back to article Photon scattering puts a shine on CERN ATLAS boffins' day

Large Hadron Collider boffins in charge of the ATLAS experiment reckon they've seen photons interacting at the quantum level for the first time. This isn't something that happens at everyday energies: if, for example, you shine two beams through each other in a dark room, you'll see two spots on the wall. However, direct …

  1. MaxRock

    "... predicted by quantum chromodynamics."

    Typo? I didn't think photons had much to do with QCD (quarks and gluons).

    1. Destroy All Monsters Silver badge
      Windows

      Very perceptive.

      You can read the whole paper at nature here.

      Indeed, QCD is not involved. We stay in QED and use virtuals particles from the weak force ("heavy light", innit) or fermions to interacdt with:

      One of the key features of Maxwell’s equations is their linearity in both the sources and the fields, from which follows the superposition principle. This forbids effects such as light-by-light (LbyL) scattering, γγ right arrow γγ, which is a purely quantum-mechanical process. It was realized in the early history of quantum electrodynamics (QED) that LbyL scattering is related to the polarization of the vacuum1. In the standard model of particle physics, the virtual particles that mediate the LbyL coupling are electrically charged fermions or W± bosons.

      So.... electromagnetism starts to get into the nonlinear regime, a bit like gravity.

      (This also explains the lightshow under space-orbital lasers about to fire as seen in "Akira", I'm sure)

      1. werdsmith Silver badge

        If I could have chosen my career I would have wanted to work at the bleeding edge of particle physics more than any rock star / move star/ sports star job. Even more than being a fast jet pilot or an astronaut.

        Huge admiration for the enormous reach that these people are achieving at CERN and Culham.

        1. Hans Neeson-Bumpsadese Silver badge

          RE: career

          If I could have chosen my career I would have wanted to work at the bleeding edge of particle physics

          Me too...unfortunately I reckon that no matter how long I studied and how much I trained, I'd still never be able to understand more than one word in five.

          1. Dagg

            Re: RE: career

            If I could have chosen my career I would have wanted to work at the bleeding edge of particle physics

            Me too, problem I had a prof whose standard phase was "Intuitively obvious" like f*ck it was. I now suspect that he was not that good and "Intuitively obvious" was an excuse for "I have no clue so by asking you will appear to be an idiot, so don't ask"

          2. IT Poser

            Re: RE: career

            Me too...unfortunately I reckon that no matter how long I studied and how much I trained, I'd still never be able to understand more than one word in five.

            Give your self some credit. I'm certain you'd be able to understand the various definitions of the words. What is uncertain is which definition to use.

        2. anothercynic Silver badge

          Don't forget Harwell...

          ... The big round building also does pretty funky things, as does the other (not round) building on the other end of the campus.

        3. Inventor of the Marmite Laser Silver badge

          Ditto

          Unfortunately being thick enough to give pairs of short planks a run for their money doesn't help.

  2. Justin Case

    Stupid me

    I love reading about this stuff, but it makes me realise that I can't understand it and never will.

    Good work - carry on.

    1. Ken Hagan Gold badge

      Re: Stupid me

      Feynmann's benchmark was that if you couldn't turn it into an undergraduate lecture then you didn't understand it. (I think he was specifically referring to "spin", having rashly promised to deliver such a lecture as proof that it could be done and belatedly conceeding not only that he couldn't give the lecture but also that this meant he didn't understand it.

      So I guess you are in good company.

      1. John Mangan

        Re: Stupid me

        I always loved Feynman's distinction between measuring, characterising, predicting (mathematically) something and 'understanding' it.

        1. Destroy All Monsters Silver badge
          Linux

          Re: Stupid me

          Well, pace Feynman, "understanding" just means creating a syntax processor inside your head (aka. "program") that can simulate what's going in the problem domain you want to be able to handle (whether the problem domain is correctly described or underspecified by the information you have about it is another matter).

          Some people are just unable to do so for complex-enough problem domains (this can be seen in undergrads quite clearly, which is why 50% drop out each year and some barrel through leisurly at 18). So sorry, mission impossible in general, Feynman.

          Interestingly, you can go recurisve and blackbox the blackbox, maybe leaving out detail until the person in front of you "gets it".

          (Whole populations seem to be predisposed to being better/worse at blackboxing some problem domains, this is probably why the "Journal of Computational Intelligence" is now dominated by Chinese, oops, getting into HBD here, better shut up. No Golden Retriever icon? Penguin, then!)

          1. RavingDaveD

            Re: Stupid me

            Sorry, didn't understand a word of that.

            QED

            Dave

        2. Anonymous Coward
          Anonymous Coward

          Re: Stupid me

          "I always loved Feynman's distinction between measuring, characterising, predicting (mathematically) something and 'understanding' it."

          Actually, this is sort intrinsic to the process of top-down analysis that we generally use to gain understanding of things and which naturally results in a why/what hierarchy where why something happens on one level in the hierarchy is explained in terms of what happens on the level below.

          Thus, the end result of any top-down analysis, where there is no hierarchical layer below to explain why, must be something that is essentially abstract in that it can only be explained or described in terms of itself. So, as you and Feynman point out, there's a difference between characterising and measuring something and understanding it.

  3. Stoneshop Silver badge
    Coat

    Heavy Metal?

    "Photon Scattering" sounds more like an Indie band

    1. molletts

      Re: Heavy Metal?

      > "Photon Scattering" sounds more like an Indie band

      They would probably play an interesting mix of heavy metal and light music.

      1. HieronymusBloggs

        Re: Heavy Metal?

        "They would probably play an interesting mix of heavy metal and light music."

        Ion Maiden?

  4. steelpillow Silver badge

    I think you will find that "heavy photon" theory is a good deal more exotic and speculative than the photon-on-photon scattering predicted by good ol' QED.

    What we have here is just a late tick-box on the Standard Model, not a first glimpse into a "hidden sector". Still, nice to know Richard Feynman was right - again.

    1. Destroy All Monsters Silver badge

      No, not that "heavy photon". Just the W.

  5. Black Betty

    Could this be a case of non-mutual anihilation?

    ie. each photon spontaneously forms a particle-antiparticle pairs (p1-a1, p2-a2) which then cross annihilate p1-a2 and p2-a1.

  6. allthecoolshortnamesweretaken

    "CERN explains that the phenomenon happened during experiments in the organisation's ATLAS experiment, in which they fired high-energy lead ions at each other."

    They crossed the streams?!?

  7. Anonymous Coward
    Anonymous Coward

    QED, the quantum theory of electromagnetism

    So it's a QED for QED? What's that, QED squared?

  8. jayeola

    Ruddy hell. I went to the CERN Open Day a few years ago, promised that I would brush upon my physics and I still don't understand much of this apart from...

    * the universe is big, very big.

    * made up of stuff that is small, very small

    * and it's moving fast (i think)

  9. Roj Blake Silver badge
    Coat

    Photon at the Airport

    A photon arrives at the airport and goes up to the check-in desk to collect its boarding pass.

    After handing it over, the lady behind the counter asks him "do you have any bags to put in the hold?"

    "No thanks" replies the photon, "I'm travelling light."

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