Recent content by qinglong.1397

Wald and Zoupas discussed the general definition of ``conserved quantities" in a diffeomorphism invariant theory in this work. In Section IV, they gave one expression (33) in the linked article. I cannot really understand the logic of this expression. Would you please help me with this?

Thanks! But why does B contain [a,c)?

I am reading H. Croom's Principles of Topology and in page 139, he gave an example 5.2.5 to show that two points in the same member of any separation of the topological space X, might not belong to the same component of X. In this example, the space X is a subspace of 2 dimensional Euclidean...

Hi WannabeNewton, I know it's been late, but I haven't been able to figure out how to solve the problem 7.4. Can you help me out? Thank you!

Sure. I'll try to solve all of them before the end of the next week.

Thanks! Never thought of this. Great!

Hi, everybody. I have some problem with Wald's statement shown in the picture. This is from the last paragraph in Page 178. He claimed that there are only solutions with two of the p_{\alpha} positive and one negative. But it's easy to find out that if two of the p_{\alpha} are negative while...

Hope there is someone answering this problem soon :)

Hi, Pervect. Thanks for sharing your idea! I'd like also provide a different point of view which sound trivial from a guy in a different forum. She simply interprets the "massless string" as something which doesn't consume any work done by the observer. That's how she understands...

The argument in Poisson's text is interesting. Sadly, it is for static case and seems not general. I think the energy Wald referred should be the one measured by the observer sitting next to the particle. This makes sense because in GR, you can't compare two vectors at different events.

Thanks, WnnabeNewton! I read some of the posts in that link and #65 and got inspired by your discussion. I think I can explain the meaning of conservation-of-energy argument now. I think, the correct the wording should be conservation-of-mass. Mass of a particle is a constant. But how to...

Hi all, I am working on the problems of Wald's General Relativity. I came across this difficult problem: the 4th problem in Chapter 6. Part (a) is easy, but I cannot figure out how to prove part (b). Prof. Wald suggested to use the so-called conservation of energy, but u^{a} isn't a...

Haven't pay much attention to the development of LQG. Looks it's made some progress. I'm so glad.

Great! Thank you very much!

Hey, thanks for your reply! But what is "the next equation", the second equation in the first attachment? If so, I cannot agree with you, because there is no a pullback of a right action.