On Fri, Jan 3, 2014 at 12:20 AM, meekerdb <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> wrote:
>>   On 3 January 2014 14:31, meekerdb <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)
>>   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?

> 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. 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"?

>   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)


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