It is well known that at the foundations of contemporary physics there are quandaries that inhibit the inner workings of nature from being understood at a deeper level. These quandaries are manifested most evidently in quantum mechanics, particle physics, and gravitation and cosmology. Against that background, presented here is photodynamics, a deterministic theoretical framework within which the many unanswered questions in foundational physics can be resolved comprehensively. Photodynamics is conceptualized via four core postulates: (i) all of space and matter is composed fundamentally of photinos, indivisible primordial particles that are the source of inertial mass and energy, with a unit photino defined by the elementary quantum of action given by Planck’s constant h; (ii) photinos are distributed spatially in the form of cells, contiguous photino packets that are autonomous, elastic, and mobile; (iii) the universe evolves synchronously in discrete time steps; (iv) all dynamic activity in nature arises from the behaviors of physical systems induced by the innate elasticity of their cellular elements. These postulates are formulated into a systematic and coherent mathematical framework that is then applied to the full spectrum of physics from subatomic to cosmological, yielding remarkable results. Notably, Coulomb’s law of electrostatics, Bohr’s formula for the hydrogen spectrum, the Schrödinger equation, Newton’s law of gravity, Maxwell’s electrodynamics, and nuclear forces all emerge naturally as consequences of photodynamics, which also settles the measurement problem in quantum mechanics and offers insights into the dynamics of cosmic structures and the origins of dark matter and dark energy.