@ArnoldNeumaier Great, thanks! I have not time to start reading books (I have a backlog--Dirac, Thorne/Misner/Wheeler, and lots of others), but I'll keep that in my list!

Note that I do not know Group theory--the title of your book suggests it's required. Is that true?

I am trying to calculate Christoffel symbol for ds2=−(1+2ϕ)dt^2+(1−2ϕ)(dx^2+dy^2+dz^2) using variational principle but I don't know I am not getting the desired result

Using Euler Lagrange method I end up getting zero as Christoffel symbol

@Manishearth: No, you don't need any group theory; what is needed for the book is introduced in Part I. But as I said, Part II (on statistical mechnaics) is essentially independent of Part I. It uses from Part I only the conventions introduced in the motivational Chapter 1, which assumes nothing. Of course, statistical mechnaics has the flavor of Lie algebras, so if you know more about it, it is easier to appreciate why I do things the way they are done.

''the title of your book suggests it's required'' - I realize that the title may be deterring people from reading it, though I even have responses from 16 year olds having read large parts of it with profit. The next version of the book will therefore simply be called ''Coherent quantum mechanics'', and will have lots of material added about coherent states and their use. But it will take me one or two more years to be that far.

@ArnoldNeumaier great! I may even read part one (after a few months--like I said, too many things going on now), I'm pretty interested in group theory--just never knew where to start.. And I'm not that far off from a 16-yr old (I'm 17) ;)

@Manishearth: Actually, the 15 pages of the motivational Chapter 1is bedtime reading, not more demanding than most answers here on physics.SE, with a small formula/text ratio. It is an invitation to quantum mechanics, giving an overview of some of the important topics and how they are encoded into formulas.

@ArnoldNeumaier 15 pages? Alright, that looks fun! I have enough time to read THAT, thank god!

Vote for the RDS community ad!

Normally I wouldn't canvas, but given the lack of meta activity, this proposal will never get ad status (10 votes iirc) unless it gets a nudge now and then :/

Aah, its 6 votes..

can anyone please help me with this? physicsforums.com/showthread.php?t=587482

@Qubit why not ask it as a question on p.se? I doubt anyone will mind you crossposting from Pforums...

Its fine if it looks like a homewk question but is a comparison of two methods that give different results

As long as it doesnt sound too 'check my work'y

I think I am not getting the math right here..I know my concepts about spacetime geodesic is correct

@Ma

Aah...

@Manishearth I would love to put this question on SE but I really do have time to write it up...if someone could just look at it once and suggest something would be great

Cant you just copypaste the code"

?

Νοτε τηατ ι δοντ θνδερτανδ τενσορ αναλυσις

Oops

Clicked the keyboard language button

I meant to say "note that i dont understand tensor analysis"

So i can't do much about that question

As a matter of fact it's about derivative more than tensor...I don't know why I am not being able to wrap my head around this derivative

What do you want to differentiate?

The ds^2?

Im not sure if you can divide squared differentials in multivariable calc

Multiplying/dividing differentials is an abuse of notation, but it works

But i dunno how far it goes...

When you have a function of the variable times a squared differential in multivariable, there may be an issue

May be.

Thats all i can think of

Just checking, you differentiating wrt τ, right?

I mean the dots mean differentn wrt proper time?

yep

Otherwise tdot=1

Gotcha

Wait is your el correct?

The rhs should have a x alpha

Not x

And theyre partial derivatives

which one?

All of them, the rhs should have del L/del x^\alpha in the first one

And del L/del t in the second

(del=rounded d partial derivative symbol)

No mathjax here, so linkylink: en.wikipedia.org/wiki/Euler–Lagrange_equation#Basic_method

Im talking about the two statements of EL eqns

@Qubit ping

I know it's partial derivative...the reason I didn't use partial derivative notation is because I didn't see partial derivative notation in physics forum symbol list...I thought people will get it

What about the equation RHS?

The time-EL should be d/dtau(dL/dtdot)=dL/dt

And the general one is d/dtau(dL/dxalphadot)=dL/dxalpha

The RHSs are different

@Qubit

sorry that's a typo

In both places?

Even in the time EL?

And you forgot to diffentiatr phi by tau..

It seems as if you don't know phi...

ya that was my problem...I know phi is dependent on r and r is dependent on x, y, z ...and using proper time I can relate r and t..but I was just lost...I couldn't differentiate

Whats the relation?

(i know no GR either, so all these things are half-familiar... )

In Short: In GR we try to study different space or spacetime.... the one I am trying to study is a general weak field space time... I am trying to find Christoffel symbol for that spacetime, which is actually a easy task if I use general formula for Christoffel symbol

....but you can read of Christoffel symbol from the geodesic equation... and you can get geodesic equation from EL (because El gives you equation of motion)....I am trying to use variation principle to get geodesic and then find Christoffel symbol..which I haven't succeed yet

Basically I don't get how you got from the EL equation to -(1+2phi)tdotdot^2=0

Cos phi isnt constant

Even if phi was constant, it should be -(1+2phi)x2

Whoops -(1+2phi).2tdotdot

I know that...that's a wrong solution..phi is not constant...right now I am trying to do it using chain rule to account for the fact that phi is dependent on r

Is r dependant on tau? If so, whats the relation?

i think dtau^2 = dt^2 - dr^2

Isnt ds^2=dt^2-dr^2 ? Atleast in SR.. Oh wait theres a metric

Hmmm

And youll need the reln between phi and r as well..

Well, this is beyond me... Too many squared differentials....

(unofficial) update on the neutrino fiasco blogs.discovermagazine.com/cosmicvariance/2012/03/16/…

(by sean carrol)

*carroll

Aah and official update arxiv.org/abs/1203.3433

Officialish anyways

But the sean carroll one has a funkier title "Superluminal neutrinos are so 2011" ;)

hi. I've got a quick question. So I've just read Arnold Neumaier's description on virtual particle in physics.stackexchange.com/questions/4349/…. How wrong is it to claim that we can only see virtual particles appearing in our equations when we have at least 2 quantum objects in our system? In normal 'semiclassical' QM e.g. quantum electron in classical potential, the electron is on-shell all the time. Once resolved, I'll append the answer as a comment later.

Why don't you ask it as a regular question? Answer space here in chat is confined to a few lines....

ok, wait a moment

hmmm physics.stackexchange.com/questions/22458/…

ok, I'll write an answer.

thx

Hi, do you know if we have a site for an applied chemistry question?

I thought that you people may know a place where you send questions if they are not physics-related enough.

iirc, there is a beta version of chemistry stackexchange

Ah, found it. It is in Area 51 :(

@Manishearth It links to the paper so it's good enough as far as I'm concerned

Sean Carroll's blog post is the one I tweeted a link to

@Qubit Looks like you got some help there

For future reference, it's fine to cross-post from Physics Forums as long as the question is suitable for our site (e.g. no "do my homework" questions and no "check my work" questions)