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?"