In The Hitchhiker's Guide to the Galaxy, by Douglas Adams, the number 42 was revealed to be the "Answer to the Ultimate Question of Life, the Universe, and Everything". But he didn't say what the question was! I will reveal that here. In fact it is a simple geometry question, which then turns out to be related to the mathematics underlying string theory. For more see: http://math.ucr.edu/home/baez/42/ and for the slides of this talk see: https://math.ucr.edu/home/baez/42/