The h Bar

12:38 AM

So apparently string theory because if you truncate $e^{-x} = 1 - x + \dots$ at a finite number of terms, the truncation goes to infinity, but keeping all terms means it stays finite, in this case going to zero, but for the 'hadronic mass spectrum'?

0celo7

that does not seem to be a coherent sentence

bolbteppa

1:03 AM

summerstudents.desy.de/hamburg/e246457/e247841/Stringintro.pdf

Between equation 0.6 to 0.7 it says it

Cows

1:25 AM

Guys, I need some web dev help. Having some kinks with basic auth

0celo7

1:47 AM

@Cows what math?

@bolbteppa Hmm. What about it?

bolbteppa

explain it

it's crazy

0celo7

@bolbteppa look, I’ve read your sentence like 5 times and you’re missing several words

“so apparently string theory” is not English

bolbteppa

It is perfect Eenglish

0celo7

whatever

Cows

@0celo7 oh I meant "basic auth" for API access

@0celo7 but I think I figured it out

@0celo7 can you help me understand the difference between adiabatic and diabatic?

bolbteppa

2:06 AM

@0celo7 'so apparently string theory (is a thing, is true, exists, is a theory worth considering, etc... etc...) because if you truncate...'

parvin

hi guys, can some one explain to me how a capacitor can let current flow through it? or better to say, how can it have the effect of a current flowing?

bolbteppa

@Cows en.wikipedia.org/wiki/…

Cows

@bolbteppa awesome! looking at it now

bolbteppa

@parvin coulomb's law en.wikipedia.org/wiki/Capacitor#Theory_of_operation

0celo7

@bolbteppa you can't leave out multiple words and have it be perfect english

bolbteppa

2:11 AM

@0celo7 you can according to linguists since perfect English is amorphous and malleable depending on social consensus

0celo7

well this guy's social consensus is that you're wrong

Semiclassical

2:25 AM

@bolbteppa so English is a glassy language. Neat

bolbteppa

Sandy enough yes

parvin

@bolbteppa if in an insulator the charges are not uniformly distributed, does it create a field ?

cuz I thought of field as a property of a charge, not a temporary state that they have

and that the insulator in a temporary non uniform charge distribution is in neutral position, how can it create any field?

bolbteppa

As the wiki link says, you can have a dielectric (~ insulator differencebetween.info/… ) between your conductors and end up with the dielectric developing an electric field because "When a dielectric is placed in an electric field, electric charges do not flow through the material as they do in an electrical conductor but only slightly shift from their average equilibrium positions causing dielectric polarization"

Dielectric

A dielectric (or dielectric material) is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material as they do in an electrical conductor but only slightly shift from their average equilibrium positions causing dielectric polarization. Because of dielectric polarization, positive charges are displaced in the direction of the field and negative charges shift in the opposite direction. This creates an internal electric field that reduces the overall field within the dielectric itself...

parvin

2:44 AM

can I describe some thing then you -please!- tell me if it's correct?

it's like, if there is a circuit with a battery source and a capacitor, from one side, the battery start giving out charges, and they flow until they reach to one of the capacitor's plates, but do not flow further cuz capacitor don't let them.

instead, the charges distribution cause the other plate bring opposite charges close to the dielectric in between. when taking the capacitor out,connecting it to another circuit with a consumer, it causes potential difference and with that it can act like a battery, until the potential difference between its plates are zero

is that right?

bolbteppa

I think so, this seems like what you're trying to describe

How a Capacitor Works - Capacitor Physics and Applications

►

parvin

thank you!

vzn

3:02 AM

in theory salon, 2 mins ago, by vzn

This Game Teaches You How to Build a Quantum Computer / motherboard

Anonymous

@Curio $\tau=I\omega$

vzn

in theory salon, 1 min ago, by vzn

New silicon structure opens the gate to quantum computers / physorg

parvin

do electrons have energy?

Anonymous

@parvin Of course

parvin

how do they have?! I mean, how can they transfer energy?

do they actually "have" energy or is it like they can cause attraction or potential difference and cause forces on other chargeS?

Anonymous

3:09 AM

@parvin Yes, the former

Anonymous

I suggest doing some basic reading from Wikipedia first

parvin

on what? what should I search in it?

Anonymous

Electron

Anonymous

Also Kinetic Energy

parvin

thank you

DanielSank

3:23 AM

ZOMG I NEED HATS

@heather give me hats!

DanielSank

3:41 AM

@0celo7 hats.

@BernardoMeurer

anyone

Anonymous

Upvote questions from the SE app. You'll get a hat :P

Anonymous

Or vote to close a question

Anonymous

Or...

Downgoat

4:12 AM

Queston: why did alpha particles get their own designation? What is so special about 2 protons + 2 neutron, why didn't a hydrogen nucleus get its own name?

0celo7

@Downgoat we knew about alpha particles way before protons, neutrons, or nuclei

Downgoat

I assume that is because we observed them during nuclear decay?

0celo7

yes

Downgoat

Why are He-4 nuclei emitted in nuclear reactions, why isn't it energetically favorable to emit a Li-6 nuclei?

Anonymous

Binding energy

0celo7

4:25 AM

@DanielSank "if you ever see DanielSank online can you ping him and tell him "ooolb got banned by rob when he logged off right after the conversation that night""

2

- ooolb

Anonymous

@0celo7 It seems ooolb is stretching it again. Not a very respectable thing to do.

0celo7

Stretching what?

enumaris

5:11 AM

weez

Cows

5:45 AM

So i have been reading all sorts of things in my spare time

I wonder how time ordering is done in weird space though

Just a thought than ran across my mind while struggling with basic QM concepts lolz

At any rate finally got to read on time-independent perturbation theory and some other things like Fermi's (Dirac's ?) Golden rule

Interesting stuff

I'm curious how time ordered exponentials work in curved space. If you know, ping me. I will read on this next month.

0celo7

@Semiclassical paging

Cows

Ordered exponential

The ordered exponential, also called the path-ordered exponential, is a mathematical operation defined in non-commutative algebras, equivalent to the exponential of the integral in the commutative algebras. In practice the ordered exponential is used in matrix and operator algebras. == Definition == Let A be an algebra over a real or complex field K, and a(t) be a parameterized element of A, a : K → A . {\displaystyle a{\mathrel {:}}K\to A.\,} The parameter t in...

Semiclassical

@0celo7 ?

0celo7

@Semiclassical it worked!

Semiclassical

What did?

0celo7

5:54 AM

@Semiclassical I'm trying to get a horrible (but probably elementary) inequality

mathematica seems to imply it's correct, but the form has me raise an eyebrow

Semiclassical

how horrible are we talking?

0celo7

@Semiclassical getting the last one from (6.5) i.gyazo.com/53210b0ffcaafa027c699cc6f0466143.png

$R,\lambda,\rho\ge 0$

Semiclassical

...yeah, that's not nice looking

0celo7

$\epsilon\in (0,2)$

yeah, so here's the weird thing

note that $B$ has that $1+\epsilon^{-1}$ term in it

but then in (6.5) that's divided by $4-2\epsilon$

and somehow that disappears

so you'd expect it to have the wrong blowup, but I'm not sure

Semiclassical

weird

Cows

5:57 AM

@0celo7 the equations you are sharing look awesome. May I ask what you are working on. I am just curious

0celo7

@Cows Cheng-Li-Yau gradient estimate for elliptic equations

Cows

@0celo7 very cool

0celo7

@Semiclassical also the sign of $\lambda$ seems to be wrong...

it's a strange looking thing

dmckee

6:10 AM

::facepalm::

The author of

0

Q: Neutron Source from ionised Helium?

Reading the question about Is there any way to attract or push away a proton? I’m wondering would it be possible to ionise Helium atoms completely and to separate some electrons and protons in an electric potential field. If this is possible, what happens to the neutrons? Edit: It is possible to...

neutrons

has managed to accumulate more than three thousand rep.

SkyWalker

7:37 AM

@TomNeiser You are a student of UCLA ?

Have you met Terry Tao ?

Slereah

8:23 AM

mornin

Slereah

8:39 AM

"A mathematician might find Notation 3.31 objectionable on the grounds that the operator X does not actually have any eigenvectors."

SHOCKING

"The fact that δ(x − x0) is not actually in the Hilbert space L2(R) does not concern the physicist"

That bloody physicist

Tom Neiser

9:04 AM

@SkyWalker Yes, I'm at UCLA. Yes, I have been to one of his talks on finite time blowup of the Navier-Stokes equation (terrytao.wordpress.com/2014/02/04/…). He seems like a very down-to-earth person. Still has an Australian accent

Slereah

In a Hilbert space, is $\langle a, b \rangle + \langle c, d \rangle = \langle a + c, b + d \rangle$?

Captain Bohemian

10:42 AM

@Slereah I think I know too little about conformal field theory. I used to see a book with a chapter conformal field theory, but I didn't read it much bevause I don't know where conformal field theory is applied in physics.

Slereah

11:00 AM

String theory for a start

Captain Bohemian

11:29 AM

but I don't know if I can get a position in a string theory group.

I think loop quantum gravity is closer to GR, but there are not many groups in it.

Emilio Pisanty

@dmckee I've been saying this for ages

data.stackexchange.com/physics/query/393837/…

it's a design flaw in the applicability of the SE rep-accounting model to science

Slereah

all quantum gravity stuff is full of groups

Emilio Pisanty

and now that user is actively participating in the close review queue

@Slereah let's not

Let's create community mechanisms, working within the software that we have, that will clearly mark BS and pseudoscience as such and will make it clear that this site isn't the place to post it.

Slereah

Well I tried that but it never works!

Even just changing the ratio of points gained and lost never went anywhere with SE

Or adding a rule to delete answers that are plain wrong

So welcome to the status quo

Emilio Pisanty

11:49 AM

@Slereah indeed

user929304

12:08 PM

@ACuriousMind hey, let me know if you have some time later, wanted to ask something. it s essentially about: why "relational QM" is an interpretation? as in, how does it deviate from the conventional/standard description of QM, for it to qualify as "an interpretation" like many others.

Slereah

"To that end we introduce the anticommuting socalled Faddeev-Popov ghosts
- henceforth abbreviated $\Phi \Pi$ ghosts"

$\Phi$addeev $\Pi$opov

Emilio Pisanty

@Slereah well, that does seem like a reasonable acronym for Фадде́ев-Попо́в ghosts

Slereah

What do people call a gauge transformation, anyway

Is it just the principal bundle business or does it hold for any underdetermined Lagrangian system

"BRST theory uses crucially cohomological ideas and tools."

noooooooooooo

David Z

12:42 PM

@Slereah do note that deleted message was highly inappropriate

Slereah

I guess I'll just have to do it myself!

Slereah

1:02 PM

@0celo7 what does the cohomology of a nilpotent operator $D$ being $\mathrm{Ker}(D) / \mathrm{Im}(D)$ mean

What's the equivalence relation

I know that Im is a subset of Ker since $D^2 = 0$

Physics Meta

1:13 PM

0

Q: Crackpots and links to crackpot articles in their profile

So I see that this website is tolerant of people (which I choose to call "crackpots") which have links to their own dubious work in their profile. These people even have thousands of points of reputation (I bet most of them from members upvoting their reasonable questions), but the minute you che...

discussion user-accounts non-mainstream-physics profile-page

GPhys

@Slereah To get a Cartesian r^2 if I have a r^2 in Boyer-Lindquist coordinates I just add a^2 right?

ACuriousMind

@Slereah I don't quite understand your question

It's the quotient of the kernel by the image, just a standard vector space quotient

user929304

1:31 PM

@ACuriousMind i ask because I recently came across this recent paper arxiv.org/pdf/1712.02894.pdf

ACuriousMind

@user929304 I'm afraid I don't know anything about relational QM

And I don't care enough about interpretations to change that :P

user929304

@ACuriousMind same :)

@ACuriousMind just wondered what the big deal is about it

0celo7

@Slereah what ACM said

Slereah

@ACuriousMind Oh are they vector spaces

user929304

it s the one that says the state is only defined relative to another system

Slereah

1:35 PM

And so you just collapse the $Im$ dimension?

ACuriousMind

@Slereah Sure, the BRST operator is an operator on a (pseudo-)Hilbert space.

Slereah

That was the part I was missing

Was not aware the two were vector spaces

Though I guess it should be obvious for a linear operator

0celo7

What the hell is a pseudo Hilbert space

ACuriousMind

@0celo7 One where you can have null/negative norms :P

0celo7

Oh, right

Slereah

1:39 PM

I guess it's the BRST space where the states are shitty because of the gauge symmetry

And you have to get rid of them or something

Wait

That article on BRST quantization is also by Henneaux

I can't escape him

0celo7

@ACuriousMind urgh halp

(Typing doubt)

It’s a long one

Slereah

Is there a good intuitive meaning behind what the cohomology is

Like why the quotient of the kernel

ACuriousMind

@Slereah Gauge invariant states with the gauge redundancy removed.

Slereah

Well I meant more generally

ACuriousMind

That is, the kernel of the BRST operator are the gauge invariant states because the operator basically implements the (infinitesimal) gauge symmetry, and its image are precisely the analogue of the spurious states from Gupta-Bleuler that are "there" but decouple from all physical processes.

Slereah

1:45 PM

though henneaux is giving an example here

With the exterior derivative

Let's see if it illuminates

GPhys

Am I understanding that correctly?

ACuriousMind

@GPhys Understanding what correctly?

0celo7

@ACuriousMind Define $$B=C(1+\epsilon^{-1})\rho^{-2}-4\lambda\sigma +(2(n-1)^2+\epsilon)R,$$ $R,\lambda,\rho>0$, $n\ge 2$, $0<\epsilon<2$, $0\le \sigma\le 1$. The claim is that $$\frac{B+\sqrt{B^2-4(2-\epsilon)\lambda^2 (2\sigma^2-\epsilon)}}{4-2\epsilon}\le \frac{(4(n-1)^2+2\epsilon)R}{4-2\epsilon}+C'((1+\epsilon^{-1})\rho^{-2}+\lambda)‌$$

ACuriousMind

I'd rather not

0celo7

So I can see one has to get a $2B$ in there somehow, probably by estimating that square root from above

@ACuriousMind :(

Slereah

1:52 PM

@ACuriousMind Is the cohomology (for the exterior derivative) inexact closed forms?

Or something similar?

0celo7

@Slereah yes

Slereah

ah, some progress

I mean, I still need to find out one would care about it

But still

0celo7

@Slereah because it's dual to homology

Slereah

Yeah I'm up to the Poincaré lemma part

0celo7

one could almost say it's a co-homology

@ACuriousMind pleeeeease

Slereah

1:56 PM

one might

Why is $H^0(d) = \mathbb R$

What's the set of inexact $0$-forms?

0celo7

it's that for a connected manifold

Slereah

Oh wait

I guess trivially

They're all inexact

0celo7

it counts the constant functions

ACuriousMind

@Slereah It's just (locally) constant functions

Slereah

Since there's no -1 forms

(It's for $\mathbb R^n$)

0celo7

1:58 PM

@Slereah Prove: a locally constant (continuous?) function on $\Bbb R^n$ is constant everywhere

Slereah

Is that the identity theorem or something

0celo7

you don't need continuity

identity theorem?

Slereah

Wait what

How would a locally constant function be constant everywhere

0celo7

hint: R^n is connected

Slereah

What about $f(x) = 0, x < 0$ and $f(x) = 1, x > 0$

Wait what does locally constant mean here

0celo7

2:01 PM

how is that locally constant at $0$

Slereah

Oh is that constant on every neighbourhood

0celo7

@Slereah each point has a neighborhood on which the function is constant

Slereah

ah yes

0celo7

not every neighborhood

Slereah

that would make more sense

0celo7

2:01 PM

why?

take the neighborhood to be the whole thing and it's a trivial condition

Slereah

I thought it meant like functions constant on some neighhourhood

0celo7

that's what I said

Slereah

Not quite

I thought it was like

Only constant on a finite range

Is what I meant

Ironically the next section of the article is "local functions"

0celo7

@BalarkaSen pls chat.stackexchange.com/messages/41742876/history

Slereah

that's what I get for not reading the whole thing

Balarka Sen

2:05 PM

NO GOD! PLEASE NO!!! NOOOOOOOOOO

►

Slereah

what

Balarka Sen

damn son where d'you find this

@0celo7 Do you beremeber the homological definition of Euler class

the $H_n(E, E - \mathbf{0})$ business

ACuriousMind

@BalarkaSen It's, uh, the official SE guide to the level of content allowed in user profiles :P

Balarka Sen

lol

0celo7

@BalarkaSen I'm pretty sure the one I learned was using Cech cohomology but if you want me to remember anything more I'm screwed

Slereah

2:14 PM

0

Q: Crackpots and links to crackpot articles in their profile

So I see that this website is tolerant of people (which I choose to call "crackpots") which have links to their own dubious work in their profile. These people even have thousands of points of reputation, but the minute you check their profile, you're baited to go to "CrackpotLandia" (such as aca...

discussion user-accounts profile-page non-mainstream-physics spam

The basic proof of the Poincaré lemma is basically just finding an $\alpha$ such that $\omega = d\alpha$?

(for $\mathbb R^n$, anyway)

0celo7

yes

Slereah

Aight

So far so good

Balarka Sen

@0celo7 Hm

0celo7

@BalarkaSen Yeah looking at Bott and Tu there's a bunch of spectral sequence diagrams and tic tac toe lemma stuff

This was where I decided algebraic topology was not my cup of tea :)

Balarka Sen

Hah

0celo7

2:28 PM

I don't think that inequality above is true

At least not according to mathematica

not the first error in this book

Balarka Sen

@ACuriousMind Inspired by the answers to that question, I shall include a link to njwildberger's Algebraic Topology courses on youtube in my profile

ACuriousMind

@BalarkaSen ¯\_(ツ)_/¯

Slereah

Is the algebraic poincaré lemma supposed to apply to... functionals?

Space of functionals?

ACuriousMind

@Slereah What's the "algebraic Poincaré lemma"?

Slereah

Not a clue

saalburg.aei.mpg.de/wp-content/uploads/sites/25/2017/03/…

3.6

"The algebraic Poincaré lemma gives the cohomology of d in the algebra of local forms"

0celo7

2:33 PM

sounds like some physicist crap

ACuriousMind

Ah

Slereah

Who knows

Ah, there's the BRST

ACuriousMind

No, strictly speaking local functions/forms are not functionals

0celo7

what the hell is a local form

Slereah

And there is the BRST differential

Which I never heard of

but is apparently our nilpotent operator

ACuriousMind

2:34 PM

@0celo7 Basically Lagrangians and other functions you eventually want to feed a field and its derivatives to

0celo7

hmm

Slereah

Why does it work differently than $n$-forms, though?

ACuriousMind

@Slereah Well, they basically are $n$-forms on the jet bundle :P

Slereah

They have a different cohomology group it seems

Oh god

0celo7

@ACuriousMind trol

Slereah

2:36 PM

Not the jet bundle again

Balarka Sen

jets4life

ACuriousMind

@Slereah I think Henneaux is talking about them this way explicitly not to introducethe bundle!

0celo7

@ACuriousMind isn't it a jet bundle of some other bundle on which the fields live?

Slereah

even worse

He's sneaking it in

I guess there's no escaping the jet bundle

ACuriousMind

@0celo7 Yeah, I think it's the jet bundle of the "configuration bundle"

Slereah

2:37 PM

Also "Henneaux" makes me think of Heino

Heino - Die Schwarze Barbara

►

0celo7

Lmao

Abhikumbale

Hi, what is a good book to understand the mathematics behind special and general theory of relativity?

I'm currently studying from Gregory L Naber

And Callahan

Slereah

Which mathematics

There's a lot of it

If you just mean tensor calculus it's in basically every GR book

Balarka Sen

@0celo7 I want to write down a question on the issue with holonomic approximation theorem that we were facing and post a self-answer to it

Just to get all the details documented somewhere (and reviewed by other people)

Slereah

You know who wrote a great list of GR books though

@0celo7

30

A: Getting started self-studying general relativity

This list is extensive, but not exhaustive. I am aware that there are more standard GR books out there such as Hartle and Schutz, but I don’t think these are worth mentioning. Books with stars are, in my opinion, “must have” books. (I) denotes introductory, (IA) denotes advanced introductory, i.e...

Anonymous

2:53 PM

@JohnRennie Are you around? We could do the dual booting now, or tomorrow, as you wish. I got the USB ready

Anonymous

@BalarkaSen I'm reading Hirsh-Smale, now :) First chapter

Anonymous

Finally free!

Balarka Sen

Cool

Sid

@blue exam over? How did it go?

Anonymous

@Sid Yes, over! They asked questions like "Write a short note on basic Sociology" XD.

Anonymous

3:01 PM

No idea how much I had to write, but more or less it was okay. If we get like 70+ out of 100, that gets converted to a 10 grade....so I don't need to worry I guess :P

Sid

@Blue ...what?

Anonymous

@Sid Yeah, for humanities 70-100 is 10/10. 65-70 is 9/10. 60-65 is 8/10...something like that

Sid

@Blue ...for us, >90 is Ex, 80-90=A and so on till 35. <35=Fail.

Fortunately, I will not fail in anything this semester

Anonymous

@Sid It's similar here, for other subjects. Humanities is an exception

Anonymous

>90 (10/10) >80 (9/10) and so on...

0celo7