Doubtful bit of logic there but I think I see what you mean
Not my logic. Einstein's, according to various P S books. Perhaps it looks better the other way round. Gravity is not a force, therefore it does not expend energy. Seems much the same to me though.
Because the effect of the moon's gravity becomes greater than the earth's only when you're up close.
Suddenly gravity becomes a force? The moon attracts the spacecraft without the craft having been lifted off the moon?
Where does the energy come from?
Yes but the rock already had some extra potential energy before you picked it up, just by being on the ground above the bottom of the well. It's that energy that's released.
That's where the "other thoughts" were leading. It seems as though everything has sufficient gravitational potential energy to bring it into contact with everything else in the Universe, but where does the energy come from? How's this for an idea?
Gravity is the curvature of spacetime, and it appears that the degree of curvature is directly related to both the mass and density of the body causing the curvature. For example, a body of the mass and density of the sun will cause relatively gentle curvature over a large area. If this mass were compressed to the size of the Earth, the curvature of spacetime around it would be much more severe.
Given a situation in which an enormous mass, such as the total mass of the Universe, is compressed into an unthinkably small “speck”, with a diameter no greater than the Planck distance, we might just be forgiven for referring to the resulting curvature of spacetime as “infinite”. (:P) This, we are told, approximates to the state of the Universe at the instant of the Big Bang. If this is the case, it follows that every particle of matter and energy in the Universe, at the start of its life – or of this cycle of its life – occupied the same point in spacetime. The energy, whatever its source, that caused this infinitesimal, primordial speck to expand, transforming itself into billions of light years of spacetime would also have caused the curvature of spacetime to expand as well, and to “soften”, but, it would always remain curved, thus it would always tend to return to its original condition, like the rock falling back to Earth once the restraining force has been removed. This would mean that the energy which drives gravitational attraction is the potential energy imparted to every particle in the Universe by the Big Bang. Thus, there is sufficient potential energy within the Universe to bring every particle back to an infinitesimally small speck.
