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.
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.