The h Bar

12:01 AM

*lecturers

:-)

Hi, Can someone provide me some self reading material for Condensed matter theory? I've done QFT previously for which I could happily read Peskin supplemented with David Tong. Can you please suggest some references along those lines? Thanks

Mithrandir24601

@skullpatrol The second one was in my MSc and covered considerably less than my first and (I felt) didn't do it in any particularly great way, so distinctly average. The third was pretty decent - I liked the way he did things and was essentially a more mathematically detailed version of the first :)

0celo7

12:23 AM

@Mithrandir24601 Who was it?

Let's see. You're a Brit, so...Hughston or Tod?

Felice/de Clarke?

user685252

12:39 AM

Sounds like the first guy was a real gem.

user685252

1:32 AM

She wins $250,000 in educational prizes for this??

skullpatrol

1:51 AM

@heather^

Anonymous

2:29 AM

@SaiKrishnaDeep Shankar's new book has a few chapters on CMT. Heard it's good but haven't used it.

ooolb

@SaiKrishnaDeep i can

still there?

Anonymous

@ooolb Just type it. He can read your message later :) I'm interested in this too

ooolb

well i need to know what level he is at

or what he wants to learn

Anonymous

He said he knows QFT...

Anonymous

@ooolb Ya, that is true

Anonymous

2:41 AM

CMT is too huge a field

Anonymous

*broad

ooolb

@Blue not enough information

Anonymous

@ooolb Agreed.

0celo7

Blue acting like he's a physician

Anonymous

@0celo7 "physician" ?!

0celo7

2:48 AM

someone who does physics

Anonymous

...

0celo7

@Blue yes?

Anonymous

Yes?

enumaris

not sure that word means what you think it means

0celo7

I agree @enumaris

@Blue mb look it up

enumaris

2:56 AM

I turned my neural net into a 37million parameter beast...takes forever to train it now

Avantgarde

Hi physics

well, see you

ooolb

3:36 AM

see you later space cowboy

0celo7

@ooolb are you at perimeter?

ooolb

right now?

no

0celo7

If so, I need you to find Carl Bender and interrogate him at gunpoint about matched asymptotics

ooolb

oh i know that dude

he wrote that book

on approximations

0celo7

ok go find him

ooolb

3:40 AM

what's in it for me?

0celo7

my love and admiration

ooolb

i already have that.

0celo7

you wish

ooolb

also is he at perimeter right now? i'm pretty sure he was just visiting back in 2013.

0celo7

oh, was he?

ah

he's at St. Louis

ooolb

3:42 AM

ooo the h bar is quite empty right now

we're basically alone

kinky

0celo7

I'm leaving now

ooolb

😢

0celo7

oooooooooooooooooooooo

I have two perturbation terms

there's two boundary layers

do your homework, kids

ooolb

if you do your homework at school is it schoolwork or homework?

0celo7

homework

@ooolb do you want an exercise?

ooolb

3:47 AM

send on discord.

save me the public embarrassment thanks

Secret

Last night dream has a lot of crazy scifi stuff:

1. A strange warp drive geometry and JohnRennie's comment on it

0celo7

@ooolb it's there

Secret

2. A weird particle or state that is made of a superposition of a torus region with clockwise momentum and anticlockwise momentum, resulting in one that has no momentum along the major circumference of the torus but still nonzero momentum in directions that are not pointing along the torus

0celo7

@ooolb sorry now it's there

ooolb

k

i never did LSD before but if I do I'll make sure to do it with @Secret

Secret

3:59 AM

I take no drugs. unless my kidney medicine cyclosoprine A has strange side effects of creating strange dreams

0celo7

@ooolb so did you see it?

the computations involved are formidable

ooolb

take drugs all the time, cause I like to lose my mind, every day, edge close, to the day you overdose.

Secret

As will be elaborated with some annotated pictures later, the particle like state mentioned in 2 seemed to behave like a gravitational analogue of anapoles

where imagine a region of spacetime that got simutaneously frame dragged in the clockwise and anticlockwise direction

Since gravity does not obey superposition, I am not even sure if the result of having two opposite directions of frame dragging will cancel each other out

The dream also mentioned of some GR simulator that can simulate any type of spacetime

0celo7

@Secret I need this

Do you know how awesome that would be

one could test many conjectures

ooolb

is it not on steam?

Secret

4:07 AM

Same thought as you, however I think the major challenge of such simulator is the computational cost. GR calculations with its highly nonlinear nature, might be more costy than a computation of a protein.

However I can see some ways approaching it. Recall how Slereah was building some kind of spaceitme database, that could be the first step. Next, one might be looking for machine learning techniques to help on the simulation by using the classifications of spacetimes as machines are known to perform very well on sign problems as a recent paper has shown

Since GR equations are ultimately a system of 10 nonlinear PDEs, it might be possible the solution strategy has some relation with the class of spacetime that is under consideration, thus that might help heavily reduce the parameters need to consider to simulate them

0celo7

I once asked how hard it would be to do a GR sim of something with just discrete symmetry (cubical) and two people said it would be a very hard PhD thesis

enumaris

actually 6 nonlinear PDEs right

ooolb

we can sleep with secret tonight and figure out how the sim works in his dream.

free Phds

0celo7

@enumaris don't forget the constraints

and the gauge conditions

and matter equations if you have them

enumaris

that's what I mean tho, the 10 PDE's can be reduced to 6 due to "gauge symmetries" right

unless I remembered wrong

0celo7

4:15 AM

@enumaris Yeah but you still have to solve the gauge constraints

It's a giant mess because those also depend on the solution

you need background metrics and the whole thing is pretty bad

But I don't know anything about the numerics. I should take a class in grad school

enumaris

I just mean this: The EFE is a tensor equation relating a set of symmetric 4 × 4 tensors. Each tensor has 10 independent components. The four Bianchi identities reduce the number of independent equations from 10 to 6, leaving the metric with four gauge fixing degrees of freedom, which correspond to the freedom to choose a coordinate system.

there aren't actually 10 independent equations

0celo7

@enumaris But choosing the right coordinates is a nontrivial task

You want wave gauge

So to pick the coordinates you have to solve more PDEs

Secret

@ooolb Even if that is really possible (I always can talk about things in a non joking perspective), the issue is that 1) Unlike other people, I cannot incubate my dreams for a certain topic due to Mechanism 1 (consicous desires have reduced probability of appearing in dreams), and 2) For 6 years, my dream still yet to show any sign of revisiting the exact same idea, and there are no known instance of either sequel dreams nor recurrence dreams

enumaris

mmm

ooolb

it's not impossible unless it's impossible.

where are you should I bring my pillow

enumaris

4:20 AM

impossible is nothing

-adiddas

adidas*

I can't spell -.-

0celo7

@enumaris we used to have a numerical GR guy who complained about the constraints being very hard to maintain throughout the solution

you have to trim in a clever manner to keep the constraints fulfilled without killing the solution

Secret

@0celo7 I felt this aspect can be helped by machine learning. You can train a neural network with some PDEs of a known class with some known constraints, and let it figure out the best solution for some new PDE after say training it on 1000 different PDEs

Actually that makes me wonder, are the space of all coordinate choices more than all possible moves of Go?

o.o

what?

hwat?

4:27 AM

hwta?

Secret

ok, let me ask in a different way. What are the possible number of gauges modulo isomorphism?

enumaris

uncountably infinite?

x->x+a for any real constant a consitutes a valid coordinate transformation

well

constrain that to a neighborhood

0celo7

what does he mean by isomorphism though

enumaris

i dunno

Secret

say something like x->xsin^2x+xcos^2x is isomorphic to x->x

so the isomorphism here is some given function that can be represented as different expressions

enumaris

4:33 AM

isomorphic = one to one and onto mapping? All coordinate transformations are diffeomorphisms of the manifold...as such...they are also isomorphisms...and so...1?

Secret

right, I see, so it's not a very useful notion in counting number of coordinates in the context of manifolds

enumaris

I think the answer is either 1, or uncountably infinite depending on what you mean...

Secret

I am trying to find a good way to sort the gauges in equivalence class that are easily manageable but so far I can only think of the class of gauges related by linear or affine transformations

enumaris

I can't imagine a way to preferentially pick out only a finite number or even a countable infinite set of coordinate transformations...

maybe

like...

uh....

There is a maximum number of symmetries of a manifold, i.e. the number of killing vector fields admitted by a manifold.

in 4 dimensions the maximum number for that is 10

given by the 10-dim Poincare group

0celo7

5:01 AM

@Semiclassical :)

ooolb

@0celo7 hyperbeam?

0celo7

@ooolb fluid flow over a plate

enumaris

kamehameha?

Secret

5:27 AM

The following is what the warp drive saw in the dream look like. Red denote regions where the spacetime is expanding and blue denote the region where the spacetime is contracting

and, don't ask me why it has those weird portals or tube like geometries, it is simply what it looks like in the dream

though given the original alcuberrie drive can actually host CTCs, it may be not that far fetched

enumaris

If the universe can have CTC's it's bad news for 0celo!

orbit-stabilizer

@Secret I didn't know you ventured here

Secret

enumaris: From what I understood from the dream, the warp drive showed here may be some variation of the alcuberrie metric with a global topology that has 4 holes in it whereas the original alcuberrie drive, if I recall, don't have holes

orbit stabilizer: h bar is my home chat, because this is the first SE chat I joined. Maths chat is the 2nd one I joined, followed by periodic table, biosphere, factory floor and many others

enumaris

5:44 AM

can't really do ADM GR without global hyperbolicity afaik

bad news for 0celo indeed

Secret

also another interesting thing is that Dream Johnrennie has a remark about the flat spacetime bubble in the middle:

He said that the bubble of that radius [of the order of a starship] cannot be stable with spherical geometry

As for the real Johnrennie, I am not sure what he will say, but from what I knew, I don't recall anything controlling the size of the flat spacetime region of any warp drive metrics

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