The Interval in Space Time

There are two different possibilities as to the relation between them. It may be physically possible for a body to travel so as to be present at both events, or it may not. This depends upon the fact that nobody can travel as fast as light. But there is a physical fact which can be inferred from the distance in time together with the distance in space. This is what is called the Interval in Space Time. For example, if we were to send out a flash of light and have it reflected back from the Moon, this would take about two and a half seconds. Nobody could travel so fast as to bepresent on the Earth during any part of those two and ahalf seconds because