Question

What discovery did Newton argue was a main force in the universe?

Answer 1

Newton argued that all heavenly bodies have gravity.

The gravity is a natural phenomenon by which the objects with mass are attracted to each other, effect mainly observable in the interaction between the planets, galaxies and other objects of the universe. It is one of the four fundamental interactions that cause the acceleration experienced by a physical body in the vicinity of an astronomical object. It is also called gravitational interaction or gravitation.

Isaac Newton was the first to state that the force that causes objects to fall with constant acceleration on Earth (earth gravity) and the force that keeps the planets and stars in motion is of the same nature. This idea led him to formulate the first general theory of gravitation, the universality of the phenomenon, exposed in his work Philosophiae Naturalis Principia Mathematica.