On 24 Nov 2017, at 15:59, Lawrence Crowell wrote:
On Thursday, November 23, 2017 at 5:53:14 PM UTC-6, Bruce wrote:
On 24/11/2017 10:15 am, Lawrence Crowell wrote:
On Wednesday, November 22, 2017 at 9:37:48 AM UTC-6, Bruno Marchal
wrote:
On 20 Nov 2017, at 23:04, Bruce Kellett wrote:
You clearly have not grasped the implications of my argument. The
idea that "MWI replaces all nonsensical weirdness by one fact
(many histories)" does not work, and is not really an explanation
at all -- you are simply evading the issue.
Without collapse, the apparent correlations are explained by the
linear evolution, and the linear tensor products only. I have not
yet seen one proof that some action at a distance are at play in
quantum mechanics, although I agree that would be the case if the
outcome where unique, as EPER/BELL show convincingly.
Aspect experience was a shock for many, because they find action at
a distance astonishing, but are unaware of the many-worlds, or just
want to dismiss it directly as pure science fiction. But after
Aspect, the choice is really between deterministic and local QM +
many worlds, or one world and 3p indeterminacy and non locality.
Like Maudlin said, choose your poison.
Bruno
Bruce
I am new to this list and have not followed all the arguments here.
In weighing in here I might be making an error of not addressing
things properly.
Consider quantum entanglements, say the entanglements of two spin
1/2 particles. In the singlet state |+>|-> + |->|+> we really do
not have the two spin particles. The entanglement state is all that
is identifiable. The degrees of freedom for the two spins are
replaced with those of the entanglement state. It really makes no
sense to talk about the individual spin particles existing. If the
observer makes a measurement that results in a measurement the
entanglement state is "violently" lost, the entanglement phase is
transmitted to the needle states of the apparatus, and the
individual spin degrees of freedom replace the entanglement.
We have some trouble understanding this, for the decoherence of the
entangled state occurs with that state as a "unit;" it is blind to
any idea there is some "geography" associated with the individual
spins. There in fact really is no such thing as the individual
spins. The loss of the entangled state replaces that with the two
spin states. Since there is no "metric" specifying where the spins
are before the measurement there is no sense to ideas of any causal
action that ties the two resulting spins.
This chaffs our idea of physical causality, but this is because we
are thinking in classical terms. There are two ways of thinking
about our problem with understanding whether quantum mechanics is
ontic or epistemic. It could be that we are a bit like dogs with
respect to the quantum world. I have several dogs and one thing
that is clear is they do not understand spatial relationships well;
they get leashes and chains all tangled up and if they get wrapped
up around a pole they simply can't figure out how to get out of it.
In this sense we human are simply limited in brain power and will
never be able to understand QM in some way that has a completeness
with respect to causality, reality and nonlocality. There is also a
far more radical possibility. It is that a measurement of a quantum
system is ultimately a set of quantum states that are encoding
information about quantum states. This is the a quantum form of
Turing's Universal Turing Machine that emulates other Turing
machines, or a sort of Goedel self-referential process. If this is
the case we may be faced with the prospect there can't ever be a
complete understanding of the ontic and epistemic nature of quantum
mechanics. It is in some sense not knowable by any axiomatic
structure.
Hi Lawrence, and welcome to the 'everything' list. I have come here
to avoid the endless politics on the 'avoid' list.
The issue that we have been discussing with EPR pairs is whether
many worlds avoids the implications of Bell's theorem, so that a
purely local understanding of EPR is available in Everettian models.
I have argued that this is not the case -- that non-locality is
inherent in the entangled singlet state, and many worlds does not
avoid this non-locality. I think from what you say above that you
might well agree with this position.
Bruce
Of course MWI can do nothing of the sort. MWI suffers from much the
same problem all quantum interpretations suffer from.
I don't see this. the MW theory (that is the WWE without the collapse
axiom) explains the violation of inequality in a way which avoids any
action at a distance, but when we assume one universe, like Einstein
explains very clearly already in 1927, you get a notion of
simultaneousness incompatible with special relativity and very minimal
form of realism.
For me, as a logician, I consider that SWE and SWE+collapse are
different theories. The first is local, deterministic and admits a
local physical realism, the second is not intelligible at all, as the
notion of observer is unclear and dualistic.
Bruno
With MWI there is a nice idea of the world continuing on as a
complete pure state quantum system, but it has the problem that we
observers have some restriction on our observational domain. This is
because we are thrust into some subset of the Hilbert space of
evolution. It really is a sort of collapse, but rather than of an
epistemic wave function it is within a map on the ontological domain
an observer can access.
LC
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