In my earlier discussion of space travel in our own future, I mentioned wormholes as one of the varieties of travel my Shine Cycle predicts we will eventually use to travel in our own universe. But in my writing such junctions between disparate locales are not always restricted to two places within one universe; by using wormholes, or other methods (largely what I call “applied metaphysics”), it is possible to send information or even fleets of ships from one universe to another.
Naturally occurring interuniversal wormholes are even rarer than the ordinary interstellar variety, and are tremendously valuable, since they make regular, comparatively cheap trade between universes possible. Aside from those fortunate worlds—and the even rarer places where metaphysical costs are low enough to even think about building artificial wormholes, or gates, for non-emergencies—sending even only a small message from one universe to another is quite expensive, and transporting people or supplies is a major undertaking, so anything that isn’t both important and urgent usually waits until there’s enough to justify the cost. (I allude to this in the first chapter of my novel-in-progress Sunshine Civil War.)
These gates connect more worlds—universes—than just ours and the world in which most of the series is set. There are wormholes connecting it to Reignalmia, several that we might consider “alternate histories”, most likely the Waste, the battered peninsula on which “A Backwater Rebellion” is set, and more. But gates can also be constructed into places or worlds that we might consider fictional or legendary (it becomes even less clear whether the worlds or the fiction caused the other); most of these, many “alternate histories,” and some others are known as “postulated universes” (since each answers a “what if?” question, and first contact from them to the rest is vanishingly rare), while the remainder (including ours) are called “standard system” universes.
Oddly, while physical and even metaphysical laws and constants are not necessarily quite the same from one universe to another, technology, techniques, and even tradition developed on one world tends to work (if not quite optimally) on other, different worlds, but defy attempts to integrate the principles behind them with those of the other world. (You could put the Vorkosigan Saga‘s Necklin rods, RCN sidereal sails, and the Dillingham hyperdrive of Piper’s future history on one ship, but it would probably end in disaster.)
What do you think?