Prakriti means matter or nature. It is derived from the etymology pra+kriti, pra means to issue forth and kriti means to create or act. Therefore prakriti is the source from which all created thing have arisen. It is due to this productive quality of prakriti that prakriti is seen as a feminine principle and deified in Hinduism as the divine mother ([wiki]shakti[/wiki]). Although the concept of Prakriti has Vedic origins, the yogic theory of prakriti is developed by the formal Samkhya school of Hindu philosophy.
Prakriti is constituted of the three [wiki]gunas[/wiki] which are described as infra-atomic strand like constituents which undergo vibrations(similar to the modern notion of quantum strings in string theory). They are are the inherent drives within matter which causes its motion, activity and cause it to change and transform. The gunas are recognised to be three types based on their manifest effects physically and psychologically: [I]sattva guna [/I]is the neutral state and is psychologically experienced as brilliance, stillness; [I]rajas guna [/I]is the active state and is psychologically experienced as passion and desire and [I]tamas guna[/I] is the inertial state and is psychologically experienced as stupour and lethargy. The gunas never act in isolation, but always in relation to one another to maintain a balance. All activity is said to be nothing more than the vibrations of the gunas.
Prakriti can exist in two states: unmanifest ([wiki]avyaktam[/wiki]) and manifest ([wiki]vyakta[/wiki]) In the unmanifest state the gunas are in a super-equilibrium. This equilibrium is then collapsed by [I]purusha[/I] the original and pure consciousness, through simply the act of observation(similar to the observer effect in quantum theory) causing the gunas to vibrate and causing matter to manifest and then expand outwards. When the the gunas begin to lose their momentum over time, the reverse occurrs and matter begins to contract inwards and returns to its unmanifest state. This is known as the cycle of evolution and involution.