Modeling in Physics: A Story of Scales

HiPhiS (History & Philosophy of Science) Lecture by Annick Lesne, theoretical physicist and CNRS research director at the LPTMC Paris-Sorbonne and the IGMM Montpellier. Free admission.

Abstract

The starting point of this presentation is to show how our understanding of a real system using models fundamentally depends on the scales at which we observe it, the scales of the phenomena we wish to predict, and the intrinsic characteristic scales of the system. I will illustrate this point using several now-classic examples: diffusion processes, the DNA molecule, and the Brittany coastline. We will see that this perception of different scales is put to the test for fractal structures and, more generally, for systems exhibiting scale invariance; and conversely, how the detection of scale invariance is limited by the scales of observation. Clearly distinguishing between different scales and levels of organization is also essential for understanding the concept of emergence and studying the complex systems where it manifests, such as a crowd or a dune.