Material substance that constitutes the observable universe and, together with energy , forms the basis of all objective phenomena.
mass , inertia , and gravitation . Matter in bulk occurs in several states; the most familiar are the gaseous (see gas ), liquid , and solid states ( plasmas , glasses , and various others are less clearly defined), each with characteristic properties. According to Albert Einstein 's special theory of {{link=relativity">relativity , matter and energy are equivalent and interconvertible (see conservation law ).