Defining and Testing the Foundations of Physics: A Constraint-Based Framework

This article addresses a persistent ambiguity in contemporary physics: what it actually means for a framework to qualify as a foundation of physics. The term is frequently applied to interpretations, reformulations, and speculative proposals, yet rarely defined with operational precision. Rather than proposing a new physical theory, this paper develops a constraint-based framework for evaluating foundational claims. It argues that genuinely foundational structures must be judged not by explanatory narrative or empirical fit, but by the constraints they impose on physical theory-building. Central criteria include ontological minimality, the primacy of conservation laws, the derivation (rather than postulation) of dynamics and geometry, reduction consistency, overconstraint, parameter economy, structural uniqueness, and resistance to ad-hoc patching. The paper clarifies the distinction between theories, interpretations, and foundations, and applies the proposed criteria to major existing frameworks such as classical mechanics, quantum mechanics, and general relativity. It concludes that, while these theories are extraordinarily successful within their domains, none currently satisfies all requirements necessary to function as a complete foundation of physics. By making foundational criteria explicit, the article provides a reusable diagnostic tool for assessing foundational proposals and for clarifying debates across physics, philosophy of physics, and related fields. Its aim is to sharpen foundational discourse, not to replace existing theories or advance a specific alternative.