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Hugh Everett | Reviews of Modern Physics | (1957)
Primary Link DOI Openalex

Abstract

The task of quantizing general relativity raises serious questions about the meaning of the present formulation and interpretation of quantum mechanics when applied to so fundamental a structure as the space-time geometry itself. This paper seeks to clarify the foundations of quantum mechanics. It presents a reformulation of quantum theory in a form believed suitable for application to general relativity. The aim is not to deny or contradict the conventional formulation of quantum theory, which has demonstrated its usefulness in an overwhelming variety of problems, but rather to supply a new, more general and complete formulation, from which the conventional interpretation can be deduced. The relationship of this new formulation to the older formulation is therefore that of a metatheory to a theory, that is, it is an underlying theory in which the nature and consistency, as well as the realm of applicability, of the older theory can be investigated and clarified.

Tags

Sample Definition And Size

This is a theoretical physics paper; no empirical sample or sample size is involved.

Study Type

The paper presents a theoretical reformulation of quantum mechanics (a conceptual/theoretical study), not an empirical or experimental study.

Conflicts Of Interest

No conflicts of interest are declared in the paper; standard for theoretical physics publications of the era.

Results Summary

The key result is the formulation of quantum mechanics without the collapse postulate (“pure wave mechanics”), introducing the concept of relative states. Everett shows that observers, treated as physical systems, will have determinate relative measurement records, and that in the limit of many measurements, almost all relative sequences exhibit the standard quantum statistics via a typicality measure. Thus, the conventional probabilistic predictions are recovered as subjective appearances within a deterministic, no-collapse framework. ([plato.stanford.edu](https://plato.stanford.edu/archives/win2017/entries/qm-everett/?utm_source=openai))

Referenced In

StarTalk

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.

youtu.be

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?

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