That doesn't work -- not surprisingly, since H0 is inverse time units, not distance -- unless there has been some change to units since I branched so that it automatically inserts factors of c as needed.

    H0 = 70 * u.km / u.s / u.Mpc
    (1/H0).to(u.Mpc)
    ERROR: UnitsException: 'Mpc s / km' (time) and 'Mpc' (length) are not convertible [astropy.units.core]