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ELI5: if the human body regenerates every single cell within it every seven years, then why do tattoo's remain throughout our life? | does the pigmentation get copied by new cells?
does it just stain the flesh itself & seep through?
[here is the source for the seven year regeneration information.](http://stemcell.stanford.edu/research/)
/u/thisisntnamman explained quite well & has the most upvotes, here's the answer:
"Your skin has layers. ... | 356 | Your skin has layers. The two big ones are the epidermis and the dermis. The epidermis is the highly cellular one with lots of cell division and shedding. The dermis is blow that layer. It is not nearly as cellular. There is a lot of non-cell connective tissue, fibers and elastics that hold skin together and support al... | 200 |
Why do we go into "food comas" after eating large amounts of food? | 27 | The hippocampus gets overloaded with serotonin, causing an immunogenic cascade reaction which activates numerous platelet factors. Consequently, the SPF-15 receptors are then filled which will send a signal (complex) causing the leptin hormone to inactivate. This will remove the feeling of hunger. These events in succe... | 14 | |
ELI5 why deer behave differently when confronted | Deer are known to be extremely cautious creatures and even the slightest sounds can spook them. However deer often freeze up when cars are riding by. Are they scared and freeze up or are they curious and waiting to see what will happen? | 19 | Scared perhaps and also waiting.
Deer will run fast away like you said. But they also will lay completely still if a potential predator is nearby and they think that the predator doesn't see them.
Once they feel they are spotted they will likely take off.
I've had deer do this many times. Young fawns especially... | 13 |
[The Walking Dead] How is Michonne keeping those katanas so damn sharp? | Cutting heads off is hell on a blade, even the best ones. And sharpening katana's is a pretty arduous process that takes a bit more than a whetstone. Considering how many heads she must have chopped off, how the hell are those blades not dull as cheap machetes by now? | 26 | Correction: Cutting off *human* heads is hell on a blade. Decomposition takes a lot of the structural integrity of a body away. Decapitating a walker is both less wearing on a blade, and doesn't require the blade to be sharpened as often or as well. | 22 |
CMV:People are too obsessed with prestigious universities. | This obsession is something I don’t understand. Sure , people who graduate in Harvard will get a better starting salary than someone from an average university.But that’s only because the people who get into Harvard usually are not average people. They work hard, intelligent, or they have some family connections.
But ... | 107 | Have you heard about signaling theory in economics?
Basically, it says that education doesn't have any incentric value but only servers as a signal to future employers about your quality.
So companies don’t hire you because your skills (things you know) but because who you are (good studier, hard worker, family conne... | 11 |
[Rick and Morty] How is getting the Szechuan Sauce such a big problem? | I mean Rick said it himself often enough, every possible event exist somewhere in the Multiverse.
How difficult can it be to find a Universe in which the Szechuan Sauce was never discontinued, or to find a Universe where the Mulan film just came out so they still serve Szechuan Sauce at McDonald? | 58 | That's much easier said than done. There is no guarantee that a universe exists in which the exact same recipe of Szechuan sauce is still available. And if that universe does exist, there is no time efficient way in which to find it with his existing technology. It's basically trial and error.
Finding it is going to t... | 34 |
[Death Note] Why didn't L just check Light and Misa's handwriting? | 53 | At one point in the manga, Light says he's been intentionally writing differently in the Death Note to his normal handwriting.
Misa is no genius, but we see she is pretty good at disguise. She probably had the same idea. | 44 | |
ELI5 - why do people at the equator (spinning 1000 mph with the earth) and the poles (not spinning almost at all) experience gravity the same? This feels like it would have a massive difference on just walking around! | 53 | There is actually a difference! It's a very minor difference, amounting to less than half a percent, but at the poles you *do* exert just a bit more force on the ground under you.
Since the surface speed of the earth spinning is so high, you might think the force felt due to centripetal acceleration might also be a lo... | 87 | |
[Star Wars] What was Yoda's relationship with the wookies and how did that relationship form? | 546 | Both Yoda's species and Wookies are very long lived. Jedi do a lot of diplomatic missions and over the decades/centuries he's been a consistent point of contact for the various tribes and helped them build their place and reputation in the Galaxy. | 476 | |
[MCU] What's up with my living situation post-blip? | So i'm taking out the trash right, and all of a sudden my arms start turning to dust! I scream in terror but then my whole body fades away. Like half a second later, i'm back, and i'm freaked out at whatever just happened. As I run back to my house, I find that the door is locked. I bang on the door in frustration, but... | 40 | I guess become a supervillain now.
Seriously now, get in contact with the authorities and ask them for help. You're not the only blip returner, so they're probably setting up places for you all to stay at. People may be driving around now looking for resurrected folk to tell them where to go. | 25 |
ELIM How the Republican party went from abolishing slavery to not being able to get the minority vote | I'm Canadian I don't know a lot about the history or evolution of the American political system. I just know the Republicans were the driving force to pass the amendment to abolish slavery and now they can't get support from minorities | 27 | In the 1960s, the Democrats were the driving force to pass civil rights laws. Now, up until this point, the Democrats *had* been the traditional party of white racists. But many of those people were angry about civil rights, and abandoned the party. Republican leaders saw that getting all the racists into their party w... | 16 |
[Star Wars] At the duel on mustafar why doesn't one side just start force flinging lava at the other? | 49 | Because of a variety of reasons.
One, because that takes concentration and effort, which their opponent isn't going to give them when they're in range of a lightsaber.
Two, because Anakin is clearly not thinking about using the environment as a weapon.
Three, because despite everything, Obi-Wan still is trying to st... | 45 | |
ELI5: Does the immune system get weak or “rusty” having not had to fight off human spread infections for over a year while in quarantine? | 106 | It really depends upon the organism being bacteria or virus. Nobody knows how long Covid-19 vaccines will offer immunity, yet. Also different vaccines will vary. Chicken Pox vaccine (varicella) lasts \~40-50 years, then immunity lessens, that's why there is a Shingles vaccine for elders. Measles last your lifetime.... | 72 | |
Why don't electrons traveling in the orbitals of atoms lose energy, although they are a mass traveling a narrow space which should require some kind of acceleration to stay close to the atom? | As I learned in physics the acceleration of a mass (and the change of direction is an acceleration) results in a change of kinetic energy, so traveling in a narrow space like an electron around an atom requires acceleration to change the direction of the electron to stay around the atom, so then why are atoms stable at... | 3,109 | This is a good question, and one of the questions that led us away from the classical model of the atom and towards the quantum model. You are correct that the classical way we think of an atom (positively charged nucleus, negative particle in a circular orbit around it) would emit radiation, causing the electron to de... | 1,941 |
ELI5: Whenever I buy a video game disc, (Xbox, Ps4, etc.) It says it needs to download the game into the console. Isn't the game already on the disc? | 16 | On modern consoles it has to install the data from the disc onto the console's hard drive. That's because blu-ray drives are just too slow to load data for modern games, so it has to be installed on a faster (although still pretty slow to be honest) hard drive.
Usually you also have to download patches, even if the ga... | 43 | |
ELI5 what makes a Pub different from other bars. | The Irish pub owner's AMA had an interesting comment "all pubs are bars, but not all bars are pubs". Being Canadian I love going to chill bars, and one of these that I go to is an irish free house...a pub...but others are just, bars...what exactly constitutes a pub?
*edit: It seems that historically speaking, there wa... | 1,920 | A pub is somewhere you should feel comfortable to spend the whole day and even take children during earlier hours. It should be a cosy place, decorated in a friendly and welcoming manner, if a little naff. There should be games available such as pool, darts and a quiz machine. The better ones will even have dominoes, c... | 2,834 |
[Alien] Why not just study the xenomorph in deep space far from Earth? | Based off an earlier question I saw, considering Weyland wants the xenomorph so bad and clearly has the money and resources to make friggin colonies and massive space stations, why not just study the xenomorph out in space? Make multiple stations and position most arpund gas giants, that way, should things go wrong, th... | 65 | Because the good scientists like all professionals in high demand want to live in places with something to do outside of work. You have multiple PhDs in biology, xenobiology and medicine. Do you want to live on a planet with no breathable atmosphere, inside a 10x10' cell, with your only social outlet the techs who work... | 49 |
ELI5: What exactly is a partial derivative? | What exactly is a partial derivative? I have a basic idea of a derivative i.e, I know that dy/dx is rate of change of y with respect to x and that it represents the slope of a curve
Thanks! | 45 | It’s still a slope. But when you multiple variables then you have a surface instead of just a curve. You can hold all but one variable constant then take the derivative to find the slope in only one direction. | 42 |
Why do tornadoes seem to avoid Chicago? | I live in Chicago, and as you probably know a huge storm system came through the Midwest today and caused significant damage to a few small towns in Illinois. Although I recall tornadoes hitting the outlying suburbs before, I don't remember the last time one actually hit Chicago. A lot of Chicago's weather is strongly ... | 34 | While there is some minor justification for believing that urbanization can cause storm-splitting, the more likely scenario is that you are simply paying attention to Chicago, so you notice every time it doesn't get hit. If you paid close attention to a particular (arbitrary) location on a dart-board, you'd notice it ... | 33 |
Why is Watson considered the father of behaviorism? |
I'm taking AP Psych, and I can't figure out why Watson is regarded as the father of behaviorism when Pavlov experimented with classical conditioning before Watson and helped in switching the focus of psychology from introspection to objective observation. Does anyone know why Watson is considered the father of behav... | 19 | Watson was the first person to identify reinforcement/punishment (operant conditioning principles). Essentially, he realized if good things followed behavior, the organism would do it more and if bad things followed, they would do it less
Pavlov was the first person to identify respondent conditioning, but this part i... | 22 |
ELI5: How can some remote controls still work even when the LED is not pointed directly at the TV? | 44 | LED is not laser. It's like a small bulb, just glowing and sending light everywhere. You can see LEDs on your devices (tv, router, usuall power on/off on everything), even if they are not directly pointing at you, right? | 16 | |
ELI5: How come blowing fire makes the flame stronger but blowing candles makes it die? | I actually wanna know because fires at camps and stuff grow when you blow\* but blowing at a candle puts it out. Imagine it's the same size as a campfire, so you can't just say because it's small. | 25 | To make a fire you need three things; fuel, oxygen, heat or ignition source.
When you blow out a candle you are cooling it off, thus the paraffin vapors don't ignite.
When you blow on a campfire, you're adding extra oxygen. | 19 |
ELI5: how did the sizes of mattresses become standardized? Is there a regulation authority for such things? | 10,402 | There is no standard, it’s cultivated from years and years of different companies selling different products.
For example, if a mattress manufacturer’s 60x80” mattress (Queen) sells very well, the company that manufactures bed frames will want to sell frames that fit this size, as well as the company that sells sheets... | 3,082 | |
ELI5: /r/darknetplan | 39 | So websites have names. The place that has all these names is called ICANN. When you type in a website name, ICANN tells you the address for you to go to so you can get to that website. A lot of other fancy stuff happens that makes the information get from one place to another.
This is good most of the time. Remem... | 10 | |
ELI5: what do they mean when they say that spider webs are stronger than steel? How is that possible? | As in the title. | 24 | It’s based on tensile strength when compared to effective diameter. Spider silk is only microns in diameter, so if you could extrude a steel specimen at the diameter of a strand of spider silk, the spider silk would take more force to break | 42 |
[Game Of Thrones] What if Joffrey was nice? | What if Joffrey wasn't an evil psychopath? What if he was a kind, friendly kid?
How would this have changed things? | 26 | If Joffrey were nice, the world would actually be a much much much better place. But by insisting on the glorified tradition of putting children and morons on the Throne, the world has created it's own destruction.
Remember that Joffrey's Misogyny and Anger that originally lead to Ned Stark's execution. This even star... | 28 |
[Spider-Man] Is Peter special, or would the bite have worked on anyone? | Is there something special about Parker's DNA that let the spider affect him the way it did, or would anyone who got bit develop spider powers? Did he have a dormant X gene or something? | 41 | Peter was chosen. In J. Michael Straczynski’s (and John Romita Jr.’s) Run on the Amazing Spider-Man they delve into the history of it and the Spider-man is a bit like the Vampire Slayer (Buffy) is so much as there have been numerous Spider-men through different times and cultures all the way back to the African spider ... | 39 |
ELI5 How does digital clock work? | How does digital clock counting time? Not display i wonder how they can know how much time pass? | 16 | There is a special elements called a quartz. It is the same thing that beach sand is made of. It has a special property of converting different Energies. With pressure it turns into heat, with light it splits light, and with electricity it creates a vibration.
Some quartz crystals make a very stable vibration. Imagine... | 26 |
[DOOM] What was the Doom Slayer doing in between DOOM 2016 and Eternal? | I always thought this little interlude would be shown at some point during one of the DLCs, but they ended up not going there
At the end of DOOM 2016, the Slayer was teleported away/imprisoned by Samuel Hayden. At the start of Eternal, a couple months later, the Slayer has escaped/been released from wherever Hayden se... | 21 | The slayer was ejected from hell or stumbled through the same portal he went through after the doom 64 ending. The sentinel codex mentioned finding the slayer lost and delirious in the wastes of their world with strange weapons and armor to them. He probably knew how to escape hell already and given that the seraphim h... | 20 |
Can we make sugar, in vitro, out of CO2 and water--with sunlight or any other kind of energy input--any more efficiently than plants can? | 26 | The short answer is: No, we cannot make sugar out of CO2 and Water more efficiently than photosynthetic organisms.
There are a couple things to think about this question though. First off, we can't do it more efficiently than plants, but turning CO2 into sugars is something that *could* in principle be done with our c... | 14 | |
ELI5: How we know that there isn't another planet in the exact same spot as Earth on the other side of the Sun. Like 6 Months behind? | 19 | Pick up a bucket of water and spin around, holding it out at arms length. Notice how you're wobbling as you spin?
Now, take two buckets of water, one in each hand, and spin around. They are balancing each other, and you are no longer wobbling.
The sun is "wobbling" because of all of the planets that circle it. Sci... | 49 | |
If free neutrons decay in 15 minutes how are neutron stars stable? | I assume the neutrons in the star are unbound so what mechanism is keeping the neutrons from decaying? | 15 | For the neutron to decay
N -> P + e^- + antineutrino
and for this reaction to be energetically favourable, the electron has to have an unoccupied low energy quantum state to fall into. But all these states are already occupied by the free electrons which are highly degenerate. So the reaction cannot proceed in an ... | 12 |
ELI5: Where do deleted files go? | Where do deleted files go? | 17 | They actually don't go anywhere unless you tell them to very specifically.
Imagine you have a book full of random words. The first word is #1, the second word is #2 and so on. Say the first page looks like this:
cat had a dog Jill
You can tell a story: *Jill had a cat*, by telling the reader to go to words 5, 2, 3, ... | 24 |
ELI5: What does it mean to say the earth is tilted on its axis? Tilted with respect to what? | 296 | >ELI5: What does it mean to say the earth is tilted on its axis? Tilted with respect to what?
Tilted with respect to the ecliptic, the plane defined by the Earth's orbit around the sun.
You can grab a pen and draw a circle on a piece of paper. That pen could be held perpendicular to paper while you're tracin... | 857 | |
Is It True Helium Is a Liquid At 0 Kelvin? | 70 | At atmospheric pressure it is, but if you turn up the pressure to an insane amount you'll turn it onto a solid. From a quick look at a phase diagram you'll need over 25 times atmospheric pressure to turn Helium into a solid. | 44 | |
CMV: There is no reason why PC games can't have unlimited save slots | In many of the games I played, one can create a folder, move all of one's saves there and then all the save slots would be free for use again. No game I tried, however, lets you actually do this simple file manipulation from within the game, and no game does it for you automatically when saving.
There are games that ... | 20 | Some PC games do offer unlimited saves. The Civilization series is the first to pop to mind. The limited saves isn't usually due to restraints in memory. It is usually for strategy. Unlimited saves reduces your risks.
I remember the old days of PC gaming, MS-Dos, Commodore, and the rest. Using hex editors on saves ... | 12 |
[DC Comics] If there is only ONE Darkseid, no matter the reality, why doesn't he conquer Golden Age Earth? | There's supposedly only one Darkseid, the same version. Why doesn't he conquer Golden Age Earth where the Golden Age heroes, such as gravity-fueled Superman, wouldn't stand a chance against him and his army? | 402 | If he entered a universe, it would crumble under his might. That's why he relies on avatars as they're all tendrils of his power. Not every universe is the same, some can only handle a certain amount of power, so his avatar reflects the power of the universe. Golden Age Earth can't handle as much as Silver Age or Rebir... | 618 |
Why do economists not look at income data at the individual level? | Edit: Please ignore my claim that the UK provides long term income data at the percentile level- I misspoke (aka was stupid and wrong) and the closest I can find to this now is annual income by decile. Apologies for any issues/trouble.
​
I am a political science grad and one of the things that has been bug... | 89 | Data tracking individuals over time is called "panel data," and there are some studies that analyze it. Try searching for "panel data" and whatever your topic of interest is. For the US, the National Longitudinal Study of Youth has high-quality panel data covering a wide range of topics.
I think I've heard of research... | 105 |
CMV: The popular response to the Paris Massacre makes me feel like we're watching recent history repeat itself. | If you look in the most popular comments on any of the main threads about the recent Paris attacks you'll see calls for us to 'get serious' with ISIS, and that we should roll in there guns a'blazing and stomp them out, and that killing them to a man is the only way to get rid of this problem. And this makes me sad, I f... | 116 | Actually, post 9/11 things were going great.
We dismantled the Taliban and gutted Al-Queda. They were completely defeated and on the verge of being wiped out.
The entire international community was in Afghanistan ready to contribute soldiers and resources to rebuilding it as a modern democracy.
And then George Bush ... | 71 |
How do you cool things to extreme low temperatures +1-2K? | 19 | For anything below liquid helium temperature, generally laser cooling is used. There are many different mechanisms for exactly what physical properties are used. The general principle is that you shine photons at very specific frequencies, so that the material is more likely, on average, to give momentum to the photo... | 18 | |
CMV: "Cash" or "Money" should be acceptable responses for when asked what one (adult) wants for Christmas. | **Title correction (grammar):** CMV: "Cash" or "Money" should be acceptable responses when asked what one (adult) wants for Christmas.
CMV spurred by being on the cusp of thirty and still making Christmas lists for my mom because she thinks monetary gifts are too impersonal. Also I love my mother very much and appre... | 61 | What if two people exchanging gifts both want money? If one avoids the potential conflict by giving a gift instead of cash, then the recipient is disappointed because they got something they didn't want.
If both give each other money in the same denomination, nothing was truly exchanged. If both give each other differ... | 22 |
[Teletubbies] What exactly are the Teletubbies and Teletubbie Land? | They have vague human characteristics, even different genders and races. And they possess some rudimentary form of intelligence on par with a human toddler. But who created them and why?
Then there's the question of their technology. They have a vacuum with artificial intelligence, their home has automated food dispen... | 87 | They are the product of a child's imagination. The child is the baby in the sun. The world is the child's interpretation of the world around him. The teletubies are his various emotions as he interacts with various toys and objects that his parents leave with him. The tv segment is either when his parents leave the TV ... | 77 |
Eli5: Are people that live alone in the woods breaking any laws(hunting, building, etc) or are they "immune" to said laws? | 19 | Living alone in the woods does not exempt one from the applicable laws. Whatever is illegal for the federal, state, county, local government that has jurisdiction over the area is illegal regardless of where the person lives.
Having said that, it is possible that people in those circumstances will get away with it jus... | 42 | |
ELI5: why does the arm feel like static when you hit your elbow on a corner? | 34 | At the elbow end of your humerus, there's a bit of a groove where your ulnar nerve passes over the end of the bone, so the nerve's pretty exposed there. If you bang your elbow the wrong way, you'll hit that vulnerable nerve and pinch it against the bone, and it causes a bunch of spurious sensations from all along wher... | 36 | |
[Star Wars](Rule of Two) Why should I take up a Sith apprentice and teach him the force? That guy wants to kill me! | Here I am thinking being a Sith is about amassing power and dressy all spooky, but these holocrons I'm reading not only say I need to have an apprentice, but *that apprentice has to try to kill me!* Why are all these Sith Lords even worrying about teaching someone else in the first place? Shouldn't they be looking out ... | 319 | You would be a coward, then. Avoidance of conflict causes stagnation and weakness; the Sith rise above this by proving themselves in struggle. Either you kill your apprentice, therefore claiming your rightful place as the Master, or your apprentice kills you, thereby keeping the Sith Order and it's ideals strong and al... | 300 |
[Star Trek] Holodeck question: Can one Holodeck connect to another, so the occupants have "online" experiences? Or are Holodecks only capable of working alone? | 41 | Yep. The Federation briefly used this for teleconferencing purposes, and set up little mini-holodeck projectors on ship bridges. (This was a technology they used instead of viewscreens for like two episodes on DS9, and then quietly stopped using again.) | 16 | |
Can you explain in simple terms, why can nothing travel faster than light? | 203 | For me, the simplest way to explain it is that experimentally, we have measured the speed of light to be always the same value - 3 x 10^8 m/s, otherwise known as c. What does that mean?
It means that if you shoot a beam of light, it will always be traveling away from you at c. Even if you have a rocket ship, and manag... | 185 | |
ELI5: When I drank for the first time, 3 drinks made me feel drunk. 4 years later I can probably drink 3x that and feel the same (thanks college). If these two me's were breathalyzed, would we both produce the same BAC, or is my body now just more used to the feeling of 3 drinks? | 45 | Your BAC is constant; tolerance merely refers to how much a given amount of alcohol affects your judgment, inhibitions, etc. So drinking the same amount of alcohol with the same body mass will yield the same BAC, but you won't feel as drunk.
This is also assuming that your metabolism has not changed in how quickly it ... | 28 | |
[Phineas and Ferb] has doctor D ever created a ‘useful’ (helpful) inator or is every invention just meant to cause a minor inconvenience? | 34 | he did create the all you can eat inator that causes your metabolism to speed up so you could eat a lot but not gain any weight.
He also made the age acelerator inator that sped things up age wise. It was used to speed up the process to make cheese. It could be used to speed up other products that require waiting time... | 41 | |
Salt Water Crocodiles are said to have changed very little since 'dinosaurs roamed the earth,' is this exclusively because of their apex position in the food chain, or do their offspring show a lower rate of genetic mutation? | As in the title, 'lower rate' as compared to higher mammals, which developed more recently. | 32 | Actually, this is a misconception. What we'd recognise as 'modern crocodiles' actually appeared *after* birds and mammals. It's just that the crocodile body plan has been copied by a lot of their relatives.
The first recognisably crocodilian crocodiles- the eusuchians- evolved about 130 million years ago. Archeopteryx... | 34 |
How does a lightning bolt create thunder? | I don't understand how a bolt of light creates sound. | 17 | A lightning strike consists of a high current running through a small channel of ionized gas in the atmosphere. Normally, our atmosphere is a very poor conductor, but if sufficient charge builds up in a cloud, the electric field might become strong enough in some places to start creating a conductive channel. Once this... | 27 |
[Indiana Jones] Could any contraption conceived in the late 1930's (or earlier) be so sensitive to light disturbance that it could trigger a booby trap? | 20 | It was really a pressure trap triggered by stepping on a floor tile. Much like a magician using misdirection, Indy stepped down at the same time is putting his hand in the light because he suspected he would be double crossed. Upon running out the other guy avoided the light but stepped on the wrong stone. | 37 | |
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These changes... | 53 | These sound like really welcome changes.
> Outright removal of repeat threads within a certain timeframe. Ex. if we see two abortion threads within the same day, then we remove the second one posted. Pros: greatly cut down on repeat questions. Cons: many topics have subtle differences that could be erased by remov... | 13 |
Should I go with a Prestigious school or debt-free route?. | I’ve recently been offered admission for an MA in political communications. One in Canadian university with full funding for two years and one at the London school of economics - one year, no funding and hefty tuition. I’m leaning towards LSE because I want to pursue a future in academia and I feel like it might look ... | 16 | I vote go the debt free route. A lot of big name universities (e.g., University of Chicago) have "cash cow" master's programs which are large, impersonal, and provide poor training. Basically, they're just trying to get money from you and get you out the door quickly.
I had 5 friends in a program like this-- it did w... | 47 |
ELI5:Why are moths attracted to bright lights ? | Title says it all | 53 | Moths use lunar navigation. They look up in the sky and use the moon to traject where they are and where they are going. Man made lights mess with that cause they can seem like moonlight to the moths.
| 23 |
ELI5: why do gravitational forces create rings on a single plane, rather than a globe? | 160 | It's not gravitational forces that do this, it's collisions.
Orbits at the same distance in anything *except* a single plane will collide. When that happens, the particles exchange momentum and tend to come out closer to an "everage" orbit, with a plane between the two incoming particles'.
Repeat lots of times for m... | 62 | |
The tensor is property of many fundamental forces in QED, but it is not explained in readily graspable terms... | Does anyone here have a good way to explain what a tensor is, what the different ranks and classes of tensors in normal terms?
Thanks in advance. | 17 | A tensor is basically the general term for vectors and matrices. A tensor has a rank which is the number of dimensions it has: a rank zero tensor is a scalar (number), a rank one tensor is a vector, a rank two tensor is a matrix, and higher rank tensors don't have fancy names.
Generally in physics, each row or column ... | 11 |
[Justice League movie] Why was superman's death the ideal time to attack earth? | Yeah yeah, superman has died and it's set everyone in to a world wide panic which activates the mother boxes and allows the parademons to feed on the fear. Cool.
But come on, 73 years ago mankind was fighting among itself in a global war, had significantly weaker technology and was virtually weaponising fear in the f... | 17 | 1. Why was it a good time to attack?
I don't know, maybe Superman and his battles brought attention to Earth
2. Why was his death mourned?
Unsure, but probably because Superman had protected Earth even for a short time, and that must have meant something | 17 |
ELI5: Why did Ancient Rome use a solar calendar instead of a lunar one? | Lunar calendars seem like they make more sense from an ancient standpoint, in that the phases of the moon are a natural indicator of the passing of time. Solar seems to make much less sense in that the months have inconsistent days and don't really track to anything external.
So I'm curious if Rome always used a solar... | 31 | Solar calendars are better at tracking seasons. People in regions that get the 4 standard seasons tended to develop solar calendars. People close to the equator who tend to get wet/dry seasons instead tended to make lunar calendars. Some cultures made both, and the Maya had very complex calendars that were lunar and so... | 18 |
[Legend of Zelda] How do the locks know all the nearby monsters have been killed, and why are they designed this way? | From the "secret staircase" blocks in the original, to the keys and chests that fall out of the sky in Link's Awakening, to even the boxes in Boko campus in Breath of the Wild. The land of Hyrule send to be littered with locks that just spring open when all the monsters in their vicinity have been killed.
How does a ... | 33 | Hyrule is clearly not a naturally evolved area, as it shows many signs of artifice in its composition. The ecologies, geographies and astronomy, even its causality are all patently absurd, suggesting the entire area was created by an agency significantly in excess of the (admittedly great) powers of the denizens of Hyr... | 32 |
CMV: I think the idea of a life after death is far more frightening than simply ceasing to exist | As frightening as it is to think that nothing comes after death, at least that would also means no more suffering and pain. The afterlife on the other hand could be far worse than our wildest imaginations.
Just consider what terrible things are happening in this world, who knows what could happen in the world to come.... | 67 | It's a a bit tricky to compare absolute nothing with infinite possibility. At least with infinite possibility we could get lucky.
If you died and awoke in a white space with two doors. One has a sign that says that if you cross the threshold, you will cease to exist. The other has nothing else on it. There exists not... | 22 |
[Marvel] What characters or abilities would *not* gain an appreciable boost from being bonded with a symbiote? Are there any? | 88 | Most symbiotes are weak to sonic waves and heat, so characters whose powers are based on sounds (Banshee, Siryn, etc) and ones whose powers are based on heat (Human Torch, etc) would probably not mesh well with a symbiote. | 104 | |
ELI5:If the US and Iran come together, how will the Middle East power balance change? | 102 | There are a few reasons it will change, maybe for the better and maybe for the worst... I'll list a quick few, and hopefully others can expand.
There is no black and white changes that will happen. America wants influence there without needing to deploy an army.
1) it can force down oil prices to hurt Russia
2) Iran... | 26 | |
ELI5: How did they calculate a single sperm to have 37 megabytes of information? | 14,590 | DNA is coded with 4 letters: A, T, G, C.
A byte can hold 4 pieces of these letters. A byte can contain for example "ATTG".
If you know how long your data is, then you know how much byte you need. For example "AATGCCAT" is 8 code long, than you need 2 bytes.
37MB is appr. 37 Million bytes. That means the genetic code... | 9,981 | |
CMV: Drugs shouldn't be criminalized unless you're a danger to the public. It should be treated and not punished. | Addiction is a disease/mental illness that needs to be treated, not criminalized/punished. Instead of being in jail, you should have to log a certain amount of court ordered hours in mandatory programs like rehab, drug and alcohol counseling, probation which includes drug tests (duh)
DUIs and child endangerment due to... | 3,862 | Are you advocating that Drugs be treated like how we currently regard alcohol? Where possession in itself is not illegal but regulated? Surgeon General warnings, open restrictions on public use, age restrictions etc? If so what would be the point of outright making it illegal to sell drugs? | 394 |
ELI5: Why does draining a large body of water cause it to form a vortex? | 58 | The vortex that forms is caused by the physical principle called angular momentum. Let us assume a straight walled circular pond, with a drain at the center bottom. As the water begins to drain, the flow of water comes from the edges towards the center. This creates momentum at an angle from the direction the water is ... | 11 | |
[Pokemon] I fought in the Pokemon war under the command of Lt. Surge. What was the world like? | What nations were at war?
Whose side were we on?
What was being fought over?
What were the weapons used?
Where was the war-front? | 58 | From the official cannon, Surge is American. For the timeline to work out, it would have had to have been the Gulf War. He was, officially, a member of the Army, a pilot, and his electric Pokemon saved his life.
Since we know the avionics of Gulf War aircraft, it must be that he suffered an electrical failure that wa... | 37 |
[LOTR] Does destroying the One Ring cure addiction to the One Ring? | Did Frodo or Bilbo continue to crave the One Ring after the ring was destroyed? | 34 | Gandalf says that "Some wounds never heal," and it's implied that he's speaking of the addiction to the Ring and the actual damage that it does to the soul, along with the other wounds that Frodo has from the Morgul-blade at Weathertop and from Shelob's sting. Bilbo also mentions missing the Ring when he and Frodo reu... | 66 |
The outer electron of a Cesium-133 atom reverses its direction of spin when exposed to microwave radiation of precisely 9.19263177 GHz, which is the basis of the atomic clock. But what happens if the frequency is off slightly? What if it's a Hertz or two too high or too low? How does the atom react? | 415 | Take a stream of cesium is sent past the microwave radiation. the closer the radiation is to the proper frequency, the more cesium atoms will transition to their higher state. The atoms then pass a filter which removes non-transitioned atoms from the stream, and the rest (the atoms that did transition) hit a detector... | 101 | |
CMV: Kyle Rittenhouse has no grounds for his defamation lawsuit against any media outlets or celebrities, and comparing himself to Johnny Depp is laughable. | *Edit:* I forgot to change the title right as I posted, but I guess it's too late for that now.
The newer title would have been **"Kyle Rittenhouse is incorrect to compare himself to Johnny Depp in regards to defemation by media and celebrities"**
**All I want to be challenged on is whether or not Rittenhouse has any... | 410 | How do you explain so many people still being completely wrong on the facts of his case?
It was purposefully reported vaguely that he killed “black lives matter protesters” without clarifying that they were white, to the point where many people still believe the people he killed were black.
It was repeatedly reported... | 267 |
Why do we feel itches? | 37 | There are many, many reasons why we itch. Itch researchers break them down into 4 main classifications of itch:
* First is called "pruritoceptive itch", which is just a fancy word for itching that originates in the skin. This is the most common type of itch and can be caused by stimuli such as insect bites or poison i... | 16 | |
ELI5: Why do Christians think there are no prophets after Jesus (Muhammad, John Smith, etc.) even though they believe in the prophets that came before Jesus (Adam, Noah, Abraham, and Moses)? | I'm not Christian, but this is one thing about the faith that has always baffled me. | 46 | You might also ask why Muslims and Mormons don't recognize prophets after Muhammad and John Smith. It's just the most recent update on the religion that is compatible with their faith. Believing in some prophets doesn't require one to believe in all prophets. Religion tends to be heavily discretionary. | 27 |
CMV: commenting in medium to large comment sections anywhere is stupid | Case in point, YouTube. I spend a lot of time time watching videos and or listening to things relevant for me but i'd never get into commenting. It's useless, top dogs are usually cringey one liners or the uploader themselves adding another closing remarks like "also don't forget to do that and that", so your comment i... | 15 | Just because you don't read the comment section doesn't nobody else does. Even if only a handful of people read your comment, you still conveyed your message and exposed people to your ideas. That's the point of any type of communication. | 11 |
ELI5: How did a shaved head become synonymous with the white power movement? Why are they called skinheads? | 39 | "Skinheads" is a subculture originating in Britain in the late 60s, it resulted from a split in the "mods" subculture and was formed from the more violence-prone "hard mods" portion of the subculture where the fashion was for guys to have shorter hair and a working-class style(as opposed to the "peacock mods" who wore ... | 22 | |
ELI5: The difference between a .Torrent file and a Magnet link | 16 | Imagine you want to go to Chuck E. Cheese but don't know where it is or what it looks like, just the name. Luckily, you have a friend who specializes in this kind of thing. He is a torrent search engine.
You ask him and sure enough he gives you a piece of paper with a phone number and a pass phrase on it. When you cal... | 10 | |
[Family Guy] When did Brian lose his integrity? | I would love a specific event or series of events, but whatever is fine.
I was watching an old episode, the one where Peter is stranded on an island, and Lois remarried with Brian. Brian did a very noble thing by breaking it off with Lois so she could get back with Peter. He didn't even push too hard for sex, despite ... | 55 | Brian was always the smart one in the house, because he was unchallenged. Early on he was flexing his muscles and managed to weasel his way into tight-knit groups like the new rat pack.
As time went on, people began to see him for what he really was. His drinking and drug abuse began to catch up and he became more an... | 91 |
ELI5: What goes into mens' cologne that makes them smell "manly". What about these fragrances/chemicals makes them masculine? | 73 | It's contextual. In western culture most women's perfumes have fruit, flower, and vanilla notes. Men's cologne generally have earthy notes like pine and musk.
By context you think of it as smelling one way or another because you've always associated certain smells with perfume and others with cologne. | 36 | |
ELI5: How big does a landmass have to be for it to no longer be considered an island? | 18 | It has to be "sub-continental", basically, not a continent itself.
They generally define it based on what chunk of earths crust it sits on, called a "tectonic plate". Ocean plates look different then continental plates. If it's surrounded by water and isn't a continental plate, then it's an island, or if it's on a c... | 11 | |
[Marvel] How dangerous would a lethal Spider-Man be? | Say, that he's still a good guy at his heart, but isn't so concerned with holding back and has few to no qualms with taking the lives of his foes. | 57 | He would instantly become one of the most dangerous human beings alive. What holds Spider-Man back is his innate sense of morality. When called upon he easily holds his own among some of the Avengers' greatest threats but he spends his time doing things like chasing down muggers and rescuing people from burning buildin... | 74 |
ELIF why Chernobyl is inhospitable radioactive wasteland yet people live without problems at Hiroshima and Nagasaki? | Conventional maxims say that nuclear weapons make land inhospitable for something like 20,000 years but people live in Nagasaki and Hiroshima without problems yet Chernobyl, which wasn't a nuclear explosion but a meltdown of a nuclear reactor is too dangerous for human life? | 281 | Lets say you have an ice cream cone and you drop it on the floor. You get a bit of a mess but it's not too bad. If you leave it alone it dries up after awhile. That's Hiroshima and Nagasaki.
But what if you had a whole great big freezer of ice cream and it stopped working? The ice cream starts to melt and get everywhe... | 275 |
ELI5: Why is light considered analogous to time? | In every video I see about time relativity, they explain it by showing that light bends due to gravity. But why does that imply that time bends as well? Isn't light just a collection of photons? | 64 | The light is just there as an example. If the light were not there, space itself would be bending. Space and time are part of the same thing:spacetime.
By having the light be present, you can see the path and curvature of spacetime. The speed of light is the speed of all causality (it’s just that light is the most ob... | 68 |
ELI5: How did wheels work before we invented wheel bearings? | I watched a program last night which showed a wheelwright recreating an old fashioned cart wheel and slipping it straight onto a thick wooden axle. It made me wonder just how easy it would have been to pull, and why the wheel and the axle didn't burst into flame from the friction?
I guess they probably lubricated it ... | 45 | Yes they relied on two surfaces rubbing together, and yes those surfaces were often greased. A lot (probably the majority) of rotating objects still rely on plain bearings with sliding contact like this.
Regarding the resistance, note that the sliding surface is quite a small diameter, and cart wheels tend to be very ... | 49 |
ELI5:why does the Swiss army guard the Vatican? | I was told that it was historical reason. If so why do they guard the Vatican today and why doesn't the Italian army guard? | 46 | The short answer is that the Swiss Guard are mercenaries. The Vatican has continued to pay to extend the Swiss Guard contract for over 500 years. At this point it's mostly just tradition, however, those guards are well trained. | 57 |
ELI5: Why do our energy levels go down when we're depressed? | Depressed people I've seen generally feel more tired and fatigued than usual and end up sleeping more than usual. Why is this? | 18 | Depression in many ways puts your body through the same processes that a lot of physical illnesses do. One part of that is that both are associated with the release of what are called pro-inflammatory cytokines in your body. Like the name implies, these are chemicals that cause inflammation in your body. Evolutionarily... | 17 |
[Naruto] How does Nagato (after Impure World Reincarnation) still have Rinnegan despite the fact that Tobi removed them?Would someone revived with Rinne Rebirth also come back with their Rinnegan intact? Do eye powers become part of your soul or something? | 18 | Im pretty sure that Edo Tensei returns people to life the way they were when they died.For example when Madara died he had given his rinnegan to Nagato,so when he was brought back with Rinne Rebirth he lost his rinnegan because they were fake(they crumbled away). | 18 | |
ELI5: why don't grocery stores and restaurants give unsold food to shelters? | Why don't places like fast food restaurants and grocery stores that cook food donate the unsold (but still good) food at the end of each day? Why not give to a homeless shelter instead of throwing away? | 18 | This practice, while charitable and laudable in theory, is a liability nightmare. Even if the stores do comply with local food safety regulations, they're going to be subject to frivolous lawsuits and legitimate lawsuits (if the food harms someone).
Additionally, some nanny state mayors (like Michael Bloomberg) have d... | 36 |
ELI5: Why was Mylan's CEO forced to testify before congress over EpiPen prices? As a private company, aren't they allowed to charge whatever they think people will pay? | 17 | there's a little bit more to it. Her father is in congress, and he was critical in a process that created a government requirement to keep a supply of epi-pens in all public schools, shortly before the price hike.
now, some people feel like this may be some corruption at work, for obvious reasons. | 33 | |
CMV: Not knowing Mandarin Chinese in 2050 will be the same as not knowing English in today's international job market, and I should learn it. | I'm a journalism student who wants to work overseas covering stories all over the world. Right now, the richest countries are english-speaking, and so if you want to be a foreign correspondent (or almost any other job) the most marketable/profitable language for you to know is English.
[By 2050 the Chinese economy wil... | 17 | You need an empire to export your language and culture. The last two, The British and the American, have been exporting English for the last 400 years. The global-ish empire before that, the Romans spoke Latin which was commonly taught in high school through the 80's.
Also, the Chinese haven't been real great at expor... | 19 |
ELI5: why does sour candy give you sores in your mouth? | I ate a bag of sour skittles on one side of my mouth earlier today and now my tongue is sore on that side. Why does this happen? | 21 | Acidic foods taste sour to us. So if you eat a lot of acidic food you literally damage the skin of your mouth via the acid.
Think of a lemon. Lemons are sour because they have a lot of "citric acid" in them. | 21 |
[Westworld] I get that Guests can't shoot each other and Hosts can't hurt guests, but what stops Guests from stabbing or otherwise physically hurting each other? How has that not happened, by accident, in 30 years? | 236 | Generally, the hosts' Samaritan Reflex prevents guests from harming one another.
But, the disclaimer on the Delos website says that accidents and murder *do* happen...they're just rare.
Relevant quote:
>Statistically speaking, you are more likely to die from lightning strike than to die while in a Delos park. Howe... | 175 | |
[Marvel/DC] How does the rest of the world feel about the USA having basically a monopoly on superheroes? | 236 | It oftentimes results in an arms race. Other world powers try to develop heroes of their own or try to build up deterrents against US hero aggression, such as massive nuclear arsenals. It's not that these countries want war, it's that they don't trust the US to not abuse its access to metahumans.
The result of the... | 176 | |
CMV: Voter registration is a good thing | There was a post yesterday on r/politics regarding automatic voter registration when a person turns 18. I posted a tongue-in-cheek comment somewhere around the lines of, "if you don't take the initiative to register beforehand, I don't want you voting the day-of."
So during the time that I was down-voted to oblivion, ... | 109 | There are things like voter roll purges where they remove registered voters. You may not realize you're not registered until you show up to the polls.
You're really just rewarding people with good organization skills who don't have a complicated situation (for example by living in the same place for the last X years)... | 91 |
[ELI5] Why are most screws either flathead or Phillips? Why not just one or the other? Are there advantages to different head types on screws? | 16 | because they're designed for two different things. flatheads are for manual screwdrivers. philips are for power screwdrivers on assembly line. phillips are self centering and self cam-out so it doesn't overtorque the screw. phillips can apply more torque but easy to slide out of the slot.
square bit or roberts... | 19 | |
ELI5:Why is virtually every claim about human nutrition controversial? | First calories were bad. Then it was fat. Later it was carbs. Why is it so hard to identify the ideal human diet? | 72 | Because you can't put a human in a locked cage for 80 years and feed it an experimental diet. We can use animal models, we can use short tests, we can ask people what they ate, but you can't definitively prove nutrition requirements or long-term effects without experimentation. | 111 |
[Warcraft] Say I am a middle class human living in Stormwind. Is it completely impossible for me to become a shaman or a druid? | Would it ever be possible for me to harness the power of the elements or nature and become a fully fledged shaman or druid? If not, why can't I? | 46 | It took ages of living close to nature for the Tauren, Orcs, Trolls and so on to learn and respect nature and the elements, you can't cut a process like that short. And it's not a simple process like learning to cast a fireball, it's about mutual understanding between the people and the land.
unless you are a goblin, ... | 45 |
What are the advantages for a base 12 system? | People who want everyone to change to a base 12 system are often portrayed as crazy. What are the advantages for this system? Is it only because it's easily divisible by a lot of numbers? | 30 | One major advantage is that 12 is divisible by 2, 3, 4, 6 and 12. 10 is only divisible by 2, 5 and 10.
So 12 can be divided into thirds easily, quarters, halves, three quarters... 10 does not quarter easily. Thirds, quarters and halves are units we find easy to work with.
| 23 |
CMV: The Common Sentiment against the "9 to 5 job" is naive and unrealistic. | I've seen this time and time again in both online self-improvement circles and among friends who've recently graduated college but haven't obtained full time work, and I actually think it's not only an attitude that's bad for society and a person's personal development. It seems to have lead to a culture among some cir... | 38 | The fundamental reason 9 to 5 jobs are degrading is the lack of respect implicit in the hierarchical system behind them.
You're not being paid for achievement. You're being paid to be there during set hours. Of course your work is evaluated on a periodic basis, but the primary quantitative metric of performance is ph... | 36 |
[Dragonball Z] Can Cell become stronger through training, or is his power set, and can only rise through absorption or Zenkai? | Then only times we've seen Cell gain any strength is through absorbing thousands of people, the Androids, or getting a Zenkai. Does that mean he can't train to become stronger? In his mind he's perfect in his final form and doesn't see a reason to train anyways. | 48 | Cell is part saiyan, so he to can utilize their ability to get stronger after nearly dying. This is heavily hinted at when he exploded himself. This pushed him to near Gohan levels of power PLUS gave him the ability to use instant transmission.
That said, he lacks the mentality to get stronger.
He feels he is perfect... | 44 |
ELI5: Why do all kids around the world like sugary food (like candy, chocolate, sugary drinks, etc.) more than anything else, and when reaching adulthood, most don't get obsessed with it that much? | Even if they're not hungry, they would eat candy at any time
Also, how much is too much for children? | 17 | Evolution and experience.
Sugary foods are loaded with energy.
Most of our existence, we could not get enough food, so when we found something like berries, loaded with energy, it was beneficial to eat them as much as possible. So we evolved to crave those kind of foods.
Now that we have a surplus of food, we don't ... | 18 |
[Spider-Man: Far From Home] Issues with EDITH augmented reality facial recognition | SO Edith can scan a room and identify everyone there--Cool, but how come it didn't recognize a TOP EXECUTIVE from Stark industries? (Mysterio) or all of the employees in the fake bar? Also, how come it was fooled by the hologram? Wouldn't Advanced AI say to Peter, there is something wrong with the faces around you--ie-... | 31 | He scrubbed his presence and image from the internet before he enacted his plan.
Mysterios whole plan was to present himself to the world as a new hero who came from a whole other dimension to be the savior of the world. How would that work is anyone could just look at him and say "Hey wait a minute, you're this guy."... | 42 |
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