On 5/9/2013 11:28 AM, Jason Resch wrote:




On Thu, May 9, 2013 at 1:11 PM, meekerdb <meeke...@verizon.net <mailto:meeke...@verizon.net>> wrote:

    On 5/9/2013 10:02 AM, Jason Resch wrote:
    Von Neumann thought the extra baggage was required to make the model match 
our
    observations, but Everett later showed that step was unnecessary.  The 
model (free
    of additional baggage) predicts the same observations as the model with it.

    He showed that IF the wave function separates into orthogonal components (an
    irreversible process) then FPI explains the observations.  But the model 
says it
    never does that; it only approximates that, in certain bases.


Could you explain this? I don't understand in what sense the Schrodinger equation can only approximate itself?

If you include the observer and the system observed then when the observer interacts with system in superposition the observers state becomes a superposition in the same basis. The cross-terms in the superposition are not zero. They can be shown to become approximately zero if you include interaction with an environment that has a large number of degrees of freedom and you trace over the environment variables. But that last step isn't part of the Schrodinger equation, it's a separate assumption comparable to Boltzmann's assumption of molecular chaos.

      Decoherence theory tries to fill in the process by which this occurs give 
a
    statistical mechanics type account of irreversibility.


It gives an account of the appearance of an "irreversible wave-function collapse" without their having to be one. It is derived entirely from the theory of QM and is not an extra postulate.

It depends on the choice of basis. In general there's other some basis in which state is pure. Decoherence says the density of the subsystem is approximately diagonal in a particular basis. This involves assumptions about the environment and is not part of the wave function.

      But you could also take the epistemological interpretation of Peres and 
Fuchs
    instead of inventing other worlds just to save the determinism of an 
equation.


The other worlds are a required element of the theory, unless you deny the reality of superposition. I think Everett's thought experiment explains the situation the best:

Imagine a box with an observe in it who will be measuring the state of a particle and writing the result in a notebook. This box is entirely sealed off from the external world such that the internal result of the experiment remains in a superposition until it is opened. Now a second, external observer models the entire evolution of this box over time, including before and after the observer inside measures the state of the particle and records the result in a notebook. He determines the superposition of all the possible handwritings of all the possible results in the notebook. Is the internal observer not conscious in each of the various superpositions resulting from the measurement?

Depends on what you mean by THE internal observer. There is a superposition of states that represents the external observers theory of the internal observer.


Epistemological interpretations seem to deny there is any fundamental reality at all, aside from what we can see and learn, which to me seems like a dead end in the search for truth.

Shifting the truth off to undetectable realms doesn't help much.


      I like MWI and Bruno's FPI idea, but without some testable prediction (not
    retrodiction) I don't find them compelling.


Why do you find compelling about the idea that all other superpositions (except for one) vanish?

It comports with experiment. What do you find compelling about the idea that the unity of your consciousness is an illusion.

Brent

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