The Sleepwalkers

The Sleepwalkers is a 1959 book by the Hungarian-British writer and journalist Arthur Koestler, which traces the history of Western ideas about the cosmos from ancient Mesopotamia to Isaac Newton. Its central thesis is that scientific discoveries arise in a manner akin to sleepwalking: not by chance, but guided by intuitions that the scientists themselves do not fully understand, and without full awareness of what their findings will imply.

The narrative begins in antiquity with the Ionian school of early philosophers, such as Anaximander and Anaximenes, to whom Koestler attributes the first mechanical, non-religious model of the solar system. After a brief period of progress, the tradition in his account slipped back into superstition and mysticism. He then examines the lasting influence of Plato, particularly his insistence that the world must be a perfect sphere and that the heavenly bodies must move in perfect circles at uniform speed, a notion Koestler describes as a curse that weighed on astronomy for two thousand years.

The heart of the book is the story of how that curse was broken. Koestler is notably critical of the modern image of Copernicus as a revolutionary, arguing that his heliocentric model still sought circular motion and was at least as complicated as Ptolemy's. He instead highlights Tycho Brahe, whose vast and meticulous observations provided the indispensable basis for Johannes Kepler, who discovered that planetary orbits are elliptical. The work closes with Newton's law of universal gravitation, which explained both advances.

The book enjoyed notable reception. The mathematician Alexandre Grothendieck drew on its title for a metaphor about scientific creativity, and the novelist John Banville acknowledged its influence on his Revolutions trilogy. The historian of astronomy Owen Gingerich, however, found it highly questionable, especially in its treatment of historical figures and in claims about Copernicus that later scholarship has qualified.