Why do photons behave differently than particles in scattering processes?

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Discussion Overview

The discussion centers on the differences in scattering processes between particles and photons, particularly why photons do not scatter in photon-photon collisions under certain energy conditions. It explores concepts from quantum electrodynamics (QED) and the mechanisms behind particle interactions.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions why particles scatter in particle-particle collisions while photons do not in photon-photon collisions, assuming insufficient energy to create particle-antiparticle pairs.
  • Another participant inquires about the forces responsible for scattering in these processes.
  • A different participant notes that photons have no mass, which may contribute to their scattering behavior.
  • It is proposed that photons can scatter indirectly through intermediate virtual electron-positron pairs, although this process has a very small probability due to the complexity of the involved Feynman diagrams.
  • One participant expresses limited knowledge of QED and seeks clarification on what dictates the exchange of bosons or electrons in scattering processes, requesting additional resources for understanding.

Areas of Agreement / Disagreement

Participants express differing views on the mechanisms of scattering, with some asserting that photons do not scatter directly while others suggest indirect scattering is possible. The discussion remains unresolved regarding the specifics of these interactions.

Contextual Notes

There are limitations in the discussion regarding the assumptions about energy levels required for photon interactions and the definitions of scattering processes. The complexity of the Feynman diagrams and their implications for scattering probabilities are also noted but not fully resolved.

CassiopeiaA
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Why do particles scatter in particle-particle collision while photons don't in photon-photon collisions, assuming that photons don't have enough energy to create particle anti-particle pairs?
 
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What force would do the scattering ?
 
ie.. they have no mass
 
CassiopeiaA said:
Why do particles scatter in particle-particle collision while photons don't in photon-photon collisions,

Photons can in fact scatter off each other "indirectly", via intermediate virtual electron-positron pairs. See e.g. page 4 (problem 3) of this document:

http://faculty.ucmerced.edu/dkiley/Physics161Fall2011HW2solns.pdf

The cross-section (i.e. the probability) is very small because the Feynman diagram has four vertices as opposed to only two in electron-electron scattering.
 
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I have very little knowledge of QED, but can you tell me what dictates exchange of bosons (particle-particle interaction) or electrons (in case of photon-photon interaction) in scattering processes? It will be helpful if you provide some links to further illustrate the point.
 

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