= Open matter-dominated Friedmann solution
{title2=$a\propto\cosh\eta-1,\quad t\propto\sinh\eta-\eta$}
A negatively curved universe with <pressureless matter> and no dark energy expands forever. With $a_0=1$ and $0<\Omega_{m,0}<1$, its <scale factor> is $a=\Omega_{m,0}(\cosh\eta-1)/[2(1-\Omega_{m,0})]$ and its <cosmic time> is $t=\Omega_{m,0}(\sinh\eta-\eta)/[2H_0(1-\Omega_{m,0})^{3/2}]$. The parameter is <conformal time> scaled by $\sqrt{-K}$ and measured from the <Big Bang>.
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