B-Theory of time

The B-theory of time is the name given to one of two positions regarding philosophy of time. B-theorists argue that the flow of time is an illusion, that the past, present and future are equally real, and that time is tenseless. This would mean that temporal becoming is not an objective feature of reality.

B-theory is often drawn upon in theoretical physics, and in theories such as eternalism.

The labels, A-theory and B-theory, are derived from the analysis of time and change developed by Cambridge philosopher J. M. E. McTaggart in "The Unreality of Time" (1908), in which events are ordered via a tensed A-series or a tenseless B-series. A-series is closely related to presentism while B-series is closely related to eternalism.

Events (or "times"), McTaggart observed, may be characterized in two distinct, but related, ways. On the one hand they can be characterized as past, present or future, normally indicated in natural languages such as English by the verbal inflection of tenses or auxiliary adverbial modifiers. Alternatively events may be described as earlier than, simultaneous with, or later than others. Philosophers are divided as to whether the tensed or tenseless mode of expressing temporal fact is fundamental. Some philosophers have criticised hybrid theories, where one holds a tenseless view of time, but asserts that the present has special properties, as falling foul of McTaggart's paradox.

The debate between A-theorists and B-theorists is a continuation of a metaphysical dispute reaching back to the ancient Greek philosophers Heraclitus and Parmenides. Parmenides thought that reality is timeless and unchanging. Heraclitus, in contrast, believed that the world is a process of ceaseless change, flux and decay. Reality for Heraclitus is dynamic and ephemeral. Indeed, the world is so fleeting, according to Heraclitus, that it is impossible to step twice into the same river. The metaphysical issues that continue to divide A-theorists and B-theorists concern the reality of the past, the reality of the future, and the ontological status of the present.

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