افق ِ کیهانی
ofoq-e keyhâni (#)
Fr.: horizon cosmologique
The → observable region of the → Universe,
limited in extent by the distance → light has traveled during
the time elapsed since the beginning of the Universe
(→ Big Bang). No signal from the objects lying beyond the cosmic horizon
can be received because light has not yet had enough time to travel the distance.
The cosmic horizon can be defined in two ways:
1) The size of the → observable Universe
as derived from ct, where c
is the → speed of light and t is the
→ age of the Universe, 13.8 billion years, hence 13.8 billion
2) The → comoving distance. The distance given above
corresponds to the size Universe had 13.8 billion years ago. Since then
the Universe has been growing at a rate of 3.52c. Therefore,
the current radius of the
observable Universe is about 48 × 109 light-years.
Same as → particle horizon,
→ Hubble distance,
→ Hubble radius, and → Hubble length.
See also → sound horizon.
→ cosmic; → horizon.