What of Lazarus?

And Roddenberry's original 1964 series prospectus included among its "story seed" premises "The Mirror," in which the starship Yorktown came upon its exact duplicate, but only one of them could survive. Although that's more like Voyager's "Deadlock" than "Mirror, Mirror," I guess.

I'm sure there were a lot of SF stories about alternate worlds that were a "mirror" of our own -- in some ways, it goes back to Lewis Carroll's Through the Looking Glass and the like. DC Comics introduced their "evil twin" universe Earth-Three in 1964.

 

It certainly wasn't a new story idea. I was just pointing out that, in an early iteration, "The Alternative Factor" had elements similar to "Mirror, Mirror" in it.

 

^And I was expanding on your point with other, reinforcing examples, not questioning it. Taken together, the examples demonstrate that the basic idea of a "mirror" or "anti" universe was not unprecedented and multiple different people came up with forms of it independently. As, indeed, is almost always the case with just about any idea.

 

I assumed the odd void they were in is like the Phantom Zone in Superman and Superboy in that time and ageing cease as do concomitant needs such as food, water, et al.

 

I assume that the void exists outside of space-time, or something, and they only observe a few minutes at most before entropy of the multiverse in quadrillions of years (our time) breaks through their protective bubble, and they explode or suffocate or something.

 

Which is a trope that doesn't make sense. If there were no time, there'd be no life, no thought, no movement, because all those things require the passage of time. There's no picking and choosing which actions occur and which are suspended, because time is part of everything. If time doesn't pass, everything's frozen in a single instant forever.

 

^ If there's no time, there's whatever the writer says there is. There are no rules at play here.

Hell, we're already into the realm of fantasy by that point anyway.