‘Stranger Things’ Season 5: What is the Abyss?

“Everything we have ever assumed about the Upside Down has been dead wrong,” Dustin (Gaten Matarazzo) says in Stranger Things Season 5, Volume 2. And how right he is.

The latest batch of Stranger Things episodes blows the show’s world-building wide open, revealing what, exactly the Upside Down is. But that’s not all. It also gives us more detail into the mysterious dimension where Henry Creel/Vecna (Jamie Campbell Bower) has been hanging out, which Dustin coins “the Abyss.”

So what’s the deal with the Abyss, and how is it connected to our world and the Upside Down? Let’s break it down.

What is the Abyss?

In the world of Dungeons & Dragons, the Abyss is “a realm of pure chaos and evil,” as science teacher Mr. Clarke (Randy Havens) describes it. That makes it the perfect namesake for the alternate dimension that Henry has made his home. Before the release of Season 5, Stranger Things fans referred to this world as “Dimension X,” a name that comes not from any dialogue in the show, but from the released script for the Season 4 finale.

Separate from the Upside Down, the Abyss is a yellow-tinged world full of bleak mountains and floating rock formations. It’s also the original home to creatures like the Mind Flayer and the Demogorgons. As Holly (Nell Fisher) discovers in Season 5, Volume 2, if you go through one of the rifts in the ground in the Abyss, you’ll find yourself falling through the Upside Down.

The Upside Down is a wormhole, not an alternate dimension.

Randy Havens in “Stranger Things.”
Credit: Netflix

For Stranger Things‘ whole run, our heroes have assumed the Upside Down is an alternate dimension, like the Abyss turns out to be. However, that couldn’t be farther from the truth. Instead, using Dr. Brenner’s (Matthew Modine) notes from Hawkins Lab in the Upside Down, Dustin realizes that the Upside Down is actually a wormhole connecting our dimension and the Abyss.

Stranger Things has been hinting at this reveal throughout Season 5. Look no further than its references to A Wrinkle in Time, which features wormhole-like tesseracts. Or how about Mr. Clarke fully teaching a class on Einstein-Rosen Bridges, aka wormholes?

Henry, the Mind Flayer, and the Demogorgons have been using the Upside Down as a path to get to our world. And if they’re ever gravely wounded in our world or the Upside Down, as Henry was at the end of Season 4, they can always retreat back up into the Abyss. That explains why none of the crawls ever located Henry: He was biding his time up in the sky.

How was the Upside Down wormhole created in the first place?

Credit: Netflix

Presumably, the Abyss has always existed in parallel with our world, but how did they end up connected? The answer: Eleven (Millie Bobby Brown).

In 1979, following the massacre at Hawkins Lab, Eleven banishes Henry to the Abyss. It’s not the first time he’s been there. As the play Stranger Things: The First Shadow confirms (and Volume 2 hints at), young Henry found himself teleported there while exploring a Nevada cave system.

After Eleven banishes Henry, Dr. Brenner focuses on trying to get her to find him psychically. Those experiments led her to make contact with a Demogorgon back in the void, all the way back in Season 1. When she did, that created not just the gate to the Upside Down, but the Upside Down itself, bridging the two worlds.

Great, so what does exotic matter have to do with all of this?

Credit: Netflix

Dustin doesn’t just discover that the Upside Down is a wormhole. He also learns that the entire bridge is being held together by exotic matter, which is the roiling ball of energy he, Steve (Joe Keery), Nancy (Natalia Dyer), and Jonathan (Charlie Heaton) discover hovering over Hawkins Lab in Indiana.

Exotic matter is a real scientific term. According to BBC Science Focus, “It’s the generic name physicists give to matter with weird properties. Exactly how weird depends on the area of physics.”

For the purposes of Stranger Things, though, exotic matter is the source of energy that keeps the walls around the Upside Down wormhole together. If it’s destroyed, the whole bridge goes down — along with anyone in it. The destruction of the bridge will prove crucial to our heroes’ plan to stop Vecna from joining the Abyss to our world.

So now that we’ve gotten that impromptu physics lesson out of the way, the stage is set for what’s shaping up to be a massive finale. Here’s hoping everyone makes it out alive.

Volumes 1 and 2 of Stranger Things Season 5 are now streaming on Netflix. The series finale premieres Dec. 31 at 8 p.m. ET on Netflix and in theaters.