[Warning: The following contains spoilers for Stranger Things 3. Read at your own risk!]

Stranger Things' third season was a fun adventure filled with exploding rats, child spies, and have we already mentioned the exploding rats? But the season finale delivered a devastating twist: the only way for Joyce (Winona Ryder) to close the gate to the Upside Down and stop the Mind Flayer meant sacrificing Hopper (David Harbour), who was seemingly killed when Joyce blew up the Soviet machine in the lab underneath Starcourt Mall.

A three-month jump forward in time revealed everyone moving on in the wake of Hopper's death, with Eleven (Millie Bobby Brown) now living with the Byers and moving with them far from the supernatural troubles of Hawkins. But a cryptic mid-credits sequence revealed that the Upside Down hadn't been completely shut out of our world, with the Soviets raising a demogorgon in Kamchatka, Russia. More interestingly, the scene also revealed that the Soviets are keeping an unseen American captive.

Stranger Things 3 Recap: Here's Who Died This Season

So, what if Hopper isn't dead? What if he's being held captive by the Soviets because instead of killing him, the machine's explosion actually transported Hopper through space and/or time?

It sounds crazy, even by Stranger Things standards, but people have been speculating there will be a time travel element in the series for a while. There are theories that that the gate to the Upside Down doesn't take you into a parallel universe, but into a future version of Hawkins. Season 2 also included references to The Terminator, which was playing at the Hawkins theater in Episode 1 and which was the focus of a commercial Eleven watched in Episode 2. More notably, one of the Season 3 influences was Back to the Future, perhaps the most iconic time travel movie and the flick that a very stoned Steve (Joe Keery) and Robin (Maya Hawke) watched after escaping the Soviet lab. Then again, most of the times a film has been referenced in Stranger Things, it hasn't been very literal. Ghostbusters was a big influence in Season 2, but it's not like we saw ghosts, and the George Romero influence this season didn't mean the show featured literal brain-eating zombies.

But even if we ignore the time travel-centric pop culture references, the letter Hopper wrote to address Mike (Finn Wolfhard) and Eleven's burgeoning relationship is extremely focused on the idea of time, both moving forward and the desire to go back. "I know you're getting older, growing, changing, and I guess if I'm being really honest that's what scares me. I don't want things to change," Hopper wrote. "So I think maybe that's why I came in here, to try to maybe stop that change, to turn back the clock, to make things go back to how they were. But I know that's naive. It's just not how life works. It's moving, always moving, whether you like it or not. And yeah, sometimes it's painful. Sometimes it's sad. And sometimes it's surprising. Happy. So you know what, keep on growing up, kid. Don't let me stop you."

Here's What Hopper Wrote in His Letter to Eleven in Stranger Things 3

While Hopper resigned himself to the natural progress of time in the heartwarming letter, this message could be setting up the introduction of time travel and our heroes attempting to change events for the better in the next season. But to find the biggest clue that Season 4 might introduce time travel, one has to go all the way back to one of the original inspirations for the show: the Montauk Project. Not to be confused with MKUltra, the Montauk Project is a conspiracy theory that the government secretly experimented with teleportation, mind control and -- you guessed it -- time travel in Long Island, New York. The original pitch for the series, then called Montauk, also mentioned time travel. So while introducing time travel in the show's fourth season might feel a bit random after years without previously venturing into that sort of territory, it could be something the Duffers have been planning from the start -- and something David Harbour is personally hoping to see in the series.

"I don't know [if time travel is possible in Stranger Things] because I don't have any spoilers," Harbour told TV Guide. "The great thing is, I'm fascinated by what the hell the Upside Down is. I know a lot of things about Stranger Things, but I don't really know what the Upside Down is. But people have speculated online that it may be the future or it may be the past or it may have some time component. I love time travel movies. I would love to see time travel in it. ... Time travel is profound. It would be hard to find actors that look like Millie Bobby Brown when she was 11 or Gaten Matarazzo when he was 12. But yeah, I love time travel. I would love to see it in the show."

But even if we accept time travel is possible in the Stranger Things universe, there's still the question of how it might connect Hopper and his potential survival. Our theory? Whatever malfunction Hopper set off in the machine when he threw the Soviet assassin into it, thus creating that electricity barrier that prevented him from getting back to Joyce and to safety, may have also saved his life. We saw that everyone else who entered the lab floor was disintegrated when the machine exploded, but we notably didn't see Hopper's death or any evidence of his body afterwards. Could the fact that Hopper was on the other side of the energy barrier -- and on the side closer to the Upside Down -- mean he was affected by the explosion differently? Could it somehow have transported him through time, thus saving his life? And if he did go back in time, but not by much, that could also explain how the Soviets could have easily captured him and taken him back to Russia where they then imprisoned him. Or perhaps he went really back in time and was able to reconnect with his now-dead daughter Sarah, finally giving viewers closure on that storyline.

Then again, there is also a slight chance that instead of transporting Hopper through time, the machine explosion transported him through space instead. David Cronenberg was one of the influences the Duffers listed for Season 3; most likely, they just were inspired by the director's exquisite use of body horror in his films, but Cronenberg's most famous movie, the 1986 classic The Fly, did feature Jeff Goldblum's character inventing a teleportation machine -- one that went horribly awry when he used it while a fly was also inside the device, thus merging their DNA.

Stranger Things 3 Is Proof Popular Shows Can Also Be Very, Very Good

If the Duffers really wanted to pull more direct inspiration from Cronenberg, and specifically The Fly, then maybe Hopper's life was saved by the machine teleporting him away, perhaps even to its sister machine in Russia that we saw in Season 3's opening scene. And while we doubt this would happen, imagine if Hopper somehow merged with the Upside Down in the process. (Not that we hope or even think that would happen, but it is fun to picture a Hopper with extra limbs growing out of him like the Mind Flayer or a mouth like a demogorgon.)

We know this all sounds crazy and that people say the simplest explanation is often the truth. However, until they show us Hopper's dead body, we can't believe he's actually dead. Plus, when has the simplest explanation ever been the case in Stranger Things? So until Season 4 premieres and proves us wrong, we're going to continue to believe Hopper is alive and that teleportation or time travel saved the day.

Stranger Things 3 is available to stream on Netflix.

Additional reporting by Lindsay Macdonald

PHOTOS: Joyce and Hopper's Best Moments



Other Links From TVGuide.com Stranger ThingsDavid Harbour