Eddington introduced the concept of the arrow of time - the one way flow of time as events develop and our perceptions evolve. He pointed out that the origin of such an arrow appears to be a mystery in that the underlying laws of physics (at least at the time of Eddington) are time symmetric and would work equally well if run in the reverse time direction. The laws of classical physics follow from the minimization of the action and are indeed time symmetric. This view has been beautifully captured by Carlo Rovelli , who writes: "The difference between past and future, between cause and effect, between memory and hope, between regret and intention...in the elementary laws that describe the mechanisms of the world, there is no such difference." But what picks out only those solutions running forward in time?I think this paper is correct in that (1) a common view today is that the thermodynamic arrow of time is the only one; and (2) this view is mistaken.
By now, there is a large literature on the arrow of time [1-10]. Essentially all of the literature accepts the proposition that the fundamental laws of physics do not distinguish between past and future and could equally well be run backwards. There is also a recognition that the second law of thermodynamics does distinguish between these directions as it states that entropy cannot decrease in what we refer to as the future. This leads to the idea of a thermodynamic arrow of time. Many view this thermodynamic arrow as the origin of the passage of time, or at least of our consciousness of that passage.
Our point in this paper is that the basic premise of such reasoning is not valid in quantum theory. Quantum physics in its usual form has a definite arrow of causality - the time direction that causal quantum processes occur. ...
The basic statement saying that the fundamental laws of physics do not differentiate an arrow of time is not correct. At the microscopic level, reactions run in one direction but not the other.
Monday, March 30, 2020
The quantum arrow of causality
A new paper argues that Quantum causality determines the arrow of time: