Viewpoint: Yes, history, recent advances, and new technologies provide reasonable hope that a grand unified theory may be within reach.

Viewpoint: No, a grand unified theory of the fundamental forces is not within the reach of physicists today.

The belief that a small number of organizing principles underlies the immense variety of phenomena observed in the natural world has been a constant theme in the history of science. One of the first unification theories was introduced in the fifth century B.C. by Empedocles: a system of four elements—air, earth, fire, and water—with qualities of coldness or hotness and moistness or dryness. This system soon was supported by a geometrical model outlined in Plato's Timaeus (ca. 360 B.C...