...would the world be a very different place? Quantum theory originally had to deal with huge problems in classical physics, above all the stability of atoms. The particle theory of light evolved in the context of experiments like the photo-electric effect and the Compton effect. In pre-Schroedinger days, these phenomena did indeed seem like compelling evidence for the particle theory. Later developments showed, however, that they could also be explained with classical light. Write the Hamiltonian and put in a sinusoidally varying electric field, and pretty much everything works as it ought to: the photo-electric effect, the Compton effect, etc. Nowadays the strongest evidence for photons comes from recent experiments on anticorrelation statistics of single-photon detection. My question is then: to what end? Suppose the anti-correlation experiments had been done and the opposite result were obtained...consistent with classical e-m. Would that result have been such a disaster? Would it have implied any irreconcilable contradictions with the universe as we know it?