V.—Symposium—The Time Difficulty in Realist Theories of Perception

Abstract

Is the time intervening between stimulus and perception an obstacle to a realist theory of perception ? The question is not a new one. It is one of the ordinary difficulties that the idealists have urged against the realists, but it has a special significance in relation to recent developments of physical theory. The electro-magnetic theory has established the fact that there can be no immediate action at a distance, a time interval intervenes between the emission and the reception of a luminous or any other kind of signal. Neither light nor gravitation nor any other kind of influence of one object on another is instantaneous. When the rays from a luminous point impinge on the different parts of my retina I perceive the point whence the rays are coming. The perception seems to me the immediate apprehension of this point, and to be there in space where the point is. But this is impossible, for the rays I perceive are not at this point when I perceive it. The object of visual perception can never be actually present to me, for no signal can travel more quickly tharl light and so make me aware of the object before I receive the luminous signal. If the point is on the sun, the light wave takes eight minutes, if it is on Sirius it takes about eight or nine years, and if on more distant stars, hundreds or thousands of years. On the other hand, however close to me it is, it must occupy some time, even though it be the quite inappreciable infinitesiinal fraction of a second.