Third Stone from the Sun

No one knows who they wereor what they were doingBut their legacy remainsHewn into the living rock…Of Stonehenge

– Spinal Tap

Picture yourself on a train in a station. The presence or absence of Plasticine porters with looking-glass ties is irrelevant.¹ For some reason, the station is called Entity. Entity Junction, in the county of Anywhere.

There are two platforms in Entity Junction, and they consist just of the two sides of the concrete sliver on which the very occasional passengers pace up and down—after all, it's just a junction. Rather than having numbers, the platforms have names. As you stand looking out towards the crisp blue sky of Anywhere in one direction, trains arrive on the platform called Platform Past. As you stand looking the other way, you see trains arriving on the platform called Platform Future. The station is quite narrow, which means that passengers in the train arriving at Platform Past can easily see the passengers leaving from Platform Future as the train begins to pull slowly out of Entity station.

If you are sitting on one of the trains, or on one of the very few benches on this mysterious, rather empty junction in the middle of Anywhere, you can get the strange feeling that you are moving even when you are still. You experience relative motion. When the train on Platform Past starts to move, the people on the train that's waiting on Platform Future can feel as if they are moving.

You start to wonder, where is Platform Present? According to your habitual image of how time works, Platform Present should be smack in the middle between Platform Past and Platform Future. But there is no Platform Present. There is just the concrete sliver, that small junction called Entity, just a name and a couple of benches—it's that kind of train station. The search for a terminus might be fruitless.

Like all analogies, this analogy for how actual entities are (the study of which is called ontology) doesn't really work—we can't help visualizing the platform of a stable present that we can point to and walk up and down on. But the analogy does allow one to see how the present could be reconfigured as a relative motion between past and future rather than something that exists by itself. One often imagines the present as a thing that exists all by itself, like some kind of bubble. It doesn't matter what size the bubble is—it could be a nanosecond, it could be three million years. Whatever size the bubble of the present is, it is subject to paradoxes that make it very unlikely. For instance you can infinitesimally subdivide it, so that movement across it becomes impossible (Zeno's paradox). Or if the bubble has no parts whatsoever—this in itself is paradoxical because if the bubble has any size at all, how come it can't be measured?—then movement across it is impossible in another way.

Trains arriving at Platform Past are very vivid for some reason. They are brightly painted. They have well-tuned, distinct whistles. All the door handles are brilliantly polished brass. The trains that arrive at Platform Past are called Appearance. Appearance trains are always very distinct like this, and you can see all the work that went into them. You can see the old dusty seats in Carriage A; where the door between Carriage A and Carriage B was broken by someone trying to rush through the train; how someone replaced one of the doors in Carriage C with a differently painted one; how the breaks squeak on Carriage D.

There is something strange about trains arriving at Platform Future. You can't see them so clearly. Something makes them appear blurred, as if there is always more to what you are seeing than you can discern at any one moment. The trains that arrive on Platform Future are all called Being. While Appearance trains seem very vivid and obvious when you look at them, Being trains seem to evaporate the...