The Interval Between Two Events

The interval between two events is a physical fact about them, not dependent upon the particular circumstances of the observer. There are two forms of the theory of relativity, the special and the general. The former is in general only approximate, but is exact at great distances from gravitating better. When the special theory can be applied, the interval can be calculated when we know the distance in space and the distance in time between the two events,. estimated by any observer. If the distance inspace is greater than the distance that light would have traveled in the time, the separation is space-like.