Glossary
Phi (φ ≈ 1.618)
Definition
The golden ratio — The irrational number to which a self-similar split of any quantity tends when each part is to the smaller as the whole is to the larger.
Why it matters
Andrei's 2026 Frontiers in Human Neuroscience paper reports that human resting EEG theta-alpha frequency ratios show robust φ-organization across two independent datasets (N = 320). The Phi Coupling Index measures whether an individual's alpha/theta spectral-centroid ratio is closer to φ than to the harmonic 2:1 ratio, and shows a strong association with theta-alpha convergence near the 8 Hz boundary. The Phi System uses φ as a single proportion connecting Andrei's research, brand grid, and decision-making heuristics.
Example
A subject whose alpha-to-theta spectral-centroid ratio sits closer to 1.618 than to 2.0 — For example theta centred near 6.2 Hz and alpha near 9.8 Hz — Shows stronger theta-alpha convergence toward the ~8 Hz boundary.