 The Causal Principle has been the subject of extended criticism. (We addressed objections to the Causal Principle as subsumed under the PSR from a philosophical perspective earlier in  4.4.)  Some critics deny that they share Craig’s intuitions about the Causal Principle (Oppy 2002). Morriston (2000) argues that, for one thing, it does not seem to be an a priori truth, for not only does it lack “a kind of ‘luminosity’ that makes it impossible not to believe it, but closer inspection does not make it clearer that it is true” (2000: 156–59). He points not only to the presence of serious doubters (which he thinks he should not be able to find were it truly an a priori truth), but also to quantum phenomena, and thereby joins those who raise objections to the Causal Principle based on quantum physics (Davies 1984: 200). On the quantum level, the connection between cause and effect, if not entirely broken, is to some extent loosened. For example, it appears that electrons can pass out of existence at one point and come back into existence elsewhere. One can neither trace their intermediate existence nor determine what causes them to come into existence at one point rather than another. Neither can one precisely determine or predict where they will reappear; their subsequent location is only statistically probable given what we know about their antecedent states. Hence, as Smith argues, 