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## Main Question or Discussion Point

As is well known, David Deutsch is a leading proponent of the interpretation of Quantum Mechanics stating that the universe somehow branches into all the possibilities represented by the wavefunction; an ever-evolving multiverse, known as the Many Worlds Interpretation(MWI) or Everettian Interpretation.

In his book "The Beginning of Infinity" he introduces a core principle to derive his justification for probability in these Many Worlds: there exist an infinite amount of

The concept of

In his book "The Beginning of Infinity" he introduces a core principle to derive his justification for probability in these Many Worlds: there exist an infinite amount of

**fungible**universes. So there is no new universe magically spawned each time there's a quantum event, rather they were always there, an infinite identical set of them, but they are**fungible**. What does this mean? According to Deutsch 'fungibility' means that just like 1 dollar in your bank account is the same as any other dollar you have in your bank account, so is true for all particles in this fungible-multiverse. So the electron you are observing also exist in all the other corresponding universes, this is naturally the main axiom of MWI, however Deutsch makes a point about them not only being identical but**fungible**.The concept of

**fungibility**makes perfect sense to me in economics or other human constructs, but is it a property of physics? When we think back to the dollars in your bank account, they are fungible in the minds of everyone participating in the economy, they exist as neural patterns in our brains and as 1s and 0s made up of logic gates in the computers that hold them. I came across someone reviewing Deutsch's book who said lasers are fungible, but I am struggling to find any proof that there exist**fungible**properties in the real world that are not constructs of other complex processes. The reason this is a point of contention for me is that it underlies Deutsch's entire view of reality, which is quite a postulate to support ones quantum interpretation if it does not exist in known physics.