Dimension 1138

For all intents and purposes, the Dimension 1138 appears similar to our real dimension, with the exception that humanity as a whole is more innovative and creative, making common knowledge out of things that were ground-breaking an era later in our world.

The progress timeline that D1138 involves (based off of Cyberpunk and its derivatives) is as follows:

The Stone Age

The Mythic Age

The Clock Age

The Steam Age

The Deco/Diesel Age

The Atomic Age

Essentially, the story of Earth to Sender takes place as the end of WWII has caused society as a whole to find extremely high value in nuclear power. It's destructive capabilities were seen as a means to immense constructive capabilities. With humanity's enhanced technological prowess, nuclear engineering is taught as early as elementary school, with those who have a passion for the craft leading the economic and technological charge.

Though every "modern" creation is powered by atomic fusion, from small fusion cores to enormous reactors, there are still elements of earlier eras to be seen. Machines run by gasoline can still be found, though they are widely considered inferior and are mainly used for decoration or scrap. Steam-powered devices are rare, and therefore valuable. Purely-clockwork designs are almost extinct, Mythic designs are legend, etc.

With the ChronoCaddy MK IV's dimension hopping capabilities, the band is able to move between dimensions. This allows them to not only evade the ever-persistent Transgalactic Federation, but also allows them to see things that, to put it lightly, most beings just don't get to see.