Btheory

Btheory, often written B-theory of time, is a philosophical account according to which temporal relations between events are tenseless. In this view, the truth conditions of statements about time depend on the ordering of events, not on a moving present. An event can be described as earlier than, later than, or simultaneous with another event without invoking any privileged present moment. As such, there is no objective flow of time in the fundamental structure of reality; becoming is not a fundamental feature but may be explained as a feature of language or as a description of relations among events.

The B-theory is contrasted with A-theory, which treats time as tenseful: past, present, and future are real and time passes in some objective sense. Proponents of B-theory typically hold that statements about times and events can be expressed without reference to a now, often aligning with a four-dimensional view of spacetime in which all moments are equally real.

In physics, B-theory is closely associated with the block universe concept, where all points in spacetime are equally real. Special and general relativity support the idea that simultaneity is relative and that temporal relations are structural features of spacetime rather than aspects of a flowing present. Some philosophers argue that this does not undermine our experience of duration or causation, which can be interpreted as relations among events within the block.

Critics argue that B-theory undermines the apparent passage of time and the personal sense of becoming, while supporters maintain that the theory preserves a coherent account of change and causation without recourse to an absolute present. The distinction between A- and B-theories originates with J. M. E. McTaggart and has been developed by philosophers and physicists to interpret time across different frameworks.