Who gets to decide the truth?

Until the 1600s, the average annual rate of economic growth in human history was approximately zero, on a per capita basis. Economies developed haltingly and, by today’s standards, minimally. Politics consisted of a long and bitter series of wars, revolutions, and coups, punctuating variously short or long periods of oppressive and corrupt rule. Regimes came and went, and borders were redrawn, and politics staggered from one empire, invader, or upheaval to the next. Doctors and scholars knew barely more than the ancients had known—in some respects, less. The word scientist did not exist; neither did the concept of science as we know it today.

Knowledge existed, of course, and impressive kingdoms appeared, and new technologies emerged. But an objective observer would probably not have said that the Europe of the late medieval period was better organized or more advanced than the Europe of the Roman Empire at its height. In the year 1500, alien visitors might reasonably have pegged Homo sapiens as a stuck species. “Come back in another 100,000 years,” they might have concluded, “and maybe these goofballs will be interesting.”

And then it all changed.