A detailed description of Olbers' paradox allows you to conclude that if the universe
(a) were big enough so that every line of sight ended in a star,
(b) were infinitely old,
(c) were static and not expanding and
(d) if several other simple assumptions were satisfied,
then the entire night sky would be roughly as bright as the surface of our sun!
Therefore, the simple observation that the night sky is dark allows us to say something very profound about our universe: it cannot be infinitely big, infinitely old and static all at the same time! Many people used to believe that the universe was this way, and it turns out that all they would have had to do to convince themselves otherwise was think carefully about a simple question that every child asks: "Why is the sky dark at night?" This is definitely an argument for the old adage that there's no such thing as a stupid question! As it turns out, we still don't know whether the universe is infinitely big (but most of us think not), but we do have a good grasp on the age of the universe and we do know that it is expanding, and of the two, it is the finite age of the universe which seems to provide the main explanation for Olbers' paradox.