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If life has a single origin, when did plants evolve into animals? | [Phylogenetic tree of life](_URL_5_) which is the best visualization for how evolution shook out. You should also look at [Eukaryote](_URL_4_) which has sections on differences among eukaryotic cells and on origin and evolution. |
If all life in Earth originated from the same source, what is the common ancestor between animals and plants? | It was a single-celled lifeform 1.6 billion years ago. _URL_0_ You share some 44% of your genes with a cabbage because so many are to do with microscopic processes such as cell respiration. Our common ancestor would be a load of single-celled organisms which hadn't settled on which genes to activate for pattern formation I.e. which end is the head or the tail, which bit is the flower or the root. Different individuals within this collection of single-celled organisms mutated different methods of pattern formation (activating different genes which both plants and animals have)and plants and animals embarked on their divergent paths. |
Is it possible for a moon to also have its own moon? | It is possible for a moon to have it's own satellite, yes. Whether it would be classified as a "moon" or not would be up to the academics, but a loose definition is: * A distinct, whole object * A solid object * In orbit around a more massive body The mass of the satellite orbiting a moon would most likely be very small in relation to that moon. |
Is it possible for a moon to have its own moon? | Two factors I think are worth mentionig. 1. The Roche Limit describes the distance from a celestial body at which a satellite will be torn apart by tidal forces. It's approximate and depends somewhat on composition, but it is very roughly 2.5 radii of the main body. [Source](_URL_1_) 2. The sphere of influence is the distance at which, in this case, the moon's gravity is less of a factor on an object than the earth's gravity. Any further from the moon than this and the object would no longer orbit the moon, but rather orbit Earth. Our moon's SOI is about 38 lunar radii [source](_URL_0_). So a satellite of the moon needs to orbit at a distance greater than 2.5 lunar radii but less than 38. Closer and it would break up, further and it would drift away. Of course, as others have said, a subsatellite would not stay in this zone, as it's an unstable orbit. |
What makes the gas around Jupiter and Saturn part of the planet and not the atmosphere? | I think you're just a bit confused with the terminology. Technically, most scientists would consider the Earth's atmosphere to be part of the planet Earth. You are right that what you see when you see pictures of Jupiter is basically just an extremely thick atmosphere. What is at the core to the planet was actually being [debated as of 2008](_URL_0_). |
How is the surface of a gas planet like jupiter? | As far as we know, for most gas giants, the upper layers of the atmosphere are gaseous (as the name suggests), a combination of mostly molecular hydrogen and helium with traces of ammonia and water. As you get closer to the planet's core the gas would gradually transition to a layer of liquid due to the immense pressure, eventually reaching a molten, rocky core. Put briefly, there probably wouldn't be a "surface" in that sense, though that said gas giants are quite poorly understood objects and as such we can't really be entirely sure what you'd find inside one. |
Do anti bacterial soaps and hand sanitizers create worse bacteria? | Yes but if you use a sanitizer that uses alcohol as it's sanitizing ingredient then there is no worry. |
What will the James Webb telescope allow us to see that Hubble cannot? | One major difference is that JWST will be an infrared telescope: it won't look at optical light like Hubble does. With regards to exoplanets - one of the major goals of JWST is to measure the atmospheric components of exoplanets - something we can't do very accurately with today's telescopes! |
Does the moon have earthquakes? | Quakes could in theory occur in all major rocky bodies of the solar system, but in the case of the Moon we have good evidence thanks to the seismometers placed by the Apollo astronauts. Yes, they happen. They are weaker than Earth's but last longer (like an hour) since the Moon's surface doesn't damp energy very easily. _URL_0_ |
Does Mars have tectonic activity? | Tectonics happen when the core is a different temperature than the surface. Mars doesn't have any as that planet's dynamo died over a billion years ago (the hot liquid metal core spinning also produced the magnetic fields that once protected Mars' atmosphere). As it cooled, tectonic shifts would have slowed and weakened in direct correlation. |
Why is so much of Venus's atmosphere CO2? | Lack of surface water (Oceans) eliminates a huge carbon sink into which CO₂ could dissolve and precipitate out as carbonate compounds. Lack of apparent tectonic activity (sub oceanic crustal subduction) would preclude the sequestering of such carbonaceous crustal material deeper under the surface. This would allow the ocean to desaturate and continue act as carbon sink. The presence Carbon-sequestering life would possibly reduce the CO₂ concentration by a few percent, depending on the steady state biomass supported by the planet |
When people say stars and nebulae are formed by gas and dust, what exactly is the dust? | Carbon compounds and silicates are still around in space, and they can form *very* complex structures. The environments where they form can allow for very different chemistry than is encountered on Earth, even at high vacuum, and the structure and formation of dust remains a large and active topic of research. It also scatters and absorbs light in different ways than gas, so it's important to understand the dust in order to correctly remove its effects when doing all other areas of astronomy. Dust is ubiquitous, causes important effects, and is poorly understood. |
How does churning cream into butter reduce its lactose concentration? (4%-1%) | Lactose is sugar. Sugar completely dissolves in the liquid. Cream is an emulsion (homogeneous mix of fat and liquid). Churning won't extract the sugar that has dissolved in the liquid, it will only separate the fat (butter) from the liquid (buttermilk). In the end, almost all the sugar will be still dissolved in the buttermilk and almost none in the butter (only a bit remains, because not all moisture will be extracted). That's why the percentage of lactose in butter is so low, and the percentage of lactose in buttermilk is higher than in cream (same amount of sugar concentrated in less mass because all the fat is gone). Edit: removed the practical example, it was too silly. |
Do all stars have planets? | There were a handful of papers published within the past 3 years that suggest nearly all stars have at least one planet. Based on current understanding of the process of stellar formation, there will always be some matter that is gravitationally bound to the protostar but is not pulled into the star. This matter would form planetesimals and planets. Further reading: _URL_0_ _URL_1_ |
Why is the air that you exhale warm when your mouth is open wide while it's cooler when you blow the air through pursed lips? | Contrary to what people in this thread are saying, this has nothing to do with the speed of the air, improved convection or wind chill. When you exhale onto your hand with your mouth open, most of the air that hits your hand came from your lungs. Conversely, blowing through pursed lips forms a narrow stream of air from your lungs which drags cool air from the surrounding atmosphere with it. Edit: this effect is called entrainment. |
Why do you blow warm air when your mouth is wide, but cool air when your lips are closer together? | It is due to a process called entrainment. A fast moving jet of air from your mouth draws colder, room-temperature air along it, so the overall temperature of the air is lower - it doesn't just _feel_ cooler; it _is_ cooler. |
Why does the hair on the average human head continue to grow while all other primates have hair that stops naturally at a relatively short length? | This may be close to layman speculation, but I recall asking this question in a science forum many years ago and got this answer from someone supposedly educated in the matter Hair does continue to grow indefinitely, however there is a maximum length that hair in certain places can get before falling out. Hair on the human head can grow very long before falling out, whereas human arm hair will generally not reach more than 15mm before falling out It's not like your arm hair, underarm hair or pubic hair stops growing at a certain length, it merely falls out before it can become Rapunzel like. Hair on different species is the same thing. Bobo the Chimp, would be regularly losing his hair once it reaches standard chimp length. Because this is happening randomly over the chimps body and regrowing quickly it is never noticable (it's not like all the hair grows exactly evenly then sheds in one day then starts growing back) Please someone correct me if I'm misinformed, as I've repeated this to many people |
How do eyelashes “know” when to stop growing? | The growth of eyelashes occurs in three phases, when these phases start and stop is genetically controlled. See the published report below, scientists 'know' some aspects of the process, but some details are currently unknown: _URL_0_ |
"For reasons even a chemist is hard-pressed to explain, ring shaped gasoline molecules are higher in octane", is this still true ? | That line doesn't make very much sense. Gasoline is a mixture of several molecules, mostly hydrocarbons of varying sizes and structures. One such hydrocarbon is octane, an 8 carbon linear chain. By definition octane is not and cannot be a ring. My guess is that they may be saying that ring structures found in gasoline can provide more energy, although this would not be true. |
TIL that early Homo sapiens interbred with the Neanderthals up north. Does this mean that people whose ancestors stayed in Africa are more "purely" human? | Neanderthals can also be considered as humans. If they were still around today and interbreeding was possible, they would be probably be considered a subspecies, or perhaps a race. This viewpoint isn't widely accepted yet but there may be some kind of racist factor which contributes to the idea that they were inferior to us. There is evidence that they had developed tool use, art, trade and some kind of culture before they died out. Their decline may have been due to being more pacifist than homo sapiens, rather than being subhuman. |
If space is primarily empty vacuum, do gas particles such as those in nebulae diffuse into said vacuum? | Yes. Due to the random movement. But that nebulae has mass and therefore gravity which holds the gas in. It the same as asking why air doesn't escape earth's atmosphere. Because it is held by gravity. But some air does escape. |
What causes planets in a solar system to orbit on a "plane" instead of in any direction like electrons around a nucleus? | Do electrons even actually "orbit"? I thought that was the simplistic grade school explanation, but they actually live in a probability sphere around the nucleus, and we can't tell if they are actually "orbiting". Intuitively it would seem that this sphere implies that there is no defined orbit. |
Why is it so hard to cure baldness? | our current advances in medical science excel at repair. if you broke your leg, we can easily repair it. if you cut your finger off, we can likely repair it with some luck and skilled surgeons. what we cannot do is grow a leg or finger back. on a similar vein, we have products like rogaine that can be used to maintain the current hair follicles but we do not have the tools to grow them back where they've died/atrophied (apart from a hair follicle transplant). |
Why don't the bubbles (head) created when pouring a beer dissolve quickly like bubbles produced when pouring pop? | Beer, unlike soda, contains a melange of proteins from the grains and the yeast. Many of these proteins are amphipathic (i.e. they have sections that are hydrophilic, and sections that are hydrophobic, similar to soap), and, similarly to soap, these proteins help to stabilize gas bubbles. (I hope that someone can elaborate on the mechanism by which this happens, as I can't) |
Why didn't the asteroid belt coalesce into a planet, like elsewhere in the solar system? | The gravitational pull of Jupiter is sufficient enough to disrupt the formation of anything that gets too big and simply rips it apart. And if you think about it, there's actually not that much material in the asteroid belt. [Ceres](_URL_0_), a object that has not even 2% of the Moon's mass, is 25% of the total mass of the whole belt. Coupled with the fact that this mass is so spread out (a 'close encounter' could be a couple of hundred thousand kilometers away from any two asteroid, with collisions really unlikely) planet formation is physically impossible. [More sources](_URL_1_) |
Where does blister fluid come from/go to? | It's [lymph](_URL_0_) (_URL_1_), which is the water part of the blood. |
If A Microwave Oven's door prevents the leakage of microwaves due to the holes being smaller than the wavelength, how then, do radio waves make their way into my house, allowing me to listen to the radio/tv? | Because your house is not made of metal. The concept being explained on that page is a so-called [Faraday cage](_URL_0_). Faraday cages can only be made out of materials that conduct electricity well (such as the metal case of a microwave oven), so the non-conducting wood/concrete/brick of your house is not going to block electromagnetic waves in this manner. |
If a human was cloned, would the clone have the same fingerprints? | [This article](_URL_0_) is about identical twins, effective clones; it states, in part: > To a standard DNA analysis, they would be indistinguishable. Yet the parents of twins can usually tell them apart by subtle visual cues, and, **while their fingerprints are generally similar, they are not identical.** |
Why are there so many more islands in the Pacific than any other ocean? | The Pacific is extremely geologically active relative to the other oceans. See the [ring of fire](_URL_0_). This provides many more opportunities for island formation via direct volcanic activity and crustal uplifting at a convergent plate boundary. |
Why are there thousands of islands in the Pacific, but only a handful in the Atlantic? | Mid-ocean volcanoes make islands. That's why. Look up "Ring of Fire." That's the name given to the land masses that encircle the Pacific Ocean, where volcanoes are found on the West Coasts of the Americas, as well as in Japan (Fuji) and other Asian countries. Look up earthquakes on land around the Pacific. You'll find that this area is unstable, and has been shaking and squirting up volcanoes for millenia. The Atlantic is a quiet old maid compared to the vivacious movers and shakers that are the tectonic plates under the Pacific. |
Do animals perceive any difference between languages? | If the dog is mature yes. The dog has to adapt how he interprets different words/sounds as a dog does not only learn some commands but also picks up the mood of humans or other stuff. If the dog is not mature it would not make any difference at all because the dog did not learn to understand any phonetics. |
Obviously the moon has no atmosphere, but given that the surface does have a higher gravity than the rest of space, is there a slightly higher quantity of gas than ordinary space? | Yes, the the moon contains more gas than the vacuum of space. I would expect some of it to come from material released from the surface by incoming radiation. It's too hard to check on my phone but I believe the wiki page will tell you about it's composition and origins. |
What is 'Space' expanding into? | It's not expanding into anything, rather, the distances between separate points is increasing. |
Why does food and drink taste different depending on it's temperature? | Certain chemicals contained in foods change in solubility as temperatures change. Say, for instance, a soft drink. A soft drink is carbonated (added CO2) that makes it fizzy, but it also enhances the flavour by giving a slight tart taste. In lower temperatures, the solubility of CO2 is increased via a chemical equilibrium: CO2(g) < -- > CO2(aq) (exothermic). Meaning, when your soft drink is cold, its fizzier and tastes better. That's just one example, of course, but the principle is the same for other foods, I assume. |
Lunar dust on Earth's moon is jagged because there is no weather to wear it into roundish shapes. But why is the surface dusty? Why isn't it one solid rock? | Ah, I know this one. Meteors! Or... would that be meteorites? It didn't pass through an atmosphere though... ah, whatever. Anyway, the meteor would hit the otherwise solid rock surface and break it, fracture it, melt it and turn it into shards of glass. That settles back down, and is repeated a billion more times over a long time until the entire surface is jagged broken crust sand. Unfortunately for us, it never stops being jagged. |
Why does the sun appear orange at sunset and sunrise but during the day appear white? | As photons from the Sun pass through the Earth's atmosphere, they experience Rayleigh scattering, whereby low-wavelength (bluer) light is preferentially scattered compared to redder light (Rayleigh scattering depends on 1/wavelength^(4)). This is why the sky appears blue during the day- since blue sunlight is scattered every which way, we see it coming from the whole sky whereas the longer-wavelength light appears to mostly just come from the Sun. At sunrise and sunset, these photons must travel through more atmosphere to get to the observer, and thus the blue light is all but completely scattered away, leaving the Sun and the sky surrounding it to appear red. |
How much volume does the dissolved gas take up in carbonated water? | I don't know the answer to this question, but there is a simple way to find out. For this experiment, you will need: 2 graduated cylinders or some kind of volume measuring device 1 can of carbonated water a glass of non-carbonated water Fill one graduated cylinder up to a certain volume with carbonated water, and the other up to the same mark with normal water. Let the two cylinders sit overnight. By morning, the CO2 should have come out of solution. See if the volume in the first cylinder has gone down. Edit: clarity |
Why does the moon have so many impact craters compared to the Earth? | Because earth has an atmosphere that destroys most impacters before they hit the surface, oceans that absorb impacts without creating craters, and weather, glaciers, volcanoes and plate techtonics that erase evidence of impact craters. When you look at the moon, you are looking at 4 billion years of impacts. On earth, it's rare to be able to find a crater a few million years old, and the ones older than that no longer really look like craters. The rest have been erased by a living planet. |
Why is there so many impact craters on the Moon comparing to Earth? | The earth atmosphere protects us from most impacts. Furthermore our plate tectonics and the changing of terrain over the centuries has worn down the lesser craters earth would probably have developed early on. The moon does not benefit from such things. I am sure there is more to it but this is based on my rudimentary knowledge. |
Why can I not see many stars? | > I see pictures like this: _URL_0_ and long to see this sight for myself. I think those types of pictures are taken using decent cameras with high ISO settings and a long exposure time (maybe 25 seconds or more). They don't reflect what you'd see with the naked eye, unfortunately. Here's one photographer's rendition of what he saw vs. the picture from his camera: _URL_1_ |
If the big bang expanded faster than the speed of light, doesn't that contradict the fact that "nothing travels faster than the speed of light"? | The constraint on velocity regarding the speed of light is a product of special relativity, which does not apply to distant objects in between which space itself is expanding. Indeed, when taking the expansion of the universe into account, there are galaxies receding away from us faster than the speed of light. Unless the expansion slows down, we will never observe their current state. |
What do blind people see when they dream? Assuming they were blind from birth. | Surveys have been done on this very subject. A lot of the results found that people with congenital blindness often report experiencing other senses while dreaming while almost none experienced any visual dreams. For example a lot of studies using participants of three different categories (congenital blindness, later onset blindness, and those not blind) reported that those with congential blindness often had dreams where they had sensations of smell, taste, touch, and mostly sound while almost none of them reported having any visual aspects to their dreams at all. People with later onset blindness after age 1 found that the longer they were blind, the less visual representations they found in their dreams. |
Why doesn't the earth rotate around the centre of the milky way, but instad rotates around the sun? Wouldn't the centre of the galaxy have a larger gravitational pull? | The earth does rotate around the center of the Milky Way, along with the Sun and everything else local. Keep in mind that the center is *really* far away - and since gravitational attraction goes as 1/distance^(2), it's significantly less of a factor than the Sun's pull. According to Wolfram Alpha, the difference is about [19 orders of magnitude](_URL_1_), while the difference in mass is about [12 orders](_URL_0_). Hence, the gravitational attraction from the center of the galaxy is (very) roughly 10 million times weaker than that of the Sun. |
How excentric is the solar system's orbit around the gravitational center of the milky way? | The words you are looking for are apogalacticon and perigalaticon. The eccentricity of the sun's orbit about Sagittarius A\\\*, (the center of the Milky Way galaxy) is 1.07, which leads to a difference of about 15% between apo- and peri- galacticon. This leads to the two points being about 27,0000 and 31,0000 light years away from the center point. |
Does our sun have gravitational pull on the closest star? What about very far away stars? | Yes, there is no limit to the range of gravity. However, the strength falls off with the square of the distance, which means that the gravitational pull between two stars is extremely low. The gravitational acceleration felt on Proxima Centauri, the nearest star other than the Sun, due to the Sun is 16 orders of magnitude (that's a factor of 1 with 16 0's) smaller than the surface gravity we feel on Earth and about 13 orders of magnitude smaller than the gravity the Sun exerts on the Earth. |
Do planets have an effect on the stars they orbit? Or are they largely irrelevant as far as the star is concerned? | They do have a small effect. A planet doesn't just orbit a star; the planet and star orbit each other. Since the star is much more massive, its orbit is very small, usually smaller than the diameter of the star itself. But by very carefully measuring either the position or velocity of a star we can sometimes detect the small movements caused by the gravity of its planets, which allows us to indirectly detect the planets. This is what the Sun's orbit looks like compared to the size of the Sun (the curved line is the path of the barycenter relative to the Sun, so if you imagine that point as stationary the Sun is moving around it). Most of this is due to the gravity of Jupiter, but all the planets contribute: _URL_0_ |
Why is it that sunburns aren't as prominent on scar tissue as on "normal" skin? | Scar are actually more susceptible to sunburn than regular skin. I cannot say whether it shows more or less but I can say that skin scars are damaged more in sunlight as they may have less protective features. Sunlight [damages collagen](_URL_1_) and [scars](_URL_0_) (and skin) contain a lot of it as well as doing lots of other damage to DNA and other molecules. Sunburnt skin looks red and feels warm because of increased blood flow to the site of injury (slight swelling probably also occurs). Scars may not look as bad because blood flow might not be increased to the same extent. Scar tissue does not have the same vasculature and so would not appear as red but I can assure you is it damaged. |
High Fructose Corn Syrup is about 55/45 fructose to glucose, and sucrose is 50/50 but a disaccharide. In a mildly acidic environment (the stomach), the disaccharide is cleaved. Is there any merit to hating HFCS? | There is a doctor at UCSF who has gotten a lot of press about this. He claims that it's not only the higher amounts of fructose, but the fact that when you eat sugary foods that are more naturally occurring with fructose, that you also consume fiber with it. In my experience, most highly processed foods with HFCS do not have significant amounts of fiber. I'm not a biochemist, but he goes through some simplified example biochemical cascades caused by consumption of fructose and how the harmful effects of this can be somewhat offset by fiber. He has a youtube video giving a talk about this, if you want to understand his point: _URL_0_ Edit: added UCSF |
What do the true orbits of planets and around the Sun look like? | It's pretty close to a flat plane for the planets _URL_0_ There's a lot more variation for dwarf planets, asteroids, and comets, though even then most orbit in more or less the same plane. What you probably don't have is a true sense of scale (because most people don't). Space is *really big*. _URL_1_ gives a great perspective. |
Why is water in oceans/seas salty? | All natural water has some salt content, but in fresh water it's just too little to notice. Lakes have rivers/streams that take water out to keep salt from building up. In the ocean, there's no flow of water out, just evaporation, so the any salt dumped in there from the rivers stays there and doesn't go it. It just keeps building up. Some lakes that have no water flow out are also salty, (Great Salt Lake, Dead Sea, etc.) |
How exactly is vitamin D absorbed through sun light? | There precursor to vitamin D can be found in the skin (7-dehydrocholesterol). When it interacts with UV light, a reaction occurs that converts 7-dehydrocholesterol to vitamin D3 (cholecalcipherol). This is not bio active though. Cholecalcipherol then goes to the liver where it is hydroxylated to 25-hydroxycholecacipherol. THEN it goes to the kidney where it is again hydroxylated to make 1,25 dihydroxycholecacipherol . . . otherwise known as bioactive vitamin D |
How do we 'hear' our own thoughts? | A similar thing I often wonder is how do we "see" images that we are imagining or remembering? For example, if I'm caught in a daydream, I not only feel like I am looking at the image, but that I am *not* looking at whatever is actually in front of my face. |
Why is the ocean blue? | When you look at something, the color you see is the color of all the light that *wasn't* absorbed by that object. Similarly, water looks blue because it tends to absorb all colors of light very well except for blue light. |
For other planets, how do scientist determine which pole is the North one? | [Here](_URL_1_) is the International Astronomical Union's definition for bodies in the solar system. Perhaps a similar definition could be applied to other bodies not in our solar system, using the galactic plane as a reference (potential problem: I'm not sure if we have accurate measurements of the invariable plane of the galaxy though, so I'm not sure if this could be done)? I really don't know. I haven't been able to figure out how or if it's done for bodies outside of our solar system, so here's how I would imagine doing it: Perhaps you could simply define the geographic north pole of a whole star system to be that around which the orbit of the planets is seen to be counter-clockwise (like it is in our solar system), when viewed from "above". Then you could simply reapply the IAU's definitions to that star system to identify north and south poles of planetary and smaller bodies. |
How often do asteroids impact the sun? What happens when they do? | Comets have been observed and recorded impacting the Sun, see e.g. [SOHO spacecraft sees two comets plunge into Sun](_URL_0_). [This article](_URL_1_) describes a case where a comet impact "appeared to interact with plasma and magnetic fields in its surroundings as it fell apart." (That's distinct from the above example, also mentioned in the article, which was followed by an apparently unrelated coronal mass ejection on the other side of the Sun.) Other than that sort of interaction, comets and asteroids are very tiny compared to the Sun, and such impacts have no lasting effect. |
Which uses more energy, an empty refrigerator or a full refrigerator? Or does it matter? | Assuming the system is at steady state, both will use the same amount of energy. |
What is the octane number mean for petrol? | Octane number tells you how resistant is the petrol to premature combustion. In the engine, when piston is pushed in the cylinder, the petrol may combust before the piston s pushed to the limit, which is not cool for the engine. There is a thing called iso-**octan** (to be more specific - [2,2,4-trimethylpentane](_URL_0_)) and it doesn't like to combust much, it's octane number is 100 (just by universal agreement, it's a relative number). And there's another thing called [n-heptane](_URL_1_), which combusts at any little given reason, it's octane number is 0. When your petrol's octane number is 95 it means that if I mix 95% of octane and 5% of heptane, my petrol will combust just as likely as yours. BTW, there are plenty of things with octane number more than 100 or less than 0. |
Why do bubbles in carbonated drinks or beers form from imperfections or scratches in glass? What causes them to form from surface imperfections vs randomly within the liquid? | Those imperfections act as nucleation sites. In your example they help with the physical separation of the gas (carbon dioxide) from liquid (water). When you open the bottle some of the carbon dioxide dissolved in the water wants to leave (pressure change) and go into the air but it can't because the individual CO2 molecules cannot overcome the viscosity of the water. The nucleation site provides a place for CO2 molecules to aggregate and form bubbles capable of breaking the hydrogen bonds of the water molecules. Without the imperfections there is nowhere for the CO2 molecules to coalesce. |
Has sleep paralysis been observed in a scientific setting? | Yes, in fact [sleep paralysis has been experimentally induced](_URL_0_). Basically what was seen from objective measures is that the brain appeared awake, while muscle activity was suppressed. The measure of brain activity in this study, however, was just two EEG leads (central and occipital). While this is sufficient to discriminate sleep from wake, identify sleep stages, and has good temporal resolution (i.e., can detect high frequency oscillations) it does not have good spatial resolution, so it can't tell you what is going on in very specific areas of the brain in the same was as fMRI can. |
How come giant meteors never hit the earth anymore? OR Statistically, when will the earth get hit by a giant meteor next? (BONUS: Is 'meteor' the right word to be using?) | > or we're due for one. This simply isn't true. The probability of being hit by a large meteor has nothing to do with how long it's been since the last hit. It's a great example of the [gambler's fallacy](_URL_0_). |
Does outside noises and other stimuli impact the dreams I have? | Yup. In [this study](_URL_3_), they randomly spoke names as people were sleeping, which were then incorporated into those dreams. Even other kinds of stimuli will work. [Dement and Wolpert](_URL_2_) were able to successfully incorporate water and light into people's dreams. And then there's [this study](_URL_0_). What they did here was to present a mild electrical stimulus to the median nerve as the participants slept. The stimulation would cause the person's finger to move by activating the nerve (and provide feedback to the brain of the movement, but not the motor plan to cause the movement). Even this type of stimulus was incorporated into the participants' dreams. Just a note that none of these techniques work 100% of the time, and they were all induced during [REM sleep](_URL_1_). |
What percentage of dry matter in plants is carbon from CO2 origin? | It is not necessary for any carbon to originate from the soil. For example, [hydroponics](_URL_0_) can grow plants without a soil medium. |
What fraction of a plant or tree’s mass comes from carbon fixation in photosynthesis? | Essentially, all of it minus the water (of course there are minerals, nitrogen, etc. that would’ve been taken up from the soil, oxygen from the air, but that would likely be negligible) - essentially all of a plant’s biomass is derived from fixed carbon. It’s also going to differ from species to species and plant to plant. For instance, seaweed or moss would be almost completely water, while a tree, which puts much more effort into developing thick cell walls would have a greater proportion of its weight derived from carbon sequestration. The same plant in drier/wetter periods will also differ depending on how much water it has absorbed/stored. So yeah, there’s no universal answer |
Why does olive oil make paper a lot more transparent than water does? | The reason is that there is a better match of the refractive indices of olive oil and the fibers in paper than is the case with water. First, let me backtrack a bit to explain why paper is opaque in the first place. It turns out that the fibers in paper don't absorb light strongly in the visible. However because the medium is so inhomogeneous (e.g. see [this picture](_URL_0_)), there are a large number of scattering centers such that most of the light ends up being scattered before passing through the paper. Now what happens when you put oil is that because it has a similar refractive index to the fibers (about 1.5), you essentially create one effective medium that is much more homogenous, which in turn reduces scattering significantly such that the paper becomes quite transparent. Now water has a smaller refractive index (1.3), albeit one still larger than air (1), which means that scattering is still reduced, just not to as large an extent as when oil is used instead. |
Is it possible for a high powered laser to burn through a mirror (or other highly reflective surface)? | Yes. A sufficiently high power laser would produce enough heat to quickly destroy the reflectivity of the mirror. Additionally, you could use a laser of a wavelength that the mirror does not reflect (e.g., an IR laser on a non-IR reflective mirror). |
If Solar panels were at 100% efficiency, would putting one on the roof of an electric car be enough to keep it perpetually running? | A car engine's power output is measured in horsepower. 1 hp = 745 Watts. Most cars have upwards of 50 hp (small engine, small car) and typically over 100 hp. On a sunny day with no clouds and with the Sun high in the sky you can get around 1000 Watts per square meter (less if the Sun is low or there is cloud cover). A typical car takes about 7-8 square meters. So the total energy that falls on the car is around 10 hp. So, it would depend on the weight of the car. And you won't be able to run it any longer than there is Sun out. |
Is our universe rotating? | This is actually a very deep question that physicists have struggled with for a long time: _URL_0_. For example, there are ways to tell that you are on a rotating planet, even if you were deep in a cave without any ability to reference the ``fixed'' stars in the sky: _URL_1_. Great question. |
Is reading a text while listening to an audio version of the text any more beneficial for the uptake of information than just reading alone? | I would say the opposite as /u/Science4Neon. Hearing the text would evoke certain responses in the brain - different connections and memories, painting a certain picture. Reading the text would likely evoke some of the same responses, but odds are there will be some that are much different. A good example would be hearing a song versus reading the lyrics. A person can know all of the words to a song, but until they see them written, the meaning may be lost. The opposite may be true as well. Yes, if you are a visual learner, reading may be more beneficial than hearing, but what is the harm in doing both? Especially in the case of Shakespeare where the inflection and context of what is written may not be immediately obvious (unless you are familiar with the older English style of writing...) |
What distinguishes a tensor from just being a fancy way to define a matrix? | Just like a vector is not just an ordered set of numbers, a tensor is not either. Vectors and tensora are geometric objects, whose components transform a certain way. A matrix or a row/column are just ways of representing the components of a tensor or a vector in a given basis. |
What happens to a fruit when it gets bruised at the molecular level? | The cell walls in the bruised area rupture, allowing the sugars and other organic molecules inside to leak out. This creates the soft texture of bruised fruit. Oxygen molecules from the air diffuse in and react with the organic molecules via an oxidizing enzyme ([polyphenol oxidase](_URL_0_)). The enzyme acts like scaffolding, holding the oxygen and the organic molecule close to each other in such a way that the reaction energy barrier is low. The resulting oxidized molecules are often brown in color, leading to the characteristic bruised appearance. _URL_1_ |
Why was entropy so low at the beginning of the universe? | We have no idea! This is one of the great mysteries of cosmology. You'll hear it argued that this is even the reason we have an arrow of time: time goes in a particular direction (that is to say, forward) because of the second law of thermodynamics, but we need to start off in a special low-entropy state in order to even have that evolution in the first place. For now, that low entropy has to take the form of an initial condition. One would hope that whatever Final Theory of Absolutely Everything we find one day will explain that in a nice and natural way. But that is a long way off. Sean Carroll's book "From Eternity to Here" is supposed to be an excellent and well-explained discussion of this for laymen. In fact, he loves talking about this stuff, so you might consider reading his [FAQ](_URL_0_) on it (not to mention his many blog posts on the subject) or a [video](_URL_1_). Because frankly, Sean's been thinking about this stuff for a lot longer than I have and will explain it much better! |
Why isn't the sky completely white at night? | You've hit upon a very old question called ["Olbers' Paradox"](_URL_0_). The solution relies on the fact that the universe is not infinitely old, so only finitely many stars and galaxies are observable and they collectively subtend an angle on the sky much smaller than the full sky. |
Why does milk help with spicy foods/sauces? | Capsaicin (the chemical compound that is "spicy") is a base that binds to certain receptors in your mouth. These receptors are activated when that binding occurs, and stay activated until the capsaicin is removed. Milk has a protein called casein that strips away the capsaicin, turning off the receptors and giving you some relief. |
If you rubbed sunscreen on a window and stood behind it, would it protect your skin from UV rays? | Most glass already filters out the majority of harmful UV rays, however it would in fact work. Sunscreen works simply by adding an opaque-to-UV layer on top of your skin, so doing the same to a pane of glass would have the same effect. |
If a sufficiently large asteroid came close enough to Earth to interact with the atmosphere, but didn't collide with Earth itself, could it heat the atmosphere to a catastrophic degree? | It would have to be a planet sized object (or a very dense object like a neutron star) to disrupt the moon's orbit. As for heating the atmosphere anything large enough to heat it would be large enough to impact. Take the Tunguska asteroid, it caused massive devastation, but not enough to be catastrophic (and also was luckily in Siberia) and not globally, it was very localized. |
Since heat is lost very slowly in space, do asteroids have any of their "original heat" left from their formation or collisions? | The original heat as you call it would be the gravitational potential energy that get released when the parts of the object fall together an form the planet/moon/asteroid. While it takes time to dissipate this heat it works best for smaller bodies as they have higher surface to volume ratio. As Heat is lose is proportional to the surface area while heat capacity is to volume. That's why you get bigger penguins in the Antarctic compared to the ones further north. For heavenly bodies this means asteroids will be cold very soon after they have formed. For Earth sized objects the value is somewhere around 20-400Myr* if accounting for potential energy only. Jupiter and Saturn show some excess radiation that isn't accounted for by solar energy input. As far as I know one theory is that it's left over formation heat that gets released. |
Why can't I remember being an infant if I remember the language I learned at the same age? | If you learned a language as an infant and stopped using it before about 3 years of age, I would be surprised if you could remember any of it. Language is something that you're constantly drilled on in daily life, just by the process of interacting with people around you. You learned it then, but you're still having it reinforced now. |
How can very small children remember language, people, etc. and yet not retain any memories? | Associative learning is intact even in baby insects. Babies *are* forming and retaining memories, but they're doing it at the same time that they're forming a hippocampus, the structure that will be used for conscious learning and memory down the road. It's present at birth, and used off and on throughout infancy, but takes a while to shape up and become the default assembly tool of sensory information. tl;dr: They retain memories, even at birth, but they aren't consciously learned, or even consciously accessible till the brain structures are in place. |
Why do the sounds of rain seem to help humans sleep? | In [this(pdf alert)](_URL_0_) study they found that 80% of babies fell asleep with white noise as opposed to 25% when white noise was not present. Like white noise, the sound of rain is (ideally) an unchanging constant source of noise which can cause the brain to "override" other noises that occur that may cause a person to wake up. In addition to that, many people simply find rain to be comforting and soothing, and so they will be in a more relaxed state as they try to go to bed. Based on that I would say that if you find yourself being woken up by random noises during the night or have a hard time turning you brain "off" at night, then pulling up sounds of rain may indeed be helpful for you. |
What is happening when gasoline "goes bad"? | The gas we put in our cars is a very carefully balanced compound of chemicals, intended to work with carefully engineered engines. When it sits there for too long, some parts (lighter hydrocarbons) will evaporate, leaving a mixture of gasoline that your engine may not be able to handle. Also, don't forget that chemical reactions will happen to the gasoline as it's sitting in the sealed environment. If there's air in the tank with the gas, it will start oxidizing, possibly even forming a solid gum that can constrict or block the gas line. _URL_0_ |
What are the physical differences between 'cheap' and high quality vodka? | The ingredients play a big part. While you might imagine that no-taste means it is the best vodka, many would disagree. Selection of ingredients and the process usually determine the quality and taste of the vodka. While Grey Goose is wonderfully tasteless, Chopin, or some other high quality vodka is far smoother because of the slight flavouring. If you asked what these added flavours are, you would probably be told they were a secret. Of course, lack of fusal oils (unwanted byproducts of productions) does remove some of the nasty tastes associated some cheap vodkas. |
How does soap wash away bacteria? | There are 2 main categories of contaminants that you can have on your hands. There are water soluble contaminants and fat soluble contaminants. Rinsing with water is sufficient to remove water soluble contaminants. However, unless soap is used, fat soluble contaminants will largely remain on your hands. Bacteria can live in oils//fats on your skin. The purpose of soap is to wash away fat soluable contaminants. You are incorrect that bar soap is self-cleaning as bacteria can and do live on the surface. Soap does not kill bacteria unless it is antibacterial soap. Antibacterial soap is not recommended as hand soap because it is bad for the skin. Realistically, it is unlikely that your friend will have harm befall her as the result of her refusal to use the bathroom bar soap. As most people are aware, the majority of bacteria are harmless. |
What is the effective actual brightness in relation to the human eye of planetary objects in the distant solar system? What I mean is: are photos of Saturn the brightness they are due to long exposures or would they actually be relatively dim objects due to their distance from the sun? | You can see most of the planets with your bare eyes on a dark night, except Mercury (because of its small size and because it is usually only visible at twilight due to its proximity to the sun) and Uranus/Neptune (too far away, but you can see with a good pair of binoculars). Most pictures of outer planets are taken with a good zoom lens and a long exposure. If you stay up until about 5am tonight you should be able to see Saturn. If you have good vision you might be able to make out its rings. |
Why do animals yawn? | _URL_1_ [Wikipedia](_URL_2_). One theory is, when our blood contains increased amounts of carbon dioxide an influx of oxygen (or expulsion of carbon dioxide) is required to prevent oxygen starvation of brain tissue. Other theories claim the yawning helps regulate body temperature when the subject is not perspiring. Since dogs do not perspire, I'm more inclined to agree with the first theory. _URL_0_ |
Can Astronomers actually see other galaxies rotating, other stars moving, and other such events in "real-time" or does space appear to stand still? | [These](_URL_1_) are the remnants of the supernova that exploded in 1987. [These](_URL_0_) are the locations of stars around a very massive, invisible object in the center of our galaxy. [Barnard's Star](_URL_2_) is moving pretty fast, by star standards. In all of those you'll notice that things are changing over the course of several years. If you're lucky enough to be looking at a galaxy as a supernova explodes you'll see [a very bright star appear](_URL_3_) and then fade over the next few weeks. You won't see galaxies rotating or anything like that. That takes millions of years. If you watch Alpha Centauri for long enough, you'll see the two stars rotate around each other in 80 years. |
Does the heat from other stars affect our temperature on Earth? | Technically yes, since energy is arriving on Earth, but the effect is negligibly small. A quick approximation is "how bright is a moonless night compared to daylight?" That gives you a zeroeth order idea of how much of a difference it makes. There are other things to include if you really wanted to, like light in other wavelengths than optical, which for the most numerous stars (red and brown dwarfs) is most of what they emit, but it's going to be an adjustment to the baseline answer of "Not really." The small changes in the Sun's luminosity cause a larger effect on Earth's temperature. |
[Biology] What is that tingly chill sensation you get in your nose before you sneeze? | Well there seems to be a lot that goes into a sneeze. Muscus linings being irritated, nerve endings being stimulated, chemicals like histamine being released, muscles in your neck and head being activated, and a psychological component. I'm not entirely sure which part the tingle happens, but here's a link on the science of a sneeze. _URL_0_ |
Why is thunder often a long and low rumble with multiple "impacts", when lightning itself is a very quick event? | * Lightening [isn't a single event.](_URL_0_) There are typically 3-4 strikes in a single "lightening bolt". * The sound from a single bolt doesn't reach you all at the same time. The top of the bolt is farther away from you than the bottom of the bolt, and the sound takes longer to reach you. * Echos. Thunder bounces off of everything. A significant amount of what you're hearing is an echo. * Refraction. The different layers of the atmosphere have different densities and sound propagation, which means they will bend sound. The conditions that lead to a thunderstorm results in even greater differences in refraction than normal. The sound from the part of the lightening bolt in your layer will travel to you relatively directly, while the sound from the top of a lightening bolt will often take a rather arching path to get to you. |
Why does thunder rumble for several seconds when the lightning strike is only a fraction of a second? | Even normal sound compresses air. That's how the wave works. The thing is, when a gas is compressed, it heats, causing it to rebound faster than it was compressed. Lightning heats up local air _a lot_, causing a local expansion that kind of 'reverberates' as the heat spreads out slower than the speed of sound. Another factor is that the flash is only the middle part of a lightning strike. Electricity is conducting and heating air before and after the strike, but at levels that aren't producing light you can see. The strike isn't as brief as we imagine. Finally, lightning is not a _point source_ of a sound. It's this big winding column or web in the clouds that can be very long indeed. Sound from different parts are reaching you at different times. |
Can a laser cut a mirror? | Three answers for you today: 1) Theoretically no, not if you had a perfect mirror that reflected 100% of light. However this is currently impossible. 2) Theoretically yes if you have a strong enough laser, and a thin enough mirror. Mirrors do not reflect 100% of light especially the shorter wavelengths. The light which is not reflected is absorbed and would heat up and cut the mirror much like typical laser cutter cuts plastic. 3) Realistically no. To date even high end laser cutters have difficulty cutting through metal unless it is thin gauge. An impressive commercial laser cutter can cut through up to 0.1875" mild steel, but only .075 Stainless steel, and even less for brass (.040"). *Note not all of the thicknesses here are based solely on the reflective properties of the metals, but that is a big part of it. Also those thicknesses are based on the manual I have for a Kern Laser System. |
Why is the boiling point of hydrogen higher than helium? | Helium is less polarizable than hydrogen (or H2) because its nucleus has double the charge, yet its electrons lie in the same shell. The same effect makes helium atoms smaller than hydrogen atoms. |
If the universe is expanding at an incredibly fast rate then why do nearby celestial bodies (such as the sun and the moon) stay the same distance from Earth? | It has an effect, but the solar system is (comparably) so small that it produces effects that we cannot in any way measure. The distances over which expansion is significant is much much bigger than the distances in the solar system (to give you a hint, the hubble constant which governs the expansion of the universe is measured in km/s per megalightyear. The solar system is not even a light *day* across). To add to that small effect, gravity works against the expansion. This means that the effect on the solar system becomes negligible. So small in fact that over the lifetime of the solar system the fractional change of the radius is in the order of 10^-24 . edit sauce _URL_0_ |
Is a bottle of still water heavier than one of sparkling water? | I believe that a saturated solution of carbon dioxide in water is very slightly more dense than plain water (about 1.01 or 1.02 g/mL). |
Why is plant DNA so much more complex than animal DNA? | Their genomes can be larger, but larger did not necessarily mean more complex. That being said, there tend to be fewer constraints on the genes of plants. Animals, at least bilateral animals, have very tightly-regulated developmental plans involving large numbers of genes that must work in concert. Plants, on the other hand, have much more flexible developmental plans. This means they are better able to cope with copies of genes, new genes from other organisms, or even entire extra chromosomes without suffering negative effects. This will tend to result in having more genes, more duplicate or closely-related genes, and more "dead" genes in their genomes on average than bilateral animals under otherwise similar conditions or constraints. |
Are there significant and recognizable differences between the structure of most plant and animal genomes? | So I'm far from an expert on plants, but I'm going to link some cool review articles below. Feel free to PM me if you have any questions. _URL_2_ _URL_0_ _URL_3_ _URL_1_ |
Do animals with short life spans (like insects) evolve more rapidly than animals with longer life spans? | The two major factors are 1. population size and 2. generation time. Turns out that rates across all kinds of groups tends to be somewhat similar because the two factors work in opposite directions. Large population sizes mean slow evolution, but these also tend to be small organisms with a short generation time. Small population sizes are typical of large organisms with long generation time. |
How far up the atmosphere does helium rise, and what happens to it? | A large part of it disappears into space. There is only a finite amount of Helium on this earth as it is formed from Uranium decay and/or in suns (there are perhaps other processes that do the same but these are the main ones as far as I know). This is why we should only use Helium for serious things - floating balloons are bad. |
How can humans share 60% of our genes with bananas? | One way to think about it: how much does a smart phone have in common with a refrigerator? Basically nothing, right, they're totally different in size and purpose. But think about it. Both contain steel, plastics, and glass. Both have circuit boards. Those circuit boards have fiberglass, copper, gold, and semiconductor chips that contain silicon and plastic. Remember, DNA describes *everything*, both the big obvious shape stuff you can see, and the basic chemical structures you can't. The DNA sequences that humans share with bananas include instructions on how to build a cell membrane, how to create the amino acids that form proteins, how to assemble those proteins, how to build DNA itself, how to replicate and maintain it, etc. |
Whitening tooth paste | Whitening toothpaste and floss do not whitening your teeth. The two requirements for whitening to occur are 1. contact time and 2. concentration. You do not get the adequate contact time or high enough concentration for whitening to occur during your 2 minutes ( if you even brush that long) brushing time. |
How is the sun even formed when the same process forms planets? | Massive planets the size of our Sun can't exist. This is because gravity causes mass to be attracted to mass and, within a uniform sphere (by Newton's Shell Theorem) this means that gravity gets stronger as you get to the middle. So at the middle of the Earth is molten rock due to the extreme pressure due to gravity. For larger objects more of the middle is molten rock. For an object as big as the Sun, the middle isn't just molten rock but it is hot enough for nuclear reactions to occur. All of this heat escapes to the surface via heat transfer which also melts (or even ionizes in the case of the Sun) the surface material. It becomes a ball of plasma due to heat due to the pressure of gravity and is no longer considered a planet but a star. |
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