“Yay!” she shouted – “which ones?” She loves a long list of them, and eagerly consumes everything ridiculous and grotesque about them – Egyptian mummies, Aztec sacrifices and mad Roman emperors.
We’ll start with the earliest and work our way up, I said, but first I want to show you something about every empire ever. Can you draw a timeline, a long line with little marks to represent centuries?
She did so, and said, “What are the years?”
They can be any years, I said – the same thing happened several thousand years ago as happens now. First, do you remember the yeast in the bottle?
She remembered the example well – a single yeast cell was dropped into the bottle at noon, double every minute, and the bottle was full at midnight. She had learned that the bottle was half full not at 6 pm, as seems intuitive, but at one minute to midnight. The bottle was about one per cent full at seven minutes to midnight, and so on.
Do you remember why they multiplied that way? I asked. “Well, they could eat the sugar,” she said.
Right, I said – they found a new resource, and it made them multiply. Do you remember how to draw their growth? I asked.
“Sure,” she said – “It’s exponential.” Can you draw that kind of curve over the timeline? I asked, and she did, starting with a low straight line right over the timeline and then sweeping upwards.
Good, I said – that’s what happens when a certain group of humans finds a new resource. Why won’t the exponential growth curve go on forever? I asked.
She looked at me like I was crazy. “Because exponential growth always ends in a die-off,” she said, looking bored; we’ve done that lesson many times.
Well, it has to end somehow, anyway, I said. So how does the curve end? I asked, and she drew the rising curve peaking and plunging down again.
Excellent, I said. What you’ve just drawn is an empire. That’s what an empire is.
“What, they multiply like yeast?” she asked.
Maybe not quite so dramatically, I said, but it grows all the same, and then hits a peak and declines. It starts when a group of people can tap a resource that no one else could. Maybe they bred a certain kind of plant into a crop, or tamed a certain animal, or found a new land where the animals never learned to be scared of humans and didn’t run away. It can be a new technology, like the Romans put iron shields together into a wall, or like the Vikings developed ships that could brave the far seas. It could be a new religion.
“Wait – what?” she said. “Even if everyone turned to a new religion, they’d use the same energy as before.” Yes, I said, but a religion can change the way people live, and encourage some people to give their lives or go evangelising.
Thing is, look at the timeline below it – what do you notice?
“It doesn’t take long,” she said, “just a few hundred years.”
It can take longer or shorter, I said, but even if it’s just a hundred years, that’s slow by human standards. In the rearview mirror we can look and see that it was a rise and fall, but we don’t really see it happening, or understand while we’re seeing.
She nodded thoughtfully, and then asked, “Can we pretend to be people in one of the empires? Like can I be the queen of the Persians, and you be one of the Spartans?”
You can absolutely be queen of the Persians, I said – you don’t want to be a Spartan yourself?
“Not a Spartan woman!” she said. “I don’t want to be kidnapped on my wedding day and shave my head.”
Fair point, I said. Okay, you’re queen of the Persians. We spent the next five minutes sword-fighting with cardboard rolls, until she curled up with a book and was ready for bed.