When Physics Demands Its Own Beginning: The Initial-Conditions Regress and the Limits of Presuppositionless Explanation in Cosmology

This paper develops a claim-level diagnostic protocol for assessing when cosmological explanatory demands — particularly the demand for a presuppositionless account of initial conditions — exceed the conditions under which physical explanation can operate. It introduces diagnostic signature S6 (Initial-Conditions Regress), which formalises a distinctive regress pattern: explanatory work is displaced onto a new starter package without a physically licensed interface anchoring the restart. The core argument rests on a single constraint: every physical derivation presupposes a non-empty set of applicability conditions (a ‘starter package’). Under this constraint, the demand for presuppositionless explanation generates an unavoidable regress, terminable only by postulation, circularity, or dissolution (the EPM-Lemma). Applying the protocol to seven prominent cosmological claims — including inflation, the Hartle–Hawking no-boundary proposal, conformal cyclic cosmology, cosmological natural selection, the string landscape, and the strong anthropic principle — yields structured verdicts (PASS / PASS* / OPEN / Loss of Applicability) that populate all four verdict classes, demonstrating that the protocol discriminates rather than uniformly rejects. The contribution is methodological, not ontological: no position is taken on the truth of any cosmological proposal. A formal statement of the EPM-Lemma is provided as an Online Supplement.