The biological sciences have been dominated by 'classicist' science-predicated on the post-Enlightenment belief that a real world exists, which behaves according to notions of causality and consistency. Although medicine, and by implication psychiatric nursing, derives its explanatory power from such a science, much of its focus-illness-is not amenable to causal explanation or prediction. The theoretical developments of the 'new physics' have been used to redefine science and, as a result, have challenged traditional constructions of reality. The new physics are usually framed in terms of the physical world, or to construe consciousness. In this paper I shall consider the implications of chaos-a relative of the new physics-for psychiatric nursing practice. As nursing appears to crave a 'certainty principle' to govern the theoretical underpinnings of practice, this study considers how chaos might contribute to a metaparadigm of nursing.