• Question: happens when particles of light smash together

    Asked by grew354bat to Philippe, Lucy, Joanna, Harrison, Edoardo on 17 Jun 2019.
    • Photo: Philippe Gambron

      Philippe Gambron answered on 17 Jun 2019:


      Particles of light, photons, do not interact with each other. However they can produce things that will interact with each other. For example, photons can fluctuate and form particle-antiparticle pairs that will interact by exchanging photons.

    • Photo: Edoardo Vescovi

      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).

    • Photo: Harrison Prosper

      Harrison Prosper answered on 17 Jun 2019:


      Philippe and Edoardo have given very nice answers. Let me just say that it is a very good thing that light under ordinary circumstances does not interact with light, otherwise our view of the world would be extremely fuzzy! But shine two sufficiently high powered lasers at each other and you can create particles from the colliding light!

    • Photo: Lucy Budge

      Lucy Budge answered on 18 Jun 2019:


      As the others have said – under normal circumstances nothing at all! If they did it would make being able to see anything essentially impossible, as light would no longer travel in a straight line from the object to our eyes.

      However, take two really powerful lasers and some strange stuff can happen, though it’s never the particles of light interacting directly with each other, but particles they produce interacting.

Comments