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Why do we breathe out of a dominant nostril which also changes throughout the day? And why does this dominance change? | This is the [nasal cycle](_URL_0_) (also see [here](_URL_1_) for recent review and [here](_URL_2_) for the classical study). Congestion of the mucosa in the nose goes up and down throughout the day, usually up in one nostril and down in the other. A variety of reasons have been proposed. [This](_URL_3_) recent article proposes the nasal cycle strikes a balance between airflow, which dehydrates the mucosa but allows better air passage, and hydration, which reduces airflow but results in better clearance of contaminants. |
Why don't planets lose centrifugal force until they fall into the sun? | The balls in the video loose their energy because: 1) it's converted into heat due to friction, 2) the material (spandex) is elastic and thus it starts vibrating. When it comes to planets, stars and other astronomical objects, their orbits shrink, too, and this is due to gravitational radiation (emission of gravity waves). For planets and stars the effect is insignificant, but it can be observed in systems comprising compacts stars (e.g. neutron stars). |
why do bubbles form when boiling water | The other answers miss one small bit. The first bubbles that form when you heat up water is actually dissolved air. They form even before water reaches the boiling point because the solubility of gases decreases with increasing temperature. |
Why does a toaster make bread crispy, but a microwave makes bread soft? | Microwave ovens heat food by jiggling molecular bonds in water and fats. This process tends not to get foods to the elevated temperatures needed for the [Maillard reaction](_URL_0_) to take place and browning to occur. |
Why do candles stay lit so long? | The wax melts and is absorbed by the wick, the flame heats the wax causing it to vapourise and the resulting gas is burned. So the flame is not actually the wick burning. (The wick will smoulder at the tip, but the wax is continually absorbed which prevents the wick from igniting). |
What's the largest organism that doesn't need sleep? | This is probably not what you had in mind, but the largest organism that doesn't require "sleep" is also the largest organism - honey fungus. Plants, protists and fungi are all organisms, and to my knowledge don't exhibit sleep patterns in the way that vertebrates do. If you're question was about animals in particular, we may need to better define sleep. Dolphins, and by extension likely whales (largest animals) are able to rest half of their brain while still maintaining basic movement (i.e. swimming, breathing). It is likely a different state than what humans would define as sleep, thus it could be argued that these animals don't sleep either. |
Why are galaxies circular and not spherical? | Some elliptical galaxies are, in fact, quite close to spherical, a sphere merely being a special case of an ellipsoid. Spirals just get all the attention, 'cause they're so purdy. |
What created moon dust? Why isn't the moon just one giant rock? | Bits of material flying around in space at great speed end up hitting the moon and blasting craters in the surface. Over time this leads to the surface being pulverized into dust. There had been a *lot* of time. |
How is the Moon covered mostly fine dust if the erosion forces of wind, water, and plate tectonics do not exist? | Meteors are enough to create the regolith. The moon (and the earth) are constantly bombarded with them, the earth has an atmosphere that burns most of them up before they hit the ground. The moon having no atmosphere has no such protection. |
Are all meteorites and asteroid gray like seen in the pictures? if so, why? | Well, [here's a picture](_URL_0_) of a pallasite meteorite. These show up with green areas because of the minerals present. A lot of what we find in meteorites is iron and nickel, and those are both gray/silver, and so that does skew meteorites somewhat to the easy ones to identify. |
Why is it that the lenses on most cameras are round but when we view the pictures/video taken theyre rectangular? Why dont we have square lenses? | Generally the film or the digital detector is laid out in a square (Edit: or rectangular) shape. The actual field of view of the camera is circular. A square lens would be terrible to engineer and would not actually make the field of view square. |
Do insects grow tired the same way as us? | Insects certainly do get muscle fatigue. However, they are built to greatly resist fatigue. For a fly, they have evolved to fly for hours upon end, they can't get tired from just a short flight. The big difference relates to [respiration and circulation](_URL_0_). In humans this process is centrilized in our torso, whereas insects perform respiration all over their body through [Spiracles](_URL_1_). Each segment acts somewhat autonomously to take care of these processes. Insects and humans have scary similar parts, insect muscle fiber and activating neurons & junctions between the too are very similar. But in general the organization is very different. When an insect is caught in a spiderweb, the spider will let the insect fatigue before it goes in for the kill. The spider web's stickiness causes the insect muscles to try to do more "work" as it tries to break free, and this reduces the time it takes to make the muscles fatigued. Edit: Suggested spelling change |
Do insects get tired? | Like all organisms insects do not have access to unlimited energy. They cannot fly/run around forever because they need to consume food. Whether or not they "feel" tired is nearly impossible to say as we cannot enter the "mind" of an insect. However, it is certain that insects will eventually cease activity when their energy reserves are low. Insects do enter a sleep-like state and can suffer from sleep-deprivation. [Popular Source](_URL_0_) [Primary Source](_URL_1_) |
If identical twins are thought to NOT be hereditary (unlike fraternal), why do some families have so many through the generations? | There appears to be some hereditary element: A quick search revealed this document _URL_0_ They cited two studies that found an increased chance of identical twins having more indentical twins. However, only in the maternal line... See in particular p. 183 and References to Lichtenstein 1996 and Parisi 1983 |
Are there any stars that aren't part of a galaxy or cluster of other stars? | Yes, there are stars that aren't part of any galaxy. They are known as [intergalactic stars](_URL_1_) or sometimes rogue stars, but usually they form large groups such as those in found by Hubble in the Virgo cluster. As for stars that aren't part of a cluster, they have been also. These are stars which have been ejected from their host galaxy, usually by a gravitational sling-shot from their local supermassive black hole. [These have been found in the Milky Way](_URL_0_). |
Why does air make things taste better (or worse)? | Oxidation is the culprit. The chemical reaction produces byproducts that either enhance or degrade flavor. |
How does odor escape apparently air tight containers? | The only truly air-tight seals I know of are knife edge seals where even atoms of helium cannot go through. These seals are made by crushing a softer copper gasket against a very sharply machined, hard stainless steel edge. It is also possible that the dog is smelling some bomb residue that made its way onto the concrete block while the bag was being sealed up. In any case, mother nature's chemical sensors are incredibly, incredibly sensitive. We still have much to learn from these types of examples. |
Humans replace the cells in their bodies very frequently. How come the new cells don't "remove" old scars or imperfections? | Scars are mostly composed of protein, without much cellular content. To degrade this material and replace it with normal tissue is an energy expenditure without any real benefit, as the scar is doing a fine job of holding things together. Furthermore, degrading the scar tissue could potentially render the injury more prone to re-opening. |
How big would the sun appear to the Voyager 1 at the distance it's at now? | It would appear about the same *size* as the diameter of a human hair, held at arm's length. _URL_0_ |
How long before Voyager is closer to another star than our Sun? | According to [this article](_URL_0_), Voyager 1's encounter with another star will be in about 40,000 years. At that point it will come within 1.7 light-years from it. The star is Gliese 445, which is around 17 ly's from the Sun. I don't know exactly when the halfway point is but I guess that would be when it's closer. |
How is autism diagnosed? | In a recent /r/science AMA about autism, Dr. Tristram Smith [explained](_URL_0_), "There is no lab test for Autism, so the diagnosis is based on careful assessment of the person and getting a thorough history and ruling out possible other medical issues." |
What would happen if I ran a microwave without a door on it and stood in the same room? | Not a direct answer to your question, but [here](_URL_0_) is an article from 1980 about the proposal by Robert Pound (very prominent Harvard physicists, just died in 2010) to use microwaves for residential heating. I realize this doesn't answer the question of how much heating you would feel near a standard kitchen microwave oven, but it is worth knowing about if you're interested in this question. |
Can high frequency sounds outside human perception damage hearing? | When previously asked, the consensus was that the risk of damage was relatively low: _URL_0_ _URL_2_ _URL_1_ |
How do scientists determine the age of a star? | While I agree with the other responses that composition can tell a lot about the age of the star, one needs to be careful. For example, in the Large Magellanic Cloud, the metallicity is 1/3 that of the solar metallicity, meaning that a star in the LMC may appear to be "older" than those in the Milky Way, though they very often aren't. [30 Doradus](_URL_1_) is a mecca of starburst activity, generating new stars that have lowish metallicity. A cute way to figure out a star's position in its life is by comparing it with an evolutionary track on what's called an [H-R diagram](_URL_2_). Evolutionary tracks are generated with theoretical models from modern and somewhat older ([Salpeter IMF](_URL_0_)) astronomy, and can be plotted on the H-R diagram to compare with the stars. These models are called [isochrones](_URL_3_). This is one of the most common research approach to figuring out stellar ages. |
How is the age of a star determined? | We’ve looked at enough stars that we can figure out how big, how hot and what’s in it. From that and current theories on stellar evolution (and looking at a lot of similar stars) we can work backwards to how old it is. Look up “main sequence” to get an idea for how stars change as they age |
Is it possible for a comatose woman to become pregnant? | First off, note that ['coma' is a very vague term](_URL_1_) that encompasses a wide range of physiologic states. But there's no intrinsic reason why a 'comatose' woman would be unable to conceive (unless whatever caused the coma is also affecting her endocrine function). There have been numerous [case reports](_URL_2_) of [pregnant women receiving injuries that lead to coma](_URL_0_), and subsequently delivering a healthy baby. The literature does note that some cases result in fetal demise shortly after the onset of coma (though of course we cannot say anything about causation based on just case reports). Also note that delivery must be by cesarean section, if women are unable to participate in labor for a spontaneous vaginal delivery. |
Is the universe expanding due to angular momentum? | This is one of those questions where the answer is just no. Perhaps you could elaborate on why you think angular momentum would cause the universe to expand? |
Can a planet rotate on its major axis WHILE simultaneously rotating on its minor axis? | What iorgfeflkd is talking about is called "precession", all planets have it to some extent, and it is exactly what you're talking about. |
If the cold weather doesn't make you ill/sick, why does it give you a runny/blocked nose? | The purpose of the nose when breathing is to add water to the air you breathe in. This is better for your respiratory system as it prevents cells and mucous drying out and stops your body getting cold. Cold air can't hold much water so your nose produces excess fluid in an attempt to add as much water to the cold air as possible. This is why you find your nose running in cold air. |
How or why are yawns 'contagious'? | A hypothesis suggests that [contagious yawning](_URL_2_) is connected to the activity of [mirror neurons](_URL_0_), found in primates. A quick search also turned up [this](_URL_1_) paper. |
How much oxygen can one tree produce in a day? | Related question, but how much oxygen does one average adult human consume in a day / year? |
What is the difference between Embryonic and Fetal stem cells? | [Embryonic stem cells](_URL_1_) are recovered from the blastocyst stage of an embryo, from extra embryos created during an in vitro fertilization process. Thus, ESC lines are generated from extra materials left over from IVF treatments, and were not implanted within a person. [Fetal stem cells](_URL_0_) are stem cells recovered from fetal tissues, such as fetal blood, bone marrow, liver, etc. They are typically extracted from deceased/terminated fetuses. |
How can the universe be 150 billion light-years across and only 13.7 billion years old? | Light rays can reach us from a distance greater than 13.7 billion light-years because the universe has been expanding while the light ray has been travelling. While the ray of light itself can't have travelled further than 13.7 billion light-years, the universe is still expanding *behind* it, so by the time it reaches us, the distance between us and the object it came from is greater than 13.7 billion light-years. |
Are solar systems moving towards or away from the center of a galaxy? More detailed question inside. | Our solar system actually isn't outside, [we're right in the meat of the galaxy.](_URL_2_) But yes, solar systems can move all around within a galaxy. Because of the way mass is distributed in the galaxy, their orbits aren't necessarily nice circles, [but can weave closer and farther from the center](_URL_1_). Furthermore, when stars get close to each other, they can cause large changes in each other's orbits. Just like how planets can slingshot space probes, stars can slingshot other stars out of a galaxy or toward its center. Also, galaxies collide with each other from time to time, [and that can fling large numbers of stars away.](_URL_0_) |
How does momentum affect a flying insect inside of a moving vehicle? | The fly is working against the air currents in the car, which accelerate along with the rest of the car assuming you have the windows closed. If you jam on the gas, luckily the air in the car doesn't all pool at the back. It's similar how we can walk around on the Earth even though it's travelling ~30km/s. |
What happens if you take antidepressants and you're not clinically depressed? | Reuptake-inhibitors like Prozac are better thought of as drugs for bringing neurotransmitter levels to a normal level, not necessarily to a higher or lower level. Though they certainly inhibit reuptake, your body responds to this inhibition by modulating its own synthesis of neurotransmitters. This is why they can simultaneously act as antidepressants and anxiolytics. If your levels are already normal, you might experience some ups and downs during that first month or two as any user would, but you should eventually normalize afterwards. Source: I'm a synthetic medicinal chemist with an interest in psychopharmacology. |
If you shot a gun in space, what would happen to the bullets? | They would travel with constant velocity until they hit something that stops or slows them. |
Why do some stars in the night sky rapidly change colour from red to blue to white and yellow? | As suggested already, if the color changes are very intense, it might actually be some kind of flying vehicle, such as an airplane or helicopter. Otherwise, you're probably looking at a bright star (Sirius) or planet through a very turbulent atmosphere. Due to the uneven conditions, light gets refracted and dispersed. The colors appear through the same mechanism that splits sunlight in a prism and generates colors out of white light. |
Do artificial sweeteners aid in weight loss, inhibit weight loss, or do they not come into play? | There are not many well-designed studies to answer this question in general ([_URL_4_](_URL_4_)). That being said, a recent study of Dutch kids showed that artificial sweeteners in soft drinks do promote weight loss, contradicting lower quality evidence from previous studies. _URL_5_ There is also some evidence in adults that substitution of artificially sweetened beverages does assist with weight loss in the short term at least. |
Is it the case that the photon hitting my eye when I look at a star in the night sky originated in a star hundreds or thousands of lightyears away? | Yes, as to see the star the photon must have been either emitted by the object (either by absorption/remitting or through a process that releases energy like nuclear fusion). The photon hitting your eye is the same photon (being emitted/remitted a couple of times along the way) that came from the object hundreds or thousands of light years away. |
Why is Graphene so strong? | Lots of layers of graphene make up graphite. Now within a sheet of graphene all the atoms are bound to each other strongly by covalent bonds. To break the sheet you have to put in lots of energy to break the bonds. However the layers aren't connected together with localised bonds. The layers can slide over each other without any bonds breaking. This means that the layers can slide over and off each other. This is how the lead in your pencil works. Layers of graphite come off the pencil and stay on the paper. In diamond all the carbon atoms are joined together with strong covalent bonds. This is why diamond is stronger than graphite EDIT: Adding some images [Graphene](_URL_0_) [Graphite](_URL_1_) [Diamond](_URL_2_) |
Would a mirror reflect radiation from a nuclear disaster? | the first picture of the elephants foot at Chernobyl had to be taken using a mirror so that the radiation would not wipe the film clean. So yes I assume it would greatly diminish any radiation that you would otherwise receive. |
Would a mirror reflect radiation? | Simple answer: Not with conventional mirrors, and with great difficulty regardless. So gamma radiation (the type of radiation most people refer to) is made up of photons, just like visible light, except of much higher frequency (and thus energy). Their wavelength is so short they will pass through material, or be absorbed by it due to the high energy. The thing is, conventional mirrors typically only reflect radiation around the visible light range (and as an unintended consequence some lower and higher frequencies (IR, UV)), as they're not built to reflect gamma radiation. You can get mirrors that reflect gamma radiation but they are prohibitively large as the angle of incidence has to be almost 0 degrees. Best way to get in and out of Chernobyl 20 years ago was inside of a thick lead box. Regardless of this, extra layers of anything would block **some** radiation. |
why does head hair and facial hair continue to grow long while hair on other parts of the body stop growing at a maximum point (arm, chest, armpits, etc.)? | I just added this one to the sciencefaqs here - _URL_1_ The reason is because of hair follicle cycling - _URL_0_ |
Do astronauts get sick in space/stop getting sick over a period of time? | Well you've pretty much answered your own question, eventually they would become immune to all present bacteria and viruses assuming that the people had good immune systems that completely removed the pathogen from their system. You do have to allow for mutations in the pathogens which could cause another infection. However, astronauts don't just stay isolated in space for long periods of time, they get deliveries from earth all the time bringing possible new bacteria. In my non professional opinion, I think they would get just as many colds etc as normal people on earth |
Can astronauts get sick while they're in space? | You're right, the ISS is an isolated environment and so they cannot get a disease if they didn't take the pathogen with them. However that's not the only way to get sick. There are lots of microorganisms that aren't pathogenic under normal conditions but can get activated when your immune system isn't working properly. They are called [opportunistic infections](_URL_0_). They can happen on Earth for a variety of reasons, but they are more common in imunocompromised patients. In long-duration spaceflight, the immune system is weakened by microgravity effects, giving a chance for pathogens to start reproducing out of control. |
When a person suffers a severe case of amnesia, will they have interests in the same things that they had before their amnesia? | It depends. Retrograde amnesia (the most common type of amnesia) only impairs ones memory for events. Skill related memory (muscle memory) is not affected. That is why a person with amnesia can still speak English. So, if ones preferences come from a particularly traumatic event, then they might not have the same hatred for that thing because they may not remember this event. On the other hand, if a particular preference has been had since birth because of a genetic predisposition, it will not be affected. |
Is it at all beneficial to blow your nose when you have a cold? Are you reducing the net amount of mucus in the sinuses or is more just produced to replace what was expelled? | I am not aware of any good clinical studies looking at the benefit of nose blowing. There are case studies showing that doing it vigorously can cause injury, but these are only individual case studies. However, it is a good idea to get the accumulated mucus out of the sinuses, as when it doesn't clear it can become a nice home for bacterial infections. You do need to clear it, and the disgusting truth is that our respiratory tract is set up for you to do it the other way....that is, swallow it. You know how you just kind of reflexively swallow from time to time? That's mostly mucus that has come up from your lungs or down from your nasal area. |
In social settings, I stutter because I get anxious, and get anxious because I think I'm going to stutter. Why? | This could be caused by the anxiety triggering yourself to start physically giving commands to your mouth to say. I know that failure under pressure (what I would call "choking under pressure) is very often caused by you physically trying to do the actions yourself, instead of letting your body naturally doing it. For example, a baseball pitcher can pitch in practice fairly well without "trying", but when he enters a game, he will be in the mindset of being extra careful and cautious, so he will start to "try" to pitch well. This causes him to perform worse because he isn't following the same form and motions that work well. As he begins to do worse, he will continue to "try" more and more, leaving any form that he naturally had that worked for him in practice behind. Hope that helps, I'm no expert, but I read an article in my paper a while back that related to this. I might be able to answer questions if my explanation was bad. |
What is going on inside my head that gives me a headache? | Why does sleeping for an extended time (e.g. 12-16 hours) cause headaches? Seems to happen to me every weekend lately. |
What is the difference in shampoo and conditioner? | Shampoo is used mainly for its detergent/cleaning effect of removing oils and dirt from the surface of your hair. Conditioner is adding a coating of shiny oils/waxes/polymers to your hair to make it look and feel smoother. Neither is better nor worse as they are for different purposes. A good mini-recap is about halfway down [here](_URL_0_). Hope that helps! |
How does shampoo/conditioner work? | Take a look at the ingredients on your shampoo bottle. Most likely you will see Sodium Dodecyl Sulfate or Sodium Laureth Sulfate or one of their derivatives. These compounds are surfactants. Surfactants have heads that are attracted to polar subtances like water and tails that are attracted to nonpolar substances like oils. When you rub shampoo on your hair, the hydrophobic tails grab onto the excess oil in your hair and orient themselves into little spheres with the hydrophilic heads pointing outwards and the hydrophilic tails, and the oils that they can mix with, on this inside of the sphere. This structure is called a micelle, and it gets washed away when it comes into contact with water. Most of the other ingredients in your shampoo are fragrances. Some surfactants are too zealous in their removal of oils and end up making your hair brittle and weak, however. |
Can single-celled organisms get cancer? | Well, let's look at the six hallmarks of cancer: * self-sufficiency in growth signalling - already present * insensitivity to anti-growth signals - not really applicable * evasion of apoptosis - probably possible * enabling of a limitless replicative potential - already present * induction and sustainment of angiogenesis - nope, can't happen * activation of metastasis and invasion of tissue - nope, can't happen So, you see, they can't. Can they get something similar? Sure, a virus infection can be analogous to cancer to a single cell organism. But they can't get cancer |
Can single-cell organisms get cancer? | [_URL_0_](_URL_0_) No, not "cancer" by definition, but they could get a mutation that makes them "immortal" and reproduce without limit. Such a colonly would probably kill itself off by using up all its resources too quickly, though. |
Does a ball ever stop bouncing? | In the magical world of ideal classical approximations and fantastical physical properties, the ball would never stop bouncing. Classical mechanics carries no notion of a quanta of energy, so you could continue to cut it in half indefinitely. Bisecting the bounce height will never get you to zero height until you take a limit to infinite time. In the real world, things aren't nearly as simple as the simple "drop a ball, it rebounds to half the original height". Energy is lost to a myriad of places such as sound and heat that will eventually sap any kinetic energy the ball originally had. There are other effects that will work to stop the bouncing, but non-ideal materials and interactions will be the major factors. e: This sounds great, but is mostly wrong. The bouncing ball converges to zero even when using classic approximations and perfect collisions. So there's your answer, as long as you believe in this newfangled "math" stuff. |
Where do mosquitoes go when it rains? | Apparently they go where ever they want. _URL_0_ If you are having problems with mosquitoes, you really need to destroy where they are laying their eggs. Empty out any standing water containers near your place, even little ones, and forget about the poisons. They won't help. |
where do mosquitos hide during the rain? | Mosquitoes have quite hard exoskeleton that helps to protect them from raindrops. Their exoskeleton and low mass makes them *almost* impervious to falling raindrops. To put this achievement into perspective, a single raindrop can weigh 50 times more than a mosquito. During downpour, they take shelter in grooves or holes in tree trunks or hide under things like leaves or rocks. Mosquitoes in cities do the same thing as their counterparts in rain forests - take refuge under rocks, in people's homes, in knots of trees etc. |
Is honey bee colony collapse affecting other insects? | There isn't any evidence that the collapse of honey bee colonies per se adversely affects other organisms. Its important to keep in mind that in most parts of the developed world, honey bees are an introduced species (originated in Africa, domesticated in Egypt/The Levant/Europe in ancient times). They are often brought to agricultural areas for pollination services (literally a truck full of hives) and removed afterwards. They are not natural members of the ecosystem. If anything, they are invaders who displace native pollinators. In terms of pesticides/fungicides affecting other insects, there have been many studies showing the adverse effects of pesticides on native pollinators. In general, intensive agriculture is damaging to natural ecosystems. |
How powerful is the radiation from a phone/wifi compared to everyday objects such as an electric stove, hair dryer, microwave, the sun? | I don't know about that specially. But i do know of an event here in Germany there the Telekom (a german telecomunication enterprise) put up a cell phone tower. The people as always started complaining about the "smog" (they could not sleep, ..) as soon as it was physically there. Actually, the technical equipment to even send out data was installed some time later (as in weeks). As it was installed, no new complaints were raised in that event. I guess, that shows pretty good that most of the wifi-hating is due too fear for technical new things rather than actual effects. |
Why do some people experience clinical depression when other people don't? (plus more questions inside) | > Are people prone to clinical depression from a pre-existing deficiency in their endocrine or neural systems? Studies on twins separated at birth suggest that genetic factors (presumably involving the nervous system) do play a significant role in risk of depression. _URL_2_ Exact genes responsible are quite difficult to pin down, as common single nucleotide variants are not significant predictors of risk _URL_2_ and the newer work on copy number variants hasn't come up with anything too exciting yet. |
Why can we see fire? Isn't it just heat? | Hydrogen and Carbon burn invisible. When you see a flame, say on a candle, the actual visible flame is made up of small particles of non-combusted soot that's glowing brightly due to the heat. |
How much time do we have to build a telescope large enough to observe the events immediately following the Big Bang, and how big would that telescope need to be? | We don't need particularly fancy telescopes to detect the cosmic microwave background, and recent missions like WMAP have given us pictures of it with extraordinary resolution. Too see farther back than the CMB (about 400,000 years after the big bang), we can not longer use light (or any EM radiation) because the universe was opaque. Neutrino or gravitatioonal wave observatories could bypass this, but our capability in those areas is much much worse than with light telescopes. |
Would a hot object retain its heat longer in space? | its not *quite* a vacuum, there are still errant molecules wandering around, even if there might be miles between them. but alas, this wouldnt make for very effective cooling. So you will also express heat through IR radiation. This is the method that space craft use to diffuse all of that heat generated by its electrical devices. |
Why do fluorescent things glow under UV light? | Fluorescence is the ability of an object, or rather the material it's made of, to absorb light and then re-emit them. They way this works is usually via the absorption of photons by the material to promote electrons into higher energy levels. Then, these electrons relax back to ground state, emitting photons in the process. In a normal case, one high energy photon will be absorbed and then a lower energy photon will be emitted. This is because when the electron relaxes back to the ground state, some of the energy will be lost as heat. This is why UV light (high energy) is usually used to shine fluorescent objects that will then emit visible light (lower energy) back to us. There is also another mechanism in which 2 photons are absorbed in order to promote a single electron. In this case, the emitted light can be of a higher energy than the absorbed light. However, not very many photons can be absorbed this way and the absorption is much lower than the typical case above. |
The sun emits UV rays, so why don't fluorescent things visibly glow in sunlight? | You are misunderstanding a lot. Not all flurophores need uv light to fluoresce. Gfp for example uses blue light to emit green. Rfp uses green light to emit red. The reason we typically can't see fluorescence is because of light saturation that makes seeing the fluorescence impossible. Remember the scene in Apollo 13 when jim lovell talks about seeing the algae (or something) fluorescing after his cockpit lights failed? You can see fluorescence when there is no ambient light flushing it out. |
Why can't/don't primates hibernate? | you may find [this nytimes article](_URL_0_) interesting. Apparently in medieval Europe, peasants would hole up for the winter with their livestock and sleep most of the time as a way to conserve energy. It's kind of like hibernation. |
Autism is a spectrum. Is there a spectrum for people with sociopathy and psychopathy? | The only correct answer to this question is we don't know. Mental processes and diseases just aren't well understood. The standard for defining mental illness is a book called the DSM. They are on the fifth edition of the book, you can see it here _URL_0_ The biggest complaint with that is that it classifies mental illness in terms of its symptoms. It would be like if we said that a heart attack is similar to heartburn, they just lie on different ends of a spectrum. An alternative to classifying mental diseases is being developed by research scientists, called the Research Domain Criteria. This effort is trying to classify mental diseases using genetics, imaging, biomarkers and other quantitative tools. Here's a good article about it _URL_1_ |
Diluted red wine changes color at a certain concentration. What's happening here? | Red cabbage has an anthocyanin, flavin, that is a terrific pH indicator (which can be the basis for a nifty demonstration for school children). According to my very brief search, grapes have flavin, too, so I might suspect that it (or another anthocyanin) makes it into the wine intact, causing the effect that you saw. Way to go on noticing that - it's awesome! |
How come clouds alone are white but a sky full of clouds is grey? | The darkening of clouds is caused by shadows, either from other clouds or the cloud itself being thick enough to extinguish more light than the surrounding skies. Of course, this depends on the angle of the sun relative to the clouds and your direction of observation. If you're looking at distant clouds and the sun is generally behind you, those clouds will appear white because they are scattering sunlight back toward you. |
How did pre-clothes era humans survive temperature changes? Were they capable to survive winter naked? | We didn't survive in cold temperatures without clothes, actually! It's important to note, also, that our ancestors had a lot more body hair than modern humans do. Even now, people who have historically lived in colder climates tend to be more hairy than people in warmer climates. But that's pretty much why we started wearing clothes. We started off in Africa and were only able to survive in colder climates after we started making clothes. Our ancestors who wore clothes survived the colder temperatures and reproduced, and the ones who didn't make clothes presumably died off. I doubt that ancient humans bothered to kill animals solely for fur - it's more likely that while they were already killing or scavenging them for food, they also used the inedible fur to protect themselves from the cold. *edited for clarity |
Excluding the Sun, if all of the remaining mass that exists in our solar system were combined, would it be enough to collapse into another star? | No. [The graphs here](_URL_0_) show why pretty nicely. Also, brown dwarfs, the least massive stars, are ~100 Jupiter masses. |
Why does my sub-zero beer turn solid AFTER I've opened it? | The carbon dioxide is the main reason this occurs. When the beer is closed the carbon dioxide is under pressure which forces it to dissolve in the beer. This reduces its freezing point. When you open it the CO2 is no longer under pressure and now can escape from the beer. (Which usually gives beer its foam) This does three things for the system. First the act of removing CO2 from the solution cools the beer because the CO2 takes energy with it as it changes to the gas phase. Second by removing the CO2 you remove impurities in the water which in turn removes raises the freezing point (Look up freezing point depression for more about this). Thus with the combination of effects you have ice form. Third the CO2 escaping typically is very chaotic which "stirs" the beer heavily. This aids nucleation. The reason it overflows is when you start freezing the beer, ice expands which pushes the remaining liquid out of the bottle. You can easily do this with other drinks containing CO2. |
Does most atmospheric oxygen come from plants or bacteria? | Actually, in terms of simple volume the vast majority of the atmospheric oxygen on earth (70-80% of it ) is created by marine algae. There are around 7,000 different species of algae on Earth and they collectively produce over 330 billion tones of oxygen each year. Since water covers about 71% of the planet it is not surprising the volume of oxygen produced is proportionate. However, when you consider the vast areas of land that support little to no plant life, it is clear that, on a basis of volume, the algae in the ocean is more productive than the plants and trees on land. |
Why do I sneeze if I look into the sunlight/a bright light? | There is something called the [photic sneeze reflex](_URL_0_). Best answer: the reason why photic sneezes occur is unclear. The linked Wiki page gives a nice overview of the different theories. \- ice |
Are there stars that are not part of any galaxy? | Our models show that it should be possible for stars to get ejected from their galaxies. For instance, this might happen as a star orbits a black hole and is slung shot away near the speed of light. As far as I know, we have yet to observe such a star. |
Why is it that if you look directly at some stars you cannot see them? | Because the center of your vision has high resolution and color sensitivity, but poor light sensitivity (compared to your peripheral vision). See _URL_0_ and _URL_2_ for more. Using [averted vision](_URL_1_) to observe very dim objects in darkness is a well known technique. |
Why do celestial bodies form an orbit instead of falling directly into its source of gravitational pull? | Actually they are falling ! Circular orbits would be such that, in the time it takes the satellite to fall a certain distance down, it has also moved another distance to the side such that the distance to the center has remained constant. Elliptic orbits are deformations of circular orbits, and are such that this is slightly false most of the time, with the satellite sometimes gaining and sometimes loosing in distance. |
Can someone with autism be a psychopath or a sociopath? | I had a look on scholar and couldn't find any papers looking at the comorbidity of autism with antisocial personality disorder (the diagnosis that psychopathy falls under in the DSM). This probably reflects the diagnostic differences between these disorders. [This paper](_URL_0_) found that the lack of empathy observed in children with autism and children who exhibit psychopathic tendencies are actually quite different. The lack of empathy in autism comes down to the difficulty in understanding what others think (lack of [Theory of Mind](_URL_1_)). The psychopathic tendencies appeared to be underpinned by an inability to reason about others' emotions. The main conclusions of [this paper](_URL_2_) are the same. |
Is there a spectrum to psychopathy as there is to autism or are you either a psychopath or not one at all? | Yes there certainly is a spectrum, there isn't even a clear 'flag' that can diagnose psychopathy. It's formed by personality traits that don't necessarily stand out as 'bad', but when it interferes with normal functioning and social interaction (or more popular known, causing criminal behaviour) it becomes a 'disorder', with all the ambiguity other mental disorders can have like AD(H)D and Autism. I would recommend this excellent Ted talk on the subject: [Strange answers to the psychopathy test](_URL_0_) |
When people say the universe is expanding do they mean empty space is being created or the actual "fabric of space time" is expanding? | If everything was getting bigger, we wouldn't be able to tell that anything was happening! Space is stretching but objects are not. Objects are pulled along by the stretch, but they are only pulled *apart* if they are not stuck together by sticky forces such as gravity or electromagnetism. |
How is it possible that the big bang expanded faster than the speed of light? | It didn't. The universe doesn't have an expansion speed - it doesn't make any sense to say the universe is or isn't expanding faster than the speed of light. By [Hubble's law](_URL_0_), what happens is that the further away two galaxies are from each other, the faster they expand away from each other. So there are always some galaxies receding less quickly than the speed of light, and some expanding more quickly. That was true in the early universe and is still true today. This doesn't violate the laws of physics because nothing is moving *through* space faster than light, but rather, space itself is expanding. That circumvents the usual prohibition against faster-than-light motion. One way to think of it is that you're not allowed to send a *signal* faster than light, but you can't use the expansion of the universe to send a message, so it's alright. |
How environmentally friendly is recycling? | It depends. For metals: absolutely. Mining is a very energy-intensive and environmentally harmful process. Especially for the exotic metals in batteries or catalytic converters. Aluminium is also very energy-intensive to mine, but a breeze to recycle. For Plastics: borderline. Some plastics can be re-melted and turned into fabrics or other materials, some cannot. When you enter in the burning of fossil fuels to transport those plastics from bins to recycling centers to factories, it becomes really tough to justify. Paper/cardboard: usually not worth it. Plant materials are a fully renewable resource. We have tree farms that supply the pulp. It's better to recycle wood from old furniture or demolished buildings because we have to cut down forests to get those materials. Glass: depends. Glass is easy to clean, so turning in used bottles for reuse saves the need to manufacture new ones. But glass in general isn't valuable or scarce. |
Since there are gaseous planets, can there be gaseous moons? | The issue is that small bodies don't have the gravity to permanently trap gas around them. Unless the body is at least a certain size, IE very large, you'll get a rocky body instead of a gas giant. At which point is it really a moon or is it a binary planetary system? |
If space is expanding outwards, would part of the night sky eventually get darker? | Our galaxy is not expanding, because its stars are gravitationally bound. The sky will go dark eventually, but because of the decrease in available fuel for fusion reactions, not because of the expansion of space. |
Why galaxies form discs when smaller objects form spheres? | Thanks for asking this question, was also curious and learned many things from the educated replies given. |
When the Vikings visited mainland North America circa 1000 AD, why didn't they carry over so many deadly diseases to the natives as other Europeans did in the late 1400s and early 1500s? | Because the Norse themselves were largely lacking in epidemic disease, due to living on the periphery of Europe. Vinland was mostly contacted by people sailing from Greenland, which was itself largely populated from Iceland. Iceland didn't encounter smallpox until [1241](_URL_0_) and the disease was never endemic there...it swept through periodically and died out. The population in Iceland is just too small to support that kind of disease for long periods. The populations on Greenland were even smaller and less able to support such diseases. There's just no good route for disease transfer from small population to small population via infrequent visits between populations. Contrast this with Spanish who were sailing directly from some of the largest cities in Spain to the new world. That kind of direct trip from major disease centers just wasn't happening with the Norse. |
What happens to a photon when it hits the surface of the sun? | The surface of the sun is a very good black body. This means that almost all photons that arrive at the surface will be absorbed. If you shine a lot of photons this absorption would heat up the surface and cause the sun to glow brighter, but you would need an extremely bright light source to achieve this. |
Why do birds bob their heads when they walk? | They do it to freeze a frame of reference, like a footstep, where the depth of field is static while the body moves. Must be like living in a strobe light |
Why do birds bob their heads when they walk? | *If you look closely, or take videos and watch them in slow motion, you will see the head actually stays in one place while the body walks past it. It then is jerked forward and put in front of the body and the body walks past it again. What this behavior does is keep the head still and in one spot as long as possible. By keeping the head still, the bird gets a better look at the world and is able to see things more clearly. It can focus on one spot for a longer period of time*. Source: _URL_0_ |
Why do singers lose their accent when they sing? | That's not true for all singers. David Bowie, for example has a very strong accent while singing. EDIT: Also pretty much every country music singer. |
If we should use antibiotics sparingly, why is daily antiseptic mouthwash OK? | An antiseptic is not an antibiotic. Alcohol is a common antiseptic, bacteria are not going to build up and immunity to alcohol. |
Is their credible science behind putting fluoride in a water supply? | Yes, there is. The idea to add fluoride to drinking water came from the observation that communities which had drinking water that naturally contained higher amounts of fluoride had lower rates of dental caries (cavities). You may find this article from the British Medical Journal helpful: [Systematic Review of Water Fluoridation](_URL_0_) |
What effect does the heat produced by internal combustion engines have on the planet's weather? | Any good climate model incorporates it, but it is probably less of an effect than you think. _URL_0_ What's really interesting that people don't consider enough is the urban heat island effect. The fact that your house has a black roof probably adds more to net heat to the planet than your car. The black asphalt parking lot. |
Does the heat produced by combustion engines have an effect on Earth's temperature? | Just made a quick calculation. [The world's yearly energy consumption is 104,426 TWh](_URL_0_). That's 375\*10^18 J. Just 60 minutes of sunlight on Earth deliver 624*10^18 J (oversimplified Earth as a flat disc of 6371 km radius facing the Sun perpendicularly, solar power is 1360 W/m^(2)). So, really, even if heat from engines does warm the environment up it's not by any significant amount. The real issue is trapping energy from sunlight and that happens because of greenhouse gases. |
How do sodas/other beverages become "zero calorie"? | Most use sweetners that humans cannot derive nutrition from. For example, sugarless gum uses xylitol (a sugar alcohol). Xylitol is sweet and actually helps prevent proliferation of oral pathogens as they can't use the xylitol either. |
The planets revolve around the sun a plane (give or take some) but how does this plane relate in position relative to the galactic plane? | The plane of the solar system is inclined about 60 degrees relative to the galactic plane. |
When a fruit or veggie is "unripe" when picked, how does it ripen? | Well most plant structures (starch and what we would call fiber) are composed of just long chains of glucose. The amounts and variety (amylose and amylopectin) and the ripening conditions vary from plant to plant. For example, avocados will never ripen on the tree, while tomatoes only ripen while still on the vine (the color can change, but there is an alleged negligible effect on taste or texture). Another interesting one is lemons, since they actually get less sweet when they ripen since the acid content increases. These changes are usually determined by the "target" animal for seed dispersion and the amount of time for the seed itself to mature. But by-in-large, ripening is not too dissimilar from muscle degradation during starvation. But instead of breaking down muscle for amino acids, it's starch and fiber for glucose. Also this really doesn't apply to vegetables where we eat the plant body itself (i.e. asparagus) or flowering body (artichokes). Several Edits for clarity and spelling. |
Are all numbers infinite? | Besides the fact that the quotation provided is obfuscating word-play, the argument isn't valid: > But if you divide a non-infinite number an infinite number of times the resulting pieces are non-infinitely small. This sentence simply isn't true. Divide a number n by x. The limit of that quotient as x approaches infinity is zero, meaning the quotient is not "non-infinitely small" - whatever that means. You add all those pieces back together and, _by definition_, you'll get your original number n back. |
Is it possible to synthesize ozone and get it into the atmosphere? | It is possible to synthesize ozone, unfortunately, this is a question of scale. The mass creation of ozone and then facilitation to the correct altitude would be an astronomical cost. Ozone can be created through arcing electricity through oxygen; however, ozone in the troposphere is actually a pollutant and acts as an irritant to humans. |
Are children demonstrably that much better at picking up new languages than adults could be? | There is a 'critical age for language acquisition'. Kids do pick up languages far more quickly than adults, who tend to translate everything when learning a new language rather than just picking up the meaning. It's especially obvious when you look at accents. Children will learn the accent of their environment, adults tend to never really pick up the accent even if they've been living in a new country for a long time. |