Cosmological concept · Cosmology
The Observable Universe
Cosmology & UniverseEstablished Science
Definition
The region of the Universe from which light has had time to reach us since the Big Bang.
Scientific overview
Because light travels at a finite speed and the Universe has a finite age, we can only see out to a certain distance. Owing to expansion, the edge of the observable Universe now lies about 46 billion light-years away, giving a sphere roughly 93 billion light-years across — a tiny, and possibly infinitesimal, part of the whole.
Current measurements
| Diameter | ≈ 93 billion light-years | NASA |
Open questions
- Is the Universe finite or infinite beyond what we can see?
Related topics
Knowledge connections
- Related toThe Cosmic Horizon
- Related toThe Expansion of the Universe
- Related toThe Cosmic Horizon
Sources & references
The primary and reference sources this topic draws on.
- NASANational Aeronautics and Space Administration
Mission data, planetary science, space telescopes, and public-domain imagery.
Most NASA-produced imagery is in the public domain; individual items are checked for usage terms before publication.