On 26-10-2022 07:45, Brent Meeker wrote:
On 10/25/2022 4:15 PM, smitra wrote:
On 26-10-2022 00:14, Bruce Kellett wrote:
On Wed, Oct 26, 2022 at 9:00 AM John Clark <johnkcl...@gmail.com>
wrote:
On Tue, Oct 25, 2022 at 5:31 PM Bruce Kellett
<bhkellet...@gmail.com> wrote:
_> One of the main troubles with this is that the Copenhagen
Interpretation, insofar as there is any such thing, does not
entail that the wave function collapses when the result enters
consciousness. This was a mad idea put forward by Wigner, and it
was soon realized that the idea was just silly, and could never
work. So that idea has long been abandoned. Deutsch's attempted
proof involves comparison with an abandoned idea of quantum
mechanics, so it doesn't really prove anything. Besides, the whole
set-up involves assumptions about quantum computers and
consciousness that are far from obvious, and probably not even
correct._
OK, so forget about consciousness, the fact remains that If you see
interference bands on Deutsch's photographic plate then that would
prove a universe can split and, provided the difference between them
is very small, can under the right conditions become identical again
and thus merge back together. That is the key part of the multiverse
idea and if it's true then there is no need to indulge in the
mumbo-jumbo of Copenhagen quantum complementarity.
That is as much mumbo-jumbo as anything in Copenhagen. For instance,
what determines if the difference between the worlds is small
'enough'? You are using the result of no divergence between worlds to
conclude something about a divergence that probably never occurred.
It
is simpler to state that no measurement was made in the Deutsch
set-up. Measurement, after all, involves irreversible decoherence,
and
such cannot be 'quantum erased'. So no which-way measurement would
have been made in the Deutsch experiment. "Measurement" requires the
formation of permanent records in the environment (and many copies of
the result can be formed as well).
There is no such thing as irreversible decoherence in unitary QM. Now,
you and Brent have invoked the expansion of the universe in past
discussions to argue that fundamentally irreversible phenomena do
exist. However this reasoning is flawed, because you then assume a
semi-classical model where the expansion of the universe is described
in a classical way. If QM is fundamental, then the entire state of the
universe, including the space-time geometry is part of that quantum
description. You then have a wavefunctional that assigns a complex
amplitude to the entire state of the universe that includes al the
fields of all particles and also the space-time geometry.
That assumes that the long sought quantum theory of gravity will not
break unitarity. There are already proposals for this
https://arxiv.org/pdf/2201.11658.pdf
Brent
It's not clear that generalizing from unitary to isometric transforms
makes much of a difference here for the purpose of getting to a real
collapse of the wavefunction. ALso, in the article they
Thing is that the laws of physics are what they are. You cannot demand
that you require measurement results to be truly permanent and that
they therefore arise due to irreversible processes. Whether that's the
case or not is determined by the laws of physics, not by us.
Also, in the article they threat the space-time geometry as a classical
background field, the consider the problem of QFT in an expanding
universe. It's not clear at all from their proposals how in their
proposal where the dimension of Hilbert space increases, one would
quantize gravity.
Saibal
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