On 28 Dec 2011, at 06:28, Joseph Knight wrote:

On Mon, Dec 26, 2011 at 3:44 AM, Bruno Marchal <marc...@ulb.ac.be> wrote:

On 26 Dec 2011, at 05:47, Joseph Knight wrote:

On Sat, Dec 24, 2011 at 9:05 AM, Bruno Marchal <marc...@ulb.ac.be> wrote:

On 23 Dec 2011, at 20:16, Joseph Knight wrote:

The same problem arises in Part 2. Bruno claims that we are forced to accept that Alice’s consciousness supervenes on the film.

No. On the projection of the pellicle on the Boolean graph, and then on the Boolean graph missing part. The idea is that we built again the right physical activity, with the projection of the film playing the role of the cosmic rays.

What is a pellicle? (Sorry) I understand this part, however. My objections arise later.

A film. (But in french "film" is for cinema (movie?)).

OK, there was no confusion.


but (film + optical graph) is certainly changed, and Alice’s dream turns out differently (if it occurs at all).

With comp + sup-phys, it can't.

Why? If we assume sup+phys, then some changes in the physical system on which the dream supervenes certainly will lead to changes in the dream.

I don't think so. Remember that we suppose comp (and sup-phys). So we already agree that we can change the physical implementation if it runs the computation at the correct level. So, we can change the physical implementation as we wish, below the substitution level without changing the first person private consciousness.

I think I wasn't clear here. I didn't mean changes in the particular physical system consciousness is supervening on -- of course by comp that doesn't matter. I meant that, assuming sup-phys on physical system X, there must exist some changes in X which lead to changes in consciousness.


Bruno isolates the film and thus reaches his apparent contradictions. But this is not a permissible move.

I think that the term "film" could have different meaning in french and english. But the film here means the projection of the pellicle on the glass/crystal medium. This one is never broken. It is a process which takes time, and occur in some place.

Not only is the definition of supervenience violated, but his principle of irrelevant subparts is violated as well – for the optical graph is not irrelevant for the execution of Alice’s consciousness.

Of course, but once we put away the nodes, the physical activity corresponding to the computation are not changed. The optical graph becomes irrelevant for the physical activity on which Alice's consciousness is supposed to supervene, by comp+sup-phys.

This is where my problem lies. Of course the physical activity of the system is changed when you (invalidly) remove the optical graph from the system. It is far from irrelevant. For example, what mechanism causes the light to triggers the lasers? There must be some "internal" mechanisms at work as well. The nodes aren't "connected" to one another, but it matters whether or not the recording is being projected on an optical graph, vs. a concrete wall, vs. movie screen....

Why? The relevant physical activity is the same.
Obviously I agree with you (the projection of the film does not instantiate consciousness). The point is that if comp and sup-phys are maintained, and if 323 is correct, then there is nothing different from projecting the film on the glass crystal with the boolean laser graph removed and a wall.

I have no problem with 323. My argument is that consciousness never supervenes on the film/movie/recording.

I agree with that. If only because there are no more any computation done "in time and space" (the original abstract computation does not disappear, of course, so with comp, we will have to attach consciousness to it, and not to its particular "concrete implementation".

So there is something different between projecting the film on the glass crystal, and the wall. The relevant physical activity, in the two cases (glass/crystal vs wall), is not the same. In the first case (and not the second) the light interacts with the crystal medium and triggers the lasers. How can you argue that this interaction is irrelevant and can be removed?

Because that special activity has nothing to do with the original computation. If it were, I could not have said yes to the doctor at the start. Once the boolean graph is remove, we just get a special weird screen. And the absurdity is still there: there are no computation done when we project on that weird sort of screen.

You can still say yes to the doctor. But that activity does have something to do with the computation. Suppose the film were projected upside down, or equivalently that the boolean graph were turned upside down (no change in the physical state of the film). Unless we assume some incredible symmetry in the layout of the graph (contradicting comp), there would most certainly be a change in computation!

Which computation? I don't see any computation in the projection of the computation-movie. The Boolean graph nodes are broken. The light patterns is exactly the same, with the boolean graph turned, or not, upside down. You argument seems to rely on non relevant (with respect to the possible computation) idiosyncracies of this thought experience implementation. I will think about a version of MGA making this more obvious.

It does matter for the computation what the light lands on.

But what is the computation in this case?

This doesn't violate 323, or comp. It means that the whole system (crystal/glass+film) must be taken into account in your analysis.

The whole system is considered, and then changed in a way which does not change the physical activity, except for operating nodes which are retreived, and this to show that the physical activity does not implement the computation, but is only a mimicking of non relevant appearances associated accidentally with the "original computation".

It is no better than taking half of the brain and ignoring the other half. It isn't a matter of substitution level.

OK. But you have to explain me the role of the broken node, in the computation, or even in the light patterns. You might try, as an exercise to refute your own argument by changing the original device.

Let me restate my concern: Consciousness supervenes on the optical graph+the recording, even when the nodes are completely disconnected. It is true that "most of the work" is being done by the recording, but not all of the work. The optical graph still matters, and the "physical activity" of the system is not solely provided by the recording, as it still depends on how the projected light interacts (physically) with the glass/crystal surface.

But this is no more relevant in term of the computation, which is supposed to be a copy of the brain processing at the right level or below.

There is a point in the argument at which you ignore the glass/ crystal system and focus solely on the movie/recording, claiming that Alice's consciousness supervenes on the movie/recording. But this is false. At no point does Alice's consciousness supervene on the recording, not even when the nodes are completely disconnected.

Yes. That's why it is a reductio ad absurdum.

Its a reductio ad absurdum only if you artificially ignore the interaction between the projected light and the crystal medium and lasers. Because consciousness supervenes on crystal/glass/nodes +film, it is not meaningful to make this move.

What is removed does not change the light pattern. The nodes are broken and play no role in that computation, in case we could find one (as opposed to find just a description of a computation, for which the nodes are also irrelevant).

Consciousness changes do not imply film changes (even though the converse may well be true). You have isolated a subsystem from the machine, mistaken this subsystem for being sufficient for consciousness to supervene on -- little wonder an absurd conclusion follows!

I could because all this is supposed to be done below the substitution level.

I understand that, but I don't understand how it addresses my point.

If the boolean graph is no more working, to insist we don't remove the nodes gives them a special role not accounted in original computation, which can be said to exist (relatively to us) by the fact the nodes did operate the relevant elementary computable steps defining the (relative) implementation of the computation. The role you give to the node, for making the projection conscious seems magical and unrelated to the original computation.

I am trying to think of an analogy to another system which would make my argument clearer (and in the process learning how tricky the concept of supervenience can be).

Actually, I do the same. I search a system where I can make it clearer why the idiosyncrasies of the movie-graph are simpler to evacuate. But in the present case, it seems rather obvious to me that the absurdity is already there, before replacing the glass+smoke by a usual screen. There is already no more computations, we can already use the stroboscopic argument to make that absurd.

I am not familiar with the stroboscopic argument.

It is an argument used to show (if that was necessary) that a movie of a computation is not a computation, nor even a well defined physical reality. Instead of moving the film behind a lamp, we move the (stroboscopic) lamps and the observer along the film. Then the existence of a movie is shown to be relative to an observer, making the idea that a consciousness supervene on the movie non sensical. I think this should work also with the situation where the broken nodes are not removed. Such an argument avoid some special tailored critics based on that type of thought experiment, like the heap sand critics (which by itself leads to the absurd notion of partial zombie, which some materialist accepts, but just as way to avoid the consequence of comp). Anyway, the stroboscopic argument shows that a projection of a movie is not even a well defined physical events, as needed for a primitive supervenience thesis.




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Joseph Knight

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