It's theoretically possible to create a wormhole whose end points are at different moments in time. If you could somehow accelerate one end of the wormhole away at relativistic speeds and then back again, you'd create a one-way time machine. Time Dilation would cause the end that moved away and returned to "age" less than the other end, similar to the concept behind the Twin Paradox. You'd end up with a very limited "time machine" in that endpoint A is some amount of time "behind" endpoint B. Traveling from A to B would essentially move you into the past by a tiny amount. Traveling from B to A would move you into the future by the same amount. If you went from A to B and back to A all via the same wormhole, the time you gained and lost would cancel out.
A clever person (and anyone capable of creating wormholes is more than likely very clever) might set up two such wormholes. One from A to B that saved you a few minutes of time when traveling that direction. The other goes from a point near A (we'll call it A2) to a point near B (which we'll call B2). This one we accelerate the other end (A2 instead of B2) and return it, so that when you travel from B2 to A2 you go back in time by a tiny amount. Let's say we step into the first wormhole at point A at the present moment, and arrive at point B approx 1 minute in the past. We walk a couple steps from B to B2, and enter the wormhole there. When you enter B2 you arrive at A2 1 minute before you left. We've now traveled a total of two minutes into the past. If you stepped from A to B again, you'd be three minutes into the past, and from B2 to A2 again would make it four minutes. By continuing to travel through the ring, I'd be able to travel further and further into the past, though I can't move to a time before the wormholes were created.
If you travel in loops in the opposite direction, you could use the "roman ring" of wormholes to go into the future. Not that you'd want to, but similar arrangements can be built with more complex configurations than two wormholes, provided they are symmetric and appear in a multiple of two.
There remains a possibility that the math behind the Roman Ring is actually just taking advantage of a flaw in our current mathematical models of gravity, and that experimenting with such a wormhole-turned time machine would fail to get the predicted results. Since stable wormholes may require more energy than the output of our Sun, it seems unlikely this will be tested in our lifetimes in the real world. See also Chronology Protection Conjecture for additional arguments why such loops may prove impossible. Don't let that stop your gaming, however. Time Travel is fun.
Game and Story Use
- An inventor / scientist working on teleportation or wormhole production might accidentally create a time machine.
- In a setting where spatial wormholes exist naturally, but are beyond our technology to create or manipulate, one may be able to chart out a route that transits between multiple natural wormholes to get the effect of a Roman Ring. They probably won't be as conveniently arranged as artificial ones would be, however, so it may take years of your life (spent piloting a space craft on a specific course) to move back in time.
- In other words, not worth it for vacation or petty dabbling, but still within the realm of possibility for a mad scientist, the unhinged obsessive time-traveler with an axe to grind, or a sufficiently motivated time abyss.
- Or, such routes might be utilized by temporal refugees fleeing the end of the universe. Yes, it sucks to lose 10 years of your life aboard ship, but if it means dodging the bullet that wipes out humanity, and thereby assuring another 30 to 50 years of life for yourself, it may be worth it.
- A Roman Ring can create a fun sort of chase scene or adventure towns scenario, where you travel back in time between the same two or four locations repeatedly, seeing them in progressively earlier eras.
- Creating a Roman Ring would definitely take Sufficiently Advanced Technology and a huge power output. So don't piss off the folks who made it, because they'd got the resources to take care of themselves.
- A Roman Ring might be housed in some sort of stellar megastructure, and left behind by the Precursors.
- It starts off looking like a dungeon romp in space, but if the PCs figure out that the two "teleporter" stations are actually a Roman Ring, they could travel back in time and visit the civilization that built the place.