Many Worlds

I'm a third of the way through The City We Became and while I'm enjoying the story so far, the exposition has reminded me that I'm a little weary of the many worlds theory. It seems to be the go-to pseudo science behind a whole lot of the science fiction I've read or watched recently, and I'm finding it hard to believe that there could be a new universe for every decision that every living creature that ever lived or could have lived. It just doesn't seem plausible. I believe there is only one universe, other than the current one, and that universe is identical to this one except I have a goatee.

I'm pretty sure that even if there was an infinite number of universes, every decision by every living being would get made the exact same way. After all, free will is an illusion. The only way you could change the past is with a time machine that fills up with gummy juices and encapsulates so none of your gut microbiome get left behind.