Have you met my Anti?

What happens when matter meets antimatter? Theoretical scientists have addressed this issue by deriving the first analytical expression for the stability of matter-antimatter molecules. Dima Gridnev and Carsten Greiner of the Institute of Theoretical Physics, Frankfurt, Germany, looked at systems containing two positive particles and two negative particles that interact with each other through Coulombic forces. According to Gridnev, the hydrogen-antihydrogen molecule turns out to be unstable because the proton and antiproton approach each other too closely and are "seen" as a neutral combination by the other particles.