Parallel Worlds Probably Exist. Here’s Why

I was introduced to quantum mechanics through the traditional Copenhagen Interpretation. In this view, we use the Schrödinger equation to calculate and evolve wave functions—mathematical descriptions of quantum systems. These wave functions behave like waves when left undisturbed, embodying the famous concept of wave-particle duality. A particle such as an electron or photon can act like a wave when it’s not being observed.

But here’s the twist: when we perform a measurement, this wave function is said to collapse—instantaneously—into a definite state. We see a particle, not a wave. And if we repeat the experiment many times, the distribution of outcomes matches the square of the wave function’s amplitude. This became known as the Born Rule, which states that the wave function doesn’t describe physical reality directly, but instead encodes the probability of different outcomes.

This marked a major philosophical shift in science. It meant the universe, at its most fundamental level, was probabilistic, not deterministic. Unsurprisingly, this didn’t sit well with great minds like Einstein and Schrödinger, who believed there must be something deeper at work—perhaps hidden variables that could restore determinism beneath the apparent randomness.

Then, in the 1950s, Hugh Everett proposed a radical alternative: the Many-Worlds Interpretation.

Looking back, it seems almost obvious. But given how deeply the early physicists were rooted in classical thinking—focused on measurement, instruments, and definite outcomes—it’s understandable why they didn’t arrive at this idea.

Everett’s proposal is elegant in its simplicity: there are no special rules for measurement. The Schrödinger equation always applies, without exception. What we call "measurement" is just one quantum system interacting with another. When that happens, the systems become entangled, and the observer becomes part of the quantum system.

The result? Branching realities.

Each possible outcome of a quantum event actually happens, but in separate, non-interacting branches of the universe. From the perspective of any single observer, it appears as if the wave function has collapsed. But in truth, nothing has collapsed—you’ve simply become entangled with one outcome.

The reason the other versions are inaccessible is due to environmental decoherence—the interaction of quantum systems with their surroundings causes the branches to evolve independently, making it impossible for them to interfere with one another again.

What Everett proposed wasn’t just an interpretation. It was a reimagining of what reality means.