Editing Lambda-CDM model (section)

== Historical development ==
The discovery of the [[cosmic microwave background]] (CMB) in 1964 confirmed a key prediction of the [[Big Bang]] cosmology. From that point on, it was generally accepted that the universe started in a hot, dense state and has been expanding over time. The rate of expansion depends on the types of matter and energy present in the universe, and in particular, whether the total density is above or below the so-called critical density.{{citation needed|date=February 2024}}

During the 1970s, most attention focused on pure-baryonic models, but there were serious challenges explaining the formation of galaxies, given the small anisotropies in the CMB (upper limits at that time). In the early 1980s, it was realized that this could be resolved if cold dark matter dominated over the baryons, and the theory of [[cosmic inflation]] motivated models with critical density.{{citation needed|date=February 2024}}

During the 1980s, most research focused on cold dark matter with critical density in matter, around 95% CDM and 5% baryons: these showed success at forming galaxies and clusters of galaxies, but problems remained; notably, the model required a Hubble constant lower than preferred by observations, and observations around 1988–1990 showed more large-scale galaxy clustering than predicted.{{citation needed|date=February 2024}}

These difficulties sharpened with the discovery of CMB anisotropy by the [[Cosmic Background Explorer]] in 1992, and several modified CDM models, including ΛCDM and mixed cold and hot dark matter, came under active consideration through the mid-1990s. The ΛCDM model then became the leading model following the observations of [[Accelerating universe|accelerating expansion]] in 1998, and was quickly supported by other observations: in 2000, the [[BOOMERanG experiment|BOOMERanG]] microwave background experiment measured the total (matter–energy) density to be close to 100% of critical, whereas in 2001 the [[2dF Galaxy Redshift Survey|2dFGRS]] galaxy redshift survey measured the matter density to be near 25%; the large difference between these values supports a positive Λ or [[dark energy]]. Much more precise spacecraft measurements of the microwave background from [[WMAP]] in 2003–2010 and ''[[Planck (spacecraft)|Planck]]'' in 2013–2015 have continued to support the model and pin down the parameter values, most of which are constrained below 1&nbsp;percent uncertainty.{{citation needed|date=February 2024}}