Science Fair Project Encyclopedia
In the sci-fi television show, Stargate SG-1, the "iris" (of the Stargate) is a large, metal protective device, similar to the shutter of a camera, which was invented by Stargate Command to prevent unwanted travelers from emerging through the Stargate's wormhole.
When closed, the iris forms a barrier within 10 μm of the wormhole's event horizon, thereby preventing most forms of matter from properly reintegrating. Objects coming through the wormhole are destroyed instead, accompanied by a ringing thud against the iris. Radio signals are able to penetrate, however, allowing SG teams to request the opening of the iris using their GDOs. The iris also suppresses the destructive "kawoosh" (the unstable wormhole) generated when the Stargate opens, apparently as a side effect.
The System Lord Sokar devised a means to breach the iris by firing a particle beam through the wormhole, the subatomic particles being small enough to reintegrate in the space between iris and event horizon and heating the iris up with the intent of eventually melting it. The SGC used this technique themselves in a later episode to penetrate a "natural iris" that had formed over a distant world's Stargate after it had been buried while still active.
Instituted in the pilot episode, the original titanium iris was destroyed in the episode "A Matter of Time" by a black hole's gravity leaking through from the other end of the wormhole. It was replaced with a new iris made of a trinium alloy.
It is not clear how the iris is installed into the stargate, nor how it is opened or shut. Earth seems to have the only Stargate with an iris. None of the more advanced races do, though the Stargate in the Ancient city of Atlantis has a force field that can serve the same function.
Iris Deactivation Code
The Iris Deactivation Code is a code transmitted through an open stargate to request that the iris be opened to allow travellers through. IDCs are transmitted using a GDO.
Early portrayals of its use even had it deactivating the iris against Stargate Command's wishes, such as in the Season 1 episode "Cold Lazarus". The stargate in Atlantis is not protected by an actual iris, but the term has been carried over to apply to the protective force field that fills the same role.
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