= Einstein-de Sitter round-trip message time
{c}
{title2=$t_n=t_0[1+n(1-(1+z)^{-1/2})]^3$}
For two <comoving observers> in an <Einstein-de Sitter universe>, light observed at redshift $z$ today fixes their separation through the past <null geodesic>. A newly sent signal needs the same <comoving distance> for every one-way leg. Since $a=(t/t_0)^{2/3}$, each leg adds a fixed <conformal time> interval, producing the displayed reception time after $n$ legs when replies are immediate. At $z=1$ the first round-trip wait is $[(3-\sqrt2)^3-1]t_0$. There is no finite count limit because future <conformal time> diverges, though infinitely many legs require infinite cosmic time.
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