On 5/9/2013 12:40 PM, Jason Resch wrote:




On Thu, May 9, 2013 at 2:08 PM, meekerdb <meeke...@verizon.net <mailto:meeke...@verizon.net>> wrote:

    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


I follow you so far. To confirm we are on the same page, so you think observers are special in any physical way from any other "non observer" in a physical system?

    in the same basis. The cross-terms in the superposition are not zero.


Do they need to be, what if they are not zero? How does a single-universe interpretation avoid this issue?

    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.


Earlier you said it can be shown, so how is it an assumption? Or do you mean it is an assumption that the environment has a large number of degrees of freedom?

That and that the interaction is such that it diagonalizes in the variable(s) 
of interest.



        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.


It doesn't matter which/whose basis you use though, does it?

It's not "whose" but "which". Most measurements are modeled as position measurements but you can invent ones that are measurements in momentum space too. But in general you can't create a measurement to determine the pure state which includes the environment.


        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.


Okay, then from the view point of the external observers, shouldn't the various internal observers who remain in a super position, include observers each with a memories of recording one of the results in the log book, and in their brain? What happens to these memories (and presumably the experiences) when the external observer opens the room and collapses the superposition? Are we to believe all the memories and experiences that internal observer had are retroactively erased from existence and in fact, never happened at all?

No, we believe the external observer needs to update the wave function he's using to describe the internal observer, based on his new information.




    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.


They are implied by the model of reality.

They are implied by ONE model of reality.

Just like the galaxies beyond the cosmological horizon are implied by some models of inflation. Why contort a perfectly good and simple theory to make it match our (known) limited perceptive capacities? To me, single universe theories are as silly as any theory of inflation which said: "Once a galaxy crosses beyond our cosmological horizon, it ceases to exist, and any life forms that might have been in those galaxies cease to be."

Except there are no galaxies that are observed to cross the Hubble sphere.




        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 experiment even hints that other superpositions vanish?

"Vanish" = no longer seen.


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


Is this the real source of your resistance to MWI, that you do not feel yourself split when your intuition suggests you should feel it?

No. It's that it makes no testable predictions. It's just metaphysics to satisfy a demand for determinism - unless it can predict something.


Don't worry, you don't need to condemn your copies to a superposition with 0 amplitude to explain why you (in this branch), do not have access to the memories/experiences of the other yous (in other branches).

This is the same error presentism makes: believing we must make all other points in time non-real to explain why we feel ourselves to be in this single point in time.

So to answer your question, what I find compelling is not contorting a theory to solve imagined problems.

I think of non-determinism as an imagined problem.

Brent

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