An Experiment with Time is a book by the British soldier, aeronautical engineer and philosopher J. W. Dunne about his precognitive dreams and a theory of time which he later called "Serialism". The book discusses two main topics. The first half of the book describes a number of precognitive dreams, most of which Dunne himself had experienced. His key conclusion was that such precognitive visions foresee future personal experiences by the dreamer and not more general events. The second half develops a theory to try and explain them. Dunne's starting point is the observation that the moment of "now" is not described by science. Contemporary science described physical time as a fourth dimension and Dunne's argument led to an endless sequence of higher dimensions of time to measure our passage through the dimension below. Accompanying each level was a higher level of consciousness. At the end of the chain was a supreme ultimate observer. An Experiment with Time has influenced imaginative literature ever since it was published.