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 compensations of calamity are made apparent to the understanding also, after long intervals of time. A fever, a mutilation, a cruel disappointment, a loss of wealth, a loss of friends, seems at the moment unpaid loss, and unpayable. But the sure years reveal the deep remedial force that underlies all facts.”
—Ralph Waldo Emerson (1803–1882)
“The bird is lost,
Dead, with all the music:
While sunsets heard the brain’s music
Faded to last horizon notes.”
—Owen Dodson (b. 1914)