4 ms·

The article strikes me as crackpottery, but this statement > A lot of physicists also don't see any value in MW's interpretation since it offers no predictive

The article strikes me as crackpottery, but this statement > A lot of physicists also don't see any value in MW's interpretation since it offers no predictive value is not entirely correct either. This is the probably best "explain like I am an undergraduate not in Physics" article on Everett's proposal. https://plato.stanford.edu/entries/qm-everett/ https://plato.stanford.edu/entries/qm-everett/ To further summarize the value of Everett's proposal: In the standard von Neumann-Dirac collapse formulation of QM, a collapse happens when we measure it. But what a measurement event looks like and conditions when it occurs are not described by the theory at all. This is one reason why QM cannot completely describe the universe, or approximate it. Note that even if we can describe what a collapse is, this+QM still fails to model parts of the world, only approximating it. But one can try to propose a formulation of QM that agrees with the collapse formulation, that does not have that collapse, so that it is closed in the sense that for each system of observers observing a quantum system collapsing, that system can be modeled as quantum system itself. That is Everett's proposal. From the linked article, > Everett’s solution to the problem was to drop the collapse postulate from the standard formulation of quantum mechanics then deduce the empirical predictions of the standard collapse theory as the subjective experiences of observers who were themselves modeled as physical systems in the theory. The result was his relative-state interpretation of pure wave mechanics.

kgwgk 7y ago
The “no predictive power” is beyond what is predicted by standard QM, because the MWI is supposed to recover the same predictions. And it’s not clear how does it so, because if standard QM has an issue with “what a measurement event looks like and conditions when it occurs” then exactly the same problem remains in the MWI if the same predictions have to be recovered. Even though there is no collapse in the MWI it looks like there is a collapse, even though you don’t have to specify when the collapse happens you have to specify when does it look like a collapse does happen.
- jhanschoo 7y ago
  > even though you don’t have to specify when the collapse happens you have to specify when does it look like a collapse does happen. In MWI there is no collapse event, because there are no observers in the traditional sense that may collapse the system. In MWI we resign and just say that observers are subject to QM, and when a "measurement" is made, what happens is that observers and the observed system get entangled so that certain combinations of properties of the observer-observed system are not possible. This entanglement of two projections of a composite system can be described in the language of QM. > what is predicted by standard QM, because the MWI is supposed to recover the same predictions. MWI recovers the same predictions. Where in standard QM if one says an observer observes that a system may collapse 40% in state a and 60% in state b, MWI says that in systems (of the observer and the observed) where the observer makes the observation in the same exact manner, the observer will record state a with the system in state a 40% and the observer will record state b with the system in state b 60%, and there are no states where the observer observes something and the subsystem is in the other state. Of course, you can simply model the entire system of observer and observed in standard QM and recover the same relative predictions without invoking the absolute observation of an observer. In MWI we do away with the conceit that there is an absolute observation of an absolute, but ill-defined observer.
  - kgwgk 7y ago
    The point is that if standard QM has a problem to make predictions, then the MWI would face the same problem to make the same predictions starting from a universal wavefunction. If standard QM has no problem to make predictions then I agree than in principle the MWI could make the same predictions (but it seems to me that in practice it can only make predictions by using standard QM and saying that those are the same predictions that could in principle be derived).
    - jhanschoo 7y ago
      Can you clarify what you mean by standard QM? I had taken your usage of "standard QM" to mean, as you used it in context, to be collapse interpretations, but strictly speaking standard QM just concerns itself with quantum systems and is not incompatible with MWI. Edit: it's too late to alter my original ancestor comment, but I think the way I wrote it may have yielded a misunderstanding. I didn't mean to suggest that MWI has value because it can predict phenomena. I meant to say that it has value because it is a metaphysically cleaner model of reality than the collapse interpretations.

kgwgk 7y ago

The “no predictive power” is beyond what is predicted by standard QM, because the MWI is supposed to recover the same predictions. And it’s not clear how does it so, because if standard QM has an issue with “what a measurement event looks like and conditions when it occurs” then exactly the same problem remains in the MWI if the same predictions have to be recovered. Even though there is no collapse in the MWI it looks like there is a collapse, even though you don’t have to specify when the collapse happens you have to specify when does it look like a collapse does happen.

jhanschoo 7y ago
> even though you don’t have to specify when the collapse happens you have to specify when does it look like a collapse does happen. In MWI there is no collapse event, because there are no observers in the traditional sense that may collapse the system. In MWI we resign and just say that observers are subject to QM, and when a "measurement" is made, what happens is that observers and the observed system get entangled so that certain combinations of properties of the observer-observed system are not possible. This entanglement of two projections of a composite system can be described in the language of QM. > what is predicted by standard QM, because the MWI is supposed to recover the same predictions. MWI recovers the same predictions. Where in standard QM if one says an observer observes that a system may collapse 40% in state a and 60% in state b, MWI says that in systems (of the observer and the observed) where the observer makes the observation in the same exact manner, the observer will record state a with the system in state a 40% and the observer will record state b with the system in state b 60%, and there are no states where the observer observes something and the subsystem is in the other state. Of course, you can simply model the entire system of observer and observed in standard QM and recover the same relative predictions without invoking the absolute observation of an observer. In MWI we do away with the conceit that there is an absolute observation of an absolute, but ill-defined observer.
- kgwgk 7y ago
  The point is that if standard QM has a problem to make predictions, then the MWI would face the same problem to make the same predictions starting from a universal wavefunction. If standard QM has no problem to make predictions then I agree than in principle the MWI could make the same predictions (but it seems to me that in practice it can only make predictions by using standard QM and saying that those are the same predictions that could in principle be derived).
  - jhanschoo 7y ago
    Can you clarify what you mean by standard QM? I had taken your usage of "standard QM" to mean, as you used it in context, to be collapse interpretations, but strictly speaking standard QM just concerns itself with quantum systems and is not incompatible with MWI. Edit: it's too late to alter my original ancestor comment, but I think the way I wrote it may have yielded a misunderstanding. I didn't mean to suggest that MWI has value because it can predict phenomena. I meant to say that it has value because it is a metaphysically cleaner model of reality than the collapse interpretations.