The h Bar

bolbteppa

16:00

I skimmed tiny bits of it hoping for some hand-waiving from him and it seemed like every other book, sometimes he gives you an astounding way to look at something formal, but couldn't find it in what I looked through :p I still have hope It'll have something good!

0celo7

@bolbteppa link to this new book?

bolbteppa

books.google.ie/…

0celo7

@bolbteppa I'll probably get it

holy shit it's long

why isn't it on Amazon

Danu

Oh god :P

In a nutshell for physicists

Will it be high school level? :P

0celo7

It'll probably he harder to read than e.g. Fulton & Harris

:P

FenderLesPaul

16:13

I don't get the point of "group theory for physicists" books

Like what physicist actually has time to read this stuff

0celo7

because many people aren't as smart as you

FenderLesPaul

instead of just learning the necessary material as they go along

@0celo7 I don't mean it like that

just in terms of time and commitment needed to work through such a book

which grad students etc. typically don't have

0celo7

@FenderLesPaul because many people aren't smart enough to do that?

FenderLesPaul

:p

Danu

@0celo7 Eh? :P

0celo7

16:15

still waiting for those solutions...

Danu

@FenderLesPaul How about everybody

(in HEP)

0celo7

@Danu Have you read his QFT book? It's nonsensical at times

Danu

@FenderLesPaul Because "necessary material as they go along" often amounts to horrible confusion after several years

0celo7

It's not advanced, just really strange

Danu

@0celo7 Nah, I never expected it to be good :P

bolbteppa

16:16

A lot of what I wrote yesterday seems to motivate twistors as Penrose sets them up here http://users.ox.ac.uk/~tweb/00002/index.shtml
Given a 4-vector $r = (t,x,y,z)$ representing a point $R$ we find it's reflection representation
$$R(r) = tI + xs_x + ys_y + zs_z = \left[ \begin{array}{ c c } t + z & x + iy \\ x - iy & t - z \end{array} \right]$$
and say that the twistor $Z = (Z_1,Z_2,Z_3,Z_4)$ is *incident* with the point $R$ if
$$ \left[ \begin{array}{ c c } Z_3 \\ Z_4 \end{array} \right] = \left[ \begin{array}{ c c } t + z & x + iy \\ x - iy & t - z \end{array} \right]\left[ \begin{arr…

0celo7

His GR book is excellent, best one out there.

I don't know why his QFT book is so bad.

FenderLesPaul

@Danu But these "xxx for physicists" books tend to preserve the confusion haha

Danu

@0celo7 CARROLL DAMNIT :P

@FenderLesPaul Yes, sadly :P

0celo7

@Danu I use Carroll all the time.

Danu

Only GR book in my world :3

0celo7

16:17

I like Carroll because he uses indices and has rigor.

FenderLesPaul

Waaald

0celo7

I used Carroll as a reference for geometry stuff while working through exercises in do Carmo (math book)

Because I didn't want to put up with index free notation all the time

@FenderLesPaul Honestly Wald is shit for the first 5 chapters

His explanation of Riemannian geometry might be the worst out there

And don't even get me started on Appendix B

FenderLesPaul

I mean most GR books are shitty for the first few chapters

Carroll's chapter 2 is awesome though

0celo7

Not Straumann.

Danu

All GR books are shit for math :)

FenderLesPaul

16:19

but his explanation of manifolds is just as confusing for someone who hasn't seen differential manifolds before

0celo7

Straumann's first chapters are very strong.

FenderLesPaul

True Straumann is great all around

0celo7

@Danu That's a bold claim.

FenderLesPaul

but that's an advanced GR book

0celo7

Hawking-Ellis is regularly used by Lorenzian geometers.

Danu

16:20

Except perhaps the ones explicitly for mathematicians :P

0celo7

@FenderLesPaul Correct.

FenderLesPaul

I don't like HE honestly

It's too terse

0celo7

I think his "explanation" of manifolds is that they're paracompact topological spaces locally homeomorphic to $\mathbb{R}^n$ and doesn't explain any of those words.

A+ clarity for beginners.

@FenderLesPaul That it is.

You should really check out Beem et al.

If you're interested in pure geometry, that is.

They don't even pretend to be writing a physics book.

@Danu Have you looked at Straumann at all? Do you think it's shit for math?

FenderLesPaul

@0celo7 Can I read it?

or is it too mathy?

Because I suck at math

Slereah

@0celo7 Does he also have to explain what numbers are, you big baby

0celo7

16:25

@FenderLesPaul it's HE level

but they go into more detail

and they cover stuff that's probably worthless to physics

like curvature pinching theorems

Danu

@0celo7 Nope :P

Maybe it's okay---I was just making ridiculous claims for the sake of it, y'know :)

0celo7

@Danu He defines $\mathrm{d}$ as the unique nilpotent degree one antiderivation that satisfies $\langle\mathrm{d}f,X\rangle=Xf$.

Not exactly "shit for math"

FenderLesPaul

Hehe pinching

Danu

@0celo7 Not exactly how I think it should be defined, either

Why invoke a metric when there is no need to?

0celo7

@Danu metric o.o

$\langle-,-\rangle$ is the natural $T_pM$-$T^*_pM$ pairing

you could write it as $\mathrm{d}f(X)=Xf$ if you like

Danu

16:39

@0celo7 Ewwww that's some ugly-ass notation

I was already starting to wonder what the heck was going on there... taking an inner product of a form and a vector

In my world $\langle\cdot,\cdot\rangle$ is reserved for inner products

0celo7

@Danu meh, it should be clear from context

I wouldn't use that notation either if I was writing a book

Danu

@0celo7 Yeah, it should be :P I totally misread that, I'll admit it ;)

0celo7

@Danu it's a German GR book, what more could you want

Danu

I don't think Germans are particularly good textbook writers

0celo7

they're rigorous

dmckee

16:48

Anyone have a cute exercise in Lagrangian mechanics in 2 DoF? I need something make my class exercise the method.

Danu

@dmckee Spring attached to a spring (attached to a wall)?

Double Atwood machine is a classic

0celo7

@dmckee Get Arnold!

Slereah

You need a metric to map vectors to dual vectors

Otherwise there is no correspondance between the two

Or, for the same result

Musical isomorphisms!

0celo7

you can use a symplectic form too

any nondegenerate bilinear form, really

Danu

@Slereah But that's not what he's doing---he's just using forms as linear functionals on the tangent space

Slereah

16:54

Well

Forms are linear functionals?

Danu

Yes

Bernard Meurer

Hey hey

0celo7

@Slereah Huh?

Of course they are

Slereah

Well yes

That is what I am saying

0celo7

why is that a question though

an element of $\Omega^1$ at a point is just a covector

Bernard Meurer

16:58

I just got myself them downvoting rights. Where's that proof of yours @0celo7?

0celo7

@BernardMeurer hidden

I'll delete it if you downvote

Bernard Meurer

:p

I wouldn't, it's too nice of a proof

Slereah

Down to 63 kg B)

I dunno why the murcans complain that dieting is hard

It is not fun but it's easy as shit :V

0celo7

Not in America

Everything is made with extra fat

Bernard Meurer

@Slereah How tall are you?

Slereah

17:02

Is there butter in the atmosphere

1.72 m

Bernard Meurer

I'll take my 79Kg and hide in the corner

Slereah

Well depends how you're built

But I got sticks for arms currently :p

Bernard Meurer

I'm 1.82 tho

I just have to overcome my Schweppes addiction

Slereah

Chocolate bars and juice were pretty hard to quit

yuggib

79 kg and 1.82 seems pretty ok

Bernard Meurer

17:05

Yeah Cranberry juice too

0celo7

look at all you skinny fuckers

Bernard Meurer

I drink a box every 2 days of that thing

@yuggib Not in a country where everything orbits around the beach :p

Slereah

Not everyone has your American heft

0celo7

one of the German math profs is addicted to cranberry juice

has a crate in his office

Slereah

All that bacon belly

yuggib

17:06

@0celo7 how much do you weight? I hope more than 100

Bernard Meurer

gotta keep it under 75

0celo7

@yuggib kg?

yuggib

yep

Bernard Meurer

Yeah @0celo7 we use real measurements

0celo7

@yuggib no

Slereah

17:07

How many Planck masses

0celo7

@Slereah a lot

Bernard Meurer

How many stones?

yuggib

@0celo7 then you're skinny too

0celo7

how much is the Plank mass?

@yuggib not really

Slereah

About $10^{-8} kg$

0celo7

17:08

@Slereah ok so I'm a few billion Planck masses

Slereah

fatty

So many protons

Bernard Meurer

@0celo7 How much in pounds then?

0celo7

not telling you

Bernard Meurer

Sigh, let me ask Michelle

0celo7

@BernardMeurer why would my sister know how much I weigh

Bernard Meurer

17:11

@0celo7 Cause she knows everything?

0celo7

@BernardMeurer she knows what I tell her

Bernard Meurer

Wait a second, when you vote down an answer you loose rep?

John Rennie

17:25

@BernardMeurer rep and karma ...

Slereah

Yes

But you regain it back if the answer is deleted

Bernard Meurer

Hell I ain't ever downvoting stuff again

Slereah

You should

Lots of chaff around

John Rennie

@Slereah you don't get the karma back though. You'll be reincarnated as a social scientist.

DanielSank

@ACuriousMind I hardly think the fact that a lot of books start QM with a single massive particle in a square well is a good reason to say that this should be the case. Note also that we get raising/lowering operators in the second chapter of Griffiths (a very common 1st quantum book) yet he continues to use the ridiculous first quantized notation when introducing multiple particles.

Slereah

17:34

Infinite potential well is the simplest QM thing

DanielSank

@Slereah 100% false.

Two level system is the simplest thing.

Slereah

Well then what is!

How do you make a two level system

DanielSank

Why Griffiths starts off using the wave equation is completely beyond me.

@Slereah You go find an electron.

Bernard Meurer

Sigh, when you come up with a nice answer and someone gives the exact same answer a second before you

DanielSank

@BernardMeurer #justphysicsstackexchangethings

Slereah

17:35

I have an electron

DanielSank

@Slereah See? There you go.

Bernard Meurer

@DanielSank stackoverflow tho.

DanielSank

@Slereah How do you make a particle in an infinite square well?

Slereah

But electrons have like spinors and shit

Bernard Meurer

At least my function is shorter and uses proper enumerate

Slereah

17:36

@DanielSank : Free Hamiltonian with boundary conditions?

DanielSank

@BernardMeurer I don't like what OP asks there. That data structure probably shouldn't ever come up.

@Slereah Uh, yeah... then I don't understand your question "How do you make a two level system".

I thought you were asking how to make it in real life.

Bernard Meurer

@DanielSank I have no idea what he's doing to be honest, and he not being able to predict the depth of nested lists is bad in itself

Slereah

Well how is it simpler

Bernard Meurer

But I liked how recursion served there

Slereah

Than a point particle

In a bounded space

DanielSank

17:38

It's a two by two matrix instead of a differential equation.

Slereah

Well gee then why not a ONE LEVEL SYSTEM

Bam

Everything is simpler

What about the VACUUM

DanielSank

Why Griffiths starts off with partial differential equations in his quantum book is entirely beyond my comprehension.

Slereah

0 level system

DanielSank

@Slereah -_-

Bernard Meurer

I started reading Griffiths, but then I couldn't solve the integrals

DanielSank

17:39

I take it that you're resorting to jokes because you realize I'm right.

Slereah

You rapscallion

DanielSank

@BernardMeurer Griffiths is a terrible quantum book, IMHO.

Bernard Meurer

@DanielSank but when I tried Shankar everyone said the notation was horrible and told me to try Griffiths :p

DanielSank

@BernardMeurer WHAT!?

Hari Prasad

@0celo7 sin(0) = 0

DanielSank

17:40

Shankar is great!

Slereah

I use Landau

Landau is best

DanielSank

@Slereah Griffiths puts the Schrodinger equation expressed in an infinite dimensional space (i.e. position space) and in a particular basis (the position basis) on the first page. Why? Why does he do this?

Slereah

It doesn't even use Hilbert space shit :V

Bernard Meurer

@DanielSank even you did with the $\langle 0\rangle$ being the null vector

Slereah

That's pretty standard?

DanielSank

17:41

@BernardMeurer excuse me?

Bernard Meurer

Yeah, he notates the null vector as a ket at the beginning of the book as opposed to just 0

DanielSank

So?

That's a reasonable choice.

Bernard Meurer

and then everyone got nuts over $\langle 0\rangle$ being the ground state of a system

DanielSank

pffft, ok whatever.

Bernard Meurer

and told me to use Griffiths

so on I went

DanielSank

17:42

Real physicists use $|\Omega \rangle$ as the vacuum anyway.

Bernard Meurer

But now I'm switching back to Shankar because I didn't like Griffiths

DanielSank

@BernardMeurer Griffiths royally sucks.

That book manages to completely ignore the way quantum mechanics is done in real life because of its fetish with the wave equation in the position basis and in making students do a ton of integrals.

Bernard Meurer

@DanielSank When I opened the pdf there was a tsunami of formulas already I thought that was pretty gandalf of him. (As in You shall not pass!)

DanielSank

@BernardMeurer Yes.

I think the first problem you should solve in quantum mechanics is the black body spectrum because it proves that classical mechanics is wrong and gives you a reason to pay attention.

Slereah

@DanielSank Only for the interacting vacuum

DanielSank

17:46

@Slereah Oh who cares.

At least that way it's unambiguous.

Oh oh wait I see your point.

Yes ok that could be confusing.

Slereah

Who even uses the 0 element of the Hilbert space, anyway

It's not even a ray

Bernard Meurer

@DanielSank I'll go back to Shankar tonight, specially now that I get what linear dependence and independence is

I still have a little trouble seeing matrices as vectors tho

Hari Prasad

@BernardMeurer why?

Bernard Meurer

@HariPrasad Well because I can't visualize it, I still think of vectors as arrows even though I'm trying to kick that off my mind

Hari Prasad

@BernardMeurer You can think matrices as arrows!

Bernard Meurer

17:54

@HariPrasad But how will a matrix be an arrow?

Hari Prasad

@BernardMeurer Think like this. A matrix tells you about how a vector behaves

@BernardMeurer Know programming?

Bernard Meurer

@HariPrasad Yeah, mostly Python and C, why?

0celo7

@BernardMeurer :/

@DanielSank People think your notation is terrible too, FYI.

Hari Prasad

@BernardMeurer OK here it goes: A scalar is a single number. A vector is a list of numbers. A matrix is an array of numbers

@BernardMeurer (just an analogy)

Bernard Meurer

An array being defined by a collection of lists?

Hari Prasad

17:59

@BernardMeurer yes that's ok

0celo7

@DanielSank uhhh

Hari Prasad

@BernardMeurer Its just a differnt way to imagine vectors

0celo7

I think you're biased because of your work

My PDE prof keeps saying one of the best reasons to learn PDE is to do QM

Bernard Meurer

So wait, is a matrix just a different type of vector or is a matrix a group of vectors?

0celo7

@DanielSank Sadly 0 books actually do this...

Hari Prasad

18:01

@BernardMeurer hmmm... "Both"

0celo7

@HariPrasad what?

that's not what he means

Hari Prasad

@0celo7 sorry

0celo7

He has a hard time visualizing e.g. $\mathrm{Mat}(n,\mathbb{R})\cong\mathbb{R}^{n^2}$

which is fine

but he shouldn't need to visualize it

Hari Prasad

@0celo7 that's oK for a mathematician but not ok for a physicist or an engineer

Bernard Meurer

I just like visualizing stuff

0celo7

18:03

@HariPrasad I'm an engineer and I survive

Hari Prasad

@BernardMeurer that's a good habbit

@0celo7 which branch of engineering?

0celo7

@HariPrasad nuclear

Bernard Meurer

He's in kaboom-engineering

0celo7

@BernardMeurer Why are you doing QM before you've learned calculus properly?

Hari Prasad

@0celo7 Any idea of "Sensitivity analysis of linear and non-linear systems"?

Bernard Meurer

18:07

@0celo7 Wanna teach me proper calculus as well?

John Duffield

@bolbteppa : I'm not denying QM, I'm saying the experimental evidence makes it clear that electron spin is real. See this old version of the Wiki Stern–Gerlach article. It repeats the faster-than-light non-sequitur that says _ the electron can't be rotating like a planet, so it can't be rotating at all_. Of course it isn't rotating like a planet. It's a spin ½ particle.

0celo7

@HariPrasad no

Hari Prasad

@0celo7 OK leave it

0celo7

@BernardMeurer not really

Hari Prasad

@JohnDuffield why does it take so much time for you to respond? do you read the whole article before posting?

0celo7

18:09

oh just let him be

John Duffield

@bolbteppa : uhhn, not the amplitudehedron. The repeated theme of our "conversations" here is that people will not believe in hard scientific evidence, but their belief in things that do not exist is utterly unshakeable.

Hari Prasad

@0celo7 Have you learnt abstract algebra?

0celo7

@HariPrasad taking a course right now

John Duffield

@HariPrasad : respond to what? I'm sometimes slow to respond because I work for living, and I have a wife and family. And apologies, my wife is calling me now for a glass of wine and tagliatelli. I have to go.

0celo7

lol

Hari Prasad

18:13

@JohnDuffield Please! you are free to go

DanielSank

@BernardMeurer Dude, make sure you get a good linear algebra course.

@0celo7 Who are "people"?

0celo7

@DanielSank ACM, CW

DanielSank

Notation can be a religious issue. The most important thing is consistency.

Bernard Meurer

@0celo7 Thought so

@DanielSank I damn sure will, still waiting on college answers. Georgia Tech is out tomorrow

dmckee

@JohnDuffield Stern-Gerlach shows that various particles have magnetic moments, and that measurements of those moments along a selected axis are quantized. Nothing more.

0celo7

18:27

@dmckee No, I'm pretty sure it says that it's of the same nature as orbital angular momentum.

dmckee

But interpreting that magnetic moment as a result of spinning balls of charge has a big problem: the quantization you calculate for spinning balls of charge is different than that measured for many materials (integer versus half-integer).

0celo7

The Wiki article says so!

no_choice99

hi people, do you have any idea in which stack exchange website the following question could be asked : "how can scientists trust closed source programs?"

Bernard Meurer

@no_choice99 Dunno, I almost on use Open Source stuff

apart from my phone and this site, and I don't trust either

0celo7

cuz you're a scrub

Bernard Meurer

18:34

@0celo7 I'm a believer, asshat

0celo7

what did my sister say

Bernard Meurer

I didn't ask her, got busy fixing some stuff

dmckee

@no_choice99 Trust in what way? I mean, in particle physics we do validation on all the software no matter who writes it.

Over time must things are really run through the wringer and weakness noted and spread around.

no_choice99

@dmckee I was about to mention "tests" to make sure the program works fine and returns the numbers it should. Trust that there's no bug or malicious code. Trust that the program does what it claims

I would like to post the question somewhere on stack exchange but I'm clueless as to where

dmckee

Roughly the same way that anyone trusts any software, then. By a combination of testing and reputation. In truth that is how most open source software is trusted too.

Sure, you could look at the code, but few people do. And if you bother to look up where someone did look at the code you are just trusting them.

Not that I'm defending closed source practices, just that the on the ground practice doesn't distinguish much.

On the up side and large fraction of the software used in particle physics is open, and those closed tools that see much use are used widely in industry too, so there are a lot of people with experience with them.

In any case, there are a number of software related questions on Academia and on Computational Science. I'm not sure if either would accept your question. In the wider context you might poke around Programmers but I'd look for a duplicate before considering asking there.

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