On 12/10/2012 5:41 AM, Jason Resch wrote:


On Mon, Dec 10, 2012 at 12:32 AM, meekerdb <meeke...@verizon.net <mailto:meeke...@verizon.net>> wrote:

    On 12/9/2012 5:03 PM, Jason Resch wrote:


    On Sun, Dec 9, 2012 at 6:51 PM, meekerdb <meeke...@verizon.net
    <mailto:meeke...@verizon.net>> wrote:

        On 12/9/2012 4:37 PM, Jason Resch wrote:


        On Sun, Dec 9, 2012 at 5:40 PM, meekerdb <meeke...@verizon.net
        <mailto:meeke...@verizon.net>> wrote:

            On 12/9/2012 12:08 PM, Jason Resch wrote:

                And without a doubt the most popular interpretation of Quantum
                Mechanics among working physicists is SUAC (Shut Up And 
Calculate),


            That's not an interpretation at all.

            Well for a more philosophical statement of it see Omnes.  His view 
is that
            once you can explain the diagonalization of the the density matrix 
(either
            by eigenselection, dechoherence, or just assumed per Bohr) then you 
have
            predicted probabilities.  QM is a probabilistic theory - so 
predicting
            probabilities is all you can ask of it.


        Is science just about its applications or about understanding the 
world?  I
        would argue that science would not progress so far as it has if we 
thought
        finding the equation was the be all and end all of science.  The "shut 
up and
        calculate" mindset can be translated as "don't ask embarrassing 
questions", it
        is the antithesis of scientific thinking.

        Student in the 1500s: Does the earth move about the sun, or do the 
planets
        merely appear to move as if earth moved about the sun?
        Professor in the 1500s: We have all the formulas for predicting 
planetary
        motion, so shut up and calculate!

        Fortunately, Copernicus wasn't satisfied with that answer.

        So what's your objection to Omnes?  That the world just can't be
        probabilistic?  So instead there must be infinitely many inaccessible 
worlds -
        which happen to mimic a probabilistic world.


    It is fine if QM is a probabilistic theory.  Where I disagree with him is 
in his
    belief that we can never go beyond that in our understanding of it.  I am 
not sure
    how accurate this statement is, since it is a secondary source, but
    http://en.wikipedia.org/wiki/Roland_Omn%C3%A8s says: "We will never, Omnès
    believes, find a common sense interpretation of quantum law itself."  To 
me, it
    almost seems as if he says it is not worth trying to find an answer.

    Suppose he'd said in 1400CE, "We will never find a common sense 
interpretation of
    the sphericity of the Earth."  He'd have been right; we didn't, instead we 
changed
    'common sense'.


I don't know, I think Sagan's explanation fits most people's common sense:

http://www.youtube.com/watch?v=Jwr8CLX3NJA&t=1m19s <http://www.youtube.com/watch?v=Jwr8CLX3NJA&t=1m19s>


    I lean more towards David Deutsch who says science is about finding good 
explanations.

    But why isn't "It's a probabilistic world and it obeys the Born rule." a 
good
    explanation.


It is worse than that.  From: 
http://lesswrong.com/lw/q7/if_manyworlds_had_come_first/

"All right," says Nohr. He sighs. "Look, if this theory of yours were actually true—if whole sections of the wavefunction just instantaneously vanished—it would be... let's see. The only law in all of quantum mechanics that is non-linear, non-unitary, non-differentiable and discontinuous. It would prevent physics from evolving locally, with each piece only looking at its immediate neighbors. Your 'collapse' would be the only fundamental phenomenon in all of physics with a preferred basis and a preferred space of simultaneity. Collapse would be the only phenomenon in all of physics that violates CPT symmetry, Liouville's Theorem, and Special Relativity. In your original version, collapse would also have been the only phenomenon in all of physics that was inherently mental. Have I left anything out?"

The page also asks:

But suppose that decoherence and macroscopic decoherence had been realized immediately following the discovery of entanglement, in the 1920s. And suppose that no one had proposed collapse theories until 1957. Would decoherence now be steadily declining in popularity, while collapse theories were slowly gaining steam?

    I'm all for finding a better explanation, i.e. a deterministic one.  But 
simply
    postulating an ensemble of worlds to make the probabilities "deterministic" 
in
    arbitrary way doesn't strike me as any improvement.



MWI follows directly from a literal reading of the equations, which contain no mention of collapse or only applying only at certain scales.

No it doesn't. It is no more than decoherence, which means that in a selected basis the reduced density matrix becomes approximately diagonal. At that point Everett says the different diagonal eigenvalues are the probabilities of projections onto orthogonal subspaces, which being orthogonal can be regarded as different 'worlds'. But this suffers the same problems as other interpretations (which is why Omnes says there isn't any intuitive interpretation). First, there has to be a selection of a basis, which in an experiment is made by a choice of instrument (what does your detector detect?). Whether this is part of theory or a boundary condition depends on whether you include the experimenter in the Hilbert space. But if you include the experimenter, you've just backed out the boundary condition one step - you haven't eliminated it. Once the instrument is modeled, then (in theory) you can calculate decoherence in the selected basis and the *reduced* density matrix will become *approximately* diagonal in the selected basis. But notice that there is nothing in the bare mathematics that tells you the reduced density matrix gives you the probabilities. It is a choice based on the instrument/environment division. The density matrix becomes (almost) diagonal when you trace over the environment part (otherwise nothing has happened - or more precisely it could unhappen). Performing this trace operation is a mathematical calculation, not part of the physical evolution, and it philosophically equivalent to choosing a basis in which to collapse a wave-function.

Brent

Even better, the Born rule falls out as Everett himself noticed. If anyone is performing a stretch (postulating new things), it is those in the collapse camp who add new conjectures to the theory in an unjustified effort to preserve the notion of a single universe. The theory itself explains why the other universes are not observed, so pretending we have to augment the theory by adding new postulates (observers, collapse, born rule) to make it agree with our observations is somewhat absurd.

In the history of science efforts to keep humanity on the center stage seem to always fail ( http://www.youtube.com/watch?v=o8GA2w-qrcg ). I think that very reason, to keep the Earth near the "center of the universe", was and is the basis for collapse theories.

Jason


    Brent
    "As to the fable that there are Antipodes, that is to say,
    men on the opposite side of the earth where the sun rises
    when it sets to us, men who walk with their feet opposite
    ours, that is on no ground credible. Even if some unknown
    landmass is there, and not just ocean, "there was only one
    pair of original ancestors, and it is inconceivable that
    such distant regions should have been peopled by Adam's
    descendants."
          --- St. Augustine



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