Modeling in physics: a story of scales

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

Summary

The starting point of this talk is to show how the understanding of a real system by means of models depends fundamentally on the scales at which it is observed, the scales of the phenomena we wish to predict, and the intrinsic characteristic scales of the system. I'll illustrate this point using several classic examples: diffusion processes, the DNA molecule and the coast of Brittany. We'll see how this perception of different scales is put to the test for fractal structures and, more generally, systems exhibiting scale invariance; and conversely, how the detection of scale invariance is limited by the scales of observation. Distinguishing between different scales and levels of organization is also essential for considering the notion of emergence and studying complex systems where it occurs, such as a crowd or a dune.