[jdbburg]

The Breit-Wheeler process (convert two photons into electron+positron) has been one of the most elusive fundamental processes in electromagnetism. This prediction came when quantum mechanics was first being developed in the early 1930s but was not observed for more than 80 years after its prediction, since high energy photons are hard to come by. In contrast, many of the other fundamental processes were discovered fairly quickly after their predictions (the photo electric effect was discovered even before its quantum interpretation was given by Einstein, for which he won the nobel prize)