Why does the force of gravity decrease with increasing distance?

Answer 1

If you ask Isaac Newton, he'll tell you that the force of gravity obeys a law which says gravity decreases with the square of the distance, and that's all he knows.

If you ask Albert Einstein, he'll tell you that mass warps space-time, and the effect reduces by the square of the distance for reasons having to do with the number of dimensions and the consistency of space-time math.

If you ask a modern particle physicist, he or she will explain that graviton particles carry the force of gravity, and they spread out as they travel away, so that the density drops with the square of distance. Then they will start arguing with Albert about the details, and both of them will get very frustrated because not all of their predictions match perfectly.

The string theorist will pipe up at this point and claim to have ways to make Albert's results agree with the particle physicist's, but very few people can even understand their math, and no one has a good way to test the string theorist's ideas.

So while we know gravity does decrease with distance, and we some ideas about how, we don't have all the details yet about why.

(Cross-posted from Quora)