God said, 'Let there be light'; "Against the Day" collects ways our ancestors attempted to track light back to its source and replaced religion with alternative lights. There is the light of relativity, the odd light of electromagnetic storms, the light of the mysterious Tunguska event of 1908, when a meteorite struck Siberia or God announced a coming apocalypse. [...] the dynamite flash, the diffracted light of Iceland spar, the reflected light of magicians' mirrors, the 'light writing' of photography and movies, the cities' new electric lighting that makes the heavens invisible at night.