BACK IN 1996, while perusing an issue of Guitar for the Practicing Musician magazine, I stumbled upon a lesson called the “The Warp Refraction Principle” by columnist Jon Finn. An esteemed player, author and Berklee College of Music professor, Finn is obviously a fellow avid sci-fi fan and knew how to draw me in with that title. In that gem of a lesson, Jon explained that the guitar fretboard is divided into two separate and similarly ordered universes. The line between them is drawn by a lone interval within the five pairs of adjacent strings produced by standard tuning: (low to high) E, A, D, G, B, E. In examining each adjacentstring pair, you’ll observe that all but one are a perfect 4th, or two and one half steps, apart —…