"... predicted by quantum chromodynamics."
Typo? I didn't think photons had much to do with QCD (quarks and gluons).
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 …
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)
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.
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"
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.
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.
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!)
"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.
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.
Biting the hand that feeds IT © 1998–2020