John McPhee, in trying to fathom the extraordinary age of the earth, speaks of deep time.1 The metaphor of depth describes a temporality so distant from the present that its very presence among us in rocks and fossils seems quite alien. By examining layered geological formations, analysts can interpret a past that is nonetheless present with us. "You begin tuning your mind to a time scale that is the planet's time scale.'2 As we have seen in chapter 2, the narrative that astrophysical cosmology has told about the universe as a whole is similar. By looking into the night sky, astronomers begin at such a temporal distance that the presence of background radiation noise as a "present' phenomenon, however measurable, seems thin. Nonetheless, deep time appears to us, narrowly discernible, as a past yet contemporary light.