Buzz
The notion that reality, or 'Creation,' could encompass multiple realms is an ancient one. Religions such as Hinduism, Buddhism, Judaism, Christianity, and others have been contemplating the idea of parallel planes of existence for thousands of years, often in the context of life before and after death.
As noted by Danish scholar Helge Kragh, even pre-Socratic thinkers like Anaximander and Anaximenes were exploring similar concepts. Subsequent generations of influential philosophers (such as Thomas Wright and Immanuel Kant, to name just a few) have continued to delve into this idea.
The term 'multiverse' itself was first introduced in 1895 by American philosopher William James, although with a slightly different interpretation than what we understand today. He described a world he viewed as 'all plasticity and indifference,' seemingly governed by a multitude of forces.
In contemporary times, physicists, cosmologists, and philosophers use the term (broadly speaking) to describe the potentially infinite number of universes that could exist, each one representing every possible variation, situation, and more throughout all of time and space, extending even to the quantum (think subatomic) level. This means everything that could happen or exist is realized in at least one universe—maybe even fairies!
WHAT DOES THE MULTIVERSE REALLY LOOK LIKE?
Scholars who embrace the multiverse theory are now striving to figure out what shape this multiverse might take and how it would operate. For example, they are questioning whether the multiverse originated from a single Big Bang, multiple Big Bangs, or perhaps an ongoing sequence of them.
In recent years, two prominent models for how the multiverse is structured have been proposed: one by Max Tegmark, a cosmologist from the Massachusetts Institute of Technology, and the other by Brian Greene, a theoretical physicist and string theorist at Columbia University.
Tegmark, in his essay for *Scientific American* titled 'Are Parallel Universes Unscientific Nonsense? Insider Tips for Criticizing the Multiverse,' outlines four models within his multiverse taxonomy. He argues these models are all suggested by existing theories in physics and are grounded in ideas of an expanding universe, a landscape of expanding universes, quantum mechanics free from collapse, and an external reality.
Tegmark’s Level I multiverse, for example, describes 'a single space so vast that it includes numerous universe-sized regions.' In contrast, his Level II multiverse involves 'a single space that holds universe-sized regions, each featuring its own distinct type of space.' With his Level IV model, Tegmark introduces the argument 'that if there exists an external reality completely separate from us humans, then there must be a fourth type of multiverse, one that realizes all mathematically possible universes.'
Greene, conversely, presents nine potential forms of the multiverse in his book *The Hidden Universe*, some of which overlap with Tegmark’s. These include: a quilted multiverse, where an infinite sequence of events occurs repeatedly across infinite universes (but the layers are invisible to us due to the speed of light); a quantum multiverse, where new universes are born each time a 'divergence in events' happens (imagine a universe where you chose to read a different article, perhaps with Schrödinger's cat curled up on your lap); and a cyclic multiverse, where multiple universes (as three-dimensional branes) collide, reset, and reform through Big Bangs, repeating the cycle.
Some of these multiverse concepts have been staples in science fiction for years, while others are only beginning to capture our imaginations. For instance, the TV show *Futurama* explores a version of Greene’s cyclic multiverse idea in an episode where three characters are stuck in a time machine that only moves forward in time. Upon discovering that their universe is cyclical, they manage to return to their original time (or a nearly identical version of it) by completing a few full loops through the universe.
One of my personal favorites, drawn from Greene’s list, is the concept of the *holographic principle*. As *Motherboard* explains, 'some researchers think [it could bridge] Einstein’s theory of relativity and quantum mechanics' by suggesting that 'every three-dimensional object we know and love is actually a projection of tiny, subatomic packets of information stored in a two-dimensional Flatland.' If true, this idea would be 'a really important insight,' as theoretical physicist Daniel Grumiller put it in the article.
Much of this imaginative work, according to Greene, is inspired by string theory, a broad field of research that might serve as the 'theory of everything.' Among its many suggestions, it posits that one-dimensional strings of matter could stretch throughout the universe, connecting it under a unified set of physical laws (possibly extending to other laws beyond our current understanding).
According to Greene, these unifying strings may not just take the form of strings. The theory 'also allows for objects resembling large flying carpets, or membranes, which are two-dimensional surfaces,' he explained to NPR. 'What this suggests within string theory is that we could be living on one of those massive surfaces, with other surfaces floating out there in space.'
SO, WHERE DOES OUR UNIVERSE FIT IN?
One way to explain this idea is to consider that if all possible combinations of universes are unfolding—universes where the Earth is covered in hydrochloric acid, or where there’s sunlight and water but no breathable atmosphere, etc.—we must be in one that has all the factors necessary to support life, existing due to physical and mathematical necessity.
Having trouble imagining infinite habitable Earths? To help visualize this, Greene suggests we think of a deck of playing cards:
'Now, if you shuffle that deck, there are so many possible orderings that could happen. Eventually, after enough shuffles, the orderings will have to repeat. In the same way, with an infinite universe and a finite number of arrangements of matter, the way matter organizes itself must eventually repeat.'
Take the movie *Groundhog Day*, for instance, where Bill Murray’s character Phil relives multiple versions of the same day—a day spent indulging in diner food, a day where he takes a *Thelma and Louise*-style dive off a cliff, and so on. If we imagine for a moment that Phil is navigating a series of possible February 2nds by leaping between universes where he is the only differing factor. In this corner of the multiverse, each universe has had its deck of cards shuffled in exactly the same way—until that fateful winter day when Phil’s group arrived in Punxsutawney.
NOT EVERYONE IS CONVINCED BY THE MULTIVERSE THEORY, HOWEVER.
Some detractors of the multiverse dismiss the entire concept as nonsense, arguing that since the idea isn’t falsifiable (i.e. it can’t be proven false through the scientific method), it doesn’t warrant further exploration. Still, Greene has proposed a method for verifying its existence using the Large Hadron Collider.
In response to such criticism, Tegmark cites cosmologist Sean Carroll, who 'believes we need to reconsider the entire theory-testing process,' Tegmark says. Carroll argues that the 'relationship between theory and experiment' is currently being misinterpreted (at least in this universe), as he explains in an essay:
'We can’t (as far as we know) directly observe other areas of the multiverse. But their existence significantly impacts how we interpret the data from the part of the multiverse we can observe. The value of the idea isn’t in how neat or logically fulfilling it is, but in how it helps us make sense of the data. Even if we never get to visit those other universes.'
Greene also mentioned to *Fresh Air's* Terry Gross that, even though theories about the form and characteristics of the multiverse are tough to prove, the potential impact of validating them makes the efforts of him and his team worthwhile:
'You almost can't avoid including some form of the multiverse in your research if you delve deep enough into the mathematical descriptions of the physical universe... Many of us are exploring different versions of parallel universe theory. If it all turns out to be nonsense, then it’s a lot of effort wasted on a far-out idea. But if it's correct, it would completely transform our understanding.'
WHAT CAN THE MULTIVERSE DO FOR ME RIGHT NOW?
Next time you're out on a date with someone who doesn't seem too impressed, try telling them that, in the universe next door, they find your wit and charm absolutely irresistible, and that all these universes (including yours) are stacked together like flying carpets. They might believe you, or they might not.
Either way, you can rest easy knowing that, in at least one other universe, they did.
