 Second, the expansion rate varies as different types of matter come to dominate the dynamics. As shown by (\(\ref{eq:cons}\)), the energy density for different types of matter and radiation dilutes at different rates: for example, pressureless dust (\(p=0\)) dilutes as \(\propto R^{-3}\), radiation (\(p=\rho/3\)) as \(\propto R^{-4}\), and the cosmological constant (\(p=-\rho\)) remains (as the name suggests) constant. The SM describes the early universe as having a much higher energy density in radiation than matter. This radiation-dominated phase eventually transitions to a matter-dominated phase as radiation dilutes more rapidly, followed eventually, if \(\Lambda &gt; 0\), by a transition to a \(\Lambda\)-dominated phase; if \(k \neq 0\) there may also be a curvature dominated phase.