----- Original Message ----- 
From: "Brent Meeker" <[EMAIL PROTECTED]>
To: "Saibal Mitra" <[EMAIL PROTECTED]>
Sent: Wednesday, June 08, 2005 02:23 PM
Subject: RE: Observer-Moment Measure from Universe Measure


>
>
> >-----Original Message-----
> >From: Saibal Mitra [mailto:[EMAIL PROTECTED]
> >Sent: Wednesday, June 08, 2005 1:16 PM
> >To: Patrick Leahy; Hal Finney; [EMAIL PROTECTED]; [EMAIL PROTECTED]
> >Cc: everything-list@eskimo.com
> >Subject: Re: Observer-Moment Measure from Universe Measure
> >
> >
> >I think one should define an observer moment as the instantaneous
> >description of the human brain. I.e. the minimum amount of information
you
> >need to simulate the brain of a observer. This description changes over
time
> >due to interactions with the environment. Even if there were no
interactions
> >with the environment the description would change, but this change is
fixed
> >by the original description.
>
> That means that, supposing the brain is a classical, the "moment" cannot
be
> defined by a description of values, omitting rates; just as the path of a
> ballistic projectile cannot be specified by it location, omitting its
velocity.
> But to include rates means an implicit introduction of time and continuity
of
> OMs.  This implies that OMs form causal chains and it makes no sense to
talk
> about the same OM being in two different chains.


That's true in an isolated personal universe that is not interacting with an
'outside world'. I could, e.g. take your brain and simulate that on a
computer. The evolution equations for your brain are deterministic, so the
simulation will describe a unique chain of causal links provided you fix the
boundary conditions.

If the personal universe is embedded in another universe (like in our case),
then the evolution equations will be constantly perturbed.




>
> But a lot of the motivation for OMs comes from the brain *not* being
classical;
> from the idea that the brain gets "copied" into Everett's multiple
relative
> states or MWIs.  Decoherence in the brain is very much faster than the
> neurochemical processes - that's why it's approximately classical.  So
what is
> going on when QM predicts different OMs?  From Everett's point of view the
> brain must be treated as part of the QM system and it gets "copied" - but
not
> by itself.  Its description must include its entanglement with the quantum
> systems observed.  So it seems that in either case, classical or quantum,
an OM
> as a description of a brain state, has links outside itself.  In the
classical
> case it has casual links in time.  In the QM case it has Hilbert space
links to
> what has been observed.


I agree. But the entangled state of a brain with the rest of the universe in
the MWI corresponds to an ensemble of different worlds such that in each
member of the ensemble the brain is in some definite state.


>
> >So, I see no problem with Hal's way of thinking about OMs....
> >
> >
> >Observers are can be thought of as their own descriptions and thus
universes
> >in their own right. Observer moments are observers in particular states
i.e.
> >their ''personal'' universe being in a certain state. The causal relation
> >between successive states is already defined when we specify which
observer
> >we are talking about. i.e., we have already specified the laws of physics
> >for the personal universe of an observer which defines the observer.
> >Specifying the initial state of the personal universes thus suffices.
>
> That would hold for a classical brain in a classical universe.  But does
it in
> a QM universe?  I see a tension between the idea of "personal universe"
and
> quantum entanglement.

I don't see problems here. If you assume that our universe is described by
some fundamental laws of physics then those laws of physics also describe
our brains. The way a particular brain works is thus fixed. This then
defines the personal universe. Entanglement of the brain with another system
can only happen if there are interactions with the outside. Even in the
classic case these intercations make the evolution of the personal universe
nondeterministic.



Saibal

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