
4.1 Vibrational Entropy in the Thermodynamic Limit
As illustrated in Figure 2, the topological difference lies entirely in the stacking sequence:
the FCC lattice is structurally isotropic due to its cyclic (ABCABC) sequence, while the
HCP lattice possesses a preferred vertical axis due to alternating (ABAB) stacking.
In the statistical mechanics of hard spheres, the FCC lattice possesses a higher vi-
brational (phonon) entropy than the HCP lattice [7, 8]. Applying this classical result to
a quantum tensor network is structurally robust because the phononic density of states
is a direct group-theoretic consequence of the local potential well’s symmetry. Because
the FCC geometry possesses a higher point-group symmetry (O
h
) than HCP (D
6h
), its
perfectly isotropic potential natively accommodates a wider, more symmetric spectrum
of transverse zero-point fluctuations. This geometrically enforces a higher vibrational
entropy regardless of the specific microscopic bond interactions.
While this entropic advantage is famously microscopic locally (on the order of 10
−3
k
B
per particle), phase transitions in the early universe are collective, global phenomena.
Because Γ ≫ H, the crystallization front propagates adiabatically, allowing the causal
patch to maintain thermal equilibrium where the total free energy difference scales as
∆F = −N(T ∆S
vib
). In the thermodynamic limit (N → ∞), the probability of the
universe falling into the HCP state over the FCC state is given by the Boltzmann weight:
P
HCP
P
F CC
= exp
−
N∆S
vib
k
B
→ 0 (9)
The massive scale of the universe transforms a microscopic local advantage into a deter-
ministic outcome in the thermodynamic limit. Random stacking faults are exponentially
suppressed, strictly driving the selection of the isotropic FCC state.
4.2 A Discrete Variational Principle for Geometric Extension
Beyond simple density and entropy, the selection of the FCC lattice satisfies a discrete
topological variational principle. When transitioning from the 2D boundary to the 3D
bulk, the Hamiltonian seeks to minimize spatial shear by matching the zero-stress 2D
Euler ground state (⟨k⟩ = 6) as closely as possible along any continuous cross-section.
To establish uniqueness, we restrict our search to the set of K = 12 close-packed
Euclidean vertex figures. Distorted or non-regular geometries inherently require unequal
bond lengths, invoking a severe harmonic elastic energy penalty that scales as ∆E ∼
κ(∆l/l)
2
per bond. In the high-tension environment of the expanding early universe,
this immediately removes distorted geometries from the low-energy ground state. The
minimum-energy candidates are thus strictly restricted to the three maximally symmetric
contact graphs for 12 uniform spheres: the Icosahedron, the HCP Twisted Cuboctahedron,
and the FCC Cuboctahedron.
The Icosahedron entirely lacks regular planar equators, geometrically forcing k
i
= 5
across all skewed intersecting planes. The HCP figure contains exactly one regular k
i
= 6
equatorial plane, breaking spatial regularity along its vertical axis. The FCC Cuboctahe-
dron is mathematically unique in possessing exactly four regular k
i
= 6 equatorial cross-
sections (the {111} crystallographic planes), perfectly satisfying the discrete ⟨k
2D
⟩ = 6
minimum-energy condition across all spatial axes simultaneously.
8