"In a series of remarkable developments in the twentieth century, elementary particle physicists, astronomers, and cosmologists have removed much of the mystery that surrounds our understanding of the physical universe. They have found that the cosmos is, on the whole, comprehensible. Of course, no one can claim to understand or explain every facet of the structure of reality. However, we now have theories—mathematical models—that describe the general character of that reality. At this writing, these theories are consistent with all observational data, including measurements of incredible precision. While they will undoubtedly be superseded by better theories as science continues to advance, the great success of current schemes makes it likely that they are on the right track. The broad picture that is drawn by modern particle physics and cosmology is very probably the way nature is, and what we have yet to learn may be expected to fit comfortably on its foundation—just as these sciences fit comfortably on the foundation of Newtonian physics.

We now have a deep and revolutionary understanding of the true nature of the mathematical quantities and theories of physics. We have realized that they are basically human inventions, including the notions of time and space. The quantities of physics are defined operationally by how we measure them. The laws of physics are not, as usually assumed, restrictions on the behavior of matter—handed down from above. Rather, they are restrictions on the way that physicists can formulate their theories.

Of course, the laws of physics must agree with observations. But, beyond that, they are formulated in such a way as to assure, as best as possible, that they do not depend on any particular point of view. Otherwise they cannot be expected to faithfully describe an objective reality. When these requirements are met, the laws, as we know them, appear naturally. Furthermore, the forces that account for the interactions between bodies are introduced in the theory to preserve that theory’s independence of point of view.

Not everything in the universe is thereby "explained." In this regard, "explanation" is taken to mean a statement accounting for all details on something, while "understanding" or "comprehension" is taken to mean the perception of the nature of something. The hope of any ultimate, complete theory from which everything may someday be derived is dimmed by the new developments. Instead, the structural details of the universe, including basic facts like particle masses and force strengths, can be understood as accidents. The origin of this structure may be likened to the origin of biological structure, the combined result of tautological necessity, random chance, and natural selection.