In 1543 a church administrator in a cold corner of Poland published a book claiming that the ground beneath our feet is in motion. Everything you have been told about what happened next is wrong.

He was not persecuted. He was not mocked. His system was not simpler than the one it replaced, and it was not more accurate. Sixty years after publication, the number of astronomers in all of Europe who accepted it could be counted on the fingers of two hands, with fingers to spare. The central idea was not even his: a Greek had proposed it eighteen centuries earlier, and the mathematical machinery came out of Damascus. Every test we instinctively apply when we ask whether someone is a genius or a crank would have returned the wrong answer in 1543.

And yet something separated Nicolaus Copernicus from the many confident men of his century who were simply wrong. Something visible at the time, on the first listening, to anyone who cared to look. This book goes looking for it.

The search turns out to concern everyone. A three-year-old who asks why the moon follows the car stands in precisely the position Copernicus occupied: holding an observation that does not fit the accepted picture, with no way to tell whether the picture is wrong or he is. So does the professor with a stubborn anomaly in her data. So does the man who arrives at a newspaper office with a notebook proving that Einstein was mistaken. At the moment when nothing is yet known, all three are indistinguishable, and so is everybody else who has ever asked how the universe works.

Rivalry with Copernicus is a field guide to that moment. It dismantles the legend piece by piece, follows the real canon through his sieges, his lawsuits, his currency reforms, and his forty years of silence, and arrives at a single test that does not care about your credentials, your confidence, or the eventual verdict of history.