In
general relativity, an
event horizon is a boundary in
spacetime beyond which events cannot affect an outside observer. In layman's terms, it is defined as "the point of no return", i.e., the point at which the gravitational pull becomes so great as to make escape impossible. An event horizon is most commonly associated with
black holes. Light emitted from inside the event horizon can never reach the outside observer. Likewise, any object approaching the horizon from the observer's side appears to slow down and never quite pass through the horizon, with its image becoming more and more
redshifted as time elapses. The traveling object, however, experiences no strange effects and does, in fact, pass through the horizon in a finite amount of
proper time. From here to the central singularity will take 0.0001 seconds in proper time, in free fall, for a 30 solar mass black hole. This infall time is proportional to the mass of the black hole.
