Different universes?

Hi All,

In this post I'm focusing on the science fiction aspect of this subject, although people are free to look up modern-day scientific hypotheses (e.g. Evertt's many worlds)   on multiverses , first thought of by Schrödinger in 1950s Dublin.

In science fiction parallel and alternative universes are often used interchangeably , although sometimes people have noted that  there are some subtle differences  (if one reads Wikipedia or any sci fi forum) between the two  and the overall encompassing universe is called the multiverse. 

Broadly speaking an alternative universe deals with the micro of the world and  is a place which is similar to our own, i.e. the laws of physics are still the laws of physics,  humans are around,  but the place different in some way.  For example fixed wing aircraft may never have overtaken airships as a way of travelling or maybe history is different e.g. Rome never fell,  the Nazis won the war etc. 

 As a corollary to alternative universe , one can say that not only do they exist all at once, but are constantly being created by the tiniest of details, which can have profound effects. Take by way of example throwing a stone on a pond. The initial plop creates waves and ripples than effect more than just the initial spot in which it landed.  You go out , you meet someone, that someone becomes a friend then a lover. You have children, one of which becomes a great physician , musician, or world leader. Or maybe even there's a darker outcome : that child becomes a monster, a war criminal or some other tyrant. But it all happened because you stepped out one day.  If you didn't then it never happened, but there's an alternative reality where it did happen.

By contrast a parallel universe is implied to be in parallel to our own , but different in the grander scheme of things ,  at a macro level,  e.g.  the abovementioned laws of physics don't apply and therefore you can have stuff like comic book  superhero powers,  magic, maybe Elves and Orcs as well. In one sense the "wizarding world"  of Harry Potter 's a parallel universe or for classic literature maybe Tolkien or CS Lewis in Narnia. Presumably even in parallel universes there are alternatives ....

The possibilities are endless. I wonder if God see a them all?