Macroscopic Quantum Coherence at 300 K and Many-Worlds Bifurcation in the Exciton-Polariton Soliton:from the direct soliton–Schrödinger mapping to admissible branch selection

Abstract

This paper addresses a foundational question in quantum mechanics: can an effective Hilbert subspace describing a macroscopic collective degree of freedom take the place of the single photon in the double-slit experiment while retaining full mathematical consistency? The answer is affirmative, and rests on a definite construction. The central result is a direct mapping between the solitonic state and the linear Schrödinger equation — with no intermediate variational steps — formulated as an exact identity under the condition of internal adiabaticity. The physical structure that realizes this construction is here termed the NESS (Non-equilibrium Self-confined Soliton): a self-organized, self-confining exciton-polariton soliton that generates its own coherence without external traps or coherent lasers, sustained by an incoherent ambient energy flux that offsets its losses. The NESS unifies three properties never before combined in a single theoretical object: spontaneous self-confinement at 300 K through Kerr nonlinearity (n₂ ~ 10⁻¹⁴ cm²/W), dissipative persistence sustained by ambient flux (the physical analogue of biological metabolism), and exact reduction to a rigid collective coordinate X(τ) governed by Gross-Pitaevskii dynamics. The construction admits two tracks of physical realization — the ideal bright soliton (Route A, falsifiable on its existence at 300 K) and the nonlinear soliton-like wave packet in room-temperature polaritonic fluids (Route B, falsifiable on indivisibility) — sharing a common formalism, exact for the former and to first order in ε for the latter. Upon this substrate we introduce an admissibility operator, mathematically associable with a constrained projection map — not a collapse operator — as an original instrument for selecting which branches (generated by unitary evolution) are physically realized. It follows that the transition between the schools of thought associated with the classical Copenhagen approach and the multiversal one of Hugh Everett III emerges as a necessary structure of NESS dynamics rather than as an interpretive choice. The broader framework from which this construction arises — the Multiverse in Vertical Time Theory (MVTT) [DOI n.10.5281/zenodo.19630208] — is referenced in the concluding sections.