Mohammad Namjoo

We argue for the claim that spacetime singularities in general relativity (GR) signal _indeterminism_, broadly construed. We first develop a schema for diagnosing a type of indeterminism for physical theories, which we denote by Indeterminism. Such indeterminism involves a broader notion of a _lack of a determination_ than the usual Laplacian one. More precisely, Indeterminism arises in a model of a physical theory whenever future (or past) states of the model are (i) not unique, (ii) not specified, or (iii) ‘incoherent’—that is, they fail to satisfy desiderata that the theory should reasonably satisfy. We then apply our schema to salient features of spacetime singularities in GR. We establish that, indeed, singularities signal a type of indeterminism that cannot comprehensively be understood as a variety of Laplacian indeterminism: namely, spacetime singularities in GR signal Indeterminism.

In Defeating Dr. Evil with Self-Locating Belief, Adam Elga proposes and defends a principle of indifference for self-locating beliefs: if an individual is confident that his world contains more than one individual who is in a state subjectively indistinguishable from his own, then he should assign equal credences to the hypotheses that he is any one of these individuals. Through a sequence of thought experiments, Elga in effect claims that he can derive the credence function that should apply in such situations, thus justifying his principle of indifference. Here we argue, using a Bayesian approach, that Elga’s reasoning is circular: in analyzing the third of his thought experiments, he uses an assertion that is justifiable only if one assumes, from the start, the principle of indifference that he is attempting to justify. We agree with Elga that the assumption of equal credences is a very reasonable principle, in the absence of any reason to assign unequal credences, but we do not agree that the equality of credences can be so derived.