Dr. Alexandre Deur (TJNAF): A Glance at Non-Linear Dynamics in Nature
The relative simplicity of linear systems has made them privileged in Physics studies and teaching. Non-linear systems are much less tractable, and yet they constitute the majority of systems encountered in Nature. Even at fundamental level, all forces of Nature display non-linear behavior, sometimes relatively discreetly, e.g. with electromagnetism (QED), sometime prominently, e.g. with the strong nuclear interaction (QCD). Therefore, understanding non-linear dynamics is an essential and critical part of our endeavor to understand Nature both at fundamental and applied levels. In this seminar, I will first recall what linear and non-linear systems are. I will then discuss how non-linearities emerge, in particular in QCD and gravity (General relativity, GR). After reviewing the basics of QCD and GR, as well as their phenomenologies, we will find that there are intriguing parallels between QCD and GR. These parallels may help understanding the observations at the origin of the standard model of cosmology (the Lambda-CDM model), viz. a Universe model largely dominated by dark matter and dark energy. We will then see how GR's non-linear behavior may dispense --- partly or totally --- with dark matter and dark energy.