5:01 AM
@JackRod Hi :-)
15 hours ago, by Jack Rod
actually why earth crust does not melt? and what make it temp so high?
The Earth is heated at its centre by radioactive decay and it cools at its surface by radiating heat into space. So the temperature decreases as we move from the centre to the surface.
And at the surface the temperature has decreased to, well, 20°C in Chester this morning.
The crust doesn't melt because the temperature has decreased to below its melting point.
If there was a sudden huge increase in the energy from radiation at the core then I guess it could raise the temperature at the surface enough to melt the crust, though we would care becaue we'd be cooked well before the crust melted :-)

5:22 AM

5:46 AM
Happy Krishna Janmashtami :)

1 hour later…
6:57 AM
@user250478 to be fair it is hard to see how any natural process could ever form a geon. You mention black holes, but for those there is an obvious and natural way for them to form. If stable geon solutions exist they are likely to be highly contrived and wouldn't exist outside of some theorist's fevered mind :-)

7:48 AM
What does a relative boost map look like in matrices?

4 hours later…
11:51 AM
@ACuriousMind I figured it out, a solution that we both can be happy with. There's a way in which you can not produce and not starve - listen to this, this is groundbreaking - you can't starve if you don't need food to live.
Transfer human minds into computer boxes each with a little solar panel on top and blast them into orbit XDDD
Or just have machines produce everything ig

Without embarking on that discussion, is transferring human minds into computers even theoretically possible? Even supposing you could copy one's memory, what would happen to consciousness? D:

Not really a physics question

Who mentioned Physics? :P

refer to this if you are worried about the persistence of the self :

@Slereah Many thanks, this looks very interesting

12:04 PM

Before that I'm reading that comic and the devil has a point

@Feynman_00 for that to be answerable, we'd have to understand what consciousness actually is :P

I will need a new definition of self in terms of continuity of time evolution of the human being
@ACuriousMind Yeah, we talked about that once
Existence is truly wonderful, isn't it?
Maybe that's the most obvious thing I've ever said and yet every time I come to think of this I'm amazed

@Slereah The inventor is the real og

@Feynman_00 It is a violent and irrepressible miracle, yes
(with apologies to Disco Elysium, where I stole that line from :P)

12:14 PM
tf is that

That is the game from which you propics come, right?

yep

It's been only a week since I discovered ACM's profile is not community-invariant

at some point I started only changing it on physics.SE when I change it, so for many other communities it is whatever it was when I first created an account there
not all of them are DE pictures

some are merely the game that inspired it

12:20 PM
I'm waiting for the right moment to change my username to qfieldtheory
Just kidding :P

3 hours later…
3:01 PM
Many thanks for your reply @JohnRennie , you, the moderator and the users of this quantum room are friendly. I disagree that this is feverish speculation, I disagree meanwhile that we don't know how is our solar system, or for example the dark matter.
I disagree to critic the work of other persons (due my perspective and my knowledges), I don't like that people think that we can to warp the space-time,
I don't like that people think that could to exist a primordial black hole as explanation of certain anomaly of our solar system, I don't like that the pedestrian thinks that we can to travel using wormholes (see the reference [1]), I prefer add contructive feedback in the way that I think, and I clair that the authors of these theories made a great effort.
[1] See the second claim by Renate Loll from last section of the article George Musser, La paradoja más famosa de la física se acerca a su fin, Investigación y Ciencia (this journal is the Spanish edition of Scientific American), Febrero 2021, Nº 533. This article was also published in Quanta Magazine.
There was a typo in "..and I clair that the ....", I want to say "..and I claim that the ...." Many thnaks.

3:56 PM
5-10% of the people on Earth don't have access to electricity, is that for real?
Most of it seems to be concentrated in Africa

damn
just imagine how many more scientists and engineers the world could have if they had access to electricity and whatnot

Ugh. People don't need to potentially become scientists and engineers to be worth caring about. They're people.

How do you determine what is worth caring about?

4:21 PM
@ShikiRyougi What a great video, I complete agree with it
@ACuriousMind Given the selfish altruism argument, isn't it better for places like the West and Europe to lift African people out of poverty, to get them educated, and to get them producing at a much higher level so we can all benefit that way?

The problem is whether or not there should be some benefit for us in order to care for the ''poor''. ACM (if I understood correctly) points that we shouldnt have a personal motive, instead, everyone should be well off just because they are humans.

I already said that I find this way of looking at the world deeply distasteful. The argument in the video is correct, I just fundamentally disagree with the idea that altruism needs to be conceived of as selfish.

@ACuriousMind I don't entirely disagree with your view but I don't entirely relate to it either. In what part or aspect of a human being is the value concentrated in your opinion? Something must differentiate a human being from a rock for example, unless you care about rocks just as much as you care for humans. If it's not the productivity, is it the potential to be productive, is it the body, is it the brain, is it the spirit?

4:41 PM
@JingleBells It is the ability to feel joy and to suffer, the ability to have hopes and dreams, the existence of the conscious mind. The things that make us human, the things we tell stories about. Is "potential to be productive" really the only thing you could come up with?
Is death for you just the end of productivity? Nothing more but a cold, unfeeling 0 in the productivity column of the eternal spreadsheet of the universe? ::shudder::

5:07 PM
@ACuriousMind No, it is not the only thing I could come up with, I didn't want to go on and list a ton of stuff because I was curious about what you had to say. Death for me is not just the end of productivity. The reason I value productivity and innovation is precisely because it leads to more joy, less suffering, better hopes, and better dreams, and it leads to the survival of more conscious minds, it might even lead to the creation of new digital minds. That's why I value productivity.
In this universe of atoms, it's precisely the rise in complexity of minds that makes it meaningful to me, the fact that we even exist and that the universe exists makes me curious and makes me want to explore it more, and the tool that has been able to push us the most in that direction is productivity and cooperation.

5:21 PM
@JingleBells And yet you are willing to let those suffer that do not "produce", or do not produce "enough". At some point along the way it seems you forgot why you ostensibly cared about productivity in the first place. All production and innovation in the world is pointless if we forget what it is supposed to be in service to - a means to an end, not an end in itself.

5:31 PM
@ACuriousMind I'm not willing to let them suffer, it's just that I don't know how to help them without doing it on the backs of people producing or incentivizing more unproductivity. And since now that you know why I value productivity, you know why I'd place a higher value on a person producing than on a person that doesn't. An unproductive person's sole value is the mind, the rise in complexity, while a productive person has that + the value of contributing to all the stuff I stated above.
Note: I'm not taking into account the potential to produce here
If I had to save either a productive human or a human that's certain will never be able to produce, I will save the productive human, I hope there's no controversy here and I believe this is what you'd do as well.
(holding everything else the same of course)

ah yes, all these rich capitalists producing by owning stuff, we really can't help anyone without doing it on their backs :(
@JingleBells I reject the idea that this is a trolley problem. We can and should provide for everyone. And no, "productive" is not the criterion I'd use to resolve problems of this kind, and I find the suggestion deeply offensive.
Like, actually offensive - I'm horrified by the idea anyone could think I'm like that, and you've just ruined my day. Goodbye.

@ACuriousMind Bruh I said everything else held the same, which means productivity is the only difference, I don't see how else you can solve the problem besides throwing a dice. And I never said that the real world represents such a trolley problem.
I wasn't trying to offend you, I was just giving an example that productivity to me holds more value than unproductivity, if everything else is held the same. I was suggesting that you'd do the same because given the constraints given (in this unrealistic hypothetical example) there's no other reasonable way to act (if you value productivity more).
If you want to twist my words, change the constraints of the example, or pretend as if I said the example represents reality, and then get offended by it, you can do so but just know that this was not my intention at all, sorry.

6:06 PM
@JingleBells I am not "twisting your words", I am taking offense at precisely what you said. If you, after all I've said, really cannot figure out why I find it offensive, I have nothing more to say to you. I won't respond to any further messages.

Hi everyone, is there someone who can help me understand how to write a proper post suitable for physics.SE ? I've had my most recent question closed due to it being "homework-like": physics.stackexchange.com/q/723764/342681

@Nalt Sure: In general, questions that ask us whether or not something is "correct" are a poor fit for our site, as discussed in the post that's also linked in the closing notice
I think your question was perhaps a bit unfairly closed due to its formatting

Perhaps I should just remove the "my attempt" portion.

because the underlying question - "what does 'project' mean in this context?" is certainly on-topic here

I think my post was poorly written then. The user who provided an Answer did not address the question I wanted answered. Instead, they saw my "is my attempt correct" statement.

6:13 PM
I really think it's the formatting - people tend to expect the question at the end of the post
I also think it's perfectly fine you have your attempt in there; what's perhaps distracting is that the quote is bigger than it has to be - you could cut the latter half and it would still be clear what you're asking about

I thought about doing that, but was worried there may be context crucial there for those examining the question.

Anyway, I have submitted for the post to be reopened given some edits. Thank you for your time and input.

@ACuriousMind I can figure out why you took offense to it, I believe it's because you are an incredibly moral, emotional, and caring person, and the mere thought of having to make such a trolley problem choice makes you feel sick, regardless of what the constraints are. I didn't know that this is how you'd react to it and I feel guilty for putting that thought in your mind, I genuinely feel sad because you've helped me out so much throughout the years, and you don't deserve this. :(
I'm sincerely sorry for making you feel bad, I shouldn't have given the example at all and I went too far with it.

7:03 PM
Hi,
In the above link, on page 37, there is a figure of a potential energy function of a harmonic oscillator (say a particle), specifically figure 23.22. In the figure there is also an indication of the total energy E. Is it possible for a particle to exist at the unstable maxima where the potential energy is greater than the total energy? The kinetic energy would have to be negative, which is impossible. Yet, isn’t the unstable maxima also a point of equilibrium?

@schn that is not the potential energy function of a HO
but aside from that, if $E$ was greater than $U(2/3x_1)$, then a particle could rest at the unstable maximum
you are correct that kinetic energy can't be negative

@ACuriousMind ok, thanks. So is the unstable maximum a point of equilibrium?

yes - but unstable equilibrium

And in this case, an unattainable one, or? The particle can never reach it.

if you restrict the total energy to $E$, then yes, it can't be attained

7:18 PM
Ok.

7:29 PM
@JingleBells Although I do understand that in a problem such as the trolley problem you would like to have a trait that would help you choose between humans lives, and although I do not find the idea that productivity should be that trait (looking it purely from a philosophical point of view), I believe that this ideology is very wrong.
If you were to say that this trait should be for example ''potential to do good in the world'', I think that it would be more acceptable as an idea (although still controversial). For example, choosing between the life of a mass murderer and the life of a ''normal'' person would be fairly easy with this viewpoint. (Disclaimer: I do not support this idea, just stating what would may be more acceptable as an ideology)
You may find this video useful: youtube.com/watch?v=A1x7FqXRy9c
I think that productivity is not a good measurement of value for a human life

7:52 PM
I do not find this offensive to be honest, but some very close people to me are what you would call ''unproductive'' and its just sad to think that they would have less value than someone ''productive''. An even bigger issue is how to measure ''productivity'', who is in a position to say that someone is not useful? Lets say that a friend of mine is an ''unproductive'' person, I can claim that her mere existence helps a ''productive'' person like ''me''.
I put quotetion in ''me'' because who can judge that I am ''useful''? This ideology fails in a lot of ways...

2 hours later…
9:38 PM
Is there a moderator who can help me understand what is wrong with my post here: physics.stackexchange.com/questions/723764/… My submitted edits were insufficient for having the post reopened
" Your question can be reopened if suitably edited to ask about the underlying concepts — please read the links above carefully to learn how." is written, but to my understanding my post satisfies that.

@Nalt The problem is likely that this question sounds very much like a homework question: You talk about "instructions", and their mathematical meaning, that's exactly what someone trying to get us to solve an exercise would write. Unless one clicks on the link you provided, one won't know you're actually quoting part of a paper (btw: I cannot find the exact quote you provide in the article you link - where are these "instruction" from?) rather than e.g. instructions in a lab manual.

Why is sometimes the evolution operator written as $e^{-\imath H t}$ while at other times it's written as $e^{-\imath H t -\epsilon H}$?

there is also no context provided - you just drop the quote on us without any explanation of the context or what you're trying to do

They are from one of the authors via email correspondence. Do you have any edit suggestions?

I had provided context, but was told it was unnecessary by a different person. Honestly, I am getting quite frustrated with this website.

@DIRAC1930 Who writes "the evolution operator" as the latter?

9:49 PM
I think when you're considering the Schwinger-Keldysh contour

@Nalt what you had provided was your own attempt; not context. So...the "instructions" come from private correspondence, but you prominently claim the "source" of these instructions are the link to the article, where these instructions don't actually appear?
I'm not sure how you expect anyone to understand that

Ah, that was not my intention.

I think a brief explanation of how you (apparently) emailed the authors and they gave you this description of their procedure but you don't understand what they mean by "project" might go a long way here - but then again, the question remains why you don't ask the authors what they meant... :P

because I want to exhaust my own resources before I bother them. They are my final option

@DIRAC1930 In the context of propagators and such, we often encode the instruction of how to evaluate the contour as $\lim_{t\to \infty+\mathrm{i}\epsilon}$ - this has to do with thinking about the different ways to shift the poles; if you are looking at the SK contour you should be familiar with this from ordinary QFT and the Feynman propagator

9:58 PM
@ACuriousMind Thanks, I need to brush up on this