Is the Universe a string-net liquid?

The first hint that a new type of matter may exist came in 1982. "Twenty five years ago we thought we understood everything about how matter changes phase," says Wen. "Then along came an experiment that opened up a whole new world."

In the experiment, electrons moving in the interface between two semiconductors behaved as though they were made up of particles with only a fraction of the electron's charge. This so-called fractional quantum hall effect (FQHE) suggested that electrons may not be elementary particles after all. However, it soon became clear that electrons under certain conditions can congregate in a way that gives them the illusion of having fractional charge - an explanation that earned Laughlin, Horst Störmer and Daniel Tsui the Nobel prize (New Scientist, 31 January 1998, p 36).

Wen suspected that the effect could be an example of a new type of matter. Different phases of matter are characterised by the way their atoms are organised. In a liquid, for instance, atoms are randomly distributed, whereas atoms in a solid are rigidly positioned in a lattice. FQHE systems are different. "If you take a snapshot of the position of electrons in an FQHE system they appear random and you think you have a liquid," says Wen. But step back, and you see that, unlike in a liquid, the electrons dance around each other in well-defined steps.