There’s a long-running joke that the process of getting a PhD requires that you know more and more about less and less, until eventually you know everything about nothing.
When I was in CS grad school, some of my
fellow underpaid teaching slaves colleagues and I spent some time thinking about all the different types of nothing there were in the world. We wound up with a long list on the whiteboard, among them:
Zero (floating point/real)
Zero matrix (we decided somewhat arbitrarily that matrices and vectors were different for the purpose of this discussion)
Null pointer (points to nothing)
Void pointer (may point to something, but you can’t tell without further information)
Fixed-point combinators (considered different from identity functions for similar reasons to vectors and matrices)
Nil (in the Lisp sense)
Blank storage media (have capacity but no content)
Vacuum (has extent but no content, esoteric physics theories about vacuum energy aside)
Empty database tables (have structure but no content… arguably similar to null vectors/matrices)
Code segment that has no effect (similar to identity functions, but not quite the same)
I’m sure there are others. Feel free to add suggestions in the comments.
Update: Chip suggests the addition of Seinfeld plots.