Theory of Gravity

My latest personal pet theory is that gravity is caused by the expansion of the universe. Imagine a rope with a knot in the middle. When you apply a force to the two ends of the string, the center gets tighter. The idea is that space works the same way.

This theory is not based on any real understanding of cosmic physics.
If I knew more about physics I could prove or disprove this to myself quite quickly or could properly attribute this to physicists who have already explored this concept. If anyone has those references, pass them along!