There are many theories about the origin of the subway. By choosing, and dogmatically sticking to one of the theories below, you instantly become a guru in bleeding-edge physics:
- The subway has always existed. It‘s a natural part of the fabric of the universe. (Think Swiss cheese, or the underground tunnels that form in limestone as a result of erosion)
- The subway was built by a very powerful, almost god-like civilization. (There‘s no trace of them now.)
- The subway was built by a great federation of many advanced civilizations. (No trace of them either, nor any left-over ‘scaffolding‘ used during construction.)
- Insert your own pet theory here.
Anyway, though the possibilities of the subway seem endless, the problem has always been to find the entrances. The entrances are small, and very far apart for slower-than-light travel. Of course, being made of dark matter, they‘re pretty near invisible too, so they are extremely difficult to find. Once found however, the finder must immediately report the coordinates to GAIA by law. Gaia, consisting of extremely risk-averse AI‘s, decided that all subway strings first need to be scouted out to see where they lead before making them generally available. Even though finders are rewarded most handsomely, there are still those who elect not to give up their private subway entrance. The reasons for such selfish behavior are many and varied.