00:00 - 16:0016:00 - 00:00

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'?

that does not seem to be a coherent sentence

1:03 AM
Between equation 0.6 to 0.7 it says it

1:25 AM
Guys, I need some web dev help. Having some kinks with basic auth

1:47 AM
@Cows what math?

explain it
it's crazy

@bolbteppa look, I’ve read your sentence like 5 times and you’re missing several words
“so apparently string theory” is not English

It is perfect Eenglish

whatever

@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?

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...'

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 awesome! looking at it now

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

2:11 AM
@0celo7 you can according to linguists since perfect English is amorphous and malleable depending on social consensus

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

2:25 AM
@bolbteppa so English is a glassy language. Neat

Sandy enough yes

@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?

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"
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...

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?

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

thank you!

Anonymous
@Curio $\tau=I\omega$

do electrons have energy?

Anonymous
@parvin Of course

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

on what? what should I search in it?

Anonymous
Electron

Anonymous
Also Kinetic Energy

thank you

3:23 AM
ZOMG I NEED HATS
@heather give me hats!

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...

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?

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

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

yes

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

Anonymous
Binding energy

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.

Stretching what?

5:11 AM
weez

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.

@Semiclassical paging

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...

@0celo7 ?

@Semiclassical it worked!

What did?

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

how horrible are we talking?

@Semiclassical getting the last one from (6.5) i.gyazo.com/53210b0ffcaafa027c699cc6f0466143.png
$R,\lambda,\rho\ge 0$

...yeah, that's not nice looking

$\epsilon\in (0,2)$
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

weird

5:57 AM
@0celo7 the equations you are sharing look awesome. May I ask what you are working on. I am just curious

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

@0celo7 very cool

@Semiclassical also the sign of $\lambda$ seems to be wrong...
it's a strange looking thing

6:10 AM
::facepalm::
The author of
0

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...

has managed to accumulate more than three thousand rep.

1 hour later…
7:37 AM
@TomNeiser You are a student of UCLA ?
Have you met Terry Tao ?

8:23 AM
mornin

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

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

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

2 hours later…
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.

11:00 AM
String theory for a start

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.

@dmckee I've been saying this for ages
it's a design flaw in the applicability of the SE rep-accounting model to science

all quantum gravity stuff is full of groups

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.

Well I tried that but it never works!
Even just changing the ratio of points gained and lost never went anywhere with SE
So welcome to the status quo

11:49 AM
@Slereah indeed

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.

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

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

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

12:42 PM
@Slereah do note that deleted message was highly inappropriate

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

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 $D^2 = 0$

1:13 PM
0

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...

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

@Slereah I don't quite understand your question
It's the quotient of the kernel by the image, just a standard vector space quotient

1:31 PM
@ACuriousMind i ask because I recently came across this recent paper arxiv.org/pdf/1712.02894.pdf

@user929304 I'm afraid I don't know anything about relational QM
And I don't care enough about interpretations to change that :P

@ACuriousMind same :)
@ACuriousMind just wondered what the big deal is about it

@Slereah what ACM said

@ACuriousMind Oh are they vector spaces

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

1:35 PM
And so you just collapse the $Im$ dimension?

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

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

What the hell is a pseudo Hilbert space

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

Oh, right

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

@ACuriousMind urgh halp
(Typing doubt)
It’s a long one

Is there a good intuitive meaning behind what the cohomology is
Like why the quotient of the kernel

@Slereah Gauge invariant states with the gauge redundancy removed.

Well I meant more generally

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.

1:45 PM
though henneaux is giving an example here
With the exterior derivative
Let's see if it illuminates

Am I understanding that correctly?

@GPhys Understanding what correctly?

@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 $$\frac{B+\sqrt{B^2-4(2-\epsilon)\lambda^2 (2\sigma^2-\epsilon)}}{4-2\epsilon}\le \frac{(4(n-1)^2+2\epsilon)R}{4-2\epsilon}+C'((1+\epsilon^{-1})\rho^{-2}+\lambda)‌​$$

I'd rather not

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

1:52 PM
@ACuriousMind Is the cohomology (for the exterior derivative) inexact closed forms?
Or something similar?

@Slereah yes

ah, some progress
I mean, I still need to find out one would care about it
But still

@Slereah because it's dual to homology

Yeah I'm up to the Poincaré lemma part

one could almost say it's a co-homology
@ACuriousMind pleeeeease

1:56 PM
one might
Why is $H^0(d) = \mathbb R$
What's the set of inexact $0$-forms?

it's that for a connected manifold

Oh wait
I guess trivially
They're all inexact

it counts the constant functions

@Slereah It's just (locally) constant functions

Since there's no -1 forms
(It's for $\mathbb R^n$)

1:58 PM
@Slereah Prove: a locally constant (continuous?) function on $\Bbb R^n$ is constant everywhere

Is that the identity theorem or something

you don't need continuity
identity theorem?

Wait what
How would a locally constant function be constant everywhere

hint: R^n is connected

What about $f(x) = 0, x < 0$ and $f(x) = 1, x > 0$
Wait what does locally constant mean here

2:01 PM
how is that locally constant at $0$

Oh is that constant on every neighbourhood

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

ah yes

not every neighborhood

that would make more sense

2:01 PM
why?
take the neighborhood to be the whole thing and it's a trivial condition

I thought it meant like functions constant on some neighhourhood

that's what I said

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"

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

what

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

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

lol

@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

2:14 PM
0

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...

The basic proof of the Poincaré lemma is basically just finding an $\alpha$ such that $\omega = d\alpha$?
(for $\mathbb R^n$, anyway)

yes

Aight
So far so good

@0celo7 Hm

@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 :)

Hah

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

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

@BalarkaSen ¯\_(ツ)_/¯

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

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

Not a clue
3.6
"The algebraic Poincaré lemma gives the cohomology of d in the algebra of local forms"

2:33 PM
sounds like some physicist crap

Who knows
Ah, there's the BRST

No, strictly speaking local functions/forms are not functionals

what the hell is a local form

And there is the BRST differential
Which I never heard of
but is apparently our nilpotent operator

2:34 PM
@0celo7 Basically Lagrangians and other functions you eventually want to feed a field and its derivatives to

hmm

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

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

They have a different cohomology group it seems
Oh god

@ACuriousMind trol

2:36 PM
Not the jet bundle again

jets4life

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

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

even worse
He's sneaking it in
I guess there's no escaping the jet bundle

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

2:37 PM
Also "Henneaux" makes me think of Heino

Lmao

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

Which mathematics
There's a lot of it
If you just mean tensor calculus it's in basically every GR book

@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)

You know who wrote a great list of GR books though
@0celo7
30

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!

Cool

@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

@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

@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...

3:11 PM
wonder if I should shlepp my computer home
I'll probably get more work done if I don't

Why'd you want to get work done over Christmas ;P

@ACuriousMind to increase the GDP

Anonymous
@Sid Doing math doesn't increase GDP :P

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