In general relativity, an apparent horizon is a surface that is the boundary between light rays that are directed outwards and moving outwards, and those directed outwards but moving inwards.
Apparent horizons are not invariant properties of a spacetime. They are observer-dependent, and in particular they are distinct from absolute horizons.
See, however, the articles on ergosphere, Cauchy horizon, the Reissner-Nordström solution, photon sphere, Killing horizon and naked singularity; the notion of a horizon in general relativity is subtle, and depends on fine distinctions.
Read more about Apparent Horizon: Definition, Differences From The (Absolute) Event Horizon
Famous quotes containing the words apparent and/or horizon:
“The trouble with kingdoms of heaven on earth is that they’re liable to come to pass, and then their fraudulence is apparent for all to see. We need a kingdom of heaven in Heaven, if only because it can’t be realised.”
—Malcolm Muggeridge (1903–1990)
“Elvis’ disappearing body is like a flashing event horizon at the edge of the black hole that is America today.”
—Arthur Kroker (b. 1945)