Hi Richard,

On 28 Oct 2012, at 21:01, Richard Ruquist wrote:

Bruno, But it seems that the Gleason Theorem assigns probabilities to
the different universes in the multiverse that are not there in
Everett's MWI in the first place. Richard

?
I don't see that, nor why you say so. can you elaborate? Gleason theorem just makes unique the usual Born rule, and justify a literal reading of the quantum amplitude as relative (infinite) proportions. It is quite similar to the Deutsch Hayden justification, in decision theoretical terms, of such amplitude reading, in the Heisenberg picture.

Bruno





On Sat, Oct 27, 2012 at 9:46 AM, Bruno Marchal <marc...@ulb.ac.be> wrote:

On 26 Oct 2012, at 15:52, Richard Ruquist wrote:

Well Bruno,

If the "measure problem" (which I take to be the assignment of
probabilities) is intrinsic to Everett's MWI, does that not amount to
negating it?


Why? I think that it is beautifully solved by Gleason theorem, for the
Hilbert space of dim bigger or equal to 3.



I did not suggest that it negated comp, which is what you
responded to.


I think comp will confirms Everett QM, and this would make our sharable
human or animal substitution level very plausibly at the Heisenberg
uncertainty level, this for surviving even a long run, without detecting any
difference.

In that case, the Gleason solution will be the solution for comp. For this the X and Z logics (alreeady extracted) must conforms to some desiderata, already expressed by von Neumann, for a quantum logic, and which is that
mainly it defines the searched measure.

I m not sure I can understand string theory or any fundamental QM without
Everett.

I agree that the idea that we are multiplied by infinities at each instant is not attractive, but science is not wishful thinking, and besides, I don't
take any theory too much seriously (we don't know). I also know that
different theories can happen to be equivalent.

Of course, to be sure, comp has also many attractive features, mainly its conceptual simplicity and naturalness. It really explains almost why there is something instead of nothing, as it assumes only 0 and the successor and
the very simple laws, and explain from that how that very explanation
emerges in some collection of stable numbers' dream.

Bruno






Richard

On Fri, Oct 26, 2012 at 9:35 AM, Bruno Marchal <marc...@ulb.ac.be> wrote:

Richard,

On 25 Oct 2012, at 18:42, Richard Ruquist wrote:

Bruno,

Doesn't the Gleason Theorem negate MWI by assigning probabilities?
Richard



On the contrary. Gleason theorem solves the "measure problem" intrinsic
in
the Everett MWI, it makes the probabilities into comp (or weakening)
first
person indeterminacies.

Unfortunately, comp necessitates a version of Gleason theorem for all
comp
states, not just the quantum one, as the quantum law must be derived from
the 1p indeterminacies, occurring in arithmetic.

The advantage is that comp provides the theory of both quanta and qualia
(and a whole theology actually).
Unfortunately, it is not yet clear if those quanta behave in a
sufficiently
quantum mechanical way, like making possible quantum computers, hydrogen,
strings may be, etc.

Bruno





On Thu, Oct 25, 2012 at 9:38 AM, Bruno Marchal <marc...@ulb.ac.be>
wrote:



On 24 Oct 2012, at 19:53, meekerdb wrote:

On 10/24/2012 4:31 AM, Bruno Marchal wrote:


On 23 Oct 2012, at 14:50, Roger Clough wrote:

Hi meekerdb

There are a number of theories to explain the collapse of the quantum
wave
function
(see below).

1) In subjective theories, the collapse is attributed
to consciousness (presumably of the intent or decision to make
a measurement).


This leads to ... solipsism. See the work of Abner Shimony.




2) In objective or decoherence theories, some physical
event (such as using a probe to make a measurement)
in itself causes decoherence of the wave function. To me,
this is the simplest and most sensible answer (Occam's Razor).


This is inconsistent with quantum mechanics. It forces some devices
into
NOT
obeying QM.


No, it's only inconsistent with a reified interpretation of the wf.
It's
perfectly consistent with an instrumentalist interpretation.
Decoherence
is
a prediction of QM in any interpretation. It's the einselection that's
a
problem.






But instrumentalism is just an abandon of searching knowledge. There is
no
more what, only how.
An instrumentalist will just not try to answer the question of betting
if
there is 0, 1, 2, ... omega, ... universes.

And the einselection is not a problem at all, in QM + comp. It is
implied.
And, imo, the QM corresponding measure problem is solved by Gleason
theorem
(basically).

And then, keeping that same 'everything' spirit, the whole QM is
explained
by comp. We have just to find the equivalent of "Gleason theorem" for
the
"material hypostases".

Bruno








3) There is also the many-worlds interpretation, in which collapse
of the wave is avoided by creating an entire universe.
This sounds like overkill to me.


This is just the result of applying QM to the couple "observer +
observed".
It is the literal reading of QM.




So I vote for decoherence of the wave by a probe.


You have to abandon QM, then, and not just QM, but comp too (which can
only
please you, I guess).

Bruno


http://iridia.ulb.ac.be/~marchal/



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