On 06 May 2016, at 01:13, Bruce Kellett wrote:
On 5/05/2016 10:57 pm, Bruno Marchal wrote:
On 05 May 2016, at 01:31, Bruce Kellett wrote:
This is where your fascination with the 1p-3p notion gets you into
trouble. If the third person view (3p) means anything at all, it
means simple intersubjective agreement. The third person is one
who stands outside the particular experimental situation and
observes the outcome. In the 'Quantum Darwinism' of Zeh, this
corresponds to the fact that decoherence leaves many traces of a
particular experimental result in the environment; this result can
be shared among many 'third persons' without degradation -- hence
intersubjective agreement.
There is no 'person' who has the 'bird' view -- there is no-one
who continues to see the superposition after dechorence has had
its way. Your 1p-3p distinction works for person-copying, as in
taking copies of a computer program, because there can be a third
person who sees both copies, the one in Washington and the one in
Moscow. Nothing similar is possible in the quantum case, so your
continued use of the 'peepee' language in discussions of quantum
mechanics is just confused.
I will at the positive aspect. You seem to agree with the
computationalist FPI. That is a progress. Now just reread Everett.
Pure state evolves in pure state, and never becomes mixture in the
MW. The third person view is given by the wave or matric formalism.
The relative state are given by partial trace. We can define a
world by a set of things close for interaction, this automatically
ensure locality.
MWI with the partial trace, required in order that experiments give
definite results, does give the transition froma pure state to a
mixture. Certainly, the only sensible definition of a wolrd is a set
of things closed for interaction -- this requires the partial trace,
by the way, To claim that this automatically ensures locality is
just nonsense.
...........
As I said, there is no 'person' who has the 'bird' view. It is
just your belief that this is the fundamental ontology. You have
absolutely no direct evidence for this, nor could you have. The
fundamental ontology could just be one world, with the universal
wave function as nothing more than a calculational device -- you
could not know the difference.
But this does not work, as Feynman and Everett already explained
with the double slit. In "Fabric of Reality" David Deutsch made it
even clearer using for slits.
You are confusing the Feynman paths of the path integral formalism
with separate worlds.
I did not.
David Deutsch is famous for this particular idiotic confusion. You
have just defined a 'world' above as a set of things closed for
interaction. On that definition (with which I agree), the paths
through the separate slits in a two-slit set-up cannot be separate
worlds -- they are just separate paths in the Feynman sense.
All they need to be are different terms in the wave expansion. They
are superposed states/worlds/situations/whatever.
..........
As I expected, you simply duck the problem and make a fatuous
appeal to authority. I have shown explicitly that the argument
given by Tipler fails.
You have to rebut my argument.
I did. The error is in factoring Alice (+) state, which is
impossible as her memory has changed in the two branches.
Rubbish. You seem to forget the argument that Tipler actually made.
I reproduce it here:
here I was referring to the debunking of your idea that Alice cannot
get right the result of repeated measurement.
You come back on a different thread.
There is a widely cited paper by Tipler (arxiv:quant-ph/0003146v1)
that claims to show the MWI does away with non-locality.
I read it a long time ago, but I have stopped to believe that MWI can
be non-local before. If you agree that a world is a sect of object/
event close for interaction, then Jesse mazer argument directly leads
to locality. Where Alice is separated from Bob light cone, she can be
in the same world at all. There will be no action at a distance
because there will no interaction possible. The correlation will not
be confirmed by them, but only by their respective doppelganger which
will inhabit their worlds soon or later.
It is instructive to go through his argument, and to see how he has
managed to deceive himself. We start with the singlet state:
|psi> = (|+>|-> - |->|+>)/sqrt(2)
and then expand the state for the second particle in a different
basis (at relative angle theta):
|+>_2 = cos(theta/2)*|+'> + sin(theta/2)*|-'>,
|->_2 = -sin(theta/2)*|+'> + cos(theta/2)*|-'>.
Substituting this into the singlet state above, we get
|psi> = -[ sin(theta/2)*|+>|+'> - cos(theta/2)*|+>|-'> +
cos(theta/2)*|->|+'> + sin(theta/2)*|->+'>]/sqrt(2),
which exactly represents the requisite four worlds, corresponding to
the (+,+'), (+,-'), (-,+'), and (-,-') possibilities for joint
results, each world weighted by the required probability.
OK, but you cannot look at them like if it was a mixture. No collapse
has ever occurred, nor will ever occur.
Tipler claims that this shows how the standard statistics come about
by local measurements splitting the universe into distinct worlds.
He is, of course, deluding himself, because the above calculation is
not local.
That does not make sense to me. The calculation is local. What it
depicts is a coherent whole which behave thorugh local interactions,
with the apparition of phenomenological indeterminacy and non locality
due to the fact that the observers differentiates.
It is, in fact, nothing more that the standard quantum calculations
(with the projection postulate evident)
Yes, but the projection is only a first person (plural intra world)
view.
that I gave above for the possible (+) and (-) results for Alice,
combined in the one equation. It still uses the fact that Alice's
measurement of particle 1 affects the quantum state for particle 2
(which is, by then, a large spacelike distance away).
I don't see that.
Tipler utilizes the non-local nature of this change to extract
theta, the relative orientation of magnets -- a relative orientation
that can only be known by comparing orientations at A and B
directly. So Tipler's derivation is every bit as much local or non-
local as the conventional calculation -- he has not eliminated non-
locality by his trivial reworking of the derivation.
But non-locality never entered in the picture. It is only the
abstraction of the parallel states which make us feel something has
acted at the distance, but what the many Alice and Bob are doing is
just localizing themselves in the universes (first person plural view)
that they can share.
Tipler's calculation is exemplary in every way as a standard quantum
calculation on this entangled state. He has merely ignored the
effects of decoherence in order to retain the full superposition.
Decoherence is only superposition contagion. It is done as sublight
speed, and differentiate the stories, providing new bits of
information to the participant. for the outer picture, it is only a
rotation in some complex space, without leading to any new bit of
information.
There is nothing wrong with this if you want to work in the many
worlds paradigm. His problem, as I have pointed out, is that this
standard quantum calculation is irreducibly non-local:
The problem would be if the physical get non local. "local" does not
apply to the calculation done by the observer.
The question Tipler (and you) must answer is where the angle theta
in the above calculation comes from? Theta is the angle of the
relative orientation of Alice and Bob's polarizers -- an angle
chosen only after the two entangled particles are widely separated.
This angle can only be known by having information about both
polarizer angles to hand, and these polarizers are at spacelike
separation when the angle is needed for the above clculation. The
calculation therefore, involves an essential non-locality. Doing the
standard calculation in the many worlds paradigm has not removed
this non-locality.
This is the analysis that you have to rebut,
The angle theta comes from Alice choosing a measurement angle. Bob
might make a measurement, giving him a differet theta', if he is
spacelike separated from Alice. In that case both will localized
themselves in different differentiation of their environment, and they
will never discover the discrepancy between theta and theta', as both
are entangle with the corresponding doppelgangers provided by the
singlet state.
To sum up, your mistake, I think, consists in deriving a physical
mixture from the projection postulate. At no points the MWI ever
becomes a mixture. It is one wave all the time. We are just relatively
embed in it. The same with the sigma_1 complete space
(computationalism).
Bruno
Bruce
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