The Left-Handed Universe: An Evidential Audit of the Broken Symmetry Assumption

The Standard Model treats the left-handedness of the weak interaction as a spontaneously broken symmetry — the remnant of an originally parity-symmetric universe whose symmetry was hidden by the Higgs mechanism. This paper audits the evidential basis for that assumption. The TWIST experiment measured the parity asymmetry parameter in muon decay to P_μ^π·ξ = 1.00084 ± 0.00029, consistent with exactly 1 — maximal parity violation with zero right-handed component to six decimal places. Every weak interaction ever observed is exclusively left-handed. No right-handed neutrino has been detected. The minimal sterile neutrino model was excluded by MicroBooNE in December 2025 (95% CL). Neutrinoless double-beta decay remains unobserved after decades of searches. The neutrino-Higgs coupling is at least seven orders of magnitude weaker than any other fermion. Against this evidence, the assumption of prior parity symmetry rests on theoretical aesthetics, not observation. No experiment has detected a symmetric precursor state. No right-handed weak current has been measured. The "broken symmetry" framing is acknowledged within the community as "an act of faith" motivated by the expectation that fundamental laws should be mirror-symmetric. This paper does not propose an alternative framework. It compiles the evidence, identifies the untested assumption, and poses the question: at what point does an act of faith become an impediment to progress? Part of the Bootstrap Universe series (Paper 91). An alternative theoretical framework addressing the questions raised here is developed in the author's Bootstrap Universe series on Zenodo (ORCID: 0009-0003-6828-2155).