[ajross]

Yeah. The article is a little confused with terminology. Photon/photon interaction is "illegal" in QED in the same way and for the same reasons that wave solutions to classical electromagnetism don't interact (well, except to propagate). What's happening here are interactions between the two photons and the vacuum.

So the new science here isn't unexpected confirmation of new physics, it's our ability to probe our existing understanding of the vacuum with new interactions.

[rrmm]

Right, the new physics the wikipedia article is alluding to is that in previous experiments indirectly measuring two photon interaction cross-sections, the cross-section was higher than what the standard model would predict (but those experiments didn't have tight enough error bounds to say anything definitive).