= Particle creation and annihilation
https://en.wikipedia.org/wiki/Annihilation
Predicted by the <Dirac equation>.
We've likely known since forever that <photons> are created: just turn on a light and see gazillion of them come out!
Photon creation is easy because photons are massless, so there is not minimum energy to create them.
The creation of other particles is much rarer however, and took longer to be discovered, one notable milestone being the discovery of the <positron>.
In the case of the electron, we need to start with at least enough energy for the mass of the electron positron pair. This requires a photon with wavelength in the <picometer> range, which is not common in the thermal radiation of daily life.