Complementarity

The interrelationship, completion or perfection brought about by one or more units supplementing, being dependent upon, or standing in polar opposition to another unit or other units. In atomic physics, for example, conflicting evidence of behaviour or characteristics obtained under different experimental conditions cannot be comprehended within a single picture, but must be regarded as complementary in the sense that only the representation of the totality of the phenomena exhausts the possible information about the objects observed. This implies the impossibility of any sharp separation between the behaviour of atomic objects and the interaction with the measuring instruments which serve to define the conditions under which the phenomena appear. The situation in quantum physics has been considered one reflection of the application of an all-pervasive principle determining the approach to the unity of knowledge. Complementarity is seen characteristically in the behaviour of light as a wave and as photon particles. Situations in psychology and biology also present equivalent complementary aspects; and the considerations of such analogies in epistemological respects in turn illuminates unfamiliar physical problems.