A.T.

I think his point is that in General Relativity gravity is not an interaction force (real force) like in Newtons theory, but an inertial force (fictitious force). http://en.wikipedia.org/wiki/Fictitious_force What is "holding us down" is our inertia, or the tendency to follow a geodesic path in space-time. It is the same thing that holds an astronaut against the rear wall of an accelerating rocket: http://en.wikipedia.org/wiki/Equivalence_principle One can describe those effects in non-inertial frames by inertial forces, or distorted coordinates like shown in the clip below. Note that in Einstein's model there is no "force of gravity" because this representation uses only (real) interaction forces :

They are advancing straight in space-time. But since space-time is distorted, the projection onto space advances non-uniformly. It is best explained with graphics: Here some more visualizations: http://www.physics.ucla.edu/demoweb/demomanual/modern_physics/principal_of_equivalence_and_general_relativity/curved_spacetime.html http://www.relativitet.se/spacetime1.html