Dear 22nd century,

I have no doubt that many of you have lived in, worked in, or at least visited space. To us, it seems likely you'll have at least one moon base, that you're mining ridiculously mineral-rich asteroids, and that the long hard work of terraforming Mars has begun. You've probably set foot on the more interesting moons of Jupiter and Saturn. Space may even seem a bit mundane to you — the solar system variety, at least.

The real space question is this: Have you given up on the whole idea of traveling farther, of visiting or settling planets other than the ones in our solar system? I fear you have.

I'm not talking about the faster-than-light dream. The speed of light is likely just as impassable in your century as it is in ours. Science fiction that says otherwise is mostly magical thinking. It's likely we can't even get close, given the titanic amounts of energy it takes to accelerate to even a fraction of the speed of light.

No way around it, each light year — or 6 trillion miles — will take decades to cross, and there are barely any stars in a 10-light year radius. We're in a celestial suburb. The only way humans have ever seriously considered getting to the realm of other star systems is in vast starships designed to run for a century or two. Because they would probably take multiple generations to reach their destination, space nerds call them generation ships.

But the last few years have not been kind to the generation ships dream. The science seems to be telling us that generation ships are a dream too far — and science fiction is starting to follow suit.

This is a wrenching thing to have to write. Tales of generation ships have fired my imagination for as long as I can remember. I love all the tropes — the ones where the Earth-like ships are so vast and old that the inhabitants, descendants of the original crew, have forgotten they're on their way to another star (such as Robert Heinlein's classic Orphans of the Sky, in which the vessel is launched in the 22nd century). Or the ones where the colonists are all in cryogenic storage and one is accidentally woken decades early (like Chris Pratt in the much-maligned 2016 movie Passengers).



