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Next: Objection 7 Up: Dialectic Previous: Objection 5

Objection 6

The next objection marks a return to physics: ``You assume that all physical processes are irreversible. But they are not. In fact, under certain conditions, namely those where the system is allowed to move from state A to state B in such fashion as to always be arbitrarily close to thermodynamic equilibrium, it's possible to execute a reversed process. All we have to do is avoid generating or allowing the system to generate an entropy increase which is transferred to the environment and is thus not retrievable. One way to do this is to proceed very slowly so as to not generate heat, in other words, we execute an adiabatic process."

This objection flies in the face of what we said above in Objection 2 regarding Max and ballistic computers, which are designed to capitalize on such tricks as adiabatic processes.gif But let's suppose for the sake of argument that the barriers to real, physical irreversibility described in connection with Max and ballistic computers can somehow be surmounted. Under this charitable supposition, how does the present objection fare? Not well; here's why.

Again, let's suppose for the sake of argument that an automaton can be made reversible at every step in the real physical world, and that this allows not only an in-principle thermodynamically reversible automaton, but a ``real world" one: a concrete one that saves all intermediate results, avoids irreversible erasure, prints the desired output and reversibly disposes of all undesired intermediate results as it retraces the machine's configurations in reverse order. To accomplish this, in keeping with the ideas behind ballistic computers, the automaton must be kept or keep itself arbitrarily close to thermodynamic equilibrium. For erasure to be thermodynamically reversible, the initial ensemble of memories must be distributed equally among possible states of phase space. Let's call such a process r.w.i, for ``real-world irreversible." . Now, given that consciousness isn't currently associated with r.w.i. processes, why isn't the objection a complete non-starter? The answer must be that somehow -- at least in the realm of thought and thought-experiment -- the processes associated with consciousness can, at least in principle, become r.w.i. But notice that since the objective of our opponent is to show that reversing consciousness is doable, if the present objection is to have a chance of succeeding, it must assert not only that the neurological processes in question can become r.w.i, but also that they could become r.w.i. without thereby preventing the rise of the consciousness with which they are connected. And so a natural question arises: Is there any reason to think that the speed at which neurological processes unfold can be inseparably bound up with the consciousness they underlie? Indeed there is, as we now proceed to explain.

Suppose that Sandra enjoys a stretch of consciousness from tex2html_wrap_inline1149 to tex2html_wrap_inline1197 which centers around an appreciation of her own brain activity during this time. (In order to make it easy to envisage the situation, imagine that Sandra's doctors are concerned that she might have a brain tumor, and hence submit her to various brain scanning technologies.) Suppose, in addition, that she not only observes her brain activity during this time, but that she apprehends the speed at which these neurological processes proceed. (To make the scenario vivid, you might think of her watching a PET scan as a digital readout ticks off the scan's duration.) It's impossible, ex hypothesi, that Sandra's brain processes through tex2html_wrap_inline1391 be ``r.w.i.-slowed" without destroying the consciousness with which they are associated in the ``normal speed" mode. The problem, specifically, is that if `Bob' is replaced with `Sandra' in the Argument From Irreversibility (see the ``double-boxed" version of the argument given above), the present objection is impotent.gif

Generally speaking, could a mind/brain ever meet r.w.i. conditions or their equivalents? In particular, could the mind/brain be kept at or near equilibrium so that a mentation could be reversed? Given that the firing of a single neuron is decidedly not an adiabatic process, and given that a mind/brain at or near equilibrium is a dead brain (or, at best, a ``blank" mind), we are compelled to conclude that cognition cannot be reversed because the initial conditions required for reversal cannot be met. It seems very unlikely that the physical processes of the central nervous system which sustain P-consciousness can be adequately modeled even by the most sophisticated ballistic computer (Brownian computer, etc.).

In sum, the difference between computation and cognition is this: Computation is logically reversible à la Theorem 1. And computation can be modeled by devices (e.g., the ballistic computer) which approximate r.w.i. processes. Cognition, however, including as it does P-consciousness, is phenomenologically, experientially, and conceptually irreversible, and cannot be modeled by devices which approximate physical reversibility.


next up previous
Next: Objection 7 Up: Dialectic Previous: Objection 5

Selmer Bringsjord
Fri Sep 6 11:58:56 EDT 1996