The Ontology of Vacuum: The N = 0 Ground State of the Constraint Network

This document establishes the constitutional ontology of vacuum within the Energy-Efficiency Theory (EET) framework. The vacuum is defined as the N=0 ground state of the constraint network---the state of the energy substrate with zero persistent Type I constraint nodes. It is not quiescent: deep transient constraint events (S₃ S₂ S₀) occur at an irreducible frequency governed by the minimum action quantum A₄₄ₓ = /2, producing a universal fluctuation spectrum S_ () = (/4) || (Vacuum Unquiescence Theorem, CLOSED-in-EET). The vacuum's transient dynamics are described by the weak Euler representation (e^i without persistent modulus), the mathematical signature of non-Being---the substrate operating in its default, unconstrained mode. Version 2. 1 is a v6. 1 constitutional alignment, companion ontology synchronization, and constitutional deepening upgrade. It incorporates the Being/non-Being framework (Two Forms of Energy v3. 4, 2--5), establishing the vacuum as the purest expression of Existence and the physical specification of non-Being. It registers the vacuum as the pre-bifurcation substrate---the physical state prior to the energy bifurcation into free-state and constrained-state forms. It establishes the vacuum as the five-channel zero baseline of the complete constraint Second Law (Constraint Network Dynamics v4. 0, Part III-C. 2) ---the unique physical state in which all five entropy production channels have zero mean, with only the Transient channel possessing non-zero variance. It formalizes the vacuum as the constitutional null test of the EET framework (2. 8): the single physical state in which every ``N 1'' constitutional structure undergoes systematic degeneration, confirming the integrated architecture of the EET constitutional system. It provides the vacuum's sevenfold ``pre-'' identity (pre-bifurcation, pre-constraint, pre-Being, pre-time, pre-space, pre-information, pre-interaction), identifies the vacuum as both the fixed point of the EET explanatory chain and the unique pure state without internal contradiction, and establishes the universal calibration baseline principle. It adds a comprehensive Appendix H, Providing detailed EET resolutions of sixteen major vacuum-related open problems in contemporary physics, with constitutional anchoring and priority registration. Appendix I documents the vacuum's philosophical resonances---from Hegel's dialectic of Being and Nothing to Aristotle's first matter, from the ancient void/plenum debate to Kant's limits of observation---as structural parallels grounded in the N=0 vacuum's physical constitution. The vacuum ontology maintains 29 interfaces to 24 companion ontologies, establishes the jurisdictional boundaries of all ``N 1'' constitutional concepts, and provides the physical foundation for EET's treatment of the cosmological constant problem, the ontological status of virtual particles, the ``something from nothing'' problem, and the origin of irreversibility. All v2. 0 constitutional content is retained and expanded. Keywords: Vacuum ontology; N=0 ground state; constraint network; non-Being; pre-bifurcation substrate; transient constraint events; Vacuum Unquiescence Theorem; weak Euler representation; transient constraint template spectrum; five-channel zero baseline; constitutional null test; definitional domain boundary; primordial formation (N: 0 1) ; cosmological constant problem; virtual particles; Casimir effect; Being/non-Being framework; Existence; Difference Precedes Constraint; constitutional singularity; universal calibration baseline; vacuum--causality--CND constitutional triangle; three arrows of time.