Originally Posted By: Bill S.
Originally Posted By: redewenur
I like that. It's exactly right: "always be in a state of freefall" = "always follow a timelike geodesic". Ín other words, unless acted upon by a force, the vector of the object is determined solely by the geometry of space-time.

I like it too, but it still leaves unanswered the question as to how the geometry of spacetime is altered without energy being transferred/used.

Nobody has more than a clue. Perhaps the beginning of the answer, from Frank Wilczek:

“How is it possible to construct heavy objects out of objects that weigh nothing?,” he asks. Only by “creating mass out of pure energy.” These particles are essentially “excitations in otherwise empty space.”

- Which, again, comes back to m=E/c2

“That suggests something …beautiful and poetic: the masses of particles [such quarks and gluons] are not like, or similar to or metaphorically suggested by — they are the tones or frequencies of vibration patterns in dynamical voids.”

- Sounds like M-Theory doesn't it. And the bottom line:

“in cosmology, we meet our match, and don’t know what’s going on.”

http://www.learnoutloud.com/Free-Audio-Video/Science/Physics/The-Universe-is-a-Strange-Place/15576

"Time is what prevents everything from happening at once" - John Wheeler