The h Bar

Slereah

17:00

I seem to recall that it has a bunch of solitons

FenderLesPaul

QFT in curved space-time doesn't have poorly defined particles in the same sense

in that case there is no global time coordinate in general and you need a time coordinate in order to define your positive and negative frequency modes

even when you do have a global time coordinate you can always just transform to another time coordinate so there isn't a preferred notion of particle either

ACuriousMind

@Slereah QFT in curved spacetime has a different reason - you have no unique choice of mode functions $u_j$ since there's no unique choice of frame, which leads to Bogolyubov transformations being allowed/introduced when you switch frames, so what's a particle state in one frame might not be in another (cf. Unruh effect)

Slereah

I see

ACuriousMind

@Slereah Even for exactly solvable models, the Hilbert spaces are rarely examined, and I believe, also unknown. The only theory where I can with confidence say that the Hilbert spaces are known is 2D CFT.

Huy

What is the physics.SE opinion of QFT in a nutshell?

0celo7

17:02

1,100 page Java book? Well I'm not doing Java my first year, I can leave that.

Slereah

Are they rarely examined or isz it like peering into the eye of madness

Do they try to examine them but never come back

0celo7

@Huy I don't like it.

Huy

@0celo7: Why?

FenderLesPaul

@Huy it's a pretty shitty book

way too whimsical

Huy

@FenderLesPaul: Why?

ACuriousMind

17:03

@Slereah Hm, it looks like we at least know the "particle spectrum" of sine-Gordon/Thirring

0celo7

@Huy I want to like it, but mainly Zee flies over so many details.

FenderLesPaul

doesn't teach you how to do any computations

poorly organized

it starts from the path integral approach but doesn't do path integrals properly

0celo7

He flies so fast by things and the exercises are hard.

ACuriousMind

But I can't tell you whether this means we know the Hilbert space, unfortunately

FenderLesPaul

i.e. it barely if at all mentions BRST quantization

and ghost fields

0celo7

17:04

@FenderLesPaul He does not.

ACuriousMind

As said, if you want nice models with well-defined Hilbert spaces, do CFT ;)

0celo7

@FenderLesPaul He does.

Slereah

Does it need ghost fields?

Thirring isn't a gauge theory

I do want to learn about AdS/CFT

0celo7

@Slereah BBS is good, but I can't vouch past chapter 6.

Slereah

BBS?

FenderLesPaul

17:05

@Slereah I don't see how you can do path integral quantization of gauge fields properly without ghosts

0celo7

Becker, Becker, Schwarz

Slereah

Well yes but Thirring isn't a gauge theory!

Neither is Sine Gordon

ACuriousMind

@Slereah They're not talking about your damn Thirring model :P

0celo7

I'm going to leave Zee's GR book. I have a legit e-book of it.

Slereah

oh

FenderLesPaul

17:06

@Huy but yeah I do agree with 0celo7 in that it's very rushed

0celo7

Single Variable Calculus has served me well, but ultra-gloss pages are heavy :(

FenderLesPaul

I never got anything out of it

I like Ryder a lot better but it doesn't have exercises

at the end of the day I found Srednicki the most useful as far as actually learning how to QFT goes so you could just try combining those two

0celo7

I'm going to re-read Weinberg sometime in the future. Will read Zee alongside to see if I can get anything out of it.

FenderLesPaul

yeah Weinberg is definitely on the bucket list

Slereah

I wonder if some people just read physics books like regular books

Cover to cover

0celo7

17:08

@FenderLesPaul I've used him as a reference.

@Slereah I've read some like that.

FenderLesPaul

@0celo7 his notation is just so impenetrable sometimes

0celo7

7 books have been removed from the box.

I want to finish Weinberg G&C but I have no clue when.

FenderLesPaul

@0celo7 going off to college

sniff they grow up so fast

2

0celo7

@FenderLesPaul yeah I have to start packing! I ain't got shit together

skill patrol

and the real growing is just about to begin :P

0celo7

17:11

I have BLT, BBS, Straumann, Hawking, Wald PDFs but I can't leave my babies

FenderLesPaul

Get your shit together man

Can't be leavin Wald behind

0celo7

I could leave behind most of my books and just use the iPad.

:(

skill patrol

you can always come back later for the ones you need...or have them shipped to you

0celo7

brb lawn mowing

FenderLesPaul

@0celo7 but it's just not the same :(

lies and slander!

skill patrol

17:17

:-)

happy now?

FenderLesPaul

yes :D

skill patrol

:D

Huy

@0celo7: What exactly is it you are doing with those books? Selling? :P

FenderLesPaul

@Huy he's going to college

lol I can imagine @0celo7 standing right by a really shady alley dressed all sketchy lookin like he's selling drugs but when someone comes up to buy some he tries to sell them copies of random physics books

ACuriousMind

@FenderLesPaul ...and then uses the money to buy drugs?

skill patrol

17:22

psst...wanna quick quantum fix?

FenderLesPaul

@ACuriousMind ooh that's a good plot twist

skill patrol

...and then uses the drugs to bribe his way into med school?

Slereah

Med school seems pretty shit

8 years of memorizing whole textbooks

skill patrol

hence the drugs

anyone remember the name of that TV series named after one of their textbooks?

set in a Seattle hospital...

Grey's Anatomy

Grey's Anatomy is an American romantic medical drama television series that premiered on American Broadcasting Company (ABC) as a mid-season replacement on March 27, 2005. The series has aired eleven seasons, and focuses on the fictional lives of surgical interns and residents as they gradually evolve into seasoned doctors, while trying to maintain personal lives and relationships. The title is a play on the name Gray's Anatomy, an English-language human anatomy textbook originally written by Henry Gray. The show's premise originated with Shonda Rhimes, who serves as an executive producer, along...

FenderLesPaul

"Romantic medical drama"

lel

Slereah

17:34

Nothing gets you in the mood quite like dysentry

skill patrol

Gray's Anatomy. The book is widely regarded as an extremely influential work on the subject, and has continued to be revised and republished from its initial publication in 1858 to the present day. The 40th edition of the book was published in 2008, the year of its 150th anniversary.[1]

FenderLesPaul

wtf 40 editions

even Stewart's calculus book isn't up to that

skill patrol

Gray's Anatomy

Gray's Anatomy is an English-language textbook of human anatomy originally written by Henry Gray and illustrated by Henry Vandyke Carter. Earlier editions were called Anatomy: Descriptive and Surgical and Gray's Anatomy: Descriptive and Applied, but the book's name is commonly shortened to, and later editions are titled, Gray's Anatomy. The book is widely regarded as an extremely influential work on the subject, and has continued to be revised and republished from its initial publication in 1858 to the present day. The 40th edition of the book was published in 2008, the year of its 150th anniversary...

150 years worth of students memorizing that^

Slereah

40 editions?

That's nothing

The Handbook of Physics and Chemistry is up to like

96?

skill patrol

only a chemist would memorize that

:P

0celo7

17:50

@FenderLesPaul It's a great show.

Should I take Abramowitz & Stegun?

@ACuriousMind ::sweats:: Be glad ::sweats:: you don't have a lawn ::sweats::

Slereah

A&S is a nice book to have

Then again

It's free on the internet

Public domain

0celo7

I'm really slimming down my book collection for transport.

Slereah

just buy the Book of All Physics

0celo7

how long is it

I want ACM to write Quantum Physics and add a volume every few years until he dies

@skillpatrol I don't need very many of them.

I have PDFs of pretty much every book I own physically.

skill patrol

oh

ACuriousMind

17:56

@0celo7 As Danu once said, they'd probably be among the driest books you've ever read ;)

0celo7

@ACuriousMind Doubtful, you're a good writer and I imagine it would be full of random references.

@FenderLesPaul How much did you get into Zee's QFT book?

@ACuriousMind How much do you know about anyons?

ACuriousMind

@0celo7 As much as anyone

0celo7

@ACuriousMind I know that's an actual saying, but I have no clue what it means D:

ACuriousMind

@0celo7 I thought it meant "as much as some random person on the street", but I could be wrong

0celo7

@ACuriousMind I think so too, but the random person on the street might be a genius :/

ACuriousMind

18:00

"as much as the average over random persons on the street", then

0celo7

@ACuriousMind ...so nothing

@ACuriousMind Let me rephrase: how much do you know about Chern-Simons

ACuriousMind

@0celo7 Exactly, I don't anything about anyons (except that they occur in 2D because the universal cover of the rotation/Lorentz group is not a double cover)

@0celo7 Ehhh...I can write down the Chern-Simons form, but that's about it, I don't know anything specific

0celo7

God dammit can someone please tell me what's in X.G. Wen & A. Zee, J. de Physique, 50; 1623, 1989???

Slereah

science

ACuriousMind

@0celo7 Title or DOI?

Slereah

18:05

Aren't anyons those weird 2D fields that are in between fermions and bosons

0celo7

@ACuriousMind everything

I just need the paper D: this exercise has ruined this book for me

the answer is in there

ACuriousMind

@0celo7 No, I want to know whether you can tell me the title or DOI, I can't find the paper at all

0celo7

DOI?

Slereah

It's a fancy identifier for papers

0celo7

no, that's all I have

ACuriousMind

18:06

@0celo7 Digital Object Identifier

Slereah

Just go to the Journal de physique website

And check what's in volume 50

Loong

dx.doi.org/10.1051/jphys:0198900500130162300

ACuriousMind

@Loong Yeah, I found that right now, too

Hm, I don't see any way to get access to that except individual subscription, that's a really bad thing to use as reference

Slereah

coughsci-hubcough

Loong

hal.inria.fr/file/index/docid/211021/filename/…

0celo7

18:11

@Loong thank you kind sir!

Loong

@0celo7 you are welcome

Slereah

One thing I wonder is, what's the oldest bibliographical reference someone has been able to sneak in

0celo7

Probably Euclid

Slereah

Like can you publish an archeoastronomy paper and put as a biblio item "Astronomical tablet of Utshipa, 2500 BCE"

I'm not sure in what journal people published tablets

0celo7

Actually Zee references a Babylonic Taylor series

Slereah

18:16

The Sumerian Physics Journal

0celo7

@ACuriousMind what is the Landau gauge

oh it's a variant of $R_\xi$

ACuriousMind

@0celo7 Do you really expect I can answer that off-hand? It's either $\xi = 0, 1$ or $\infty$ for this EM gauge parameter, I think.

Slereah

I think it's the infinity one?

Or is that Coulomn

I forget

I remember Landau being extreme

So either 0 or infinity

0celo7

coulomb is $\nabla\cdot\mathbf{A}=0$

@ACuriousMind Actually yes...

@Loong well thanks again

Slereah

Isn't there also one that's like

3

Or some weird number

0celo7

18:21

Yennie

according to Wiki

oh god I need the effective action?

ugh why does QFT suck so much

Slereah

Effective actions are the easiest man

Just pick like one term that's gauge invariant

That will be your action

Like Tr(dF²) or some shit

0celo7

yeah the result doesn't look anything like that

Slereah

Or something I dunno

Tr(dF²) is for meson interactions

0celo7

time to change my avatar

ACuriousMind

@0celo7 Why's that?

0celo7

18:29

@ACuriousMind because Einstein is so cute and I just took a picture of him that's so cute

vzn

@Slereah what does?

0celo7

Slereah

The effective Lagrangian

I forget the exact formula

It had some exponential of SU(N) matrix

vzn

for what type of scenario?

ACuriousMind

@Slereah Sleerah, look at what vzn referenced.

They're asking about the solitons you mentioned far upstream.

Bro, do you even chat?

0celo7

18:33

@ACuriousMind #rekt

my picture has been changed

Slereah

vzn : SU(2) effective Lagrangian

For pions

Like you pretend there are only two quarks of the same mass

and find the most general lagrangian for it

And that's the lowest order term of that

vzn

the pions (or quarks) are seen as solitons, or something else?

Slereah

They're just doublets of SU(2)!

1/2 + 1/2 = 0 + 1 kind of stuff

vzn

this is hard to follow. generally interested in soliton connections to particle physics. hence the curiosity.

Slereah

0 is... rho meson?

It's not soliton related

1 is the pion triplet

vzn

18:36

@Slereah you mentioned solitons above (click on the gray left arrow). caught my attn. parachuted in. couldnt follow the thread.

2 hours ago, by Slereah

I seem to recall that it has a bunch of solitons

Slereah

Oh

ACuriousMind

@vzn: We were talking about the Thirring or Sine-Gordon models, which have classically solitonic solutions

Slereah

I meant the solution to the Sine Gordon model

0celo7

@ACuriousMind is that a missing texture?

Slereah

That seems to be quite a jaunty chapeau

vzn

18:38

@ACuriousMind wrt particle physics or some other context?

ACuriousMind

@vzn QFT. It's not exactly "particle physics", but you find that these solitons show up in the particle spectrum of the theory, yes.

@0celo7 You mean the oddly colored elongated shape?

It...could be, but I'm not sure

0celo7

@ACuriousMind Yes.

vzn

@ACuriousMind has anyone measured them? or are they more theoretical?

0celo7

I imagine it was like a cigar or something.

ACuriousMind

@vzn Neither of these models describe an actual physical system in the sense that the particles would be real particles. I think you get them as condensed matter description of some crystals, where solitonic quasi-particles (or "crystal lattice excitations") are nothing unusual

Slereah

18:42

For a start they are 2D theories

We have too many dimensions!

0celo7

do anyons have any relevance to us at all?

unless of course one puts anyonic excitations on 2-branes and solves the universe

vzn

@ACuriousMind are the solitons in the EM field (of the crystal) or something?

ACuriousMind

@0celo7 The fractional quantum Hall effect is connected to them, I think

Slereah

Well they're solvable models

Which is nice to have

vzn

@Slereah Sine Gordon/ Thirring are 2D?

ACuriousMind

18:44

@vzn No, rather think of actual vibrations of the crystal lattice, but since the theory is 2D as Sleerah said, they, if at all, would only describe thin-film crystals.

0celo7

more like thin-line

it's 1+1, right?

vzn

@ACuriousMind soliton patterns in the (2D) crystal lattice?

Slereah

Yes

ACuriousMind

@0celo7 Oh, right.

Slereah

1+1 indeed

Sine Gordon is solved with inverse scattering transform, which works best for 2D systems

And there's a theorem linking Thirring and Sine Gordon

0celo7

18:46

@vzn 1D

Slereah

Hence the solutions.

ACuriousMind

@vzn The "crystal" here is essentially just a string with a certain behaviour.

So...it's a solitonic wave travelling along a certain kind of string, I think

vzn

had heard more about korteweg-devries but not these other eqns much.

ACuriousMind

(string not as in string theory, string as in actual, physics string)

vzn

@ACuriousMind lol you say that like theres a difference :P

0celo7

18:48

string theory strings are not actual, physical strings TIL

@ACuriousMind is an anti string zealot

vzn

@0celo7 no kidding eh? never noticed that!

0celo7

@vzn that sounds sarcastic

ACuriousMind

Sigh...string theory strings are fundamental building blocks without substructure. Actual, physical strings are made out of particles with bonds, etc, etc...

0celo7

@ACuriousMind that's right backpedal

vzn

@0celo7 seriously. hadnt seen/ noticed antistring sentiments. thought he was only an anti-interpretations zealot lol

0celo7

18:49

the Czech Fleck is on your ass now

ACuriousMind

@vzn He is kidding, I am not "anti-string" (not fervently "pro" them, either)

0celo7

"string not as in string theory, string as in actual, physics string" - ACM, string hater

lel you're intellectual garbage now :D

vzn

0celo is always such a troublemaker. have noticed that.

ACuriousMind

@vzn It's Ocelo-7 because we've disposed of the even more troubling models Ocelo-1 through Ocelo-6 ;)

0celo7

does no one know 1337 speak anymore

seriously

vzn

18:52

@ACuriousMind still working on that buggy programming or something eh? :|

> thats not a bug! thats a feature!

ACuriousMind

@vzn Self-awareness of the AI comes with a certain payload, apparently :/

vzn

@ACuriousMind lol reminds me of Independence Day (movie) ... & probably others ... eg Transcendence (more recently)

ACuriousMind

Wasn't ID that one with aliens? My memory for movies is very bad

0celo7

I prefer to think of myself as Cortana

ACuriousMind

..."that one with aliens", most specific description ever, I guess :D

Slereah

18:56

People only speak leet ironically now

0celo7

ID did have aliens

vzn

@ACuriousMind ID is pretty old at this pt (uh oh, my secret is out) but it had will smith. part of the plot was an alien (computer?) virus iirc.

ACuriousMind

Ah, yes, the Wiki summary talks about a computer virus

0celo7

@Slereah I would have chosen Ocelot if that were available

been on 0celo7 for 4 years now

0celo7 is very natural to type now

ACuriousMind

...but doubling of names is allowed here, you can call yourself Ocelot if you want, even if there's another one.

Slereah

18:58

Zeroceloseven

Einstein vs Stephen Hawking -Epic Rap Battles of History #7

►

have a science debate

0celo7

@Slereah one of the best by far

Slereah

It's breddy good

0celo7

when will people learn not to build shit on top of ancient nordic ruins

FenderLesPaul

19:49

@0celo7 sorry I had a meeting; I didn't get too much into the book

at best I got use out of reading random bits here and there

I didn't go through it systematically if that's what you're asking

idkfa

20:05

@KyleKanos I tried to rephrase my question (physics.stackexchange.com/questions/197812/calculate-potential) here but in the end it just comes down to the fact that I did not knew how to calculate the derivatives. I doubt that would benefit physics.SE and to that specific excersise I don't have questions regarding potentials. What would be the right way to go on about this? It's the first time I asked a question that I can't rephrase to fit the Q&A format.

Slereah

20:43

Is the Fourier transform to solve field operators always justified

I mean, I know that there are solutions that aren't square integrables

ACuriousMind

@Slereah What do you mean by "solve field operators"`, and what classes of theories do you mean with "always"? ;)

Slereah

Hm, it's true that the example I have in mind is not free!

But if you have a free theory, why can we assume that it's always square integrable

And hence can be Fourier transformed

Like say, Klein Gordon

$(\square + m^2) \phi = 0$

Will all the solutions be square integrable

ACuriousMind

Formally, a quantum field is an operator-valued well-tempered distribution on spacetime, where "well-tempered distributions" are roughtly those that can be fourier transformed

You must bear in mind that a quantum field is not a quantum state, hence why would you demand square-integrability?

Slereah

Well because Fourier transforms can only be performed on square integrable functions, no?

Or is it just L^1

I forget

ACuriousMind

@Slereah The space of well-tempered distributions carries a Fourier-transform, and it is larger than any $L^p$-space

Slereah

20:49

Good to know, I s'ppose

Is it because non-L^p functions can have fourier transforms that are distributions?

0celo7

"well-tempered"

sounds like a sward description

Slereah

*sord

ACuriousMind

Rigorously speaking, you shouldn't even write stuff like $\phi(x)$ for a quantum field - only things like $\int f_x(y)\phi(y)\mathrm{d}y$ are well-defined for smooth functions $f_x$.

Slereah

"Let me not specify what the vector Gj actually is. "

Well gee how helpful!

ACuriousMind

@Slereah A distribution is not really a function at all - it acts on functions, instead. You should think of $\phi(x)$ as the distribution applied to a smooth function sharply peaked around $x$.

Slereah

20:51

I know

0celo7

@ACuriousMind I thought they had to be Schwarz functions

ACuriousMind

@0celo7 Yes, they have, you are right.

Slereah

Can you have a field that is just like

phi = 1

Constant over all space

Or phi just being an infinity of compact support functions sprinkled over all space

ACuriousMind

$\phi = 1$ is possible only when the space is compact, I think, but I'm not sure

Also, what do you mean by "compact support functions". It's operator-valued!

0celo7

compact support operator :D

Slereah

20:56

Well yes but as you may remember there's a mapping from functions to distributions!

You nitpicky grump

0celo7

#rekt

ACuriousMind

What? No, the operator-valued-ness has nothing to do with it being a distribution

0celo7

ACM is a pedant confirmed

Slereah

Just picture a compact support function f(x) and the operator phi |a> = f(x) |a> or something

I dunno

ACuriousMind

You could say you just define the operator assigned to a point to be non-zero on only a compact set, but you can't just write down "functions" for a quantum field because it has to take values in the operators on the Hilbert space

There's a reason you don't see many "solutions" of the field equations in papers that are full quantum and don't do anything classical - you can't just write down the classical solution because $x$ is not a good operator

And this is also why the path integral formulation is so nice because it circumvents dealing with the operator formalism

0celo7

20:59

you heretics and your Hilbert spaces

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