question
stringlengths 19
300
| answer
stringlengths 28
1.02k
|
|---|---|
If you were to travel to another star at near the speed of light, would you see events occurring on the star twice as fast as the normally would be? | The speed of light is the same in all reference frames. Therefore, even if a person is moving at near-light-speed, the light from that star will arrive at the same rate. The changing variable is the amount of time that passes for each observer. The person traveling at high speed will not see as much time pass, while the observer on the 500-light-year-away planet will see at least 500 years pass. It's difficult to think of these issues in terms of ideas like "light catching up" because time itself shifts. |
Did the big bang occur in all directions? I often hear that we can only see 13.?? billion light years before we can't see anymore, but isn't there technically another 13.?? billion light years worth of material beyond the initial bang, just in the other direction? | The misunderstanding here comes from your idea of the "center" if the universe. There isn't one. Every point in the universe appears to be moving away from every other at the same rate. The *observable* universe " on the other hand is spherical centered on the earth, because light has only had the age of the universe to reach us we can only see the age of the universe in every direction, making a sphere (called a Hubble sphere) If you were on any planet in the universe you would only be able to see the age of the universe away from that planet. |
The oldest known star has recently been discovered. Scientists believe it is ancient because of its low iron content. Why do old stars have a low iron content? | Shortly after the big bang the universe was about 75% hydrogen, 25% helium, and very small amounts of lithium. That was all that there was to form the first generation of stars. As these large massive stars went through their life cycle they fused these primordial elements into heavier elements in their cores, just like stars today. Large stars go supernova when they start producing iron and when they explode they seed the gas and dust clouds around them with heavy elements. This means that later generation stars have a higher metallicity than early generation stars, since the later generations are formed from these seeded clouds. |
"Our Sun is unusually metal-rich for a star of its age and type." -- What does this mean? | Metals come from supernovas, so the presence of metals in stars means that the star was formed from the nebula of a previous star that died. The more metal, the more generations have come and gone before it. So when they say it's unusually metal rich, they could be saying that our galaxy went through many quick successive generations of large, short-lived stars before our star was born. |
Is it possible for organic life to exist that isn't carbon-based? | No, by definition. Organic materials must contain carbon. As for carbon based life, it's possible in theory. Silicon is the most likely contender since it can form similar molecules to carbon. |
Does fruit lose some of its nutritous value when it is blended into a smoothie? | No, why would it? You essentially "blend" the fruit in your mouth while chewig it. The chemicals that make up the nutrition in fruits are stable enough to withstand the kinetic energy applied by the blender. That is of course only the case if you drink it right away, because blending a fruit practically destroys the protective shell of the fruit, so the chemical compounds get broken down by bacteria and light more easily. TL;DR: The fruit doesn't lose anything if you consume/conserve it after the blending. |
Are the orbits of the solar system coplanar to the Sun's orbit around the milky way? | I'm seeing a lot of responses here based on some popular YouTube videos that are based off of a gross misunderstanding of even the most basic principles in physics. I found a site that explains why these ideas are wrong and how somebody could make such mistakes. _URL_1_ |
Can anyone explain in simple terms how the CRISPR technology works in gene editing? | CRISPR uses a protein (cas9) to make double stranded cuts in DNA. The natural double stranded DNA repair mechanisms in the cell, chew the DNA back from the break to generate the single stranded DNA ends needed to complete the repair. The result of this is that he DNA at the site of the damage is lost. Cas9 requires a guide RNA to direct it to the DNA. The guide RNA matches a unique sequence in the DNA. In this way you can make Cas9 cut the DNA anywhere you choose by selecting the sequence of the guide RNA. CRISPR gets fancier too. You can include various other components that match the region of the DNA you are causing the double strand break in. These will be used as templates to repair the DNA. You can include new DNA in these regions to introduce a gene, or even a mutation in an existing gene. |
Can fire burn things in space? | [On the right](_URL_0_) is what a flame looks like in microgravity. The hotter gas no longer rises, so it stays in that spherical shape. The blue part of the flame is the hottest, so that could definitely burn something. Of course, this is all within an enclosed oxygen filled environment. Out in the vacuum of space there is no oxygen so fire chemistry doesn't occur. |
Why does certain skin get sunburned, yet other skin (i.e. your hands, toes) does not? | I'm no expert, but my theory is that some skin is less exposed to sunlight. I've definitely gotten sunburned on the tops of my toes after spending a day barefoot at the beach, and I've gotten sunburns on the backs of my hands too. Generally, the soles of your feet and palms of your hands are shaded by the rest of your body, so they don't get burned. |
How much plant matter could be made from the carbon contained in a diamond. | Plants are mostly linked cellulose fibres (C6-H10-O5)*n, which is 44% carbon by weight. 0.5 grams of carbon could be combined with some hydrogen and oxygen used to create 1.12 grams of plant. |
Would it be possible to make a much harder material than diamond by forming an allotrope of a different element, or is Carbon the best option? | There are other materials that have a hardness greater than diamonds, though most are some allotrope of carbon. A pretty good summary of four can be found [HERE](_URL_1_). Scientists can produce substances harder than diamond, but it takes a lot of effort and energy. Diamond has a moh reading of 10. Pure, lab created [Lonsdaleite] (_URL_0_) has a moh scale reading of 15.8! Much harder than diamond. Unfortunately, when it forms naturally it forms with lots of impurities and only when a giant meteor crashes into the earth. |
If 25% of a liver can regenerate into a whole liver, can you cut out 25% of your own liver and save it if you ever needed a new one? | Assuming you could store it safely for long enough, probably. I know that it's possible to take 50% of someone elses' liver and transplant that into another person rather than moving the whole liver, so that part of the procedure is sound. You'd need a pretty nifty way of storing it for any length of time though, and it'd probably be fairly expensive. |
If livers regenerate, would it be possible for me to donate half my liver, grow it back, then donate it again? If so, how many times can one repeat this process? | No, you can only donate your liver once, mostly limited by the fact that not just any part of the liver can be sliced off and be able to fully regrow. There are two (main) lobes in the liver and each has a full set of connections needed to connect to the rest of the body (an artery, vein and bile duct). They take one of the lobes, and the remaining one just gets bigger to compensate, the taken one does not grow back. |
Why does pouring boiling hot water sound different than pouring cold water? | Because water is a rather odd material; the speed of sound changes very dramatically inside water between 0-100C (over 100 m/s diff.). This effects sounds that interact with the fluid (such as it travelling inside a pipe into a glass). _URL_0_ |
Does alcohol really kill your brain cells? | No. Over-consumption of alcohol does impair communication between brain cells by damaging the dendrites (the part of the brain cell that receives messages from other brain cells), but it does not kill the cells outright. However, severe alcoholism can lead to a disease called Korsakoff's syndrome, which can cause loss of brain cells in certain parts of the brain and thus lead to cognitive decline. It isn't caused by the alcohol itself, but rather by thiamine deficiency which is common in malnourished chronic alcoholics. Alcohol impairs the body's ability to absorb thiamine. TL;DR: Not directly, but too much alcohol + nutritional factors might. |
Could a moon have its own moon? | Seems like it would be difficult, but not impossible. [Article](_URL_0_) |
How does the ozone layer heal itself? | Radiation from the sun is absorbed by diatomic oxygen molecules in the upper atmosphere and the energy breaks the molecular bond. Some of those free oxygen atoms recombine with diatomic oxygen to create ozone (O3). |
How does the ozone layer “heal” itself? | Lightning creates ozone naturally. Possibly other phenomena does so too. Ozone doesn't last forever with or without CFCs, but with CFCs in widespread use it was depleted far faster than it was created. Now, it is being created faster than it is being depleted. This will continue until a new equilibrium is reached (likely very similar to pre-CFC levels). |
If gravity and light propagate at the same speed why does light come from where the sun use to be but we are orbiting where the sun actually is? | Check out [all these past threads](_URL_0_), and the [astronomy FAQ](_URL_1_). The short answer is that even though changes in gravitational fields propagate at the speed of light, [there are velocity-dependent terms that cancel out aberration](_URL_2_) such that you're orbiting where the sun "would be" based on 8-minute-old information. |
Why does the moon go red during an eclipse? Why not black? | It's the same thing that makes sunsets red: [Rayleigh scattering](_URL_0_). Think about it from the perspective of the Moon: the Earth is blocking out the Sun, but there's still some sunlight diffusing around the edges of the Earth's atmosphere and therefore visible to someone on the Moon. However, since this light has traveled through the atmosphere, the blue photons have mostly been scattered whereas the red photons are mostly still traveling in the same direction. So the light that reaches the Moon is red because the Earth's atmosphere filtered out the blue. |
Why does a lunar eclipse turn the moon red and not completely black? | Atmospheric refraction/lensing. Light that passes through the Earth’s atmosphere that doesn’t hit the surface will be bent around the curvature of the Earth by refraction and leave the atmosphere at a different angle. Here’s a decent diagram demonstrating this: _URL_0_ |
It has been reported that the cancer death rate in the U.S. has declined 20 percent over the last 30 years. Why hasn't life expectancy increased? Have we reached a fundamental limit? | Actuarial analyst here. We work with mortality all the time. Yes, life expectancy is growing slightly every year. New mortality tables are published every ten years and projected for years in between. However, if someone doesn't die from cancer, they'll just die from something else. Avoiding cancer doesn't necessarily mean you'll live longer. |
Why are our sneezes so powerful? | Sneezes use the diaphram... and yes you can produce this own power consciously. To answer the question of why, it's because it helps force out whatever's caught in your nose. |
Petroleum on Earth was created from living organisms. How was the petroleum on Titan created? | Petroleum does come from living things, you're right. The catch is that the liquid on Titan isn't petroleum, just a liquid formed by the gas molecules in Titan's atmosphere that were hit by solar UV radiation and stuck together. |
If I would to left a refrigerator open in a room, would the room temperature drop or rise? And why? | A fridge is a [heat pump](_URL_0_). It takes heat from inside it and dumps it outside, into the room. But this effort generates heat over and above the amount of heat moved, regardless of size, type, power etc, so the room warms up. |
Are there natural oil spills? | Yes, there are actually a lot of natural oil seeps. There are several offshore [California](_URL_0_), and many in the Black Sea on the Russian, Ukrainian and Georgian coasts. Oil naturally migrates upwards and if there is a pathway for it to reach the surface, it will. |
Can oil spills happen naturally? | Oil 'spills' would not be the best word for it. There are places on the southern coast of California and in the gulf of Mexico where oil seeps out of the ground, but its often unnoticed and occurs at a very slow rate. Also, this usually isn't pure crude oil, but a mixture of natural gas and other oils. A few species are able to consume the oil as well and live around these places. |
Does the sun have a solid and liquid surface like Earth? | The Sun has no liquids or solids. The entire Sun is plasma with the exception of some of the atmosphere (the outer few hundred km of the Sun) which is cool enough that not very much of it is ionized. There isn't any clear "surface" to the Sun, either. We often define the surface to be the photosphere, the place at which the optical depth & tau;=2/3, because this results in roughly one-half of the light we see coming from layers below the photosphere and one-half coming from layers above the photosphere. But there's no actual physical boundary at the photosphere. |
How does leg hair know to grow back when shaved? | Hair growth doesn't stop. The hair on your legs falls off long before it has a chance to get as long as the hair on your head, for example. See explanation here : _URL_0_ |
With space expanding everywhere, how is it that andromeda is on a collision course with the Milky Way? | This question is a very common one is one of our [Astronomy FAQS](_URL_0_) - the answer is located [here](_URL_0_/expansion_gravity). |
If the universe is expanding and there is nothing outside of it, then where do parallel universes (multiverse) exist? | Well I see it a bit like this: When you are on a planet and you go to the north pole, you cannot go further north. When you go to the south pole you cannot go further south. On another planet there exists another north and south pole. This is just an analogy. The north and south poles represent the boundaries of this universe, which is the planet in the analogy. The other planet is outside of the first one. The thing about the universe is that it encompasses everything that we know and have some understanding of. Another universe will be so outside of ours that we cannot know if it even exists. |
If the universe is still expanding, then how can there be parallel universes next to us? | It depends on what you mean by parallel universe. If you're talking about the many-worlds interpretation, where there's a "world" for each possible outcome of a quantum measurement, then those "worlds" all occupy the same physical space and should *not* be thought of as other universes. If you're talking about brane-world cosmologies as in some string theories, then it's kind of hard to visualize but the idea is that they're separated in a dimension other than our three spatial ones. For example, imagine that our universe were a two-dimensional surface. Maybe an expanding infinite flat piece of paper. The "other universes" here would be like other sheets of paper stacked above ours. |
Why does soft plastic packaging leak when thawed? | Are you sure it is not water condensing on a cold surface or a layer of ice on the surface melting? |
Why do bridges become icy/freeze before the regular roads do? | It's quite simple really: in the winter, unless you live in a polar region, the ground is warmer than the air. So a bridge that has cold air surrounding it on all sides will cool down faster than a road surface that is only being cooled down from above. |
How can my monitor show videos in 1080p, when its max resolution is 1440*900? | It can't show the videos in 1080p. What the monitor (or rather the graphics card) is doing is scaling the 1080p video down to 1440 by 900, typically by averaging multiple pixels in the source video in to the single pixel on your monitor. |
Is the Milky Way generally rotationally aligned the same way our solar system is? | No. The celestial equator (plane containing Earth's equator, separating the night sky into the Northern and Southern halves), the ecliptic (plane containing the solar system), and the galactic plane (containing the stars of the Milky Way) are all unaligned with each other. The relative angles are 23.4°, 60.2° and 62.9°. [_URL_0_](_URL_0_) Btw, there is only one "solar system", i.e., the system around "Sol", the other name for the Sun. Systems around other stars are called stellar systems. |
Can candles burn in zero gravity? | Yes. It was tested on a Space Shuttle flight once. [Here's](_URL_0_) a picture (on the right). |
Are there any moons we know of that rotate the planet at the same rate that the planet spins? | There is no planet like this, but [Pluto](_URL_1_) and its moon [Charon](_URL_2_) have this property. They are mutually [tidally locked](_URL_0_). |
Do atoms have color? And if not, where do colors come from? | Think of light as a portion of the EMR spectrum, so light of different colours has different wavelength, and different energies. Atoms/molecules/etc. can absorb certain wavelengths of light, and then when you minus out that wavelength (and respective colour) the remaining light will be the colour you perceive an object. For example, Copper Sulphate absorbs heavily at 570nm and slighty at higher wavelengths. This corresponds to yellow and oranges. As a result, Copper Sulphate appears bright blue. |
Will we ever be able to view exoplanets with a telescope? | Aloha... I work for an observatory where we do (among other things) exoplanet hunting (_URL_0_). As lorgfefikd mentioned, it has been done. We routinely find new exoplanets. However, our method for finding them currently revolves around watching for periodic disturbances in a stars brightness that indicate orbiting planets. That given, new instruments already in the design stage will allow us to get closer images - and more importantly, spectroscopic analaysis of the planets. While not as interesting, for most people, as a visual picture of trees and galloping alien beings - a spectroscopic analysis of a exoplanet will tell us things like does it have oxygen and water, does it support life. Does it support intelligent (industrialized) life, etc. |
Why are planets not tidally locked with the sun? | Given enough time, all the planets will become tidally locked with the Sun. The timescale involved though are in the billions - trillions of years (for the outer planets). How fast a planet becomes tidally locked depends on the mass of the star and the distance from the planet to the star. We have found exoplanets [tidally locked](_URL_0_) to their stars because they are so close to their host stars (some up to 1/5 the distance Mercury to the Sun). PS: Have included more material to help you understand tidal locking. [/u/Das_Mime 's great visualization of tidal locking](_URL_1_) Note that the Sun can raise tides on planets, as Earth does on the Moon and vice versa. The separation between the Earth and the Sun is on average ~149 million kilometres; the distance separating Earth and the Moon is ~380 000 km; the distance separating Pluto and Charon is ~19 640km (doubly locked, i.e locked to each other). |
Do octopuses have dominant tentacles like people have dominant hands? | Great question. Yes, it is quite possible that cephalopods, including octopodes, have a "handedness" to their tentacles. It appears to be related to their dominant eye and field of vision on an object they are interacting with. _URL_1_ _URL_0_ |
Are skinny or wide tires better in the snow? | Car nerd here: though a wide tire *does* give you more grip on an even, smooth road, such tires have real problems with hydroplaning on wet, snowy, and icy roads. Thus, [snow tires](_URL_1_) are narrow to try get maximum force at a small area (biting into the snow more effectively) and have less water under the tire (reducing the chance of hydroplaning.) Even rally cars, that typically carry some serious rubber when on tarmac, have narrow snow tires ([example](_URL_0_)). |
Why are narrower tires better in the snow? | Narrower tires means that cars weight is distributed to a smaller area of tire contacting the ground. So with weight staying the same and area decreasing, you are increasing the amount of pressure exerted on the ground in a given area. Also instead of just plowing through snow/ice with your tires, a thinner wheeler cuts through it instead of just pushing it. |
Whatever happened to the hole in the ozone layer? | CFC's are no longer really manufactured, due to the [Montreal Protocall.](_URL_0_) [Ozone depletion](_URL_1_) is still an issue, but we no longer massively produce most of the chemicals that were making it worse. Now that we've stopped, there's nothing more to do. |
Whatever happened to the hole in the ozone layer? | Ozone is naturally created by ultraviolet radiation hitting the atmosphere. As a result, once we slowed down the pollutants that deplete it, it started reforming. There's not as much ozone as there is naturally, but there's more than there was ten years ago. |
Why do babies cry so much for no obvious reason? | babies cry because they cannot communicate, so when one of their needs is not being met they do the only thing they can: cry. there are many "needs" that will cause crying, such as: being hungry, tired, uncomfortable (due to positioning or perhaps a dirty diaper), pain (breast milk is hard on the stomach and causes pressure and gas, also sickness or teething pain), or they might not be getting enough attention and so they "need" to be held or comforted to establish an emotional connection with the parent/caregiver. source: experience, I work as an infant caregiver. |
If breaking the sound barrier results in a sonic boom, would going faster than the speed of light have a similar effect? | There actually is such an effect in the right context, and it manifests as Cherenkov radiation. In a vacuum, light travels at speed *c*. In a transparent material, light will travel at a slower speed. (This is what the index of refraction measures.) Let's call that slower speed *v*. If a charged particle travels in that transparent medium at speed greater than *v* but, of course, less than *c*, it will produce Cherenkov radiation, the electromagnetic equivalent of a sonic boom. Cherenkov radiation is key to certain detectors (for proton decay and neutrino observatory experiments like Super Kamiokande); they have large underground areas filled with water and detectors set up to detect any Cherenkov radiation, which would then indicate that certain particle physics phenomena had occurred. |
Why do humans have eyebrows although we have lost most of our body hair? | I don't know how effective eyebrows are at preventing sweat from entering the eye, but eyebrows have a conserved function in many primates; non-verbal communication. The use of eyebrow signalling has been recorded in most [human cultures](_URL_0_). Without uttering a word, we can express a friendly greeting, surprise, anger, distrust or displeasure. Eyebrows may also play a role in facial recognition in [primates](_URL_1_). |
Brown Hair, Red Beard. Why??? | To be frank, I don't have a great answer for you, but I can summarize my response to a [similar question](_URL_0_) as part of this [previous thread](_URL_1_). So what I remember of hair color genetics is that there are several genes involved in the pigmentation of (head) hair color, at least two if not more. Hair associated with secondary sex characteristics (facial/genital hair) doesn't always follow the same phenotype as head hair and often demonstrates at least part of the recessive genetic trait (red/blonde). As I last understood this (and through a quick search) it seems the genes for this aren't entirely understood, and it seems this phenotype is more complicated than head hair pigmentation. Sorry I don't have a better answer for you, though maybe a geneticist will come along and help out. |
When we "lose" fat, where does the fat really go? | Fat is stored in cells in many forms, for instance [triglyceride](_URL_0_) which is basically 3 fatty acids connected together with a glycerol molecule. When your body needs energy your fat cells use Lipase to break apart the fatty acids and release them into your blood. fatty acids move into other cells from the blood just like sugar does where hey are consumed by mitochondria to produce ATP through beta oxidation. That's where they are combined with Oxygen and release Carbon Dioxide + energy for your cells. **In other words** your body tears the fat molecules down to their individual carbon atoms, attaches them to oxygen and you exhale them. **TL/DR** You exhale it. When you exercise and you breath heavy you are literally exhaling your fat ass. **[Edit]** Thanks for gold! Please don't try heavy breathing as a weight loss technique. That's like repeatedly flushing your toilet to cure constipation, except it can result in raising your blood pH. |
Are all stars exponentially large? How do their properties change as they get smaller? | > exponentially 'exponentially' refers to a rate of change. We would say a variable X grows exponentially if the rate of change of X is proportional to the value of X. To put that another way, the larger X is, the faster X grows. 'exponentially large' doesn't mean anything, though...do you mean 'extremely large'? Also, I'm not sure what you're asking. Do you want to know how our solar system compares to the same system for other stars? |
If cameras having more resolution than the human eye are made, could we tell the difference between them and a camera with the exact same resolution as the human eye? | The resolution of a human eye is a lot more complicated than that. They're not like cameras. Each receptor only gives a signal once every second or so, but they don't all do it at once. As such, you can't really say the resolution or the frame rate. To make things worse, the receptors aren't spread out evenly. They're mostly in the middle. Your brain tricks you into not realizing how bad your vision outside of that is, but try reading something you're not looking directly at. You also can't directly compare the pixels in a photograph with your field of view. The photograph probably doesn't cover your whole field of view. But if you're looking really close, your whole field of view isn't going to cover the whole photograph. But if a picture has a higher angular resolution than your eye, it will theoretically be slightly better if it has a higher resolution, but it's not going to make much of a difference. |
Why do humans need to brush their teeth while most animals seem perfectly healthy without doing so? Has brushing prevented us from evolving a natural defense to bacteria that harms our teeth? | Question: What makes you think that most animals are perfectly healthy without doing so? I'm not attacking you. Just curious because I've always thought the opposite. |
Do insects sleep, or have any comparable process? | /u/jokerzwylde's answer is not correct. Insects do have a type of rest that resembles vertebrate sleep in various physiological measures, and is distinct from torpor. For example, rhythmic and endogenously driven neural activity, increased threshold for response to stimuli, changes in breathing, changes in posture and reduced motion, regular circadian rhythm to sleep/wake patterns, and rebound sleep (increased sleep the day/night after being deprived of sleep.) In honey bees, there is some really cool work to show that sleep deprivation results in poorer learning the next day. See a related comment on a related question earlier today: _URL_0_ |
Why are girls (and possibly also boys) entering puberty significantly earlier than several decades ago? | From what I've been told in medschool (in OBGYN), increased obesity rates means increased adipocytes, which produce a hormone called estrone. Estrone is an oestrogen, thus stimulating secondary sexual characteristic (fat redistribution, development of mammary glands etc.). Can't really provide a tangible source because this was said in a seminar. As to why boys puberty earlier.. don't know. |
If the active ingredient in Marijuana is THC, why are there different effects depending on the different strains? Are there more chemicals at play here? | There are as many as 85 active compounds in marijuana, THC happens to be present in the highest concentrations and THC levels are used to measure potency. The effects of many of the other compounds aren't well understood. (_URL_0_) |
Why do flames always burn vertically? | As the fuel burns -- combines with oxygen in the air -- the resultant gases are hotter and therefore lighter, and so rise. In fact, there are different temperatures within a flame, the middle blue part being the (relatively) coolest and the tip of the flame being the hottest. In zero-G (free fall), because the gases do not rise, candle flames are spherical. _URL_0_ |
Does hair grow at a constant rate? | No, hair does not grow at a constant rate. Hair is made of keratin, which is a protein. Diet plays an important part in how quickly your hair grows. If you are eating a low-protein diet, your hair will grow more slowly, while a high-protein diet will facilitate faster growth. Age and genetics also play an important role. Hair growth tends to slow down in old age, while some people just have the genetic tendency towards faster or slower growth. The average rate of hair growth is about 1cm per month, but that can vary quite substantially. |
How and why do bruises form? | Bruises result from trauma to a region of your body. If powerful enough, this causes the capillaries underneath the site of trauma to rupture and for the blood to leak out into the surrounding tissues. Consequently, you get this purple-bluish colour that fades after a couple of weeks. The darker colour is from the red blood cells losing their bound oxygen. Essentially, as the bruise changes from blue, to green, to yellow, and then fades, you are seeing red blood cells being broken down into its constituents to be exported and reused. |
How long must a car idle to use as much gas as when starting the car? | Click and Clack the tappet brothers from Car Talk addressed this question. The story about the amount to start the car really based on old carburators which tended to put a big slug of gasoline into the engine on starting. Fuel injectors have brought this down to almost nothing (4 seconds, 6 seconds, etc). However, if you're looking at it from an overall economics standpoint, there is more to consider than just the gas used in the start. It takes energy from and puts wear on your battery, starter, flywheel, & piston rings (for initial movement before the oil is circulating). They recommend only turning off/restarting if you're going to waiting longer than 3-4 minutes, based on the average life/usage rating of these other components |
How true is the plane of planetary orbits in the solar system? | Essentially yes. But none of their orbits are perfectly level. If we define level as the plane of the sun's equator, then _URL_0_ tells you by how much each planet is off level, "Inclination to Sun's Equator". Space Trivia Point: The moon's orbit around the earth is not level either, at least not in the same plane as the earth's orbit around the sun. For if it were, we would have eclipses twice a month. Do you see why that would be the case? |
If Silver is the most conductive element, why don't we use it in electronics as opposed to Copper and Gold? | Silver is the best conductor, but is expensive and oxidises easily, making it unsuitable for uses where it's exposed to oxygen or large amounts are required. Gold doesn't oxidise*, but is expensive, which is why it's often used as a coating for electronic connections like HDMI cables. Copper is abundant and has good conductivity and oxidation resistance for its price, making it the most cost effective for general use, especially when it's not exposed to air (for example in rubber coated wires). *it does, but negligibly under standard conditions. |
Were plants larger or smaller on earth two hundred million years ago as compared to today? | Just to correct a misconception: we do not have evidence that dinosaurs were larger because of higher oxygen levels. We have a [number of posts in our FAQ](_URL_0_) about this that go into details. |
Why does hot water sound different when it's poured? | The viscosity of water changes significantly with temperature (hot water "flows easier" than cold water). Viscosity and speed of sound are related, and the propagation speed of sound waves is an important factor in the sound it makes when poured. |
What determines the size of a given star? | A star is a competition between the inward force of gravity, and the outward pressure caused by the fusion reactions. Quite simply, if a star is formed from more available material, it will be more massive. But mass is not always proportional to the physical volume. [This website](_URL_2_), while ugly, does go over some of the different stages, and the relative effect on the size of the star, of the star lifecycle. |
Six year old asking: How do we know plants feel no pain? | Because plants do not have a nervous system or brain. |
Does fire take up space? | > but I was always confused of how a chemical reaction is seen. Sometimes when a chemical reaction takes place light is released, and this light happens to fall in the visible part of the electromagnetic spectrum. > Is fire made up of matter? Yes. It is made of molecular fragments, many of which are highly energetic and unstable. > If so, is it made of something like plasma, the same way lightning is? Yes I think this is reasonable to say so. A plasma is a gas of positive and negatively charged particles, and these ions are in the flame. However, not all the particles in the flame are charged, some of them are neutral. [I'll let this link do the explanation](_URL_1_). |
Why do epileptics get seizures because of strobe lights? | The majority of people with epilepsy (PWE) do not have seizures because of strobe lights. Those with specific conditions, usually reflex epilepsy or juvenile myoclonic epilepsy, are at higher risk of photosensitive seizures. It's not well-known why some PWE are photosensitive. It is well-known that at rest there is a posterior dominant rhythm to EEG activity—a regular sinusoidal voltage fluctuation in the 8.5–13 Hz range best seen over the primary visual areas in the back of the brain. While a bright light flashes repetitively, it can cause regular evoked potentials in the visual cortex, time-locked at the frequency of the flashes. Since seizures are themselves overly-synchronized and self-sustaining bursts of brain cell potentials, it's not a huge leap to consider that causing synchronous potentials with light may lead to a seizure in a susceptible individual. The actual down-to-the-membrane details are still to be worked out. |
Why do lights in the distance flicker? | It's due to the turbulence of the atmosphere. The optical index of air (the way it refracts light) depends on the temperature: you can see it above a road during summer for example. Because of the turbulence, the light goes through different air layers and it changes with time. So the quantity of light you receive varies. The effect is more important when the distance of air is bigger: for distant objects or for stars near the horizon. |
Why is it that we can take clear pictures of things like galaxies and nebulas, but not planets or moons that are nearby? | Because they're tiny. Their angular size is much, much smaller than the angular size of galaxies or nebulae. See [this question](_URL_1_) as well from the [FAQ](_URL_0_). |
How can the Universe be larger than the observable universe? | If you lived in a space in which the geometry is flat, you would be absolutely right. But when we talk about expansion, it doesn't mean that objects are literally moving away from us. The distance is increasing, but only because the space itself is expanding in between the objects. The objects themselves remain static with respect to this background, but the distance we measure changes due to gravity. In this way, two objects can be effectively out of causal contact without actually moving away from each other faster than the speed of light. |
Why is Europe considered a continent if it's attached to the rest of Asia? | The Ural mountains, the Volga-Don river system, the Caspian Sea, and the Caucasus Mountains all provide large–scale natural boundaries between Europe and the rest of Eurasia. Köppen climate maps show that most of Europe (being in some sense a large peninsula) has a distinctively maritime climate, unusually mild and wet for the latitude, whereas northern Asia has a much more strongly continental climate. And there are the cultural differences. *Edit:* This [wiki article](_URL_0_) says that the Ural river, somewhat to the east of the Volga and draining into the Caspian, not the Black sea, is preferred. |
Since there is no light pollution on the surface of the moon or certain comets, how come the sky isn't filled with stars and galaxies? | While there is no light pollution on the moon or on a comet, there is a lot of light. Coming from either the sun or the Earth (in the case of the moon). The camera has its exposure settings chosen to ensure that the surface of the moon/comet is properly exposed and this surface tends to be rather well lit. Since cameras only capture a limited range of brightness, the much dimmer stars don't register. If you would set the exposure settings to capture the stars and point the camera at the sky, you'd capture a lot of stars, more than you would from most places on Earth. |
What makes a material sticky? | The general answer to this would be adhesion (when two dissimilar material stick together). There are however many different ways in which adhesion could exist. For example two materials could slightly dissolve into one another and basically weld to each other, or it may result from electrostatic interactions, or as the result of inter-molecular forces such as Van der Walls forces. Check out the wiki page on [adhesion](_URL_0_) |
If the sun emits heat into our solar system like a giant space heater then why is the universe so cold if it has trillions of stars like the sun? | The nearest star to the Sun is a few light years away. We're about 100 million miles away from the Sun, about a millionth of the distance to the nearest star, and even here the Sun barely warms space. The Earth is warm because it has an atmosphere to trap the Sun's heat, but leave the atmosphere and you'll freeze your buns off. And that's a millionth of the distance to the next star over! |
Why is the expansion of the universe accelerating? | We don't know. All we know is that there is something that is overcoming that force of gravity on larger scales which is called dark energy. |
Why is the hole in the ozone layer over Antarctica? Why does the ozone not diffuse into an even layer around the Earth? | The reaction that depletes the ozone happens most easily on the surface of microscopic ice crystals. The atmospheric conditions required to form these crystals and break down ozone occur every spring in Antarctica due to temperature, humidity and amount of sunlight. Those conditions aren't as common in other regions. |
Is a coconut a fruit or a nut? | Botanically speaking, a coconut is a fibrous one-seeded drupe, also known as a dry drupe. However, when using loose definitions, the coconut can be all three: a fruit, a nut, and a seed. Botanists love classification. [Source](_URL_0_) |
Is UV light reflected by a mirror - or is it absorb into the actual glass? | Most mirrors are made of soda-lime glass backed with a reflective surface. This surface tends to be either silver or aluminum, but other layers are added to increase adhesion to the glass as well as to modify the reflective surface's optical properties. Soda-lime glass absorbs light very strongly below 300 nm, but the total amount absorbed depends on the thickness of the glass. The reflective coating itself, however, probably reflects a large portion of the incident UV, although it's impossible to say without knowing the manufacturing specifications of your mirror. |
Does mirror reflect UV light? | A surface-silvered one does. I've constructed and used UV spectrometers with those to direct and concentrate the light. Much below 200 nm, other factors come into play though. Normal household type mirrors have the silvering behind glass for robustness. Ordinary glass cuts off the shorter wavelength end of the UV spectrum. |
How many flu strains does a typical flu vaccine affect? | Most vaccinate for either three or four specific strains. But there is also some protection for strains similar to or closely related to those, even if they are not the specific ones included. If you want the four-virus version, ask for the "quadrivalent" or "tetravalent" vaccine. They seem reasonably common now in the US-- my local walgreens had it. Might as well! |
Why do my speakers "toot toot toot" whenever a mobile phone comes near? | Your phone sends and receives electromagnetic signals in the air. These signals are waves that can interfere with and slightly change the current of electricity going to your speakers and cause it to make the sound. On a side note if you want to see something cool put your cellphone underneath an oldskool CRT computer monitor and send it a text message. |
How is destruction of a nuclear explosion filmed? | There was a special type of film created for the intense exposures; a type of film that only the intense radiation from a nuclear test could expose. Also the [Rapatronic Camera](_URL_0_) was developed for ridiculously high shutter speeds. |
How are nuclear explosions filmed? | The camera sends an electrical signal to a receiver in a safe location. |
Why does our body make longer, darker hair under a cast? | [Your hair is bleached by exposure to the sun.](_URL_0_) Sorry for the weird source, but I think it suffices. |
Why doesn't a star's gravity disturb its planets' moons? | There's the concept of the [sphere of influence](_URL_0_) where the gravity of a planet, despite being weaker than the star, is locally dominant due to the short distance. Therefore a moon or an artificial satellite can still be in orbit around a planet despite the presence of a much larger attractor. The star is still attracting the moon and the moon is still orbiting the star. But the planet-moon system is still attracted as a whole, so in a reference frame centered on the planet you can still see the moon orbiting the planet. Earth's sphere of influence is more than twice the distance to the Moon. If you place an artificial satellite at this distance it will be too unstable to orbit the Earth. |
Why are men much more prone to suicide compared to women? | As it happens, both genders are equally prone to suicide. The difference is the methods. Women have a tendency to choose less violent methods, such as poisoning or overdosing. Because of this, they have a higher rate of survival. Whereas men choose more violent methods such as guns or vehicles, and as such are more "successful." More or less. |
The asteroid belt...is it a sphere? | The asteroid belt is pretty flat, you can imagine it like one of the rings of Saturn in shape. The reason for this is that all the planets/asteroids etc in the solar system formed inside a spinning ring of matter (an accretion disc) around the very young Sun, so are all orbiting roughly the same way (interactions between bodies since then has scattered some out, hence the rogue asteroids we worry about hitting the Earth, but the majority of stuff is still merrily spinning on round the Sun in the same plane we are). |
Why are some bruises purple and some are brown? | The purple, or blue color happens because damage occurred, but the skin isn't broken. Essentially you're bleeding under the skin resulting in clots. The brown color is essentially an almost healed bruise, or a less serious bruise where not much damage occurred thus less bleeding under the skin. For serious bruising you will notice that it is red at first, once blood fills the damaged area it turns purple/blue indicating that clotting has begun. As the bruise heals it will turn yellow/green and finally brown until it's healed. [_URL_0_](_URL_0_) |
When you shine light at a mirror, does the amount of light in the room change? | The number of photons emitted - what you perceive as "light" - would be unchanged. The mirror would only distribute them differently. So the perceived increase in brightness from the reflection in the mirror is offset by the shadow the mirror casts. |
Why does the Earth not spiral to the Sun if it emits gravitational waves during its revolution? | Because the power output from gravitational waves is ***incredibly*** tiny for systems other than say rapidly spinning neutron stars. The [power](_URL_0_) radiated has a factor of G^4 / c^5 out front which is incredibly tiny and it drops off in output by 1/r^5 with distance. |
If photosynthesis uses sunlight and carbon dioxide to make sugar, why don't leaves taste sweet? | Glucose is produced in photosynthesis but if it is not used in respiration is it converted into starch so that it can be stored for later use. Testing for starch is a classic way to test for photosynthesis taking place (many will remember a high school experiment where a stencil placed over a leave causes starch to only be produced in the areas that are open to sunlight. This starch can be detected using iodine.) |
This is probably a really dumb question but, can plants get cancer? | This is a good basic answer I think: _URL_0_ Essentially the answer is, yes, sort of, but it's not as deadly because plants don't have circulatory systems that can spread metastases (i.e. blood). |
Can tendrils in nebulae form planets without a parent star? | Gas clouds usually don't have enough pull to converge into planets on their own, if they aren't extremely large or dense. And as tendrils, their parts are already likely to be moving apart from each other in one of the three dimensions. So it will usually only happen when the tendrils are extremely dense, extremely massive, or get pushed together by an outside disturbance, like the blast of a supernova. Edit: The first two cases would be likely to leave stars nearby. Only with some disturbance I'd expect 'free' planets to develop. And there's probably quite a few sub-brown dwarf gas giants between the stars. |
How can a photon have a mass of zero without violating the mass - energy equivalence? | Yes, everything you've said is correct (for a particular choice of "system" versus "surroundings"). It's because mass is not exactly what you think it is. Mass isn't simply "the amount of stuff" in the system like you might've learned in introductory science classes. Mass is just energy **not** due to the overall motion of your system as a whole. Since a photon has no mass, all of its energy is energy of motion (you could call it kinetic energy). The mass of a system of particles is not simply the sum of the masses of the particles. So while photons have no mass, adding or removing photons from your system can change the total mass of the system. |
Do Aquatic Animals Yawn? | Fish yawn as territorial or mating displays it's commonly accepted that all vertebrates yawn. Nobody knows why though here's an article on [why we think people yawn](_URL_0_). [Here is an article about fetal yawning](_URL_1_) |
If stars in a galaxy increase in velocity the further they are from the center, why do galaxies have spirals? Wouldn't spiral arms indicate slower speeds as you approach the edges of a galaxy? | Despite normal intuition when looking at a face on picture of a spiral galaxy, the spirals aren't exactly what they would seem. They are not concentrations of stars as you might assume and they have little to do with the motion of the stars. They are in fact density waves with in the material of the galaxy, namely gas and and dust. The slightly higher concentrations of particulate matter lead to the formation of larger, brighter stars. This leads to the characteristic spiral, not the motion/velocity of the stars. |
Are galaxies more likely to spiral a certain direction? | Clockwise *is* anticlockwise if you look at it from the other side, which you can do with a galaxy. Therefore the question implies that there is a "correct" side to look at a galaxy from, which there isn't. The ones observable from earth have the appearance of being roughly half-and-half from our viewpoint. |
Subsets and Splits