• Choose a category
• All
• Classic-Fiction

That is the same with all our other laws—they are not exact. There is always an edge of mystery, always a place where we have some fiddling around to do yet. This may or may not be a property of Nature, but it certainly is common to all the laws as we know them today.

Yet in its unfinished form the law of gravitation explained so much. To a practicing scientist, that validated it. The same small parcel of mathematics explained Tycho Brahe’s nightly observations of the planets in the sixteenth century and Galileo’s measurements of balls rolling down inclined planes, timed against the beat of his own pulse. The planets are falling, Newton reasoned; the moon feels the same force as an earthly projectile, the force weakening with the square of the distance. A law is not a cause—philosophers still wrestled with this distinction—yet it is more than merely a description. It precedes the thing explained, not in time but in generality or in profundity. The same law explained the earth’s symmetrically bulging tides, rising both toward and away from the moon, and the newly measured orbits of the moons of Jupiter. It made new predictions that scientists could confirm or disprove with experiments on balls hanging delicately in a laboratory or observations of majestically rotating galaxies a hundred million million times larger. “Exactly the same law,” Feynman said, and added—having struggled to find the right wording—

Nature uses only the longest threads to weave her pattern, so each small piece of the fabric reveals the organization of the entire tapestry.

Meanwhile, why does an object in motion tend to travel forever in a straight line? That, Feynman said, nobody knows. At some deep stage, the explanations must end.

“Science repudiates philosophy,” Alfred North Whitehead had said. “In other words, it has never cared to justify its truth or explain its meaning.” Feynman’s colleagues liked to think of their gruffly plain-spoken pragmatist hero as the perfect antiphilosopher, doing rather than justifying. His own rhetoric encouraged them. He lacked patience for the now-popular What is reality? brand of speculation arising from quantum-mechanical paradoxes. Yet he could not repudiate philosophy; he had to find ways to justify the truth that he and his colleagues sought. The modern physics had banished any possibility of discovering a system of laws unambiguously tying effects to causes; or a system of laws deduced and conjoined with perfect logical consistency; or a system of laws rooted in the objects that people can see and feel. For philosophers, these had all been marks of a sound explanatory law. Now, however, a particle might or might not decay, an electron might or might not pass through a slit in a screen. A minimum principle like the principle of least action might be derived from laws of forces and motion, or those laws might depend on the principle: who could say with logical certainty? And the basic stuff of science had grown inexorably more abstract. As the physicist David Park put it: “None of the entities that appear in fundamental physical theory today are accessible to the senses. Even more … there are phenomena that apparently are not in any way amenable to explanation in terms of things, even invisible things, that move in the space and time defined by the laboratory.” With all these traditional virtues removed—or worse, partly removed while still partly necessary—it fell to science to build a new understanding of the nature of explanation. Or so Feynman argued: the philosophers themselves, he said, were always a tempo behind, like tourists moving in after the explorers have left.

Scientists had their own forms of blindness. It was often said in the quantum-mechanical era—Feynman had said it himself—that the only true test of a theory was its ability to produce good numbers, numbers agreeing with experiment. The American pragmatism of the early twentieth century had brought forth views like Slater’s at MIT: “Questions about a theory which do not affect its ability to