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2:12 PM
Sigh, for some reason it won't let me sign up for analysis
 
measure theory is fun; vector measures are (maybe only apparently) complicated; integrating vector functions wrt vector measures is shit
 
What? I'm not doing measure theory
 
I am
sadly
right now
 
I have a list of 6 questions for my advisor on GR shit
I need to track him down now
 
What are the questions
 
2:27 PM
The ones you can't answer.
The thing with double coverings
HE prop 4.5.10
The causal curve spacelike curve thing
How to check if globally hyperbolic
Is Schwarzschild globally hyperbolic
Transitivity of causal relations
And one other thing
Oh the Ellis proof
 
Well Ellis pretty much said "OH WAIT I'M BUSY NVM"
So I guess it's up to him to solve this mystery
I guess I could ask that one guy who wrote a paper referencing a similar theorem
 
Which one
Not the German I hope
I left a comment on your post about that IIRC
 
2:42 PM
The one that's like
"Is the operation of time machines forbidden"
Or something
One of the footnote basically states that theorem
No foliation for time oriented simply connected manifolds with CTCs
 
"Any strongly asymp­totically flat, maximal initial data set that satisfies the global smallness assump­ tion, stated in the introduction, leads to a unique, globally hyperbolic, smooth, and geodesically complete solution of the Einstein-Vacuum equations, which is foliated by a normal maximal time function t, defined for all t > —1."
 
Yep
 
wot
what is global smallness
 
That's the Choquet-Bruhat theorem
 
is everything tiny
 
2:44 PM
Or some strange formulation of it.
 
aka the only GR lady
 
it is actually the Christodoulou-Klainerman theorem
 
Proof?
Since when do you give a shit about GR
 
of the theorem?
look at the paper
I do not give a shit, but you asked whether Schw is globally hyp
since it is a solution of Einstein eqns, it should be such if the initial conditions satisfy the assumptions of the thm
 
Being foliated isn't the same as being globally hyperbolic, though
Altho...
Time function...
What's the time function condition for GH
I forget
 
2:48 PM
it says unique, globally hyperbolic etc solution
 
Oh
Well Schw. is asymptotically flat
What is global smallness tho
 
Hm
3 downvotes in a row this afternoon
I wonder who it could be~
 
the downvote fairy
 
@yuggib I checked out that book from the library
It's fucking scary
 
2:53 PM
of course it is
it's some sort of holy graal of the analysis of PDEs applied to relativity
 
But your theorem doesn't help
 
why? the thing you have in mind do not fit in the assumptions?
 
Schwarzschild isn't geodesically complete
So it must fail one of the assumptions!
 
:-D
I see
 
Dunno which one
 
How the fuck did you find that
 
I used
The google
 
Dammit now I need O'Neil
Time to buy more books.
Might as well get Kobayashi-Nomizu, Spivak and Evans.
Reed and Simon
Choquet Bruhat
All Rudins
Steenrod
Are there any other good books?
 
The Bible
It is The Good Book
 
I have that memorized.
 
3:04 PM
If you want math, though, the Veda is the one you want I think
 
I'm not a heathen, after all.
 
IIRC the Veda has some math in it
Bible does have an approximation of pi
but that's about it
 
lol
 
We need more holy books with some proofs in them really
Eternal life and the Cauchy-Schwarz theorem
 
fucking prof doesn't have his office number listed
what's up with that
 
3:09 PM
Schrödinger's office - you only know if any particular office is his after you've looked inside.
 
Who the fuck puts this in their CV
@ACuriousMind No, I have to find the elven prof
his wife does QFT
huh
I can't find his CV
help
ah, found him in the campus directory -- ridiculous
I'm like one room over from him right now, lol
Not there, of course, when will I learn that profs are never in their offices
 
@GPhys which two universities?
 
3:24 PM
@Slereah Very interesting, and I'll be stealing that for a Q&A
unless you want to do it
seriously, what did you google
 
globally hyperbolic schwartzschild metric proof
 
but what about the interior
maximally extended schwarzschild
@Slereah I googled that exact thing
 
mb google better
 
and now it comes up in google because I clicked on your link
@ACuriousMind I think Google just doesn't work correctly for me
 
do some google lifts
 
3:27 PM
not smart enough, apparently
@Slereah what about maximally extended though
 
Dunno
 
well what are the null geodesics in KS coordinates
those coordinates are good across the horizon, right
 
yeah
and since it has null coordinates IIRC
Should be easy enough?
 
GR is literally the worst
@ACuriousMind is QFT more fun than this
 
Oh wait no
Which one is the Schw. with null coordinates
I think it's basically a null version of Kruskal
U = T - R, V = T + R
Or something
 
3:34 PM
wait
schwarzschild is not a warped product
yup, this is some BS
 
So this just blew my mind
83
Q: Auto-inserting Stack Overflow affiliate into all Amazon book links

Jeff AtwoodWe have officially discontinued the Amazon book affiliate remnant ads, since despite our best efforts they don't perform well for our audience and cannot be made to perform well. We've often wondered, Would it be a problem if all Amazon links were converted to affiliate links? I'm thinking this...

for your enjoyment
 
oh wait
I'm stupoid
@ACuriousMind Ahhhhh, $S^2$ is complete (in the Riemannian sense) by Hopf-Rinow since a compact metric space is complete (in the topological sense), right?
 
@EmilioPisanty What blows your mind? That they have a script that automatically does that? That they're doing it at all?
 
holy crap why is O'Neil $70
bah, not getting that
 
I have no idea what drives prices for physics books
Some are $20, some are $200
 
3:45 PM
it's a math book
I don't get physics books anymore
If we extend the Schwarzschild spacetime down to the singularity, it's still topologically $\mathbb{R}^2\times S^2$, right?
 
Well if we add a point it will have a different topology
 
0
A: Wave equation for de Sitter invariant Green's functions

Han YanThe master thesis by J. Hartong, On problems in de Sitter spacetime physics has some detailed explanation from Eq 2.5 to 2.6. I was able to get the final answer following his notes. Two important intermediate steps are: $\partial_aZ=-l^{-2}(\frac{X^d(y)}{X^d(x)}X_a(x)-X_a(y))$ and $(\partial...

@Danu I like how this guy did 6 pages of calculations and was ignored
@Slereah oh no, without the singularity
just extend past the horizon
I wonder...can you argue that the exterior is glob hyp and the interior is glob hyp
so the whole thing is glob hyp?
not sure if I buy that.
 
Tough sell
I would ask proof
Since there's not even an overlap between the two
 
yes
I have to work in some messed up coordinates I bet
Damn, I should have brought Zee from home.
he really explains the various coordinate systems well.
 
Eddington mb
It's null and crosses the horizon
 
3:54 PM
well what are the coordinates in the Penrose diagram
the one that JD loves so much
See, there's a Cauchy surface
I just how to show that it actually is one
and the theorem in O'Neil, which I just found in BEE as well, makes things a lot easier
 
Kruskal I think?
Hm Kruskal is not quite conformal to Minkowski
 
Danu is gonna be pissed when he sees this
wtf is a Borel measure, anyway
in theory we can prove the glob hyp with Borel measures
according to BEE
 
wot
 
HE apparently messes around with Borel measures in chap 6
they define a volume measure so that $\mu[M]=1$
 
Is that some partition of unity business
I dunno
 
4:01 PM
we basically define a function $$t(p)=\log \frac{\mu(I^-(p))}{\mu(I^+(p))}$$
 
Is that the time function?
 
then check for any inextendible curve $\gamma$, that $\operatorname{im}(t\circ\gamma)=\mathbb{R}$ and that $t$ is continuous
@Slereah yup
then the spacetime is globally hyperbolic
 
So basically you check literally how much spacetime is in the future
 
mb
Shit, the proof is in a German PhD thesis
 
Well you read german
 
4:03 PM
yes, but I can't get the paper
I'd have to email the librarian there
and I probably would not understand all of the technical terms
so we'd need @ACuriousMind to help
 
der spacetime
raumzeit
 
they missed the great chance to call it zaum
 
@0celo7 That's already a word.
 
I know
Tame, right?
 
No, that's zahm
A Zaum is a bridle
 
4:09 PM
Oops
I don't know what that means in English
lol
 
The hmong
The empire everyone forgot
 
yeah, no clue what "bridle" is
never heard of it
 
It is a horse thing
 
I already googled it
 
Also : a horse hairdo is called a mane
 
4:13 PM
I knew that
who doesn't know that?
 
bald horses mb
 
do horses speak English
@Slereah Dude, why is $\{I^+(p)\mid p\in M\}$ an open cover
I know why it's open
 
We discussed this a while ago didn't we
 
nope
 
A point $p$ is always in the future of another point bc normal neighbourhood
 
4:17 PM
Why does every point have a normal neighborhood though
 
Because it is a spacetime
On a manifold
And not a manifold with boundaries
 
I'm not convinced
Don't make me say it
 
Manifold with boundaries, $I^+$ isn't a cover
Check HE mb
It discusses the hood a lot
 
so do Jost, do Carmo, all of the Riemanian books
 
Well then look there mang
What do you ask me for
 
4:19 PM
doesn't mean I believe them
 
Do I look like I'm made of topology
 
Yes!!!!
 
Do you see any open sets on my face m8
 
Yes, your eyes are open and convex
 
@ACuriousMind
 
4:21 PM
@DeNiSkA He's got you on ignore.
 
@0celo7 ya i was checking :( [this is making me quite upset]
just because of my stupid exclamation marks
 
@Slereah this is coming out soon
lots of global geo, p. cool
 
But
Riemannian
Instead of Lorentzian
 
Riemannian geometry is still pretty cool
 
How many big theorems apply to Riemannian and not Lorentzian?
Outside of all paracompact manifolds having a metric
 
4:25 PM
@Slereah None.
What I was wondering is this
Has anyone taken spacetime $(\mathcal{M},g)$, then Wick rotated to space $(M,h)$, done crazy shit on this space, then rotated back?
like Seiberg-Witten theory
 
Probably
 
we have spinors and shit on spacetime already
 
Problem is like
you can't guarantee that it will be nice
Rotating a Lorentzian spacetime won't necessarily give you a real riemannian space
and vice versa
 
proof?
 
Iunno
Probably not too hard to make up an example I guess
 
4:28 PM
I've heard $g=\mathrm{d}t\otimes \mathrm{d}\theta$ is Lorentzian
allegedly
yeah, $\det g=-1/4$
 
yeah you can see that a wick rotation is gonna make that shit complex
 
@ACuriousMind What exactly was Donaldson's work on
Real manifolds?
Wait was that even Riemannian geometry
 
What part of Donaldson's work? :P
And why can't you look that up yourself?
 
@ACuriousMind He did more than one thing?
@ACuriousMind How?
 
^this
 
4:30 PM
Huh?
 
I know you never saw any movies but I won't believe you don't know Donald Duck
 
@0celo7 I dunno, by reading his Wikipedia page, for example?
 
Oh, is he the Looney Toons thing?
@ACuriousMind he has a Wikipedia page o.o
I don't know his first name
 
You don't need to! Just type "donaldson math" into Google!
 
Can someone ban @0celo7
 
4:33 PM
What the fuck
@ACuriousMind huh
 
You really need to learn to look things up on your own.
 
shakes old man fist
Yeah really @0celo7
You need to improve your googling
Maybe take one of those classes for old people on how to use the internet
 
:(
They never taught us in school how to Google things...
How am I supposed to have figured it out by myself
@Slereah why do you want me banned
 
For pretending you don't know Donald Duck.
pretty heinous crime
 
@0celo7 Trial-and-error.
 
4:38 PM
@ACuriousMind I don't know how to do that
 
@ACuriousMind How would someone have known to google "donaldson math" if they didn't know that was Donald duck?
 
^
 
Well maybe it's time to go back to primary school
Learn about shapes and colors
 
what's that
 
@HelkaHomba lol, what? Ocelot asked me "What exactly was Donaldson's work on?", he already knew that was a mathematician.
 
4:40 PM
Ah, I see
 
OH WAIT
It's 17:41
Gotta skedaddle!
 
...
 
Smell ya later jerks
 
?
does @Slereah ever work while at work
 
that is part of the mystery
 
4:41 PM
I think he's either here or eating reindeers :P
 
lol
For the record, I do know of the Donald duck
@ACuriousMind why can't I google
even when I google, I can't find the answer
 
How many different combinations of keywords do you try before declaring "I can't find the answer"?
 
In Soviet Union, answer always find you.
 
@ACuriousMind I seriously searched for that Schwarzschild thing for 30+ minutes
Read a half a dozen papers on arXiv
Then the Frenchie finds it instantly!
 
@ACuriousMind That they're doing it at all
 
4:52 PM
Damn, new shoes are giving a blister on my right foot.
@Slereah Visser hasn't even shipped yet :/
 
5:30 PM
@ACuriousMind why do people have such a hard time typing "0celo7"
 

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