= Condensed matter
<Condensed matter> comprises physical systems such as <solids> and <liquids> in which interactions among many constituents determine the observed properties. The term refers to the material system; <condensed matter physics> studies its structure, dynamics and phases.
A <crystal> illustrates the change of viewpoint. Its <chemical atoms> can have collective vibrational modes described as <phonons>, while its electronic response can involve <energy bands> rather than isolated-atom <energy levels>. <Collective excitations> and <phase transitions> show why a many-constituent system can display useful organizing principles that are not apparent from one atom alone.
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