This is yet another delayed response; the story of my life really ...

Jason: "By physically reversible I don't mean we as humans can undo 
anything
that happens, rather physical interactions are time-invertible.  If you
were shown a recording of any physical interaction on a small scale, an
elastic collision of particles, the decay of a nucleus, burning of
hydrogen, it would be impossible for you to tell if that recording were
being played in reverse or not, since it is always possible for that
interaction to occur as it does in either direction of time."

MP: This is only true for 'individual' reactions on the micro scale, but 
even then the 'truth' about the reversibility can only really be 
maintained by hiding the truth about the context. For example, it is 
logically possible for certain atomic nuclei to collide at just the 
right velocities and fusion will occur. In reality however the 
probability of what are normally fission products coming together to 
make a uranium nucleus is so close to zero you are never going to see 
it. [I don't know much about the physics but my casual believe is that 
heavy elements are created through various long and complex 'ratchet' 
accretion pathways in which nuclear isotopes of H or He enter heavier 
nuclei.] Like wise the burning of hydrogen; it seems simple enough and 
yes it is 'reversible', but does the reverse occur? Not where you and I 
can see it.

Jason: "Quantum mechanics makes the universe seem random and 
uncomputable to
those inside it, but according to the many-worlds interpretation the
universe evolves deterministically.  It is only the observers within
the quantum mechanical universe that perceive the randomness and
unpredictability, but this unpredictability doesn't exist at the higher
level where the universe is being simulated (assuming many-worlds). "

MP: I don't think I can accept this. Maybe I sound arrogant in saying 
this, but I think the idea of simulation is used a bit too loosely. I 
know there are those lurking on the Mind & Brain list and JCS-online who 
would say I am 'the pot calling the kettle black', because I am always 
asserting what I call UMSITW [pronounced um-see-two for English 
speakers] - updating the model of self in the world - is the basis of 
consciousness. But they misunderstand me, because I do not say there is 
anyone else doing simulation, merely that we experience being here 
because the universe has evolved self sustaining regions within itself 
which maintain their structure by means of dynamically modelling 
themselves and their local region so as to avoid fatal dangers while 
obtaining everything they need from their environments. My point here is 
simply that the universe is its own best simulation and that any ideas 
of something greater, such as a Matrix type operation, are science 
fiction only. Why? Because for a feasible universe like the one we seem 
to inhabit to be deterministic does not require that it is predictable 
nor that it can be repeatable. Nobody knows to what extent quantum level 
events are intrinsically random as opposed to being _pushed from 
'behind' or 'below'_ so to speak.

That is one thing. Another thing is that no entity or set of entities 
could know if their 'simulation' attempt was doing what they wanted in 
every detail because to attempt to find this out would interfere 
irreversibly with the unfolding of the world. This latter objection can 
be sidelined by accepting that there are no entities with any such 
intention therefore it is irrelevant. For those who would be 'believers' 
in Sky God, as well sceptics, this puts divine intervention pretty much 
off limits.

OK, that leaves the concept of pseudo-emulation: another hidden 'level' 
of structure embodied in calculation. I guess this can be represented by 
either
1/ the movie '13th Floor' - which I think much better than 'Matrix' 1, 
2, and 3 in terms of its encapsulation of interesting philosophical 
questions - or
2/ Bruno's 'Yes Doctor' hypothesis.

These might seem to be very different but I don't think so. The key 
point is that a wilful entity or conspiracy seeks to emulate all or part 
of another wilful entity's world to the extent that the latter can't 
tell the difference when the change is made. Doubtless Bruno has a far 
more exacting definition and sets of caveats, but I insist on 
plain-English. As far as I can see, the assertion that this MUST be 
possible in principle because 'we' can imagine a mathematical 
implementation, just begs the question. I do not think there is anything 
shameful in 'reifying' physics, because if we exist and know that we do 
it has to be because we BELIEVE in ourselves and our world. Believing in 
something IS reifying it. When we understand that the basic mechanism 
underlying this process is the activation of a model of whatever it is, 
the whole question of mind and consciousness is demystified. This does 
not remove the wonder, or the challenges, of living in the amazing 
universe. It should mean that we spend less money on snake oil though!
 
Regards
Mark Peaty  CDES
[EMAIL PROTECTED]
http://www.arach.net.au/~mpeaty/
 


Jason wrote:
>
>
> Mark Peaty wrote:
>> Hello Jason,
>> please excuse my ignorant interjections here but, as a
>> non-mathematician, non-philosopher, I need to work things into a plain
>> English version before I can feel that I understand them, and even then
>> the edges of things get fuzzy with far more ease than they get straight
>> and clear cut. Furthermore I am beginning to wonder if the apparently
>> 'straight' and clear cut boundaries to concepts and so forth are not
>> merely figments of my imagination. I don't think I go anywhere as far as
>> John M. in this but then maybe that is just because I fear to let go of
>> my sceptical reductionist walking stick. :-)
>>
>> Jason: 'perform an infinite number of
>> computations with a finite amount of energy, but only if the
>> computations done on that computer are logically reversible.'
>>
>> MP: Surely 'logically reversible' does not necessarily imply no entropy,
>> just that for the purposes of the concerned observer, the computing
>> system can return to a state that is sufficiently close to the original
>> state so that the inputs can be discovered. More or less by definition,
>> entropy increases and manifests as deterioration of the substrate and as
>> the need to supply more energy to travel through the system than
>> otherwise is calculated to be necessary to obtain the minimum changes
>> needed to embody the changes of state in the calculating system.
>>
>
> Right, logically reversible computations on their own do not imply no
> increase in entropy by the computing system, but for a computing system
> to operate with no net increase in entropy, the computations it
> performs must be logically reversible.  This is because: "For a
> computational operation in which 1 bit of logical information is lost,
> the amount of entropy generated is at least k ln 2, and so the energy
> that must eventually be emitted to the environment is E   kT ln 2." (
> http://en.wikipedia.org/wiki/Reversible_computing#More_on_Landauer.27s_principle
>  
>
> )  Note that the computing substrates needed to implement such an
> efficient computer are well beyond our current level of technology and
> are only theoretical.  However there is as of yet, no known reason why
> an arbitrarily efficient computer could not be built.
>
> A reversible computation is one that has a 1 to 1 mapping between input
> and output.  For example if if I compute x=x+3, every input has a
> unique output, given the function and the result it is possible to
> determine the input.  However the same could not be said of a function
> defined as x=x modulo 3, or x=0, where there are a finite number of
> outputs.  These computations are not reversible because it is
> inpossible to get the input given function and the output.
>
>> Jason: 'The physical interactions that occur in this universe are also
>> reversible.  e.g. An electron can accept a photon and move to a higher
>> energy state or an electron can emit a photon and move to a lower
>> energy state.  Does reversible physics imply that a computational model
>> of said physics would involve entirely reversible computations? '
>>
>> MP: This concept of 'reversible' is very useful, but to how great an
>> extent is it just a convenient fiction? My understanding is that you
>> can't fire *a particular* photon at a particular atom and guarantee that
>> your favourite electron will rise to the predicted level. I mean it
>> either will or it won't.
>
> By physically reversible I don't mean we as humans can undo anything
> that happens, rather physical interactions are time-invertible.  If you
> were shown a recording of any physical interaction on a small scale, an
> elastic collision of particles, the decay of a nucleus, burning of
> hydrogen, it would be impossible for you to tell if that recording were
> being played in reverse or not, since it is always possible for that
> interaction to occur as it does in either direction of time.
>
>> Conversely as I understand it [AIUI] the
>> subsidence of an electron to a lower orbital is only predictable in a
>> statistical sense. Once again is it not that the real world entities
>> must be dealt with in a statistical manner, either as bulk substances,
>> predictable due to the averaging of activities of the individual quantum
>> particles, or as individual quantum items manifesting radical
>> indeterminacy?
>
> Quantum mechanics makes the universe seem random and uncomputable to
> those inside it, but according to the many-worlds interpretation the
> universe evolves deterministically.  It is only the observers within
> the quantum mechanical universe that perceive the randomness and
> unpredictability, but this unpredictability doesn't exist at the higher
> level where the universe is being simulated (assuming many-worlds).
>
>> Either way AIUI, the computational model will manipulate
>> symbols denoting the real world physics and there is no guarantee that
>> any such computing system could overcome the limits imposed by entropy
>> and quantum indeterminacy.
>>
>
> I'm not sure what you are saying here.  Are you saying that a perfectly
> efficient computer could not be built or that the physics of this
> universe are not computable?
>
> Jason
>
>
> >
>
>

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