Univers

The universe is the totality of space, time, matter, energy, and the physical laws and constants that describe them. In cosmology, one distinguishes the observable universe—the region whose light has had time to reach us since the beginning of the cosmological expansion—from the larger, possibly infinite, universe beyond. The observable universe spans about 93 billion light-years in diameter and is limited by the finite age of the cosmos and the speed of light.

Current consensus around a standard cosmological model, Lambda-CDM, describes the universe as composed of ordinary matter, dark matter, and dark energy, with radiation significant in the early universe. The large-scale structure forms through gravity, giving rise to galaxies, clusters, and the cosmic web. The laws of physics—general relativity for gravitation and the Standard Model for particle interactions—apply across the cosmos, though their integration at the earliest moments remains a focus of research.

Observational evidence for the Big Bang includes the expansion of galaxies, the cosmic microwave background radiation, and the abundances of light elements. Space-based missions and surveys support an age of about 13.8 billion years and a history of expansion from a hot, dense state. Yet questions remain, including the nature of dark matter and dark energy and the behavior of gravity under extreme conditions.

Some theories in physics propose a multiverse—an ensemble of universes with varying properties—though this remains speculative with limited empirical access. The word “universe” derives from Latin universus, meaning “all things,” from uni- meaning “one” and vertere meaning “to turn” or “to become a whole.”