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)
“Four spectres haunt the Poor—Old Age, Accident, Sickness and Unemployment. We are going to exorcise them. We are going to drive hunger from the hearth. We mean to banish the workhouse from the horizon of every workman in the land.”
—David Lloyd George (1863–1945)