The h Bar

@ACuriousMind Hm... ok I hear you on there being no ground for saying "should."

By specifying these inputs to the theory, are we coercing the system to evolve in such a way that we get what we want out if it? Does the need to specify these parameters place any limitations on the theory?

ACuriousMind

@LukeBurns I don't understand the question. Of course we are building our theories such that they correctly predict the results of experiments. I don't know what you mean by "coercing" the system.

DanielSank

@ACuriousMind any thoughts on standing up for mod?

0celo7

please don't

I don't want to have to make an ACM doll :(

ACuriousMind

@DanielSank It's still 7 days till nomination starts

DanielSank

@ACuriousMind Indeed true.

user218912

12:30 AM

@0celo7 what?

DanielSank

That is a thought.

Anything else?

Look, here's the thing. I don't want to do it because I think it will lead to me generating less content.

However, I want whoever does it to be good at it.

I like the way you reason about site policy.

Your communications are clear.

Luke Burns

@ACuriousMind The values for mass and charge are given by experiment, and we've "tuned" the theory to work by selecting the right values. That's what I mean by coerce.

DanielSank

In a nutshell, I agree with your approach to policy, so I want you to run so I can vote for you.

0celo7

@IceLord Nothing.

user218912

@0celo7 you make dolls of moderators?

DanielSank

12:33 AM

Gotta go, getting on a plane. @ACuriousMind think about it.

user218912

what do you do with them? @0celo7

0celo7

@IceLord no

user218912

ok

ACuriousMind

@DanielSank Well, thanks. I can't promise you either way because I'm not sure yet, but since our last discussion I've moved more towards "will run".

@0celo7 I don't even want to know what you would do with a "ACM doll"

0celo7

@ACuriousMind Nothing good, which is why I don't want one.

user218912

12:36 AM

@0celo7 ( ͡° ͜ʖ ͡°)

Luke Burns

@ACuriousMind Yeah I'm not exactly sure I know what's holding me up here. I appreciate your help.

user218912

ever since my macbook got wet from my water bottle the battery runs out faster.

ACuriousMind

@LukeBurns You're probably expecting something from QFT that it isn't designed to do - it's meant to predict a large amount of data from only very few inputs, but there are these experimental inputs

user218912

@0celo7 do you know why that could be the case?

0celo7

you rboke it

ACuriousMind

12:41 AM

A theory with no experimental input is both the holy grail and probably unattainable

0celo7

@ACuriousMind String theory.

According to Lubos...it must be correct.

ACuriousMind

@0celo7 Still has string tension

Also, which of the compactifications is realized, although that might be dynamical

0celo7

@ACuriousMind Proof?

Luke Burns

@ACuriousMind I don't know if it's that I'm expecting more from it than it was designed for... More that I'm trying to get a sense of whether there are explicit limitations that arise out of the need for experimental inputs.

0celo7

Maybe string tension is linked to the compactification

Which is in turn linked to Witten's gut size

DanielSank

12:43 AM

@ACuriousMind very good

0celo7

@ACuriousMind Sigh. You'll win.

user218912

duh

user218912

everyone loves ACM.

0celo7

I don't love him, that would be weird.

user218912

when I search up a question on stackexchange and look at the answer it's written by ACM (70% of the time).

0celo7

12:44 AM

Start asking harder questions

ACuriousMind

@IceLord Now that is definitely not true, there are users on this site who rather strongly dislike me

0celo7

I can come up with 5 questions he can't answer

@ACuriousMind JD doesn't count.

user228700

Hello :) I was wondering if u guys had any suggestions as to how to get really comfortable with solving free body diagrams involving constraints and all...

user218912

@ACuriousMind who cares doood.

user218912

ignore them

ACuriousMind

12:46 AM

@0celo7 Not talking about him. There was this example, for instance

user218912

page not found.

0celo7

Dude, I have 4k rep

DanielSank

@KaumudiHarikumar practice?

user228700

@DanielSank Yep. I'm finding that I really suck :/

DanielSank

@IceLord answering lots of questions is not the same thing as modding.

@KaumudiHarikumar oh no!

user218912

12:48 AM

@KaumudiHarikumar or be like me and use lagrangians in your newtonian mechanics class and get no marks.

user228700

@IceLord Dunno what you meant.

user228700

@DanielSank Yep :'-(

user218912

because I'm really bad at visualizing stuff like vectors.

user228700

@IceLord Oh, that's gotta be a problem :/

DanielSank

@ACuriousMind hahahahaha amazing!

Your comment is excellent.

Bernard Meurer

12:49 AM

Page not found :(

0celo7

can someone link the comment

DanielSank

@BernardMeurer you need more rep.

user228700

@DanielSank To be fair though, I only just started this stuff...

user218912

@KaumudiHarikumar basically any problem in newtonian mechanics can be solved using something called the euler lagrange equations which are equivalent to $f=ma$. if you solve them you get the equation of motion you find using free body diagrams but without drawing any diagrams, and you can solve it to get the same answer.

Bernard Meurer

@DanielSank Too much work

DanielSank

12:50 AM

@IceLord True but, dude...

0celo7

can you really @IceLord

how do you know what $V$ is without a diagram

user228700

@IceLord Wtf?! Wow. Sounds interesting but it's not for the me right now.

user218912

@0celo7 well basic diagram

0celo7

also I'd like to see you solve one of my statics homeworks from last semester

14 constraints

user218912

@0celo7 lol

DanielSank

12:52 AM

@ACuriousMind can we start a club for people who have been victims of personally directed abuse through the site?

ACuriousMind

@DanielSank Sure, your sockpuppet-accuser beats what I've got by several orders of magnitude, though

DanielSank

@KaumudiHarikumar yeah Lagrangian mechanics is very useful.

Remember the other day I asked if you knew about Lagrange multipliers...?

@ACuriousMind ok well you can still join the club. Your rank is "sock puppet" ;)

ACuriousMind

Yay!

DanielSank

The FAA is now making me turn off my phone's communication capabilities.

Ciao

ACuriousMind

see ya

0celo7

12:56 AM

why do they let an octopus on a plane

user218912

lol

ACuriousMind

@0celo7 Because he paid for the ticket? :P

DanielSank

^ That

0celo7

@ACuriousMind I messed up.

user218912

@0celo7 @ACuriousMind I'm being dumb but given a lagrangian for a real vector field how can you impose the lorentz gauge condition on the vector field, or show that it satisfies it?

0celo7

12:57 AM

I'm too far down the rabbit hole of compact open topologies, lie transformation groups, etc. to give up now.

But I really want to give up.

I'm very sorry for what I said to you.

ACuriousMind

@0celo7 That's called the sunk cost fallacy. Just give up if you want to

0celo7

@ACuriousMind I took economics.

I don't want to give up.

It's like the Lorentz stokes theorem -- I will eventually write a full proof of this.

Although this is considerably harder.

I need to get Montgomery-Zippin.

ACuriousMind

@IceLord 1. You can only impose gauge conditions on massless vector fields. 2. You impose it usually by adding a Lagrange multiplier for it.

user218912

@ACuriousMind oh

ACuriousMind

@0celo7 Well, now I'm confused, do you or do you not want to give up?

0celo7

1:01 AM

What's a Lagrange multiplier?

user218912

seriously? I'm pretty sure you told me to do the same thing last year for this problem.

ACuriousMind

@0celo7 A multiplier named after Lagrange.

0celo7

I've heard about them, but they seem really hard. I never learned about them.

user218912

but I forgot how I did it.

0celo7

@ACuriousMind What?

ACuriousMind

1:03 AM

5 mins ago, by 0celo7

But I really want to give up.

3 mins ago, by 0celo7

I don't want to give up.

???

user218912

@ACuriousMind if I'm given a real vector field lagrangian and asked to show it satisfies some equation of motion, I just plug it into the euler lagrange field equations right?

user218912

is there an easier way to do it, assuming I'm given the EOM and the lagrangian?

ACuriousMind

Lagrangians can't satisfy equations of motion, but the field by definition has the E-L equations as its equations of motion, yes.

user218912

@ACuriousMind yes that's what I meant.

user218912

@ACuriousMind

user218912

1:07 AM

2 mins ago, by IceLord

is there an easier way to do it, assuming I'm given the EOM and the lagrangian?

ACuriousMind

I don't see what's hard about computing some E-L equations.

user218912

because the lagrangian is so big

user218912

unless some terms disappear somehow

user218912

it will be a long calculation

ACuriousMind

Well, long calculations are something to get used to, not something to be afraid of

user218912

1:09 AM

okay. xP

0celo7

@ACuriousMind Well...I wish someone could explain this.

Mike gave me a paper and a 700 page book to start.

My prof sent me a page from some old topology book

I should just read the original paper in full...

user228700

@DanielSank Yes, I remember, but like I keep telling you, it's too advanced for the level I'm at right now.

0celo7

No one really knows this proof

@ACuriousMind So I really want to know how it works.

user218912

@KaumudiHarikumar no such thing as too advanced. just try to learn it. even if it seems hopeless.

user218912

and ask help here.

ACuriousMind

1:12 AM

^bad advice. Knowing what you can and can not digest is a valuable skill

user228700

@IceLord No, it isn't that I don't want to. I would if I could; I just don't have the time, among everything else I gotta learn.

user218912

@ACuriousMind but you're forgetting that with indefinite time spent on something you can digest anything.

0celo7

But I really don't want to go through the pain of figuring it out

@ACuriousMind It will probably take a few weeks for me to understand all the analysis and functional analysis, before I even get to the geometry.

ACuriousMind

@IceLord So? No one has infinite time or infinite patience at their disposal.

user218912

@ACuriousMind I kind of do. because I am irresponsible and don't prioritize things properly.

user218912

1:15 AM

and so far it works well.

0celo7

does it

user218912

yes.

user218912

I am learning so much everyday.

user218912

(thanks to you guys)

0celo7

I don't learn things any more

I slowly come to accept things as true

ACuriousMind

1:17 AM

@IceLord Your day doesn't have more than 24 hours either, and I doubt that this is an efficient way to do things anyway

0celo7

@ACuriousMind I wish I had your ability to accept black boxes.

I've lost so much time this past month chasing black boxes.

@ACuriousMind How do I do it?

ACuriousMind

@0celo7 Just...let go

user218912

@ACuriousMind if you add a self interacting term to the lagrange density for a scalar field does it change the dimension of the lagrangian or is it still $d$?

0celo7

@ACuriousMind Screw you Elsa

ahhh now I've got that fucking song stuck in my head

user218912

I think it's still $d$

0celo7

1:21 AM

@IceLord dude

ACuriousMind

@0celo7 lol

Didn't even think of that

0celo7

you need a coupling constant

that coupling constant makes the dimensions work out

user218912

we didn't learn coupling constants yet.

user218912

we didn't even begin field theory yet, I'm just using my past knowledge of it but I don't remember coupling constants.

ACuriousMind

How can you know what a "self-interacting term" is but not what a "coupling constant" is?

0celo7

1:23 AM

@IceLord Sigh.

Your method of learning has not been working so far

forgive us for being skeptical

user218912

dude I'm working ahead

user218912

I didn't even read the notes

user218912

I'm just randomly guessing

ACuriousMind

Why? Why would you randomly guess instead of trying to systematically work something out?

0celo7

lol

user218912

1:25 AM

because

user218912

I didn't learn it yet

0celo7

@ACuriousMind ok let me randomly guess

uhh, let's work out some differential Harnack estimates for noncompact Ricci flow on spheres

I'll just take some shots in the dark and see if they stick

user218912

@ACuriousMind I'm sorry :(

0celo7

@ACuriousMind How do I use A-A to show that a group action is proper o.o

srs question this time

ACuriousMind

How am I supposed to know that?

0celo7

1:27 AM

because you know A-A?

I don't really have an appreciation for how one uses it.

ACuriousMind

Yeah, but we used it to show shit in function spaces

user218912

@ACuriousMind I did a search of the pdf for the course notes and there is no word "coupling constant" or "self"

user218912

is that bad?

0celo7

Wait

ACuriousMind

I don't know what it's supposed to have to do with a group action

user218912

1:28 AM

how am I supposed to learn it then.

0celo7

What does equicontinuous even mean

@ACuriousMind Does it mean that the functions are all $\epsilon$-close?

ACuriousMind

I don't know what $\epsilon$-close means, but why don't you just look up "equicontinous"?

0celo7

@ACuriousMind Is a uniformly converging family automatically equicontinuous?

@ACuriousMind I know what it means, no need to look it up

user218912

@ACuriousMind it does not mention coupling constants or self interactions in the lecture notes but the problem uses it.

user218912

what in the world do I do?

ACuriousMind

1:31 AM

@0celo7 Yes

0celo7

@ACuriousMind Good.

Compact-open means uniform convergence on compact sets. This also means I can use A-A. I think this means an equicontinuous sequence of diffs/isos converges to a diff/iso. Also I think I can get local compactness from this.

Local compactness might give compactness of the isotropy subgroup.

ACuriousMind

@IceLord Well, I can't do anything about that. Since I also don't know how "complete" your notes are supposed to be, I also can't say whether that's bad or not.

0celo7

@IceLord Read Weinberg.

It's the best QFT book.

user218912

@ACuriousMind do you explain it in any of your answers on pse?

user218912

@0celo7 my prof said to stay far, far away from weinberg until you finish QFT I and II.

user218912

1:34 AM

idk how you used it as your first book

user218912

you're weird

0celo7

I also hate physics with a passion now

So maybe your prof has a point

Burning passion, really.

user218912

but your interests include solid state physics and general relativity, and you're taking QM, and engineering courses which use physics.

user218912

and you work in a physics lab.

ACuriousMind

@IceLord Explain what? Even if your course doesn't explicitly use the word "coupling constant", that's just a name for the $\lambda$ in a $\lambda\phi^n$ term in the Lagrangian.

user218912

1:37 AM

@ACuriousMind oh so I was right it is the coefficient.

user218912

that's the only think that I could think of it to be.

0celo7

@IceLord I don't consider it physics like what you're doing

But I must be careful not to offend @ACuriousMind

I am basically saying I hate what he loves

which is not good

But I cannot help it

user218912

@ACuriousMind why do coupling coefficients have to have mass dimension $2$?

0celo7

@IceLord And I'm not taking QM.

user218912

@0celo7 you finished it?

0celo7

1:39 AM

@IceLord they do?

ACuriousMind

@IceLord they don't

0celo7

@IceLord No, why would I take QM?

user218912

@ACuriousMind it literally says check your answer by using the fact that the coefficients on the self interacting term have mass dimension $2$

user218912

the self interacting term is

0celo7

in dimension 4 and with a cubic term, perhaps

but certainly not in general

user218912

1:41 AM

$\sum_{n\geq 2} a_n \phi^n$

user218912

does that explain why?

0celo7

in $d$ dimensions?

user218912

in any dimensions

0celo7

ok that's certainly false

user218912

oh, it says $a_2$ has it only.

user218912

1:42 AM

:|

user218912

sorry

0celo7

@ACuriousMind ...is it just me or does he misread all the time?

user228700

@JohnRennie: Whenever you're here, the next time, would you mind discussing a homework-tsy problem with me? (Involving free body diagrams). I dunno how to make the concepts clear in my head w/o actually specifying a problem.

user218912

:/

user218912

I'm not dyslexic I just skim, that's why. @0celo7

user218912

1:44 AM

I'll try my best not to anymore. sorry.

0celo7

I'm dysexic

user218912

are you?

0celo7

yes

user218912

then how do you easily blast through books?

user218912

and type in LaTeX really fast.

Sir Cumference

1:47 AM

You know what I wonder?

Wait, now I just realized how incredibly stupid my question was...

Forget that

user218912

what was it?

Sir Cumference

I stupidly asked why we didn't define the speed of light as exactly 300,000km/s, but then I realized we'd need to make the meter way, way way way way way way way bigger

user218912

xD

Sir Cumference

Wait, actually, maybe not

user218912

@ACuriousMind does EACH term in the lagrangian have to have dimensions $d$?

Sir Cumference

1:51 AM

$300,000,000/299,792,458 = 1.00069229$

So we'd make the meter 1.00069229x bigger

If I didn't screw up my math

user218912

so why is it a dumb question?

Sir Cumference

Guess it isn't

user218912

looks reasonable to me but i'm dumb so...

Sir Cumference

Now I want to know why we didn't just call the speed of light 3 * 10^8 m/s

Since we redefined the meter in terms of the speed of light a few decades back

user218912

I bet you there are tons of questions answered about that on PSE.

user218912

1:53 AM

just search it

Sir Cumference

Not that I see

user218912

@ACuriousMind to find the dimensions of the coupling constant do I just write out the dimensional analysis equation with $[\mathcal{L}] = d$ which I am assuming is right always?

user218912

so for my lagrangian is it right to say $d = [a_n] + n[\phi]$ ?

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