On 24-04-2022 06:18, Brent Meeker wrote:
On 4/23/2022 1:31 AM, smitra wrote:
On 21-04-2022 22:37, Brent Meeker wrote:
On 4/21/2022 1:27 PM, smitra wrote:
On 21-04-2022 20:18, Brent Meeker wrote:
On 4/21/2022 1:32 AM, smitra wrote:
On 21-04-2022 02:53, Bruce Kellett wrote:
On Thu, Apr 21, 2022 at 10:05 AM George Kahrimanis
<gekah...@gmail.com> wrote:
On Tue, Apr 19, 2022 at 11:09 AM Brent Meeker
<meeke...@gmail.com>
wrote:
The only purpose of the box in Schroedinger's thought experiment
was
to put off the observers perception. Really the thought
experiment
is over when the radioactive decay occurs. That atom has
transitioned to a different nuclear state which is entangled
with
and recorded in the environment.
On Tuesday, April 19, 2022 at 4:20:49 AM UTC+3 Bruce wrote:
Yes. Schrodinger had the cat in a box to emphasize the idea that
the
cat was in a macro-superposition of alive/dead. This misled
Wigner
to the extent that he thought the state collapsed only when the
box
was opened. All of this was made redundant when it was realized
that
decoherence rendered the state definite almost instantaneously.
Saibal makes the same mistake when he claims that Alice, after
her
measurement, is still in a superposition until Bob sees her
result.
The idea that the superposition still exists since decoherence
is
only FAPP is something of a red herring -- in MWI, Alice has
branched according to her result into up and down branches that
no
longer interfere. There is no macro-superposition.
This is wrong, because inability to demonstrate interference does
not mean that there is no superposition.
Alice does not branch due to decoherence. It is true that there
are two branches where the results of Bob are different due to
rapid decoherence. But before Alice knows the result of Bob, the
state of the algorithm that represent Alice's mind will be
identical in both branches. What matters is whether or not
information about Bob's result can change Alice's subjective
state. Only then can the two branches from Alice's point of view,
diverge. If this were possible, then that means that Alice could
obtain information about Bob's result without even looking at his
result. So, Alice would have psychic abilities.
Of course she can obtain information about Bob's result without
looking at it. That's what decoherence does, spread information
into
the environment so that there is a fact-of-the-matter as to the
result.
You've apparently bought into the Many Minds interpretation of MWI,
so
the cat isn't dead, the vial isn't broken, and the atom isn't
decayed
until Wigner's friend looks in.
Yes, the Many Minds version of the MWI makes the most sense. The
mind as defined by the algorithm the brain is running is the same in
the different sectors.
-1- Decoherence (by a chaotic environment) turns an entangled
superposition into a non-coherent density matrix, only if we
subsequently omit the environment from the description of the
system.
(Not if we keep the environment in the description.)
FAPP is for a reason -- we automatically trace out unneeded
environmental variables.
-2- The "box" (in which Scroedinger's cat is enclosed, with the
lethal apparatus) contains also its "environment", so a quantum
descrition of this box describes the environment also. Therefore
I
do not agree that decoherence INSIDE THE BOX will ruin the
superposition ASSESSED FROM OUTSIDE THE BOX. So, Wigner was
right. I
suppose that Saibal also is right, though I have not checked
that
message (sorry).
Unfortunately for this idea, decoherence does not stop at the
box. In
the time that Wigner thinks about this before he opens the box,
decoherence has enveloped essentially the whole world, so Wigner
himself has decohered into either a world with a dead cat or a
world
with a live cat. He can't dissociate himself from the split that
occurs, so from his point of view outside the box, the
superposition
is long gone, and he has to deal with a simple classical state of
either a dead cat or a live cat -- no superposition remains.
The superposition does remain, it's just that it cannot be probed
in interference experiments. Before Wigner knows the result, his
subjective state of his mind is the same in both branches. It
doesn't matter that everything in his environment including the
atoms in his brain is entangled with the state after the
experiment. What matters is that Wigner cannot know the result
without observing it. The bitstring that contains all the
information he is aware of, is the same in both branches.
What if he forgets what he saw?
If he forgets, then he'll merge with the versions in the other
sectors that also forgot what he saw. What matters is the bit string
that represents everything she is aware of at a certain moment. When
he remembers again then he'll spit again.
This splitting an merging dozens of times per second. But merging
with what or whom. Is Bob merging with other Bob's who have
different
memories but aren't recalling them at the moment?
Yes. In principle one has to start with a definition of Bob as an
algorithm (in practice one then assumes that such a definition exist
without one being able to specify it explicitly). When the algorithm
is run by a brain or some other machine, it will take in information
and change as a result. So, the Bob of now is not the same as the Bob
of one second later, these are different algorithms, albeit it very
similar ones.
So, what we have is a large set of algorithms. Some algorithms have a
working memory and for those algorithms it makes sense to talk about
their subjective past This is then defined by the algorithm itself.
For each algorithm there then exist a set of possible future
algorithms that are one computational step away from it. This then
follows from applying the algorithm itself to data that has yet to be
processed by the algorithm and is therefore unknown to it. This
uncertainty leads to the multiple future states.
You do realize don't you that if you take this view you've made QM
personal and epistemic so we can forget all the MWI muddle and adopt
QBism whose only problem is that what you think reality is, is
personal.
One may get to something that looks like QBism, but one cannot
conclude that reality is personal within the framework that I suggest.
Why not. Each algorithm has it's own data, it's own prior, and so
it's own idea of reality. Sounds like QBism to me.
Yes, but QBism is more than just that, it makes assumptions like there
not being a universal wavefunction.
Remembering is the result of consulting the memory and the memory
was in a superposition entangled with the environment. If
information in the memory is processed by the algorithm that
represents the mind of the person, then the person's mind will split
again.
But then you've completely forsaken physics, which depends on
inter-subjective agreement about events.
The universe is what it is. We can try to find out how it works by
doing experiments according to rigorous protocols that we've designed
that are good at distinguishing rival models from each other. But
there is no guarantee that the way the universe works at the
fundamental level will itself be consistent with our own protocols. It
may be that at the macro level FAPP things do work out that way, but
that in principle, there is a tension between the way we do physics in
practice and how the universe works.
The universe is what it is. Which means the job of physics is to
describe it, not to invent stories to make it conform to equations we
invent.
The equations we've found are based on experiments. Explore the
consequences of those equations is also physics.
Inter-subjective agreement about experiments is something that arises
FAPP when we do experiments in practice. This is not going to be
violated when doing those experiments that are needed to find the
fundamental laws of nature. But those laws may then tell us that a
multiverse exists and events in one branch may then be different from
events in another branch.
You say physics is not engineering. But it's not mathematics either.
In physics one needs to work from within consistent mathematical models.
So, one should strive to make models we use better defined. There is
then nothing wrong with discussing unitary QM. If one criticizes the MWI
but one does not specify a well defined model for collapse, then that's
inherently problematic. Take e.g. the example of the photon mass and
charge. One may think that one can do experiments and get to constraints
on the photon mass and photon charge without having to specify a
detailed model. As pointed out in https://arxiv.org/abs/hep-ph/0306245
the mechanism for photon mass does matter, and as pointed out here
https://arxiv.org/abs/hep-ph/0505250 experimental limits on the photon
charge do not make any sense due to a lack of a consistent theoretical
model.
Saibal
Brent
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