In Star Trek, a quantum fissure is a fissure on the quantum level in the fabric of space-time, a spatial anomaly. It serves as a fixed point across the space-time continuum, intersecting countless other quantum realities. In 2370, Lieutenant Worf, while returning from a bat'leth tournament on Forcas III in the shuttlecraft Curie, passed through a quantum fissure and found himself shifting to different realities. This shifting was caused everytime he was close to Geordi La Forge, who's VISOR emitted a subspace field pulse. He eventually returned to his own reality. (TNG: "Parallels").

The 'quantum relatities' intersected by this phenomenon appear to correspond to the parallel universes in the many-worlds interpretation or MWI of contemporary quantum mechanics. Many-worlds claims to resolve all the "paradoxes" of quantum theory since every possible outcome to every event defines or exists in its own "history" or "world." This means that there is a very large, perhaps infinite, number of universes and that everything that could possibly happen in our universe (but doesn't) does happen in some other universe(s). The fundamental idea of the MWI, going back to its first proponent Hugh Everett in 1957, is that there are myriads of worlds in the Universe in addition to the world we are aware of. In particular, every time a quantum experiment with different outcomes with non-zero probability is performed, all outcomes are obtained, each in a different world, even if we are aware only of the world with the outcome we have seen.

While some physicists have speculated that it might be possible to move 'between' these universes, others believes that travel or communication between worlds is impossible. The interfering worlds can't influence each other in the sense that an experimenter in one of the worlds can arrange to communicate with their own, already split-off, quantum copies in other worlds. Since each component of a linear solution evolves with complete indifference as to the presence or absence of the other terms/solutions then we can conclude that no experiment in one world can have any effect on another experiment in another world. Hence no communication is possible between quantum worlds.