John K Clark (johnkc@well.com)
Tue, 29 Jul 1997 10:36:56 -0700 (PDT)


EvMick@aol.com On Tue, 29 Jul 1997 Wrote:

>parallel Everett universes, Since my first name is Everitt I find
>myself facinated by this term...would you pleas elucidate?

The name comes from Hugh Everett, best known for the Everett, or many worlds
interpretation of Quantum Mechanics. Everett has been dead for many years now,
at least in this universe. He was disappointed at the poor reception his
theory received and lost interest in Quantum Mechanics, he spent most of his
life writing nuclear war games for The Pentagon. In his youth Everett was
interested in the philosophical aspects of Quantum Mechanics and in the last
few years his theory has increased in popularity.

Quantum Mechanics has been more successful, over a wider range of conditions
than any theory I know of, but it has always suffered from philosophical
problems. Is that a wave or a particle? In what direction is that photon
polarized? The standard Copenhagen interpretation, believed by most
Physicists, is that nothing is anything until a measurement is made and the
wave function collapses. If you decide to use a photographic plate, an
electron is a particle. If you decide to use an interferometer, an electron
is a wave. This works fine except its a bit vague about what a measurement
is and who is taking the measurement. Are Human Beings the only ones able
to make an observation and change a potential reality into a actual one?
What about a chimp, or a dog, or a bug?

In 1957 Hugh Everett solved the measurement problem but at a very high price,
too high most thought. He said that when any particle undergoes the smallest
detectable change ( a quantum jump ) the entire universe, including you the
observer, duplicates itself and splits in two, but we have (almost) no way
of communicating with the other universe. If true this would mean there is an
infinite number (some say just an astronomical number) of universes.

Many universes would differ from this one in only one tiny detail, but some
would be very different. Even EXTREMELY unlikely events would happen in one
of them. In one I was just elected The Pope, in another I graduated from
Ringling Brothers Clown Collage, and in yet another one all the molecules of
air diffused by chance to the other side of the room as I type this and I

Today David Deutsch is probably the leading advocate of Everett's ideas. In
response to critics who say the theory is untestable he maintains that an
intelligent quantum computer could detect these worlds, if they are there.

A conscious quantum computer shoots electrons at a metal plate that has
2 small slits in it. It does this one at a time. After leaving the plate the
electrons hit some photographic film, but do not look at the photograph until
later. The quantum mind has detectors near each slit so it knows which slit
the various electrons went through. The quantum mind now signs a document
saying that it has observed each and every electron and knows what slit each
electron went through. It is very important that the document does NOT say
which slit the electron went through, it only says that they went through
one slit only, and the mind has knowledge of which one. Now the mind uses
quantum erasure to completely destroy his memory of the experiment. The only
part remaining is the document. Now look at the photographic plate. 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. 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,
so you get no interference. In the many worlds model all the other worlds
still exist in parallel and will converge and interfere with each other when
the electrons hit the photographic film.

Deutsch thinks an experiment like this will actually be performed in the
first half of the next century. The reason it is so difficult is that the
conventional view says that conscious observers obey different laws of
physics, many worlds says they do not. To test who is right we need a mind
that uses quantum properties.

It will not be easy to erase memories completely with nothing leaking out to
the rest of the universe, but recent developments suggest that it may be
possible. This sort of quantum isolation would not just be needed to test
many worlds, it would be essential if you want to make a quantum computer .

John K Clark johnkc@well.com

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