On 09-05-2022 01:00, Brent Meeker wrote:
On 5/8/2022 1:50 PM, smitra wrote:
On 08-05-2022 06:03, Brent Meeker wrote:
On 5/7/2022 6:21 PM, smitra wrote:
On 05-05-2022 00:04, Brent Meeker wrote:
On 5/4/2022 12:27 PM, smitra wrote:
In
fact, that idea introduces a raft of problems of its own -- what
is
the measure over this infinity of branches? What does it mean to
partition infinity in the ratio of 0.9:0.1? What is the mechanism
(necessarily outside the Schrodinger equation) that achieves this?
That simply means that there is as of yet no good model for QM
without the Born rule.
But there is no mechanism for the Born rule. It is inconsistent with
pure Schroedinger evolution of the wave function. I think the
problem
of measures on infinity is overcome if you simply postulate a very
large but finite number of branches to split. Or why not not an
continuum probability and just measure by the density around the
eigenvalue...the measured values are never exact anyway. I don't
these things are wrong or show MWI is inconsistent, but I think they
show it has just moved the problems it purported to solve off to some
unobservable worlds, which is no better than CI.
Born rule is not inconsistent with the Schrödinger equation, it just
tells you that the wavefunction gives you the probability amplitudes.
This is better than the CI, because the CI is inconsistent with the
Schrödinger equation.
Because?? It takes one more step and says "probability means
something happens and other things don't." It's not called the
"Copenhagen Equation". It's called the "Copenhagen Interpretation",
i.e. how to _INTERPRET_ the Schroedinger equation and so it is
consistent with it.
It's called an interpretation just like the MWI, but these are
actually different theories that make different predictions, albeit in
a domain that cannot easily be accessed experimentally.
That the CI is inconsistent with the Schrödinger equation is easy to
see. If the Schrödinger is valid, then the state of a system evolves
in a unitary way. But after a real collapse the state changes in a
non-unitary way.
Which is only a problem if one insists that the Schroedinger equation
is the whole of the theory and it is ontic. CI denies the first and
says that measurements are projection operators because a measurements
is necessarily a classical-like result. QBism says the whole theory
is epistemic.
Yes, but this mans that CI is not compatible with QM as a fundamental
theory. You can't have a fundamental Schrödinger equation and then have
it not apply to some special cases.
If we consider measuring the z-component of a spin polarized in the
x-direction using a Stern-Gerlach apparatus, then the entire system
of the spin the experimental set-up, the observer and local
environment consists of particles that should evolve according to the
Schrödinger equation.
"Should"?
If MWI is correct.
If the measurement takes one minute, then the initial state of a patch
of one light-minute diameter around the location of the experiment
maps to a final state of that patch in a unitary way.
You seem to overlook that this one-light minute sphere also had
incoming particles and radiation which could not be accounted for the
Schroedinger equation.
Yes, so one can imagine a shield keeping particles from outside that
region from interacting with particles inside the region. Weakly
interacting particles like neutrinos can enter, but they don't interact
with what's inside the interior region. So, the state of the universe
factors into a part for the inside and outside regions (where the
outside region also incudes weakly interacting particles that have moved
inside). Both parts evolve in a unitary way.
But CI says that this does not happen because the internal observer in
the system performed a measurement that causes the state of the system
to collapse.
Yes, that's a problem although CI+decoherence doesn't depend on an
observer. The effect of the incoming radiation is also a problem. But
MWI doesn't solve the problem, it just assumes that the correlations
are created which have the same effect as collapse as far as the
instruments and observers are concerned. Decoherence goes part way to
solving the problem by quantifying how the "collapse" occurs
statistically in time.
Yes, one needs to consider correlations between the states of the
measurement devices and the measured systems.
Saibal
Brent
The issues with branches etc. are likely just artifacts with making
hidden assumptions about branches. At the end of the day there are
only a finite number of states an observer can be in. If an observer
is modeled as an algorithm, take e.g. Star Trek's Mr. Data then it's
clear that there are only a finite number of bitstrings that can
correspond to the set of all possible things Mr. Data can be aware
of.
But different Mr. Data's and different instruments can have different
number of states. So what you're suggesting is QBism.
It may fall under QBism, the question is if this is going to cause
problems that cannot be resolved well.
Saibal
Brent
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