Everett and Nash: Two Ways of Thinking About Possibility

Two names from different corners of intellectual history capture something I keep returning to. John Nash studied what happens when people make decisions in a world shaped by other people's decisions. Hugh Everett asked how quantum theory should describe an observer and the full range of possible measurement results. The formal links between their ideas are slim. Together, though, they inspire a question I care about: what if life is best understood as an ongoing process of possibility, choice and learning?

What each of them actually did

Hugh Everett III (Hugh Everett: Quantum Measurement Without Collapse) published a paper in 1957, based on his doctoral thesis at Princeton, that he called the "relative state" formulation of quantum mechanics. Textbook quantum theory uses two rules: one for how a system changes smoothly over time, and a special "collapse" rule for the moment a measurement is made. Everett asked what happens if you drop the collapse rule and describe the observer and the measuring device with the same physics as everything else. In his account, each possible result ends up paired with a version of the observer who recorded that result. Other physicists later popularized this as the idea of "many worlds" (The Many-Worlds Reading of Quantum Physics), a way of talking that Everett himself carefully avoided. Experts still disagree about how to read his work, especially about how probability fits in.

John F. Nash Jr. (John Nash: When No One Gains by Switching) published a two-page paper in 1950 showing that every game with a limited number of players and options has at least one stable point, as long as players are allowed to mix their choices at random. At that point, now called a Nash equilibrium, no player can do better by changing only their own choice while everyone else keeps theirs. Stable does not mean best: in many games the stable result leaves everyone worse off than if they had found a way to cooperate. In 1994 Nash shared the Nobel Memorial Prize in Economic Sciences for this work on games in which each player chooses independently.

Life as possibility, choice and learning

I picture reality as a series of unfolding journeys. At each moment there are options, limits, unknowns, and other people whose choices also matter. Whatever happens becomes part of what I carry into the next moment. In that sense the self is not a finished object; it is changed by the path it takes (Life as an Evolving Game). Game theory gives me a language for how my choices depend on other people's. Probability gives me a language for uncertainty (Probability, Risk & Uncertainty). The image of branching worlds gives me a language for paths not taken (Mapping the Futures a Choice Opens).

My curiosity goes further than those formal tools. I sometimes imagine that separate conscious lives could be different viewpoints of one larger awareness, learning through experience (Many Minds, One Shared Awareness, A Soul That Learns Along the Way). I do not claim that physics proves this or that Nash's work implies it. It is an open philosophical possibility, and an image that encourages me to take decisions, empathy and personal growth seriously.

Where the comparison stops

Because the pairing is a personal metaphor, it matters where it breaks down (Where Physics Ends and Philosophy Begins).

• Branches are not decisions. In Everett's account, branching comes from physical interactions such as measurement. Nobody chooses a branch, and thoughts or wishes do not create one.
• An equilibrium is not a destiny. Nash's idea applies to a clearly defined game with players, options and payoffs. It says nothing about souls, consciousness or the meaning of a life.
• Two different kinds of chance. Quantum theory has its own precise rule for the odds of measurement results (The Rule Behind Quantum Probabilities). The odds I put on my own choices are personal estimates. One cannot stand in for the other.
• Attention is not a quantum measurement. In double-slit experiments, the interference pattern fades when a physical record of the particle's path exists, whether or not anyone looks at it (The Double-Slit Experiment, What Observing Means in Quantum Physics). Attention matters a great deal in a human life, but not through quantum physics.

So what I take from Everett and Nash is not a new theory. It is a pair of lenses: one for the many ways things could turn out, and one for how my choices meet other people's. Neither man proposed the link I draw between them, and I hold it as a philosophy still under construction (A Philosophy Under Construction).

A family naming story

These two inspirations also live in a family naming story (A Family Name Inspired by Everett and Nash). For me, a family name inspired by Everett and Nash stands for curiosity, humility in the face of uncertainty, and the courage to shape a meaningful journey through the choices we can actually make. Like any name, it leaves room for others to find a completely different meaning in it.

Sources

• Jeffrey Barrett, “Everettian Quantum Mechanics,” Stanford Encyclopedia of Philosophy (revised 2023) — A careful overview of Everett’s no-collapse formulation, its 1957 publication and the competing ways it has been read since. It notes that Everett avoided talk of splitting worlds.
• “Many-Worlds Interpretation of Quantum Mechanics,” Stanford Encyclopedia of Philosophy (revised 2026) — Explains the many-worlds family of interpretations, including the open question of how probability fits in and the criticisms the view still faces.
• John F. Nash Jr. — Facts, NobelPrize.org — The 1994 Prize in Economic Sciences in Memory of Alfred Nobel, shared with John C. Harsanyi and Reinhard Selten “for their pioneering analysis of equilibria in the theory of non-cooperative games.” The link nobelprize.org/laureate/712 redirects here.
• Lin, Lu, Fedoseev, Lee, Lyu and Ketterle, “Fringe visibility and which-way information in Young’s double-slit experiments with light scattered from single atoms,” Physical Review A 113, 022219 (2026) — Analyzes two recent experiments in which single atoms act as the slits. When information about a photon’s path can in principle be obtained, here recorded as a change in an atom’s motion, the interference fringes fade. The journal page blocked automated access, so the title, authors and abstract were checked through the DOI registry and the arXiv preprint instead.
• arXiv:2507.19801, free preprint of the Physical Review A paper above — Same title and authors; the abstract can be read here without a subscription.
• Hugh Everett III, “‘Relative State’ Formulation of Quantum Mechanics,” Reviews of Modern Physics 29, 454–462 (1957) — The original paper. Citation details match the DOI registry; the publisher page blocked automated access, so the page itself was not checked.
• John F. Nash Jr., “Equilibrium points in n-person games,” Proceedings of the National Academy of Sciences 36(1), 48–49 (1950) — The original two-page proof that every finite game has an equilibrium. Citation details match the DOI registry; the publisher page blocked automated access, so the page itself was not checked.

These sources support the descriptions of the physics and the game theory. They do not support my personal interpretation, and I do not claim they do.