You may have seen one or the other adventurous character suddenly appear in a “parallel universe” by some strange magical or extremely high tech “portal”. You might’ve wondered about it at some point. What exactly is a parallel universe? How are they supposed to exist?
The idea was originally conceived by Isaac Newton in his book Optiks. In an excerpt from the book, he writes:
And since Space is divisible in infinitum, and Matter is not necessarily in all places, it may be also allow’d that God is able to create Particles of Matter of several Sizes and Figures, and in several Proportions to Space, and perhaps of different Densities and Forces, and thereby to vary the Laws of Nature, and make Worlds of several sorts in several Parts of the Universe. At least, I see nothing of Contradiction in all this.
It gained traction with Erwin Schrodinger described how his equations led to multiple histories and that they didn’t happen alternately, but simultaneously.
The multiverse theory has been explored in many fields aside from the most obvious fields of physics, astrophysics, and cosmology. Even religion has considered the idea of a multiverse.
The physics community, however, is divided in opinion about multiverse theory. Some prominent physicists believe that it is a futile direction. Others, however, have tried to improve upon the technicalities of parallel histories and find evidence either in the universe or through experiments.
Multiverse theorists have classified multiverse sin many different ways. Brian Greene has classified them into nine types whereas Max Tegmark has suggested a four-level classification.
Exotic physics theories suggest various ways in which the existence of a multiverse can be justified. M theory and string theory postulate that parallel universes could exist in higher dimensions (since they deal with 10 or 11 dimensions as opposed to the 3+1 dimensions we are used to). Black hole theory suggests that our universe is actually situated in the singularity of a black hole. This inherently means that there may be other universes hidden away in the singularities of all the millions of black holes in our universe itself.
There is much work to be done in this field. In fact, it is still unclear whether the multiverse theory is a figment of our imagination or a physical reality we are unaware of. The cosmic scale of the problem challenges the best of the best in the field and will continue to challenge them in the most intriguing ways possible.
Some might even argue that knowing the nature of our own reality is impossible. It is beyond the scope of our human brains and we cannot unearth the truths about our own maker, exactly how one can not definitively prove or disprove the existence of God.
Reality or not, however, fiction writers take this extreme of human conceptualisation to even greater levels in their stories and films. And I believe that in itself is a marvellous feat, every story a parallel universe in itself.