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:
“If we ever feel discouraged by the apparent constraints on humanity, about its lack of elbowroom and freedom of action, we should think of the Jews and the Greeks, insignificant, powerless, and tiny in the age of the dinosaur empires, yet providing the growing points for the next stage in human destiny.”
—Barbara Ward (1914–1981)
“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)