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Why does sleep paralysis cause people to have terrifying visions instead of just visions? | You may have it backwards: During REM sleep the brain is pretty much acting out the movements you're dreaming, but also [blocking the actions](_URL_1_). A [part of the brain](_URL_2_) is associated with the blocking. In other words, *every* time you're dreaming, your body is paralyzed. At least some theory suggests that during sleep paralysis you're having a stressful or frightening dream and your brain is waking up in the wrong order: You're conscious, but the chemical signals produced by the Pontine tegmentum [haven't worn off yet](_URL_0_). |
When the universe expands and the galaxys move away from each other quite fast, how can it be that andromeda and milky way will collide anyways? | Both the Milky Way and Andromeda are part of the Local Group, a cluster of over fifty galaxies. The galaxies are close enough to be gravitationally bound together. As the galaxies orbit the center of gravity of the Local Group, some of them are moving toward each other because that's the path of their orbits. The Milky Way and Andromeda just happen to be on a collision course. The Local Group is itself part of the Virgo Supercluster, which is also gravitionally bound. At greater distances, gravitational attraction between galaxies is much weaker, so it is believed that dark energy takes over. The existence of dark energy is not yet proven but the evidence is very strong. It is believed that dark energy is driving the accelerating expansion of the universe. tl;dr Over large scales, dark energy is causing galaxies to move away from each other, while gravity is more dominant at smaller (but still mid-bogglingly large) scales, causing some closely neighboring galaxies to move towards each other. |
Why do scars never heal? | This is my understanding. The difference in texture you notice between your regular skin and scar tissue is because of the way that the collagen is deposited by the fibroblasts that are healing the deep wound. Normally it is random, but in the case of scar tissue all of the fibres are aligned in the same direction. Even if cells are replaced they are still constrained by the extracellular matrix that has been laid down. But sometime scars do fade a bit, even collagen slowly gets altered by the various cell movements that keep epidermises intact throughout an organisms life. |
Why do scars never heal? | The way scars heal is different than the formation of regular skin. The wound is filled with a dense connective tissues and elastic tissues that creates a scar. It does not have the same layers as normal skin which are epithelial tissue and will never grow into regular skin. I have had a scar on my knee for 22 years that still looks the exact same, just a little lighter in color. The body does this in order to further protect the damaged area. |
What is the .01% of germs that can't be killed by most cleaning products? | I read somewhere that these kind of products actually kill ALL germs, but manufacturers say that they only kill 99.99% to cover themselves should something bad happen like a bacterial infection to someone who washed his hands with such a product. That person can't go and sue the company then because the company could then say that it was the .01% that it does not kill. |
Why can't I teach my dog language? | Dogs only respond to those commands because they've learned they'll get a reward when they hear that particular sound. They don't actually know what they mean. You might as well ring a bell to get them to sit provided you give them a treat when they do. Language involves understanding multiple contexts and levels of abstraction that are way above the cognitive capacities of our canine comrades. There are some extraordinary dogs that can learn ~100s of commands, but it's still just about responding to a familiar sound that reminds the dog that a treat is about to follow (even if you don't give it up, they still hope). |
If Earth is moving, the Sun is moving, and our galaxy is moving.. are we not closer to the speed of light than we think? | Relative to what? There's no such thing as absolute speed. To high-energy cosmic particles we are moving very close to the speed of light indeed. |
Which plant is the most effective at converting CO2 to Oxygen? | [Photosynthetic efficiency](_URL_0_) is the proper term for this and it's actually measured as sunlight to biomass. The reason is because the same amount of CO2 + (other stuff^1 ) = O2 + (other stuff^1 ), so efficient is always 1-to-1 ratio if you measure CO2 to O2 conversion. In any case, the most efficient plant is sugar cane at around 7%. However, plants are put to same by algae have efficiency rations of up to 30%. ^1 I know "other stuff" this is not very scientifically accurate but I'm trying to simplify things. |
Why can't I cleanly wipe the condensation off my bathroom mirror after a shower? | Condensation is caused by the relatively cool surface of the mirror pulling moisture out of the air. The water vapor in the air essentially loses energy, that is, cools off and phase changes into water, when it encounters this surface. When you wipe it, you get rid of the droplets that have formed on the surface of the mirror. What you haven't addressed is whats causing it in the first place - the cool mirror. So a new layer of droplets quickly forms. If you take a hairdryer on hot and blast the mirror THEN wipe it, it will no longer form condensation. This is known as the female solution. You can also spit on the mirror and wipe it around. The body temperature phlegm should slow/stop the condensation. This is known as the male solution. Some fancy hotels actually have mirror heaters to avoid this problem altogether. |
Why do animal eyes (like dogs, cats, spiders, sheep etc.) reflect bright direct light at night but human eyes don't seem to? | Nocturnal animals (and deep-sea animals) have a layer of reflective tissue behind the retina called the tapetum lucidum. It's purpose is to act like a mirror and send light back through the retina, giving it twice the chance to hit it.... And thus making the eye twice as sensitive. We don't have it because we're not nocturnal. |
What are the physics behind different baseball pitches? | I'd recommend *The Physics of Baseball* for a detailed look at the game. |
What are the physics behind different baseball pitches? | The spin in which the pitcher imparts on the ball as they release it. So the way they hold their fingers causes the ball to rotate. The friction of the air on the ball spinning causes draft and thus ball moves oppositely |
What prevents a large rotating disc from exceeding light speed at the edges? | The disc could not maintain structural integrity. _URL_0_ |
If a disc is spinning near the speed of light at the furthest edge, would the innermost portion exist at a different time due to its spinning at a slower speed? | Time would pass differently on the edge, yes. You're not an idiot at science, AT ALL. This is an EXCELLENT question to ask and one not a lot of laymen/laywomen would think to ask. Trying to reconcile spinning discs and special relativity were one of the things that led to the general theory of relativity, which upended three centuries of gravitational thought. Keep thinking these thought experiments, and don't put yourself down! |
Why did a massive hole in the ozone layer form over Antarctica as opposed to places where excessive amounts of pollution are being given off? | [This column, from the University of Hawaii Dept. of Geology & Geophysics *Ask an Earth-Scientist* series](_URL_1_), may answer your question. |
What, if any, plants could survive on mars? | No known species of plants would be able to survive direct exposure to the Martian conditions, such as extremely low temperature, thin air, high levels of solar radiation, and low amount of minerals and nutrients in the Martian soil. However, scientists are working on removing useful genes from extremophiles through gene splicing and adding them to plants, which could then be housed in little greenhouses on Mars. See more [here.](_URL_0_) |
When can a plant be officially considered dead? | What you have here is an interesting question because science doesn’t have a concrete definition of life. Biology is “the study of life” but a more accurate definition would be “the study of the physical and chemical processes of life”. We can study the processes, like a heart beat or brain wave function. We can determine when they have ceased, to declare someone dead. But we cannot study the life as it leaves them. We can only study the signs that tell is that the life is leaving them. Plants have a few processes that I could think of that could be determinate like that. Xylem and Phloem tissue activity, photosynthesis activity. It could be dead when these stop, but sometimes the plant could be brought back after these processes have stopped. I’m not sure if anyone has officially issued a definition of plant death. Probably not because it’s not a very lucrative definition to propose. |
Could humans still breath our atmosphere if there was no nitrogen? | Yes, any gas mixture is fine as long as the partial pressure of oxygen is correct and the other gases are inert. Pure oxygen is fine, but it would have to be at lower pressure than the atmosphere. Some spacecraft have used pure oxygen. Scuba divers sometimes use mixes of helium with oxygen to avoid nitrogen narcosis. |
Why do some people sneeze when they look at the sun? | Genetics! Photic sneeze reflex occurs in around a quarter of the population, and thought to be autosomal dominant. In fact, it is listed in [disease databases](_URL_0_) as "ACHOO (Autosomal-dominant Compelling Helio-Ophthalmic Outburst) syndrome". A [recent published study](_URL_1_) found genetic variants near the genes *ZEB2* and *NR2F2* are associated with the trait, at least in Europeans. These genes have been also been shown to be associated with seizure disorders (e.g. Rett syndrome and Mowat-Wilson syndrome), suggesting perhaps there is a link between photosensitive epileptic seizures and photic sneeze reflex. |
Can one fall into coma while being asleep (directly transitioning from sleep to a comatic state)? | You can fall into a coma while being asleep. A common cause is diabetes. According to the article it can be reversible. _URL_0_ |
Could an exoplanet orbit two stars at the same time? | Yes, this is called a circumbinary planet and a few have been discovered, such as Kepler-16. |
Why don´t planets orbit the sun like electrons orbit the nucleus of an atom? | Well as far as we can tell, electrons -don't- orbit the nucleus, in a classical sense; rather, there's a probability of an electron being in any one 'orbital' at any one point. But the answer you're looking for is because the electron has very, very little mass, while a planet is uh. Quite a bit bigger |
Can water be compressed to a solid? | Keeping it at room temperature, you'd have to compress it to a pressure of about 10,000 atmospheres before it solidified. It wouldn't form regular ice, it would form something called Ice-VI with a different structure. |
can water be compressed into a solid? | Yes it can. Look at [the phase diagram of water](_URL_0_). As you can see, at any temperature lower than the critical point a solid phase of ice will be thermodynamically stable, which means that you can solidify liquid water by just increasing the pressure sufficiently. Note, however that this phase while solid would be different from the type of ice you obtain by cooling down water at atmospheric pressure below 0C. As for the ice being "cold," well, that depends on what temperature you keep the solid at. There is nothing inherently "cold" about ice. |
Is time truly another dimension or is it a description of the other three? | Yes, time is a dimension just like the other three, with the exception of one small, technical difference in its mathematical description. Spacetime is a four-dimensional surface on which all physics takes place, and depending on your speed through spacetime, which directions correspond to time and which to space will vary and become intermingled, much how when you rotate a sphere, the new latitude coordinate is a combination of the old latitude and longitude coordinates. |
Does heat change the taste of food? | I’m not quite sure about food but heat affects the taste of drinks for sure. The colder the drink, the more your tastebuds become suppressed. Imagine an ice cold beer vs a room temperature beer. Same beer, but one goes down a little bit easier. So to answer your question, I would assume heat only affects the way that the food is perceived by your tastebuds. Could there be a potential chemical difference within food at different temperatures? I’m not sure. Maybe someone more knowledgeable would be able to answer that |
Is there any difference between water boiled in the microwave vs boiled on stove top? | It's possible that the pot/kettle is imparting some taste to the water. It's also possible that the average temperature in the water is different using the two methods; when I make tea using the microwave, I find it's impossible to heat the water uniformly. Our sensitivity to flavors does change with temperature. |
Is there a difference between water that was heated in a microwave and water that was heated on the stove? | Probably not. The heating of the water is absolutely not going to impact how it tastes. If there is a taste change, that indicates a change in the chemical makeup of the water. The only way that I can think of that happening is if you heat the water in the microwave with some really thin, cheap plastic container that wasn't suitable for use in a microwave. In that case, it is possible for plasticizing agents like phthalates to leach into the water, but even then I doubt that you would be able to taste them. As long as you use a container that is microwave-appropriate, there should be no change in the taste of the water. --edit-- Actually, /u/Twistentoo is probably right. |
Why do my eyeballs feel sore when I come out of the dark into the sunlight? | There are two sets of muscles in your iris(the colored part of your eye), one to dialate(in response to low light) and another to constrict(in response to bright light) to ensure the approriate amount of light reaches the retina. As these are muscles, an abrupt change in brightness will force then to rapidly constrict which puts strain on them, and can be painful. |
What, if any, Native American diseases were spread to Europeans after contact in the new world? | Syphilis was carried from the new world to the old _URL_0_ |
In all the star gazing we have been doing in the last few hundred years, have any stars mysteriously appeared or disappeared? | Enough dust to fill an entire solar system mysteriously disappeared around star [TYC 8241 2652](_URL_0_). There is no definitive explanation for the disappearance because current theories suggest that planets form over millions of years. The current theories as to the disappearance are not sound. |
Is there a difference in the quality of gas based on where it's sold. Is exxon gas better than walmart gas,etc.? | Some gas stations add 10% ethanol to their gas. This makes the fuel cheaper but also makes it burn less efficiently causing you to lose mpg. |
Can someone fully explain why an orange LED appears to change color when placed in liquid nitrogen? (video inside) | The light from an LED is generated when an electron moves from a high energy state to a lower energy state. This difference in energies between these two states is referred to as the band gap. The larger this gap, the more energy an emitted photon has when an electron makes the transition. The higher energy the photon is, the more "blue" it will appear. From low energy to high, the visible spectrum runs from red > orange > yellow > green > blue > violet. As the temperature decreases, the gap becomes larger, and the photons become more energetic as a result. In this case, the shift is quite dramatic, and we see the wavelength shift from ~600 nm to ~550 nm. |
Why does LED glow brighter in Liquid Nitrogen but only for a moment? | First you made a faulty assumption. That all objects have less resistance as the temperature decreases. Semiconductors don't do this. They have less resistance at higher temperatures. This is because at higher temperatures more charge carriers go from the valence band to the conduction band because they have more energy. It's an exponential relationship. The current is proportional to e^(eV/kT) - 1 _URL_2_ _URL_3_ _URL_1_ OK, so what are we seeing? Notice the color of the LED changes form red to yellow. As the LED cools, the crystal shrinks and that changes the band gap which changes the color. Human eyes are more sensitive to yellow so this is probably part of the reason it appears brighter even though its intensity might decrease. Eventually it gets so cold that the current drops enough that it appears dimmer. _URL_0_ |
If all the planets stopped revolving around the sun and if they all were the same distance from the sun, would they all fall towards the sun at the same rate? | Actually, no. Although mass doesn't matter on the small scale, it does on the large scale. Acceleration of a golf ball on earth is practically the same as a bowling ball on earth because there's pretty much no difference between the mass of earth+golf ball and earth+bowling ball. However, Jupiter+Sun would have a much greater mass pulling each other together than say Mars+Sun |
Is there any known correlation between smell or flavor (bitter, sweet, etc) and nutritional value? | Yes, that’s the whole point of taste buds (evolutionarily). Small carbohydrates (sugars) bind to sweet-tastebuds, signalling the brain that ’this must be good nutrition’. The weird thing is that most lipids (fat, oil) don’t taste that good even though they are extremely nutritious. Also, animals have during their evolution learnt to associate bad tastes with toxic compounds. For example, bacterial and fungi toxins taste extremely bad (e.g. milk gone bad or moldy bread). |
Can humans actually smell "sweetness" or is it an association with an already learned smell thatakes something smell sweet? | You can't smell sweet. Things also don't smell sour, bitter, salty, or umami. These five cardinal tastes are things that we perceive with our tastebuds. Our nose, however, is picking up aromatics that we may associate with certain tastes. So...no you can’t but you can smell things that can be associated with sweetness. Hope this helps. |
Why are gases more soluble in cold liquid, but solids are more soluble in warm liquid? | I'm not seeing anything like correct answers but the solution to this eludes me at the moment. Gas dissolves in cold liquids primarily because that provides more state spaces. Gibb's free energy is minimized and entropy delta are maximized by the gas dissolving. It doesn't dissolve in hot liquids primarily because other state spaces are available and are taken first. |
Why are some alleles more dominant than others? | The dominant gene codes for a functional protein. The recessive gene codes for a non-functional protein or no protein at all. Brown hair is brown because there is pigment because there's a gene that codes for a protein that makes the pigment. If there gene doesn't code for a functional protein, no pigment makes it to the hair, so it is pigmentless, aka blonde. The gene is dominant because if even just one allele codes for the functional protein there's still pigment being made. Same thing with blue/green eyes vs brown, yellow peas vs green, etc - the 'colored' version is the dominant trait as a result of a single or double copy of a functional color-producing protein while the 'colorless' version is the recessive trait from a complete lack of color-producing protein. |
Why do ice cubes have bubbles in them? | Gases (such as air) are soluble in water. However, in ice they are not (barely) soluble so when water with dissolved gas is frozen the gas leaves and is trapped by the forming ice. You can make (almost) perfectly clear icecubes if you boil the water before filling the ice tray (let the water cool down before you fill the tray, some trays are not suitable for boiling water). The solubility of gasses in water decreases with rising temperature so boiling it basically "degasses" your water. |
Why do your eyes have to switch focus between things that are near and far in a mirror if a mirror is flat? | Largely because a mirror is not a magic box that just displays the information you are seeing like an LCD TV. The mirror is just reflecting light and lines of vision. It does not change to focal lengths or points of any of the information it is redirecting. |
Why is it that when I'm sick I lose my appetite? | When your body's immune system is activated to fight off an infection, different chemicals are released. Cytokines are involved in this process, and they release chemicals that do a bunch of things (won't get into the details of that). Just know that some of those chemicals will tell your brain you aren't hungry anymore (satiety). The thing too is that viri/bacteria may feed off the glucose and nutrients you digest...feeding it further. So it can sometimes be a good thing depending on what pathogen you're fighting off. However that is not to say you should NOT eat. Still eat food, stay hydrated, etc. Just know that if you don't, our body is still able to find energy elsewhere to fight off the infection...such as by burning your fat stores and such. |
why is the moon so spherical if it doesn't spin on it's own axis? | It does spin on its own axis. In any case, a spherical shape is the most energy-efficient configuration. Any object large enough to be significantly affected by its own gravity will ultimately collapse into a sphere under the influence of its gravity. |
Does a solar eclipse happen everyday somewhere on the planet? | No. For a solar eclipse to happen, the moon must be directly between the sun and the earth. For a lunar eclipse to happen, the earth must be directly between the sun and the moon. These alignments are somewhat rare events, happening only a few times a year. |
If table salt (NaCl) dissolved in water is present as sodium and chloride ions, why can I taste salt when I drink the water? | So the "taste" of salt is mainly the sodium ions. Try dissolving a teaspoon of baking soda (sodium bicarbonate) in some water and see how awfully salty it tastes. The carbonate gives it a chalky flavor (or maybe it's more of a feel) as well, but the sodium is unmistakable. |
why does sticking your finger in soda fizz make the fizz go away faster than normal? | The oils on your skin lower the surface tension of the soda, causing individual bubble walls to thin and burst sooner/faster. If you have very clean hands (like washed with an anti grease soap like dish soap, rinsed thoroughly, you'll have comparatively less oil and the effect will not happen nearly as noticeably. *Edit- the oils on your skin act as a surfactant in this case. _URL_0_ Happy micro bubble popping! |
how is there so much helium in nebulas? | Helium also formed during the big bang, along with small quantities of other elements. That raises the question of why it stopped at helium. [This seems to explain it in detail.](_URL_0_) The short version is that by the time the universe was cool enough for deuterium to stay fused, the pressure and temperature were low enough for fusion to stop at helium. |
If bacteria prosper in warm environments, why does our body raising its temperature kill off most harmful pathogens? | Remember that proteins all have an optimal temperature range to maintain their proper shape. The raising of your body temperature is not what actually kills the bacteria; that is done by your white blood cells. Raising the body temperature makes the bacterial proteins (enzymes in particular) less efficient - or that's the goal anyways - slowing their replication and allowing your white blood cells to attack them with more ease. |
Why does your metabolism slow down with age? | During puberty, the brain flips a switch to "flood" the body with hormones such as testosterone and/or estrogen, to induce physical and mental developments to the body. The increased flux of hormones in the body is the reason why growing boys and girls have fast metabolisms. The hormones have different effects based on gender, as boys significantly gain muscle mass, while girls significantly gain body fat, which is ideal for reproduction. There are many factors we can consider why someone in their thirties gains weight much easier than during their teenage years, and metabolism is not a major one. Yes, metabolism is indeed fast during puberty, but it is suggested that we gain weight during our adulthood because we get less active, muscle growth slows down, and the calories we need to consume is now far less than during our teenage years, but our eating habits remains the same. The primary factor suggested that induces weight gain during adulthood is our lifestyle. |
Why is yellow a primary colour in paint and not in light? | See [additive color](_URL_1_) vs [subtractive color](_URL_0_). > Subtractive color systems start with light, presumably white light. Colored inks, paints, or filters between the viewer and the light source or reflective surface subtract wavelengths from the light, giving it color. If the incident light is other than white, our visual mechanisms are able to compensate well, but not perfectly, often giving a flawed impression of the "true" color of the surface. Conversely, additive color systems start without light (black). Light sources of various wavelengths combine to make a color. In either type of system, three primary colors are combined to stimulate humans’ trichromatic color vision, sensed by the three types of cone cells in the eye, giving an apparently full range. |
Why is yellow a primary colour when we talk about paints/pigments but is replaced with green when we talk about light? | Primary colours are not something that is fixed. Any set of colours that can be used to reproduce the colour spectrum can be called a set of primary colours. Usually RGB (red green blue) is used when using additive mixing (light is a typical example, using all colours results in white) and CMY (Cyan, Magenta and Yellow) is used for subtractive mixing (adding all colours yield black, mostly the case in printing). However, the precise colour of these primary colours is subject to change and depends on what is accessible. _URL_1_ _URL_0_ |
Why do objects like wheels appear to spin backwards as they speed up? | It is a light phenomenon, not a brain phenomenon. It happens in movies because of the frame rate of the video (rapid series of photos) being taken. If the spokes move at the same rate as the frame rate then the wheels won't look like they are turning at all because every time you take a photo the wheels have rotated to the exact same spot they were previously. If there is a difference in rate, optical illusions occur. This only occurs in real life when the car is under lights that blink. Many street lamps for example blink so rapidly that the blinking can't be perceived. If the rotation of the wheel mathematically aligns in a specific way, the wheel will appear to be moving backwards. The same effect can be achieved in a dark room with a strobe light and ceiling fan. |
If the universe is expanding and galaxies are flying away from each other at accelerating rate, how can they collide? | Because they're close enough that their mutual gravitational attraction prevents expansion from driving them apart. Expansion is real but it's not insurmountable. |
What makes paper so weak (what makes it tear so easily) when wet? | I can't address the molecular level stuff, but at the macro level, it's just the fibers are too short to resist the shear forces. When dry, the short, rough fibers have more friction to resist the shear forces. When wet, the fibers float away from each other and the wetting agent lubricates the fibers. I'll speculate that there is some kind of mild adhesive used in the manufacture of most papers, perhaps just some starch from the vegetable feed stock. This adhesive helps maintain the relative position of the fibers, which improves their mechanical strength. If the water degrades this adhesive, then the geometry of the fibers is easier to compromise and energy will not transfer evenly across the sheet. SOURCE: much destructive testing of fiber reinforced materials (not paper). |
Is there a clear barrier between stars and space? | At least regarding the earth's atmosphere, it does slowly transition to space, but there's also an altitude that is generally considered the boundary of space: the Kármán line. The definition of the Kármán line is based on airplanes. As you go up in altitude, the air gets thinner and you have to fly faster to generate enough lift to stay up. At a certain point, you would have to fly at orbital velocity to stay up. That point is the Kármán line. The definition itself is fairly arbitrary since there is still more air above that height, but it works for what we need it to |
Why is there a difference between kinetic and static friction? | The answer is (partially) in the name. When an object is stationary, enough time passes for the atoms at the interface of the two objects to settle into a local energy minimum and establish thermodynamic equilibrium. Once settled into this energy well, a larger push is necessary to break out and start sliding again. Kinetic friction, on the other hand, applies in the kinetic regime, wherein the atoms at the interface do not have time to settle into equilibrium but instead experience some average higher-energy interaction. Since not enough time is given to settle, the relatively strong bonds that would form in equilibrium need not be overcome and the job is easier. |
Why does metal feel colder than plastic when they're both sitting in the same cold room? | Metal has a higher [Heat Transfer Coefficient](_URL_0_) than plastic so even though the temperature difference between your skin and the 2 materials is the same heat will flow more easily to the metal giving the impression that it is colder! |
Why does metal feel so much colder than plastic? | Your nerves sense temperature *changes*. When you touch metal, its high thermal conductivity allows heat to flow out of your finger and into the metal more quickly than plastic. Metal has a higher thermal conductivity than plastic, so it pulls more heat away from your finger, so the temperature of your finger changes faster, so it feels colder. It's the same reason a windy day feels colder than a still one, even at the same temperature, and the reason why 350^0 F air in the oven doesn't burn you very quickly while 212^0 water will burn you very quickly. |
Can mosquito bites provoke reactivation of dormant viruses (e.g. cold sores)? | If the mosquito bite provokes an immune response then sometimes it can. Mosquito bites usually only provoke a minor immune response that doesnt usually involved the T-Cells or B-Cells. It involves mostly the humoral immune response (neutrophil, macrophages, etc.). Usually when the adaptive immune system becomes activated there is a great deal of cytokine signaling going on and sometimes this can signal to latent viruses that they have an opportunity to begin their lytic lifecycle. This is sometimes why someone who has a cold may have a resurgence of the herpes simplex virus, while the immune system is busy dealing with the rhino-virus the factors that were holding the herpes in check have gone to be allocated to the more pressing threat and then herpes begins its lifecycle. |
Why does "freezer burn" have a smell and taste to it? | "Freezer burn" is a problem where repeated slight thawing and freezing (opening/closing the door frequently, smaller freezers, et cetera) have leached the fluids out of food products and into the ice crystals. The change in taste is due to the cells being ruptured in this process, and the change in liquid content. This problem is less common in freezers that are kept at more static temperature for long periods of time - freezers that aren't opened and are large enough/well insulated enough to maintain temperature. |
If the sun is mostly made up of Hydrogen and Helium, why is sunlight display light over the full spectrum? | Sunlight is [blackbody radiation](_URL_0_), which emits at all wavelengths. You're thinking of electrons excited between orbitals, which isn't what produces light in the sun. |
Why isn't sunlight just the hydrogen and helium emission lines? | Emission lines are due to electrons within atoms moving between energy states. This is why the energy of the photons (and therefore colour) are quantised - the energy state must be well defined. There will be a colour for n=2 to n=1 transition, one for 3 - > 2, etc. What occurs in stars is super heated matter (plasma) where the elements are already ionised - the electrons are not bound to the nuclei and can have any amount of energy (sort of; the point is it's a continuous scale, not quantised). Therefore, particles in the plasma will emit light as they bump into each other, or any other energy transfer process (fusion, deionisation, etc.) and this light can have any amount of energy. Hence full spectrum radiation. EDIT: I put the transitions the wrong way round for emission. Idiot. |
How do seedless fruits reproduce? | They don't. Seedless fruits (in every case I can think of) are a human invention. We selectively bred for smaller and smaller seeds until we got a fruit tree without them. It's "children" are actually clones made by taking a part of the tree and planting it and having it grow into a full tree. Another possibility is what's done with watermelons. Seedless watermelons are made by crossbreeding two different species of seeded watermelons, and like many hybrids, their offspring are sterile. |
How do they reproduce seedless fruits/vegetables ? | See _URL_1_ For [watermelon](_URL_0_). They take the pollen from the seedless watermelon and pollinate a conventional watermelon flower. This produces seedless watermelon seeds. |
If a soap doesn't foam, is it less effective? | Soaps and detergents are chemicals with a polar end which binds with water, and a non-polar end that bind to fats and oils. The soap molecule this firms s bridge between water and oil, allowing the oil to mix with the water and get washed away. Soap foams when there is no oil around. The polar ends are binding with water, but there is no oil for the non-polar end to bind to. So the soap/water complex forms spherical bubbles, with the water on the outside, and all the non-polar ends of the soap molecules bunched up in the middle. If there is more oil that the soap molecules can handle, it won't foam because every soap molecule is used up with an oil molecule. So: soap foaming essentially means that you have more soap than oil. Another way of saying that is that you have used too much. If your washing machine foams like crazy, use less washing powder next time. |
Is soap required to "foam" in order to work properly? | Nope! Two soaps that don't foam are laundry detergent and the type of soap that goes in dishwashers. If you put a foaming type of soap in either of those machines, it will cause a huge mess. However, those soaps still clean dishes and clothes just fine. Lots of cosmetics companies actually add things (like sodium dodecyl sulfate or ammonium lauryl sulfate), to soaps to make them foam more, because many people associate foam with cleanliness. |
Why is an ordinary old computer able to beat an average-decent chess player, while it takes a supercomputer to beat a grand master? | It doesn't take a supercomputer to beat a grandmaster anymore. You're probably thinking of Kasparov's match, but remember he was playing against a supercomputer from the 90's. A good chess engine running on a normal PC can easily beat today's top ranked players. The software has also gotten a lot better. An HTC Touch HD reached grandmaster level in a tournament. |
Why does my microwave use interfere with my WIFI? | Wifi works on the 2.4 GHz band. Microwave ovens work on the same band as well. The reason why WiFi uses it is because due to microwaves and such it's an unlicensed band, and anybody can use it (within limits). The downside of that is that there's plenty intereference. Normally I don't think a microwave oven should be causing enough interference to cause serious issues with WiFi. I've experimented with it and can pick it up on a scanner, but I've not seen it actually break a wifi connection, unless you have a very weak signal already. If it does that you should check the oven's door and make sure it closes properly. |
What is the liquid inside blisters? | It depends on the type of blister. If you're talking about clear blisters, it's blood plasma - everything that isn't a red blood cell in blood, such as water, nutrients, clotting agents, drugs, proteins, hormones - filtered out of the bloodstream. A blood blister is filled with, well, blood. Infected blisters can be filled with pus - dead white blood cells and waste products. |
Why does eyesight change as you get older? | The eyes have seen to much brother. They just can’t do it any longer. But seriously it’s a condition called presbyopia. It has to do with the inability of hardening the crystalline lens in the eye. Age-related changes also take place in the muscle fibers surrounding the lens. With less elasticity, the eye has a harder time focusing up close. There are other theories that are genetic and environmental based. So pick your poison. |
"Why" does a two-photon system have mass? | This has a *ton* of significance. Hugely significant. Consider an atom. electrons are about 1/2000 the mass of the proton. So nearly all the atom's mass is in the protons and neutrons that make it up, no? A proton or neutron has about 940 MeV/c^2 in mass, and they're made up of 3 valence quarks. But the valence quarks aren't ~300 MeV/c^2 in mass... they're closer to 3 MeV/c^2 ! So where does all the mass of the proton come from? It comes from... the gluons. Massless particles, like the photon is massless, acting as a whole system of particles that impart mass to the proton. By extension, most of the mass of the nucleus, the atom, molecules, every bit of normal matter in the universe... All gluons. All massless particles in a system that has a mass. |
How do mosquitoes know what blood type you are? | most people (85%) secrete a chemical marker of their blood type. Mosquitoes apparently prefer type O blood 2 to 1 over type A - with type B falling in the middle they are predominately attracted to emission of carbon dioxide though _URL_0_ |
How do mosquitoes sense blood? | They are attracted to mostly CO2 and heat, if you refer as to how do they find the blood vessels then the answer is literally poking around. Their proboscis numbs out the sting pain and well... you know the drill. [Here](_URL_0_) is a more detailed video. |
Is it possible that there are more planets on our system? | I'll gloss over the fact that Pluto isn't defined as a planet anymore and inform you that it's actually in good company in the outer solar system: > The classical (low-eccentricity) belt is home to at least three dwarf planets: Pluto, Haumea, and Makemake. The [Kuiper belt](_URL_1_) is full of remnants of the formation of our solar system, it wouldn't surprise me in the least if we find more Pluto-sized objects floating around out there. But don't hold your breath waiting for Earth-sized objects to be found: we would have seen the gravitational effects of any such large body long ago. |
Have astronomers found any stars that they are certain do not have planets orbiting them? | Don't forget that with our current level of technology we're still finding new "planets" in *our own* solar system _URL_0_ so we're certainly not in a position to be making definitive statements about other solar systems |
Why do all the planets with substantial axial tilt have such similar angles (besides Uranus)? | It is mostly luck. Neglecting planet-planet or planet-star or planet-disc interactions you would expect that the spin axis would align with the axis of the protoplanetary disc they formed from. With planet-star tidal interactions you would expect a reduction of obliquity due to tidal effects resulting in either a prograde or retrograde spin aligned with the orbital axis. Planet-planet and planet-disc interactions can excite obliquity. So basically we should expect planets subject to strong tidal interactions to have near zero obliquity. Of course impacts can do the same thing but far too many things in planets get attributed to impacts when other process can achieve the same thing. |
If helium-3 is so energy dense as fusion fuel, shouldn't we need very little of it? | A Deuterium/Helium-3 mixture produces approximately 384 TJ/kg. Compare that to Uranium which produces 80 TJ/kg. Yearly Uranium consumption is about 60 million kg, if you wanted to replace all of that with Helium-3 you'd still need thousands of tons each year. From 1955 to 1996 only 225 kg of tritium were produced in the USA. 150kg of which have since decayed into Helium-3. So no, tritium decay would probably never be able to meet demand. |
Is Helium-3 a viable fuel source? | That would perhaps have a semblance of truth if we had working fusion power plants, but we don't. The ones that do exist, which don't produce more energy than they consume, use deuterium and tritium as their reactants and not helium-3. One would need about 20 tons of helium 3 per year in order to power the United States (calculations based on energy yield per fusion reaction and some assumptions about power efficiency). The space shuttle is not huge, the cabin is about 75 cubic meters which would only be a few kilograms of helium at normal pressure, so you would have to jack the pressure pretty high to get a few tons. Helium 3 right now is extremely important for low-temperature physics, and very hard to get. |
Chemically, is there any discernible difference between a 12 year scotch and a 21 year old scotch? | Older scotches taste different because they have been sitting around in a oak barrel for all those years absorbing the flavors of the wood (also scotch is aged in pre-used barrels, usually bourbon but also sherry etc). Single malts are a self explanatory - made from malted barley at a single distillery. In a blended malt the malt can be from various cereal grains but also a large amount of the mix could be just grain whiskey. This is distilled differently in a process similar to vodka (continuosly operating column still rather than a copper pot still as is done for single malts) which is cheaper and gives a lighter flavour Once in a (practically) inert glass bottle the liquid should stay pretty similar to how it was when bottled except for some molecular breakdown and oxidation over time, especially if exposed to light or heat |
What is the difference between liquor aged 10 years and one aged 40 years? What changes it? | When a bottle says aged 12 year they mean 12 year in a barrel not the bottle. Liquor, for example whiskey, picks up flavor from the cask/keg it is barreled in. The cask/keg can impart very subtle textures and flavors to a whiskey. Wine, on the other hand, ages differently than liquor. As wine ages, a chemical called 'tannins' breaks down and the result is a "smoother" tasting wine. |
If somebody gets a new organ and you check ~50 years later, will the organ still have the DNA of the donor? | It depends on the organ, and on what cells you look at. Some cells (monocytes, for exemple) are able to migrate inside tissues, and they would have the DNA of the host. However, the huge majority of the cells would have the donor's DNA, yes. |
If someone gets an organ transplant, and you took a tissue sample from that organ Sample years later. Would the DNA be the recipients DNA or the Donor's? | Depending on the organ, it would most likely be the donor DNA. But, host cells can infiltrate and become part of the organ. Some tissues would convert over completely like a skin graft. Others would be partial like a heart. Liver and Kidney would probably stay mostly just donor. |
Why do Humans need to brush their teeth to fight infection and bacteria , while other animals do not ? | Keep in mind that our modern diet makes us more prone to dental caries than most animal diets; [sucrose](_URL_0_) is the primary dietary component responsible for the formation of cavities. Evidence suggests that human populations (eg, [Eskimos](_URL_1_), had very few cavities per person prior to contact with Europeans. |
Why do two stroke gasoline engines have to use mixed fuel? Why aren't they designed with a separate oil system? | Two-stroke engines can have a separate fuel and lubrication systems. This is common in marine 2-stroke diesel engines. (Marine 2-stroke diesels also aren't small.) The lubricant-in-fuel thing does make for a simple engine. |
(Astronomy) Why is the sun white? | The HR diagram was created in 1910 when we knew much less about stars and their spectral power distributions. The color range on the diagram was arbitrarily based on visual observations. There are a lot of traditional holdovers like this in astronomy that remain because they don't really get in the way of the science. You're correct that the sun is white but appears yellow or orange due to atmospheric scattering. |
Why don't we consider vastly different breeds of dog different species? | The tl;dr answer is, they are capable of producing viable (able to reproduce) offspring with each other, therefore they are the same species, even if their phenotype is dramatically different. |
Are rogue planets more spherical than planets that are orbiting a star? | The spericalness is mainly driven by the total mass of the object. The higher the mass the more spherical as surface gravity is highest. For this reason we see the largest mountain in the solar system on Mars and smaller bodies like moons or dwarf planets are even less spherical. |
If photons have no mass, why does a black hole trap them? | A photon does not require mass to be affected by gravity as the source of gravity is not mass, it is energy and momentum, which a photon definitely has. MinutePhysics has a great [video](_URL_0_) explaining this and some other common physics misconceptions. |
Why can noise cancelling headphones only cancel at low freqs? | It's a problem with electronics. To cancel a wave you need to be able to synthesize an identical but opposite one. If you have a 100 Hz wave the Whole wave is 10 ms long. So, if you sample the signal, invert it and reproduce it with a lag of less than 1 ms or so you're almost set. If you have a 1 kHz wave (which is "mid range" in audio) the Whole wave is 1 ms long. You'd have to reproduce the signal identically in less than 0.1 ms. Which is basically impossible. Also, mantaining phase coherence is not that easy at higher frequency. |
How do stars and planets first start spinning? | Stars and planets form out of huge gas clouds as you may know. These gas clouds have some natural motion (swirling), this is where the initial motion comes from. As the cloud collapses to form a star, the radius of the cloud decreases. Conservation laws tell us that the angular momentum before the collapse and after the collapse must be the same. Since the radius of a collapsed cloud is so much smaller, it must spin much faster in order to have the same angular momentum. The solar system forms during the process of star collapse, so the bodies in the solar system will rotate in the same direction for the same reasons mentioned above. |
Do people who are "tone deaf" have problems when speaking tonal languages? | There was a study of Chinese people who spoke Mandarin, language that requires pitch when speaking, and evaluated them for amusia (inability to differentiate pitch and sounds accurately). The researchers were able to identify some participants as having amusia, who were significantly worse than others at recognising pitch, even when raised in a tonal-dialect society. The amusia-participants however were seemingly unaware of their difference and were able to reproduce tones successfully. This would suggest that though unable to identify tones, they did not suffer from communication issues. The paper is [here](_URL_0_) and a neat summary can be found [here](_URL_1_) |
Why does planets have planar orbits rather then spatial orbitals? | I am not sure what "spatial" means in this context but, I'll answer why the planets in our solar system are in a plane. The sun and all the planets were formed from a big ball of gas (the proto-solar nebula), that slowly collapsed in on itself due to its own gravity. At some point, the fact that the gas was slowly spinning generated a force that was comparable to the gravitational collapse, and the system formed more into a plate-like shape. Most of the gas stilled flowed toward toward the center, and formed the early sun. Some of the rest of it, especially the sooty particles we call astrophysical dust, agglomerated into the planets. The planets retained the motion of the gas and dust they were born from, and thus all orbit in the same plane, which has the same sense of rotation as the sun itself. I am not up on all the recent results from Kepler and other planet finding missions, but I do believe that not all systems have all the planets in a relatively flat plane, though most do. |
If a woman has slept with identical twins during the same time period, and becomes pregnant, is it possible for her to tell who the father is? | This [actually happened](_URL_0_); it came up in a paternity suit. |
Is it possible to make a "silicon diamond?" | They don't look like diamonds. They look like [this](_URL_0_). |
Why do motorcycles produce more pollution than cars despite having better gas mileage? | One means of fuel efficiency and it answers you second question is the power to weight ratio. Motorcycles have much more power compared to weight than a car. As the weight increases, more power is required to maintain a given speed which consumes more gas. There are many other efficiencies gained with smaller engines resulting in better gas mileage. The amount of gas consumed is not the whole story though. The engines are quite different in almost every way. Pollution is not about how much gas you burn. Pollution is about the byproducts of said combustion. Mythbuster's data said that modern motorcycles are 30% more fuel efficient than cars. If the exhaust of the motorcycle contains greater than 30% more pollutants per gas unit then the Motorcycle pollutes more. Plain and simple. |
When our vision is blurry, what happens inside of our eyes when we squint to “clarify” the images we see? | When you vision is blurry (due to the lens not focusing correctly due to various reasons) and you squint your eyes, your eyelids come closer together and reduce the aperture of the light coming in through the pupils. This effectively makes the eye almost become a pinhole camera which can focus images without the aid of a lens. You can find out more about why a pinhole camera works the way it does [here](_URL_0_). (effectively it cuts out a bunch of extraneous rays and keeps only the ones that will focus on the image plane...the closer you get to a perfect pinhole camera, the dimmer the image gets though). |
Are there numbers like pi, as in infinite non-repeating decimals, that can be expressed rationally in a non-base 10 system? | > Also I don't know a whole lot about the non-repeating element of pi, and how that plays into the whole question. How can we even tell it will never repeat? We know it will never repeat because we know that it is irrational. The proof that it is irrational is rather involved and involves a little bit of higher level math, but it is possible to show that there are no integers a and b such that pi=a/b. The fact that it will never repeat follows from this. Note that all of this is irrespective of your choice of representation; integers are integers are integers, in any base. |
Why can we see the moon during the day sometimes? | [Here](_URL_0_) I made you an image. It depends on the position of the moon relative to the earth and sun. When the moon is behind the [terminator](_URL_1_) (seen in the illustration I made) we see the moon at night. When it is in front of the terminator we see it during the day. |
Why are galaxies not spherical? | The same reasons solar systems aren't spherical. The laws governing angular momentum. Basically, a spiral galaxy is flat(ish) for the same reason a solar system flat(ish). Averages and gravity! There are many galaxies, called [elliptical galaxies](_URL_1_), which are amorphous blobs. and even spiral galaxies have a [bulge](_URL_0_) in their center. Edit: Downvote? This is ask science, if you think I'm wrong about something don't down vote and run, tell me why. |
Why do hard plastics become lighter in color when bent? | You are introducing a whole bunch of dislocations and other defects into the structure of the solid and these things tend to reflect light differently than the normal plastic, an effect we call crazing. It is also possible that you are doing something like stress induced ordering of the polymer which can happen in rare cases but it is most likely an abundance of defects which you are observing. |
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