Matter

One contemporary view on matter takes it as all scientifically observable
entities whatsoever. Commonly, the definition is limited to such entities
explored by physics.

The definition pursued here is of matter as whatever the smallest, most
fundamental entities in physics seem to be. Thus matter can be seen as
material consisting of particles which are fermions and therefore obey the
Pauli exclusion principle, which states that no two fermions can be in the
same quantum state. Because of this principle, the particles which comprise
matter do not all end up in their lowest energy state, and hence it is
possible to create stable structures out of fermions. In addition, the Pauli
exclusion principle insures that two pieces of matter will not occupy the
same location at the same time, and therefore two pieces of matter in which
most energy states are filled will tend to collide with each other rather
than passing through each other as with energy fields such as light.

The matter that we observe most commonly takes the form of compounds,
polymers, alloys, or pure elements.

In response to different thermodynamic conditions such as temperature and
pressure, matter can exist in different "phases", the most familar of which
are solid, liquid, and gas. Others include plasma, superfluid, and
Bose-Einstein condensate. When matter changes from one phase to another, it
undergoes what is known as a phase transition, a phenonmenon studied in the
field of thermodynamics.