Zygma energy

Zygma energy and radiation was a form of energy used for time travel which may have been made up of double nexus particles.

In the 51st century, Doctor Sa Yy Findecker conducted time experiments for Minister of Justice Magnus Greel. He discovered the double nexus particle and developed zygma beams as a method of travelling from one point in time to the other. (TV: The Talons of Weng-Chiang) Zygma energy created a drop in quantum pressure which lead to turbulence in the Time Vortex. (AUDIO: The Butcher of Brisbane)

Later on, it was determined that the safe limit for time travel using zygma energy was 200 years for an average human mass. (PROSE: Emotional Chemistry)

The Vaults on Gallifrey contained objects propelled through time by zygma energy. (AUDIO: Fractures)

Other Information
Humans did not develop time travel until the botched sigma experiments of the 30th century. (PROSE: Transit)
 * ''Presumably, "sigma" was a typo for "zygma."