This article contains spoilers for Stranger Things season 4 volume 1.
Stranger Things season 4 volume 1 finally reveals the origin of the Upside Down, showing the moment when Eleven created the first Gate. The mysterious realm known as the Upside Down is the key to Stranger Things, a twisted version of Hawkins that is home to monstrous beings such as the Mind-Flayer and the Demogorgon. The origin of the Upside Down has long been something of a mystery — but, given Stranger Things season 4 is marketed as "the beginning of the end," it's no surprise the Duffer brothers have decided now is the right time to provide some answers.
An important clue to the Upside Down's origin was provided in the Stranger Things: Kamchatka miniseries by Michael Moreci, Todor Hristov, Dan Jackson, and Nate Piekos, released ahead of season 4 as an official tie-in. This introduces readers to Russia's version of Dr. Brenner, Dr. Boris Orlov, whose theories appear to be directly related to the creation of the Upside Down. Like Brenner, he has been conducting experiments in telekinesis; significantly, he believes this power can serve to open doorways to "infinite worlds." It seems Stranger Thingsis embracing the multiverse.
Related: Why Stranger Things' Season 4 Episode Lengths Could Be A Major Problem
This fits perfectly with Stranger Things season 4, episode 7, which finally reveals Eleven's true origin story. It seems the first "window" to the Upside Down was created in the aftermath of a telekinetic battle between Eleven and Number One, with Eleven tearing open one of Dr. Orlov's "doorways" — and blasting her opponent into it. Another connection was forged some years later, when Eleven opened the first Gate - bringing the two dimensions more
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