Popper: Of Clouds and Clocks - Freedom and Determinism

This is the central philosophical problem Popper aims to solve: How can abstract meanings, ideas, promises, or theories - which have no mass, no energy, no physical properties - causally influence physical behavior? Compton's example: He traveled from Italy to Yale to deliver a lecture because of a *promise* he had made. But a promise is an abstract entity - just marks on paper or sounds in air. How can these abstractions make a physical system (his body) travel thousands of miles? A strict physicalist would have to say: A physicist who knew Compton's exact physical state could have predicted his journey purely from particle positions and velocities, without knowing anything about promises, meanings, or Yale lectures. The promise is just an "epiphenomenon" - a byproduct with no real causal power. But this seems absurd. Clearly the *content* of the promise (not just its physical embodiment) matters causally. If the promise had been to meet in Paris instead of New Haven, Compton would have gone to Paris. The abstract content controls the physical behavior. How is this possible without postulating mysterious mental substances or violating physical laws? This is Compton's Problem, and it's more fundamental than the traditional mind-body problem. It's about how the abstract realm of meanings, arguments, and ideas can have genuine causal efficacy in the physical world.