Some actors are just plain wrong for some roles. Bella Thorne as a quantum physics whiz kid is one of them (and it’s not an issue or gender or looks; attractive women can and do play science types convincingly — Jodie Foster and Laura Dern come to mind).
It would help if Vivien (Thorne) sounded like she knew what she’s talking about, but quantum physics serve no purpose in this movie other than as a clumsy metaphor for falling in love. Vivien herself seems ambivalent about her chosen field of study, describing it on separate occasions as "simple" and "complicated," as well as "fascinating" and "exhausting," but all the proof we get of this is her bedroom mirror scribbled all over with equations of whatever — so I guess she’s supposed to be a regular Will Hunting.
Moreover, Vivien refers to herself as a "numbers girl" (I assume it’s the kind of numbers that follow the phrase 'for a good time call...'), and when asked "What's math got to do with love?," she replies "Well, there's all these numbers that surround the word 'love', and it used to make so much sense to me ... Now I'm not so sure."
I’m not so sure either. What are these numbers, and how and why do they surround the word love? Then again, Vivien fails at least once some big test (often mentioned but never explained) for which she’s been studying for over a year, so maybe she’s just a victim of the Dunning–Kruger effect