The concept of parallel universes—sometimes referred to as the “multiverse”—has long fascinated both scientists and science fiction enthusiasts. For centuries, the idea of multiple realities existing simultaneously alongside our own was relegated to the realm of fantasy. However, in recent decades, the idea has shifted from wild speculation to a hypothesis under serious scientific scrutiny. With the development of advanced physics and the design of revolutionary experiments, the possibility that the multiverse theory may not be the stuff of science fiction, but perhaps an essentially fundamental constituent of our reality, is slowly beginning to dawn on us.
What Are Parallel Universes?
Succinctly put, the theory of parallel universes postulates that beyond our own, there could exist other universes-each with their own laws of physics, constants, and even histories-existing parallel to our own. These universes could almost be parallel to our own but at the same time be very different. Of these other dimensions, some may contain other versions of ourselves who made different choices or may even be living completely different lives, while others may be radically different, with totally new forms of life, or perhaps none at all.
Discussion regarding the parallel universe generally happens in the parallel universe of quantum mechanics that describes the rules of how particles can behave at incredibly small scales. Quantum theory asserts that a particle may exist in numerous states, an occurrence known as superposition. Applied to the universe as a whole, this might be understood, by some people, as if the principle expands in the macro-world-that is to say, in the case that every possible result of every incident actually happens within a separate and coexisting universe. That is to say, there would be a different universe created on each occasion the outcome could differ.
Probably the most famous and widely discussed model of parallel universes emanates from the so-called Many-Worlds Interpretation of quantum mechanics. Inspired by physicist Hugh Everett III in 1957, the theory states that every possible outcome related to a quantum event, each corresponding to a different universe or world, does take place but in a separate, non-interacting branch of the universe.
To see what this means, let’s return to a famous thought experiment called Schrödinger’s cat. In it, there is a cat in the box who is in a superposition of states, both alive and dead until the cat is observed. It means, in MWI jargon, upon opening the box to look, the universe “splits” into two branches, wherein one has an alive cat and another in which the cat is dead. In that respect, according to this view, action by the observer does not really collapse the wave function of probabilities for alive or dead into a reality; both realities continue their life in parallel separate universes.
While this may sound like the stuff of a science fiction novel, many physicists take it seriously because it offers a coherent and mathematically viable explanation for the strange and counterintuitive nature of quantum mechanics.
Theoretical Models Supporting the Existence of Parallel Universes
Besides, there are a few more theoretical approaches in physics alluding to the existence of parallel universes; each provides a different perspective regarding how and for what reasons these universes could exist.
1. Cosmic Inflation and the Multiverse
Probably the strongest theoretical framework supporting parallel universes is based on the theory of cosmic inflation, which proposes that the universe went through a period of exponential expansion during the very first moments following the Big Bang. That same theory stated that the fast, exponential expansion of space-time creates small, bubble-like regions of space that grew and would grow to form this huge universe that we find ourselves in. Some variants of the inflationary theory even allow for universes to be infinite, each formed by eternal inflation and hence possessing its unique laws of physics-its own set of physical constants. It is precisely this that the so-called eternal inflation suggests: it claims that the observable universe we live in may turn out to be only one bubble in a far larger-easily infinite-multiverse. Each separate bubble can, therefore, be regarded as another universe, fully complete with its separate laws of physics, and perhaps, just perhaps life forms totally incomprehensible by us.
2. String Theory and the Landscape Multiverse
Another framework that supports the idea of parallel universes is from what is called string theory, which is a candidate ‘theory of everything’. That is, string theory attempts to bring together general relativity and quantum mechanics. String theory postulates that the basic entities underlying the universe are not point-like particles but tiny vibrating strings. When.
The vibrations of the strings are possible in such astronomically large ways, it results in exponentially huge numbers of solutions or “vacua” for the structure of the universe. Various theories say the universe we see is just one of these incredibly vast solutions to the equations of string theory. This collection of universes is called the landscape multiverse . Each universe in this landscape could have different physical constants, leading to different forms of life and different physical laws.
3. The Simulation Hypothesis
The wildest-but-increasingly-discussed-idea of all is the simulation hypothesis: the idea that our entire universe could be some kind of computer simulation run by some more advanced civilization. This hypothesis has been popularized by philosopher Nick Bostrom, who’s argued that, if it were possible to simulate the actions of conscious beings in a computer sophisticated enough, there might be innumerable simulated universes-and potentially even an infinite number.
It is not, however, a variant of the multiverse hypothesis, although it does entail that our universe might be one of many different simulations by different simulators for various reasons. Our universe, in this case, would be just one of several parallel simulations going on that could develop along the way.
Evidence to Support It
For a long time, the concept of parallel universes was no more than a philosophical speculation, with only scant direct evidence. However, recently, the advancement in the study of physics and cosmology has been slowly making this theory nearer to testability. Since other universes cannot be observed directly, there are indirect ways that scientists have sought to garner proof of the existence of the multiverse.
1. Cosmic Microwave Background (CMB) Radiation
One such possible clue could come from the investigation of the cosmic microwave background-the faint radiation left over from the Big Bang. Some cosmologists have suggested that if our universe is part of a larger multiverse, there might be observable evidence of interactions between different universes in the form of anomalies in the CMB.
A 2007 research team from the NASA Jet Propulsion Laboratory, under the lead of Ranga-Ram Chary, reported the discovery of some bizarre CMB anomalies for which they didn’t have full explanations. Considering some of the above-mentioned to be statistical anomalies, some believe this might be faint traces of our universe colliding with other universes.
2. Gravitational Waves and the Multiverse
Another direction in which verification of the multiverse hypothesis can be obtained perhaps concerns the detection of gravitational waves: ripples in spacetime from massive objects accelerated to high speeds, such as black holes and neutron stars. Among the produced patterns, a number are supposed to exhibit some hint at extra universes or dimensions.
In 2016, gravitational waves were first detected, and the discovery won physicists the Nobel Prize in Physics. These first detections had nothing to do with parallel universes, but in the years to come, experiments could start to search for a pattern within gravitational waves that may be suggestive of other realities.
3. Quantum Experiments and Interference Patterns
On a smaller scale, experiments in quantum mechanics continue to probe the strange behaviors that underlie the multiverse theory. One of the most well-known experiments concerns what is known as quantum interference patterns, whereby particles such as photons or electrons appear to be able to exist in multiple states all at once. These interference patterns suggest that particles can exist in superposition-a key idea in the Many-Worlds Interpretation.
With scientists continuing to push the boundaries of quantum mechanics, it is possible that future experiments will have more concrete evidence of parallel universes-or at least new insights into the strange nature of quantum reality.
Parallel Universes and Our Place in the Cosmos
As we delve deeper into the realms of theoretical physics, the possibility of living in a parallel universe becomes quite plausible.
The concept of parallel universes dares to contradict the very principle of our existence, forcing us into profound questions about the nature of life, our choices, and even how the universe came to be. Whether the parallel universes are there or not, the search for proof has kept science on its toes, beckoning us to revisit all that we knew about the cosmos.