Season 17, Episode 4: The Many-Worlds Interpretation’s Solution to Quantum Weirdness

Hey StarTalkians! In the last post, we delved a little deeper into Neil, Chuck and guest Sean Carroll’s discussion of the Copenhagen interpretation of quantum mechanics. But the original listener's question was actually about something else: the many-worlds interpretation.

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Sean Carroll gives a fantastic explanation in the podcast, but this post will take a closer look at the interpretation, guided by Hugh Everett’s "Relative State" Formulation of Quantum Mechanics. Schrodinger’s cat laid bare the problems with the Copenhagen interpretation, and Everett’s answer is now the leading alternative.

Trusting the Math: The Core of Everett’s Approach

Everett’s approach can be summarized as “trusting the math.” On the podcast, Professor Carroll makes this clear too: the “many worlds” exist in some form in the math, whether we like it or not.

In a way, the Copenhagen interpretation second-guesses the math, inserting this unnatural process of wavefunction collapse when we make an observation. The cat suddenly becomes alive or dead, or the electron suddenly materializes in one place and all alternatives disappear into the ether.

In the paper, Everett contrasts this “discontinuous change” in the wavefunction with the “continuous, deterministic change” described by the Schrodinger equation of quantum mechanics.

Everett’s idea, simply put, is to say: If the math says there are multiple outcomes, maybe we shouldn’t be forcing it into a single outcome?

He approached this ingeniously. His paper includes the observer in the mathematical description of the system. Think about it like this: if a detector activates with a certain quantum event, the state of the detector itself is also in a superposition.

So the math suggests there are also two detectors: one activated and one not. Everett originally called this a “splitting” of the universe.

This is illustrated beautifully in a figure attached from an article on Everett in Scientific American .

Solving Schrodinger’s Cat: Many-Worlds in Practice

We can now tackle Schrodinger’s cat in a many-worlds framework, and it’s actually pretty easy.

There is one world where the radioactive atom decays and the cruel contraption kills the cat, and one world where it doesn’t. Both things actually happen to the cat somewhere – all opening the box does is tell us which world we’re in. 

The real question is: did Everett solve the problem, or just create an even bigger one?