I read in Asimov's magazine, in the eighties or nineties. The author was French. The concept was not exactly the same. But the protagonist found three mirror worlds, her own, and two others. She was a person with different character traits in each world. It is not exactly what you describe, but the story came to mind when I read your post. I wish I could remember more.

When I worked at a bookstore, his backlist took up practically a whole display bookcase.

one of my favorite sub-genres in science fiction.

Depending on exactly when and what kind of a change is postulated, and how carefully it's thought through, alternate history can be a delight.

Most of the people who write it tend to go with: what if the South and won the Civil War, or What if Hitler had won WWII. Although there are also lots and lots of others. I haven't yet seen an alternate history novel or story that goes with the What if Al Gore had become President in 2000, although there is one out there called Christian Nation by Frederic C. Rich in which John McCain wins the 2008 election, but dies a few months later, and Sarah Palin becomes President. So the extreme fundamentalist Christian right gets in charge, with the sorts of consequences you'd expect. It is plausible and scary.

A different alternate universe one is The Mirage by Matt Ruff. In this one, on November 8, 2001, Christian extremists hijack four planes in the Middle East. Two are crashed into the Tigris and Euphrates World Trade Center in Baghdad, one into the Arab Defense ?Ministry in Ryadh, and the 4th is crashed by its passengers in the desert. A decade later mysterious artifacts have begun showing up which seem to be from a world in which the United States, which in this world is a collection of backward Christian theocracies, is the only super power and a similar attack had occurred there. It's quite well done and I liked it.

Sometimes the concept is that people can somehow move from one parallel universe to another. The best example of that is Alternities by Michael Kube-McDowell. In that one a man stumbles across a portal to another universe, and it winds up being controlled by the repressive authoritarian government of that world. During the time frame of the novel, which is set in the 1970's, they only know of six other universes, all of which are sufficiently close to our own (and yet very different in many ways) that operatives from the home universe can travel and conduct business in the others. Very, very good.

Harry Turtledove is the master of alternate universe novels. He has several different series going on, so you might want to look him up also.

fantasy or science fiction. There are so many directions for the imagination to go. However it's interesting to think about it as a real possibility too. The blog I was referring to posited that science is coming close to proving it but it had so much other far out stuff on it that I decided not to link to it.

are divided on whether alternate universes actually exist. There's one theory out there that every single small decision anyone makes results in a branching off of another universe, so that new universes are coming into being all the time. Others say, no, it doesn't happen.

And if there really is a multiverse, there's also divided opinion about whether or not we could ever cross over into another one. It seems to me, without actually researching this very much, that the consensus is that there may very well be other universes out there, but we will never know for sure because we will never be able to directly observe or interact with them.

That's why I like science fiction, especially alternate history. That and time travel.

like Bridge Across Forever ... hmm, that's may not be the title - it was by Richard Bach. Let me see if I can find. Yep, it is right. The Bridge Across Forever: A Love Story.

So many possibilities. I wish we could find a way to get into one of those universes. Like right now, I wish I could switch over to a happier universe where the past election went in a much better direction for us Dems. Sigh.

A universe where Gore became president is definitely interesting to think about. Also, Stephen King wrote a story recently that somewhat touched on the subject of parallel universes. It was a story about where JFK's presidency would have went if he hadn't been assassinated.

I also like to think about a universe where Bush and Cheney didn't finish out their second term as they were brought down by scandal and personal difficulties. Some of us felt so certain that that would be the reality we'd experience, but I guess we may have just overindulged in wishful thinking a bit much. Sigh again.

Yeah, so many possibilities to think about.

One of my favorite movies that touch on the parallel universe/time travel concept is Donnie Darko. I love that movie.