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22:15
@ACuriousMind Is the Hodge theorem here the same one as Hodge decomposition theorem $\Omega^p=d\Omega^{p-1}\oplus d^\dagger\Omega^{p+1}\oplus \text{Harm}^p$?
@ACuriousMind 10/10
@0celo7 Depends on the context, could also be this one, for example
@Qmechanic Not the hero we deserve, but the hero we need!
@ACuriousMind Eww, I don't understand any of that!
Context = link
@0celo7 Ah, didn't see the link
22:19
@ACuriousMind Ah, I found it in Frankel, although he chickens out on the proof.
@0celo7 Yes, I think "Hodge's theorem for functions" from Mike there is a special case of the general Hodge decomposition. The vanishing of the integral there shows there's no component of $\rho$ in the $\mathrm{d}^\dagger$-part, I think
@Jimnosperm :)
@ACuriousMind The proof of the "sufficient" part is elusive.
Necessary is simple to prove.
God, you care too much about proofs. Just trust that the mathematicians are correct :D
@ACuriousMind W...wait, what?
HE'S ONE OF US!
22:22
lol
I've always had this attitude, sort of. But I always felt bad about it, too
I usually try to see why it should be true
and if I manage, I just skim the proof :P
Well that went straight over my head.
@Danu This.
For instance, it bothers me that I've never seen a proof of Gauss-Bonnet.
@Danu Heh, yeah. I'm not advocating to take that stance in general, but there has to be a certain effort/usefulness ratio for it to be worth understanding such a proof.
@ACuriousMind Yeah, agreed. If I really don't see it, I try to resort to technicalities
Unless the proof is "beautiful". Then it needn't have use ;)
22:25
@0celo7 I don't believe you. If it did, you'd have googled it.
::googles what the heck Gauss-Bonnet is::
@Danu Don't believe me all you want, doesn't change anything.
@ACuriousMind Even I've heard of that
Ah, just a special case of Atiyah-Singer :D
Friggin index theorems
I wish I'd know something about them
Did we end up agreeing on any good sources for Homology & cohomology?
22:28
Fine, I'll do it.
@Danu Not that I'd recall
@Danu Would it be a good idea to talk to your QFT and ST profs?
@0celo7 no?
I'm not looking for a physics treatment
(for now)
I don't see why you can't just talk to a math grad student at your school.
I could, when I get back to uni
22:32
@Danu Do you want it from the rather topological or the rather algebraical viewpoint, btw?^^
Honestly though, I don't think a lot of math grad students know it either
@ACuriousMind Algebraic
I have this book by Bredon - Topology and Geometry
which presumably does it from a topological POV
(It has full chapters on both homology and cohomology)
But I probably first need things like fundamental group, homotopy theory and stuff to really "get" it right?
So maybe I should push for a more topological approach after all... hmmm
@Danu The Wiki article has Hatcher as a reference.
Topological for me would mean simplicial/singular/cellular homology + Eilenberg-Steenrod axioms.
@ACuriousMind ::stares blankly::
@ACuriousMind Hey I know one of those!
22:34
Algebraic would mean chain complexes and their homologies, resolutions, spectral sequences.
@0celo7 I have the Hatcher book
@ACuriousMind I want chain complexes.
Okay, honestly
I really want to have a strong motivation for caring about e.g. De Rham cohomology as it came up in my diffgeo course
I think the motivation is topological
@Danu Henneaux/Teitelboim rehash it in the course introducing BRST symmetry, but I guess it isn't enough if you don't know it already
But the presentation I saw there was very algebraic
@Danu deRham is definitely rather topological, I'd say
Right, but my prof only gave that background after a purely algebraic introduction
Also, I think I'm better at algebra than topology as of right now
22:37
Well, there'll always be algebra beause homology is algebraic topology, after all^^
Anyways, thanks for the reminder about Hatcher, @0celo7. It seems quite relevant
Ideally, I'd have a Russian-style book like Vinberg. It seems to suit my needs very well
@Danu Well it's on my list of books that I want to read but never will.
What does "Russian-style" mean?
@0celo7 It's a very distinctive type of mathematics
@0celo7 In Soviet Russia, textbooks read you.
Very physical and intuitive
22:40
@ACuriousMind Crap, there goes 25 points.
You lured me into a dual comment...I could have answered.
Who cares? :P
@Danu I'm less than 100 away from VTC privileges.
@0celo7 I understand the excitement, but it's really not fun lol
@Danu I was just about to say that staring at that gif any longer would drive me nuts :P
But I appreciate the sentiment ;)
22:43
I cannot resist:
@0celo7 With great power comes great responsibility.
@ACuriousMind 2/10
@Danu I rate your 2/10 5/10
@ACuriousMind 8/10
It seems Sakurai (rather, the editors) took out the discussion of Young Tableaux in the 2011 revision of Modern Quantum Mechanics.
@0celo7 That's a shame. I'm gonna find and compare the editions now!
22:56
@Danu I noticed that Qmechanic referenced Sakurai in the context of Young tableaux, and I know my version did not discuss that at all.
That's the 1994 edition that discusses it.
I know
I commented on QMechanics' post
@ACuriousMind haha. Totally pointless, but I couldn't resist :)
Oh well, I think anyone interested in the Young tableaux stuff can find it him/herself
I hate daylight savings time
I like having the feeling that it's "late in the evening" while it's still light outside
23:05
But I had gotten used to the SE day starting at 1am! Now it's 2am! ;(
/care
@ACuriousMind every time day light savings happens I hear the number of accidents goes up because
Sleep cycles get off
And people don't drive well then
Good thing I don't drive, then
Also, you look different again, @StanShunpike :D
I know! The last few days have been crazy!
Its gone so many different colors. Red, green, tan. Its awesome
23:14
It still bores me a little, tbh
What does?
the picture
Well, I admit mine isn't as shapely as yours :D
Guess the pun was a bit third class
Real manifolds have curves
@StanShunpike: You don't want to have one of these, I guess?
@Danu $\mathbb{R}^n$ is crying in the corner now.
23:20
I was gonna add "unless they're trivial"
But thought that'd ruin the fun
Luckily, we've got our German friends for that :)
Nitpicking runs in our blood, I guess
@ACuriousMind nope, I kinda like the changing backgrounds. I'm afraid if I post a picture it will stop doing it.
@Danu @ACuriousMind A curve is defined on Wikipedia as a map from an interval onto a topological space. Can that interval be a single point?
@StanShunpike It's kind of a trivial curve then, isn't it?
@StanShunpike Since that'd be equivalent to the map being constant on a larger interval, yes, unless you demand the map to be injective (which isn't done in general).
Whether or not you include it in your definition will not matter much
23:30
Sometimes the constant curve provides a needed identity element or something like that
@ACuriousMind Well, I think it's rather usual to define it from an open interval
@ACuriousMind Of course, constant curves are important. But 1-point curves, not so much
But like I said, this does not appear to be an important point
(pun intended)
Hahaha
Not bad
:)
@Danu I think the interval is usually closed, how else are you gonna get "start" and "end" points?
yeah I thought it was too
23:31
@Danu 7/10
@ACuriousMind This was discussed briefly in my diffgeo course, I think. Certainly, Lee's book uses open intervals.
@ACuriousMind Start points are easy: $\gamma(0)$.
Wikipedia uses closed I think.
@Danu And 0 is part of what open interval?
@ACuriousMind $(-\epsilon,\epsilon)$
It's just called a starting point by convention, not because the curve is undefined before it
(in Lee)
In my course, we used $[0,\epsilon)$ lol
Lee is an active SE user
23:34
Best (or worst?!) of both worlds
@StanShunpike Before you go asking him something though, let me do some fact-checking lol
I'm not going to, I will let you do it. You will ask better. :p
Puns? Really?
@Danu Oh...I think you use that $\epsilon$ way for germs, when all the stuff you want to do is local (which is usually the case in DiffGeo).
Yeah okay, checked.
@ACuriousMind Yeah, exactly.
Not just for germs though.
@0celo7 not a fan of puns?
23:35
Integral curves, for instance
@0celo7 Don't you find them punny?
@ACuriousMind No. 76 to go.
What kind of manifold would only have single point curves?
@StanShunpike The point :D
2
@ACuriousMind Sigh :P
23:39
@0celo7 I'm interested whether you'll be glad of this eagerness to reach 3k after you've reached it ;)
@ACuriousMind My activity on this site will plummet again.
@Danu Truth must be spoken! ;)
So if I had a collection of single point curves....each would be a separate manifold unconnected to the others? Does a lattice work that way?
0
Q: What is it like being a theoretical cosmologist?

SirSuperiorMy dream is to become a theoretical cosmologist. I love math and physics and I am incredibly curious about the mysteries of our universe. What is it like to be one (specifically research)?

@0celo7 Ah, c'mon keep answering stuff. Perhaps look at a few questions which don't require much formulae at all - those usually get many votes, and need not be boring.
23:42
@0celo7 what happens when an unstoppable force meets an immoveable object? It gets posted on SE and put on hold by QMechanic.
@ACuriousMind Oh, the corruption of the pure spirit of SE :P
That was another dumb one earlier....wtf
@ACuriousMind I don't like conceptual questions though, there are actual physics students who can answer those.
@ACuriousMind did you see my question above about the lattice? Just curious if u had a thought about it.
@Danu I just wanted to get @0celo7 to talk a bit about physics and not just calculate stuff :P
23:44
@StanShunpike Countable collections of points are 0-D manifolds, if that's what you're asking
They're also smooth and orientable
@StanShunpike No, and I don't see it. Perhaps I'm blind
@ACuriousMind It's too bad nuclear physics is rarely brought up on SE, that's where I'll be able to BTFO you people in 3-4 years.
5 mins ago, by Stan Shunpike
So if I had a collection of single point curves....each would be a separate manifold unconnected to the others? Does a lattice work that way?
@ACuriousMind
Ehhh. Well. Not really.^^
@0celo7 I think you're doing a lot of BTFOing as it is :p
23:47
@StanShunpike Nah, I have no clue what I'm doing
@0celo7 None of us have. That's called life.
How is a lattice different then?
@StanShunpike You have a notion of "nearest neighbour" and an analogue of the derivative, for example.
How you define the derivative is actually related e.g. to ordering issues in the path integral formalism.
@ACuriousMind You mean forwards, backwards, or whatever the other thing is called?
@Danu Exactly.
23:51
I see that the choice is superficially the same as ordering
But it doesn't appear to be deep at all... is it?
@Danu Sidewards is the correct term.
@Danu, my batch of honey wine is done.
it's pretty good.
@DanielSank how did you make it?
@Danu Deep...I wouldn't call it deep, I guess.
@DanielSank Kool!
abt
abt
23:54
@0celo7 my dream is to become (x), though I do not know what (x) is. tell me about it.
@StanShunpike Yeast, water, honey, time.
@ACuriousMind I mean, is there something more interesting than the obvious forwards = $\hat p$ first, backwards = $\hat x $ first?
@StanShunpike (plus some toasted oak and a vanilla bean)
@abt Dude, I'm in high school, I have no clue
abt
abt
no i was being sarcastic
whatever nvm
23:56
@Danu Well, you can also do symmetric. But no, I don't know of any interesting consequences of it, it's just something you need to be aware of when quantizing a theory.
abt
abt
@0celo7 I was just generalizing a common statement that is made a lot.
(AFAIK, of course)
@ACuriousMind I know, I just didn't want to type it out and thought it was obvious from my previous comment :P
@ACuriousMind I do think there are very interesting things to be said about this. I think the entire program of "geometric quantization" is based on the idea that it provides a good motivation for one choice. Or at least that's what one of my professors told me.
@ACuriousMind I was still asking about the analogy with the derivatives btw. But you don't think it's more than just superficial, then?
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