Did I mention I was doing this course with the OU this year? It's quantum theory. Having read the odd book for the layperson about the subject - and found that the concepts have a habit of completely dribbling out of my ears within a couple of months of completing said books - I decided to give it a proper go from a more mathematical/scientific viewpoint in order to try to nail the concepts into my head more securely. The OU does online tutorials now, and one of those has just finished, covering some pre-requisite maths of the sort I've done before but not for ages.
Anyway, it turns out quantum theory's quite tricky. I mean, it's not rocket science. It's much harder. It being less brain-friendly than that kind of classical mechanics and all.