• 300

# Aristotle

At first astronomers thought that all planets fell into the Earth. Then they thought that all planets rotated around Earth. Also Earth had the most of all four elements.
• 400

# Cladius Ptolemy 2nd Century A.D.

From Aristotle's idea he created a complex system of circles and epicycles describing the movement in the sky. If a disagreement occurred, than another circle was added.
• # Isaac Newton

Came up with the universal law of gravitation. He thought he came up with the law because an apple fell onto his head. The law explains that any objects in the universe exert gravitational attraction on each other, with the force having a universal form. Fg=G m1*m2 /r^2
• # Henry Cavendish

Found the value of the constant in Newton's law of universal gravitation (G) 6.67X 10^-11 m^3kg^-1 s^-2 He found this out in an experiment to directly find the gravitational attraction between objects.
• # Albert Einstein

Added to Newton's theory of the motion of falling bodies at high speed. Assumed that the speed of light was constant no matter what location. Was the first person to expand on his zero acceleration to non-zero acceleration.
• # ALbert Einstein

Found out that a gravitational field and constant acceleration are equivalent. Mass and energy affect a gravity field. Also a gravitational field isn't a force, so Newton was incorrect.