The theory based on the idea that objects with mass move toward each other is Newton's Law of Universal Gravitation.

Here's why:

* Newton's Law of Universal Gravitation: This law states that every particle in the universe attracts every other particle with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between their centers. This means that objects with more mass exert a stronger gravitational pull, and objects closer together experience a stronger force.

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