Universe
Observable Universe
The Observable Universe is the cosmic setting studied by cosmology, whose history extends from early inflation to the present accelerating expansion.
Overview
The Observable Universe occupies the broadest level in this hierarchy of cosmic structures. Cosmology examines its origin, evolution, and nature; current theories describe stages of its history, while many questions remain open. In those theories, a brief episode of cosmic inflation about 13.8 billion years ago magnified density differences that could later help create large-scale structure.
When inflation ended, its driving energy transferred to matter and light in the big bang. Early nucleosynthesis produced hydrogen, helium, and traces of lithium and beryllium. About 380,000 years later, recombination allowed light to travel long distances and produced the cosmic microwave background, the oldest light that can be observed. Stars, galaxies, and the cosmic web formed later. Cosmic expansion is accelerating, with dark energy proposed as an explanation.
Essential data
- Key fact
- Cosmic inflation is described as occurring about 13.8 billion years ago.
- Key fact
- The cosmic microwave background dates from the epoch of recombination.
- Key fact
- Early nucleosynthesis produced hydrogen, helium, and traces of lithium and beryllium.
- Key fact
- NASA’s account describes cosmic expansion as accelerating.
Sources and references
- The Universe — NASA Science NASA Science