On 09-02-2020 11:37, Bruce Kellett wrote:
On Sun, Feb 9, 2020 at 7:48 PM smitra <[email protected]> wrote:
On 08-02-2020 07:00, Bruce Kellett wrote:
On Sat, Feb 8, 2020 at 4:21 PM smitra <[email protected]> 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. 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.
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.
The trouble is that even postulating the Born rule, ad hoc as in
Copenhagen, does not get you out of the problems with Everett. As long
as one follows Everett and assumes one branch for each component of
the superposition, one is going to fail to explain normal scientific
practice. If one follows Brent and Bruno and assumes that there are
multiple branches for each experimental result, then one has lost
touch with the Schrodinger equation anyway, Everett is out of the
window, and there are still problems with the definition of
probability.
It is probably a matter of which is the least bad theory at the
moment. None of the available approaches is entirely satisfactory. But
that is not an unusual situation in the development of physics.....
This is an artifact of promoting "normal scientific practice" to a more
fundamental law of Nature than the actual laws of physics. Scientific
practice is an imperfect method, it may well have flaws, it may not
always yield toe correct outcome. So, being able to construct a
counterexample where some observers would draw the wrong conclusion if
the laws of physics would have a certain structure, is is not evidence
that the laws of physics cannot have that structure.
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.
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
There is not evidence for any of this type of worry, either. So why
bring it up?
Quantum non-equilibrium is not just something that has not been
detected, it would also violate basic physical principles. This simply
illustrates that there are no good ways to get to a single world theory.
The laws of physics would have to be radically different from anything
we've seen.
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.
Who says so? Sounds like special pleading to me.....
Unitary time evolution would have to fail at larger scales where the
known dynamical laws of physics are even more solidly established.
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.
Maybe single world theories are better adapted to explaining our
ordinary experience -- and explaining everyday experience is, in the
final analysis, the aim of any scientific theory.
Appealing to ordinary experience is bad science. This is why it took
Lorentz several years to accept the Einsteinian interpretation of his
transformation laws.
Bruce
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