Question: happens when particles of light smash together

Edoardo Vescovi answered on 17 Jun 2019: last edited 17 Jun 2019 6:37 pm

Let me say few facts (1) and come to a short answer (2) and experiment (3).
1) Typical experiments, like those in particle accelerators in CERN, take particles far apart and smash them. Particles interact by sending each other “virtual particles”, which survive for a split second. As a result, the initial particles can turn into other particles or simply bounce off untouched. We measure particles flying away and study the forces in the game.
2) Photons are the particles of light and don’t usually interact. When light is very intense, photons are energetic enough to interact by exchanging virtual particles. It is rare because virtual particles must be created (like “out of a hat”) and immediately destroyed. Two drawings borrowed from Wikipedia help you to see how.
— Photons can simply bounce off like billiard balls. This
https://en.wikipedia.org/wiki/Two-photon_physics#/media/File:Photon-photon_scattering.svg
shows 2 photons (wavy lines on the left) that fly away (wavy lines on the right) after an intermediate time when 4 virtual particles (edges of middle square) existed.
— As said in the answer above, they could also produce other particles. This
https://en.wikipedia.org/wiki/Two-photon_physics#/media/File:Photons_interaction_for_fermion-antifermion_pair.svg
shows 2 photons (wavy lines on the left) that turn into 2 new particles (straight lines on the right) after an intermediate time when 1 virtual particle (vertical line) existed.
3) I’m not involved in experiments, but understand in
https://home.cern/news/news/experiments/atlas-observes-direct-evidence-light-light-scattering
that CERN scientists saw the first type (= simple bouncing off).