|Image (c) Lydia Chai|
Einstein recognized that temporal specifications, too, are relative and depend on the observer. In everyday life, the impression that we can arrange the events around us in a unique time sequence is created by the fact that the velocity of light - 186,000 miles per second - is so high, compared to any other velocity we experience, that we can assume we are observing events at the instant they are occurring. This, however, is incorrect. Light needs some time to travel from the event to the observer. Normally, this time is so short that the propagation of light can be considered to be instantaneous; but when the observer moves with a high velocity with respect to the observed phenomena, the time span between the occurrence of an event and its observation plays a crucial role in establishing a sequence of events. Einstein realized that in such a case, observers moving at different velocities will order events differently in time. Two events which are seen as occurring simultaneously by one observer may occur in different temporal sequences for others. For ordinary velocities, the differences are so small that they cannot be detected, but when the velocities approach the speed of light, they give rise to measurable effects. In high energy physics, where the events are interactions between particles moving almost at the speed of light, the relativity of time is well established and has been confirmed by countless experiments.
- Fritjof Capra