The h Bar

ACuriousMind

00:03

The hats are here!

0celo7

@ACuriousMind wat

ACuriousMind

@0celo7 The hats are here!

0celo7

wtf

is that some Heidelberg thing?

ACuriousMind

No, that's an SE thing

Mikhail

winterbash2015.stackexchange.com

0celo7

00:10

what?

can someone please explain?

ACuriousMind

@Mikhail's link is the official explanation, what confuses you? ;)

Mikhail

also the train goes into a house

0celo7

@ACuriousMind o.o

@Mikhail ??

Mikhail

look at the animation in the link.

0celo7

just a bunch of people

ACuriousMind

00:16

@0celo7 There's a freaking train at the top of the page, how can you not see it?

0celo7

@ACuriousMind huh

don't know

ACuriousMind

It drives from left to right, behind/through the houses

0celo7

yes, I saw it once you pointed it out

ACuriousMind

Ah, alright

0celo7

watching the Bourne Supremacy, getting hyped for Germanland

@ACuriousMind you guys expecting snow?

ACuriousMind

00:24

Not that I'd know :(

0celo7

you don't go outside, so it doesn't concern you

ic

ACuriousMind

Didn't really snow here last winter, either.

0celo7

:P

oh god your avatar

it's scary

@ACuriousMind what is that

ACuriousMind

@0celo7 A "hat"

Symbolizing the Greek muse of tragedy, apparently

0celo7

lol you got the close one

naturally

@ACuriousMind fancy talk for a sad mask

ACuriousMind

00:29

@0celo7 It's a tragic mask, not a sad mask! :P

0celo7

if Herr Rademacher could not explain it to me I don't think you can either :P

looks like a sad mask to me

@ACuriousMind do you have to equip the hat

where is the SE inventory screen

ACuriousMind

lol

Yes, you need to equip it, just click on the message that says you earned it, it takes you to the inventory screen ;)

0celo7

ok

yay

now we're both sad

hmm, @ACuriousMind, it looks like they're not in the same position

ah, one can move it!

Mikhail

01:20

2

Q: Why electric pickle only glow at one end?

The electric pickle is often used as an example of a non-ohmic resistor. In the experiment, electric current excites the sodium ions inside pickle, producing very bright and intense light effect. What I am wondering here is that why in many experiments only one end of the pickle glows?

kevin Tah N.

03:17

hey there, anyone available

?

start ChatJax

$\alpha$

start ChatJax $\alpha$

\alpha

dmckee

04:23

@kevinTahN. Go here: math.ucla.edu/~robjohn/math/mathjax.html

dmckee

In any case, the last of my grades for fall semester have been submitted.

For reasons outside of my immediate control it's been the worst upper-division bloodbath I've even presided over.

If one student will agree to finish the work, I can change him to a incomplete and then I'll be failing fewer than a third of my juniors and seniors.

Yikes!

I need a drink, but I have a cold and shouldn't have one.

DanielSank

Anyone know how to think about this:
$\int dx \delta(x^2 + y^2 - r^2)$?

dmckee

04:42

@DanielSank Er ... the delta function is non-zero in a circle, but you integrate along the x-axis, so you encounter it twice.

But I'm not sure exactly what the properties of $\int dx\,\delta(x^2-x_0^2)$ are. I'd hesitate to assume they are the same as $\int dx\,\delta(x-x_0)$.

I'm sure I knew that stuff in grad school. Or at least the week I passed the comps.

Physics Meta

05:43

0

Q: second quantization and elementray questions

I want your opinions on how useful it is to throw second quantization at students when they have not understood first quantization. I tend to add a simpler answer when I see this. Also the emphasis on second quantization and statements of the type "all space is filled with electron fields /parti...

discussion

kevin Tah N.

08:02

@dmckee awesome, very interesting info

skill patrol

10:16

Anyone interested in Literature?

0celo7

10:56

@skillpatrol No, and I'm dreading the Lit class I have to take next semester.

skill patrol

Then don't take it.

0celo7

11:13

@skillpatrol I want to graduate.

skill patrol

Why don't you have advanced credit for it?

0celo7

@skillpatrol Lack of intelligence.

skill patrol

Live and learn pal.

0celo7

@dmckee There's a formula for the delta of a function. @DanielSank should know it...

The Dark Side

Some hat secrets:

David's hat store

The Winter Bash 2015! We talk hats, period... and more hats. w...

:D

skill patrol

11:31

Hat Admiration Group

HATS

This^ just started too.

0celo7

11:55

Hats do not show up on mobile.

DanielSank

12:31

@0celo7 Yes yes, the business with the Jacobian.

Bass

12:41

does anybody know a way to type a Feynman slash in MathJax?

the only thing I found is \ not: $\not\partial$

0celo7

12:57

@Bass $/\!\!\!\partial$

Bass

$/\partial$, $/\!\partial$, $/\!\!\partial$, $/\!\!\!\partial$

cool thanks! :)

0celo7

13:26

@Bass test: $/\!\!\!\partial\psi$

in some typsetting programs you can push the $\partial$ into what is next to it

looks like chatjax is free from this

Bass

@0celo7 not sure what you mean.. here (Firefox) it looks perfect. thanks for the hint

0celo7

@Bass I'll find an example...

@Bass chap 10 in Jost if you have it

can't take a screenshot of my e-copy right now

Bass

14:01

@0celo7 nope.. don't have Springer access at the moment

0celo7

Shing

14:25

oh man, I love the new hat function on stack exchange

Slereah

14:47

Is that a fancy formula for hermitianity

hermitianness

hermititude

0celo7

@Slereah dunno

vzn

16:06

in theory salon, Nov 20 at 17:10, by vzn

Babai breakthru: graph isomorphism in quasipolynomial time / Tmachine blog

Moses

Hi

Illustionist

16:38

Hi

can somone provide me with reference of how to construct Hamiltonian from Lagrangian using matrix method ?

or provide me with reference

Illustionist

16:59

@0celo7 physics.stackexchange.com/questions/224025/…

0celo7

@Illustionist The kinetic energy is, in general, a quadratic form.

Illustionist

I see

how can you get the Hamiltonian from this

Slereah

what is this "winter bash" thing on SE

o, they are Achievments

0celo7

17:14

@Illustionist from what

I'm not sure what your question is

@Huy finish that calculation yet?

Huy

just got home from the geometry class

that was some sick shit

shit

now I need to eat dinner and prepare for pedagogy exam tomorrw

how was ur day @0celo7

0celo7

it's 12AM

day has not started

>pedagogy

implying that's a real thing lol

Huy

idk

they call it that way

it's a joke really

it was 3 hours per week for 12 weeks or so

and I went through everything in less than 2 hours

0celo7

@Huy sounds like a standard course

Huy

yeah

I did two such pedagogy courses already

0celo7

17:27

@Huy sounds like a standard course

Huy

was always similar

0celo7

@Huy you wanna watch me play BF4, I recorded some gameplay

Huy

pretty much the biggest waste of my life

0celo7

dunno what to do with the footage now

Huy

@0celo7 if you wanna watch me play LoL I recorded some too

0celo7

17:28

ok

post.

Huy

@0celo7: youtube.com/watch?v=N_2ofWcVKkU starts around 8:30

0celo7

with voice?

Huy

I don't speak when I play by myself

but later some German fag joins me on TS and talks to me

ryan u trol

0celo7

@Huy who is ryan

@Huy uploading

the quality is crap because of reasons

increasing the recording quality from now on

ACuriousMind

17:49

@Qmechanic: I am confused. I'm trying to help @EmilioPisanty with his zilch conservation, and I agree with your repeated statement in your answers that an on-shell symmetry is a vacuous notion.

However, the derivations in one of the papers seems to use that if I get $\delta S = \int \mathrm{d} C = 0$ for any on-shell transformation (and I will get that for every on-shell transformation, as you say), then $C$ is a conserved current form. Is there something wrong with it, i.e. is such a conserved quantity somehow inferior to a "true" conservation law derived by Noether's theorem, or is this reasoning flawed altogether?

0celo7

Zilch conservation?

ACuriousMind

If there is nothing wrong with it, what's so brilliant about Noether's theorem? It would seem such a reasoning somehow renders it moot to look for symmetries if I can get on-shell conserved quantities by any old transformation

0celo7

Why is an on-shell symmetry vacuous?

ACuriousMind

@0celo7 Because "on-shell" means "the variation of the action is a boundary term for any variation of the path/fields".

And symmetry means "the variation of the action is a boundary term for the variation of the path/fields under the symmetry transformation".

0celo7

Oh yeah.

@Huy glorious murder

@Huy good round I had this morning, randomly decided to record it

ACuriousMind

17:54

I'm currently thinking that since Noether's theorem uses off-shell identities that just become conservation laws on-shell, those contribute "additional information" about the system, while if I use the equations of motion to get the identity in the first place, then I've gained no new information

This, however, would render this whole business about "conserved quantities of Maxwell's equation" pretty boring from a theoretical point of view.

0celo7

What are the conserved quantities of Maxwell's equations?

ACuriousMind

@0celo7 An infinite hierarchy, apparently, beginning with the energy-momentum tensor and the zilch tensor, just look at Emilio's recent questions

0celo7

@ACuriousMind Hmm

ACuriousMind

If what I'm thinking is correct, naming that thing "zilch" was quite appropriate because what it adds as information is...zilch :D

0celo7

Seems boring :P

@ACuriousMind What's some good Bavarian food

I need to make a list of things to eat in the old country

ACuriousMind

17:58

Also cc @Danu, see above for my recent confusion about that zilch thingy.

0celo7

Leaving in one hour

ACuriousMind

@0celo7 I'm not a Bavarian.

0celo7

@ACuriousMind I thought Westphalia was Bavaria

guess that explains my geography grades in middle school...

@ACuriousMind you've certainly heard of some Bavarian foods, right?

ACuriousMind

18:26

@0celo7 Not really, actually

My contact with Bavaria so far has been absolutely minimal, I have no relatives there

0celo7

hmm

@ACuriousMind have you ever been there?

ACuriousMind

Nope

0celo7

have you been outside of Germany?

ACuriousMind

Yes

0celo7

but not to the land of the free

@ACuriousMind do you like Leberkase

Emilio Pisanty

18:44

@0celo7 Ooooh, Leberkäse is not bad

At least when compared with British food, so take that with a grain of sand.

The statement, not the leberkäse

@ACuriousMind Yeah, if you're confused then I've got very little chance, it's way more technical on those Noether fronts than I'm used to at the moment so I'm slogging through this stuff.

ACuriousMind

@0celo7 Ew, no

0celo7

Is that for America or Leberkase

Danu

19:18

Oh, god, hats...

@ACuriousMind I don't really like this terminology/way of thinking about stuff so I can't help you. What paper exactly are you referring to?

I hope you agree that at least the conserved quantities derived from $Z$ are indeed conserved, no?

@EmilioPisanty Do not despair quite yet!

ACuriousMind

@Danu Look in the other room for a bit more, I'm talking about this. I agree that they are conserved, I disagree that that particular paper uses a "symmetry" and "Noether's theorem" to derive that.

Danu

@ACuriousMind This paper is not really something I'm taking all too seriously at the moment anyways...

Why don't we stick to Kibble and Anco's papers?

ACuriousMind

Because Emilio wants a Noetherian formulation and Anco is completely on the level of the e.o.m.!

Also because Anco is full with arcane terminology and techniques, I guess :P

Danu

I'm pretty sure Anco is the way to go.

Why would we hope for a Noetherian formulation when we know the required symmetry only holds on the level of e.o.m.?

ACuriousMind

@Danu Look at e.g. Philbin - there is a symmetry corresponding to this!

Danu

19:27

@ACuriousMind I'm pretty sure we agreed it's related to duality which is not a symmetry of the action.

ACuriousMind

@Danu Yes, the duality is not a symmetry of the action. That does not prohibit the zilch from being the Noether current of another actual symmetry.

Danu

@ACuriousMind I thought we agreed it had to come from duality---I see things have changed (I didn't look at the chat yet).

0celo7

19:45

@Danu what's some good Bavarian food

Danu

Nothing really, in my opinion. Kartoffelknödel are kind of funny---other than that it's mostly dough, meat and fat.

It's very unrefined.

(like their beer)

0celo7

What is wrong with dough and meat

Are you gluten free vegan

Danu

No, it's just boring.

There are no really interesting flavors involved.

I should note that my food standards a higher than most people's.

0celo7

@Danu what German food do you like

Danu

@0celo7 German pie and/or cookie recipes can be quite good---though I haven't had anything good here.

Emilio Pisanty

19:52

@ACuriousMind Yeah, Anco is a lot to digest

0celo7

You have not had any good German food?

Emilio Pisanty

Particularly when compared with Barnett

Danu

@0celo7 While living here? Neh, not really.

0celo7

How am I the snob in this room??

Danu

I don't know. Who said that?

me?

0celo7

19:54

What food do you like

Danu

Too much to enumerate...

0celo7

Examples?

Danu

Oh btw if you want to have something nice yet basic to eat here you could just buy some nice Brezen, those are pretty good.

@0celo7 Many types of Asian food, Latin-American food when done well, Medditerranean etc

I tend to get a bit bored when eating typical West-European food because of the lack of interesting flavors (of course, this completely depends on the price level you're looking at, but that goes without saying).

0celo7

@Danu I know what a pretzel tastes like

I'm asking you because all my mother is going on about is Leberkase, which is nasty

Danu

Leberkase is pretty fucking shit :P

It's delicious in a disgusting way, if you know what I mean.

You can enjoy it like you can enjoy McDonald's

0celo7

20:01

I love McDonalds

Danu

I am starting to doubt that anyone called you a snob.

0celo7

I will put a Schnitzel on a piece of bread and be happy

Danu

That's already a lot better than McD's

0celo7

Will probably get a thing of nuggets before I get on this plane

I don't know why people dislike McD

It's great

Danu

It's a matter of time before you start disliking it (or it was for most people I know, anyways).

Mikhail

20:07

Danu

^what's this?

Mikhail

explains how big macs are a rip off

0celo7

Time to get fisted by the TSA

Big Mac? Lol I get the $1 double cheeseburger

Mikhail

first the big mac then the 1 dollar cheeseburger

0celo7

Although Chick Fil A is better...

Mikhail

20:13

Burger King

0celo7

But a lot more expensive! I'm a destitute college student.

ACuriousMind

20:27

@ChrisWhite Now even the Area 51 discussion zone was done before us!

Mikhail

Anybody have appendix 1 of "Handbook of Optical Systems"?

0celo7

@ACuriousMind why is The Man mad at us

ACuriousMind

@0celo7 Uh, what?

0celo7

@ACuriousMind we're last for some reason

We made the SE government mad

ACuriousMind

Or we're getting an extra fancy new design :)

I'm ever the optimist

Bass

20:46

1

Q: How to prove $d\omega=(\nabla_\mu\omega)_\nu dx^\mu\wedge dx^\nu$ without using coordinates

This is exercise 7.8 b) of Nakahara's GTaP: Let $\omega\in\Omega^1(M)$ be a 1-form on a Riemannian manifold with Levi-Civita connection $\nabla$. Prove that $$ \mathrm{d}\omega=(\nabla_\mu\omega)_\nu\, \mathrm dx^\mu\wedge\mathrm dx^\nu $$ I proved it using the fact that $\mathrm dx^\mu\wedge\m...

differential-geometry riemannian-geometry differential-forms

anyone versed in coordinate-free notation?

ACuriousMind

@Bass 1. Just use that the contraction of a symmetric object (that $\Gamma$) and an antisymmetric object is always zero (although this just hides your explicit argument there, everyone just proves that once generally and then just uses it precisely to not quit the summation convention) 2. The r.h.s. has picked coordinates, how do you think you can prove that in a coordinate-free way?

Bass

@ACuriousMind with 1., I get rid of the second line, but what about the 3rd one?

2. I just thought maybe there is a coordinate-free way to express the r.h.s., then there might be a way to prove it coordinate-free.. apparently there isn't?

ACuriousMind

@Bass The third is just $\partial_\mu \omega_\nu \mathrm{d}x^\mu \wedge\mathrm{d}x^\nu$.

Bass

oh! of course

thanks!

ACuriousMind

@Bass Well, I'd say the l.h.s. is the coordinate invariant way of writing this :P

Probably it's something like $\mathrm{d}\omega = (\nabla \omega^\sharp)^\flat$, though

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