If you haven’t seen the Netflix Original Series STRANGER THINGS, then stop reading this right now, and go watch the entire series. I’ll wait… Done? Good. It’s about time you did that.
In addition to its homages to horror and science fiction of the 1980s, STRANGER THINGS posits several scientific theories involving an unseen world known as the “Upside Down”. You can’t complete a binge watching session of the series without being extremely curious about the existence of such a place. Fortunately, there are several scientific theories which might explain what the “upside down” actually is and if it could really exist. (All from the viewpoint of a non-scientist.)
A parallel universe exists outside of our own universe, but is created out of random quantum-mechanical events. These random quantum-mechanical events are like a fork in the road. A parallel universe can be created when a situation has multiple approaches, each one of which could produce multiple outcomes. Every plausible approach creates a new universe parallel to our own with the only difference being that in this “new” universe, a different approach was chosen. From that point on, our universes diverge down different paths and become unrecognizable to each other.
In STRANGER THINGS, it is possible that some kind of cataclysmic event made the Earth unsuitable for humans or caused them to evolve into monsters. An event such as a nuclear war (the show is set in the 80’s after all) could have occurred in the world of the “upside down”. This would explain the continual snow fall that could have been from a nuclear winter.
There are a number of random quantum-mechanical events which could have been responsible for such a difference. For instance, imagine if Ronald Reagan woke up one morning and had the choice of wearing a blue tie or a red tie. In our universe, he chose a red tie and everything was fine. In the upside down, Reagan decide to wear a blue tie and then started a nuclear war.
Incidentally a collection of these parallel universes would be the multiverse. Watch RICK AND MORTY for the best explanation of multiverse theory.
An alternate dimension differs from a parallel universe in that it contains extreme variations in the actual structure of the universe, itself. In organisms, this variation could be slight differences in chromosomes which account for abilities in another dimension which do not exist in our own. Perhaps the “upside down” is a dimension where telekinesis is one of those structural variations. If we follow this theory, then we can conclude that Eleven was able to steal telekinetic powers from this alternate dimension by merely being able to exist there momentarily.
Quantum Subspace is a theory that all realities interact. Under this theory, there are multiple universes existing beneath our own observable universe. Unlike parallel dimensions, these multiple realities have unseen crossing points which allow for interaction. Hawkins, Indiana may be a point in quantum subspace where crossing over is possible. This explains how these two worlds are able to interact with each other. For example, when Will makes the lights turn on in his mother’s house, this would be a cross point where the two universes intersect. It’s entirely possible that Dr. Brenner’s experiments tore the universe a new one at the exact point where one of these crossing points previously existed, thus allowing more interactions between worlds.