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Why is it only recently that we are discovering stars being "closer than ever" to earth, wouldn't we have noticed these closer stars first? | The object mentioned wasn't spotted for a long time as it is a [brown dwarf](_URL_0_), which are incredibly hard to see due to being incredibly dim. These are very small and cool objects, and are actually unable to fuse Hydrogen in the normal fashion due to their lack of mass (they are, however, thought to fuse Deuterium, a heavier isotope of Hydrogen). The brightness of a star is very strongly related to its temperature, with the power emitted going as T^4 - that means that an object that is double the temperature will be 16 times as bright. In the case of WISE 0855-0714, its measured temperature is actually below the freezing point of water - that means that, per unit area, you are actually shining about twice as brightly in the infrared as this object! Considering that fact, it's pretty darned amazing that it was spotted at all. |
How much longer will the Hubble Space Telescope remain operational? | As long as NASA finds a way to use it. They are expecting that it will fall back to Earth [between 2030 and 2040](_URL_1_). It could fail due to other issues before, of course. [BFR](_URL_0_) could potentially bring it back in one piece with an acceptable cost. |
Can you get burned by sunlight through a window? | Ordinary glass absorbs 97 per cent of the UVB rays that cause sunburn and some skin cancers, and 37 per cent of the less harmful UVA radiation. This translates to a protection of about SPF30, so you can still get burned with long enough exposure. Car windscreens have a plastic layer bonded between two layers of glass and this blocks all the UVB and 80 per cent of the UVA, making sunburn very unlikely. _URL_0_ |
Are neonicotinoids 'bee killing' pesticides? | "Neonics" are insecticidal chemicals that will kill pretty much any insect including bees. The problem is with application. No one is spraying bees with insecticide (maybe some peoole are idk) but their use leaves large residual ammounts in the environment which eventually get back to the bees since they tend to get around. Neonics are used to protect crops from crop pests but guess who is pollinating thise same crops? Its the bees. So even without targeting bees with insecticides they still get adequate contact and dosage to have an effect on their health. Source: Im an entomology grad student that works on how to kill social insects (ants). |
If a photon is a "particle" that is all energy and without mass, is there an equivalent "particle" that is all mass and without energy? | No, because the energy of a relativistic particle is E = sqrt(m^2 + p^(2)), where c = 1 and p is the 3-momentum. So E > = m for all values of p. |
Is a headache where i think it is? | The brain itself has no pain receptors and cannot feel pain. Rather, headaches are things like blood vessels around your skull hurting. While it's true that you could be imagining pain, most headaches are actual pain receptors, even if their ability to sense pain is heightened from a purely psychological reason like stress. |
Do bacteria develop resistances to the soaps we use? | Hand soaps are surfactants, they work by making the surface they're applied to too "slippery" for germs and particles to stick to. This is why the proper way to wash your hands is to soap up to a lather, then rinse away the lather down your hands to your fingertips and off, rather than just washing it away. In reality I suppose they could develop a resistance to this, but it's probably less likely than something that attempts to destroy the germs. |
Is there any truth to the common "opinion" that balding indicates higher levels of testosterone? | Male pattern baldness is in fact androgen related-but it's because of DHT (dihydrotestosterone), a testosterone metabolite, not testosterone itself. That's why Propecia (finasteride) works as a hormonal treatment-it blocks 5-alpha reductase, the enzyme that converts testosterone to DHT. |
Why does glass become a mirror when there is no light? | The glass reflects light all the time, but when there's a bright enough light on the other side, the light coming through completely overwhelms the light being reflected. |
Where does dust come from and why is there so much of it? | Living stuff is losing cells, objects rubbing at each other can release smaller fragments, there is a lot of erosion of various objects from weather and so on. It also doesn't go away unless something eats it (for organic material), it melts, it gets included in some other material or something like that. |
Can Alcohol Melt Ice Quickly? | I'm not so sure the answer of which would be faster is as clear cut as it seems. Water has a higher thermal conductivity than alcohol, which means if both were at the same temperature, water would be able to extract roughly twice as much heat than alcohol. However, as noted below, alcohol will induce a phase change by depressing the freezing point. It's not immediately obvious to me which factor would be more important in terms of time, so hopefully someone with more chemical knowledge will step in. For example, if the temperature of the ice is 10F, the water will have to heat it up to 32F to melt it, whereas alcohol may only have to heat it to 20F. So even though the water is faster at heating, it has a further distance to go. |
Does ice melt more quickly when mixed with alcohol? | Yes it will, especially if the glass is not chilled. The heat will conduct through the liquid and into the glass much faster than the gas (air) surrounding just the ice. There is also a greater surface area of the cold system after the liquid pours over it and heat transfer is proportional to boundary area. Finally, water vapour can absorb into the concentrated alcohol and this will raise the temperature somewhat over time as well (as it is like the opposite of evaporation of a hot liquid which effectively cools it). This will be more effective over the boundary surfaces of the liquid-glass-ice system (i.e. liquid surface and glass surface) compared to the air-glass-ice system, where condensation will occur on the ice, and other heat transfer would be pretty limited |
How accurate is carbon dating? | At the long end of its range (40,000 years) its accuracy may be down to one or two thousand years. At the younger end of its range its accuracy is better, with iron age dates (~3000 years ago) being accurate o usually +/- 50 - 100 years. |
How accurate is Carbon dating? | Carbon dating is fairly accurate. We aren't sailing blind here, we calibrate carbon dating with tree rings that fairly directly tell us how much of what isotope of carbon we should find in material of certain ages. For larger time-scales, we use other things like uranium-lead dating. Here we find certain isotopes that we know "shouldn't be there" - these elements just "don't fit" when the rock initially forms, they can only get there if they were originally another element that decayed into that element. > nobody's been around long enough to know how long it takes the isotopes to decay, so we can't be sure it's accurate This is kind of a silly thing to say: there's no reason to assume that physics suddenly changes its rules when we're not looking. |
If phytoplankton contribute to half of the global oxygen output, has declined by 40% since the 50's, why is atmospheric oxygen not dropping noticeably? | So there are a couple of factors at play here. Atmospheric O2 is decreasing over time, as can be [seen in this chart from Scripps](_URL_0_) (compare to the [Keeling Curve, which monitors CO2](_URL_1_)). This is largely due to burning of hydrocarbons, a general form of which could be given as CH+O2- > CO2+H2O. While decreasing phytoplankton counts may also play some role in this decrease, it is important to note that atmospheric O2 has a residence time of ~4500 years, and one source dropping by half over 60 or so years is not going to have immediate impacts. |
how come our hearing nearly fails when we stretch or yawn? | I answered this a while back with regards to yawning. Check it out [here](_URL_0_). As for the stretching, it is also likely that you activated the tensor tympani muscle. |
Regarding the Google Fiber announcement: What is the theoretical maximum bandwidth of fibre optic internet? | Paraphrasing the abstract of a talk that Peter Winzer from Bell Labs gave here last march, commercial wavelength division multiplexing (WDM) systems can acheive 10 Tbit/s, and research experiments have approached the 100 Tbit/s mark over a single fiber. Recent fundamental studies have shown that those experimental results are very close (within a factor of 2 or 3) to the "Shannon limits" of (nonlinear) optical fiber transmission. He concludes that space is the additional degree of freedom required to achieve higher transmission, whether it's multiple single mode fibers, multimode fibers, or various coupled mode configurations. In a different talk given by Cedric Lam from google fiber, he addressed some of the more practical issues with fiber to the home (FTTH). I don't have the abstract, but one bit I remember was that he encouraged the academic community to try to develop low power, stable, tunable lasers for the next generation of dense WDM systems to be practical. |
How does Google Fiber significantly increase download speed? | Google owns the backbone infrastructure for their fibre network. Generally broadband connections slow down at a much more local network, and in improving the connectivity at this level they improve end user speed. Imagine a water pipe that has to supply a whole neighbourhood, and everyone trying to use that. Google effectively hugely increased the size of the water pipe to that area. Further up the chain, the pipes have been big for a while now. |
Does our solar system rotate about a particular point, or does it just rotate around our galaxy's center? | I think the simplest way to look at it is: Every massive particle is gravitationally attracted to every other massive particle. Everything in the solar system orbits the sun, and everything in the solar system including the sun also orbits the galactic centre. But there's more. The sun orbits Jupiter a bit, but only enough to cause a slight wobble in its position. Earth also affects both of these bodies, but its effect is insignificant. Other bodies in the Solar system act under the combined influence of the Sun and the planets, and also interact amongst themselves. This includes the moons, planetary rings, comets and asteroids. Not every orbit is stable because there are not only two bodies in each interaction. So sometimes things collide, or sometimes they attain a trajectory which sends them out of the Solar System. |
Why do babies never cry or make noise in the womb? | There is no air inside womb. The first cry is also the first time air come inside their lungs. |
How much fuel is consumed per second of idling a typical passenger car and/or SUV? | Half a milliliter or less. According to the [U.S. Dept. of Energy](_URL_0_), > Idling can use a quarter to a half gallon of fuel per hour, depending on engine size and air conditioner (AC) use. A gallon is 3.78541 liters, so fuel consumption in gallons/hour is roughly the same number of ml/sec. |
I accidentally bought organic milk and the expiration date is two months from now. How is this possible? | Organic milk is usually more heavily pasteurized. It's the same reason those little cups of creamer can sit out at room temperature forever. |
Why are pistol bullets usually more round-shaped while rifle bullets are usually pointy? Shouldn't they all be pointy for better aerodynamic properties? | There are a couple of considerations here. First, handgun rounds are generally used at shorter ranges, so their long-range performance is obviously less critical. Second, handgun rounds must generally be more compact than rifle rounds, meaning they tend toward a stubby shape. There are, of course, handguns chambered for rifle rounds and vice versa, however. |
Why handgun bullets are rounded? | My educated guess is that rifle rounds are meant to travel distances over 100 yards. Not that they can't be used in closer situations, they can, but if you do need to make a longer shot you need to have an aerodynamic bullet. Handgun rounds are not meant to be used for distances past 50 yards (this is an approximation). Can they be? Yes. You can use a handgun round either in a sidearm or carbine and hit a target at 100 yards (easier with the carbine, difficult with a sidearm). But handgun rounds are usually not meant or required for "long distance" shooting. |
What is carbon fiber, how is it made, and why is it so strong? | Carbon fiber is essentially the same as fiberglass, but instead of using woven glass fibers, you use fibers made of carbon. These are usually made from long chain molecules that contain a lot of carbon. They spin it together like cotton or wool, but on a molecular scale, then cook it to drive of anything that isn’t carbon. The individual fibers are usually woven into sheets, then laid on a mold and covered with resin. Carbon fibers have a huge tensile strength and are very light, and the resin locks the fibers together, so the resulting material has an incredibly high strength-to-weight ratio. Basically, the material can’t stretch or bend easily in most directions because of the carbon fibers, and any direction the fibers don’t cover the resin does. |
If the sun were to explode, how long would the planets in our solar system maintain their orbits? | They would never slow down because there is no air resistance in space. They would shoot off in the direction they were traveling in (minus the gravitational pull of the sun which no longer exists) at the same velocity forever unless they got 'caught' by the gravity of some larger stellar object. |
Why can you see better when you squint? | When you focus on an object at a certain distance, your lens in your eye is adjusted so that all the light rays coming from a specific point of that object and that go through your pupil, are focused to a single point of your retina. When you're not focusing (or if you have bad eyesight) the different rays are projected at different points of your retina and you see a blurry image. Now, if you squint (or if you make a tiny hole with your fingers to look through), your drastically limit the amount of rays coming through your pupil, so even if your lens does not focus, the image will be less blurry because there are less places on your retina the light reaches. In the extreme case, there is only one ray of light per point of the object and the image will be crystal clear, even without a lens. This is the idea behind a [Camera obscura](_URL_0_). |
I know the difference between venomous and poisonous, but does this distinction only apply to animals? Are there venomous plants? | Only animals are considered venomous. I feel the need to point out though that, as multiple dictionaries(Oxford and Merriam-Webster at least) define it, venom and poison are not mutually exclusive. Rather all venom is poison, but not all poison is venom. |
[Physics] Why does refrigerating food make it last longer? | This is a biology question. Bacteria and all the other life forms use enzymes to break down food into fundamental ingredients. These enzymes work only in a specific temperature range, for example 10 degrees above and below the room temperature. When food is stored in the refrigerator where temperatures are much lower, the enzymes become inactive. Even the enzymes that are responsible for regular cell activities (like multiplying and metabolism) are rendered inactive. This causes the bacteria, fungi and any other microbe to go into a dormant stage where they are unable to multiply, perform cellular activities or consume nutrients. This prevents food spoilage and makes the food last much longer. |
How does one lose their voice, physically speaking? | So what it basically comes down to, is a process of inflammation. [These are normally functioning vocal cords](_URL_0_) now when you overuse them lets say at a concert, the soft tissue around the vocal cords actually becomes inflamed. This inflammation basically reduces the ability for the muscles to move in the required pattern to produce sound. So with time, your body naturally reduces the inflammation in the area and your voice returns. This is a similar mechanism that happens when you have acute laryngitis (throat infection). Except this time the inflammation is being caused by an infection not overuse. |
How do candles burn for so long? | Ever notice how you end up with a lot less candle after it's done burning? It's the wax that burns. The heat from the flame melts some of the wax, which gets drawn up the wick and acts as fuel for the flame. |
If two sets of identical twins married each other and had kids, would the cousins be genetically similar enough to be considered "siblings"? | Short answer: Yes. Long answer: Since the Mothers and Fathers are genetically identical, then genetically, the children have the same parents. Of course, blood siblings can (theoretically) be as genetically distinct from each other as their parents are from each other, but that's *really* unlikely. (something like 2^-46 unlikely) |
If telomere length is a primary factor in aging and cell division stops when telomeres run out, wouldn't we see a shorter average lifespan among monozygotic twins than among the general population (or among non-monozygotic twins) due to the "extra" division before each zygote begins to develop? | All vertebrates posses the genes for an enzyme known as telomerase, which has the ability to add nucleotides to the ends of chromosomes to prevent chromosomal shortening. Embryonic stem cells actively express telomerase, so that one extra division would likely have been compensated for by addition of extra nucleotides by telomerase. Upon differentiation, most cells cease production of telomerase as a protection against proliferative disorders (primarily cancer). Some rapidly proliferating cells (such as adult stem cell lines that maintain the lining of the cut) still possess telomerase throughout their lifespan. Source: _URL_0_ |
With all these beautiful colors you see in pictures of nebulas in /r/space, what colors will your eyes actually see of those objects in space? | We image the sky in the entire spectrum of light; may it be microwave, gamma, infrared, UV, radio, visible, etc. Each apparatus is different of course. So if the picture is taken in the visible spectrum those indeed *are* the *real* colours. We humans see a very small piece of the entire light spectra, but to observe and better understand the pictures taken in other regions, they are false coloured.(usually an index or legend accompanies the picture for guidelines for observations, it also usually accompanies the region in which it was as captured). We can't see the other frequencies, the brain has no colour for it, hence there is no 'colour' in the sense of it. |
Do isotopes have the same absorption spectra? | There are some subtle differences. For the main spectral lines, the energies depend on the effective mass of the electron, which is related to the mass ratio of the electron and nucleus, and if the nucleus has a different mass then the spectral energy changes. For fine and hyperfine splitting, there may be a more direct effect because the nucleus has a different magnetic moment. For example, a hydrogen alpha line has a wavelength of 656.4 nm while the same line for deuterium is 656.3 nm. |
Do different isotopes (e.g. Carbon 12 and Carbon 14) have slightly different electron emission spectra? | Their atomic spectra will be slightly different due to *isotope shift*. The nucleus is not actually a point as we often pretend in chemistry; it has some extended spatial structure. And different isotopes of the same element have different nuclear structure. The finite size of the nucleus has a small influence on the atomic level structure, so if you change the structure of the nucleus (for example by adding a few neutrons), you change these very small shifts in the atomic spectrum. |
Given the current level of computing power (easily available to all, not supercomputers), how long would it take to break the Enigma code by brute force techniques? | According to the internet, a 180-character ciphertext took about 400 CPU days (which isn't a very accurate unit) to crack in 2006. Considering the enormous rise in computing power since then, especially with the rise of GPGPUs, I can't imagine it taking too many weeks to do it on a home computer with a beefy GPU, assuming the software for it is relatively efficient. There's still an element of chance involved. Sometimes you get "lucky" and solve it fast, sometimes it takes longer. It's also worth mentioning that there are several versions of the enigma cipher machines, some considerably more advanced than others. |
How do quantum computers perform calculations without disturbing the superposition of the qubit? | It seems to me you are asking two distinct questions > How do quantum computers perform calculations? Calculations are achieved by the application of [operators](_URL_0_) on quantum states. These can be applied to the entire superposition at once without breaking it. > How can you retrieve information without collapsing the superposition? As has been correctly answered by /u/Gigazwiebel below, you cannot retrieve information without collapsing the superposition. This is why quantum algorithms are so clever and so hard to design, by the time of measurement your superposition should be in a state so that it gives the correct answer some high probability of the time when measured. & #x200B; Even if somehow you managed to measure the whole superposition without breaking it (which of course is against the laws of quantum mechanics), you would be restricted by [Holevo's bound](_URL_1_), which says you can only retrieve n classical bits of information from n qubits. & #x200B; |
Water is clear. Why is snow white? | Water is clear, why are frothy waves white? Glass windows are clear, why is a pile of shattered safety glass white? All for the same essential reason. Something clear is clear because its structure is well aligned to allow light to pass through with**out** lots of refraction or absorption. Snow flakes (and bubbly water, and glass shards) provide millions of surfaces, all pointing different directions, sending light bouncing and bending and absorbing in all sorts of ways. The light gets diffused into what you see as white. |
Two astronomy questions: Why does dark matter need to exist? What does the night sky look like without any light pollution? | Here's a nice image that shows how light pollution affects the night sky: _URL_0_ |
Why do illnesses seem to intensify at night/in the morning, for example if I have a sore throat why does it feel more painful just before I fall asleep? | If I could possibly add on to this question...if I've been working out or running then sleep, why do I feel the soreness after I wake up while if I go running then sit in a chair for several hours I'll feel perfectly fine getting back up? |
Is it possible for a planet to consist solely of liquid as opposed to a solid or a gas? If no, why not? | Yes, Jupiter might even be one. Even if it is not then other gas giants could be formed by gravitational instability in which there is no solid core (at least at the early stages but there are processes which may form one later). |
What are the reasons why we keep the eyes closed while sleeping?(Not counting keeping the eyes from drying) | Generally speaking it`s required. Closing your eyes is the first part of the falling asleep process. It removes the visual stimulus. Some people are able to sleep with their eyes open as a result of a condition called [Lagophthalmos](_URL_0_) |
Why does it sometimes foam up in the toilet when you urinate like a head on a draft beer? | Medical lab Scientist, Protein in your urine. Not exclusively from semen, can be for more serious reasons too. [Here] (_URL_0_). |
Do insects have the ability to "get fat"? | [This thread](_URL_0_) contains a good comment string based on /u/Redwing999 experience and some written sources on insect obesity. |
Is it possible to make a synthetic flawless gemstone quality diamond? | Yes, [it's been done for over 40 years](_URL_0_). It's just not economically viable make large diamonds for use as gems; almost all synthetic ones are used as abrasives or for other industrial uses. As for the vending machine, it's actually possible to create small diamonds in either [hydraulic presses](_URL_2_) about the size of vending machines or [DACs](_URL_1_) which are much smaller. |
In what way is time a dimension? Why is it called the fourth dimension? | You define something's location with coordinates. On a line, you need one number. This is one dimensional. On a sheet of paper, you need two numbers - two dimensional. In a three dimensional world you need three numbers to define where something is. Now, what if we had things like photons that can be absorbed and emitted? Three numbers is great, but it can't tell us anything about when that photon was emitted. So we add another number, time. A fourth dimension. It's like saying "I'll meet you at the train station at noon." The train station has three numbers to define where it is. But you have to add another number for the time that you'll be there. |
Will frozen gasoline burn? | Gasoline only burns as a vapor. The term flash point means the temperature at which a substance forms a flammable vapor at its surface. Below the flash point, the material cannot be ignited. However, if you introduce a heat source, you can warm part of the material, produce a flammable vapor, and ignite it. If you've produced enough extra heat to warm more of the material, the reaction can become self sustaining. _URL_0_ |
If Earth is twice the size of Mars, then why are we able to see Mars as a bright star from Earth, but in all the pictures of Earth from Mars, Earth appears as a tiny dot and not twice as large? | Taking photos of the night sky is not easy. You can see what looks like a brilliant night sky, and then lift up your phone and it just looks like a black smudge. Yes, the Earth should be brighter from Mars than Mars is from Earth. But the cameras on these rovers & landers are not designed to take high quality pictures of the night sky through the Martian atmosphere, so their images of Earth aren't impressive. It isn't the main purpose of the Mars missions, so they haven't put a lot of time and technology into trying to do this anyway. |
Do stars turn into planets? | Stars throw off gases and metals at the end of their lifespan (By "metals" I mean anything heavier than hydrogen or helium) These things go on to produce both stars and planets as they condense into a new star system. As for the remaining core, it turns into a stellar remnant. _URL_0_ Typically this is a white dwarf. If this stellar remnant was captured by a star's gravity, or somehow formed as part of a binary star system, then it would be a planet. I'm not sure likely it is for a star to turn into a planet while part of a binary system--unless it was captured by a younger main sequence star. This is because heavier stars burn hotter and die faster. If two stars form together, then the the bigger one would die first and probably blow away it's partner. |
Why Can't We See the Bright Light from Our Galaxy's Center? | Too much dust to see it in the visible spectrum. Are you sure the photos of other galaxies are visible light images? [Here](_URL_0_)'s what our own looks like when you use other wavelengths. |
How complete is our Periodic Table of Elements? | In the periodic table, the element is defined by the number of protons in its nucleus. ~~Chromium~~ Cobalt has 27 of them and Nickel 28, so no, there can't be an element between them. And the numbers are continuous throughout the table, with the possible exception sometimes at the very high end where someone might synthesise a new element with a high number of protons before all the ones before it have been synthesised. So other than discovering new very heavy elements out of order, you won't find new elements between any already discovered elements. And you can't extend the table in the other direction either, hydrogen has just one proton so there can't be anything before it. |
Why do our voices "crack"? | The pitch of your voice is determined by a number of things: the length (and thus thickness) of your vocal chords, the size of your larynx and (for a lesser part) the position of the larynx and the shape of your pharynx. When going through puberty, the larynx, pharynx and oral cavity all grow/change. This has a large effect on how your brain needs to control the muscles in these areas. A cracking voice is just a mistake on your brain's part. Since emotion, stress and nervousness can have a significant effect on your muscles (shaking hands, not being able to walk) they can also affect the muscles controlling your voice. A cracking voice is the result. edit: minor spelling mistakes |
Where does our atmospheric oxygen come from? | I'll hazard a guess and say that it's not that you're incorrect, but rather that the professor thought that the mention of the source of atmospheric oxygen was not appropriate for the talk. I don't know what level you're at, or what level you'll be presenting to, but based on the use of the word "populistic," it sounds like the professor thought that the tidbit was meant to "wow" more than to inform. I admit that I'm speculating, though. I don't know what your professor wanted. But Photosystem II is present in cyanobacteria, so I would assume you're correct about it being responsible for breathable oxygen. |
If light is an electromagnetic wave , just like infra red or radio, can we use non optical instruments like Antennae to detect it ? | The principles are the same but the frequencies and wavelengths are very different. Visible light has wavelengths of about 500 nm or 1/20000 of a mm. You’d want pretty tiny antennas. Still, I remember a paper once where someone had realized that a microscopic organism was doing exactly that. It had an “eye” which was an antenna for light. Also we can’t yet build circuitry fast enough to keep up with optical frequencies the way we can with radio frequencies. I think we’re within a factor of 100 so it’s not totally inconceivable we’ll get there someday. Just not yet. As for going the other way, building lenses for radio waves, there’s no reason you couldn’t. You need something with a different index of refraction than air, but also not too absorbent, analogous to glass for light. And the size would have to scale up to meters to accommodate the larger wavelengths of radio. |
Why does soap form bubbles? | To have a bubble form, air needs to be trapped inside the bubble walls. If the structure of the bubble walls collapses, then the wall breaks quickly and the bubble pops. This is what happens with pure water. Ironically, it's the strong attraction between the water molecules that cause them to pull back together quickly and thus collapse the bubble walls. It's basically impossible to form bubbles faster than they pop if you have pure water. Soap molecules will strengthen the bubble walls so that the bubble lasts longer. Part of how they do this is by decreasing the surface tension of the water so the water molecules take longer to run out of the bubble walls. This means the bubble walls last longer and it's possible to form the bubbles faster than they pop. |
When I get a big blister but don't pop it, after a few days it is dry. Where does the liquid inside go? What is it made of? Where did it come from? | The liquid is basically plasma and dead cells that were trying to fight possible infection. It is also possible that the irritation stimulated inflammatory effects that allowed more cells to migrate to that area to fight off possible infection. The fluid drains into your lymphatic system, which then dumps into the venous system at the superior vena cava so you don't lose the fluid. |
If the the Twin Jet nebula is 1,200 years old then how can we see it if it's 2,100 light years away? | Because when we discuss how old something is in the sky we're generally referring to local time. Not the time of the event plus its distance from us. Thus the Nebula was created 1200 years ago our time, or 3200 years their time. So Supernova 1987a occurred 28 years ago is accurate from our perception, we dont say 1987a occurred 168,028 years ago. This is due to several factors, firstly we've only been able to date things in the sky with any accuracy over the last 100years or so, and we're often not sure how far away things. So saying 1987a occurred 28 years is very accurate (from our local perspective), saying it occurred 168,028 years is probably quite innacurate as the distance/time is an approximate. It just makes it easier all round. People understand the difference between when we saw it and when it actually happened. |
Can someone validate this claim that we have been losing oxygen levels due to burning of fossil fuels. We used to have 21.4% oxygen only a century ago. Should the oxygen level fall down below 19% then we would suffocate? Are oxygen levels are still decreasing today? | The volume fraction of oxygen in the atmosphere is certainly less now than it has been historically, but this is nothing new. In prehistoric eras, we had things like giant 24" insects because the high oxygen concentration permitted efficient respiration of such animals. The change has little to do with the burning of fossil fuels, and more to do with the abundance of oxygen producing plankton, bacteria and vegetation on earth varying over time. At present, humans experience hypoxia at about 0.16 absolute atmospheres partial pressure of oxygen, and the volume fraction is about 20.9%. |
Why do certain mental illnesses or physical conditions cause us to experience clear sensory hallucinations (people's faces, voices speaking in sentences, etc.) rather than just sensory garbage? | I can't offer an explanation as to how complex hallucinations originate (although I will mention that the [Wikipedia article](_URL_0_) has a lot to offer). I do want to point out though, your assumption that we don't hallucinate jumbled crap may be driven by confirmation bias. Ie: people are more likely to tell you about the time they hallucinate that they had a conversation with *literally god* vs hallucinating noise. Although this is anecdotal, I myself have hallucinated plain noise on a handful of occasions, either hallucinating from drug use, or once from oxygen deprivation. The latter I remember particularly well, I had been surrounded by a loud crowd at first, and suddenly the entire crowd was drowned out by this inexplicable incomprehensible scratchy noise, a lot like when old TVs had bas signal. Sorry for the lack of an answer, hopefully a better one will come our way soon. |
By what mechanism are zero-calorie sweeteners thought to cause "weight gain?" | There is epidemiological evidence of an association between artificial sweetener ("AS") use and weight gain. This doesn't mean that artificial sweeteners cause weight gain. There is animal evidence (rats) but animal evidence isn't nearly so helpful as you would think (humans and rats are quite different). Speculative mechanisms for the association between AS and weight gain are: * No cause, just an association. Maybe people with weight problems take more AS. * a lack of satiety from the sweetener so the person may eat more, * overestimation of the caloric savings and so the person eats more, * taste distortion because the AS are sweeter than sugar, so you want sweeter foods, * decreased metabolic rate from using AS to decrease caloric intake in the short-term [Ref](_URL_0_). |
Male pattern baldness is usually determined by the mothers side. Are there any other traits that are dominated by one parent or the other? | A rather dramatic example of a syndrome (actually a pair) that depends on which parent a chromosomal anomaly is inherited from is [Prader-Willi](_URL_1_) vs [Angelman](_URL_0_). In either case, genes on chromosome 15 from one parent are deleted or inactivated, while the genes from the other parent are suppressed through [genomic imprinting](_URL_2_), which is an [epigenetic phenomenon](_URL_3_), i.e. it doesn't actually change the DNA, it just changes what sections are activated. It is amazing to me that such a seemingly minor difference of which parent contributes the chromosomal section in question can lead to such vastly different outcomes. The wiki links for the two syndromes give nice, concise overviews of the problems and challenges each condition entails. |
How does Venus retain its atmosphere? Does it have a magnetosphere? | Venus doesn't have a magnetic field. However, it's not because of the slow rotation. Its rotation is slow, but still fast enough to generate a magnetic field. So the slow rotation explanation is a bit of a misconception. What we think is happening is that since Venus doesn't have plate tectonics, it's not removing heat efficiently. (In order to generate a magnetic field with the core, there needs to be a sufficient amount of heat flowing out at the core-mantle boundary.) One reason Venus kept its atmosphere was because of volcanic out-gassing. (Although we haven't observed anything live, there are many calderas and lava flow streams) Venus also has a much stronger gravitational field than Mars, which helps to keep the atmosphere. |
How does Venus have the atmosphere that it does when it has no magnetosphere to shield it, like Earth does? | Venus doesn't generate its own magnetic field, although it does have a [weak induced magnetic field](_URL_0_) because of the interaction of the solar wind with the ionosphere. This provides some protection for the atmosphere. Another thing Venus has going for it is that the atmosphere is mostly made of relatively CO2 rather than lighter molecules like O2 and N2. You need more energy to lift those heavy molecules away from the planet. On the other hand, lighter elements like hydrogen have been stripped away and are nearly gone from the atmosphere. |
What causes the difference between kinetic and static friction? | The friction itself is caused by the interaction of elements of the surfaces essentially locking in, like teeth that fit together more or less. Mostly less when they're moving. When neither object is moving relative to each other, the rough bits will be pushing against each other in a set position. This causes them to lock in tighter, as they're going to deform slightly to match each other and sort of stick together. Now you have to overcome these bits that have been pushed together before you start again. By this explanation, if you were to stop moving for an infinitesimally small period of time, the surfaces wouldn't have a chance to mold together you'd still have kinetic friction when you get going again. |
What would happen to a dead body floating in space? Would it decompose at all? | If the body was not in a space suit and assuming it wasn't near a heat source it would likely freeze in short order preventing any decomposition. In addition any water would boil off in the low pressure leaving the body a dry frozen husk. Quiet possibly it would then last indefinitely as none of typical biological processes involved in decomposition (mainly bacteria) could occur. |
Why do human lips have very few to no pigments? | This is because the melanocytes, which produce the pigment, are mostly present in the skin (in the epidermis near the bottom layer stratum basale). The lips, however, change from skin to mucosa, and there are very few, to no, melanocytes in the mucosa. |
How come when your eating a spicy food and you stop eating it, it becomes more spicy? | Because you're eating other things along with the capsaicin-including ones and those are calming your taste receptors. Once there isn't a large volume of fats, carbohydrates and fluids washing through your mouth you're left with capsaicin free to irritate your nerves until saliva finally (and quite slowly) washes it away. |
Can a moon have a moon that has it's own moon? | Sure, why not? If you substitute 'satellite' for 'moon', we've seen this in our own solar system: Sun --- Earth --- Moon --- Lunar Orbiter So empirically, we see that we can have a 'moon' with it's own 'moon, which in turn has it's own 'moon'. I'm not aware of us finding this configuration in nature yet, but there's not reason for it not to exist. Although I imagine the size of the final moon will be quite small relative to the main parent. |
Can you get hearing loss from exposure to loud noises outside our hearing range? | Could someone familiar with sound transduction mechanisms in the ear comment on this? I thought hearing loss due to loud sound exposure was due to what is essentially excitotoxicity in the frequency-tuned transducer cells. That is to say, while ultrasound could still damage hearing via cavitation-related cytotoxicity, it would occur by a different mechanism than would normally operate for loud-noise induced hearing damage. |
Why are some people more susceptible to mosquito bites? | It's important to clarify whether this is a question of likelihood of being bitten or severity of reaction. Some people react very strongly to mosquito bites, while others have little response at all, and so might mistakenly think they are not being bitten. |
Why is life based on carbon | Carbon is capable of forming stable chains of essentially arbitrary length and complexity. No other element does so in the same way. Silicon can form similar structures but they're much less stable and nothing else really comes close. Complexity is fairly essential for anything you'd call life. |
[Astrophysics] Is an Elliptical Orbit with an equal pericenter Possible? (Picture Example) | > Most orbits that I've seen in diagrams are either circular or elliptical with a different r1 and r2. That's because Kepler's laws say that bound planetary orbits are ellipses with the "sun" at one of the foci of the ellipse. If the ellipse is not a circle, it will have two foci, and neither one lies at the centroid as you've drawn it. |
Why is dust able to gather on my electric fan, instead of being blown out with the force of the airflow? | Two reasons. Static electricity. This is especially so if your fan blades are plastic. This causes dust to collect on the blades when the fan is not switched on. There is a boundary layer when the blades are spinning. In fluid dynamics, when an object is moving through a fluid, there is a boundary layer of extremely slow moving fluid close to the surface of the object and a layer of non-moving fluid at the surface. In this case, the surface is the fan blade. Any dust already trapped there would not get blown off as they are not experiencing any wind. In fact, the centripetal acceleration experienced when the fan is on should keep them on fairly well. |
Do other animals get ticklish like humans do? | Rats are ticklish and emit ultrasonic "laughter" chirps when tickled. It used to be something of a novelty in labs, but has gotten some serious study the past ~10 years or so. [Here's an accessible Scientific American post discussing some of it](_URL_0_) |
What color is the Sun, really? | This is also biased by the mediums it is being viewed on, as neither our eyes nor camera equipment is entirely impartial. Such pictures as you are talking about are actually filtered to show a different part of the spectrum and artificially colored. It can be artificially colored in other ways as well- _URL_0_ For example |
If the ozone layer is made of O3. Why then does it not burn up? | In order to "burn up" there must be something to burn with. Combustion being the reaction of an oxidizer (ozone or oxygen) with a fuel. There is nothing for it to burn with in the ozone layer. That being said, ozone is unstable and breaks down into oxygen with time. The ozone layer is still there because ultraviolet light photolyzes the oxygen and regenerates the ozone. So while it might be decaying, it's constantly being replenished. (as a side note, ozone depleting chemicals causes the break down to occur much faster, faster than it can be regenerated and thus why the concern for ozone layer depletion.) Interestingly enough, ozone is indeed [explosive](_URL_0_) on its own (no fuel needed), but this only happens at very high concentrations, above 10%. The ozone layer doesn't explode because the actual concentration of ozone in that region is only ~10 ppm (0.001%), the rest being oxygen and nitrogen. So there just simply isn't enough concentration for it to explode. |
This may seem like a very stupid question, but why isn't water flammable? | Essentially, water is the *product* of burning hydrogen. Burning is an oxidation reaction (a reaction with oxygen to produce an oxide). Burning carbon produces carbon dioxide, burning hydrogen produces dihydrogen monoxide (water). |
In most models of the solar system, the planets are all show on the same flat plane - are they? | There is a reason for this - when planets form there is usually a larger structure influencing the patterns. For instance, the dust planes of most proto systems we've seen tend to follow the Milky Way plane. I am not sure if we have seen this happen in other galaxies yet (they are kinda far...) - but it figures to follow the pattern. As the dust in the galaxy has this flat shape and the dust in the young solar systems have the same shape - the planets tend to form within the shape of the dust. You get an alignment. This is also why most things rotate and revolve in the same direction. The general motion of the system of the Milky Way is one direction (not sure if clockwise or counter). The star follows that, the dust follows it, the forming planets follow it, etc etc. |
What is the Difference between a Photon and an Electron? | Electrons are not excitations of the EM field, photons are. Electrons just interact with the EM field because they are charged. |
What's the smallest number that we don't know whether it is prime or composite? | There's no real answer to this. No one is keeping a definitive list, and checking primality is pretty fast. Probably millions of primes numbers are newly discovered and forgotten forever every day for encryption. |
When a car wheel turns, it initially blurs, and then appears to turn slowly in the opposite direction. Why is this? | From [here](_URL_0_): > There are two broad theories for the wagon-wheel effect under truly continuous illumination. The first is that human visual perception takes a series of still frames of the visual scene and that movement is perceived much like a movie. The second is Schouten's theory: that moving images are processed by visual detectors sensitive to the true motion and also by detectors sensitive to opposite motion from temporal aliasing. There is evidence for both theories; as of 2011, the debate is not completely settled although the weight of evidence favours the latter. |
Do children who speak different languages all start speaking around the same time, or do different languages take longer/shorter to learn? | Basically, all the languages in the world have approximately the same difficulty level, so you'll see that child language development happens at the same rate regardless of the language being learned. It just seems to us that some languages are harder because of how different they are from the language we grew up with. A child under six months has the ability to distinguish between phonemes that an adult would not be able to. After that six month mark (approximately. It varies from person to person) the brain starts to recognize the specific phonemes it needs to learn the language it's exposed to. Simply put, it cuts out the phonemes it doesn't need, which is why as an adult, it's much harder to learn a language with a lot of phonemic differences from your own. |
How do the iPod to cassette adapters work? | Cassettes use magnetic tape, so this converts the signal from your iPod into a magnetic signal (like cassettes) so it will work just like a normal cassette. It's a really simple device, actually. |
Why does the sun make colours fade? | UV radiation breaks down chemicals (pigments) which color objects. |
Why do colors fade when left in the sun? | Typically, the culprit is [UV degradation](_URL_0_). This is a specific example of [photochemistry](_URL_1_), which is the study of chemical reactions triggered by light absorption. |
Is it possible for dogs to learn commands in 2 languages? | Hi there. Veterinarian here. Absolutely. For a dog, they don't actually hear differences in language. They hear a "cue", and that cue can be anything from a hand gesture to a word, to just a sound or a look. All you need is patience, and a good training regimen. [Positive reinforcement](_URL_0_) training is the best method. A great book to look into regarding training methods is [Don't Shoot the Dog](_URL_3_) by Karen Pryor. It really breaks down the differences in training techniques and explains them in a very approachable way. The Wikipedia page for [dog training](_URL_1_) is exhaustive, but the Pryor book is better. Also, as a side note, please don't use any of Cesar Millan's methods for training. They do not work effectively. They may train the dog what not to do, but often only create frustration and [learned helplessness](_URL_2_) in the animal, which could easily eventually cause the dog to become aggressive. Edit: spelling, clarification |
Why does Helium exist as a liquid at zero Kelvin? | There is also a concern of pressure. What pressure is the Helium at when at 0K? To determine state we need to know pressure as well. For example, if you put water in a bell jar and through vacuum decrease the pressure as it nears 0 atm the water will boil. Temperature is not the only factor for a material's state. As for the specifics of Helium, I've not a bloody clue, but I'm sure if the pressure were appropriate we could form a solid substrate of helium of some sort. Though there are others here who will have a much better answer than I will. |
Is It True Helium Is a Liquid At 0 Kelvin? | At atmospheric pressure it is, but if you turn up the pressure to an insane amount you'll turn it onto a solid. From a quick look at a phase diagram you'll need over 25 times atmospheric pressure to turn Helium into a solid. |
Do animals ever suffer from mental illness? | Yes. Inbreeding in dogs has lead to instances of inherited mental illness. Some bull terriers will compulsively chase their tails, sometimes for hours a day. As for wild animals, mental illness would likely face severe selective pressures making it unlikely to propagate. |
Do animals suffer from mental illness? | We can't be sure. We diagnose depression and other mental disorders by means of communication in humans. However, the widely popularized theory is that animals do indeed suffer from mental illness. One observable state is depression. Alot of what we know could be based on primates and their behavior. [Example](_URL_0_), moreover, there is also [this](_URL_1_) BBC Earth article that will have alot of what you seek., |
Why does my plate get boiling hot, but my food hasn't even thawed out when I put it in the microwave? | Microwaves work by zapping a particular frequency of microwave radiation at your plate and food. I have never had this problem but would be willing to bet that your plate is made with a mineral that contains chemical bonds with the same energy as water, that resonate at the same "pitch", so to speak. So while the water in your food is being excitated and evaporating, the lattice of your ceramic plate just gets really hot. |
Is there a reason for soap to foam up? | Water is a polar solvent, and is thus ineffective at cleaning non-polar substances like oils, fats, etc. Soaps and detergents work (usually) by the use of surfactants that have a hydrophobic end and a hydrophillic end. The hydrophillic end always maintains contact with the water and the hydrophobic avoids it, enveloping things that otherwise wouldn't dissove and letting it exist as an immersion. This also naturally makes these products foaming agents to varying degrees. Sodium laureth sulfate does this and it's a really cheap detergent. Things that would dissolve fats and other non-polar substances, i.e. non-polar solvents, are horrible for you (you're made of fats and etceteras). |
Are radiowaves also comprised of photons? | a 'radiophoton' would just be a photon with a different energy than the 'standard photon' you are thinking of. |
Are radio waves also photons? | All EM radiation is comprised of photons, including radio waves. If you emitted radio waves into a dark room, it would just be radio waves. If you switched the frequency of what you're emitting to ~400-800 THz, you would be emitting visible light (and NOT radio waves) and achieve your goal. I suspect what you actually mean is changing the frequency of the radio waves while in transit through the room. If you had a magical device that could do that, then yes, the room could be lit. The caveat is that radio waves have much lower energy than visible light, meaning that changing the frequency of the photons is equivalent to changing their energy, which is really, really tough to do without absorbing the photon. |
How do flies not get sick from the bacteria and mold that grows on old food? | Fly physiology is so completely different than our own that any comparisons outside of genetics or general cell biology are pretty difficult to make. The fact of the matter is that flies have all sorts of their own pathogens. Because their physiology is vastly different, the pathogens on flies rarely affect humans, and human pathogens have little effect on flies. For example, many human pathogens exploit cell division or cell division machinery, but most parts of the average fly are postmitotic. Furthermore, flies are actually adapted to eat bacteria and mold. Experimental fruit flies generally need yeast in their nutrient media in order to survive and reproduce effectively. [Here's a very old paper that examines yeast digestion in fruit flies.](_URL_0_) |
Do insects rot, and if so, why can't we smell it? | Insects definitely rot. As an entomologist and pet insect keeper, I have experienced the smell of rotting insects a lot. Especially decaying larvae/caterpillars smell, as do large insects such as stick insects and praying mantids. When mounting large specimens, I typically remove the contents of the insects abdomen/gut. The reason you do not smell this in your house is that most insects that will be living in your house are small and dehydrate very rapidly after dying (due to not having much tissue). But if you stumble upon a cupboard full of dead cockroaches for sure you will smell them while cleaning. |
Why does hair growth stop at a certain point on your arms, legs etc., but not your head? | Hair follicles never stop growing, they just die, fall off, and start growing again. The faster they die, the less time they have to grow, which makes the length of the hair shorter on average. The only difference between the hair on your body and the hair on your head is how long it can grow before it dies. |
Why do people say time is the 4th dimension? | Just to take the first line of the wikipedia page on dimension: > In physics and mathematics, the dimension of a mathematical space (or object) is informally defined as the minimum number of coordinates needed to specify any point within it. You seem to understand that we need three coordinates to describe something's spatial position but I could go to that position and the object not be there. That's because you didn't specify when (think about arranging meeting somebody at a specified place with no specified time, that'd be useless). That is the simplest sense in which time is the fourth dimension. |
Why do we produce mucus when we have a cold? | Mucus prevents the entry of other viruses while we deal with the sickness we already have. It also contains enzymes that slow the progression of the virus so we can fight it off better. |
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