A Hubble constant of 50 km s−1 Mpc−1 corresponds
to a Hubble time of about 20 billion years.
What would be the Hubble time for a Hubble constant
of 100 km s−1 Mpc−1? 75 km s−1 Mpc−1?
If the rate of expansion of the universe is slowing
down with time, will the Hubble time over- or underestimate
the age of the universe?