Can't attribute, found it floating around in several places. It had a choirmate (theoretical physicist) in stitches, will tell it at her next conference.
Heisenberg, Schrodinger and Ohm are in a car
They get pulled over. Heisenberg is driving and the cop asks him "Do you know how fast you were going?"
"No, but I know exactly where I am" Heisenberg replies.
The cop says "You were doing 55 in a 35." Heisenberg throws up his hands and shouts "Great! Now I'm lost!"