Final answer:
Ulam's notion of physical complexity does not directly relate to the set-theory axiom of regularity, but his ideas imply the existence of order within complex physical systems, which might indirectly align with principles found in set theory.
Step-by-step explanation:
Ulam's ideas about physical complexity focus on the inherent complexities found within certain systems in physics, where simple laws are applicable but complex systems can manifest unique patterns unlike simpler systems. These complex systems have the fascinating capability to adapt and evolve, demonstrating a level of organization and self-organization that is not typically present in simpler systems observed under traditional physics. The field of complexity in physics, therefore, takes into account behaviors such as non-equilibrium phenomena, heat transfer, phase changes, crystal growth, and the cooling of iron into magnetic domains — all characteristic examples of complex detailed systems that suggest underlying order and organization.
While Ulam does not directly address the set-theory axiom of regularity in his discussion of physical complexity, his ideas implicitly suggest the intricate balances and underlying order present within seemingly random complex systems that could offer further insights into areas like thermodynamics, statistical mechanics, and non-equilibrium phenomena. It aligns with the overall human effort to make sense of and systematize the vast, complex universe around us, partly through the discipline of physics.