Optical illusion
From Tardis Wiki, the free Doctor Who reference
The Brigadier at first believed the TARDIS's dimensional transcendentalism to be an optical illusion. (TV: The Three Doctors)
In early 2020s, Gabriela Camara also thought the TARDIS to be an optical illusion. When she asked Ryan Sinclair about it, Ryan wasn't sure. (TV: Praxeus)
