A shared universe is a set of creative works where more than one writer (or other artist) independently contributes a work that can stand alone but fits into the joint development of the storyline, characters, or world of the overall project. It is common in genres like science fiction. It differs from ‘collaborative writing’ where multiple artists are working together on the same work, and from ‘crossovers’ where the works and characters are independent except for a single meeting.
The term shared universe is also used within comics to reflect the overall milieu created by the comic book publisher in which characters, events, and premises from one product line appear in other product lines in a media franchise. The term has also been used in a wider, non-literary sense to convey interdisciplinary or social commonality, often in the context of a ‘shared universe of discourse.’
Fiction in some media, such as most television programs and many comic book titles, is understood to require the contribution of multiple authors and does not by itself create a shared universe and is considered a collaborative art form. Incidental appearances, such as that of d’Artagnan in Cyrano de Bergerac, are considered literary cameo appearances. More substantial interaction between characters from different sources is often marketed as a crossover. While crossovers occur in a shared universe, not all crossovers are intended to merge their settings’ back-stories and are instead used for marketing, parody, or to explore ‘what-if’ scenarios.
It can become difficult for writers contributing to a shared universe to maintain consistency and avoid contradicting details in earlier works, especially when a shared universe grows to be very large. The version deemed ‘official’ by the author or company controlling the setting is known as ‘canon.’ Not all shared universes have a controlling entity capable of or interested in determining canonicity, and not all fans agree with these determinations when they occur. Fans also create their own unofficial contributions to a shared universe in the form of fan fiction. While never regarded as canonical, certain ideas may become influential or widely accepted within fan communities, who refer to such ideas as ‘fanon.’
Some writers, in an effort to ensure that a canon can be established and to keep details of the setting believable, employ tools to correct contradictions and errors that result from multiple contributors working over a long period of time. One such tool is ‘retconning,’ short for ‘retroactive continuity,’ which resolves errors in continuity that came about through previously-written conflicting material.
The expansion of existing material into a shared universe is not restricted to settings licensed from movies and television. For example, novelist Larry Niven opened his ‘Known Space’ setting to other writers initially because he considered his lack of military experience prevented him from adequately describing the wars between mankind and the Kzinti. The degree to which he has made the setting available for other writers became a topic of controversy, when Elf Sternberg created an erotic short story set in ‘Known Space’ following an author’s note from Niven indicating that ‘[i]f you want more ‘Known Space’ stories, you’ll have to write them yourself.’ Niven has since clarified that his setting is still to be used only ‘under restricted circumstances and with permission,’ which Niven granted to the several authors of the ‘Man-Kzin Wars’ series.
A setting may also be expanded in a similar manner after the death of its creator, although this posthumous expansion does not meet some strict definitions of a shared universe. One such example is August Derleth’s development of the ‘Cthulhu Mythos’ from the writings of HP Lovecraft, an approach whose result is considered by some to be ‘completely dissimilar’ to Lovecraft’s own works. Less controversial posthumous expansions include Ruth Plumly Thompson’s and later authors’ sequels to L. Frank Baum’s ‘Oz’ stories and the further development of Isaac Asimov’s ‘Foundation’ universe by Greg Bear, Gregory Benford, and David Brin.
By 1961, Marvel Comics writer and editor Stan Lee, working with artists Jack Kirby and Steve Ditko, merged the bulk of the publisher’s comics characters into the ‘Marvel Universe.’ Marvel sets its stories in an increasing number of alternate realities, each with an assigned number in a greater ‘multiverse.’ DC and Marvel have also periodically co-published series in which their respective characters meet and interact. These intercompany crossovers have typically been written as self-limiting events that avoid implying that the DC Universe and Marvel Universe co-exist. Exceptions include the twenty-four comics released under the metafictional imprint ‘Amalgam Comics’ in 1996, depicting a shared universe populated by hybridizations of the two companies’ characters. Marvel has since referred to this as part of its setting’s greater multiverse by labeling it ‘Earth-692.’