Up until the 20th century, virtually the only application of the wheel in Tibetan culture was the use of mani, or prayer, wheels in spiritual blessings. This fact stresses the inward nature of the society, one that places a stronger emphasis on the exploration of consciousness and spirituality than the material world.
Make no mistake: Science has its place in Tibetan culture. The region's warrior kings of the seventh and eighth centuries imported a great deal of mathematics, medicine and architecture from neighboring areas. They also introduced Buddhism and its emphasis on karma, reincarnation and the middle path between extreme ideas.
Enter any Tibetan Buddhist monastery, and you'll see a representation of the Sipa Khorlo or Wheel of Life, which resembles a terrifying monster chewing on a pie graph. Also known as a Bhavacakra, the wheel is far more than mere decorative art, however. It illustrates Tibetan Buddhism's complex take on the endless cycle of death, life and rebirth known as samsara.
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The wheel illustrates the six ways in which desire shackles us to the vicious circle of samsara and the six realms through which every life passes in an endless chain of death and rebirth. These six segments include three upper realms of humans, gods and demigods, as well as three lower ones of animals, hungry ghosts and hell beings. Buddhists believe that a person remains bound to this chain until, through Buddha's noble eightfold path to enlightenment, he or she achieves Nirvana and rises above the wheel.
Look again to those lower realms of misery and longing, as well as to the great demon Yama, the Lord of Death who grips the wheel, and we see the crucial interplay of karma, merit and death. You can think of karma as a kind of psychic string that runs through all the forms that a life takes in samsara. You might have been a preta, or hungry ghost, in the last life, a human in this one and a goat in the next, but the same string of karma runs through all these forms. It continues in every form you've ever embodied. What's more, karma permits your actions in one incarnation to influence the next. As such, Tibetan Buddhists emphasize the accumulation of merit. Only through a lifetime of compassion and acts of devotion can they avoid incarnation into the lower realms.
This is why Yama is so terrifying to behold: He represents not only impermanence, but also the incessant danger associated with the death journey. According to eastern religion expert Robert Thurman, this aspect of Tibetan spirituality cannot be overstated. While he acknowledges that metaphorical interpretations of samsara's lower, hellish realms are not without merit, avoidance of these realms is a true motivator to the believer. Death in Tibet is far different from the nihilistic view of dying as a plunge into nothingness or an endless, peaceful slumber.
Death, as we'll learn next, is a serious journey for the Tibetan Budhhist soul.