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In the physical sciences, a state of matter is one of the many ways that matter can interact with itself to form a macroscopic, homogenous phase. The most familiar examples of states of matter are solids, liquids, gases, and plasmas; the most common state of matter in the visible universe is plasma. Less familiar phases include: quark-gluon plasma; Rydberg matter; Bose-Einstein condensates and fermionic condensates; quantum spin Hall state; degenerate matter; strange matter; superfluids and supersolids; and possibly string-net liquids.

Bose-Einstein condensate is a state of matter that occurs at extremely low temperatures, near absolute zero. These temperatures are too low to occur anywhere on Earth except in laboratory experiments. The very slow motion of molecules at these temperatures allow some of the more bizarre aspects of quantum mechanics to manifest themselves in the form of novel macroscopic properties.

Under extremely high pressure, ordinary matter undergoes a transition to a series of exotic states of matter collectively known as degenerate matter. These are of great interest to astrophysics, because these high-pressure conditions are believed to exist inside stars that have used up their nuclear fusion "fuel", such as white dwarves and neutron stars.

When in a normal solid state, the atoms of matter align themselves in a grid pattern, so that the spin of any electron is the opposite of the spin of all electrons touching it. But in a string-net liquid, atoms are arranged in some pattern which would require some electrons to have neighbors with the same spin. This gives rise to some curious properties, as well as supporting some unusual proposals about the fundamental conditions of the universe, itself.

One of the metastable states of strongly nonideal plasma is Rydberg matter which forms upon condensation of excited atoms.

Main article: List of states of matter

Physical organology (Physics-based musical instrument classification) is based on the state-of-matter (Classical Element) in which the instrument produces the initial sound.

State-of-matter has been used as a classification scheme for musical instruments. The first example of state-of-matter instrument classification was Schaeffner's 2-class Solid Instruments versus Gas (Wind) Instruments categorization scheme. Instruments are ordinarily classified by how the intial sound in the instrument is produced. In the state-of-matter classification, instruments are categorized based on the state-of-matter of the initial sound-producing element[1], as follows:

• Solid instruments, such as the piano in which sound is made by matter in its solid state;
• Water instruments, such as the hydraulophone in which sound is made by matter in its liquid state;
• Wind instruments, such as the flute in which sound is made by matter in its gaseous state;
• Plasma insruments, such as the plasmaphone or ionophone in which sound is made by matter in a higher-energy state such as plasma, quark-gluon plasma, or other higher energy state.

A fifth category, quintephones (from "quint", Latin for "fifth", and "phone", Greek for "sound"), is included for instruments such as computational sound synthesizers in which the initial sound production is synthetic rather than acoustic.

There are four broad categories of electro-acoustic transducers: geophone, hydrophone, microphone/loudspeaker, and ionophone:

• 2005-06-22, MIT News: MIT physicists create new form of matter Citat: "... They have become the first to create a new type of matter, a gas of atoms that shows high-temperature superfluidity."
• 2003-10-10, Science Daily: Metallic Phase For Bosons Implies New State Of Matter
• 2004-01-15, ScienceDaily: Probable Discovery Of A New, Supersolid, Phase Of Matter Citat: "...We apparently have observed, for the first time, a solid material with the characteristics of a superfluid...but because all its particles are in the identical quantum state, it remains a solid even though its component particles are continually flowing..."
• 2004-01-29, ScienceDaily: NIST/University Of Colorado Scientists Create New Form Of Matter: A Fermionic Condensate

• Phase (matter)
• Condensed matter physics
• Cooling curve
• Supercooling
• Superheating