Time past

BC and AD seem at first glance confusing, because there's no "Year Zero", you go from AD1 from 1BC without stopping anywhere that's neither. But there is a Point Zero and it's the only one in history as we reckon it. Or is it?

Two things we need to be clear on to begin with. First, what does a clock tell you? What is 3pm? 3pm is "three hours after midday". So 3:00 is the end of the third hour. Because it begins with a 3, it would be easy to confuse it for the first moment of the fourth hour. But it isn't. It's the end of the third.

The other is that Jesus can be thought of as having an "official birthday". The queen of England was actually born on 21 April at some hour in that day. But she has an official birthday, on which we are bid to celebrate her, on usually the second Saturday in June.

And we all understand the concept that our birthdays begin at some point around 00:00:01 (I'll come back to that) on the anniversary of our day of birth, regardless when we were actually born. I was born at 9:30pm but like everybody, I start to be a year older after midnight on 11 October.

So Jesus was born a few years BC, according to the story. But his "official birthday" is Point Zero.

Now, think about my birthday. When does it actually begin? It cannot be midnight because that belongs to October 10. It cannot be 00:01 because it has already existed for a minute. It can't be 00:00:01 because it has already existed for a second.

So when we reckon the beginning of my birthday we enter a Zeno's paradox. No matter how close we approach the beginning it has still already begun. We can get as close as the Planck length to midnight and we still haven't quite reached its beginning.

So in fact the start of my birthday, and yours, and the queen's, and in fact Jesus', must be considered an abstract that is neither within yesterday nor within today. It is the very moment the clock ticks past midnight but that moment does not have any physical reality.

AD and BC work in exactly the same way.

AD1 is the year after Jesus was "born". 1BC is the year before. There cannot be an actual 0BC or AD0 because the Zero is entirely abstract. So BC becomes AD in exactly the same way that yesterday becomes today.

But why isn't AD1 AD0? After all, no years have passed, right? It should match a clock, where the time it tells is how much is passed. Or 0BC?

Well, it would be rational, of course. But we don't measure years in that way and never have. We label which year it is, not which year it has been, whereas we label which hour has passed. You can consider it "illogical" that the two systems don't work the same way but it isn't. Both are perfectly logical. They're just different. You put yourself in the position of arguing that English is correct and French is wrong, which is understandable to believe, but of course nonsensical.

So in fact, today is the 23rd day of the ninth month in the 2017th year after the official birthday of Jesus. But the time now is 11 hours have past and 21 minutes. But if we measured it in the same way we do years, we should say it is 11:22 or 12:22 or...

posted by Dr Zen @ 8:22 pm