Conversion of Muonium into Antimuonium

A detailed analysis is made of the possible conversion of muonium into antimuonium in various environments. An assumed $\overline{\mu }e\overline{\mu }e$ weak interaction of the usual form and strength gives a probability of 2.5×${10}^{-5\mathrm{}}$ in vacuum, even in the presence of reasonable external electric fields. In a solid the probability is less by at least 10, and probably 20, orders of magnitude. In an inert gas the probability is roughly to be divided by the numbers of collisions during a muon lifetime, and hence is quite small unless the pressure at room temperature is less than about ${10}^{-4\mathrm{}}$ atm. Lowering the temperature does not help. A possible experiment is suggested.