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. The most common case of an event horizon is that surrounding a black hole. Light emitted from beyond the horizon can never reach the 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.
More specific types of horizon include the related but distinct absolute and apparent horizons found around a black hole. Still other distinct notions include the Cauchy and Killing horizon; the photon spheres and ergospheres of the Kerr solution; particle and cosmological horizons relevant to cosmology; and isolated and dynamical horizons important in current black hole research.
Read more about Event Horizon: Event Horizon of A Black Hole, Particle Horizon of The Observable Universe, Apparent Horizon of An Accelerated Particle, Interacting With An Event Horizon, Beyond General Relativity
Famous quotes containing the words event and/or horizon:
“It is known that Whistler when asked how long it took him to paint one of his nocturnes answered: All of my life. With the same rigor he could have said that all of the centuries that preceded the moment when he painted were necessary. From that correct application of the law of causality it follows that the slightest event presupposes the inconceivable universe and, conversely, that the universe needs even the slightest of events.”
—Jorge Luis Borges (18991986)
“Dark times is what they call it in Norway when the sun remains below the horizon all day long: the temperature falls slowly but surely at such times.A nice metaphor for all those thinkers for whom the sun of mankinds future has temporarily disappeared.”
—Friedrich Nietzsche (18441900)