Water might secretly be a mix of 2 different liquids, scientists say For decades, scientists suspected water secretly behaves like two different liquids. A new AI-powered study has finally caught it happening at the molecular level. For years, scientists have suspected that, at the molecular level, water is two different liquids — a denser one and a less-dense one — that are constantly switching places. Catching real molecular evidence of this microscopic transformation has been hard. But now, with help from artificial intelligence, researchers say they've finally found it. "It's hard to imagine — here is just one water, right?" said Xiao Cheng Zeng, a physical chemist at the City University of Hong Kong and co-author of the new study, told Live Science while holding a water bottle in the air. That puzzle sent him digging through scientific literature, where he found the possible explanation: the two-state hypothesis. "That got my attention. We have literature to talk about it but no evidence." The findings, published June 4 in the journal Nature Physics, could not only prove this long-sought molecular change is real, but also help to explain dozens of water's weird behaviors. Most liquids become denser as they cool, but water behaves differently; it becomes denser until about 4 degrees Celsius, then starts to expand, which is why ice floats. Water also resists temperature changes better than similar liquids and has a viscosity that decreases under certain pressures. Scientists have documented various anomalies related to water and suspect they may be interconnected. The two-state model is an attempt to be that unifying explanation. A 30-year hunch Zeng has been studying water since his postdoc days in the late 1990s, when he worked on liquid freezing. The two-state hypothesis itself came onto his radar later — around 2006, when he first