Category
page 1Physical horizons
event horizon
boundary of a region of spacetime from which one cannot escape once entered
particle horizon
the maximum distance from which light from particles could have traveled to the observer during the age of the universe
Cauchy horizon
light-like boundary of the domain of validity of a Cauchy problem in general relativity
cosmological horizon
horizon appearing on a cosmological scale
absolute horizon
boundary in spacetime, defined with respect to the external universe, events inside which cannot affect an external observer
apparent horizon
surface that is the boundary between light rays that are directed outwards and moving outwards, and those directed outward but moving inward