There is no problem here because in practice MWI is nothing more than
the usual QM formalism to compute the outcome of experiments where you
then assume that the ensemble of all possible outcomes really exists.
Locality then follows from the fact hat the dynamics of the theory is
manifestly local. The Hamiltonian only includes local interactions and
observers are part of this dynamics. Although observer are not
explicitly treated as being part of the wavefunction that describes the
entire system, the assumption is that in principle, this is the case. In
practice, one can then proceed according to the usual QM formalism.
John points out the thought experiments by Deutsch makes it clear that
the usual QM formalism will not work in certain cases, that will then
falsify the ad hoc collapse postulate. If you then believe that MWI
cannot account for violation of Bell's inequalities while ordinary QM
can, then that begs the question of how removing the FAPP unobservable
sectors where all other outcomes are realized, could matter at all.
Saibal
On 31-08-2023 00:55, Bruce Kellett wrote:
The many worlds idea has already been falsified because it cannot
account for the observed violation of the Bell inequalities for
entangled particles. MWI is supposedly a local theory -- where is the
local account of the correlations of entangled particles?
Bruce
On Thu, Aug 31, 2023 at 12:39 AM John Clark <johnkcl...@gmail.com>
wrote:
The short answer is yes, Many Worlds is falsifiable. For example,
right now there are experiments underway in an attempt to prove that
the GRW theory of objective quantum wave collapse makes predictions
that Many Worlds does not, if they are successful it will prove that
Everett was dead wrong, it's as simple as that. GRW claims that
Schrodinger's equation is incomplete and that another very complex
term needs to be added to it because it's the only way they could
think of to get rid of all those worlds that for some reason they
dislike, there was simply no other reason to add that extra term.
With this new term Schrodinger's equation is no longer completely
deterministic because a random element is added such that the larger
the wave function is (the more particles it has) the more likely the
quantum wave function will objectively collapse. They carefully
tuned their very complex extra term inserted into Schrödinger's
equation in just such a way that, because an individual electron is
so small the probability of you being able to observe one
objectively collapse is almost but not quite zero; but the
probability of you NOT observing something as large as a baseball
NOT collapsing is also almost, but not quite, zero. Despite heroic
efforts. up to the present day nobody has found a speck of
experimental evidence in support of the GRW theory of objective
quantum wave collapse, and until and unless they do Many Worlds must
be the preferred theory according to Occam's razor because it makes
fewer assumptions, it has no need to complicate matters by adding
that extra term to Schrodinger's equation.
But GRW is not the only or even the most popular competitor to Many
Worlds, that honor would have to go to the Copenhagen
interpretation, and there is certainly no way to falsify that, but
back in 1986 in his book "The Ghost in the Atom" David Deutsch
proposed another way to falsify Everett's Many Worlds; the
experiment would be difficult to perform but Deutsch argues that is
not Many Worlds fault, the reason it's so difficult is that the
conventional view says conscious observers obey different laws of
physics, Many Worlds says they do not, so to test who's right we
need a mind that uses quantum properties.
In Deutsch's experiment, to prove or disprove the existence of many
worlds other than this one, a conscious quantum computer shoots
electrons at a metal plate that has 2 small slits in it. It does
this one at a time. The quantum computer has detectors near each
slit so it knows which slit the various electrons went through. The
quantum mind now signs a document for each and every electron saying
it has observed the electron and knows which slit it went through.
It is very important that the document does NOT say which slit the
electron went through, it only says that it went through one and
only one slit and the mind has knowledge of which one. Now just
before the electron hits the plate the mind uses quantum erasure to
completely destroy the memory of what slits the electrons went
through, but all other memories including all the documents remain
undamaged. After the document is signed the electron continues on
its way and hits the photographic plate. Then after thousands of
electrons have been observed and all which-way information has been
erased, develop the photographic plate and look at it. If you see
interference bands then the Many World interpretation is correct. If
you do not see interference bands then there are no worlds but this
one and the conventional interpretation is correct.
Deutsch is saying that in the Copenhagen interpretation when the
results of a measurement enters the consciousness of an observer the
wave function collapses, in effect all the universes except one
disappear without a trace so you get no interference. In the Many
Worlds model all the other worlds will converge back into one
universe when the electrons hit the photographic film because the
two universes will no longer be different (even though they had
different histories), but their influence will still be felt. In the
merged universe you'll see indications that the electron went
through slot X only and indications that it went through slot Y
only, and that's what causes interference.
I know that what I said in the above is a fair representation of
what Deutsch was saying because some years ago I wrote to him about
this and he said it was an accurate paraphrase.
It must be admitted that like every theory Many Worlds makes
predictions that cannot be tested, but a theory is not judged on the
basis of what predictions it makes that have neither been confirmed
nor falsified experimentally, instead they are judged by how well
they conform to experiments that HAVE been performed, and in Many
Worlds case it conforms to every physics experiment that has ever
been made up to the present day. Yes Everett's idea produces a lot
of worlds, but Occam does NOT say the best theory is the one that
produces the simplest outcome, the best theory is the one that makes
the fewest assumptions and still agrees with experimental
observations.
John K Clark See what's on my new list at Extropolis [1]
fwm
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