Universe
The universe is the totality of space and time, together with all the matter and energy they contain. It includes:
- matter and energy, both in the ordinary forms we see around us, and in the "dark" forms, known as dark matter and dark energy, whose existence is inferred mainly from their gravitational effects. Matter and energy are organised on the largest scales into a structure known as the cosmic web;
- Spacetime, the four-dimensional continuum in which matter and energy exist, move and interact.
Origin of the universe
The Big Bang theory
As of August 2026, the most accepted theory of the origin of the universe is the Big Bang: which states that the universe began about 13.8 billion years ago in an extremely hot and dense state, and has been expanding and cooling ever since.[1][2]
Alternative theories and hypothesis
Although The Big Bang theory is by far the most supported, it is not the only scientific theory on the origin of the universe: alternative proposals, such as the ekpyrotic universe theory,[3] the BVG unified cosmology,[4] and the bilobular collision model,[5] are under active research.
Observing the early universe
The early universe can be observed today via the cosmic microwave background (CMB), the light released when the universe had cooled enough to become transparent a few hundred thousand years after its formation.[2]
The universe today
The universe is constanly expanding
On the largest scales, the distances between galaxies grow with time, and the more distant two galaxies are, the faster they recedes from each other.[6]
The rate of expansion of the universe is described by the Hubble-Lemaître law.[2]
The majority of matter and energy in the universe is invisible to us
According to the standard model, the universe today consists of:[2]
- about 68% dark energy
- about 27% dark matter
- about 5% ordinary (baryonic) matter and energy
The universe is organised into large-scale structures
Matter in our universe is far from spread uniformly: gravity has gathered it into galaxies, groups, and clusters, which in turn form superclusters, walls, and filaments. On the very largest scales these structures arrange themselves into the cosmic web, a pattern of filaments and walls surrounding vast, nearly empty voids, formed as gravitational attraction draws matter into ever larger concentrations.[7]
References
- ↑ Johnson, C. (2017). An Introduction to Geology. In An Introduction to Geology. OpenGeology.
- ↑ ↑ ↑ ↑ Planck Collaboration. (2020). Planck 2018 results (Scholarly article). In Astronomy and Astrophysics (Vols. 641, p. A6). https://doi.org/10.1051/0004-6361/201833910
- ↑ Gunn, A. (2025). This bold theory says the Big Bang wasn’t our beginning. In BBC Science Focus.
- ↑ Varnam, B. (2026). The BVG Unified Cosmology: A Complete Field-Driven Alternative to the Big Bang. Zenodo. https://doi.org/10.5281/zenodo.20591798
- ↑ Aldana, A. D. (2026). The Origin of the Universe Without a Big Bang Singularity: The Bilobular Collision Model as a Cyclic Anisotropic Alternative to ΛCDM. Zenodo. https://doi.org/10.5281/zenodo.20487411
- ↑ Hubble, E. (1929). A Relation between Distance and Radial Velocity among Extra-Galactic Nebulae (Scholarly article). In Proceedings of the National Academy of Sciences of the United States of America (Vols. 15, Issues 3, pp. 168–173). https://doi.org/10.1073/pnas.15.3.168
- ↑ National Aeronautics and Space Administration. (n.d.). Large Scale Structures (Webpage). In NASA Science (Website).
Further reading
- The Universe, NASA Science
- Planck, European Space Agency