The View from Within and the View from Above: Looking at van Fraassen’s Perrin

Abstract

Bas van Fraassen has usefully contrasted two ways to view the relation between theory and measurement: from above and from within. Roughly put, “from above” is the perspective in which we view measurements from the point of view of the finished theory aiming to examine how the measurement is related to the theory. “From within” is the perspective in which we see measurement as a means for the development of the theory. van Fraassen warns us that we need a “synoptic vision,” one that combines both perspectives. In this chapter, I argue that this synoptic view can be had without forfeiting important conclusions about how theory and experience and observation are related to reality. I make my case by looking in detail into an important episode in which the two views should clearly be in play: Perrin’s work on the Brownian motion. This case has been recently studied by van Fraassen too. There are significant elements of disagreement in the ways we look at this case. I argue that Perrin’s case shows that it is unreasonable to defend the superiority of the molecular theory c. 1912 without defending its likely truth. There is an important point of contact with van Fraassen: we both take measurement to be a vehicle of representation. But we disagree on the role of instruments as means for representation. After having presented my own way to bring together the view from within and the view from above in Perrin’s case, I take issue with his account of instrument-driven measurement as a case of public hallucinations.