So recently I was asked for my opinion on alternate timelines and alternate universes, particularly as used in comics. This is really a big topic to tackle all at once so I thought I would break it down into two parts. This week I wanted to look at what kinds of alternate universes there are, just so we’re all on the same page, and then next week I’ll give my opinion on the usefulness of each in telling a story.

Let me start by defining what’s not an alternate timeline for the purposes of this discussion, namely anything like alternate history fiction. If we were to accept that definition then all fiction counts as an alternate timeline of some sort and the term just stops being useful. Yes, there are genres of fiction that are deliberately structured to be to our world as some of the following definitions of an “alternate timeline” are to fictional worlds but when you get down to basics you’ll realize all fiction does fit that description to some extent so you just have to ask how much the creators intended for that to be true. If that makes sense.

Let’s just move on.

For a story to have an alternate universe premise it must have two separate worlds that are somehow the same (a shared history, shared characters or something similar) and then make the characters of those two worlds aware of each other. That’s a little dense, I know, but maybe I can clear up what I mean by giving some examples of the four prevailing types of alternate universe.

The first, and probably best known kind of alternate universe is the Baileiesque alternate universe. This kind of alternate universe I’ve named for George Bailey, the protagonist of It’s a Wonderful Life. George’s story is one of the biggest, best known examples of the type in popular culture and most people probably know the story already, how George Bailey was contemplating suicide and callously tells his guardian angel that the people who know him would have been better off if he’d never been born.

So Clarence, George’s angel watchman, takes his charge to a twisted, darkened world where George meets people and sees places that should be familiar but seem to have been robbed of something that made them good and vital. It’s a world where George Bailey was never born.

Baileiesque alternate timelines are always defined by the person who visits them and exist to show them something about themselves. They’ve been used in everything from simple morality stories like It’s a Wonderful Life to iconic science fiction like the Star Trek episode Mirror, Mirror. These alternatives are narrative devices that let characters and audiences explore some path not taken and strive to make sure that both audience and character see as much as possible from their “home” world reflected in the alternative timeline.

The second kind of alternate universe is the Narnian alternate universe. These kinds of places are entirely different from the world as we know it, possibly even having different rules governing them from the beginning of time. As the name implies, Narnian universes are best embodied in C.S. Lewis’ fantasy series The Chronicles of Narnia. They are places of wonder visited by (usually) more mundane people who become something more than they were as a result of their visit.

Unlike Baileiesque stories, Narnian alternate universes serve to build something new in characters, rather than reveal something that is already true about them. Narnian stories are hero’s journeys, rather than opportunities for introspection. As a result there’s as little overlap between people, places and histories as possible between most Narnian alternate universes and the homes of the characters who visit them.

The third kind of alternate universe is an Ultimate universe. The name is derived from Marvel’s Ultimate line of comic books, where that publishing house completely reimagined its heroes with modern backstories and a more tightly written continuity. Characters were reworked to fit new sensibilities or storytelling conventions. Then the whole thing eventually crossed over into the main Marvel timeline before Mainline Marvel, Ultimate Marvel and a few other Marvel ideas got mashed into an incomprehensible mess that’s supposed to be the new continuity going forward.

Confused? I am too.

Let me try and give a better illustration of the Ultimate alternate universe phenomenon. Get on Netflix and watch Star Trek, both the original TV series and the movie Wrath of Kahn, then the two recent J.J. Abrams films. If anyone accuses you of wasting time tell them it’s for science.

Back? Good. You’ve now experienced the Ultimate phenomenon in a very limited case. When Star Trek was rebooted the studio couldn’t resist using Leonard Nimoy to tie-in for all the fans of the classic series. But the way this reboot reinterprets the characters, particularly in the case of Uhura and Spock, and casts the entire crew of the Enterprise as misfits rather than the cream of Starfleet is done entirely to make the narrative more exciting for modern viewers. The very long shadow Star Trek: The Wrath of Kahn casts over Star Trek: Into Darkness is another classic hallmark of Ultimate alternate universes and the existence of Nimoy-Spock solidifies the modern movie franchises as true alternate timelines, since they’ve interacted with the original.

Unlike Narnian and Baleiesque alternate universes, which exist primarily as narrative devices, Ultimate universes exist to allow a popular story that has grown out of hand or out of relevance to take the highlights and rebuild the story and characters into something new and easier for new audiences to get into. At least, in theory.

The final kind of alternate universe is the quantum alternate universe or the more commonly used term multiverse. You know how I said Baileiesque universes show how the world would be if one thing were different? Quantum universes assume that all the different things that could happen did happen and each has its own universe. Basically, a quantum universe is the ultimate attempt to answer “what if?”

Now the thing that makes multiverses tick is that lots of people travel around in them – there’d be no point, narratively speaking, otherwise. The alternate possible universes are open to everyone, so they don’t have a character building purpose as a set piece. Rather they are almost always the central lynchpin of the plot, the thing that makes everything else interesting and effective. The many alternate universes in a quantum universe is somewhere between MacGuffin and Deus Ex Machina, driving the plot forward and bringing it to a close.

So these are the four broad types of alternate timelines that exist in modern fiction. How good or useful are they? Tune in next week and we’ll hash that out – but if you want the short version it’s “depends.”