The theory predicts that the next season will take place around April 1986 when the Chernobyl disaster occurred.
There’s a theory doing the rounds about Stranger Things that we’re really hoping doesn’t come true.
The third season ended in October 1985, so this would place the action a whole six months later.
This thought lends credence to the theory that “the American” mentioned in the mid-credits sequence is indeed Chief Jim Hopper who is presumed dead at the end season three.