Timelike geodesic in the expanding flat slicing of de Sitter spacetime (source code)

= Timelike geodesic in the expanding flat slicing of de Sitter spacetime
{c}

For a timelike geodesic moving in the $x$ direction with $t(0)=x(0)=0$ and $\dot x(0)=v_0>0$, spatial translation symmetry gives $e^{2Ht}\dot x=v_0$. Proper-time normalization then gives
$$
\dot t=\sqrt{1+v_0^2e^{-2Ht}}.
$$