Taking to Instagram, user @noahschhnapp explained his theory referencing the film Interstellar: “It all starts at ST 1 where Clarke does the same explanation of the portal.
“But add The Flea and the Acrobat. Acrobat needs a portal to enter upside down.
“If you paid attention in the series you know that the monster dies when the portal closes.”
The fan theorises that the explosion during The Battle of Starcourt Mall didn’t actually kill Hopper, instead it transported him in time.
“In the movie Interestellar it happens that we have a flea that walks between dimensions after an accident. It interacts in both worlds through time-space at random.”
The fan concluded: “Hopper is lost in space-time, where he has already transited between the two worlds, helping throughout the show in small acts.”
Stranger Things seasons 1-3 are available to stream on Netflix.