It is easy to guess from the title of this article that its content will deal with the current changes in the foundations of physical sciences—the changes which are far-reaching enough to be called revolutionary. But the full significance of this intellectual upheaval will become clear only if we compare it to another scientific revolution which took place in the sixteenth and seventeenth centuries. The significance of this first scientific revolution is fully recognized by the historians of science and historians in general; if I shall recall its main features, it will be only to provide us with a contrasting backdrop against which the salient features of the contemporary transformation of physics will stand out more vividly and more suggestively. The comparison between what is going on now and what went on three centuries ago will clearly show that the distance along which physical science moved in the last fifty years is not only greater than that covered in the last three centuries, but also—and this is far more significant— greater than the distance separating the science of Newton from that of Aristotle. In other words, the twentieth century revolution is far more profound than what was rather inappropriately called “the Copernican revolution;” the intellectual distance between Aristotle and Newton is far smaller than the distance separating the world of Newton and Laplace from that of Einstein, Planck, de Broglie, and Heisenberg.