Hello everyone and everything,

I have pompously made my own thread for this, even though we have another
MGA thread going, because the other one (sigh, I created that one too)
seems to have split into at least two different discussions, both of which
are largely different from what I have to say, so I want to avoid confusion.

Here, I will explain why I believe the Movie Graph Argument (MGA) is
invalid. I will start with an exegesis of my understanding of the MGA, so
that Bruno or others can point out if I have failed to understand some
important aspect of the argument. Then I will explain what is wrong. I
believe confusion regarding the concept of supervenience has been
responsible for some invalid reasoning. (At the end I will also explain why
I find Maudlin’s thought experiment to be inconclusive.)

As it is explained
the MGA consists of three parts. Throughout the argument we are assuming
comp and materialism to be true.

*The MGA*


In *Part 1*, Bruno asks us to consider Alice. Alice is a conscious being.
Alice already has an artificial brain, to make the reasoning easier. We are
assuming here (with no loss of generality) that, under normal
circumstances, Alice’s consciousness supervenes on this artificial brain.
Alice is taking a math exam, when at a certain moment one of the logic
gates A fails to signal logic gate B. At this precise moment, however, a
particle arrives from some far-away cosmic explosion and triggers gate B
anyway. Assuming comp we (pretty safely) conclude that Alice’s
consciousness is unaffected by this change in causation – after all, the
computation has been performed.    Moreover, we can assume any number –
thousands, say – of such failures in Alice’s brain, with lucky cosmic rays
arriving to save the day. Indeed, *all *of Alice’s neurons could be
disabled, with cosmic rays triggering each one in just the right way so as
to maintain her consciousness. Bruno (wisely, in my opinion) likes to end
the steps of his argument with questions. At the end of MGA 1, he asks, is
Alice a zombie during the exam? We are really forced to say that she isn’t,
because of our comp assumption. So Alice is just as conscious as she was
before her brain started short-circuiting.

In *Part 2*,* *we build on the ideas of part 1 but without cosmic rays.
Bruno assumes for the sake of argument, again with no loss of generality,
that Alice is dreaming and that her brain has no inputs or outputs. Now,
Alice’s (artificial) brain is a 3D Boolean graph (network being the more
common term), which, with a few wiring changes, can be deformed into a 2D
Boolean graph and thus laid out on a plane. Next Bruno asks us to imagine
us instantiating Alice’s 2D graph-brain as a system of laser beams
connecting nodes (instead of wires, and with destructive interference
helping out with NOR, etc.), all in some special material. The graph is
placed between two glass plates, and a special crystalline material is
sandwiched between the plates which has the property that if a beam of
light connects two nodes, the “right” laser is triggered to signal the
right node at that location. (Unlikely, but conceivable and valid, which is
all we intrepid philosophers need anyway!)

So Alice is dreaming (conscious), with her dream supervening on the 2D
optical graph, and with no malfunctions. Suppose we film these computations
with a video camera. Now suppose Alice begins to dream the same dream again
but after a while, Alice’s 2D graph begins making mistakes, i.e. not
sending signals where signals should be sent. But if we, in all our
humanitarian goodwill, project the (perfectly aligned) film onto the
optical material/graph, we can preserve Alice’s consciousness completely.
If it worked with the cosmic rays from part 1, it works here too, by comp.
Alice remains conscious.

Finally, in *Part 3*, we reach some apparent contradictions. Bruno
introduces a (safe) principle at the beginning, namely that if some part of
a system is not used for the functioning of that system in some given task,
then it can be removed and still complete that task. If Alice doesn’t use
neuron X to complete her math exam, we can remove neuron X during the exam
and she will perform the same way. I will call this the principle of
irrelevant subsystems.

So, back to Alice and the filmed 2D optical graph. We are apparently
forced, at this point, to conclude that Alice’s consciousness supervenes on
the projection of the movie. In Bruno’s words:

Is it necessary that someone look at that movie? Certainly not. No more
than it is needed that someone is look at your reconstitution in Moscow for
you to be conscious in Moscow after a teleportation. All right? (with MEC
[comp] assumed of course). Is it necessary to have a screen? Well, the
range of activity here is just one dynamical description of one
computation. Suppose we make a hole in the screen. What goes in and out of
that hole is exactly the same, with the hole and without the hole. For that
unique activity, the hole in the screen is functionally equivalent to the
subgraph which the hole removed. Clearly we can make a hole as large as the
screen, so no need for a screen. But this reasoning goes through if we make
the hole in the film itself. Reconsider the image on the screen: with a
hole in the film itself, you get a "hole" in the movie, but everything
which enters and go out of the hole remains the same, for that (unique)
range of activity.  The "hole" has trivially the same functionality than
the subgraph functionality whose special behavior was described by the
film. And this is true for any subparts, so we can remove the entire film

In short, we are forced to accept that Alice’s consciousness supervenes on
a vacuum. Of course, we don’t really have to go this far, because already
we have Alice’s consciousness supervening on a film which performs no
meaningful computations, i.e., is “inert” – an absurdity. There are several
other ways of stating this part of the argument, none of which changes the
result, and if anyone is confused I recommend reading the links above. But
otherwise this concludes the MGA. It has apparently been shown that there
is a contradiction between computationalism and materialism.

*The Problem*


I said initially that my concern was with the treatment of the
supervenience concept. This term is often thrown around on the Everything
list. It is an important concept. What is supervenience? If system X
supervenes on system Y, then there cannot be a change in X without a change
in Y. Note that there can be a change in Y without a change in X. In other
words, IF change in X, THEN change in Y. (Supervenience is silent on issues
of entailment/causation, etc.)

Bruno’s (and Maudlin’s, for that matter) argument hinges on the issue of
supervenience, specifically: on what does consciousness supervene? If it
can be shown that, assuming computationalism and materialism, that
consciousness supervenes on a vacuum, or on a “causally inert” object, then
we have shown something important. But it matters how we get there.

In *Part 1*, when the neurons (nodes) in Alice’s brain are all
malfunctioning, she is saved by the cosmic rays. The rays trigger the
neurons precisely when and where they must be in order to instantiate
Alice’s consciousness. But Alice’s consciousness *does not* supervene on
the cosmic rays. Nor does her consciousness supervene on her damaged brain.
Her consciousness supervenes on the system (brain + cosmic rays). There *can
*be a change in consciousness without a change in the cosmic ray pattern:
Alice’s consciousness might change, say, if a neuron (node) from the brain
is removed, preventing the corresponding cosmic ray from triggering it and
leading to an alteration in her consciousness. Likewise, there *can *be a
change in consciousness without a change in her (damaged) brain, say, if
the cosmic shower had occurred in a slightly different way.

Bruno’s argument is a conflation of necessary and sufficient conditions, as
well as a conflation of supervenience and entailment. The cosmic rays are
necessary to execute Alice’s consciousness, but not sufficient. It would be
an invalid move to remove her brain (however faulty it may be) and focus
exclusively on the cosmic particles as a cause of her consciousness. By
this fallacious reasoning, we might conclude that because the left
hemisphere of someone’s brain is necessary for their consciousness, it is
also sufficient. It is the confusion of “IF change in (relevant) cosmic
rays, THEN change in consciousness” with “IF change in consciousness, THEN
change in (relevant) cosmic rays”.

The same problem arises in *Part 2*. Bruno claims that we are forced to
accept that Alice’s consciousness supervenes on the film. But this is not
correct – Alice’s consciousness supervenes on (film + optical graph), for
the same reasons as above. There *can *be a change in consciousness without
a change in the film: suppose I destroy a portion of the glass/crystal
medium, hence some of the nodes in the graph. The film is unchanged, but
(film + optical graph) is certainly changed, and Alice’s dream turns out
differently (if it occurs at all).

Bruno isolates the film and thus reaches his apparent contradictions. But
this is not a permissible move. 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. We certainly cannot remove it and expect Alice to remain
conscious, any more than we can remove the artificial brain of *Part 1 *and
expect Alice to pass her exam – in both cases, we are left merely with an
interesting light show. In conclusion, we are *not *forced to conclude that
Alice’s consciousness supervenes on a vacuum, or on an inert film reel.

Please discuss, and tell me if I myself have made any errors.

Regarding Maudlin’s argument: Russell has recently stated that Maudlin’s
argument doesn’t work in a multiverse, and that consciousness is thus a
multiverse phenomenon. I disagree for the same reason that Bruno disagrees:
the region of the multiverse on which consciousness supervenes can just be
Turing emulated in a huge water/trough/block computer, and Maudlin’s
argument can be reapplied. I realize that this could lead to an infinite

The real reason I don’t find Tim Maudlin’s argument convincing is largely
due to recent comments made by Brent. It is not patently absurd that a
constant program/algorithm cannot be conscious – it is for intelligence,
however. For all I know, this has not been decided either way. Maybe in the
future a “consciousness theorem” will decide the matter one way or another,
but until then I don’t think that Maudlin has demonstrated a contradiction,
just an irritating fact. (It seems to me, and is worth noting, that if the
principle of irrelevant subparts is true, then we are forced to conclude
that a constant program/algorithm can be conscious, rendering Maudlin’s
paradox, well, not a paradox.) Intelligence is tricky, as it has the notion
of counterfactual bound up within its definition. But there is no *a priori
*reason to assume this to be the case for consciousness.

Joseph Knight

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