Einstein didn’t care much about experiments. Of the three tests he proposed for general relativity, the first—that clocks should tick slower in a gravitational field—wasn’t satisfied until after his death. Early experiments tended to contradict the prediction. His second prediction, that light from distant stars would be deflected by the warped space-time around the sun, catapulted him to world fame in 1919, when observations of a solar eclipse seemed to confirm his prediction. But as historians have since shown, the 1919 measurements were equivocal at best.
The one unequivocal verification of Einstein’s theory during his lifetime was his explanation of a tiny anomaly in the orbit of Mercury. When he finally got that calculation to work, that was the only evidence he needed that space and time really were warped. “Nature had spoken to him,” wrote biographer Abraham Pais. “He had to be right.”
We now know he was. Just ...
