On 4/25/2018 6:57 AM, agrayson2...@gmail.com wrote:
On Wednesday, April 25, 2018 at 10:51:13 AM UTC, Bruce wrote:
From: *Bruno Marchal* <mar...@ulb.ac.be <javascript:>>
On 22 Apr 2018, at 01:47, Bruce Kellett <bhke...@optusnet.com.au
<javascript:>> wrote:
From: *smitra* <smi...@zonnet.nl <javascript:>>
On 22-04-2018 00:18, Brent Meeker wrote:
On 4/21/2018 12:42 PM, smitra wrote:
That's then an artifact of invoking an effective
collapse of the wavefunction due to introducing the
observer. The correlated two particle state is either
put in by hand or one has shown how it was created. In
the former case one is introducing non-local effects in
an ad-hoc way in a theory that only has local
interactions, so there is then nothing to explain in
that case. In the latter case, the entangled state
itself results from the local dynamics, one can put
ALice and Bob at far away locations there and wait
until the two particles arrive at their locations. The
way the state vectors of the entire system that now
also includes the state vectors of Alice and Bob
themselves evolve, has no nontrivial non-local effects
in them at all.
Sure it does. The state vector itself is a function of
spacelike
separate events, which cause it to evolve into orthogonal
components...whose statistics violated Bell's inequality.
Brent
There is no non-locality implied here unless you assume that
the dynamics as predicted by QM is the result of a local hidden
variables theory.
Saibal
There is no need to suggest local (or non-local) hidden
variables. The non-locality we are talking about is implied by
the quantum state itself -- nothing to do with the dynamics.
But that type of non-locality has never been questioned, neither
in the MWI, or a fortiori in QM+collapse. But the MWI explains
without the need of “mysterious” influence-at-a-distance, which
would be the case in the mono-universe theory, or in Bohm-De
Broglie pilot wave theory. Without dynamic we have “only”
d’Espagnat type of inseparability.
Bruno
It seems that you are starting to see it from my perspective.
Non-locality is just another way of emphasizing the
non-separablity of the quantum singlet state. As you say, this is
true in MWI as in collapse theories. In my extended development of
the mathematics in another recent post, I demonstrated that there
is actually no difference between MWI and CI in this regard. All
that we have is the non-separability of the state, which means
that a measurement on one particle affects the result of
measurements on the other -- they are inseparable. This is all
that non-locality means, and this is not changed by MWI. An awful
lot of nonsense has been talked about this -- people trying to
find a "mechanism" for the inseparability -- but that is not
necessary. Quantum theory requires it, and it has been totally
vindicated by experiment. That is the way things are, in one world
or many.
Bruce
You place great faith in the singlet wf. But how can you legitimately
treat the system quantum mechanically if you assume zero uncertainty
in the total spin AM? AG
Zero spin is insured by conservation of angular momentum. There are
limitations imposed on the measurement by the uncertainty principle as
shown by the WAY theorem, but the constraint isn't of practical
significance for typical laboratory measurement because the apparatus is
so big (in action) compared to the variable measured:
In 1952 Wigner [2
<http://iopscience.iop.org/article/10.1088/1367-2630/15/1/013057/meta#nj454968bib02>]
provided analysis that showed that in the presence of a conservation law
it is impossible to perform an ideal measurement of an observable/L/_/S/
that does not commute with the conserved quantity. Specifically, Wigner
showed that if one has an additive conservation law of some
quantity$N_{\mathrm{tot}}= N_S\otimes \mathbbm{1} + \mathbbm{1} \otimes
N_{\mathrm {A}}$ over the composite system (such as angular momentum or
baryon number), and an observable/L/_/S/ for which [/L/_/S/ ,/N/_/S/
] ≠ 0, then there cannot exist a von Neumann–Lüders measurement that
respects the conservation law with$[V,N_{\mathrm{tot}}]=0$ . *Wigner
demonstrated, however, that an****/approximate/**measurement
of**/L/**_/S/ **can be performed, with the error decreasing as a
function of the size of the apparatus system.
*http://iopscience.iop.org/article/10.1088/1367-2630/15/1/013057/meta**
**Brent**
**
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