The basic notion of the stargate concept is to have at least two mechanical devices (stargates) in two distant positions, such that, when active, the rings of each become similar to a physical, singular gateway or door-frame between the two locations. The concept was developed by the writers of the feature film Stargate, Dean Devlin and Roland Emmerich. Similar devices had been seen in previous fiction, but their complete conception as seen in the film was quite original — though there has been contention as to whether they plagiarized the idea from a previous script submission.[5]
The idea of a "portal" for travelers has been seen often throughout the history of both fantasy and science fiction, often taking a similar form, a device or magical object shaped as a regular or irregular closed geometric form filled with a water-like, rippling puddle that represents the boundary point between the two locations. The stargate picks up heavily on this conception, emphasizing the "watery puddle" for the sake of an alien mystique.
Much of the inspiration for the functioning of the device is drawn heavily from theoretical astrophysics, particularly that of black holes and wormholes, a staple of science fiction, often used to create "shortcuts" through space. Although these may exist in reality, it is not widely held to be true that any such phenomenon could safely transport a human being,[6] as such wormholes would most likely be created by excessive gravity (e.g. from a black hole) which would destroy any potential traveler.[7] In Stargate however, this is circumverted by transporting a traveller through as an energy signature, and reintegrating him at the other end.
Surrounding plot
The Stargate film begins in 1928, when the titular alien device is first discovered and unearthed at Giza, with a young Catherine Langford watching as her father, the archaeologist who found it, directs its unearthing. Stargate SG-1 has since revealed more of the backstory of the Earth Stargate. The American ship Achilles brought the gate to America in 1939 to prevent it from falling into the hands of the Nazis.[8] The United States Air Force then stored the device in various locations —including Washington, DC (Episode 1969)—before installing it at its location of the film and series. The Stargate was studied in the 1940s as a potential weapon and was later mothballed,[9] As the Stargate film quickly skips to the "present day" (1994), an unsuccessful archaeologist Daniel Jackson is giving a lecture about his outlandish theories that the Great Pyramid of Giza was not built by the pharaoh Khufu. After he is laughed away, an aged Catherine Langford meets with him, and recruits his egyptological talent, taking him to a top-secret military base at Creek Mountain, where he is instructed to decipher the unique Egyptian hieroglyphs present on a set of cover-stones. He realizes that the indecipherable glyphs are in fact not words but images of constellations, such that by identifying 6 of them a position in space can be extrapolated. He is then shown the stargate itself, uses his new understanding to identify the 7th symbol (the point of origin allowing a route to be extrapolated), and the gate is opened for the first time.
Because thousands of combinations had been previously tried and had failed, it was believed at the time that only two stargates existed, connecting Earth and the planet Abydos, which was visited in the film. At the beginning of the Stargate SG-1 series, however, a large set of additional valid coordinates were discovered engraved in ruins on Abydos. Because the coordinates pick out stars, and because time leads to stellar drift, other addresses were impossible to dial until Samantha Carter reworked the dialing system on Earth to account for this movement. After this, a massive network of possible connections suddenly became available. Even more addresses were later uncovered by Colonel Jack O'Neill from a repository of Ancient knowledge.
The alien race encountered in the original movie is later developed in SG-1 as the Goa'uld, the dominant evil power in the Milky Way. The leaders of this race, the System Lords, pose as gods and use the stargates to transport slaves between worlds. This has resulted in a large number of planets throughout the galaxy sporting human life, often in civilizations more primitive than Earth. The majority of these civilizations, descended from former Goa'uld slaves, treat the stargate as a religious relic, often as a source of long-forgotten fear and evil.
For most of the run of Stargate SG-1, Earth was under constant threat from the Goa'uld, and is no match for their superior technology. In the face of this threat, the US Air Force established a top-secret base, the SGC (Stargate Command), as a frontline defence. Multiple teams are formed and sent on missions through the stargate, their primary objective being exploration, and through it the discovery of intelligence, technology and allies to help the fight against the Goa'uld. The primary team is called SG-1, and the series follows their adventures.
For a long time it was thought that the Goa'uld were the builders of the Stargate Network, but it was later discovered that they had merely made use of the relics left behind by a different and extinct race, the Ancients. At the climax of SG-1's 6th season, Daniel Jackson discovers that the Earth myth of Atlantis is in fact founded upon the Lost City of the Ancients, and Season 7 is spent trying to locate it. At the beginning of the show Stargate Atlantis, which coincides with the beginning of SG-1's 8th season, the city is found in the Pegasus Galaxy, and 8 chevrons are dialed to send an expedition there on what could be a one-way trip. It is there that they discover a new network of stargates, and are plagued by the nemesis of the Ancients, the Wraith. During the events of The Ark of Truth it is revealed that the pre-ascended Ancient known as Amelius originated the concept of the Stargate and wormhole travel.
Internal names
The Ancients call the Stargates the "Astria Porta".[10] The Goa'uld and the Jaffa refer to it as the "Chappa'ai" (Cha-Pa-Eye), a term also used by the human inhabitants of many worlds such as Abydos.[1] The Wraith and some Pegasus human civilizations call Stargates "Portals".[11][12] Stargates have also been referred to as the "Ring of the Gods",[13] "Circle of Standing Water",[14] "Doorway", "Stone Ring", "Gateway",[15] "Annulus",[16] "Ring of the Ancestors",[17] "Wraith Well",[18] "Circle of Darkness" (particularly by primitive societies that fear or revere the device),[19] and even (in a deliberate self-parody) as "The Old Orifice".[20]
Operation
The film Stargate rushed very quickly over how a stargate actually works and is operated, but the subsequent television shows go into this area in a great amount of detail. In SG-1, it is explained that a stargate's destination is not fixed, but is singled out by a process known as "dialing".[1] Once a destination is selected by the traveler, the stargate generates a wormhole between itself and a complementary device at the destination, by being supplied with a threshold amount of raw energy.[21] Objects in transit between gates are broken down into their individual elemental components, and then into energy as they pass through the event horizon, and then travel through a wormhole before being reconstructed on the other side.[22]
Dialing
Each location served by a stargate has its own unique "address", which is a combination of seven or more non-repeating symbols appearing on the dialing stargate.[23][1] By "dialing" these symbols in the correct order, the traveler selects a destination.
The show is consistent with the mechanics of address-dialing. The process involves associating a unique symbol of the inner ring to each of at least the first seven of the chevrons on the outer circumference. The main "address" is invariably dialed first, and the last symbol is the "point of origin" " representing the gate being used, which acts as the final trigger for the completion of the address sequence.[24] As each symbol is dialed, the chevron is said to "engage" or "encode" and usually responds by lighting up or moving. When the final symbol of an address is dialed, that chevron is said to "lock" and the wormhole opens (this terminology is arbitrary and often interchangeable, but preferred by the recurring character Walter Harriman).[24] If the address is incorrect or does not correspond to an existing or otherwise functional stargate, the last chevron will not lock, and all of the chevrons will disengage.[21]
Addresses
The symbols used to comprise addresses are actually pictorial representations of star constellations. By identifying six constellations in space, a single point can be extrapolated that corresponds to the destination desired.[22] It is assumed by the show that this is enough to identify the position of any stargate within a galaxy. The symbols dialed are often referred to as "coordinates", and are written as an ordered string; for example, this is the address used in the show for the planet Abydos: 
(corresponding to the constellations of Taurus, Serpens Caput, Capricornus, Monoceros, Sagittarius and Orion). As explained by Dr. Daniel Jackson in the movie, the stargate requires seven correct symbols to connect to another stargate. As shown in the picture opposite, the first six symbols act as co-ordinates, creating three intersecting lines, the destination. The stargate uses the seventh symbol as the point of origin allowing one to plot a straight line course to the destination.
Eight-symbol addresses were introduced in "The Fifth Race", opening up new plot lines by connecting stargates to different galaxies. The additional symbol acts as a type of "area code".[4] Such connections, in comparison to seven symbol codes, required substantially more energy to complete a functional wormhole — much more than any standard dialing method can provide. Opening an intergalactic wormhole has been shown to require large amounts of power compared to a regular wormhole. This has been generated in a variety of ways in different episodes, although the main way is using a Zero Point Module (ZPM).[25][26][4][17]
The show has never featured a nine-symbol address, so the purpose of the ninth chevron is unknown. However, Robert C. Cooper has stated that the purpose of the ninth chevron will be revealed in the upcoming series, Stargate Universe.[27] One of the purposes proposed for the new series is that the ninth chevron connects it with an Ancient ship that seeds stargates throughout the universe, and was abandoned after the ancients ascended. It is unknown if this will be the final idea.[28] The extra chevrons are so rarely used that stargates are often seen with those two chevrons embedded within the stone platforms that hold many of the gates upright (see the image at the top of this article). This has often led to the misconception that a stargate only has seven chevrons.
Dial-Home Device {DHD}
There are a handful of methods used in the shows to dial a stargate, and the most common is with the use of a Dial-Home Device. Almost always referred to as the "DHD" for short, it is depicted as a pedestal-shaped device with a round inclined control panel on top, consisting of two concentric circles of "keys", and a translucent red (Milky Way) or blue (Pegasus) hemisphere in the center; the keys represent the symbols on the rim of the stargate. By pressing these keys a traveler builds an address. The central hemisphere serves as an "E as acivate the stargate once a destination has been dialed.
In the Milky Way, the Dial-Home-Device contains 38 of the 39 symbols on the stargate, meaning there is always a missing glyph on each DHD. This missing glyph however is not the point of origin for that planet. It has been confirmed that the missing glyph on numerous DHDs differs on each planet because of that planet's stargate position in the galaxy. In other words, it acts as a default setting to prevent bad connections to obstructed stargates in the Milky Way. The glyph that is hidden under the pedestal of the stargate, unseen along with the extra two chevrons, cannot be dialed by that stargate's DHD. This states that only certain addresses can be reached in certain positions in the galaxy. The only way to intervene and reach all destinations in the Milky Way is to manually dial the gate, or use an alternative dialer, such as the one at the SGC. [29]
The Atlantis DHD is more similar to the Earth's dialing computer than an actual DHD, and looks more like a set of crystal panels. It can block out certain gate addresses.[30] The Atlantis DHD also has an extra control-crystal allowing the dialing of an eighth chevron during the dialing sequence and is the only DHD in the Pegasus Galaxy capable of dialing Earth.[31] A similar DHD is also used on Puddle Jumpers, where the set of used glyphs corresponds to the galaxy of the Puddle Jumper. The Wraith also travel through Stargates in small spacecraft called darts and have some means of remote-dialing them in a manner similar to Ancient ships.[32] According to Dr. Zelenka, dialing an address leaves a small imprint on the control crystals of the DHD, and about fifty addresses can be recovered from a DHD using the proper equipment. However, this gives no indication of the order in which the addresses were dialed, and no guarantee can be made as to the accuracy of the recovered addresses.[32]
The show makes it clear that every stargate originally had its own DHD, located directly in front of the gate and facing it.[21] Over time, however, some DHDs have been damaged or lost. This has been the source of plot-difficulties for the protagonists on several occasions, as it is still possible to travel to a stargate that lacks a DHD, meaning that dialing home again will be much more difficult, if not impossible. One of the primary functions of the MALP that precedes an SG team is to confirm the presence of a DHD.[21] In the absence of a DHD, a user must manually select the address through sheer force and an external power-source.[21] Pegasus Galaxy Stargates do not have a movable ring, so manually dialing these is impossible. Travelers can also emulate a DHD through a Dialing Computer like Stargate Command has. Remote dialers have been used by several races like the Goa'uld and Asgard in various episodes.
[edit] The Wormhole
Once an address is dialed, the gate is said to have created a "stable wormhole" between itself and the gate dialed. The creation process is depicted with great consistency, and hence has become one of the defining motifs of Stargate, at times being central in both the SG-1 and Atlantis title sequences. It involves the generation of the "puddle of water" portal which lasts roughly 2 seconds, and is completed by the ejection of an unstable energy vortex resembling a surge of water or quicksilver. The vortex is portrayed as a symbol of the stargate's power, invariably causing characters to be awed.[33] Any matter which comes into contact with the vortex is annihilated on a molecular level, as is dramatically demonstrated by a pair of smoking shoes in the episode "Prisoners".[34] This aspect has been used in some cases to dispose of highly hazardous materials.
The actual portal of a stargate appears inside the inner ring when an address is correctly dialed. This has the appearance of a horizontal puddle of water which represents the "event horizon" in the show. In non-fictional parlance, an event horizon is the perimeter around a black hole or wormhole through which once one had crossed, the gravitational pull of the singularity would be too strong to overcome. The wavering undulations characteristic of water are supposed to represent the "fluctuations in the event horizon".[1] This puddle may then be entered (usually accompanied by a water-like sound), and the traveler will emerge from a similar pool at the destination stargate. The show makes it clear that transit is strictly one-way; an attempt to travel "backwards" causes the traveler to be destroyed[35] (though during the episode "New Ground" and in the first episode a man partially puts his hand through the event horizon of the destination gate and pulls it back with no apparent issues[36] However, as matter is only transmitted through a stargate once the whole object has passed the event horizon (except in the same "A Hundred Days" episode where Teal'c dangled from a rope secured to a ceiling on the other side) the stargate would not have started to try to deconstruct him, instead waiting until he was entirely inside). Additionally, the outgoing gate is invariably entered from the same side as the unstable vortex present during stabilization of the wormhole.
Passage through a Stargate's wormhole is depicted as a visual effect of shooting through a tunnel in space, although this is just a visual aid as travelers are not conscious during the trip. The average travel time between Stargates is 6 seconds. In the movie and early SG-1 episodes, travelers exit from the Stargate "frozen stiff" and feeling as though they have been on a "rollar coaster ride". The character Charles Kawalsky describes Stargate travel as like pulling "out of a simulated bombing run in an F-16 at eight-plus g".[1] In later episodes the experience is no different than stepping through a door,[37]explained as a result of refinements made in the Stargate interface at the SGC.
Under normal circumstances, a wormhole can only be maintained for slightly more than 38 minutes.[38] Extending the wormhole duration beyond this requires tremendous amounts of power, such as that provided by a nearby black hole,[39][40], energy beings,[41] or advanced technologies.[3][42]
While the kawoosh effect in the movie was created by filming the actual swirl of water in a glass tube, and looked like a vortex on the back of the Gate,[43] however on the TV series, this effect was completely created in CG by the Canadian visual effects company Rainmaker.[44] At the beginning of Season 9, the original movie wormhole sequence was substituted by a new sequence similar to the one already used on Stargate Atlantis, but being blue as it was in the movie and SG-1, whereas in Atlantis it's green.[45
