Are we alone in the universe? Or is the cosmos teeming with life? And what difference would it make if we found the answer? Those are just some of the questions we address in this week's show.

Does science progress in a cumulative way?  In other words, do later scientific theories build upon earlier ones by keeping older established truths about the world, and adding us more truths?  The standard answer, familiar from Whiggish history and brief historical asides in scientific textbooks, is that it does.