Homework 20, Day 22, Due Nov 9
    Solve HW17 for the case of non-equilibrium time dependent ionization.

    Plot H+/H and H0/H as a function of redshift, for 100 < z < 1e5. Include the equilibrium solution from HW17 or HW18 on the same plot, but with different line styles.

    Find the recombination and ionization timescales. Make a plot showing these timescales together with the age of the universe.