According to relativity, gravity is a curvature of space rather than a "force" proper. Also according to relativity objects travel in a straight line and the effect of gravity is that the object moves in a straight line in a curved space. So I was just ruminating over this notion and hit a conundrum.

 

Let's say you have two bodies in space. The first object is the Earth (but we've stopped its rotation) and the other is a bowling ball. In this thought experiment I want to see what happens when there is no initial relative motion between the two bodies. So at T=0 we set it up so the two bodies are moving through space in perfect synchrony. Relative to one another there is no motion.

 

Now if the bowling ball is sitting "perfectly still" how is it that it begins to fall towards the Earth? Why is it that the Earth, the curved space, and the bowling ball do not all work together as a single unit with no motion occurring between them?

 

Is it merely that the proximal side of the bowling ball is closer to the Earth, and therefore occupies a more curved space-time, while the distal side of the ball occupies a lesser curvature? Or is it related to the thermodynamics / electromagnetism of the ball, such that although the macro-body that we call a "bowling ball" appears to be motionless, its constituent sub-particles are in constant motion?

 

As an aside, is there anything in this thought experiment that gives insight towards a quantum theory of gravity, or has string theory got it pretty much sewn up?

 

I look forward to the group's insights!

Now if the bowling ball is sitting "perfectly still"

 

Aha! There's your mistake! You assumed that because the object isn't moving in space, that it is prefectly still. In GR you have a non-euclidean space-time manifold. You have to consider all the components!