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. 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.
..........
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:
There is a widely cited paper by Tipler (arxiv:quant-ph/0003146v1) that
claims to show the MWI does away with non-locality. 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. 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. It is, in fact, nothing more that the standard quantum
calculations (with the projection postulate evident) 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). 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.
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. 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 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,
Bruce
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