The Puzzle of Conscious
Experience (Pt 2)
by David J. Chalmers
A True Theory of Everything
In searching for an alternative, a key observation is that not all entities in science are explained in terms of more basic entities. In physics, for example, space-time, mass and charge (among other things) are regarded as fundamental features of the world, as they are not reducible to anything simpler. Despite this irreducibility, detailed and useful theories relate these entities to one another in terms of fundamental laws.
Together these features and laws explain a great variety of complex and subtle phenomena.
It is widely believed that physics provides a complete catalogue of the universe's fundamental features and laws. As physicist Steven Weinberg puts it in his 1992 book Dreams of a Final Theory, the goal of physics is a "theory of everything" from which all there is to know about the universe can be derived. But Weinberg concedes that there is a problem with consciousness. Despite the power of physical theory, the existence of consciousness does not seem to be derivable from physical laws. He defends physics by arguing that it might eventually explain what he calls the objective correlates of consciousness (that is, the neural correlates), but of course to do this is not to explain consciousness itself. If the existence of consciousness cannot be derived from physical laws, a theory of physics is not a true theory of everything. So a final theory must contain an additional fundamental component.
Toward this end, I propose that conscious experience be considered a fundamental feature, irreducible to anything more basic. The idea may seem strange at first, but consistency seems to demand it. In the 19th century it turned out that electromagnetic phenomena could not be explained in terms of previously known principles. As a consequence, scientists introduced electromagnetic charge as a new fundamental entity and studied the associated fundamental laws. Similar reasoning should apply to consciousness. If existing fundamental theories cannot encompass it, then something new is required.
Where there is a fundamental property, there are fundamental laws. In this case, the laws must relate experience to elements of physical theory. These laws will almost certainly not interfere with those of the physical world it seems that the latter form a closed system in their own right. Rather the laws will serve as a bridge, specifying how experience depends on underlying physical processes. It is this bridge that will cross the explanatory gap.
Thus, a complete theory will have two components: physical laws, telling us about the behaviour of physical systems from the infinitesimal to the cosmological, and what we might call psychophysical laws, telling us how some of those systems are associated with conscious experience. These two components will constitute a true theory of everything.
Searching for a Theory
Supposing for the moment that they exist, how might we uncover such psychophysical laws? The greatest hindrance in this pursuit will be a lack of data. As I have described it, consciousness is subjective, so there is no direct way to monitor it in others. But this difficulty is an obstacle, not a dead end. For a start, each one of us has access to our own experiences, a rich trove that can be used to formulate theories. We can also plausibly rely on indirect information, such as subjects' descriptions of their experiences. Philosophical arguments and thought experiments also have a role to play. Such methods have limitations, but they give us more than enough to get started.
These theories will not be conclusively testable, so they will inevitably be more speculative than those of more conventional scientific disciplines. Nevertheless, there is no reason they should not be strongly constrained to account accurately for our own first-person experiences, as well as the evidence from subjects' reports. If we find a theory that fits the data better than any other theory of equal simplicity, we will have good reason to accept it. Right now we do not have even a single theory that fits the data, so worries about testability are premature.
We might start by looking for high-level bridging laws, connecting physical processes to experience at an everyday level. The basic contour of such a law might be gleaned from the observation that when we are conscious of something, we are generally able to act on it and speak about it - which are objective, physical functions. Conversely, when some information is directly available for action and speech, it is generally conscious. Thus, consciousness correlates well with what we might call "awareness": the process by which information in the brain is made globally available to motor processes such as speech and bodily action.
The notion may seem trivial. But as defined here, awareness is objective and physical, whereas consciousness is not. Some refinements to the definition of awareness are needed, in order to extend the concept to animals and infants, which cannot speak. But at least in familiar cases, it is possible to see the rough outlines of a psychophysical law: where there is awareness, there is consciousness, and vice versa.
To take this line of reasoning a step further, consider the structure present in the conscious experience. The experience of a field of vision, for example, is a constantly changing mosaic of colours, shapes and patterns and as such has a detailed geometric structure. The fact that we can describe this structure, reach out in the direction of many of its components and perform other actions that depend on it suggests that the structure corresponds directly to that of the information made available in the brain through the neural processes of awareness.
Similarly, our experiences of colour have an intrinsic three-dimensional structure that is mirrored in the structure of information processes in the brain's visual cortex. This structure is illustrated in the colour wheels and charts used by artists. Colours are arranged in a systematic pattern - red to green on one axis, blue to yellow on another, and black to white on a third. Colours that are close to one another on a colour wheel are experienced as similar. It is extremely likely that they also correspond to similar perceptual representations in the brain, as part of a system of complex three-dimensional coding among neurons that is not yet fully understood. We can recast the underlying concept as a principle of structural coherence: the structure of conscious experience is mirrored by the structure of information in awareness, and vice versa.
Another candidate for a psychophysical law is a principle of organisational invariance. It holds that physical systems with the same abstract organisation will give rise to the same kind of conscious experience, no matter what they are made of. For example, if the precise interactions between our neurons could be duplicated with silicon chips, the same conscious experience would arise. The idea is somewhat controversial, but I believe it is strongly supported by thought experiments describing the gradual replacement of neurons by silicon chips. The remarkable implication is that consciousness might someday be achieved in machines.
|Information: Physical and Experiential
The ultimate goal of a theory of consciousness is a simple and elegant set of fundamental laws, analogous to the fundamental laws of physics. The principles described above are unlikely to be fundamental, however. Rather they seem to be high-level psychophysical laws, analogous to macroscopic principles in physics such as those of thermodynamics or kinematics. What might the underlying fundamental laws be? No one knows, but I don't mind speculating.
I suggest that the primary psychophysical laws may centrally involve the concept of information. The abstract notion of information, as put forward in the 1940s by Claude E. Shannon of the Massachusetts Institute of Technology, is that of a set of separate states with a basic structure of similarities and differences between them. We can think of a 10-bit binary code as an information state, for example. Such information states can be embodied in the physical world. This happens whenever they correspond to physical states (voltages, say), the differences between which can be transmitted along some pathway, such as a telephone line.
We can also find information embodied in conscious experience. The pattern of colour patches in a visual field, for example, can be seen as analogous to that of the pixels covering a display screen. Intriguingly, it turns out that we find the same information states embedded in conscious experience and in underlying physical processes in the brain. The three-dimensional encoding of colour spaces, for example, suggests that the information state in a colour experience corresponds directly to an information state in the brain. We might even regard the two states as distinct aspects of a single information state, which is simultaneously embodied in both physical processing and conscious experience.
A natural hypothesis ensues. Perhaps information, or at least some information, has two basic aspects: a physical one and an experiential one. This hypothesis has the status of a fundamental principle that might underlie the relation between physical processes and experience. Wherever we find conscious experience, it exists as one aspect of an information state, the other aspect of which is embedded in a physical process in the brain. This proposal needs to be fleshed out to make a satisfying theory. But it fits nicely with the principles mentioned earlier - systems with the same organisation will embody the same information, for example - and it could explain numerous features of our conscious experience.
The idea is at least compatible with several others, such as physicist John A. Wheeler's suggestion that information is fundamental to the physics of the universe. The laws of physics might ultimately be cast in informational terms, in which case we would have a satisfying congruence between the constructs in both physical and psychophysical laws. It may even be that a theory of physics and a theory of consciousness could eventually be consolidated into a single grander theory of information.
A potential problem is posed by the ubiquity of information. Even a thermostat embodies some information, for example, but is it conscious? There are at least two possible responses. First, we could constrain the fundamental laws so that only some information has an experiential aspect, perhaps depending on how it is physically processed. Second, we might bite the bullet and allow that all information has an experiential aspect - where there is complex information processing, there is complex experience, and where there is simple information processing, there is simple experience. If this is so, then even a thermostat might have experiences, although they would be much simpler than even a basic colour experience, and there would certainly be no accompanying emotions or thoughts. This seems odd at first, but if experience is truly fundamental, we might expect it to be widespread. In any case, the choice between these alternatives should depend on which can be integrated into the most powerful theory.
Of course, such ideas may be all wrong. On the other hand, they might evolve into a more powerful proposal that predicts the precise structure of our conscious experience from physical processes in our brains. If this project succeeds, we will have good reason to accept the theory. If it fails, other avenues will be pursued, and alternative fundamental theories may be developed. In this way, we may one day resolve the greatest mystery of the mind.
Dancing Qualia in a Synthetic Brain
Whether consciousness could arise in a complex, synthetic system is a question many people find intrinsically fascinating. Although it may be decades or even centuries before such a system is built, a simple thought experiment offers strong evidence that an artificial brain, if organised appropriately, would indeed have precisely the same kind of conscious experiences as a human being.
Consider a silicon-based system in which the chips are organised and function in the same way as the neurons in your brain. That is, each chip in the silicon system does exactly what its natural analogue does and is interconnected to surrounding elements in precisely the same way. Thus, the behaviour exhibited by the artificial system will be exactly the same as yours. The crucial question is: Will it be conscious in the same way that you are?
Let us assume, for the purpose of argument, that it would not be. (Here we use a reasoning technique known as reductio ad absurdum, in which the opposite hypothesis is assumed and then shown to lead to an untenable conclusion.) That is, it either has different experiences - an experience of blue, say, when you are seeing red - or no experience at all. We will consider the first case the reasoning proceeds similarly in both cases.
Because chips and neurons have the same function, they are interchangeable, with the proper interfacing. Chips therefore can replace neurons, producing a continuum of cases in which a successively larger proportion of neurons are replaced by chips. Along this continuum, the conscious experience of the system will also change. For example, we might replace all the neurons in your visual cortex with an identically organised version made of silicon. The resulting brain, with an artificial visual cortex, will have a different conscious experience from the original: where you had previously seen red, you may now experience purple (or perhaps a faded pink, in the case where the wholly silicon system has no experience at all).
Both visual cortices are then attached to your brain, through a two-position switch. With the switch in one mode, you use the natural visual cortex in the other, the artificial cor tex is activated. When the switch is flipped, your experience changes from red to purple, or vice versa. When the switch is flipped repeatedly, your experiences 'dance' between the two different conscious states (red and purple), known as qualia.
Because your brain's organisation has not changed, however, there can be no behavioural change when the switch is thrown. Therefore, when asked about what you are seeing, you will say that nothing has changed. You will hold that you are seeing red and have seen nothing but red, even though the two colours are dancing before your eyes. This conclusion is so unreasonable that it is best taken as a reductio ad absurdum of the original assumption-that an artificial system with identical organisation and functioning has a different conscious experience from that of a neural brain. Retraction of the assumption establishes the opposite: that systems with the same organisation have the same conscious experience.