From the latest Marvel’s Doctor Strange movies to Everything Everywhere All At Once, we see the concept of “multiverse” entering the pop culture scene more often than before. As the name implies, Multiverse is a concept that says there are an infinite number of universes, and perhaps we’re living in just one of them. 

Before being introduced in pop culture, the theory was represented by a small community of scientists to understand hard-to-explain, observable properties of our universes. It implied the existence of other worlds besides the one we’re in, set in completely different environments.

Multiverse Theories

In 2003, MIT physics professor Max Tegmark proposed four types of multiverses, each explaining how the multiple worlds are formed and what they are like. 

The first type is called the regions beyond our cosmic horizon, talking about the existence of infinite universes with only different initial conditions, provided with identical laws of physics as our universe. We can only observe the universe we inhabit, but there are multiple versions of ourselves (or alter-egos) living across the unobservable universes.

The second, reportedly the most scientifically accepted idea is the “inflationary cosmology”. The theory suggests that each universe is a “bubble” with infinite size and growth, and an uncountable number of bubbles have been created since the big bang. As these bubbles constantly expand in size, they are pushing each other further away at the “speed of light”, making it impossible for us to travel to another one. The ever-inflating bubbles may not have the same laws of physics as ours, either.

Another popular type of multiverse theory talks about the statistical behaviour of matters from quantum mechanics, introduced by Hugh Everett in 1957. Every decision, or quantum event, branches out another universe; if the branches reach far, the produced universe may look wholly different from what we live in. An example of quantum events is explained in the famous thought experiment “Schrödinger’s cat”, where the probability of a cat inside the box being dead or alive exists at the same time until we open it and observe the outcome.

The last level of a multiverse, which Tegmark calls Level IV, equates every valid mathematical question to a universe. He assumes “mathematical existence” means “physical existence” and aims to explain how some maths are “unreasonably effective” when discovering mathematical structure that perfectly fits our universe.

Fascination With Multiverse Theories

Although conceptual and theoretical, the science community (including fiction) has studied Multiverse for many years. Despite theoretical studies, the existence was not evidenced with empirical data; we have never observed another universe yet, and no one can confirm how much it would take for humans to travel across multiverses like in fictional worlds.

Then how can multiverse theories fascinate scientists (and writers) with bright minds? 

As for scientists, especially those who studied quantum mechanics, it can provide an explanation of what happens to “unobserved” scenarios. According to the traditional interpretation of quantum mechanics, the universe has overlapping dimensions, but according to a certain selection, the universe follows only one path. However, once we do an experiment and get probabilities, the randomized matters (even the ones hundreds of light years away) come into one region and draw a certain outcome. 

“It’s kind of a strange feeling that the quantum mechanical state that was so far away suddenly disappears by what we observe,” Kim Beom-jun, a physics professor at Sungkyunkwan University, told SBS. 

These disappeared matters, or untested scenarios, can be explained in Everett’s multiverse theory – they are played out in other multiple universes. As it sounds too imaginative and improbable, the theory is still controversial among scientists when it comes to proving scientific value.

For writers, the disciplines of the Multiverse give food for the imagination. Many ask the question “What if?” – wondering if there would have been different outcomes under different situations drawn by different decisions. The Chronicles of Narnia, Star Wars, and many pieces of pop culture take on this question and asks us how we would have behaved if the alter-universe existed.

Although we won’t be able to travel across bubbles or alternative scenarios in tens or hundreds of years (or maybe we will), we still can use the power of imagination to ask ourselves about hypothetical situations. Also, remember, just because there are many universes out doesn’t mean that our universe is not special. It is still a one-of-a-kind, unparalleled universe that shines in the flock of ever-expanding worlds.