question
stringlengths 19
300
| answer
stringlengths 28
1.02k
|
|---|---|
What percentage of stars are not part of a galaxy? | [Free floating planets](_URL_0_) may be [more common than stars](_URL_1_). |
Why does a beer can sound different from a soda can when you open it? | Wow something I can actually chime in on in Askscience! I feel so privileged! So yeah, obviously the sound you hear comes from the rush of CO2 escaping. The source of CO2 in most beers (and ciders) is directly from the actual fermentation process itself, whereby the yeast eats sugar and converts it to alcohol and CO2. In soda, CO2 is injected by machine, and in much higher concentrations. Interestingly, a lot of large-scale commercial brewers will inject CO2 as well, though they inject less CO2 to mimic the levels gained through fermentation. |
Dissolving gas in a liquid. Help me explain to a friend why nitrogen won't keep carbon dioxide dissolved in beer. | He needs to understand [Raoult's Law](_URL_1_) and [Henry's Law](_URL_0_)! Basically, the amount of dissolved gas in a liquid is going to be proportional to the amount of that *same gas* in the gas phase above the liquid. Also Dalton's Law if he doesn't understand how partial pressures sum to total pressure |
Why did my apple juice only freeze after I poured it in a cup? (see pic inside) | This happens when you supercool a solution beow it's freezing point. I answered a similar question [recently](_URL_3_) and I'll copy from that answer: If there's no point at which ice crystals can start to form (this can be a point on the edge of a container, speck of dust, or other impurity), you can cool water below the freezing point. This is known as [supercooling](_URL_1_). If you then nucleate the formation of ice, the entire liquid will snap freeze rapidly. Many people see this when they [over- cool beer in the freezer](_URL_4_), or use it to build [really interesting ice sculptures](_URL_2_). This also happens at the boiling point, which can be extremely dangerous. Anything that disrupts a [superheated liquid](_URL_0_) can drive it to all spontaneously boil into steam, which can lead to severe burns, or a jar of chemicals exploding in your face (happened to me in the lab once. Not recommended). |
Planetary Science: What keeps the magma inside rock planets hot? Why doesn't it ever cool down? | Not all rocky planets need to have molten cores, and they do cool down over time. The cooling process can be very slow, however. Even though space is very cold, there isn't much in it to absorb heat. The only way for a planet to cool is through black-body radiation, and this becomes less efficient as the outer layers of the planet cool and act as insulation. There is also some "fresh" heat being generated inside the earth through the decay of radioactive elements. This isn't enough to keep the planet from cooling, but it does slow it down a bit. |
Why dont plants suffer from the effects of aging and cancers like mamals do? | Trees can get cancer, but because of harder cell walls in plants, they can't traverse throughout the "body". As for old age, technically nothing dies of old age. People die of pneumonia or heart attacks or stroke, which is attributed to old age. Similarly, a long lived tree is more likely to be burned down or struck by lightning or get a deadly fungus. |
How does fuel burn in space without the presence of oxygen? | Spacecraft carry their own (liquid) oxygen with them. It is then mixed with the (liquid) hydrogen in the combustion chamber of the rocket engine. |
Reading recent articles, I get that we recently spotted the most distant/oldest galaxy ever, 13.4 billion light years away. With my understanding of the expansion of the universe, this galaxy was much closer to us than 13.4 bn ly, at the time it looked like what we see of it today. Am I correct ? | So you are on to a subtle point about distances. As a photon is emitted from galaxy A and travels to us at B the distance increases. When we say 13.4bn ly we mean the distance that the photon detected today has traveled is 13.4bn ly. 13.8bn ly as the size of the universe (radius) is the most common figure given. However we do recognize that in the intervening 13.8bn years the universe has grown and as such it is currently ~45bn ly in radius (however if a photon was emitted today it would take more than 45bn ly to cross that distance since the distance would continue to grow). The actual number doesn't really matter though, all that matters is that we are consistent and we generally are. |
Is handwriting genetic? | I'd vote for it being mostly a learned behavior. However, aspects such as fine motor skills and dextrous control of your hands may certainly have genetic components but this would expand to more than just handwriting. |
Why does every person have unique handwriting? | I'm no professional, so I shouldn't really 'answer.' Regardless, this was up this week: _URL_0_ The top comment as least explains the boy/girl difference pretty well. |
Why is monogamy more common in birds than in mammals? | It depends on what type of monogamy you mean. Birds tend to be socially monogamous, which means they find a mate, have children, and raise them with the same partner. However, birds typically aren't sexually monogamous. For example, the scissor tail flycatcher has a "cheating" rate as high as 70% some seasons. This is due to seeking out the most "fit" mates, so one can have better offspring. As for being socially monogamous, the theories I've read believe it has to do with birds requiring more help early on compared to mammals. Where most mammals are walking within hours of being born, it takes birds several weeks before they're flying. Since breeding is all about continuing on your genetic line, it would make sense for bird fathers to hang around to ensure their success. |
What is it that makes food stale, and does that process reduce the calories in said food? | What's happening, generally, in things like bread, for example, is the transformation of starches. When starches are at room temperature and below, they will begin to crystallize which consumes water from other nearby compounds in the food. This essentially "sucks" the moisture out of a food by binding it in the crystallized starches. |
Why do all kinds of vertebrates have tails? | Evolution doesn't select for useful traits, but rather select against traits that reduces the chances of an organism to pass down their genetic material. So in the case of the pig it is possible that having a tail did not give them a disadvantage in term of survivability and thus chances to pass down their genetic material, whereas for humans having a tail might have some detrimental effect on survivabilty. Hopefully this is somewhat helpful, I am sure someone else can answer your question better. |
Gas giant and ice giant planets exist, but is it possible for "liquid giant" planets to form? | “The term gas giant was coined in 1952 by the science fiction writer James Blish and was originally used to refer to all giant planets. Arguably it is something of a misnomer, because throughout most of the volume of these planets the pressure is so high that matter is not in gaseous form. Other than solids in the core and the upper layers of the atmosphere, all matter is above the critical point, where there is no distinction between liquids and gases. Fluid planet would be a more accurate term.” |
If the Universe is infinite then why isn't Heinrich Olbers right? | The universe is probably (although by no means certainly) infinite in volume. However, it has existed for only a finite amount of time, which means only a finite volume is visible to us. The 'edge' of the visible universe roughly corresponds to the time when the universe's energy density became low enough that atoms could form and the hot proton plasma became transparent. Also, it turns out that the distribution of matter in our universe is nowhere near so uniform as Oilbers was probably imagining. It's very plausible that even a static, infinite universe like he was imagining could have gaps in its stuff. |
When experiencing Sleep Paralysis some people feel like they can't move while others instead are met with a feeling of deep fear. What is the cause of that? | This 2011 study talks about noth SP and Fear. It may help. _URL_1_ |
With high magnification and low exposure, can telescopes see the shape of the nearest stars to the Sun (like the Alpha Centauri system, or Barnard's Star)? Or are these stars still too far away and appear only as points? | Larger stars can be resolved, for example [Betelgeuse](_URL_0_). Sirius, a large and close star, when imaged with Hubble, basically looks like a point spread function. _URL_1_ |
With a powerful telescope, is it possible to see the 'outline' of certain stars? Or are they all simply too far away for them to appear as anything else other than a point of light no matter the magnification? | [There are some stars that we can very roughly resolve](_URL_2_), e.g. [Mira (Hubble Space Telescope)](_URL_0_) or [Pi1_Gruis (Very Large Telescope)](_URL_6_). The limit for resolution comes from the [diffraction limit](_URL_5_). So for more and better resolution pictures of other stars we will need bigger telescopes. Fortunately, [these telescopes are being built right now.](_URL_4_) Furthermore other smart techniques exist to get over the diffraction limit. For example it is possible to use the rotation of stars to extract the surface distribution of [chemicals] (_URL_1_) using doppler imaging or even [magnetic fields](_URL_3_) using Zeeman-Doppler-Imaging. |
Why is the surface temperature on Venus hotter than Mercury? | I read somewhere that this is caused by greenhouse effect. Mercury, while closer to the Sun than Venus, has basically no atmosphere, while Venus has very dense atmosphere (atmospheric pressure on surface of Venus is 90 times larger than on surface of the Earth), and this atmosphere is mainly composed of carbon dioxide, a greenhouse gas which absorbs the IR radiation emitted from the surface of the planet, and reemits it back thus raising the temperature. |
Cleaning products can kill 99% of bacteria. What is that last 1% and why haven't we killed it yet? | I think a logical answer to this can be explained on the basis of statistics. No matter how poisonous a substance can be for germs/bacteria , the germs are capable of forming a cyst and save themselves. So this 1% is left out on the benefit of doubt. Survival of the fittest indeed! |
Carbon Fiber vs. Carbon Nano-tubes | What is commonly referred to as "carbon fiber" is usually in reality a [carbon-fiber-reinforced polymer](_URL_0_), which is basically a composite material consisting of sheets of [carbon fibers](_URL_2_) and some sort of epoxy bonding them together. Actual carbon fiber sheets are essentially "blankets" of mostly carbon atoms in a hexagonal matrix. Carbon nanotubes, on the other hand, are a [fullerene](_URL_1_) which means they are composted purely of carbon atoms. In the case of nanotubes, they're analogous to a carbon fiber sheet being rolled up into a miniscule tube (only a handful of atoms in circumference), giving them incredibly high tensile strength. A "sheet" of carbon nanotubes would actually consist of many tubes woven together, but not chemically bonded as in a sheet of carbon fibers. |
What is happening in an operating system when a process is "Not responding"? | [Here](_URL_0_) is a nice post from Raymond Chen explaining part of your question. Generally, the OS checks if an app hasn't retrieved messages from the message queue in a long time (a couple of seconds) and if it hasn't - the app is "not responding". Usually the app is stuck performing a heavy computation on the main thread and is unable to retrieve messages from the message pump. Such computations may be heavy calculations or using a blocking API to write to the hard disk/network. This can be avoided by performing heavy calculations on a separate thread, in order to keep the main thread free to respond to messages. |
Why is it impossible to read things in our dreams? | There are numerous accounts by persons that report lucid dreaming that they enter lucidity by reading something, reading it again and noticing that the text has changed. To this end I'd suggest that it is possible to read items in our dreams; however is obviously dependant on the individual. I am on mobile just now, but I recall an article on Neuroscience Nature. I shall look that up when I return home, although that is in a few days. |
Would it be better for one to play the lottery with the same numbers, or to randomize their choice each play? | The winning numbers today are independent of yesterday's. Each day, the winning string of numbers is chosen randomly from all possible strings. So there is no difference whether you play the same numbers every day or you change them up. You have the same chance each day of matching the winning numbers. |
How good were the optics in Galileo's telescope compared to today's cheap telescopes? | Galileo's telescope could not resolve the planet Saturn, he saw the rings as two fixed moon like globs on either side of the planet. Today's cheap 2.4" refractor can easily resolve Saturn's rings so it shows you how bad Galileo's optics were. Galileo's did not have the lenses we have today, his telescope used simple lenses so they produced horrible color fringed images. Even cheap modern telescopes use two glass achromatic lenses to focus most of the color - Galileo never had that... achromats would not show up till 150 years later. Galileo did understand that stopping a lens down made it work better so he stopped down the objective lens to 12mm...... meaning he had a 1/2 inch telescope that was a meter long... making it somewhere around f/80. |
Can we use the sun's gravitational lensing as a telescope? | in theory, yes, but in practice it wouldn't have the right "focal length". or in other words, the geometry of the system star-sun-earth is bad enough not to make it possible. the earth would have to be 500-1000 times further from the sun to make it work. and, of course, there is also the little problem of sun emitting much more light than you would receive from the observed objects. however, i remember reading about mission proposal, that could use sun as gravitational lens to enhance signal from the probe, once it reaches the distance of about 400 AU. |
What is the theoretical limit to the quality of images we can take of planets orbiting other stars? | Here's the kind of quality we can currently achieve: _URL_5_ |
Would there be any advantages to using the gravitational lensing of the sun as a telescope? | Yes! Yes there would be. The advantage would lie in the huge amplification of microwave signals. The spacecraft should be placed at around 542 AU from the Sun, sort of a "focal length" (but not the same). Einstein was the first to realize this and compute this distance. Weird thing is you don't need to stay there. You can go further, and it gets better. This is where a gravitational lens differs from an actual lens. This distance is massive, though. It's outside our possibilities for now. But there is work on designing a mission and making it plausible in the (near?) future, see FOCAL. |
What is happening when something is sticky? What causes stickiness? Is it Viscosity? | If you're touching something like honey or a sugary solution, and it's sticky, it's because the molecules are forming interactions, like hydrogen bonds, with the molecules on your skin. Hydrogen bonds are what keeps oxygens and hydrogens together to form water, and they're also involved in keeping proteins and DNA together. Honey is made of fructose and glucose, which both have lots of sites that can hydrogen bond. |
What makes stickiness sticky? | Many kinds of non-permanent adhesives work by forming relatively weak chemical bonds between molecules. So in that sense, it is a kind of electrical attraction that only applies at close range. There are also adhesives that work mechanically, like microscopic velcro. This wiki page gives a good list of different methods: _URL_0_ |
Why can't we see the flag on the moon using telescopes from earth? | The best resolution of an optical telescope is about 0.1 microradian, limited by diffraction. This implies that when looking at an object on the Moon (about 400,000 km away), it cannot resolve objects that are smaller than 10^(-7)\*4\*10^(8) m = 40 meters. I obtained 1 microradian (10^(-7)) by dividing the wavelength (2*10^(-7) m, in the near UV) by the Hubble telescope mirror diameter (~2 m). |
Is it possible to see the American flag on the moon via telescope? | No, at least not a telescope on Earth or in Earth orbit. Hubble needs objects to be about the size of a football field to be discerned. Even the previously proposed 100 meter aperture OWL telescope would not have been able to see the flag, though it might have been able to resolve the landers and rovers. |
Why do we get stuffy/runny noses when we cry? | It's because tears flow across your eye and down into the [nasolacrimal duct](_URL_0_), where they're carried into your nasal cavity. |
Why can I see star clusters better when they’re in my peripheral vision? | There are 2 types of photoreceptor cells in the eye: rods and cones. Rods are more sensitive to light than cones, and they are more concentrated on the edges of the retina. Thus peripheral vision is more sensitive to faint lights. When you look straight at the stars the light falls on centrally located cones which are less sensitive to light, and you can't make out the stars. |
What natural things cause wildfires, besides lightning and volcanoes and meteorite impacts? | In at least [one rare instance,](_URL_0_) a landslide uncovered shale with high concentrations of pyrite. Oxidation of the pyrite generated enough heat to cause low-grade coal to burn. [American Geophysical Union](_URL_1_) notes on the landslide. Highly recommended on the subject: [Tending Fire,](_URL_2_) by Pyne. |
If caffeine is flavorless, why do uncaffeinated sodas taste differently than their caffeinated counterparts? | Caffeine is not flavorless; quite the opposite, in fact. In its pure form caffeine is quite bitter. That said, the caffeine concentration in soda is generally overpowered by the sugar (though the absence of caffeine could certainly change the taste profile of the beverage). |
What is the cause of a photographic memory? | The existence of true photographic (eidetic) memory is controversial, and it is not at all apparent that it actually exists outside of legend and hoax. See the Wikipedia page on the controversy surrounding it for an overview. |
Why do some foods go bad, but others go stale? | Bacteria generally need moist environments to live in. Meatloaf, milk, and mayonnaise are moist enough to allow bacterial growth. As for your potato reference, a potato is a type of seed, and as such has to protect itself from bacteria in the wild. Its skin acts as a barrier against bacteria. Also, when you buy them, potatoes are still alive. So they fight bacteria actively. However, when you cook it, you kill the potato and create ruptures in its protective skin, allowing the bacteria in. Foods that go stale tend to dry out. Once they're dry, they can't be eaten by most bacteria. Without water, bacteria dehydrate and die kind of like we do. This is why people try to tell you how bad McDonald's hamburgers are for you by saying they don't decompose. They are just too dry to harbor bacteria. They certainly do decompose, it just takes the addition of other creatures (animals, insects, etc.) to break them down to the point where bacteria can affect them. |
Why do galaxies form into a disc shape rather than a perfect sphere such as a star or planet? | I'd recommend watching the PBS Space Time video series on YouTube. It is a pleasure to watch, and they explain things in enough detail for laymen to understand while not misrepresenting the facts. In fact, they have a video which answers your exact question: _URL_0_ |
What are the possibilities of Jupiter igniting into a star? | Zero. Calling Jupiter a failed star is like calling a greyhound a failed elephant. It is not big enough. Not nearly big enough. As for your second question. I have no idea. ....calmly waits for someone smarter than me to answer. |
Is it possible to build an underwater speaker that compensates for the sound disortion due to the water? | As mentioned before, underwater speakers already exist. They mainly deal with the issue of water dulling our ability to perceive audible vibrations. The frequency of a sound wave only depends on the original wave and since frequency determines the note we hear, underwater speakers don't have to adjust the frequency. Of course the timbre - this is the quality or characteristic of a sound wave, or what allows you to distinguish between a trumpet and a violin - will be distorted. And you may lose stereophonic sound, or the ability to hear in stereo, under water. Also the sound will be incredibly dull since the bones in our inner ear that we normally use to hear with are not vibrated as effectively. The way we hear underwater is primarily through vibrations of the skull. Source: _URL_0_ It is not possible for underwater speakers to change the way we perceive sound underwater. But they can produce louder waves to compensate for the vibrational loss. |
Why does facial hair grow faster then Arm [body] Hair? | Your hair grows in a cycle with 3 phases. There's a growth phase, a resting phase, and a falling out phase. Your hair on your head has a long growth phase, and shorter other phases. Your facial hair is similar in nature with a longer growth phase. Same with your underarms and other hairy places. Your arms/legs/other parts of your body have shorter growth phases with longer of the other two phases. That's why the hair there seems to always stay so short comparatively. Check out the part where it mentions [Hair-follicle Cycling](_URL_0_) |
Why are our Solar System planets in the sequence they are from the sun? What does it tell us about initial conditions? | The simple answer is that it originally formed from a spinning disk of dust. This dust clumped together, eventually forming planets as all of the dust within a ring formed into one big clump that orbits within that ring. |
If the Hubble telescope captured an exploding star 2 million light years away, does that mean that the star may have already exploded... 2 million years ago? | Not just "may have...2 million years ago". It *did* explode 2 million years ago. |
Why do all impact craters look round? | 1) All impact craters aren't round. Impacts into a surface obliquely (i.e. striking near parallel to a surface) produce oblique impacts (e.g. _URL_0_). 2) For a hypervelocity impact (i.e. ~15km/s average in our solar system), the geometry of the projectile matters very little. During the impact process, the projectile is entirely melted within fractions of a second. The shock wave generated by the impact would propagate roughly hemi-spherically into the target. Material in the upper layers of the target will be ejected, forming what is called the transient cavity (roughly bowl shaped). However, the impactor has very little to do with the ejecta, or the subsequent modification due to gravity; it's all about the shock wave. Refer to Melosh, H. J. "Impact Cratering: A Geologic Process", Oxford Univ. Press, New York (1989). |
What is the difference between astronomy, astrophysics, and cosmology? | Astronomy and astrophysics study everything in space. Cosmology is a subset of that which focuses on the early universe and the large scale structure of the universe. "Astrophysics" is often taken to refer to the theoretical side of things while "astronomy" is often taken to refer to the observational side of things, but in practice they are often used interchangeably. Depending on who I'm talking to, I will either introduce myself as an astronomer or an astrophysicist. |
Why did Africans develop dark skin? | Africans didn't develop dark skin - all homo sapiens had dark skin at one point, as we all originated from africa. It was europeans that developed lighter skin, one of the theories for why this happened was because in the less sunny climates, natural selection tended to whiter people as darker people would have a harder time getting enough vitamin D. |
Could the universe (as we know it) exist with multiple time dimensions? | Most likely not, or at least not *our* universe. Here's a neat diagram describing the difficulties inherent to universes that [differ from 3 spatial + 1 time dimensions.](_URL_1_) * Tegmark, (1997) "On the dimensionality of spacetime" _URL_0_ This plot refers to "non-compactified" dimensions, ones which behave in a simple and sufficiently large manner like we are used to, this doesn't exclude the possibility of compact dimensions such as those in String Theory. The differing universes are as the paper puts it, "dead worlds" unable to generate physics or behavior as seen in our own. We must however restrict ourselves to the mathematical consequences as no evidence exists for the physicality of such universes. |
Why is there a flu season, how does cold weather benefit the influenza virus? | The virus itself is probably less effective when cold, but cramming people indoors for three months straight helps it spread faster. You can get the cold or the flu any time of the year. It's also hard to "plan ahead" for a virus because it's constantly mutating into a new strain. Vaccines only work for a while until the virus has changed enough to require a new one. |
Flu and colds are caused by viruses. But why are they "in season" during cold and damp weathers? | Another compounding factor is proximity to others. We spend more time inside during colder/inclement weather, thus providing us with longer and more frequent interpersonal contacts. I've seen numerous theories about viral persistance, fomites, and weather effects on the body, but the Public Health folks I work with generally agree that it's the increased frequency and duration of person to person contact that is responsible for the increases in infection rates. |
Hydrogenation increases the boiling point of a vegetable oil. Is there a inverse process that decreases the boiling point of a vegetable oil? | I'm a biologist so my organic chem isn't the best, but I think I can answer this one. The melting temperature of fats depends on the length of the fatty acid chain and the degree of saturation. Double bonds between two carbon have different geometry than single bonds, so when there are double bonds, the fatty acid chains don't stack together as well, thus lowering the fat's melting temperature. Hydrogenation works by reducing the double bonds to single bonds, which raises the fat's melting temperature. To oxidize single bonds, you can halogenate the alkanes by adding chlorine, iodine, or bromine under high temperature. Then you can add a strong base to perform an elimination reaction which will remove the halogen and a hydrogen on an adjacent carbon, leaving a double bond instead. I'm not sure if this would be a safe product to eat though. |
why is it that water makes a paper towel cloudy but oil makes it clearly transparent? | So you can think of a paper towel as being made of two things, the fibers, and the air between the fibers. These two mediums each propagate light differently, and because there is no regularity, its just a mix of air and fibers, the light scatters significantly. Why does it scatter? Well when ever light passes through a boundary between two mediums, it bends. Stick a pencil is a glass cup of water and you will see it's image "shift" as it enters the water. The number that describes this behavior is called the "index of refraction." So the mix of air & fibers has lots of boundaries so you get lots of scattering. The oil will replace the air, and the oil is closer to the fibers in terms of index of refraction,so light feels less of a shift when passing between oil & fibers so does not scatter as much so is more transparent. Water is probably not as close, so a wet towl is more opaque. |
How does humidity affect how sound travels? | It only has a very slight effect. At 20 ºC sound travels at 343.4 m/s @ 0% relative humidity and 344.6 m/s @ 100% relative humidity. |
What would cause stars to appear to flicker different colors? | [The atmosphere.](_URL_0_) This also answers why stars twinkle and not planets. |
Why do fluorescence microscope have a higher resolution than optical microscopes, when both of them use light? | Most fluorescent microscopes have the same resolution as standard optical microscopes. However, there are some interesting tricks that it's possible to do with fluorescent samples to improve resolution beyond the diffraction limit. These methods are collectively known as "super-resolution microscopy." One widely used super-resolution method is STED (stimulated emission depletion). In this method, a pulse of light is used to deplete fluorescence in the area around the point being imaged, allowing greater resolution to be achieved. |
Why is there only the 2 two types of radio signals, am and fm? | There are many other kinds of analog signal encoding - phase modulation, pulse width modulation, interrupted continuous wave ... In principle, any of these could be used to deliver audio signals. AM and FM as you know it happened to be early winners because they were well suited for voice and music and were within the ability of the technology of the day to implement. |
Is it possible that some pathogens or viruses have evolved to cause coughing/sneezing symptoms in its victims to encourage it to spread? | I'd say the other way around, to be pedantic. Some pathogens evolved traits that lead to coughing/sneezing and could travel well in air/mucous, thus were spread extensively, and thus the trait perpetuates. They didn't develop the trait *to* do a thing, but the trait mutated randomly and *did* lead to success, thus it persists. |
If time is the fourth dimension, shouldn't it contain the first three as well? | Width and height and length don't contain each other, they are linearly independent. |
Why do we consider time to be the fourth dimension? | You need 3 spatial coordinates and 1 temporal coordinate to specify your location in spacetime. Which one is the first, second, third, or fourth is irrelevant. All that matters is that there are 4. |
Why are the Middle East and North Africa deserts? | In addition to the conditions suggested by u/Astromike23 there are also human caused ecological changes that occurred more recently. You may have heard the Middle East referred to as the fertile crescent, some regions of it were lush and fertile but the sheperding livestock by humans in the region since the development of agriculture has led to its biomass becoming depleted. So the fragile ecology of the region was wiped out by the early human technology of goats. This can be seen in other fragile biomes such as Iceland, areas of which sheep have turned into moonscape. tl;dr: fragile ecosystems have existed in the past in those places, but human exploitation has caused or amplified desertification. |
Are stealth planes really 'stealthy', or are they vulnerable to low-frequency and bistatic radars? | I read an [article recently in Popular Mechanics]( _URL_0_ ). Basically, there are emerging technologies to defeat low radar signatures, but none seem to be proven. I think one interesting point is that the planes are only designed to defeat a certain range of common radar frequencies. So if you make a effective radar based on another frequency (VHF, UHF, GHz, etc), you may be able to detect the aircraft. However, each frequency band has its own limitations that would need to be overcome before an effective radar could be created. |
What makes a stealth plane 'stealth'? What is the technology involved and why can these planes be invisible to radars etc? | Two different ways. One being radar absorbing material. The other is the use of flat surfaces and sharp edges, it reflects the radar so that the full signal doesn't go back to the receiving station. They won't actually be invisible, but can reduce the signature of the F117a down to that of a small bird. |
Are the current health food trends such as non-GMO and organic better or worse for the environment and sustainability? | GE crops currently on the market have, on average, increased yield while reducing pesticide use. They have also allowed farmers to use safer herbicides. Organic farms have about 20% lower yield on average, so to grow the same amount of food you need to use more land and inputs. |
How do insects regulate their body temperature? | Insects have traditionally been considered as poikilotherms (animals in which body temperature is variable and dependent on ambient temperature) as opposed to being homeothermic (animals which maintain a stable internal body temperature regardless of external influences). |
Does the expansion of spacetime happen at every scale of the universe? | In the presence of matter, no. Einstein's field equations are non-linear. They include contributions from both matter/energy and dark energy. So at small scales (matter dominated) there is no expansion; at large scales (dark energy dominated) there is expansion. This may seem contradictory, but in GR superposition doesn't hold as the equations are non-linear. |
Does cannabis suppress your immune system? | It would probably depend on what you're taking it for. If you're taking it because you're a nervous wreck w/o it (anxiety), the stress itself could be much worse for your immune system. I don't think these questions are simple to answer. |
Do cannabinoid receptors degrade with cannabis use? | Pharmacology 101: drugs act on receptors. Receptors cause changes in a cell. Cells tend to resist prolonged changes from their 'normal' state, so if they have intense and prolonged receptor activation, they decrease the number and/or effect of the drug's receptor. This process is called tachyphylaxis and it occurs at different rates for different receptors. Cannabis use does build tolerance, presumably via tachyphylaxis although there may be other mechanisms involved. Cannabis tolerance is largely, and possibly completely reversible, but can take several weeks or months. |
When a wheel or anything circular spins really fast, why does it sometimes look like its spinning backwards and then spin forwards again? | This is known as the wagon-wheel effect. It is most commonly observed when viewing a video recording of a spinning wheel. In this case, it is a result of a strobe-like effect caused by the fact that a video is actually made up of a series of discrete frames. It can also happen in real life viewing, though. In this case, it's not always clear what the cause might be. One known (and reproducible) cause is subtle vibration of the eyes. This is why the effect is most often noticed when viewing a rotating wheel from a moving vehicle, such as a car. The engine imparts a subtle vibration to a viewer inside the car, which then causes the effect when a rotating object outside of the vehicle is viewed. It can also happen when perfectly stationary. In this case, the cause is unknown. There have been some proposals related to neural cyclic sympathy, but it's not conclusive. We know that the effect can happen after a rotating object is viewed continuously for a while, but the exact cause is still debated. |
Why does melanin make skin darker? | It doesn't have anything to do with heat. As I understand it, melanin is produced in response to ultraviolet radiation. More UV will lead to more melanin being produced. That's why you tan. Melanin will block UV from reaching the delicate underlayers of your skin, because too much UV is bad for you. However, UV in some amount is necessary for your body to produce vitamin D in your skin. Too little vitamin D can cause rickets and other diseases. So if your ancestors came from an area with high levels of UV, such as areas around the equator, they will tend to have higher levels of melanin so as to block more of the UV. If your ancestors came from higher (northern or southern) latitudes, there isn't as much UV, so you won't need to block as much, and will need to absorb more of it. So you make less melanin. |
Do other animal species have an eye colour diversity similar to humans'? | I don't know about eyes specifically, but differences in coloring (or indeed expression of individual traits) of any external body part within a species is just part of the normal genetic diversity. Just look at the different color schemes in horses (even within a single breed). So if this can be true for hair and skin it'll be reasonable to assume somewhere it happens for eyes as well. |
Could gravity in space bend the light coming from stars so much that where a star appears to be isn't actually where it is? | This is exactly the effect that was measured by Eddington and Davidson back in 1919 that make Einstein world famous. During a solar eclipse, when the Sun is dimmed, you can see the starlight near it. If you record the positions of those stars and compare them to their locations when the Sun isn't in the way, there is a bending of light or shift which occurs because of the Sun's gravitation. Here's some info about it with a diagram, * _URL_1_ The actual paper, * _URL_0_ And the even more impressive and related effect of the Einstein Ring, * _URL_2_ |
I understand that the Sun, once you leave our atmosphere, appears white rather than yellow. With this in mind, what colour do other stars (red giants, blue giants, etc) appear in space? (Additional details and questions inside) | It also appears white while you're in the atmosphere as long as it's high in the sky. [Here's a picture that shows the color of black bodies of different temperatures.](_URL_0_) The chart you linked to has a temperature axis, so you can work out what color they should have drawn those stars. I don't know why people keep insisting the sun is yellow, or calling [G-type main-sequence stars](_URL_1_) yellow dwarfs. |
Is the Sun hot simply because of high pressure? | > He said that the fusion in the core of the Sun supplies an outward pressure that supports it against gravitational contraction (this I already knew), but it contributes very little to the temperature. How accurate was he? I don't know whether that's an exact quote, but as you wrote this it is a very strange thing to say. *The fusion per se* does not supply an outward pressure, it is the *heat* released by the fusion that keeps the pressure up and maintains hydrostatic equilibrium. This released heat is what replaces the energy lost to space. I have a feeling that this is one of those situations where someone was saying something quite specific but it is getting misinterpreted as being more general, but I don't know what that specific thing could be. Maybe it's a chicken and the egg thing with the original stellar nebula collapsing and warming before fusion is initiated? |
Is the sun hot because of gravity itself, or because of the nuclear fusion ? | The heat from gravity would have been radiated away a long time again. It maintains its temperature through nuclear fusion. |
Does playing music for plants really help it grow faster? | No. Playing music for plants doesn't do anything to increase the growth rate. |
Do other animals laugh? | Laughter is by definition just the audible expression of excitement so yes, many animals laugh. It's been studied in chimps, dogs and rats from what I've turned up and anecdotally I have tickled a chimp and she definitely laughed.. |
Immediately following the big bang, did the universe grow faster than the speed of light? If so, how come the speed of light is treated as an absolute and unbreakable "cosmic speed limit"? | First, the universe doesn't grow at a rate that can be expressed as a speed; the "rate of expansion" depends on how far apart two things are. Second, as it's popularly put, nothing can move through space faster than the speed of light, but there's no limit to how fast *space itself* can expand. See [this comment](_URL_0_) for a more detailed version of that. Because of that, there can be (indeed, there are, and have been since at least inflation) objects that are receding from us at "speeds" well above the speed of light as they are carried away by the "flow" of the expanding universe. |
Are most nutrients in fruit and vegetables really in or under the skin or peel? | It really depends on the fruit or vegetable in question, as well as the nutrient. Apples contain most of their fiber in the skin, but the vitamins and minerals are present throughout the flesh. Sweet potatoes and carrots carry their vitamin A all through their flesh, but a skinned Russet potato is basically nothing but starch. Citrus skins are not particularly useful from a nutritive perspective, but the pulp and juice definitely are. |
How does squinting help you see? | When you wear glasses you correct light refraction reaching your eyes. When you squint, you reduce the amount of light being refracted, therefore, making it easier to see. There is something called a pinhole occluder that does the same thing. You essentially look through a tiny hole and, if you wear a prescription, it makes your eyesight seem clear. Basically just poke a hole through an index card using a paper clip and look through the hole. You will be able to see perfectly. |
Are there any elements or compounds that were first discovered in space, other planets, comets? | Helium was first discovered on the Sun! (sort of) Using spectrometry of sunlight, they found that the wavelengths correlated to an element not yet observed on earth. [Wiki](_URL_0_) |
Why is the light-gathering power of a telescope proportional to the surface of its mirror? | > ... and it's this probability amplitude that gets evenly spread in space. No, a photon that is send out between t_0=0 and dt from the star will be at time t at a distance between r=c*t and r+dr=c*(t+dt). So the propability is spread over 4pi r^2*dr. The propability not the wavefunction, since the photon has to be somewhere in this volume. Also since light has no dipersion i vacuum, dr=c*dt is constant for all r, so probability spreads with r^2. |
Do fingerprints heal when scarred? | Fingerprints usually do regenerate enough to allow identification, unless there is severe damage to the tissue. So it is possible to intentionally "erase" them. I do not have information to answer if it is possible to develop a new set of fingerprints. You can check [this article](_URL_0_). PS I'm new to providing scientifically accurate answers, so please let me know if I am doing it wrong. |
Why is it that the sun looks different during sunrise and sunset even though they are at same distance from horizon? | The colors you see during sunset/rise are due to the scattering of light as it collides with particles in the atmosphere. The slight difference between the colors at sunrise and sunset then is due to a differing atmospheric composition between these times. There is typically more humidity in the evening than in the morning, so the sunset tends to bring out the longer wavelengths (red) best able to penetrate. The relatively lower humidity in the morning causes the sunrise to display colors more towards the blue side of the visible light spectrum. This could also explain the overall difference in light level as well I guess. This phenomenon is also seen through long term weather changes as well. Dry winter months tend to produce 'bluer' sunsets/rises, while the hot humid summer months tend to produce 'redder'. |
If a photon has no mass, then how can it transfer momentum? | To explain the same thing as /u/Fenring in fewer words: massless things have momentum proportional to their energy. I bet you've been led astray by the formula p=mv, but that's only an approximate formula that works for massive objects traveling at low speeds. |
What would happen if you "carbonated" soda with helium instead of carbon dioxide? | At 5C, about refrigerator temperature, CO2 has a solubility in water of around 3g/L of gas, giving around 1.5L of gas per liter of carbonated water at room temperature. By comparison, at 5C, helium only has a solubility of 0.00165g/L, but since helium is so much lighter than carbon dioxide, you'll still get close to 10L of gas once it comes out of solution. I really wouldn't want that sort of expansion going on in my stomach. |
About how much light does Pluto receive from the sun? | About 1/1600th as bright as it is on Earth. That is still much brighter than the moon. |
What percentage of the light produced by the sun hits Pluto? | If you have a sphere whose centre is at the sun and whose surface is at the orbit of Pluto (roughly, it's an ellipse IRL), the answer to your question is the fraction of this sphere's surface area that is occupied by Pluto. That is the ratio of Pluto's radius to its orbital radius squared. This is about 0.04 trillionths. The images you see rely on long exposure times and significant post-processing. |
How do we communicate wih people who are blind and deaf? | First of all, it is very uncommon to be born both deaf and blind: mostly people are born deaf and gradually become blind or vice versa. Therefore, they start with learning special sign language and/or braille at a young age. Communication with deaf-blind people usually goes through special interpreters (deaf-blind); they make signs with the hands of the deaf-blind person, or spell letters in the hand of the deaf-blind person. In answer, they do the same. Communication therefore is slow but not impossible. Source: sister is a deaf interpreter who did a minor in deaf-blindness. |
If I was able to look 13,8 billion lightyears out in the galaxy, I would theoretically be able to see the Big Bang, but would it matter which direction I looked? | You would see the cosmic background radiation, which is basically the universe as it was about 300,000 years after the big bang when protons and electrons joined to become hydrogen and the universe became opaque. It looks mostly the same in all directions, but if you look very carefully (e.g. with the WMAP telescope) you can see variations in it. |
Why, when stirring a cup of instant coffee with a spoon, does the sound of the spoon scraping around the edge of the cup get more high pitched the more the coffee granules dissolve? | The phenomenon is called [hot chocolate effect](_URL_4_), and is due to the changing density of your liquid when the powder is dissolving. You can also find past threads on this as well: _URL_3_ _URL_0_ _URL_2_ _URL_1_ |
Why is there still helium on Earth? Shouldn't it all have ended up in the upper atmosphere by now? | Helium is produced by the alpha decay of heavy elements, and the Earth is full of lots of heavy elements. A lot of it becomes trapped in small pores underground, like oil does, and when oil is extracted helium comes out and is captured. |
How come, when we rub our eyes hard enough we see those weird colors and patterns? | What about those really faint, amoeba-like, transparent globs floating around your vision? They look like microbes as seen underneath a microscope. It's kinda hard to describe but they're definitely there. Debris floating on the cornea?? |
Why can’t we remember much from our infancy? | Short term memories are formed by transient synaptic plasticities and Long term memories are formed from these short term ones by Long Term Potentiation (its the most well accepted neural correlate for memory formation as of now). The short term memories are formed in the hippocampus which is very robust starting early age but the frontal cortex (also called as the neocortex where most of the long term memories are thought to be stored) develops even until the mid-20s in humans. From this perspective, infants may not consciously remember anything as the short term memories cannot easily get translated to the long term memories and get stored in the brain (we don’t truly know the chemical/physical nature of memory yet). |
What is the most Distant Star that We can See with the naked eye? | Any star you can see with your naked eye is in the Milky Way. A person with good eyesight can see stars down to about mag 6.5 under great seeing conditions. The furthest object from earth that can be seen with the naked eye is the Andromeda Galaxy which is 2.5 million light years away. As for a specific star, well that's really tricky because there are factors like observing point and even the fact that the farther away a star is the harder it is to pinpoint its distance. One really far away star that can be seen with your naked eye is Deneb. |
Whats happening when a sonic boom occurs? | When an object passes through the air it creates a series of pressure waves in front of it and behind it. These waves travel at the speed of sound, and as the speed of the object increases, the waves are forced together, or compressed, because they cannot get out of the way of each other. Eventually, when the speed is Mach 1, they merge into a single shock wave, creating the boom. [Diagram](_URL_0_) [The cloud is caused by rapid condensation of water vapor in the air](_URL_1_) |
I just read that silver is the most conductive metal. So why do so many electrical connectors use gold? | Silver is also very reactive. It combines with oxygen in the air and turns a kind of brown. The word for this is tarnishing. A tarnished silver surface does not conduct electricity. That means that connections to silver are not as reliable as other conductors. Gold does not tarnish, so its connections are always good. A better conductor that does not connect is not as good as a lesser conductor that stays connected. |
Why is gold used on connector ends, like on usb-connectors for gaming mice, when copper has lower electrical resistivity? | Gold does not tarnish or corrode, while copper corrodes very rapidly, and the actual conductivity of gold is not significantly lower than copper, but the kicker is that the coating is so thin that it does not increase the resistivity of the whole circuit by any relevant amount. & #x200B; There is absolutely no benefit gained by keeping the last 0.1mm of a cable copper, when the benefits of anti tarnish/corrosion are so important to the reliability and lifespan of a product, |
Why do snowflakes form such unique and symmetric shapes? | Because they are crystals. Crystalline substances follow geometric patterns because it minimizes the energy of the molecular configuration, a beautiful example of spontaneous order. In the case of water, the water molecules align according to hydrogen bonding, forming "hexagonal" shapes (in 3D space, though). The way these shapes lock is rather fixed, but they are flexible in their growth, giving raise to many possible shapes. Chaos theory does the rest. |
Would a corpse decompose in outer space, or say the surface of the moon, as it does on Earth? | No the body would dessicate and mummify, similarly to what happens to corpses at very high altitudes. Decomposition is mediated by bacteria which cannot live in a very low pressure, low temperature environment. Even if the integrity of the suit were maintained, temperature would drop below freezing quickly and all biological activity would stop. |
What would happen if the universe were expanding into a finite space? | Our best understanding of the universe is not just that the matter inside it is flying apart, it's that space itself is expanding. It's not expanding *into* anything. It's expanding more in the sense that a rubber band expands if you stretch it. If some constraint appeared that suddenly caused the expansion to stop, that wouldn't mean that there is suddenly a physical wall in the universe. |
Subsets and Splits