The h Bar - 2021-04-10

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3:10 AM

@Semiclassical these might be fun/handy for remote physics teaching/learning falstad.com/mathphysics.html

there's also some links to more of the same kind of stuff on other sites

3:21 AM

though seeing is believing, and i like your idea of physically building them at home

4:01 AM

Does anyone have a good explanation for why the existence of a possible gauge anomaly is characterised by the fifth homotopy group of the gauge group being non-trivial

I know that such groups have to have a complex rep for the fermions to live in, are they related?

4:42 AM

@antimony i'm fond falstad's circuit simulator

5:35 AM

nice :)

5:59 AM

@ACuriousMind with strong nuclear force i guess you can at least make the argument that, without it, nukes wouldn't be possible (though we hardly understood it when we made them). but what grand human transformation would you ascribe to the weak nuclear force?

6:09 AM

in Physics noob tries to get better (ft.John rennie), 4 mins ago, by John Rennie

Or I guess it's fairer to say that both QED and Maxwell's equations are derived from the same Lagrangian.

can anyone tell me what is this lagrangian?

Quantum electrodynamics

In particle physics, quantum electrodynamics (QED) is the relativistic quantum field theory of electrodynamics. In essence, it describes how light and matter interact and is the first theory where full agreement between quantum mechanics and special relativity is achieved. QED mathematically describes all phenomena involving electrically charged particles interacting by means of exchange of photons and represents the quantum counterpart of classical electromagnetism giving a complete account of matter and light interaction. In technical terms, QED can be described as a perturbation theory of the...

6:29 AM

@satan29 you only need the $-\frac14 F_{\mu\nu}F^{\mu\nu}$ part of the QED Lagrangian for Maxwell's equations

7:21 AM

@Semiclassical there are methods these days to detect reactors using neutrino detectors

7:31 AM

@Slereah do you mean mostly for compliance and intel, or also scientific insight into reactor processes? or both?

whatever you need it for!

cool

Never worry too much about applications, in my opinions

Twin primes were discovered in the 17th century and it wasn't until cryptography in the 60's that they became "useful"

thats the beauty of it imo :D

ehh

number theory would still be beautiful even if it never became useful

7:40 AM

and yet people would still bitch

between a universe where number theory is lovely but irrelevant, and a universe where the NSA has a material interest in what progress is made on the Riemann hypothesis

i'm not sure we got the better deal

Why ask about the standard model, then

Isn't it beautiful on its own

you're talking to a guy who did condensed matter theory. defending the beauty of the standard model is happily outside my jurisdiction

but apparently questioning its utility is!

lol

i don't think the standard model needs defending. It Just Works. (Except To The Extent That It Doesn't But We Don't Really Know About That.)

7:52 AM

Many things work but are of questionable utility

1 hour later…

9:20 AM

@Semiclassical nuclear power (and weapons) were made possible mostly by understanding the weak force, no?

1 hour later…

10:26 AM

If the process of constructing an "extended $\mathcal N$-supersymmetry algebra" involves giving the supercharge an additional index that runs to $\mathcal N$, does this mean that the spinor index on it is always two component?

So the supercharge for the $\mathcal N=4$ supersymmetry algebra for example is sort of a four-component vector with each component being a two component spinor

@fqq I'm pretty sure we had only the Fermi theory of $\beta$-decay when we built nuclear reactions - the modern understanding of the weak interaction as the result of the spontaneously broken electroweak theory hails from the 60s (Glashow model, Goldstone with spontaneous symmetry breaking, Glashow, Weinberg & Salam w/ electroweak theory).

The first proposal of W/Z bosons as force carriers seems to be from around 1949 according to this, so no, we really built nuclear bombs and reactors without really understanding what we were doing.

@Charlie don't think of it as "the supercharge" - you're just introducing $\mathcal{N}$ supercharges and numbering them

and yes, each supercharge is still a spinor

ok ty

6 hours later…

4:14 PM

Any good books, or articles explaining the Jamin interferometer?

1 hour later…

5:40 PM

@ACuriousMind I think for a while the weak interaction was a 4-fermion thing

With harsh points rather than propagators

That was the 60's idea I think

Yo, everyobe

Muon G-2 Results out today!!!

was waiting for it, tho, I admit I don't understand a single thing of it.

@JohnRennie @Slereah you understand that?

damn ugly! going to sleep at 3 and waking up at 5...

I'm on sleep medications

that sucks

life, covid and all

I don't touch experimental

It is a scary place

Me too....

beli scary

I prefer to stay in the platonic realm thank you

Belcom vro

Anyone here watching Match tonight?

lol

very interesting match actuallie

nop

5:49 PM

imagine having to keep track of $10^{80}$ particles and pretend most of them aren't influencing each other

Imagine having a slight problem in tracking system and the particles influencing each other.

→ 4 messages moved to Trashcan

@ACuriousMind What was moved? I wanted to see them

I could be looking at a star right now that's 30 parsecs away and if I post about it it would be an influence on local experiments

Luckily, unlike in our previous study, we have no reason to believe Evangeline the Adulterator gained access to our stored doses.

What if George tampers data according to astrology????

I've a cool idea

of an alternative formulation of theory of everything

@Slereah u there>

?

5:53 PM

No.

@Slereah that's the Fermi theory, no?

@ACuriousMind I think so?

Let's mix all pseudoscience, homeopathy, alchemy, astrology, NLP and everything and make a new theory of everything pseudoscience version, then we'll publish and sell our generalization

I don't remember much about it

hehehe d(^_^)b

5:55 PM

I think it was just $\psi^2 \eta^2$

just bumping spinors

$\psi^2 \eta^2$

cool theory

electron spinor and neutrino spinor

that sort of thing

okay, I understood everything

Good, because I don't remember a lot of places that talk about Fermi theory

okay sir, I understand

5:57 PM

Cool neutrino dudes might but I only remember it from that weird article about black holes radiating neutrinos

okay sir, I understand

@Slereah What is your IQ Score?

(turns out they do not radiate neutrinos even if Fermi theory is true)

@RewCie 1

@Slereah Damn! That's very sad... that made me emotional too.

It's in "Magic without magic", if you want the emotional rollercoaster

@Slereah Hey king, you forgot couple of zeros in the end

5:59 PM

a bunch of papers in honour of Wheeler, which is a weird theme for a physics book

Just In: India became the country with fastest vaccination rate today.

The rate after end of the month is projected to be 3x of the rate now

user image

@ACuriousMind Google Suggests ACM Profile Pic

user image

Google suggests Slereah Profile PIC

Damn! I was searching for Profile Pic for me and then suddenly, This came to me - > reddit.com/r/IndiaSpeaks/comments/lhkyvk/…

Goosebumps all over my body

My viral twitter thread which got me 700 followers in 24 hours has been viral in Reddit too

I guess, I should make a new reddit account then

reddit.com/r/india/comments/lhecjj/…

check that too

I've multiple viral reddit threads on me

damn! I'm feeling myself as a celebrity

whatever, fsfsfsfsfsfsfs ignore

user image

source - techncyber.com/2021/02/koo-app-false-data-leak-claim.html

Twitter made me famous.

Calm down.

okay vro

no viral threads from now

6:36 PM

@ACuriousMind yes I agree. My point was that the Fermi theory is a first understanding of the weak interaction, not the strong one

7:00 PM

the early form of the strong interaction was the Yukawa theory, I think

Which is kind of valid in the simplest approximation?

If you assume everything mediated by spin 0 mesons

I don't know how much this is related to actual nuclear power, though

I'm not big on engineering history

7:26 PM

@Slereah I think Meitner and Frisch had correctly identified the fission process and estimated the energy simply using a classical model using charge and radius.

Like the liquid drop model?

idk

yes

And chain reactions were already known from chemistry.

Szilard had already thought about doing the same with neutrons before fission was discovered.

So next they had to confirm that there are really neutrons produced by fission.

experimentally determine the relevant cross-sections and discover a way to slow down neutrons

so then Chicago Pile number 1 would be the next big step

100 point bounty that may be of interest to people here!

5

Q: Example of a standard/archetypal/simple 4-band gapped condensed matter model with analytic results?

I am looking to study Berry phase-like phenomena in a gapped 4-band material model. In particular, I want to numerically and analytically calculate the Abelian Berry curvature integral of each band over some region of k-space. It should be easy to calculate the Chern number of this system. Howeve...

condensed-matter model-hamiltonians solid-state-physics topological-insulators berry-phase

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