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Danu
Danu
12:02 AM
Why would anyone ever visit 4chan.org/pol/
 
ACuriousMind
ACuriousMind
@Phonon Great, now I am looking up Morse theory.
 
Phonon
Phonon
@ACuriousMind glad to see you so motivated at 2 am haha
@Danu btw give chess24.com a try later, good alternative to our usual blitz sites, (average 2k players online)
 
Danu
Danu
@Phonon I really like their streams, but never played there
 
Phonon
Phonon
@Danu same, but when I tried it, it was nice, good interface, board, etc.
 
Danu
Danu
I'll give it a shot sometime
 
Physics Meta
Physics Meta
12:13 AM
0
Q: What the hell, I just lost 582 reputation points

Rob JeffriesWTF? Users removed? Seriously thinking of quitting this site for good.

discussion
 
ACuriousMind
ACuriousMind
Apparently, they liked Rob more than me. A lot.
 
Phonon
Phonon
@ACuriousMind this happened to you recently as well?
 
ACuriousMind
ACuriousMind
@Phonon Yes, but I gained about 30 rep from that.
 
Phonon
Phonon
@ACuriousMind :O some bug?
 
ACuriousMind
ACuriousMind
And if you look at the latest meta posts, you can see who was removed
@Phonon No, a bunch of trolls were thrown out, if you ask me :P
 
Phonon
Phonon
12:18 AM
ah k, gonna have a look
 
Danu
Danu
@ACuriousMind I got -10, lol
 
Sean
Sean
@ACuriousMind if yu had downvoted the users answers, I suspect you could get your -1s back from that
 
ACuriousMind
ACuriousMind
@Sean They didn't have much answers, and I don't think I downvoted those they had.
Also, wow, they really liked John, -1741 rep total today for him
 
HDE 226868
HDE 226868
@ACuriousMind AnnaV lost 1500+.
 
ACuriousMind
ACuriousMind
@HDE226868 No surprise, after all, since this meta post basically gives a list of people they upvoted in particular.
"John Rennie, Lubos Motl, AnnaV, Rob Jeffries etc."
And, yep, Lubos lost ~400
 
Sean
Sean
12:26 AM
How do you know who the removed users were?
 
ACuriousMind
ACuriousMind
I'm psychic, haven't you noticed that yet? ;)
 
HDE 226868
HDE 226868
> I thought that it's inappropriate to humiliate a scientist and a lady with more than one negative vote
Anna's a scientist. Don't be sexist.
 
ACuriousMind
ACuriousMind
@HDE226868 I kinda expected her to react to that statement, but she perhaps didn't read it.
 
Danu
Danu
So... this is coming from the removal of a handful---or less---of users?
 
Sean
Sean
How do you know who the removed users were?
 
HDE 226868
HDE 226868
12:29 AM
@Danu 9, it looks like. Minimum.
 
ACuriousMind
ACuriousMind
@Sean Because they've been all over meta in the last week or so, and now their accounts are gone (for example the writer of the meta post I linked there).
 
HDE 226868
HDE 226868
Actually, all the major losses max out at 9 users removed, so perhaps that's all.
 
ACuriousMind
ACuriousMind
Would fit the odd 5-8 upvotes their ridiculous comments got
 
Danu
Danu
@HDE226868 How do you know?
Ah, yeah get it
 
HDE 226868
HDE 226868
@Danu I checked Rob, Danu and Anna's.
 
Danu
Danu
12:33 AM
Okay, so I think it was a case of sock-puppeting then
 
HDE 226868
HDE 226868
You think?
 
Danu
Danu
I only had one removed, lol
 
HDE 226868
HDE 226868
Same. Only -28 for me.
 
Sean
Sean
I had two users removed affect me. Roughly -50. Annoying but not as bad as some of the high rep users
 
ACuriousMind
ACuriousMind
@Sean Well, arguably, it doesn't matter at all for John, Lubos or Anna whether they lose 1000 points or not :P
 
Stan Shunpike
Stan Shunpike
12:48 AM
In the definition of Levi-Civita connection, i often see $$(\partial_k g_{rj} + \partial _j g_{rk} - \partial _r g_{jk})$$. are these indices $k,r,j \in \lbrace t,r,\phi,\theta\rbrace$?
 
Danu
Danu
Spacetime indices, yes
I think those are terrible indices though
$\mu,\nu,\rho,\sigma,\kappa,\lambda$ are the ones I'd use
That's typically enough
 
ACuriousMind
ACuriousMind
@StanShunpike I would refrain from choosing $t,r,\phi,\theta$ as explicit labels (unless you know you are in such a chart), but these should be spacetime indices. Didn't @0celo7 tell you that a bit ago?
I seem to recall you asking the same question
Or I'm going crazy
 
Stan Shunpike
Stan Shunpike
No, he got distracted by indices. Or then I missed what he said. one or the other
Either way, it is the exact same question
But now I understand
 
Danu
Danu
Also, the fact that that was not obvious to you tells me you should be studying more basic stuff than the connection
 
0celo7
0celo7
@StanShunpike What else would they run over?
 
NeuroFuzzy
NeuroFuzzy
12:56 AM
@HDE226868 I got -46 heh
 
0celo7
0celo7
I actually considered chat.stackexchange.com/transcript/message/20850374#20850374 as an answer to your question.
 
NeuroFuzzy
NeuroFuzzy
@ACuriousMind Hahahah oh lord I got one of those too (weird comment on meta w/ good replies) that really annoyed me. But now it's gone.
 
Stan Shunpike
Stan Shunpike
@0celo7 Well, if we are working with spacetime manifolds, it's obvious. But I'm always reading about the levi-civita connection in math books and they never specify what the indices stand for. Didn't @ACuriousMind say I shouldn't assume it unless I know the chart is locally $t,r,\theta,\phi$?
 
0celo7
0celo7
@StanShunpike You generally know the chart in GR.
 
Stan Shunpike
Stan Shunpike
Yeah, somehow my knowledge of manifolds and knowledge of indices weren't synching on that fact.
I didn't get why they were using different indices if $\lambda, \mu,\nu$ all fall in $\lbrace t, r, \phi, \theta\rbrace$. But I guess they couldn't write $\Gamma^\lambda_{\lambda\lambda}$ as that would imply they were all the same index.
@0celo7 ^
@0celo7 So I found the exterior solution for the Schwarzchild metric. Is the interior solution significantly harder? Wald has a section on it I haven't read yet. going to soon.
 
0celo7
0celo7
1:18 AM
Idk, neither is very hard.
 
ACuriousMind
ACuriousMind
@StanShunpike That's because the indices don't stand for anything specific. The equations you write down with indices are supposed to hold in every chart (unless specified otherwise)
 
Stan Shunpike
Stan Shunpike
@ACuriousMind ah, that makes sense.
 
ACuriousMind
ACuriousMind
So, you can take any set of coordinates, not just $t,r,\phi,\theta$, plug them in there, and the equations hold.
 
0celo7
0celo7
The Christoffel symbols in particular are defined chartwise.
 
Stan Shunpike
Stan Shunpike
@ACuriousMind But they would all be part of the same set right? Even if I had $x_1, x_2, ...., x_n$ indices, then for $\Gamma^\lambda_{\mu\nu}$ $\lambda,\mu,\nu \in \lbrace x_1, x_2, ...., x_n\rbrace$. Correct?
 
ACuriousMind
ACuriousMind
1:23 AM
@StanShunpike Yes. And in every "slot" that one of $\lambda, \mu, \nu$ represents, you can choose anew which of the $x_i$ to put there, but you must put the same at every occurence of $\lambda$, for example.
 
Stan Shunpike
Stan Shunpike
@ACuriousMind So, whatever choice I make, it must come from the set $\lbrace x_1, x_2, ..., x_n \rbrace$. Right?
 
ACuriousMind
ACuriousMind
@StanShunpike Yes.
 
Stan Shunpike
Stan Shunpike
Sweeet. that's awesome. I've been confused about that for a while. Great!
 
ACuriousMind
ACuriousMind
@0celo7 Yeah, the symbols, as things with indices, are defined chartwise, like all things which you define only in their "indexed form" are.
 
0celo7
0celo7
@ACuriousMind Most introductory texts define the affine connection as a combination of derivatives of the metric.
 
ACuriousMind
ACuriousMind
1:28 AM
That's why it is ugly to define them without properly defining what a connection on a bundle is - you don't see that they're just components of a single object :P
@0celo7 As you might imagine, my dislike for indices makes me also dislike most introductory texts ;)
 
Stan Shunpike
Stan Shunpike
Wait, I don't understand your point @ACuriousMind
Can you elaborate a bit
 
ACuriousMind
ACuriousMind
@StanShunpike The thing what I say about the Christoffels? Don't worry about that. You're fine without understanding it.
 
Stan Shunpike
Stan Shunpike
@ACuriousMind I agree for now. I want to get used to calculating before I try to step up to that. I'm very pleased I calculated the interior solution for the Schwarzschild metric. That was a goal of mine.
 
ACuriousMind
ACuriousMind
And I can't explain it without explaining how you see a connection on a bundle abstractly, and that feels to me much more intuitive than it actually is when I try to explain it.
 
0celo7
0celo7
@StanShunpike Now you know more GR than @ACuriousMind :P
@ACuriousMind So I posted 5 answers today...that's more than the rest of the month combined.
 
Stan Shunpike
Stan Shunpike
1:32 AM
LOL I doubt it.
@0celo7 why today?
 
ACuriousMind
ACuriousMind
@0celo7 I noticed. I wondered whether I should ask you what insanity befell you ;)
 
Stan Shunpike
Stan Shunpike
or was it just the questions that came up
 
0celo7
0celo7
@StanShunpike They complained about needing more 3k rep users.
 
Stan Shunpike
Stan Shunpike
Ah, yeah i've heard that
 
0celo7
0celo7
Figured I'd get back in the game.
I should have a shot at getting a sweet 50 bounty
1
A: How does Dirac define the representative of $\{\langle\phi\frac{d}{dq}\}\psi\rangle = \langle\phi\{\frac{d}{dq}\psi\rangle\}$

0celo7I believe the difficulty stems from the archaic notation. What he is trying to do is show that $-\mathrm{i}\mathrm{D}$ is Hermitian, where $\mathrm{D}=\mathrm{d}/\mathrm{d}q$. Note the first equation you wrote. It is just saying that $\mathrm{D}$ acting "backwards" on the bra is equivalent to $\m...

 
ACuriousMind
ACuriousMind
1:33 AM
@StanShunpike Nah, you probably do know more GR in some sense. I can do DiffGeo, but when it comes to actual physical content, I know very little of GR, or its peculiar solutions.
 
0celo7
0celo7
I'm 99% sure that's the right answer.
@ACuriousMind Fun GR fact: it is possible for a Kerr back hole to have a sweet spot of parameters so that a photon on its surface looks stationary to an observer at infinity.
 
ACuriousMind
ACuriousMind
@0celo7 Since that user has asked multiple questions that essentially just reduced to translating Dirac's old-fashioned notations and notions into the modern speech, I think you're probably correct. Although I'd also say you're correct without considering that.
@0celo7 What does it mean for a photon to "look stationary"? It's not as if I can see photons unless they hit my eye
 
Stan Shunpike
Stan Shunpike
@ACuriousMind You sound like Ted Shifrin on Math Chat. He said he abhors indices and just prefers to use DiffGeo
 
0celo7
0celo7
@ACuriousMind Lol, don't worry about that!
They just do!
 
ACuriousMind
ACuriousMind
@StanShunpike lol...perhaps we are soulmates
 
0celo7
0celo7
1:37 AM
The geodesics have constant radial coordinate, essentially.
 
ACuriousMind
ACuriousMind
Yeah, I figured I'd be something like that :P
 
0celo7
0celo7
@ACuriousMind You can tell that to laypeople, they won't ask that question!
Then you don't have to grumble about null infinity and whatnot.
 
ACuriousMind
ACuriousMind
@0celo7 I know. I've trained myself to always ask these kinds of questions since I learned that you don't see the length contraction, but instead the Terrell rotation.
So I've grown careful about what "observers see"
 
Stan Shunpike
Stan Shunpike
What is Terrell rotationn?
 
ACuriousMind
ACuriousMind
@StanShunpike It's what describes what you would actually see if a relativistically moving object passed by you. You don't see it shorter, but it appears weirdly rotated/distorted.
 
0celo7
0celo7
1:42 AM
@ACuriousMind I'm sure you know that a lot of these back hole curiosities are not very relevant.
 
Stan Shunpike
Stan Shunpike
@0celo7 Relevant for what?
 
0celo7
0celo7
Particularly because if they are ever observed, you will die horribly and never get anywhere with the information.
@StanShunpike Experimental physics.
 
ACuriousMind
ACuriousMind
@0celo7 I know, but still, we need to know what we mean when we say "it would look like X".
 
0celo7
0celo7
@ACuriousMind Well the technical term is stationary limit surface.
 
ACuriousMind
ACuriousMind
Also, interesting typo there :P
 
0celo7
0celo7
1:44 AM
@ACuriousMind From Wiki: "At the static surface, a particle, moving against the flow of space at the speed of light, is static relative to a distant observer."
It's a common error, I'm sure.
@ACuriousMind If you let a(n) (alcoholic) spirit air out, does it lose potency?
 
ACuriousMind
ACuriousMind
@0celo7 Uh...no idea, I'd think not, at least not very fast
 
Stan Shunpike
Stan Shunpike
My pet peeve is when people use technical terms they cannot define. This processor today kept saying he "studies the mind" but never defined what it was.
 
ACuriousMind
ACuriousMind
Your processor can speak? ;)
 
Stan Shunpike
Stan Shunpike
Lol
 
0celo7
0celo7
@ACuriousMind Found it. In Boyer-Lindquist coordinates, the stationary limit surfaces are $r_{\pm}=M\pm\sqrt{M^2-a^2\cos^2\theta}$
$a=J/M$ where $J$ is the angular momentum of the black hole.
 
Stan Shunpike
Stan Shunpike
2:05 AM
@ACuriousMind You know Hooke's law? Did you know Hooke discovered the first cells?
 
0celo7
0celo7
@StanShunpike Do you mind accepting my answer to your $\Phi$ question if you don't have any more questions?
 
ACuriousMind
ACuriousMind
@StanShunpike No, I didn't know that!
 
Stan Shunpike
Stan Shunpike
@0celo7 not at all. Can u give me the link? Glad to do it
 
0celo7
0celo7
0
Q: Where do we get the terms involving $\Phi$ in parentheses come from in the static weak field metric?

Stan ShunpikeI am confused about the static weak field metric. As written in Hartle, it reads \begin{equation} ds^2 =-\left(1+\frac{2\Phi(x^i)}{c^2}\right)(cdt)^2 +\left(1-\frac{2\Phi(x^i)}{c^2}\right)(dx^2+dy^2 +dz^2) \end{equation} From what I read, he doesn't derive it and I can't seem to find a derivati...

general-relativity newtonian-gravity approximations
 
Stan Shunpike
Stan Shunpike
If I missed any others, let me know and I'll do those too.
Done
 
0celo7
0celo7
2:10 AM
thanks
I'll look through your other stuff, perhaps answer stuff that I know.
@StanShunpike What is wrong with this guy's answer? physics.stackexchange.com/questions/171828/…
 
Stan Shunpike
Stan Shunpike
Nothing, I accepted it. I was told initially not to accept to quickly. I periodically go through them and accept ones.
I just do them all at once. It is more efficient. Brb
 
Stan Shunpike
Stan Shunpike
2:57 AM
One of my recent question in the biology forum seems to be eliciting very diffefent answers. biology.stackexchange.com/q/30928/11652
I was stretching last night and questioning why I do it without warning up.
 
 
2 hours later…
abt
abt
4:52 AM
Hello!
 
Stan Shunpike
Stan Shunpike
5:18 AM
@DavidZ That biology question on Bio SE I asked above elicited widely divergent responses (at least it seemed that way). From your experience on PSE, does that mean the topic I asked about was too non-mainstream? Or do some topics just elicit differing opinions sometimes?
 
David Z
David Z
5:43 AM
@StanShunpike I can't comment on whether it's too non-mainstream because bio.SE is a different site with a different scope. But I don't think it makes sense to assume anything about your question simply because it got widely varying responses.
 
Stan Shunpike
Stan Shunpike
Okay, I think that answers what I was asking you then. I haven't encountered that much so I was just curious. Usually when I have asked questions here pn PSE people have given a definitive answer and not much debate was needed.
@DavidZ
 
David Z
David Z
6:01 AM
I do think biology is more susceptible to having different explanations for the same effect, and thus multiple answers to one question
0
Q: Difference between quantum numbers j and m and the four other: principal quantum number n, angular momentum m, and etc

GuestI am confused about what is the difference between the quantum number j and m and the other four quantum numbers: the principal quantum number n, angular momentum m, and etc.? From "Quantum Mechanics: Concepts and Applications" by N. Zettilli, it says: Where J is the general angular momentum op...

quantum-mechanics angular-momentum
too lazy to transcribe that at the moment
 
Stan Shunpike
Stan Shunpike
6:23 AM
@DavidZ I did half of it.
@DavidZ I think the way I spaced the equations though failed. If you see the edit and know how I can do it better in the future, let me know what Latex commands I should have used.
 
Stan Shunpike
Stan Shunpike
6:50 AM
I am reading Landau and he says Born's formula $$E = -\frac{Z^2 m e^4}{8n^2 h^2 \epsilon_0^2}$$ isn't relativistic. Is there a relativistic version?
 
 
1 hour later…
David Z
David Z
7:54 AM
@StanShunpike I figured it was easier to just finish editing than to explain
Actually this one is kind of tricky because the equations are boxed. Usually you can just use \begin{align}...\end{align} for spacing equations like that though.
 
 
2 hours later…
David Z
David Z
10:23 AM
The only joke paper I've found on arXiv today: arxiv.org/abs/1503.09109
 
Emilio Pisanty
Emilio Pisanty
 
 
3 hours later…
Jimnosperm
Jimnosperm
1:01 PM
What's with all the recent "user was removed"s? Did we have a sockpuppet infection or something? I had 2 at the same time, both for -28. That means both users gave me 3 upvotes and 1 downvote and were deleted simultaneously. I've seen others who had it worse with 4 or more removed users at once (albeit some made off with a net gain)
I think security has dropped the ball. Who needs to be fired?
Nvm, checking meta first seems to be what I should start doing
 
Jiminion
Jiminion
1:30 PM
@Jimnosperm Sorry, I've already disappointed you today. Also, I lost 10% of my rep due to user deletions. And now you are the second person I've seen with a 14K+ rep complaining about losing less than 1%.
 
Jimnosperm
Jimnosperm
Actually, I don't have 14k rep yet, but that's not the point of your valid argument
But about your answer
There is no center. And if there were a center, it wouldn't be defined by the location where no external gravitational fields influence it. There is also no absolute right time. You could call time experienced along a comoving geodesic as the right time, but that's still not an absolute thing. Also, you should know better than this. You've been around enough and you participate in chat. You should know that whatever you've always felt is irrelevant to what mainstream physics says.
Andiamo, minion! Get your head in gear today. I expect this stuff from other new users, but not from you
 
Jiminion
Jiminion
@Jimnosperm Wouldn't there be a place in the universe where time is moving slower than any other? And given that the universe is expanding (generally) would this place (or places) be relatively stable?
@Jimnosperm Your rep says 14.1K. (Gee, you are a bit crabby today....)
 
Jimnosperm
Jimnosperm
@Jiminion No there is no place where time is moving slower than any other because if there was then at that place an observer could still watch something go past at relativistic speeds, which would appear to that observer to be progressing slower through time.
@Jiminion Chat rep adds together all rep from SE sites where you have 200 or greater. On Physics.SE, I currently have 13613. (And yeah, I may be a bit crabby today. Today is Wednesday. I'm usually in a poor mood on Wednesdays. Sorry if I was too harsh on you)
 
Jiminion
Jiminion
1:48 PM
@Jimnosperm Oops, I meant FASTER than anywhere else. Gravity slows time. I think of time running slower near a schwartzchild radius. [No problems about the crabbiness. You are Canadian. Deep down, there are 300 million obnoxious people south of you that care about you all very much.]
 
Jimnosperm
Jimnosperm
There both is and is not a point that progresses through time the fastest
By definition, a geodesic represents the maximum amount of time that can be experience between any two events
So, in a way, that is the location where time moves the fastest
But to any other set of two events, observers on the second geodesic may observe the first geodesic as moving slower through time. More than this I can't say because there isn't any way of talking about time dilation beyond that
 
LeGrandDODOM
LeGrandDODOM
2:05 PM
Hey guys
Is the homework PhysicsSE policy "no homework whatsoever" ?
 
Jimnosperm
Jimnosperm
@LeGrandDODOM no
55
Q: How do I ask homework questions on Physics Stack Exchange?

David ZWhat is the policy on asking homework questions on Physics Stack Exchange? What kinds of questions are considered homework questions? Are homework questions allowed? What should I include in a homework question? Why don't you provide a complete answer to homework questions?

discussion faq homework
 
Jiminion
Jiminion
@LeGrandDODOM It's more important to show what you have done and perhaps get help/insight on a particular part you have trouble with. Broad homework questions are frowned upon.
 
LeGrandDODOM
LeGrandDODOM
@Jiminion Do you mean they're tolerated when given enough details about where one's stuck ? Reading meta.physics.stackexchange.com/questions/6631/… made me understand homework questions should always be closed no matter what
 
Jiminion
Jiminion
@LeGrandDODOM Yes. They can be a bit harsh about closing homework related questions, in my opinion.
 
Jimnosperm
Jimnosperm
@LeGrandDODOM The closer you are to asking a question like that first one, the happier we will be.
Here is another excellent guideline: meta.physics.stackexchange.com/q/5958/23473
 
Jimnosperm
Jimnosperm
2:46 PM
28
A: Why CAN we see the new moon at night?

yachadhooI stumbled across this question, and while it is an old question and there are some halfway decent answers, I think it deserves a more in-depth response. I completely understand the question, which I think is am excellent question. Trying to understand the phases of the moon is much more diffic...

One more vote gives this user a well-deserved populist badge
And someone ruined it by voting on the accepted answer. Alright, 2 more votes for that user then
 
Jiminion
Jiminion
@Jimnosperm Oops. I think that was me. I'm really a thorn in your side today....
 
Jimnosperm
Jimnosperm
No, it makes no difference to me if that user gets a gold badge. I just thought with being 1 vote away and writing such a good answer that I'd help them out a bit
 
 
1 hour later…
The Dark Side
The Dark Side
4:02 PM
How do you know you are not contributing enough answers to the site?
Of course, look at your answers tab.
But a less trivial way --
When the recent user removals cost you -40, while it is an order of magnitude higher for regulars.
That's simultaneously both :) and :(
 
0celo7
0celo7
I lost 0 from that.
 
Jimnosperm
Jimnosperm
Mine only cost 56
 
The Dark Side
The Dark Side
Hey that's very comforting :)
Thanks
 
Jimnosperm
Jimnosperm
Mind you, I'm one of the less frequent answerers of the regular users
 
0celo7
0celo7
Only 409 till VTC privileges.
 
The Dark Side
The Dark Side
4:05 PM
:)
 
Stan Shunpike
Stan Shunpike
@0celo7 I am reading Landau and he says Born's formula $$E = -\frac{Z^2 m e^4}{8n^2 h^2 \epsilon_0^2}$$ isn't relativistic. Is there a relativistic version?
 
0celo7
0celo7
@StanShunpike Uh, probably. What formula is that :P
@StanShunpike Try asking @dmckee . I think he's the particle physicist in the room.
 
Stan Shunpike
Stan Shunpike
Will do. I think that's the basic one you derive from particle in a box or the SHO, I can't remember which. I can get the name when I get home. I don't know why Landau didn't include it.
 
0celo7
0celo7
@StanShunpike $Z$ and $n$ means it has to do with atoms.
 
Stan Shunpike
Stan Shunpike
Yeah, exactly
 
abt
abt
4:12 PM
@0celo7 I can chat now, furthermore am I not welcome here until I read more books?
 
0celo7
0celo7
@abt You're welcome here at all levels.
I've found you're not welcome if the questions you ask can be found on the first page of a Google search, however.
@abt I got my first theoretical physics book in October (?) of 2013. That was Zee's Einstein Gravity in a Nutshell.
A complete list with times will be impossible. Some books I read one section in for a few hours and then put away, others I read cover to cover spread out over months.
 
abt
abt
@0celo7 What do you suggest that I do right now? I was thinking of spending from now until the end of April to further my foundation before moving on. Would you recommend that?
 
0celo7
0celo7
@abt I seriously recommend getting Shankar and Zee now.
 
abt
abt
How about for my maths? Should I continue reading Artin and also read a book on linear algebra such as by Incel?
 
0celo7
0celo7
Don't bother with rigorous analysis. I don't think anyone in this chat knows any, and we get along just fine.
I've heard good things about "Linear Algebra done right"
 
abt
abt
4:20 PM
That one is too basic I think, I've read some parts a year ago.
I want to learn some multilinear algebra and forms because I'm kind of lacking.
and did you ever try analysis though?
 
0celo7
0celo7
Yeah.
It's really hard and unenlightening.
Unless you want to get into hardcore quantum mechanics or rigorous field theory, it's not necessary.
 
abt
abt
Where did you learn about differential forms of electrodynamics? Like hodge stars and forms? It's not in griffiths as far as I've seen. Though I've read about it in penroses book.
 
0celo7
0celo7
Uh, you'll learn that in your study of differential geometry.
 
abt
abt
Fair enough.
 
0celo7
0celo7
Lee covers that in Smooth Manifolds.
 
abt
abt
4:25 PM
Can you look at the contents of this book? crcpress.com/product/isbn/9781466510005
 
0celo7
0celo7
Alternatively, I recommend Nakahara, Geometry, Topology and Physics.
 
abt
abt
Is that worth a read for gr and forms? It was a gift.
 
0celo7
0celo7
The ToC looks fine, but without reading any of it, I can't say much.
I think Nakahara with Lee's books as references for some topics will give you a good understanding of geometry.
I wish I had done that to begin with.
 
abt
abt
I asked someone before, and they mentioned that learning GR without index gymnastics is not good, and that I should not read that books since it avoids it.
 
0celo7
0celo7
@abt You will learn that some of us don't like indices.
By the same token, some do.
 
abt
abt
4:29 PM
Sorry I've really taken a lot of your time asking these questions, thanks though.
If I hadn't met you then I would be on a completely different path, as strange as it may sound.
 
0celo7
0celo7
@abt The biggest thing is not to jump between books.
That's a lot harder than it sounds.
 
abt
abt
Are exercises obligatory for understanding?
I tend not to
 
0celo7
0celo7
I think so, yes.
 
abt
abt
Furthermore, is everyone here aware of these free online lectures by perimeter institute that are graduate level? perimeterinstitute.ca/training/perimeter-scholars-international/…
A lot of people don't know about them, so I thought I should link it just in case.
 
0celo7
0celo7
I think most of us do.
 
Jimnosperm
Jimnosperm
4:34 PM
@abt Aware of them? I'm in some of them
 
abt
abt
You're in PSI right now?
 
Jimnosperm
Jimnosperm
No, not right now
 
abt
abt
You used to be?
 
Jimnosperm
Jimnosperm
Or ever. I wasn't part of PSI
 
abt
abt
Then you are implying that you are currently watching them.
 
Jimnosperm
Jimnosperm
4:36 PM
My supervisor was joint with PI and so I attended lectures there last year as well as working out of an office there once in a while
 
abt
abt
@0celo7 have you sat through all of them? I've done 2-3.
 
0celo7
0celo7
@abt I've not seen any of them.
 
abt
abt
@Jimnosperm do you live in Canada?
 
0celo7
0celo7
I know of them though.
 
Jimnosperm
Jimnosperm
@abt Ya, eh?
 
abt
abt
4:37 PM
@Jimnosperm I live near Perimeter Institute by the way, so we're close.
 
Jimnosperm
Jimnosperm
OMG another Canadian. This is a surprise
 
abt
abt
@Jimnosperm Are you at UofT?
 
Jimnosperm
Jimnosperm
Right now I'm unaffiliated, but I was York
 
abt
abt
0celo7 mentioned that you're into cosmology I think, can you recommend me any books or lectures?
By the way I'm also 17 (98), though currently not even close to 0celo7's level.
 
Jimnosperm
Jimnosperm
Any particular topic in cosmology you looking for? Or just some general stuff? And video lectures or pdfs?
Have you done multivariate calculus yet?
 
abt
abt
4:43 PM
Yes, since you're in Toronto, I can tell you how much I know from UofT's course codes.
My current level is MAT257, MAT267, PHY250/2/4/6.
 
Jimnosperm
Jimnosperm
Woah now! I was at York, not UofT. They have a completely different course code system
 
abt
abt
and PHY354 because I've done classical mechanics and calculus of variations.
 
Jimnosperm
Jimnosperm
But it sounds like you have some basics
 
abt
abt
For reference
 
DanielSank
DanielSank
I tried having a conversation on /r/philosophy. Big mistake.
 
Jimnosperm
Jimnosperm
4:46 PM
Just so you know, cosmology is at graduate level for a reason. Maybe it's not as math intensive as QFT/EFT, but you're going to want some good preparation
 
DanielSank
DanielSank
Folks were talking about quantum mechanics.
 
abt
abt
Yes though I'm not that good in them, I know enough to tackle differential geometry or general relativity without any problems, though for some reason I don't know where to start.
 
Jimnosperm
Jimnosperm
Sean Carrol's book provides a great intro to GR
I recommend learning that first because everything in cosmology is based on knowing GR
This means learning tensor calculus
 
abt
abt
@DanielSank You cannot be that impartial of the philosophers, there are some good ones like Tim Maudlin. Some of them though what they are talking about.
know*
@Jimnosperm Is tensor calculus usually taught in most GR books? I don't think I need to read an entire book of the subject as most universities do not have a tensor calculus or analysis course.
 
0celo7
0celo7
@abt If you want to study string theory cosmology, you'll of course need more than just tensor calculus.
It's called "Riemannian Geometry" if you're looking for a course
 
Jimnosperm
Jimnosperm
4:51 PM
@0celo7 Let's start with the basics
 
DanielSank
DanielSank
@abt I know there are good philosophers. /r/philosophy was the mistake :)
 
0celo7
0celo7
@Jimnosperm Yes, but he mentioned he wants to learn string theory.
 
abt
abt
@0celo7 Yes exactly, I know that part enough.
 
0celo7
0celo7
My big mistake was buying a string theory book before I knew what a topology is.
 
Jimnosperm
Jimnosperm
@abt A good GR book will teach you most of what you need to know about tensor calculus. But it still takes some getting used to
 
abt
abt
4:52 PM
@0celo7 I've read munkres topology somewhat, is that good enough?
 
0celo7
0celo7
@abt Never read it.
 
abt
abt
There is a course in topology at UofT starting in may, and I was thinking of auditing it.
 
Jimnosperm
Jimnosperm
Bah. String theory is so last decade
 
abt
abt
@0celo7 @Jimnosperm Speaking of which, I was speaking to a professor at CITA and he told me not to get too interested in String Theory as it's probably wrong.
 
0celo7
0celo7
@abt I don't think there's much use in sitting down with a math text and reading the whole thing. You're very likely to pick up a lot of unnecessary material.
 
DanielSank
DanielSank
4:53 PM
@abt Dude, be careful with math courses. You can spend a lot of time and energy and not learn anything useful.
 
abt
abt
What is faulty about that statement if anything?
 
DanielSank
DanielSank
Check with the prof ahead of time. Ask what the flavor of the course will be.
 
0celo7
0celo7
@abt If anything, the "probably"
I don't think we know either way.
There's no evidence either way.
 
Jimnosperm
Jimnosperm
String theory has been explored all it pretty much can be. There's not much more to do with it and most are moving away from it
I've been told many times that you should only get into it if you're really dedicated to it. Even then you should consider something else
 
abt
abt
@0celo7 Then why are you studying it? Could you not have spent the time to further your knowledge in QFT and GR, or even any maths that you have not covered.
 
0celo7
0celo7
4:58 PM
@abt I'm doing physics as a hobby, not a career. I can study anything I want to.
I happen to think string theory is cool.
 
abt
abt
@0celo7 Also why do you want to study nuclear engineering? You are all set to be a great theorist already. This was unexpected for me. If you don't mind me asking, why are you not studying physics as a career?
 
0celo7
0celo7
@abt Fusion.
Money has a lot to do with it too. I don't want to have a degree that barely puts food on the table.
 
abt
abt
@0celo7 A lot of people mention this, though for me money isn't really a priority. I only want to discover something fundamental and I would be content with that alone.
@0celo7 Though I'm not sure if I will come to regret it.
 
Jimnosperm
Jimnosperm
@abt Only that?
 
0celo7
0celo7
@abt I can always do like Jim, he started as an engineer and became a theorist. (I think.)
 
Jimnosperm
Jimnosperm
5:04 PM
Nobody discovers fundamental things anymore
 
abt
abt
@Jimnosperm that's the point entirely.
 
0celo7
0celo7
I just want to have a degree that will allow me to find decent work in some capacity. Last year my department had a 100% employment rate for students not going to grad school.
For sure I'll be getting a minor in physics.
 
abt
abt
@0celo7 Are you even going to attend any of your lectures? It will be ridiculous.
 
Jimnosperm
Jimnosperm
@abt So you're saying "I'm not in it for the money, I'm only in it to become famous to the point where I'd have money thrown at me anyway"
 
0celo7
0celo7
@abt Of course. I attend school now, don't I?
I'm not a bum :P
 
abt
abt
5:08 PM
@Jimnosperm not like that, seriously I am not interested in that.
@0celo7 How are you able to listen in class?
 
0celo7
0celo7
@Jimnosperm The goal is to solve the Riemann hypothesis, Yang-Mills mass gap, Navier Stokes, dark energy and dark matter in one paper.
Can you get multiple nobel prizes?
 
Jimnosperm
Jimnosperm
Yes, you can
But only one per paper, I think
 
abt
abt
@0celo7 knowing the Nobel committee, you probably won't even win any for that.
Until you're almost dead at least.
 
0celo7
0celo7
Still, solve three Clay problems at once and then retire.
@abt Einstein is still salty.
@abt I sent you my book list btw.
 
abt
abt
@0celo7 True, and thanks.
 
Jimnosperm
Jimnosperm
5:11 PM
@0celo7 Retire after that? No! I thought I'd cure cancer first
 
0celo7
0celo7
@Jimnosperm "A proof on the cure of cancer using the Hodge conjecture"
 
Jimnosperm
Jimnosperm
Grrrr.... I'm doing our stack egg and some fools are always choosing exactly the wrong options every time. So much so that they seem to be trolling
 
0celo7
0celo7
Go for 4 Clay prizes.
 
abt
abt
If 4, then you may as well just go for 6.
 
0celo7
0celo7
@abt Note that the list is in no particular order.
 
abt
abt
5:15 PM
@0celo7 If you don't mind me asking, what got you into physics and maths in the first place, and when?
 
0celo7
0celo7
You can see baby 0celo7 asking dumb questions in the comments!
 
abt
abt
@0celo7 For me, I first begin studying by myself in my 9th year, for the chemistry olympiad, and I made it to the final round though I did not know enough biochemistry or organic mechanisms to make the team. After that I started reading physics from halliday/resnick and also calculus to prepare for the physics olympiad, though I lost interest in that as I continued on. This was all before my 10th year.
 
0celo7
0celo7
Although here I point out a mistake in the video. Since the guy who posted the video did not notice it, I think he's a fraud.
 
abt
abt
You didn't have many good lecture resources back then did you?
 
0celo7
0celo7
@abt Nope, I had no clue what to do. So I bought a book that had good reviews on Amazon.
That doesn't always work btw.
I don't know why anyone would like Zee's QFT book.
 
ACuriousMind
ACuriousMind
5:21 PM
Well, that was interesting...I had been evacuated from my home for the last hours because a dud bomb from WWII had been found nearby. Fun times.
 
0celo7
0celo7
@ACuriousMind Do you know what an orbifold is?
 
ACuriousMind
ACuriousMind
A...manifold with corners :D
 
0celo7
0celo7
So you don't know anything about their holonomy?
 
ACuriousMind
ACuriousMind
No, certainly not
 
alarge
alarge
@0celo7 Not all physicists work in theoretical physics (indeed most don't). The guy might well have seen that there were not many videos on YouTube about the technical side of GR and as he had taken one class on it during grad school, decided to make a video. Fraud is a rather strong word to use here.
 
0celo7
0celo7
5:23 PM
Also, please assure @abt that mathematically rigorous analysis is hardly needed for most physics.
@alarge He said that the difference between co- and contra-variance is like the difference between $x$ and $1/x$.
A lot of stuff he says does not make sense.
 
ACuriousMind
ACuriousMind
Mathematically rigorous analysis is rarely seen in most physics, and even more rarely needed.
 
0celo7
0celo7
@ACuriousMind What is your criterion for upvoting answers?
Do you read the answers to every question?
 
ACuriousMind
ACuriousMind
On questions where I know the answer and which I don't find interesting I will skim the answers - if there are many answers, I will upvote the one or two best of them, otherwise I vote answers to these up only if they are exceptionally well-stated.
On questions where I know the answer and which I do find interesting I will vote up most answers that are correct and useful to people who didn't know the answer, and perhaps write my own.
On questions where I don't know the answer I will vote up any answer which makes me feel that I now know (a substantial part of) the answer, and which seems to be correct.
But I don't read the answers to questions which don't interest me at all unless I had another reason to visit the question, I think
 
alarge
alarge
@0celo7 I don't see how this changes anything. The sad truth is that you can't retain all this information if/when you don't need it. You're probably right in that he hasn't used GR in any serious manner (research), but my point is that he could still have a PhD in physics and calling him a fraud is a bit much (I dare you go ask your local physics faculty about GR and see how much of an insight they have on average). Not that any of this really matters.
 
0celo7
0celo7
5:59 PM
@alarge Point taken.
 
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