"One of the audio sources Lipsett sampled for 21-87 [a film that had a great influence on Lucas] was a conversation between artificial intelligence pioneer Warren S. McCulloch and Roman Kroitor , a cinematographer who went on to develop IMAX. In the face of McCulloch's arguments that living beings are nothing but highly complex machines, Kroitor insists that there is something more: 'Many people feel that in the contemplation of nature and in communication with other living things, they become aware of some kind of force, or something, behind this apparent mask which we see in front of us, and they call it God.'"
"When asked if this was the source of "the Force," Lucas confirms that his use of the term in Star Wars was 'an echo of that phrase in 21-87.'" .
The Force has a "dark side", which feeds off emotions such as anger and fear, whereas the Jedi use the Force only for peaceful purposes. The series' villains, the Sith, embrace the dark side in order to seize power. The Jedi's compassionate and selfless use of the Force has come to be known by inference as "the light side", although that term is not used in the films.
The prequels introduced the idea of midi-chlorians, microscopic organisms that reside in living cells and communicate with the Force. A being's potential to use the Force is correlated with the number of these organisms residing in its blood.
Midi-chlorians (also spelled "midi-clorians" or "midichlorians") are a microorganism in the fictional Star Wars galaxy, first mentioned in Star Wars Episode I: The Phantom Menace. They are microscopic life-forms that reside within the cells of all living things and communicate with the Force. Midi-chlorians compose a collective consciousness and intelligence, forming links between everything living and the Force. They are symbionts with all other living things; that is, without them, life could not exist. The Jedi have learned how to listen to and coordinate the midi-chlorians. In order to be a Jedi or a Sith, one must have a high enough concentration of midi-chlorians in one's cells.
The word "midi-chlorian" appears to be a portmanteau of "mitochondrion" and "chloroplast", two organelles found in real cells and thought to have evolved from bacteria as endosymbionts inside other cells, as purported in the endosymbiotic theory. Creator George Lucas has indeed stated that the midi-chlorians are based on the endosymbiotic theory (Rolling Stone, June 2005), and it appears that in the story of Anakin Skywalker, he wanted to create a more modern "virgin birth" in the Star Wars saga that was as much based in "science" (albeit fictional) as in philosophy and religion, with the mythic "givers of life" being microscopic life-forms, rather than gods.
An ancient prophecy foretold the appearance of a chosen one imbued with a high concentration of midi-chlorians, strong with the Force, and destined to alter it forever. Anakin Skywalker was believed by many to be the chosen one. He had the highest concentration of midi-chlorians the Jedi Council had ever seen. He was possibly conceived by the midi-chlorians; Anakin was born without the assistance of a male. Lucas has said in interviews that Luke Skywalker had the same total midi-chlorian count that Anakin did at birth, though this does not necessarily make him the chosen one because Anakin did exactly what the prophecy foretold by coming back from the Dark Side and destroying Emperor Palpatine.
In Star Wars Episode III: Revenge of the Sith, Palpatine states that a Sith Lord, Darth Plagueis, had the ability to use the Dark Side to influence midi-chlorians to create life and to prevent people from dying.
The Force can enhance natural physical and mental natural abilities, including enhancing strength (such as during a 'Force jump' or to slow a fall from an otherwise dangerous height) and accuracy (as when Luke Skywalker (Mark Hamill) was able to launch proton torpedoes into a small thermal exhaust port on the Death Star in A New Hope). Within the film series, a number of other force powers are demonstrated, those include but are not limited to telekinesis, telepathy, enhanced empathy and precognition. The Jedi were also able to influence and control the minds of others by making use of the Jedi mind trick. The Sith can sometimes use the Force to create harmful energy to attack others. Darth Sidious, 'the Emperor' is able to conjure a lightning-like attack using the force.
The term 'Force power' originated in the Star Wars Roleplaying Game, by West End Games. Later, it was used in Jedi Knight: Dark Forces II, where they could be gained via a system of Force 'points'. The names are often preceded by Force.... For example, Grip is mostly known as Force Grip.
Within the Star Wars expanded universe, a number of other powers have been demonstrated, those include the ability to heal or drain the life-force of others, increase resistance to attack, dissipate energy attacks and warp space.
When the planet Alderaan is destroyed in A New Hope, Obi-Wan senses "a great disturbance in the Force, as if millions of voices cried out in terror and were suddenly silenced". In Star Wars Episode V: The Empire Strikes Back, Palpatine (Clive Revill in the original version, Ian McDiarmid in the special edition) tells Darth Vader (David Prowse and James Earl Jones) that he has felt a disturbance in the Force upon realizing that Luke Skywalker poses a threat to him. In Star Wars Episode II: Attack of the Clones, Yoda (Frank Oz) feels a disturbance in the Force when Anakin, enraged by his mother's death, slaughters a tribe of Tusken Raiders.
Yoda is seen to be visibly disturbed after the deaths of many Jedi during the Great Jedi Purge in Star Wars Episode III: Revenge of the Sith. He falls to his knees and grasps his chest, as if in pain himself. This shows the interconnected nature of the force, especially its bond with the Jedi that were killed. In episode IV, Darth Vader was able to sense Obi-Wan through his interactions with the force, and in episode VI, Vader and Luke Skywalker were able to sense each other.
Force-sensitivity is a condition in the fictional Star Wars universe where a life form possesses a natural connection to the Force. Though the Force flows through all life, with only rare exceptions (such as the Yuuzhan Vong), outright sensitivity to it is a more uncommon trait. Force-sensitivity is a trait established at birth, and is revealed in Star Wars Episode I: The Phantom Menace to be the product of midichlorians, microscopic beings that exist symbiotically with other life forms, and allow the Force to flow through their hosts. There also appear to be varying levels of Force-sensitivity, or "Force potential". This could range from a relatively modest level (such as Tionne, one of Luke Skywalker's first Jedi students), to very high levels (such as Yoda and Darth Sidious) to exceptionally rare beings of astronomical power (such as Darth Nihilus, Anakin Skywalker, Luke Skywalker, and perhaps the Solo children).
Force-sensitivity is partly genetic, as the children of Anakin Skywalker both have high force-sensitivity themselves. It is also 'the will of the force', as in the case of Anakin Skywalker himself. While potential for force-sensitivity is established at birth, awareness, experience and training are necessary to harness the power of the force. Yoda implies that this training is most effective in childhood.
The first appearance of a force ghost is in the film The Empire Strikes Back, although Obi-Wan's voice is heard after death in _A_New_Hope. In the Return of The Jedi, the ghosts of Yoda and Anakin Skywalker are also seen. While the first two are seen to vanish upon death, it is unclear if Vader's body actually vanishes as he dies. It certainly does not disappear or dissolve onscreen (unlike those of Yoda or Obi-Wan Kenobi the other two Jedi to die in the original trilogy) and Luke Skywalker is later seen burning Vader's armor. There is no indication onscreen whether this armour still contains the Dark Lord's body or not.
Questions arose after the release of The Phantom Menace, when Qui-Gon Jinn's body did not vanish after his death fighting Darth Maul and, perhaps more importantly, none of the other characters expected it to. Qui-Gon's remains were burned on a Jedi funeral pyre on Naboo. In the film's DVD commentary Lucas indicated that this apparent discontinuity was a plot point that would be returned to .
In Revenge of the Sith it is made known that the ability to return as a Force Spirit is not in fact something which happens to every Jedi, but a recently discovered and complex discipline. The late Qui-Gon Jinn is said to have discovered "..the path to immortality", the secret of how to retain his identity after death and absorption into the Force, a process which requires the attaining of a state of unconditional compassion. It is also stated that his spirit will instruct Yoda and Obi-Wan in this discipline during their exiles. This scene sets up the ability both characters demonstrate in later episodes.
George Lucas has since indicated (on the Episode III DVD commentary) that the appearance of Vader's former self, Anakin Skywalker, as a Force Spirit at the end of Episode VI is due to combination of Anakin's own latent Force ability, his achievement of a moment of unconditional compassion at his death and redemption and Yoda and Obi-Wan's spirits helping him extend his identity out of The Force.