Theoretician Jokes

The difference between theory and experiment:
A guy was walking along the street one night, when he came upon a man-a
theoretical physicist-on his hands and knees under a street light, searching
the street. The fellow asked him what he was looking for, and the theoretician
replied, "I'm looking for my car keys." Being a helpful sort, the fellow
started searching, too.
After a time he asked, "Are you sure you lost them here?"
"Of course not" replied the theoretician. "But at least there's light here."