The cosmic horizon, also known as the cosmological horizon or particle horizon, is the maximum distance from which light or any information could have traveled to an observer since the beginning of the universe. It marks the boundary between the observable and unobservable regions of the universe, effectively defining the size of the observable universe at any given time
. Because the universe is expanding, the cosmic horizon is not a fixed distance but a dynamic boundary that grows over time. Currently, this horizon is approximately 46.5 billion light years away from Earth, meaning we can observe objects whose light has traveled that far since the Big Bang
. There are related concepts such as:
- Particle Horizon: The furthest distance from which particles' light could have reached us since the Big Bang, setting the limit of the observable universe
- Hubble Horizon (Hubble Sphere): The distance at which objects recede from us at the speed of light due to cosmic expansion. Objects beyond this horizon move away faster than light relative to us, but may still be observable if their light was emitted earlier
In summary, the cosmic horizon is the ultimate observational limit set by the finite speed of light and the universe's expansion, beyond which we cannot receive any information or signals
