[System] Given the following post, respond as if you're commenting on Reddit:

[User]
ELI5: What is the difference between desert and ocean sand?

This is my first ELI. I am trying to follow the rules. I searched for ELIs on sand. I could not find an answer from the last 6 months. Also my internet skills are failing me.

My question in more details: Over the last couple years sand as a resource has become more expansive due to shortages. I am wondering whether transportation is the issue or if there is something that makes desert sand useless to the building and silicone industry.

[Assistant]
The difference comes from how the sand is made. Desert sand is made by wind, and makes each grain smooth. Ocean sand is made by water, and makes each grain rough. The rough sand can stick together easier, and so is better for building.

Edit: Spelling.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
[Star Wars] How did Luke never find out that Starkiller Base was llum?

Considering its an important planet to the Jedi and Luke was studying them after ROTJ, how come he never went to planet where Jedi get their kyber crystals and saw what the Empire/First Order were doing?

[Assistant] Ilum had been extensively mined by the Empire to build the Death Stars, so there wasnt a huge reason for Luke to go there. And according to Wookiepedia, the location of Ilum was unknown to the First Order for a long time after the fall of the Empire, which means it was probably unknown to Luke as well.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
[Superman] Why didn't the Kryptonians take over a planet with a yellow or blue star earlier?

I know General Zod's whole thing is basically this, but why didn't it happen before?  There's also other yellow stars out there. Why do Kryptonians choose to live on a planet where they have no powers?

[Assistant] Depending on the continuity, that's exactly what they did. Then they had some disagreements among themselves. Imagine a civil war between an interstellar empire of Supermen. They shocked themselves with their own brutality, and settled on Krypton and *only* Krypton.


[System] Given the following post, respond as if you're commenting on Reddit:

[User] ELI5 - how does charcoal work? How do you burn something and expected to burn later?

[Assistant]
Charcoal isn't burnt. It's pyrolysed, which is a different process.

Plants are made mostly of cellulose and (in the case of wood) lignin, which are complex molecules that contain a lot of carbon. Burning a plant reacts those molecules with oxygen in the air to produce mostly carbon dioxide and water, which are both gases at the temperature of a flame and thus fly away into the air. (In practice, flames are usually a bit 'dirty' and contain a number of other things too.)

There are two steps to this chemical reaction: *breaking* the bonds in the molecules that already exist (which consumes some energy) and then *recombining* the resulting parts with oxygen (which releases more energy than the first step consumed, so both steps together produce energy on net).

In charcoal, wood or other organic material is heated, but not supplied with enough oxygen for a true flame. For example, it might be buried in a pile below ground with only a little oxygen available. This heating causes the first step of the reaction, breaking down the complex organic molecules into mostly free carbon + other stuff. But there's not enough oxygen for much of the second step to take place, so it stops there. (In practice, a little oxygen is introduced - just enough to allow enough of the second step to happen to keep the pile of material hot enough to continue breaking down.) This first step alone is called *pyrolysis* (Greek: *pyro* "fire" + *lysis* "to break down").

The resulting charcoal is effectively a chunk of mostly-pure carbon, which burns with a cleaner and hotter flame because many impurities have been removed (particularly water, which takes a lot of energy to evaporate) and because it doesn't have to consume energy to allow the first step of the reaction.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
Is it possible to accurately predict the death of a given star?

If you were close enough to a red giant star would it be possible to accurately predict the point at which it would go super nova? How accurate could that prediction be? Would you be able to pinpoint the precise minute, year, decade? And from how far in advance? Also, same question for a smaller star collapsing into a white dwarf.

[Assistant]
No.  The problem is that the changes which will result in the star exploding all occur deep within the core of the star, and it takes of order a million years for structural changes in the core to be visible on the surface.  This not coincidentally about the same amount of time it takes for the thermal energy in the core to make it out to the surface.

Supernovae in massive stars occur because the core has fused up to iron and doesn't have another energy source to fall back on and support the star against gravity.  There are five or six fusion stages the star goes through, roughly H -> He -> C, O -> Ne, Mg, Na -> Si -> Fe -> kaboom.  For a massive star like Betelgeuse, the first step takes 2-3 million years.  Helium to carbon/oxygen, another hundred thousand to million years.  Going up the alpha chain from oxygen takes no more than a few hundred.  After that, you get a silicon core in a few months to years, and an iron core in just a few weeks, if that.  This is because each rung of the nuclear burning ladder releases less and less energy per reaction and requires much higher temperatures to proceed, so the star goes through its fuel faster and faster.

And therein lies the problem.  Once the star moves off the main sequence and becomes a red supergiant (red giants don't go supernova, as a rule), all you know is that it has at least started burning helium in its core.  You have no real idea how far along it is in that process because the energy released by carbon burning and higher simply has no time to make it to the surface and produce visible changes in the structure of the star.  Now, you might have a shot if you were really close to it by detecting neutrino emission, since neutrinos stream freely out of all stars - in fact, solar neutrinos are some of our best physical evidence for the fusion processes occurring in the core of the Sun.  But you'd never see a high enough neutrino flux when viewing the star from afar.  Once the star goes supernova, you would get some slight amount of warning from an enormous surge of neutrinos resulting from the formation of the proto-neutron star at the center of the core, but that's it.  And it only amounts to a couple hours' warning before the supernova shockwave makes it to the surface and finishes blowing up the star.

Similar story for low-mass stars destined to become white dwarves.  Although we can definitely classify stars as being asymptotic giant branch (AGB) stars, which are no longer burning helium in their cores and are well on their way to completely shedding their outer layers, this phase is still very long (AGB stars are still burning hydrogen and helium in shells around the inert core).  The process by which an AGB star ejects its envelope and becomes a white dwarf takes of order 10-100,000 years.  This is blisteringly fast on an astronomical timescale, but we humans really can't say anything until a star is already well into this phase.  This is accentuated by the fact that this phase is so comparatively short, so there just aren't that many stars out there currently in it and thus we don't have a great handle on what they should look like.


[System] Given the following post, respond as if you're commenting on Reddit:

[User] [Borderlands] Why are there so many midgets on Pandora?

[Assistant] Pandora's 90 hour day subjects its population to increased radiation exposure from the planet's star.  This increased radiation exposure causes a higher rate of mutation in the FGFR3 gene, which is responsible for Achondroplasia, the most common cause of dwarfism.  Because of the harsh nature of society on Pandora, people born with this obvious morphologic abnormailty are frequently the subject of scorn and ridicule, which enventually results in criminality and insanity.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
[General] How would a modern Vampire operate?

Where would they most likely be hunting? Would they live in groups? What should they fear the most about modern humans?

[Assistant] Assuming we're talking about intelligent vampires like Dracula and lestat.  They'd absolutely love modern society over the old world.  Settle into a city like Vegas or Shanghai or Paris that's known for operating late hours and unlike smaller cities.  Purchase a condo through a familiar are through online transactions. Make some minor modifications like black windows.  And high speed internet service. They'd prowl online forums and chat rooms looking for victims and grooming potential victims to the idea that they are real vampires and lure them in.  Online dating and anonymous hook up apps will become a buffet for them.  Once too many people begin to ask questions they simply move to another city or even just across the city.  Large homeless populations will provide a quick meal as well. And in today's day and age any evidence brought to light will be discredited and called fake or considered the work of a serial killer or lunatic rather than a monster living down the street.


[System] Given the following post, respond as if you're commenting on Reddit:

[User] ELI5: Why do we feel jealousy?

[Assistant]
It's all wired in us. We feel jealous to encourage us to be better than that person.

Let's go back in time about half a million years ago...

Oog and Gork are neighbours. They are hunting buddies and they have known each other for years. The two go on a hunting trip. Oog is bigger and stronger and can throw the spear further and faster than Gork. Gork took down a 300lb deer while Oog took down a 600lb deer.

Gork will obviously be jealous.

Suddenly, a group of females nearby notice Oog carrying the freshly killed deer on his back and start flocking towards him. They then go back to Oogs's cave and start mating.

Now Gork will be very jealous.

Simple enough?


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
Does time travel into the past imply the Halting Problem is decidable?

Rule: Assume that there are unbounded resources including time.

If the message will be sent by ourselves, we will receive the YES **instantly.** If we do not receive the answer, then the algorithm does not halt.

Basically, if there is no possible future where the algorithm halts, then we will not be able to send a message back in time. **And the lack of a message means it will not halt.**

[Assistant] It isn't an area with a lot study. However, it has been argued that a Deutschian closed-time loops allows effectively for the construction of a halt oracle (not by the means you mention but you can read Aaronsen's paper if you want).


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
ELI5: How does a voice commentary for sports videogames (ex. NBA 2K12) actually get recorded? How does it actually work?

Well, explain like I'm 8 would be adequate. My nephew is constantly amazed that the commentators seem to almost always be saying the right thing whenever he plays his NBA 2K12 on his Playstation. I notice that the comments may get a bit repetitive at times, but it also still quite blows my mind. So how do they do it? Do they record thousands of lines, each time saying every specific player's name? I just can't imagine what's happening behind the scenes.

Edit: I realized that I used the word "actually" twice. Lol. Anyway, thank you for all the replies!

[Assistant]
They don't record every line for every player. They'll record each player's name in a couple of tones of voice, and then plug the recording of the name into a longer line of commentary.

However, some of the lines that are specific to a individual player are recorded with the player name in full.

As for how the game knows what to say and when to say it: any event in the game can trigger commentary, and the game will choose from a selection of lines that will fit the current situation.

You're right though, it is pretty incredible how far video game commentary has come over the years. Back in the early 2000s, things were even more repetitive, to the point where I'd play most sports games with the commentary off!


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
Returning to Academia

As of 2008, I had my bachelor's and master's in history. I had a full ride lined up to go to Purdue to start the Phd program. Due to starting a family, I decided not to pursue it at the time and instead worked in other field where I have some skill which is IT.

While working my way up in the IT field, I started an adjunct position at a nearby community college and have been doing that nearly every semester since 2010. IT has been good to me and I have a high paying position for my area.

At the end of 2020, I left my employer and while I took on an IT consulting gig, I decided it was time to try doctoral school again as it was a passion and still is. I received one acceptance with no funding and a letter saying that I would have gotten in if the pandemic hadn't caused the university to lower the number of new candidates. For the acceptance without funding to St. Louis University, I deferred my enrollment and continued with my IT career. In that time frame, I bought new things and took on new debt since I thought it was over.

Now.... SLU has funding for me to start my program. At 37... I feel like it is now or never.

How do I justify taking a MASSIVE pay cut and ask my wife to become the sole breadwinner while I pursue something I think is my dream? Is it worth it? Am I giving up too much? How do I juggle being a Dad while going to school.. doing an assistantship.. still teaching online courses.. and maybe even do a little consulting to make ends meeting? I still have student loan debt from my first round of college.

I keep telling myself that with all of my IT experience, I could easily find another good paying job in the field if it doesn't work out, but the unknown is scary.

I'm not even sure what I am asking this community, but I wanted to put it out in the ether that is Reddit...

Thanks for reading.

[Assistant]
Don't do it.  You can still go to academic conferences, you can still read journal articles, there are loads and loads of amazing lectures online.  Heck, start a podcast or a YouTube channel about the area of history you are interested in.

Your work life balance, sanity, ability to be a good parent/partner, and financial situation are going to be so much better if you let IT pay the bills and keep history as one of your passions.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
[Star Trek] Where the Hell are the Xindi?!

Since Captain Archer stopped the war with the Xindi, they've been dead silent.  Even during the Dominion war, when the entire Alpha quadrant was at risk, the Xindi remained quiet.  Apparently, the Xindi are meant to join the Federation by the 26th century, but I haven't seen or heard a thing from the Xindi throughout TNG, DS9 or Voyager.  So where the hell are they?

[Assistant]
Best bet? After learning of the Sphere Builders' treachery, they took stock of what had happened and chose to retreat deep into their own space to attend to old wounds and rivalries. While the original Xindi Council was a massive step forward in unification and peace, the actions of the Insectoids and Reptilians revealed that they had not progressed as far as they thought, and that, absent the false threat of Earth, they needed to go back to square one.

Azati Prime became a neutral territory, where any Xindi could live and work. Generations went by as the Xindi learned how to live with one another, how to give up on their ancient tribalist ways, how to become one people. Because of the social instability, technological advancement slowed. Integration programs were put in place, to ensure diversity in Xindi environments for all of the species.

It wasn't until a few hundred years later that the Xindi finally emerged a unified race. They opened up talks with Earth, now the Federation, and were allies for some time, before the invasion of the Sphere Builders brought them together and the Xindi applied for membership.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
How do snakes move?

How do snakes move forward? Watching them, it seems like they move forward by slithering their body back and forth, but I can't see how that moves them forward.

[Assistant]
Snakes have four ways of moving around.  Since they don't have legs they use their muscles and their scales to do the "walking".

Serpentine method:  This motion is what most people think of when they think of snakes.  Snakes will push off of any bump or other surface, rocks, trees, etc., to get going.  They move in a wavy motion.  They would not be able to move over slick surfaces like glass at all.  This movement is also known as lateral undulation.

Concertina method:  This is a more difficult way for the snake to move but is effective in tight spaces.  The snake braces the back portion of their body while pushing and extending the front portion.  Then the snake drops the front portion of their body and straightens an pulls the back portion along.  It is almost like they through themselves forward.

Sidewinding: This is a difficult motion to describe but it is often used by snakes to move on loose or slippery surfaces like sand or mud.  The snake appears to throw its head forward and the rest of its body follows while the head is thrown forward again.

Rectilinear Method:  This is a slow, creeping, straight movement.  The snake uses some of the wide scales on its belly to grip the ground while pushing forward with the others.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
[XMEN] Shouldn't Magneto get helmets for his whole team?

I mean, all Professor X has to do is get one of his goons to slap off the helmet quickly and then he's vulnerable.

[Assistant]
Okay, first off, the helmet is magnetically stuck to his head. You'd need high-level super-strength to pull it off.

Ultimately his team is expendable, and he is strong enough to insta-kill most of his minions if they are mind controlled. Although afterwards he would feel guilty about having to sacrifice them for "the greater good."

Of course, Xavier knows that Magneto is willing and able to kill *anyone* to achieve his goals. That's why Xavier doesn't push Magneto very frequently. For example, in Fox's X-Men 1, Magneto points guns at an entire police squad when Xavier has Sabretooth's claws around Magneto's throat. Xavier backs down.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
If the Sun were to suddenly disappear how long would it take for the Earth to freeze?

Title pretty much. Question came to me when watching a Doctor Who episode.

Edit: From a few comments, I think I need to be more specific. My freeze, I mean be unsuitable for human life without technology. I don't mean it as in walk out of a heated house and die. How long would it take for earth to be inhabitable by humans without any forms of technology.

Thanks!

[Assistant]
Your question should be clarified as:  If the LIGHT from the sun were to stop reaching earth (for some unexplainable reason).

If the sun actually vanished, the planets would abandon their orbit and well...it will not be a fun time.


[System] Given the following post, respond as if you're commenting on Reddit:

[User] How long can bacteria survive on everyday household items without nutrients and water?

[Assistant]
Depends on the strain and species. If it's a spore forming bacteria, it can survive for almost forever.

Normal households won't be free of water or nutrients, as there are naturally in the air. But in ideal conditions, as to your question, a few days to a few weeks.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
ELI5: Why is it hard for rural areas to get home internet even if they have good phone service?

Edit: *good cellphone data service*

What's the difference between watching Netflix on mobile vs home internet? Why can't a similar technology of radiowaves or satellite be used?

[Assistant] Good phone service just needs cellular towers, which is a few connections to service a large area. Good internet, cable or fiberoptic, regulars direct connection from the residence to the provider. So they'd need to run cabling to each house, along all those rural roads, to provide good internet, which is an expensive upfront cost for a small benefit (a few customers).


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
ELI5: Why do people like Ron Paul? What does he want to do if he becomes president?

First of all im from Europe and know nothing about US politics but what i've read is that people like Ron Paul, why?

[Assistant]
Ron Paul is a social and economic libertarian.

It can be confusing because the the terms liberal, conservative, and libertarian are slightly different in the US than they are in Europe.

In the US, liberals are on the left of the political spectrum and generally believe in things like unions, progressive taxation, social equality, financial regulation, etc. Liberals are more often found in the Democratic Party.

Conservatives are on the right of the political spectrum and generally believe in less progressive taxes, less financial regulation, religious values, etc. Conservative are more often found in the Republican Party.

Libertarians in the US are sort of a mix in that they fall on the extreme right economically and on the far left socially.

Ron Paul is further unique in that he falls on the far right economically, but socially spans the entire political spectrum.

So Paul believes in the complete deregulation of business and financial markets, the dissolution of our national bank, returning our currency to be tied to gold, removing a bunch of government institutions and generally removing as much power from our federal government as possible.

Socially he believes that drugs should be legal, but he also thinks that abortion should be illegal, so he sort of spans the spectrum.

So people generally like him because they ideologically agree with a number of his beliefs and above all else think the federal government exists to take rights away from people.

People don't like him because they think his views are extreme, impractical, irrational, and ideologically think that government exists to protect the rights of people.


[System] Given the following post, respond as if you're commenting on Reddit:

[User] When I breathe casually, why does my stomach move in and out.  But when I breathe deeply my chest expands?

[Assistant] When you inhale normally, your diaphragm drops displacing the contents of the abdominal cavity. When you do a forced inhalation, you utilize your external intercostals and other accessory muscles, allowing for further expansion of your chest cavity until your inspiratory reserve capacity.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
ELI5: Why do we get hungry every few hours, even when we haven't burnt all the energy/calories from our previous meal(s)?

I'm sure there's something very obvious that I'm missing, but I don't get why humans get hungry all the time even if there's plenty of energy left to burn. For instance, if we eat a breakfast that's 1500 calories and then sit on the couch all day and only burn maybe 700 calories, why do we feel hungry again a few hours later, even though there's still 800 calories left? If I had to guess, I would guess that the feeling of hunger (like stomach growling)is a technique our body uses to tell us that we need more food and more energy. But why does our body make us feel hungry even if there is leftover food that we haven't burned yet?

[Assistant]
We get hungry when our body is about to start the process of warming up the furnace to burn fat.

There may be plenty of calories available in our bodies, enough to last for days, but we get hungry when we run out of the "easy to access" energy and our blood sugar level gets low.

Blood sugar levels have a certain safe range -- too low and we're weak, too high and the blood turns toxic.  When we eat, blood sugar levels rise as food gets digested and sugars get added into the bloodstream.  If it rises above a certain point, our body starts skimming off the top and putting the excess into fat.  If it falls below a certain point, we get hungry, and if it falls even further, we start burning off that fat to return those sugars to the bloodstream.

Hunger fades once the fat is burning and sugar levels rise.  When the fat calories run out, we just get tired not hungry because the body is already in "fat burning" mode.

As soon as we eat anything (edit: anything with any sugar), our body immediately stops burning fat and switches to using the incoming food instead.  When that runs out, you get hungry again as part of flipping the switch back to fat use.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
[Warhammer 40k] Describe the typical process of a planet falling to Papa Nurgle

Hello everyone. I am a lowly member of a small cult and would like a guide pretty please.

[Assistant]
Nurgle is the beginning and the end, he is both life, death and everything in between. Like those he will come to everyone, and that makes him different to his chaotic brethren.

Tzeentch favors the smart and cunning, the ones with ambitions that span across the whole galaxy. His followers are the intellectual elite.

Slaanesh favors the decadent and the desperate. Rich oligarchs that wish to end their continual boredom as well as the poor living in the gutters of the hive city that long to drown out their bleak reality.

Khorne is war and burning wrath. He favors only power and those willing to use it. Righteously vengeful or hateful and indiscriminate, he represents both. His followers are those both powerful and willing to crush their enemies.

Malal is pure destruction. He destroys everything but himself. That's it.

Nurgle on the other hand doesn't care about a specific characteristic. If anything is alive it falls in his domain and he has things to give that everyone want. He will lessen the pains of life, both physical and mental, and even take your fear of death. Among his followers may be a the graying business man, that fears death slowly creeping towards him and making all his lively possessions pointless or the suffering and abandoned mutant, cowering in the sewers praying for a few friends to make his existence bearable, or the guardsman at the front-line when he sees the endless slaughter and just wants back home and live happily ever after. He is not as excessive as the others, no unspeakable pleasure, no glorious vengeance, no big twisted schemes; just the contentedness life can give you, the joy of friends and family, birth and finally a fulfilled death.

When he decides to take a world it won't be spectacular. A dying man begs for help and Nurgle hears him. He is generous, as he always is, and quickly bestows the man with his gifts. The man feels better, happy and loved like he hasn't been since his childhood. The nasty cough and his bloating stomach don't bother him, no, they are signs of his 'fathers' affection. He obviously wants to share his new found happiness with the world, so he walks around  the hive, coughing his lungs out but smiling broadly. Withing week everyone dies painfully, convulsing in their bodily fluids and the man rejoices. Who would he be to deny them entry to Nurgles garden after all. They deserved it.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
Nothing is unnatural. CMV

Everything in the universe is nature (meaning it is part of the physical world). Anything produced in the universe is natural. Genetically modified organisms were produced or engineered by humans, who are part of the universe. You can't say something is unnatural or unnaturally occurring, unless you're talking about something supernatural. Also, something that is "man-made" is still natural since humans are part of nature. I really can't see how this can be disputed. In day to day life, when people refer to something unnatural, they are making up their own definition or using their own parameters for determining whether something is natural or not. Instead of using the word unnatural when talking about man-made things, shouldn't people be using "man-made"?

EDIT:

The definition of natural:

>Existing in or caused by nature; not made or caused by humankind.

Humankind is part of nature so doesn't the definition contradict itself? It's like saying:

>Existing in or caused by nature; not made or caused by nature.

Shouldn't the definition be:

>Not made or caused by humankind.

[Assistant]
Technically, you are correct, but this would render the words 'natural' and 'unnatural' useless, so we have a kind of loose definition for the purpose of conveying information

For examples: ''This shirt is made of polyester and this one is made of natural fibres'' or ''This woman has dyed her hair blonde and this woman has naturally blonde hair''


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
ELI5:Why does the US Armed Forces have an Army, Navy, Marines, and Coast Guard, instead of just an Army and Navy.

It seems unnecessary to have all these branches when the Navy can just absorb the Coast Guard and the Army can absorb the Marines. To me it seems counter-intuitive for these specialized branches to exist when in reality they are essentially the same branch.

For example, Marines are supposed to specialize in invasion and ground combat, but so are Army Rangers. The Navy reigns in international waters but both the coast guard and the navy perform the same tasks with the same equipment.

To me, it seems expensive and overly complicated to keep 4 branches instead of 2.

[Assistant]
Back when they first started making militaries, there were two kinds of fighting people:

* People who fought on land. When they got around to inventing the English Language, they called them *Armies*.

* People who fought on water, from ships. We call them *Navies*.

Now around the time of the American Revolutionary War (late 1770s), navies fought using wooden sailing ships with lots of cannons firing solid iron balls. These guns were pretty powerful, but they were pretty inaccurate unless you got really close, and unless you got really lucky and blew up the enemy's gunpowder magazine, they couldn't really do enough damage to sink another ship quickly.

So if you were willing to sail through cannonball fire for a little bit, it was possible to get close enough to the enemy ship to board it with your own men. However, most sailors were good at sailing, and not as good at shooting or hand-to-hand fighting, so they decided to create groups of soldiers who specifically trained to fight from ships. These are called *Marines*.

Some countries kept them as part of their armies or navies, but in the US, they put them specifically under the authority of the Department of the Navy, and slowly over time they gained more and various responsibilities- Presidential guard, Embassy guard, etc.  Also, because they were on Navy ships all the time, they were usually the first ground troops to show up when the government was trying to flex its power overseas, so they also started doing amphibious warfare (invading beaches from ships), which is their primary mission today.

Around the same time, many countries saw a need for a nautical police force. Using the Navy for that was in most cases overkill; you want to enforce tariffs and catch criminals, not blow merchant ships out of the water. So *Coast Guards* started becoming a thing, tasked with seagoing law enforcement and search and rescue. In the US, it was put under the authority of the Department of Transportation in peactime, and the department of the Navy in wartime. (there was no Department of Defense then). Recently they've been put under the Department of Homeland Security.

So, finally, years later, airplanes were invented. Immediately all the armed forces saw a use for them; mainly spotting for big guns at first (Navy battleships and Army artillery), but later they started carrying guns and bombs and torpedoes and missiles. In some countries, they managed to create a separate *Air Force* right away (the UK did this with the RAF), but in the US, the Army and Navy each handled their own aviation, arguing (accurately enough) their needs were different. So it wasn't until after World War II that the Air Force was split off from the Army into a final branch. The Army still maintains its helicopters for transport and close air support, and the Navy argues that aircraft carrier operations are too different from the land flying that Air Force personnel are used to, so they each have their own aircraft. The Coast Guard needs aircraft for long-range search and rescue. And the Marines have their own aircraft because they're supposed to be a self-contained, independent and fast-moving fighting force once the Navy drops them on the beach.

As for why they haven't merged them back? Politics, money, and tradition. There have been several attempts made--the Air Force argued in the 50's that nuclear weapons made all surface forces obsolete; the Army has tried to absorb the Marines several times; the Air Force has tried to take the Navy's planes, etc. But it seems unlikely in the near future.


[System] Given the following post, respond as if you're commenting on Reddit:

[User] ELI5: How do diesel engines work? Why would they be preferred?

[Assistant]
Diesel fuel burns differently than gasoline.  It's a thicker, less volatile fuel that burns more slowly than gasoline (think of the difference between setting a cup of gasoline on fire, and the ease of doing so, compared with doing the same thing with a cup of oil).  So, when the gasoline in a cylinder burns, it does so very quickly.  It only provides propulsive energy when it burns, so it only provides that oomph for a very short time, so you need to have more repetitions of this to get things moving, hence the higher comparative rev rates of gasoline engines.  Diesel burns more slowly, so it ignites and it keeps pushing for longer.  So, you don't need as many revolutions of the engine to get the power out of it.  This longer push in the cylinders also results in the engine creating more torque.

Diesel is also ignited differently.  It isn't ignited with a spark like gasoline is.  Rather, it is compressed to a very small volume, until that compression creates enough heat to cause ignition.  This high pressure means that diesel engines have to built very strong, to withstand that pressure.  The end result is that you have a very toughly built engine that revs low and creates a whole lot of pull out of those low revs.  So... diesel is preferred in those situations that benefit from those characteristics.  And that means hauling, where you have a lot of weight that you need to get moving and keep it moving.  You don't need the high-revving horsepower of a gas engine for that.  You need that slow-burn torque of a diesel for that.  Yank all that weight off the line and just get a head of steam going and keep going.  That's hauling, and that's diesel.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
Why are the Galapagos Islands specifically so important to study?

I always see the Galapagos Islands as the big place that people are studying.  I realize there are major historical discoveries that have happened there, but aren't there likely to be many archipelagos that are near a mainland that display the same amounts of natural selection and adaptive radiation?  Are they just the "famous" archipelago?  Is there a really unique situation there?  Or are people building upon 100+ years of research in that specific place?

[Assistant] It's for a number of reasons. Largely because of the fact that the Galpagos is a volcanic landmass that was never connected to any continent. This means that all the species there had to migrate there, and there are no natural large predatory mammals, so they're able to survive there. Because of this, and because of how different the Galpagos landscape is compared to anywhere else, species were able to adapt in ways that we haven't seen before. There are many species there that can't be found anywhere else in the world. For instance, there's a native species of Iguana there that's adapted to aquatic life, which is something we've never seen from Iguanas.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
ELI5: How is the Earth's core still hot 4.5 billion years into its existence?

I mean, I get that it's pressurized and all, but how does it maintain enough heat to keep iron melted?

[Assistant]
The earth is actually still heating itself. We're not just a bunch of rock, the core and mantle actually have atoms breaking down, releasing heat. We are effectively sat on a nuclear reactor set to slow.

Early earth was hotter, and has lost a LOT of heat over time, but the amount we have left isn't just here form the start, our planet is effectively burning fuel to keep active.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
Why do we only see one big rainbow instead of myriad of very small ones? Every drop of water in the air kind of creates its own small rainbow by refracting the light, so why don't we see all of those individually?

Question has been answered, but feel free to add onto any dicussions or bring up points not yet mentioned.

[Assistant]
A water droplet is a sort of mirror prism. A ray of light comes from the Sun, enters the droplet and changes its angle due to refraction, reflects off the inner wall of the droplet (at least partially), and comes out at a different angle. Different colours come out at different angles.

If you imagine a triangle from the Sun, to the droplet, to your eye, this is the path the light goes. You will get a specific colour if the angle between the Sun-droplet line and the droplet-eye line is just right. What this means is that all droplets in the same line-of-sight will give you the same colour, because the Sun->droplet->eye angle is the same along that line, and the light has been bent by the same angle for all those droplets.

A rainbow is (in principle) circular, centred on the point exactly opposite the Sun, because it doesn't matter which direction the light is bent, as long as the angle is right. So a full circle of lines-of-sights of droplets will cause rays of light of a specific colour to hit your eyes. Of course, the ground is in the way most of the time (the Sun is above ground, so the centre of the rainbow is below ground), and the rainbow ends up looking like an arc.

You also get double & triple rainbows etc because light can bounce more than once within a droplet, and will come out at a different angle after each bounce. But some light leaks out after each bounce, which is why the second + third + above rainbows are quite dim - and also why clouds aren't completely dark!


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
[Star Wars] What makes falling to the dark side of the Force more serious than a non-Force-sensitive becoming evil?

How is it any different from a regular person doing evil stuff and why is it considered harder for a Jedi to stop doing evil things than a regular person? Isn't someone like Jango Fett or Tarkin just as or even more dangerous than a Jedi? What makes an evil Force user a more important target than a known vile criminal like Jabba who is known to cause widespread suffering?

Yoda: Once you start down the dark path, forever will it dominate your destiny, consume you it will.

[Assistant]
1)non-force sensitives don't have freaky superpowers.

2)a force user's life is dominated by their connection to the Force. Misuse of it will seep into them and cling to them.  IOW: being evil taints your soul. Being Dark Side taints your soul AND poisons the Force around you.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
[MCU] The Asgardians, an incredibly advanced species, couldn't find a way to safely remove the reality stone from Jane. So how did Tony, with comparatively lesser technology, do it so easily?

In TDW, the Asgardians made a big deal about how it would be extremely difficult to safely separate the reality stone from Jane. And yet, in 2023, Tony managed to create the technology to do it, with relative ease; how?

[Assistant]
I think it's a combination of three things:

First, the Asgardians had *very* little time between rediscovering the Aether and being invaded by Dark Elves. Nobody had seen it for eons. The knowledge Odin inherited was a flat-out lie regarding whether the Aether still existed and certainly did not include details like how to remove it.

Second, there was little incentive for Odin to extract the Aether while it was contained. Removing the aether may have been a very bad idea without a sure way to destroy it (a mistake Thor makes later on). Odin would have had no problem sacrificing Jane if necessary. He regularly sacrifices Asgardians to achieve goals and he values humans far less.

Third, the Aether has its own intent and seemed both hostile to Asgardians/Humans and 'friendly' to the Dark Elves. Two Asgardians got thrown across a room just for touching Jane while it left willingly for Malekith. It's possible that this was taken advantage of in some way to extract it or, at least, that Malekith possessed the knowledge of how to control it (indicating that it was a matter of technique rather than pure technological ability).


[System] Given the following post, respond as if you're commenting on Reddit:

[User] ELI5:Why is bottled water often more expensive than Coke (or other fizzy drinks) which, as well as containing water, contain lots of ingredients which need to be bought and paid for while water is just, water?

[Assistant]
When you buy a bottle of Coke, it comes from a local bottling plant.  Coke only has to ship a very highly concentrated syrup containing the flavor across the country & somebody adds water to it locally & then distributes it to stores.  Many bottled waters come out of the same factories - they just don't bother adding anything to the water.

If you want a 'special' bottled water those have to be bottled at a single location and then shipped all around the world.  Shipping is expensive, water is heavy & Evian has to come all the way from France.

Then there's always the idiot factor.  If you put a fancy label & a high price tag on some tap water, you can probably get people to buy it because they just assume that the more expensive product is higher quality.


[System] Given the following post, respond as if you're commenting on Reddit:

[User] What is the difference between genetic mosaics and chimera?

[Assistant] Mosaics and chimeras are animals that have more than one genetically-distinct population of cells. The distinction between these two forms is quite clearly defined, although at times ignored or misused. In mosaics, the genetically different cell types all arise from a single zygote, whereas chimeras originate from more than one zygote.


[System] Given the following post, respond as if you're commenting on Reddit:

[User] ELI5: Why is there serotonin in snake venom if that chemical is the chemical that makes us happy?

[Assistant]
Your body repurposes the same chemicals for multiple uses.

Serotonin is used in the brain to modulate your mood, but its also used in the circulatory system to control blood vessel constriction and blood clotting.

The snake doesnt much care about your mood, but it does want to blow up your circulatory system with a huge dose of chemicals that interfere with normal behavior.


[System] Given the following post, respond as if you're commenting on Reddit:

[User] ELI5: What does hacking actually LOOK like? For example, what interface is the hacker using, what's their goal, and are they typing in a bunch of passwords like in the movies?

[Assistant] Nothing like the movies. Most of it is writing a program at your leisure, depending on what youre doing. Its just exploiting over sights or weaknesses in a code or system. Very little is done in real time, and even that is more more mundane, just exploring directories for data you want, etc.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
CMV: Nuclear waste isn't really a big problem.

So my train of thought goes as follows: The uranium mined for nuclear energy is already radioactive to begin with. In the power plant, it decays into much more radioactive isotopes, but these have really short half-lives, so it will just take a couple months for them to decay into isotopes just as weak as the uranium that was originally mined.

So why do we need final disposal sites where this weak radioactive material can stay for thousands of years? If we just dumped them deep into the ocean for example, what would happen? Wouldn't they just dilute to the point of not being noticeable at all?

It's really hard to get information on this online, but I gotta be wrong in some way, otherwise people wouldn't have this argument, right?

[Assistant]
It's true that the diffusion of radioactive matter into the sea will dilute it, but it comes from a very concentrated source to begin with, thus harming aquatic life nearby. It's not so much that entire oceans are affected significantly, but the immediate area is.

However, like you say, encasing waste in concrete is a pretty inexpensive and safe way to dispose of the waste, so there shouldn't be much of an incentive (if any) to just dump it in the sea.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
ELI5: How can cars like the Honda CR-X get 52 mpg in 1984 but average cars now get the mid 30's?

Explain?

[Assistant]
Weight and Emissions requirements.

Cars have progressively gotten heavier for safety reasons such as mandatory air bags, and higher crash test requirements.

Car engines also have much more restrictive emissions laws influencing their design. Things like catalytic converters affect horsepower and efficiency.


[System] Given the following post, respond as if you're commenting on Reddit:

[User] ELI5 : why do buses make that "PFSSSST" sound when they stop?

[Assistant]
Many large vehicles have a system of brakes actuated by compressed air instead of hydraulic fluid or cables you would find in a lighter vehicle or passenger car.

Parking/emergency brakes on such vehicles are usually "normally closed": to release the brake, air pressure must be applied to the brake.  For these, a sudden release of air pressure will quickly activate that brake, but also will create a little bit of noise.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
[Harry Potter] Bone marrow transplants for leukaemia sufferers results in the patient producing new blood that is genetically the same as the donor. If a Muggle received marrow from a compatible wizard donor could they potentially gain some magical ability from it?

I'm don't know if wizards can cure leukaemia but if not I could envision a plausible scenario where a muggle born wizard is the best compatible donor available for a non-magical sibling and having no hesitation about going through the procedure for them. Given the emphasis that the wizarding community places on the magical nature of wizard blood (indeed their blood has been involved in a few spells) and the established fact that magic has a genetic basis then a muggle who has received marrow from a wizard will now be producing genetically pure wizard blood.

Could this potentially open the door to some aspects of magical ability to them?

[Assistant]
Wizard blood, while containing magic, doesn't necessarily mean it is the source of magic.

And we have no idea how much epigenetic is involved in gaining the magical talent, or if genetics is even involved at all. For all we know, even if you clone a wizard, the clone might not have magic.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
CMV: There is no viable free market solution to climate change

According to the most recent reports we're already in a climate crisis. People are already protesting enmasse for drastic changes. The free market is not a system that handles drastic change well. If there is drastic change that fundamentally, and systematically shuts down certain types of businesses, and revenue streams the markets tend to go into free fall and crash. Still, we do need to change our ways in a fundamental and systemic way. So I dont think there is a way you can come up with a free market solution that would adequately address the problem and still have a fully functioning free market.  I am open to ideas and would like to hear what you think.

[Assistant] Slavery used to be legal and commercially viable.  The abolition of slavery was disastrous for the legal slaving industry; good riddance.  The markets continued to function.  The markets are not only capable of handling change, the markets enable change.  The capital market is the tool we use to funnel capital to productive uses society wants.  If society decides it wants to stop using hydrocarbons and start using nuclear energy instead, the markets may be used to facilitate that change.


[System] Given the following post, respond as if you're commenting on Reddit:

[User] ELI5 how does submarines sink when its full of air?

[Assistant]
The hull is very heavy and so they just barely float normally.

They have big chambers inside called ballasts that are filled with air when they are at the surface, but when they want to sink they let seawater into them and pump the air that was in them in to compressed tanks. Compressed air is more dense so it effectively makes the entire vessel less buoyant, making it sink. When they want to rise they decompress the air in the tanks back in to the ballast, pushing the water back out to the ocean.


[System] Given the following post, respond as if you're commenting on Reddit:

[User] Is it possible to have planets with shapes other than spheres? e.g. a cube or two spheres combined?

[Assistant]
Such configurations would not last for long. The reason why large celestial objects are spheres is because this is the most stable configuration for an object held together by its own gravity. If the object is massive enough, its gravity will cause it to eventually collapse into a spherical shape (though rotation of the object around its axis can cause the shape to deviate from a perfect sphere).

Smaller objects, such as the moons of Mars, may exist in non-spherical form because their gravity is not strong enough.


[System] Given the following post, respond as if you're commenting on Reddit:

[User] ELI5: Do fish get 'out of breath' when they swim really fast?

[Assistant]
Same way humans do - they don't got enough oxygen. Of course, they don't *breathe* though.

To become out of breath, you must exert your muscles, such as by doing exercise. Muscle use requires energy. This energy can be produced in two different ways - aerobic respiration and anaerobic respiration. Aerobic respiration is what cells do normally because it produces a lot more energy and doesn't poison you. However, it requires oxygen. A cell that doesn't have enough oxygen can only use anaerobic respiration, which produces less energy and creates a toxic byproduct called lactic acid, that builds up in your muscles.

Lactic acid can be converted to a non-poisonous molecule using oxygen, which is what being out of breath is - after you do some anaerobic respiration, you need even more oxygen than you normally do, because you need the normal oxygen for aerobic respiration *plus* the oxygen needed to clear the lactic acid. This happens to fish too, but where we get oxygen using our lungs by breathing, fish get it using their gills by moving water across them.

Fish have a particular disadvantage when it comes to being out of breath. If you think about the anatomy of a fish, they're pretty much entirely muscle, right? They also have a ridge of darker meat.  Most of the time, the fish is only using that small ridge of dark muscle, that's optimised for regular use. This is the same kind of muscle we have everywhere. The white meat is only used by the fish when it needs a rapid burst of speed, but it runs out of oxygen faster than the dark meat does, so it builds up lactic acid really fast if it's used for too long.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
[Elder Scrolls.] I've somehow stumbled onto an Ebony Bow.

My first question is: How "strong" is this bow?
Or in other words, how fast can the arrow shoot,
and how much force does this produce? (Piercing and all the like)

Secondly: How does this Ebony Bow compare to a modern Bow?
(Any kind of modern bow I suppose.)

Any thoughts??

[Assistant]
It's kind of hard to imagine a Bow made from ebony. What is it? Stone? Metal?...anyway that bow is going to be *immensely* stiff.

You're going to need immense upperbody strength to even draw the thing.


[System] Given the following post, respond as if you're commenting on Reddit:

[User] ELI5: Why are astronaut's movements in space seemingly slow motion when there's no air/water resistance to slow them down?

[Assistant] There are a few reasons. Their suits are pressurized. The joints of these suits want to fully extend due to this pressure. This makes it difficult to move and do things, and reduces precision substantially. Not only this, but the suits are quite heavy, and have inertia to slow movements. Lastly, the astronauts do not have anything to stand on. Fast movements will make their bodies start to rotate and further reduce the precision of their motions.


[System] Given the following post, respond as if you're commenting on Reddit:

[User] ELI5: How does the pump at the gas station know when to stop putting fuel in your car?

[Assistant]
Up inside the handle there's a venturi nozzle (a smooth restriction in the tube) that causes a low pressure spot in the fuel line. That venturi is connected by a small tube to a hole near the end of the nozzle. The hole is on the side of the nozzle, not the big hole that the fuel comes out of. While you're pumping fuel the venturi pulls air into that small hole.

When the tank gets full enough that the fuel level comes up to the end of the nozzle, fuel starts to get sucked into that little hole. Fuel is way denser than air. This causes a pressure change inside the handle that actuates a spring-loaded mechanism to shut off the valve inside.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
[Mass Effect] How did Illium get a Hanar to portray Blasto in the Blasto movies?

Hanar are supposedly all very peaceful and were seriously offended by the movie,  yet they bost having a Hanar in the leading role.  Is there any indication as why or how this happened?

[Assistant] Just because an entire species is thought of as being one thing, doesn't mean they won't have their exceptions.  *Most* Hanar are peaceful and offended by the movie, however apparently one played a little fast and loose with it's society-driven morality and decided to become famous.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
ELI5: How did countries of the world come about deciding on a universal measurement for time?

I know there is a slight when considering military time, but every one agrees that there are 24 hrs in a day. How did we all come to agreement on this fact?

[Assistant]
Europeans used it and conquered the rest of the world and converted everyone else.  Formally, of course there have been international standard organizations that codified everything eventually, but those came long after the practicalness of European mass expansion across the globe spreading their time systems, calendars, and much more to every corner of the earth.

If China conquered the world instead, we would be using their system, which is different.

Our current time system is a descendant of ancient Egyptian and Babylonian time systems which was changed and altered in various  cultures to get to what we have now.


[System] Given the following post, respond as if you're commenting on Reddit:

[User] Why was Curiosity such a big deal if Opportunity and Spirit were already on Mars?

[Assistant] It's bigger. It has more experiments. It has more cameras and shit. It has a motherfucking laser cannon. It's in a new location. It's powered differently so it can theoretically last longer. Spirit's already done and Opportunity is coming to the end of it's life. It's already well beyond what it was designed to do.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
ELI5:How a person who commits horrendous acts against humanity, such as Albert Speer get 20 year sentence while illegally downloading documents, such as done by Aaron Swartz, holds a potential for 35 years ?

I saw two documentaries back to back. One on Aaron Swartz and then the Nuremberg trials. This confused me.

[Assistant]
In most jurisdictions, the maximum penalty that can be issued by a court is much more severe than the typical penalty. The maximum penalty is usually reserved for only the most heinous of crimes or repeat offenders of serious crimes.

Also, sometimes the maximum penalty is exaggerated because it reflects the maximum penalty of each charge put back-to-back consecutively (e.g. serving 5 years on one charge, then 3 years on another etc.). In reality, many jurisdictions allow for multiple sentences to be served concurrently so that someone like Aaron probably wouldn't have had to serve consecutive sentences for each individual violation.

In sum, it's highly unlikely that Aaron Swartz would have actually served (or even have been sentenced to) anywhere close to 35 years - if any prison time at all.

The other issue at play is that the maximum possible sentence for a given crime varies widely by jurisdiction. In many jurisdictions in the US, people can be sentenced to death for murder. In many other countries, however, the maximum penalty for a murder charge may be considerably less severe (e.g. 20 years).


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
[Harry Potter] Would Parseltongue be able to distinguish between a Slow-worm and a "true" snake?

Technically, slow-worms are limbless lizards instead of snakes.

[Assistant]
Parseltongue is a language. It's not sentient. Your question is flawed. You should ask, "Can a slow-worm understand Parseltongue?" The answer is no.

You may as well ask if your glass mug can distinguish between a full-grown dragon and some butterbeer. No, but butterbeer will fit in the mug and a dragon would not. This is a very Muggle sounding question. Are you a Mudblood?


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
[Star Wars] Was food produced on the Death Star? Did it have a certain area for growing food, or was it delivered from somewhere else?

Considering the size of the station, it would be a huge benefit to grow food there using artificial light.

[Assistant]
No, no food was grown there.  You don't put a farm on your battlestation.
The Empire has entire worlds dedicated to feeding the rest of the galaxy, Death Star included.  They ship the food in by freighter, much like they do with Coruscant.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
Why do they stop space launch countdowns?

I'm not sure that this is totally appropriate here, but I couldn't think where else to ask.

Sometimes, when reading about space launches(specifically NASA in this case) I see a statement like this:

"We're going to count down to T-2, then we're going to stop the countdown there for fifteen minutes while we work on something."

I don't get the stopping of the countdown.  Isn't the point of the countdown to tell you how much time you have before something happens?  Why stop the clock at T-2 for 15 minutes?  Why not just make the countdown T-17?  Wouldn't that be more useful?  A stopped T-2 could start in two minutes or in two days.

[Assistant]
Everything must go as close to perfect as it can.

There is a T clock - T for test, where everything is checked against a list and the T clock has built in holds for double checks, confirmations and go/no-go decisions.

The L clock - L for launch, is the time remaining before the scheduled launch. Because of orbital mechanics issues, sometimes delays will exceed the launch window and there has to be a delay until the next day.

The US Space Shuttle had holds at T-27 hours, T-19 hours, T-11 hours, T-6 hours, T-3 hours, T-20 minutes, and T-9 minutes.

For Shuttle, the T-9 hold came up the most because during launch coverage the T-9 was usually during the live broadcasts. During the T-9 NASA would do the following:

* During the hold, final launch window determination

* Activate flight recorders

* Final "go/no-go" launch polls conducted by NASA Test Director, Mission Management Team and launch director

So why is there a T-2 hold - to do all the last minute things, the verifications, flight data recorders, get the radio telemetry going, fire up APUs, all sorts of things.

Here is a list of all the stuff they had to do past T-9 for Shuttle

* Once the countdown resumes, start automatic ground launch sequencer

* Retract orbiter access arm (T-7 minutes, 30 seconds)

* Start auxiliary power units (T-5 minutes, 0 seconds)

* Arm solid rocket booster range safety safe and arm devices (T-5 minutes, 0 seconds)

* Start orbiter aerosurface profile test, followed by main engine gimbal profile test (T-3 minutes, 55 seconds)

* Retract gaseous oxygen vent arm, or "beanie cap" (T-2 minutes, 55 seconds)

* Orbiter transfers from ground to internal power (T-50 seconds)

* Ground launch sequencer is go for auto sequence start (T-31 seconds)

* Activate launch pad sound suppression system (T-16 seconds)

* Activate main engine hydrogen burnoff system (T-10 seconds)

* Main engine start (T-6.6 seconds)


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
ELI5: If human body regenerates cells all the time, how memories persist in brain?

If brain cells also undergo the life-and-death (or regeneration) cycle - how are stored memories or electrical impulses carried forward?

[Assistant]
"You" are not the molecules that make you up, but rather the arrangement of those molecules. The same applies to your memories - memories are the pattern of connections between brain cells. If all the cells in a connection are replaced, but the new cells are connected in the same way, then the memory remains the same, because the memory is the pattern of the connection, not the molecules that make it up.

If that's not clear enough, take an analogy. You have a lego set, let's say it's the Batmobile. If you take it apart, you still have all the pieces, but you no longer have the Batmobile. If you buy a copy of every piece separately and swap them into the model one by one, you still have the Batmobile, but none of the pieces are the original pieces. Your memory is the Batmobile, not the pieces.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
Why can't the three-body problem be solved?

In school teachers always said it was unsolvable and left it at that and I am now doing second year physics in uni and it's again taken as axiomatic that we cannot solve it. What is it about it that presents a problem?

[Assistant]
It isn't a direct answer to your question, that has been answered elsewhere in the thread.

The correct statement is the three body problem can't be solved *analytically*. It is very routine to solve n-body problems numerically with a differential equation solving routine. Although the answer can never be as precise it can be very accurate. All the spectral lines from ions who have lost more than one electron for example is an n body problem and yet we know the spectral lines of Iron XIV etc very accurately.


[System] Given the following post, respond as if you're commenting on Reddit:

[User] ELI5: If a nuclear Football is ever stolen, why can't they just change the codes?

[Assistant]
In addition to having a person holding the nuclear football, the president carries a card with a series of codes on it, one of which is necessary to prove that the person ordering an attack is actually the president.  If someone stole the nuclear football, that would be insufficient to launch an attack without the president's identification card.  Additionally, authorizing an attack requires permissions from both the president and the secretary of defense.  This means that in order to actually order a nuclear strike, someone would have to acquire the nuclear football, the president's  gold code (which isn't apparent just from stealing the card it's on), and whatever the secretary of defense uses for identification.  (I don't know what the secretary of defense has, but it's probably like the president's card, which doesn't have an easily interpreted code on it.)  Presumably the time it would take to steal and interpret all those items would be long enough for government officials to call, email, or otherwise contact the relevant personnel to inform them of the situation. Also, there are lots of trained people with guns who are willing to risk their lives chasing people who steal the nuclear football, which would further reduce the chances of anything disastorous occuring.

Also, there's probably some other emergency plan for this scenario that's classified for national security purposes.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
ELI5: Why do people trace the lineage of Jesus back to King David through Mary's husband Joseph since they do not share the same genetics, per the story of the Virgin birth?

Tis the season!

[Assistant] Ancient people didn't know anything about genetics. But inheritance - in this case, a metaphorical inheritance of the Kingdom of Israel - would be passed down male-line. Adoptive children, which would include Jesus to Joseph, were perfectly eligible for inheritance. That was actually how Roman emperors would name their successor for a while - they'd adopt whoever they wanted.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
ELI5: If nearly all the countries are in debt or in a financial crisis, where is all the money going?

Like say how the U.S. is in debt to China. And if China has a debt to Japan. And Japan to France so on an so forth. How is there money circulating if we're all in the red?

[Assistant] Countries owe money to other governments, their own government, and people (both within the country and elsewhere).  The majority of US debt (for example) is owed to US government and private American citizens.  Only about 9% of the US debt is held by China.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
[World War Z novel] What was the status of the United States Marine Corps during the duration of the American campaign?

The Navy, Air Force, and presumably Coast Guard were all grounded since Secretary Sinclair didnt believe that it was worth it trying to fuel, maintain, and arm a billion dollar warship or multi-million dollar fighter jet. The Army ended up taking the brunt of the march to New York.

But what about the Marine Corps? What was the role and status of the Marine Corps during the War? A couple of Marine combat engineers made E-Tools but was that really all we did?

[Assistant]
The United States Army saw massive reorganization throughout the war. Early on in the war the "Alpha Teams" were made most likely of elite marine units. While those teams were successful once the outbreak in New York got out of control the Alpha teams were unable to keep the outbreaks under wraps.

 After the battle of Yonkers which was primarily the Army (but probably had some marine units) the U.S. defense force fell apart and a there was a massive exodus to the west. This is probably where most marine units ended up disorganized, lost or dead. Once the west coast was secured the armed forces had to completely evolve, as you mentioned this meant no substantial machines would be used. In the novel they mention that they had to walk across the country.

The Marines that were left were adopted into this new armed forces. The modern marines love their machines and that's not what World War Z was won by. That said the steady trigger finger and great discipline lends itself to the new methods of warfare quite well. Many army units were augmented with marine veterans.


[System] Given the following post, respond as if you're commenting on Reddit:

[User] ELI5: How can "power naps"(10-30m) be more effective than longer naps? (1-3h)

[Assistant]
A Power Nap ends before you enter the phase of Deep Sleep.

 Sleep occurs in four cycles of around 90 minutes each-

+ Light Sleep Cycle

+ Deep Sleep Cycle

+ Dream Cycle

+ Light Sleep Cycle

*(repeat)*

If you wake up in b/w a cycle (before it's finished, but after it has started), you'll feel very tired. Which is why you should sleep for either six hours, seven-and-a-half hours, and nine hours.

______________

The power nap is thought to maximize the benefits of sleep versus time. It is used to supplement normal sleep, especially when a sleeper has accumulated a sleep deficit.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
ELI5: How can car insurance companies adjust their prices for people based on age/sex and not be sued for discrimination? What stops them from adjusting rates based on race?

I know they base their rates on actuarial information, but what is to stop them from doing the same thing with regards to race? It seems like insurance companies are allowed to exercise a degree of prejudice that most other businesses would never get away with.

[Assistant]
Two things that are relevant:

1. They can discriminate on any factor if they have scientific evidence that it increases or decreaes the cost of insuring you. There is clear evidence that younger drivers are more likley to be involved in a crash; therefore it is legal to charge them more.

2. The legal standard for discrimination is different depending on what the basis for the discrimination is. Legally race is extremely difficult to justify (almost impossible), sex is difficult but possible, and age is relatively easy to justify.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
[Star Wars] Mace Windu vs. Palpatine.

Mace Windu blocks Palpatine's lightning, and now Windu, Anakin and Palpatine are there with Windu ready to drop the final blow.

Now Windu, instead of saying that awful "he's too dangerous to be kept alive", says something more sensible. "He's killed countless Jedi, he tried to kill Obi-Wan [through Dooku], he would kill anyone to get what he wants". This causes Anakin to doubt that Palpatine has any intention of saving Padme. In his confusion, he fails to act. Windu goes to strike. What happens next?

[Assistant]
Windu goes for a death blow and catches a blast of Force Lightning square in the chest, blasting him out the window.  During the split-second distraction, Anakin lops off Palp's head.  The Jedi congratulate him on his service.

Deep down though, the Dark Side has found a place in Anakin's heart.  He executed Dooku at Palpatine's command.  He killed a disarmed Palpatine.  Corruption within the Senate remains unchecked.  Anakin begins to consider the points made by the Separatists.

With Padme's support, Anakin leaves the Order and is elected as a Senator himself.  He tracks down the Sith knowledge hinted at by Palpatine and begins his training, as his fear for Padme's death gnaws at him.  His Force power grows by leaps and bounds as he isn't maimed, and the Dark Side is quicker, easier, more seductive.  Windu's Juyo style becomes more attractive to him.  Eventually, not even Yoda can match him in power or swordsmanship.  He supports unethical activities by the Senate to support his view of order and promote his own personal power.

Eventually Padme discovers this and leaves him with Luke and Leia.  In his rage, he takes on a secret apprentice of his own, outside the Jedi Order.  Slowly Anakin moves to have himself made Chancelor.  Thanks to his service in the Clone Wars, he builds a small cadre of men loyal to him and him alone.  Political opponents begin to disappear.  Anakin learns the history of the Sith and begins to see Empire as the most logical system of government...


[System] Given the following post, respond as if you're commenting on Reddit:

[User] [Lord of the Rings] Which members of the original Fellowship were virgins?

[Assistant]
Probably only gandalf and legolas simply due to how their races treat sex like marriage.

The rest are pretty middle age by now, all the hobbits are in around the 40s or above, boromir too, with aragorn and gimli much older. Odds are they have had sex at one point or another.


[System] Given the following post, respond as if you're commenting on Reddit:

[User] ELI5: Why is League of Legends so popular?

[Assistant]
First of all, it's free.  You can download the game and immediately play the game without paying anything.  There are a number of people who continue to play for months or years without ever buying anything.  That's immediately going to make a game popular.

There are things you can buy within the game, but individual champions and runes, which buff up the characters you play can both be bought with in game currency, which you earn as you play.  A lot of money is actually spent on cosmetic items like skins for champions, but these don't improve the strength of your champions.

There is a weekly rotating schedule of free champions that you can play in normal games, so even if you don't own many, you can try new champions every week.

The games are fairly short, most lasting around 30-40 minutes.  So, you can queue up for a game, find one in about a minute, play with people and be done under an hour.  If you immediately queue up for another one, or play the next day, or come back weeks or months later, there may be small changes, but the basic games stays the same and you won't necessarily be behind other people who play all the time (except that they're more likely to have refined their skills).


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
If we're able to identify the position once of a quantum particle, would it not then be feasible to time a ton of pictures to happen at nearly the same nanosecond on the same quantum particle to track it's 'position'?

1) Why is it not possible to measure the position of a single quantum particle multiple times? (aka a video) Would we be able to then track it's momentum?
2) If the answer to the above is that it pops in and out of existence, how exactly does that happen?
3) How large of a field would you need to track a single quantum particle?
4) Would that be able to be done on Earth? Would we have to develop a large science facility in space somehwere?
5) Would it even be possible to build a machine large/small enough to do this?

[Assistant]
>Why is it not possible to measure the position of a single quantum particle multiple times?

We **can** detect the position of a particle multiple times.

>Would we be able to then track it's momentum?

Yes, although this does not allow for violations of the uncertainty principle. And anyway the product of the experimental uncertainties on the position and momentum will be much larger than the Heisenberg uncertainty lower limit anyway.

>If the answer to the above is that it pops in and out of existence, how exactly does that happen?

It's not the answer to the above. It doesn't really make sense to consider a real particle popping in and out of existence.

>How large of a field would you need to track a single quantum particle?

Particle detectors in experimental particle and nuclear physics come in various sizes. Some can fit in your hand, and some are huge arrays of many detectors, much larger than a human body.

>Would that be able to be done on Earth? Would we have to develop a large science facility in space somewhere?

There's no need to be in space, unless you're specifically interested in particles of extraterrestrial origin. Even then sometimes you can detect them from the ground.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
[Stargate] Where does the iris go when it is open?

There is no housing of any kind around the gate, would such an advanced piece of technology have a massive cavity inside conveniently located to allow for the installation of a metallic shield?

[Assistant]
You remember the Jaffa Guards from the first film? They had Eagle and Jackal helmets that could completely fold in to themselves without any apparent space to hide them?

This is one of the first technologies the SGC got from the program and utilised when they build there Iris to protect earth.


[System] Given the following post, respond as if you're commenting on Reddit:

[User] [Avengers] How much stronger is Thanos than the Hulk? Is he naturally stronger or was it because of the infinity stone?

[Assistant]
Its not only Strength its training.

The Hulk fought with brute force and rage, the hulks only power is the madder he gets the stronger he gets.

That isn't exactly helpful in a tight space hand to hand combat.

Thanos' first strike was pinpointed, Thanos knew precisely where to strike.

But for Thanos to pull apart Hulk's hands was just a raw display of over powered strength.

For Thanos to pull apart Hulk's hands , when Hulk's Hands had all the leverage.

Hulk was in shock.

No one , no one had ever stood up to hulk like that.

Hulk was afraid.

Hulk's only weapon was diminished.

So Hulk needs anger to get stronger.  Hulk couldn't be stronger, because Hulk became afraid of Thanos.


[System] Given the following post, respond as if you're commenting on Reddit:

[User] [The force awakens] How did the first order manage to perfectly aim the starkiller base to where it would shoot down all 5 hosnian planets?

[Assistant] They didn't really aim it so much as bend it around in hyperspace. The beam entered hyperspace and portions were allowed to splinter off into real space. It technically was aimed near Hosnian and grazed each planet and moon as it passed by.


[System] Given the following post, respond as if you're commenting on Reddit:

[User] [Santa Claus is Coming to Town] Did Burgermeister Meisterburger have the legal authority to not just ban toys, but search all of the houses of the citizens of Sombertown to find toys?

[Assistant]
[](/communerd)Sombertown ran under a political ideology that theorists describe as a "cynicocracy," which is defined by the governance of cynics in order to create a more cynical society. The idea that whimsy is of an existential threat to a pragmatic, well-ordered civilization is intrinsic to this form of political system; just as fascism cannot allow free journalism to exist and critique it, cynicocracy cannot allow a whimsical mode of life to critique the drab mode of life that its citizens otherwise are forced to endure.

Fascism justifies the suppression of individual rights with the welfare of the state; cynicocracy behaves similarly but with more of an emphasis on the welfare of order as an abstract concept, as opposed to a specific nation. The denizens of Sombertown, by and large, had been taught from an early age to believe that the government had the best interest of order in mind, and that any actions it took were not to be questioned or opposed.

And just as fascism ceases to ask questions of legal authority and individual rights in favor of the cult of personality and the emotional assumption that the leader can do no wrong, so too does cynicocracy behave. It isn't a question of whether the Burgermeister had the right to do what he did. Almost none of the adults of Sombertown would ever have thought of that question. What matters is that the Meisterburger dynasty in times past had sculpted a society which would accept just about *anything* in the name of suppressing child-like emotions in favor of a solely pragmatic and undistracted society.

Sources: *Christmas Against Kings: An Examination of the Holiday's Effects on World Politics* by Snowy the Frostman, *On the Ramifications of a Whimsy-Led World* by Comet, and *A Comprehensive History of Meisterburger Politics* by Jingleshoes Elfmann III.


[System] Given the following post, respond as if you're commenting on Reddit:

[User] ElI5: Why does wasabi burn your sinuses and not your tongue/mouth?

[Assistant] The chemical that makes wasabi spicy doesn't get absorbed by the tongue like the chemical that makes peppers spicy. Wasabi spice is also less hot by eating it with water or watery liquids like soy sauce, whereas hot pepper spice is not. You need alcohol or something fatty like milk to lessen the spiciness of peppers.


[System] Given the following post, respond as if you're commenting on Reddit:

[User] Are colorblind people able to watch 3D movies with the red-green glasses?

[Assistant] Theoretically, yes. The lens of the glasses filters out some of the light so that one eye gets one image and the other eye gets another. If the person is red-green colorblind, that doesn't mean that red or green are invisible, just that there are wavelengths of light that they cannot distinguish. The 3D effect arises from your two eyes getting different images, not because they are processed as being different colors. This would still be the case for a colorblind individual.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
What is wrong with String Theory?

I've always been under the impression that String Theory was incomplete, but conceptually intact. (If that makes any sense). But, as I look into it more, it seems like a lot of string theorists may have all of the math worked out, but their only problem is that it is extremely difficult to test whether or not there actually is 11 dimensional hyperspace.

**So, is the difficulty of testing the theory its only downfall?**

I am quite obviously a layperson.

Separate question: By accelerating subatomic particles to near that of the speed of light and smashing them into each other, is the collision expected to produce enough energy to truly gain any real insight on extra dimensions? Or are we simply doing the best we can?

Thanks to anyone who read this.

Edit: Thanks so much for the responses! I now have a lot more to read up on just to try to further understand the concepts at play.

[Assistant]
>So, is the difficulty of testing the theory its only downfall?

Yes. If it cannot be examined or of use experimentally, it's a useless theory to science.

String Theory has more in common with abstract Mathematics than present-day Physics.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
ELI5: Why is x/0 undefined while 0/0 is undetermined?

What's the difference between the two anyway? Aren't both inapplicable?

[Assistant]
The first thing to note is that we can never divide by 0. So both of these expressions are undefined, technically.

However, in the context of limits (I'll explain in a second) when things look like they're going to x/0 or 0/0 we do different things.

To start, a limit is simply explained as what does a function look like its doing as we get close to a point. We typically introduce limits by picking points closer and closer to a value and see where these results looks like they're going.

So, we want to know what's going on around x = 1 of the function (x^2 - 1)/(x-1). We try to plug in x = 1 but we quickly realize that we see 0/0.  So we pick the point 0.9 and plug it in then 0.99 and 0.999 and numbers closer and closer to 1. Then we point 1.1 and 1.01 and 1.001 and number closer and closer to 1 from the other direction and get this table

    x       f(x)
    0.9     1.9
    0.99    1.99
    0.999   1.999
    1       0/0???
    1.001   2.001
    1.01    2.01
    1.1     2.1

and we can easily see that in this case 0/0 meant 2.

In another case: (x^2 + x - 6)/(x^2 - x -2) as we get close to 2. Well, plugging in x = 2 gives us 0/0 again. But a table analysis like above will tell use that this is really 1.666

Yet another case: (e^x -x -1)/x^2 as x gets close to 0. Plugging in 0 tells us 0/0. But a table analysis (taking a limit) tells us 0.5

So 0/0 can really mean anything!

----

Alternatively, let's look at things that end up as x/0. First example is (x^2 )/(x-2) as we get closer to 2. We try to plug in 2 and we get 4/0. Let's do a table:

    x      f(x)
    1.9    -36.1
    1.99   -396.01
    1.999  -3996

Things are going way off to negative infinity! Let's try the other direction:

    x      f(x)
    2.1    44.1
    2.01   404.01
    2.001  4004

Things are going way off to the positive infinity!

Okay... maybe it was a fluke. Let's try another limit of the form x/0: say... 2/(e^x -1) as we get close to x=0. Plugging in x =0 tells us 2/0. Right form. But building a table gives us infinities again!

So, we can see from a few examples here that x/0 means infinities, while 0/0 can mean anything. So, we call one of them undefined (or really infinite) and the other we call indeterminate because it can be anything, we just don't know what. (There are advanced ways of determining the "what" without building a table, but this should convey the point.)

----

But really, what does all this mean? Why do we care about limits? Well, limits are the foundation for modern calculus. They can explain how rockets fly, how fireworks explode, nuclear reactors, electrical circuits, and many many more things.

----

TL;DR: This deals with the calculus topics of limits. Which is the question "what happens when we get close to _____". And if it looks like x/0 then we get an infinity (undefined) and if looks like 0/0 we can get anything (undetermined).


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
[Marvel/DC] Would the Punisher Kill Amanda Waller?

If Punisher was dropped into the DC universe, would he consider the choices and actions made by Amanda Waller worthy of punishing?

[Assistant]
Yes.

She is very much on the evil with good intentions side. Castle has shown repeatedly that he does not hold with that excuse.

Waller is responsible for a HUGE number of innocent deaths and is behind some seriously heinous shit. Castle would put her down a thousand time over, especially as shes repeatedly shown to cause more issues than she solves.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
[Star Wars] Why exactly does Anakin begin acting so differently after being put in the suit?

It seems like his entire personality is very different after being put in the armor. Suited Vader, for instance, acts far more statistically than he had prior to the Mustafar fight. In ROTS, everyone Vader kills were people he was ordered to kill, where as in the comic immediately afterwards he seemingly can't get enough of the violence and keeps on killing and killing, even beyond any real point. That's just one thing I thought of, Vader also talks differently, has different body language, etc. Why?

[Assistant] He is emotionally and physically shattered. He realized his place and stayed within it. He also was always a skilled commander and cunning tactician before when he wasn't whining about not being a master. He was still that angry, confused boy who slaughtered the Tuskens, he just was more scary looking.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
ELI5: How can martial arts specialists punch through rock or wood?

How can some people punch through bricks or wood boards without getting hurt. What's the scientific explanation behind this?

[Assistant]
The trick is you have to break it or you're really going to hurt yourself.

Let's say that you have a block of wood. That block of wood will break if you apply enough force to it. Let's say you need to apply 100 pounds of force to break it. You could rest 100 pounds of weights on it or you could hit it with your 1 pound fist going really fast.

But, let's say you only hit it with 90 pounds of force. You'll probably bend the wood some but the majority of the energy will bounce back into your hand, possibly causing injury. If you hit it with 100 pounds of force or more then the energy will be used to break the fibers of the wood and it won't rebound into your fist.


[System] Given the following post, respond as if you're commenting on Reddit:

[User] Is the Big Bang theory the only scientifically supported theory on the origins of our universe? Do we have ideas of other ways it could have conceivably happened that would make as much sense?

[Assistant] Note: The Big Bang theory does not really attempt to explain the Big Bang as "origin of the universe". It rather describes the early development of our universe. It doesn't state that the universe came from nothing or something like that.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
Why are C API functions are badly named?

As an example consider the function `strstr()`. How is one supposed to understand the usage of this function solely by its name? Had I wrote such function my pull request would have been rejected for bad naming of a function.

Why is that so in the C standard library?

[Assistant] because C was invented in a time and on a machine where memory and computing power was scarce and extremely expensive, so short names made sense. Shorter names meant saving on compile time and memory usage. Also input methods were very clunky back then, that also might be one of the reasons.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
ELI5: Why did humans evolve mentally when every other species evolved physically?

Why did we evolve for intelligence instead of strength, speed or some other physical trait?

**Edit:** I know I phrased this question awkwardly, I'm not the best with words. And although the question has been answered I still love to read all the new well explained and thought-out responses to this question, but please stop telling me that human's also evolved physically and that animals also evolved mentally. I know this, I'm not oblivious, I just was speaking broadly in the sense that a Shark or Lion's most advantageous quality lies in their strength while a humans most advantageous quality is our mind.

[Assistant]
Essentially every evolutionary niche that could provide an advantage got filled by something. It's not that we evolved for intelligence instead of strength, it's that we happen to be the ones that evolved for intelligence so we can even ask the question...other animals went for strength (or speed or camoflage or...).

Humans are, physically, actually quite astounding in terms of endurance. If we're in good physical condition, we can run many other land animals to exhaustion.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
Why does salt melt ice and mess up slugs?

What allows it to have these properties?

[Assistant]
Salt doesn't really melt ice like heat does. When you add salt to water, it lowers the temperature that it freezes at. So when water would normally melt/freeze at 32F, it now happens at, say 5F

So, if you wanted to have a salt popsicle, you would have to make your freezer a lot colder in order to freeze them.

Slugs die when you put salt on them because too much water leaves their body and they dry out and die (called osmosis). There's a simple saying "water follows salt". You could also kill them by pouring sugar on them, but it might not be *as* efficient.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
When an electron and positron annihilate, they give off two gamma rays - is it always exactly two? Might it be more?

And what if a proton and an antiproton annihilate? Will that also usually be two gamma rays?

[Assistant]
>When an electron and positron annihilate, they give off two gamma rays - is it always exactly two? Might it be more?

It's *at least* two, but it can be more, with small probability.

>And what if a proton and an antiproton annihilate? Will that also usually be two gamma rays?

With protons and antiprotons, there are more channels open even at zero relative kinetic energy. So you don't have to get gamma rays, you can, for example get various mesons. Those mesons then decay to leptons, photons, etc. So proton-antiproton annihilation is more complicated than electron-positron annihilation.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
ELI5: Why do we keep our belly buttons for life?

Why do belly buttons heal and leave behind a hole (or bump) that never goes away? Shouldn't they leave a surface scar on the skin that eventually fades like other injuries?

[Assistant]
Nothing on your body will regrow after you've been born - at that point the basic layout of your body is set in stone and nothing that's missing or damaged will regenerate beyond creating scar tissue.

The umbilical cord tunnels all the way through your abdomen, extending through your skin and subcutaneous fat.  Because of its position, that skin and fat just never forms.  The skin will "heal" through the formation of a scar, so you don't end up with a big hole in your stomach (though that's not really the same thing as healthy skin).  But there's no similar process to fill the space of the underlying fat, which causes your belly button to dip inward into the gap caused by the missing fat.

Other injuries that destroy subcutaneous fat later in life, such as animal bites, produce scars that look like shallow belly buttons.  These injuries destroy the subcutaneous fat, which never comes back.  The scar tissue that forms above then "falls" in to the hole left by that missing fat, creating a pit like scar.

The belly button happens to be really prominent because of how much fat there is surrounding it, which results in an extremely deep pit.  But again, any scar that destroys the underlying fat will look like that down to the depth of the surrounding fat in the area of the scar.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
CMV: A committed open relationship doesn't exist.

I've been thinking about this a lot lately. I asked my girlfriend of six years what her thoughts were on open relationships. She said she might be into it if I was capable, but my personality being what it is, it would probably would not work. It's a sacrifice she's not willing to make.

Sure, I get jealous easily. But that aside, it seems to me that being "committed" to someone means you lend yourself to them entirely. It seems mathematically impossible to give 100% of one thing (yourself) to two or more different things (other people). You commit to someone you think is worthy; someone who is special. That being said, and in relation to how much of yourself you can give, either one person is special to you, or nobody is.

Edit: My view has been changed. I think what I've learned from everyones varied responses is that when it comes to interpersonal relationships the only rules that exist are those which you and your partner (or partners) agree on, and that such agreements or disagreements result from how each individual feels on a solely personal level. So basically, the rules are made up. This leads me to question the validity of marriage, as marriage is just another set of rules, but hey... I can save that for a later post. Thank you everyone for the responses.

[Assistant]
If your definition of "committed" is "exclusive", then by definition you can't have a committed open relationship.

But looking for another angle, you don't share everything 100% only with your SO. For example you sometimes go eating with friends, or have activities for other people, don't you ?

For most people that are in an open relationship, sex is at the same level that eating a good burger or playing video games: it's pretty cool, but not sacred at all. As such, they can do it with people that want to share that with them, without restricting it exclusively to their SO. But if you think that sex is more than something pleasant and that it's something that define a couple, then sure you're not going to share this with other people.


[System] Given the following post, respond as if you're commenting on Reddit:

[User]
[The First Purge] About the government's role...

I wasn't sure if this would be considered a spoiler, so I thought I'd play it safe. My question:

Why did the government want to kill the poor, criminals, minorities, etc...?

[Assistant]
Because the government is *seriously* corrupt. They're more worried about their investors  and special interest groups, who have taken the reins of power and shifted the guiding purpose of authority from helping the people to helping line the pockets of a few mega-billionaires who don't give two shits about the people at the bottom of the pile.

This has always been the way to keep society in line. Create arbitrary "classes," make the people in the middle feel like they're superior to *someone.* Then turn them against each other. The people in the middle are too worried about the people "beneath" them to notice the fact that you're fucking them all over the same. In Purge-America, they've taken the "turn them against each other" and dialed it up to eleven.