Originally Posted by
wogoga
The existence of coherent sun light consisting of more than one photon (in the same way as induced emission in general) is strong evidence that also photons are "social" particles, interacting with each other.
Because of cohesion forces between molecules, water molecules are not homogeneously distributed in the atmosphere, but can often be found in groups (droplets). Reasoning from analogy could suggest the hypothesis of small cohesive forces between photons.
You don't need to reason from analogy. If there is a force between photons, we would be able to measure it. Many, many experiments have searched for this "force" at optical wavelengths, and all have shown that photon-photon interactions are incredibly small. The force was finally observed in a special case (inelastic gamma ray interactions) and it agreed with all theoretical predictions.
Thanks for the hypothesis, Wogoga! Unfortunately it has been falsified by these experiments.