http://en.wikipedia.org/wiki/Topology
“There’s an old joke among mathematicians that topologists (who study deformations of space) can’t tell a coffee cup from a donut. In physics, topology is used in several areas such as quantum field theory and cosmology.”
From link:
A topological quantum field theory (or topological field theory or TQFT) is a quantum field theory which computes topological invariants.
Although TQFTs were invented by physicists, they are also of mathematical interest, being related to, among other things, knot theory and the theory of four-manifolds in algebraic topology, and to the theory of moduli spaces in algebraic geometry. Donaldson, Jones, Witten, and Kontsevich have all won Fields Medals for work related to topological field theory.
In cosmology, topology can be used to describe the overall shape of the universe.[18] This area is known as spacetime topology.
I knew that. I just thought it was too old a joke to be worth commenting on...