Sally Riordan, Stanford University
5.15pm in room LAK2.06 (formerly T206).
Evidence that the fine structure constant is increasing over cosmic time-scales has recently reignited a debate in the physics community regarding the existence of fundamental units of nature. Some physicists see the variation of the fine structure constant as evidence for a decreasing speed of light. They argue that black holes provide a way to discriminate between a world in which the speed of light is increasing and one in which the electron charge is increasing. Others hold firm to the conventionalist view that only dimensionless constants can properly be said to change. A proper understanding of Mach’s principle, they argue, makes it meaningless to talk about the variation of a dimensionful constant. The speed of light is nothing but a conversion factor between metres and seconds. As a result, the standard view that there are three fundamental units of nature has been challenged: there are, under this view, none.
Taking inspiration from an episode of metrological history, I argue that we more properly end this argument by concluding that there is only one fundamental unit of nature. One measure of the world is necessary in order to inject meaning into our system of measurement and to connect our experimental results to scientific theory. I’ll be looking to the ideals that brought about the creation of the metric system in the 1790s. Considering why Lavoisier, Borda, Couloub, Monge, Condorcet, Laplace and Lagrange (amongst others) believed the kilogram and the metre to be “not in any way arbitrary” and “taken from nature” will lead us to a pragmatic, operationalist understanding of “fundamental”, under which it is meaningful to say that there is only one fundamental unit of nature.
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