Double nexus particle
From Tardis Wiki, the free Doctor Who reference
The double nexus particle, Findecker's Folly, was a particle discovered by the scientist Sa Yy Findecker at some point in the 51st century. While one nucleus existed in the material universe, the other mirror nucleus existed outside of time and space altogether. (AUDIO: The Butcher of Brisbane)
It led to the development of practical time travel through the formation of zygma energy into a beam as a power source applied to the time cabinet. However, it ultimately proved to be a technological cul-de-sac, as time travel in this way led to horrible and life-threatening mutations. (TV: The Talons of Weng-Chiang)
