# Re: Quantum Time Travel

From: Russell Standish <R.Standish.domain.name.hidden>
Date: Mon, 1 May 2000 12:10:11 +1000 (EST)

Jacques Mallah wrote:
>
> --- Russell Standish <R.Standish.domain.name.hidden> wrote:
> > > You're playing with words. The point is a
> > > measure distribution must be measure *of
> > > something*. Thus it makes no sense to speak
> > > of "the measure distribution"
> > > given a wavefunction, unless you state what it is
> > > measure *of*. The only measure distribution we
> > > have been dealing with in that context is of
> > > observer-moments. I call that M(c)
>
> > Not at all true. A lot of discussion has taken place
> > in this list re
> > measure of strings in a Schmidhuber plenitude.
>
> Which is not in "that context", of a wavefunction.
>
> > Measure is always taken to be the strength or
> > density of a particular object from within an
> > ensemble (continuous or otherwise) of
> > objects. It is readily related to a sampling
> > probability when the
> > measure distribution is normalisable.
> >
> > Schroedinger's equation gives a measure distribution
> > for outcomes of particular observables, given
> > certain constraints (a Hamiltonian and a
> > boundary condition).
> > An observer moment must be the conjunction of
> > some vast array of observables having particular
> > values.
>
> Really? Are you saying that the Sh. eq. gives a
> measure distribution for "outcomes" of "observables"
> even when there are no obserrver-moments? What is
> that supposed to mean?

Of course. Anyone can construct a system with no observers in it. eg a
cubic metre of Titan's ocean. That system will have observables eg
temperature, density etc, but presumably no observers (until we send a
space probe), and hence no observer moments. The SE is well defined
given our state of knowledge of Titan's surface, and one can compute a
measure distribution of observable outcomes if an observer were to be
present.

> If by "observables" you mean Hermitian operators,
> how does the Sh. eq. do the above?

If A is your observable, x is the state your system is in, and y
indexes the set of outcomes, the distribution <y|A|x> is the measure
distribution of outcomes fro that observable. Surely, you know this already.

> My view, as I have stated repeatedly, is that it
> should be possible to derive a measure distribution
> for computations implemented by a physical system and
> that given a wavefunction & the Sh. eq., it should be
> possible to show that the ratios of the measures of
> appropriate computations that could be conscious (if
> present, e.g if there is a brain in the system) to the
> total measure of such are the usual effective
> probabilities.

I guess we differ here. I don't believe a computation can ever be
conscious. Rather I believe the converse - a consciousness can always
implement a computation.

>
> > My own preference is to talk about a quantum
> > history, which under some
> > (perhaps rather flaky) assumptions, could be
> > identified with the concept of observer moment.
>
> What's a "quantum history"? Any relation to the
> "consistent histories interpretation"?

Perhaps, although I'm not familiar with this term.

>
>
> =====
> - - - - - - -
> Jacques Mallah (jackmallah.domain.name.hidden)
> Physicist / Many Worlder / Devil's Advocate
> "I know what no one else knows" - 'Runaway Train', Soul Asylum
> My URL: http://hammer.prohosting.com/~mathmind/
>
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>

----------------------------------------------------------------------------
Dr. Russell Standish Director
High Performance Computing Support Unit, Phone 9385 6967
UNSW SYDNEY 2052 Fax 9385 6965
Australia R.Standish.domain.name.hidden
Room 2075, Red Centre http://parallel.hpc.unsw.edu.au/rks
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Received on Sun Apr 30 2000 - 19:08:41 PDT

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