4 ms·

I feel like there isn't really, not anymore, and most of the semblance of a debate is people reporting on historical debates. Although hard to be sure without,

by ajkjk 2y ago

I feel like there isn't really, not anymore, and most of the semblance of a debate is people reporting on historical debates. Although hard to be sure without, like, a survey. At least in what I read it seems like the remaining debate is over how literally to interpret the words "many worlds", rather than whether the basic idea is correct. Ideas like entangling with the experiment and the decoherence of quantum states are very well-established.

deleted 2y ago
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pdonis 2y ago
> Ideas like entangling with the experiment and the decoherence of quantum states are very well-established. Yes, but neither of those explains why we observe measurements to have single results. The MWI "explains" that by saying that actually, measurements have all possible results (which is what a straightforward application of the Schrodinger equation says), but we don't experience that, we experience a single result in each branch of the overall entangled wave function. This "explanation" is treated with skepticism by many because it is completely different from how we treat individual branches of an entangled superposition in any other context besides "measurement". Normally, when two quantum systems are in an entangled superposition, we say that neither of them individually has any well-defined state at all; only the total joint system containing both of them does. We don't say that each branch of the entangled superposition is a different "world" in which each individual system has a well-defined state. The MWI has to claim that somehow when a "measurement" involved we can say that.
- notfed 2y ago
  > Yes, but neither of those explains why we observe measurements to have single results. IMO Everett is in fact the only interpretation that explains this quite clearly. "Why do we observe measurements to have single results?" "Because when you entangle with (an observable in a superposition), you enter a superposition. I.e., a mapping from states of you to states of (observable)" People who don't believe it's possible for themselves to enter a superposition should ask themselves whether they believe atoms may, and whether they (themselves) are made of atoms.
  - pdonis 2y ago
    > "Why do we observe measurements to have single results?" "Because when you entangle with (an observable in a superposition), you enter a superposition. I.e., a mapping from states of you to states of (observable)" This doesn't explain why we observe single results. A single result is not an entangled state. Mathematically, it's just one term of the entangled state: so observing a single result would mean the entangled state would be replaced by just one of its terms. This is what "objective collapse" interpretations say happens. But it's not what the MWI says happens. > People who don't believe it's possible for themselves to enter a superposition "Superposition" is not the correct term here; "entanglement" is. "Superposition" is basis dependent. "Entanglement" is not. The relevant question is not whether people can become entangled. A state in which a measurement has a single result is not entangled. At least, not if you interpret the math the way standard QM normally interprets the math. Edit: I should add here that this whole discussion is assuming a "realist" interpretation, where the quantum state describes the actual physical state of an individual quantum system (which might consist of subsystems, such as a measured object and the measuring device and the brain of the person reading the result off the measuring device). Not all interpretations are like that; for example, ensemble interpretations or statistical interpretations. In those interpretations the issue we are discussing doesn't even arise and "many worlds" seems like a straightforward confusion of concepts, like thinking that (to use an example from Beyond the Fringe) Venezuela must be all blue because it's colored blue on a map.

by ajkjk 2y ago

deleted 2y ago

[deleted]

pdonis 2y ago

> Ideas like entangling with the experiment and the decoherence of quantum states are very well-established. Yes, but neither of those explains why we observe measurements to have single results. The MWI "explains" that by saying that actually, measurements have all possible results (which is what a straightforward application of the Schrodinger equation says), but we don't experience that, we experience a single result in each branch of the overall entangled wave function. This "explanation" is treated with skepticism by many because it is completely different from how we treat individual branches of an entangled superposition in any other context besides "measurement". Normally, when two quantum systems are in an entangled superposition, we say that neither of them individually has any well-defined state at all; only the total joint system containing both of them does. We don't say that each branch of the entangled superposition is a different "world" in which each individual system has a well-defined state. The MWI has to claim that somehow when a "measurement" involved we can say that.

notfed 2y ago
> Yes, but neither of those explains why we observe measurements to have single results. IMO Everett is in fact the only interpretation that explains this quite clearly. "Why do we observe measurements to have single results?" "Because when you entangle with (an observable in a superposition), you enter a superposition. I.e., a mapping from states of you to states of (observable)" People who don't believe it's possible for themselves to enter a superposition should ask themselves whether they believe atoms may, and whether they (themselves) are made of atoms.
- pdonis 2y ago
  > "Why do we observe measurements to have single results?" "Because when you entangle with (an observable in a superposition), you enter a superposition. I.e., a mapping from states of you to states of (observable)" This doesn't explain why we observe single results. A single result is not an entangled state. Mathematically, it's just one term of the entangled state: so observing a single result would mean the entangled state would be replaced by just one of its terms. This is what "objective collapse" interpretations say happens. But it's not what the MWI says happens. > People who don't believe it's possible for themselves to enter a superposition "Superposition" is not the correct term here; "entanglement" is. "Superposition" is basis dependent. "Entanglement" is not. The relevant question is not whether people can become entangled. A state in which a measurement has a single result is not entangled. At least, not if you interpret the math the way standard QM normally interprets the math. Edit: I should add here that this whole discussion is assuming a "realist" interpretation, where the quantum state describes the actual physical state of an individual quantum system (which might consist of subsystems, such as a measured object and the measuring device and the brain of the person reading the result off the measuring device). Not all interpretations are like that; for example, ensemble interpretations or statistical interpretations. In those interpretations the issue we are discussing doesn't even arise and "many worlds" seems like a straightforward confusion of concepts, like thinking that (to use an example from Beyond the Fringe) Venezuela must be all blue because it's colored blue on a map.