 One of Lakatos’s key examples is the predicted return of Halley’s comet which was derived by observing part of its trajectory and using Newtonian mechanics to calculate the elongated ellipse in which it was moving. The comet duly turned up seventy-two years later, exactly where and when Halley had predicted, a novel fact that could not have been arrived at without the aid of Newton’s theory (S&amp;P: 5). Before Newton, astronomers might have noticed a comet arriving every seventy-two years (though they would have been hard put to it to distinguish that particular comet from any others), but they could not have been as exact about the time and place of its reappearance as Halley managed to be. Newton’s theory delivered far more precise predictions than the rival heliocentric theory developed by Descartes, let alone the earth-centered Ptolemaic cosmology that had ruled the intellectual roost for centuries. That’s the kind of spectacular corroboration that propels a research programme into the lead. And it was a similarly novel prediction, spectacularly confirmed, that dethroned Newton’s physics in favour of Einstein’s. Here’s Lakatos again: