The interphase phenomenon has been described as a "flaw" in the fabric of space-time. It is a pocket outside of known reality, and even provides a doorway to alternate universes. Prior to 2269, such an area was only closely observed once, in an area on the fringes of Tholian space, by the crew of the U.S.S. Enterprise NCC-1701. At that time, the interphase area was in deep space, apparently a natural phenomenon. It was believed by Starfleet astrophysicists, however, that such an area could be created artificially by rapidly shifting gravitic and magnetic fields of great strength. The U.S.S. Defiant NCC-1764 was transported via interphase into the Mirror Universe, as well as more than a century into the past. The U.S.S. Hood NCC-1703 was also caught in an interphase rift in 2269, but was recovered when it reappeared nearly a year later.
When in the close proximity of an interphase area, the synapses of the humanoid brain seemed to be subtly affected. Sensory distortion resulted after a time, leading eventually to madness, with the victim most often becoming violent—even homicidal. Drugs were developed that inhibited this effect, but these drugs would lose their effectiveness after a time. Within the actual interphase area itself, an object is caught between universes. Any use of large amounts of power (including the use of beamed weaponry and warp drives) disturbed the interphase area, and could cause objects to shift back and forth randomly between universes. Such objects could appear and disappear at random, or appear only as ghostly images.
- Roddenberry, Gene (Executive Producer) and Freiberger, Fred (Producer). "The Tholian Web." Star Trek, Season 3, Episode 9. Directed by Herb Wallerstein and Ralph Senensky. Written by Judy Burns and Chet Richards. Paramount Pictures Corporation, 15 November 1968.
- Berman, Rick & Braga, Brannon & Coto, Manny (Executive Producers). "In a Mirror, Darkly, Part I." Star Trek: Enterprise, Season 4, Episode 18. Directed by James L. Conway. Written by Mike Sussman. Paramount Pictures Corporation, 22 April 2005.
- McLimore, Guy W. Jr., Poehlein, Greg K., and Tepool, David F. "Ghosts of Conscience." Star Trek: The Role Playing Game, Book 2001B. Illustrations and Drawings by Mitch O'Connell and Jordan Weisman. FASA Corporation, 1983.