I seem to remember doing a similar problem in an order of magnitude astrophysics class I took. We calculated that there were good odds that at least one person

I seem to remember doing a similar problem in an order of magnitude astrophysics class I took. We calculated that there were good odds that at least one person on the planet detected a neutrino from Tycho's supernova when it interacted with the vitreous body of the eyeball. (This is from memory, so don't quote me on it --- I may have remembered the sign wrong!)