Isaac Newton defined gravity as being force between two objects. He figured out the laws that gravity appeared to follow: gravity causes objects in the universe to be pulled toward one another. Gravity is also responsible for the formation on Earth, moon and other planets. Planets are able to revolve around the Sun because of gravity. Aristotle was one among the first people to understand the theory behind gravity. Galileo was an Italian physicist who made telescopic observations that proved what goes up must come down. He discovered that objects of different weights will fall toward the Earth at the same force. Without gravity everything would float off into the atmosphere. Some scientists believe that gravity is carried by a particle called the graviton.