Bruno Marchal wrote:
> Le 21-août-06, à 16:01, 1Z a écrit :
>
> > Exactly. And if non-phsyical systems (Plato' Heaven) don't
> > implement counterfactuals, then they can't run programmes,
> > and if Plato's heaven can't run programmes, it can't be running us as
> > programmes.
>
> I would say that only non-physical system implement counterfactuals.
A counterfactual is somethingthat could have happened, but didn't.
A static, immaterial systems can only handle counterfactuals by
turning them into factuals -- everything that can happen does
happen. It can fully capture the *conditional* structure of a
programme,
(unlike a "recording") at the expense of not being a process.
A programme is not the same thing as a process.
Computationalism refers to real, physical processes running on material
computers. Proponents of the argument need to show that the causality
and dynamism are inessential (that there is no relevant difference
between process and programme) before you can have consciousness
implemented Platonically.
To exist Platonically is to exist eternally and necessarily. There is
no time or changein Plato's heave. Therefore, to "gain entry", a
computational mind will have to be translated from a running process
into something static and acausal.
One route is to replace the process with a programme. After all, the
programme does specify all the possible counterfactual behaviour, and
it is basically a string of 1's and 0's, and therefore a suitabale
occupant of Plato's heaven. But a specification of counterfactual
behaviour is not actual counterfactual behaviour. The information is
the same, but they are not the same thing.
No-one would believe that a brain-scan, however detailed, is conscious,
so not computationalist, however ardent, is required to believe that a
progamme on a disk, gathering dust on a shelf, is sentient, however
good a piece of AI code it may be!
Another route is "record" the actual behaviour, under some
circumstances of a process, into a stream of data (ultimately, a string
of numbers, and therefore soemthing already in Plato's heaven). This
route loses the conditonal structure, the counterfactuals that are
vital to computer programmes and therefore to computationalism.
Computer programmes contain conditional (if-then) statements. A given
run of the programme will in general not explore every branch. yet the
unexplored branches are part of the programme. A branch of an if-then
statement that is not executed on a particular run of a programme will
constitute a counterfactual, a situation that could have happened but
didn't. Without counterfactuals you cannot tell which programme
(algorithm) a process is implementing because two algorithms could have
the same execution path but different unexecuted branches.
Since a "recording" is not computation as such, the computationalist
need not attribute mentality to it -- it need not have a mind of its
own, any more than the characters in a movie.
(Another way of looking at this is via the Turing Test; a mere
recording would never pass a TT since it has no
condiitonal/counterfactual behaviour and therfore cannot answer
unexpected questions).
> That counterfactuality is the essence of (immaterial) comp. Although
> here Russell has a point: the quantum multiverse seems to handle
> counterfactual.
Multiverse theories seek to turn the 3rd-person "X could have happened
but didn't"
into the 1st-person "X could have been observed by me, but wasn't".
> Now if comp is correct, I cannot distinguish a
> "genuine" quantum multiverse from any of its emulation in Platonia,
A quantum multiverse is sitll only a tiny corner of Platonia.
Physical many-world theories have resources to keep counterfactuals
unobserved that immaterial MW-theories lack (including the simple
of one that many mathematical possibilities do not
exist physically).
For instance, even if their are two informationally identical me's
in different branches of a phsycial universe, it is not
inevitable that any sharing or corss-over of
consicousness would occur, because in a phsyical
universe, cosnciousness would have something other
than informational structures to supervene on.
Thus me might
well be able to tell that we are in a quantum multiverse rather than
Platonia, on the basis that we just do not observe enough weirdness.
Too broad: If I am just a mathematical structure, I should have a much
wider range of experience than I do. There is a mathemtical structure
corresponding to myself with all my experiences up to time T. There is
a vast array of mathematical structures corresponding to other versions
of me with having a huge range of experiences -- ordinary ones, like
continuing to type, extraordinary ones like seeing my computer sudenly
turn into bowl of petunias. All these versions of me share the memories
of the "me" who is writing this, so they all identify themselves as me.
Remember, that for mathematical monism it is only necessary that a
possible experience has a mathematical description. This is known as
the White Rabbit problem. If we think in terms of multiverse theories,
we would say that there is one "me" in this universe and other "me's"
in other universes,a nd they are kept out of contact with each other.
The question is whether a purely mathematical scheme has enough
resources to impose isolation or otherwise remove the White Rabbit
problem.
Too narrow: there are a number of prima-facie phenomena which a purely
mathematical approach struggles to deal with.
space
time
consciousness
causality
necessity/contingency
Why space ? It is tempting to think that if a number of, or some other
mathematical entity, occurs in a set with other numbers, that is, as it
were, a "space" which is disconnected from other sets, so that a set
forms a natural model of an *isolated* universe withing a multiverse, a
universe which does not suffer from the White Rabbit problem. However,
maths per se does not work that way. The number "2" that appears in the
set of even numbers is exactly the same number "2" that appears in the
list of numbers less than 10. It does not acquire any further
characteristics from its context.
The time issue should be obvious. Mathematics is tradionally held to
deal with timeless, eternal truths. This is reflected in the metpahor
of mathematical truth being discovered not found (which, in line with
my criticism of Platonism, should not be taken to seriously). It could
be objected that physics can model time mathematically; it can be
objected right back that it does so by spatialising time, by turning it
into just another dimension, in which nothing really changes, and
nothing passes. Some even go so far as to insist that this model is
what time "really" is, which is surely a case of mistaking the map for
the territory.
Consciousness is a problem for all forms of materialism and physicalism
to some extent, but it is possible to discern where the problem is
particularly acute. There is no great problem with the idea that matter
considered as a bare substrate can have mental properities. Any
inability to have mental properties would itself be a property and
therefore be inconsistent with the bareness of a bare substrate. The
"subjectivity" of conscious states, often treated as "inherent" boils
down to a problem of communicating one's qualia -- how one feels, how
things seem. Thus it is not truly inherent but depends on the means of
communication being used. Feelings and seemings can be more readily
communicated in artistic, poetic language, and least readily in
scientific, technical language. Since the harder, more technical a
science is, the more mathematical it is, the communication problem is
at its most acute in a purely mathematical langauge. Thus the problem
with physicalism is not its posit of matter (as a bare substrate) but
its other posit, that all properties are physical. Since physics is
mathematical, that amounts to the claim that all properties are
mathematical (or at least mathematically describable). In making the
transition from a physicalist world-view to a mathematical one, the
concept of a material substrate is abandoned (although it was never a
problem for consciousness) and the posit of mathematical properties
becomes, which is a problem for consciousness becomes extreme.
The interesting thing is that these two problems can be used to solve
each other to some extent. if we allow extra-mathemtical properties
into our universe, we can use them to solve the White Rabbit problem.
There are two ways of doing this: We can claim either:-
White Rabbit universes don't exist at all
White Rabbit universes are causally separated from us (or remote in
space)
The first is basically a reversion to a single-universe theory (1).
Mathematical monists sometimes complain that they can't see what role
matter plays. One way of seeing its role is as a solution to the WR
problem. For the non-Platonist, most mathematical entitites have a
"merely abstract" existence. Only a subset truly, conceretely, exist.
There is an extra factor that the priveleged few have. What is it ?
Materiality. For the physicalist, matter is the token of existence.
Maerial things, exist, immaterial ones don't.
The second moves on from a Mathematical Multiverse to a physical one
(3). The interesting thing about the second variety of
non-just-mathematical monism is that as well as addressing the White
Rabbit problem, it removes some further contingency. If the matter,
physical laws, and so on, are logically possible, then the general
approach of arguing for a universe/multiverse on the grounds of
removing contingency must embrace them -- otherwise it would be a
contingent fact that the universe/multiverse consists of nothing but
mathematics.
> and
> the physical laws must take that into account.
All forms of physics handle counterfactuals.
Or do you mean it handles them in the sense of making them real -- as
Deutsch insists.
Multiverse theories claim that all possible worlds exist; but
"possible" has more than one meaning, so there is more than one
multiverse theory. Logical possibility simply means that something is
not self-contradictory. Physical possibility means something is not
contradictory to the laws of physics. "Five-sided square" is
self-contradictory. "Water runnig uphill" is not, but it is physically
impossoble.
'And, as I argued in FoR, the reality of universes in which we chose
differently makes sense of (some) formally 'counter- factual'
statements that don't make sense in single- universe physics, which can
only help in making sense of free will.
We are forced to conclude that, in spacetime physics [i.e. without a
multiverse], conditional statements whose premise is false ("if Faraday
had died in 1830 ...") have no meaning. '[Fabric of Reality, D Deutsch,
p. 275]
Suppose we agree. What is Deutsch himself to make of the
counterfactuals we need to discuss the consequences of the laws of
physics themselves, such as: "If charge were not conserved, the world
would be a very different place"? The multiverse is no help, for by
definition, it contains no worlds in which the laws are different.
Deutsch's view thus implies that these essential claims about how
things would have been had the laws of nature been different "have no
meaning". The moral is that if we want to give truth conditions for
counterfactuals in terms of possible worlds, we need the set of all
ogically possible worlds, not the set of physically possible worlds.
Indeed, Deutsch's whole multiverse probably counts as a single possible
world in David Lewis's account, to which Deutsch later compares his own
view: "The fruitfulness of the multiverse theory in contributing to the
solution of long-standing philosophical problems is so great that it
would be worth adopting even if there were no physical evidence for it
at all. Indeed, the philosopher David Lewis, in his book On The
Plurality of Worlds, has postulated the existence of a multiverse for
philosophical reasons alone." [pp. 339,40], my italics. Note that it is
doubtful whether the italicised counterfactual is itself meaningful, on
Deutsch's view! In fact, what Lewis postulates is not a multiverse
theory, in Deutsch's sense.
from:-
http://www.usyd.edu.au/time/price/preprints/DeutschReview-bjps.html
Under David's interpretation, conditional statements whose antecedents
are false in all physically possible universes, such "as there is a
perpetual motion machine..." are meaningless.
So are positive statements about things that don't exist in any
physical universe, eg "there is a perpetual motion machine"
So are negative statements about things that don't exist in any
physical universe, "there is no perpetual motion machine". But, of
course, we would regard the last as meaningful and true.
There is in fact a whole bunch of reasons for thinking that statements
don't require real-world referents to be meaningful. We judge the
meanings of statements by their semantic and syntactic makeup. we don't
judge them by peeping into the universe next door. We can make sense of
"there is life on other planets" without knowing whether there is in
fact life on other planets. If we couldn't make (linguistic,
comceptual) sense of "there is life on other planets", we wouldn't know
how to go about verifying its truth.
The kind of linguistic/semantic meaning I have been talking about is
called "sense", as opposed to reference, the real-world object a
statement is about, if it is about one. The distinction originated with
the Frege
David's contention seems to be based on the idea that "all meaning is
reference". However it is arbitrary at best. It suggests statements
like "if MWI is false.." are meaningless unless there is a world where
MWI is in fact false. But how can that be if there is in fact, more
than one world ?
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Received on Tue Aug 22 2006 - 07:47:32 PDT