Nugatory, thanks again. I understand now. I didn't imagine that the de-warping space-time in the wake of the moving mass would return any and all energy to the mass that was transferred to the space-time in front.
But one more question:
You write "or you could say that there is no net...
Thanks for your reply.
I understand everything you've said, but I don't understand why an action (mass distorts space-time) doesn't result in an equal and opposite reaction which would cause the velocity of the mass to be altered.
A mass moves through space-time at constant velocity. Space-time around this mass is warped by the mass and as the mass moves through space-time it causes unwarped space-time to warp and already warped space-time to warp more. In addition, the space-time it has moved through de-warps. Why...