Quantum physics
Quantum physics revealed that particles changed their behaviour when observed. Ng theorised that the experience of "shoulder creeping" was related to quantum phenomena. (AUDIO: ScrapeJane)
Quantum theory was one of the subjects studied by Susan before she and the First Doctor settled at Totter's Lane. (PROSE: Losing the Audience)
While waiting for Clara Oswald to finish her day of work at Coal Hill School, (PROSE: The Day of the Doctor) the Eleventh Doctor read a book on Advanced Quantum Mechanics, (TV: The Day of the Doctor) which bored him after he failed to find Wally anywhere and had to resort to reading the text. (PROSE: The Day of the Doctor)
Behind the scenes
The 2019 Companion Chronicles audio story Daybreak establishes that fixed points in time are only created "once a waveform has collapsed". This is a clear allusion to wave function collapse, a concept in quantum mechanics. This is when a wave function in a superposition (ie. with multiple possible quantum states) is "observed" (measured), and thus collapses into only one possibility.
Ng in ScrapeJane is stretching this meaning of "observation", in the context of quantum mechanics. In the real world, a measurement in quantum mechanics is not the same as mere observation through sight.
