Water and the supercritical world

We all know how water works. When it's cold and hard we put it in drinks; a bit warmer and we can drink it; warmer still and the kettle whistles. Most of us understand how water changes between its solid, liquid and gas states as temperature changes. Or at least we understand it within the ranges of temperature (and pressure) we are used to.

But outside these limits weird stuff happens: there are sixteen different types of ice that form at various combinations of low temperatures and high pressures (fever-tree marketeers could make a fortune); there's a particular combination of temperature and pressure - the Triple Point of water - at which it's possible for ice, water and steam to exist at the same time; and there's another pressure/temperature combination - the Critical Point - beyond which it behaves as a liquid and a gas at the same time - a Supercritical Fluid.

Plenty of parallels exist. Whilst few people are capable of understanding how or why, most of us do know that Newtonian physics doesn't apply at very large or very small scales. As cool as these ideas have become, they don't affect our decision-making very much.

But the political, social, environmental and technological temperatures and pressures in our world are getting beyond the limits we're familiar with. These do affect our decisions and our, often subconscious, mental models of how things work are important.

When we find ourselves blusteringly arguing that water is incompressible (or similar); we should take a look at the thermometer and the barometer; and be prepared to examine our stock of universal truths.

See From big data to important information - by Yaneer Bar-Yam - that inspired this post. Interestingly the branch of mathematics initially used by physicists to understand complex behaviours at extremes of scale (Renormalisation Group) is also being applied to biological and social systems.