Langdon was surprised. “Your grandfather taught you about the number PHI?” “Of course. The Divine Proportion.” Her expression turned sheepish1. “In fact, he used to joke that I was half divine...you know, because of the letters in my name.” Langdon considered it a moment and then groaned. s-o-PHI-e.
He felt himself suddenly reeling back to Harvard, standing in front of his “Symbolism in Art” class, writing his favorite number on the chalkboard. 1.618. Langdon turned to face his sea of eager students. “Who can tell me what this number is?” A long-legged math major in back raised his hand. “That's the number PHI.” He pronounced it fee. “Nice job, Stettner,” Langdon said. “PHI's ubiquity2 in nature, clearly exceeds coincidence, and so the ancients assumed the number PHI must have been preordained3 by the Creator of the universe. Early scientists heralded one-point-six-one-eight as the Divine Proportion.”
“Hold on,” said a young woman in the front row. “I'm a bio major and I've never seen this Divine Proportion in nature.” “No?” Langdon grinned. “Ever study the relationship between females and males in a honeybee4 community?” “Sure. The female bees always outnumber the male bees.” “Correct. And did you know that if you divide the number of female bees by the number of male bees in any beehive in the world, you always get the same number?” “You do?” “Yup. PHI.” The girl gaped. “NO WAY!”
“Way!” Langdon fired back, he began racing through slides now—spiraled pinecone petals, leaf arrangement on plant stalks, insect segmentation—all displaying astonishing obedience to the Divine Proportion. “This is amazing!” someone cried out. “Yeah,” someone else said, “but what does it have to do with art?” “Aha!” Langdon said. “Glad you asked.” He pulled up another slide—Leonardo da Vinci's famous male nude-The Vitruvian Man. “Nobody understood better than Da Vinci the divine structure of the human body. He was the first to show that the human body is literally made of building blocks whose proportional5 ratios always equal PHI.” Everyone in class gave him a dubious6 look.
“Don't believe me?” Langdon challenged. “Next time you're in the shower, take a tape measure.” A couple of football players snickered. “All of you. Guys and girls. Try it. Measure the distance from the tip of your head to the floor. Then divide that by the distance from your belly button to the floor. Guess what number you get.” “Not PHI!” one of the jocks blurted7 out in disbelief. “Yes, PHI,” Langdon replied. “One-point-six-one-eight. Want another example? Measure the distance from your shoulder to your fingertips, and then divide it by the distance from your elbow to your fingertips. PHI again. Another? Hip to floor divided by knee to floor. PHI again. Finger joints. Toes. Spinal8 divisions. PHI. PHI. PHI. My friends, each of you is a walking tribute to the Divine Proportion.” Even in the darkness, Langdon could see they were all astounded9. He felt a familiar warmth inside. This is why he taught.
“Come on,” Sophie whispered. “What's wrong? We're almost there. Hurry!” Langdon glanced up, feeling himself emerge from a schooling thought. He realized he was standing at a dead stop on the stairs, paralyzed by sudden revelation10.
Sophie was looking back at him. It can't be that simple, Langdon thought. But he knew of course that it was. There in the bowels of the Louvre...with images of PHI and Da Vinci swirling through his mind, Robert Langdon suddenly and unexpectedly deciphered11 Saunière's code. “Fibonacci numbers only have meaning in their proper order. Otherwise they're mathematical gibberish12.”