Question: why does gravity exist??

Marcus Gallagher-Jones answered on 19 Mar 2012:

That may b one of the biggest problems in physics at the moment. A lot of much smarter people than I are looking into it but right now no one really knows. The theory proposed by Einstein in general relativity is that gravitation occurs due to the curvature of space-time by mass. Einstein described objects as moving through space in a straight line however when they encounter something with mass this line becomes curved, a force will therefor act on the object to cause it to maintain a straight path. The list of theories surrounding gravity is however longer than both my arms so I’m afraid I don’t understand more than that at the moment.