Everything You Need to Know About the Upside Down, the 'Stranger Things' Parallel Universe

Stranger Things
This post contains major spoilers for Stranger Things Season 1.

“The Vale of Shadows is a dimension that is a dark reflection or echo of our world. It is a place of decay and death. A plane out of phase. A place of monsters. It is right next to you and you don't even see it.”
Stranger Things, Chapter 5: “The Flea and the Acrobat”

Imagine a world exactly like our own, but distorted by time and space. You can still access familiar places, but they're askew, empty; they lack the principle of formality, and appear as mere simulations. This is, in essence, the Upside Down of Stranger Things, another dimension that is presented to us as a membrane-dripping, shadowy version of the world we know and inhabit.

The first season of Stranger Things keeps the Upside Down shrouded in mystery beyond being an alternate dimension that resembles our own. It is inhabited by a humanoid monster (nicknamed the Demogorgon) that feeds on eggs and abducts children. It is dark, blue-hued, and can, to the best of our knowledge, only be accessed by people with telekinetic properties or through energy-induced portals.

Stranger Things returns to Netflix with Season 2 (and a clear promise of Season 3), and if the trailers are any indication, the line between our world and the Upside Down will be flimsier than ever before. Is Will Byers experiencing visions of that world, or was his return from the Upside Down a dangerous way of binding our dimensions, perhaps detrimentally?

Here's a breakdown of everything we know about the Upside Down, including what the show, mythology, and real-world science tell us about alternate dimensions.

Eleven Stranger Things

Eleven was the first to brush up against the Upside Down

The opening moments of Stranger Things Season 1 offer a look at the horrors unleashed from the Upside Down. On November 6, 1983, in the bowels of the Hawkins National Laboratory, an unnamed scientist runs through a corridor, pursued by some unseen monster – undoubtedly the Demogorgon, that evil monstrosity who escaped from the alternate dimension with the help of Eleven. Will Byers is soon captured by that same monster, which sets in motion the events of the show. But how, exactly, was Eleven able to summon this evil thing and transfer it from one world to another?

We're never given a clear-cut explanation to how the science works, but flashbacks in later episodes inform us that Eleven is the daughter of a woman who participated in an MKUltra-like experiment or, a government-facilitated test on willing subjects to mine the limitations of mind-control. Eleven (real name: Jane) was born during these tests and given over to Hawkins National Laboratory scientists. From a young age, she showed signs of being telekinetic, and able to manipulate energy. She was used to perform a variety of experiments, including one that saw her successfully eavesdropping on a Russian spy. During this same experiment, Eleven unwittingly came across the Demogorgon. Dr. Brenner, a leading Department of Energy scientist, was intrigued by Eleven's encounter with the monster, and urged her to revisit it. She later made contact with the beast; the connection was so extreme that it cracked a wall in the deprivation tank she was using to access other worlds. This created a hole between universes that the scientists could not control.

Stranger Things

The Vale of Shadows

Will Byers' friends Mike, Dustin, and Lucas use knowable metaphors (e.g. Dungeons & Dragons references) to explain the unexplainable after Will goes missing. They name the creature stalking Hawkins the “Demogorgon” after a monster in the game, and call the alternate universe “the Upside Down” after Eleven flips their D&D board over as she tries to explain the physics of the other dimension. Dustin compares the Upside Down to the “Vale of Shadows,” a parallel world mentioned in D&D lore. (Turns out the Vale of Shadows is a Stranger Thingscreation, and not something from the actual game.)

“It is right next to you and you don't even see it,” their fictional D&D Expert Rulebook explains. This goes in tandem with what we know of the Upside Down, which seems to butt heads with our world; it's why Will can communicate with his mom via Christmas lights without physically being in the same room. The worlds occupy the same space, but don't share matter.


The acrobat and the tightrope

Mike, Dustin, and Lucas eventually prod their science teacher, Mr. Clarke, for a possible explanation of the Upside Down. He uses a simple, but confusing, analogy: He tells them to picture our dimension as a tightrope and the people in it as acrobats. We're able to walk forward and backyard across the rope, but we cannot turn upside on it without losing balance and falling. He then tells them to picture a flea on the same tightrope. The flea isn't bound by the same gravitational properties because of its physical makeup: it's smaller, more agile, and go all around the rope. The flea, per this metaphor, can access "the Upside Down.”

That's not a super great explanation, considering both a human and flea would occupy the same three-dimensional world. But, in an interview with Business Insider, physicist Paul Steinhardt used a better analogy. Instead of a tightrope, he suggested picturing a sandwich, with each dimension represented as a piece of bread, separated by a layer of hummus. The hummus is the binding between these worlds that makes it difficult for the two to converge; it would require a great deal of energy – like a large finger pressing the two layers together, creating a hole – for them to combine and occupy the same space. In this analogy, Eleven is the finger; she uses her bounty of telekinetic energy to merge the universes together until they create a hole, allowing the physical beings on either side to cross between both planes.

But why does the Upside Down exist?

Who knows. Perhaps it always existed, or perhaps it was created by other Hawkins National Laboratory experiments. In reality, there are multiple theories about the possible existence of other universes, and none really come close to explaining the Upside Down. Is it part of a multiverse, one of an infinite number of other worlds? Or is it merely a pocket universe, a projection of our own observational plane? We're not given enough information to summon a guess. If we had to, we'd say it's the latter, and that Season 2 will go deeper into the mythology of the Upside Down's creation.

Stranger Things Season 2

Speaking of Season 2...

The first season teased an entirely different ecosystem in the Upside Down. There's the Demogorgon monster, the eggs, and those weird sticky webs. The monster also seemed to use humans as incubators for slug-like creatures that possibly birth new monsters. The biology remains unclear; the eggs and slugs appear to be two different organisms, and it's hard to discern from which – if either – the monster grows from. (Probably the slugs, considering we see it feasting on the eggs in Season 1.) The Demogorgon died last season, but we ended on the image of Will Byers barfing up the slugs in his bathroom sink and subconsciously flashing back to the other side. Does this mean there are baby Demogorgons growing in the sewers of Hawkins?

And what is with that giant, Lovecraftian tentacle monster we see marching in the distance of the Season 2 trailers? Is that an evolution of the Demogorgon, another breed of monster from Upside Down, or something else entirely?

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Lindsey Romain is a writer and editor living in Chicago. She covers politics for Teen Vogue and has also appeared in Vulture, Birth.Movies.Death, and more. Follow her on Twitter @lindseyromain.