Officially there is a single explanation to the origin of the Space Quest Universe. The subject is only briefly mentioned in the Space Quest games, canon or otherwise. Much comes from the Space Quest Companion.
According to Space Quest Companion and occasional line in the series. The humans of Xenon are in fact Human colonists from Terra III (Earth) who grew apart from the motherworld. Supporting evidence for this is given from various minor references from the games, including various sightings of Federation vessels, a similar culture, references to historical events, the various calendars, allusions in the Galactic Inquirer and others (see timeline).
According to the Companion the wormhole traveled by Roger and the Two Guys in Space Quest 3 was a space-time anomaly transporting them back to 20th century Earth. Space Quest III refers to the travel between the blackhole into a parallel universe. Though time travel and parallel universe travel are not mutually exclusive (in some theories of quantum mechanics connected together like the coils of a spring).
Infact Roger Wilco and many of the characters in the game are infact said to be "human" by the narrator and other references within the series. A line in SQ6 suggests that many humanoids in the galaxy are actually of earth origin.
Another theory that appears in fan fictin, is that Space Quest universe is an alternate universe, claiming that the ignorance of the Xenonians as to Earth indicates that they did not originate there (they infact know Earth as "Terra III"). Evidence for this side is much more abstract, usually claiming that the many Earth and culture references are goofs slipped in by the writers trying to create references. They claim that the wormhole was an inter-dimensional portal and exists chronologically parallel to modern earth (rather than being set in the future).
Many varying theories abound not only about the origins of the Space Quest universe and how it relates to our universe within fan fiction, but also whether (if it is an alternate universe) if Xenonians are in fact analogous to humans, and whether the calendar system is based on similar events.
- ↑ Through the passage of time some personal habits haven't changed with humanoids of earth heritage. Although no one knows the true origin, people have been hanging rolls of flimsy paper called azwipe next to their extruded item disposal units. Since no one is certain of its actual use, it is a mere cultural decoration in most circles.