Many clues throughout four seasons have been hinting at this possibility, as it turns out.
A new theory described on the YouTube channel 'Flicks and the City' suggests that 'Stranger Things' is heading to officially make time travel possible within its universe, and it's going to be the only way for Eleven to defeat the main villain.
Time has become somewhat of a center point in season 4, but it's not like 'Stranger Things' did not flirt with the idea of time travel earlier. Rich in 'Back to the Future' Easter eggs, the show also hints that Number 8 – Eleven's fellow laboratory kid from the second season – is actually named after Kali, the Indian goddess of time.
The show's villain, Vecna, has also been focused on the idea of time and how humanity forces itself into artificial limits with it. At some point in the show, young Henry Creel even makes the clock hands go in the opposite direction.
Besides, one of the most intimidating symbols of season 4 is an actual vintage clock – the very same that young Henry made go backwards, later to use it when haunting his victims as Vecna.
So it would be reasonable to think that Eleven will have to team up with Number 8 in order to somehow make time travel possible and use it to resolve the show's main conflict. One of the ways she could do that is to undo the banishing of Number One.
Many fans seem to be ready to believe that the show is heading towards time travel.
"I feel like season 5 should have a way where time travel is somehow introduced – or maybe the series finale can go back in time completely but only the people who were affected by the upside down – know of it – even the deceased that would come back," – @b4tjokez.
Some theories even seem to be getting way too far.
"I'm betting they're gonna pull an attack on titan with stranger things. Will is the endgame villain, time travel is somehow involved and he's known everything about the upside down from the start," – @mattwrightHQ.
But some fans argue that time travel will actually ruin the show, as it is very paradoxical and is deemed by many as a "cheap" way to resolve conflict or spark dramatic events.
Still, we'll have to wait until July 1 to watch Volume 2 of season 4 and see whether there will be a time travel cliffhanger.