Re: Question on quantum computing and many-worlds interpretations of Quantum Mechanics

I've noted this before here but I'll be happy to send a copy of the paper I
gave at the 1987 ASA meeting, "Parallel Worlds, Quantum Theory, and Divine
Sovereignty" to anyone who wants it & gives me a snailmail address.

Shalom
George
http://web.raex.com/~gmurphy/
----- Original Message -----
From: "Loren Haarsma" <lhaarsma@calvin.edu>
To: "_American Sci Affil" <asa@calvin.edu>
Sent: Thursday, March 02, 2006 8:40 PM
Subject: Re: Question on quantum computing and many-worlds interpretations
of Quantum Mechanics

>
>
> I agree that there might be theological issues to worry about in a
> many-worlds interpretation of quantum mechanics.
>
> But I want to focus just on a scientific issue.
>
> Someone might have told you:
>
>> The success of a quantum device therefore
>> necessitates the existence of parallel universes ( multiverses ) in order
>> for all the computations to be carried out in parallel.
>
> But that is false.
> Absolutely, positively, false.
> A successful quantum computer will not in any way necessitate the
> existence of parallel universes or the Everett "many worlds"
> interpretation of quantum mechanics.
> I'd stake my Ph.D. in atomic physics on it.
>
>
> There are many different interpretations of quantum mechanics. Four
> general categories are (1) standard "Copenhagen" interpretations; (2)
> Everett-type "many worlds" interpretations; (3) "non-local"
> hidden-variable interpretations; (4) "local" hidden variable
> interpretations (i.e. hidden variable interpretations which don't allow
> changes in the wave function to propagate faster than the speed of light).
> The "Bell Inequality" is a famous theoretical prediction which describes
> and experiment in which "local hidden variable" interpretations make a
> different prediction for the outcome of an experiment than the other three
> interpretations. The experiment has been done, and local hidden variable
> interpretations have been shown to be inconsistent with data.
>
> There is, as of now, NO experimental or theoretical observational way to
> distinguish between the other three interpretations (Copenhagen
> interpretations, many-worlds interpretations, and non-local
> hidden-variable interpretations). All three classes of interpretations
> make identical predictions for how quantum computers should work.
>
>
> Quantum computers work by utilizing cleverly designed Hamiltonians in
> _this_ universe, not by using anything from other universes. (In
> classical or in quantum mechanics, a Hamiltonian is an equation or a
> functional operator which describes the energy of the system in terms of
> variables such as position, momentum, angular momentum, etc.)
>
>
> Here's an analogy. A few decades ago, people built some sophisticated
> "analog computers" by combining resistors, capacitors, inductors, and
> transitors in clever circuits. Analog computers are not as versitile as
> digital computers. They cannot solve _any_ sort of mathematical problem
> the way digitical computers can. But there there are certain classes of
> problems (e.g. second-order differential equations) which analog computers
> can solve much more quickly than digital computers. The electrons in
> analog computers don't do anything special -- they just obey the same old
> laws of motion that they always do in any circuit. But the circuit is
> cleverly designed so that, when the electrons move according to their
> regular old laws of motion, their behavior matches the solution to a
> particular mathematical problem.
>
> In the same way, quantum computers are much less versitile than ordinary
> digital computers. However, there are certain very restricted types of
> problems on which they (like analog computers) out-perform digital
> computers. Electrons in a quantum computer aren't doing anything weird
> (or perhaps I should say, not doing anything weirder than they do all the
> time in any ordinary atom or molecule). However, in a quantum
> computer, the clever designers set up the system so that when the
> electrons (or photons) obey the same old ordinary laws of motion that they
> always do, their behavior matches the solution to a particular
> mathematical problem.
>
> When someone builds a clever classical-physics device such that its
> mechanical or electrical behavior matches the solution to a tricky
> computation problem, we don't feel any need to invoke parallel universes.
> Nor should we. Nor is there any such need when someone builds a clever
> quantum-physics device such that its behavior matches the solution to a
> tricky computational problem.
>
> Someday, physicists might find a way to distinguish experimentally
> betwen Copenhagen, many-worlds, non-local hidden variable, and other
> interpretations of quantum mechanics.
> But we haven't yet.
>
>
> Loren Haarsma
>
Received on Thu Mar 2 22:34:57 2006