Comment on “ Exclusion of time in the theorem of Bell ” by K . Hess and W . Philipp

– A recent Letter by Hess and Philipp claims that Bell's theorem neglects the possibility of time-like dependence in local hidden variables, hence is not conclusive. Moreover the authors claim that they have constructed, in an earlier paper, a local realistic model of the EPR correlations. However, they themselves have neglected the experimenter's freedom to choose settings, while on the other hand, Bell's theorem can be formulated to cope with time-like dependence. This in itself proves that their toy model cannot satisfy local realism, but we also indicate where their proof of its local realistic nature fails. Introduction. – The recent papers [1–4] by Hess and Philipp have drawn a lot of attention, especially since the work was featured on Nature's web pages and from there reached the popular press in many countries. In this comment we would like to point out a number of fatal errors in the work, of which the most serious is the lack of recognition of the choice which an experimenter is free to make in the laboratory, and which a theoretician is free to make in a Gedankenexperiment. We shall convert this freedom into a statistical independence assumption, and show how it plays a vital role in obtaining Bell's theorem: quantum mechanics violates local realism. In fact, Hess and Philipp criticize Bell's proof of the theorem on the grounds of a quite different independence assumption made by Bell whose only role is to enable him to cover stochastic as well as deterministic hidden variable models (his hidden variables λ are not assumed to be localized, see [5] p. 153, paragraph 4 of " Bertlmann's socks and the nature of reality "). They claim that time variables should be included in the proof but as we show below, this is untrue. Hess and Philipp's proof that their toy model of the EPR correlations satisfies local realism is incomplete (and uncompletable). It is perhaps difficult to appreciate