''For other articles with similar titles, see Time Stream (disambiguation)''
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.〔Science fiction scholar Paul Kincaid comments, "The time machine allows not movement in time (we already live in time, and a novelist has always been able to set a story in any future or past era), but transposition in time." 〕
* 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..."
Brian Stableford writes of the historical and philosophical concepts of time (and using the terminology of "flow"),
Like space, it is a basic aspect of experience; early philosophical treatments of the idea hesitated in a similar fashion over the question of whether time could be said to exist apart from the objects manifesting its effects. The manner of time's experience is, however, markedly different from that of space; time appears to 'flow' unidirectionally from the past into the future, bearing all existence with it, encapsulated in the momentary present.
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 () 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'...) ..."
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