Imagine waking up one morning and sensing something different. Your phone’s wallpaper isn’t what you remember setting. Your morning coffee tastes slightly different, just a little off. A friend swears they never had the conversation you vividly recall from yesterday.
Could these be mere glitches in memory? Or fleeting glimpses of another reality, one where your choices led you down a different path?
According to the Many-Worlds Interpretation (MWI) of quantum mechanics, every possible outcome of every decision actually happens, just in a different universe. This means that in another reality, you took that job offer, pursued that relationship, or even became a completely different person.
But how did this theory emerge? And could it be true?
A Battle Over Reality
Do Choices Create Parallel Universes?
Before the Many-Worlds Interpretation, the dominant explanation for quantum mechanics was the Copenhagen Interpretation, formulated by Niels Bohr and Werner Heisenberg in the 1920s. This theory stated that a quantum system exists in multiple states (superposition) until it is observed, at which point the wave function collapses, and only one outcome remains.
But in 1957, a 26-year-old Princeton physicist named Hugh Everett III had a radical idea:
“What quantum mechanics tells us is that everything that can happen does happen in some world.”
Hugh Everett III
Instead of the wave function collapsing, Everett proposed that every quantum event causes reality to split, creating multiple parallel universes where every possibility unfolds simultaneously.
At first, his theory was dismissed. Bohr and his colleagues rejected the idea, and Everett, frustrated, left academia in 1959 to work in military research. He would never see his work fully recognized in his lifetime.
But today, scientists are taking his idea more seriously than ever.
A Struggle Against Scientific Orthodoxy
In 1957, a young physicist named Hugh Everett III stood before a panel of experts at Princeton University, defending a theory so radical that it defied everything quantum mechanics had accepted for decades. He proposed that the universe does not “choose” one outcome over another when observed. Instead, it splits, creating multiple realities where every possible outcome actually happens.
Everett’s dissertation, The Theory of the Universal Wave Function, challenged the mainstream Copenhagen Interpretation, which had been the foundation of quantum mechanics since the 1920s. According to the Copenhagen view, a particle exists in multiple states at once (a phenomenon called superposition) until it is measured. The moment an observation occurs, the wave function collapses, and the particle “chooses” one state to exist in.
But Everett refused to accept the idea that a measurement had such a magical effect on reality. Instead, he argued that the wave function never collapses at all. Each possibility plays out in a separate, coexisting reality. In one world, a photon travels through one slit of an experiment, while in another, it travels through both. In one universe, you choose a career in medicine, while in another, you become an artist. Nothing is lost every version exists somewhere.
His mentor, the famous physicist John Wheeler, found the idea fascinating yet unsettling.
“I think your idea is crazy, but not crazy enough to be correct.”
John Wheeler
Despite this backhanded encouragement, Everett’s theory was met with skepticism. The reigning authority on quantum mechanics, Niels Bohr, dismissed his ideas outright. Bohr and his colleagues believed that wave function collapse was an inherent part of quantum physics and saw no need for an alternative explanation. The Copenhagen school, deeply entrenched in traditional quantum mechanics, saw Many-Worlds as unnecessary and overly speculative.
The Unexpected Revival of Many-Worlds
For more than a decade, Everett’s theory remained buried in academic obscurity. Then, in the early 1970s, physicist Bryce DeWitt rediscovered his work. DeWitt was intrigued by the idea that the universe could split into infinite branches, coining the name “Many-Worlds Interpretation.”
“Everett’s interpretation is not just a mathematical trick. It suggests a real and infinite multiverse, where all things that can happen do happen.”
Bryce Dewitt
Everett, however, never returned to quantum physics. He died in 1982 at the age of 51, never knowing that his ideas would later influence some of the most groundbreaking discoveries in physics.
Quantum Experiments That Hint at Many-Worlds
As the 20th century progressed, One of the most famous was the Double-Slit Experiment, originally performed by Thomas Young in 1801 and later re-examined in 1927 by Clinton Davisson and Lester Germer. This experiment demonstrated that light behaves both as a wave and as a particle, depending on whether it is observed.
When a single photon is fired through the slits without being measured, it interferes with itself, acting like a wave. However, when the experiment is set up to detect which slit the photon travels through, it acts like a particle, as if it “knows” it’s being observed.
Many-Worlds offers a striking explanation rather than collapsing into one state, the photon takes all possible paths in separate realities.
A few years later, physicists tackled another paradox, quantum entanglement. In 1935, Einstein, Podolsky, and Rosen proposed the EPR paradox, arguing that if quantum mechanics were correct, two entangled particles should be able to influence each other instantaneously, no matter how far apart they were. Einstein, deeply uncomfortable with this idea, famously referred to it as “spooky action at a distance.”
For decades, scientists debated whether entanglement was real. In the 1960s, physicist John Bell developed a test for it, and in the 1980s, experiments confirmed that entangled particles really do influence each other instantly. If Many-Worlds is true, entangled particles exist in different universes, but their correlations remain across realities.
In 1999, an even stranger experiment emerged, the Delayed-Choice Quantum Eraser, led by physicist Yoon-Ho Kim. This experiment suggested that a decision made in the present could influence an event that had already happened in the past. Many-Worlds provides an elegant answer: both possibilities exist in different branches of reality, but we only experience one outcome.
“No phenomenon is a phenomenon until it is an observed phenomenon.”
Later wrote by Jhon Wheeler – Once who had doubted Everett
What If It’s True?
If the Many-Worlds Interpretation is correct, reality is far more intricate than we perceive. Every choice creates a parallel version of you, living out a different path. Somewhere, another you exists with an entirely different life.
This raises profound questions if infinite versions of us exist, does free will truly matter? Are all possibilities equally real? While proving Many-Worlds remains a challenge, its implications continue to shape modern physics and philosophy. As quantum research advances, we may one day unlock the secrets of the multiverse.
“If all outcomes exist, what makes the version we experience special?”
Hugh Everett III
A Universe That Branches Like a Tree
The Many-Worlds Interpretation suggests that reality functions like an ever-growing tree, where every decision causes a new branch to form. In one reality, you chose to study physics; in another, you became a musician. These versions of you exist independently, unfolding their own experiences.
A classic thought experiment illustrating this is Schrödinger’s Cat. In 1935, Erwin Schrödinger imagined a cat inside a box with a poison-triggering quantum event. The Copenhagen Interpretation claims that, until observed, the cat is both alive and dead. Many-Worlds suggests that the universe splits, one where the cat survives and another where it dies.
Physicist Sean Carroll explains:
“When you open the box, you don’t collapse the wave function. You simply find out which version of the cat you are experiencing.”
This theory forces us to reconsider what we call “reality.” If every possibility exists, what makes the version we experience unique?
Why This Matters
Beyond physics, Many-Worlds has influenced quantum computing, technology, and pop culture.
Quantum computing relies on superposition, where a qubit exists in multiple states at once. Physicist David Deutsch argues that Many-Worlds provides the best explanation for how quantum computers operate, calculations may be occurring across multiple universes simultaneously.
In Everything Everywhere All at Once, Evelyn Wang experiences multiple realities where she made different choices. In one, she never immigrated to the U.S. and became a martial arts movie star. This aligns with Many-Worlds each decision creates an alternate version of her life.
Similarly, Interstellar explores quantum mechanics through Cooper’s experience inside a black hole’s tesseract, where time is non-linear, hinting at realities unfolding simultaneously. Even the Marvel Cinematic Universe has explored parallel realities, with Doctor Strange and Loki interacting with alternate versions of themselves.
If Many-Worlds is real, then every choice we make isn’t just a possibility, it actually happens somewhere.
Does Consciousness Split?
If reality constantly branches, does our consciousness split across these versions? Or does each version of “you” exist independently?
“Your consciousness does not split, you just exist in the version where you are aware of your choices.”
Neuroscientist Max Tegmark
Physicist Sean Carroll supports this view, stating:
“There’s no special, privileged ‘self’ that moves between worlds. Every version of you simply exists in their own reality, unaware of the others.”
Sean Carroll
This means that while multiple versions of us may exist, we only experience one path. If Many-Worlds is real, then our choices don’t just shape a single future, but infinite versions of it.