Asked by: Edward Seymour, Hove
There are now as many as eight: the number creeps up as science advances. Schoolkids are taught about three physical states: solid, liquid and gas. A fourth is hot, charged gas (plasma), which consists of positively charged ions and free electrons.
In 1995, scientists created a new state called ‘Bose-Einstein condensate’ by cooling gas to within a few degrees of absolute zero (-273°C), at which point molecular motion almost stops and the atoms behave en masse like a single atom. Earlier this year, researchers reported another new state for certain metals, where atoms exist as both solid and liquid at the same time.
Two other states are space-related: ‘quark-gluon plasma’, which made up the Universe up to a few milliseconds after the Big Bang, and ‘degenerate matter’, a highly compressed state that’s found in stars.