In 1964, John Bell showed that quantum mechanics is incompatible with locality and causality. Most physicists currently accept quantum non-locality, without pausing to question causality, i.e., the microscopic arrow of time. Indeed, causality is so fundamental to scientific thinking that it was not explicitly included when the assumptions corresponding to "local realism" were enumerated in the original work of Einstein, Podolsky and Rosen. However, as causality contradicts time-reversal symmetry, it is questionable in the context of a microscopic theory. In this talk, a version of Bell's theorem adapted to photons will be proved. One of the simplest retro-causal models available, one which is stochastic and provides an appealing description of the correlations discussed by Einstein, Podolsky and Rosen and by Bell, will be discussed. Generalizing this model remains a challenge.