Question regarding Light by Light Scattering

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    Light Scattering
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Discussion Overview

The discussion revolves around the phenomenon of Light by Light Scattering, particularly in the context of recent observations at the Large Hadron Collider (LHC). Participants explore the implications of photons interacting and the historical context of this effect within quantum electrodynamics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses confusion regarding the excitement over Light by Light Scattering, questioning why it is considered a new discovery if photons are known to behave as both particles and waves.
  • Another participant clarifies that photons are better described as quantum fields and mentions that photon fields can scatter off each other, referencing a related effect known as Delbruck Scattering.
  • A participant notes that direct photon-on-photon scattering was previously too weak to detect with earlier experimental equipment, highlighting the significance of the LHC's findings.
  • Another participant argues that the effect has been predicted for decades and that the LHC's measurements align with expectations, suggesting that it is not surprising or new.
  • One participant points out that the ATLAS collaboration had announced measurements related to this effect as early as November 2016.

Areas of Agreement / Disagreement

Participants exhibit disagreement regarding the novelty and significance of the findings related to Light by Light Scattering. Some view it as a groundbreaking discovery, while others assert that it was anticipated and not surprising.

Contextual Notes

There are unresolved aspects regarding the historical predictions of photon interactions and the limitations of previous experimental capabilities that may have contributed to differing perspectives on the significance of the recent observations.

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?
 
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Curious13 said:
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.
 
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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.
 
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