metastable

Metastable describes a state of a system that is not the most stable configuration but can persist for a long time because it sits in a local minimum separated by an energy barrier from more stable states. It is distinct from equilibrium in the sense that, given sufficient time or perturbation, the system will relax to a more stable state.

In chemistry and physics, metastability refers to local but not global minima of a potential energy landscape. Diamond is metastable at room temperature and pressure: graphite is thermodynamically more stable, but diamonds can persist for long periods. Supercooled liquids and supersaturated solutions are other classic examples: they remain liquid or supersaturated despite conditions that would ordinarily trigger a phase change. Metastable crystal forms can be produced and stored temporarily, and certain alloys contain metastable phases such as martensite, which can transform under heat or stress.

In cosmology and particle physics, metastable states can occur as false vacua in quantum fields; decay proceeds via tunneling or thermal fluctuations, with a lifetime that can be exceedingly long or short depending on the energy barrier.

In electronics, metastability describes a state in a digital circuit where a component briefly settles in an indeterminate voltage level, often due to timing violations. Systems are designed with synchronization stages to reduce the chance of metastable outputs.

Metastability is a key concept across disciplines, linked to energy landscapes, kinetic barriers, and the practical impact of long-lived nonoptimal states on material properties, reactions, and device behavior.