Take the 2-minute tour ×  In the process of pair annihilation an
electron and a positron annihilate each other to produce a pair
of photons, conserving momentum and energy. As the oppositely
charged particles approach each other, the field around them
decreases. We may consider them as a dipole with a decreasing
dipole moment and radiating energy. As the field decreases the
value of E changes. Consequently, B should change: $$ \nabla
\times \mathbf{B}=\epsilon_0\mu_0\frac{\partial
\mathbf{E}}{\partial t}$$ and $$ \nabla \times \mathbf{E} =
-\frac{\partial \mathbf{B}}{\partial t}.$$ So we have a Poynting
vector that drives energy in the outward direction (If it was in
the inward direction the field would grow stronger with the
approach of the particles which is not the case). By the time
the electron and the positron are close enough to clash the
classical self energy (electromagnetic self energy) has moved
out to an infinite distance.  Quantum Mechanical Picture:Virtual
photons emitted by the electron (or the