In cosmology, a cosmological horizon marks a limit to observability, and marks the boundary of a region that an observer cannot see into directly due to cosmological effects. Jump to: navigation, search Cosmology, from the Greek: κοσμολογία (cosmologia, κόσμος (cosmos) world + λογια (logia) discourse) is the study of the universe in its totality and by extension mans place in it. ... The word Boundary has a variety of meanings. ... Possible meanings: In general, an observer is any system which receives information from an object. ...
The existence, properties, and significance of a cosmological horizon depend on the particular cosmological model being discussed.
An example of a cosmological model with an event horizon is a universe dominated by the cosmological constant (a de Sitter universe).
For the case of a horizon perceived by an occupant of a de Sitter universe, the horizon always appears to be a fixed distance away for a non-accelerating observer.
For the case of the horizon around a fl hole, observers stationary with respect to a distant object will all agree on where the horizon is. While this seems to allow an observer lowered towards the hole on a rope to contact the horizon, in practice this cannot be done.
The particle horizon in physical cosmology is the maximum distance from which particles (of positive or zero mass) can have travelled to the observer in the age of the universe.
The particle horizon is defined as the largest comoving distance from which light can have reached the observer — at the present moment.
The event horizon is defined as the largest comoving distance from which light can ever reach the observer — at any time in the future.
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