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A system is in a metastable state when it is in equilibrium (not changing with time) but is susceptible to fall into lower-energy states with only slight interaction.
See also metastability.
Metastable Systems[edit]
Almost any system can demonstrate metastability, but it is most prevalent in systems of weakly interacting particles. Often, the weak interaction between particles is the only energy barrier that must be overcome to reach a lower-energy state.
Some common examples of metastable states are:
- Supercooling. Here, molecules of water are the particles, and the Van der Waals force is the weak interaction between them. Supercooled water can exist in liquid form at temperatures below freezing, and will remain there until external interaction (vibration or introduction of a seed particle) causes the water to crystallize.
- Sandpiles. Here, sand grains are the particles, and they interact via Friction. It is possible for an entire large sand pile to reach a point where it is stable, but the addition of a single grain causes large parts of it to collapse. This is similar to...
- Avalanches. Here, snow and ice crystals are the particles, and in dry conditions snow slopes act similar to sandpiles. An entire mountainside of snow can suddenly slide due to the presence of a skier, or even a loud noise (vibration).
Behaviors of Metastable Systems[edit]
Systems prone to metastable states tend to exhibit power law behavior when measured over time. This is because the interactions are scale invariant. For instance, adding a single grain to a sandpile can result in anything from a small local disturbance (common) to the collapse of almost the entire pile (rare). The distribution of these effects follows a power law distribution.