It is well recognized that there are unanswered questions in the foundations of physics—most evidently in quantum mechanics, particle physics, and gravitation and cosmology—that currently prevent a fuller understanding of the workings of nature. Against that background, presented here is photodynamics, a deterministic mathematical model via which the quandaries in foundational physics can be resolved comprehensively. The core hypothesis of photodynamics is that Planck’s constant his not merely a natural constant; rather, it is the numerical measure of the magnitude of a photino, a primordial particle of static-form radiant energy of which all of space and matter is ultimately composed. Three postulates define the framework in which all physical interactions associated with photinos take place: (i) photinos are distributed spatially in the form of cells, contiguous photino packets that are autonomous, elastic, and potentially mobile; (ii) the universe evolves recursively in discrete time steps; (iii) all dynamic activity in nature arises from the behaviors of physical systems induced by the innate elasticity of their cellular elements. These foundational axioms are systematically formulated into a universal mathematical model that is then applied to the full spectrum of physics from subatomic to cosmological, yielding remarkable results. Notably, Bohr’s formula for the hydrogen spectrum, the Schrödinger equation, Newton’s law of gravity, nuclear forces, Coulomb’s law, and Maxwell’s electrodynamics all emerge naturally as consequences of photodynamics, which also settles the well-known measurement problem in quantum mechanics and offers insights into cosmic dynamics and the origins of dark matter and dark energy.