Fine-tuning as Old Evidence, Double Counting, and the Multiverse

Abstract

The idea that there might be multiple universes with different parameters of nature is often considered an attractive response to the finding that various parameters appear to be delicately finetuned for life. The present paper investigates whether the appeal to fine-tuning can legitimately be combined with an appeal to independent empirical evidence for other universes or whether, as suggested by Cory Juhl, combining such appeals inevitably results in illegitimate double counting of the finding that the parameters are right for life. In doing so, the paper takes into account the fact that the parameters' life-friendliness is old evidence for us, which makes Bayesianism's problem of old evidence relevant to Bayesian analysis of its evidential impact. Ultimately, the verdict reached is that the warning of double counting is helpful, but that double counting can in principle be avoided. The paper highlights remaining independent challenges against the fine-tuning argument for the multiverse.

God in dialogue with His creation

“…The works of Friederich (2017), Barnes (2020) and Loke (2022b, pp. 175-181) deal intensively with the counter-arguments against the view that the fine-tuning of natural constants requires a creator.…”

Uniform probability in cosmology

“…Our review of various ways to model a fair lottery on the natural number does not directly help to answer a number of additional questions that arise in the context of the cosmological measure problem and that need to be analysed step by step, such as: how to factor in observer selection effects (which already occur in the finite case), how to apply typicality reasoning (in the sense of Hartle and Srednicki (2007) and Garriga and Vilenkin (2008); or whether this is useful in the first place), and how to confirm a theory of this type given that we use data from our only observable universe both for theory building and for confirmation (doublecounting, in the sense of Friederich, 2017). Offering such a full analysis goes well beyond the scope of this contribution.…”

A New Fine-Tuning Argument for the Multiverse

“…unaware that there is a life-friendly universe. Concerns on the possibility of rational probability assignments in this situation are articulated in [25] and taken up in [26]. The posterior probabilities P + (T M ) and P + (T U ), in turn, are supposed to reflect the rational credences of an agent who not only knows that a life-friendly universe requires fine-tuning, but also knows R, i.e.…”