Past and future of an event

Given an event P, one can divide the other events in the universe into three classes. Those events that can be reached from the event P by a particle or wave travelling at or below the speed of light are said to be in the future of P. They will lie within or on the expanding sphere of light emitted from the event P. They they will lie within or on the future light cone of P in the space-time diagram. Only events in the future of P can be affected by what happens at P because nothing can travel faster than light. 

The past of P can be defined as the set of all events from which it is possible to reach the event P travelling at or below the speed of light. It is thus the set of events that can affect what happens at P. 

The events that do not lie in the future or past of P are said to lie in the elsewhere of P. 

What happens at such events can neither affect nor be affected by what happens at P.