星門(Stargate)

Conceptual origin

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. This is achieved by the creation of a stable wormhole between the gates.


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.
The developers of the concept have also made some attempt to explain how Stargates work in terms of soft science fiction. Their explanations are based heavily in theoretical astrophysics, particularly that of black holes and wormholes. A wormhole is held to be a warping of spacetime that causes space to become "folded", supposedly allowing for "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, as such wormholes would most likely be created by excessive gravity (e.g. from a black hole) which would destroy any potential traveler.
The means by which the gates operate as described by the series is fairly coherent; there are perhaps three major reasons why the Stargate deserves the label of soft science fiction:-
1) Although the gates are described as "giant superconductors," no explanation is given of the extradimensional medium through which the electrical current would have to move. 2)Naquadah, the material from which the Stargate is made, is fictional. 3) Wormhole theory is exactly that, and many of the specifics (such as the specific material required to hold a wormhole open at each end) have not been resolved.

Operation

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.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 chevron on the outer circumference. The main "address" is invariably dialed first, and the last symbol being the "point of origin" " representing the gate being used, which acts as the final trigger for the completion of the address sequence. As each symbol is dialed, the chevron is said to "engage" 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). 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.

Addresses

The symbols used to comprise addresses are actually images of constellations. By identifying six constellations in space, a single point can be extrapolated that corresponds to the destination desired. 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 you 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". 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).
The show has never featured a nine-symbol address, so the purpose of the ninth chevron is unknown (fan theories inlcude other galaxy clusters, time travel, alternate timelines, and completely alternate universes). However Robert C. Cooper has stated that the purpose of the ninth chevron will be revealed in the upcoming series, Stargate Universe. 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 gate 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

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 "Enter" key to activate 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 the planet. It has been confirmed that the missing glyph on numerous DHDs differs based on how each stargate is positioned on different planets. The glyph that is hidden under the pedestal of the stargate, unseen along with the two chevrons, cannot be dialed by the DHD. This states that only certain addresses can be reached in certain positions in the galaxy as a safety mechanism. In one episode of the SG-1 show, the team, because they did not have a DHD on the Stargate on Earth, overrode the mechanism, passing through the center of the star almost destroying that system. The mechanism in this case, was only activated temporarily because the star's orbit would have intersected the Stargate for a short period of time. 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.The show makes it clear that every Stargate originally had its own DHD, located directly in front of the gate and facing it. 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 functioning DHD.

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 called the "kawoosh" (since Crusade),resembling a surge of water or quicksilver. The "kawoosh" is portrayed as a symbol of the Stargate's power, invariably causing characters to be awed, reflecting or imbuing the awe of the audience, and any matter contacted by the "kawoosh" effect is destroyed, save for the inevitable smoking shoes. Power for the wormhole can be drawn from both the point of origin (the dialing Stargate's power source) and the destination. One of the most basic and repeated axioms of Wormhole Physics, the (fictionalized) field of study pioneered by the character Samantha Carter, is that unless an extraordinary amount of energy is being generated at either end, a wormhole can only be maintained for 38 minutes at a time.
The actual portal of a Stargate appears inside the inner ring when an address is correctly dialed. This has the appearance of a vertical 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". 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(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 issuesHowever, 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 gate's "kawoosh"; the show has not demonstrated what happens if a traveler enters from the wrong side.

Passage through a Stargate is usually accompanied by a visual effect of shooting through a tunnel in space, though it is just meant to be a visual aid. The representation of the transit is sometimes almost instantaneous, and other times it appears to last up to 20 seconds. This is thought to be just a representation of how it might look. Since they are disintegrated, it would be impossible to truly see the inside of a wormhole or travel through it. The actual time the travel takes on average 6 seconds. Novice travelers often emerge from the gate trembling as if they've been on a "roller coaster ride", and although later often omitted, they are covered in ice crystals from the reintegration. The character Charles Kawalsky compares Stargate travel to pulling "out of a simulated bombing run in an F-16 at eight plus g" because of the energy going through the wormhole at such speed and then being "reintegrated". In other episodes, however, gate travel is superficially no different to stepping through a doorway. This has since been explained as problems with the man-made interface on the Earth gate, and has mostly been fixed over the years of Stargate operations. The visual effect resembles a spinning wispy tube, and was in Season 9 (and the first season of Atlantis) revamped to resemble a misty tunnel lit by shooting rings of light. The Atlantis wormhole is significantly greener in colour whilst the new-style Milky Way wormhole was blue. The film depicted the first moment Daniel Jackson entered the pool, walking through and remaining in apparently physical form as if the pool was in fact simply a covering for the black of the wormhole beyond.

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Milky Way

A Milky Way Stargate has thirty-nine inscribed symbols on the inner ring. When dialing, this inner ring rotates until the dialed symbol is aligned with the seventh chevron, at which point the ring pauses, the seventh chevron moves down and up, and the appropriate chevron in the sequence engages. In the Stargate SG-1 series, an engaged chevron glows red. In the original Stargate film, all of the chevrons use this motion, and none of them glow red.

With 38 symbols, the Stargate Network in the Milky Way has: (38×37×36×35×34×33) = 1,987,690,320 possible addresses.
8-symbol addresses will yield: (38×37×36×35×34×33×32) = 63,606,090,240 possible addresses.
If a 9-symbol address operates like 8-symbol addresses it will yield:
(38×37×36×35×34×33×32×31) = 1,971,788,797,440 possible addresses.

However, not all points in space represented by these addresses have stargates, in fact, there are sufficiently few valid coordinate sets that randomly dialing the Stargate is largely futile. If the person dialing does not know the point-of-origin symbol, there are many more possible combinations. Because the gate on Earth was found without a DHD, the Stargate team on Earth developed the technology to interface with the gate in order to power it and dial it by the use of computers. (Essentially an automated version of 'manual dialing'.) When using a DHD, however, each chevron is activated immediately upon entry of the symbols, without the inner ring spinning. This allows for a much faster dialing process.

Pegasus galaxy

In the spinoff series Stargate Atlantis, an expedition dials the 8-symbol address from Stargate Command to travel to the Ancients' Lost City of Atlantis, located in the Pegasus Galaxy. They find that the Ancients seeded planets throughout the Pegasus galaxy with Stargates too, but used gates of a slightly different design. As these gates were built at a later date than the original Milky Way network, they may be of more advanced design, however at this point the differences appear mostly cosmetic. The alternative Stargate design in the Pegasus galaxy is one of many things the producers of the shows employed to differentiate the sister shows SG-1 and Atlantis. Pegasus Stargates are designed with blue chevron lights instead of Red ones, and the address symbols are groups of small blue lights (rather than embossed figures) that light up sequentially instead of rotating. In SG-1 it is stated that the rotating section of the gate unlocks when sufficient power to dial has been fed to the gate, allowing manual dialing in case the DHD is damaged or not present, as on Earth. In "Phantoms", an off world DHD is destroyed, and Dr. McKay states that there is no way to manually dial the gate. Presumably this is because the Pegasus gates lack the free-rotating central ring.

Schematic diagram of the Atlantis stargate with glyphs
Unlike the Milky Way gates, Pegasus gates are depicted with 36 symbols. 7 symbols are still required to dial an interplanetary address, adhering to the same constraints as a Milky Way gate.

With 36 symbols, the Stargate Network in the Pegasus Galaxy has: 35×34×33×32×31×30 = 1,168,675,200 possible addresses.
8-symbol addresses will yield: 35×34×33×32×31×30×29 = 33,891,580,800 possible addresses.
If a 9-symbol address operates like 8-symbol addresses it will yield: 35×34×33×32×31×30×29×28 = 948,964,262,400 possible addresses.

Thus there are fewer possible addresses in the Pegasus Galaxy, although it may still be the case that there are more Stargates there if more of the possible addresses are utilized than in the Milky Way. In a departure from the definitive "anywhere to anywhere" ethos of SG-1, the only Stargate in the Pegasus galaxy capable of reaching Stargates in the Milky Way is the one located at Atlantis. This is due to a special "control crystal" unique to the Atlantis DHD, without which a Pegasus Stargate cannot encode its eighth chevron. Unlike any other known gates, the Atlantis Gate can also identify the point of origin of the gate that tries to dial in, and can block an incoming wormhole. An orbital Stargate in the Pegasus Galaxy
Some Pegasus Stargates are orbital: they lead to open space, something never seen in the Milky Way. This is again a departure from the "personal travel" rather than "starship travel" ethos of SG-1, as these gates are used solely for space-faring vessels and never for humans. It is possible that the Ancients created these gates for localized travel to worlds where ground-based gate travel would be hazardous, either due to climate or atmospheric difficulties or due to native creatures. Orbital gates are depicted without a DHD, being powered by three power nodes spaced equally along the outer ring (see image). In the show, Puddle Jumper vessels have built-in DHDs to explain how a craft would return through an orbital gate.
In "Irresistible", a plan was put in place to create a bridge of linked Stargates in the void between the Milky Way and Pegasus galaxies to circumvent the need for a ZPM to effect travel between Atlantis and Earth (see McKay-Carter Intergalactic Gate Bridge below).
One concept directly ported from SG-1 to Atlantis, and that was the idea of an "Iris" that allows wormholes to form but stops anything trying to emerge. The Atlantis Stargate has a force field that serves the same function. As with SG-1, only the protagonists' gate has this capability, being the singular real defense they have against major attacks (thus allowing the shows to continue despite having insuperable enemies).

Reference:

http://en.wikipedia.org/wiki/Stargate_(device)

http://en.wikipedia.org/wiki/Dial-Home_Device