
Originally Posted by
swansont
No, it will not attract the universe more. Looking at the contribution from that one rock: it moved away from half of the universe, and closer to the other half. No net effect. Far from the earth, the net attraction hasn't changed.
That is true, but only true without the earth involved. Like you said: it's the contribution of that one rock. But the earth compresses the rock more when it's closer to the earth's centre of gravity, which gives them both more gravity force. It's an exponentially cumulative force: two object close together, somewhere in universe, have more gravity together than when they're farther apart. Together they can shrink more space than the plain sum of both forces. That's because we're talking about
acceleration. There's already a 'square' in it.