Astrophysics (Index)About

particle horizon

(cosmological horizon, comoving horizon, cosmic light horizon)
(furthest point from which light can reach us)

The particle horizon (aka the cosmological horizon, comoving horizon, or cosmic light horizon) is the boundary in the universe defined as the furthest distance from which light could travel through the age of the universe to you, taking into account the speed of light and the expansion of the universe. As such, it constitutes a similar limit on any particle whose motion is bounded by the speed of light. The observable universe is all the universe within this boundary. The distance through which such light would have traveled is called the horizon distance.

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