When the TARDIS lands on prehistoric Earth, both the Doctor and Susan are surprised that the exterior of the ship still looks like a police ... ‘Time and Relative Dimension in Space’.

The key insight that enabled their explanation was that quasicrystals were, in fact, periodic—but in a higher dimension than the ... An example of a four-dimensional object is the tesseract ...

Jo comments that it looks different and the Doctor tells her that he’s been doing a spot of redecorating. The circular patterns on the wall are still there, but here they appear to be more like ...