How and why to embed surfaces in 4-dimensional spaces

This talk is part of the Nonlinear Algebra Seminar.

Geometric topologists like to study spaces of arbitrary dimensions. Fortunately, we at least limit ourselves to studying manifolds, which locally mimic Euclidean space. Dimension four forms a "phase transition" between low- and high-dimensional manifolds, exhibiting unique behaviour and necessitating bespoke tools. I will describe the source of this curious phenomenon, giving a few guiding examples and constructions. The key source of the problem or appeal, depending on your perspective, of 4-dimensional manifolds turns out to be the difficulty in embedding surfaces therein.