The h Bar

0celo7

14:02

@yuggib Not understanding projective reps is the reason why I don't get half of what @ACuriousMind says

ACuriousMind

@0celo7 Chapter 2.7 is titled "Projective representations".

2

0celo7

14:32

@ACuriousMind I've read it twice.

I don't see your point.

BBS is titled "String Theory and M Theory" but they do a shit job of explaining.

ACuriousMind

@0celo7 Well, you might say he explains it badly (and I would agree), but "not at all" is not a fair characterization.

yuggib

when I was a physicist, I learned QFT on Weinberg, Itzykson-Zuber and later Fields by Siegel

by the last is a little bit peculiar as a book

Slereah

Hm, Siegel

sounds familiar

Oh wait

Is he the FIELDS guy

yuggib

as a friend of his has to say, it is orthogonal to other presentations

0celo7

@ACuriousMind How about this: Weinberg allows you to read Weinberg, but nothing else will make sense. And then you realize Weinberg never made sense to begin with.

yuggib

14:38

insti.physics.sunysb.edu/~siegel/Fields3.pdf

Slereah

Yeah that one

He also wrote the Stuperspace paper

"Instinct is claimed as a basis for most discussions of quantum field theory, though clearly this topic is too recent to affect evolution"

:D

One day we will evolve with an instinct for QFT

QuantumMechanics

Does anyone know what kind of function that I_\alpha is? upload.wikimedia.org/math/0/9/4/…

yuggib

he is a funny guy (at least from what they told me, never met him in person)

Slereah

@QuantumMechanics : Seems to be some Bessel function shit

Bessel function

Bessel functions, first defined by the mathematician Daniel Bernoulli and then generalized by Friedrich Bessel, are the canonical solutions y(x) of Bessel's differential equation for an arbitrary complex number α (the order of the Bessel function). Although α and −α produce the same differential equation for real α, it is conventional to define different Bessel functions for these two values in such a way that the Bessel functions are mostly smooth functions of α. The most important cases are for α an integer or half-integer. Bessel functions for integer α are also known as cylinder functions...

that's the one

Modified Bessel

Always remember all the Bessel functions

0celo7

Gwen Stefani - Used To Love You

►

Slereah

14:42

It's basically the only special function in physics

0celo7

Worst music video of all time?

QuantumMechanics

Thank you! :-) Getting not easier...

Slereah

@0celo7 : youtube.com/watch?v=x4sqMNHZxjI

0celo7

@Slereah Lol

Slereah

I do love Roki Vulovic

Much better than Lepi Mica

Slereah

15:12

The problem with doing path integrals by hand is that you have to know your infinite product rules

0celo7

just derive them

oh, very nice

0celo7

15:34

@ACuriousMind @DanielSank @dmckee Does the average physicist know what an abelian group is?

QuantumMechanics

@0

Slereah

QFT people certainly

And probably a few more people working with group stuff

QuantumMechanics

@0celo7: Yes

0celo7

@QuantumMechanics Does the average physicist know what Hausdorff is

Slereah

This is a Hausdorff

3

0celo7

15:37

@Slereah Any GR person, certainly

Flows are an abelian group of diffeomorphisms, after all.

Slereah

Hausdorff property probably less so

QuantumMechanics

@0celo7 not by heart

Slereah

Hausdorff property is pretty much always assumed and not really mentionned

(in manifolds, anyway)

0celo7

Anyone who reads HE knows what it is

Slereah

Eh

It's mentionned but it's the kind of thing you read and forget

It's never really used anywhere

Except for the Taub NUT spacetime

0celo7

15:39

It's used elsewhere.

In the Cauchy chapter IIRC.

Perhaps even Chapter 8, but I only skimmed that one.

Slereah

Also maybe to prove that they all admit a metric?

Or does he throw that back on the bibliography

0celo7

He uses the partition of unity, but does not show paracompactness + Hausdorffness $\Leftrightarrow$ PoU

Then again, no one shows that.

Slereah

I had to show it once

0celo7

I think the proof is in Lee.

Slereah

During my brief stint as a mathematician

0celo7

15:42

Why would you ever show that

Slereah

I had to do a class in topology

Where I didn't understand anything

b/c I'm a poor physicist

And we had to pick a presentation topic

They were all awful

Suddenly

"Differential geometry!"

I'll pick that thank you

0celo7

Don't you just hate when you listen to an artist and that one song is good, but all others are terrible

@Slereah should've done Stokes

Slereah

It was fine.

Got a good grade on it

Unlike the exams D:

dmckee

@0celo7 I'd have to look it up. And I'd feel stupid when I did that, because I did know. But it doesn't come up in my work.

0celo7

I remember "abelian group" as simply the additive group of reals.

Slereah

15:46

I remember it because of the joke

What is purple and commute

0celo7

I think any abelian group is homomorphic to that one anyway

Slereah

The trivial group is abelian

is it homo to the reals

0celo7

It's homo to $0\in\mathbb{R}$

i.e. a subset

Slereah

I GUESS

0celo7

@Slereah what

Slereah

15:47

An abelian grape

0celo7

grapes are green

Slereah

What is yellow and complete

(some grapes are purple)

0celo7

Hilbert cheese

Slereah

No

A bananach space

0celo7

someone is spying on us...

ACuriousMind

15:50

@0celo7 Most certainly not (and not even to subgroups of it)

0celo7

@ACuriousMind whaaaaat

like what

Slereah

What would $Z_2$ be homo to

ACuriousMind

@0celo7 $\mathbb{Z}/n\mathbb{Z}$.

0celo7

@ACuriousMind o

Hmm, did we have this discussion once

I recall $\mathbb{Z}_n$ coming up recently

GBeau

@0celo7 if by $\mathbb{Z}_n$ you mean $\mathbb{Z}/n\mathbb{Z}$, you should know the former is ambiguous

but it's not too much of an issue since it's normally obvious from context, unless you're intending to refer to $\mathbb{Z}/p\mathbb{Z}$ with the notation, then it's just confusing

Slereah

15:58

What's the difference between $Z_n$ and $Z/nZ$

0celo7

I think one is p adic integers or something

Slereah

Which one is just a cycle of n elements

ACuriousMind

@Slereah $\mathbb{Z}_p$ is also used for the p-adic integers

$\mathbb{Z}/n\mathbb{Z}$ however is unambiguous.

Slereah

What's a p-adic integer

0celo7

^

Slereah

15:59

Aren't p-adic numbers specifically a completion of $Q$

ACuriousMind

You don't want to know

Slereah

And would have the same integers

0celo7

It's unambiguous because I don't know what they are.

Bass

@ACuriousMind Isn't the canonical projection $\mathbb Z\to\mathbb Z/n\mathbb Z$ a group homomorphism?

ACuriousMind

@Bass It is

0celo7

16:01

I'm so confused

Bass

@ACuriousMind So $\mathbb Z$ is homomorphic to $\mathbb Z/n\mathbb Z$. Which means, $\mathbb Z/n\mathbb Z$ is not a counter-example for your statement that not all abelian groups are homomorphic to a subgroup of $\mathbb R_+$.

ACuriousMind

@Slereah Well, they are. But you can also define the p-adic numbers without any metric: The p-adic integers are the elements of $\varprojlim_{k\in\mathbb{N}} \mathbb{Z}/p^k\mathbb{Z}$. Then $\mathbb{Q}_p$ is just the quotient field of this ring.

They are "integers" because just like the rationals are the quotient field of the integers, the p-adic numbers are the quotient field of the p-adic integers.

0celo7

On mobile, no clue what \varprojlim is o.o

ACuriousMind

A projective limit, obviously ;P

0celo7

Is this all standard algebra stuff?

Slereah

16:06

PhD level algebra

0celo7

Wau

It might snow some more

ACuriousMind

Define "standard". Projective and injective limits are something that comes up in algebra, but you don't need them for everything

0celo7

I'll never have algebra again

So the professor didn't do the paperwork and I'm not an employee. Great.

Slereah

Pretty sure Al-Khwārizmī would say "what the fuck is all this"

3

0celo7

Time to email him and swing by his office like a parasite

Bass

16:19

@ACuriousMind What's an example of an abelian group that is not homomorphic to a subgroup of $\mathbb R_+$? I cannot think of one. Finitely generated abelian groups are homomorphic, since you can project onto the subgroup of one generator (which is homomorphic to $\mathbb Z$ or $\mathbb Z/n\mathbb Z$), and real/complex vector spaces are homomorphic too, by projection.

ACuriousMind

@Bass I think you took "homomorphic" to mean the wrong thing. I'm pretty sure 0celo7 and Slereah we talking about being isomorphic, because "being homomorphic" is not a thing.

Bass

@ACuriousMind Oh I see. IMO they are pretty different things. Is "homomorphic" used that way often?

ACuriousMind

@Bass No. One doesn't say at all that two things are "homomorphic" (but coming from topology, one might confuse that with "homeomorphic", which is the topologist's "isomorphic")

Mike Miller

The only context I've ever seen someone say "homomorphic" is when wants to say "homomorphic image". One might say "$G$ is the homomorphic image of $H$" to mean that there is a surjective homomorphism $p: G \to H$. This is awkward and undesirable. If this is what you mean, a more natural phrasing is "$H$ is a quotient of $G$"

Bass

Just realized that there exist trivial homomorphisms between every pair of groups. So all groups are "homomorphic" to each other in that sense.

Mike Miller

16:24

Oh.

Bass

I meant it in the sense of: Isomomorphic $\Leftrightarrow$ there exists an isomorphism. Homomorphic $\Leftrightarrow$ there exists a homomorphism.

But the latter is a tautology.

ACuriousMind

Yes, there's always the zero homomorphism.

GBeau

@FenderLesPaul see grad cafe for ann arbor

interview, dated today

Danu

@yuggib Hahahahahahahaha "talks are usually good"

@yuggib I'm technically a student of both.

yuggib

o.O

why?

@Danu come to see my talk on the 3rd of February, and then you can judge :-P

Danu

16:31

@yuggib Whose seminar?

Siedentop?

yuggib

no

duerr/pickl/etc

Danu

@yuggib It's a feature of my study program.

@yuggib Link or something?

yuggib

I actually know siedentop as well

Danu

Oh Duerr is this Bohmian guy right

@yuggib Okay.

yuggib

duerr seminar

Danu

16:32

I don't like him :P

yuggib

mathematik.uni-muenchen.de/~bohmmech/Teaching/OberseminarWS1516

I don't know him at all

Mike Miller

@yuggib I'll be there.

yuggib

and I don't like bohmian shit too

I've been invited by Pickl

Danu

About the Nelson model?

yuggib

yes

not gonna talk about the Nelson model much however

:D

Danu

16:34

I think there is little chance of me attending, since that is my finals week.

GBeau

@FenderLesPaul and UCSB interview, also dated today

Danu

Topology is on the 5th

yuggib

just saying for info

Danu

Thanks for the invite :)

yuggib

@MikeMiller you're in germany?

Danu

16:36

@MikeMiller You will? :P

Bernard Meurer

Americans, I have a question; why is it that so many people hate on Cornell?

yuggib

I thought it was a joke, however

you may never know

Danu

@BernardMeurer Do they?

AFAIK it's pretty respected, but I'm not an American ;)

Mike Miller

I've never heard of that, @Bernard.

GBeau

@BernardMeurer I don't know where you would get that impression

Bernard Meurer

16:37

@Danu @MikeMiller Recently I've met quite a few people who disliked it

GBeau

an anecdote does not a pattern make

Bernard Meurer

Not as in they are bad academically, but just rated the college badly somehow

Some dude from Rensselaer Polytechnic even went on to brag about having a better physics course some while ago

Mike Miller

ok

Bernard Meurer

So I wondered if it was an actual thing or I just met weird people

GBeau

that feel when your advisor comes over and opens emacs but you use vim

Bernard Meurer

16:41

@GBeau I almost have a convulsion when too close to emacs

GBeau

I guess I need to find a new advisor

yuggib

how could you do without auctex?

Danu

@GBeau I'm still doubting whether to start using either

yuggib

emacs+auctex+orgmode

what else?

Mike Miller

just use notepad : - )

GBeau

16:45

@Danu emacs has a significantly smaller learning curve if you're serious

I'm definitely much faster/happier than I was using other editors though, and I use it for everything

Danu

@GBeau I'm still on texstudio

But I spend a lot of time typing

so maybe it's worth it to try and get just a little faster

Bernard Meurer

I like Atom

And use VIM when on the terminal

Emacs seems nice but the learning curve is ginormous

GBeau

@Danu I (somehow) managed to learn LaTeX without ever using one of the IDEs

keeping around old example files, probably

Danu

What are IDEs

GBeau

"integrated development environment"

Bernard Meurer

16:50

@Danu It's the sign that you've become weak

Mike Miller

that's a severe case of lmgtfy bro

Bernard Meurer

On a serious note it's a text editor on steroids

GBeau

well that's just because you haven't seen how much time people have put into vim and emacs extensions, or, hell, the default client

Danu

@MikeMiller No, I tried that first.

Try googling "IDEs"

Of course, "ide" does work ;)

Mike Miller

the integrated development environments of marhc

ACuriousMind

16:52

@Danu Uh...the third and fourth hit are the German and English Wiki articles about IDE for me.

Mike Miller

but hugs all around in any case.

Danu

@ACuriousMind Oh, not for me...

I get pretty US-oriented stuff on my googlz. :(

This is a higher-ranked hit:

Ides

Ides may refer to: == Calendar dates == Ides (calendar), a day in the Roman calendar that marked the approximate middle of the month. For March, May, July, and October it is the 15th day of the month (Dictionary.com). For other months it is on the 13th (Dictionary.com). Ides of March, a day on the Roman calendar that corresponds to 15 March; it was marked by several religious observances and became notorious as the date of the assassination of Julius Caesar in 44 BC == People == Saint Ides, an Irish saint == Acronym IDES == Intrusion Detection Expert System SAP AG's IDES, Internet Demonstration...

ACuriousMind

Interesting, that's not even on my first page

GBeau

I have my google apps/work account set to administratively disable all search customization for all accounts in my "organization", and otherwise my first hit is Illinois Department of Employment Security

followed by @Danu's wiki article

(google apps used to be free...and still is if you have an account from when it was)

@Danu but if you're looking to try something, I'd probably recommend trying emacs over vim since you'll get usable with it a lot faster

(that is, reach workflow parity with your old solution much faster, and probably a lot faster before you'd get to the same place with vim)

FenderLesPaul

@GBeau yeah I saw

no emails for me

fucking sucks ugh

GBeau

17:02

ditto

FenderLesPaul

I want an interview from UCSB :(

GBeau

but...it's only 11 am so maybe

FenderLesPaul

idk if this means my chances are over or if I still have a chance

if more people start posting about UCSB then I know I'm fucked haha

my friend at UCSB said they hadn't sent out any rejections or acceptances yet yesterday

and a post-doc friend of mine said the same for Caltech

but they didn't say anything about interviews

GBeau

:<

FenderLesPaul

dude look at the stats of the guy that got the UCSB interview

990 PGRE and 4.0 GPA

990 PGRE ughhh

if that's what they're looking for then I'm kissing UCSB goodbye

Mike Miller

17:05

stop

Danu

Just chill man, I know it's tense and scary etc etc but perhaps just take stock when the day is over :P

GBeau

@Danu but that's not for like 6 weeks

FenderLesPaul

it's an emotional roller coaster :p

Mike Miller

do you have things to learn? focus on those

remember that your future grad school will like you better if you'd gotten a lot done this semester

Danu

@GBeau I've been through it too; but just filling this whole chat up with the emotional rollercoaster is maybe not the best thing ^^

FenderLesPaul

17:08

fine :3

GBeau

@Danu takes it to another chat

Is physics pedagogy on topic in physics.se?

Mike Miller

I hope one day there's a metaphysics.se

FenderLesPaul

isn't there a philosophy se?

Mike Miller

meh

it's the crucial difference between metaphysics.se and meta.physics.se that's funny

GBeau

@MikeMiller is metamathematics on topic in math.se?

Mike Miller

17:19

Not sure what that is, but my money's on no.

Bernard Meurer

@FenderLesPaul waiting for college apps is THE emotional rollercoaster

graduate school or not

FenderLesPaul

well that and when a girl invites you to a movie with just her but her best friend crashes

such a struggle

Mike Miller

also, mad max

Bernard Meurer

@FenderLesPaul ::hugs::

FenderLesPaul

@BernardMeurer d'aww <3

Bernard Meurer

17:26

There should be a support group for waiting for applications

0celo7

@ACuriousMind Ohhhhhh

@FenderLesPaul Wow

Did you hear my James Bond story?

FenderLesPaul

17:43

@0celo7 I did not

what happened?

0celo7

17:57

@FenderLesPaul I went to see Spectre and her SJW roommate came along

I got to hear all about how the series promotes misogyny and Bond is a rapist

+her constant sighing and huffing during the movie

FenderLesPaul

I mean it's true that the old bond movies were very misogynistic but the newer ones are better

progress is obviously happening

DanielSank

@0celo7 In my experience that one is like 50/50 in terms of known the definition. However, I'd be surprised if explaining index notation requires talking about abelian groups.

Danu

@DanielSank In fact, I think the two are quite unrelated ;)

Also, what do you think about this claim: One should always capitalize words derived from names (in scientific writing) in order to avoid confusion (e.g. Abelian, Abelianization, etc.).

DanielSank

18:12

Ehhh, no opinion.

I think having a standard and sticking with it is important though.

ACuriousMind

@Danu Either always do it or never do it, but be consistent

DanielSank

Maybe I'll have an opinion later.

Ha, see that? +2 for consistency.

Danu

@ACuriousMind Of course.

@DanielSank But that's a no-brainer.

On a tangentially related note, people always ask me why I insist on making all my pictures in TikZ...

DanielSank

@Danu I recently used TikZ for a circuit diagram. That was cool.

Danu

I recently used it for...

DanielSank

18:15

FOR?!?!?

Mike Miller

@Danu: If no-brainers didn't need to be stated then people wouldn't still be doing the opposite.

Danu

FenderLesPaul

@Danu dude TikZ is awesome

Danu

@MikeMiller This particular one did not need to be stated in this particular conversation :P

FenderLesPaul

especially since I don't have to learn an entire external drawing program

DanielSank

18:16

@Danu Rose petals...

Danu

@FenderLesPaul It is.

DanielSank

You call that physics?

Danu

@DanielSank Hah, who cares about physics when you can do algebraic topology? ;)

Makes for much nicer diagrams ;)

Emilio Pisanty

@Danu Not a lot of algebraic topology on phys rev kaleidoscopes

Danu

@EmilioPisanty That's what you think ;D

...but this is just for some course I'm taking.

Emilio Pisanty

18:18

@Danu would be happy to be proven wrong.

It's a pretty objective claim.

Danu

I think I'll soon start working on my thesis: It will probably be on 2-dimensional SUSY ;)

DanielSank

@Danu Well, I never thought about it like that.

Danu

Physically physicsy physics :)

DanielSank

What have I been doing with my life?

Danu

Anyways, hope you're impressed by the diagrams ;)

DanielSank

18:20

^ Am impressed.

Danu

Thanks :)

How complicated was your circuit diagram? Did you need the "full power", or was it pretty chill?

DanielSank

@Danu Relatively chill.

We had beers after.

Danu

good

0celo7

18:37

@DanielSank Oh, I just realized my definition of vector space includes "abelian group"

@DanielSank There's a partial new paragraph I added at the end

Is it superfluous?

"End" being right before your comments

So it's on the second page (I think)

DanielSank

19:16

Every time I see "Raman spectroscopy" I ask myself why someone is measuring spectroscopic response of noodles.

@0celo7 Ehhh what was that link again?

Bernard Meurer

My dedicated h-bar computer seems to be en-route to death

I don't think it's handling @0celo7's messages too well

2

GBeau

20:04

my old computer was named nike because all it did was win but then it died

ironically, my new primary computer is named styx

pictorexcrucia

20:17

Hi guys I just asked a question related to finding an electric field in a certain type of capacitor. It's not a homework question, rather it's for my job. I work in a lab and I need this electric field. My question was "put on hold" for being too "off topic" or something. I really was just asking for what books I could look at to help me solve my problem because I am genuinely at a loss as to where to start.

0celo7

20:56

@DanielSank I emailed it to you for future convenience.

@DanielSank Oops, I sent that to your work email...I don't have your personal. Hope it's not an issue.

Transcript for