General relativity

Why shouldn't gravity be a force? I am interested to know the reasons why we shouldn't treat gravity as a force in, for example, General Relativity. Won't we be able to model it accurately by... more

I am no Physicist, but I enjoy reading about Physics. However reading about leading theories such as M-Theory and others they speculate about the existence of the Graviton. In my past reading of... more

How can astronomers say, we know there are black holes at the centre of each galaxy?What methods of indirect detection are there to know where and how big a black hole is?

>> [General Relativity] basically says that the reason you are sticking to the floor right now is that the shortest distance between today and tomorrow is through the center of the... more

I understand that people explain (in layman's terms at least) that the presence of mass "warps" space-time geometry, and this causes gravity. I have also of course heard the analogy of a blanket or... more

I have studied some of Einstein's Theory of General Relativity, and I understand that it states that gravity isn't a force but rather the effects of objects curving space-time. If this is true,... more

The most oft-cited [triumphs](http://en.wikipedia.org/wiki/Tests_of_general_relativity) of GR are things such as the shifting perihelion of Mercury, gravitational redshift experiments, and... more

Just what the question asks. Assuming the Friedmann-Rovertson-Walker (FRW) metric, what measurements can be performed to determine the spatial curvature of the universe.

Einstein's Theory of Relativity, When objects travel faster time slows down for them relative to other people. People say "Astronauts age slower because they travel faster in space, obviously by... more

you can connect a car heater to the car of a power 2,0kw to a 230V power outlet in the garage if the socket is protected by a 10 A fuse? only responses are not accepted

Calculate the rest energy and the kinetic energy of:a) A 100g ball travelling with the speed of 100m/sb) An electron travelling at a speed of 0.999c. Which one has greater rest energy? Which one... more

We learned about the Einstein train that travel nearly the speed of light and it's just said that the time slows down when you get close to the speed of light. But I don't understand how did they... more

A rod of proper length l0 is at rest in a frame of reference S travelling at a speed v relative to the reference frame S' of a brick wall. The rod collides end-on with the wall, which brings that... more

A spacecraft is in a circular orbit around a schwarzschild black hole of mass M. a) find expressions for the orbital period as a function of r determined by an observer at rest at infinity and an... more