The Duality of Time Theory

In 1998, from the observations of distant Type Ia supernovae, in addition to the data from the cosmic microwave background and large galaxy redshift surveys, the expansion rate of the Universe was found to be accelerating. According to General Relativity, the accelerating expansion can be accounted for by a positive value of the cosmological constant, equivalent to the presence of a positive vacuum energy, dubbed as dark energy, which apparently permeates all of space. The observations suggest that dark energy is 73% of the total energy density. This led to the current standard model of cosmology, the Lambda-CDM model as described in 6.6, which has generally been accepted from 2003 through the present, since it is the simplest model in good agreement with a variety of recent observations.

The expansion of the Universe is thought to have been accelerating since the Universe entered its dark-energy-dominated era roughly 5 billion years ago. The most important property of dark energy is that it has negative pressure which is distributed relatively homogeneously in space. The simplest explanation for dark energy is that it is a cosmological constant or vacuum energy.