PTOLEMY’S WINDING PATH
RECENTLY, I FELL IN LOVE. It was a whirlwind romance that caught me completely off guard, but there I was, entranced by Ptolemy’s 1870-year-old astronomy treatise, Almagest. (Or rather, by GJ Toomer’s 1984 English translation of Ptolemy’s ancient Greek tome.)
Before then – and like most of us, I’m guessing – I knew little about Ptolemy and cared even less. After all, he’d created an overly complicated model of the Solar System with the Earth, not the Sun, at the centre, and Nicolaus Copernicus and his followers had proved him wrong. Ergo, who cared about Ptolemy?
How greatly I’d underestimated him! I now think of him as a man of the moment, because he was a key pioneer of empirically based mathematical modelling. We hear a lot about that these days, with models offering our best hope for successful planning in the face of climate change and COVID-19. But as far as modern science goes, it all began with Almagest. It’s an extraordinary book, and not just because it’s the oldest surviving comprehensive treatise on mathematical astronomy. Its systematic presentation of a sophisticated, observation-based, predictive model of the motion of each planet is a masterpiece, a founding blueprint for theoretical science itself.
The story of Ptolemy’s astonishing work is not just scientifically significant: it also has something of the flavour of a mystery novel.
PTOLEMY LIVED IN ALEXANDRIA in the second century, 250 years before Hypatia, the famous female mathematician. Founded as a Greek city in 332 BCE, Alexandria was under Roman rule in Ptolemy’s time, although he was part of the Greek-speaking community there. No-one knows the exact dates of his life and work, although it is generally suggested that he was born around 100 CE and died around 170 CE. The latter date suggests that this year is, to all intents and purposes, the 1850th anniversary of his death.
Ptolemy offers us a glimpse into the kind of creative thinking needed to do science – even
