Hardy’s Paradox
March 13, 2009

I just read about a crazy quantum mechanical thought experiment from 1992 called Hardy’s Paradox, wherein electrons and positrons can essentially undergo incomplete annihilation. As far as I can tell, it’s not quite a true paradox: it’s a prediction of quantum mechanics that is perfectly mathematically consistent, it just happens to completely defy our physical intuition. I’ll provide my attempt at a summary of the paradox below, and describe a ridiculous experiment that has just been published which offers a direct observation of the effect. If you want a more thorough explanation of Hardy’s Paradox, I refer you to “The Mystery of the Quantum Cakes”, an article (available free here, for some reason) aimed at an audience of science teachers.