Introduction to Astrophysics II, 29:120
Spring, 2007
Eleventh Homework Set...April 26, 2007. Due May 4, 2007

(1) Consider a universe in which $\rho=0$ (this is an approximation for one in which the mean density is very low compared to closure density.)
(a) What must the sign of $k$ be? Give your reason.
(b) What is the functional form of $R(t)$, i.e. how does $R(t)$ depend on $t$?

(2) Assume a cosmology in which $k=0$ (this is believed to be the true state of affairs). The present distance to the Virgo cluster is 22 Mpc. To answer the questions below, you must identify a key missing parameter (number) and find a value for it.
(a) How far away was the Virgo cluster 10 Gyr ago?
(b) How far away will it be 10 Gyr from now?
(c) What was Hubble's constant 10 Gyr ago?
(d) What was the missing datum that you need to answer the three questions above?