ABSTRACT
In the standard model, known as ΛCDM, this tensor’s components are largely empirical, without much input from theory, of which we are reminded by the rather emphatic inscription of its contents across its name, ‘Λ plus cold dark matter.’ The standard model thus derives from an unavoidable compromise: rather than aiming to find the ultimate description of everything, ΛCDM seeks to identify a metric that approximates the observable Universe as well as possible. All three Sakharov conditions can be satisfied with the standard model of particle physics. The problem may reside with the standard model of particle physics, rather than the standard model of cosmology. The ΛCDM model described thus far is foundational and quite successful in accounting for many cosmological observations. A pivotal turning point in the establishment of the ‘standard model’ was the serious attempt at addressing a persistent inconsistency—known as the ‘horizon’ problem—towards the end of the 1970’s.
