I just found the following discussion that, IMHO, bears on the
ideas in the thread on "Computational irreducibility and the
simulability of worlds".
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
>I began with a short note and it turned into a sermon,
>not all of which may apply to your inquiry.
>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.
>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.
>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
>"Collapsing wave functions" are exactly analogous to
>"collapsing average value of a Lotto ticket" when the drawing
>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
>****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
>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.)