Zero - Charles Seife [23]
The lack of a year zero began to cause problems two centuries later. In 731 AD, about the time Dionysius’s Easter tables were set to run out, Bede, a soon-to-be-venerable monk from the northern part of England, extended them again. This is probably how he came to know of Dionysius’s work. When Bede wrote a history of the church in Britain, the Ecclesiastical History of the English People, he used the new calendar.
The book was a huge success, but it had one significant flaw. Bede started his history with the year 60 BC—60 years before Dionysius’s reference year. Bede didn’t want to abandon the new dating system, so he extended Dionysius’s calendar backward. To Bede, also ignorant of the number zero, the year that came before 1 AD was 1 BC. There was no year zero. After all, to Bede, zero didn’t exist.
At first glance this style of numbering might not seem so bad, but it guaranteed trouble. Think of the AD years as positive numbers and the BC years as negative ones. Bede’s style of counting went…, –3, –2, –1, 1, 2, 3,…. Zero, whose proper place is between –1 and 1, is nowhere to be seen. This throws everybody off. In 1996, an article about the calendar in the Washington Post told people “how to think” about the millennium controversy—and casually mentioned that since Jesus was born in 4 BC, the year 1996 was the 2,000th year since his birth. That makes perfect sense: 1996 – (–4) = 2000. But it is wrong. It was actually only 1,999 years.
Imagine a child born on January 1 in the year 4 BC. In 3 BC he turns one year old. In 2 BC he turns two years old. In 1 BC he turns three years old. In 1 AD he turns four years old. In 2 AD he turns five years old. On January 1 in 2 AD, how many years has it been since he was born? Five years, obviously. But this isn’t what you get if you subtract the years: 2 – (–4) = 6 years old. You get the wrong answer because there is no year zero.
By rights, the child should have turned four years old on January 1 in the year 0 AD, five in 1 AD, and six in 2 AD. Then all the numbers would come out right, and figuring out the child’s age would be a simple matter of subtracting - 4 from 2. But it isn’t so. You’ve got to subtract an additional year from the total to get the right answer. Hence, Jesus was not 2,000 years old in 1996; he was only 1,999. It’s very confusing, and it gets worse.
Imagine a child born in the first second of the first day of the first year: January 1 in 1 AD. In the year 2, he would be one year old, in the year 3 he would be two, and so forth; in the year 99 he’d be 98 years old, and in the year 100 he’d be 99 years old. Now imagine that this child is named Century. The century is only 99 years old in the year 100, and only celebrates its hundredth birthday on January 1 in the year 101. Thus the second century begins in the year 101. Likewise, the third century begins in the year 201, and the twentieth century begins in the year 1901. This means that the twenty-first century—and the third millennium—begins in the year 2001. Not that you’d notice.
Hotels and restaurants around the world were completely booked well in advance for December 31, 1999—not so for December 31, 2000. Everybody celebrated the turn of the millennium on the wrong date. Even the Royal Greenwich Observatory, the official keeper of the world’s time and arbiter of all things chronological, planned to be swamped by the revelers. While the atomic-precision clocks ticked away in the observatory on the hill, the masses down below awaited a state-sponsored Millennium Experience, complete with a “spectacular opening ceremony” that the organizers scheduled for—you guessed it—December 31, 1999. The exhibit’s close on December 31, 2000, is just when the astronomers on top of the hill crack open their champagne bottles to celebrate the turn of the millennium. That is, of course, assuming that astronomers care about the date at all.
Astronomers can’t play with time as easily as everyone else