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 Originally Posted by Renton
Suppose that the earth is the only massive object in the universe. It doesn't orbit anything and it doesn't rotate. Under these conditions, if i picked up an apple and released it, apply no forces to it, would it remain motionless in mid air?
If the Earth is the only massive object in the universe, the what are "you" and what is an "apple". They are massless objects, which would not experience a gravitational force.
Otherwise, both you and the apple are massive objects which are accelerating.
The Equivalence principle broadly states that gravitational forces are indistinguishable from other forces in the way they accelerate masses.
Meaning that if I'm in a closed room, and I experience 9.8 m/s^2 of acceleration in 1 direction, then I can't perform any test inside the room that can say whether I'm in a uniform gravitational field or if I'm somehow being accelerated by some other means (a rocket or the hand of god).
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For the record, this notion of 2 stationary objects alone in an otherwise empty universe is griefing me, but not troubling me. Clearly the objects would attract each other by Newtonian mechanics. I just don't know how Einstein's Relativity explains it in terms of geodesic lines in curved spacetime.
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