The h Bar

Mostafa

20:00

Holy moly @0celouvskyopoulo7 is back. No more dead chat

0celouvskyopoulo7

I don't think the chat was dead

Mostafa

It was

0celouvskyopoulo7

not according to @Secret

Mostafa

not always but most of the time

Danu

It was less distracting than usual :P

0celouvskyopoulo7

20:03

if y'all want to ship this over to math, feel free

1

Q: Density of analytic functions in Sobolev spaces

I've seen this mentioned in a few physics books (Hawking-Ellis, Stewart), but never with any details. Let $(M,g)$ be an analytic Riemannian manifold, and $U\subset M$ an open set with compact closure. Define the Sobolev space $H^k(U)$ as usual. Is $C^\omega(\bar U)$ dense in $H^k(U)$? I think a p...

Mostafa

Domestic moderators should lobby in such cases to end the suspension sooner,

bolbteppa

A nice motivation for weak derivatives is that integration ignores a function on a set of measure zero, but derivatives can't even handle $|x|$, why can't a derivative ignore a function on a set of measure zero also

Mostafa

especially @ACuriousMind

We've voted for you, even rallied and campaigend and expect you to represent us in the moderators club

0celouvskyopoulo7

@Mostafa meh, let it be

bolbteppa

Thus you want to define your derivatives in terms of integrals to achieve this via ibp

0celouvskyopoulo7

20:05

I was able to talk to the people I needed to talk to

Balarka Sen

I think mod suspensions are usually unanimous. But yeah, better to not let that topic come up again.

I can work on easy math, learn foliations, or try to watch a movie. What will I do?

Mostafa

A strange mix of Closed time-like curves, causality, depression, suicide, etc.:

vimeo.com/33367784

10 minutes.
Strongly suggested to ya'll especially @Slereah @Secret

0celouvskyopoulo7

@BalarkaSen I am watching a movie

Balarka Sen

which

0celouvskyopoulo7

Full Metal Jacket

bolbteppa

20:10

@0celouvskyopoulo7 it's good, what is boundary straightening

Balarka Sen

Kubrick eh

Not a big fan of that man, but he's good

bolbteppa

Zizek - Full Metal Jacket

►

Danu

FMJ is really great

Balarka Sen

Is that... Zizek sitting on a toilet?

bolbteppa

Never watch the movie in the same after thinking about it like that

haha

Yes

Balarka Sen

20:11

@Danu I watched 2001 and never really liked it.

Although I like it from the artistic perspective. Not my favorite, though.

bolbteppa

2001 was horrible, but FMJ and some others are amazing

Still want to watch Barry

Danu

2001 was good.

Balarka Sen

Plan to watch A Clockwork Orange someday.

bolbteppa

Fell asleep to 2001, Clockwork is great

0celouvskyopoulo7

@bolbteppa cut up the boundary and map it to pieces of the half-space

Balarka Sen

20:13

@Danu I dunno, have you read Tarkowskij's criticism of it, and his "response movie"? :P

0celouvskyopoulo7

you can do the estimates in the half space, then get an estimate on the error you get from the coordinate change

Balarka Sen

*seen his

bolbteppa

I wish I had read en.wikipedia.org/wiki/Regularization_(mathematics) a long time ago

Danu

@BalarkaSen No, but I honestly feel like it's not nice to let your opinion be determined by meta-context (such as criticism from some other director)

Balarka Sen

@Danu I am not basing my opinion on Tarkosvky's. My opinion on that movie just happen to be identical to him :)

I found his interview long after I thought I did not like 2001.

And why, etc

Mostafa

20:16

@blue Something strange happened: I wanted to buy an animation tonight. There was an option on their website saying if you've paid but haven't recieved the download link, send number 8 to number xyz....

I sent it and they sent me back the download link!!!!!
(didn't pay)

Bernardo Meurer

@bolbteppa @BalarkaSen Zizek asked me out for lunch when I go to Ljubliana today :P

bolbteppa

Wow, tell him his insights about movies are awesome, but Chomsky is right :p

Balarka Sen

I did not like Zizek's insight on Stalker.

Bernardo Meurer

I don't like Chomsky :P

Balarka Sen

But that's the only review of him I have read, so there's that.

Bernardo Meurer

20:18

(as a philosopher)

Balarka Sen

@Bernardo Neato!

Danu

@bolbteppa But isn't this sort of... the "standard" interpretation?

bolbteppa

No idea

It's like a Freudian/Lacanian take on it

Danu

Is it? I don't know

This you-need-to-be-humiliated-to-belong thing is super well-known and common to many hierarchically structured organizations

bolbteppa

Yeah but what he says about the ironic distance and efficiency is pretty interesting

Slereah

20:25

You can't say that here @Danu

not until you have kissed the goat!

Danu

@bolbteppa Mhm, he puts it nicely

bolbteppa

Slavoj Zizek - Blue Velvet

►

Balarka Sen

Oh, let's see what he has to say about that.

Blue Velvet is an interesting movie but not Lynch's best to me.

(Indeed, might be the weakest in all of what I have watched from Lynch so far)

Abcd

The characteristic $X$ rays wavelength for the lines of the $K_{\alpha}$ series in elements X and Y are 9.87 $A^o$ and 2.29 $A^o$ respectively. If the Moseley's equation $v^{1/2} = 4.9*10^7 (z-0.75)$ is followed, what are the atomic numbers of X and Y?

0celouvskyopoulo7

seems like a homework question to me

Abcd

20:33

@0celouvskyopoulo7 No. Practice question.

I have tried many times

And I dont ask HW questions!

Can someone please help??

0celouvskyopoulo7

people in this chat don't know actual physics

4

sorry

Abcd

@0celouvskyopoulo7 Are you being sarcastic?

Why?

0celouvskyopoulo7

I am being 50% sarcastic

Slereah

what is the other half

Abcd

@0celouvskyopoulo7 Please don't be rude then

I just asked coz I was unable to solve

You could have said a simple no if you didnt want to answer!

0celouvskyopoulo7

20:37

@Slereah milk

ACuriousMind

@Slereah Implying the theory some of us do is not "actual physics", I'd wager :P

Mostafa

@0celouvskyopoulo7 bring it down to %10

0celouvskyopoulo7

@ACuriousMind hello

Slereah

Can't be, since he's not a physicist

ACuriousMind

@Abcd Well, even if such questions are not forbidden here, it would be nice if you told us what you've done and where you are stuck, specifically

0celouvskyopoulo7

20:38

@Danu I have something that will trigger you

Slereah

unfortunately the days where it was cool to mock string theorists for not doing real physics is gone

I mean you still can, but the competition isn't looking good

ACuriousMind

@0celouvskyopoulo7 heyhey

0celouvskyopoulo7

@Danu this is one theorem:

Balarka Sen

@bolbteppa Interesting. Of course, the whole character of Frank is full of Freudian subconsciousness and the film does have an Oedipal connotation. I think he really does a good job at summarizing that.

Danu

@0celouvskyopoulo7 That's incredibly badly written, then.

0celouvskyopoulo7

20:41

@Danu The book is a bit of a troll, there's an introductory part where he states the main result

the proof is spread out over a few hundred pages

Danu

ok...

0celouvskyopoulo7

but!

Notice the various symbols

\mathsf, \mathfrak

Danu

terrible

0celouvskyopoulo7

the notation is pretty darn strange

the use of \mathsf, especially

Balarka Sen

(I am also impressed that he mentioned that Dorothy's apartment is the hellish room of fantasies, and is the root of the primal instincts of the characters of the movie, in contrast to it being a "disease" of each of those individuals or something)

Ugh, my internet.

0celouvskyopoulo7

20:44

@ACuriousMind If I have a question about the chat, am I to direct it to the meta room?

Slereah

I'm reading on the link between the stress energy tensor and the Belinfante tensor

It's not pretty

bolbteppa

@BalarkaSen any opinion on this youtube.com/watch?v=qPsgsuSvbXo

ACuriousMind

@0celouvskyopoulo7 Yeah, start meta conversations in the meta chat if you can help it (no issue in pointing others here once to the fact there's a conversation happening there, though)

0celouvskyopoulo7

How do I even get there

ACuriousMind

Backup Room – The h Bar

A backup room for when The h Bar is busy. (chat.stackexchange....

If you want to hear my input on something, you'll have to wait a bit though 'cause I gotta hunt some food

0celouvskyopoulo7

20:47

good luck in the Heidelberg wilderness

Balarka Sen

@bolbteppa Heh, I know of his transcendental meditation business, but I don't know much about it to comment on anything. I am a contrarian, so of course I am skeptic about this, but hey he does seem good at managing his ideas - he makes great movies!

I liked one comment of David Cronenberg on him though. Upon asked if he could beat Lynch at wrestling he remarked "I think so. Especially if he was doing one of those meditations at that time."

:P

0celouvskyopoulo7

@Danu So did you ever get a handle on the heat flow proof of AS?

Danu

I'm still in the seminar, yes

Mostly learned that Roe's book is absolutely garbage if you don't already know the analysis

0celouvskyopoulo7

Aha. Is the approach via pseudodifferential guys?

Danu

I don't know what that is supposed to mean

It is about asymptotic expansions of the heat kernel

0celouvskyopoulo7

20:51

Yeah, but what part of the analysis were they assuming?

Danu

idk exactly, but too much for me haha

At least all the Sobolev embedding stuff

0celouvskyopoulo7

Yes, one of the least fun but most useful parts of analysis

Danu

But more too... whatever

The seminar is pretty disappointing.

0celouvskyopoulo7

Shame

I'm taking an "advanced analysis" seminar next semester, it looks really good. Operator algebras, representation theory, ergodic theory.

Bernardo Meurer

@0celouvskyopoulo7 Good lord

0celouvskyopoulo7

20:57

@Slereah What do you make of this definition?

If $(M,g)$ is a GH and future causally geodesically complete spacetime, late time observers are oblivious to topology if there is a Cauchy surface $\Sigma$ s.t. there is no causal curve whose past contains $\Sigma$?

Slereah

How can you have a causal curve whose past doesn't contain $\Sigma$

That would be a bad Cauchy surface

0celouvskyopoulo7

that's what I'm wondering

Bernardo Meurer

@0celouvskyopoulo7 What's an operator algebra?

0celouvskyopoulo7

an algebra of linear operators on a Hilbert space

Bernardo Meurer

What's Operator Theory?

0celouvskyopoulo7

21:06

the theory of operators on Banach spaces

Bernardo Meurer

It's specific to Banach Spaces, always?

0celouvskyopoulo7

Probably not, but Banach/Hilbert spaces are the most common

Slereah

@Qmechanic what the hell is that page setting

7

A: Stress-energy tensor for a fermionic Lagrangian in curved spacetime - which one appears in the EFE?

$\require{cancel}$I) OP is considering Dirac fermions in a curved spacetime. OP's action has various shortcomings. The correct action reads$^1$ $$ S~=~\int\!d^nx~ {\cal L}, \qquad {\cal L} ~=~e L, \qquad L~=~T-V,\qquad e~:=~\det(e^a{}_{\mu})~=~\sqrt{|g|}, $$ $$ T~=~\frac{i}{2} \bar{\psi} \s...

0celouvskyopoulo7

via the Gelfand-Naimark theorem, one can also abstract and talk about $C^*$ algebras without reference to a space

Slereah

What is that vile block of equations

0celouvskyopoulo7

21:08

I don't know much about operator theory proper

I know standard functional analysis

operator theory is orthogonal to my main interests for the most part

Slereah

QFT stuff always seems weird to me because everyone wants bounded operators but literally none of the QFT operators are bounded

I know you can kind of make them bounded, but then how do you transform it back

If you bound your operator $X$ with $e^{-X}$, is the expectation value just $-\ln(\langle e^{-X} \rangle)$?

Also is there a standard notation for converting distributions to functions if such a mapping exists?

0celouvskyopoulo7

@Slereah what do you mean, bound it by $e^X$?

@Slereah The embedding $L^1_{\mathrm{loc}}\to \mathscr D'$ is usually just $f\mapsto T_f$ if you need a symbol.

Slereah

@0celouvskyopoulo7 Are you asking or are you disapproving of not checking if $e^{-X}$ exists first

0celouvskyopoulo7

I am asking what you are talking about

Slereah

@0celouvskyopoulo7 I need the opposite one

0celouvskyopoulo7

21:23

$e^{-X}$ exists in many circumstances

@Slereah Not all distributions are represented by functions, so there is no notation

Slereah

Not all numbers have an inverse and yet there is a symbol

0celouvskyopoulo7

Touche

I don't know of a symbol

Why do you need one?

Slereah

If the operator $\langle \psi, X \psi \rangle$ is unbounded, $\langle \psi, e^{-X} \psi \rangle$ isn't

(I don't know if it's always true but it's commonly used in QFT)

0celouvskyopoulo7

if $X$ is self-adjoint...probably.

Slereah

@0celouvskyopoulo7 To convert the stress energy tensor operator in semiclassical gravity into an actual stress energy tensor

0celouvskyopoulo7

21:25

@Slereah I don't think there's a notation

Just use words

bolbteppa

@BalarkaSen my concern is the people who apparently went nuts after it and what it really does

Slereah

@0celouvskyopoulo7 What am I, an english major?

0celouvskyopoulo7

I'd imagine $||e^{-X}||\le e^{-\inf \sigma(X)}$

@Slereah no, a French major

Slereah

I am neither

My last french class is quite a while back

0celouvskyopoulo7

then suffer

Slereah

21:27

Over 10 years ago

I think that if semiclassical gravity isn't too dumb, the renormalized stress energy tensor should always be a function

or at the very least, it should be a function if it is for the classical theory

Qmechanic

@Slereah : Do you have display/rendering problems? Or you are talking about the mathematical content?

Slereah

Is this supposed to be the way it looks?

Qmechanic

@Slereah : Yes.

Slereah

Bit hard to digest if compact

Hm

If I have $\partial_\mu \langle \phi(x) \phi(y) \rangle$, is it equivalent to $ \langle \partial_\mu(\phi(x) \phi(y))\rangle$

I guess it would be, by linearity?

Although that sounds slightly harder to prove for distributions than for functions

Since I can't just write $\partial \phi(x) = [\phi(x + \varepsilon) - \phi(x)]/\varepsilon$

Qmechanic

21:49

@Slereah : What is $\langle\ldots \rangle$ in this context?

Slereah

Also I'm not 100% sure that $$\langle \lim_{\varepsilon \to 0}\partial [\phi(x + \varepsilon) - \phi(x)]/\varepsilon \rangle = \lim_{\varepsilon \to 0} [\langle \partial \phi(x + \varepsilon)\rangle - \langle \phi(x)\rangle ]/\varepsilon $$

Not sure that putting the limit out of the product is kosher

@Qmechanic The expectation value with respect to some state

But of course the real case is going to be $$\partial_\mu \langle \phi[f] \phi[g] \rangle = -\langle \phi[\partial_\mu f] \phi[g] + \phi[f] \phi[\partial_\mu g] \rangle $$

Which I'm even less sure if it's true

Although I guess the same argument applies here, except with even more expansion

and I'm also not 100% sure that $\phi[\lim f] = \lim \phi[f]$

Qmechanic

@Slereah : It could include a time-ordering that mean that time differentiation acts differently inside and outside $\langle\ldots \rangle$.

Slereah

Time ordering I can deal with but I mostly wonder about it from an analysis point of view

bolbteppa

If I say 'phenomenological theories', what do you think of

Slereah

@bolbteppa stamp collecting

0celouvskyopoulo7

21:57

GDP

bolbteppa

Fermi model is phenomenological, I guess they mean a vague model/guess

Slereah

Phenomenological model is a model where you just fit your equation to a curve

you don't try to grasp at any underlying theory

bolbteppa

That's a good way to put it

0celouvskyopoulo7

@Slereah that's kind of the definition of what a distribution is...

if the limit is in the $\mathscr D$ topology...

Slereah

There's that at least

What about the limit of a Hilbert product?

0celouvskyopoulo7

22:06

Hilbert product?

Slereah

Sesquilinear product

0celouvskyopoulo7

Do you mean the tensor product?

Slereah

of a Hilbert space

0celouvskyopoulo7

Oh, the inner product.

What about it?

Slereah

Does the limit commute too in that case?

0celouvskyopoulo7

22:07

Are you asking if $(x_n)$ is a sequence, $x_n \to x$, $y\in H$, then does $\langle x_n,y\rangle \to \langle x,y\rangle $ hold?

Slereah

Hm, i guess put that way

it should yeah

0celouvskyopoulo7

Yes, because $|\langle x-x_n,y\rangle|\le ||y||||x_n-x||\to 0$.

Slereah

Semiclassical gravity is safe for another day

Jesus Christ this book never ends

0celouvskyopoulo7

that's what Spivak said when he finished volume 3

Slereah

Now I'm trying to prove that the semiclassical stress energy tensor of the scalar field can be expressed by the propagator

And the expression of that stress energy tensor is literally 5 lines

0celouvskyopoulo7

22:11

is the latest version on github?

Slereah

Last version was put on github 7 hours ago

0celouvskyopoulo7

also did you fix the log files

Slereah

It's not gonna be terribly different

log files?

0celouvskyopoulo7

the overwrite issue

Slereah

Oh yeah I need to find out how to remove them

Not so far though

0celouvskyopoulo7

22:13

Ah, the fabled Einstein-Vlasov equations

or the models for them at least

Slereah

0celouvskyopoulo7

Visser?

Slereah

Look at this beast

yeah

I think it's in Birrel too

What is even $g^\alpha_\mu$, does he just mean $\delta^\alpha_\mu$

Balarka Sen

@bolbteppa shrug. I think it's all a bit unintelligent.

Slereah

Wait what is $g^{\alpha \beta}(x,y,\gamma)$

I need to reread this a bit I think

0celouvskyopoulo7

22:21

a metric

Slereah

Yeah but why is it a bitensor

0celouvskyopoulo7

page?

Slereah

285

"The bivector $g^\mu_\nu(x,y,\gamma)$ parallel transports a vector at $y$ to a vector at $x$ along $\gamma$"

Why call it $g$ you lunatic

0celouvskyopoulo7

lol

Slereah

Calling a rank 2 tensor $g$ that's not the metric is certifiably insane

0celouvskyopoulo7

22:26

yeah i can't think of a good reason for that.

Slereah

journals.aps.org/prd/abstract/10.1103/PhysRevD.46.3388

To this day I still find new papers on CTCs

there's a neverending amount

bolbteppa

More word-interpretation, 'chiral' in SSB, chiral symmetry relating different numbers of pions?

0celouvskyopoulo7

$L^2L^1_\mu$

what madness is this space

Slereah

journals.aps.org/prd/pdf/10.1103/PhysRevD.43.3878

0

Q: Fluid gravity equivalent to relativity?

Fill a balloon with water and poke a hole. Water will be forced toward the hole. The hole is a gravitational body, the forcing is gravity. Is this a valid analogy? Can gravity be accurately understood as simply a fluid dynamical phenomenon, without resorting to any newtonian concepts or spaceti...

gravity

best question

0celouvskyopoulo7

2

Q: How stupid is this theory of gravity?

As will be evident, I am not a physicist. I've always been interested in physics but my education tapered out with general relativity and basic quantum mechanics, years ago. Several years ago a sort of thought experiment began to nag at me and I've wanted for those more knowledgeable to basically...

gravity

@Slereah this notation is a bit much

Slereah

22:35

which

0celouvskyopoulo7

$$||D_\mu^0f||_{L^2_{\bar p}L^\infty_{\bar x}}=\left(\int_{\Bbb R^n}\langle \bar p\rangle^{2\mu}\left(\text{ess sup}_{\bar x\in\Bbb R^n}f^2(t,\bar x,\bar p)\right) d\bar p\right)^{1/2}$$

so cluttered

not sure how to make it better

Slereah

What is that ass

ass sup

0celouvskyopoulo7

aka vrai max

essential supremum

Slereah

What makes it truer than the regular supremum

0celouvskyopoulo7

$\text{ess sup}_{x\in X}f(x)=\inf\{k\in\bar{\Bbb R}:\mu([f\ge k])=0\}$.

$f$ equals a larger number only on a set of measure zero

Slereah

22:42

Ah ok

what to use for the interior product

$i_X$ or $\iota_X$

0celouvskyopoulo7

it's the measure theoretic sup, since sets of measure zero are forgettable

$i_X$

@Slereah isn't $E=mc^2$ a worthless expression

what does $E$ even mean there

Slereah

it's the Hamiltonian

Or timelike component of the stress energy tensor in the rest frame

0celouvskyopoulo7

but why is it an "energy"

what does energy even mean?

if you say Nother charge I will slap you

Slereah

Historically it's just some conserved quantity that people noticed converted into different forms across theories

That's the historical reason for energy to be a thing

Conserved quantities of mechanics, electromagnetism, thermodynamics, etc that could turn into one another

I don't think people really cared about "energy" until those things became big

Energy was probably in the equations somewhere but nobody made a big deal

and that is also true of $E = mc^2$

There is some equivalence between that energy and binding nuclear energy and radiation energy

and then pop science got a hold of the word and now nobody can shut up about energy

0celouvskyopoulo7

"Since there is an error in the proof of the existence of a maximal globally hyperbolic development, a complete proof (as well as an explanation of where the error occurs) can be found here."

Jeez, you write a book on the Cauchy problem and can't even get the main theorem right?

Slereah

22:54

lawl

Slereah

23:06

I don't know why we say there aren't any quantum gravity experiments, really

There's a few

They're not all glamorous but still nice

0celouvskyopoulo7

@Slereah Aha. He knew about the error in his first book, so the second one has the complete proof.

Apparently Geroch and Yvonne had an incorrect proof :o

Slereah

not an easy proof, I assume

0celouvskyopoulo7

It is not, and the argument in HE is not great either

HE is pretty sketchy

I still do not understand that analyticity thing

Just win baby

23:32

yo

Emilio Pisanty

@JohnRennie Possibly, but mostly I think is my naturally low tolerance for BS.

Just win baby

BS has its own reasons for existing, no? @EmilioPisanty

0celouvskyopoulo7

@Justwinbaby who are you?

Just win baby

23:47

a raider fan

who r u?

0celouvskyopoulo7

@Justwinbaby A Russian

Just win baby

cool

0celouvskyopoulo7

Oh, do you know the old woman?

Just win baby

I know the old man and the sea

is a good book

0celouvskyopoulo7

Moby Dick?

Just win baby

23:52

too long

0celouvskyopoulo7

Thailand Street Food - HORSESHOE CRAB Salad

►

Backup Room – The h Bar

Transcript for