Why is it called Many-Worlds? AIUI (which may be completely wrong, as I know nothing of quantum mechanics) there is a single, deterministically evolving wave function. No splitting. The puzzle is why no-one ever perceives a system to be in a superposition. Suppose that a particle is flying towards a pair of detectors, in a superposition of states that will trigger one of them or the other. I will only perceive one of the detectors firing, never a superposition of both of them firing. From the point of view of the universal wave function, I am in a superposition along with the particle and the detectors, but such superpositions are never part of my experience. The part of the wave function representing my consciousness has a part with the experience of seeing one detector fire, and a part with an experience of seeing the other fire.
Perhaps it should be called the Many-Minds theory.
Many worlders are pointing at something in the physics and saying “that’s a world”… but whether it qualifies as a world is a separate question , and a separate kind of question, from whether it is really there in the physics. A successful MWI needs to jump both hurdles.
The issue is not whether superpositions exist, but whether they qualify as worlds.. it’s a conceptual issue.
There is an approach to MWI based on coherent superpositions, and a version based on decoherence. These are incompatible opposites, but are treated as interchangeable in Yudkowsky’s writings.
Deutsch uses the coherence based approach, while most other many worlders use the decoherence based approach. He absolutely does establish that quantum computing is superior to classical computing, and therefore that underlying reality is not classical. But showing that reality is not a single classical world is not the same as showing that it consists of a number of quasi classical worlds in superposition.
Superposed states lack a number of features that one would typically associate with a world: objectivity, size, causal isolation, and permanence.
Decoherence has the opposite problem: decoherent worlds can be large, can be objective, can be permanent for all practical, purposes, are causally isolated by definition.
But there is no obvious mechanism for decoherence within core QM. A coherent quantum state that evolves according to the Schrodinger wave equation remains coherent. Some additional mechanism for decoherence is required, and the complexity of the that mechanism must be factored into an assessment of which theory is simplest. (Why assume a coherent starting state? Well, maybe the universe started in a decohered state.. that’s actually a popular suggestion … but it requires its own explanation and adds own complexities).
There is an approach to MWI based on coherent superpositions, and a version based on decoherence. These are incompatible opposites
They’re not opposites, they’re two different ways of analyzing the same situation. Examining the local density matrices at various places, we may find decoherence has occurred, even while the global state is in a coherent superposition.
Why is it called Many-Worlds? AIUI (which may be completely wrong, as I know nothing of quantum mechanics) there is a single, deterministically evolving wave function. No splitting. The puzzle is why no-one ever perceives a system to be in a superposition. Suppose that a particle is flying towards a pair of detectors, in a superposition of states that will trigger one of them or the other. I will only perceive one of the detectors firing, never a superposition of both of them firing. From the point of view of the universal wave function, I am in a superposition along with the particle and the detectors, but such superpositions are never part of my experience. The part of the wave function representing my consciousness has a part with the experience of seeing one detector fire, and a part with an experience of seeing the other fire.
Perhaps it should be called the Many-Minds theory.
Many minds is a thing
https://en.wikipedia.org/wiki/Many-minds_interpretation
...But appealing to special properties of of observers is one of the main things many worlders are trying to getaway from them.
Many worlders are pointing at something in the physics and saying “that’s a world”… but whether it qualifies as a world is a separate question , and a separate kind of question, from whether it is really there in the physics. A successful MWI needs to jump both hurdles.
The issue is not whether superpositions exist, but whether they qualify as worlds.. it’s a conceptual issue.
There is an approach to MWI based on coherent superpositions, and a version based on decoherence. These are incompatible opposites, but are treated as interchangeable in Yudkowsky’s writings.
Deutsch uses the coherence based approach, while most other many worlders use the decoherence based approach. He absolutely does establish that quantum computing is superior to classical computing, and therefore that underlying reality is not classical. But showing that reality is not a single classical world is not the same as showing that it consists of a number of quasi classical worlds in superposition.
Superposed states lack a number of features that one would typically associate with a world: objectivity, size, causal isolation, and permanence.
Decoherence has the opposite problem: decoherent worlds can be large, can be objective, can be permanent for all practical, purposes, are causally isolated by definition.
But there is no obvious mechanism for decoherence within core QM. A coherent quantum state that evolves according to the Schrodinger wave equation remains coherent. Some additional mechanism for decoherence is required, and the complexity of the that mechanism must be factored into an assessment of which theory is simplest. (Why assume a coherent starting state? Well, maybe the universe started in a decohered state.. that’s actually a popular suggestion … but it requires its own explanation and adds own complexities).
They’re not opposites, they’re two different ways of analyzing the same situation. Examining the local density matrices at various places, we may find decoherence has occurred, even while the global state is in a coherent superposition.
Local decoherence with global coherence is hardly many worlds. Global decoherence with local coherence would be a much better fit.