On 10-02-2020 08:17, Bruce Kellett wrote:
On Mon, Feb 10, 2020 at 5:08 PM smitra <smi...@zonnet.nl> wrote:
On 09-02-2020 11:37, Bruce Kellett wrote:
On Sun, Feb 9, 2020 at 7:48 PM smitra <smi...@zonnet.nl> wrote:
On 08-02-2020 07:00, Bruce Kellett wrote:
On Sat, Feb 8, 2020 at 4:21 PM smitra <smi...@zonnet.nl> wrote:
On 08-02-2020 05:19, Bruce Kellett wrote:
No, I am suggesting that Many-worlds is a failed theory,
unable
to
account for everyday experience. A stochastic single-world
theory
is
perfectly able to account for what we see.
Bruce
Stochastic single word theories make predictions that violate
those
of
quantum mechanics.
No they don't. When have violations of the quantum predictions
been
observed?
A single world theory must violate unitary time evolution, it has
to
assume a violation of the Schrodinger equation. But there is no
experimental evidence for violations of the Schrodinger equation.
While
one can make such assumptions and develop a formalism based on
this,
the
issue is then that in the absence of experimental proof that the
Schrodinger equation is going to be violated, one should not
claim
that
such a model is superior than another model that doesn't imply
any
new
physics.
So what. If Everettian QM doesn't work, as it has been shown to
fail
in that is does not recover normal scientific practice, then one
must
look to alternative theories. I have not advocated any particular
theory, but a break down of unitary evolution is not such a big
deal
-- it is what we observe every day, after all. This is the heart
of
the quantum measurement problem.
The focus on Everettian QM to argue against MWI in general is a
straw
man attack.
That would not be the way most physicists would see it. They take
Everettian QM as basic. Unfortunately, Everettian QM has hit a
catastrophic train wreck -- it is clearly not viable as an
understanding of quantum physics. The reason for this is a clear
corollary of Kent's argument. Simply put, Everett takes the
Schrodinger equation as basic. Acting on a general quantum state with
the Schrodinger equation gives the relative states, and there can only
ever be one relative state for each term in the expansion in terms of
some set of basis states. The amplitudes of interest are the
coefficients in this expansion. However, these coefficients or
amplitudes, are just ordinary complex numbers, so are completely
transparent to the SE. The set of sequences of outcomes of repeated
trials (measurements on replications of the initial state) is then all
n^N sequences of outcomes (labelled by 0 - n-1 for the n possible
outcomes for N trials). This set of sequences is independent of the
amplitudes in the original expansion of the state of interest in terms
of the set of basis states. Consequently, the data one obtains from
this set of experiments is one of the set of possible sequences of the
integers 0 to n-1, is completely independent of the amplitudes in the
original expansion. One can, therefore, gain no information about
these amplitudes from the set of N trials. The Born rule is
irrelevant, because the data are necessarily independent of the
coefficients/amplitude.
This proves that Everett's approach from the SE, where there is only
one branch for each possible outcome in a single trial, cannot account
for the way in which experimental results are used in practice. Given
Everett, experiments cannot reveal anything at all about the original
state. So Everett fails as a scientific theory. End of story. Period.
Nothing more to be said.
This no go argument against Everett has no bearing on the Many Worlds
aspect of QM. Clearly one cannot ignore amplitudes without getting a
contradiction with the probabilistic interpretation of QM.
The main issue is unitary time evolution. This is a rather
unambiguous thing that one can check in experiments. A breakdown of
unitary time evolution has never been observed.
As Brent has pointed out, unitary evolution breaks down every time we
observe a particular result for a measurement (to say nothing of black
holes). Your focus on unitary evolution is misplaced -- it is not
universally observed.
This has no bearing on the unitary time evolution of an isolated system.
We can infer from measurements that an isolated system does evolve in a
unitary way. Non-unitary time evolution would violate the known laws of
physics. The information paradox involving black holes is a problem
precisely because of this. No one believes that the solution involves a
non-unitary evolution. Even Hawking who originally did propose such
ideas later reversed himself.
Many-worlds theory might be salvageable from the train wreck of
Everett, but it is not clear how. It seems to be widely assumed that
there is more than one branch for each basis state, even though that
is not what Everett or the SE say. It is not clear how this could ever
happen in a principled way: it certainly is not consistent with
unitary evolution via the Schrodinger equation. There may be a way out
of this, but none has been offered to date, and I would not hold out
many prospects for success in such venture.
I believe that one has to be more pragmatic. One can make reasonable
assumptions like that an arbitrarily large quantum computer can be made
to work arbitrarily close to the ideal limit. One can then consider
thought experiments involving the quantum computer simulating an
effectively classical observer doing measurements. This then goes a long
way to resolve the interpretational problems with unitary QM.
Bruce
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