The h Bar

get the physics package and then \dd{x}

9:27 PM

Maybe that will work, but it gives an error on stack, $\dd{x}$, risky if I write everything using it then want to copy it to other places and it fails :(

Some good lazy shortcuts though apparently tex.stackexchange.com/a/275048/111183

This is actually an awesome package, is there a way to make $\pdv{x}$ $\pdv{f}{x}$ work on stack

Finally \tr gives trace, this is the best package ever

@bolbteppa indeed it is

@BalarkaSen what a nightmare i.gyazo.com/e82adde0e92784b6b29c5b10e3d208a0.jpg

Shortcuts really are a problem if you want to share the code though

\pdv*{f}{x} genius

To use '\dd x' or \dd{x}, that is the question

9:43 PM

@bolbteppa \dd{x} puts the right spacing.

I was never able to get the right spacing, this is a nice fix, but stress of { }

It turns out the light-cone gauge is not evil and horrendous, it's actually absolutely vital

Also I'd advise that once you find your ideal dx

Make a new command

So you can just type \dx

@bolbteppa it can be both

I really hated the light-cone gauge, but now it's like the coolest thing ever, you need it to throw away a load of quadratic oscillators in the $\hat{L}_n \sim \hat{p} \cdot \alpha_n + \text{terms quadratic in oscillators}$ to make sure you can throw away ghosts!

Not explained well in Scherk but in GSW it is

light-cones > ghosts

Yeah \dd{x} is so good, can set up \dd{x} e^{-i\dv{f}{x}} so quick, now we use that insane delta method to solve it and then up is down, black is white!

10:09 PM

putting the measure before the integrand is degenerate

@Slereah Someone did a study a few years ago of what topics ought to be in a introductory physics course for people going into health related fields.

Relativity seems like a distant candidate

They thought it weird that the topics we teach in those courses almost exactly match the ones taught in the first course for engineers and physics majors, and wanted to know what could be dropped.

I mean, I guess time dilation might be a good solution to keep patients living longer

They surveyed thousands of professionals in those fields. Very few individuals used more than a few topics. But every topics in the standard course was important to a few people.

10:14 PM

Is the QM part for radiation doctors

Relativity is critcal in understanding beam mechanics for radiation physics, for instance.

So they ended the project with no useful recommendations, alas.

But when I'm running out of time I drop QM and relativity. I figure they are going to need a refresher when they start to specialize anyway.

can't do QM without functional analysis or relativity without geometry

you can't do anything without algebra

what about gender studies

the amount of algebra most people need is very minimal

I don't actually know what one does in algebra

10:22 PM

you learn the addition

my main shelf has three sections

geometry, analysis, and physics

and the physics is all geometry and analysis

Get some logic books

^

Ahah

The gruppenpest begs to differ

Someone once said to me only half-jokingly all of physics is representation theory

the uninteresting parts, perhaps

GR is well defined and completely independent from algebra

amazing

Einstein knew de wae

10:25 PM

Said the diffeomorphism group representer

lol

@0celo7 tensor algebra

A: Relation b/w Dirac Algebra and Lorentz group

Understanding tensors in terms of representations of GL(N) and Young diagrams and whatever else is involved is impossible

1

It's pretty annoying that P&S just give you $$S^{\mu \nu} = \frac{i}{4} [\gamma^{\mu},\gamma^{\nu}]$$ from thin air, here is a way to derive it similar to Bjorken-Drell's derivation (who start from the Dirac equation) but from the Clifford algebra directly, assuming that products of the gamma ma...

@Slereah that's not real algebra

One of my master thesis was Young diagram stuff

The $SU(2)$ part was alright

10:28 PM

real algebra is homological galoid functors on derivative Grothendieck sheaves

Then I had to do $SU(3)$

And all went to hell

I find it impossible

Young Diagrams arise in multiparticle QM very naturally and I still can't make sense of this stuff

yeah they pop up a lot for like

Baryons and mesons

Since you can do decomposition of products of $SU(N)$

And the composite particles are $\approx$ the irreps

I've managed to avoid it all and it's getting more annoying avoiding it, really want to get this stuff down

It's like

If you pick some sigma model of two particles

For quarks

Then it's some $SU(2)$ vector

The product of two such vectors will be $\frac 12 \otimes \frac 12 = 1 \oplus 0$

The vector part is composed of the three pions

And the scalar part some other meson

10:33 PM

I'm happy breaking up a 3 x 3 matrix into it's trace, a symmetric matrix, and an anti-symmetric matrix, which is a $3 \times 3 = 1 + 5 + 3$ or whatever

yeah that's the real thing behind it

It's like $q_\mu q_\nu = q_{[\mu}q_{\nu]} + q_{\{\mu}q_{\nu\}}$

It gets much more annoying for $SU(3)$ though

just get Zee's book

I bet it's nonsense but gives formulas for this shit

Clebsch–Gordan coefficients for SU(3)

For the SU(3) part i had to read the worst book in the world

The math book written entirely in Penrose notation

In mathematical physics, Clebsch–Gordan coefficients are the expansion coefficients of total angular momentum eigenstates in an uncoupled tensor product basis. Mathematically, they specify the decomposition of the tensor product of two irreducible representations into a direct sum of irreducible representations, where the type and the multiplicities of these irreducible representations are known abstractly. The name derives from the German mathematicians Alfred Clebsch (1833–1872) and Paul Gordan (1837–1912), who encountered an equivalent problem in invariant theory. Generalization to SU(3) of...

And now, 6 years later, there's just a wikipedia article about it

hmm

is there automatically a maximum principle when the first Dirichlet eigenvalue is positive?

Jake Rose

Anyone free for a quick wave and sho conceptual question?

10:49 PM

$$|y, \gamma, {i^2}, {i^z}, c^1, c^2\rangle =\sum_{y_1, y_2}\sum_{{i^2}_1, {i^2}_2}\sum_{{i^z}_1, {i^z}_2}\langle y_1, y_2, {i^2}_1, {i^2}_2, {i^z}_1, {i^z}_2|y, \gamma, {i^2}, {i^z}, c^1, c^2\rangle |y_1, y_2, {i^2}_1, {i^2}_2, {i^z}_1, {i^z}_2\rangle$$

What is this madness

I mean it's just the old completeness thing

still

quite awful

Hook length

God

@Slereah nice

@Slereah how many pages was your thesis?