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Naturalness, Extra-Empirical Theory Assessments, and the Implications of Skepticism

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Abstract

Naturalness is an extra-empirical quality that aims to assess plausibility of a theory. Finetuning measures are often deputized to quantify the task. However, knowing statistical distributions on parameters appears necessary. Such meta-theories are not known yet. A critical discussion of these issues is presented, including their possible resolutions in fixed points. Both agreement to and skepticism of naturalness’s utility remains credible, as is skepticism to any extra-empirical theory assessment (SEETA) that claims to identify “more correct” theories that are equally empirically adequate. The severe implications of SEETA are set forward in some detail. We conclude with a summary and discussion of the viability of three main viewpoints toward naturalness and finetuning, where the “moderate naturalness position” is suggested to be most appealing, not suffering from the disquietudes of the extreme pro- and anti-naturalness positions.

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Notes

  1. Italicized words appearing in this article are defined in more detail in [1].

  2. For future discussion, the distinction between “testable” and “falsifiable” theories will be important. A “testable” theory is “one that contains at least one point in parameter space that is capable of yielding evidence for new physics beyond the standard theory in future experiments,” whereas a “falsifiable theory” is one “whose entire parameter space could conceivably be ruled out (i.e., shown to be non-concordant) by a specified collection of experiments and analysis that can be done in the future” [1]. A falsifiable theory is a testable theory, but a testable theory might not be falsifiable.

  3. In [1] an authentic theory is defined to be “... one that has a point in its parameter space ... that is concordant with any conceivable experiment that could possibly be performed in the theory’s domain of applicability.” More colloquially, it is the “correct theory” or, in the case of a less ambitious effective theory, a “more correct theory” or “deeper theory.”

  4. Diversity is highlighted here, since its useful role has not been emphasized directly in the literature. Of course, many others extra-empirical preferences have strong claims too, such as a coherent and efficient explanation of causal mechanisms, etc.

  5. For example, all superpartners are degenerate in mass at 1 TeV.

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Acknowledgements

I am grateful for discussions with A. Hebecker, S. Martin, A. Pierce, and Y. Zhao. This work was supported in part by the DOE under Grant DE-SC0007859.

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  1. Physics Department, Leinweber Center for Theoretical Physics, University of Michigan, Ann Arbor, MI, 48109-1040, USA

    James D. Wells

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Wells, J.D. Naturalness, Extra-Empirical Theory Assessments, and the Implications of Skepticism. Found Phys 49, 991–1010 (2019). https://doi.org/10.1007/s10701-018-0220-x

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