R,C,H,O number systems, spinors, triality and spacetime

QG group meeting.
Speaker: Yasha Neiman.
Title: "R,C,H,O number systems, spinors, triality and spacetime".

In lieu of the QUAST seminar today, I'd like to tell some fun stories I've been learning about the reals/complexes/quaternions/octonions, and how they're related to things we like, e.g. spinors.