{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"358ca0f65bfe9dc362d108f525dc58ee4597d96605cc174df52a6213cecf6ee9","created":"2026-10-03T07:17:58Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011","7634b50edcbbf83ae2f2e94062090f3ca3a29492f52eba44d36c9538b21bda62"],"salt":"4b0901c43aa45ff768663540b5c5223d8fb419724e93862d69d18730de056caa","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"yes-no","assisted_by":[],"external_id":"bio.supercooled-water.llcp-existence","kind":"well-posed","literature_status":"partially-resolved","n":"1","parents":[{"note":"","parent_revision":"7634b50edcbbf83ae2f2e94062090f3ca3a29492f52eba44d36c9538b21bda62","relation":"special_case"}],"plain":"The proposal is that deeply cooled water can exist as two liquids of different density, separated by a phase transition that ends at a critical point. Computer models of water show this, and a 2026 experiment reported seeing it in real water, but an independent confirmation is still missing.","posed_since":"1992","precise":"Determine whether H2O (and D2O) has a first-order transition between a high-density liquid (HDL) and a low-density liquid (LDL) ending at a liquid-liquid critical point (LLCP), versus the singularity-free scenario, a critical point at negative pressure, or the stability-limit conjecture. The LLCP is established in several classical and machine-learned first-principles water models, and ultrafast heating of amorphous ice with X-ray scattering has reported a discontinuous-to-continuous crossover with critical fluctuations. An answer is an independent confirmation, by a different technique or group, of critical scaling (diverging correlation length with 3D Ising exponents) in metastable bulk water with crystallization excluded.","problem_ref":null,"references":"","settled_by":"Independent measurement of critical scaling or of a density discontinuity in bulk metastable water inside the region where ice forms rapidly, with crystallization excluded, consistent with the 2026 report.","status_note":"A 2026 ultrafast X-ray experiment (You et al., Science 2026, https://doi.org/10.1126/science.aec0018) reported a discontinuous-to-continuous liquid-liquid transition with critical divergence near $210 \\pm 8\\,\\mathrm{K}$, following a 2020 report of the transition under pressure; independent confirmation and an equilibrium measurement in bulk water are still lacking.","title":"Does real water have a liquid-liquid critical 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