The Sleepwalkers: A History of Man's Changing Vision of the Universe is a 1959 book by Arthur Koestler, and one of the main accounts of the history of cosmology and astronomy in the Western World, beginning in ancient Mesopotamia and ending with Isaac Newton.
The book challenges the habitual idea of a progressive science working towards a definite goal. The suggestion of the title is that the scientific discoveries and the geniuses that come to them are like a game of sleepwalking. Not that they come by pure chance, but that often the genius doesn't really know that he has discovered, as it is evident for instance in the three Laws of Kepler.
A central theme of The Sleepwalkers is the changing relationship between faith and reason. Koestler explores how these seemingly contradictory threads existed harmoniously in many of the greatest intellectuals of the West. He illustrates that while the two are estranged today, in the past the most ground-breaking thinkers were often very spiritual.
Koestler also casts doubt on the firm beliefs that today people hold as truth without even understanding them. For instance, he says, "I am sitting on a chair made of molecules, which consist of atom, which are formed by subatomic particles, but the distance between these particles (he refers to protons, neutrons and electrons) is so huge relative to their sizes that it would be better compared to the distance between stars. So basically I am sitting on a chair made of nothing"
To this point is important to note that another recurrent theme of this book is the breaking of paradigms in order to create new ones. People - scientists included - hold onto cherished old beliefs with such love and attachment that they refuse to see the wrong in their ideas and the truth in the ideas that are to replace them. "The conclusion he puts forward at the end of the book is that modern science is trying too hard to be rational. Scientists have been at their best when they allowed themselves to behave as "sleepwalkers," instead of trying too earnestly to ratiocinate.