On 05 May 2016, at 01:31, Bruce Kellett wrote:
On 5/05/2016 5:17 am, Bruno Marchal wrote:
On 04 May 2016, at 01:25, Bruce Kellett wrote:
On 4/05/2016 3:41 am, Bruno Marchal wrote:
On 03 May 2016, at 00:32, Bruce Kellett wrote:
On 3/05/2016 1:49 am, Bruno Marchal wrote:
On 02 May 2016, at 07:54, Bruce Kellett wrote:
On 2/05/2016 3:15 pm, Jesse Mazer wrote:
On Mon, May 2, 2016 at 12:13 AM, Bruce Kellett <[email protected]
> wrote:
No, I disagree. The setting b has no effect on what happens
at a remote location is sufficiently precise to encapsulate
exactly what physicists mean by locality. In quantum field
theory, this is generalized to the notion of local causality,
which is the statement that the commutators of all spacelike
separate variables vanish -- as you mention below.
And if you used full quantum description of the measuring
apparatus and experimenter, and didn't assume any collapse on
measurement, then there would in general be no single
"setting b" in the region of spacetime where one experimenter
was choosing a setting, but rather a superposition of
different settings. Do you think your preferred definition
can be meaningfully applied to this case, and if so how?
I do not know what you here mean by "collapse on measurement"?
It seems that you might be confusing a collapse to a single
world after measurement with the projection postulate of
standard quantum theory. The projection postulate is essential
if one is to get stable physical results -- repeated openings
of the box in Schrödinger's cat experiments would result in
oscillations between dead and alive cats.
The projection postulate is replaced by the FPI in Everett, and
as I explained yesterday, it is just self-entanglement, or what
I call often the contagion of superposition:
Alice * (up + down) = Alice * up + Alice * down.
If Alice look, as many times as she want at the up/down state
of the particle, she will find up (and always up) *and* down
and always down. The reason is that once she find up, Alice
becomes Alice-up, and that state does no more factor out the
particle state (unless memory erasure).
That is just the projection postulate, it cannot be replaced if
you want to agree with observation.
Well OK. If that is the projection postulate, then it is a
theorem in QM-without collapse, through the direct use of the
First Person Indeterminacy.
As I thought, you have confused this with the collapse of the
wave function to a single world.
That is the confusion of the Copenhagen people, who believe
(correctly) that a measurement select one world among many, but
believe (incorrectly) that the other worlds, or wave suterms,
have mysteriously disappear.
With Everett analysis of measurement, we have:
Alice * (up + down) = Alice * up + Alice * down. (linearity of
tensor product),
and it becomes:
Alice-seeing-up * up + Alice-seeing-down * down (linearity of
time evolution)
With the copenhagen collapse of the wave, we have:
Alice * (up + down) = Alice * up + Alice * down. (linearity of
tensor product),
and it becomes
Alice-seeing-up * up (non-linearity of time evolution)
or
Alice-seeing-down * down (again with a non-linearity of time
evolution)
The proportion of worlds, or the probability of results being
given by the (square-root of 1/2)^2 (= 1/2), square root hidden
above for reason of readability.
When it is boiled down, this is nothing more than a matter of
taste. By concentrating on the individual worlds, so that
A(|+>|-> - |->|+>) --> A(+)|+>|-> OR A(-)|->|+>
where A(+) means "Alice sees + as her result", and so on, the
conventional understanding simply implements the insights coming
from decoherence and wider entanglement with the environment,
leading to the emergence of disjoint worlds: the
original pure state reduces to a mixed state (represented by the
use of 'OR' in the above equation) as a result of the partial
trace over environmental degrees of freedom. The alternative
formulation (where 'OR' is replaced by '+') simply retains the
original pure state and does not represent the formation of
disjoint worlds following environmental decoherence.
?
You talk like if the conventional understanding as many-worlds, and
the MW was not leading to Many worlds.
I find it difficult to parse this sentence. The conventional
understanding is that decoherence and the partial trace reduces the
original pure state to a mixture. This is necessary if one wants the
theory to produce definite results from experiments, rather than
superpositions. The resulting 'worlds', if you want to call them
that, are disjoint and do not have any influence on one another. If
you want to believe that all the 'worlds' exist, then feel free, but
that belief has no operational consequences -- Occam's Razor is the
usual way of dispensing with such redundancies.
This is sometimes referred to (following Tegmark) as the
difference between the 'frog' and 'bird' views.
(It is more precisly the difference between the first person view
and the third person view. It is not a question of scaling.
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.
Nothing substantial hangs on this -- it is just a difference of
perspective which adds nothing to the state. The 'frog' view is
what you would call a result of FPI:
OK. Nice you see that.
I see it as a result of the formation of actual disjoint worlds
that continue to evolve separately, never to influence one another
again. The 'bird' view is an abstraction that never actually
influences anyone or anything.
The bird view is the universal wave, or the universal deployment or
the sigma_1 truth/reality. It is the basic ontology. The first
person views are the internal espistemologies.
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.
The only real problem of Everett is that it must be extended on the
sigma_1 truth, not just the quantum one. The quantum aspect must be
explained phenomenologically too. (well, that is not obvious at
all, but that is what explain).
Unless you sort out this confusion you will never understand
quantum mechanics.
You see a confusion, because sometimes I talk about the
projection postulate in the copenhagen frame, where it is
associated with the collapse during the corresponding
measurement, and sometimes I talk about the projection postulate
in the frame of the non-collapse formulation of QM (Everett), in
which case there is no collapse associated of course, but the
differentiating or bifurcating realities/computations (relative
terms of the linear wave).
See Price for the analysis of the singlet state in those terms.
Or Tipler, that you interpreted incorrectly apparently by
avoiding the first person indeterminacy.
I did not misinterpret either Price or Tipler -- they both make
the same elementary mistake, and neither sees that they have, in
fact, built non-locality into their analyses.
?
You need to make good your claim that my analysis is a
misinterpretation.
? (Jesse Mazer did, and I did, and Price did, and Tipler did,
Maudlin did, even Susskind and Friedman did). Let us say that we
disagree on this. If I find a better pedagogy I will try it.
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.
Bruno
I suggest that you are unable to do this.
Bruce
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