Does real water have a liquid-liquid critical point? · revision history

Revision 2

Accepted · core change · record

Changes against revision 1:

Title · changed
Revision 1: Does real water have a liquid-liquid critical point
Revision 2: Does real water have a liquid-liquid critical point?
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.
Precise · changed · core
Revision 1: 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.
Revision 2: Determine whether $\mathrm{H_2O}$ (and $\mathrm{D_2O}$) 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.
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.
Kind
well-posed
Answer type
yes-no
References
(empty)
Literature status
partially-resolved
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.
Posed since
1992

Decisions