A metastable system with a weakly stable state (1), an unstable transition state (2) and a strongly stable state (3)

Metastability is a general scientific concept which describes state of delicate equilibrium. 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. It is analogous to being balanced precisely at the top of a round hill, rather than safely at the bottom of a valley.

Almost any system can demonstrate metastability, but it is most prevalent in systems of weakly interacting particles in physics and chemistry. Physics (Greek Physis - φύσις in everyday terms is the Science of Matter and its motion. Chemistry (from Egyptian kēme (chem meaning "earth") is the Science concerned with the composition structure and properties Often, the weak interaction between particles is the only energy barrier that must be overcome for the system to reach a lower-energy state.

In phases of matter

Metastable phases of matter include those which are supercooled or superheated. In the Physical sciences a phase is a Set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties See Superheater for the device used in Steam engines In Physics, superheating (sometimes referred to as boiling retardation For example, 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.

In aggregate matter

Small avalanches demonstrate metastability at Mount Baker Ski Area. The Mount Baker Ski Area is a Ski resort located in Whatcom County Washington, United States.

Sandpiles are one system which can exhibit metastability if a steep slope or tunnel is present. In Physics, the Bak–Tang–Wiesenfeld sandpile model is the first discovered example of a Dynamical system displaying Self-organized criticality Sand grains form a pile thanks to friction. Sand is a naturally occurring Granular material composed of finely divided rock and Mineral particles Friction is the Force resisting the relative motion of two Surfaces in contact or a surface in contact with a fluid (e 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.

The avalanche is a well-known problem with large piles of snow and ice crystals on steep slopes. This article refers to the natural event For other uses see Avalanche (disambiguation An avalanche is an abrupt and rapid flow of snow often 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 or vibration.

In electronic circuits

Metastability in electronics is usually seen as a problem. Metastability in electronics is the ability of a non-equilibrium electronic state to persist for a long (and theoretically unlimited period of time (see Asynchronous circuit A changing circuit is supposed to "settle" into one of a small number of desired states, but if vulnerable to metastability, can get "stuck" in an undesirable state.

In computational neuroscience

Metastability in the brain is a phenomenon which is being studied in computational neuroscience to elucidate how the human mind recognizes patterns. In the field of Computational neuroscience, the theory of metastability refers to the human brain’s ability to integrate several functional parts and to produce Computational neuroscience is an interdisciplinary science that links the diverse fields of Neuroscience, Cognitive science, Electrical engineering, The term "metastability" here is used rather loosely. There is no "lower energy" state, but there are semi-transient signals in the brain which persist for a while and are different than the usual equilibrium state.

In chemical systems

A metastable system with a weakly stable state (1), an unstable transition state (2) and a strongly stable state (3)

In chemistry, a system of atoms or molecules involving a change in phase of matter, crystal structure, or chemical bond can be in a metastable state, which lasts for a relatively long period of time. In the Physical sciences a phase is a Set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties In Mineralogy and Crystallography, a crystal structure is a unique arrangement of Atoms in a Crystal. A chemical bond is the physical process responsible for the attractive interactions between Atoms and Molecules and which confers stability to diatomic and polyatomic Molecular vibrations due to heat make chemical species at the energetic equivalent of the top of a round hill very short-lived. In Physics, heat, symbolized by Q, is Energy transferred from one body or system to another due to a difference in Temperature Metastable states that persist for many seconds (or years) are found in energetic valleys which are not the lowest possible valley (point 1 in illustration).

For example, diamond is a metastable form of carbon at standard temperature and pressure. In Mineralogy, diamond is the allotrope of carbon where the carbon atoms are arranged in In Physical sciences standard conditions for temperature and pressure are Standard sets of conditions for experimental measurements to allow comparisons to be made It can be converted to graphite (plus leftover kinetic energy), but only after overcoming an activation energy - an intervening hill. The Mineral graphite, as with Diamond and Fullerene, is one of the Allotropes of carbon. In Chemistry, activation energy, also called midnight energy, is a term introduced in 1889 by the Swedish scientist Svante Arrhenius, that is defined Martensite is a metastable phase used to control the hardness of most steel. Steel 035 water quenchedpng|thumb|200px|035%C Steel water-quenched from 870°C]] Martensite, named after the German metallurgist Adolf Martens (1850–1914 The bonds between the building blocks of polymers such as DNA, RNA and proteins are also metastable. A polymer is a large Molecule ( Macromolecule) composed of repeating Structural units typically connected by Covalent Chemical bonds Deoxyribonucleic acid ( DNA) is a Nucleic acid that contains the genetic instructions used in the development and functioning of all known Ribonucleic acid ( RNA) is a Nucleic acid that consists of a long chain of Nucleotide units Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl

Being "stuck" in a thermodynamic trough without being at the lowest energy state is known as being "kinetically persistent". The particular "motion" or "kinetics" of the atoms involved has resulted in getting "stuck", despite there being preferable (lower-energy) alternatives. Chemical kinetics, also known as reaction kinetics is the study of rates of chemical processes

The stability or metastability of a given molecule depends in part on its environment, including temperature, pressure, and the presence of catalysts or seed crystals (in the case of a solid state system). Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature Pressure (symbol 'p' is the force per unit Area applied to an object in a direction perpendicular to the surface Catalysis is the process in which the rate of a Chemical reaction is increased by means of a Chemical substance known as a catalyst A seed crystal is a small piece of Single crystal material from which a large Crystal of the same material typically is to be grown Solid-state chemistry is the study of the synthesis structure and physical properties of solid materials The presence of a liquid layer can help facilities transitions between crystal states. The difference between producing a stable vs. metastable entity can have important consequences. For instances, having the wrong crystal polymorph can result in failure of a drug while in storage between manufacture and administration. Polymorphism in Materials science is the ability of a solid material to exist in more than one form or Crystal structure ^[1]

Reaction intermediates are very short-lived, and are actually thermodynamically unstable rather than "metastable". A reaction intermediate or an intermediate is a Molecular entity that is formed from the reactants (or preceding intermediates and reacts further to give the directly The IUPAC recommends referring to these as "transient" rather than "metastable". The International Union of Pure and Applied Chemistry ( IUPAC) (aɪjuːpæk or ay-yoo-pec) is an international Non-governmental organization ^[2]

Non-equilibrium thermodynamics includes the study of chemical systems which are in unstable states. Non-equilibrium thermodynamics is a branch of Thermodynamics concerned with studying Time -dependent Thermodynamic systems irreversible transformations

Metastability is also used to refer to specific situations in mass spectrometry^[3] and spectrochemistry^[4].

See also: Chemical stability

See also: Chemical equilibrium#Metastable_mixtures

In nuclear physics

An atomic nucleus can achieve a number of different energetic states, known as nuclear isomers. Chemical stability when used in the technical sense in Chemistry, means thermodynamic stability of a chemical system In a Chemical process, chemical equilibrium is the state in which the chemical activities or Concentrations of the reactants and products have no net change The nucleus of an Atom is the very dense region consisting of Nucleons ( Protons and Neutrons, at the center of an atom A nuclear isomer is a Metastable state of an Atomic nucleus caused by the excitation of one or more of its Nucleons A nuclear isomer occupies Some of these states are metastable, meaning that there can be relatively long-lived nuclei of the same isotope in different energetic states. Isotopes (Greek isos = "equal" tópos = "site place" are any of the different types of atoms ( Nuclides

Further information: Nuclear isomer#Metastable_isomers

See also

• Metastasis (Xenakis composition), a musical composition
• Hysteresis

References