|WARNING - REFEREES ONLY|
If you're going to play a character in this setting DO NOT READ ON - there's information in this section which may spoil your enjoyment and will certainly ruin many of its surprises.
Think about that for a minute. Ships are going into the past. Once there they're isolated, can't get help in an emergency, and have no way of returning if the displacer is destroyed and another can't be built. But they nearly always come back. There's something odd about that, isn't there? The idea that the past can't be changed is just that. An idea. There is no evidence that the past has been changed, even after attempts are made to change it. Therefore, it's assumed, time can't be changed. It's an assumption, and it's wrong. The adventurers come from a world at the extreme edge of a probability curve.
Whenever someone goes back in time, whether they're trying to change history or not, the arrival of the time ship and the events that occur when it's in the past must inevitably cause changes. But the universe doesn't tolerate events with multiple outcomes, so what happens is that each change creates new timelines without destroying the original timeline. Depending on events there can be tens, thousands, or millions of new lines, each of them containing the time travellers. But the time travellers continue to exist in their original timeline too, and when they go home they'll find that nothing has changed. They don't know - they can't know - that their world is the freak. The original timeline (or more likely one that was modified by time travellers who weren't recorded in the history books) is surrounded by near-identical doppelgangers, each with at least one historical change if you know where to look.
The diagram to the right is an extremely simplified view of just a few of the changes produced by the cruise of the Corinthic mentioned in the opening text.
- She travels back from "now" A to 1588, where her tourists spend a day or two exploring London. As a result dozens or millions of time lines form (an example is 1588 to "now" B), in all of which a ship-full of strangers from the future appeared in 1588 and made an enormous stir. If the Corinthic were to return to "Now" at this point one version of the ship would return to "now" A and find it unchanged, but the overwhelming likelihood is that the ship will return to one or another version of "now" B.
- In most time lines she carries on into the past, as promised in the prospectus for the trip, with her next port of call in 1000 AD. Here another group of time lines form, 1000 AD to "now" C, in many of which the Vikings hear about the wonders of North America and go in to colonise it. In some of them time travel is invented at some point and another group of time lines form, ending at "now" D.
- Going on to 75 AD the Corinthic causes another enormous stir, and there will be endless tales of the strangers who arrived in a floating island and warned of the devastation to come. As a result in many worlds there are far fewer casualties in Pompeii and Herculaneum, with an enormous effect on all subsequent history. Call the resultant worlds E through G (with a few million others) since time travel will probably be invented early and often.
- Next stop 500,000 BC, where there are fewer opportunities to mess up history, but any lasting effect will probably be major. For example, one of the tourists might accidentally infect a tribe of Homo Erectus with influenza, leading to an epidemic which wipes out a large percentage of the species. As a result the history of Homo Sapiens is a little different, forming more timelines leading to "now" I, which will be unrecognisably different from "now" A. Or something might help Erectus, eliminating Homo Sapiens altogether.
- Similarly, in 150 million BC most of the things the travellers can do have minor effects... but there might be a few timelines where the dinosaurs were never wiped out, where they were wiped out early and the mammals weren't under extreme pressure to survive, or where the Corinthic came to grief in this period and her passengers and crew colonised 150 Million BC. One of these timelines leads to "now" H.
- On the timelines where the Corinthic survived she probably heads for 500 BC, where there's another chance of divergence.
- In the original timeline ending at "now" A one spinoff might lead to "now" J.
- In the timeline where history changed in 500,000 BC (leading to "now" I) the alarmed travellers find a world that is nothing like they remember. Maybe there are no Greeks, maybe there are no humans - perhaps Homo Erectus is still the dominanant species. Their arrival in this line can precipitate yet more time lines, such as line K which will eventually lead to its own "now".
- In the timeline where history changed in 150 Million BC (leading to "now" H) there are no humans - or if the world was colonised by humans in the deep past they have by now evolved to something totally unrecognisable. Again, the arrival of the the Corinthic creates yet more time lines, one of which is L.
While in the timeline ending in "now" A the Corinthic returns home to find nothing changed, in every other timeline the passengers and crew will find changes, some subtle and others devastating.
That's what I've written so far this evening. The next bit will be rules for handling this, how to give the players a bit of a chance to survive, etc. All comments VERY gratefully received.