The idea that
events in the future may or may not
affect you. If an event is not in your event cone, it will not affect you.
|X...a.X
T| X...X
I| X.X b
M| X
E| X.X
| X...X
|X..c..X
----------
SPACE
The "shaded" region inside the X's is your event cone. Events within this area can possibly affect you. Anything outside that cone cannot.
Example: A can possibly affect you. It has the time needed to cover the space to affect you. C has already affected you and is in your past. B cannot affect you, since it does not have the time to cover the distance needed.
I learned this all in
physics the other day and thought it was pretty darn
neato.