Re: Many Worlds

From: scerir (
Date: Wed Jul 25 2001 - 10:14:13 MDT

> This idea was proposed by Princeton graduate student Hugh Everett III in 1957.

Everett III proposed a different idea: the Relative State Interpretation (RSI).
As far as I know the MWI says that, during a quantum measurement,
the quantum chain (particle + pointer + reader) splits up (in many parts,
many worlds, even many minds - MMI). The whole effect is, of course, nonlocal.
And according to Deutsch......

> "Quantum theory leaves no doubt that other universes exist
> in exactly the same sense that the single Universe that we see exists,"
> he says. "This is not a matter of interpretation. It is a logical consequence
> of quantum theory."

The RSI says that the quantum chain splits up, during the quantum
measurement, but each part (world) comes with some *probability* attached.
So the RSI is compatible with the Decoherence Interpretation (by Zeh,
and Zurek, et al.), which forbids the reality of many worlds.
Deutsch seems to be aware of these problems when he says that ...

> Free will might have a sensible definition, Deutsch thinks, because the
> alternatives don't have to occur within equally large slices of the multiverse.
> "By making good choices, doing the right thing, we thicken the stack of universes
> in which versions of us live reasonable lives," he says. "When you succeed,
> all the copies of you who made the same decision succeed too. What you do
> for the better increases the portion of the multiverse where good things happen."

The Interpretation of Quantum Mechanics: Many Worlds or Many Words?
Max Tegmark (IAS)
Journal-ref: Fortsch.Phys. 46 (1998) 855-862
As cutting-edge experiments display ever more extreme forms of non-classical behavior,
the prevailing view on the interpretation of quantum mechanics appears to be gradually
changing. A (highly unscientific) poll taken at the 1997 UMBC quantum mechanics
workshop gave the once all-dominant Copenhagen interpretation less than half of the votes.
The Many Worlds interpretation (MWI) scored second, comfortably ahead of the
Consistent Histories and Bohm interpretations. It is argued that since all the above-mentioned
approaches to nonrelativistic quantum mechanics give identical cookbook prescriptions for
how to calculate things in practice, practical-minded experimentalists, who have traditionally
adopted the ``shut-up-and-calculate interpretation'', typically show little interest in whether
cozy classical concepts are in fact real in some untestable metaphysical sense or merely
the way we subjectively perceive a mathematically simpler world where the Schrodinger
equation describes everything - and that they are therefore becoming less bothered by
a profusion of worlds than by a profusion of words.
Common objections to the MWI are discussed. It is argued that when environment-induced
decoherence is taken into account, the experimental predictions of the MWI are identical
to those of the Copenhagen interpretation except for an experiment involving a Byzantine
form of ``quantum suicide''. This makes the choice between them purely a matter of taste,
roughly equivalent to whether one believes mathematical language or human language
to be more fundamental.
Worlds in the Everett Interpretation
David Wallace
To appear in Studies in the History and Philosophy of Modern Physics
This is a discussion of how we can understand the world-view given to us by
the Everett interpretation of quantum mechanics, and in particular the role played
by the concept of `world'. The view presented is that we are entitled to use `many-worlds'
terminology even if the theory does not specify the worlds in the formalism; this is defended
by means of an extensive analogy with the concept of an `instant' or moment of time in relativity,
with the lack of a preferred foliation of spacetime being compared with the lack of a preferred
basis in quantum theory. Implications for identity of worlds over time, and for relativistic
quantum mechanics, are discussed.
Against Many-Worlds Interpretations
Adrian Kent
Journal-ref: Int.J.Mod.Phys. A5 (1990) 1745
This is a critical review of the literature on many-worlds interpretations (MWI),
with arguments drawn partly from earlier critiques by Bell and Stein.
The essential postulates involved in various MWI are extracted, and their consistency
with the evident physical world is examined. Arguments are presented against MWI
proposed by Everett, Graham and DeWitt. The relevance of frequency operators to
MWI is examined; it is argued that frequency operator theorems of Hartle and
Farhi-Goldstone-Gutmann do not in themselves provide a probability interpretation
for quantum mechanics, and thus neither support existing MWI nor would be useful
in constructing new MWI. Comments are made on papers by Geroch and Deutsch
that advocate MWI. It is concluded that no plausible set of axioms exists for an MWI
that describes known physics.
Progress in a Many-Minds Interpretation of Quantum Theory
Matthew J. Donald
In a series of papers, a many-minds interpretation of quantum theory has been developed.
The aim in these papers is to present an explicit mathematical formalism which constitutes
a complete theory compatible with relativistic quantum field theory. In this paper, which could
also serve as an introduction to the earlier papers, three issues are discussed. First, a significant,
but fairly straightforward, revision in some of the technical details is proposed. This is used as an
opportunity to introduce the formalism. Then the probabilistic structure of the theory is revised,
and it is proposed that the experience of an individual observer can be modelled as the experience
of observing a particular, identified, discrete stochastic process. Finally, it is argued that the formalism
can be modified to give a physics in which no constants are required. Instead, `constants' have to be
determined by observation, and are fixed only to the extent to which they have been observed.
On Many-Minds Interpretations of Quantum Theory
Matthew J. Donald
This paper is a response to some recent discussions of many-minds interpretations
in the philosophical literature. After an introduction to the many-minds idea, the complexity
of quantum states for macroscopic objects is stressed. Then it is proposed that a characterization
of the physical structure of observers is a proper goal for physical theory. It is argued that an
observer cannot be defined merely by the instantaneous structure of a brain, but that the history
of the brain's functioning must also be taken into account. Next the nature of probability in many-minds
interpretations is discussed and it is suggested that only discrete probability models are needed.
The paper concludes with brief comments on issues of actuality and identity over time.
Does Quantum Nonlocality Exist? Bell's Theorem and the Many-Worlds Interpretation
Frank J. Tipler
Quantum nonlocality may be an artifact of the assumption that observers obey the laws
of classical mechanics, while observed systems obey quantum mechanics. I show that,
at least in the case of Bell's Theorem, locality is restored if observed and observer are both
assumed to obey quantum mechanics, as in the Many-Worlds Interpretation. Using the MWI,
I shall show that the apparently "non-local" expectation value for the product of the spins of two
widely separated particles --- the "quantum" part of Bell's Theorem --- is really due to a series
of three purely local measurements. Thus, experiments confirming "nonlocality" are actually
confirming the MWI.
Observational Consequences of Many-Worlds Quantum Theory
Don N. Page (CIAR Cosmology Program, University of Alberta)
Messages from Jerry Finkelstein and Jacques Mallah have led me to realize that,
although I stand by my prediction that in a many-worlds theory you will be alive in the
year 2100 in some worlds, paradoxically the evidence you will have then will not
support many-worlds quantum theory over single-history quantum theory, since
in either theory it will be evidence of very low measure and likelihood for a random
observation. Therefore, I deleted this part of the paper (and shortened other parts)
Contrary to an oft-made claim, there can be observational distinctions (say for the
expansion of the universe or the cosmological constant) between "single-history"
quantum theories and "many-worlds" quantum theories. The distinctions occur when
the number of observers is not uniquely predicted by the theory. In single-history theories,
each history is weighted simply by its quantum-mechanical probability, but in many-worlds
theories in which random observations are considered, there should also be the weighting
by the numbers or amounts of observations occurring in each history.

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