Stone Tape theory

The Stone Tape theory was a speculative explanation for ghosts. It speculated that physical matter, especially stone, could absorb energy from living beings, thus "recording" them. Under certain circumstances, those stored echoes could be played back. Sarah Jane Smith, who did not believe that ghosts were the souls of the departed, was a proponent of that theory. While investigating the case of Ashen Hill Manor, Sarah briefly explained the theory to her young companions Rani Chandra and Clyde Langer. (TV: The Eternity Trap) She also mentioned it to Emily Morris during a time-travelling trip in 1889. On that occasion, Sarah discovered that the fabric of a building could transmit echoes not only from the past, but also from the future. (TV: Lost in Time)