Baryon charge (baryon number, B), one of the internal characteristics of elementary particles, different from zero for baryons and equal to zero for all other particles. The baryon charge of baryons is taken to be unity, and that of antibaryons — minus unity. The baryon charge of a system of particles is equal to the difference between the numbers of baryons and antibaryons in the system. In particular, the baryon charge of atomic nuclei is equal to their mass number. Until the 1970s the baryon charge was held to be a strictly conserved quantity, whose conservation law holds for every type of fundamental interaction. With the creation of various models of a unified field theory (the so-called “grand unification”, which takes in the weak, electromagnetic and strong interactions), however, this has been called into question. In particular, the proton is predicted to be able to decay, for example through the channel p→e+ +π0, with a lifetime τ of between 1030 and 1032 years in different models (according to experimental data, τp>1030 years). Some versions of the theory predict that a neutron can turn into an antineutron (the so-called neutron oscillations).