Stories We Like: A Guide to the Comma
|time reversal |
A mathematical operation on the description of a physical system in which the signs of variables representing time are reversed. Also called time conjugation. See more at invariance.
in physics, mathematical operation of replacing the expression for time with its negative in formulas or equations so that they describe an event in which time runs backward or all the motions are reversed. A resultant formula or equation that remains unchanged by this operation is said to be time-reversal invariant, which implies that the same laws of physics apply equally well in both situations, that the second event is indistinguishable from the original, and that the flow of time does not have any naturally preferred direction in the case of fundamental interactions. A motion picture of two billiard balls colliding, for example, can be run forward or backward with no clue to the proper time direction of the event