Naturalness and Emergence

Abstract

I develop an account of naturalness (that is, approximately: lack of extreme fine-tuning) in physics which demonstrates that naturalness assumptions are not restricted to narrow cases in high-energy physics but are a ubiquitous part of how interlevel relations are derived in physics. After exploring how and to what extent we might justify such assumptions on methodological grounds or through appeal to speculative future physics, I consider the apparent failure of naturalness in cosmology and in the Standard Model. I argue that any such naturalness failure threatens to undermine the entire structure of our understanding of intertheoretic reduction, and so risks a much larger crisis in physics than is sometimes suggested; I briefly review some currently-popular strategies that might avoid that crisis.

Responses

“…When they hold, they can legitimately be exploited in inferences. Assumptions concerning the absence of various sorts of special tuning are common in many areas of science and, as argued in Wallace (2019), it is not clear that science can proceed without reliance on some of them. Although I don't have space to argue this in detail, a great deal of causal reasoning in science including physics seems to rest on assumptions about the absence of special tuning of various kinds-a point that is suggested both by JZ's and KZ's discussions as well as that of Porter Williams, to which I now turn.…”

Quantum Gravity at Low Energies

“…for anthropic considerations see (Polchinski 2006); see also (Wallace 2019b) and references therein.…”

Determinism Beyond Time Evolution

“…Indeed, this approach has the interesting consequence of dissolving the distinction between initial conditions and parameter values. Wallace has observed that the physical content of a theory has three aspects: the qualitative form of its dynamical equations (in which the coefficients are unspecified parameters); the actual, numerical values of the parameters (expressed as dimensionless ratios); and the initial conditions [45]. As Wallace notes, it is common to consider that the parameter values are 'lawlike' while the initial conditions are merely 'contingent' -that is, parameters and initial conditions are usually thought to have importantly different modal status.…”