A Romantic Comedy, as told by Newton

Over the (southern) summer, I am digging into N-body dynamics as I start work on a couple of new research problems. To warm up, I wrote a simple code which tracks the motion of a handful of particles interacting via their mutual gravitational attraction. 

Watching the intricate dance the particles made in my simulations, it struck me that I had also inadvertently invented an algorithmic story-generator. 

Projecting a story onto moving dots makes about as much sense as giving names to patterns of stars in the sky or finding shapes in the clouds — which is to say, quite a bit of sense. After all, making up stories about the material world seems to be one of the few universal human activities, and is perhaps one of the human instincts that has led to us become a scientific species. 

Like the physical world, stories have rules. Take the rom-com, for example — girl meets boy, but then some other boy (or girl, but always exciting and wildly unsuitable) gets in the way; misunderstandings abound and hilarity ensues. Whatever happens along the way, the film ends with the happy couple happily coupled while the unsuitable suitor slinks off into the distance and/or conveniently pairs-up elsewhere. 

Here’s a classic three-body rom-com. Physics-wise it shows the interactions between three planets (or stars, gravity does not discriminate) with identical masses which are initially at rest. This system is chaotic — a tiny change to the initial arrangement can make a huge difference to the subsequent story. 

In this movie, a brief but promising dalliance between Blue and Green is interrupted by Red, who is mad, bad, and dangerous to know. Blue and Red fall into a swirling, tempestuous relationship (warning: purple prose!). But just as the rejected suitor seems to be leaving forever, a last-minute change of heart brings Green back to the centre of the action, and this time, Blue is definitively attracted. The story ends with Red wandering off, footloose and fancy free, while Blue and Green join the ranks of the celestial Smug Marrieds. 

Call it Bridget Jones’s Orrery.  

Happy holidays.