On 10-02-2020 07:37, 'Brent Meeker' via Everything List wrote:
On 2/9/2020 10:17 PM, smitra wrote:
On 09-02-2020 19:16, 'Brent Meeker' via Everything List wrote:
On 2/9/2020 12:48 AM, smitra 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.
Except for every measurement ever made of a quantum variable.
This os also explained by unitary time evolution as there observed
system is not an isolated system.
Which just pushes the problem off to another place.
Brent
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.
The MWI may have some philosophical weaknesses like the derivation
of the Born rule but the pragmatic variant of it where you just
assume the Born rule is clearly superior to any other model where
you're going to just assume that the known laws of physics are going
to be violated to get to a model that to you looks more desirable
from a philosophical point of view.
If the MWI (in the general sense of there existing a
multiverse rather than any details of how to derive the Born rule)
is
not correct, then that's hard to reconcile with known experimental
results.
All experimental results to date are consistent with a single-world
theory. There are several possibilities for such a theory, but to
date, experiment does not distinguish between them.
Single world theories require a violation of unitary time evolution of
a perfectly isolated system. No experiment has ever observed this.
Because a perfectly isolated system can't be observed.
Observers interact locally with the observed system, so nothing would
change if the observed system plus observer were located inside a
giant isolated system. So, whatever observation is cannot
funbdamentally depend on the system not being perfectly isolated.
That's funny, since 20 lines above you invoked the_ lack_ of
isolation to explain measurements.
Brent
Measurement can be fully described by local interactions, so it's
compatible with the entire system comprising of measured system plus
observer, being completely isolated.
New physics that so far has never been observed needs to be
assumed just to get rid of the Many Worlds. Also, this new physics
should appear not at the as of yet unprobed high energies where the
known laws of physics could plausibly break down, instead it would
have
to appear at the mesoscopic or macroscopic scale where the laws of
physics are essentially fixed.
Bohm's theory does not require as-yet-unobserved new physics. GRW do
postulate a new physical interaction, but that is below the level of
current experimental detectability.
Bohm theory is not equivalent to QM, it only becomes equivalent to QM
if one imposes a condition known as "quantum equilibrium". In general,
Bohm theory in a condition of quantum non-equilibrium leads to
violations of the Born rule. See here for details:
https://en.wikipedia.org/wiki/Quantum_non-equilibrium
Then without any experimental evidence for the additional features of
Bohm theory such as the signatures of quantum non-equilibrium, why
would be prefer it over and above a theory that doesn't make such
assumptions? One would have to have very strong theoretical objections
against the theory. In case of the Standard Model one can predict that
it will break down at very high energies. But I don't see why the MWI
in the pragmatic sense where one assumes the Born rule is so bad that
it merits considering alternative theories, particularly if those
alternative theories make lots of unverified assumptions about new
physics in domains where new physics is thought to be unlikely to
appear.
Besides, why should you assume that the Schrodinger equation is the
ultimate physical law?
It may be false, but absent experimental evidence that it is indeed
false, theories that imply that it's false shouldn't get the benefit
of the doubt just because they imply a single world.
Even though a single world is a well confirmed and often repeated
empirical observation?
It's not confirmed and repeated. One has to do an experiment that can
distinguish between the alternative theories. Unitary time evolution
is easily falsifiable. What's wrong is to claim that an experiment
that on its own would be consistent with collapse is somehow evidence
for collapse if it is also consistent with unitary time evolution when
unitary time evolution and not collapse theories are consistent with
the totality of all the experimental results.
Collapse theories are also consistent with fairies erasing the other
possible results. Unless MWI can produce a result inconsistent with
SWI then it is just adding otiose unobservables. There are infinitely
many ways to add things that can't be observed. The promise of MWI
was that everything would be explained by the Schroedinger equation
alone. But it turns out that you still need to postulate the Born
rule and then you still need to some yet unexplained axiom to say when
a measurement has occurred and the Born rule can be applied. In other
words MWI didn't deliver on its promise...although it led to some
interesting research.
Brent
While in the MWI the Born rule may need to be postulated, no ad hoc
assumption on measurements is required. The observer is described by a
wavefunction, and therefore whatever it is aware of is in a
superposition of all possible states. So, if we model the observer as a
computer, the mind of the computer being whatever algorithm the computer
is running, then we end up with a superposition over a set of
algorithms. We then do have a preferred basis, which is the basis of the
algorithms. Each algorithm unambiguously defines what the observer is
aware of.
Saibal
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