The Many Worlds interpretation of quantum mechanics

Demystifying the Many Worlds theory

By Patrick Regan


From ‘Doctor Who’ to ‘Narnia’, ‘Back to the Future’ to ‘Rick and Morty’, parallel universes are a mainstay of pop culture. The concept is now so ubiquitous that everyone has a notion of what it entails. But do parallel universes really exist? Is there another version of you who has had an identical life up until this moment, the only difference being that you chose to read this article and they didn’t?


Imagining multiple universes can be difficult to understand. Think of it like this: for any given interaction, there are a variety of different outcomes. Before the interaction, any of the outcomes is possible. A popular thought experiment demonstrating this is Schrödinger’s cat. Imagine that you have a cat locked inside a box with a vial of poison, the poison will be released and kill the cat at a random time. The only way we can know whether the cat has been poisoned is by interacting with the box by removing the lid. In Quantum Mechanics this means that the cat is in a superposition of states – the cat is simultaneously both dead and alive at the same time. By opening the box, we see one of these results but not both. So how does the cat go from being in a combination of two states at once to being in just one?


The Many Worlds interpretation of Quantum Mechanics tells us that whenever different outcomes to an interaction are possible, our universe splits into a number of parallel universes, each with corresponding to a different outcome. In the case of Schrödinger’s cat, both possibilities happen; there is a universe where the cat died, and one where it lived. The timeline of history branches in order to accommodate every possible result. Theoretical Physicist Brian Greene described the Many Worlds interpretation like this: “every potential outcome sees the light of day; the daylight each sees, however, streams through its own separate universe”.


This idea was first proposed in 1957 by a graduate student named Hugh Everett. He believed that the Many Worlds interpretation was the best way to explain the phenomenon of wavefunctions collapsing upon observation. The wavefunction—a mathematical description of all the properties of a wave —can collapse into one of many different states. The act of observing and measuring the wavefunction, causes this collapse leading to the creation of many different worlds, wherein each of the likely outcomes occur.. These different worlds exist simultaneously but can never interact. So unfortunately, physics won’t ever find a way of transporting you to a parallel universe where you’re a rockstar. Many people are irritated by this concept, as it suggests that what we see is only a small sliver of all of existence.


It’s worth noting that Everett’s view is, of course, one of many interpretations of Quantum Mechanics. It agrees with the data and there is mathematics which supports it, but there are also several other theories such as the Copenhagen Interpretation which go against the Many-World theory.


There is currently no majority consensus as to which interpretation of Quantum Mechanics is correct. Each is merely a different way of interpreting the results of experiments, but the model you believe in makes no change to the hard data. Many scientists believe that this makes the Many-Worlds interpretation more philosophy than physics.


From Issue 18

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