The problem with crossovers between SF/fantasy universes, even aside from licensing issues, is that they can really only work as "imaginary stories."
stories basically imaginary?
That's what Alan Moore said...
("Imaginary story" was the term used by DC Comics in the '50s through the '70s for out-of-continuity stories about situations that weren't intended to be "real" within the series' main continuity, like Superman dying or getting married -- the same sort of thing Marvel did in What If...?
The greatest "imaginary story" was "Whatever Happened to the Man of Tomorrow?" by Alan Moore, which came out at the time that DC's whole continuity was being rebooted and was basically the final adventure of the Bronze Age or "pre-Crisis" Superman. Moore's narration contained the classic line, "This is an imaginary story... but aren't they all?")
Agreed. That's why I NEVER want to see a Star Trek/Star Wars crossover. I can only enjoy Star Wars as a strict fantasy; there isn't a shred of actual SCIENCE in it anywhere. Some argue the same is true of Star Trek, but I disagree. Some of the Star Trek episodes have been inspired by real science, and some of them have gone on to inspire future real science. And at least Star Trek never used the word "parsec" as a unit of time!
was meant to be science fiction in the vein of the prose works of the '50s and '60s. Star Wars
was meant to be "space fantasy" in the vein of Flash Gordon
and John Carter of Mars
. ST hasn't always lived up to its aspirations of credibility, but SW has never had any to begin with, being essentially a sword-and-sorcery epic dressed up with space-opera trappings.
The only way I could even begin to make my Sliders/Xena crossover make sense was to have an AU where Alexander the Great didn't die young, but made it all the way across Asia and over to North America. And since the time setting of Xena skips around from biblical to current year with NO attempt to explain the discrepancy, I figured I didn't need to worry too much about the Xenaverse showing up in modern-day California instead of ancient Greece.
Well, as long as you're treating the Hercules/Xena
universe as the "home" universe, you can accommodate just about anything, since those shows embraced their origins in mythology and folklore and often basically admitted that they were pure fiction, playing fast and loose with reality and blurring the lines between reality and fiction.
Although you could borrow the conceit from the Sliders
episode "The Guardian" that time flows at different rates on some worlds, so that even though it's technically the present, events on that world might be very far behind where they are on "our" Earth.
Conversely, you could play off the Xena
clip shows that had clones or reincarnations of the main characters existing in the present day (in fact, in a present day where Xena
is a TV show).
So you can combine unlikely SF universes if you anticipate the problems and come up with a creative, in-universe solution...
Yeah, it helps gloss over the historical differences if you go the alternate-universes route, although it's harder to use that to justify the whole geography and alien population of the galaxy being completely different (I don't remember there being any Vulcans or Klingons in the universe of Arrakis), let alone the laws of physics being different. Ideally I'd prefer a case where you can just do an honest crossover and treat shows as part of the same reality and timeline. But that's very hard to find in science fiction.