Double nexus particle
From Tardis Wiki, the free Doctor Who reference
The Double nexus particle was a particle discovered by Findecker some point before the 51st century. It lead to the development of practical time travel trough the application of a Zygma beam as a power source. This was put to use in devices like the time cabinet. However, it ultimately proved to be a technological cul-de-sac, as time travel in this way leads to horrible and life-threatening mutations. (DW: The Talons of Weng-Chiang)
