Rene Descartes was sitting at a bar. The bartender came over and asked if he would like another drink. He replied, "I think not." And he vanished.
Heisenburg was also sitting at the bar. After Descartes vanished in a puff of smoke, the bartender walked over to him and asked, "Did you see that?"
Heisenburg replied, "I can't be certain."
The bartender then noticed Einstein was there. So he asked him if he could believe what had just happened.
Einstein replied with a shrug, "Well, to me it's all relative."
And so it goes...
Richard