Mark Peaty wrote:
> 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). "

This is mixing Everett's relative state interpretation with the idea that the 
world is a simulation.  These are not the same and maybe not even compatible.  
The world evolves deterministically in Hilbert space and the "many-worlds" are 
projections relative to us.  Whether this can be simulated, except in a quantum 
computer, is questionable because the Hilbert space is infinite dimensional.  
Is some fixed finite resolution sufficient for simulation?

> 
> 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 assumes that the simulation must be quantum mechanical - but I think that 
would defeat the whole point of assuming a simulation.  If the world can be 
simulated classically, then it can be monitored without interference.

Brent Meeker


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