Rick said:
If you want a way of quantifying the multiverse in a way that makes sense from a roleplaying perspective - try the 'Luther Arkwright' graphic novel series. On one parallel they identify the different parallel universes with a numerical code, using their own parallel as a baseline, 'zero-zero'. So, for example, 00-00-00-05 might only differ from your own parallel slightly (e.g: Napoleon forming a world-spanning French Empire after conquering Russia in 1812), whereas 00-00-01-00 might differ significantly - neanderthals might be the dominant human form, for example and 00-01-00-00 might not have an earth present at all. 99-99-99-99 would be a complete opposite to your baseline, where the physical laws of the baseline parallel might not even work and the universe is markedly different in all respects).
The point being, you will get many parallel worlds where the 'divergence' from our own is comparatively recent and will differ from ours in many respects, but the further back in time the divergence happened, the more differences there will be.
I did a bit of that a while back, thing is, I'd have to write a whole timeline from the divergence point to the present for each universe, and there is no concise way to represent each Universe unlike the 6 attributes for the UWP. I am a fan of Sliders, but that is not what I had in mind here, basically its another means of interstellar travel, but one that completely ignores the local stars around Sol. I've read about wormholes how if you created one assuming the ends start out close together, you could accelerate one end to near the speed of light, say to Alpha Centauri, lets say from the end's point of view it takes a year of accelerating and decelerating to arrive at Alpha Centauri, whereas in the outside universe the end is seen to take a bit over 4.4 years to get there. (Through hard acceleration!) The people back on Earth however only have to wait one year, they can then step through this wormhole to arrive at Alpha Centauri 3.4 years in the future, but they also can step back through the wormhole and end up a moment just after they left, in this case the time travel doesn't matter because the distance in light years is greater than the distance in years. But from Alpha Centauri A you could create another such wormhole and accelerate and decelerate it back towards Earth and it arrives 3.4 years later as seen from the outside, but only 1 year after that as seen through the second wormhole. One can then step through the first wormhole from Earth to Alpha Centauri and arrive 3.4 years in the future, then one can walk to the second wormhole opening at Alpha Centauri and step through that and end up back on Earth another 3.4 years in the future, for a total of 6.8 years in the future on Earth, and by retracing ones steps through the two wormholes one can walk 6.8 years back in time just moments after one left. Now you have a two-way time machine with these two wormholed. One can go back and forth and change history endlessly and either it causes paradoxes or the universes split off from one another both universes being mostly identical except for the tiny changes wrought by the time traveller's meddling with history and of course the butterfly effect that follows. If you go onb making these timelines, you end up with a lot of universes that end up looking much the same with an endless number of parallel Earths, and you can have trade and commerce between them through these wormholes, and each Earth ends up pretty much like any other, so as before you had 8 billion people on Earth, with these two wormholes, you now have 16 billion people on two parallel Earths, and each individual or almost each will have his near identical counterpart in the other Earth, though one being 6.8 years older than the first. This doesn't to me look like a very interesting cosmos. With parallel universe, no chance of a time paradox, there is no reason for each Universe not to interfere with any other, unlike a time travel campaign with paradoxes, where there is an effort to preserve history.
So to start all over with wormholes and make a consistent universe with a bit of strangeness and newness to it, instead of a series of almost identical carbon copies of Earth, I change my first assumption about wormholes, namely that you can create a wormhole with both ends close together in the same Universe, what if you can't?
What if you can create a wormhole, but the other end ends up somewhere else, you can't control where or when that other wormhole opening ends up. Sensors and probes are sent through the wormhole, and most often the other end is in intergalactic space. The Hubble constant is measured (the rate at which the Universe expands) and in each case it is a little or perhaps a lot different, some Universes are big and old, while other Universes are smaller and young, they all seem to have originated in a Big Bang, but each Big Bang seems to have occured in a different moment in the past. The game mechanic is roll 3d6-4 to determine how many billions of years old the Universe is, this will produce a range of from 0 to 20 billion years. Our Universe is about 13 billion years old. Astrogation checks do no good, it is hard to tell whether it is the same Universe at different times or different Universes and different Big Bangs altogether. People tend to shrug it off and say, "Hey, there are stars and planets here we can colonize!" The same effect I mentioned with the first wormhole operates here, except both wormhole ends effectively start out in different Universe, they are not casually connected. The fact that the other end of the wormhole appears in intergalactic space is of no consequence, galaxies can be seen, a telescopic observation determines which Galaxy is the nearest one, and the starship at the other end carrying the wormhole end starts accelerating there, no need to worry about fuel, as it can be pumped through the wormhole as needed.
There is this website which calculates travel times:
http://www.convertalot.com/relativistic_star_ship_calculator.html
Let say you had to travel 2,000,000 light years to reach the nearest galaxy to start exploring, and lets say you had a ship which could accelerate at 6 gs, this calculator says it would take 5.2751665975024125 years of ship time to reach that Galaxy. As I said before there is no artificial gravity in this setting, but then there is no need for anyone to be on that ship at the other end, it can be piloted remotely through the wormhole, the pilot can remain on Earth if he likes, fuel would be fed through the wormhole to the ship at the other end, and it constantly accelerates at 60 meters per second squared.
according to the rules of the calculator:
1. The star ship accelerates continuously from the origin to the midpoint of the mission.
2. At the midpoint, the ship turns its thrusters to face the destination.
3. The ship decelerates continuously from the midpoint to the destination.
So the people back on Earth wait 5.275 years for the other end of the starship to arrive at the Galaxy they are intersted in, it does not matter how much time elapses in that other Universe due to time dialation, as there is nobody they care about observing that trip. So they wait 5.275 years look for a near Earth like planet, one that is almost like Earth, and with all these stars to observe, you can get a planet that comes pretty close, they want a primitive atmosphere like the Earth had about 4 billion years ago, and then they introduce Earth life to it rather that wait for evolution to create its own complex life, this life is largely single-celled plants algae optimized for photosythesis, and then the ship takes off and leaves, they go on a 1,000,000 light year journey in a near circle, while keeping track of that planet they left behind. This second Journey takes another 5.051281901423193 years from their perspective, a little more than 10.32 years is required for the entire project to come to fruition back on Earth, and then comes landing day, the ship lands on an Earthlike planet with a breathable atmosphere, the life is still rather primitive, but now the atmosphere will support higher life forms from Earth, so those are sent through the wormhole, trees and grasses are spread to every continent, wild life is distributed, and then the ship takes off again on a shorter journey, this time they travel a circle that is 100,000 light years in circumference. This takes another 4.307553805162063 years their time or a total of 14.63 years their time to accomplish, finally the ship lands one final time, and colonists step through to a planet with virgin forests and lots of wild life, or that is the hope anyway. Little is known about this Universe they travelled to, no one know who or what else lives there. Plenty of opportunities for adventure. Obviously this setting is tailored to the Scout Career, much of it has to do with exploration. There is no true predictable faster than light drive, if you want to visit a neighboring star to this world, you have to go by slower than light travel.
I hope I've made this setting clear to you.