In Principia, its full title is the Mathematical Principles of Natural Philosophy, Newton lays out his laws of motion, law of universal gravitation and an extension of Kepler’s laws of planetary motion. It is a book that helped define the Age of Reason and it is Newton’s most celebrated achievement.
He proposed that the universe is mainly empty space criss-crossed by powerful but invisible gravitational forces. Whether tiny atomic particles or giant planets, the attractive pull between two objects is proportional to the product of their masses and decreases with the square of the distance between them.
In 1684, Newton was living in self-imposed isolation at Cambridge. Approached by young astronomer Edmond Halley, Newton answered a question that the curve to a mathematical formula was an ellipsis. Dr Halley asked for his calculation without delay.
Halley continued to manoeuvre with great diplomacy, coaxing Newton through the process of getting the three parts of the Principia finished. Halley went to great lengths to bring Newton’s work to paper, paying for the publication himself as the Royal Society had run out of funds.
British astronaut Tim Peake named his 2015 mission to the International Space Station ‘Principia’.
