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

[User]
Where do light or photons come from?

It's a question that I never thought about, but I can't reason out where exactly it comes from. In a circuit, for instance, I know that there are particles like atoms in the filament, and there is the movement of electrons which moves in opposition to the electric charge. I know that light is a form of energy, so electric energy is turned into light energy (primarily), but I'm confused with where exactly do the photons come from? Where do these EM waves suddenly come from? There is no particle that acts as a stationary 'photon' in a circuit.

[Assistant]
Photons don't have a conversation law. You can create and destroy them, unlike electrons for example (except in very extreme cases that don't apply here). So in a circuit we need to move existing electrons, but we don't need "stationary" photons.

The way photons are created is the following: you put electricity in the system, a wire, or a gas for example. This gives energy to the system. The atoms in the wire, gas etc. Have electrons and the energy in the system can "excite" the electrons. Basically it gives them a little energy. The electrons don't want to have that energy, so it goes back to a lower energy state. But because energy cannot be destroyed it has to get rid of the extra energy. It does that by emitting a photon, so we get light!


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

[User]
[Star Wars: Rogue One] Two ISDs couldn't take down the Rebel Fleet, but Darth Vader's Could?

During the fleet battle, we see that there were two Star Destroyers engaging the Rebel Fleet. One was eventually disabled by Gold Squadron which led to the other being destroyed.

However, when Vader enters the battle his ISD obliterates the fleet with impunity.

Why the difference?

[Assistant]
Scarif was a pretty cushy posting, and a lot of officers (especially higher up the chain of command) were pretty lax in enforcing proper training and preparedness - there was zero expectation of experiencing any actual combat, much less a full on fleet action and ambush.

So the Star Destroyers were caught off guard, out of position, and with crews asleep at their stations. That said, they did do a number on the Rebel fleet before their destruction.

Then in comes Vader and the Devastator. His crew are already among the best of the best, they're a well oiled fighting machine, and they're coming in hot and ready to jump into combat. The Rebel fleet has already taken a pounding and is preparing to fall back, and their fighter/bomber wings have already dropped their ordinance on the prior Star Destroyers and the Shield Station.

Vader's really just coming in as a cleanup crew, and if the local Navy detachment were doing their jobs properly, would never have been necessary in the first place.


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

[User] ELI5: What exactly is white chocolate, why is white chocolate white?

[Assistant] NPR had a short radio piece about white chocolate this morning on Weekend Edition. Chocolate uses both cocoa butter and cocoa solids to make traditional brown chocolate. White chocolate uses the cocoa butter, but replaces the cocoa solids with milk solids.


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

[User]
If you're deeper into the earth, how does it affect escape velocity?

Hello! I have been watching Cosmos by Neil DeGrasse Tyson again recently and, after he sparked my interest about escape velocity, I began to Google and try to find what it would take for the sun to escape the Milky Way. The equation for escape velocity being 2GM/r, and knowing that the Sun does not sit at the edge of the Milky Way, I began to wonder: If you're deeper in the ground (on Earth) does the escape velocity change. The radius effectively lowers, which would make the escape velocity more. However, the mass put into the equation also lowers, which will make the escape velocity less. So, what would happen in a realistic scenario? Would the escape velocity be higher or lower or am I completely wrong about this whole thing? If you have any ideas, I'd love to know.

[Assistant]
Escape speed at distance *r* is found in the same way as for the exterior escape speed. A particle escapes to infinity if its total energy is 0. (The zero of the potential is set at infinity and total energy E = 0 means the particle is at rest at infinity.) The deeper inside the potential well the particle is, the higher the escape speed. The interior of Earth has a higher potential than its exterior. So the interior escape speed continues to increase as r --> 0. Precisely, we have the following.

---

To lowest-order, Earth is approximately a homogeneous sphere of mass *M* and radius *R*. Hence the gravitational potential is

> U(r) = (-GM/2R)(3 - r^(2)/R^(2))    if r < R

> U(r) = -GM/r    if r > R

 If the particle is initially at some interior distance *r*, then its total energy is

> E = mv^(2)/2 - (GMm/2R)(3 - r^(2)/R^(2))

Setting E = 0 and solving for *v* gives the interior escape speed.

> v*_esc_* = [(GM/R)(3 - r^(2)/R^(2))]

Of course, this treats the mass of Earth as if it were interacting only gravitationally. That is, we pretend particles can orbit inside Earth and that there really isn't any interior structure like a molten core.


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

[User] [Back to the Future] Why didn't Sam (Marty's grandpa) take him to the hospital when he hit him with his car?

[Assistant]
This was back in the day when all you did with most injuries was rub some dirt in it and then move along with your day.

Sure, Marty got knocked unconscious for several minutes and had to be dragged from the street long enough to be disrobed by Sam's daughter in a private bedroom, but that type of thing builds character, ya know?


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

[User] ELI5: Why isn't minimum wage in the US tied to the dollar inflation rate?

[Assistant] Because a large enough group of politicians believe that raising the minimum wage at all is bad for the economy, so they make sure it can't be raised. Allowing it to automatically be raised is even more egregious to them.


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

[User] ELI5: How did ancient people know that the earth was round?

[Assistant]
The two major arguments known to the ancients were these:

* Observing that if you travel northwards or southwards by any specific distance, the angle of the North Star above the horizon will also change by a specific predictable amount, implying that the Earths surface has a consistent curvature, like a sphere.

* Observing that the shadow the Earth casts on the Moon during a lunar eclipse is always a circle, and realizing that the only shape which always casts a circular shadow is a sphere.


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

[User]
[LOTR] Why did Sauron have his minions worship Morgoth instead of himself?

Morgoth is out of the picture so Sauron doesn't need to worry about being put in his place by Morgoth.

[Assistant]
From Letter 183:

> When [Sauron] found how greatly his knowledge was admired by all other rational creatures and how easy it was to influence them, his pride became boundless. By the end of the Second Age he assumed the position of Morgoth's representative. By the end of the Third Age (though actually much weaker than before) he claimed to be Morgoth returned.


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

[User]
ELI5: Why does it seem like people are more religious in rural or impoverished areas?

Just something I noticed while driving through a lot of small towns this weekend. A lot of the signs for the city had a list of all the churches.

[Assistant]
There are multiple reasons that all contribute.

Religion gives people hope, and is something to lean on in hard times.

Another is that smaller towns generally don't have enough of a population to support parks, bars, nightclubs, or theaters. Which means that the churches take on the role of gathering spots within those communities.

Rural communities also tend to be more conservative, and churches are an old institution. So it's more acceptable in the community to spend money on an old institution than a new on.


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

[User]
ELI5: What is actually happening in my body when I build a tolerance to something like alcohol?

Is the digestive system just recognizing what I am taking in faster or is my liver storing up what it needs in anticipation of more alcohol or what?

EDIT: I am truly sorry. I see numerous good responses to this, but have yet to determine whether or not this is actually answered due to drinking. I will flag it as soon as I am sober and feel that I am clear-headed enough to make such a decision.

[Assistant] It's a physical response. When your body is introduced to a toxin (alcohol), it responds by making more of the enzyme that gets rid of it. This is regulated epigenetically. Your body literally gets better at dealing with it which is why it takes more and more to get drunk.


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

[User]
[MCU] Is Captain America strong enough to cut somebody in half by throwing his shield?

I know he would probably never do it but is he capable?

I'm thinking he would have no problem cutting an Outrider in half.

What about Captain America from Earth-616? Has he or can he do it?

[Assistant]
Like bare chested average human absolutely yes if he really wanted to. He isn't peak human in the movies he is superhuman.

He survives a fall from like 150 feet.

Tanks a genade launcher blast with his shield

Curls a helicopter

 flips and launches a bike over his head and smashes it into an oncoming truck etc.

He is very very clearly super human in the MCU. It's weirdly enough arguable that MCU cap is stronger than the comic version.


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

[User]
[Hitler] Why are fictional Nazis always so concerned with cloning/preserving/bringing back Hitler?

I mean Hitler certainly was the most iconic Nazi leader and perhaps the most powerful and charismatic one, but he was not the entirety of the Nazi movement. Why do we never see any Nazis who want to bring back Ernst Rhm, Dr. Goebbels, the Strasser brothers or Rudolf Hess?

[Assistant] He more or less *was* the entirety of Nazism. There was an unwritten policy in the Nazi hierarchy called the *Fhrerprinzip*, or that Hitler's word was more or less law, and always took priority over the law as it was written. There was also the idea of "working towards the Fhrer" (popularized by historian Ian Kershaw). Hitler was a notoriously hands-off ruler in most fields of administration, content to give vague orders and let his underlings handle it. As a result, Nazi officials were left trying to determine the best way to fulfill Hitler's wishes, or what they perceived Hitler's wishes to be. As a result, this led to a culture of constant infighting and one-upmanship between officials trying to prove that they knew what Hitler wanted better than everyone else.


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

[User]
[Star Wars galaxy] What makes the Unknown Regions so "unknown"?

Have they just not been explored for hyperlanes yet? Is it not feasible for the central galactic polity to try to extend that far?

[Assistant]
There are "walls" of almost impenetrable hyperspace turbulence dividing the galaxy, with access available only by a few (generally secret) bottlenecks.

^(*See - Rebels, Outbound Flight, Aftermath, X-Wing, Vector Prime*)


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

[User]
Question about Judith Butler's performativity theory

When Judith Butler says that gender is strictly performance, and that it's not related to internal states, is she really saying that gender performance has nothing to do with what feels "natural" or "right" to a person? I feel like I must be misunderstanding something, because, if that's the case, how do you explain trans people? Why would someone choose a gender performance different from the one they were assigned at birth? I think it'd be easy to argue that trans people are people whose performances failed to live up to social expectations, but, a) that's not necessarily (or even usually) true, b) it wouldn't explain why someone would choose the even less socially acceptable option of transitioning, and c) it still leaves you with the question of why some people aren't able to meet social standards for performance.

Am I misunderstanding something here? If so, could someone please set me straight?

[Assistant]
You're making a classic error in your reading of Butler, which is that you mistake performativity for a synonym of performance. They're really quite different.

Performativity is to do with the philosophy of language, and it comes from the work of J.L. Austin. It has to do with the relationship between language and the very horizon of choice itself. Language, in short, structures both social and intimate horizons. It's not merely a means to describe things, but rather something that *does* things.

Because language structures both the social world and the subject (i.e. the individual who speaks), the repetitive iterations (i.e. the saying over and over again, which is also necessarily a doing over and over again) of sex and gender impact on our very notion of what is possible in/for human life. "Choice," therefore, is a notion that's overdetermined by the parameters of language: none of us are "perfectly sovereign" subjects.

To better understand this, you might refer to something that may at first seem quite far afield: the discussion of interpellation in Althusser's "Ideology and the Ideological State Apparatuses." What Althusser says of ideology is not self-same with Butler's argument, but it comes a lot closer to performativity than you'll come if you try to understand her in terms of performance. As Althusser says of the subject:

>his ideas are his material actions inserted into his material practices governed by material rituals which are themselves defined by the material ideological apparatus from which we derive the ideas of that subject

To begin to understand Butler's argument, one needs only a slight modification, which is that what Althusser says of the "material" is also in and of language.


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

[User]
[Spiderman No Way Home] Why doesnt a lawyer affiliated with Stark Industries/the Avengers take on Peters case?

Matt Murdock has a good reputation, sure, but youd think the immediate choice would be someone already involved with the Avengers legal team rather than contacting a small law firm that does mostly local cases. Even Hogarths law firm might have more precedent with hero cases.

[Assistant]
Tonys gone, its ambiguous how much Pepper is still involved and while Happy was very ready to help, he doesnt have nearly the pull and resources of the Starks as evidenced by his concern over his own potential problems from his involvement.

We know the Parkers are relatively poor so Murdock makes perfect sense.


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

[User]
I think that the backlash to Sochi 2014 Olympics over gay rights is more US Russophobic propaganda than genuine concern for human rights. CMV

The reason why I say this, is there are MANY MANY countries in the world that have made homosexuality illegal, even punishable by death or imprisonment: Russia is not one of them.

The US allies and partners Saudi Arabia, Pakistan, Kenya, UAE, Qatar, India (nominally) Jamaica have made homosexuality a criminal offense! India outlawed homosexuality outright only a month or two ago, and yet the focus is on Sochi because 'The Olympics suddenly make homosexuality punishable by death or imprisonment less important than a vague law that makes homosexual sex practices (this is what the actual law says, I speak Russian, it's on the Kremlin's website if you're interested and can read Russian) being taught to children, when those same people would be killed in Pakistan or Saudi Arabia? Comment sections across the internet on Russophobic articles often echo the same questions (and indeed, many Russians have an increasingly negative view of gay people that ironically didn't exist before because now they see gay NGOs as persecuting them unfairly--and given their lack of activity in Saudi Arabia or Jamaica, they may be right)

Tl;Dr if Obama really cared about gay rights as much as they say they do re: Russia, why doesn't he send an openly gay ambassador to Saudi Arabia, for example?

[Assistant] Its not being anti-Russian, its because the focus of the Olympics is on Russia and the law was introduced just recently.  If the Olympics were in Saudi Arabia or Jamaica or any other country you mentioned, the criticism would be on their recently passed laws too.


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

[User] ELI5: Why is it that sometimes when you swallow something like a lozenge or capsule of some kind, it feels like its stuck in your throat for some time after? I mean, it cant actually be, because it feels that way long after the thing wouldve dissolved, so what is giving that distinct sensation?

[Assistant]
Your throat is very sensitive. That feeling of something 'stuck' is actually a generally universal feeling that your body signals to indicate 'irritation'.

When you swallow a medicine cap, tablet or suck on a lozenge, your throat may just not be that used to swallowing something that isn't as soft as chewed food. The texture and dryness may also play a part, and it registers as a sign that you may have swallowed something unnatural.

Another thing that causes the 'something stuck in throat' feeling is acid reflux, where your stomach acid comes back out and gives you burns in the esophagus. The irritation can feel like a mild blockage to having a ball there that no matter how you try you can't 'swallow' down and can get extremely infuriating.

In other words, that feeling is triggered for ANY time your throat has discomfort and irritation. You're just used to associating it to stuck food because that's happened the most.


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

[User]
Does the wealth of the ultra wealthy actually harm normal people?

When people have a bunch of wealth (on paper), but they aren't actually chewing up resources, does it even matter to poorer normal people? Are poorer people actually getting deprived of goods and services? What is the effect of people  accumulating enormous amounts of wealth on paper?

[Assistant]
Wealth can be invested in making new goods and services - e.g. building a factory, or a piece of software or it can be invested in buying existing assets.

Building factories, software etc, typically results in hiring workers, paying them wages, paying other firms for parts and so forth, and thus the money circulates.

Buying an existing asset for, say, $1m, means that someone must have sold said asset for $1m. Therefore the seller has $1m in money to do something with (this probably includes the seller paying costs like commission, legal fees, taxes, etc). While they might turn around and buy a new asset of their own, at some point the $1m is going to be spent on investment in new assets or on consumption.

That said, the processes that produce paper wealth can be harmful - for example the restricted housing supply that drives up house prices deeply effects poorer people. The issue there is the housing shortage in and of itself. In other words, deeper details matter.


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

[User]
ELI5: The Limitations of Diplomatic Immunity

As the title says, what are they? Do diplomats get full immunity from all transgression within a host country or is that only when performing official duties? According to the Vienna Convention on Diplomatic Relations of 1961 Article 31.1c diplomatic immunity doesn't apply to activity outside of a diplomat's official functions, but is that the current case. Do diplomats have carte blanche within a host country just by being diplomats?

[Assistant]
It's worth noting that even if a diplomat / embassy claims immunity, the host nation is not required to take it on the proverbial chin.  They can declare the diplomat unwelcome (persona non grata) and expel the diplomat from the country if the host nation so chooses.  Similarly, the diplomat's home nation can recall said diplomat (or prosecute the diplomat themselves) to avoid or curtail an international embarrassment.  There are certainly scenarios where diplomatic relations have become strained because diplomats do really stupid / criminal things.

In short, diplomatic immunity is not an absolute blanket to do whatever you want and get away with it.


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

[User] ELI5: Why does the heart beat slower, on average, for athletic people compared to less athletic people?

[Assistant]
As you improve your athletic fitness, your cardiovascular system becomes more efficient.  Put another way, your body becomes better at taking the oxygen you breath in, and using it to make energy for your muscles to perform their job.

The human heart naturally adjusts based on the need to get oxygen and other supplies to tissues in the body.  When you're exercising and your muscles are doing a lot of work your heartrate goes up; when you're resting, your body is doing less work so your heart rate goes down.  But because athletes condition their body to efficiently provide and distribute oxygen and other nutrients through the bloodstream, they don't need as many beat cycles to provide their resting body with the supplies they need.

Think of it like a bunch of firemen in line passing along buckets of water to put out a fire.  If the buckets were smaller, you'd need more buckets to get the water necessary to put out the fire.  If the buckets are bigger, you need fewer buckets to get the same amount of water.

When you get in shape, it's like you have big buckets that don't spill.  When you're out of shape, it's like you have smaller buckets that may spill and not get all of their water to the fire.


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

[User] How does a broken bone connect again once the two healing pieces reach eachother?

[Assistant] It depends on various principles, including where the bone is and how they connect to each other. If anatomic reduction is achieved and the segments are compressed, then you get primary bone healing which is direct growth of the osteons on each other. If the segments are not compressed and there is micromotion at the site, you get callus formation and the bone remodels itself. Children are better at this than adults - hence why children get casted more than surgically fixed.


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

[User] Can the COVID-19 have enough variants where it would be considered something new/different and not be detected by the current tests? How do the tests not detect other types of coronavirus?

[Assistant]
The PCR tests use specific primers that recognize certain sequences unique to SARS-CoV-2 and absent from other coronavirus types.

Mutations are a concern for this testing, but they do try to pick parts of the viral genome that are more conserved (mutate less often). Beyond that, there's also an ongoing effort to sequence viral samples so we would know if we had to adjust the primers for the PCR test.

There are also antigen tests, which rely on antibodies to recognize viral proteins. This is perhaps a little less vulnerable to mutations, but you still want to keep an eye on it.


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

[User] ELI5: How legit is Judge Judy? (TV personality)

[Assistant]
From a legal point of view, Judge Judy operates as an independent mediator between two parties. The parties are asked to sign an agreement before going on the show, agreeing that whatever Judge Judy decides will be the final decision. This has all the same weight in law as any written contract - in other words, it is legit.

The show sometimes accepts requests from people to appear on it. But they also search through court listings and approach people to ask if they want to appear on it. In return for appearing on the show, the parties have their transport to the studios paid for, and are put up in a hotel for the duration of filming.

The other thing which encourages people to appear, but which makes the show less-than-legit, is that when Judge Judy orders one party to make a payment to the other party, it is actually the show which makes this payment, so no one will be financially out of pocket as a result of the show.


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

[User] ELI5: Why do we feel the urge to destroy stuff when feeling frustrated/angry?

[Assistant] Well, anger is one of the strongest emotions, and one of the emotions that get you into fight & flight mode. This releases a load of hormones, that make you pumped up and ready to fight, whatever that made you angry. A normal way of getting this feeling out, would be breaking ("fighting") stuff, even if its an inanimate object, which would explain why you can often find yourself grabbing the nearest thing, and throwing it into the ground.


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

[User] ELI5: Are "natural" sweeteners like honey and agave really better than just regular sugar or corn syrup? Why or why not?

[Assistant]
They all vary in their fructose/glucose/sucrose ratios, so aside from that, no, one is not better than another.

Also, stop calling stuff "natural". It's a shitty weasel word that advertisers use to make you think it's better.


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

[User] ELI5: why do people care about the difference between shaken and stirred?

[Assistant]
Without getting into personal opinions, which are subjective, there's a difference between shaking and stirring.

Shaking agitates the ice in the drink more, which causes it to melt faster. This results in a colder, more diluted drink. It also introduces air into the drink, which can make it frothier or fizzier, especially if there's something in there like dairy or egg.

Stirring mixes the ingredients together in a calmer manner, so less ice melts and air isn't introduced. Stirring results in a slightly warmer, but less diluted drink without foam or froth.

For most drinks that are just liquor and mixers, you probably want to stir so you don't dilute them (they'll still be pretty cold). For most drinks that involve dairy or egg or are supposed to be light and frothy, you'll want to shake to aerate them. For drinks that you want to be really cold and don't mind if they get diluted some (e.g., a martini for some people), you can also shake.


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

[User] ELI5: Why can animals drink dirty water safely but humans can't?

[Assistant]
Animals cannot drink dirty water safely. Humans also cannot drink dirty water safely. As many humans have access to alternatives (clean safe water) we do not tolerate the risk unless forced to do so.

Animals have no choice but to tolerate the risk, and so they risk contaminants, toxins, parasites, and disease because the alternative is dying of thirst. Many animals are rife with parasites and other conditions we would not ordinarily tolerate.


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

[User] [Dr. Who] If the doctor can reincarnate *and* time travel, why doesn't he team up with all of his other selves at once to be a more effective team?

[Assistant]
With certain *strange* exceptions, a Timelord cannnot cross his own timeline. Causes big gluts of time paradox.

Any why waste your life doing the same thing over and over.... Doctor #13 would have already done all this 12 times.


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

[User]
How can I as a non-academic know if a book is widely used and well accepted by scholars?

I am referring to the Humanities and Social Sciences (HSS) area.

[Assistant]
An easy way would be to track citation metrics. Search for the book in google scholar and look closely at the entries. That won't work if the book is very new as it takes time for research to get published.

Another method would involve searching for a review of the book in journals. Reviews are generally positive for academic texts, but it at least gives you more context.


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

[User]
ELI5: If William Shakespeare's works contained 100s of words that he made-up, then how were they able to be understood?

Works with so many made-up had the potential to be dismissed as the ravings of a lunatic, but instead, his were seen as genius.  Why?

[Assistant]
He didn't just create words out of thin air, he coined (or at least was the first to print) words based on existing words.

For example, he's credited with coining the word "bedroom."  It's pretty easy to understand what he meant by that since the words "bed" and "room" already existed.  Or the word "invulnerable" which was based on the already-existing "vulnerable."


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

[User] ELI5: How does wifi work on airplanes?

[Assistant] Depending on the set-up, the plane either has a satellite receiver pointing up or a cell phone antenna pointing down to get Internet. That connection is plugged into a wireless router, not all that much different from what you get at home.


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

[User] ELI5: Why do many different animals all have white bellies?

[Assistant]
It is primarily a form of defense from predators. A larger animal looking down on a smaller one would see the dark color of the preys back which would help camouflage it with the ground or whatever is underneath. A predator looking up at the white/ light colored underbelly would see it blending in with the sky.

Eg: think of the black and white of killer whales. Dark to hide it against the ocean floor from the top. White to hide it against the the sky from the bottom.


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

[User] If seawater is much more abundant than fresh water.. why did we evolved to not being able to drink it?

[Assistant]
We actually sort of did.

Our lineage (the chordates) first appears at the basal Cambrian about 540 MY ago. Back then, our ancestors were aquatic and pretty much  confined to salt water environments. It isn't before the Devonian, roughly 170 MY later, that one of the lineages within the chordates (the tetrapods) began transition towards land.

Now moving inland requires a the acquisition of a certain number of specialised caracters, one of which is the ability to use fresh water. So the ability to use seawater was pretty much discarded in exchange for the necessary capacity to survive on fresh water at that point.

This adaptation is by no way trivial, BTW, as anybody which has transferred oceanic lifeforms to freswater aquaria can attest. Unless you have some adaptive mechanism, osmosis will just bloat you up till you explode.

Also worth noting that some members our tetrapod lineage have since moved back to the ocean (Cetaceans and pinnipeds) and have had to reacquire the ability to drink seawater.


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

[User] Eli5: How do farmers keep poisonous plants from growing in crops and being harvested and packaged with edible plants?

[Assistant]
The combine harvester machine actually helps take care of this. You can set the head height to be above where a lot of those are if present, and the internals of the machine are already designed to pick out the useful parts like corn kernels or grains and throw away the rest.

For stuff like strawberries etc thats usually handpicked.


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

[User] [Lord of the Rings] If Sauron getting his ring back would spell certain doom for Men, Elves and Dwarves, why was he originally defeated in the first place?

[Assistant]
Men and elves were both stronger at the time of the Last Alliance. The elves were certainly in their autumn compared to past Ages but were more numerous and powerful than at the end of the Third Age, which is really their last hurrah.

While Men had also declined from their height in the golden age of Numenor, they were still led by full-blooded Numenoreans, bolstered by prosperous and populous colonies that were also either Numenorean or recent descendents. While Gondor remembers those glory days, they're really just keeping the lights on and sweeping the floors.

Even with both of those, it still took a ~~year~~years-long seige to finally draw Sauron out of Barad-Dur. After his fall, his servants spent millenia weakening the Free Peoples. Moria and Erebor both fell, the elves of Mirkwood were isolated and harassed. Both Arnor and Gondor were wracked with internal and external enemies; the Northern Kingdom fell/dissolved entirely into roving bands of Rangers, while Gondor as mentioned is a shadow of itself.

On top of everything else, almost all the former alliances have broken. The Rohirrim regard the Lady of the Wood as a dangerous and vaguely hostile sorceress. Dwarves were always a bit isolationist but are now largely traveling craftsmen, never staying in any one place for long. What few elvish strongholds remain largely keep to themselves too. But even if they could present a unified front, at the end of the Third Age the Free Peoples couldn't put up a fraction of the power they did in the Last Alliance.


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

[User]
CMV: Shows which depict the prosecution/investigators as always right, as well as forensic shows which misrepresent forensic science as infallible (and pseudo-scientific often, have led to a perversion of the justice system, such as NCIS, Criminal Minds, CSI, Bones, etc.

Many shows likes Criminal Minds, CSI,  NCIS, Bones, Cold Case Files, *(ad nauseum)* , always "get their man" so to speak.

I feel this like this biases the general public against primary suspects (not charged with anything *yet*) and defendents (on trial). The idea that forensic science is infallible and incapable of any errors (human or otherwise)  lowers the average personal level of confidence required to find someone guilty of a crime (beyond reasonable/showdow of a doubt).

This had led to a perversion of the justice system.

[Assistant]
Your view is part of what is referred to as "the CSI effect", though it's the less prevalent belief.  The larger part--the part that is widely believed by lawyers--is also sort of the opposite. The notion is that the shows you're talking about always have conclusive forensic evidence or a confession.  So, the belief goes, these shows are training juries to expect a higher standard of proof before they are willing to convict.

Studies on the CSI effect have failed to show any significant evidence for it in terms of links between watching these shows and having preconceptions about forensic evidence.  Studies *do* show that over time people tend to expect and demand more of scientific evidence and trust it more when it is present but they have been unable to find a link to viewership of these shows or the "always get their main" aspect to which you refer.  Based on studies it actually appears to just be a "tech effect" which is essentially that as technology improves people expect forensic technology to improve also.  It also seems to be the case that if forensic shows are contributing to this at all it's merely on account of showcasing technology of which the public was previously generally unaware.


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

[User] [Aliens] What do the xenomorphs eat?

[Assistant]
This is an open question. Some xenomorphs have been seen consuming the corpses of their victims. Dragon, for instance, was interrupted at one point while eating a corpse. It's often presumed that chestbursters feed on their former hosts post-birth, but on LV-426, there were many bodies in the hive whose only visible wounds were from the actual birth. We know that the xenomorph ~~initially encountered by the *Nostromo*~~ on LV-1201 fed on a cat at one point, during the chestburster stage. The weird thing is, it gained *way* more mass than the cat had. It was well over 100% efficiency. This suggests that it had some other source for mass, much less for energy.

They may feed off of some sort of radiation, they may be able to consume non-organic matter like metal, or they may have some sort of access to energy/mass that we simply don't understand. It's really, really hard to say.


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

[User] When I pee, why does it feel near impossible to simply stop peeing half way through and just finish the rest some other time?

[Assistant]
You've got a muscle that controls your bladder, and to urinate you need to relax it.

Imagine you're arm wrestling with someone. They're applying a pressure on your arm, and your arm muscle is resisting that pressure. Now, if you relax your arm, they'll push it onto the table, and it's really hard to recover and force your arm back up. You need to be really strong to recover from that position. It's easier if they let go.

The same thing applies with the muscle controlling your bladder. You can train it to shut off the flow off urine, but it needs to be strong enough. The stronger this muscle is, the easier it will be to stop urinating. When all your urine is gone, there's no more pressure, and your bladder muscle can seal up.


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

[User] ELI5: How did sheep shed their wool before the emergence of humans?

[Assistant]
Humans have selectively bred a small number of species to help provide better for human needs at the expense of the animals natural survival. Sheep are one of those species.

Prior to domestication sheep would have grown a much smaller amount of wool up to the point where it served their needs, like the hair on a bear or a wolf. It doesn't grow indefinitely.

Then humans came along and found these relatively docile sheep sitting around and someone realised their wool was very useful to make things like clothing out of. Over many generations humans captured and bred these sheep to harvest their wool from. Humans also realised that by breeding the males and females with the most and best wool, the offspring would usually end up with even more wool than the parents. By repeating this process over time we ended up with the types of sheep we have today, who are completely reliant on humans to regularly shear them and remove the wool. This is domestication and selective breeding. Without us they would suffer many problems like overheating and being far too heavy.


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

[User]
ELI5: Why does it feel cold when I set my air conditioning to 70 degrees in the summer, but when I set my heat to the same temp in the winter it is nice and toasty warm?

Just wondering why the same temp feels so much different.

[Assistant] Your body acclimates to the seasonal normal temperatures.  If it's 50 F in July everybody is looking for a jacket, but if it's 50 F in January, people are getting out their shorts. The human body does a lousy job at determining the actual temperature.


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

[User]
ELI5: The IRS scandal and Obama's connection

I have seen a lot in other subreddits and on the news concerning this scandal dealing with the IRS but haven't picked up on what exactly is going on.

[Assistant]
Certain non-profit organizations that raise money (mostly through donations), are allowed to claim a tax exemption with the IRS, when they file their taxes, they file as a 501(c)(4). Traditionally, this has been things like Volunteer Fire Departments or the Salvation Army. They provide a service to their community and use the funds in this manner, and hence are exempt from taxes.

However, after the Citizens United case, a new type of group was formed called a Super Political Action Committee, or a Super PAC. Super PACs used this 501(c)(4) exemption so they could raise unlimited amounts of donations, while keeping the identity of their donors secret. They did this by using the "social benefit" claim for the (c)(4) exemption.

So, the IRS began examining (c)(4) groups more carefully, to make sure groups were not abusing this tax exempt status. There is nothing wrong with this, it is their job. However, the "scandal" is that since 2011, a few individuals in the IRS began scrutinizing specific types of groups, mostly those with affiliation to Right Wing or Tea Party ideologies. Had they simply scrutinized EVERY (c)(4) group, or did it at random, there would be no scandal, but since they singled out certain groups, some people are outraged.


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

[User]
ELI5: Why does giving birth hurt, even though it harms reproduction? why was it not removed through natural selection?

don't give me stories about the first woman eating a weird fruit please.

[Assistant]
Human reproduction is limited by two of humanity's most useful advantages: We stand upright and are very intelligent.

Standing upright requires a relatively narrow pelvis. Being very intelligent requires a relatively large brain, and therefore skull. Yet the skull must fit through the pelvis at birth! So a middle ground is found and we are adapted to have babies born relatively undeveloped, so their skull bone plates are not fused yet and their brain is smaller. It hurts, but pain isn't a limiting factor on reproductive success.

A consequence of being born undeveloped is that human children are vulnerable and delicate. They need constant care and protection to survive, and so have frequent cries that their parents are biologically wired to respond to.

So we have covered why childbirth is painful and babies are annoying little shits.


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

[User] Does a blackhole rotate? And if so, why?

[Assistant] Black holes have the same angular momentum as the precursor object had before it collapsed into a black hole. So if there was a rotating neutron star that accreted enough mass from a neighbouring star to collapse into a black hole, the black hole would be rotating like the pulsar was before.


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

[User]
ELI5: What do the numbers after a crime mean?

So I've been watching Law and Order: SVU and something I have always wondered is what the numbers after the crimes mean (Rape 3, Murder 1 etc.). I gather that the lower the number the more severe the crime. But is there an overall method to the numbers (like it goes from 2 to 1 if malus aforethought intends to be proven in the court)?

[Assistant]
The number is the "degree" of the crime. Murder, for example, includes:

* **First-degree murder** is any intentional murder that is willful and premeditated with malice aforethought. Felony murder is typically first-degree.
* **Second-degree murder** is an intentional murder with malice aforethought, but is not premeditated or planned in advance.
* **Voluntary manslaughter** (also referred to as **third-degree murder**), sometimes called a crime of passion murder, is any intentional killing that involved no prior intent to kill, and which was committed under such circumstances that would "cause a reasonable person to become emotionally or mentally disturbed". Both this and second-degree murder are committed on the spot, but the two differ in the magnitude of the circumstances surrounding the crime. For example, a bar fight that results in death would ordinarily constitute second-degree murder. If that same bar fight stemmed from a discovery of infidelity, however, it may be mitigated to voluntary manslaughter.
* **Involuntary manslaughter** stems from a lack of intention to cause death but involving an intentional, or negligent, act leading to death. A drunk driving-related death is typically involuntary manslaughter. Note that the "unintentional" element here refers to the lack of intent to bring about the death. All three crimes above feature an intent to kill, whereas involuntary manslaughter is "unintentional", because the killer did not intend for a death to result from their intentional actions. If there is a presence of intention it relates only to the intent to cause a violent act which brings about the death, but not an intention to bring about the death itself.

So, to answer your question, yes - the lower the number, the more severe the crime, thus the more severe the punishment.


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

[User]
ELI5: When a stock market crashes and everyone is desperately 'selling', who is actually willing to 'buy'?

Wolf of Wall Street got me thinking about this.

[Assistant]
The fact that not many people are willing to buy is what *causes* the crash. If as many people were buying as selling, the price would stay about the same. The fact people are desperate to sell means there are more sellers than buyers, so the price drops.

The few people who are buying are either ignorant of the crisis, or buying speculatively thinking that he stocks will rebound at a later date. Shares that crash to near zero will either rebound, or become completely worthless if the company involved goes bankrupt and has no positive assets.


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

[User] ELI5: How come we still have bad eyesight passed down genetically to today if early human ancestors depended on eyesight for survival such as hunting?

[Assistant]
We have lots of different eyesight problems then in the past.

1. We live for a longer period of time and eye problems can be exagerated with age.

2. Many current environmental impacts on our vision (artificial light, eye strain, computer screens, chemicals we encounter, etc.

3. Depending on your vision you could still probably hunt or at least find a use in an ancient tribe - gathering berries, tending fires, building huts, or more.


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

[User] [MCU] If the Guardians of the Galaxy had not stopped Ego's plan to absorb everything in the universe, how would Thanos have altered his goals now that over 99.99% of life in the universe had be destroyed rather than just 50%?

[Assistant] With Ego controlling almost all planets it's highly unlikely Thanos would have been able to amass all the infinity stones.  Ego can probably take Thanos in a fight if Thanos doesn't have access to his core.


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

[User]
[Star Wars] How are invasive species not super prevalent and destroying all the eco-systems in the galaxy?

It doesn't look like there is a customs at any of the ports, and there are obviously several of the same animal species, as well as plants, all over the galaxy. How is there able to be healthy biodiversity with so much xenocontamination?

[Assistant]
[](/scootaplease)Do you know how many planets have rancor populations these days? All the main species that could be considered invasive spread around the galaxy thousands of years ago. No one's worried about customs because all the worst ecological damage was done millennia before would-be customs workers were born.

Besides, there really aren't that many species capable of taking over a variety of different planetary ecosystems. Tiny adaptations for minute variances in gravity, atmosphere, and native virus resistance can make all the difference when it comes to indigenous species holding their own against invaders.


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

[User]
[MCU] Would Mijonir allow a worthy wielder to do something that would make them unworthy?(while wielding it)Or would they suddenly NOT be able to lift it.

Example. A very worthy Thor suddenly has the urge to bash a kids head in with the hammer. Would mijonir suddenly become "too heavy" for him?

[Assistant]
I imagine part of 'being worthy' is not being the kind of person that would suddenly do something that would make them unworthy.

For Thor to suddenly go and do that would be such a shift in personality that effectively wouldn't be the same Thor anymore. So he wouldn't be able to lift the hammer.


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

[User] ELI5: Why is India so bad at Olympic sport?

[Assistant]
Mostly due to infrastructure.

In India sports has a relatively low level of investment, public interest, social involvement besides cricket and to a lesser extent field hockey, volleyball and badminton.

Most high level sports people train from a young age through several layers of clubs/teams with coaching and leagues of various levels. It is a big machine of development and talent discovery/grooming.

In India this is not the case for many sports.

Grassroots training, nurturing talent and structural competitive systems are very rare outside of cricket or wealthy individuals.

There is some social stigma against professional sportsmen outside of the larger sports. Generally it is not government priority, it can be rare to get proper funding and therefore in the family structure of Indian life, sports can be seen as wasting time/ fun for children.

TL;DR: lack of financial investment in structure. Lack of financial incentive. Social stigma. Lack of facility access - high level of poorer people have little access to sports facilities. Lack of participation.


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

[User] [Men In Black] So is it the Men In Black's mission to just keep humanity in the dark about aliens forever? At what point do they decide Humanity has progressed far enough to deal with it?

[Assistant]
Considering they're a secret NGO with no oversight and are considered the defacto world government by visiting aliens, they probably try to keep it secret for as long as they can.

Their mission statement is to keep earth safe from alien interference. At inception, they thought the best way was to make earth a planet of political refuge, so it was safe as long as everyone respected the neutrality. That means earth is only safe as long as the aliens it harbours are safe.

Letting the general populace know that aliens having been living amongst us for 50-60 years is going to cause mass hysteria and put all those aliens at risk. Possibly distabilise society enough that Earth loses its protected status. Too unpredictable.


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

[User]
CMV: Voicing your virtuous opinion through social media is nothing but narcissism.

I don't really use social media often, especially not to post anything. I am usually "tagged" or "checked-in" to places. I do scroll through on an evening, but really that is just to see funny videos or see an interesting story.

What really annoys me the most, is that people will latch on to ANY trending news story to voice their virtuous OPINION on the subject matter. This is surely only an attempt to gain validation from strangers online, and only serves to improve or cement your opinion of yourself, or to think that you, solely, have the almighty world view and you should repeat this rhetoric for all to hear.

Either way, clearly every person on this planet wants the world to become a utopia, the elysium, so why do you feel the need to voice that you also have this opinion?

The bit that further adds insult to injury, is that they will never voice opinions of matter from the around the world that have not been given social attention. People won't be talking about war torn countries, famine, slavery in other countries, because frankly they don't care. They only want to talk about their first world, privileged problems because they think it gives them something to further raise the pedestal they perch themselves so high upon.

[Assistant]
>The bit that further adds insult to injury, is that they will never voice opinions of matter from the around the world that have not been given social attention. People won't be talking about war torn countries, famine, slavery in other countries, because frankly they don't care.

Ignoring the fact that people talk about goings-on in other countries all the time, you're saying you'd be okay with people posting their virtuous opinions on social media but only if it were about these issues?

If so, what makes you the arbiter about what it and what isn't worth talking about?


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

[User] [40k] What kind of stuff does the Tau speculate about regarding the imperium, and the vast, ancient, malevolent galaxy around them?

[Assistant]
The Tau are actually pretty familiar with the Imperium and its customs, given that they've shared border territory and even coexisted (to a degree) for some time. It's not even remotely friendly relationship, of course, but it's not uncommon for some of the more disenfranchised members of the Imperium to actually go over to the Greater Good, and the Tau have learned quite a bit about the culture and day to day workings of the Imperium from them. Not to mention of course the fighting and any ambassadororial contact with official Imperium representatives.

As for everyone else, well, the Tau aren't *uninformed*, really. They are just relatively new to the galactic.stage. They know all about Orcs and Eldar and Tyranids and all those good physical threats but the function and particulars of the Warp tend to ellude them, as their own contact with it is basically non-existent. Your average Tau couldn't tell what the real difference between a Space Marine and Chaos Space Marine was, for instance, apart from the obvious culture difference. Or the Eldar and Dark Eldar. They are aware of daemons but not really the scope or the extent of what they imply; to them they are just another xenos species to either induct or exterminate.


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

[User]
What happens if a researcher doesn't fulfill the aims put forth in their proposal? (NIH)

I am a senior undergraduate student. In class we have to write a mock grant proposal. I was assigned NIH.

While writing it, I began to think about what would happen if a researcher couldn't complete all of the aims before the grant period ends? It seems like while writing the grant, it may be easy to over shoot a reasonable aim. What happens in that case?

[Assistant]
A grant is not a contract. As long as you can demonstrate honest effort and reasonable progress towards the stated research objectives, nothing will happen if some targets are missed.

The system is self-correcting, in that the likelihood of getting the next grant will strongly depend on what you've done with the previous one.


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

[User] ELI5: Why is a high IQ score directly correlated to a propensity for alcoholism/drug addiction?

[Assistant] Imagine looking at a painting of a flower, where everyone sees the flower, you see every brush stroke, every meaning behind each brush stroke, feel what the artist felt when painting it. Sometimes, it's too much. You dull things, you escape the fact that everything around you is both mundane and complex at the same time. You try to shut it off, escape, become closer to your peers by not being better than them.


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

[User]
How are gas lines in cities secured from chain explosions?

I would imagine a fracture in a gas line that results in an explosion should ideally not result in a whole city blowing up due to the explosion traveling through pipes. How is that ensured though? Through using non-flamable gas concentration or some sort of blast preventing valves?

[Assistant]
You need both a combustible material and an oxidizer to get fire/explosions.

There is no oxidizer present in the lines, and thus a flame can't travel through them.  However this doesn't stop a fire burning where the leak is exposed to oxygen - but this could at worst make the pipe slowly melt if the leak weren't noticed and shut off upstream.


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

[User]
Are there any real and tangible examples of the Butterfly Effect?

For those that haven't heard of it, here's the definition from Wikipedia.

In chaos theory, the butterfly effect is the sensitive dependency on initial conditions in which a small change at one place in a deterministic nonlinear system can result in large differences in a later state. The name of the effect, coined by Edward Lorenz, is derived from the theoretical example of a hurricane's formation being contingent on whether or not a distant butterfly had flapped its wings several weeks earlier.

[Assistant] A pendulum consisting of two rods (so basically a pendulum with a pendulum attached to it) is an easy example. Small differences in the initial state will make the system behave completely differently. It is still a predictable system though, but in order to make any senseful predictions one would need very accurate data on the starting conditions. A small difference would completely change the movement.


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

[User]
If water boils away instantly in the vacuum of space, how did ice comets and the like form?

And when water boils in a vacuum, where does it 'go'? Does it just disperse as atomized H20?

[Assistant] Water boils away in space, but it doesn't just disappear; it's still there, in it's molecular form, floating in space. The cloud can disperse, but if the molecule interacts with a microscopic speck of dust, it might attach itself. If this happens enough times, with enough specks of dust and molecules of water, a comet can form. Gravity will keep it marginally attached, and electrical forces between the atoms will prevent them from flying off into space.


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

[User] ELI5 How do companies get gases like oxygen and helium into canisters?

[Assistant]
There are two ways to put gasses like He and O into bottles. Firstly, you can liquify them by cooling them under high pressure. Then you can put the liquid into the high pressure bottles, seal them, and allow them to warm up. The contents will then enter a state called 'super-critical', where they are neither liquid nor gas.

Secondly, you can take the gas and simply compress it, It will get hot as you do this, and you have to get rid of that heat. If the pressure is high enough, it will again become a super-critical fluid.

Lastly, there is another way to store and transport oxygen or helium. You can liquify it, and place it in a *dewar flask*, which is a container that is insulted by a vacuum. (A Thermos flask is a domestic dewar flask, and, indeed, they are often used to hold small amounts of liquefied gasses). The insulation is good enough to slow the boiling of the liquefied gas so that you can transport them long distances without losing too much of it.


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

[User]
Does the clock arms (seconds, minutes, hours) ever split the clock face in three equal areas?

This is a hypothetical clock where the arms move around the middle axis with constant speed, so no tick tocks. If you extend the lines of the clock arms, do they perfectly split the clock face in three thirds at any point during the 12 hours?

[Assistant] No. Consider a clock that rotates counterclockwise at exactly the rate the hour hand moves, so that the hour hand always points up. Now the minute hand goes at a rate of 1/60min - 1/12hr = 11/720min and the second had at a rate of 1/1min - 1/12hr = 719/720min. Any perfect split will happen when the second hand has gone around a multiple of 1/3 times, say n/3 for some integer n. At that time, the minute hand will have gone around 11/719\*n/3 times. We need this to also be a multiple of 1/3, so 11n/719 must be an integer. Since 11 and 719 are coprime (11 is prime and doesn't divide 719; in fact, 719 is prime), this only happens when n is a multiple of 719. When n=3, the second hand has gone around 719 times, which takes 720 sec = 12 hr, a complete cycle. So we only need to consider n=1 or n=2. For n=1, the second hand has gone 719/3 = 239+2/3, so the second hand is pointing 2/3 of the way around the circle (i.e. 8 o'clock, but the 8 will have moved). The minute hand has gone 11/719 * 719/3 = 11/3 = 3+2/3, so the minute hand is also pointing at 2/3, so this is not the split you want. Similarly, when n=2, both hands point at 1/3. So there is no such perfect split.


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

[User] ELI5: How do you measure stuff in space? How do we know this star weighs x-times the weight of the sun? And how we know how much the sun weights. Same goes for distances. How can you tell how far something is?

[Assistant]
# Measuring Distance:

There are several methods to calculate the distance of a celestial body. Which one is used depends on the exact circumstance. Here are some of the most important methods:

---

* **Parallax**: Earth orbits the sun. In the process of this orbit, we change our position in space relative to a celestial body (just like you see a nearby tree in a different position if you move 10 steps to one side) Using trigonometry, we can calculate the distance to the celestial body in question.
 * Advantages: very precise for close objects, no complicated instruments needed.
 * Disadvantage: only possible for close objects

---

* **Spectral emission**: Stars emit photons with specific wavelengths based on the material they are fusing in their core. We can identify the composition of a star by analyzing those photons.  Due to the expansion of space, however, the wavelengths of photons emitted very far away get redshifted. That means, their wavelengths get longer the further they travel. By comparing the wavelengths of the photons we *measure* to the wavelengths the photons *should have* we can calculate the distance those photons traveled. And thus the distance to the celestial body.

 * Advantage: Possible over longer distances

 * Disadvantage: The object has to be bright enough so we can measure spectral lines reliably

---

* **Standard candles**: Standard candles are celestial bodies of known luminosity (~brightness). We know this luminosity due to the characteristics of some bodies (special types of super novae etc.) By comparing the absolute brightness to the apparent brightness (the brightness the object has vs the brightness we see from the distance) we can calculate the distance to the standard candle. By identifying standard candles in distant galaxies and nebulae, we can infer the distance of those structures.

 * Advantage: Possible over long distances

 * Disadvantage: We need to find standard candles

# Measuring Mass:

---

* **Orbital Mechanics**: Since we have a fairly good understanding of orbital mechanics in well-behaved spacetime (that is: spacetime that is not curved too much), we can use orbital mechanics to determine the relative mass of two orbiting bodies. That is, if we know the mass of Earth, we can use the shape of the Earth's orbit to determine the mass of the Sun.

----

* **Gravitational Lensing**: Einstein's Theory of General Relativity tells us, that gravity is the curvature of spacetime. As such, the path of photons moving through such curved spacetime appears to be curved to an outside observer. As the curvature at a given distance to an object is proportional to the mass of that object, we can use the path of photons passing by a celestial body to calculate the mass of the body.

---


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

[User] [The A-Team] Was Murdock driven crazy or further crazy in Vietnam?

[Assistant] It's not explicitly stated, but it is implied that Murdock isn't really full-throttle nuts, he's just an eccentric who managed to bullshit his way into (and then in later seasons out of) an asylum in lieu of a military prison. A person who was really as nuts as H.M. pretended to be would be completely useless in any kind of high-pressure situation, and be a liability to the team instead of an asset. Murdoch, meanwhile, was consistently able to perform on demand as both a pilot and a con artist regardless of whatever quirky behavior he was engaging in during any particular episode. He may say 'je suis Napoleon", but somehow "Napoleon" still knows his way around the controls of about every craft that can or would fly in American airspace.


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

[User]
[Jurassic World/Park] Alan Grant discovered that the dinosaurs were breeding in the park. Was InGen able to correct and prevent this after the first incident? Are all the dinosaurs in Jurassic World female?

Have the first natual-born dinosaur populations continued to breed? Are there breeding populations on Isla Nublar?

[Assistant]
I found it a bit sad that there's only one T-Rex at Jurassic World. That's what the official site says. Maybe they are raising young ones somewhere away from the visitor centre.

And regarding the others, maybe they started sterilising them?


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

[User] [Marvel Comics] If adamantium is poisonous how does Bullseye have his whole skeleton cased in it without a healing factor?

[Assistant]
There's a difference here. First, Wolverine's skeleton is bonded to the adamantium perfectly. It even created a new form of adamantium that acts nearly organic, allowing the blood to flow from his marrow into his body. A solid coating wouldn't allow that, meaning that he'd have no new blood in his system. But the important thing is that his bones still act like bones, and one of the most important things your skeleton does is that the marrow inside *creates blood cells*.

Bullseye, on the other hand, had a few bones *destroyed*, and then replaced by adamantium. There's no blood coming from them, they're purely there to support his body. So not only does he have less adamantium, he also isn't pushing blood through this poisonous layer of metal.


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

[User]
[Punisher/Dexter] What would the Punisher's opinion be of Dexter?

Both the Punisher and Dexter kill criminals. Would the Punisher see Dexter as similar to him. Or would he see him as another criminal that he needs to kill?

[Assistant]
In Garth Ennis' Punisher storyline "Welcome Back, Frank", there's a running b-plot of three vigilantes who want to start their own vigilante squad with the Punisher leading them.

At the end of the arc, the Punisher shoots and kills them all.

Punisher would probably hunt down and kill Dexter.


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

[User] ELI5: How does YouTube handle millions of video notifications at once, while Discord can barely send out a couple thousand @everyone?

[Assistant]
YouTube is owned by one of the largest tech companies on the planet. Discord was started 7 years ago and, while popular, is quite small in comparison.

Google has 23 data ~~servers~~ centers worldwide, likely with *billions* of dollars of equipment in each one, Discord is worth around $15 billion total. They might have worldwide servers through cloud services, but they can't compete with what Google has access to.


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

[User]
Can a planet sustain life without a hot core?

I was under the impression that any heat the planet core provides is negligible compared to the heat from the sun. Does the core's heat significantly affect life on the planet?

[Assistant]
The actual heat is totally inconsequential. At the surface, geothermal heat is less than 1/10,000th the strength of sunlight.

However, Earth would be *very* bad off if the interior cooled to the point that the mantle solidified. That would mean no more plate tectonics, and that would be a lousy day for things that like to live.

The problem is the carbon cycle. Carbon dioxide is continually replenished into the air through volcanic outgassing and carbonate rock weathering, but then gets sequestered by chemical reactions in the ocean to eventually get subducted by tectonic plates back into the mantle.

If the mantle cools, that means no more volcanoes outgassing...but that also means no more plate subduction. All that leaves is carbonate weathering - we've essentially just turned our carbon "cycle" into a carbon "arrow" that only flows one way, from rocks to atmosphere. That weathering would continue unabated will nothing to pull that carbon dioxide back out of the atmosphere.

We're actually fairly sure this is exactly what's happened to Venus - tons of carbonate weathering, but no plate tectonics to pull that carbon back out of the atmosphere. The end result is an incredibly thick CO2 atmosphere, with accompanying runaway greenhouse effect that would raise global temperatures 500 degrees.


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

[User] [Star Trek] How does a civilian obtain a starship of his own in the federation?

[Assistant] Money. The federation still uses money, latinum, it's just that you don't need it. But companies still exist, and there is still money to be made. Typically, you'll do something like take a contract, meaning that a company will give you a ship and funding in exchange for a certain period of service. Basically, the company technically owns the ship, but the captain will run it. Then you can work your way up to buying your own ship. They aren't that expensive, the equivalent of a pretty nice car in the early 21st century for an old beaten-down one.


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

[User]
[VENOM] Why does Eddie constantly reply out loud to Venom when he can reply mentally?

We saw them talk mind to mind right when they met. Why does he feel the need to reply out loud especially when other people are around to hear it? Just enjoys coming across as a crazy person?

[Assistant]
Im just rereading Forever War and this is a very very minor spoiler.

The Colonial soldiers have computers implanted in their brains that allow communication, act like a HUD and can download info right to their brains. In that fiction humans go their whole life communicating via language, only when they are elderly and they get a new body with this brain tech in it are they exposed to non verbal communication. They still prefer to speak, its what they know.

There are a type of soldier who is "woken" up one day with the implant ready to go. All they know is brain to brain communication and despise having to talk verbally to other people, they view it as slow and not nuanced.

Eddie has spent his entire life verbalizing to external people, the Symbiote knows and prefers to vocalize internally.

tldr; Eddie has old ingrained habits.


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

[User]
Can this type of attack actually happen?

So, I know that this idea is most likely completely ridiculous, but I'm going to ask this anyways:

Can a foreign government launch several hostile takeover attempts on another country's biggest companies through the stock market either directly through government funds or through intermediaries?

For example, can China launch this type of attack on some American companies either directly or through some of their billionaires? ( they can probably force them to go through with it anyway)

Just a shower thought.

Edit: the comment review system of this sub is beyond ridiculous. Who got this genuis idea? I don't want to see the answers to my questions 2 days after the fact.

[Assistant]
It's a possibility, but a well known one, so there are robust defences in place:

 - Most countries have legislation that allows the government to block mergers & acquisitions deemed harmful to the national interest.

 - In certain strategic industries, like defence contractors, they often have either direct stakes or "golden shares" that given them veto powers over certain strategic matters. Some countries, like France, have rather broad definitions of what they consider to be a strategic industry.

 - In other industries, foreign ownership its restricted - in the EU, it's a condition of an airline's operating licence that it remains majority EU-owned. The US restricts foreign ownership of airlines to 25%.

 - They can also forcibly nationalise companies that are perceived as acting in a hostile manner - for example, Gazprom controlled a key gas distributor in Germany. It was believed to be harming German gas security, so the regulator seized control of it.


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

[User]
Would taking anti-histamine drugs like cetirizine for allergies daily would make a person more susceptible in getting COVID-19?

Reasoning is that it slows down one's immune system response, which is important in evading coronavirus.

[Assistant]
Anti-histamines don't slow the immune response, exactly.

Histamine has three major roles as far as immune response goes.

A) it increases local inflammation (which increases permeability of tissue to immune cells.)

B) signals to immune cells increasing chemotaxis - the movement of immune cells into the affected tissue.

C) increased nocireceotor activity (causing sensitivity, pain and itch). Designed to encourage you to stop using the area or move away from the cause.

Now while B is useful, it's an "all or nothing" response so hyper release of histamines doesn't provide benefit. C only affects symptoms. That means only A plays an ongoing role in immune function.

Now while that's useful, to a point, it also becomes inhibitory very quickly. Inflammation is a double edged blade, it helps the immune system a little, but if also damages tissues and organs - as an example, so called "long covid" is an example of chronic inflammation.

Anti histamines don't completely block the action of histamine, instead they mediate it. Slowing it down a little and limiting the ongoing activation of histamine receptors.

This means the important bits still happen, but the over-the-top extreme reaction is impeded and the consequences of that reaction are balanced out.

Ultimately, antihistamines may actually be of BENEFIT to covid by reducing some of the excess inflammation that can be caused by the disease as well as reducing symptoms like runny-nose, post nasal drip and excess respiratory secretions.


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

[User] Eli5: How did humans think before language?

[Assistant] Concepts. If you ever get the chance with family or friends, spend some time talking with little kids who haven't been talking long. They *know* what they want to say, but they simply don't have a way to communicate it yet. You don't need to know what "fear" or "dark" is to know you're scared when there's no light. You don't need to know what "happy" or "cake" is to know you like the feeling you get when eating it. The emotions and observations are the same, it's the communication that breaks down without a verbal or visual way to inform others of your position and thoughts.


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

[User]
[The Prestige] If the Tesla hint was a ruse, how did Tesla know what machine Angier was talking about?

Only two things are possible: either Tesla and his assistant react honestly: "what machine are you talking about? to do what?" or they jump immediately on the chance of deceiving a random man asking for stuff by going "of course".

(Since Tesla was in financial trouble and did take Angier's money, we're lead to believe the latter, although I guess that the idea is that he didn't defraud Angier, since Tesla did build a machine, just charged him "too much", which is no fraud considering it's a unique machine that could be built by only one man in history and worth more than anything else in the world, probably. Or maybe the "fraud" part would have been in Tesla using most of his time still to work on his projects while leaving Angier's machine as a little side project for little time. )

We're  never shown the former.

 The problem is, the latter can't be accomplished without knowing what he's talking about. And yet we're never shown them asking "what did the machine do again?". This would have obviously tipped off Angier too much.

So in the end, it seems that the movie doesn't show either and tricks the audience because it doesn't have a believable answer.

[Assistant]
We only see snippets of the conversations between Angier and Tesla, but it appears that Tesla was hosting him. So presumably they had several days to really drill down into what Angier was looking for. Also, the rivalry between Angier and Borden might have been widely known, so Tesla may have figured it out based on the nature of their competition.

It's possible that Borden's ruse was based on some subconscious association he had about Tesla's actual experiments.  He might have heard him speak or heard someone talking about his theories and internalized the knowledge. Then when writing his coded journal, he pulled what he thought was a completely false lead,  but it was in fact his brain making the connection between his trick and Tesla's actual work.


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

[User]
What is the likelihood that the key to my house is also a key to a lock I don't know exists?

There can only be so many variations on a key, right? So what's the likelihood that the key I have to open my house is also a key to something completely different, like a shed in Ireland, or a bike lock in Japan? I know this isn't too science-y, I just kinda wanted to know, and there's no "AskStatisticians" that I could go to.

Edit: My god, all these posts just make me want to try my key on everything in my town. I won't, because that'd be super sus with or without context, but I wish I could try.

[Assistant]
Extraordinarily common. If you go through a display rack of exterior door locks at a big box stores, you will find they have the "bitting" code on each package, and you can buy multiple locksets with the same key.

The chances of someone not only having your matching key, but finding your specific house and using it are so ridiculously low as to make it irrelevant.


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

[User]
Is there a chemical way to supress sexual feelings?

Wasn't sure if this was a better question for askreddit, but i'd like some more intelligent suggestions based off psychological knowledge or chemical/hormonal expertise. Have there been any drug studies of the sort?

[Assistant] Yes, several medications have been investigated for this purpose, and some are used.  Certain anti-depressants were found to have a common side effect of diminished sexual arousal/desire and are used for treatment of things like premature ejaculation.  Androgen antagonists are also used to treat more significant hypersexual disorders, especially in cases of criminal sexual deviance.


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

[User]
[Harry Potter] Why didn't the Dursleys gladly ship Harry off to Hogwarts?

They hate him right, 9 months whitout harry per year most have been a dream.

[Assistant]
They were so anti-magic that it actually overrode their desire to get rid of him.

After all, for Petunia, she had a lot of trauma tied up in magic.  She felt rejected that she wasn't invited to Hogwarts like her sister, and that resentment drove a rift between her and Lily that lasted the rest of their lives.  And was probably a factor in her marrying the most normal, uninteresting, non-magical guy she could find.

To her, having Harry be a wizard was a constant reminder that she wasn't special, and likely a reminder of the time she lost with her sister.  And to Vernon, it was a reminder that the world wasn't simple and boring as he wanted it to be - not to mention the embarrassment of public incidents in front of his boring friends and family.  So they abused him his whole life, hoping to stamp the magic right out of him.


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

[User]
[Star Trek/The Stand] The Federation finds an alternate Earth in the middle of the Superflu, do they break the prime directive?

Let's say for all intents and purposes, that the Federation is capable of curing the plague, and recognizing it for what it is, a bioweapon which will kill nearly everyone.

Do they step in? Do they let everyone die to preserve the Prime Directive?

[Assistant]
Since the bio-weapon was created by the native inhabitants of the planet, then the PD still applies.

This disaster was of their own making, and part of their natural development as a species.  If it causes them to go extinct, that sucks, but it was their own fault it happened.


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

[User] ELI5: Bernie Sanders wants to 'break up' the big 6 corporations on Wall Street.... What does this actually mean?

[Assistant]
A large corporation has many business units. For example GE makes many consumer electronics. They make electrical components, they make military equipment, they make equipment for power & water, airplane engines and a few other industries, plus GE capital that does a lot in the financial sector.

Maybe each of those can be broken up into 7 smaller independent companies. That would reduce the size and political influence of GE, since each individual new company would have different political goals and motives. GE Aviation wouldn't care about a new law to regulate railroad engines, and wouldn't spend money to lobby influence on it, while GE Transportation would.

Before GE as a master company, would.


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

[User]
Assembly Code

This may be a very general or very loaded question, but how does a computer actually convert assembly Code to binary, or more high abstraction language into assembly Code?

[Assistant]
You should take a look at the Nand2Tetris course. A great majority of your questions would be answered doing the projects.

Assembly to machine code is straightforward - theyre 1 to 1 and based on the hardware. Its a simple translation.

High level programming language to assembly is trickier, and depends on the hardware and the operating system. A compiler will convert the HL code to either byte code, or portable code, which is run by a virtual machine like the Java VM, or assembly, in the case of languages like C++ and Swift.

This process requires taking high level constructs like functions and classes, and converting them into imperative memory and physical structure conscious code that can be executed line by line by a processor. This requires knowing the language you are translating from, like C++, to the language youre trying to convert to, like x86 assembly.


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

[User]
ELI5: Why does a web page that takes too long to load suddenly pop up for a split second when I hit the back button?

It's happened to all of us.

[Assistant]
It's a setting in your browser that prevents the page from displaying until enough has been downloaded to cache or else images like banners would pop in after text has loaded.  This is undesirable because it could cause the text to move around while your browser suddenly makes space for the image.  A good visual would be to imagine copy-pasting a picture into a Word document.

You can actually go into a browser like Firefox and turn this feature off to see the page elements render as soon as they are downloaded, but then pages that load slowly can be unusable as clickable elements get shoved around as room is made for things like images or flash windows.

When you press the Back button, the flash of the webpage that you see is probably the portion of the page that has been cached.

tl;dr: The browser is waiting for all the pieces of the page to download before lifting the curtain and showing you the whole page in all its glory.  When you press 'back' the curtain flickers and you are seeing the elements of the incomplete page.

[edit: Forgot to add in the part about the Back button]


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

[User] ELI5: Why do we as humans have to keep our teeth clean, whereas other animals do not?

[Assistant]
Animals will eat until their teeth have been ground down and then slowly starve to death, or at least get so weak that they get ripped to shreds by predators or succumb to disease they have no medicine for.

Humans prefer to die of other things.

Also we eat way more sugar.


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

[User] [Marvel/ Civil war] how fast do captain america, black panther and Winter solider run in the highway scene?

[Assistant]
If we go with the idea that they are peak humans, then their top speed is around 30 mph and maybe as high as 40.

Cap and Panther also both seem to know that if they're going to close the gap with the Winter Soldier and conserve their strength, they'll need a car.


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

[User] [DC] Are there any superpowered heroes who would be on par with Batman if they lost their powers?

[Assistant]
Mr. Miracle is a New God and as such has immortality and superhuman strength, endurance, etc. But his main thing is being a brilliant inventor and escape artist, and in those fields he could likely equal or surpass Batman.

**Edit:** For that matter, a lot of the New Gods probably would still be damn formidable even if they became human. They're a little like Marvel's Asgardians, even the minor ones are much tougher than a human, and their champions tend to either have additional powers or just be exceptionally good warriors. The Female Furies for example, are mostly just a group of exceptional fighters by New God standards. No reason to assume Lashina or Mad Harriet or even Big Barda wouldn't be very dangerous humans, since as it stands they are very dangerous Gods.


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

[User]
Why is Ayn Rand's concept of objectivism hated so much?

**EDIT** - Like many of you already pointed out, it is better for me to read a bit about philosophy first a bit more before understanding Ayn Rand. Sorry if I appeared as someone who is ignorant but as much as I love philosophy, I will admit that I am no philosophy student which made me fall into the trap of "you are not a philosophy student, you are stupid" kind of criticism.

________________________________

I have a very general and mild understanding of Ayn Rand's concept of objecitivism which based on what I learned so far, is basically a philosophy involving selfish desires *(as in being a person with your own desires and morals)* and doing whatever you can to endulge your happiness as much as possible

*(to put it in a general sense, it can be seen as generally being a selfish a*****e  which is a concept that the video game "Bioshock" used this philosophy as inspiration a very twisted manner. She also saw the concept of altruism as a flawed concept which is somehow both true and not true considering while we live in a world where there is concept need for survival, meaning that you have to focus on your own desires first, humans are a also social species which also helped maximise their chances of survival)*

This concept seems very similar to that of Nietzche's concept of the Ubermench or the Will to Power, a concept where every human individual should live by their own morals regardless of what society says.

However, in comparison to Ayn Rand, Nietzche is loved and respected among many philosophers while Ayn Rand is mostly hated in general or expressed with contempt by others.

So why is this? Why do people hate Ayn Rand and her concept of objectivism in general?

[Assistant]
I'd say it's largely because she's had a huge influence on real life american politics but possess little to no actual philosophical merit or originality. Everybody hates people who write 'pop' books in their field which badly mislead the public, or gain attention above and beyond people doing serious work.

 Rand has senators and important political actors citing her as a major inspiration, yet you rarely hear about people who contributed in far more significant ways to political philosophy or science.

She never really had original ideas, presenting a sort of vulgarized Aristotle and Nietzsche, and all the real problems she confronted she basically ignores.


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

[User]
What could replace oxygen as a metabolic agent for extraterrestrial life?

I've seen a lot of topics about how carbon could be replaced (by silicon, usually) as a biological building block. What elements could replace oxygen or CO2s (and let's even include water) roles in the metabolic process for, say, life on a planet with no oxygen?

[Assistant]
Great question!  Among other purposes, a major role of oxygen is to serve as a final electron acceptor during aerobic respiration.  In short, because it is a pretty electronegative element, organisms are able to generate energy by shuffling electrons to oxygen gas.

Many organisms on Earth have found ways of using other elements as electron acceptors (i.e., anaerobic respiration).  The energy that organisms acquire from these reactions is related to the electronegativity of the final electron acceptor.  Some common substitutes for oxygen are iron (as ferric iron; Fe^3+ ), nitrogen (as nitrate; NO3^- ), sulphur (as sulfate; SO4^2- ), and even carbon (as CO2 or even as organic compounds).

Anaerobic respiration is very important to biogeochemical cycling in ecological systems.  For example, nitrate reduction and carbon reduction ultimately produce nitrogen gas and methane, respectively, which serve as mechanisms for the export of nitrogen and carbon from ecosystems into the atmosphere.  As a greenhouse gas, methane production from warming arctic wetlands has implications for climate change around the globe -- all because bacteria living in oxygen-free soils use a different electron acceptor to survive!


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

[User] ELI5: Why do certain body muscles get stronger with stress and healing (including broken bones), but others like eye muscles get weaker?

[Assistant] It's a different type of stress, so to speak. If you over-exert yourself in any endurance training you will lose muscle mass as well. The reason it recovers and grows stronger is because you're pushing the muscles' limit for a brief period of time and letting it rest, while when you "exercise" your eyeballs you're doing nothing more than make them work for much longer periods of time than they can handle. If you go marathon running out of the box without proper escalation and without rest you will start the catabolic state and your leg muscles will get smaller (along with many others).


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

[User] [Pirates of the Caribbean] In PotC 2: Dead Mans Chest, Elizabeth is repulsed by Jacks bad hygiene and breath as they flirt and almost kiss. But its not like she has Crest TP so isnt her breath awful too?

[Assistant] People cleaned their teeth before toothpaste.  Also, they were more tolerant of bad breath (the very concept of bad breath came from marketing campaign intented to sell a failed women's hygiene product as a mouthwash.  The company was called Listerine.  They weren't around back then.) so Jack's breath is far worse than anything normal, likely as the other person said, because of too much alcohol, but who knows exactly.


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

[User]
[X-Men] Are the X-Men prequel stories taking place in alternative universe from the original X-Men movies?

If not, why is Professor X alive, when he died and projected his mind into some comatose patient at the end of Last Stand?
Why do Wolverine have his adamantium claws, when he lost them in last Wolverine movie? How is Magneto even alive and have his powers back, when he must be around 90 years old and he lost his powers in X3?

Is this just an (extremely) lazy film writing or is this a different universe from the original X-Men movies?

[Assistant]
They changed the future in Days of Future Past. I've always understood that the implication of Mystique saving Logan at the end of the film (the past Logan) is that he's able to warn them of the things to come. Of course, whatever happens in Apocalypse could change all this - but the logical explanation is that the butterfly effect of changing the past was *huge*, meaning that the events of the original trilogy of films never remotely happened.

It's why they don't show Magneto, because now his future is uncertain, meaning they can do whatever they like with the past Magneto. Arguably, he can even die now.


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

[User]
Why does my intermediate microeconomics course say the marginal cost curve slopes upward if there are also Economies of scale?

Is the MC curve assumed short term while capital is fixed but over the long term does it flatten or invert due to economies of scale?

[Assistant]
<Argh, posted instead of hitting return. Should be finished now.>

You're close: In the short run, production is assumed to be at an efficient scale, which means that the marginal cost is always increasing. Think of it as your base line of production is running at what your factory is designed to produce at your current staffing level. If you want to produce more, you'll have to run overtime, or add a shift, or cut into maintenance periods.

If you aren't currently running at capacity, then the marginal cost can indeed decrease: That's what happens when you pay less per unit if you order in bulk. Set up costs are the majority of the cost for small, custom orders, so the more you order, the longer they can run without changing the setup and the more efficiently they produce until they hit their optimum production rate.

So, the full production function looks more like a ski jump: It slopes up, then down, then starts going back up again. Most of the time were looking at the area where it's turning back up because if you're not there, you have other problems.

In the long run, the production function is not fixed because you choose your parameters when, for example, building a factory. It becomes fixed in the short run because, after you've built your factory, it takes a lot of resources to change production significantly beyond the levels it was designed for.

Efficiencies of scale are a long run thing: E.g. if you build a larger factory that has more machines per person, you can produce more units at a lower cost per unit than if you're producing in your garage with machines that take up a person's entire time. So, even when you're taking advantage of economies of scale, your shirt run production function should be increasing on the margin, because you want to produce at an efficient scale _for that production function._


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

[User]
ELI5: If two rockets move away from each other at 0.75 the speed of light, would each appear to be going faster than the speed of light from the other rocket?

And if not, why not?

[Assistant] No, they'd see each other moving at 96% of the speed of light due to special relativity. Strictly speaking, if the rockets were moving at 100mph then they'd see each other moving at very slightly less than 200mph, but it's so close as to make no difference. Once the speeds get higher, you start having to worry about the difference.


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

[User]
ELI5: What makes "alternative" music different from other genres like rock and pop?

That new Twenty One Pilots song (Stressed Out) is at the top of alternative charts, but to me it sounds the same as any song you'd hear on a mainstream pop station.

[Assistant]
Pop is short for popular, and so any song that is marketed toward a mass audience or any song that gains popularity is "pop". Music does not have strict definitions, it is implicit. You know it when you hear it, and you can usually identify pop music by catchy, simple lyrics, non-offensive broad ideas often concerning topics of love or happiness/having fun, usually with guitar, drums, and clean synthesized melodies.

Alternative music (or alternative rock) distinguished itself from pop by having distorted melodies, lyrical content that was more edgy or subversive, and generally appealed to a smaller audience of people who thought of themselves as outcasts. However, this style became very popular over time, to the point where many "alt" songs are very popular and thus very "pop". Today it is mostly a marketing term, which ironically labels the music as being non-mass-appealing in order to actually give it mass appeal. It turns out basically all teenagers think of themselves as "alternative" rather than "popular", and thus some of the most popular songs are alternative.