On Saturday, December 16, 2017 at 6:47:22 AM UTC-6, Lawrence Crowell wrote:
>
> On Friday, December 15, 2017 at 1:17:09 PM UTC-6, Bruno Marchal wrote:
>>
>>
>> On 15 Dec 2017, at 06:20, Brent Meeker wrote:
>>
>>
>>
>> On 12/14/2017 6:27 PM, Jason Resch wrote:
>>
>>
>>> *I don't see how Wigner's friend presents a problem for Copenhagen.
>>> According to the CI, the wf collapses when the system measured, which is
>>> when the box is opened. What am I missing? The issue of the cat's memory is
>>> a different matter, problematic IMO. AG *
>>>
>>>
>>
>> The problem is according to the CI, an isolated system evolves according
>> to the Shrodinger equation, and therefore does not collapse. But it also
>> says observation causes collapse.
>>
>>
>> That is not CI. CI always supposed there is a classical realm in which
>> measurements and observations were made by classical devices. Wigner toyed
>> with the idea that consciousness was required, but that was never Bohr's
>> idea of CI. In a sense, decoherence filled in CI by providing the
>> mechanism of collapse.
>>
>>
>> I would say that decoherence explains the illusion of a collapse in the
>> mind of the machine keeping a diary of the results of measurement.
>> Decoherence is relative entanglement, and the tracing-out by the relative
>> observers.
>>
>> The decoherence theory explains that the universe differentiation is
>> quite speedy, and why macroscopic coherence is hard to be maintained,
>> although possible for some material, and quantum topology promises
>> theoretically possible "solid" qubit, etc. Like you said; it is only a
>> matter or isolation. Now, the lack of isolation makes coherence easy lost,
>> but that means only the quasi-irreversible lack of interference with some
>> terms of the universal wave, not their genuine disappearance, which would
>> contradict linearity, unitarity, well, the SWE-or DIRAC-or Feynman.
>>
>> Bruno
>>
>
A small correction below in red font.
LC
>
> You wrote a part on this with respect to Godel's theorem a few weeks ago,
> which I lost in the huge sea of posts on this thread. I was going to
> respond but lost the post.
>
> Quantum mechanics is independent of measurement. Quantum amplitudes evolve
> by unitarity or Schrodinger type of evolution and this is perfectly
> deterministic. Once one throws a measurement or decoherence into picture
> things become less clear. We might then invoke Kant's *noumena* and
> *phenomena* as a way of thinking about this. Decoherence is just a way of
> looking at what happens to a quantum wave that is disturbed by the
> environment, which can include a laboratory measurement. Given that an
> optical photon is about .1eV in energy a 100 watt light source produces
> then around 10^{22} photons every second, which in the Fermi golden rule
> are emitted by spontaneous emission and thus their wave functions are
> decoherent. This is a numerically massive process in the universe at large.
> We have these various interpretations of what happens with these decoherent
> events, which are described phenomenologically. These various
> interpretations are putative noumena for the processes of decoherence or
> measurement.
>
> If we think of a measurement as a large system with many quantum states,
> say a mole ~ 6x10^{23} of states, that couples to a system with a small
> number of states. In a measurement the large number of states produce a
> classical(like) outcome for the occurrence of the small number of states.
> The process appears to involve a type of self reference as well as the
> necessity for einselected quantum states (Zurek etc) that define a
> classically stable needle state and its outcome. The process appears to
> require that states involved with the needle state encode quantum numbers
> as Godel numbers, which in general leads to a breakdown of computability.
> The quantum classical dichotomy here may reflect a sort of axiomatic
> incompleteness; the physical axioms of quantum mechanics are unable to
> compute how a macroscopic outcome, such as a needle state or a particular
> state in a decoherent set occurs.
>
> I proposed something of this sort a long time ago, around the same time I
> illustrated how the Schild's ladder in general relativity and quantum spins
> had the same Galois field representation. In the latter case I got a muted
> response, and of course now the idea general relativity and quantum
> mechanics are categorically equivalent is a hot topic. The idea that
> quantum outcomes are not computed by quantum evolution, say the quantum
> computer executing operations on qubits, was met by horror. "Oh the
> humanity" and so forth was sounded. However, it seems plausible to me to
> this day that all we can ever have is phenomenology on this, but we will
> never understand the noumena according to some set of postulates or
> physical axioms that are complete and consistent in QM. If GR = QM in
> quantum gravity this has an impact there as well, in particular with the
> problem of the firewall.
>
> LC
>
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