Question Are alternate universes possible?

We know that canonically, time travel is possible, but we'll basically never see it do big things like change history, 'cause it's too complex or something. Although we did see it when Fey and Toni fought their future selves...

How about alternate universes? Are those canonically possible?

Basically, "time travel is not possible for regular people" -- you have to be a Mythos-level character to be able to do it, and even so it has limitations (otherwise the Bastard would simply go to the past and kill his opponents as toddlers) -- probably related to how the Sundering fractured the timestream.

Alternate universes? Hmmm... I don't remember this having been explicitly touched upon in canon. But there are pocket universes, as seen in "Sit In", and extradimensional spaces, such as wherever Phase moves mass to, and wherever Tennyo's "real" body is located. I believe that the Whateley cosmology works with a manifold of at least ten dimensions as background (cf. Boston Brawl II), and Pattern Theory works with many-dimensional concepts too.

So I believe that somewhere in that theoretical framework there is room for the many-worlds interpretation of quantum mechanics. Meaning that: yes, there are probably parallel universes.

Will the characters ever be able to contact them? That's an entirely different question...