disease and can be handled by our immune system we might not notice it, while things like avian flu, ebola, and HIV are quite scary and jump out at us."
] |
[
"The two googleable terms of art here are \"evolution of virulence\" and \"emerging pathogen\" epoxymonk's answer here is excellent but really the important point is the evolution of the microbe. Barring massively deadly pandemic events like ",
"Justinian's Plague",
", ",
"the Black Death",
", and ",
"the 1918 flu",
", emerging pathogens should not exert enough selective pressure on us to produce meaningful evolutionary adaptation - but there are other important ways in ways in which populations of critters like us can adapt - like the generation of a stable group with adaptive immunity. We do also now have ways in which we should be able to account for the observation bias as even viruses that are harmless to healthy adults should still affect the large, globally distributed, and well monitored immunocompromised populations we now maintain like AIDS patients. The pathogens we see affecting them are largely ones we can tell have affected us for a long time once we know to look for them. ",
"If you want to really get into how the evolution of virulence works here are two of my most favorite papers ever that empirically define it,",
"Timing of transmission and the evolution of virulence of an insect virus.(PDF)",
"\nJC de Roode, AJ Yates, & S Altizer. Published 2002 in Proc. R. Soc. Lond. B doi:10.1098/rspb.2002.1976",
"We used the nuclear polyhedrosis virus of the gypsy moth, Lymantria dispar, to investigate whether the timing of transmission influences the evolution of virulence. In theory, early transmission should favour rapid replication and increase virulence, while late transmission should favour slower replication and reduce virulence. We tested this prediction by subjecting one set of 10 virus lineages to early transmission (Early viruses) and another set to late transmission (Late viruses). Each lineage of virus underwent nine cycles of transmission. Virulence assays on these lineages indicated that viruses transmitted early were significantly more lethal than those transmitted late. Increased exploitation of the host appears to come at a cost, however. While Early viruses initially produced more progeny, Late viruses were ultimately more productive over the entire duration of the infection. These results illustrate fitness trade-offs associated with the evolution of virulence and indicate that milder viruses can obtain a numerical advantage when mild and harmful strains tend to infect separate hosts.",
"Virulence-transmission trade-offs and population divergence in virulence in a naturally occurring butterfly parasite.",
"\nVS Cooper, MH Reiskind, et al. Published 2002 in PNAS doi:10.1073/pnas.0710909105",
"Why do parasites harm their hosts? Conventional wisdom holds that because parasites depend on their hosts for survival and transmission, they should evolve to become benign, yet many parasites cause harm. Theory predicts that parasites could evolve virulence (i.e., parasite-induced reductions in host fitness) by balancing the transmission benefits of parasite replication with the costs of host death. This idea has led researchers to predict how human interventions—such as vaccines—may alter virulence evolution, yet empirical support is critically lacking. We studied a protozoan parasite of monarch butterflies and found that higher levels of within-host replication resulted in both higher virulence and greater transmission, thus lending support to the idea that selection for parasite transmission can favor parasite genotypes that cause substantial harm. Parasite fitness was maximized at an intermediate level of parasite replication, beyond which the cost of increased host mortality outweighed the benefit of increased transmission. A separate experiment confirmed genetic relationships between parasite replication and virulence, and showed that parasite genotypes from two monarch populations caused different virulence. These results show that selection on parasite transmission can explain why parasites harm their hosts, and suggest that constraints imposed by host ecology can lead to population divergence in parasite virulence. "
] |
[
"To add - some viruses are 'unreachable' to out immune system - rabies, herpes. They sit in our nerve cells where blood cannot reach and thus our white blood cells can't as well."
] |
[
"What happens to the observable universe as you move through it?"
] |
[
false
] |
From my understanding, everything appears to be at its own center of the universe, with the most distant visible objects being aftermath of the big bang and the closest objects being ourselves. I know that the faster something moves through space, the less that object passes through time; and that the space within our universe is expanding at an accelerating rate which means it's possible or will be true that we can never see beyond a certain point. If we were to travel to a distant vantage point (eg: near another galaxy) within our lifetime for example, how would the edge of the observable universe compare to the one we see today on earth? Would we still see the same objects from the observable universe we started with but older? Or would new particles be formed (As energy isn't constant) creating the constant illusion that we're at the center of the observable universe. But these both don't make sense to me. Where could I learn this?
|
[
"Neil DeGrasse Tyson uses the analogy of a ship on the ocean with the 2d observable horizon representing the 3d observable universe.",
"If you were in andromeda galaxy you would be able to see some of the universe the milky way couldn't see. However the milky way would be able to see some of the universe the andromeda galaxy couldn't see. In the time it took you to get to the andromeda galaxy the visible universe for all observers would have grown as more time would have past to let light from distant locations reach us.",
"Since nothing can travel faster than the speed of light anything an observer can currently see they will still be able to see even if they change position. In other words the boundaries of each observer's observable universe are accelerator faster than the observer can move.",
"edit:",
"I just wanted to clarify that the universe is likely bigger than the observable universe (probably infinite) and each point ",
" a/the center (or there isn't a center); not just appearing to be one."
] |
[
"Right now, the edge of the observable universe is a lot of protons with massive amounts of energy. What happens to those as we start moving at faster speeds?",
"Not much. The cosmic background radiation would be redshifted behind you and blueshifted in front of you.",
"and/or what does the end of the universe look like because of space expanding at a faster rate than light? Does more energy suddenly appear to create more particles?",
"I'm not sure what you mean by end of the universe. There is no edge if you mean geometrically. If you mean ultimate fate of the universe then a leading theory is heat death. Basically all particles get too far away from one another to interact and there would be no ability to transfer energy."
] |
[
"Thanks!",
"Alright, so what we see now will always remain and age in our observable universe, which is technically different for any other individual point during the \"same\" time.",
"Right now, the edge of the observable universe is a lot of protons with massive amounts of energy. What happens to those as we start moving at faster speeds? and/or what does the end of the universe look like because of space expanding at a faster rate than light? Does more energy suddenly appear to create more particles?",
"I have so many questions."
] |
[
"If we put a telescope, say, 10 light years away, identical to kepler, looking at our solar system, what planets would it be able to detect?"
] |
[
false
] |
[deleted]
|
[
"Most of the planets Kepler will detect will typically be between about 100pc and 1kpc (1parsec=3.1 light years). So If someone had the equivalent of Kepler in a solar system at say 500 pc they could detect Earth. But... that star would have to be within about 1/2 degree of being along the ecliptic plane on the sky in order for them see see Earth transiting the Sun.",
"Source",
"They would be able to see Earth at roughly 1630 light years away if they are close to being along the ecliptic plane (basically have Earth be in its line of sight as it is crossing the sun) so it is very easy to assume that we could see all of the planets, again assuming we could see each planet as it passes across our sun."
] |
[
"It's not just a matter of the size of a planet, it's a matter of time. For a transit to be confirmed as a planet, it needs to be seen at least 3 times, so you need to look at the star for at least three times the orbital period of the planet. So to detect an object at Earth's orbital radius, you'd need to look for at least 3 years (actually just over 2, if you got lucky and the first transit was right at the start of your observations). Jupiter takes 11.8 years to orbit the sun according to Wikipedia, so you'd need either 24 years and a lot of luck or 36 years to spot it as a planet.",
"Obviously you also have to be looking down the plane of the system too, so that the planets pass in front of the sun for you.",
"I can't speak for which planets would be detected, but it's basically a function of the size of the planet compared to it's orbital radius, ie how much of the sun it blocks out when it moves in front of your line of sight."
] |
[
"Er, that's kind of how it works? Astronomy isn't done by staring through telescopes manually any more... But you can see more than one star at a time with each telescope..."
] |
[
"If kepler 22b is 2.5 times the size of Earth would theoretical humans living on the planet have to be 2.5 times the size of Earth humans due to gravity?"
] |
[
false
] |
How would "humans" be different if they lived on the planet? Suppose that a human species evolved in a similar fashion as we did but this process occurred on Keplar 22. *Suppose for the purpose of this question, Keplar's gravitational force is exactly 2.4x as great as Earth's.
|
[
"Kepler"
] |
[
"Gravity is more dangerous to large creatures than it is to small creatures. An ant can fall from any height and have no ill effects upon landing. If they same conditions were placed on an elephant, it would explode upon impact. Only sea creatures can afford to be immense because they are suspended in water.",
"Creatures that evolve on a planet with large gravitational forces would be motivated to be smaller than on a planet with smaller forces unless an extremely dense atmosphere, or water was supporting their bodies."
] |
[
"it is, we only know the size of the planet, not its density, so we don't know how massive the planet is. force due to gravity= G * Mass1 * Mass2 / (Distance between them)",
"or F= Mass1 g where g is the acceleration on the earths surface"
] |
[
"Do objects \"splash\" when they enter a planet's atmosphere?"
] |
[
false
] |
A thought occurred to me this weekend watching a youngster "splash" puddles... Specifically, that when one "stomps" a sufficiently shallow puddle, the water displaces to such a degree as to effectively "empty" the puddle. Can an object entering a planet's atmosphere have a similar effect? Does the entering object cause enough displacement to allow some portion of the atmosphere to "escape" the planet? If yes, could a suitably large object displace enough atmosphere to harm the planet's eco-system? If yes, could enough frequency of smaller objects displace enough atmosphere to harm the planet's eco-system? Thoughts?
|
[
"The primary reason liquids 'splash' is because liquids are incompressible, so when something (like a toddlers foot) enters a body of water, that water has to go 'somewhere'. When you do the same with a body of gas, the gas on the leading edge can simply compress to take up less volume and make enough room for the object. Also consider that the 'edge' of the atmosphere is not distinct like the free surface of a liquid pond, there is a gradual reduction in density over many kilometers of altitude - so the object doesn't suddenly hit the atmosphere, it gradually encounters increasingly dense gasses as it descends, from basically zero density in 'outer space' to the density of the atmosphere at ground level.",
"While #Idonthavethefactstobackthisup, I suspect more atmosphere could be lost when objects ",
" the atmosphere, due to viscous drag and entrained flow, than when objects enter the atmosphere."
] |
[
"gasses escape our atmosphere all the time, that's why helium loss is a big concern. They're not really 'bound' to the earth so much as they don't have enough energy to escape unless that energy is supplied to them from something external (like a spaceship exiting the planet)."
] |
[
"Yes and no. It is possible to \"skip\" along the atmosphere -- hypersonic waveriders are designed to exploit this nature of the upper atmosphere. There isn't a real ",
" however because the atmosphere compresses pretty well and just makes waves rather than actual splashes. ",
"For some \"data\" look at ",
"the altitude track",
" from a high-altitude balloon from a group I help with. The balloon payload freefalls after burst (at the maximum altitude in the google-earth picture) and once the atmosphere is thick enough to sustain significant drag from the parachute, the descent is slowed. This is usually around 50,000-60,000 ft and if you look at the ",
"other flights",
" you'll find ",
"similar trends",
".",
"EDIT: Aside from some weird flow visualization, there's not a good way to show that the atmosphere doesn't \"splash\" because you've got to recreate the exponential density gradient that you see from space to wherever you mark the \"start\" of the atmosphere where you're looking for a splash phenomena. I showed the balloon data because it's what I have and it's the easiest way to present the idea that you do indeed see a significant separation between space and the atmosphere. But only conceptually can I explain that there isn't a hard change in density like there is between air and water ergo no qualitative \"splash.\""
] |
[
"What is the medical consensus on tourniquets?"
] |
[
false
] |
I'm not referring to ones used for surgery, etc. I'm asking if it's beneficial or harmful to use a tourniquet in a survival situation, miles away from medical attention. Also, is it beneficial to use a tourniquet for short-term blood stoppage. Like if you cut yourself and were waiting for an ambulance (although I'm sure the emergency operator would tell you what to do over the phone, I can't really call 911 just to ask a question.) My reason for asking is because I've been led to believe many different things regarding tourniquets. I've heard that tying a tourniquet is an absolute last ditch effort to preserve life, by stopping blood loss. The issue, however, is that tying one likely would lead to the loss of the injured limb, due to it dying from being devoid of blood. I've also heard that tying one CAN result in limb loss, but it isn't an issue unless the tourniquet is tied for 6-8 hours. Seems plausible. I've also heard that you can leave a tourniquet applied for days with no I'll effects. Seems totally ridiculous. And, finally, I've heard that they don't even work unless applied by a medical professional. So what's the deal? Is there ever a reason for an amateur to tie a tourniquet? And if so, when would it be practical?
|
[
"Prior to the Iraqi and Afghanistan conflicts, tourniquets were considered the fourth and last resort for uncontrolled bleeding (1. Direct pressure, 2. Elevation, 3. Pressure point, 4. Tourniquet) They were considered risky due to tissue damage and release of lactic acid and other toxins when removed. During the recent military conflicts research has shown that tourniquets are not as risky as thought and are efficient and safe as long as they are removed within a reasonable amount of time. The standard medical protocol for uncontrolled bleeding now only includes 1. Direct pressure, and 2. Tourniquet if direct pressure is ineffective. Elevation and pressure points have been removed from the protocol as being unnecessary. "
] |
[
"As long as they are removed within a reasonable amount of time ",
"How is that reasonable amount of time defined? 6-8 hours?"
] |
[
"I'm not sure but 6-8 hours after a tourniquet can cause severe tissue damage. I believe that the safe amount of time for a tourniquet is somewhere between 2-3 hours. "
] |
[
"How strong of an environmental impact does discarded glass cause?"
] |
[
false
] |
I know that plastic causes a large impact on the environment, but what about glass? Glass isn't biodegradable, but you rarely hear about glass pollution. What sorts of negative impacts are caused by glass?
|
[
"It takes up space in landfills, but other than that glass is more or less harmless. Crush it up and you essentially have sand."
] |
[
"Apparently ground glass melts at a much lower temperature than sand, plus saved materials, shipping, etc. Glass is probably only behind metal in recycling efficiency. Still, glass is essentially a transparent rock, so discarded glass is really only detrimental in that loss of recycling efficiency. "
] |
[
"Weathered glass can make for a cool find on the beach.",
"Can anyone comment on the energy lost by not recycling? That is, how much energy does a single bottle have the power to save?"
] |
[
"Why prescription drugs are so expensive in US?"
] |
[
false
] | null |
[
"The free market functions for generics. After the patent period ends, anyone is free to manufacture the same drug under the generic name. A brand may still be sold as more expensive, since it has certain restrictions for the brand name (generic only needs to be within like 20% active drug accuracy).",
"Some drugs, no matter how free market you want to get, are going to be expensive to manufacture. There are also other costs involved in medicine ALL the time. Point is, if someone could dump it for cheaper and make a profit, they would."
] |
[
"Not always. Colchicine, important for gout and available for well over 100 years, recently went from about $.10 per pill to about $5 per pill.",
"http://en.wikipedia.org/wiki/Colchicine#Marketing_exclusivity_in_the_United_States"
] |
[
"But they did force people like me to buy out of Canada and ran a marketing campaign stating that the drug I've been buying for years was unsafe. And they did force other producers of the drug to not sell in the US."
] |
[
"why does water seem to stick to glass?"
] |
[
false
] |
More specifically the water I put in glass test tubes. When I pour it down the drain in notice there's still a noticeable amount left that's kinda difficult to get rid of. We use these other vials for testing and I've noticed the same thing with them too (they're made of borosilicate, not sure about the test tubes). I don't seem to notice this when washing dishes at home though.
|
[
"Adhesion.",
" Water \"seems\" to stick to glass because it does.",
"I don't seem to notice this when washing dishes at home though.",
"It certainly still does, but (a) possible you're looking at non-transparent dishes so you're not really noticing it, and (b) soap in the water will massively reduce the surface tension and reduce surface adhesion."
] |
[
"The short answer is that glass--an amorphous compound containing primarily silicon and oxygen--tends to form something known as silanol on its surface. These silanol groups are Si-OH formed when oxygen atoms dangling from the surface of the SiO4 matrix react with moisture in the air. They form hydrogen bonds with liquid water, causing it to adhere to the surface of the glass very strongly. This won't happen as much with dishes and cookware because they often receive special coatings (e.g. PTFE/Teflon) specifically to prevent this adhesion. "
] |
[
"Adding on to this, with some liquids we see the opposite effect. Mercury in a glass beaker, for example, is repulsed by the sides of the container. As a result, the mercury on the surface forms a dome instead of the bowl shape we see with water."
] |
[
"If a projectile is fired vertically and then at an angle changing nothing else, do they both travel the same distance before they lose upward momentum?"
] |
[
false
] |
This may not be worded perfectly, but if you were to fire a projectile with a force known to make it peak at say 200', and then fire the same projectile with the same force, changing only the angle of the barrel, say 30 degrees off vertical, does the projectile still travel 200' before it begins to fall?
|
[
"No. Firing straight up will make the projectile go higher.",
"If you point the projectile straight up, all its energy is directed toward making it rise upward. If you point it at an angle, some energy is directed toward making it go horizontally-- which means less energy directed to making it rise.",
"To put it another way: aim up, and you get 100% up. Aim at an angle, and may you get 80% up and 20% sideways (for example). Since 80 is less than 100, the projectile won't go as high."
] |
[
"I think you're misinterpreting the question. He's asking if the projectile has travelled the same distance through space relative to the cannon - that is, does the length of the straight line up and down equal to the arc of a projectile with a horizontal component."
] |
[
"You might want to ask this in ",
"/r/learnmath",
" or ",
"/r/casualmath",
" instead.",
"Question clarification: You're asking if the ",
"arc length",
" of the ",
"trajectory",
" is the same, right? Just clarifying that you don't mean \"do they reach the same height?\" or something else."
] |
[
"How come we can't see the milky way with special goggles or glasses the way photographers and film makers use special filters to record and capture the night sky?"
] |
[
false
] |
[deleted]
|
[
"To get these incredibly vivid pictures of celestial objects, the photographers will have exposure times of anywhere from a few seconds to many hours (in addition to being in a place with minimal light pollution). So, in order to see these same images, you'd need to take all the light that falls into your eye over the course of multiple seconds, minutes, or hours, and perceive it all at once.",
"Or put another way, you'll never be able to look up at the night sky and see images like ",
"this",
". Sorry."
] |
[
"Well first of all, you should learn about the pollution of light.",
"And of cause there are only a few times the milky way is as visible at pitch black night.\nSo, you would have to be anywhere far off other light sources, and you should check when the milky way is at best visibility.",
"So, filters aren't everything, and I would say the least important thing"
] |
[
"The filters are used to pick up different wavelengths which our eyes cant otherwise detect...fair enough, but apart from that these photographers also use extremely long exposure times to make the image \"bright\" by capturing a lot more photons than you would in a normal snapshot of when you look at it with your naked eye. ",
"Once you layer together 5 different images, all taken with long exposures, you get much more light in that photo than you would otherwise perceive in a second observing it directly. "
] |
[
"Dimensions: are they real? And if not, why do we postulate a center-less, edge-less universe?"
] |
[
false
] |
We can move left-right, up-down, and forward-backward. We can imagine a universe wherein objects lose one or two of these possibilities, as well as ones in which they gain extra possibilities for motion and length (4 and 5 dimensional universes). And to answer the question "does our universe have a center and an edge?" physicists say "neither, because our 3-dimensional space curves into a 4th dimension." I get the analogy of a sphere having a two dimensional surface curved into the third dimension, on which an observrer would never discover a center or an edge, but I get how we confidently extrapolate this thought experiment into our reality. Do dimensions actually exist? Aren't x, y, and z really just concepts?
|
[
"Dimensions actually exist insofar as they are useful constructs to describe and communicate our observations about the world. Whether we consider the concept of dimensions \"real\" or not isn't all that important. What is important is their definition helps explain physical observation, i.e how to quantify the difference between two objects that are displaced from one-another. What I wrote above applies to any concept in science. And if you asked if gravity is real or if human thought is real or if mass or force is real, we can just replace the word \"dimension\" above with those words instead.",
"physicists say \"neither, because our 3-dimensional space curves into a 4th dimension.\"",
"We wouldn't say this! Spacetime is a system of four dimensions, three spatial and one time, all of which are subject to curvature. We don't need to \"embed\" this curvature in a \"higher dimension,\" because our theory is a local theory, thus all of its geometry involves intrinsic properties. While you can represent a 2D spherical geometry on a 3D sphere, we don't necessarily ",
"We think the universe is most likely a flat-infinite universe which has neither center nor edges. I suggest you tackle the Astronomy FAQ in the sidebar for some explanations on why we think those things."
] |
[
"I ",
" that show. I've tried to like it, but against all fiber of being, I find no joy in it."
] |
[
"The big bang, despite its suggestive name doesn't actually describe the moment of creation. The big bang model describes the early universe quite accurately to just a ",
" amount of time after the initial state of the universe. For earlier times including t=0, we do not have a physical model and lack understanding.",
"Anyway, ",
" t=0 and a little bit of time thereafter, our understanding kicks in. The big bang has absolutely no problem with the idea of an infinite universe as the big bang was an event of space expansion. An analogy would be like imaging a dot sitting on every integer on the number line and then moving all the dots to sit on every ",
" integer. Now there's twice the space between any two dots, but you still have an infinite number of them like you had before.",
"In that, it's better to think of the big bang as the process where the universe went from a very hot and high density state to a much colder and lower density state. The notion that the universe was infinite at these early moments doesn't pose any challenges.",
"Mind you, even if our universe isn't infinite, like say bounded like the surface of a sphere, we'd still use this exact same description of the big bang--high density to low density by changing the distances between points."
] |
[
"Possible adverse effects of 1,3-dimethylamylamine?"
] |
[
false
] |
[deleted]
|
[
"Maybe ",
"this report from the Department of Defense",
" and ",
"this literature review",
" will help. They both give some of the history of the situation and a better understanding about from where the controversy originates.",
"The DoD article specifically mentions:",
"So, it's a bit related to the effects of other pseudoephedrine derivatives, such as methamphetamine. Generally, relatively small molecule-based amines can be thought to have some potential neurological effects, since they can usually cross the ",
"blood-brain barrier",
"."
] |
[
"That's a lot of good info thanks! "
] |
[
"i know nothing about this chemical but i am familiar with a host of others. firstly, meth(amphetamine) itself is a synthetic drug and secondly, just because a drug has 'meth' in its name it will not necessarily be relative in its properties to regular meth. MDMA = methylenedioxymethamphetamine, for example, and i do not think they're very similar at all.",
"maybe thats not what you meant though..?"
] |
[
"Why was Rhodium so expensive in the early 90s?"
] |
[
false
] | null |
[
"Rhodium has currently has very few industrial applications outside of catalytic converters for automobiles, which consumes about 80% of the rhodium supply each year.",
"The 80's saw legislation requiring all new vehicles to have catalytic converters, and the transition to the unleaded fuels that works best with them, increasing demand for rhodium.",
"The early 90's also maked the rise of the larger SUVs, which required more rhodium than smaller vehicles.",
"So, with a new global hunger for what was previously a very rare but seldom used metal, demand outstripped supply until reserves reached a critical point. Prices spiked until new supplies were tapped and a new equilibrium was reached."
] |
[
"My guess would be because Russia is the second largest exporter and that spike is during the collapse of the Soviet Union."
] |
[
"This looks like a pretty reasonable explanation. Have an orangered."
] |
[
"How does a cell know where it is and what to do?"
] |
[
false
] |
How do we get our basic body shape? When we are forming how does a cell know that its on the arm and should turn into part of the hand?
|
[
"This is a complicated question that could be answered in a lot of different ways. I will try to keep it simple and mostly technically correct.",
"All of your somatic (body) cells have the same genes. Your body makes stuff by using genes to make templates for proteins. Not all of genes are \"on\" at the same time, and what's on and what's off is called epigenetics. Stretches of DNA can have methyl groups added and be wrapped around histone proteins; they are spooled up and basically put on a back shelf. This is more or less permanent, and is what happens to genes a cell will probably never use.",
"You can also control a gene by messing with the promoter. The promoter is a region of DNA that tells the cell \"here I am, transcribe me starting here\" - sort of like a file header but more interactive. Proteins can bind to this promoter and make it more or less active.",
"The ability to control transcription of a protein with a protein lets you start making systems like logic gates and feedback loops. A cell is also a computer. The ",
"lac operon",
" is a lot like a while loop in programming.",
"Cells are also networked. They can send signals to eachother, turn on and off genes in eachother, and all that fun stuff. They do this with diffusable chemical signals, and the specific set of genes involved in controlling overall body shape is called the ",
"homeobox genes",
". Messing with these genes will result in ",
"fruit flies with fully formed legs on their faces",
" and other weird things."
] |
[
"Some cells are simply in what they can do based off their structure, this is called the ",
"potency",
" of the cell. Some stem cells have limited trees ",
"of what they can and can't become.",
" Other cells like embryonic stem cells have very large trees of potential progression.",
"However, that's not the whole story, this is just saying that certain cells have the tools to do one thing while another might have the tools to do different things. The second half of the story is the ",
"extra-cellular matrix",
" which is the tissue and chemical stew surrounding the cells. Chemical signaling from neighbor cells, cell adhesion and nutrient supply instruct the cell on what to do with the potency it has.",
"For instance, ",
"VEGF",
" is one of the chemical signals used to induce endothelial cell migration and the formation of capillaries. But tissue is complicated, the ",
" itself might tell the cell to do one thing, while the ratio between two other chemicals might tell it to do another. Some signals might even cause the cell to revert to an \"ealier\" state, divide, self-cell death or a whole host of other activities."
] |
[
"In Embryonic development, your body guides the differentiation of cells using signal compounds/proteins called morphogens. The morphogenic diffusion gradient (called a morphogenic field), is detected via amphiphillic receptor proteins, which then respond by activating or deactivating certain sensory/developmental transcriptional networks as well as some signal transduction networks in order to begin the cell's differentiation into a specialized component of a larger being. Now the actual math behind this gets a little tricky (partial derivatives mostly and multiple integrals) but once you get the basics its not that bad. For an excellent introduction into this idea, as well as systems biology in general (which looks at these networks and others) I would suggest ",
"\"An Introduction to Systems Biology\nDesign Principles of Biological Circuits\nBy Uri Alon\"",
"Great book, and perfect if you want to know more about this topic.\n(Chapter 6 covers basic regulatory motifs in developmental networks, and Ch 8 goes more into depth into the whole concept of \"robust systems\" in development."
] |
[
"If very loud noises can damage your hearing and very bright lights can damage your sight, can very strong odors damage your sense of smell?"
] |
[
false
] | null |
[
"Loud noises and bright lights are damaging because of the energy they carry; scents, on the other hand, are merely particles suspended in the air. Sure, many chemicals could do serious damage to your olfactory receptors if you inhaled them through your nose, but it would be because of their reactivity, not their pungency. In such a scenario, damage to your lungs would probably be your primary concern."
] |
[
"indeed, though the capacity of light to damage the retina also does not necessarily correlate with a strong sensation of vision. light beyond the visible spectrum in both directions is also capable of damaging tissues (including the retina). Similarly, noise, which is just pressure oscillation, can do damage beyond the 20-20,000Hz that humans are capable of hearing, and certain \"smells\", which are just chemicals, can damage our olfactory receptors but don't necessarily produce the perception of smell."
] |
[
"Olfaction (scent) and gustation (tongue) are different and follow different mechanisms of detection. Both combine to form the percept of taste. In the case of the tongue, we have five distinct taste receptors that react to various stimuli:",
"There is some debate about 'mouthfeel' and the taste of lipids. ",
"In any case, we have a very limited number of percepts available in our gustatory system. If we put very concentrated acid on our tongue, we ",
" feel it as being painfully sour and that would probably also kill the taste buds.",
"The olfactory system works on a different principle. There are >300 receptors that each accept a different odor compound. These odors are generally aerosolized solids or liquids.",
"So no, extreme reactivity does not mean extreme pungency. For example, Cesium is highly reactive but it probably would not activate any taste buds in the tongue. If anything it might taste a bit salty. "
] |
[
"Do fish make friends with eachother? Do they make friends with fish that aren't the same type of fish as themselves?"
] |
[
false
] |
Like, especially in a school of fish such as neon tetras, for a simple example. Do they have certain members of the school that they like or dislike, do they make friends and enemies?
|
[
"\"Friend\" might be too complicated of a concept for fish, and there is a huge difference in behavior between different species. But...",
"Yes, in general there are a lot of fish that will at least look like they've made friends with other species. Hang out in the same cave with each other, follow each other around and so on."
] |
[
"I'm going to go out on a limb and say that a fish like a Tetras life is pretty darn busy. probably a little too busy to make friends or form lasting relationships. One reason is they don't live very long, and they spend their entire life either looking out for predators, hiding or dodging predators, eating, mating, or getting eaten by predators. There's not much room in there for a social life poor things. Also they would make horrible friends anyway, schooling fish tend to turn on each other the moment they discover weakness."
] |
[
"There’s actually an episode of an ocean documentary where a grouper and an octopus are friends with each other and have a well formulated hunting strategy together. The octopus covers a rock formation with its tentacles, trapping small fish inside. The small fish try to escape through openings where the waiting grouper gobbles them up. The fish that do not escape the octopus are eaten and the pair make their way to the next hunting spot together.",
"Edit: I believe the nature doc was Blue Planet."
] |
[
"Why does switching the batteries around in a remote make it work for a little bit?"
] |
[
false
] |
This always seems to work with most electronic, battery-powered devices. The most obvious reference being a remote control.
|
[
"The electrical contacts on the battery and/or battery holder build up a thin layer of corrosion that resists current flow. Moving the batteries around scratches the contacts and exposes fresh metal, improving conductivity."
] |
[
"I was merely addressing the \"one battery is more drained than the other\" question. A 1.1v battery and a .9v battery will always add up to 2v, no matter what order you put them in. "
] |
[
"I was merely addressing the \"one battery is more drained than the other\" question. A 1.1v battery and a .9v battery will always add up to 2v, no matter what order you put them in. "
] |
[
"Linguists: Are there studies that look to find links between Asian language and Native North American speech?"
] |
[
false
] | null |
[
"The linguist Edward Vajda has proposed a link between the Na-Dené language family in North America and the Yeniseian languages in Siberian. (see ",
"https://www.uaf.edu/anlc/dy/",
" or ",
"https://en.wikipedia.org/wiki/Dené–Yeniseian_languages",
"). I'm not a linguist, so it's not clear to me how well-established this connection is."
] |
[
"the link has also been genetically established",
"1) \"Genetic\" connections mean something entirely different in linguistics, FYI. It only refers to the likelihood of languages being related, not any current or past speakers via their DNA. I mention this because your comment as literally taken is actually false, as there is still a lot of debate going on. However, I understand what you meant, which leads me to...",
"2) It doesn't matter if modern day speakers are closely genetically related or not. Languages don't spread the same way as genes. Squirrels don't decide to become birds over the course of several generations because it might benefit them, but populations lose and adopt other languages when it does benefit them. Cultural assimilation is a big factor in language spread and you can never discount it. As a result, genetics studies don't tell you anything useful about the history of language. "
] |
[
"I'm not a linguist, so it's not clear to me how well-established this connection is.",
"It's not well established, but it's not out of the question. If the connection does exist, there's also the debate about whether it means Yeniseian-speakers remained behind in Siberia as the Na Dene-speakers headed east into the Americas; or whether the Yeniseians are part of a migration into Siberia from the Americas. Beringia wasn't a one-way road, after all."
] |
[
"Does chewing your nails increase your resistance to disease?"
] |
[
false
] |
I have the bad habit of chewing my nails, yet I have a very strong immune system and rarely get sick, and when I do, it's usually something mild enough I can go to work with. Since nails are a breeding pot for bacteria (many harmful) and I constantly get them in my mouth through chewing, does the body respond to them by producing antibodies or something like that which increases resistance to common diseases? Hope I asked that right.
|
[
"No, things you eat, including bacteria, are typically broken down by the acidity of the stomach. There is no positive correlation between nail chewing and immune system strength.",
"You can even cause ",
"Melanonchyia",
" which looks a little strange, but does have ",
"other",
" causes."
] |
[
"It doesn't matter that you're not swallowing the chunks you tear off, you will be swallowing some of the material you chew, it's inevitable. And yes, the principle still applies, your mouth is a huge mucous membrane, the bacteria will mingle with saliva, which you swallow 1/4 cup of each day and still end up in the stomach."
] |
[
"I'm making a honest-to-goodness question. I don't think that ",
"/r/shittyaskscience",
" would be the right place to ask a genuine question like this."
] |
[
"How does NASA control rovers if theres like 5 minutes of delay?"
] |
[
false
] |
Because the radio wave thingies get sent at light speed and theres a delay, how does NASA control rovers with such precision? Sorry for being dumb and probably getting the flair wrong.
|
[
"It's not like a remote control car where you move it around and react to the environment, they send a series of commands to the rovers and they follow them.\nPlus there'll be an onboard AI in the rover to prevent it doing things like like falling down a ditch."
] |
[
"Most of what the rovers do is automated. For example, that whole entry sequence all the way to the landing was pre-programmed so that the rover and its \"helicopter\" work without any human input. The only thing that NASA tells it to do is either to move to a location and to operate its sensors."
] |
[
"Most of what they do isn't automated. The landing sequence and helicopter are automated because they have to be, no real other option. Once the rover is on the ground, it has stereo cameras to make a map. ",
"It does have an autonav mode using which it can detect obstacles and plan a path and move around, but it's not used much because it's slow and lacks perceptual context. The main control that's done isn't like a joystick or manual commands or anything, but it's more like waypoint control. It makes a map of closeby and the operators look around, tell it to go to a particular place using a particular path, and it follows that path confirming it's not too off path using visual odometry."
] |
[
"Is pouring cold water on yourself beneficial if the air temperature is significantly greater than your body temperature?"
] |
[
false
] | null |
[
"Evaporation uses a massive amount of energy, it's excellent at cooling you. Even if the water is quite hot it can still cool you."
] |
[
"Evaporation is an endothermic process, and it removes heat from the environment. ",
"It's like a cold pack of water and ammonium chloride that you can buy from the shops to cool you down.",
"http://en.wikipedia.org/wiki/Instant_cold_pack"
] |
[
"Heat and temperature are not the same thing. This might start to get a little complicated, but try to bear with me.",
"The water has a high ability to accept a lot of heat from another substance before it raises in temperature. The air has a lower capacity to accept heat before it raises in temperature. So, if your body temperature is 98 degrees, and the water on you is initially 60 degrees, the water will continue absorbing heat from your skin until it starts to evaporate. When the water evaporates all of the heat that it has absorbed from your skin is used in the process of vaporization or \"stored\" in the molecules themselves, which is in effect taking heat away from your body, lowering your temperature.",
"Again, this is a simplification, if you're interested in more in depth information peruse through these wikipedia pages: ",
"Heat Capacity",
" ",
"Specific Heat of Vaporizatiion"
] |
[
"If you got shot, how likely is it you would actually bleed from the mouth?"
] |
[
false
] |
In movies you always see people getting cut down in a line of fire and then all of the sudden bleeding profusely from their mouths. How accurate is this to what would actually happen if you were shot? If it is indeed accurate, what happens to make this happen?
|
[
"I can't give you an exact probability, but if there is tissue damage to your lungs or anywhere in your upper GI tract, this can lead to hemorrhage which could result in blood coming from your mouth. If it is in the GI tract, it would more likely be vomiting blood. "
] |
[
"Well if they're dying slowly, the character usually has something to say. Coughing and spitting up blood would make that difficult. "
] |
[
"Just consider where it would be coming from. Your lungs are relative large and cover quite a bit of your torso. A bullet is likely to damage your lungs if you're shot in the chest, and you bleed out internally. As long as you're breathing, you're creating a cycle of negative/positive pressure in your chest cavity. Breathing in, pressure's low, lots of blood spills into lungs, breathe out, some blood is brought up with the air."
] |
[
"How did the study linking MMR vaccine and autism come to be published in The Lancet if it was obviously flawed?"
] |
[
false
] |
I would have thought that a reputable journal of the calibre of The Lancet would vet any article submitted for publication very rigorously.
|
[
"So I want to preface this by stating that Wakefield's 1998 Lancet paper contained (essentially) fabricated data, and was probably influenced by unreported financial conflicts of interest, i.e. the paper is bunk.",
"HOWEVER, claiming that the paper is obviously flawed, as far as I am aware, is not accurate. It is my understanding that in reading the paper, which is essence is a series of case reports of so called \"autistic enterocolitis\", there is nothing to suggest that there is anything wrong with the paper (unless you want to argue that 'how come the link was never noted before', to which I would say, rare events ",
" be missed in underpowered clinical trials, i.e. just because a side effect has not previously been noted does not mean that the side effect does not exist). ",
"A lot of people misunderstand how peer review occurs, i.e. the process by which peers of the author, and editors of the journal, make comments on the manuscript, and decide whether it is published. In the vast majority of cases, peer reviewers and editors simple get the text and figures of the paper. The do not look at raw data, or collected samples, or equipment, or anything outside of what is presented in the manuscript. The whole process relies on good faith (which in part is why scientific fraud is far more common that a lot of people would like to admit). Hence, when the editors and peer reviewers saw Wakefield's manuscript, they saw something very interesting and potentially very concerning.",
"The cynical reader might have a slightly different thing to add. The owners of journals want their journals to have a high impact factor (basically a measure of how often the papers in the journal are read). Editors of journals can lose their job if the impact factor of a journal goes down. The journals that already have a high impact factor (like the Lancet) instead like it when their articles are in the news. One might wonder if the editors of The Lancet also considered how much press coverage this article would generate.",
"However, perhaps there is a specific \"obvious\" flaw that you know about, that I am unaware of. If so, the answer is that peer review isn't perfect. One of the many reasons why science relies on replication."
] |
[
"without making sure it was conducted the way it should be.",
"None of science works like this. I think there's an idea that when you do some $100,000 study on \"blah\" and submit the results to a peer reviewed journal that those peer reviewers, like, fly out to your lab and examine all your equipment and use $300,000 of their own to replicate your results 3 times and pour over your 30 pages of raw data looking for inconsistencies and redo all your statistics themselves to make sure it adds up.",
"In reality, they spend an afternoon reading through your manuscript and taking it at face value. Unless something immediately screams \"fishy\" about your stats they'll assume you did them as you said you did. If you say you used method X and X is well known to over-estimate Y and you say Y is high, THAT'S something they will catch you on and grill you. But if you say you use method X and actually used method Y, it's often not possible for them to know unless your results are obviously not possible using method X. All they have is what you say and how that fits with existing literature to assess and all the time they're going to spend is probably an afternoon.",
"So a peer reviewer is an expert who spends an afternoon taking your paper at face value and establishing: is the work significant, are there any methodological shortcomings as describes, are the conclusions matched by the data."
] |
[
"Nono, it didn't come across as know it all.",
"The big mistake your friend is making (and that a lot of people make) is thinking that one scientific paper by itself means anything. I'm about to say something that may seem very strange, but read it carefully: The simple statistical fact is that Wakefield's publication could, theoretically, have been generated without any wrong doing whatsoever. I say this because all measurements have error, and all samples can be far away from true population. e.g. I could set up a test to see if aspirin causes cancer, and give it to 100 people, and just by dumb luck, all 100 could get cancer. It would be extremely unlikely, but it's possible: coincidences happen. This is why we repeat things. It would be incredibly unlikely that all 100 of my patients got cancer, but if ",
" did the study again, with new patients, and all of them got cancer too... we the chance of that happening if aspirin didn't cause cancer would be astronomically low. importantly, having the study repeated by another group takes care of a lot of things: maybe I had financial interest in saying aspirin is bad. Or maybe my batch of aspirin was contaminated. etc etc etc... i.e. the repetition not only dealt with statistical problems, it dealt with other problems too.",
"That's why single papers, by themselves, are generally not of much use, especially when it comes to nasty biological things that are super messy and complex and variable. That's why policy makers, in general, don't care about the findings of one paper: the look at \"meta-analysis\" where the findings of lots of papers are combined, to give a better over all understanding.",
"And finally, the beauty of this case is that Wakefield's observation WAS repeated, in a very large study, of just under 100,000 children, in a study specifically designed to test for autism. And guess what they found? ",
"No association, even in high risk groups",
". And that is the real reason you should believe that MMR vaccines are safe: not because Wakefield was struck off, not because he had conflicts of interest, not because he misreported his study design, not because he is generally an unpleasant crook, but because science took his claims seriously, and showed that they were false in an overwhelming way. "
] |
[
"After seeing a lot of sensationalist articles recently, what discoveries, studies or inventions are LEGITIMATELY out there right now that could make huge waves for humanity?"
] |
[
false
] | null |
[
"how it really amounts to a bunch of bologna",
"I don't have an answer, but I do need to point out that bologna = lunch meat. Baloney = nonsense."
] |
[
"My Physics professor often tells us that the two fields with the most potential to dramatically alter our lives in the coming years are the fields of genetic manipulation and neuroscience. Michael Chrichton's (slightly overdramatic) sci-fi novel 'Next' is an attempt to describe the vast potential of gene manufacturing and some of the awesome (and scary) implications it could have. That, coupled with recent advances in nanotechnology indicate that we are on the brink of major breakthroughs that will lead to whole new technologies, weapons, behaviors, etc. It could transform the world. ",
"Likewise, the study of the human consciousness is perhaps the only field that has been developed for hundreds of years but still is a huge mystery to those who study it. Harnessing the power of our own brains could dramatically alter the way humans interact and think; no one knows what could happen. "
] |
[
"The ",
"national ignition facility",
" is a little behind schedule, but still has a good chance of producing the first economically viable fusion reaction. Success at NIF could potentially mean massive production scale investment in fusion power production in our lifetimes, which would eventually mean a dramatic drop in the price of electricity and corresponding increases in environmental health and quality of living."
] |
[
"When eyes adjust to the dark, is the iris just letting more light in, or does the brain behave differently too?"
] |
[
false
] | null |
[
"The pupil can adjust to let in about ten times more light from its smallest to its largest. But the eye can increase its sensitivity by roughly a million times-- so there's more at work than just the pupil. This is the part that takes 20-30 minutes to happen when your eyes \"adjust to the dark,\" and it is a ",
"chemical process.",
" "
] |
[
"A timely eg for you, sir.",
"http://www.iflscience.com/health-and-medicine/how-the-eclipse-gave-some-people-superhuman-night-vision/"
] |
[
"Thanks! "
] |
[
"How can there be a separate vaccine for shingles?"
] |
[
false
] |
I am looking at a brochure for the shingles vaccine from my local supermarket/pharmacy. It says "If you've ever had chickenpox or the chickenpox vaccine you are at risk of developing shingles." What is going on with chickenpox/shingles? How is there a separate vaccine for shingles if it's the same virus that causes both diseases?
|
[
"Chickenpox is the physical manifestation of the varicella zoster virus. Once it \"goes away\" it continues to live and replicate VERY slowly in your spinal nerve cells. The slight infection that continues is well contained by your immune system. Sometimes, as an adult, if your body is immunocompromised due to anything from drugs to stress, the virus freely migrates down a line of nerve cells and breaches the skin. Thus, shingles is usually expressed on a patch of skin on one side of the body along a single nerve. It is, however, the same virus that infected you as a kid! Just a more condensed version. The vaccines are made of the same stuff, but the shingles version is about 14x as concentrated and loaded with chemicals called adjuvants that make your body think a real infection is happening. Your body amps up its defenses, specialized B and T cells with a memory to the proteins associated with the virus roam through your blood for the next several decades just waiting for shingles to try and emerge again."
] |
[
"You can group immunity in the blood into two groups: Cell mediated and humoral.",
"Shingles happens when our cell-mediated immunity (to the VZV virus) is low.",
"Chickenpox happens if we don't have any immunity to VZV.",
"The shingles vaccine boosts our cell mediated immunity as it is a live virus. This reduces the risk of the virus coming back as shingles."
] |
[
"Thank you for answering. What you said makes sense but the brochure I have also recommends getting the shingles vaccine if you've had shingles to prevent future shingles or to reduce the severity of any future shingles. If the vaccine basically mimics a shingles episode then why wouldn't a ",
" shingles episode basically provide the same benefits as the vaccine? "
] |
[
"How does the body \"decide\" where to lose weight from?"
] |
[
false
] |
I recently lost a lot of weight, mostly due to eating right and a bit of cardio. Unfortunately it has been mostly around my neck, face, chest and breasts, leaving me still with larger legs and "love handles". So how exactly does the body "decide" where it should lose weight from? Thanks!
|
[
"One major factor is hormones. Men and women tend to store fat very differently. Men tend to store fat on their stomachs, while women tend to store fat on their breasts, hips, and rear. ",
"Interestingly enough, this is based mostly on hormones. Transgender people who undergo cross-sex hormone therapy eventually undergo a shift of body fat distribution. Over a few years, a male-to-female individual on estrogen therapy will have her stomach thing out and her hips, butt, and chest grow fatter. A female-to-male person on testosterone will see his hips, posterior, and bust shrink and start storing fat on his stomach."
] |
[
"It's well documented that localized training does not affect fat burn in a certain area; that is, doing squats or oblique exercises will not get rid of your leg fat or love handles. Fat burn is more like peeling an onion, it comes off from the entire body rather than a single area. ",
"However, there are parts of the body more prone to storing fat, including the midsection and (especially in women) the thighs. These areas have a higher amount of fat, and so it will take longer for those areas to lose much of the excess. A lot of this can be contributed by genetics, but it's relatively constant throughout our species. "
] |
[
"It doesn't! Working out certain parts of your body will not stimulate the breakdown of fat in that area alone-- fat will be broken down from stores all over your body to provide the needed energy. Certain areas of your body are more likely to accumulate fat, and each part of your body does not lose fat at the same rate. It's not the same for everyone, there's a bunch of genetic factors. "
] |
[
"Why are some people allergic to metal? What is the antigen?"
] |
[
false
] |
From the little I know about allergies, it seems that people shouldn't be allergic to metal (cheap metal usually). So what is really going on? Is it a true allergy or is it a similar reaction?
|
[
"I'm inclined to say its a \"true\" allergy, inasmuch as its the same immune response as most allergies. The response is ",
"contact dermatitis",
". There is T lymphocyte involvement and upregulation of immuno-related hormones.",
"Specifically, it looks like experimentation has repeatedly confirmed that ",
"Nickel acts on the human Toll-like receptors",
" that are key to immune reponse."
] |
[
"How nickel turns on innate immune cells",
"Nickel hypersensitivity, an example of hapten-mediated ",
"allergic contact dermatitis",
"The 'antigen' is Nickel attached to a protein. Nickel, by itself, does not elicit an immune response; nickel is a hapten. The nickel ions from the jewelry gain access to dendritic cell within the skin. The nickel ions attach to proteins and this new 'nickel-peptide' is the antigen. ",
"the majority of us do not react to nickel, despite the near-ubiquitous presence nickel in our environment. Clearly, many factors influence our immunological response to nickel, with tolerance prevailing the majority of the time. How these regulatory mechanisms break down in affected individuals remains a mystery, but their elucidation will provide the basis for future prevention strategies.",
"I am not an immunologist, but do have training in the area. Please listen to an expert in Immunology over myself. "
] |
[
"I'd like to know as well."
] |
[
"How bright is a single photon?"
] |
[
false
] | null |
[
"The faintest light that a dark-adapted human eye can detect is ",
"about 90 photons",
", so a single photon is only 1% as bright as that.",
"By the way. The link is one entry in the ",
"Physics FAQ",
", maintained by John Baez at UC Riverside."
] |
[
"From a classical optics perspective, 'brightness' is a measure of the intensity of light when it strikes a detector (like your eye). The eye isn't the greatest detector in the world because it's not quite linear (2 million photons isn't necessarily twice as 'bright' as 1 million photons after going through neural processing) but it conveys the idea.",
"So brightness is basically a count of the number of photons.",
"As a result, the brightness of a single photon is...well, the minimum brightness that can be achieved for that particular wavelength of light. I'm sorry if it seems that my answer doesn't convey any information, but I think it's because of your misconception of what brightness is."
] |
[
"They found that about 90 photons had to enter the eye for a 60% success rate in responding. Since only about 10% of photons arriving at the eye actually reach the retina, this means that about 9 photons were actually required at the receptors. Since the photons would have been spread over about 350 rods, ",
", even if the subjects were not able to see such photons when they arrived too infrequently."
] |
[
"Why is there so much mystery shrouding the Oort Cloud? Do we know anything concrete about it's existence?"
] |
[
false
] |
A quick google search shows there isn't much consensus on the topic and it seems as if we're not even sure it exists. Some articles talk about it with certainty while others vaguely mention there being controversy among experts. What are the most up-to-date theories on the Oort Cloud and are there any interesting tidbits of information anyone can share? Thanks!
|
[
"You're right, in that it's still only a hypothesis - we can't observe it yet, since it's thought to be made up of billions of small, cold, and VERY diffuse objects with maybe a few dozen Earth masses' worth of material. Turning the Hubble Space Telescope outwards and hoping to find an Oort cloud object, for example, would be like trying to see individual electrons in front of you with the naked eye.",
"Still, the main reason why the Oort cloud is often considered fact is that it's one of the most logical explanations for the existence of long-period comets like Hale-Bopp, since their orbits show that they must have originated from a region beyond the Kuiper belt. On top of that, many computer models of the Solar System's formation predict that the gas and ice giants would have scattered an enormous amount of icy planetesimals outwards in the system's early, debris-rich days. This would have ejected most of them from the system, but some would have just remained attached to the Sun and fallen into orbits thousands of times more distant than those of the modern Kuiper belt, scattered disc, and detached/Sednoid objects (assuming that \"detached objects\" like Sedna aren't actually the closest members of the inner Oort cloud). Most of those objects would have been ejected from the Solar System, but a small fraction (still comprising a numerous population) would have remained gravitationally bound to the Sun in the form of the Oort cloud.",
"As for why long-period comets are so close relative to other Oort cloud objects, it's thought to be the result of their orbits being gravitationally perturbed by passing stars."
] |
[
"The main reason is that the long period comets come in from all directions. A spherical distribution for the source of long period comets is the easiest explanation for this distribution.",
"If their source was the Kuiper belt they would all tend to orbit much closer to the ecliptic, which is the plane that all of the planets orbit the sun. Technically there is no single plane, of course. All of the planet's orbits are tilted a bit relative to each other, but they're all pretty close to the same plane. "
] |
[
"They mean there are very few objects in a very large region of space."
] |
[
"How sustainable is our landfill trash disposal model in the US? What's the latest in trash tech?"
] |
[
false
] | null |
[
"Landfill mining is worth a look, essentially digging through existing landfills and sorting things of economic value, recyclables, biodegradables, fuel sources, etc. while creating more space in the process. It is of course a costly undertaking, but there are MSW sites in the US that have profitably implemented landfill reclamation. Here's the EPA spiel on it with sources: ",
"https://www.epa.gov/sites/production/files/2016-03/documents/land-rcl.pdf"
] |
[
"I work at a waste to energy facility, and would say the landfill model is sustainable. My plant reduces every 7 tons of incoming waste to 1 ton of ash that goes to the landfill as cover. Plus we have a system to recover metal out of the bottom ash and we sell that to scrappers for recycling. Then add in that our ash can be sold for use in concrete, and the \"new\" industry of landfill mining for precious metals reduces it even further. Just in my county/city our records show that incoming waste has been leveling off and as our ability to recycle increases, I don't see any reason to say that the landfill model couldn't be sustainable. "
] |
[
"The plant I work at is in Florida, and I'm an operator there. It's an incinerator plant, we're permitted to burn about 500 tons a day. The plant has two units, each unit has an accompanying pollution control system with it. Our scrubber system injects a lime slurry into the flue gas (gas outputted from the combustor after it leaves the boiler) that helps with sulfur dioxide gas, and activated carbon that binds with mercury (which is too small to filter) which makes it into a particulate (important later). The flue gas then passes through a baghouse, which is comprised of I believe 1200 bags that catch the treated fly ash, and now enlarged mercury particulates. The rest of the flue gas passes through an analyzer which reads the chemical makeup which feeds back to the control valves regulating our lime and carbon injection, and also adjusts our air fans into the combustor to reduce CO, NO2, etc. The analyzer also reads opacity of the stack emissions. And every year we are tested by a 3rd party on our emissions for the government and have never failed a test yet. Our plant is greener than a coal plant, our fuel is free (people pay us to burn their waste), recycles, and reduces our output to the landfill by ~86%."
] |
[
"Diesel Engines get better mileage than gasoline but do they produce less Carbon Dioxide doing so?"
] |
[
false
] |
I know that Diesel engines get better mileage by volume than gasoline. But Diesel is also a large hydrocarbon than gas so I was wondering if the mileage by carbon dioxide produced is also better for diesel or is it effectively the same or is it worse? Ignoring glittery tangents like biodiesel, does a gas engine or a diesel engine produce less carbon dioxide per mile/km driven?
|
[
"CO2 emissions per chemical potential energy are almost identical between gasoline and diesel - around 73 g/MJ. Diesel engines are more efficient because they are \"lean burn\" (i.e. use more air and less fuel than dictated by the stoichiometric ratio), have high compression ratios, and no \"throttling losses\" (since they regulate engine speed by fuel delivery instead of a throttle).",
"TL;DR Yes, diesels are generally better for the environment"
] |
[
"The problem with diesel is particulate emissions (think smog), not thatthey produce more CO2 than stard gasoline engines.",
"Improvements are being made to diesel in this area however.",
"Edit: ",
"http://thinkblue.vw.com/tdi-academy-clean-diesel-vs-gasoline/#cleandieselvsgasolinefuelsemissions"
] |
[
"I didn't know that last one about diesels, so what exactly does a throttle do then?"
] |
[
"Why is it when some vaccines are administered, they require a follow up booster within a few weeks/years?"
] |
[
false
] |
As follow-up; what determines if a vaccine is "good enough" to not require a booster? Does the booster work differently than the original vaccine? Is there an ideal time between the original vaccine and the booster?
|
[
"The initial vaccination creates a bunch of T and B cells that fight off the infection, but these soon die off. They leave a small population of memory cells that can quickly recognise and mount a defence against the infection a second time. ",
"Memory cells do not proliferate without the infection to stimulate there production, and although long lived, they are not immortal. Therefore booster vaccines are administered to \"top up\" your numbers of memory cells.",
"It's not known exactly why some infections produce much longer lasting memory cells, but is thoughr to do with their \"immunogenicity\" i.e how effective an immune response they provoke. It's down to various factors, such as certain protein sequences and cytokines stimulated, but is a rather nebulous concept in my mind. ",
"Would love to hear an expert on vaccines to chime in. "
] |
[
"When mammals are born, they get passive immunity from their mothers (whether in utero or via colostrum after birth). That's great for protecting the baby, but the maternal antibodies can interfere with the baby's ability to generate their own antibodies in response to vaccines. Everyone's maternal antibodies wear off at different times. If a baby's antibodies wear off early, they benefit from the first vaccines in a \"series.\" If a baby's antibodies wear off later in life, the first vaccines in the series are ineffective, but the later vaccines protect them. That's one of the reasons babies seem to be vaccinated so frequently and for the same things repeatedly. The vaccine schedule has been developed to protect all babies - regardless of exactly when their maternal antibodies stop protecting them. ",
"Additionally, vaccines sometimes require a booster because the vaccine doesn't have great ",
"immunogenicity",
". In an ideal world, every vaccine would invoke an awesome immune response from a single vaccination, but that's not the world we live in. Sometimes the vaccine is just not very good. Sometimes people have sluggish immune systems. Sometimes their immune system randomly gets rid of the memory cells that were created by that vaccine (you only have space for so many memory cells!). Everyone is different in these regards, the typical vaccine schedule was developed to protect the greatest number of people as possible. ",
"There is no difference (in my experience) between the first vaccine and the boosters. This may not be the case with all vaccines because every vaccine is a little different. Similarly, there is no one ideal time between boosters that is perfect for everyone. Every vaccine has a different average length of protection, and every immune system is a little different. Booster frequency is dictated by statistics - how long does the first vaccination protect ON AVERAGE (and then they usually subtract a good amount of time to account for poor responders). ",
"Finally, a vaccine is considered \"good enough\" if you have developed an appropriate immune response. This isn't something we often test because the vaccine schedule is designed such that by the time you've gotten all your boosters, the likelihood that you are STILL not protected is marginal (but still possible!). If you really wanted to know if your immune status was sufficient, you would have to test your titers. ",
"I hope that answered all your questions and was readable! Please let me know if you have any follow up questions. "
] |
[
"(I don't know why I'm bothering to argue, but here's the counter argument for anybody else curious)",
"A) True, many vaccines are considered effective for a decade or so, but it can vary from case to case. Most of the time vaccines are effective for decades, or even life, but there are examples of them failing after only 5-10 years. Due to these anomalies, most estimates are low balled for the sake of conservationism.",
"The important thing is that they protect kids for their school years, as infections spread extremely through schools, and kids aren't as well equipped to fight off serious infections as healthy adults. It's also well published the need to get booster shots! ",
"B) I have found no credible peer reviewed studies showing that disease spread between vaccinated and vaccinated populations is equal. I've in fact found the exact opposite, showing that vaccination reduces disease spread from a R value of 10 to .5 Another paper estimates that 80% vaccination reduces disease spread by 93%",
"http://www.sciencedirect.com/science/article/pii/0264410X94902291",
"\n",
"http://www.sciencedirect.com/science/article/pii/S0264410X04006784",
"C) Vaccines actually save vast amounts of money each year. About $3 Billion is spent on flu vaccines each year, and vaccines only account for 0.3% of total pharmaceutical sales, they are not being pushed by Big Pharma for extra cash. It's a lot cheaper to vaccinate somebody that to treat them of a disease, it's estimated that vaccines SAVE $7 billion each year. ",
"http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6307a3.htm",
"\n",
"http://www.jhsph.edu/research/centers-and-institutes/ivac/resources/vaccine-cost-effectiveness.html",
"D) No, vaccines are not perfect, they do sometimes fail. But they are still a hell of a lot better than doing nothing! ",
"Why am I bothering to argue Anti-vaccers on the internet? -_- "
] |
[
"Have we found any stars that are definitely without planets?"
] |
[
false
] |
Since we found a planet near Alpha Centauri it got me wondering, have we found a star system that we can conclusively say do have a planet orbiting it? If so how did we prove it?
|
[
"It's pretty hard to prove such a thing. We don't even know how many minor planets our own star has."
] |
[
"This is correct. We simply don't know for certain. We can't, really. The odds of us spotting a planet orbiting a star aren't particularly high. We really have to be looking or get a lucky break.",
"Based on the observable space we've looked at so far, I would guess that the frequency at which a star exists without some number of planets is relatively low. There is nothing especially peculiar about the planet bearing solar systems we know of that should make them so unusual. The obvious circumstance in violation of that would be something like Cygnus, which is so massive it may well have devoured anything we could reasonably ever detect getting near it."
] |
[
"The most productive methods we currently have to detect extrasolar planets all rely on the orbital plane of the extrasolar planet be more or less in line with our line of sight. If the orbital plane is perpendicular to our line of sight, then most of the methods we use don't work as well.",
"If a particular star does have planets but the orbital plane is at the wrong angle, it's unlikely that we would detect the planets even if we studied the star closely.",
"We can rule out planets around some stars, but only for massive planets in small orbits. We cannot rule out stars having a low-mass planet in a relatively large orbit."
] |
[
"When one stands on the moon, would the horizon appear to be closer, since the moon is so much smaller than earth?"
] |
[
false
] | null |
[
"Yes, it does. See ",
"here",
". But, there's another thing going on that's less obvious: the lack of an atmosphere. Without an atmosphere, there are few clues for the true distance of landscape feature. Lunar material is also in a limited sense self-similar (scale invariant), meaning that larger rocks and smaller rocks look qualitatively similar. It's not easy to tell from ",
"a lunar landscape",
" how far the hills are or how large they are."
] |
[
"If you look at a picture of a ",
"mountainous landscape on Earth",
", there's the additional clue for distance that mountains farther away look significantly bluer, because of the air in between. The mountains at the horizon at left for example don't show any details anymore.",
"Second, there's something which ",
" scale invariant in this picture: tree height. In contrast, a rock could be of any size."
] |
[
"I believe that little speck 45",
" up and left of the satellite dish is the lander module."
] |
[
"Does a charged battery weigh the same as an empty battery, theoretically?"
] |
[
false
] | null |
[
"A charged battery will weigh slightly more, or as Warren puts it: ",
"Energy is stored in a battery in chemical form. In other words, the energy is stored in the chemical bonds between atoms, which involve electrons. A charged battery has many such bonds already formed, while a discharged battery contains the same atoms, but with the bonds almost all broken.",
"The question, then, really boils down to this one: does a molecule weigh more or less than the sum of its constituent atoms?",
"A molecule certainly contains more energy than does a collection of its constituent atoms. It is also true that energy and mass are both affected by 'gravitational fields,' as can be seen by the deflection of starlight as it passes near the Sun, or by the redshifting of light as it travels upwards from the floor of a laboratory.",
"A charged battery, of course, contains more energy than a discharged one -- a trivial statement. A charged battery must necessarily weigh more than an uncharged one. In the same vein, a box of mirrors full of photons will weigh more than a similar box without any photons inside.",
"However, the difference in weight is incredibly tiny, due the very large value of c",
" , the constant that associates quantities of mass with quantities of energy in the famous equation E = mc",
" .",
"From: ",
"http://www.physicsforums.com/archive/index.php/t-105483.html"
] |
[
"You aren't taking relativistic in to account. "
] |
[
"the total mass of electrons doesn't change, so the weight should remain the same. charged & empty states are just different configurations of where electrons are put."
] |
[
"Could you clone yourself by saving your semen then having a sex change and impregnating yourself?"
] |
[
false
] | null |
[
"No. Sex changes are a general term, but what you are probably referring to is genital reassignment, or “bottom surgery,” which surgically replicates the appearance of the genitalia of the opposite sex. It doesn’t actually change your biological sex. To become pregnant, you need a functioning uterus, eggs, etc. Transgender women can have vaginas that are virtually indistinguishable from “the real thing,” even by ONGYNs, but there is currently no way to surgically construct functional reproductive organs. "
] |
[
"Alright thank you for the information. I'm a theoretical point of view, the if they could get a functional women's reproductive body parts, could you clone yourself?"
] |
[
"1) I’m not aware of there ever having been a uterine transplant into a male, and ethically I don’t think any doctor would ever authorize it. Human Subjects Review Board would riot.\n2) Endocrine conditions in male bodies are fundamentally different than in female bodies, and aren’t able to change the way that women’s bodies can when they become pregnant. The way that fetuses develop, specific hormonal conditions are vital to normal development.\n3) In order to have a successful pregnancy in a biological male, you would have to transplant both urterus and ovaries, have them not reject (dicey), carefully replicate endocrine conditions throughout the pregnancy, and probably deliver via C-section.",
"While theoretically possible, there are too many variables to control, and if any of them went wrong you could potentially kill or deform either the fetus or the patient. It would be supremely unethical to attempt."
] |
[
"How do calories actually relate to weight stored in your body?"
] |
[
false
] |
Calories are a unit of energy. How does that translate into the common idea that you gain one pound for every extra 3500 calories that you eat that you don't burn off? Where does this extra weight come from?
|
[
"The energy is stored in the chemical bonds of the molecule (protein, fat, carbohydrate). The breakdown of the molecules allows the body to harness the energy to phosphorylate adenosine diphosphate (ADP) to make adenosine triphosphate (ATP). ATP is the 'currency' that the body uses for energy.",
"The idea that the body gains a pound for every 3500 excess Calories (kcal) that are consumed is a rough estimate, and can vary greatly based on how the body is storing the excess energy. The different types of storage molecules have different energy-to-mass ratios. Proteins and carbohydrates generally contain about 4 kcal per gram, while fats generally contain about 9 kcal per gram. Thus, given about 453 grams per pound, a pound of protein or carbs (glycogen) only contains about 1800 kcal, while a pound of fat contains about 4050 kcal.",
"edit - While, not what"
] |
[
"In its simplest possible form, if your body absorbs more calories than it expends, it uses those calories to synthesize and store fat as a precaution against future calorie deficit. The mass comes from the food we eat, the chemical energy necessary comes from the process of digestion."
] |
[
"I have a related question that I think is basically answered by the above, but I'm not certain of the details.",
"When weight is \"lost\", it's simply that the energy storage molecule has been broken up and the energy released. But the mass itself is still in the body. To actually lose weight, those molecules would have to be expelled. I assume this happens through urine. Is that all correct? What form do the expelled molecules take?"
] |
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