In the comment section of a newspaper article reporting on the 2015 Nobel Prize for Physics, which was awarded for work on neutrino oscillation, I found the following joke:
"I'm sorry, we do not serve neutrinos", says the barman.
A neutrino walks into a bar.
What physical phenomenon does this actually allude to? The structure of the joke seems to imply some sort of time-reversal. I realize explaining a joke kind of defeats the purpose of the joke, but I'm just curious what the point is here.
This was a reference to the apparent measurement that neutrinos travel faster than light. FTL travel can be used to travel back in time (though the procedure for doing so is somewhat involved).
Sadly the apparent superluminal speed turned out to be due to experimental errors: a fibre optic cable attached improperly, which caused the apparently faster-than-light measurements, and a clock oscillator ticking too fast. I say sadly because the result would have been tremendously exciting if it had proved to be correct. Still, grandfathers everywhere are probably quite relieved.
