The h Bar

0celo7

02:00

@NeuroFuzzy yes, and the curvature has to obey the Yang-Mills equation

do you know about curvature on principal bundles?

there's a good analogy between the gauge field $A$ and the Christoffel symbols $\Gamma$

NeuroFuzzy

I don't know what the principal bundle is, no. Is it the tangent bundle or something?

0celo7

a principal bundle is a fiber bundle where the transformation group is also the fiber

NeuroFuzzy

Egh, you know, i should focus on this general curvature stuff first

i'm getting ahead of myself

0celo7

well GR can be formulated on the frame bundle

which is a principal bundle

I think @FenderLesPaul

I have to formalize my knowledge of bundles

NeuroFuzzy

oh good, I have to unformalize mine

0celo7

02:04

I asked a topologist and a geometer how to learn about bundles and they both recommended Hatcher -> Bott-Tu -> Steenrod

also Husemoller?

then move on to some K-theory stuff if you want spin bundles

NeuroFuzzy

Well thanks, i'll keep note of those when i'm hunting for my next book

0celo7

if you want to get into string theory you need K theory

NeuroFuzzy

Erm, the keywords "principal bundle', "formulating GR on the frame bundle", and "electrodynamics is a classical u(1) gauge theory"

i have to drive home though.

0celo7

although as ACM said, 95% of physicists just believe the Atiyah Singer theorem

NeuroFuzzy

I had a three hour diversity and inclusion seminar today.

0celo7

02:07

it's apparently crazy hard to prove

oh joy

do you feel all enlightened now

NeuroFuzzy

yes

0celo7

you're now guaranteed not to oppress minorities

NeuroFuzzy

yep

that's a weight lifted

eh it was more about conflict resolution

0celo7

someone in my political group suggested we should file for minority status

conservatives at this school are a minority

NeuroFuzzy

g2g, driving home

0celo7

02:09

cya

@FenderLesPaul do you consider QFT in curved spacetime "GR"

I don't know if I should throw them out too

obe

@0celo7 You're throwing out all your GR books?

0celo7

I guess

obe

What...

0celo7

I don't think I need them

I need the shelf space

obe

You don't like GR anymore either?

0celo7

02:11

I need to learn about crystals and these books are distracting

also I have to get rid of games

obe

Crystals are cool.

0celo7

damn Germans

my Freshman research will be bombarding crystals with stupid amounts of radiation

FenderLesPaul

@0celo7 depends on the book

0celo7

well crystals and other crap

things I've never heard of

obe

'dirac crystals' lol

I baked a blueberry cake.

FenderLesPaul

02:14

Nice

how was it?

0celo7

not learning QM

smh you're going to get rekt

you're going to get blacklisted at perimeter

I can see Dr. Sakurai problems laughing right now

"haha that little Canadian kid thinks he can do QM, haha"

blueberry cake won't help you then

FenderLesPaul

wow

0celo7

@obe can you do this integral

FenderLesPaul

only ~2 weeks in college

and you're already a bitter old man

0celo7

$$\int\mathcal{D}x\,\mathrm{e}^{-\mathrm{i}\int_0^t\dot x^2/2\,\mathrm{d}t}$$

can you do it

@FenderLesPaul that is the integral I'm thinking of, right?

@FenderLesPaul it's like 3 at this point

FenderLesPaul

02:20

possibly

0celo7

that $-\mathrm{i}$ might be wrong

obe

@FenderLesPaul Idk I didn't eat it.

0celo7

I think that should be a plus

obe

@0celo7 :'(

0celo7

but in any case you should be able to do it

protip: it's a path integral

obe

02:23

are you asking me?

FenderLesPaul

I've been tasked with a really hard acoustic song to sing

I must rise to the occasion

0celo7

@obe can you do it

FenderLesPaul

wants pie

obe

Idk can I?

0celo7

Shankar has already done it for you if you're on chap 10 or 11

how come I know this and you don't

obe

02:24

It's from chapter 8?

0celo7

no cheating

obe

Idk how to do it.

0celo7

sigh

the trick is not to do it

the trick it to realize it's the free particle propagator

and then calculate it like Shankar does in...chap 6?

obe

really.

0celo7

well you can do the path integral

it's just a gaussian

obe

02:26

I didn't really follow the path integral chapter.

I'll return to it later.

0celo7

eq. (5.1.10)

obe

@0celo7 I need to read the appendix.

0celo7

appendix?

what does the appendix do

obe

Gaussian integrals.

0celo7

you really have to know that for QFT

@FenderLesPaul agrees, right

FenderLesPaul

02:28

Yes

very important

obe

What other math stuff do I need to know?

0celo7

path integrals are just huge gaussians

uh contour integrals

obe

QFT I right?

They don't do path integrals in semester I.

FenderLesPaul

yes contour integrals

0celo7

yes you need that to calculate the Feynman propagator

dude just know Gaussians

who knows what shit will be on the tests

know something about Fourier transforms

uh @FenderLesPaul what else

FenderLesPaul

02:34

everything

0celo7

yeah

obe

Ok.

0celo7

read Twistor Geometry and Field Theory

read Riemannian Geometry and Geometric Analysis

read Topology and Analysis with Applications In Gauge Theoretic Physics

read Algebraic Topology

obe

Reminds me in the GR course they do... all the problems in carroll.

0celo7

just learn some math ffs

learn about connections on associated principal bundles

learn about homology

FenderLesPaul

02:38

dude Carroll problems are seriously easy don't worry about it

obe

What should I be worrying about except QM?

0celo7

Carroll problems are easy if you're smart

they're not easy for me

FenderLesPaul

no they're just plain easy

0celo7

you should be worrying about the state of the financial system, ISIS, etc.

FenderLesPaul

ISIS is some scary shit

0celo7

02:40

radical feminism and the destruction of the nuclear family

FenderLesPaul

worry about that

forget QM

0celo7

worry about the fact that the welfare state has done nothing but enslave future generations

you know, generally good things to worry about

obe

Boring.

The only important thing in the world is physics.

0celo7

physics is actually pretty useless

it really does not matter if Hawking is right, wrong or bites the dust

FenderLesPaul

I met a guy once who said physics was his girlfriend

that's when you know shit is really bad

0celo7

02:43

I met a guy once who loves GR

he is homeless now

obe

What about a guy who loves QFT?

FenderLesPaul

dead

0celo7

he got a job flipping burgers

meanwhile his engineer friend has a good job

the string theorist got shot out of pity

obe

Is it possible to get a phd in theoretical physics and then have a job doing something else but do research at the same time?

FenderLesPaul

no

lol

0celo7

02:47

what

how would that be possible

it is possible to get a PhD in applied physics and read on the side and make money

and still be able to mentor Canadian children through the world of quantum fuckery

obe

I wanted to be a airplane control tower operator and do physics research as well.

Is that possible?

0celo7

uh no

when do you research

how are you going to manage 12 hour days and still research

obe

part time?

0celo7

what

no one hires tech people part time

obe

dammit my dreams are gone.

0celo7

02:51

if you get a PhD in theoretical physics, you're either going to do academics or engineering

and your salary will be lower than a PhD engineer either way

obe

Idc about that.

0celo7

PhDs from my department make an average of $90,000 their first year

obe

Idc how much money I make.

0celo7

lol

obe

I want to look at airplanes and do research.

0celo7

02:52

get a load of this guy

FenderLesPaul

get a load from this guy

obe

@FenderLesPaul Is there no hope for that?

FenderLesPaul

no hope dude

sorry to say

0celo7

well he won't have student loans

so he's not as fucked as, say, a Cornell GR student who doesn't have a full ride

FenderLesPaul

my parents got me covered bro

s'all good

0celo7

02:55

but what if he's not a good professor

and can't get a good job professoring

then what will he do

@FenderLesPaul you rich

don't you have like $250,000 in debt

FenderLesPaul

nah

it's like $10 grand a year for me after scholarships and grants

0celo7

dude I gotta play a game tonight

FenderLesPaul

im ordering insomnia cookies

0celo7

@FenderLesPaul stream

FenderLesPaul

its been ages

ok

0celo7

02:57

what will it be

SKYPE CALL

@StanShunpike wanna Skype call

@obe bye

obe

D:

0celo7

two minutes to live @obe

FenderLesPaul

I can't Skype because I need to practice guitar and don't wanna clog the call with guitar noises

0celo7

any last words

FenderLesPaul

but I can watch

Stan Shunpike

02:58

@FenderLesPaul I saw this in the music SE music.stackexchange.com/questions/30457/… I dunno if you're interested.

I can't lol. I'm working. Writing my book on music theory.

obe

@0celo7 Did you deliberately decide to skype at 11?

FenderLesPaul

@StanShunpike looks interesting thanks

I've been doing these yoga breathing techniques lately and they've really helped me with hitting high tenor notes in full voice

who would've thought yoga techniques would be useful

0celo7

@obe Yes

FenderLesPaul

lemme know when you stream breh

bruh

broseph

broski

0celo7

@FenderLesPaul skype and convince me not to stop learning GR

FenderLesPaul

03:05

I can't Skype tonight I gotta practice :(

0celo7

you can't talk and play

FenderLesPaul

no because I have to sing

lol

0celo7

sing about GR then

I'm gonna try streaming BF4

FenderLesPaul

lol

I heard there was a secret chord

that Einstein played and it pleased the lord

but you don't really care for geometry do yaaa

0celo7

can I make money with geometry

real math is an operator on the space of money that raises GDP

FenderLesPaul

03:09

yes

0celo7

lemme know if this works

streaming

FenderLesPaul

just a black screen

0celo7

Still

FenderLesPaul

it says untitled broadcast

twitch.tv/0celo7

this one right?

0celo7

Revolver 0celo7

FenderLesPaul

03:17

ok got it

0celo7

You can watch me suck at PC fps

FenderLesPaul

wtf why won't it play

dmckee

@FenderLesPaul Nawh. Girlfriends (well, romantic interests of the apposite sex) keep you from doing as much physics as you would otherwise have accomplished.

FenderLesPaul

@0celo7 I'm pressing the play button but nothing is happening

@dmckee haha true

dmckee

@obe It's not actually impossible, but it takes a pretty special kind of person to make it work.

And probably a lack of the aforementioned romantic interest.

FenderLesPaul

03:21

@0celo7 is it different on a mac?

0celo7

03:32

it's streaming for me

so IDK what's up with your PC @FenderLesPaul

FenderLesPaul

idk it didn't do this on my old laptop

0celo7

Well I got pissed off by metro

I'm done

FenderLesPaul

:(

Andrew G

Given the recent claims Hawking has made about one of our problems with black holes, I've been thinking about conservation of information and reversibility. Specifically, if there are any truly irreversible processes that go on in the universe.

Put simply: If I was laplace's demon, would I be able to reverse-engineer the universe all the way back to the big bang with complete certainty, or are there some processes where the final state of a system could have come about from two/more different states? Matter-antimatter annhilation comes to mind…

NeuroFuzzy

03:54

@AndrewG Something I've heard is that in quantum mechanics the past is stochastic in the same way the future is.

Andrew G

@NeuroFuzzy Interesting. Sounds many-worldsy.

NeuroFuzzy

@AndrewG It sort of is. I'm thinking from a Schrodinger's equation POV here; if you knew "the" wavefunction of the universe, which only someone sitting outside of the universe having prepared its initial state and having not observed it since [but calculating its future state exactly through Schrodinger's equation]; then you could derive the initial state of the universe

Andrew G

...but not if I was given the entire state of the universe sometime after it's creation, and asked to derive the initial state.

NeuroFuzzy

Yeah, then it would just be probabilistic, I believe.

but 1. the world doesn't follow Schrodinger's equation, and 2. observing a quantum system while sitting inside a quantum system is zany (or if you're boring 'subtle' :) )

Andrew G

Why wouldn't the world follow the Schrodinger Equation? If I was given the current state of the universe (exact location and velocity of every particle), could I not extrapolate the future state of the universe with certainty?

NeuroFuzzy

04:02

@AndrewG oh I just mean that, like...

Andrew G

(Given infinite computational power.)

NeuroFuzzy

the world isn't classical, it's quantum. But it's not "schrodinger quantum" because that violates SR

and it's better to say it's "QFT quantum" because that satisfies SR, but that can't be quite right either (I think it suffices though)

That was just a disclaimer that

I'm only familiar with schrodinger quantum and can only talk about things to that approximation!

So that all my sentences are prefaced with an implicit "in a schrodinger universe [...]"

FenderLesPaul

States still evolve under the Schrodinger equation in QFT

Andrew G

@NeuroFuzzy Ahh, understood.

NeuroFuzzy

@FenderLesPaul $\hat{H} |\psi \rangle=i \hbar \frac{d}{dt} |\psi \rangle$?

FenderLesPaul

04:06

yes

0celo7

@AndrewG well, if spacetime has a cauchy horizon, GR tells us that knowing everything in the universe at one "instant" doe not enable us to determine everything that ever was and everything that ever will be

NeuroFuzzy

@FenderLesPaul waaaaaat. Where's the catch though?

FenderLesPaul

There's no catch

The schrodinger equation is literally just the statement that the Hamiltonian generates time translation

this is the same in both QM and QFT

so states in QFT also evolve under the Schrodinger equation

don't confuse fields with states of fields

fields propagate according to various relativistic field equations like Klein-Gordon or Maxwell

but the states of these fields still evolve under Schrodinger

0celo7

what about the state $\hat\phi|\phi\rangle=\phi|\phi\rangle$

NeuroFuzzy

@FenderLesPaul so for Dirac/whatever other weird things, you just have a specific space $\psi$ lives in and a specific $\hat{H}$?

Oh boy. Yknow, I'll get there eventually. I'm going to eat and sleep.

FenderLesPaul

04:17

night

fuck these cookies are too sugary

0celo7

my sister in law made me some awesome chocolate chip cookies

and I have to sleep now, night

Secret

04:54

I read this

https://en.wikipedia.org/wiki/Principle_of_least_action

After reading the following (which is related to my honours)

http://scitation.aip.org/content/aip/journal/jcp/126/16/10.1063/1.2720838

specifically equation (4). I cannot help but have this possibly screwy picture in mind:

That there's a curve (which its length is the action) in configuration space which is like a higher dimensional version of a hilly landscape, the curve slides until it reached a valley thus it cannot change its shape anymore (since it is stuck). Then it is easy to see that the action is relatively un…

Secret

05:07

objects that are free falling follows geodesics, which is like a generalisation of straight lines on manifolds (which in the case of GR, it is the spacetime manifold),

The previous post's interpretation of mine cause me tempted to think that the trajectory in phase space of which its length is action, then the principle of least action is the same as saying to find a geodesic in phase space?

I remember that phase space is a symplectic space, but is it also a symplectic manifold?

$$\delta \int_{t_1}^{t_2}L(\mathbf{q},\dot{q},t)dt=0$$
$$\dot{\phi}=0=-\nabla V(\phi)^{\perp}-\lambda \hat{\tau}$$
$$\ddot{x}^{\lambda}+\Gamma^{\lambda}_{\mu \nu}\dot{x}^{\mu}\dot{x}^{\nu}=0$$

They seemed to based on the same principle: To minimise the arc length of a curve??

typo: They seemed= the 3 equations seemed

John Rennie

@ChrisWhite Thanks Chris. I think I'll delete my answer. I've obviously misunderstood what was being asked.

Secret

05:24

Is there any significant meaning when the classical lagrangian vanishes, other than it means the total kinetic energy has the same value as its total potential energy?

If I have a lagrangian that vanishes for all times, then the action of that system in question will be zero, what will that mean?

classic because I still yet to wrap my head around the relativistic version

*for all times in an interval [t1,t2]

*action of that system between t1 and t2

Phonics The Hedgehog

06:29

For certain physics problem you find t, which stands for time. In this example, $100 = 30*x-(1/2)*(-3.8)*x^2$. When you try to solve x in that problem, you get either -18.6166, or 2.282713. Since we are trying to find time, and since time cannot be negative, we only use 2.28 seconds. But that -18.6 can't be there for no reason at all. Is there any physics reason why there is -18.6?

Secret

07:05

@PhonicsTheHedgehog The -18.6 is a consequence of solving the maths equation (which does not know that t > 0 if you don't explicitly state that as a constraint to the equation to be solved)

If one insists on giving a physical meaning, then for the case where x in the above equation represents time, it means whatever phenomenon that the above equation is describing, it occurs 2.28 seconds later and -18.6 seconds ago

then you gave the physical meaning to the - sign in your answer. However it is not always interesting to consider what happens in the past of some given phenomenon since most p…

Slereah

08:38

@Secret : Try to cut up your posts a bit btw

I often have to click on "see full text" on your posts

Rigor

09:20

I think there already is a text limit built in...

Slereah

12:12

imgur.com/t/infographic/oNo9IvT

Ugh

The fusion doesn't power the car in back to the future

That's the whole point of the third movie

Secret

12:30

https://www.youtube.com/watch?v=VylZJrep1MM
I wonder what happens when the top slows to a stop, will it just drop down since the magnetic filed there is basically constant and uniform?

0celo7

@Secret I think so

skill patrol

@0celo7 who's your fav NFL team?

0celo7

probably Redskins but that's embarrassing to say in public

skill patrol

hmmm...

John Duffield

@0celo7 : just try to imagine what happens when you make the torus fatter and fatter.

0celo7

12:38

@JohnDuffield It will never become a sphere.

This is a topological fact.

FenderLesPaul

check your thin privilege

0celo7

wtf fuck off SJW

there's enough at my school

which is crazy btw

the student body is crazy diverse opinion-wise

FenderLesPaul

wow patriarchy

0celo7

there are anarchists and full on communists in my dorm

btw I'm not even thin

skill patrol

real commies?

ACuriousMind

12:43

...isn't a "crazy diverse opinion-wise" student body normal?

0celo7

it's not what I expected from an old southern school

skill patrol

^

ACuriousMind

Ah, ok

John Duffield

@0celo7 : the electron is a 511keV electromagnetic wave in a Dirac's belt configuration. See this water-wave gif and try to imagine what you'd have if the wave was going round and round.

Slereah

2

skill patrol

12:46

:D

John Duffield

@0celo7 : it isn't a sphere. It's a torus that's so fat it looks like a sphere.

ACuriousMind

I think tori die of clogged arteria before they can get so fat.

0celo7

@JohnDuffield Does anyone in a professional journal support this claim?

@JohnDuffield Lol what does that even mean?

@ACuriousMind They're hardy American tori. They can take it.

@JohnDuffield Hmm, how does QED work in this picture?

What's the Lagrangian?

ACuriousMind

@0celo7 I thought the "American torus" is merely a donut :P

2

0celo7

Haha

John Duffield

12:49

@0celo7 The guy who wrote this.

Slereah

Could you link the paper he wrote on the topic

0celo7

...

Please.

Slereah

And point the page where the claim is made

0celo7

Wait, do you mean the equation or the Wiki article?

Slereah

(peer reviewed paper)

0celo7

12:51

I thought the electron was the fermionic excitation of a string...

So is the string in a Dirac belt configuration?

@ACuriousMind Remind me, are the superstring fermions excitations of the open or closed string?

Also are there clopen strings.

Slereah

Open I suppose

From what I recall closed strings behave like gravitons

ACuriousMind

@0celo7 How could it? The "Dirac belt configuration" would be merely one worldsheet topology over which is summed.

Slereah

SUSY analogs are gravitinos, which are... spin 1.5?

ACuriousMind

@0celo7 Uhhhhhhhhhhhhhhhhhhhhhhhhh...dunno :/

0celo7

@ACuriousMind Damn your poor sarcasm meter...

@Slereah Also dilaton and Kalb-Ramond.

Although I have no clue what the Kalb-Ramon actually does.

Slereah

12:54

Aren't dilatons spin 0

ACuriousMind

@0celo7 It's still being repaired. They have to imports some rare parts.

0celo7

Dilaton has something to do with the...vacuum?

Slereah

Oh wait

0celo7

@Slereah Yes.

Slereah

Are strings like

Spin 0 + spin 2 thing

ACuriousMind

12:55

Kalb-Ramond is a 2-gauge field, iirc

It belongs...to 3-branes, I think, but that could be wrong

Slereah

I vaguely recall that you could have both modes, maybe?

0celo7

Uh you have the massless multiplet that splits into Kalb-Ramond, dilaton and graviton.

ACuriousMind

Or maybe 6-branes

0celo7

lol

Did Weigand even talk about that?

I haven't touched string theory since the summer began.

John Duffield

@Slereah : see The Quantum Theory of the electron. He doesn't spell it out, but he makes it clear the electron has a wave nature, and this wave is not propagating linearly at c. Doubtless somebody will now announce that the electron is a point particle.

0celo7

12:56

No, it's a string.

@JohnDuffield Wave nature does not imply it is literally a wave.

@ACuriousMind Someone needs some Heisenberg formalism.

John Duffield

@0celo7 : it works the way it works, but now we know why it works. Because the electron field is just a reconfiguration of the photon field, and the messenger particles are more fundamental than the field they're supposed to mediate.

ACuriousMind

@0celo7 Yes, at least we did in the course, briefly. Hmm, now I think it was 5-branes: 2-gauge field -> 3-curvature, canonical kinetic term is a 6-form, which is naturally integrated over a 6d worldvolume

0celo7

Decide already :P

ACuriousMind

That was one part I found actually interesting because it was not perturbative

0celo7

Are you sure?

John Duffield

12:59

@0celo7 : no, electron diffraction implies it literally is a wave.

2

ACuriousMind

@0celo7 That I found it interesting? Yes. :D

0celo7

What does it mean that it was not perturbative

Slereah

>He doesn't spell it out

0celo7

I know what "not perturbative" means

But in this case I don't know what you mean

brb LA

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