From Wikipedia: Timewave zero and the I Ching

"Timewave zero" is a pseudoscientific numerological formula that purports to calculate the ebb and flow of "novelty", defined as increase in the universe's interconnectedness, or organised complexity,^[40] over time. According to Terence McKenna, who conceived the idea over several years in the early-mid 1970s, the universe has a teleological attractor at the end of time that increases interconnectedness, eventually reaching a singularity of infinite complexity on December 21, 2012, at which point anything and everything imaginable will occur instantaneously.^[40]

McKenna expressed "novelty" in a computer program, which purportedly produces a waveform known as timewave zero or the timewave. Based on McKenna's interpretation of the King Wen sequence of the I Ching,^[41]the graph appears to show great periods of novelty corresponding withmajor shifts in humanity's biological and cultural evolution. Hebelieved the events of any given time are recursively related to the events of other times, and chose the atomic bombing of Hiroshimaas the basis for calculating his end date of November 2012. When hediscovered this date's proximity to the end of the 13th baktun, headjusted it so that the two dates matched.^[42]

The first edition of Invisible Landscapes refers to 2012 (asthe year, not a specific day) only twice. McKenna originally consideredit an incidental observation that the two dates matched, a sign of theend date "being programmed into our unconscious". It was only after hemet Jose Argüelles in 1985 that he became convinced that December 21,2012 had significant meaning and peppered this specific date throughoutthe second, 1993 edition of the same book.^[26]