On 1 May 2017 3:22 a.m., "Bruce Kellett" <[email protected]> wrote:
On Monday, May 1, 2017 at 10:41:44 AM UTC+10, Brent wrote:
On 4/30/2017 5:05 PM, Bruce Kellett wrote:
> >
> > Which is not what you said in the quote above. The quote is "first
> > person experience in physics has to be a sum on all computations".
> > Perhaps it is all just a typo -- what you meant was "that the first
> > person experience *of* physics has to be the sum on all computations.
> > But even putting aside what "the sum on all computations" might
> > possibly mean, this is still not what you say in SANE04: to quote
> > again, "Physics is, in principle reduced to a measure on the
> > collection of computational histories, as seen from some first person
> > point of view." A measure on some collection is not a sum over anything.
> >
> > There seems to be a confusion here between what is consciousness and
> > what is the origin of physics.
>
> As I understood it, Bruno's idea was like Julian Barbour's idea of
> Everettian physics: below the classical level there are many quantum
> threads which as an equivalence class constitute the (quasi) classical
> world or our experience. These are a kind of non-local, hidden
> variables - non-local in the sense that they are in different worlds =
> threads of the UD computation. But of course the UD is executing all
> possible programs, so in order that this have any explanatory power you
> need to show that the equivalence class we think of as being our world
> at least has greater than zero measure in some sense (this is like
> solving the Boltzmann brain paradox).
>
> In Barbour's image the threads are motions of the state vector in
> Hilbert space and it is physics that it is modeled; consciousness
> supervenes on the physics. In Bruno's idea the thread are...what?
> subjective states of consciousness?
>
That was one of the questions I asked: "You bet on the existence of a
substitution level at which your consciousness is unaffected by the digital
substitution, but that is just betting on the idea that your consciousness
is Turing emulable-- it says nothing about what happens below that level."
Barbour's image is of the quantum "blue mist". But Bruno does not have
physics at this stage of the argument.
But consciousness has to be consciousness OF something.
I think this is the crucial point. Saying "Yes, doctor" is the belief that
I will not be aware of any experiential change under the digital
substitution. That means, in particular, that all my memories are carried
across intact. And my memories are of living in, and interacting with, a
physical world. So a great deal of physics has to be transferred with the
substitution. Looked at in another way, the computation that underlies my
current conscious state already include a lot of physical information.
A helpful comparison might be with Tegmark's multiverse (arxiv:
0905:1238v1). In the level 1 multiverse there is infinite space, which
contains Hubble volumes realizing all initial conditions -- including an
identical copy of you about 10^{10^29} m away. This corresponds to other
threads in the UD that go through your conscious state. These are the
threads which constitute the equivalence class that Bruno wants in order to
extract physics. But in this picture, they are just identical copies of the
conscious "you" in different universes -- they are complete in themselves
and are not needed in order for the present "me" to be conscious. Of
course, when one identifies the level I and III multiverses, this just
gives FPI as the origin of quantum randomness.
Other levels of Tegmark's multiverse correspond to the other threads of the
UD which do not contain our consciousness, and which entail different basic
physical laws -- up to Tegmark's level IV, which contains all other
mathematical structures. It might be more relevant to compare the UD to
Tegmark's later idea of the "Computable Universe Hypothesis" (CUH) which
claims that all 'computable' mathematical objects are realized in some
world in the multiverse. It is hard to detect any difference between this
idea and the worlds of the UD.
In fact, Bruno's three assumptions for computationalism: "Yes, doctor",
Church-Turing, and Arithmetical realism, would lead to Tegmark's CUH just
as readily as to computationalism.
Hmm... Here's a thought that could conceivably help with grasping a crucial
distinction between comp and something like CUH at a more intuitively
illustrative level. CUH essentially leads to the notion of a "physically
computable" multiverse, with consciousness, as ever, sitting pointlessly
like a cherry on top of the physical cake. IIRC Tegmark's take on this is
that consciousness is "what data feels like when it's being processed". I
invite you to try to crowbar the tacit presuppositions out of that pithy
little slogan. The pointlessness is of course that a physical multiverse
conceived in this manner has no need of consciousness. In point of fact it
has no need of a concrete or substantial world, which is itself
(uncontroversially, I trust) a perceptual construct in any viable theory of
mind. And when I say no need, what I mean is that there is no a priori
entailment of either consciousness or concreteness based on physics;
instead there is a posteriori consistency, a somewhat different matter.
Comp by contrast entails the principled a priori prediction of
self-reflective subjectivity. This is a genuine novelty. Moreover, it is a
novelty that is capable of investigation using a precision tool: reflexive
modal logic. That this tool isn't more widely and deeply understood beyond
the professional competence of mathematical logicians is perhaps to be
regretted. ISTM that a technical exposition of interiority of this sort -
which contains the elusive possibility of illuminating the transition from
syntax to semantics - is pretty much unprecedented in the history of
thinking about consciousness. One might perhaps think it surprising that
these insights haven't been available earlier, especially given the various
controversies engendered (e.g. by the notorious Chinese Room). No doubt
technical unfamiliarity​ has been a factor militating against this.
Anyway, the point I'm leading up to is this: whereas the very notion of
consciousness is a pointless and functionless cherry on the cake of
physics, it might seem to be the very raison d'etre of computationalism.
That there be some such concrete perceptual reality as the one in which in
which we perceive and act is a direct prediction and entailment of comp.
That there be some such emergent abstract mathematical physics
encapsulating such perceiving and acting is a further prediction and
entailment. Of course it's much too early to predict the ultimate success
of such a nascent project in extracting the extended detail of its
promising early indications, although of course it's never too soon to look
for obvious refutations or flaws. But neither should we fall into the error
of demanding too much too soon. Of what use is a baby?
In a nutshell, to paraphrase something that Bruno has sometimes said, comp
leads to the vision of a kind of subjective Library of Babel. A cacophony
indeed but one, hopefully in which the viable dramatis personae typically
find themselves in consistent and robust substantive environments​. If it
were indeed so comp would also go as far as we could perhaps expect in
answering the question of how there could be anything at all. That answer
would then lie in the inherent creativity of mere arithmetic, as expressed
in the extension of a supremely creative intensional widget. And the
creator, in this extraordinary scenario, would truly neither have nor need
the merest clue of the consequences of its own creativity.
David
So the measure has to pick out not only
> coherent threads of consciousness but also complementary coherent
> threads of physics in which the consciousness can exist. Otherwise the
> consciousness can only be conscious OF stuff independent of physics;
> which Bruno thinks includes all of mathematics and I think is empty.
> It's supposed to be an empirical question. That means there is some
> consequence of the theory which shows up in the physics. An obvious
> one, is that one's ability to do mathematics should not be affected by
> the consumption of tequila.
>
You have the difficulties in a nutshell.
Bruce
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