THE
“ARROW OF TIME”
From the mathematical standpoint, the quantity that enters into such relation as the equation of motion can be either positive or negative, and the fact that time is observed to move only in one direction is frequently characterized as an anomaly, a “puzzle.” But there is nothing puzzling about the direction of time if it is viewed in physical terms. Time, as a physical quantity—the time interval between two events, for instance—cannot be less than zero. The net magnitude of a quantity of time is therefore positive in all cases. The physical arrow points forward. A related issue that remains unresolved in the present-day mathematical version of physical theory is the question as to why time has the characteristics of a continual flow. Paul Davies describes the situation in this manner: It is one of the most perplexing puzzles in physics that the elementary conscious experience of time—the flow or motion of the present moment—is absent from the physicist’s description of the objective world. The truth is that the physicists
are not entitled to expect that their theories, which |