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Photon scattering

One experiment one could imagine doing which would provide conclusive proof of a particle nature of objects is to scatter two objects off of each other, as in the collision of two billiard balls. This experiment with light and small atoms has been done, and is now called Compton scattering. The basic setup is as below.
Figure 12.8: Photon scattering
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The results of this experiment would be completely at odds with predictions made if the light was viewed as a wave - for example, one finds experimentally that the frequency of the scattered wave is changed, which does not come out of a wave picture of light. However, when the light is viewed as a photon with energy proportional to the associated light wave, excellent agreement with experiment is found.