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Except for the human flu vaccine, why do dogs/cats need vaccines boosted every year while people don’t? | The Flu vaccine is not *boosted*. Instead, the Flu mutates really fast, and you just need a new one for a (slightly) different disease each year. There are vaccines for humans that are boosted. For example, Tetanus shots only last for 10 years. After 10 years, it is no longer effective. This is why, while you got a Tetanus vaccine as a child, there is still the advice to get a Tetanus shot (which is a booster) whenever you hurt yourself on rusty material (technically you only need it once per decade, so if you did so recently, you wouldn't need a new booster). Other vaccines (like Hepatitis) need 3 shots, spread out over 6 months, for the protection to become lifelong. The Second and Third shot are boosters. |
Why aren't bald tires grippier than treaded tires? | You are right and it would be a good idea to use unthreaded tires if u are 100℅ sure of never encountering wet roads because the purpose of threaded tires is to avoid the "hydroplane" phenomenon. If an unthreaded tire is running on a wet road, water will get between tire and road, reducing friction to negligible and causing some serious control problem. In case of threaded tire water is channelled into the grooves and thus friction is maintained. So it's kind of a compromise and safety precaution. |
Why do we shiver when exposed to low temperatures? | [Wikipedia](_URL_0_) says that it's an attempt to warm up the body in an attempt to prevent hypothermia. |
If darker colors absorb more heat, why is our skin made to darken when exposed to the sun? | Because the problem with sunlight is not the heat, but the exposure to UV radiation, which damages skin cells and their DNA, leading to sunburn in the short term, and to melanoma and other problems in the long term. Melanin, the pigment responsible for the darkening of the skin, is placed above the DNA of skin cells, protecting it by converting the energy of UV rays - energy that would damage the DNA - into heat. So yes, a little more heat is produced, but that's easily dissipated and won't cause any problem. |
Does washing off fruits and vegetables before eating them actually remove much of the residual preservatives and/or pesticides? | For a big part, yes. It mainly works for residues, which are on the outer layer of the vegetable skin, where normally the biggest part of pesticides is located. A lot of studies show further, that a acidic washing solution, eg acetic or citric acid, is way more powerful, especially for organophosphorus and organochlorines. Also, peeling and cooking also have a strong effect on reducing pesticide concentration. Anyway, normally fruits and vegetables are washed in the factory before selling and shouldn‘t have residues above critical limits, theres no need to be scared, at least if you‘re in a country with proper food safety regulations. Some Papers about the topic (there are much more): _URL_2_ _URL_0_ _URL_1_ _URL_3_ Edit: spelling |
Why are most random number generators said to be "pseudo-random" rather than truly random? What is the difference between true randomness and pseudo-randomness? | Let's start with the definition of deterministic. A deterministic process or system has one future for each state. In phase-space, the trajectories don't cross. So you can usually predict the future state of a particle given the particles current state. Random processes/functions/systems (whatever) can have multiple futures for one state. On computers, random numbers typically are deterministically generated, but by a process so complex that each future state is not easily predictable (you can have determinism without predictability: see chaos for instance) and also such that their distribution obeys the statistics of the desired random process. |
I have heard it said that many computerised random number generators are never truly random. Why is that? | Because they use a deterministic algorithm to generate the number. Most generators use some function to transform the "random" output in every iteration to generate a sequence that has good enough statistical properties to be considered random, but every such sequence is finite and will start repeating. |
My understanding is that we can't see any stars older than ~13 billion years because of the speed of light and rate at which our universe expands. Is it possible that a satellite like Voyager 1 can detect older (farther?) stars and then transmit the information back to us? | Imagine if we sent a space probe 1 light year away. This probe would be able to see things that are one light year further away from us then we could see, because the light from those start would reach it 1 year before it reached us, but the probe can only send signals back at the speed of light, so by the time we get signals from the probe about the more distant stars, the light from those stars would already have reached us, providing no benefit. |
Do bugs get sick like we do, like get a cold? | An insect can't get a cold like we do because they don't have a respiratory tract that's anything like ours....but they can get infections (get sick). Just about every organism on the planet can get sick, from bacteria to trees. Insects can catch a whole range of bacteria, parasites, and viruses. We even hijack one of the viruses that tends to infect insects (Baculovirus) in the lab to get insect cells in culture to make stuff for us. |
Do insects get sick? like do ants get colds or do bees get STI's? | yes. getting sick means you get infected by bacteria or virii or parasites or ... and of course, this can happen to insects, too. however, they have a different response than humans (read mammals) do. you e.g. have increased temperature to support your immuno cells to fight the intruders. this inflammatory response (which includes many more actions) cannot happen in insects as they don't have this superb system. however, they still have basic immunity granted by a basic system. edit: got told it is viruses, not virii. |
While you are sick, where does the mucus in my nose come from? And after clearing it out hundreds of times, how/why does it refill/overflow so quickly? | > While you are sick, where does the mucus in my nose come from? There are specific cells that line the nasal passages (concentrated in little pockets known as submucosal glands) that crank out mucin by the buttload. Mucin is a sugar coated protein that makes snot, just add water. These cells can make amazing quantities, as mucus is > 90% water. > And after clearing it out hundreds of times, how/why does it refill/overflow so quickly? Because it's part of your body's attempt to expel whatever Lovecraftian horror has taken up residence in your airways. > what is the medical purpose of your body flushing this out? See above. Mucins trap bacteria and your body expels them. Think of mucin as an army of bouncers, wrapping their arms around the stage crashers and dragging them out the door. > Are there any natural remedies to combat the forever flowing nose demons? Mucus is the natural remedy that combats the forever growing nose demons. |
How dense are Saturn's rings? | It depends on what you mean by using the word enter. Saturn's rings are made up of ice, dust, water and a few other small rocky materials, ranging from micrometers to meters in width and length. The density of the rings as a whole actually vary, hence why you can see banding on them (this is why some parts may appear lighter or darker). In fact, only 3% of the total volume of the rings is occupied by the particles I mentioned earlier, the rest is simply just empty space, however, collisions often occur between the solids because of them being in such close proximity of each other. From top to bottom, the rings are only about 30-ish feet in thickness. So if you wanted to use that analogy of it being like entering clouds whilst in a plane, it’d probably be incorrect - as you’d be smashed by rocks and ice every now and again. |
How does our brain interpret wildly-different accents as the same language? | Certain sounds within a language are [allophones](_URL_0_). This means that they can be interchanged while not altering the meaning of the word. One example is /t/. If you take nearly any English word with that sound and replace it with an alveolar flap or a glottal stop it changes the accent, but not the meaning of the word. |
Spoiled orange juice can become fizzy/carbonated, but I've never noticed spoiled milk that was fizzy. What's the difference? | Fermentation. The sugar in the juice is good for a bacteria that ferments and that causes the gas. Milk spoils with different bacteria, it has lactose and so a bacteria that munches lactose takes over. It happens to not produce the same amount of gas that a yeast fermenting a juice would produce. |
How do we reconcile the ideas that (1) the universe is infinite, yet (2) the universe is expanding? | Imagine a string of beads, each equally spaced an inch apart. Now stretch the string so that the beads are two inches apart. The string has expanded yet both instances of it, stretched and unstretched, are infinite. |
Could a planet be size of a galaxy? Whats the biggest one could be? | At a certain size, the planet would have so much mass that it would collapse and form a star, and if you added even more mass it would easily become a black hole. The cutoff point between a planet and a star (specifically a brown dwarf star) is around 11-16 jupiter masses. |
When a candle in a jar is put out by placing the lid on the jar, are all of the gasses that remain in the jar after the fire is extinguished inert? | No, at least part of the gasses will be vaporized wax which is combustible. And even if you cannot (under most conditions) ignite the gas in there, it is not inert. Fun experiment to do is blowing out a candle and holding a lit match *above* the candle wick. The flame will travel down as the hot wax vapours travel upward to the burning match. |
Why is Ozone considered a pollutant even though it protects us from UV rays? | Ozone is a toxic, corrosive gas. The ozone that protects us from UV is located about 20 km above the ground. At that altitude, ozone can't harm living things, but when it's produced near the ground, that's a different story. |
Would disease really be more widespread if hand washing wasn't the norm? | Hand washing is sometimes credited to Ignaz Semmelweis, who instituted its use in doctors delivering babies. It dramatically reduced the incidence of puerperal fever. It was not uncommon at that time for doctors to participate in dissection of corpses and then go deliver babies. That's a pretty clear cut case - if you have infectious agents on your hands, antisepsic hand washing can be a big plus. |
Do any first generation stars still exist? | Possibly, but I don't think we've found any. A first generation star would be more than 10 billion years old by now. Low mass stars like red dwarfs can live for hundreds of billions, or even trillions of years, so any first generation red dwarfs should still exist. That we haven't found any red dwarfs with zero metallicity could mean that the early universe only produced more massive stars, or it could just mean that they're rare, outnumbered by the many red dwarfs that have been born since. Since red dwarfs are so dim, we can only see the ones nearest to us--with a larger sample, it's possible we'll eventually find some first generation stars. |
Where do our eyes focus when we close our eyelids? | What's annoying is that sometimes when i try to sleep and close my eyes my eyes try to focus on a point that isn't there and end up slowly looking closer and closer until they are trying to cross, or farther, i can't tell. Still starts to hurt and give me a headache after a while... |
Why is Pi infinitely long ? | Because it's not a property of *physical* circles. It's a property of *idealized* circles, which are infinitely divisible and do not have discretized metric properties. |
Why do I feel like I need to cough when I stick a q-tip in my ear? | A reflex requires nerve circuitry with a sensory input path (afferent) and a motor output path (efferent). One of the input sensory paths for a cough reflex is in the external auditory meatus, or ear canal. [This is known as the Arnold ear-cough reflex as the sensory input comes from the nerve of Arnold, a branch of the Vagus nerve.](_URL_0_) |
Do galaxies in galactic clusters orbit each other on a plane, in a similar way to planets in a star system, or stars in a galaxy? | No, galatic clusters are typically irregular and also unstable. Compared to their size, the distance between galaxies is relatively small and collisions are fairly common. |
Do groups of galaxies orbit some larger attractor? | No. [Galaxy clusters](_URL_0_) form the largest gravitationally bound objects. Superclusters are not gravitationally bound any more - their individual galaxy clusters fly away from each other over time. |
Is there any evidence that video learning is more effective than text based learning when accessing the content for the first time? | Wouldn't the relative effectiveness depend in large part on the learning style preferences of the target students? |
Why do Jupiter and Saturn rotate so quickly? | All the gas giants have broadly similar rotation periods, which aren't dramatically shorter than Earth's (or Mars'). As you move towards the inferior planets (Venus and Mercury), rotation periods are dramatically longer, 243d and 59d respectively. A degree of tidal locking with the sun may account for these relatively long rotation periods. |
What would a nebula look like to human eyes? | It's partially a post-image process, but it's more just that they can take really long exposures to get really deep images. If you were to look at it with the naked eye, you'd basically just see a bit of a faint haze. The trick is that the surface brightness of a resolved object (that is, an object that is larger than a point) does not change with distance. So if you look at nebulosity that you can resolve with the naked eye - such as within the Pleiades star cluster - then that's what it would look like if you were close to a nebula, except it would take up more of the sky. Essentially, you're get a nice white/gray cloud up there in the sky - a little like the milky way, but a different shape, and it wouldn't resolve into stars if you look at it with a telescope. |
Why are storm clouds a dark grey color whereas normal clouds are white? | more dense as they have more water in them, thus less light gets through as it interacts with the more water molecules in the storm clouds, rather than passing through and hitting your eyes :D |
Do the planets orbit the sun on a flat plane like Saturn's rings, or in three dimensions like the stereotypical atom image? | It's flat. [Here](_URL_0_) is a short explanation why. Also, electrons don't orbit like in the stereotypical atom image. |
[Space]: Do the craters on the 'light'-side of the moon (the side facing us) mean that those meteorites just barely missed us? How did this side get hit, when it's always facing earth? | Meteorites can strike the moon from many different angles. Imagine that you're on the near side of the moon. The Earth occupies about 2 degrees of arc in the sky, which leaves an enormous area from which meteorites could approach and strike the moon. |
If I hit a baseball with a bat, can the ball go faster than the speed that I'm swinging the bat? | Yes, the ball can. Assuming an elastic collision, both kinetic energy and momentum of the system must be conserved. Focusing on the small period of time surrounding the hit of the ball, obeying these two conservation laws means that the ball can shoot off with a much higher velocity than the bat, because the bat has a much larger mass (and benefits from the mass of the person holding the bat). The material matters because this determines how elastic vs. inelastic the collision (between the bat and the ball) is. More rigid materials will lead to more elastic collisions (meaning less energy is lost to heat) and hence more energy stays as kinetic energy and the ball shoots off faster. Squishier materials lead to more inelastic collisions (meaning more energy is absorbed into deformation of the materials and generating heat) and so the ball will not bounce off as fast. |
What are the factors that affext the fundamental frequency of a wine glass? | The fundamental frequency of a wine glass is dominated by standing waves in the cylindrical part of the wall. The bell of the glass flexes in and out, kind of like its being squeezed and unsqueezed repeatedly. Adding water causes the vibration to be stopped below the water level, so the cylinder becomes shorter relative to its width, which raises the frequency. Thickening the walls does the same. If you cut out any section of the glass in the bell as viewed from the side, it will look like a vertical sliver. It vibrates kind of like a ruler or a door stop. Making the sliver shorter or wider will make it less flexible, so it will vibrate faster. I hope this isn't a homework problem. |
Do Dreams Occur in Real Time? | according to [this](_URL_5_) a five minute dream takes five minutes to play out in your head. edit: downvotes? for a cite? hu? |
Do dreams happen in real-time? | The short answer is we don't know. Here is an older thread discussing what we do know: _URL_0_ EDIT: One thing worth adding is that in individuals with REM sleep behavior disorder, dreams are often physically acted out. The physical actions appear to occur in real-time and match reported dream content. |
Do ants have ears and can they hear sounds? | Ants don’t have ears, but they can hear. Ants use sound cues for recruitment to food resources and alarm signals. The most important structure for ant hearing is called the subgenual organ. "Subgenual" means "below the knee", which is where the organ is located. [(Source)]( _URL_0_) |
If your spaceship was travelling near speed of light, would hitting a piece of space dust make it explode? | Depends on how close to the speed of light. The way to approach it is to assume that the spaceship is at rest, and then take the space dust as traveling close to the speed of light. Let's say this space dust has a mass of 1 microgram (10^-6 gram). If you are traveling at 99% of the speed of light, then the space dust would contain 5.5x10^8 J of energy. In contrast, a 25 g bullet traveling at 1000 m/s has 1.25x10^4 J of energy. So that space dust would be like 10 000 bullets hitting the space ship. |
If we were able to accelerated a spaceship/probe to a fraction of the speed of light would space dust start punching tiny holes through it? | Yes. You can either try to get enough material to absorb the whole impact energy in one place or you can try to deflect or distribute most of it - a thin shield far ahead of the spacecraft, where the dust particles disintegrate and spread out. Even the ISS has shielding, although dust particles at ~10 km/s have much lower energies. In most places it has a thin outer shield which scatters the incoming particles so they don't pierce the inner shield. |
Could Earth-origin meteorites be found on the Moon and Mars? | Certainly. You are right in thinking that our atmosphere would slow down all the rocks and magma ejected in a collision event, but for the really large ones it is very likely that some chunks of Earth escaped the atmosphere and the gravitational pull of the Earth. Once they escaped, their getting to Mars would be unlikely, but definitely possible, and the process would not be too different from the way rocks from Mars make it here. As for the Moon, there are undoubtedly chunks of the Earth that that have landed on the Moon. In fact, if I'm not mistaken, the most commonly accepted theory of the moon's formation says that the moon is a chunk of the Earth. The idea is that some proto-planet smaller than the early Earth crashed into the Earth and the collision tore the Earth open, ejecting a bunch of the magma inside out into space. The debris from the collision and the magma ejected out eventually coalesced into the Moon we know today. So, in a weird sense, the Moon IS an Earth origin meteorite. |
Could a plant grow from candle light? | From my understanding Chlorophyll the primary chemical used to generate energy for a plant has essentially two peaks where light absorbtion is highest, in approximately blue/purple and red range of the visible spectrum. Anything can produce light based on the temperature. That is why the edge of a fire is red and the center is sometimes blue for a really hot fire. Most of a fire and a candles light is produced in closer to red and infrared. So my understanding is that it would be able to absorb the red light Given enough candles it could produce enough energy. My one uncertainty is if the blue/purple range is unnecessary for some reactions or simply another range that can be utilized. More than likely to have a plant grow effectively you would need to have enough candles to have a room light in the ballpark of the sun you see outside |
Can you grow a plant just by the light from a wood fire? | Photosynthesis requires at least blue and a little deep red (green is actually thrown back unused). Firelight is 1700K-2000k, very skewed towards red and infrared. There is very little blue. You might cook your plants with infrared heat before making enough blue at that color temp. |
If stars convert mass directly into energy via fusion, is there a "natural" way to convert energy back into mass? | > where all mass will be eventually pure energy running around forever? Technically there are no such things as "pure" energy nor mass. Mass and energy are properties, ability to resist acceleration (inertia) and ability to do work respectively. They are also conserved quantities which means that they can't change within a closed system. Matter though, is a real non-abstract "thing" which can have properties such as mass and energy, and it can be converted into non-massive particles with energy, such as photons. The Large Hadron Collider creates particles mostly from the kinetic energy of accelerated hadrons. The Higgs particle was [~67 times](_URL_0_) heavier than the protons that fused it. EDIT: Added some clarification of matter, mass and energy. Also, accidentally a word. |
Why does rubbing your temples during a headache seemingly help to dull the pain? | There's lots of different types of headache and (surprisingly) many are caused by muscle pain in the upper back, shoulder, neck or the jaw muscles. Physios often treat certain types of headache with neck exercises. If the headache is caused by some imbalance in the brain, then I don't know. |
Question about Hubble Telescope? | It can: see for example these: _URL_0_ The question comes down to this: what do you want to spend your (very expensive) time looking at? Planets near you, which have already been imaged and might be possible to send other probes to; or far away stars/galaxies that you don't have any other means of looking at. |
How come ice cubes don't always float 9% above water? | Can you give more details? Is there ice *under* the cubes on top? Because then the ice underneath will be pushing upwards on the ice at the surface. The weight of the ice on top is pushing down on the ice below. This probably isn't the case, but are you sure you're dealing with pure water/ice? If either is mixed with something else then it might change the buoyancy. It's also possible that you just aren't good at eyeballing 9% of a solid object. ;) Hard for me to say without a picture. |
Are terrestrials and gas giants the only two possible types of planet? | There's actually an extensive list of planetary types on Wikipedia: _URL_0_ that said some like "rogue planet" could be a "rogue terrestrial planet." However following the type theme of terrestrial and gas giant there are also ice giants, iron planets, ocean planets, coreless planets, and so on that are similar in "kind." Within our own solar system Pluto (not a planet, but a dwarf planet) has a surface composed of more than 98% nitrogen ice based on spectroscopic analysis. Although it is a combination rocky and ice body (estimates are 50–70% rock and 30–50% ice by mass.) |
Why are the great lakes not salty? | Salt lakes are found in [endorheic basins,](_URL_0_) where water accumulates at a low point and is kept level through evaporation. When water evaporates, from a salt lake, or from the ocean, the salt is left behind. The Great Lakes are constantly refreshed, about 1% per year by water from precipitation. Some salts dissolve into the water from the surrounding terrain, but that is balanced by the drainage of the water into the ocean, so salinity never reaches high levels. |
If a strand of hair starts growing gray, will that specific hair follicle only produce gray hairs in the future? | Dear AskScience denizens: anecdotes are not allowed and will be removed. Answers need to be based on peer-reviewed scientific research. Please read the sidebar and [our guidelines](_URL_0_) for more information. |
How do planets orbit Binary Star systems? Is it possible for the planet to enter a a stable orbit in a 'Goldilock zone?' | There are a variety of orbital architectures that would allow a planet to stably orbit a binary star system, but perhaps the simplest configuration would be a close binary system with a planet in a more distant orbit. In fact, [the planet Kepler-16 b](_URL_2_) is a roughly Saturn-mass planet orbiting two very close low-mass stars. There are dynamically stable, habitable zones in binary star systems as well. You can see some animations of how such zones vary with time as the binary stars orbit one another [here](_URL_0_), and you can calculate your own habitable zones [here](_URL_1_). |
Why do things become "sun bleached"? | UV and some other light wavelengths have enough energy to break bonds in the pigment molecules in whatever is losing colour. Those bonds are responsible for the original colour, and so without them the object is no longer as coloured. |
What causes objects to bleach in the sun? | I think this is an example of photodegredation. Some fraction of sunlight is made up of high energy photons such as those found within the ultraviolet region. Over time these photons break up the chemical bonds in dye and pigment chromophores causing the colours to slowly fade away. |
[physics]What would happen if the most outer part of a spinning galaxy is moving near the speed of light? Would it slow down? | The galaxy would immediately begin to fly apart. Gravity is far too weak to sustain such insane momentum unless you have a compact object such as neutron star or black hole. |
Why are moons like Titan and Ganymede larger in size but only half as massive as Mercury? | Water ice and other low density materials were mostly vaporized and blown away from Mercury by the intense solar radiation leaving a planet with a large metallic core relative to its size. It's less dense than Earth because of smaller size and gravity - if scaled up it would be denser. It's denser than Titan and Ganymede because they are mostly composed of ice and rock. |
Why will the Sun expand? | As the fusion in the sun's core ends, the non-fusing helium ash becomes *degenerate* and contracts to a ground state. As the core contracts, it releases gravitational potential energy into the sun's envelope as heat. This extra heat puffs the envelope up so the sun's photosphere expands. Core contraction - > envelope expansion. Core expansion - > envelope contraction. |
Why can't we slow down New Horizons enough to go into orbit around Pluto? | Changing speed or direction in space requires thrust. Thrust requires fuel. Fuel is heavy. Since we use rockets to put things into space, they have to be as light as possible. New Horizons is moving very, very fast and Pluto doesn't have all that much gravity, so the spacecraft would require a long rocket burn to slow down enough to enter orbit. It doesn't have a rocket engine, only some tiny maneuvering thrusters. On the other hand, we could have chosen a course for the spacecraft which didn't give it so much speed and it would have been able to enter orbit around Pluto. But then it would have taken decades, maybe centuries, to *get* to Pluto. |
Why won't New Horizons orbit Pluto? A nine years journey just for a flyby?! | Because Pluto is (a) very far away and (b) very small. New Horizons took nine years to arrive at Pluto even though it had the fastest launch velocity of any spacecraft in history--16 km/s. In order to achieve orbit around Pluto, New Horizons would need to be going (considerably) slower than Pluto's escape velocity, which is a mere 1.2 km/s because Pluto is so small. If New Horizons had been launched at a low enough velocity to make its capture by Pluto practical, it would have taken decades for it to arrive, and no one wanted to wait that long. Bringing along enough fuel to slow New Horizons down once it arrived would have made the mission prohibitively expensive. And unlike the gas giants we've put satellites around, Pluto is too small to have a thick atmosphere that can be used to slow New Horizons enough for Pluto to capture it. So we have to settle for a flyby. |
When hydrogen clumps together under gravity to form stars, where does the energy to do this come from? | It's like a roller coaster. When the hydrogen atoms are really far apart, they're at the top of the hill. As they get closer to each other, they're going down the hill. When they hit each other, they're going really fast at the bottom of the hill. Gravitational potential energy is converted to kinetic energy. So when a big mass of hydrogen is spread out into a nebula, it has a lot of gravitational potential energy. As it contracts under the force of gravity, it converts that to kinetic energy in the atoms, i.e. heat. Then kaboom. Fusion. Where does gravitational energy come from? Well, where does gravity come from? It's just there, and we haven't quite worked out the "why" yet. |
When a photon bounces directly off of a mirror and not on an angle, does it at any point stop completely? | I think it's easier to think of the process as reflection simultaneously destroying one photon and creating another that travels off in the "reflected" angle. |
Photons don't bounce - they are absorbed and later emitted by electrons. In that case, why does the angle of incidence equal that of reflection; i.e. how do mirrors work? | I'd say to be careful using "later" emitted. It's tough to get into the specific details of what "later" means here. That being said, think of a photon causing the electrons to move in the surface (like a metal with free electrons to move). But the way the electrons move creates a photon of their own that appears to bounce back at the angle of reflection. Even more complex: All we can *really* say is that at time 0 a photon is emitted with some direction, and at time t it's absorbed at another location. We can't actually sit and watch the photon as it travels through the system. We can only see photons that interact with something and scatter off into our detectors (eyes). So what you *can* do is calculate all the possible ways that light could travel between those two points, and you find out that all the paths where angle of incidence differs from angle of reflection cancel out (ie, interfere destructively), and only the classical path remains. |
When did males start growing beards and why don't great apes have them? | Orangutans have reasonably sized [beards](_URL_0_) and this one has a bit of a mustache too. And I'm sure they aren't the only ones. |
If we can see 13.2 billion light years away with the Ultra Deep Field, does that mean that the universe was that big 13.2 billion years ago? | I think the language around all topics regarding the "universe" needs to change. I think the hardest thing for people to understand is the idea of expansion. The old "if the universe is expanding, what is it expanding into?" question becomes difficult to discuss in a field where concepts such as multiverses exist. |
Since the universe is expanding and it takes distant light longer to reach us - are there any astronomical objects that we lost track of because of this? | The most distant object we've found is a [protogalaxy](_URL_0_) which we are seeing as it was 13.42 billion years ago. It is now about 32.7 billion lightyears away, and receding superluminally. This will be the first object to disappear. I am not awake enough to try the math, but if you could use the Hubble constant to work out when the expansion between us and this protogalaxy became superluminal you could then find when the last light will arrive. I guesstimate that we have a while. EDIT for partial math: At 67.8 km/s per megaparsec, you reach the speed of light after 14.4 billion lightyears distance traveled. Light leaving from this protogalaxy today will obviously never reach us. So, at what point in time did this galaxy have a distance in space of 14.0 billion lightyears? That's the last we'll ever see. |
Is it possible for a computer to be perfect at chess? | Yes in theory, that point is referred to as a [solved game](_URL_0_) As you can see on that Wikipedia link, chess is partially solved on some lesser variations, and the full game may be impossible to solve on current technology. Computers currently however, while extremely good at chess, are just using predictive branching and can only try to make the odds of winning in their favour by making moves that are more likely to lead to a favourable outcome. With 2 computers playing chess against each-other, there would still be no way to guarantee a winner of the 2. |
Why don't silicon or nitrogen make long chains easily in nature the way carbon does? | Nitrogen has an extra valence electron - it has 5. So it can't form a grid like carbon having 4 and needing 8 for a full shell. Si has the same valence configuration that carbon does, and can form chains. But because Si is heavier and the valence electrons it has are further from the nucleus and shielded by inner electrons, the bonds aren't as strong. Si still forms many wonderful compounds and is the basis of what many consider the greatest invention of the 20th century. |
Why do stars look like points of light instead of a sky full of diffused light? | The scattering you think about happens in a gas. That does happen, but in this era of the the history of the universe, interstellar gas is extremely rarefied. In empty vacuum there's nothing to scatter the light and it can travel very long distances. In an earlier era, gas in the universe was more concentrated, and in fact the glow of the earliest population III stars has been imaged: [see here](_URL_0_) |
If lactose tolerance is a genetic mutation in humans, why do mothers produce milk for babies? | _URL_0_ > Most mammals normally cease to produce lactase, becoming lactose intolerant, after weaning[citation needed], but some human populations have developed lactase persistence, in which lactase production continues into adulthood. Basically, the mutation is to continue to produce lactase into adulthood. |
What is a bose-einstein condensate? | A Bose-Einstein condensate is a collection of atoms that all occupy their ground state, exhibiting quantum phenomena on a large scale. You definitely could not hold one or really even observe one with your naked eye since they tend to be very dilute, *very* cold, and need to be confined in some way. This is why you can't find pictures of one, just illustrations and density graphs from experiments. Bose-Einstein condensation is related to superfluidity, but they are not the same thing, Bose-Einstein condensates are not necessarily superfluids. |
Are the molecules that create smells consumed when they are smelled? | The mere act of sensing them does not destroy them. Olfaction in humans works via a set of receptors called G Protein Coupled Receptors (GPCRs). Odorant molecules interact with them, causing them to change shape and in turn promote the activation of their cognate G Proteins, which activate a signaling pathway that's beyond the scope of this question. EDIT: I suppose some of the molecules can be absorbed into the blood in the lungs, but it seems like that wouldn't be a significant sink of odorants. Anyone who has done research in this field could correct me/back me up. |
Does smell always correspond to substance? | Smell is basically made of small particles of that substance detected by the nose. So if you can smell it it usually means it is there, but sometimes the nose can smell things that are not present, which has to do more with the brain than the odour itself |
Why is Bismuth, the non-radioactive element with the highest atomic number, less dense than lead, gold, tungsten and the like? | In a bismuth crystal, atoms are 4.75 angstroms apart. In a lead crystal, they are 4.95 angstroms apart. This would cause one to think that bismuth would be heavier, so we need more information. Bismuth is arranged in a rhombohedral (tilted square prism) lattice, while lead is a face centred cubic lattice (FCC). It is known that FCC is the tightest way to pack spheres, which might explain why lead is denser than bismuth. For comparison, gold atoms are only 4 angstroms apart with an FCC structure and it is much denser. Just to do a calculation, the expected density difference between lead and gold should be the ratio of their atomic weights times the cube of the lattice ratios: (197/207)x(4.95/4.08)^3 =1.69. Actual ratio: 19.2/11.35=1.69 To answer in more detail about bismuth I'd have to know more about the rhombohedral lattice than I currently do. I will add one tidbit: it was recently discovered that bismuth is in fact not stable, but actually decays very, very slowly. |
Why do some sinks pour out cloudy water when the hot dial it turned? What causes the water to be cloudy?..Why does it eventually go away and is it safe to drink? | Is it safe to drink? Probably. But is is worthwhile to note that hot water heaters are not compliant with or certified to NSF Standard 61 which is for materials that come in contact with drinking water. Faucets and valves etc are certified to this standard. Source: I used to work at a lab that tested products to this standard. |
When using speaker phone during a phone call, how doesn't the other person hear themselves? | Your guess is correct. In order to get high-quality sound, you have to perform [echo cancellation](_URL_0_). This algorithm is so essential and simple that you don't really ever see software settings mentioning it, but if you try to implement a telephony device or application, you quickly discover that you aren't going anywhere without it. |
Why does an old open glass of water taste funny | Do you have city water or a well? City water can contain things like chlorine that evaporates quickly (taste change in prob less than a day) or other longer lasting chemicals that may bind with things in the air to produce "off tastes" and other weird things. Really clean water will still taste slightly different but it is usually other things in the water reacting and making different tastes. |
Why does bright light sometimes make you sneeze? | This is a [surprisingly common question](_URL_1_)! The condition is known as the [photic sneeze reflex](_URL_0_), and affects somewhere between a fifth and a third of people. There isn't currently an accepted reason as to why it happens, though. |
If Jupiter is shrinking by 2 cm a year, would it ever be possible for Jupiter to shrink and cool, then become a solid planet? | On a side note, how are we able to measure such small variations of its diameter? |
What happens after you pluck a fruit - how long does it live, how does it get sweeter ? | [Everything you could want to know about fruit ripening](_URL_0_) |
Why does mixing different types of alcohol usually result in a hangover? | If you are mixing different types you are likely just drinking too much and that = hangover. |
If the mouth is home to huge amounts of bacteria, how is it that a cut in the mouth can heal properly when it's not particularly clean and dry? | Well, the short answer here is: Defensins. These are small proteins that are found in your saliva that kill bacteria, and serve to protect the inside of your mouth from getting infected when there's a cut. Most of your body's mucous membranes produce large quantities of these defensins in order to protect themselves. They're really quite fascinating proteins _URL_0_ |
Why do I get chills when I listen to music that I really like? | Psychologists and scientists who examine music perception and cognition often refer to this phenomenon as *frisson*. [Here is a .pdf](_URL_0_) of a chapter from the Oxford Handbook on Music and Emotion by David Huron and Lisa Margulis (2010). The phenomenon is reviewed, and specific theories are discussed on why *frisson* arises in listeners. |
Why do we get "chills" when listening to certain music we enjoy? | [Searched](_URL_10_) Relevant [discussion](_URL_8_) Original question by [Discdevil92](_URL_0_) > When I hear some really awesome music I get full-body chills that feels absolutely amazing. Why does this happen? Relevant comment courtesy [thisicouldnotdo](_URL_11_) > Psychologists and scientists who examine music perception and cognition often refer to this phenomenon asfrisson. [Here is a .pdf](_URL_9_) of a chapter from the Oxford Handbook on Music and Emotion by David Huron and Lisa Margulis (2010). The phenomenon is reviewed, and specific theories are discussed on why frisson arises in listeners. Relevant [follow-up](_URL_2_) courtesy [wnoise](_URL_3_) > _URL_7_ > _URL_4_ > _URL_6_ > _URL_1_ > _URL_5_ |
We artificially ripen fruit with ethylene or calcium carbide. Could we artificially "ripen" an entire tree to make the leaves change color and fall off sooner than normal without killing the tree? | Ethylene is a natural plant hormone that promotes the storage of sugars. It makes fruiting bodies ripen and mature, and as you know we use it to to force or hasten the ripening process. Abscission, or the process by which trees lose their leaves, and it isn't really analogous to "tree ripening." As far as I'm concerned tree ripening isn't a thing. However, the hormones that are taught to signal abscission are auxins and ethylene. The signaling pathway that leads to abscission is a lot more complex than just the two hormones. It involves a bunch of steps including environmental clues, light levels, and a lot of other little things. That said ethylene does play a role. If you're interested in the subject you may want to give this [a quick read](_URL_0_). To answer your original question... I don't know. We probably can make a tree abscess sooner than expected, but I don't know of anyone actually doing it. And more importantly, I don't know if simply adjusting ethylene and auxins would do it. |
Does sunscreen reduce or prevent your skin from producing vitamin D? | It will reduce vitamin D formation in your skin by blocking UVB bands of light. Vitamin D is synthesized in the range of 270 and 300 nm. If you happen to have a Vitamin D deficiency, this might matter, but for nearly everyone sunscreen is still a good idea to reduce the risk of skin cancer. From _URL_0_: "Sunscreen absorbs ultraviolet light and prevents it from reaching the skin. It has been reported that sunscreen with a sun protection factor (SPF) of 8 based on the UVB spectrum can decrease vitamin D synthetic capacity by 95 percent, whereas sunscreen with an SPF of 15 can reduce synthetic capacity by 98 percent (Matsuoka et al., 1987)." |
When using sunscreen, can our body produce Vitamin D? | To the extent it blocks the sun's rays from interacting with your skin, no. Here's a very recent article about Vitamin D and sunscreen. It's for a lay audience, but it references reputable research and it's extremely interesting. _URL_0_ |
What makes our hair be curly or straight? | Curly hair is caused by the formation of [disulfide bonds](_URL_0_) between keratin fibers in the hair. This is how perms work (first a reducing agent is used to break the bonds, then the hair is molded into the desired shape, and an oxidizing agent is added to reform the bonds and 'hold' the hair in place). The physical (cross-sectional) shape of hair (more circular vs more elliptical) is also associated with degree of curling. |
I've been told that diesel is "better" than gasoline. Why is this? | Diesel fuel has a higher energy density than gasoline, resulting in greater efficiency and lower fuel burn rates in comparable engines. It doesn't really burn 'cleaner' than gasoline. |
If our solar system were on the outer fringe of our galaxy, what would the night sky look like? | We are, relatively speaking, near the outer fringe of the galaxy. [Here's an illustration](_URL_0_). And it looks like [This](_URL_1_). |
If the sun was on the outer edge of our galaxy, what would our night sky look like? | Since there are no answers so far. Our solar system is placed in a very interesting spot since there are almost no Gaz clouds preventing us from looking in most directions. I have read a few articles explaning exactly this- but coudn't find any. Now to answer your question directly, Even if you were at the outer edge you woudn't necessary see more galaxies even if yes the sky would mainly be black/empty on that side. The distance from our spot, to the outer-edge won't really influece how big or small the galaxies will look to you as the change is pretty small (you can already see some.) Hope this helps. |
Why have no giant asteroids hit the earth in recent history? | Depends what you mean by giant. Given the expected frequency of getting hit by mass-extinction-causers like the one that killed the dinosaurs, we're not overdue for one or anything. The most recent asteroid to "hit" the earth was the [Tunguska event](_URL_0_) in 1911. It exploded in midair with a force equivalent to 15 megatons of TNT and leveled a huge area of Siberia. |
If a photon is massless and has no electric charge how does it transfer energy? | The energy of a photon is a function of the frequency of the photon as a wave. This is an aspect of quantum physics (wave particle duality) as opposed to Newtonian physics. |
Why do your ears have a "ringing" sound after loud noises? | The ringing you hear is [tinnitus](_URL_1_), caused by [temporary threshold shift](_URL_0_). Temporary threshold shift happens when you're exposed to loud sounds. The stereocilia of the hair cells in your inner ear, specifically the 3 rows of outer hair cells that act as an amplifier to low level stimuli, are over-stimulated and lose some of their sensitivity. The "shift", then, is a decreased sensitivity in terms of amplitude, on accounts of your hair cells being bent out of shape and not working correctly. I hope I haven't missed anything important, and I hope this helps! |
If allergies are our bodies mistakenly identifying allergens like pollen as being harmful, why can't we "retrain" our immune systems to ignore them? | You can. It's just really expensive and involves many, many injections over a long period of time so it's usually only done on children with severe allergies. It's called [immunotherapy or allergy injections](_URL_0_) |
How is the universe "flat"? | It's not spherical. Net curvature of the universe is, within error, zero. |
Are the colours of dinosaurs depicted in books accurate? | Yes and no. We don't know exactly. There are a few fossils of dinasaur skin. All we know for sure is that some had scales very similar to modern reptiles and some may have had feathers. Color we can speculate in some cases but there's no way to be certain most of the time. Tldr: maybe but probably not. |
Why are storm clouds darker than normal clouds? | Storm clouds are denser and thicker than non-storm clouds. Since its denser and thicker, a higher percentage of the light that hits it gets absorbed (as opposed to reflected back to your eye). This makes it look dark. |
Why are storm clouds darker than other clouds? | Storm clouds are filled with water. A cloud gets thicker and denser as it gathers more water droplets and ice crystals — the thicker it gets, the more light it scatters, resulting in less light penetrating all the way through it (since light comes from above the cloud, the sun). The particles on the underside of the rain cloud don't have a lot of light to scatter to your eyes, so the base appears gray as you look on from the ground below. This effect becomes more pronounced the larger the water droplets get — such as right before they're large enough to fall from the sky as rain or snow — because they become more efficient at absorbing light, rather than scattering it (to your eyes). [IMAGE](_URL_0_) |
Are some languages easier to lip read than others? | This is a bit old, but it looks like you never got an answer. So, basically if a language has lots of sounds which are distinguished by lip movement, or are near the front of the mouth, then it'll be easier to lip read as opposed to a language with sounds further back in the mouth. Tones are also difficult to detect, as is voiced (e.g. [s] vs. [z]). I don't know of any empirical evidence to rank languages with, so I can't give a good example of particularly easy languages to lip read. I would imagine that a language with a very small set of sounds would be easier. Hawaiian, for instance, only has 8 consonants. Of those, 3 make direct use of the lips and another 3 are made with the tongue near the front of the mouth. So all in all that's relatively easy. Compare that to [Georgian](_URL_0_) which has a number of velar, uvular, and glottal consonants. That's definitely not a complete answer, but hopefully it helps. |
Do all terrestrial bodies which experience a planetary wobble and orbit a star have four seasons? | The Earth's wobble (precession of the equinoxes) doesn't cause the seasons. The seasons are due to the axial tilt and the orbit of the Sun. "Seasons" isn't an astronomical term. Any planet whose axis of rotation is tilted with respect to its orbital plane will have solstices and equinoxes. If you wanted to, you could define four seasons between those solstices and equinoxes. That's not quite the same thing as "the four seasons we experience", though, since the seasons (in terms of weather and biosphere) don't have to follow the equinoxes and solstices. Also, a planet with only very slight axial tilt will have only very slight changes in insolation throughout the year. |
What is the maximum size of a rocky planet, and what happens when a rocky planet is "too large"? | We've never seen any such object, but planet formation models suggest that a very large silicate body will usually retain enough light gases to become a gas giant anyway. The clouds that planets form in are usually hydrogen and helium rich, so you'd have a tough time making a giant rocky planet without it becoming a gas giant. There's just a lot more gas than rock. Since rock has a large percentage of oxygen a large enough rocky body may actually fuse oxygen into silicon, and then fuse silicon and helium into iron and nickel. You'd need a preposterously large "planet" for that to occur though, realistically the molecular cloud that formed it would form a giant star instead. |
What is the difference between a laser pointer and and a laser that can actually cut through things? | the technological principle is the same, laser pointers are diode lasers and you can build powerful enough diode lasers to incinerate some paper for example. Really powerful lasers for industrial cutting or beyond (military for example) are typically gas or chemical lasers, since only those achieve the necessary power. So the laser medium can be solid or gaseous. [Here][_URL_1_] is the quick overview of the types that exist. The laser light beam itself is not different between different laser technologies, apart from the frequency perhaps: they are all highly coherent light beams; a stronger laser will just emit more photons per time. |
If the universe is generally thought to be about 13 billion years old, and a light year is a measurement of time and distance, how can there be stars, galaxies, nebulas, etc more than 13 billion light years old? | No galaxies or anything else are more than 13.8 billion years old. Full stop. But there are definitely galaxies that are more than 13.8 billion light years away. Why? Because the Universe has expanded since those galaxies emitted their light. In the first million years after a distant galaxy emitted a photon, that photon will have travelled a distance of 1 million light years that today could be upwards of 10 million light years, because the Universe is expanding. |
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