# Scientific Revolution

• Democritus, Empedocles, and other Pre-Socratics developed proto-scientific theories unable to make precise, testable predictions. Things changed in the 17th century.
• The Scientific Revolution began in 1543 with the publication of Copernicus’ heliocentric theory of the solar system.
• Copernicus’s system postulated circular orbits for the planets. Deferents and epicycles were used to explain their retrograde motion.
• Beginning in the 17th century, scientific theories were formulated mathematically, yielding testable predictions.
• Johannes Kepler’s Three Laws of Planetary Motion (1609-1618)
• Ellipses: the orbit of each planet is an ellipse with the Sun at one focus.
• Equal Areas: an imaginary line drawn from a planet to the Sun sweeps out equal areas in equal times.
• Harmony: (the orbital period of a planet)2 is directly proportional to (the average distance of the planet to the sun)3.
• Galileo’s Laws of Falling Bodies and Projectiles (1609)
• Falling Bodies: the (distance a body falls) is directly proportional to (elapsed time)2
• Projectile Motion: the trajectory of a projectile is a parabola
• Isaac Newton’s Theory of Gravitation (1687)
• Using the magic of differential equations (F=MA), Newton’s theory predicted, second to second, the motion of falling bodies and the orbits of the planets
• Galileo in 1623:
• The laws of Nature are written in the language of mathematics.
• A scientific theory is an axiom system:
• designed to explain certain kinds of phenomena
• defined by its postulates
• supported or disproved by its predictions