quantum

We will follow the toy model provided in Ref.22. The infinitesimal line element ds, whose coefficients determine the metric of the spacetime, in a Friedman–Lemaitre–Robertson–Walker universe is given by Refs.23,24,25,26,27,28,29: $$\begin{aligned} ds^2=dt^2-a^2(t)dx^2, \end{aligned}$$ (1) where a(t) is the scale factor, which only depends on time. We can make a change of variables to conformal time, … Read more