**A closer look at Maxwell's demons: Counterfactual measurements and finite size effects**

Prof. Dervis Vural

Department of Physics

University of Notre Dame

A Maxwell’s demon is a device that can measure the microstate of a closed system, thereby reducing its entropy, seemingly in violation with the second law. A century of physics literature modeling the measurement protocols and internal workings of the demon culminated to the conclusion that logically irreversible operations taking place within the demon such as information erasure account for the lost entropy. In this talk I will discuss three novel demon models and the interesting thermodynamic implications of their operation. First I will define counterfactual demons: systems for which micro-state information can be inferred by observing a lack of an event. As a case in point, I will show how the thermodynamics of an ideal gas should be updated if in a fragile vessel. Next, I will discuss the implications of a demon to realistically have finite dimensions and reaction time. These realistic demons will provide us an upper bound for information-driven heat/mass transport. Finally, I will compare the rate of operation of two realistic demons: one that acts solely on local information, and another that predicts the future and optimizes its actions accordingly. The difference tells us that predicting the future is not a neutral activity, but one with thermodynamic footprint.

email physics@nd.edu for the zoom link