Forty years ago, Neil Armstrong's definitive line of technical poetry, "Tranquility base here, the Eagle has landed," marked a human achievement that still inspires awe. It also challenges the twentieth century idea of progress and helps us redefine it for the future.

We often hear that progress in technology is incremental, an ever upward arc of performance. Apollo showed how a perfect storm of politics, engineering, and skilled pilots can leap ahead of ordinary rules. Yet we have not returned to the moon, not ventured to mars, and only rarely, if ever, matched Apollo's excitement in subsequent human spaceflights. Apollo remains an historical anomaly that undermines our twentieth-century notions of progress.

Public discourse today is fond of measuring progress with Moore's law about the power of the microchip. Back in the twentieth century, it was aviation and spaceflight that marked technology's advance, relentlessly breaking barriers. Leading the way, the Apollo astronauts' role was carefully crafted to epitomize the modern heroic explorer: the man who risks his life in a far away place for the national or scientific good. Apollo 11 followed Charles Lindbergh's flight by only forty two years. Higher, faster, farther were the watchwords, and history suggested the progress might continue indefinitely.

Apollo's six lunar landings seemed like a point on that upward curve, but in fact they were its apogee. For some, twentieth-century progress seemed to stop right about 1970. People assumed they would soon fly on supersonic airliners, but the American super sonic transport SST project was canceled in 1970 (even its European competitor, the Concorde, stopped flying six years ago). Apollo was celebrated as the start of a new wave of human exploration, but forty years later the six lunar landings remain the highest, the fastest, the farthest that humans have ever gone.

Did technological progress stop in 1970? Of course not, but it did take a turn, and began moving in new directions. Following Apollo's innovations, the microprocessor was invented in 1971, ushering in a world of ever expanding computing. Since then our idea of progress, rather than simply higher, faster, farther, has reoriented toward smaller, lighter, and more complex. We now focus on measures that incorporate social, informational, and economic factors rather than strictly Newtonian velocity, altitude, and distance. Companies that produce jet airliners, for example, now define progress more by increasing safety and reducing cost per passenger-mile than by increasing speed.