Multiverse:~-
Simpley stated, the Multiverse is a class of several different time period roleplays that have absolutley nothing to do with one another except for the fact that they run in a timeline sequenced pattern.
Aside from that, there may be a few things that can't be helped when it comes to them intertwining with 'Universe' [Subforum] or another. For example, Characters that exist in the Sail Era, may happen to be the great grandfather and/or grandmother of someone in the Regency or Steam Era's. Other chance crossovers may include Historical Facts, though due to events having happend differently between the two 'Universes', these archives may vary.
This is commonly refered to as String Theory. If there are any further questions, which I'm sure there will be, please feel free to ask. Another way - and might I add a wicked cool way - to check out more about String Theory and Multiverses is to go out and buy, rent or borrow the Movie 'Donnie Darko'. It covers parallel universes pretty well. Just remember: Watch Closely - You Could Miss Something.