The timestream or time stream is a metaphorical conception of time as a stream, a flowing body of water. In Brave New Words: The Oxford Dictionary of Science Fiction, the term is more narrowly defined as: "the series of all events from past to future, especially when conceived of as one of many such series". Timestream is the normal passage or flow of time and its historical developments, within a given dimension of reality. The concept of the time stream, and the ability to travel within and around it, are the fundamentals of a genre of science fiction. This conception has been widely used in mythology and in fiction. This analogy is useful in several ways: Streams flow only one way. Time moves only forward. Streams flow constantly. Time never stops. People can stand in a stream, but will be pulled along by it. People exist within time, but move with it. Some physicists and science fiction writers have speculated that time is branching—it branches into alternate universes (see many-worlds interpretation). Streams can converge and also diverge. Science fiction scholar Andrew Sawyer writes, "The paradoxes of time—do we move in time, or does it move by us? Does it exist or is it merely an illusion of our limited perception?—are puzzles that exercise both physicists and philosophers..." History Brian Stableford writes of the historical and philosophical concepts of time (and using the terminology of "flow"): The ancient Greek philosopher Heraclitus was famous for a statement that has been translated in many ways, most commonly as "No man ever steps in the same river twice," which is often called his "flux [flow] doctrine." An essayist for the Stanford Encyclopedia of Philosophy explained it in this manner: "Everything is in flux (in the sense that 'everything is always flowing in some respects'...) ..." Fiction In fiction, an alternate continuity is sometimes called an alternate timestream. Science fiction The Time Stream, a 1946 science fiction novel by author John Taine (pseudonym of Eric Temple Bell), is the first novel to see time as a flowing stream. It was originally serialized in Wonder Stories, in four parts, from December, 1931, to March, 1932. Science fiction scholar E. F. Bleiler described how Taine employed the metaphor: The basic concept is that time is a circular stream that runs eternally, with far past blending into far future. It is possible for certain individuals to enter this