Recent content by micomaco86572

Does anyone know something about this issue? Thx!

I am studying modified gravity theories, these days, and I have learned from many papers that, among various modified gravity theories, f(R) theory can avoid the Ostrogradski instability. Most of these papers cited Woodard's paper in 2007 (Lect. Notes. Phys. 720, 403 (2007)), which just gives a...

Thank u, Chalnoth. I understand it, now.

Almost all textbooks tell us that the cosmic redshift is arised from the cosmic expansion rather than the recession of the celestial objects. I think the conclusion is basically based on the assumption of Copernican Principle, i.e. there is no favored position in the whole universe. But what if...

Why isn't the FRW metric spherically symmetric? Is it one of the maximally symmetric metric of 4D space-time? thx

Why the process of recombination is called "re"combination? The process in which the nucleus and electrons combined to form neutral atoms at early times is called recombination. But why it is added an "re" to "combination"? Is there any combination process before this process? Thx!

thank u Chalnoth. I have heard about this program, but I forgot the name.

Are there any programs which could be used to fit the Supernova data to constrain the cosmological models's parameter? thx

Yeah，so I am thinking about whether the local poincare transformation includes all the continuous coordinate transformations except the scale transformation mentioned above.

yeah, I see. But if we exclude this scale transformation， can we still say the coordinate transformation could be viewed as the local poincare transformation?

Can any continuous coordinate transformation on a differential manifold be viewed as a poincare transformation locally in every tangent space of this manifold? Thx!

asymmetric metric The metric in the classic GR is always symmetric. What if it is not metric? It has to be symmetric? Does there exist some space with an asymmetric metric? Thx.

I have the same problem. There are 3 conditions in the Goldstein's proof. If we break the second condition, we cannot obtain the same equation form after the variables' transformation. What if we break the third condition? Why we have to introduce this condition? Thx.

Thx Kev!

stupid question: why a perturbative theory cannot be background independent? thx.