This is the theory’s cleanest prediction in form: the exponent and the coefficient are parameter-free. Its size, at the derived coherence length, is far below what an experiment can reach, which the numbers below make precise. Two uncharged metal plates in vacuum already attract each other, because the quantum vacuum between them holds fewer field modes than the vacuum outside. Standard physics says that force grows as d⁻⁴. PST says the substrate is not infinitely fine-grained: it has a coherence length d₀, and as the plates approach that scale, the mode count departs from the continuum answer.

• The exponent is the prediction. The correction scales as d⁻⁶, not d⁻⁴, with the coefficient ξ = 90/π² ≈ 9.12 fixed by the substrate’s projection kernel. No free parameter tunes that power law, and it is distinguishable from every known material correction, including the retarded d⁻⁷ Casimir-Polder regime. Because the exponent is fixed in advance, measuring how the force changes with the gap tests the prediction on its own terms.
• The curve is drawn at the data’s bound, not at the theory’s value. The amplitude is set by d₀. Existing 160–750 nm data place d₀ below about 2.3 nm, and that bound is what the curve uses. The theory’s own value is far smaller: canonical normalisation fixes d₀ = √2 ℏc/mₕ = 2.2 am (Computation 201), which puts the correction at about 10⁻¹⁹ of the force at 20 nm, eighteen orders below this curve. A measurement that sees no signal is therefore what the theory expects, and the book states this plainly.
• What an experiment could decide. Slide the separation down. At the bound the signal would be 0.19% at 160 nm, 1.9% at 50 nm and 12% at 20 nm, growing as (d₀/d)²: that is the sensitivity such measurements would have, not the signal the theory expects. What would decide it is the exponent and the amplitude together. A resolved d⁻⁶ component of nanometre amplitude would refute the canonical normalisation and the M* prediction with it; a component with the wrong exponent would refute the theory; a null result at any reachable precision is its prediction.