June 09, 2020
A phase transition describes a transition between different states of matter.
You may remember this from high school chemistry. As temperature increases, ice melts to water, which eventually boils to steam. As temperature decreases, steam condenses to water, which freezes to ice. The states, which are slightly different from phases, are solid, liquid, gas. In this case, the transitions are mediated by temperature.
A phase transition is just the boiling point, or the melting/freezing point, at which the two neighbouring states of matter are equally liking to exist. So precisely at the boiling point for water, an individual water molecule is equally likely to exist as liquid water, or as gaseous steam.
Elements have different melting points. Those whose melting point is below the temperatures we encounter in daily life we think of as a gas (oxygen) or liquid (mercury), while those whose melting point is above typical Earth temperatures we typically think of as a solid (iron).
Why am I writing about something you may feel that you had justifiably forgotten the minute after your final chemistry class?
It’s because I think that much, much more can be explained by phase transitions. I’ll say it now: I think that everything interesting happens around a phase transition. What is stable acts as a filter on reality.
Complexity theory observes that interesting, often life like behaviour occurs even in inanimate matter at phase transitions (also called “critical points”). A famous illustration of this is the Ising model; see this video for an illustration of what this behaviour looks like in iron atoms.
But first, I’ll write about order and disorder.