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Final Report Summary - PRESUME (Economies of Uncertainty: Epistemological Perspectives on the Reform of the Metric System)

Metrology, the science of measurement and standardization, is little known outside a small circle of experts, although its impact on commerce, industry and daily life can hardly be overstated. Metrologists are responsible for the standardization of physical measurement in accordance with the International System of units (SI) – colloquially known as the ‘metric system’. A network of metrological institutions spread throughout the globe ensures that consumer products, communication systems, environmental safety procedures, medical drugs and myriad other technologies conform to their specifications and to national and international standards.
While metrology is a well-established science, the epistemological foundations of this science are currently poorly understood. What makes measurement a reliable source of scientific evidence? What sorts of knowledge do standardization projects generate, and how is this knowledge justified? What roles should theory play in the definition and realization of measurement units? These questions are especially pertinent in light of exciting developments currently taking place at the core of the metric system. In 2018 four basic SI units - the kilogram, ampere, mole and kelvin – are planned to be redefined by fixing the numerical values of four fundamental constants: the Planck constant, the elementary electric charge, the Avogadro constant and the Boltzmann constant, respectively. As a consequence, the platinum–iridium cylinder known as the International Prototype of the Kilogram (IPK) will no longer have the mass of 1 kilogram by definition. Instead, the mass of IPK will be determined by reference to the Planck constant with the help of sensitive measuring instruments, such as watt balances and silicon spheres.
The Marie Curie IEF “Economies of Uncertainty” project (PRESUME) ran from July 2014 to June 2016 at the History and Philosophy of Science Department at the University of Cambridge. Its central objectives were to (1) develop a general conceptual framework for the epistemological study of metrology, (2) use this framework to analyze the epistemic and social impacts of the planned metric reform, and (3) enhance the visibility and understanding of the goals and contemporary importance of metrology among scientists, humanities scholars and the general public. These objectives were accomplished by a combination of philosophical analysis, empirical work and dissemination activities.
On the analysis side, a novel approach was developed for the study of metrological knowledge based on an economic analogy. Under this approach, metrologists are thought of as providers of epistemic services. An ‘epistemic service’ is a relation between agents such that one agent (the provider) affords ignorance to another (the recipient). ‘Affording ignorance’ refers to the act of relieving the recipient of the need to obtain some piece of knowledge K in order to obtain a goal G. For example, metrologists who calibrate measuring instruments relieve instrument users of the need to know the idiosyncrasies of their instruments in order to obtain reliable results. Uncertainty functions as an interface between parties of an epistemic service, allowing agents to coordinate their actions despite having disparate states of knowledge. An economy of uncertainty is the set of epistemic services provided in a community. In an efficient economy of uncertainty, uncertainties are attributed to knowledge claims in a way that maximizes the ignorance recipients can afford while still obtaining their goals.
On the empirical side, interviews were conducted with metrologists in three leading institutions in Europe: the International Bureau of Weights and Measures (BIPM) near Paris, the National Physical Laboratories (NPL) near London, and the Physikalisch-Technische Bundesanstalt (PTB) in Berlin. The interviews concerned the history and motivations for the planned redefinition of metric units. The philosophical framework was then used to analyze the data collected from interviews as well as the ongoing metrological literature on this topic.
The results of the analysis suggest that a central epistemic goal of the metric reform is to optimize the distribution of uncertainties among measurement outcomes reported under the metric system. This optimization takes the form of a shift from an operational economy of uncertainty, where uncertainty expresses the stability and reproducibility of instrument indications, to an informational economy of uncertainty, where uncertainty expresses the predictability of instrument indications under a theoretical-statistical model of the measurement process. Theory plays an indispensible role in the informational economy, as it defines the parameter space on which measurement outcomes are specified. These results contribute to a better understanding of the importance, implications and historical context of the planned metric reform.
A variety of dissemination activities were undertaken that targeted scientists, humanities scholars and the general public. These included the organization of an international conference titled ‘The Making of Measurement’, the organization of a workshop on Informal Aspects of Uncertainty Evaluation, a public talk titled ‘How Heavy is the Kilogram?’, and 16 conference and seminar presentations given in the UK, Denmark, Germany, the US and Canada. Project publications have appeared in The Stanford Encyclopaedia of Philosophy and The British Journal for the Philosophy of Science, with three additional articles currently forthcoming. A special issue of Studies in History and Philosophy of Science dedicated to measurement is currently being edited by project research staff and will appear in 2017.
To learn more about the project, please visit the project website at:

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