Here's something even crazier: Are photons in vacuum, with photon-photon scattering, IN PRINCIPLE a model with strong enough computational power? I don't have a

Here's something even crazier: Are photons in vacuum, with photon-photon scattering, IN PRINCIPLE a model with strong enough computational power? I don't have any specific application in mind, but just for the kicks, how cool would it be to create a galaxy-sized computer that has no parts other than photons? I don't mean "no _moving_ parts other than photons", I literally mean a photonic computer where even the reflectors are made of other photons.