Summary: As she and Langdon make their way toward the Louvre’s emergency exit, Sophie tells the symbologist that the pentacle was a special symbol for her and her grandfather when she was a girl: Saunière used to stack a Tarot deck so that the pentacle, the “indicator suit for feminine divinity,” would always be Sophie’s indicator. She also tells him that Saunière taught her about PHI, the numerical value 1.618, the “divine proportion” that runs through so much of nature—and so, as Langdon knows, is replicated in so much artwork, particularly that of Da Vinci. The pentacle itself is the “ultimate expression” of PHI. Langdon’s reflections on Da Vinci and PHI leads him to realize that the scrambled Fibonacci sequence indicates that the text Saunière left behind is also a scrambled code—an anagram which, when properly solved, reads, “Leonardo da Vinci! The Mona Lisa!”
Analysis: This fascinating chapter introduces readers to the mathematical concept of PHI (1.618), the “divine proportion” or “divine number” or “golden ratio.” Through a flashback to Langdon’s Harvard class, Brown succinctly and effectively communicates the prevalence of the divine proportion in nature and in art by evoking examples readers can easily conjure in their mind’s eye, such as the cephalopod mollusk’s spiral shell or the already-introduced image of The Vitruvian Man. (He even gives readers instructions on how to measure themselves to find examples of the proportion: “My friends, each of you is a walking tribute to the Divine Proportion,” p. 102). For Brown’s purposes, PHI represents the claim that “the chaos of the world has an underlying order” (p. 102). It is this organization beneath apparent chaos that Brown’s novel itself mimics: facts, events, and symbols that initially seem to bear no relation to one another are, in fact, revealed to be integrally intertwined, time after time—just as, in this chapter, the scrambled Fibonacci sequence leads Langdon and Sophie to the Mona Lisa.
PHI also serves to connect Sophie to the concept of the sacred feminine. Her first name’s third through fifth letters are a whimsical tribute to “PHI” (and a literary foreshadowing of Sophie’s significant identity, yet to be revealed). And while Langdon does not make this connection without her prompting (p. 99), he is the one who “cracks” the code Saunière left for his granddaughter, which readers may or may not feel undercut Brown’s earlier establishment of Sophie as Langdon’s intellectual peer.