Clarke's Law

Clarke's Law stated that:

"Any sufficiently advanced form of technology is indistinguishable from magic."

- Clarke's Law

The Doctor reminded Ace of Clarke's Law and stated that "the reverse is true", as was the case of the Thirteen Worlds, a parallel universe where technology formed alongside magic. (DW: Battlefield)

The Captain paraphrased this by describing now-wrecked craft had possessed technologies "indistinguishable from magic." (DW: The Pirate Planet)

Although not referenced specifically, the Sycorax proved Clarke's Law, by thinking of blood control as form of sorcery, due to it giving them power over others. (DW: The Christmas Invasion)

When Angelo Colasanto believed Captain Jack Harkness' Vortex manipulator to be magic, Jack corrected him saying it was technology, although the two could be indistinguishable. (TW: Immortal Sins)