Wormhole

In Stargate physics, a wormhole is a "tunnel" created between two active Stargates after one of them successfully dials the other, enabling faster-than-light travel in one direction.

Overview
A wormhole is a subspace bridge created between 2 locations that allow matter to be transferred through one end to the other. Although not traveling at a higher speed, a wormhole reduces the distance necessary to reach a given location within itself (similar to Hyperspace but a lot more powerful.) To put wormholes into relative place, the time necessary for the most powerful Ancient hyperdrive to reach Lantea in the Pegasus Galaxy from Earth is 4 days, if transferred through a wormhole it is less than 20 seconds, and to reach closer planets it is around 3 seconds.

Wormholes are a vacuum of matter, like space itself, and the temperature of one is close to absolute zero (which is −273.15 degrees Celsius).

The only known method of creating stable wormholes is with an Ancient Stargate. A device which when a given address is inputted, connects to that gate over a subspace link and quickly exchanges precise locational details then establishes a stable wormhole between them. Wormholes are only 1 way, and the dialing gate is the one that you must enter through. The stargate creates its own event horizon just in front of the wormhole and dematerializes any object attempting to pass through it so it is not damaged or killed by the deadly low temperatures. It then fires it through the wormhole and the other gate and rematerializes it at its event horizon. If a barrier is placed between the two layers then the matter is unable to rematerialise and is destroyed. Wormholes can also be created by starships and held open from the inside, as is the case with the Ancient Wormhole drive.

If an object or somebody walks through the incoming wormhole, it will be destroyed, or pulled back, or the receiving gates event horizon will be like a wall, as wormholes are one-way travel only, except for radio signals.

If a wormhole impacts a solar flare, the magnetic disturbances can create a time travel effect on a wormhole passing through it based on the intensity and location.

There have also been times when a wormhole has crossed into an alternate universe

Wormholes can also pickup and deposit matter from places, although the receiving gate can remove this excess matter. On one occasion, however, a superheavy material was picked up by the wormhole and deposited into a passing sun, causing it to shift to infa-red and stopping plants from photosynthesizing on the nearby planet.

The Ancients did, however, put in place effective safety protocols in their Stargates that prevent wormholes being formed if there is a high risk of any of the above happening.

Behind the scenes

 * Seasons 1-8 of Stargate SG-1 used an older wormhole CGI effect, carried over from Stargate the movie. Seasons 9-10 used a new version of the effect retrofitted from Stargate Atlantis; the difference between them is that the effect appears green in Atlantis, but blue in SG-1.
 * Though it is stated that matter can only pass through one way in a wormhole, occasionally in Stargate Atlantis, John Sheppard would fire his P90 back through the gate when "coming in hot." This could be explained by possible ignorance on Sheppard's part, due to the fact that he was mostly added to the Atlantis expedition for his ATA Gene, or a psychological want to do something, however ineffective, to the enemy.