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

  
I want to chime in and say that I whole-heartedly agree with Loren and the others who have posted on this, stating that there is no scientific reason and no appeal to elegance that favors one interpretation of QM over any other.
 
Also, MWI is not necessarily contrary to theism. Here is why. Suppose all the universes really do exist. The concept of MWI is not that the universes are separate from each other -- the concept is that they are all in the same spacetime and affecting each other constantly. The reason light diffracts through a slit is supposedly because in each world it travels a slightly different path and the diffraction is the interference of all the "worlds" with each other. But very quickly most parts of these worlds become so decoherent that you can no longer see these interference patterns -- the worlds just pass right through each other and don't measureably interact, even though they share the same space. This is why they call them many "worlds" -- when they become decoherent they keep on existing and act like separate worlds even though they share the same space and the same physics. They aren't separate like star trek parallel universes -- they are only separate in the decohe
 rence makes interaction highly improbable.
 
Well, more and more regions of the cosmic wavefunction become decoherent at every moment of time, and so the number of "worlds" grows outrageosly fast. There are like 10^100 of you right now, according to MWI. These are all possible versions of you that fit within all possible histories of the universe. Some of these "yous" might be non-Christians, and others may be Christians. But all we are talking about are wavefunctions. There is no description of spirits or souls in QM. Maybe only one of these "yous" has a soul. Maybe this vast topology of decohered worlds is like a ski slope with moguls, and human souls are skiing across the slope constantly deciding to turn left or right. So your soul slides down the wavefunction of all possible "yous" and chooses which path to follow at every moment. Thus, of all the wavefunctions of you, only **you** determine which one **you** will be! I mean, only your spirit decides which part of the physical wavefunction it will inhabit
 . There is no contradiction to physics or MWI in this concept, because quantum physics doesn't describe your spirit.
 
MWI has such a high dimensionality to its topology of "worlds" that we could each have a steering wheel and steer down the moguls together, each of us making our own choices and yet the entirety of humanity staying on the same pair of skies. This is because we coud turn in our own allowable dimensions without negating the freedom of any of the other steering wheels to turn in their respective dimensions. In this view, humanity as a whole ends up together somewhere at the bottom of the ski slope, and where we end up some of us will be saved and some unsaved. Other parts of the ski slope are the wavefunction "worlds" for when different combinations of people would be saved. But depending on how each of us steers, our souls ride this physical wavefunction with perfect freedom, not constrained by deterministic particle physics, not constrained by the decisions of others, so that we each have as much freedom as QM physics will allow.
 
Now this theistic view of MWI is really no different than CI. And at this point in science it is impossible to say whether this view of MWI (with souls riding the worlds) is true, or wether CI (where souls decide which worlds collapse and we "ride" the only one that doesn't collapse) is true. The issue is whether the decohered worlds that you don't experience really still exist or whether they have collapsed. But in any case there is no reason to believe it has a soul in it.
 
Athiests shouldn't have a problem with this. They don't even believe **this** world has a soul in it.
 
So I don't think we need to be afraid of MWI. But again, there is absolutely no scientific reason to favor MWI over CI.
 
God bless!
Phil Metzger
 
-----Original Message-----
From: Loren Haarsma <lhaarsma@calvin.edu>
To: _American Sci Affil <asa@calvin.edu>
Sent: Thu, 2 Mar 2006 20:40:10 -0500 (EST)
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 22:21:10 2006