IN JULY 1962, Michel Siffre took off his watch and descended into the abyss of Scarasson in the French Alps. There, in a cave 130 metres below the surface, he set up camp next to a glacier. With a torch as his only light source, and deprived of all reminders of the passage of time, he lived underground, alone, for 63 days.

When he emerged, wearing goggles to protect his eyes from the sun, the world’s press was waiting. Siffre was a geologist, but what he had originally planned as an expedition to study the glacier had become famous as something completely different: the first study of the human response to living with no information about time. Siffre was the first to show that our body might have its own clock. Since then, chronobiology has become a hugely important field of research.

Now nearly 80, Siffre lives alone in a small apartment in Nice. It is so crammed with souvenirs, including giant fossil ammonites, that it resembles a cave itself. A ball of energy despite his age, he apologises for the disorder, although everything here, from the framed photos of his exploits to climbing equipment hung on the wall, demonstrates how this energy has been a defining feature of his life.

As he shows me a tube of the electrode paste used on Apollo missions, he describes how the space race was his inspiration. Yuri Gagarin had just become the first man in space and the US and USSR wanted to know what effect long missions would…