The best definition of Newton's theory of universal gravitation among the options provided is:
"Every object attracts every other object in the universe, with a force that increases as the objects' masses increase and the distance between them decreases."
This accurately reflects the principles of Newton's law of universal gravitation, which states that the gravitational force between two objects is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.