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:
“O reason, reason, abstract phantom of the waking state, I had already expelled you from my dreams, now I have reached a point where those dreams are about to become fused with apparent realities: now there is only room here for myself.”
—Louis Aragon (1897–1982)
“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)