Comment by adrian_b

The sum of the conserved quantities, e.g. chromatic charge, electric charge and spin, is null for the set of 8 particles formed by the 3 u quarks, the 3 d quarks and the electron and the neutrino, i.e. for the components of a proton plus a neutron plus an electron plus a neutrino.

This is the only case of a null sum for these quantities, where no antiparticles are involved. The sum is also null for 2 particles, where one is the antiparticle of the other, allowing their generation or annihilation, and it is also null for the 4 particles that take part in any weak interaction, like the decay of a neutron into a proton, which involves a u quark, a d antiquark, an electron and an antineutrino, and this is what allows the transmutations between elementary particles that cannot happen just through generation and annihilation of particle-antiparticle pairs.

Thus generation and annihilation of groups of such 8 particles are not forbidden by the known laws. The Big Bang model is based on equal quantities of these 8 particles at the beginning, which is consistent with their simultaneous generation at the origin.

On the other hand, the annihilation of such a group of 8 particles, which would lead to the disappearance of some matter, appears as an extraordinarily improbable event.

For annihilation, all 8 particles would have to come simultaneously at a distance from each other much smaller than the diameter of an atomic nucleus, inside which quarks move at very high speeds, not much less than the speed of light, so they are never close to each other.

The probability of a proton colliding simultaneously with a neutron, with an electron and with a neutrino, while at the same time the 6 quarks composing the nucleons would also be gathering at the same internal spot seems so low that such an event is extremely unlikely to ever have happened in the entire Universe, since its beginning.