The plot outline that Nolan passed on to his composer, Hans Zimmer, didn’t mention spaceships and wormholes at all: instead, it was a single-page short story about a father who leaves his daughter to do an important job. Its central theme, Zimmer later explained, was the idea that “once we become parents, we can’t help but look at ourselves through the eyes of our children”. The story contained only two lines of dialogue. Father: “I’ll come back.” Daughter: “When?” No concrete answer is forthcoming, perhaps because even a small amount of time apart from a child can feel like forever. The easiest way to feel the relativity of time is by loving someone.