Question regarding Light by Light Scattering

[Curious13]

I recently read this article from Science Alert regarding Light by Light Scattering (http://www.sciencealert.com/light-continues-to-behave-really-weirdly-in-the-large-hadron-collider). They seemed to be astonished to witness light actually bouncing off each other, as they state that photons pass through each other. I'm rather confused, as I realized that light can behave as a particle or a wave...so excuse me for being puzzled by their excitement, but to act as a 'wave', doesn't the particles have to 'bounce off' each other? I was wondering if anyone can enlighten me on why this seems to be new discovery?

 

[strangerep]

I recently read this article from Science Alert regarding Light by Light Scattering (http://www.sciencealert.com/light-continues-to-behave-really-weirdly-in-the-large-hadron-collider). They seemed to be astonished to witness light actually bouncing off each other, as they state that photons pass through each other. I'm rather confused, as I realized that light can behave as a particle or a wave...so excuse me for being puzzled by their excitement, but to act as a 'wave', doesn't the particles have to 'bounce off' each other? I was wondering if anyone can enlighten me on why this seems to be new discovery?

Strictly speaking, photons are neither particles nor waves, but rather quantum fields. There is a higher order (i.e., very weak) effect in Quantum Electrodynamics wherein photon fields can indeed scatter off each other.

A related effect is Delbruck Scattering, in which a photon is scattered by a static electric (Coulomb) field. This was observed a long time ago, iiuc.

But direct photon-on-photon scattering was too weak for our earlier experimental equipment to detect. So it's cool that the LHC has seen it.

 

[vanhees71]

BTW the real scientific paper is open source (as anything from the LHC collaborations):

https://www.nature.com/nphys/journal/v13/n9/full/nphys4208.html

 

[mfb]

There is nothing to be surprised about. The effect has been predicted decades ago. The LHC is simply the first accelerator where the experiments have a chance to measure it. It was expected to be measured, and it was measured, at a rate consistent with expectations.

It is not news either, ATLAS announced the measurement in November 2016. I made a thread about it back then.