The Multiverse is anything and everything that does or will exist and everything that has existed. Earth-90 is just one Universe This page is specific to media produced by Brywarrior Productions, a sub-studio for 7th Planet Studios.
The Multiverse is defined as "an infinite realm of being or potential being of which the universe is regarded as a part or instance." -- Dictionary.com
The Multiverse itself if everything. Plain and simple. Earth-90 is the name of the Universe that BBO and related elements exist inside of. It is possible to travel between Multiverses,but this has nott been shown in BBO yet. Inside each Multiverse, there are sub-divisions and sub-divisions inside those that go as follows: Universes, Dimensions, then Timelines and Pocket Dimensions.
Inside the Multiverse, there are hundreds upon billions of Universes. Bryce Bowman: Origins takes place in Earth-90, aside from one episode. This universe holds everything that has happened, will happen, or could happen in the franchise. The universe is then divided into separate Dimensions, based on major or catastrophic events.
Dimensions are sometimes another name for an alternate universe, but this is different than how they operate in Earth-90. For every single event, there are hundreds if not millions of outcomes that could happen. For each of those outcomes, a Dimension forms. This continues on for each event subsequently occurring after the first. Dimensions are only formed when a major event occurs. In the starting Dimension, the event passes without consequence, and relatively nothing is changed, but a new Dimension is formed where the event had a massive impact, and thus the new Dimension is completely separate from any other. Dimension 1, or the Prime Dimension, is the Dimension in Earth-90 that the series follows. Any major alterations from this course of events are separated into another Dimension.
Dimensions can be broken down, and divided into smaller pieces called Timelines. This split occurs with every event that has ever occurred. While these events do cause a split, they are not big enough to create a whole new Dimension, so all Timelines inside each Dimension are relatively similar. As such, it should follow that all Timelines containing a "Bryce Bowman" are in Dimension 1, but this is not correct. Black Scythe is from Dimension 50, but he is Bryce Bowman of that Dimension. Black Scythe doesn't possess on Omnitrix, and this is the major change that separates his timeline from Dimension 1, thus creating Dimension 50.
The Null Void is the only known pocket dimension in Earth-90. It is specific to each Timeline, and thus cannot be used to travel between timelines. It is known that the Null Void exists for all timelines within Dimension 1, but it is unclear whether or not it is the same one.We only know that the Null Void itself doesn't exist for other Dimensions, but it is likely that something similar exists in other Dimensions.
It has been seen that people can travel between pocket dimensions, timelines, and Universes. Specifically, Bryce traveled to the Kenn 10: Omnistorm Universe, Zs'Skayr was sent into the Null Void, and Bryce traveled into the future of an alternate timeline.
It is known that the future Bryce traveled to was his own, but is not anymore. This possible future now exists as part of a separate, but similar timeline and has been replaced by a future that matches Bryce's current state. This may also change later if circumstances change for Prime Bryce.
It is known that travel between Dimensions is possible, as Azmuth is not from Dimension 1.