Overview

The years between 1900 and 1949 were a time of extremes that included two world wars, a revolution in Russia, and the Depression in the United States. Scientific revolutions brought exciting new knowledge but also called into question the most basic concepts. New technologies and materials provided more deadly instruments of war but also lengthened lives and eased the demands on raw human muscle power. Exploration in this period echoed these extremes. Since many of the easier targets had already been reached, explorers headed for the poles, ventured deep beneath the ocean's surface, and high into the atmosphere.

Scientists also explored new frontiers, introducing new concepts while at the same time upsetting much of the perceived order by which the natural world worked. Revolutions in physics drew an entirely new picture of the most basic elements of physical reality. Our knowledge of the age, extent, and history...