Four Null Causal Spacetime: Gravity, Light and Matter from Causal Fabrics

What is the minimum structure needed to describe spacetime? In general relativity, spacetime begins with a metric, a rule for measuring distances and times, and light reveals its most basic feature: which events can influence one another and which cannot. Four Null spacetime theory reverses this approach. Instead of starting from geometry and asking how light moves through it, it starts from light itself and reconstructs the geometry. The theory proposes that spacetime is built from microscopic cells, each spanned by four balanced lightlike vectors (null generators) whose directions point to the corners of a regular tetrahedron. From these four vectors alone, the local metric is reconstructed exactly, each cell acquires a unique relational clock, and the six bivectors formed by pairs of generators split exactly into three electric and three magnetic channels, the places where field strengths and curvature live. The same geometry carries Maxwell fields, spinors and the Dirac operator, giving one causal framework for gravity, light and matter. Main results. The manuscript states every result with an explicit status: exact, certified, conditional, numerical or open. Among them: Light and gravity share one causal cone. Under the composition postulate, a single discrete Huygens law is selected, with free waves on the light cone. The Einstein interaction. Under the integrability postulate, the theory gives the Einstein coupling exactly and, in the transverse traceless sector through order L_c², a unique completion with exact rational coefficients, supported by exact-arithmetic certificates. How cells join. Transport between two cells sharing a face is fixed by the geometry of that face. Exact balance leaves only discrete choices in joining cells, every hinge of a cell has corner angles of 60° and 120°, flat spacetime closes exactly, and curvature is carried by how cells meet around hinges, in units of π/3. Quantum tests. On the F4 lattice, used as a Euclidean regulator, the tested sectors contain a massless transverse photon, a chiral fermion without doublers, and two low-energy graviton modes. What remains open. The manuscript is a research-program synthesis, not a complete theory. The central open problem is the law that selects and evolves the global pattern of connections between cells, together with its quantum dynamics and large-scale limit. Also open: a physical real-time realization with Lorentz protection, unitarity at the cell scale, the dynamical origin of balance, and the size of the cell. What’s new in this version. This version derives the transport between neighboring cells from their shared face geometry, proves that exact balance fixes a neighboring cell up to a reflection, establishes the 60°/120° hinge geometry with exact flat closure and deficits in units of π/3, and introduces the combinatorial gluing route (Route A). Transport and the static geometry of gluing are therefore no longer open; the open problem is now the dynamics of the gluing complex. Reproducibility. The calculations behind the gravitational coefficients and the gluing results are archived with this record: FourNull_LawE_Package_v30.zip, SHA-256 1abc069eb02239e158764d8a77b5878ddf67cea71bb5d03aee3b075ceee417f2 FourNull_Gluing_Certificates_v31.zip, SHA-256 80912f410650b4a40fbd0ff8f5ab18b5325eb169a7496e67355304a27bc6641f Related work. Exact kinematics of the four null frame (Paper A): doi:10.5281/zenodo.23738813. Calculations were carried out with AI assistance under the author’s direction; both implementations of the key calculations were written by AI systems, so independent external reproduction is welcomed.