One thing I decided while writing my first historical novel, Another Green World, after some 20 years of writing mostly science fiction and fantasy, was that the challenge is much the same.

In each case, you’ve got to assemble — first in your own mind, then in words for the reader — a richly textured world that you have never seen and cannot hope to visit. The characters have to seem real and alive no matter who (or what) they are: nature spirits, monsters, SS officers. And in the end, the reader must feel that he or she has actually, impossibly, seen and heard and smelled this place — experienced not only its high and low points, its joys and terrors, but also its mundane, day-to-day ordinariness.

There are differences, of course. History has already happened, and so lends itself to a certain kind of intensive, fine-grained research. You can learn, for example, that if one Ingo Miller left a certain hotel in a certain city on a certain day, he could have picked up the morning edition of X and discovered a front-page story about Y. The internet is an invaluable helpmate. For the narrative purposes of Another Green World, I was able — even on the early web of the late 90s — to find photo facsimiles from the guest book at a youth hostel in Thuringia, dating from the very week my fictional flock of Wandervögel came to roost there. In some of the entries, the young German guests had drawn pictures, inscribed poetry, scrawled slogans of the day. It was like a magic portal opening directly to their thought-world. Fabulous! And cheaper than time travel.

But SF and fantasy also requires research, for most of us at least. As a kite needs its string, a successful flight into speculative fiction needs to be tethered somewhere, to some outcropping of consensus-reality upon which you and the reader can agree. Are we going to posit that fairies exist? Cool! So let’s look closely at what people have written and sung about fairies over the past few centuries. Or maybe we imagine an interplanetary fellowship based on a shared love of computer games. We might decide then to inquire into such things as universal grammar, population genetics, the physics of space travel, the fine points of game code, artificial habitats, and exobiology.

This may be a unifying principle: the farther a fictional world extends beyond our own, the harder we need to work to make it “real”. What are the seating accommodations in a Roman villa? How does a dryad unwind after a long day in the forest? What are the fondest memories of a Nazi anthropologist? Yes or no: do androids dream of electric sheep? You may not, as a writer, need or want to give us all the answers in the limited space of the narrative. But you really ought, I think, to have some pretty clear thoughts of your own. Some reader, somewhere, is likely to wonder. So you should wonder too.