Template:Quote A Matter bridge is a device which creates a link between two universes. In order to travel to an alternate reality, one must form a link, called a "trans-universal bridge" or the more commonly used "inter-universal bridge", between the two realities. Various means of creating a bridge between realities have been discovered by Stargate Command, Atlantis expedition, and several other races.
Matter bridge projectsEdit
Project Arcturus was an attempt by the Ancients to extract Zero point energy from their own universe, a source of power potentially dozens of times more potent than a Zero Point Module. However, the project suffered from a fatal flaw. By extracting zero point energy from their own space-time, it resulted in that region of space destabilizing, no longer obeying the normal laws of physics. With the creation of exotic particles inside this region no longer obeying the laws of normal physics, they interacted in ways impossible to predict, resulting in a runaway reaction in the containment chamber.
In 2005, the Atlantis expedition discovered and revived the project. Ultimately, they ran into the same problem. Dr. Rodney McKay was confident he could overcome it, but was unsuccessful. His efforts to compensate for the instability led to the destruction of an entire solar system. Template:Quote
Realizing that drawing zero point energy from their own universe was nonviable, McKay began working on a method to draw zero point energy from an alternate reality, in essence giving them all the benefits of the project while saddling the other (hopefully uninhabited) universe with the drawbacks. In 2006, Jeannie Miller provided the missing link necessary to achieve this. With her help, Project Arcturus was recreated on Atlantis and a matter bridge was established so it could harness zero point energy safely.
However, their matter bridge connected to an inhabited universe. An alternate Rodney McKay, going by "Rod", traveled across the matter bridge to stop the catastrophic effects Arcturus was having on his universe. Though the project was immediately shut down, the still-active matter bridge continued to generate exotic particles. Rod's universe devised a method by which to force all the exotic particles to the other side of the bridge to save themselves, transmitting this plan to the main reality. To preempt them, McKay harnessed the power of their one ZPM to forcibly close the matter bridge. They successfully closed the bridge, but McKay kept the energy running in order to give Rod time to beam back to his own universe, draining Atlantis' only ZPM in the process. 
Alternate SG-1's bridgeEdit
Template:QuoteIn early 2006, another means of inter-universal travel was discovered. If one were to direct a controlled energy blast within a wormhole traveling through a black hole, one could actually open a bridge into an alternate reality, which eventually cascaded into multiple realities all converging on the one point of confluence. This effect was reversed at the point of confluence with the use of an energy blast discharged in the wormhole connected to the original point of origin's corresponding Stargate. Because the Stargate's wormhole was used to create the "inter-universal bridge," travel was only one-way, or uni-directional. 
Parallel universe's bridgeEditTemplate:Quote
Another method of extracting zero point energy from an alternate reality was developed in a parallel universe. Although Atlantis had not been discovered in this reality, their Major Samantha Carter conducted an experiment to extract minute amounts of zero point energy from many parallel realities simultaneously, thus avoiding the build up of exotic particles in any one universe. However, the experiment linked to our reality's Stargate Command where our Lt. Colonel Samantha Carter was experimenting with phase-shifting using Merlin's Arthur's Mantle. While the experiment would not have an effect on normal matter, the phase-shifted Colonel Carter and her lab were not normal matter at the time and were pulled through the bridge, causing the alternate Carter's experiment to explode - killing the alternate Carter. Although Colonel Carter was eventually returned, along with the technical details regarding the experiment, this technique has not yet been tested in our universe. 
Malcolm Tunney's bridgeEditTemplate:Quote
In 2008, Dr. Malcolm Tunney created a space-time matter bridge based on the work of Dr. Rodney McKay and Jeannie Miller, which he read in classified document written by McKay under an alias. Having read about the exotic particle creation problem outlined in the paper, he used his matter bridge to transfer heat in order to avoid the problem. To demonstrate his new invention, claiming it to solve the problem of global warming on Earth, he held a scientific presentation at a Kramer Innovations facility in an undisclosed location. However, his matter bridge was unstable, drawing heat at an inconsistent rate, and became impossible to shut off. He enlisted the help of McKay to avoid disaster. Ultimately, with the help of Bill Nye, the two collapsed the bridge by opening a second one, starving both of power and causing them to collapse.