Recent content by Dreak

Hello, I have a small question about coupling of angular momenta. When you have J² with J = J1 + J2; you change it to the form (dropping the hbar in all equations): j² = j1² + j2² + j1-j2+ + j1+j2- + 2j1zj2z now it's these j1-j2+ I have a problem with. Let's say you use it on |1/2;-1/2>...

Of course! Thanks, can't believe I messed that up.

quote from my course: "A direct result of the universal movement of objects in a gravitational field is that a constant gravitation field g can always be transformed away by going to an other reference system. Indeed, if we go over to reference system S' by coordinationtrasformation: x' = x...

And what about someone falling from the sky? (let's assume that there is no fraction)? Because I'm not certain about someone in freefall? Is it ok if I write down my own thinking and you correct it? If someone stands on the ground; we can go to a reference system in freefall by x'=x-1/2gt². So...

Let's say I have my pen on my desk; does it describe a geodesic.? Or not because there is the normalforce working on it.

Hello, PF have helped me a lot understanding a lot of important things in physics, I hope you guys can help me with this too :). I have problems understand the symmetry groups. I know there are groups like SU(2), O(3).. etc. But I have no idea how they represent certain particles.So particles...

Aha yes yes! It's all falling into place now! I took huge leaps in understanding my course today. Thanks a lot guys, couldn't have don't it without you!

Unfortunatly, that's what is written in my course :(. And that it somehow tells 'spacetime how to bend near matter'. Ehm guys, another one last question (I somehow have a lot of last questions ^^). If you got the EMT and you contract it; you get T = Tμμ. But what is the meaning of this...

Ok, thanks for the conformation. I was writing it down on paper before I posted and I already thought the triple indices were something messy :). It has already improved a lot during the day by using it continually and finding all my (stupid) mistakes, but your help (and from the others) have...

It made it a bit more clear; shame I mis some basic differential geometry :(. One last thing gμεR is not the same as Rμε. Or is it? Somehow I have the feel it's not right, because you must use the same up and low indices to do this, but on the other hand i have: gμεR = gμε x gμεRμε =...

When I posted the topic, I realized I made a mistake and that I made a mistake in something I had in mind :). But thanks for the help. So... The rieman tensors tells how space is curved and the Ricci tensor tells how the EMT curves the space?

Hello.The Einstein has following definition (in my course): Gμε = Rμε - 1/2Rgμε. But why don't we just: gμεGμε = gμεRμε - 1/2Rgμεgμε. <=> G = R- 1/2 . R . 4 = R- 2R = -R? Is this wrong or.? Also, what is the meaning of the ricci scalair and tensor?

Wow thanks, very clear explenation. Thank you very much! :)

I'm starting to doubt about something: In 4 dimension, what value has δ^{λ}_{μ} in following equation: ημ\nuη\nuλ = δ^{λ}_{μ} is it 4 or 1? and IF it's 1, what is the difference that this equation: ημσημσ = 4?

Thank you very much! :)