A term used to denote the geometry of the physical universe as suggested by the theory of relativity. It is also called space-time continuum. Whereas in newtonian physics space and time had been considered quite separate entities, A. Einstein and H. Minkowski showed that they are actually intimately intertwined. I. Newton's ideas on space and time are summarized in the following list:

1. Given two events, each of which is clearly localized in space and lasts only for an instant in time, such as two strokes of lightning striking small targets, all observers of the events will be in agreement as to which of the two events took place earlier in time, or whether they were actually simultaneous.
2. If the events were not simultaneous, the interval of time between them is an absolute entity, agreed on by all competent observers.
3. The spatial distance between two simultaneous events is an absolute entity, agreed on by all competent observers.