On 11 May 2015 at 19:14, Bruce Kellett <[email protected]> wrote:
> Bruno Marchal wrote: > >> On 07 May 2015, at 14:45, Bruce Kellett wrote: >> >>> ...... >>> Now, having read this many times, and looked at the other summaries of >>> the MGA, I still feel that something crucial is missing. We go from the >>> situation where we remove more and more of the original 'brain', replacing >>> the removed functionality by the projections from the movie, which, it is >>> agreed, does not alter the conscious experience of the first person >>> involved, to the conclusion that the physical brain is entirely >>> unnecessary; indeed, irrelevant. >>> >> >> Hmm... On the contrary: the brain is necessary. It is the primitive >> physicalness of the brain which is not relevant. >> > > That is not what you say in the paper. "Hence, consciousness is not a > physical phenomenon, nor can it be a phenomenon relating to observed matter > at all." You go on to say that the appearance of matter cannot be based on > a notion of primitive matter. But these are different things. Elsewhere you > appear to agree that consciousness does depend on the observed physical > brain. In fact, it would be foolish to deny this given the weight of > physical evidence that shows this to be the case. > > The question is whether materialism is primary. Obviously consciousness is associated with brains - even Cartesian dualism wouldn't deny that. And of course any theory has to account for the *appearance* of reality, given that it will necessarily deal with entities that aren't the primary objects of our senses. (QM, for example, explains why we experience what appear to be classical objects despite everything being based on waves, fields etc.) > Now that I have had a couple of days away from the internet to think about > this, and have read other comments on this thread, I think I understand > better the point that was not clear to me from the COMP(2013) paper. What > your intuition claims to be absurd in the MGA is that replaying the film > can instantiate consciousness. The reason for this is based on your belief > that replaying the film is not a computation, and since the basic > assumption is of comp is that consciousness is Turing emulable -- is in > fact a computation -- we cannot have consciousness without the associated > computation. > Yes. > > The argument is then that if the assumption of physical supervenience > (supervenience of consciousness on a physical brain) leads to a situation > in which consciousness would appear to be supported by something (the film) > which is not a computation, then a contradiction has been reached, and the > idea of physical supervenience must be wrong (if comp is correct). > Yes. > > That makes sense, but I did not previously accept this because my > intuition was not that the projection of the film would not reconstitute > the original conscious moment. The important point that is now clear, is > that you claim that projection the film does not constitute a computation, > so cannot support consciousness. I disagree with this. As Russell has > suggested, projecting the film can very well be considered to be a > computation. > The difference is between any incidental computations required to project a film, and the computations being shown in the film. Do you think showing a computation taking place is equivalent to performing a computation? How about showing the film running a lot faster to show a complex computation that would take, say, an hour, compressed into 1 second. Can the film really perform the computation 3,600 times faster than a computer? How about showing just the input and output - did the computation take place "behnid the scenes" somehow? > > We have to ask what constitutes a computation in the context of this > discussion. The starting point is that part or all of the brain is > replaceable by a computer -- the brain is Turing emulable. So it seems > reasonable to define a computation as a mapping between some input and some > output that is Turing emulable. In other words, one can replace the device > that takes some input to produce some particular output with a general > Turing machine. That mapping from input to output would then be considered > a computation in the terms of the present discussion of the comp thesis. > > Defined in this way, it is clear that projecting the movie film on to the > physical substrate is nothing more than a general computation. The input is > a source of light directed on to the film, and the output is the image > focussed on the screen (or brain substrate). If you like, to use Russell's > terms again, the film is a program that is run through the projector as a > computer. This process is completely emulable by a Turing machine. In fact, > digital projections of moving images are routinely performed on general > purpose digital computers. The film (program) can be stored digitally, and > the light source and screen can also be realized digitally. > OK, that does make sense of sorts. If a computation is a mapping (which ignores Brent's environment objection) then anythnig that does the mapping could be called one. In this case it's also equivalent to a huge lookup table. However I don't see how the film is a general purpose computation - it is at best a specific computation, like a machine designed only to work out one specific result - say adding the numbers 12345 and 67890. A general purpose computation (as mentioned many times) involves counterfactuals - it's capable of handling arbitrary input rather than specific input. > > The claim that the film (and projection) is not a computation is thus > false. It is a computation in exactly the same way that the brain function > replaced by a Turing machine in the "yes doctor" step 0 of the argument is > a computation. That is only true if you assume the film is a general purpose computation, or that the brain isn't. The latter is simply a statement of determinism - nothing the brain (or any general purpose comupter) does is *actually* a general purpose computation, because all they really are is patterns embedded in space-time with a layout that obeys physical laws. (At least, that's true if we leave aside the Copenhagen Interpretation and the MWI. Otherwise we get a more complicated picture, but let's KISS for now.) However if we assume that the film isn't a GPC, or that the brain is, then the above statement isn't true. > So the MGA does not establish the conclusion that "consciousness can no > longer be related to any physical phenomenon whatsoever (i.e., brains in > skulls), nor can any subjective appearance of matter be based on a notion > of primitive matter." > > In fact, the MGA seems to have very little to do directly with the > hypothesis of primitive physicality. The argument appears to be that if > physical supervenience (a different notion than primitive physicality) > leads to a contradiction with the comp hypothesis, then physical > supervenience must be abandoned. Extending this line of thinking, it > appears to be suggested that if physical supervenience is abandoned, there > is no remaining role for primitive physical matter in the understanding of > consciousness. The argument is less clear at this point, but something of > the sort seems to be implied. > Yes. The choice is between consciousness not being a form of computation (Maudlin's interpretation) or consciousness not supervening on physical objects (Bruno's). If one accepts Bruno's interpretation, then the hypothesis that physical objects exist is claimed to have become superfluous, because they have no role in consciousness and all we can ever, actually, know for sure is the fact of our consciousness (as per Descartes' cogito). > > But if the notion of physical supervenience cannot be ruled out, then the > way is open for primitive physicality. The comp argument, which claims that > the appearance of the physical can be extracted from the UD running in > Platonia, has no greater claim to credence than the physicalist's claim > that mathematics is a human invention, extracted from our experience of the > physical world. > The choice is actually between whether a recording can instantiate computation and hence consciousness, or not (assuming, as usual during this discussion, that consciousness exists and is Turing emulable, which I believe means it doesn't contain oracles, hypercomputers, etc). If a recording can instantiate consciousness then physical supervenience, far from failing, is in fact strengthened, in that consciousness can supervene on more things than we imagined it could. > > The choice between these might reduce to nothing more than personal > preference. Yes, although ISTM that a recording doesn't perform a general-purpose computation, but only - at most - a specific one. But given determinism, I'm not sure whether that matters or not. -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
