Speaker: Elijah Gunther

Abstract: Brown representability tells us there’s a bijection between generalized cohomology theories and spectra, and that morphisms of cohomology theories come from morphisms of the corresponding spectra. So is the category of cohomology theories equivalent to the stable homotopy category?

No! In the spirit of Halloween there are 👻 phantom 👻 maps 👻 that are both dead ☠️ and alive ⚡️— nonzero maps of spectra inducing the zero map on homology. In this spooky talk I’ll discuss phantom maps and related topics including their non-stable analogues – non-nullhomotopic maps of CW complexes which kill each finite skeleton 💀.

Costumes encouraged.