Lambda-CDM Model

The Lambda-CDM model is the standard model of Big Bang cosmology, describing a universe composed mostly of dark energy, represented by the cosmological constant denoted by the Greek letter lambda, and cold dark matter, with ordinary matter making up only a small fraction of the total. It successfully accounts for the observed cosmic microwave background, the large-scale structure of galaxies, and the accelerating expansion of the universe using a relatively small number of free parameters. Despite its success, the physical nature of both dark energy and cold dark matter remains unknown, and the model is the baseline against which proposed alternatives and anomalies such as the Hubble tension are measured.