 Contemporary cosmology at least has a clear target for a theory of origins: the SM describes the universe as having expanded and evolved over 13.7 billion years from an initial state where many physical quantities diverged. In the FLRW models, the cosmic time \(t\) can be measured by the total proper time elapsed along the worldline of a fundamental observer, from the “origin” of the universe until the present epoch. Extrapolating backwards from the present, various quantities diverge as the cosmic time \(t \rightarrow 0\)—for example, \(R(t) \rightarrow 0\) and the matter density goes to  infinity.[30]  The worldlines of observers cannot be extended arbitrarily far into the past. Although there is no “first moment” of time, because the very concept of time breaks down as \(t\rightarrow 0\), the age of the universe is the maximum length of these worldlines.