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:
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—H.L. (Henry Lewis)
“The thought of you will constantly elevate my life; it will be something always above the horizon to behold, as when I look up at the evening star. I think I know your thoughts without seeing you, and as well here as in Concord. You are not at all strange to me.”
—Henry David Thoreau (1817–1862)