One of my favorite game worlds, by far, is the classic Traveller universe. Traveller is a table-top role playing game set in the far future, approximately 3600 years from now and the game world is truly gigantic.
For humanity to go to the stars it will take technological breakthroughs that open up fundamental aspects of our physical universe to practical use. One example of this is fusion; we see fusion in action every sunny day and every cloudless night. The sun and stars create a huge amount of energy by fusing hydrogen into helium and the ability to harness this clean source of energy could help us break free of gravity and move around our solar system. But even with an energy source like fusion the stars are very far away in space and time. What if we could harness gravity to manipulate space-time? Using gravity we could create our own singularities and use these to “warp” space-time in such a way that we could move from one point to another much faster than we can in “normal” space.
Warping space-time is of course an old idea about how to “get around” the light-speed limit so that humans could travel to other stars within their life times. This idea is the basis for the Traveller universe. Gravity manipulation is use to create singularities that surround a starship in a warp bubble (another dimension/a worm hole) allowing that starship to “Jump” several light years in space. Since the starship is using gravity to move very long distances and trying to arrive at a pretty specific location it must move away from other gravitational sources. This requires that the starship travel in normal space far from planets, stars, and other massive objects so that the warp bubble isn’t distorted and the “Jump” leads the ship where wants to go.
Using this technology humanity could travel to other stars, entirely new solar systems filled with resources and even other planets to live on. But what if we went to the stars only to find that we were already out there? In the Traveller canon that is exactly what happened; when we left Earth we found a large and ancient human empire already out there. The backward humans from Earth, that just recently figured out the “Jump” drive, weren’t that big a deal to a 1500 year old space empire. So we called ourselves Solomani (named after the ancient Roman sun god Sol) to separate ourselves from these “other” humans (who called themselves Vilani after their own home planet) and began to build our own empire. You can learn more about the “future-history” of Traveller at my web site here:
There are more links on that site that will lead you to more in-depth details about Traveller but one of my favorites is the Traveller Map. This site shows how large the Traveller universe really is and also how well developed it has become over the years. You can zoom in on this map and look at sectors, sub-sectors, and individual star-systems (with planets and asteroids and civilizations).
Traveller is the ultimate in sand-box RPG’s, there are literally thousands of worlds to be explored.