The Multiverse is the collective name of all of the alternate zones and different realities that exist in conjunction with the world of Sonic the Hedgehog. These include different versions of the same dimension or vastly different ones, often accessible only through advanced science or powerful magic.
The exact properties of the multiverse are currently unknown. The Prime Zone supposedly at the centre of it, with other realities with varying similarities to the Prime Zone surrounding it. The multiverse has been relatively unexplored for the most part, with at least two alternate realities known to exist. (SU: #55, SB: #8)
There are other multiverses that exist independently from the one containing Sonic's world, such as the dimension of Earth 20XX, amoung various others. Normally these multiverses are incapable of contact with each other, and it has only been the efforts of villains such as Dr. Eggman or Dr. Albert W. Wily, and other anomalies such as the Genesis Portals, that have made it possible. (MM: #24, SU: #51, #78, StH: #248)
- Ian Flynn revealed in a Q&A that most of the zones that existed prior to Worlds Collide have been destroyed. He has also indicated that the Sol Zone's Jeweled Scepter is the reason that zone has merely been altered, rather than wiped from existence. The Q&A also revealed that Worlds Unite may end up showing a whole new multiverse.
- However, aside from the Sonic Boom Zone, it seemed that no other zones in Sonic's multiverse appeared during the crossover. Although it did introduce the concept of a Nexus.
- In a previous Q&A, Ian Flynn indicated that if the Prime Zone were to be destroyed, no other alternate zones would come into existence. This was in response to a query inspired by the release of the recent Teenage Mutant Ninja Turtles animated film, Turtles Forever, in which the original Mirage Comics universe was deemed "Turtle Prime" and that, if it was destroyed, all others would follow.