Entropy and gravity

2019 edition

Marius Oltean

It is a manifest fact of our everyday experience that the universe is moving towards greater and greater disorder, called in physics “entropy”: smoke exits a cigarette but does not enter into it, a drop of milk spreads through a cup of coffee but does not collect itself back together. At the same time, the laws of physics at the fundamental level – at least up to a certain interpretational extent – are deterministic: knowing, for example, the position and velocity of a particle at any instant of time, Newton’s second law (F = ma) determines its motion exactly and uniquely for all time. How can laws of physics which are deterministic produce entropy? In other words, how can rules which in principle appear to be orderly generate disorder? This basic question has long been debated in innumerable variations by physicists and philosophers, with still no clear consensus today on how to satisfactorily understand it. In this talk, I will touch upon the main ideas at the heart of this problem and some of my thesis work on it in the context of general relativity.