This post falls under the “random curious stuff” category in MindBlog’s description line. Adam Frank gives an interesting account of work he has published with Woodruff Sullivan arguing that we now have enough information to conclude that alien civilizations have almost certainly existed at some point in cosmic history.

Among scientists, the probability of the existence of an alien society with which we might make contact is discussed in terms of something called the Drake equation… Drake identified seven factors on which that number would depend, and incorporated them into an equation.