Japan has paused. In preparation for the abdication of the old emperor, and the accession of the new, companies and government offices are closed, and it is the duty of dutiful workers to stay at home; even the calendar will change. Ever since 1989 (as we count), official Japanese documents have counted years up from the year Heisei 1. On 1 May the year will reset, and babies, until then born in the year Heisei 31, will instead be born in Reiwa 1; and the years will continue to be numbered through Reiwa until the new emperor dies or abdicates.

The convention of dating events by reference to reigns, or periods of office, is not unique to Japan. In fact it was once almost universal. It reaches back as far as organised politics. In Greece, the Spartans dated by their kings, the Athenians by their judges; and the Roman republic counted from the mythical foundation of the city. None of these conventions survived the crumbling of the political structures that they both commemorated and upheld. That is why later Christians, amid the chaos of local rulers that followed the fall of the Roman empire, had to invent the dating system we still use.

Even British laws were dated by the year of a monarch’s reign until 11 Eliz. 2 (or 1963). But the political structures of Japan have shown a remarkable continuity, and their use of era names as a dating system has remained the same since AD645, in a sequence unbroken since AD701. It is still used exclusively by more than a third of the population, although the proportion is falling rapidly.

All of these dating systems extend time in a linear way distinct from calendars, which repeat in cycles. None of them recognise time as we experience it, which is a quality that neither clocks nor calendars can capture and historians can only hope to reconstruct. All dating systems construct a measurement that is independent of memory and subjectivity. This is what makes them valuable and also deeply alien. The time we actually live through works like a squeezebox, expanding and contracting, so that the hours of boredom crawl through us like slugs, while moments of pleasure are as quick as kingfishers, even while the clock measures each from the outside as the same.

The astonishing precision with which time is now measured pervades modern life – the satellite-based global positioning system (GPS) depends on almost unimaginably accurate timekeeping – but we don’t measure life in nanoseconds. “The 90s” remains a much more real concept than any individual year; the dates of “austerity” are much harder to bring to mind than the way that it feels. The curious discomfort felt by some people when they feel that their chronological age is out of sync with their stage of maturity is another example of the mismatch between outer and inner time. The apparent awkwardness of the Japanese system is actually a testimony to the way in which time seems at once an element we can’t control and something entirely socially constructed.