Every Friday afternoon, a mathematician goes down to the bar, sits in the second-to-last seat, turns to the last seat, which is empty, and asks a girl who isn't there if he can buy her a drink. The bartender, who is used to weird university types, always shrugs but keeps quiet. But when Valentine's Day arrives, and the mathematician makes a particularly heart-wrenching plea into empty space, curiosity gets the better of the bartender, and he says, "I apologize for my stupid questions, but surely you know there is NEVER a woman sitting in that last stool. Why do you persist in asking out empty space?" The mathematician replies, "Well, according to quantum physics, empty space is never truly empty. Virtual particles come into existence and vanish all the time. You never know when the proper wave function will collapse and a girl might suddenly appear there." The bartender raises his eyebrows. "Really? Interesting. But couldn't you just ask one of the girls who comes here every Friday if you could buy HER a drink? Never know --she might say yes." The mathematician laughs. "Yeah, right -- how likely is THAT to happen?"