No other number attracts such a fevered following as the golden ratio. Approximately equal to 1.618 and denoted by the Greek letter phi, it’s been canonized as the “Divine Proportion.” Its devotees will tell you it’s ubiquitous in nature, art and architecture. And there are plastic surgeons and financial mavens who will tell you it’s the secret to pretty faces and handsome returns.
Not bad for the second-most famous irrational number. In your face, pi!
It even made a cameo appearance in “The Da Vinci Code.” While trying to decipher the clues left at the murder scene in the Louvre that opens the novel, the hero, Robert Langdon, “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 tells his class that, among other astonishing things, da Vinci “was the first to show that the human body is literally made of building blocks whose proportional ratios always equal phi.”
“Don’t believe me?” Langdon challenged. “Next time you’re in the shower, take a tape measure.”
A couple of football players snickered.
“Not just you insecure jocks,” Langdon prompted. “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 blurted out in disbelief.
“Yes, phi,” Langdon replied. “One-point-six-one-eight. [...] My friends, each of you is a walking tribute to the Divine Proportion.”
I tried it. I’m 6-foot-1, and my belly button is 44 inches from the floor. So my ratio is 73 inches divided by 44 inches, which is about 1.66. That’s about 2.5 percent bigger than 1.618. But then again, nobody ever mistook me for Apollo.
The golden ratio originated in the ideal world of geometry. The Pythagoreans discovered it in their studies of regular pentagons, pentagrams and other geometric figures. A few hundred years later, Euclid gave the first written description of the golden ratio in connection with the problem of dividing a line segment into two unequal parts, such that the whole is to the long part as the long is to the short.
To make this problem more vivid and tangible, let’s think of it as a carpentry job. You’re working for Euclid, a notoriously fussy customer. He hands you two boards, each 60 inches long. Your job is to cut one of the boards into a long piece and a short piece, while leaving the other board whole. Sounds easy, but then Euclid says, “Not so fast, pal. The whole board and the long piece have to be in exactly the same proportion as the long piece and the short piece.”