Five fundamental manifestations of symmetry in physics—reproducibility as symmetry, predictability as symmetry, symmetry of evolution of isolated physical systems, symmetry of states of physical systems, and gauge symmetry—are investigated for their essential meaning and physical significance. The approach is conceptual, to the complete exclusion of mathematical formalism.

Objective or subjective : that is the question -- The science of nature and the nature of science -- Theory : explanation, not speculation -- Is science the whole story? -- Our unique universe -- Nature's laws -- Facing the universe -- The hunt for reality.

The symmetry implications of the postulates of quantum theory are investigated.