States (or phases)
Matter commonly exists in four states (or phases): solid, liquid and gas, and plasma. However, advances in experimental techniques have revealed other previously theoretical phases, such as Bose–Einstein condensates and fermionic condensates. A focus on an elementary-particle view of matter also leads to new phases of matter, such as the quark–gluon plasma.
For much of the history of the natural sciences people have contemplated the exact nature of matter. The idea that matter was built of discrete building blocks, the so-called particulate theory of matter, was first put forward by the Greek philosophers Leucippus (~490 BC) and Democritus (~470–380 BC).
Albert Einstein showed that ultimately all matter is capable of being converted to energy (known as mass-energy equivalence) by the famous formula E = mc2, where E is the energy of a piece of matter of mass m, times c2 the speed of light squared.
As the speed of light is 299,792,458 metres per second (186,282 mi/s), a relatively small amount of matter may be converted to a large amount of energy. An example is that positrons and electrons (matter) may transform into photons (non-matter). However, although matter may be created or destroyed in such processes, neither the quantity of mass or energy change during the process.