Much scientific evidence supports the conclusion that we live in a quantum mechanical universe. This universe functions in many ways counter-intuitive to observations via our five senses. The reason may be a central concept at the heart of quantum mechanics. Niels Bohr called this principle "complementarity." Heisenberg considered it a foundation on which to "interpret the validity of the quantum-mechanical laws." Years later, Oppenheimer wrote that complementarity has "turned out to be the clue to unraveling that whole domain of physical experience." Recent experiments (by Alan Aspect and others) have confirmed the quantum mechanical implications of this principle and are leading scientists to new attention to its philosophic implications. Perhaps complementarity will be fundamental to our understanding of human wholeness and how we relate to each other and the world.

The principle of complementarity is the assertion that, in the quantum mechanical world, there exist pairs of quantities that are complementary in the sense that they describe a whole only when taken together, but which are mutually exclusive in that they can never be measuredsimultaneously. They cannot because the act of measuring one property creates a unity containing the part being measured, the measurement, and the experimenter. This larger whole, in turn, defines a new "part" that is separate from, but coupled to, the part being measured. These two parts are necessarily mutually exclusive. No matter what we observe or how we design experiments, the act always manifests a part that is outside the experiment, yet coupled to it. In quantum mechanics, this principle leads directly to the well-known uncertainty principle that asserts there are fundamental limits on the accuracy obtainable in simultaneous measurements.