Brownian motion, theory confirmation and the stratification of scientific knowledge
Alan Chalmers
Dates: Monday, 22 April 2024
Time: 5:30pm
Venue: New Law Building (F10), Level 3, Room 344
How to register: Free, no registration required.
Abstract: Jean Perrin’s experiments on Brownian motion are typically seen as providing especially decisive evidence for the reality of molecules. Research in the area has been raised to a new level of sophistication by George Smith and Raglan Seth in their book Brownian motion and molecular reality. In this paper I draw out and elaborate on key consequences of that work that are of general interest. I use the case of Brownian motion to argue (i) That there is more to the confirmation of scientific theories than the validation of their predictive and explanatory power. The concordance of alternative measures of a physical quantity offers a stronger kind of confirmation. Those scientists who saw Perrin’s and associated research as bringing an end to the hypothetical status of molecular-kinetic theory had a point. (ii) Perrin established knowledge of Brownian motion at various levels, some involving no theory, some assuming that the motions of Brownian granules is governed by Newton’s laws of motion and some invoking the molecular-kinetic theory. Knowledge at each level was vindicated by appeal to concordant measures of physical quantities, implying that knowledge at each level has a similar epistemological status. It is not the case that knowledge necessarily gets more speculative the further it gets from what is directly observable to the senses nor is it the case that knowledge at the atomic and molecular level is superior to that at the observable level because it can in principle explain the latter and render it redundant. Knowledge at the various levels and the relationship between them are all key elements of scientific knowledge and its mode of progress. (iii) An appreciation of the various levels of knowledge of Brownian motion helps to dispel any puzzles that arise from an alleged clash between the time asymmetry of many physical processes and the time symmetry of the laws governing the micro-processes that give rise to them.
Bio: Alan Chalmers received a PhD in HPS from the University of London in 1971. He then came to the University of Sydney as a Post-doctoral Fellow in the Department of Philosophy . He remained at that institution until his 'retirement' in 1999. In 1985 he took up the position of Senior Lecturer in HPS in the Science Faculty and started the process of converting the one-person outfit it then was into the School of History and Philosophy of Science that it has now become. His most important books are What is this thing called science? The scientist's atom and the philosopher's stone and One hundred years of pressure: Hydrostatics from Stevin to Newton. He is the author of some 70 or so articles in history and philosophy of the physical sciences.