Yes this helps, but I still find it strange to talk about offspring
universes (that by definition are independent) and yet to predict
outcomes we sum their complex valued wave functions.

While we're on the subject of interpretation of QM,  do you know about
the transactional interpretation of QM?  I find this more natural than
Copenhagen or MWI - particularly with its explanation of "spooky action
at a distance".   

I particularly like the explanation of inertia (as arising through
advanced waves sent backwards in time from the rest of the universe).
This is a simple and natural explanation of the equivalence principle in
general relativity.  It also explains why an inertial frame of reference
doesn't rotate with respect to the fixed stars.

Given the time symmetry in the laws of physics, we expect small systems
of elementary particles won't have an arrow of time - because that is
only a feature of macro systems starting in a low entropy state.
Therefore waves that travel backwards in time (ie advanced waves) must
be a fundamental (inevitable) concept.  Doesn't all QM strangeness arise
naturally from this?  Why not invoke Occam's razor and drop the idea of
"many worlds"?

- David



-----Original Message-----
From: Matt King [mailto:[EMAIL PROTECTED] 
Sent: Saturday, 8 November 2003 3:37 AM
To: David Barrett-Lennard
Cc: [EMAIL PROTECTED]
Subject: Re: Quantum accident survivor

Hello David,

David Barrett-Lennard wrote:

>Please note that my understanding of QM is rather lame...  Doesn't MWI
>require some interaction between branches in order to explain things
>like interference patterns in the two slit experiment?  What does this
>mean for the concept of "identity"?
>
>- David
>  
>
There is a technical difference between interference and interaction.

Interaction refers to two or more particles influencing each other 
through the exchange of force.  Only particles within the same universe 
(within the broader multiverse) may interact with each other in this
way.

These particles are represented by wavefunctions in quantum mechanics, 
which have wavy properties like amplitude and wavelength, and so can 
exhibit interference just like waves on a pond.  Also just like waves on

a pond, particle wavefunctions can pass through each other, even 
annihilating completely in some places, without interacting (i.e. 
without exchanging force).

Typically in single-particle experiments like Young's double slits, 
there is no interaction, and the interference arises from the sum of all

the different trajectories (or worlds if you like) that the particle may

have taken.

In experiments involing two or more particles, frequently every possible

path of each particle and every possible interaction must be considered 
as a separate world.  Interference then takes place between these 
possible worlds, and must be taken into account in order to correctly 
make statistical predictions of how the particle system will behave.

So in answer to your question, no, the MWI does not require interaction 
between branches to explain interference.  Indeed interaction (exchange 
of force) is prohibited by the linearity of the Schroedinger Wave 
Equation (SWE), which indicates that its different possible solutions 
(universes) should move through each other as easily as ripples through 
a pond.  We can only see the interference when we're not interacting 
with the rippling system.  Once we do, the rippling system expands to 
include us within its folds.  From that point on, there are multiple 
versions of us, each experiencing a different ripple, completely unable 
to interact with the other versions of ourselves moving through us all 
the time.

Hope this helps,

         Matt.

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When God plays dice with the Universe, He throws every number at once...

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