I know positronium is an unstable pairing of an electron and positron in a Hydrogen-like system with a very short lifetime on the order of around E-10 seconds (depending on its initial state). I would like to better-understand why positronium is so unstable, despite having bound energy states like those in stable atoms. I have heard that the short lifetime is due to the partial wave function overlap between the two particles (which form a particle-antiparticle pair). This, very brief, explanation makes some sense to me. If the wave function’s overlap, there is some probability of the two particles being in the same space at the same time. If this should ever occur (which it is bound to after a sufficient amount of time has passed) then the electron-positron pair will annihilate each other and destroy the positronium atom, in the process releasing a couple of photons in order to conserve energy and momentum. In order to get a better understanding (beyond what I just inferred) I asked my professor who is quite knowledgeable on the subject. The only kind of answer I could get was that ‘positronium is unstable because the electron and positron are annihilating each other’. This explanation, which feels somewhat unsatisfactorily basic, just leads me to believe that the two particles know the other is there and ‘wants’ to annihilate, so it does. Where can I find a more detailed description of the process?