# Timeline of gravitational physics and relativity

## Before 1500

• 3rd century BC - Aristarchus of Samos proposes heliocentric model, measures the distance to the Moon and its size

## 1500s

• 1543 – Nicolaus Copernicus places the Sun at the gravitational center, starting a revolution in science
• 1583 – Galileo Galilei induces the period relationship of a pendulum from observations (according to later biographer).
• 1586 – Simon Stevin demonstrates that two objects of different mass accelerate at the same rate when dropped.
• 1589 – Galileo Galilei describes a hydrostatic balance for measuring specific gravity.
• 1590 – Galileo Galilei formulates modified Aristotelean theory of motion (later retracted) based on density rather than weight of objects.

## 1600s

• 1602 – Galileo Galilei conducts experiments on pendulum motion.
• 1604 – Galileo Galilei conducts experiments with inclined planes and induces the law of falling objects.
• 1607 – Galileo Galilei arrives a mathematical formulation of the law of falling objects based on his earlier experiments.
• 1608 – Galileo Galilei discovers the parabolic arc of projectiles through experiment.
• 1609 – Johannes Kepler describes the motion of planets around the Sun, now known as Kepler's laws of planetary motion.
• 1640 – Ismaël Bullialdus suggests an inverse-square gravitational force law.
• 1665 – Isaac Newton introduces an inverse-square universal law of gravitation uniting terrestrial and celestial theories of motion and uses it to predict the orbit of the Moon and the parabolic arc of projectiles.
• 1684 – Isaac Newton proves that planets moving under an inverse-square force law will obey Kepler's laws
• 1686 – Isaac Newton uses a fixed length pendulum with weights of varying composition to test the weak equivalence principle to 1 part in 1000