In Volume 2’s “The Bridge,” it is revealed that the Upside Down is actually part of a wormhole connecting Earth and The Abyss, another dimension occupied by Vecna ( Jamie Campbell Bower ), the Demogorgons, Mindflayer, and more.

Stranger Things Season 5 Volume 2 introduces exotic matter as a key component of the Upside Down, but what is it, really?

Dustin Henderson and the rest of the squad in Stranger Things get a pretty decent briefer on wormholes by his science teacher Scott Clarke in Season 1, Episode 5, entitled Chapter 5: The Flea and the Acrobat.