One of the concepts of the show is the concept of doubles. On many parallel Earths, there will be alternate versions of the same person. The Sliders frequently encounter alternate versions of themselves. Sometimes, the doubles of the Sliders had similar personality traits and interests (for example, many doubles of Quinn Mallory had invented sliding, or were in the process of inventing sliding). Sometimes, however, the personality traits of the Sliders are entirely different. Gender and appearance of doubles is also somewhat fluid, although this is only seen in a few cases.
Some of the doubles the Sliders encounter are doubles of people they know from Earth Prime, such as Quinn's classmate Conrad Bennish, Jr. In the episodes "Dragonslide" and "The Prince of Slides", Rembrandt meets doubles of girlfriends from Earth Prime, and in the episode "Eggheads", Arturo meets a double of his late wife. Sometimes doubles of the family members of the Sliders are found during sliding; Quinn often encounters doubles of his parents, and in the episode "Season's Greedings", Wade meets doubles of her father and sister.
On some of the alternate Earths that the Sliders visit, there are alternate versions of celebrities and politicians of Earth Prime. However, celebrities on these alternate Earths sometimes have different levels of fame than their Earth Prime counterparts. In addition, some of the alternate versions of Earth Prime politicians hold different offices. For example, the Sliders find alternate Earths where Oliver North, Hillary Clinton, Jocelyn Elders, and even B-movie filmmaker Ed Wood were at one time in their respective worlds, President of the United States. In the pilot episode, the former cast of The People's Court guest starred as their own doubles in a Soviet-styled parody of the show.
Cleavant Derricks' identical twin brother, Clinton Derricks-Carroll, occasionally appeared on the show, in the episodes "The King Is Back", "Greatfellas", and "The Prince of Slides", when there was a need for Rembrandt and his double to interact.
The Sliders' vortex (EPR bridge).
The vortex, a wormhole opened by the timer that the Sliders carry around, is the means by which the Sliders travel from one parallel universe to another. In the pilot and several other episodes, Quinn refers to the vortex as an "Einstein-Rosen-Podolsky bridge," a fictitious term that may have arisen out of a confusion between the actual term Einstein-Rosen bridge (a type of wormhole in physics) and the Einstein-Podolsky-Rosen paradox (a famous thought-experiment in quantum mechanics, which is unrelated to wormholes).
The look of the vortex changes throughout the series. From the first to third season, the vortex is a bluish whirlpool, and is somewhat transparent. In the third season the vortex is a clear water-like whirlpool with random flashes of blue. The first time the sliders use their newly acquired timer in the episode "Slide like an Egyptian" the vortex appears gold in color but in subsequent episodes it returns to the colorless version. The episode "Gillian of the Spirits" also introduced an opaque red vortex existing on the astral plane. Later, Logan St Clair's timer produces a transparent red vortex in the real world. In the double episode "The Exodus", this world's own slider technology produces an opaque red vortex with lightning at the centre that is also noticeably angular compared to the expected smooth curves previously seen. The sliders' own timer then produces the same red vortex, although the only change made to it has been the installation of a program that now gives it the ability to record the coordinates of the worlds they travel to, it would appear that whenever the slide was not a random one, but a slide were the destination was known and the coordinates were put in the timer, that the Vortex would turn red. In the fourth and fifth seasons, the sliders' vortex appears as a mostly-blue whirlpool with some blue-green, and is entirely opaque.