The Origins of the Quantum Theory

culiar behaviors manifested principally at microscopic levels. From its beginning, the new regime was symbolized by Planck’s constant h, introduced in his famous paper of 1900. Measuring the world’s departure from smooth, continuous behavior, h proved to be a very small number, but different from zero. Wherever it appeared, strange phenomena came with it. What it really meant was of course mysterious. While the quantum era was inaugurated in 1900, a quantum theory would take much longer to jell. Introducing discontinuity was a tentative step, and only a first one. And even thereafter, the recasting of physical theory was hesitant and slow. Physicists pondered for years what a quantum theory might be. Wondering how to integrate it with the powerful apparatus of nineteenth-century physics, they also asked what relation it bore to existing, “classical” theories. For some the answers crystallized with quantum mechanics, the result of a quartercentury’s labor. Others held out for further rethinking. If the outcome was not to the satisfaction of all, still the quantum theory proved remarkably THE ORIGINS OF THE QUANTUM THEORY