Neutron loop
From Tardis Wiki, the free Doctor Who reference
The Tenth Doctor and Heather McCrimmon made a neutron loop in Machu Picchu in 1911 to clean up the temporal cataclysm through which Incasaurs attempted to escape from a parallel universe to N-Space. However, at the last minute, the loop was disturbed by Hiram Bingham. With the loop broken, the Incasaur empire came through to the prime universe. Heather and the Doctor were captured by the Incasaurs. History was put back on track when the prime Hiram Bingham touched hands with an alternate Hiram Bingham from the Incasaur universe, causing a massive temporal discharge. (COMIC: Hitching Point)
