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.
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.
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 suggest that you are unable to
do this.
Bruce
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