Lecturer in Creative Uncertainty
The Lecturer in Creative Uncertainty was one of many wizards residing at Unseen University. His position in the Faculty's hierarchy is unknown (uncertain?), but it is probably quite low, as he is a lecturer, and is only mentioned in passing in The Last Continent.
Every wizard's room at Unseen University has a wooden sliding device on the frame of the door, which normally contains the words "IN" and "OUT". The Lecturer in Creative Uncertainty, however, held rather smugly that he was in a state of both in-ness and out-ness until such time as someone knocked on his door and collapsed the field, and that it was impossible to be categorical before the event... one must wonder, then, what his labels are for his door.
Erwin Schrödinger, one of the founders of Roundworld's Quantum Mechanics, is famous for a thought experiment/paradox called "Schrödinger's Cat", which Pratchett is parodying here. Essentially, he came up with a complicated method of randomly killing a cat inside a box. However, the point was that the cat would be both dead and alive until you opened the box and observed it... for more information, see here. For what the cat's point of view might be about this, see here.