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Matter is ordinarily observed in three different states, or phases (see states of matter), although scientists distinguish still two more states. Matter in the solid state has both a definite volume and a definite shape; matter in the liquid state has a definite volume but no definite shape, assuming the shape of whatever container it is placed in; matter in the gaseous state has neither a definite volume nor a definite shape and expands to fill any container. The properties of a plasma, or extremely hot, ionized gas, and of a Bose-Einstein condensate, which exists only at temperatures approximating absolute zero (-273.15°C), are sufficiently different from those of a gas at ordinary temperatures for scientists to consider them to be the fourth and fifth states of matter.
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