depth and scope, but also in sheer volume. The membership of the American Physical Society, for example, increased 400-fold from about a hundred in 1900 to over forty thousand in 1997. In part this growth reflects ballooning university enrollments, but it is also a symptom of the evolution of the scientific enterprise from a genteel academic pursuit into a robust component of the world's economy. The story of the transistor illustrates the transformation. Life without computers is now as unthinkable as a computer without miniaturized transistors. Those, in turn are products of a vast applied research effort at university and industrial laboratories that was rooted in pure, basic research. The lineage of today's laptop leads straight back to Werner Heisenberg's discovery of quantum mechanics in 1925. Turning to the coming century, and trying to anticipate the future directions of science, it helps to remember that the great discoveries are rarely the outcomes of deliberate searches for universal answers, but more often the unanticipated dividends of careful research focused on modest, specific questions. Nearly four hundred years ago, for example the German astronomer Johannes Kepler struggled for four years to remove a tiny discrepancy in the calculated orbit of Mars -- and discovered the laws that govern that motions of all the planets in the universe. In this century, Ernest Rutherford was investigating the details of the passage of charged particles through matter, when he hit upon the atomic nucleus. in the 21st century the passionate pursuit of particular problems will likewise yield wonderfully unexpected universal insights. And what are the profound insights physicists could hope for? We may soon know what dark matter is, and whether the universe will continue to expand forever, but how did time begin? General Relativity teaches us what gravity is, but where does mass, which measures inertia even in the absence of gr...
