Thermodynamics Perspective on the Direction of Time

Abstract While the perceived “flow of time” has evident outcomes discriminating the future from the past, the physical mechanisms enacting the direction of time remain one of nature's most guarded secrets. Since all known fundamental laws of physics are time-symmetric (here we refer to classical, quantum and relativistic mechanics with the notable exception of thermodynamics), the physical mechanisms associated with the time arrow must be well concealed by nature, perhaps somewhere in the quantum world. The obvious inequality of the directions of time creates the sense of “time flow”, which is a very powerful illusion, but the directional nature of time is objective and is best reflected in the explicit directionality of the second law of thermodynamics. When dealing with such complex issues as the direction of time, it is important to ask the right questions before correct answers can be found. In this presentation, a set of thought experiments are explored that allow us to formulate such questions. The queries:    

·         Why do we remember the past and do not remember the future?

·         Does entropy increase forward in time or does time “flow” in the direction of entropy increase?

·         Is the low entropy origin of the Universe sufficient to explain the temporal asymmetry?

·         Is time travel possible? 

·         Can asymmetry of the directions of time and matter/antimatter asymmetry be related?

Alternative answers to these questions and their implications as well as opinions expressed by prominent scientists and intellectuals will be considered. While some of these alternatives lead to contradictions or circular logic and have limited utility, other alternatives cannot be resolved without experimental evidence and remain open. The possibility of testing the alternative answers for open questions with real-world experiments might be possible but is not going to be easy.

Alexander (Alex) Y. Klimenko graduated from a specialized (with advanced study of mathematics and physics) high school in Ukraine, later joining a university in Moscow to study aircraft engineering (Soviet-style engineering, mixed up with theoretical physics and functional analysis). He moved to Australia to pursue an academic career, worked first at the University of Sydney and then the University of Queensland. He visited Stanford many times and was appointed CTR Senior Visiting Fellow. Currently, Alex is a Reader in Mechanical Engineering, holds a High Doctorate in Engineering, and has been elected a Fellow of Combustion Institute (inaugural class). For many years, Alex Klimenko led the Combustion and Multiscale Modelling Research Group at UQ; since 2022, he has served as the Director of the Centre for Multiscale Energy Systems --- a center dedicated to energy transition with around 50 members involved.