The Janus Point summary

Let’s return to the pool table for a moment. 

Remember that the two balls colliding was a time-reversal symmetric process. But a full game using these balls doesn’t work the same way. Let’s think about a popular billiard game called snooker, for example. If you watched the whole game in reverse, you’d witness a miracle: all the red balls jumping out of the pockets to line up in a perfect triangle atop the table, with the white ball separating itself from the pack. 

How will the universe end? There are several theories. The most popular is that of heat death. It has nothing to do with global warming – no, in fact it describes the direct opposite. This theory says that the universe will, eventually, reach maximal entropy. Heat will die out completely, and that will leave the universe so cold that motion –⁠ and by extension, all life as we know it –⁠ will simply cease to exist.

This destruction of the universe through entropy is certainly frightening. But is it inevitable? The author argues that it isn’t. That’s because, in his view, entropy is not actually growing. Instead, what’s increasing is complexity, or, in other words, order. One by-product of this growth is that complex subsystems –⁠ like Earth –⁠ emerge and become self-contained. 

You’ve probably heard the famous story of Isaac Newton and the apple tree. Supposedly, Newton noticed an apple drop to the ground, and that inspired him to develop his theories of motion. 

In particular, he became famous for solving the problem of how the Moon moves around the Earth. What exactly he was solving became known as the two-body problem. It’s a subset of a larger theory called the N-body problem, which can help predict the behavior of a finite number of gravity-driven points. 

Imagine a box filled with gas. What if we suddenly removed all the walls of this box? Well, the particles would soon begin to fly off into space. This means they'd begin to occupy a larger volume. It would seem that entropy was growing. 

That’s not the end of the story, though. The particles would move away from that box in a very specific way –⁠ their trajectories would remain exactly the same. 

Let’s go back to our three-body system. In it, the particles are arranged in a sort of triangle. And what’s a triangle? A shape, of course. The three-body model is meant to represent the entire universe. By extension, that means the universe –⁠ no matter the configuration of particles –⁠ is a shape. 

Our universe, of course, has many more than three particles, but the statement still holds true. Shapes in the universe coalesce into subsystems of ever greater complexity and order.