Le 17-mars-06, à 20:27, Hal Finney a écrit :

> John M writes:
>> 1. do we have a REAL argument against solipsism?
> Let me express how solipsism can be analyzed in the model where 
> physical
> reality is part of mathematical reality.
> Let us adopt Bruno's UDA perspective: the Universal Dovetailer (UD)
> is an abstract machine that runs all possible computer programs.
> In this way it creates all possible universes, and more... it creates
> all possible information objects: all of mathematics, logic, all 
> written
> texts, everything.  In particular it creates the information patterns
> of conscious entities like you and me.
> Let us assume that this in fact represents the reality of the 
> multiverse,
> that what we perceive and experience is all caused by the operation
> of the UD, when it creates information patterns that correspond to
> those experienes.  I know that many people here reject this hypothesis,
> but let us follow it forward to see what it can say about solipsism.
> The first thing to notice is that within the UD, each person exists 
> more
> than once.  There are many programs that include a particular 
> information
> pattern in their output, in fact an infinite number of programs.  Some 
> of
> those programs will look much like the kind of model a physicist might
> construct for a "theory of everything".  It would include the physical
> laws and initial conditions that define our universe.  Running that
> program forward would create the entire history of our universe, 
> including
> the experiences of all of its inhabitants.
> However there are other kinds of programs that would also create the
> patterns of our conscious experiences.  Some might do it purely by 
> random
> chance: they might produce enormous outputs and somewhere buried in 
> there
> will be the pattern that corresponds to a portion of our experience.
> Others would include bizarre universes such as one inhabited by aliens
> who create computer simulations of other kinds of beings, and who have
> created us.  Yet another example would be a universe composed only of 
> one
> person, with all that is outside of him being supplied by the computer
> program, perhaps from some kind of table of sensory impressions, so 
> that
> only he is real within that universe.
> Solipsism is the doctrine that only I exist, that everything else is an
> illusion.  In the context of the platonic multiverse, it would 
> correspond
> to that last case: a portion of the UD program where only the one 
> person
> is in his universe, and nothing else in the universe is real.
> So this raises the question: given that I exist multiple times within
> the UD structure, and given that in some of them the universe I see
> around me is real and in some of them it is an illusion, which is the
> reality for me?  In which one do I actually exist?
> I believe Bruno argues, and I agree, that this is a meaningless 
> question.
> You exist in all of them.  There is no single instance of your 
> information
> pattern which is "really you".  Your consciousness spans all of the
> places in the UD where it is instantiated.  However, there is a related
> question which is relevant: what will happen next?  If some of your
> consciousness is in the real universe, and some of it is in universes
> where you are an alien simulation, some in a universe where it is a
> random fluctuation, and some in a universe where you are all there is,
> how can you make a prediction about the future?  In the random universe
> you would expect to disintegrate into chaos.  In the aliens, they might
> open up the simulation and start talking to you.  In the solipsism 
> case,
> various bizarre things might happen.  And in the "plain vanilla" 
> universe,
> you would expect things to go along pretty much as you remember them.
> Here is where I may depart from Bruno, although I am not sure.


> I argue
> that you can in fact set up a probability distribution over all of the
> places in the UD where your mind exists, and it is based roughly on the
> size of the part of the UD program that creates that information 
> pattern.

I will take the time to come back on this. I have a problem with this 
which is not entirely unrelated to our perennial ASSA/RSSA debate.
Another problem is related with the fact that from the first person 
point of view it is hard to distinguish big and little programs, and 
their way of recurring hyper-redundantly.

> Recall that the UD in effect runs all programs at once.  But some 
> programs
> are shorter than others.  I use the notion of algorithmic complexity
> and the associated measure, which is called the Universal Distribution
> (an unfortunate collision of the UD acronym).  Basically this says that
> the measure of the output of a given UD program of n bits is 1/2^n.

Yes. And it is even a machine independent notion (modulo some 
constant). But "big programs" cannot be dismissed "so easily", I will 
try to find a short explanation for why I think "saying yes" to the 
doctor makes, for the first person point of view,  some limiting 
behavior of the UD "hard" from the supremacy of the little programs, 
seen as possible TOE.

> This gives us a probability distribution over all the places our minds
> are implemented, such that the shortest program(s) get the bulk of
> the probability.  This has relationships to such traditional notions as
> Occam's Razor, as Russell Standish has emphasized.  Just as we say that
> the simplest explanation for our observations is likely to be correct,
> so we can say that the simplest program which creates our experiences
> is likely to be the one that governs what will happen next.
> In principle, it should become possible eventually to turn this 
> reasoning
> into at least rough quantitative form.  We will eventually have a
> complete model for our physical universe, so we can compute its measure
> and determine how big a contribution that part of the UD makes to our
> experiences.  Likewise we could create a model of the solipsist 
> universe,
> where only the person is real and all of his external experiences are
> provided by the program.
> It is very likely that it will turn out that the real-universe program
> will be much smaller than the solipsist one.  The solipsist program has
> to have an enormous table to supply all of the sensory experiences a
> person will receive.  It also needs to have some mechanism to compute
> his brain patterns, and probably the simplest will be to have an actual
> physical universe model.  Building the brain patterns into an internal
> table is another way to do it but will probably be even larger.  Any 
> way
> you look at it, the solipsist program is going to be enormous.

OK (modulo above)

> Reasoning in this way, we will not only be able to basically reject
> the solipsist hypothesis, we can actually do so in a quantitative way!


> We will be able to say, the fraction of your experiences due to the
> solipsist universe, or equivalently the probability that it is true,
> is this extremely tiny number.  And it will very likely be an 
> incredibly
> small number, 1/2^(10^20), perhaps.  (I wrote a long posting last year
> which effectively estimated this number.)
> This, then, is an example of the power of the assumption about the
> platonic universe, that physical and mathematical reality are the same.
> It not only sheds light on ancient and seemingly insolvable conundrums
> such as solipsism, it should allow us to in principle produce 
> quantitative
> estimates of the role of solipsist universes in the larger reality.
> If as I wrote yesterday we are able to eventually verify predictions of
> this model in terms of physical observations, we would have achieved
> a unification of physics and philosophy far deeper than has ever been
> accomplished before.

I agree basically modulo the reserve mentionned above. Thanks for 
helping making clearer the possible point of departure. More works need 
to be done in the bifurcating directions to see if they really 



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