Will's link to the Upside Down's timeline is made even more tragic thanks to a Stranger Things theory. The Upside Down, an alternate dimension that's parallel to the real world, has always been a major part of Stranger Things. Will has been linked to the mysterious dimension ever since his disappearance in Stranger Things' first episode. Though Will eventually escaped the Upside Down, his time there has profoundly affected his character and created a link between him and Vecna, the villain controlling of the parallel realm. It's heartbreaking to see how Will's stay in the Upside Down has taken its toll on him and affected him in the real world.
As revealed in the Stranger Things season 4 episode "Chapter Seven: The Massacre at Hawkins Lab," the Upside Down is stuck in 1983. Specifically, the dimension is frozen on the date of November 6, 1983, the day Will was taken into the Upside Down. Stranger Things season 4 doesn't answer the question of why the Upside Down is frozen in time, though in an interview with Variety, the Duffer Brothers mentioned that this mystery will be explored in Stranger Things season 5. In the meantime, there have been some interesting theories that seek to explain the mystery of the Upside Down and how its timeline relates to Will.
The Upside Down Being Stuck In 1983 Is A Metaphor For Will's Childhood In Stranger Things
A recent theory by Reddit user cece_starling hypothesizes that the Upside Down being stuck in 1983 serves as a metaphor for Will's childhood. As the comment states, "I think the Upside Down being stuck in 83 is at least partially a metaphor for Will being emotionally stunted at a time of major trauma." The theory goes on to say that the Upside Down functions as a darker version of the real world where characters' worst memories keep them "frozen in place" as a result of unprocessed trauma. Since Vecna preys on people's past traumas, this makes the connection between Vecna and Will even more interesting and tragic.
This is an interesting theory that makes sense for Will's character in Stranger Things. The Upside Down was frozen on the last day he was truly able to enjoy childhood with his friends before his life was changed when he was taken to the parallel dimension. While his friends have moved on, Will is trying to freeze his childhood, especially in Stranger Things season 3 when all he wants to do is play Dungeons & Dragons with his friends, and hasn't properly processed his time in the Upside Down. Mike, Dustin, and Lucas have all matured in their own ways, while Will remains emotionally stunted.
Will's Connection To The Upside Down Explained
The origins of the Upside Down are a mystery. However, on November 6, 1983, Eleven opened the gate separating the Upside Down and Hawkins, Indiana. While training her telekinetic powers with Dr. Brenner at Hawkins Lab, Eleven makes contact with the Demogorgon and accidentally opens a portal to the Upside Down out of fear. That same day, Will is biking home after a Dungeon & Dragons session when he encounters the Demogorgon. Will runs home and flees into a backyard shed, where he vanishes and ends up in the Upside Down. Will survives in the Upside Down for a week before Hopper and Joyce enter the dimension and rescue him.
In Stranger Things season 2, Will is still feeling the effects of his stay in the Upside Down and experiences constant visions of the two dimensions. Due to some particles from the Upside Down latching onto Will, the Mind Flayer was able to possess Will, allowing Vecna to use him as a human spy in Hawkins, though Will's family and friends eventually drive the creature out of Will and Eleven closes the interdimensional portal, cutting off the Mind Flayer's control. Will maintains the link to the other dimension, and is the one who is able to sense the Upside Down invading Hawkins at the end of Stranger Things season 4.
Why Will Always Feels "Stuck" In Stranger Things
Ever since he returned from the Upside Down, Will has felt emotionally stuck. While Will seems to be frozen in an emotionally immature state, his friends have matured and gotten girlfriends. In Stranger Things season 3, Will attempts to get his friends to play Dungeons & Dragons like old times, but Mike and Lucas are more preoccupied with their relationships with Eleven and Max. Will feels left behind by his friends; they're not interested in playing the same game they loved as kids and are more interested in girls. Though Will's lack of interest in girls is due to his sexuality, he's also trying to hang on to his childhood.
While this theory doesn't exactly explain why the Upside Down is frozen in 1983, it's a great metaphor that explains Will's character arc during Stranger Things. Will is forever changed by his experience in the Upside Down and is perhaps holding on to his childhood as a way to avoid moving on by processing trauma and accepting who he truly is by embracing his sexuality. It's tragic to see how Will feels "stuck" while his friends are growing up and experiencing relationships, though hopefully Stranger Things season 5 gives his arc a happy ending.
Sources: Variety, Reddit