Disrupting Zanzibars: The Epistemic Function of High Precision Divergence

Activity: Academic talk or presentation typesInvited talk


Recent philosophy of measurement has emphasized the importance of coherence as a value for guiding high precision measurement (Chang 2004; van Fraassen 2010; Tal 2016). If coherence substantially governs measurement, there is a risk that assigned values do not represent human-independent stability in the world, but rather contingent facts about human interests, instruments, and measurement practices. In fact, the metrology community has long been aware of these dangers, occasionally referring to such pockets of circularity or empty coherence as “Zanzibars”—a reference to a metrological parable, concerning a watchmaker on Zanzibar who sets his shop’s clock by a ship captain’s noon gun, only to discover the noon gun is itself calibrated to his own shop clock. This parable is discussed as early as Cohen et al. (1957), and the specific accusation that the measurement of fundamental constants constitutes a Zanzibar has been levelled as recently Price (2011), where it is raised as an objection to the new SI.

I argue that the metrological community implements effective strategies to avoid Zanzibars. Perhaps the most obvious candidate is the demand that measurements converge to precise values, yet this demand has been widely dismissed by coherentists as inadequate to prevent hidden Zanzibars (Chang 2004; Teller 2013). In contrast, I focus here on a different aspect of the measurement of fundamental constants, namely the detection and treatment of high precision divergence in measured values. Historically, such divergence has served to discover inaccuracies in well-regarded measurements, such as Millikan’s incorrect value for the viscosity of air in his measurement of e, and correct against spurious values from misleadingly convergent measures, such as those of c by Michelson in 1933 and Anderson in 1941 (Cohen et al. 1957).

A recent important example of high precision divergence can be found across measurements of the fine structure constant by means of the anomalous magnetic moment of the electron and by atomic interferometry. Some metrologists take this divergence to probe physics beyond the standard model (Parker et al. 2018; Cladé et al. 2019). More generally, the metrological community explicitly implements data analysis strategies designed to be indifferent between two routes to dissolving divergence: (i) identifying new systematic error, or (ii) introduction of new physics. It is strategies such as these that ensure high precision measurement can avoid the coherentist’s Zanzibar trap.
Period11 Nov 202114 Nov 2021
Event titlePSA 2020/2021: 27th biennial meeting of the Philosophy of Science Association
Event typeConference
LocationBaltimore, United States
Degree of RecognitionInternational