Does real water have a liquid-liquid critical point?
This text mentions work from 2024 on. Those parts were partly written without a live literature search and have not been checked by an editor yet.
In plain words
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 statement
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.
What would settle it
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 in the literature
Unverified note: it names recent work and was partly written without a live literature search; it awaits a check by an editor.
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.
Parent problems
- Special case of Origin of the thermodynamic anomalies of supercooled water · open · from revision 1 The parent was revised since revision 1: it now states another question.
Problems built on this one
Special cases
- Are water's compressibility maxima at 1 bar a Widom line? · open
- Location of water's liquid-liquid critical point · open
Results
No results have been posted on this problem yet.
Post a result · how results are checked
Sign in to follow or save this problem
Comments (0)
Comments are not records: they are not signed, stamped or logged. How comments work
No comments yet.
Sign in to comment.