In Volume 1 we learned that 3,000 years of classical physics finally met its match when the strange results of experiments on ever smaller "things" could not be explained. Each new finding seemed to lead to an endless series of new questions and new experiments. And each new finding disclosed ever tinier "particles" and strange new "things." Breakthrough understandings by Einstein and Heisenberg, revealed in Volume 2, left as many questions as answers. Serious inquiry in the early 20th Century, prompted by these two giants, revealed that the nature of "nature" was still largely a mystery.