  In 1995, a team of physicists from the Budker Institute of Nuclear Physics in
Novosibirsk was able to observe the splitting of a photon in the Coulomb field
of an atomic nucleus for the first time, and reported the preliminary results
of this experiment at two conferences. This was an extremely difficult
experiment as the probability of the process is very small. It took another
seven years to publish the final results. This story has been further developed
recently. The ATLAS detector at the Large Hadron Collider observed in
ultra-peripheral heavy ion collisions a process related to the photon splitting
- light by light scattering. In addition, a team of Italian, Polish and British
astrophysicists obtained the first observational evidence of the existence of
vacuum birefringence in the magnetic field of an isolated neutron star -
another physical phenomenon also related to the photon splitting. These new
developments triggered this essay, written several years ago.
