For 100 Musings on Writing Fanfiction my thoughts on writing in one of my favorite genres (by all rights I should do one of these posts for the angst genre at some point).
The distinctions between alternate universes, realities, timelines (and other more precision definitions) are inherently complex and the lines tend to change depending on what fandom you're looking at. Two sources that I've found that explain the differences fairly well are the fandom_grammer community:
http://fandom-grammar.livejournal.com/59739.html and the fanlore site:
http://fanlore.org/wiki/Alternate_Universe. If you're interested I suggest checking out both those links as they have more in-depth examples than what I'm going into here.
First, a little bizarre personal history. I never used to read AU stories. I also never used to ship, which is a whole different issue entirely, but I preferred the stories I read and wrote to be as close to canon as possible. I think Stargate Atlantis was probably where I first took the leap into full blown AUs, though I had started to reading some alternate timeline fics in the Harry Potter fandom a while back. Now, years later, AUs are one of my favorite genres, and there are very few reasons I will walk away from a deliciously angsty AU in a fandom I love.
Most of the big projects I'm working on write now are AU in some form or another. Both of the Stargate Atlantis fics for BigBangs are AU, the large Criminal Minds fic that I've been dragging my feet on is a full blown family AU, the slightly smaller Criminal Minds fic (the first of three parts) is what I would call an Alternate Timeline, since there's only one character with a changed history. On the other hand, I have an even smaller Criminal Minds story in progress that is a direct Alternate History for a specific episode. Finally, the other piece I've been working on is a sequel to my fic where everyone on the BAU team are serial killers, which is almost a Mirror AU in a way, in the traditional sense of a Star Trek mirror!verse.
So what is it about AUs that suddenly have me so desperately hooked?
For Strength of the Pack (the shifter AU I wrote) it was two things. The first was that I thought that I could write that story in 50k for NaNoWriMo and have words to spare. I was very wrong. The second was that the idea of Reid turning into a leopard cub was just too adorable to resist. After that I was flooded with ideas about what shifter politics should look like and how that effects their experience of the world, and what it means to have a pack. Team as family is a theme that I identify very strongly with and Stargate and Criminal Minds both give me ample opportunities to examine that in close detail. AUs allow that connection to be made even more explicit.
The Criminal Minds family AU that I've been slowly working on for the past 6 months has been in my head since, oh around February or March of 2011, when I was watching season 4 of the show for the first time. It took me another eight months to even start to approach it, and I realized that I wanted to work in as much of the show canon as I could.
In all of my favorite AUs they use canon in interesting ways. Minor characters, names of places, allusions to canon events all serve to make the connection to the original show stronger and for me really enhance the experience.
One of the things I love about AUs that are not possibly in our reality is the exploration of different dynamics. Full world BDSM AUs frequently make interesting and thoughtful allegories to our more gender-focused culture, Space AUs explore politics and culture with more elegance than many science fiction tv shows. AUs that allow for psychic bonding and ghosts and supernatural creatures often show relationships in a new way that still resonate deeply. Even though many many authors revisit these AUs over and over the unique details are what build the universes.
The prevalence of coffee shop AUs (with bakeries being a close second) has been disparaged lately, but I find that removing the trappings of space travel and fighting crime lends to some very interesting character studies. One thing that an AU forces an author to do is focus on character just as much as setting. These characters are still the ones from the original book or show, but bringing them back to those defining traits is incredibly powerful. The Community episode Remedial Chaos Theory explores timeline AUs, which very well drive home the point of how character dependent AUs are. In each timeline events change slightly, but the core of what drives each character remains the same. Having said that, I now am in desperate need of some fic exploring the adventures of evil!Troy and evil!Abed.
I think what AUs boil down to for me are the possibilities. With an AU anything can happen, if you can justify it. Once one of my literature professors was talking about the interpretation of stories and he said (more or less) "Not every story is an allegory of a birthday party, but if you can make a good argument for it, then go for it. There are many possible answers, but not every answer is a right answer." That probably makes a lot less sense out of context, but I look at it kind of like this. Canon stories are a little bit like math equations. You have all of the variables set out for you, and depending on what you plug into the equation you get different answers that are essentially "correct". AU stories are more like writing essays for English class. If you can make a good argument and essentially prove your case, it doesn't really matter if you're "right", you've still got a good essay.