Counterfactuals do appear in existing laws, but these laws are regarded as second class. They are not incorporated wholeheartedly. Constructor theory puts counterfactuals at the very foundation of physics, so that the most fundamental laws can be formulated in these terms. Concepts like work and heat can’t be captured fully with trajectories and laws of motion, because in the standard conception they are considered emergent and approximate. In constructor theory we can talk about them using exact statements about possible and impossible transformations.

Sabine Hossenfelder examines David Deutsch and Chiara Marletto’s constructor theory formulation of time and thermodynamics. By formulating physical law in terms of which physical transformations are possible and which are impossible, constructor theory derives the thermodynamic arrow of time from reversible microscopic physics without invoking ad-hoc cosmological initial conditions. backreaction.blogspot.com