Big History provides a sort of sketch map of the history of the Universe, and thresholds provide a sketch map of big history. They frame the story and help you navigate through it. I began thinking about thresholds as I tried to help my students at San Diego State University prepare for an exam on big history. Each threshold marks a step in increasing complexity. We start with the very simple universe created by the big bang, and then, miraculously, we watch as more complex things appear, from stars to new chemical elements to planets, then to living things then to us, the most creative, powerful and perhaps dangerous creature that has lived on this planet in almost 4 billion years.
I love the idea of thresholds because it captures the essence of the big history story: the idea of increasing complexity. Complexity increases because already existing energies and things are arranged in new ways that generate new qualities. This is what we call ‘emergence’. However, complexity increases only in those privileged places where the perfect goldilocks conditions exist. And each increase builds on the previous ones so that, if you start a Universe and wait long enough, voila! You may have something as complex as you and me. So the thresholds have a lot to tell us about what it means to be human.
As we climb the mountain of complexity we also have to wonder where the journey stops. And it looks at present as if, eventually, the universe will reach a peak and then we start going down the other side. Now the thresholds will play out in reverse as the universe gets simpler and simpler over gazillions of years.
The thresholds are fun!