[gradi3nt]

Imagine being inside of a closed box like an elevator. Without leaving the box there is no way to tell the difference from being in free fall towards Earth versus floating in interstellar space. Therefor, general relativity take the perspective that gravity is a fictitious force (like centrifugal force) that arises from the shape of spacetime.

[josu]

>versus floating in interstellar space

Versus being inside that an elevator that is being accelerated in interstellar space

This seems like a pretty good explanation: http://www.astronomynotes.com/relativity/s3.htm

[bweitzman]

gradi3nt had it right

Free fall feels like floating Standing still (in the presence of the Earth's gravity) feels like being accelerated.