This work introduces the Chi Framework as a compact structural interpretation of the shared lightlike boundary between relativistic and quantum descriptions.On the relativistic side, the massless boundary is defined by the standard relation E = pc. On the quantum side, using the standard Planck–de Broglie relations E = ℏω and p = ℏk, the same boundary yields ω = kc. This common limit motivates the introduction of the dimensionless boundary parameter χ = pc/E = kc/ω = v/c, together with the corresponding deviation parameter δ = 1 − χ².These parameters provide a compact structural language that organizes several familiar relativistic quantities, including the Lorentz factor, proper time, and mass-shell deviation, while also admitting a phase-based interpretation.The present work is intentionally limited in scope. It introduces no new equations of motion, proposes no modification to established relativity or quantum mechanics, and makes no empirical claims beyond known physics. Its purpose is interpretive and structural: to identify a shared invariant boundary principle through which familiar relativistic and quantum expressions may be organized within a single limiting framework.This paper is the first in the UNIFICATION series. Subsequent papers explore phase amplification, coupled zero-like and infinity-like limits, geometric interpretation, field-based formulations, and candidate governing equations. An, included, educational companion text, UNIFICATION: The Chi Framework — Eight Lessons on the Boundary Between Relativity and Quantum Mechanics, which is a textbook which anybody with at least a highschool level of accomplishment can understand. Currently available: UNIFICATION 0 — A Shared Lightlike Boundary for Relativity and Quantum Theory https://doi.org/10.5281/zenodo.19860494 UNIFICATION I — Phase Structure and the Lightlike Boundary https://doi.org/10.5281/zenodo.19862660 UNIFICATION II — Implications of the Lightlike Boundary and Phase Structure https://doi.org/10.5281/zenodo.19863301 UNIFICATION — The Chi Framework: Eight Lessons on the Boundary Between Relativity and Quantum Mechanics https://doi.org/10.5281/zenodo.19863601 Soon to come: UNIFICATION III - Toward a Dynamical Formulation of the Lightlike Boundary Framework - v1.00 UNIFICATION IV - Consequences and Implications of the Chi Framework - v1.00 UNIFICATION V - Chi Framework and, Concerning the Absense of a Governing Equation - v1.00 and... UNIFICATION VI - From Limit Structure to Rotational Interpretation - v1.00
Gary A. Creighton (Tue,) studied this question.