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Where is the "equal but opposite" force where gravity is concerned?

We all know that things with energy are gravitationally attracted to each other. We also know that every force has an equal but opposite reaction... Is this some special case where Newton's third law doesn't apply? Or are two bodies that are attracted to each other pushing away on the fabric of space-time or something? Non-physics-major answer, if possible please! EDIT: Answered! Thanks guys! My mistake was in viewing gravity as a one-body as opposed to a two-body system. Two forces toward each other are necessarily in opposite directions, satisfying the third law... makes sense. I guess I was overthinking it.

Newton's Third Law implies that every object that is pulled towards another object, in return also pulls that other object towards itself. Similarly, anything that pushes against an object also has the object push back with equal force. Now with gravity, the Earth pulls us towards it. But in return, each of us also exerts an equal force on the Earth. A typical adult male will exert roughly 800 N of gravity on Earth. What effect does this have on our little planet? Well, we know that force equals mass times acceleration, or *F = m a*, which you can rewrite to *a = F / m*. In this case, the acceleration experienced by the Earth due to this specific person is really small, because the term in the denominator, the mass of the Earth, is really large.

Do photons have any appreciable impact on spacecraft outside the atmosphere?

I know that photons can be used in solar sails, and that they are technically able to propel objects, albeit very slowly. But is there any consideration for photons as they relate to, say, the ISS or some other vessel in outer space? Are there any adjustments made to flight trajectories due to photons over long periods of time?

Yup. Photon pressure applies not only a change of momentum on spacecraft but also a torque. Spacecraft need to be designed to carefully minimize the torque imposed by photon pressure and to have mechanisms to counteract those torques and trajectory changes. They may be small, but they are consistent, and that can be problematic. A particular example would be the Kepler spacecraft, which spent almost all of its time pointing at one point in the sky. The problem there was that the torque imposed by photon pressure caused the spacecraft to consistently ramp specific momentum wheels which are used to counteract that torque, unfortunately the wheels were not as well made as they were supposed to be and failed earlier than desired. Instead Kepler switched to a different mission where it was pointing at a different part of the sky that caused less photon pressure torque. As for flight trajectories, some adjustments do need to be made, but they're usually fairly small, with the exception for spacecraft that fly fairly close to the Sun.

CMV: The vegans are (mostly) right (especially about pork)

If you believe causing pain and sufering is wrong, obviously causing pain and suffering is wrong, especially to animals that have a deeper capacity to feel. People have gut intuitions towards consumption of dogs because we understand them as sentient beings that can feel and think and pigs are even smarter. Vegans are disproportionately hated because people are uncomfortable with the idea that their traditions or practices are immoral. In your economic situation you might not be able to afford veganism, but to say that it's not more moral to avoid consumption of meat is wrong if you believe causing pain and suffering is wrong. To say that it's incorrect to judge people's beliefs is just wrong because no one accepts everyone's beliefs. Like maybe if you accept beliefs like the consumption of unwilling human meat or believe that animals have no inherent moral value and permit things like torturing animals for pleasure as moral. The vast majority of moral philosophers, even meat-eating ones, will agree that consumption of mammal meat is immoral. Most arguments against veganism are inconsistent at best.

> People have gut intuitions towards consumption of dogs because we understand them as sentient beings that can feel and think and pigs are even smarter. I think that's actually more of a historical development. Dogs and cats lived together with humans for a long time, because they were useful for humans to keep them around (guard dogs, shepherd dogs, cats to kill mice and rats, etc.).

What is the most culinarily elaborate “dish” made by a nonhuman animal?

Whether it involves combining two separate foods, cooking the food, or preparing it some other way, what the most complicated transformation that an animal has made to its meal?

I'd argue honey bees producing honeydew honey. First juices of plants normally unsuitable for bees are extracted from leaves by other aphids and transformed into honeydew, a thick, dark, sticky secretion. Bees collect it and transform into honey, which they then seal in the honeycombs, alongside with larvae who can feed on it. Not only is it already transformed plant product which they transform further into something pretty far from the original, they seal it in airtight containers to preserve it against contamination and leakage - and the transformation goes way beyond typical "regurgirated food for the younglings" common in other animals.

[ATLA] Any idea what happens to Azula in the end?

I mean, from what I can tell she goes into hiding but does she ever reemerge / deal with her mental issues / find happiness?

Spoilers for the comics ahead (specifically The Search)! After losing the Agni-Kai and suffering her breakdown, Zuko had her taken to a mental care facility elsewhere in the Fire Nation. She was kept there under supervision for about a year before Zuko let her out to help him search for their mother. Unsurprisingly, things were more than a little rocky between them but eventually they managed to track Ursa down. However this didn't do Azula's mental health any favours and, after another fight with Zuko, she ran off towards a place called the Forgetful Valley and hasn't been seen since.

[Batman] I'm an honest Gotham cop and I'm under immense pressure to close a case on a mid-level (non-superhuman) crook. Is there any way I can enlist Batman's help with this case without using Jim Gordon's spotlight thingie?

It depends; if he’s something like a crime boss it’s likely that another member of the bat family is already on the case. Hang around the scene of a crime for a bit for one of them to show up to collect evidence and coordinate with them. They can’t be everywhere at once and would likely cooperate with willing police officers. If he’s a lower level guy than that then quit being lazy and do your job.

Is the sound on atom bomb videos real?

Like many of you I enjoy watching atom bomb videos on YouTube. However one thing strikes me as unreal: the sound. Usually the sound of the explosion is shown at the same time of the blast. However, the recordings are made from miles away, which lead me to believe that they are edited. I wonder: are these sound recordings even real or manufactured? Can someone point me to a real video recording with a true sound of an atomic blast?

Yeah, that sucks. The sound is usually real, but the timing is adjusted for some inane reason. Before people started doing this on Youtube, one of the best things about seeing a nuclear blast in a movie or on tv was waiting for the sound, because it was stock footage and you always knew it was going to take a few seconds for the sound to arrive, thus illustrating the power of the bomb even further. This was back before the 1990s.

[DC/Marvel] Which superheroes are best able to handle natural disasters and how would they do it?

Storm and Thor from Marvel is an obvious one. But aside from them, who are some heroes who are best suited to handle things putting out wildfires, averting tidal waves or helping with civilian and property rescue? Some that come to mind are Flash, Green Lantern especially for rescue efforts. Would Mera be strong enough to avert an entire tidal wave for a prolonged period of time? Could Superman's super breath blow out entire bushfires? etc.

I don’t know if he has ever actually done it aside from situations where all the heroes turn out to help, but in any situation where normal rescue workers would be useful Multiple Man would be able to handle quite a bit of work.

[Alien] What happens to elderly xenomorphs?

So let's assume this specific xenomorph is strong and smart enough to survive for a prolonged amount of time, there is already a queen in the hive so there's no use for them to grow into one, what would happen?

The strongest and smartest ones are turned into Praetorians by the Queen. Those would be the ones who survived that long. They protect the queen, act as generals and can replace the queen if she is killed.

CMV: Libertarians should establish their own experimental society, to crash-test their ideology.

I believe that the truest test of the principles of liberarianism (by which I mean pro-capitalist libertarianism, anarcho-capitalism and objectivism influenced ideologies) would be if (sufficiently rich) libertarians and libertarian-owned corporations funded and built (or bought if possible) a small island and established their own an-cap nation there. This "Anarchotopia" could be the hub of commerce, business and technological progress not-limited by any government. The best and brightest of business and science could gather there and follow their dreams to their best ability. This could test several things: - if libertarian/anarchist society is viable - can a truely an-cap business compete against companies that have ties to various governments - can non-restricted technological R&D outcompete government funded research. - can an existence of such An-cap Nation be beneficial to humanity DICLAIMER: Im neither a libertarian, nor an anti-libertarian. I just think its a cool idea worth pursueing and allowing, and everyone regardless of their political views should be in favor of it at least being attempted. ∆ EDIT: I am now convinced that such experiment would lead to inconclusive results, as well as a disaster, if it even managed to get of the ground. Still, I believe it to be a fascinating concept, despite the fact that Im not a fan of libertarianism myself. Useful links: https://en.wikipedia.org/wiki/Seasteading https://en.wikipedia.org/wiki/Principality_of_Sealand http://www.conservapedia.com/Galt's_Gulch https://en.wikipedia.org/wiki/Atlas_Shrugged _____ > *Hello, users of CMV! This is a footnote from your moderators. We'd just like to remind you of a couple of things. Firstly, please remember to* ***[read through our rules](http://www.reddit.com/r/changemyview/wiki/rules)***. *If you see a comment that has broken one, it is more effective to report it than downvote it. Speaking of which,* ***[downvotes don't change views](http://www.reddit.com/r/changemyview/wiki/guidelines#wiki_upvoting.2Fdownvoting)****! If you are thinking about submitting a CMV yourself, please have a look through our* ***[popular topics wiki](http://www.reddit.com/r/changemyview/wiki/populartopics)*** *first. Any questions or concerns? Feel free to* ***[message us](http://www.reddit.com/message/compose?to=/r/changemyview)***. *Happy CMVing!*

Where? All viable land is claimed, save for some weird null zones on the Croatia-Serbia border which would not exactly make a country. There's not really a place anarchists could build a society free from government involvement.

[Death Note] Can the Death Note be pre-empted when it comes to a scheduled death? Is it possible to kill someone sooner and in a different manner to what has been written in a Note or does having your name in it make you effectively unkillable until the specified time and date and method?

Yes, it can. The rules specifically state that the Death Note cannot be used to prolong someone's life; if they have a knife in their chest and are hemorrhaging blood, you can't write "Tony will die next Tuesday of a pleasant opioid overdose" to save him. This is just a variation on that rule. The Death Note kills; it does not save. And if a death makes what was written in the Death Note impossible, the target will just die of a heart attack. For example, if you wrote "Tony will be murdered by his girlfriend in one hour," and his girlfriend died in a car accident on the way to his house, the Death Note would still take him, just by stopping his heart.

Why is the presence of Cadmium in cigarettes a problem when foods such as carrots contain similar trace amounts?

I found one article says that the average cigarette contains 1.56 to 1.96 μg/cigarette. The same article shows (with a very strict p-value!) that cadmium blood concentrations are higher in smokers. In another article, it says that control group wet carrots contains 4 μg/kg Many grown foods contain trace amounts of Cadmium from the soil, so it is not unreasonable to assume that smokers and healthy eaters consume Cadmium on a similar order of magnitude. So what makes the cigarette Cadmium that more dangerous than carrot Cadmium? Why do cigarette users have higher blood levels of Cadmium?

Likely something to do with it being easier to cross into the blood stream via the lungs rather than digestive tract. A quick Google says about 6% of ingested cadmium is absorbed in the gastrointestinal tract. While the lungs absorb ~40-60% of inhaled cadmium. It can also be absorbed via the skin. There are obviously lots of mitigating factors for both. Also a kilogram of carrots is a lot. A serving is in the range of 100grams. Or basically 1 largish carrot in a meal. So the dosage would be 1/10 of your 4 micrograms, or which 6% is absorbed. Coupled with the fact people tend to consume a lot more cigarettes per day than carrots at the much higher absorption rate.

ELI5: What purpose does eye movement serve during REM-sleep?

It's more of a response to REM. During REM sleep, the visual cortex of the brain is “awake,” just as it would be during an awake state. Sleep researchers believe that the eyes may be working to focus on an area “seen” in a dream, but more research needs to be done in this area. People who are blind experience REM sleep the same as people without visual disabilities. Some researchers believe that REM sleep doesn’t actually correlate with dreaming, rather, the eye movements experienced during REM sleep have to do with the brain’s memory processing. Others believe that the eyes are “exercising” during this time, toning the muscles that are used to move the eyes during the day.

How do Computer Algebra Systems, like Wolfram Alpha, solve algebraic problems?

I've been working with mathematica and maple a lot over the last week, and I still don't understand how computers can interpret and solve algebraic equations, yielding closed form solutions.

It represents the equations and has rules for how to manipulate them. For example, if you tell it "expand (x + 2)(x+3)" then it might: 1. Parse the expression into a tree representation multiply add symbol("x") number(2) add symbol("x") number(3) 2. Notice that this tree has an add underneath a multiply and apply the distribution rule: add multiply add symbol("x") number(2) symbol("x") multiply add symbol("x") number(2) number(3) 3. There's a still an add underneath a multiply. Do it again! add add multiply symbol("x") symbol("x") multiply number(2) symbol("x") multiply add symbol("x") number(2) number(3) 4. Man, so much distribution to do. add add multiply symbol("x") symbol("x") multiply number(2) symbol("x") add multiply symbol("x") number(3) multiply number(2) number(3) 5. Finally, now we can try some other rules. Oh hey, adds under adds can be flattened: add multiply symbol("x") symbol("x") multiply number(2) symbol("x") multiply symbol("x") number(3) multiply number(2) number(3) 6. Oh, and one of the multiplications can be computed: add multiply symbol("x") symbol("x") multiply number(2) symbol("x") multiply symbol("x") number(3) number(6) 7. And there are multiplies under an add that have a common term except for some numbers, so we can group those and add the numbers: add multiply symbol("x") symbol("x") multiply number(5) symbol("x") number(6) 8. Oh, and multiply something by itself is just squaring it: add square symbol("x") multiply number(5) symbol("x") number(6) 9. Hmm... can't see much else to do. Better make it pretty and print it: x^2 + 5x + 6 In summary, computer algebra systems work by applying known-to-be-good operations to a tree representation. Sometimes they will try many different combinations of operations and return the one that worked the best, sometimes they'll fall back to doing approximations, and sometimes they don't work simply because the right rewriting rule hasn't been added yet.

Why do we prefer to sleep in the dark?

I've always wondered this.

Humans are evolutionarily adapted to sleep at night (when it is dark) and be active during the day (when it is light). Chemicals that make you sleepy build up in your brain over the day until you go to sleep at night and your brain gets rid of them all. There is another chemical as well which wakes you up and stimulates you. It is triggered by bright light (especially blue coloured light) that historically would be only from the Sun (i.e. it's day time and you need to be active not sleeping). Artificial lighting simulates sunlight which in turn signals to your body that it is day time and not time to sleep.

ELI5; How do Gatling guns/“miniguns” have such reliable accuracy?

With the very manner of how they fire bullets, guns like the M134 and GAU-8 for example must create a large amount of centrifugal force, which is still in motion while the bullets are traveling down the barrel. How do they fire accurately rather than with a spray area, as a result of centrifugals upon barrel exit?

> must create a large amount of centrifugal force They don't for the simple fact that the bullets/shells are travelling at really high speeds so they spend almost 0 time in the barrel and so are barely affected by the fact that the barrel is rotating.

Do we know how long dinosaurs lived?

I'm talking about each individual dinosaur, not the time period. Did T-Rex live for 10, 50, or 100 years? Do we have this information?

Yes, we do. For some. Or at least we have an idea. Animals tend to grow seasonally, with more growth in warmer weather and less in colder weather. This results in what are called "lines of arrested growth" or "LAGs" for short. As an analogy, you can think of them sort of like tree rings for animals. Now, for some dinosaurs, we can make a cross-section of their bones and count their LAGs (note, this does not always work for a variety of reasons including bone reworking through life and such). From this we can estimate age-at-death. For example, "Sue," a large and very complete specimen of *Tyrannosaurus rex* currently on display at the Chicago Field Museum is estimated to have been ~35 years old when it (despite the name, the sex is not known) croaked. And "Sue" was an *old* tyrannosaur, practically geriatric. From bone histology and LAGs we can also make inferences of how fast dinosaurs (and other animals) grew. For many even very large dinosaurs, the answer is surprisingly fast, reaching adult size in often <10 years.

ELI5: Why is a small amount of inflation considered "good" for an economy?

I mean, it's pretty obvious why large amounts of inflation are bad. But it's much less intuitive why some amount of inflation is considered "good." Does that help money move around somehow? Or are people more motivated to spend because the value of their savings diminish over time?

Small amounts of inflation are good for the economy because it encourages investment. If you have a large sum of cash, it's losing value every day (slowly, but it's still happening). If you want to make the most out of your money, you'll recognize that you need to to put into an investment fund of some sort so your stored cash doesn't lose value. Or you'll want to buy something with it, since given more time, the same item will be more expensive. Investments and purchases are needed to keep the economy churning. If deflation is occurring, then it's a good idea for you to sit on your big pile of money Scrooge McDuck style since it's because it's worth more every day. If everyone does this, the economy stagnates.

What is the difference between "targeted relief" painkillers and the generic painkillers?

I saw an advert for Nurofen period pain targeted relief pain killers and I wondered what the difference was between that specific Nurofen tablet and the other plain version? From my knowledge, isn't there some sort of molecule in the tablet that will bind to a receptor in the brain to alleviate pain? How is the tablet specifically targeting, in this case, period pains? Does it also purposefully interact with the female reproductive system? Similarly for headaches and other problems, if I took a tablet to alleviate headache pain, would that help at all with say a sore throat?

That's actually pretty controversial. Nurofen is just ibuprofen. Ibuprofen doesn't do anything specific for pain or discomfort associated with menstruation. But the thing is, ibuprofen *has* been demonstrated to relieve pain associated with menstruation … just the same way it relieves most other types of pain. So it's entirely truthful for the makers of Nurofen to advertise that their product is for relief from menstrual pain. Because it works fine for that. No, there's no molecule in the tablet that binds to any receptors in the brain. Ibuprofen works by deactivating an enzyme called *cyclooxygenase* which is a precursor to hormones called *prostaglandins.* Prostaglandins are part of the body's inflammatory response; that response causes discomfort in varying degrees. Inhibiting the body's production of prostaglandins reduces the body's inflammatory response, which almost as a side-effect relieves the pain associated with inflammation. Basically the mechanism of all NSAIDs — non-steroidal anti-inflammatory drugs like aspirin and ibuprofen — is largely the same. The differences between them are pretty subtle. So yes, taking an ibuprofen (or aspirin, or naproxen, or any of the other zillion drugs in that class) will help relieve a sore throat. It isn't the *best* way to relieve a sore throat; other medications are better at relieving pain, but they come with various interactions and possible side-effects. So the various NSAIDs with their anti-inflammatory properties remain the best overall way to relieve minor pain.

ELI5: How much of a cold or flu virus do you have to be exposed to in order to catch it?

As I sit on a train home from work in Australian winter, half the carriage is coughing and sneezing. My understanding is that, generally, cold/flu viruses spread either through the air and being inhaled into the nose/lungs, or by being left on a surface by contact and subsequently picked up by new contact and then passed to the eyes/ears/nose by hand. I’ve read articles about how a single uncovered cough or sneeze can spread a whole heap of virus into the air. When the virus is bloody everywhere in a container like a bus or train or plane, I can’t see how the majority of people aren’t getting at least some degree of exposure to it. So why don’t the majority of people actually contract it and become sick? Ruling out pre-existing immunity to that particular virus, what determines who does or doesn’t contract a cold/flu when they are exposed to it? Is it the amount of virus which enters the body? The strength of our immune system? I’d love to know!

In terms of "how much of a virus do you need" - we don't really know, in most cases. Some viruses, such as influenza or adenoviruses, only require 10 particles to cause infection. It depends on how the virus infects (it is harder to get infect through the skin than it is to be taken in as someone breathes, for example). For "why does x person get infected over y person" - it relies on a couple of different factors, all of which are different depending on the virus and the individual person being infected: 1. If you've been exposed to the virus before, your body will have built up what is known as "immunological memory" - it has immune cells stored away from the last infection, which can prevent a second infection from building up (so effectively that you may not even know you have had a repeat infection!) 2. How contagious the virus is. Some viruses are heavy, and when in the air, can't spread well, so don't infect many people. In contrast, the most contagious virus - measles - is an extremely light particle, and can float in a room for hours after it an infected individual has been there. The letter R is used to mark how many people an infected person will infect - for measles, every person infected will infect 17 others, on average. So if the virus is extremely contagious, a lot of people are likely to get it. If not, then only an unlucky few will. 3. Personal immunity. Just like everyone has different DNA, we all have cells and receptors for things in the body to bind to. This is really diverse, even between family members. Some people have receptors for one virus or bacterium to bind to, but others do not. This is why, even between siblings and parents, some people get sick from a certain pathogen, but others don't. In essence, it can come down to luck. 4. Health. A healthy individual may have a better functioning immune system, allowing a more rapid and effective assault on a viral infection. Others who are "immunocompromised" (such as AIDS sufferers) or more elderly don't have this same functionality, so cannot so easily get rid of an infection. This is why people so often get secondary illnesses in hospitals (as well as the fact that there are many sick people concentrated in a small area) - they are already unwell, and don't have the capacity to fight off further infection. 5. Personal hygiene. One of the single biggest factors for preventing viral infection (which most effectively spreads through bodily fluids released from a cough/sneeze) is washing your hands. If someone with the flu touches the button to open the train door, then you touch that some button, and then your mouth/nose/eyes/opening... you see where this is going. When you think that a cough can release hundreds of thousands of these particles, and a sneeze millions, you can see how this could be common! But our immune system has a number of very effective techniques to prevent viruses from entry in the first place (the skin, mucous, chemicals in bodily fluids), and prevents a huge number of foreign pathogens infecting us every day.

If half of the matter falling in to a black hole during Hawking Radiation emission are anti particles and half are their particle counterparts, why does it cause the black hole to shrink?

Why aren't the effects of particles and anti particles netted out?

There is a variety of misleading information in this thread. To begin with, you are correct: the absorption of particles or antiparticles would increase the mass of a black hole. Next: this whole description you are referencing is a description of one way of calculating the existence of Hawking radiation, but you should not take the description of the calculation to be a physical description of what happens (and, in fact, there are other ways of doing the calculation). To expand: There are physical particles in nature -- things we are familiar with, like electrons and photons and so on. In certain approaches to particle theory calculations, there are separate entities called virtual particles. Virtual particles are NOT physical particles; there is no way to observe them. One way we know they are not physical is that there are ways of doing particle physics that do not use virtual particles at all! Hawking radiation occurs because quantum mechanics allows for states that start out as just a black hole and end up as a slightly smaller black hole plus an outgoing particle. The way Hawking first showed this is with the creation of a real particle/virtual particle pair near the event horizon, with the virtual particle getting absorbed, and the black hole decreasing its mass. You can also show this without virtual particles but using tunneling (à la Parikh and Wilczek). Trying to think too literally about the virtual particle calculation is problematic because you can wind up trying to reason about non-physical objects as if they are physical.

Is time quantized ?

We know that energy is quantized by the Planck constant. There is such things also for time, or time is continuous ?

We don't know. We have no evidence of any discontinuity in time down to about 10^(-28) seconds. If time is not continuous, it will show up at shorter scales. It may also be that time is not a fundamental construct, and only emerges as an effective notion.

ELI5: When you make red hot metal hotter, why does it become white hot, rather than blue hot?

Color temperatures go red->orange->yellow->white->blue. It could become blue hot if you mad it much much hotter. But in practice you can't make iron hot enough to be blue hot. 6500 K is "standard white" (color of sunlight). You'd need to make it around 8000 K hot to be blue. Iron **boils** at around 3000 K. Even tungsten boils at around 5700 K. So any metal you could be heating up would boil away before it became blue hot.

ELI5: If the Sahara desert used to be a jungle. Is there fossil fuels here? if not why

Having a bunch of vegetation in the past isn't enough. You need to 1) have a bunch of vegetation, 2) that gets buried and sealed in before it rots, 3) with a porous rock that can hold the oil, 4) with a sealed rock above that that can trap it. If any one of those things doesn't happen, you don't get an oil reservoir that we can actually recover fuel from. All that said, the Sahara has a ton of deposited limestone and other sedimentary rock so...maybe?

If men are obligated to recognize any children they have, should't they have a say in abortion?

So this question popped up in a debate I had with a friend of mine about feminism. He was arguing for the rights of men and he asked me if forced fatherhood is fair when a man impregnates a woman and she decides to keep the child but he doesn't want it considering that he doesn't have a say over abortion. ​ I have never thought this question before, but it seemed fair to me that if you must bear the consequences of supporting a child, you must have as much control as possible to its birth, the same control as the woman who bears it, while at the same time respecting the bodily autonomy of women. ​ It seems like an ethically delicate subject that is complicated. ​ What are some philosophical thoughts about this?

With the way this is framed this isn't an abortion issue, but rather a child support issue. If the man does not want the child and the consequences of supporting it, then it is possible for the child to be born while still not forcing him to have to support it. The issue isn't so much, "should men have a say in abortion if they don't want the child but have to support it", the issue is more "should people have to support a child that they do not want?"

ELI5:Why don't we like the taste of everything that's edible?

I mean from a survival view point it would be more logical to like everything; because it equals more food, which means more chances of survival.

Edible things have different nutritional values. Early humans who thought everything was delicious spent their days eating dirt and grass. This was fun but did not provide the nutrients their bodies required so those people died off. Early humans who thought meat and fruit were delicious were extra motivated to gather those foods instead of eating grass, and they received the nutrients they needed to thrive.

Evolution of Galaxies that have no Super Massive Black Holes in their centers?

It's still fascinating to me that such a HUGE galaxy like the [A2261-BCG](http://www.nasa.gov/mission_pages/hubble/science/a2261-bcg.html), which is 10 times wider than our galaxy, does not have a Super Massive Black Hole (SMBH) in its center. Will it form a new SMBH under gravity or will it eventually ~~divide into smaller galaxies~~ "dissolve"?

Ooch, this is a tough topic. We don't actually know exactly how SMBHs form. While we know that galaxies tend to have mass concentrations in the centre, so it seems likely that having all that mass in a small space will give you an SMBH, the exact process is unknown, and why some galaxies have SMBHs and others don't is still a matter of active research. But to answer your question: it looks like galaxies form their SMBHs fairly early on, so this galaxy will probably just stay as it is. Galaxies also don't ever split up. There's just not enough energy for anything more than a bit of gas and the odd rogue star to escape. Instead, galaxies tend to merge with each other, building up into progressively bigger galaxies. If this galaxy merges with another galaxy that has a SMBH, then the SMBH will "sink" to the centre of the new galaxy, and you'll have a single galaxy with an SMBH in the centre. That's the most likely way to "gain" an SMBH at this point.

What does the term Linear Independence represent graphically? And what are the implications of two things being Linearly Independent?

Two vectors are linearly independent if they are not parallel. Three vectors are linearly independent if they don't all lie in the same 2D plane. Four vectors are linearly independent if they don't all lie in the same 3D "hyperplane." ...

ELI5: How does the International Space Station have enough oxygen for all the astronauts?

How does NASA calculate the amount required? What happens in case of a leak? Do they refuel it every trip there? If that is true how come we can't setup multiple ISSs on the way to reach further into space?

**How does NASA calculate the amount required?** Decades of research by the Russians and Americans (Skylab / Salyut) **What happens in case of a leak?** They generate it on board from water and backup solid candles, also the ISS is pretty air tight. It has to be. **how come we can't setup multiple ISSs on the way to reach further into space?** It would be hugely inefficient to have multiple stations in Earth Orbit, one big one would do. Better off with things like Lunar bases.

How is it that radiation suits protect people?

Maybe this is TV magic and I don't know what a real suit looks like but it seems like people become immune to radiation when they put on these thin plastic suits. How is it that radiation can be so dangerous and yet so easily dealt with.

The radiation suits you typically see don't block a lot of radiation. To understand their purpose, you first need to know what happens in a nuclear incident or any other situation where radiation exposure is a risk. Essentially, radiation is emitted by unstable particles that decay (the radioactive material). Normally, we like to keep these particles contained, but after, for example, an explosion, these particles can be spread all around or even be airborne for some time after the event. When you enter an affected area unprotected, the amount of radiation you'll take in during your presence is only a small part of the problem. The larger issue comes from particles that end up in your clothes, on your skin or even in your lungs after you breathe them in. These particles cause a continuous exposure to radiation even after you leave the affected area. Especially ingested particles are dangerous, as the radiation emitted by those can directly affect your internal bits, whereas radiation originating outside of your body still has to pass through your skin and muscle tissue (though it can already do damage there). So the main purpose of a radiation suit is to avoid taking too much radioactive material with you.

Can I make any solid into a liquid by adding sufficient heat?

I want to know if I can take ANY sort of substance that is in a solid form and turn it into a liquid with enough heat. I do not want to burn the substance. Some examples of the substances I am interested in are Collagen, PMMA (Poly(methyl methacrylate)), PA66 (Poly Amide 66). For anyone curious, these are some polymers that I am studying. Would I have to also create an environment to prevent combustion if I am increasing the temperature high enough to change a substances state? i.e. an environment in which oxygen is not present. How would pressure affect my idea? Would a pressurized compartment be necessary?

Not necessarily. Some substances at normal atmospheric pressure will skip the liquid phase and go straight to gas. And example of this would be Carbon Dioxide. Solid Carbon Dioxide is dry ice and it doesn't become a liquid when you heat it up to room temperature.

Why is zero multiplied by infinity not defined as zero?

Infinity isn't a number (you can't point to it on a number line), and since both things that you're multiplying have to be actual numbers, you can't multiply anything by infinity. In general, infinity is not a valid term to use in any "normal" math. What you *can* do is take the **limit** of "0 * x" as x approaches infinity, and the solution to that limit is zero.

ELI5: Why is Africa always in a state of peril?

Maybe that title is a little imperfect, but I know how valuable Land and resources are, and I think Africa has a lot of that, but it always seems to be unevolved and always in disarray. Also , I know a little about most countries and continents, but not very much about Africa, why was it left out of my education. Thanks in advanced.

Plus, the continent is really fragmented. The entire continent has almost no quality natural harbors (one in South Africa, a few on the Mediterranean, and that's it.) The coastlines tend to be rather jagged cliffs, which made it hard to catch up to commerce, back in the day. Many small rivers bisecting the land, large savannahs and desert divide the continent. Africa is a continent with dozens and dozens and dozens of different cultures, heritages, and languages, and many of these groups have been historically at odds with their neighbors. All of this really prevented Africa's ability to keep up with Europe and the Western world. Plus, ya know, slave trade. All those historical divisions between peoples haven't gone away, and modern weaponry has only made old hatreds much bloodier. There are just so many different cultures that it's hard for a single nation to unify, much less a continent.

Why does Bacillus thuringiensis produce a protein that is toxic to Lepidoptera? What does Bt need to kill caterpillars for?

*B. thuringiensis* can be present on basically any surface in a caterpillar’s environment, including those it eats. Delta endotoxins paralyse the insect digestive system causing it to starve to death, providing a delicious substrate for a primarily saprotrophic bacterium.

ELI5: Why do dogs lick people?

There could be several reasons. * To show submission to someone they recognize as dominant over them * To show intimacy with something else, which they learned from their mothers while young * To gather information about you through sweat and other things your skin secretes * You might taste really good Licking also releases endorphins, which are chemicals in brains that make you feel good, so the dogs benefit even if they only lick due to instinct.

Is there any evidence of a liberal media bias in the united States? If so can anyone tell me why?

Here is the most highly cited journal article that directly addresses your question. Watts, Domke, Shah, & Fan (1999). Elite cues and media bias in presidential campaigns - Explaining public perceptions of a liberal press. Communication Research 26(2) Abstract: Public perception of a biased news media, particularly media biased in a liberal direction, has increased over the past 3 presidential elections. To examine what might be influencing this public opinion, the authors look at shifts in public perception of media bias, press coverage of the topic of media bias, and the balance in valence coverage of presidential candidates-all during the 1988, 1992, and 1996 presidential elections. Their results suggest that the rise in public perception that news media are liberally biased is not the result of bias in valence news coverage of the candidates, but, rather, due to increasing news self-coverage that focuses on the general topic of bias in news content. Furthermore, the increased claims of media bias come primarily from conservative elites who have proclaimed a liberal bias that is viewed as including the entire media industry. Now you need to decide whether you trust liberal academics to tell you the truth. Oops. You're in an epistemological quagmire.

When you donate blood, are you accelerating the depletion of valuable stem cells you will need as you age?

I was just thinking about this when I saw the blood bus today. I know blood cells come from marrow. Could losing a large amount of blood on a semi-regular basis deplete the stores you need to make more red and white blood cells in the future?

Red blood cells are manufactured in the bone marrow and are replaced every 100-120 days. Outside of some chronic disease, you have a infinite ability to manufacture them. White blood cells, or leukocytes (there are 5 different kinds), are also manufactured in the bone marrow and are replaced every few days. You also have an infinite ability to produce them, absent some chronic disease. Giving blood does not deplete your ability to manufacture either type of blood cell. You are safe to give blood, as long as you don't have a disease that affects your ability to produce either type of blood cell.

ELI5: Private equity or hedge funds that buy successful brands and drive them to bankruptcy within a few years. What do they gain by doing this?

Just thinking about JCrew, Toys R Us, Payless, Sears, Neiman Marcus and more were all bought out by funds seemingly trying to bankrupt them. Isn't the point of buying a business trying to get them to succeed?

This isn't always the case but when that's the plan, it goes as follows: - Borrow money and buyout the company. - Have the company massively go into debt and use the money to pay yourself an enormous dividend. - Use the dividend to pay back the money you (not the company) borrowed. - The company is way over leveraged, defaults on the debt and declares bankruptcy. Here's where it gets interesting, the bankrupt company now sells off it's assets (brand name, plant, etc.) and defaults on its union contracts, pension obligations (which screws the retirees and the taxpayer funded PBGC), etc. The corporate lenders are now basically the owners of a new unencumbered company with a much higher profit margin. Hostess Bakeries is a good example of this.

Where does body heat originate?

I've been wrapping my brain around this and the best I can do is that the metabolizing of proteins and sugars during digestion must create energy that provides heat for the bloodstream to carry around. Is this correct? If so, I'm thinking that blood gets warm near the digestive system but this doesn't make too much sense when you think that body heat doesn't drop during periods of fasting. Can someone shed some light on this matter?

Heat is a byproduct of inefficient conversion of energy. In most living organisms' cases the this takes form in the conversion of the chemical energy in metabolic substrates like carbohydrate, fatty acids and amino acids to the phosphodiester bond of ATP. This process is inherently inefficient due to several factors such as proton leaks from the mitochondria and inefficient transfer of electrons to carriers. Additionally, some organisms have developed proteins that are responsible for regulated uncoupling of the electron transport chain, known as uncoupling proteins (UCPs). Brown fat is very rich in these UCPs and this tissue is activated when the body must produce greater amounts of heat, such as severe cold challenges. So, though some heat is produced in the digestive processes, the majority of heat produced by the body is by the inherent inefficiency of energy metabolism in each and every cell.

ELI5: Why do my teeth hurt when my drink is too cold?

The nerves in your mouth become numbed by the cold like if you put an ice pack on a bruise, but since your teeth are more important than a bruise your body freaks out and thinks that something bad happened because it is no longer receiving a signal from your numbed teeth so it tells you that it hurts so you will figure out what is wrong and fix it.

[Endgame] (spoilers) How did Thanos know

. . , , , , , , , How did he know how to use the Pym Particles? He was only able to go into the future because he got them from the Avengers in the past, correct? via the past Nebula?

Thanos was able to access all of 2023 Nebula's memories. She may have learned quite a bit working with Banner and Stark. Additionally, he likely has access to some of the best minds and technology in the galaxy. Also, there wasn't necessarily a 1:1 correlation between elapsed time for 2014 continuum and the 2023 continuum, so he could have had more time to figure things out. Lastly, 2014 Nebula used Stark's time machine to bring Thanos. His ship literally was shrunk to the scale required for the Quantum Realm and spit out at the Avengers compound. He may not have been able to travel in the QR and traverse time without Stark's equipment.

ELI5: Does the case of Warren Vs D.C. boil down to the police not having a duty to protect us?

They don't have a duty to provide services to individuals. So if the police fail to respond to your call, or don't prioritize properly...there's nothing you can sue for. Their duty is to the public at large, and there's no duty to respond to you specifically. In practice that means if you call multiple times because someone is invading your home and the police never show up, you can't sue the police for failing to respond.

[Harry potter] why are wizards and witches auch elitist and racists?

In the past their people, a distinct minority in the human population, were heavily persecuted. This was during the medieval era. Despite being powerful, they still struggled to survive. As a result, the wizards and witches isolated themselves, forming their own ethnic (for the lack of a better term,) enclaves, preserving their own culture. Their 'racism' as you call it is arguably justified. If they suddenly reappeared, there would be mass chaos on a civilizational scale. A tiny group of people with no apparent limit to their abilities living alongside normal humans? It would be the equivalent to finding out that lizardmen exist. The elitism that exists is possibly just a natural result of that massive difference in power. A group of people with genetic superiority over another group in a way that is obvious and evident would naturally breed that kind of ideal. Just look at the slur mudblood for example.

Why does earth rotate ?

Why does earth rotate ?

Planets form out of a protoplanetary disk, which is a collection of material that’s all orbiting the sun. This disk has some net angular momentum vector, usually pointing in the same direction as the angular moment vector of the solar system. Since angular momentum is conserved, when the disk coalesces into a planet, it will rotate in the same direction, but faster because the effective radius is now smaller.

ELI5: How can cross eyed people still see straight?

Some do and others don't. If adults become cross eyed they might very well get double vision. It's usually only if the cross is quite light that they don't. In children it can depend. Some children with cross eyed will have one eye that will not be able to see in the center of their field of vision (where both eyes'vision usually overlap). The brain will basically ignore one of the doubles. But they'll still see in their periphery

[the Silmarillion] Why did the Valar ask Eru to intervene against Ar-Pharazon's fleet instead of dealing with it themselves?

Because Men are children of Eru. Despite the fact that they were afraid that Numenor could ruin Valinor, they asked Eru because they did not want to directly kill humans or indeed any child of Ilúvatar by their own hands. It was basically a problem with too much ramifications. Also, remember that Eru didn't just kill Ar-Pharazon and his fleet, he sunk the island and then turned the world round. Perhaps not actually beyond the Valar's combined power, but something they did not want responsibility for - something they did not want to get 'wrong'. So in the end they asked Eru because he was the creator of everything, they knew that what Eru did would be the correct punishment or judgement depending on how you want to look at it. Rather than them doing it and somehow they screw it up and cause even more damage down the line.

[DBZ] So if almost dying makes a Saiyan double in strength, why wasn't future Gohan on a self harming sensu bean craze to stop the androids?

The problem with abusing that ability is that there's a high risk of accidentally killing yourself. The only time it's worth the risk is when you have an incredibly short time to become powerful enough to defeat an opponent who would be impossible to defeat otherwise and retreat is not an option, like with the fight against Frieza.

ELI5: Why is there such a wide gap in the intelligence of homo sapiens and every other organism?

The answer I've been given was basically: GOD. I'm not convinced.....

Chimpanzees are actually pretty close to us. But here's the thing. Once we reached a certain level of intelligence, we adopted a way of life centered around intelligence -- notably the use of language, tools, and complex civilizations. Suddenly being intelligent was *even more valuable* because our societies were designed around it. Once society started rewarding intelligence, people with higher intelligence were *even more likely* to survive and reproduce. A self-reinforcing cycle was born.

Is it more energy efficient to leave the heater on low when nobody is home, or to heat it up from cold when you get back?

So this morning as I was the first to walk back into my freezing office after the holiday, I was reminded of an argument I used to have with my roommate when I lived in a drafty old house in upstate New York. We would both leave the house for one to two weeks every Christmas, turning the thermostat down to something like 5C while we were away, and when we returned we would have to run the furnace full blast for about three days to get the house up to 22C again. I would always suggest that it would be better leave the thermostat on something in the middle while were gone, like 15C, but he thought it was a waste of energy. I argued that it took just as much energy to run the furnace continually for those three days when we returned than it did to maintain a modest temperature while we were away. In reality, I have no idea, but I just hated those three days of feeling cold. Obviously, this depends on lots of factors, like how cold it is outside and how long we are gone. But in general, ignoring issues like pipes freezing, does it use more energy to maintain a moderate temperature for a long time and then heat it up for a short time, or to let something cool way down and then heat it up all the way?

The amount of heat lost by an object to the environment is proportional to the temperature difference between the environment and the object. So if the object is at 20C, while the environment is at freezing (0C), then the rate of heat loss will be twice as high than if the object was at 10C. If you keep heating the house while you're away, you keep the temperature higher and the total heat loss during your away time will be higher. Whereas if you turn the thermostat down very low, the rate of heat loss will gradually slow down as the house becomes colder and colder. The total amount of energy you consume during this absence and the reheating that follows will be equal to the amount lost. In the case where you keep heating your house, this energy loss will be higher than in the case where you don't heat your house at every point in time (except for the initial period where the temperature drops from the starting point to your "something in the middle" value, in which case the energy loss is equal in both cases). So from basic physics, it will be more efficient to turn the heater down as much as possible (without risk of freezing pipes) and heat it back up upon return. To overcome the discomfort of returning to a cold home, consider a smart thermostat that can be programmed to reach the desired temperature when you return (and will start to heat before you get back). Some can even "learn" how long it takes to heat up your house specifically with repeated use, so that they start at the exact right time.

Is the galaxy a mostly flat plane like it’s depicted in pictures? If so, why?

In most artistic depictions of the Milky Way galaxy, it’s illustrated as a roughly flat 2 dimensional plane. What I was wondering is if that’s really the case, or if solar bodies revolve “above” (relative to said 2D “plane”) and “below” the center of the Milky Way?

To add some numbers to the good answers here: our galaxy has some thickness to it, but it’s wider than it is thick by a factor of 10-50 depending on how you measure. Roughly the same relative thickness as a thin-crust pizza.

[MCU] Which timeline would be the least unpleasant to live in had one of the villains succeeded in their goal?

For example:. If Obadiah Stane killed Tony Stark at the end of Iron Man 1, would the long term repercussions have been better or worse than if the Project Insight helicarriers had successfully launched during Winter Soldier? Or if Ronan the Accuser had killed the Guardians of the Galaxy and purged Xandar with the Power Stone? Or if Darren Cross had killed Scott Lang and sold Pym Particles to HYDRA? Or if Hela killed Thor and continued her conquest of the universe? Which timeline in which the villain wins in an MCU film would be the LEAST bad?

*Spider-Man: Homecoming*. If Spider-Man hadn't stopped Toomes, he would've sold a few more weapons to street criminals in New York. Maybe there would've been a few more robberies before the Avengers or SHIELD stepped in.

ELI5: How can someone call a phone number they heard on the radio and get "80% of their IRS debt completely gone!"

Are you in debt with the IRS? Do you have $20,000 or more in back taxes? Call this number for IRS relief!

Some of these businesses are scams, but some are legal and just charge for a service that anyone has access to. For instance, people in a lot of debt to the IRS can make an "offer in compromise." They agree to pay a good chunk of their debt within a set time, based on their income and assets, and the IRS does not collect the rest of the debt. This is something the IRS does because a partially collected tax debt is better than nothing. Companies like these might do something like charge you up front to submit the application for an offer in compromise, even though that's something you can do yourself, if you knew about it.

Can butterflies remember being caterpillars?

During the metamorphosis of insects it seems their cellular structure is completely reorganised. How much of the memory of the individual survives this? For example, if you "trained" a caterpillar or conditioned it to respond in a certain way would the resulting imago remember this conditioning?

Yes, and it's actually quite amazing that it happens at all. The caterpillar's body breaks down to reorganize into it's adult form yet does retain memories. This was discovered using your example, conditioning. Caterpillars were conditioned to avoid a scent and remembered it as adults. However, it seems events are more likely to be remembered in older caterpillars than younger ones.

ELI5: How does simply observing a particle (like in the double slit experiment) change the way the particle interacts?

Like in this video: https://youtu.be/U7Z_TIw9InA How does a particle "know" it's being observed, and why does it act differently when being observed?

To observe something you need to whack it with something or it needs to spit out something. For example, for you to observe your fingers, you need to whack it with light to reflect into your eyeballs. To observe your screen it needs to be spitting out light. This is what they mean by "observe", whacking it with something or watching it spit something out.

ELI5: What does it mean to sing a song in a particular key?

**First and Foremost: The vast majority of people saying this have no idea what it means! Especially Singers.** Notes are Frequencies. Doubling a Frequency results in a Note that sounds "kinda the same but higher", which is why it is treated as a higher version of a lower note. Example: 440Hz is an A, but so is 880, 1760 and even 220 and 110 or 55. The same Note but higher or lower is called an Octave, which you might have heard before. Between two Notes of the same Name we divide the space into 12 Notes equally spaced called A A# B C C# D D# E F F# G G# cycling back to the A. We might also call them A Bb B C Db D Eb E F Gb G Ab, but that's a whole nother can of worms. We didn't always use the 12 tone equal temperament system, but that's how we do it now, because that way the most amount of notes appear, that sound good, "when played together with each other". It's just the most practical. The distance from one note to another is called an *Interval* with a specific name depending on how large the interval is. You might have heard about thirds, fifths, Seconds, Octaves etc. Now, when you pick any Note as your Basis for any music (We call this our *root note*) we have to look at the intervals from the root to the other 11 possible Notes in our western System. If we just play them all, then it will sound really confused, so we gotta pick some of them. A group of picked notes to be played is called a "Scale". The A Minor Scale is A B C D E F G, the B Minor Scale is B C# D E F# G A, the A Major Scale is A B C# D E F# G#, the A Locrian Scale is A Bb C D Eb F G A and there are countless others. After you got a "Scale" you want to base a song around you can say that this is the "Key your song is in" with the Root Note of the Scale beeing the "Key Center". If you now write a Melody in lets say A Minor you might go: A -> B -> D -> C -> E -> G -> A (Higher Octave) and have other Notes as chords to support the Melody. But you might Run into a Problem, because your Singer can sing the E, but not the G and high A requested, because it's too high. One Option would be to play every Note a whole Octave lower, with all the notes staying the same in name, but that just might sound way too low as a whole, so we have to change the Key. For this example i said the E is the Note the Singer can still sing, so we move the highest Note in Question down to an E, which is 5 notes (Look at the full 12 Note-names here, not just the scale). A -> B -> D -> C -> E -> G -> A becomes E -> F# -> A -> G -> B -> D -> E (Higher Octave), which our Singer can likely sing. Congratulations, we have now changed the Melody to be in E Minor instead of A Minor. All the Instruments, Chords etc. have to also be played in the new Key. *PS: Aside from Singers, Guitars (and other instruments) are also easier to play in certain Keys (A Minor, C Major, G Major, E Minor, E Major) than others (F# Major or Bb Minor). Piano is easiest on C Major / A Minor, because it's all the white Keys.*

ELI5: Why do we give North Korea humanitarian aid instead of forcing them to give up?

So, why? Why doesn't everybody just cut off them completely, forcing their government to "surrender" as it were, open their borders and join the rest of the world. I mean, their situation ain't exactly been improving over the years [while giving humanitarian aid].

If North Korea were to collapse, it would be the closest thing we've experienced to a refugee crisis from another planet. North Koreans are forced to live in a completely different reality, and China has absolutely zero interest in integrating them into Chinese society. Providing humanitarian aid is a preventative measure against a collapse that would be extremely expensive for all parties involved. The US, China, South Korea, and Russia would replace living next to a hermit state with living next to Somalia.

[Pokémon] Why do some pokémon not evolve? (Only have one "form"). And, is there any advantage to that? Or is it all disadvantage. Examples would be nice too.

In each generation there are pokémon that do not have an evolution. I'm thinking of pokemon like Taurus. Is there any in-game explanation for why some species don't evolve? (Bar them adding an evolution in a later game.) Also, for this question, I'm not counting mega-evolutions because I think those are really more akin to injecting a massive dose of steroids or PCP into a pokemon.

Why are humans born looking like small adults? Frogs are born as tadpoles, that turn into frogs as they get older, but humans never change form. Why is that? Answer that, and you'll find your answer.

ELI5:Why were some very toxic substances formerly thought of as medicinal?

This question was inspired by [this](https://www.reddit.com/r/interestingasfuck/comments/3g7689/deadliest_rocks_in_the_world/) post, which included information on the rock [stibnite](https://en.wikipedia.org/wiki/Stibnite) which is toxic but was formerly used as medicine and material for utensils. I understand that even now many medicines have terrible side effects but how were substances like mercury ever thought of as good medicine?

Most of the "medicine" back then worked by trial and error. If your medicine "cured" the sickness by placebo effect without poisoning the patient that was a success (there is a reason most doctors had a seriously bad rep in the old days).

ELI5: Why, sometimes, you dislike a song at first, but after hearing it a few more times you begin to like it.

Music is all about patterns and repetition, but just simple repetition is boring, so there is also change. So music sits on the boundary between predictable/boring, and chaotic/incomprehensible. This is something you will notice in almost all music, that it sets up a pattern, and then changes it before it becomes predictable. The music builds expectations and then either fulfills those expectations or doesn't, depending on the effect the composer is trying to achieve. Establish the pattern then break the pattern, change it into something else - familiar, recognisable, but different. The next verse is the tune you know but with new words. Then the chorus uses different chords, or the same chords but a different rhythm, or a different order, or the same thing with a new instrument, or a different melody over the same chords. Some things predictable, some things unexpected. Point being, much of the effect of music relies on expectations, so it really makes a difference whether you know the song or not. Some songs that you end up liking the most once you know them you don't like at first because they violate your expectations in ways you don't like. But once you know what's coming, you can enjoy the changes without being thrown by them.

ELI5: Why are fights between players allowed in the NHL when it is very strongly prohibited in just about every other sport?

It's just part of the game. The refs do stop fights when they go to the ground or when it gets out of hand to prevent any real injuries occuring. The players aren't really fighting to hurt eachother. It's more to show the other team that certain things won't be tolerated. It can be strategic or just because emotions are running high, but players rarely get any real injuries from a fight.

ELI5: Why can't I swallow twice in quick succession, without it being difficult?

It's because swallowing starts a chain reaction of muscle movements in the throat all the way down the digestive tract called peristalsis. So the top muscles in the throat have to wait until the adjacent muscles are ready to start again. It's like trying to start a "wave" at a sporting event when the person next to you is still standing up. It just doesnt work.

CMV: School Lockdown Procedures actually makes students less safe.

As someone who grew up in the post-Columbine world and has always known school lockdown drills, there's some things that have always bugged me about them that I could never get past, and even as a child I knew some serious flaws that never made me feel safe with them: 1. The Standard Lockdown Procedure Relies On An Open Secret Fooling People Who Are Guaranteed To Know It I don't know what your experience was, but every school I ever went to had the "close doors, shut off lights, crowd in corner of the classroom" procedure. The whole idea was supposedly that someone would just figure it was empty and move on, since they'd have a teacher violently shake the door for a few seconds as they passed by. Question: How is this fooling anyone? Most shooters are young enough to have done these drills themselves, and even if that assumption is wrong school lockdown procedures are common knowledge. Also, even if it was somehow a secret, I wouldn't really have my life depend on someone thinking that a public school at 1PM on Wednesday is just empty. Someone who wants to shoot up a place is not going to just walk around the empty halls, jangle a few doors, and then just call it quits. Nowadays, it seems as though schools have addressed the problem of "What if the shooter isn't a colossal moron?" and added some extra security like barricades of desks or some kind of last-moment combative measure like hurling books at someone who walks through the door, but having people all in a corner is just begging for a pipe bomb (something the original Columbine shooters had, it must be noted) to be hurled into the room instead. Also, the corner where people are going to be hiding is extremely easy to guess (it's always the far one), thus anyone can just put their weapon through the door and blind-fire it while they remain safe from any desperate book throwers. 2. They completely neglect protection in other areas In other words, nothing schools can do will protect students when they're all going into or out of a school. It doesn't matter if your school has bulletproof front doors when hundreds of students are cramming their way through them to get home. Also, what about fire drills? For all the protection a school may provide while students are indoors, any security protocol that requires building evacuation is an easy and obvious tactical flaw. Even as a kid, this just blew my mind. With the mere flip of an alarm switch that can be accessed by anyone, a potential murderer could get the entire school to come out of the school and (usually) cluster into the parking lot or athletic fields, after which they could find their weapon from an off-campus hiding place (i.e. like behind a tree just off school property, so they wouldn't have to have snuck it into school) and then...well...do horrible things. I don't like to talk about this stuff because I don't want to give anyone any ideas or be seen as a sociopath for thinking about this stuff, but "Pull the fire alarm to get everyone outside" is something I'm shocked (and grateful) that no one has ever tried yet. It's like how I'm baffled as to why terrorists don't just bomb TSA checkpoints (i.e. dozens of people all tightly packed in a line) rather than try to get through them. 3. Remaining in place always struck me as a bad idea. Long ago, I decided to myself that if I was ever in any danger, I would run instead of trusting the official plan. Just book it to the nearest door and fly out of the building, because I'd always much rather choose to leave a bad situation than remain in it with the vague hope that police will arrive soon enough or that the shooter will be fooled by a secret plan that everyone knows. I've never trusted lockdown drills in the first place: keeping thousands of students in a building with an active shooter always seem dubious to me regardless of how secure the classrooms are, and I've always wished they had a more proactive plan where the shooter would be locked *inside* the building as students and teachers fled the building entirely using the outer windows and doors. Locking your classroom door and heading out the outer window so the shooter is stuck inside the building just makes so much more sense than locking the door and hoping they don't try to break it down.

What works for an individual doesn't work for a crowd. The objective is to keep as many people safe as possible, and that often means making the shooter's objectives as hard as possible, hence the practices. Crowding up against the door doesn't stop a shooter from getting in, but it does make it impossible to shoot students from outside the room without forcing their way in. If the a shooter does force into one classroom, well fuck, now they've got 30+ students to deal with in close quarters. The shooter could easily be overrun by students, even if armed. The fire alarm thing is a valid concern, and a vulnerability. As for everyone booking it, this basically creates a shooting gallery for an active shooter. Again, the purpose is to slow the shooter down and obstruct his efforts to inflict harm. Everyone running for the edits means that several unlucky souls will run into the shooter they're trying to escape from. Staying in a locked room makes the shooter's task of finding students slower and more precarious for the shooter, and in that way, it's safer for *everybody* to follow the lockdown proceedures

ELI5: Unbiased explanation of Critical Race Theory?

Most of the ones I found through the search were not ELI5 at all, like they didn't even make an attempt at explaining in a simple fashion. Some others were obviously biased.

Critical Race Theory is the theory that most, if not all, aspects of modern society have racism baked in, which is why it’s been so hard to get rid of racism. For example, we tend to assume that our laws are written to be race-neutral, but critical race theorists point to the fact that people from different racial backgrounds can have wildly different outcomes while dealing with similar legal issues in the same legal system. The explanation, according to CRT, is that the laws and legal system are actually designed (consciously or not) to perpetuate racism. It’s important to note that CRT isn’t really one theory, but rather is a collection of different ideas that challenge a wide swath of intellectual and political traditions. The common thread is that they all agree that race is one of the important factors in creating and maintaining inequalities in society.

Why do people keep dreaming about their old friends/relatives even though they're no longer in touch?

I keep dreaming about my childhood friend for years. I have not seen the guy for at least 6 years and even before that we went to different high schools, so we weren't in touch since elementary school. I finished university and still have dreams about him once a month. I don't consciously think about him, I don't wonder what he's doing but I keep seeing him in my dreams. It started to freak me out. Is there a particular name for this in psychology? Why do I keep seeing him?

Because the stories of our dreams, are compiled from our memories, worries, concerns, etc.. **The only thing your brain has to use as content matter for dreams is what's already there.** If you've seen it, experienced, or have ever thought about it, it's a possible inclusion. Then, the more you worry about it, the more it is top of mind, the more you will often see it. It's just how our mind works. Dreams are nothing more than stories that our brain puts together while you are experiencing random neural firing (think of those firings like a sleep release of sorts)..... ...and what the brain pulls for content can be random or something you've thought about, but it can certainly pull from memories many years passed.

ELI5: After eating spicy food, why does breathing-in cool my mouth, but breathing-out burns it more?

most spicy foods work by activating a receptor that reflects heat. Imagine if there is a thumb print machine and the thumb that opens it is heat, the spicy food has capsaicin which also has the same thumb print. Basically activating the sensor. When you breath in, the air in ambient which your body is used to. But when you breath out it comes out around 30 degrees C. Which is going to trigger the censor which is partially opened by spicy foods.

ELI5: how did radiation destroy machines in Chernobyl?

I remember hearing that everything from cameras to trucks stopped working because of the radiation, what's up with that?

You heard something wrong about the trucks then, those certainly didn't stop working. There's a graveyard of them because the metal became irradiated, it's not so much "they don't work" as they're now unsafe to be around because they are radioactive from induced radiation. Only more sensitive stuff breaks - film in mechanical cameras gets exposed by radiation and semiconductor based things glitch out and over time degrade to malfunction permanently.

In animals like octopuses and cuttlefish that die shortly after mating, what is it that kills them?

In documentaries about cephalopods, sometimes footage is shown of octopuses and cuttlefish post-mating indicating that they die shortly afterwards. They usually look very disheveled, with their skin peeling off it looks as though they are literally disintegrating. What causes this, is it some sort of super fast aging process?

The trait you're looking for is called semelparity. A classic example is a marsupial mouse, which basically fucks its way into the grave. As it enters the mating season it starts producing a huge amount of the stress hormones adrenaline (epinephrine) and cortisol. These make fat stores more available for energy, reduce hunger, reduce pain, reduce fatigue, and kill the immune system in order to maximise the number of times it can mate in this one season. It will continue to have sex without eating, barely sleeping, until it is ridden with diseases (fur hanging off etc.), has no fat remaining and has been digesting its muscles for energy, and is completely exhausted.

ELI5: Do trees have a life span, or will they continue to grow if not damaged or diseased?

**Edited to correct stuff.** Many trees can live for an exceptionally long time. The oldest known trees are over 5,000 years old. Trees are an interesting case because, as they grow older, they also grow *faster*. This basically means that the older they get, they’re simply more and more likely to die of a disease or other event. Also, when a tree gets old, it has trouble protecting most of its inner heartwood and/or exterior. This means it cannot fight damage as well as when it was younger. The most common way a tree would die of “old age” would be through this process: > Woody plants heal through by compartmentalizing the damage, sealing it off from the rest of the plant. This is called CODIT. This process happens in four steps, called “walls“. The process happens like this: >Wall 1: The tree blocks the transport tubes surrounding the wound, thereby preventing the wound/infection from spreading further. >Wall 2: The tree then builds a ring around the wound or infection to prevent it from spreading inward. This acts as a barrier providing further protection. >Wall 3: The tree then sections the wound laterally. This prevents the infection or wound from spreading circularly, keeping it from spreading left or right. >Wall 4: As the trunk grows, the tree’s new growth rings seal off the infection or wound. This prevents it from spreading outward into the new growth. >When a tree gets extremely old, it begins to lose this ability to compartmentalize and eventually causes the tree to die. Trees that still have leaves on them but their trunks are completely hollow is an example of wall 4 beginning to fail. Unless the wall 4 step has succeeded just in the nick of time, the tree will soon die. Hopefully this makes sense? It might not be exactly what you were hoping for.

[Terminator 2] How do we clean up this mess?

So some idiots just crashed a tanker full of liquid nitrogen into the foundry where I work. I’ve hit the alarm and my colleagues and I have escaped from the spill, but that’s about 40,000 litres of liquid nitrogen sloshing around in there. Who do we call to handle that much liquid nitrogen and how will they go about cleaning up the mess? Do I even have a job to go to tomorrow or will the plant be closed indefinitely?

You don't have to worry about cleaning the nitrogen up. Its going to warm up pretty quickly and boil off into nitrogen gas once it reaches a balmy −320 °F (yes minus 320). Then dissipate into the atmosphere which is 78% nitrogen anyway. The only clean up is the tanker itself and the physical damage done. There will be a few days of inspections to make sure the cold didn't damage pipes and tanks that are meant to hold other substances at pressure. Some of them might have to be replaced as the intense cold could have made them brittle.

ELI5: How and why do almonds have a split directly down the middle?

I was eating some today and I didn't know why this was...

Almonds are seeds, almond seeds are dicots, meaning they have 2 cotyledons. When you split the seed in half you are exposing each cotyledon Therefore both sides of the almond are not completely joined

ELI5: How do electronics with battery indicators "know" how much battery they have left?

My phone has a battery icon that shows a visual representation and a percentage of battery remaining. How does it tell how full the battery is?

Batteries voltage changes slightly as they discharge. A simple way is just to measure this voltage (like a battery tester). Smarter batteries, like laptop batteries, have micro-controllers built into them that allow the device to communicate with the battery. Charge is measured in Coulombs and battery capacity can be measured by counting Coulombs. Amps, are just the number of Coulombs per second flowing, so smarter batteries can measure the current flowing out of a device and integrate this to get the amount of charge flowing into or out of a battery. Current is usually measured with a small resistor and a voltage meter using Ohm's law (Voltage = Current \* resistance) Smart batteries will also report battery degradation over time etc, so a 100% charge on an old battery might only be 80% of the original capacity. ​ Better ELI5: ​ A Coulomb (charge) counter would act like a water meter that can measure water flowing into or out of a storage tank. By keeping track of the net water in the tank, and you know the total size of the tank, you know the percentage. ​ A more simple method is to measure voltage. This would be like capping the spigot on a tank with a PSI gauge and reading how much pressure was at the bottom of the tank and therefore you can calculate the water depth and estimate the remaining capacity. ​

If the story of Adam and Eve were true, how fast would the population have to grow in order to reach 7 billion people in 6,000 years?

I'm an atheist* who ~~believes evolution is real~~ accepts evolution as fact. I'm just curious what the math would look like for my question. Edit: 1.) Thank you for help everyone. This wasn't designed to be a religious debate. I just thought it was an interesting story problem for math that I don't understand. 2.) I'm getting a lot of comments and messages about how the Bible doesn't state that the Earth is 6000 years old. I grew up in a fundamentalist Christian religion which taught Young Earth Creationism. I understand that every Christian sect is different, so no need for the apologetics. Note: Atheism is a conclusion one arrives at when they value reason and evidence. I don't believe in, or have faith in, atheism. Faith is pretending to know things you don't know.

6000 years is roughly 300 generations. Using the premise that 2*x^3"00=7000000000, this gives a rate of 1.076 per person per generation. Put in human terms, we multiply that by 2 to get the average fertility rate of 2.15, meaning each woman would need to have 2.15 children on average to attain this rate. The current global fertility rate is 2.36 and dropping, for context. This of course ignores infant mortality, which was likely high at most periods of history and could bump this number up considerably.

CMV: I think people who get noticeable body modifications know what they are doing and shouldn't be surprised or shocked when they are viewed differently because of them. CMV

_____ To start off, I don't personally judge people negatively because they decide to get body modifications, piercings, tattoos, very noticible plastic surgery. But I think that these people know what they are getting into when they make these decisions. It is your right to modify your body how you wish but you have to know when you the decision to get a giant tattoo on your neck that it might affect your ability to get certain jobs in your future. If you are gauging your ears, it takes time. You realize early on that some of the reactions that you will get from people are negative and that they will only continue to increase in number and severity as your gauges get larger. There a lot of very good, nice, upstanding citizens that have lots of body modifications and that changing peoples views is important to the progression of society. But these people know what they are getting into and even if they don't it is still a life choice that they are making and they have to live with the fact that will effect their life, for better or worse, while they have it. CMV > *Hello, users of CMV! This is a footnote from your moderators. We'd just like to remind you of a couple of things. Firstly, please remember to* ***[read through our rules](http://www.reddit.com/r/changemyview/wiki/rules)***. *If you see a comment that has broken one, it is more effective to report it than just downvote it. Speaking of which,* ***[downvotes don't change views](http://www.reddit.com/r/changemyview/wiki/guidelines#wiki_upvoting.2Fdownvoting)****! If you are thinking about submitting a CMV yourself, please have a look through our* ***[popular topics wiki](http://www.reddit.com/r/changemyview/wiki/populartopics)*** *first. Any questions or concerns? Feel free to* ***[message us](http://www.reddit.com/message/compose?to=/r/changemyview)***. *Happy CMVing!*

I think everyone who get a significant body modification *expects* to be treated differently because of it. However, i don't think anyone should *accept* that they are treated differently. It is a completely superficial aspect to judge someone for, same as hair-style, clothes or what have you. Albeit more permanent.

[X-Men, Marvel Comics] How dire does a situation have to get for Charles Xavier to go out on the field with the X-Men.

I don't know if it necessarily needs to be a dire situation, just one that requires his specific skills. It doesn't have to be a fight, sometimes it can be some kind of diplomacy or communication. Sometimes the X-Men need to appear as a united front, and for that it can help to have the guy who runs the whole thing. Otherwise, if he really needed to, he's probably powerful enough to assist the X-Men in skirmishes from the school, using Cerebro if he needs it.

ELI5: Why can't news stations (CNN, NBC, CBS) sue the President for defamation when he calls them fake news or says they don't cover certain stories?

First, it would be a poor public relations move -- it would make the media look petty and thin-skinned to attempt to sue the President over negative tweets. This would likely damage, rather than help, the media's credibility. This would play directly into the President's strategy of marginalizing and denigrating the media, and thus not be to the media organization's benefit. Second, to win a claim of defamation, the person or organization filing the claim (the plaintiff) has to prove that there has to be some harm or injury done to the plaintiff by the defendant's defamatory statements. That would potentially be difficult for the media to quantify, and, if they did, then again they would be playing into the President's strategy of marginalizing and denigrating the media, painting themselves as having been weakened or harmed by mean tweets.

ELI5: What "sins" did Jesus "die for" exactly? What would have supposedly happened to us if he didn't? (Serious)

Christians believe that after Adam ate from the tree of knowledge of good and evil, that all humanity was fallen and carried a sin nature, even the most innocent of babies carries this with them (passed from father to their children). It's this nature that causes sin to be tempting. The only way to pay for sins is via blood sacrifice (thus the reason Hebrew law required all sorts of animal sacrifice). The best analogy I've heard for a sin nature is bamboo which grows sprouts rapidly and spreads widely. The sprouts can be cut but the root remains and spreads. Jesus being born with God as his father, lacked this sin nature and offered a way to undo the curse brought on by Adam's sin. Because he didn't succomb to temptation, and lead a sinless life, his death becomes an eternal sacrifice for all who accept it. By becoming a Christian, Christains believe that they have the keys to victory over sin (not that they'll remove the root, but can machete the top effectively, and eventually the root will wither and sprouts will be less frequent). That's not really ELI5, but if you have questions I'll try to explain more clearly.

[Dragon Ball Z] How did Vegeta keep his sanity after becoming Majin?

Saiyans have a tremendous will, and Vegeta's will is extreme even by Saiyan standards. He's extremely focused on one thing: defeating his enemies. He's also extremely arrogant, and there was a part of him that just wouldn't let himself be controlled by an _inferior_ like that. He allowed himself to be controlled when it served his desire to test Goku, and the stakes were manageable, and kept his willpower and ki in reserve until the moment breaking free was a necessity. Babidi really never had a prayer of keeping him under his spell indefinitely. This is a Saiyan warrior _price_ we're talking about here.

If you break your bones to a point you need metal rods and bolts, after the bone heals do the metal implants make your bones more sturdy & less susceptible to breakage?

Nope. The metal won't break, so it is technically more sturdy there... but the attachment points through the bone weaken them quite a bit, leaving weaker points. To some degree time can fix that. Modern implants get better and better but thin bones won't become stronger after drilling holes through them. They can even split, then you're further from home. Implants with specific surface structures and eg bone matrix proteins are interesting research topics!

If Helium is so scarce, why are Helium balloons so common?

Also, if we stopped using it in balloons, would that make much of a difference in the long term?

It's not scarce yet, but the alarm is because there is only just so much in the earth and it is being used up fast, often just released into the air, where it relatively quickly floats to the top of the atmosphere and gradually gets propelled by the solar wind away from earth. It's somewhat controversial as to exactly when we'll run out of accessible helium. > if we stopped using it in balloons, would that make much of a difference in the long term? No, that's not a large usage. It's the amount being thrown away to the atmosphere that is really large. It has critical and irreplaceable use in physics and engineering and medical applications, so everyone should note that it's definitely not the party balloons that make this an important topic.

[Cuphead] If Cuphead's soul belongs to the devil, then why does his ghost float upwards, with a halo?

He still needs to be judged. There's a Tom and Jerry episode where Tom dies and goes to heaven, only when he gets there the guy at the gate looks over his paperwork and gives Tom the bad news. Everyone's an angel until they're evaluated.

ELIF: What does the phrase "corporations are people" mean and why is it significant?

"Corporations are people" is a legal fiction (that's not a derogatory term, it's just the name we use for the concept). What that means is that it's something that isn't technically true, but legally we pretend it's true because it makes things easier. We do this so that we can apply existing laws to new scenarios that may not have existed when the original laws were created. We allow corporations to "be people" legally so we can treat that as such for the purpose of enforcing contracts, and so that they can sue and be sued as if the were a person. More recently corporate personhood has been a political issue because of recent court cases involving corporations rights with respect to political speech.

ELI5 how a jet engine works

I don't understand how jet engines work. It's awkward when I'm around people that are talking about jet engines - I just have to come up with an excuse to leave or just guess how they work. Thanks for your help, webernet!

A gas turbine engine is a tube designed to take that air from the front (the intake), add fuel, burn it and the blow it out the back at a greater rate than it was sucked in, the result being called thrust. In it's very simplest form it is a tube with 3 stages, with each stage performing a task, and each stage from front to back being part of a continuous stream of air that end up with it being ejected out the rear: **Stage 1.** Compressor - This is a fan, or set of fans, all stacked up together. This is spun (we'll come back to what spins it later) and in doing so acts like a fan in your house, blowing the air in a certain direction, rearward. Due to the fact that there are a number of fans all stacked up and acting in the same direction on the air, the force of these fans squashes the air up, compressing it many times over. The air continues to move backward towards the next stage. **Stage 2.** Combustion Chamber - The compressed air is now passed onto a chamber where fuel is continuously being injected and ignited with spark plugs. You might ask how the fire isn't put out by the fast moving air, the reason is that the way the air mixes and the ratio of fuel to air means that it's perfect conditions for combustion. In the process of being burned the air is suddenly charged with a huge amount of energy that is bursting to get out somewhere. Because the fans at the front are still furiously pushing the air backwards, the air takes the path of least resistance into the 3rd stage. **Stage 3.** Turbine - This is very similar to the first stage, but whereas stage 1 (the compressor) is like a huge desk-fan, stage 3 (the turbine) acts like a windmill. It is designed to be spun up by the hot expanding and high-energy air from the combustion chamber. Here's the clever part... Because the compressor and the turbine both sit in this tube at opposite ends, we connect the turbine (being spun by the hot air) to the compressor. The hot air has so much energy it can spin up the turbine, in turn spinning up the compressor **and** still have enough energy to produce thrust out of the back.

What kinds of acids could damage a jacuzzi?

Are there any with innocuous household uses?

Chemist - There are lots of acids that could damage a jacuzzi, depending on what it's made of. There are specific interactions to watch out for, but as a general rule, higher concentrations cause more damage. Perhaps you could specify what you are doing? There are a number of acids that you can get for household use: vinegar (acetic acid), muriatic acid (HCl), battery acid (H2SO4), and many rust removers (usually phosphoric acid). Plastics and glass generally tolerate acids in low concentrations well, but plastics shouldn't be used with nitric acid, because it is a strong oxidizer. Metal components will react with strong acids like HCl and H2SO4. And if your jacuzzi is made of stone/marble, avoid acetic acid.

ELI5: if a human embryo isn't viable, by what mechanism does the body decide to terminate? What is it that goes "this isn't working, scrap it"?

Cannot add a flair but I suppose this would come under Biology

A precise answer probably wouldn't be really eli5 but basically there will be some chemical signal if the embryo isn't viable on a cellular level. When cells die they release a lot of different chemicals that signal for other cells to recover and destroy the remnants. Also, when the embryo dies it stops secreting hormones that make the uterine wall grow into the placenta which will then start to die and detach like during a regular cycle. On the other hand, if there is some major genetic defect the blastocyst won't even implant into the uterine wall from the start and after a certain point if the fetus dies in utero the body won't necessarily terminate the pregnancy which can be very dangerous for the mother.

ELI5: Why is the unit circle divided into increments of 90 degrees (90, 180, 270, 360) and not based on 100?

I'm just genuinely curious as to why we separate it like that? For example, 100 degrees would be the same as 90 based on 100 system and 400 degrees would be 360.

The Sumerians started with a base 6 numbering system. They studied circles for things like navigation and came up with 36 degrees for a circle (in base six, 36 is 100). Later the Greeks decided they wanted more degrees, but found the divisibly of 36 useful. Since they lacked the decimal point, they chose to make a circle 360 degrees. The divisibility remains useful and that's how we all learned it, so it remains.

ELI5: What happanes to someone with only 1 citizenship who has that citizenship revoked?

Edit: For the people who say I should watch "The Terminal", I already have, and I liked it.

They are considered "stateless." Countries will likely grant him certain residency statuses or asylum after they consider what exactly caused his citizenship to be revoked. Statelessness due to political conflict and ethnic discrimination, particularly in central Africa, is actually a significant issue that burdens surrounding countries with refugees and illegal migrants.

ELI5: why does any form of storage device (usb, hard drive) never have its advertised storage space available.. for eg 4 gb usb have only 3.81 available

Two things: formatting, and different definitions of MB, GB, etc. Formatting isn't the drive manufacturer's fault. When you have any storage device you need to be able to store things in some ordered way so that you can retrieve them later. To make this possible your system writes a list of where each file will be stored in the hard drive, much like the table of contents on a book. If you had a 100 page notebook and started writing data on the first place then there'd be nowhere to put the table of contents, so you'd be better off reserving the first couple of pages for that purpose. Drives do much the same thing. The other issue—different definitions of MB, GB, and so on—comes from the fact that in computer science it is very often useful to do things in powers of two, since that meshes very well with binary. It happens that 2^(10) = 1024, which is pretty close to 1000, so that became a common multiple when dealing with large numbers. Computer scientists adopted the SI prefixes for these numbers, where 1024 bytes would be 1 Kilobyte, and 1,048,576 bytes is 1 Megabyte, and so on. The problem is that with each multiplication by 1024 you get further from factors of 1000. 1 TB (using that definition) is very nearly 1.1 trillion bytes. This has led to many people rejecting the definition of kB, MB, GB, etc being factors of 1024 and calling those quantities kiB, MiB, GiB, and so on, while the SI prefixes use their SI definition as factors of 1000. When Windows reports the size of a disk it still calls factors of 1024 MB, GB, etc, but hard drive manufacturers have switched over to the use of factors of 1000. If you look on the box it will tell you "1 TB = 1,000,000,000,000 bytes" or something like that. You get the full 1 trillion byes on a 1 TB drive, but you use some of that for formatting so you can store a good amount less than 1 TiB.

CMV: The theory of evolution and Christianity are incompatible

A couple of quick notes: I am going to use the term "believe in evolution" simply for convenience. Evolutionary theory is generally not considered something that you believe in, but since some Christians deny evolutionary theory they effectively don't believe in it. Also, I am going to be using Christianity as my reference religion, but other Abrahamic religions that contain the genesis story are applicable as well. _____ The theory of evolution that gives an explanation as to our origins I believe is not compatible with Christianity. You cannot believe in evolution as well as the Christian genesis story because they directly contradict each other. The Christian genesis story states that god created man in his current form, while evolutionary theory explains that life took millions of years to evolve and that our species is descended from a common ancestor with the other primates. If you are a Christian who believes in evolution as opposed to the genesis story and claim that the Christian genesis is just a metaphor, you open the door for the entire rest of the bible to be just a metaphor as well. Beyond that, if you claim that Christian genesis is just a metaphor because it isn't actually true in a literal sense, then you can further extend that the entire bible isn't true in a literal sense. If someone were to claim that only the genesis story is a metaphor but the rest is literally true, then that person has effectively filtered the bible themselves. For a person to pick and choose what is real and what is not in a sacred book is to not hold the book sacred. Finally, for a person to not hold the bible sacred is to not be a Christian. Evolutionary theory and Christianity are not compatible. CMV! _____ > *Hello, users of CMV! This is a footnote from your moderators. We'd just like to remind you of a couple of things. Firstly, please remember to* ***[read through our rules](http://www.reddit.com/r/changemyview/wiki/rules)***. *If you see a comment that has broken one, it is more effective to report it than downvote it. Speaking of which,* ***[downvotes don't change views](http://www.reddit.com/r/changemyview/wiki/guidelines#wiki_upvoting.2Fdownvoting)****! If you are thinking about submitting a CMV yourself, please have a look through our* ***[popular topics wiki](http://www.reddit.com/r/changemyview/wiki/populartopics)*** *first. Any questions or concerns? Feel free to* ***[message us](http://www.reddit.com/message/compose?to=/r/changemyview)***. *Happy CMVing!*

> The Christian genesis story states that god created man in his current form Actually, it doesn't. Nowhere does it provide a description of early man that suggests he looked just like the humans of today. Secondly, let's stop for a moment and talk about what Christianity actually means. Christianity means believing the story of CHRIST. That he was the son of God, was sent to Earth to die for everyone's sins, and then rose from the dead to join God in Heaven. That's the entirety of Christianity. Belief in creationism is not a requisite condition for believing the story of Christ. Yes, they're in the same book, but there are plenty of Christians who completely believe the story of Christ, but not the literal story of creation put forth in Genesis. The mere existence of these scores of people disproves your claim.

Cmv: Gentrification shouldn't be demonized

I am by no means married to this idea and would love to hear from different perspectives, but as it stands now, I don't believe gentrification should be demonized. I live in a rural area but close enough to a major city to see how gentrification has turned a once desolate area into a thriving community with lots of new businesses and a much more vibrant look. In my opinion gentrification has become a buzzword often used to illicit the picture of young, affluent, white, progressive, hipsters who come in to communities and through their buying power make life for residents decidedly worse, with little regard for their wellbeing and to scare people away from change, even if it is in their best interest. I think that any situation in which more capital is being invested in an area it is a net positive. This creates new businesses, jobs, renovated housing. The only real issue I see with gentrification is that it can cause lower income residents to leave the area should there be a massive influx of investment and capital in the area over a relatively short time. While I understand the frustration this may cause, and maybe it's callous on my part, that is how it is in a capitalist society, big bank takes small bank, big income displaces small income. If we are going to start demonizing that we would need to look at society as a whole. Business mergers happen everyday, smaller companies are bought out by larger companies. Does this have the potential for lost jobs? Yes, does it suck? Yes, does that mean that we should view all business transactions involving takeovers as evil and cruel? Not in my opinion, then why is it we view revitalizing an impoverished area as such?

Do you think there is a difference between revitalization where you infuse capital while supporting the people and culture that already live there and gentrification where you put those people aside because f*** you I've got more money

CMV: The concept of gender is irrelevant.

I'll start by laying out my thoughts and please correct me anywhere I am wrong. I know I have a lot to learn about this topic and I would really appreciate if someone could show me why and where my thinking is wrong if it is. From what I understand: gender and sex are different. Sex is grouped into male, female, and sometimes intersex, and is determined entirely by biology. Chromosomes, genitalia, hormones, and the like. Gender on the other hand, exists on a spectrum and is determined by a person's internal relationship to their sex and the degree to which they conform to cultural stereotypes and expectations for their sex. I understand that gender dysphoria is a real thing and that it must suck to feel completely alienated from your body and society's expectations of how you should act because of your sex. I also am hugely in favor in transgender rights and I would never want to take away basic human dignity and liberty from anyone. That being said, it is not physically possible to change sexes. A woman has a uterus. A male has a Y chromosome. It is just not possible to physically change your sex. If that gets me downvotes or is a point of contention in any way, seriously people have lost their minds. That should not be controversial. This is not hate speech and I am tired of being labeled as a bigot for saying that. That is part of the reason I made this post. I really am trying to understand the other side but there are just some things I can't get down with like the outright denial of biological fact followed by accusations of bigotry. If you still reading, thank you, but the difficult part is not over yet. It's about to get worse. I know how terrible this may sound to people and I really want my mind changed so I can understand this topic, but as it is now I have just learned to shut my mouth when this comes up. Here it is: I believe that transgenderism is a delusional state of mind and it makes no sense whatsoever to me the degree to which it is accepted, respected, and encouraged. No matter how much a person who is a biological male wants to believe he is a female, he is not. No matter what modifications he makes to his body, he is not a female. I will call him/her their preferred pronoun, I will respect him/her, because that is the polite and kind thing to do. I will not judge him or her based off of this. But really I cannot understand how things got to this point where we openly accept and encourage a literal delusion. To me it is identical to a white person believing they are black and then trying to act like a black person and color their skin. That is horrifically unacceptable but somehow gender transformations have become mainstream. I would really appreciate an explanation of how transgenderism is OK but transracialism isn't. I fully accept transgender people and their rights. If that is what they have to do to be happy, I am all for it. I love them and respect them the same as I would anyone else. But really I just do not get it. Here's another thing I don't get which ties into the title of this post. Gender is a cultural construct, it exists on a spectrum, therefore there are a myriad of gender identities on this spectrum one can have. But you know what else is a cultural construct? Nearly everything humans do. I do not understand the hyperfocus that has been applied to this one aspect of human relations in our culture. Let's take an example. In some cultures, eating meat is forbidden. In others, it is a staple of the diet. You could now say that eating or not eating meat exists on a socially constructed spectrum. Another example: some societies encourage alcohol, music, and dancing, and others forbid these activities. If I enjoy these activities more or less than the cultural mainstream, am I now given an identity on a spectrum? Some cultures have tight familial connections and some do not, do these traits exist on a spectrum that is worth discussing the same way we discuss gender identity and the gender spectrum? In every culture there will be a mainstream expectation of behavior for a group of people and there will be people who conform to that expectation and people who do not. This is a huge concept and is not confined just to gender. That's not to say that the concept of gender isn't worth talking about, it definitely is, but I feel like when we do that we often are prone to forgetting that social constructs stretch way beyond gender. Gender expectations change across time in the very same cultures. I do not understand why gender has become such a paramount topic of conversation today. Thank you if you read this all the way through. I would appreciate any and all feedback someone can give me. I do not want to be interpreted as a bigot. If I am unconsciously a bigot, I would like to know about it. And I'll reiterate: someone please explain how transgenderism is different from transracialism. If I can get that then I can at least do away with the most offensive of my beliefs. Thank you.

Just like doctors assign your sex depending on your genitals at birth, so too do you get assigned a gender and socialized as such at birth. Gender dysphoria comes from a misalignment with the *gender* assignment, not the sex assignment. No one is trying to change their sex, a trans man will continue to have the chromosomes of a biological women. What they are trying to change is their gender. Yes, gender is a meaningless construct like race, but also like race, it determines a great deal about how people treat you and how you're expected to interact with others. It gets hyper-focus because it determines so much about your social interactions that you're probably blind to if you haven't experienced gender dysphoria. So by changing their physical appearance and taking hormones, they're going from one gender to another. Gender reassignment surgery (changing your genitals) is just another way that trans people can better fit the gender the feel more comfortable. You're conflating sex with gender.

ELI5: Why do we have to raise breast cancer awareness?

I'm all for preventing breast cancer, but I'm pretty sure most people are aware of it by now. It's not some unknown problem that nobody knows about.

Women still die all the time because they ignored a painful lump in their breast until it was too late. Having a breast removed is sucky, but it's way better than being dead. The awareness is to encourage these women to get to their doctor before it's too late.

[Lord of the Rings] Do the Uruk-Hai inherently know how to fight skillfully?

In the Two Towers, the Uruk Hai bred to attack Helm's Deep know battle formations, can wield crossbows, use siege engines, and are able to duel trained elves to the point where they can pretty much slaughter them. Were they taught how to do all that, or do they have some sort of inherent knowledge about how to fight as soon as they're born? It doesn't look like they'd get much training or instruction in, given the amount of time they had before they were expected to take over Rohan.

Sounds like "Movie Version". IIRC, there are a couple really short scenes in the movies that show them doing some form of practice against each other... usually in the scenes showing them being bred.

Can you actually create jobs?

Often times people will bring up how company x has created thousands of jobs, but they never include how many jobs were lost by company y because of company x out-competing them. Long-term is there good evidence that a company can create jobs (I'm sure in the short-term it's possible) or do things tend to normalize after time with the jobs having just shifted from one company to another?

Not really, at least not beyond the natural rate of unemployment sustainably. It's just a political talking point really. Long run increases in the standard of living are created by destroying jobs if anything (productivity growth). "Job Creation" is only really desirable in a recession or when we are otherwise below potential output anyway

Can multiple exact same sounds played over each other produce a louder decibel output than the original sound?

This is an example of constructive or destructive interference. If the waves are in-phase, this is constructive interference. The intensities of the two waves will add up and create one much more intense wave. If the two waves are out of phase, then destructive interference will be experienced. If we have destructive interference, the waves will create a lower intensity wave, but as mentioned before, it depends on where the sound is measured because it will be louder in some places, and much quieter in others.

[WH40K] What's the armament of the Phalanx? How many guns are we talking?

I mean, I know that it definitely has a ridiculous number of guns and my sources in the "Lexicanum" syndicate speak of "it's upper surface bristling with weapons and sensorium domes". Looking at the [Phalanx] (https://i.imgur.com/Cd0X7tN.jpg) this is perhaps one of the most striking, intimidating and [beautiful] (http://i.imgur.com/mSjhhLg.jpg) ships that I have ever seen. * How many guns and what kind of guns does she field against the enemies of the Emperor? * How large a force could this ship engage and be victorious?

The Phalanx is suspected by many scholars to be an original generation Starfort upon which the Ramillies class fortresses (the second picture is actually a Ramillies, not the Phalanx) were based. It is larger, has superior power systems and actually has its own propulsion, but follows the same basic structure and defensive layout. 4 quadrants, each centered around a primary docking bay and supported by lance batteries and untold amounts of.turreted firepower. The central keep (more of a small moon) contains the primary power systems and habitations, along with dozens of heavy torpedo batteries which can support any of the quadrant defenses. A normal Ramillies has the firepower of several Battleships and is used to offer heavy static support to pivotal fleet actions. They are a match for entire fleets in their own right, and are widely regarded as the heaviest space-borne assets the Imperium has (though limited by their lack of propulsion and the dangers of relocating them via-warp-jumps). The Phalanx is superior in every way. Its increased size is noted by at least 6 docking spars, similarly configured to those of the Ramillies, along with defensive rails linking them with more supporting weapons. Alone, it is likely more than a match for any Space Marine chapter fleet, and more in par with the power of a Sector Fleet. Properly supported, not even a Craftworld could stop it.

[Overwatch] Since Reaper can see (and eat) souls and both Bastion and Zenyata drop soul orbs, does this mean that Zenyata is right and the robots DO have souls?

It's unknown what exactly reaper absorbs. Outside of gameplay, there is little to suggest that he has any connection to the supernatural. So until the lore surrounding reaper is further explained, there is no clear answer.

[Star Wars] What's to stop the newly-destroyed planet of Alderaan from re-coalescing into a similar-sized planet again in a similar orbit?

Bonus question: if nothing's stopping it from re-coalescing, how long would it take?

IIRC a significant part of the mass of Alderaan was thrown into hyperspace when the planet blew up, water and other gasses would be carried away by the solar wind... if the planet reformed it would just be a cold lifeless dwarfplanet at best. RIP

[Avatar the Last Airbender] How does Toph "see" attacks coming at her?

She can only see things if they're connected to the ground right? so how does she effectively dodge/counterattack a rock flying at her?

Though the vibrations in the ground, she can track where her opponents are standing and get a clue as to which earthbending move they're using against her, since she primarily fought against earthbenders and they heavily rely on footwork and solid contact with the ground. Similarly, she'd be able to hear and feel where a pillar of stone or a thrown rock is being torn from the surface and dodge it. She can also hear their breathing, so she can predict when a big move is coming. Long years of practice have allowed her to recognize which breath means which attack is coming. The other elements are harder for her to track due to sheer inexperience, but there are some telltale clues. Water and fire make a lot of noise when bent. And fire also gives off a lot of heat, which she can feel coming her way. Breathing is also much more important to a firebender than any other, so they probably light up like a beacon before every attack for someone trained to listen for it. Again, most of her experience was fighting against Earthbenders, especially earthbenders who greatly telegraphed their moves for the best show in their wrestling ring. So she was able to learn how to predict and respond to all kinds of attacks.

ELI5: If a computer only takes an input of 0s and 1s how does it know to expect an image as supposed to text?

I get that any symbol is usually 8 characters in binary and that pixels colors in an image range from 0-255 with 255 being 11111111 using binary But how does it actually determine to either look for a letter or a colored image by just using strings of 1s and 0s if that makes sense.

It doesn't. You can interpret the same binary data multiple ways. It's up to the program that's running what it does with the data, which is why you can open binary files in Notepad. However, if the program is expecting data of a certain structure, it may fail if it sees data that doesn't fit that structure. A BMP file, for example, should begin with a header that specifies the width and height of the image and then the image data. If there isn't enough image data for the image size given in the header, a BMP loader will fail and report that the file isn't valid. Many file types begin with a "magic number" that serves to identify the file format. An ELF executable file, for example, begins with the bytes 0x7F454c46.

ELI5:why are the noses of rocket, shuttles, planes, missile(...) half spheres instead of spikes?

Blunt noses are fine if not preferable at low speeds because the airflow can start to move out of the way before it hits the aircraft. The air in front of the craft pushes on the air further ahead to allow for a smooth transition. Supersonic travel does not have this. The air is 'notified' of the oncoming plane right as the plane comes up on it because pressure waves cannot travel out ahead of the plane. This makes pointier designs better in this region. At very *very* high speed, a blunted nose forces the shockwave to form farther in front of the vehicle, protecting it from the heating of the air that forms at the shock.