Dear Freinds,

        I just found the following discussion that, IMHO, bears on the
ideas in the thread on "Computational irreducibility and the
simulability of worlds".

Kindest regards,

Stephen

On Thu, 15 Apr 2004 15:14:38 +0000 (UTC), in sci.physics.research
[EMAIL PROTECTED] (James Baugh) wrote:

>"p.valletta" <[EMAIL PROTECTED]> wrote in message news:<[EMAIL PROTECTED]>...
>> The Wave-function of the Universe is based on QM principles of probabilty
>> and thus of observertional quantities. Quantum Tunneling is a good
>> experimental method of  'Wave-function' analysis.
>> 
>> Is it true that there is a corresponding 'Particle-function', based on the
>> same variables?  and could we use this to devise an experiment whereby a
>> 'particle' tunnels outside of the Universe revealing the
>> 'Universe-wavefunction'?
>
>Pardon Me,
>I began with a short note and it turned into a sermon, 
>not all of which may apply to your inquiry.
>********
>
>[First]
>Before using such phrases as "The wave function of the Universe"
>first keep in mind what a "wave-funtion" means.
>In QM a wave function is a distribution of probability
>amplitudes over a range of possible obserables.
>(Usually but not always position observations, e.g.
>we can have a wave function over momentum space.)
>
>In other words it describes for example how likely we are to see
>a particle pass through a pin-hole.  The arguments (x,y,z,t)
>describe where the pin-hole i.e. measuring device "is" not where
>the particle "is".
>  
>In (other) other words a wave function describes 
>*What We Know* about the system w.r.t. 
>the probability of future observations.  
>Before you write down a wave function 
>of "the universe" or any other posited
>system you first need to define what 
>"the universe" means in terms of what 
>measurements you can make.
>
>[Second]
>Given we exist within "the universe" our knowledge of the universe
>cannot be complete (in the quantum sense of maximal).  A measuring
>device cannot measure itself.  (Thermodynamics is an integral part
>of the measuring process, you must have a heat sink to cool the
>amplifier which amplifies the measurement signal.  Measurement
>is by definition gain > 0 dB.)
>So at best we should only define a Density Operator for the universe.
>
>[Third]
>Having said this let me point out that "outside the universe"
>also has no operational meaning.  If we can reach it then it
>can reach us in the sense of exchanging interactions and thus
>it is part of "The Universe" where one defines "The Universe" as
>a limiting case of the largest system possible.
>
>Quantum theory does not posit extra dimensions or multiple universes.
>(Unless you need a plot device for a Science Fiction script.)
>It simply gives us a more "stable" description of what we may
>observe and how one act of observation can alter the outcome
>of future observations.
>
>Too many people have become confuse by reading 
>"Many Worlds" re-interpretations of quatum theory 
>which essentially tries to re-embed quantum theory 
>within a larger classical framework.  
>The quantum language is by definition
>a more general language than classical.  
>It simple relaxes assumptions about actions you may
>effect on a system (i.e. that all acts of
>observation commute and thus have no effect on one another.)
>
>The same sort of confusion arises when you play with relativized
>space-time but try to stick it back into a context of absolute time.
>In the example of the twin paradox the question of
>"Which twin is *really* older?" is just such a case.
>Once you relativize you mustn't frame questions in 
>terms of the old absolutes.
>
>Quantum theory relativizes the concept of physical state.
>Holding on to the same absolute assumptions that one has
>relativized again leads to a paradox.  In
>this case the EPR paradox in the form of assumptions
>about classical probabilities intrensically vested
>with a particle when the probabilities of QM are
>intrensically non-local correlations between system
>and observer.
>
>"Collapsing wave functions" are exactly analogous to
>"collapsing average value of a Lotto ticket" when the drawing
>is held.
>
>[Fourth]
>I would qualify that the above doesn't preclude
>extra "hyperspace" dimensions.  However assuming
>there are we must ask if our "universe" is a "thin membrane" or
>if rather it extends into those extra dimensions completely.
>It is one thing to posit extra dimensions
>and quite another to assume physical objects are already
>localized (i.e. thin) with respect to those dimensions.
>This is the point of string theory. (although it too has 
>serious conceptual problems.)  
>
>Our three dimensional
>spatial picture may be just a cross section of a broader
>picture where an electron is a rope looping around
>4 dimensional hyper-space (ignoring time).  But again
>these are just mental pictures.  The physics is in how
>things behave and that is described mathematically
>where one can add as many dimensions as one wants.
>Don't confuse the mathematical model for the physics.
>
>Too many people do including 
>quite a few PhD's in Physics.
>
>Finally with regard to "Tunneling".  Tunneling
>is a phenomenon where classical theory predicts
>something is impossible while quantum theory
>predicts it is improbable but not impossible.
>Think of tunneling this way.  I design an
>escape-proof prison.  Suppose that I can prove 
>mathmatically that . . .
>
>***provided the guards follow protocol***
>
>it is impossible for you to escape.
>But in the "real world" the guards 
>are only human and mistakes
>have a certain probability of occuring.
>Given this then I can only prove in the
>real world that the probability of you
>escaping is very very small.
>
>The classical potential describing
>say the binding of an electron within
>an atom is just an idealized average description
>of the quantum electromagnetic field.
>The actual electromagnetic field you
>could view as "noisy" but its better just
>to say 
>****The e-m potential only has meaning in QM 
>as defined by the probabilistic behavior of a charged particle*** 
>
>There is only a mystery when you try to
>impose a classical picture on the behavior.
>Anytime you see the word "potential" remember
>it is an artifact used to describe how something
>else behaves.
>
>Carry this back to descriptions of "The Universe"
>"The Universe" is not a four dimensional space-time
>manifold with fields affixed to it.  That is just a model.
>The universe is a bunch of interacting processes.
>The structure of their interaction we break down into
>pieces which classically we describe as localized particles
>or continuous waves.  Both are imperfect approximations and
>the "quantum wave functions" are just a bit better.
>The best description is simply to look at how different
>actions correlate.  "Look for a click here after seeing a click there"
>(where what's clicking we classically describe as a particle detector.)
>This is usually done with the operator algebras or Lie groups.
>(And usually done badly with infinite dimensional versions, hence
>the problems with divergences when quantizing gravitation.)
>
>
>Regards
>J. Baugh



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