The h Bar

0celo7

17:00

you're lucky JD isn't here

Slereah

hm

Fermi coordinates are only for geodesics apparently

I wonder what it is for a general observer

I guess you need to rewrite it so that the connection compensates the acceleration

0celo7

GR in general frames when

@Slereah what

I thought this was easy as pie

Slereah

Easy peasy lemon squeezy

0celo7

like your mom :)

@dmckee So how's the semester going for you?

obe

@0celo7 I'm lost and behind.

I'm dying.

Slereah

17:06

I think the coordinate transform may just be the equation of the curve

Huy

rip

0celo7

@obe I agree with the Swiss

rip

obe

:(

I'll make a come back.

0celo7

ok

@Huy what is the German word for "flux"

Huy

I'd guess Fluss

but I never had any physics in German

Slereah

17:11

Hm

Apparently there's a specific term for the metric for an observer

The Frenet-Serret basis

Never heard of it before

Apparently you make one of the tetrad equal to the tangent of the curve

And get three orthogonal tetrads for the rest

arxiv.org/pdf/1211.0222v3.pdf

^here for details

0celo7

@Slereah Gourgoulhon does that for SR

Slereah

I s'ppose yes

0celo7

@obe how far are you behind

Slereah

It's one of those weird things that is absent from most GR books

obe

@0celo7 3 problem sets and 3 lectures.

...rip?

dmckee

17:23

@0celo7 The usual. Had good teaching days and bad ones; made a bunch of mistakes but learned useful lessons from some of them; too busy and too stressed to reliably make good use of the time when I get a break.

Slereah

Also what kind of name is Gourgoulhon

Is he an ogre

dmckee

I've had a research student quit out from under me (sad) and another throw himself into off-campus work with the folks who gave him an internship over the summer (good!), but found a new kid some promise if more enthusiasm than sense yet.

Slereah

Hey @0celo7

Let's make a GR book

It will have ALL THE THINGS

dmckee

Committee work never seem to achieve anything, but still takes a lot of time, but by giving a single professor the authority to make a change for the department we've gotten a few things actually done. And I was only the designee once.

0celo7

Yes!

Combine HE with Straumann

Also throw in Stefani et al.

Slereah

17:27

And some Visser

And some Wald

0celo7

and throw in some general frame crap

Slereah

and Birrell

0celo7

yes QFT definitely

Slereah

Hm, what else is there

0celo7

2000 page GR book :D

obe

17:27

I would read it 100%.

0celo7

do we cover the mathematics?

Slereah

2000 pages sounds a bit short

Sure

I don't want to do Schwarzschild until chapter 40 or so

I want empty space to be an ordeal to read through

0celo7

lol

Slereah

Also, here's a rule

No "Check this book for the proof"

0celo7

veto

Slereah

17:30

NO BIBLIOGRAPHY

0celo7

I don't want to prove sobolev embedding crap

Slereah

hehh

Why do you need Sobolev, is it for the initial value problem thing

0celo7

yeah

Slereah

Also I want actual details on CTCs

Huy

@ACuriousMind: I've gotten an answer about the setup of the experiment, this is pretty much a translation of what the student wrote to me, maybe something doesn't make any sense at all. "this proton beam stuff is for proton therapy (cancer). to adjust penetration depth, there were "degraders", graphite blocks to slow down (?) the protons. after going through those degraders, the protons' energies vary. therefore they deviate differently in the magnetic field.

Slereah

17:34

Even Visser's book barely deals with them

Huy

@ACuriousMind higher energy, less deviation. hence for proton therapy it is important to know how the proton beam behaves after running through degrader and deviation magnet. to measure the "energy broadth", they led the beam through a single slit (1mm width) to guarantee a compact and precise beam.

@ACuriousMind after this, the protons hit a monitor which measures the intensity of the beam. in the experiment, the current of the deviation magnets was changed, so that protons of different energy levels pass through the slit. "

Slereah

One thing I wonder about CTCs, though

What's the deal

Aren't all hyperbolic equations supposed to have a well defined Cauchy problem?

Or am I wrong

0celo7

what visser book

Slereah

Or are EOM in CTCs not hyperbolic

@0celo7 : "Lorentzian wormholes'"

0celo7

another book I want D:

Slereah

17:37

It's a pretty good book

Not very detailed since it goes through a lot of topics

But it's a nice ressource

0celo7

ok

start a table of contents

do we review SR?

Slereah

NO

SR is just the chapter on Minkowski space

No historical route

We start straight in GR

0celo7

how many proofs of the Einstein equations do we give

Slereah

Hm

Let's see

There's the one from the Hilbert action

There's the analogy to Newton along with energy conservation

There's the Fierz-Pauli thing

There's the Lovelock theorem, kinda?

0celo7

@Slereah yes

@Slereah same as the first one

Lovelock justifies $\mathcal{L}=R$

Slereah

17:44

Oh

I suppose

0celo7

you're missing one

Slereah

We can also do the method Feynman uses

Which one is it

0celo7

Weinberg came up with a proof

it's in his book somewhere

Slereah

What book

I have his QFT book and it's already 3 books

Huy

@0celo7: you'd rather study functional analysis with me

0celo7

17:46

gravitation and cosmology

@Slereah do you have a legal copy

Slereah

No

0celo7

"legal"

Slereah

Also no

0celo7

I'll provide that, you will always have it - Nicki Minaj

I'll screenshot the relevant pages

Slereah

thx

0celo7

17:52

seems I...don't have it on my laptop

strange

probably on the ipad then

uploading

m.imgur.com/SzobqT0,ebGqInf,zmwwYHL

@Slereah

Slereah

thx

0celo7

the images are in reverse order

at least for me

Slereah

Oh wait

There's also the derivation of GR from gauge theory

Well, somewhat

0celo7

really

how

Slereah

it's not exactly a gauge theory

Well if you have a free field $\bar \psi \gamma^\mu \partial_\mu \psi$

If you want it to be invariant with the symmetry $x \rightarrow f(x)$, then you end up with the tetrad field

And if you want it to be invariant with $\psi \rightarrow \Lambda \psi$, then you need the spin connection

But that does not give you the Hilbert term, though

0celo7

18:08

are we gonna have this in the book?

start on the table of contents

Slereah

I guess the first part is constructing a spacetime

Manifolds, bundles, connections, curves and whatnot

then some general spacetime things

Geodesics, curvature, causality conditions, geodesic congruences

Symmetries I suppose too

Then the Einstein equation proper

General things on the Einstein equation

0celo7

what about forms

lie derivative

you know what

Slereah

Part of the construction of spacetime

0celo7

if we're serious about no references

we have to prove the Poincare-Hopf theorem

also the hodge elliptic theorem

D:

Slereah

The chapter after is just Stephani :p

ALL THE METRICS

0celo7

18:19

lol

Slereah

I want at least 5 derivations of Schwarzschild

0celo7

Chapter 4: Some Exact Solutions

700 pages :D

Slereah

Also chapter 5 is actually hollowed out paper and inside is an interferometer

You have to do the experiments yourself

0celo7

lol

Exercise 5.1: Prove the existence of gravitational waves.

NeuroFuzzy

@Slereah your standup routine needs improvement

0celo7

18:23

@Slereah seriously, start on the ToC

make a google doc

what level of math do we expect the reader to know?

Slereah

All the math ?

I dunno

Really there's just so much of GR you could fill a million pages

I would like more GR books to not just be the usual

Special relativity - manifolds and curvature - Einstein equations - Linear GR - Gravitational waves - Schwarzschild solution - Black holes - FRW solution - Cosmology

That's basically the layout of most GR books

Huy

we did linear GR in the end

0celo7

De Felice and Clarke do extended bodies

Slereah

They all have a special thing

But usually it is just one or two

Wald does spinors and semiclassical gravity

0celo7

HE is special

Slereah

18:29

(and causality)

Carroll does QFT in curved spacetime

Straumann does thermodynamics

MTW does whatever it is doing

0celo7

Straumann does positive energy theorem

Straumann derives Kerr

Slereah

One nice thing about MTW is that there's an exact solution for EM plane waves

0celo7

I think we should base the book off of Straumann

the way basic GR is presented in that book is great

Slereah

I do like that he actually presents experimental things and GR prototypes first

If you're going to do the historical route at least do that

Weinberg does the same thing for QFT

First chapter is all history of QFT

0celo7

who starred my Nicki Minaj quote

@Slereah are we gonna do this or not?

Slereah

18:35

Who knows

I have book ideas all the time, I rarely go far in them!

0celo7

but this will be the book

we can make some serious coin on this

Slereah

How charmingly naive :p

I think Hawking's money isn't so much from HE

0celo7

problem: no one can pronounce your last name

Slereah

Oh sure, mister Zeroceloseven

0celo7

yes

dude

the coverart should be JD's avatar :D

he should be the third author :)

Slereah

18:44

that's a bit cliché

0celo7

DLU

Slereah

"curved spacetime grid" is the cover of most GR books

Throw in an apple too

0celo7

what do you suggest then

Slereah

One book I wanted to do was just a full book on causality violations in physics

Just CTCs and tachyons

and maybe advanced waves

0celo7

would this be a series?

a new volume every 5 years or so?

Slereah

18:48

Volume 2 would just be a mystery novel

Volume 3 a children book

0celo7

sigh

we could have done something great

Slereah

Doubt it

0celo7

h8r

Slereah

Now that I work I don't really have the time for big projects D:

CTC book I would still like to do, though

There isn't a lot of good books on CTCs

it's a rich field but basically no serious book on the topic

Speaking of

Since quantum gravity is solvable in 2D

0celo7

how many pages would be need for ADM

Slereah

18:52

I wonder if there's any CTCs popping up there and what happens to them

0celo7

who wants to do Gram Schmidt for me?

Huy

@0celo7: use a calculator?

0celo7

no

Huy

why not

0celo7

bad at math

Huy

19:00

wat

0celo7

i'm bad at math

Huy

ah ok

0celo7

19:14

ffs I can't even do gram schmidt properly

Huy

19:33

nub

Physics Meta

0

Q: How can we recruit Richard Muller to this site?

I have noticed that Richard Muller (of e.g. Physics for future Presidents (both a course in qualitative physics at UC Berkeley and a book)) has recently become very active on Quora. Or it could be that I just discovered it. In any case, even the response to comments is outstanding. What could w...

discussion

0celo7

@Huy "Find numbers $x$ and $y$ so that $w-xu-yv$ is perpendicular to both $u$ and $v$." I just dotted with $u$ and $y$ and got a system for $x$ and $y$...is there a better method? Preferably involving Gram-Schmidt.

Huy

@0celo7: numbers $x$ and $y$? are you doing inner products on $\mathbb{R}^1$?

0celo7

@Huy $w,u,v\in\mathbb{R}^3$.

$x,y$ are scalars.

Huy

ah

no further impositions on $u,v,w$?

0celo7

19:45

nein

Huy

how is it possible if they all have the same direction

0celo7

Ok well that's the only restriction then :)

Linearly independent

jeez

Huy

linearly independent is huge

aren't x and y just the inner products you compute in Gram Schmidt

then compute them

0celo7

no because $u $ and $v$ are not orthogonal

Huy

hm

so what?

Gram Schmidt gives you a new orthonormal basis but it's built upon the linearly independent vectors you have

0celo7

19:50

because the GS coefficients are in front of orthogonal vectors

Huy

so the vectors you get from Gram Schmidt are just some linear combination of $u,v,w$ you already have

so you just have to add or subtract some numbers and you get $x$ and $y$

0celo7

show me please

because when I do it I just get another linear system

GS gives you $xu+yv$

but not in terms of $x$ or $y$

so you have to solve a 2x2 system

Huy

hm

0celo7

which is what I wanted to avoid

Huy

ic

ok

obviously this is an important problem that you must solve by yourself

0celo7

19:52

solving the system is not hard

Huy

I'd rather watch football

ofc it isn't

0celo7

I just want an easier method

Huy

probably does work somehow with GS

but cba thinking about it at 10pm

where's ACM

Slereah

Oh wait

Hyperbolic equations only have well defined Cauchy problems locally

I guess that is where the words "globally hyperbolic" mean

Huy

@0celo7: why is Gram Schmidt better than a 2x2 system btw?

0celo7

20:00

@Slereah That is correct

@Huy No particular reason

Huy

ah ok

Slereah

Is there a special criterion for hyperbolic equations to be globally hyperbolic

Or do you just have to wing it

0celo7

@Huy being unfaithful

Huy

-.-

0celo7

@Slereah the equations are not globally hyperbolic

I think the theorem is that hyperbolic equations on globally hyperbolic manifolds have a Cauchy problem

Slereah

20:14

Well yes but that is not my question

Generally speaking, taking a math equation, is there a special criterion to know whether or not they have a well defined Cauchy problem globally

0celo7

Dunno

Slereah

I suspect there is no general easy trick to know

0celo7

@Huy what's with the face

Slereah

So the Jacobi elliptic function solution for a scalar field is not of compact support

but on the other hand

I think a domain wall solution would be easy enough to make compact?

Or close to, anyway

Well, it's not of compact support, but

I think the front velocity would be easy enough to check

Slereah

20:42

Just the velocity of a perturbation on the domain wall or something

0celo7

21:01

CBE 529 - Application of Linear Algebra in Engineering Systems

3 Credit Hours
Fundamental concepts of linear algebra to problems in engineering systems: steady state and dynamic systems. Geometric and physical interpretations of relevant concepts: least square problems, LU, QR, and SVD decompositions of system matrix, eigenvalue problems, and similarity transformations in solving difference and differential equations; numerical stability aspects of various algorithms; application of linear algebra concepts in control and optimization studies; introduction to linear programming. Computer pr…

@Huy

That's the linear algebra class I want!

Slereah

"A class of rigorous solutions for the Einstein-Rosen nonstatic cylindrically symmetric metric in the presence of combined electromagnetic and scalar meson fields has been obtained."

That's a rather random paper

"The study of relativistic field equations in the presence of a scalar meson field
has attracted the attention of many workers."

Has it

You liar

Although I think "meson field" is secret code for "We don't want to actually use mesons but it sounds better than saying Klein Gordon"

0celo7

@Slereah probably

> Recommended Background: At least one senior-level course in differential equations or advanced calculus. Mathematical maturity.

> Mathematical maturity.

Who the hell wrote that course description?

Slereah

21:50

No math babies

0celo7

footnote in Arnold: "In almost all textbooks, even the best, this principle is presented so that it is impossible to understand." (c. Jacobi, Lectures on Dynamics, 1842-1843). I do not choose to break with tradition.

Slereah

heheh

what principle?

0celo7

22:06

Maupertuis

:O

that's...pretty damn profound if you ask me

Slereah

I think it's a pretty general thing

physical laws you can try to translate as geodesics of some metric

It's an old idea

0celo7

well excuse me for thinking that's pretty damn cool

Slereah

There's an 1872 paper about the notion that maybe EM forces are from space curvature

0celo7

they are

Kaluza Klein :^)

@Slereah link?

0celo7

22:30

@ACuriousMind How does "$\mathrm{SO}(3)$ is not simply connected" imply the theorem on the bottom of page 248?

Slereah

22:48

Fuck I can't find it anymore

It was a paper from the 1870's I think

Some conference of mathematics on non-Euclidian geometry

and he proposes that maybe forces are due to space curvature

0celo7

bah

I'll believe it when I see it

Slereah

arxiv.org/ftp/arxiv/papers/1205/1205.4909.pdf

Might be in there

0celo7

>no equations

I want the paper

Slereah

Oh there weren't equations IIRC

It was just speculation

0celo7

garbage

Slereah

22:54

Pretty good for the 19th century I say

Ah, found it

Apparently it was William Clifford

0celo7

@Slereah nah

Slereah

"Flat manifoldness (in which the curvature is everywhere = 0 may be treated as a special case of manifoldness with constant curvature"

What is a manifoldness

0celo7

lol

Slereah

"Moreover, he extended Riemann’s ideas by speculating that physical phenomena could be fully reduced to properties of space curvature varying between one portion of space to another. Heat, light and magnetism might be mere names for tiny variations in the curvature of space, he boldly hypothesized."

Going a bit too far, Clifford

Don't fly too close to the sun

It is weird to think that back then the molecular dynamics of heat was still controversial

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