On 1/2/2014 10:38 PM, Jason Resch wrote:




On Fri, Jan 3, 2014 at 12:20 AM, meekerdb <meeke...@verizon.net <mailto:meeke...@verizon.net>> wrote:

    On 1/2/2014 7:37 PM, Jason Resch wrote:



    On Thu, Jan 2, 2014 at 8:35 PM, LizR <lizj...@gmail.com 
<mailto:lizj...@gmail.com>>
    wrote:

        On 3 January 2014 14:31, meekerdb <meeke...@verizon.net
        <mailto:meeke...@verizon.net>> wrote:


            Then I'll start by saying I don't reject MWI, I just have 
reservations
            about it, not so much that it's wrong, but that it doesn't really 
solve the
            problems it claims to - which implies criticism of the position 
that MWI
            has solved all the problems of interpreting QM.  A lot of the above 
claimed
advantages knocking down straw men built on naive interpretations of Bohr. Some are just assumptions, e.g that physics must be time reversible and linear.

        I thought linearit was probabilities adding up to one, which isn't a 
radical
        assumption???


    I think you might be thinking of unitary vs. non-unitary:
    http://en.wikipedia.org/wiki/Unitarity_(physics)
    <http://en.wikipedia.org/wiki/Unitarity_%28physics%29>

        Time reversibility is an observed phenomenon in (almost) all particle
        interactions, so surely not an assumption at all?


    I agree, things like CPT symmetry, determinism, etc. aren't just 
assumptions, but
    underlie every other known physical law that is known.

    http://en.wikipedia.org/wiki/CPT_symmetry
    The *CPT theorem* says that CPT symmetry holds for all physical phenomena, 
or more
    precisely, that any Lorentz invariant
    <http://en.wikipedia.org/wiki/Lorentz_invariant> local quantum field theory
    <http://en.wikipedia.org/wiki/Quantum_field_theory> with a Hermitian
    <http://en.wikipedia.org/wiki/Self-adjoint_operator>Hamiltonian
    <http://en.wikipedia.org/wiki/Hamiltonian_%28quantum_mechanics%29> must 
have CPT
    symmetry.

    Collapse of the wave function would be the only phenomenon in quantum 
mechanics
    that is non-unitary, non-linear, non-differentiable, and discontinuous. It 
would
    also be the only principle in physics that non-local, non-causal,
    non-deterministic, and violates special relativity.

    I can understand that Brent's ambivalence toward MWI, it may not be the 
final
    answer, but I think it is a good step in that direction. However, I am 
surprised
    that anyone well-versed in the known physics of today, could consider 
collapse as
    anything but a wild, unsupported, and almost-certainly-false conjecture.

    That's what I mean by attacking a straw man.  Fuchs and Peres et al, 
including Bohr
    only considered 'collapse of the wave function' as a change in one's 
information.


I agree Bohr was closer to Fuchs and Peres, but Heisenberg, von Neumann, Wigner, etc. all believed in collapse, and CI is still taught as the orthodox interpretation in most places. It's not exactly a straw man.

To say the theory is only about our information seems like a kind of cop-out to me. We don't see other theories in science described as only speaking about the information that we can gain not about anything that real external to us. Why can't QM be a realist theory like everything else in science?

I sort of see the opposite trend. More and more physicists are looking for an information based fundamental theory.

    Bohr said QM is not about reality, it's about what we can say about 
reality.  Only
    later did people try to invent real collapse theories, e.g. Penrose, and 
while I
    don't consider any of them likely I wouldn't say they are almost certainly 
false.


Let's say someone proposed a new theory to explain why when something falls into a black hole we can no longer see it, but it ignored that other theories already explain why we can't see things that fall into a black hole.

Or how about a theory that it's both destroyed at the event horizon and also falls through to the singularity?

Moreover, imagine that this theory, if true, would require faster than light influences, as well as violations in the second law of thermodynamics and conservation of mass energy. Would you say this theory was only "unlikely"?

Are you claiming that Penrose's idea does all those things?


    There is so much well-established physics that must be given up; for 
apparently no
    other reason than the ontological prejudice some harbor for the idea that 
the
    universe is no bigger than we previously thought.

    That's as good a prejudice as every thing must be determined from the 
beginning.


Now who is fighting straw men? (You always pretend this this is the primary, or only motivation for Everett)

I don't know about you, but Bruno has said he considers fundamental randomness to be completely unacceptable. What do you think about the idea that the whole course of the universe was set at that (near) singularity at the beginning of the universe? I realize it was probably not Everett's motivation - he was more interested in the Heisenberg cut problem.

Brent

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