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In the 1990s, a lot of people had high hopes for a quantum-based explanation of consciousness. But it was never really good science, was it? Here is first an article and then a more detailed book chapter for those interested in this historical curiosity.

David Chalmers, a philospher from Washington University, jokingly calls it the law for the minimisation of mysteries. 'Consciousness is a mystery, quantum mechanics is a mystery. When you have two mysteries, well maybe there is really only one. Perhaps they are the same thing.'

That the answer to consciousness might be found in the strange world of the quantum is a suggestion that dates back at least as far as the musings of physicist, David Bohm, in his 1951 book, Quantum Theory. In the past few years, however, such speculation has taken on a new urgency. What else, ask a host of thinkers, including Roger Penrose, the Oxford mathematician famed for his work on the geometry of tiling patterns and black holes, could explain aspects of the mind such as free will, intuition, creativity and the subjective unity of experience?

In the odd world of the quantum, things appear to exist in a multitude of states - describable only as the set of probabilities known as a wave function - until tipped into a definite outcome by an act of 'measurement'. An electron or atom (and some would even argue the whole Universe) remains an open field of possibilities until forced into an interaction. It is as if the physical world wants to explore many alternative pathways before collapsing into a settled state. For the champions of quantum consciousness, this seems to be just what the creative human mind does: sample many paths and outcomes before its 'wave function' collapses into the coherent state which is our logical stream of thought. The difficulty for quantum theorists has been that while they may have found the parallels attractive, their ideas lacked an experimental basis and also went against common sense.

Most neuroscientists and philosophers of mind now believe that consciousness will be explained by the neural connectionist hypothesis. This sees the mind as the outcome of patterns of impulses dancing across the synaptic connections that make up the neural circuits of the brain; a tangled web of information rather than a special field or unknown force.

What gives the connectionists confidence is that any interference with the functioning of the brain's 50 billion nerve cells - whether from strokes, drugs, the surgeon's knife or merely sleep - tends to alter subjective experience in a rather definite way. In other words, breaking or altering connections can produce predictable effects on behaviour. By contrast, there seems to be no obvious way that quantum effects could play any part in brain activity.

'The scale's all wrong. How can something that occurs at the subatomic level influence events at the macroscopic level of the cell, where we already know something is happening?' asks John Taylor, a physicist from King's College London who is pursuing a connectionist model of consciousness. Taylor says that in the hot, sticky world of the brain, any fleeting quantum events that might carry information would be drowned out in the hubbub of background thermal noise. While neural networks are known to be robust to such noise, a quantum-based 'mind design' seems to demand a degree of biochemical precision that is utterly at odds with messy organic systems.

Such views led many to instantly dismiss the rash of quantum speculation that arose in 1989, largely in the wake of popularising books by Penrose and also Michael Lockwood of the University of Oxford and author Danah Zohar. Indeed, for a couple of years the field went relatively quiet. But this year the bandwagon has started to roll again. Penrose has written a sequel to the Emperor's New Mind called Shadows of the Mind, which extends his ideas and is due out this autumn. But supporters of a quantum explanation claim that they have a site where quantum effects may be taking place

In the past, quantum enthusiasts could be accused of merely lumping together two unfathomable mysteries. What they needed was a plausible mechanism through which quantum-level phenomena could have an effect on higher-level brain activity. Earlier this year, at a conference on the mind at the University of Arizona at Tucson, quantum enthusiasts argued that they had discovered their missing link - cell structures called microtubules.

Judging from the dismissive responses of other delegates, the enthusiasts still have a long way to go if they are to make any converts. The quantum theorists, said Taylor, were guilty of piling speculation upon speculation. Here, we look at some of their ideas and examine why they are so reviled.

Microtubules are the lattice of protein rods which fill every cell in the body, creating an inner scaffolding or cytoskeleton. Each microtubule is a hollow cylinder, 25 nanometres across, built from 13 strands of the protein tubulin. Microtubules are a common building material in the cell and clusters often form larger structures such as the beating cilia that cover the surface of some cells or the centrioles which organise cell division.

Before microtubules were discovered in the 1970s (previously, the fixatives used in electron microscopy had been dissolving them), biologists tended to think of cells as watery bags with a few organelles slopping about in a soup of enzymes. But it is now clear that cells have a well-organised skeleton made out of microtubules. This cytoskeleton not only gives cells a shape, it also appears to play a key role in the circulation of proteins and plasma products. Each microtubule sprouts a coating of thread-like microtubule associated proteins (MAPs) which some researchers believe form contractile spurs that drag plasma along, 'hand over hand', in a miniature bucket brigade.

Cell biologists feel they have only just begun to scratch the surface of the part played by microtubules. Yet quantum theorists have been quick to seize upon them as structures of exactly the right scale to act as amplifiers of submolecular quantum effects. A number of speakers at the Arizona conference shared the conviction that microtubules might form the ultimate substrate for consciousness - although their actual theories varied wildly. These ranged from the idea that microtubules might generate a coherent electromagnetic field which structures the water trapped inside each protein cylinder to the possibility that microtubules act as waveguides to photons - and so form a tiny optical computer inside each cell.

The person most responsible for this flurry of speculation about microtubules is Stuart Hameroff, an anaesthesiologist at the University of Arizona who has toyed with at least half a dozen variations of the story. Hameroff says regardless of whether microtubules prove to be harnessing quantum effects, he is convinced they must play some part in any final explanation of consciousness.

He points out that even single-cell animals such as the slipper-shaped paramecium have primitive sensory and learning capabilities. With practice, paramecia can learn to back more quickly out of narrow glass tubes. Hameroff says other experiments suggest they can even learn paths through simple mazes. Yet paramecia have no synapses or brains. Something - Hameroff believes microtubules - must be organising their behaviour.

One idea that Hameroff has developed with colleagues, including Steen Rasmussen of the Los Alamos National Laboratory, is that the surface of microtubules could ripple to act as a cellular automata computer. A cellular automata is a grid of cells where each cell switches its neighbour on or off to create complex - and self-organising - patterns of activity.Hameroff says that each protein molecule making up the strands of a microtubule wall is a C-shaped building block. He believes these blocks can vibrate rapidly, in the order of a nanosecond, and if coordinated, this contraction and expansion could send a meaningful flow of information down the flanks of each microtubule. So within each neuron - indeed, within every cell - there might be a miniature connectionist network carrying out its own level of information processing.

The cellular automata theory originally seemed to have no need for a quantum dimension. But a big problem was that some sort of time- keeping clock or long-range force was necessary to keep all the protein shape changes in step, otherwise any patterns would quickly be washed away. After a few oscillations, the patterns would degenerate into randomness.

Rather than giving up on what looked to be a rather implausible line of speculation, this difficulty led Hameroff to the controversial work of Herbert Frohlich, a physicist at the University of Liverpool. In the 1970s, Frohlich suggested that what drives the vibration of a protein molecule could be an internal oscillating dipole. That is, strategically placed at the hinge point of a large molecule might be a single trapped electron or region of electrostatic charge.

When this trapped charge made a quantum flip-flop shift of position - a quantum leap across the barrier of the hinge to a point on the other side - it might be enough to throw the whole protein into a different shape. Frohlich went further and proposed that cell membranes might create a situation where a whole series of such delicately poised dipoles lined up - like compass needles in a magnetic field - leading to a quantum coherent state on the macroscale.Such long-range alignment, producing a single quantum system covered by the same wave function equation, is well known to physics from phenomena such as lasers and superconductivity.

But most scientists dismiss the idea that the same kind of coherence can be achieved in the hot, messy realm of organic chemistry. Undeterred by what seems to be a common-sense argument, Hameroff claims that microtubules might just have the right dimensions and quasicrystalline structure to generate the fleeting regions of quantum coherence needed to keep vibrating tubulin molecules in step, making the cellular automata idea theoretically plausible.

Leaping ahead to how cellular automata computations would lead to conscious-level processes, Hameroff says thoughts and men-tal images may emerge when the coherence between the patterns rippling along the walls of a network of microtubules reaches a certain critical level. Memories could be retained as 'frozen' standing wave patterns on the surface of microtubules. Creative thought and intuition would exploit the clusters of microtubules often found lying in parallel in cells - quantum superposition allowing a cluster to exist in many states before collapsing into a favoured solution.

Hameroff admits that attributing such powers to microtubules leads to the conclusion that paramecia - or even the cells in your big toe - are in some sense conscious. But he says that brain cells are known to have unique forms of microtubule organisation and the structure of the brain probably also makes a big difference to the overall properties of the system. The higher abilities of the human mind would only emerge once microtubules were put together in the right way.

As if the cellular automata theory of consciousness were not startling enough, Hameroff has a foot in several other quantum camps. Another line of speculation is that microtubules form wave guides for channelling photons. Again, Frohlich-like states of quantum coherence are needed to create the right conditions. In this case, water inside the tubule - or possibly bound tightly to the tubule's outer surface - becomes aligned with the quantatised electromagnetic field.

Hameroff claims that there is enough physical theory to suggest that in such a structured state, the water will emit photons and that these will propagate down the microtubule without absorption, making use of properties dubbed superradiance and self-induced transparency. Superradiance emerges from the highly speculative theory that tightly confined water molecules will spontaneously line up, turning some of their chaotic thermal energy into coherent, laser-like, pulses of light.

Self-induced transparency is the still more unlikely idea that these photon pulses would not immediately be reabsorbed by neighbouring water molecules but would pass down the tube relatively unhin-dered because - like light bouncing down a fibre-optic cable - the microtubule walls would act as a conducting waveguide. In effect, the cytoskeleton becomes an optical computer, flashing messages across the cell via laser-like beams of light.

The reaction of other scientists at the Arizona conference was mixed. A few had come thinking quantum theories were rubbish and now had to admit something interesting might be happening down at the microtubule level. However, many more departed still thinking quantum theories were rubbish: there might be a lot unknown about the role played by microtubules in cell functioning, but there was no reason to think that microtubules were harnessing quantum effects to create consciousness.

Heated discussions broke out in private, with critics accusing the quantum camp of being too eager to treat speculation as established fact. Most of the important phenomena on which the microtubule theories were based, such as structured water superradiance and Frohlich's macroscale coherence, were themselves of dubious standing.

Shaking his head during a coffee break, Jack Tuszynski of the University of Alberta said he was one of many physicists who searched for evidence of Frohlich-type effects during the 1980s and found nothing. Meanwhile, Taylor echoed several others in saying it was bad science when it became hard to tell the joins between the parts of a theory which were based on established knowledge and the parts which were still guesswork.

Even more worrying for some was the apparently poor grasp of basic biology among many of the quantum proponents. John Watterson, a biologist from Griffith University in Australia, said it became clear in conversation with one leading figure that he did not know proteins were made up of amino acids: 'I was really rather shocked by that.' In another telling incident, a psychologist confided that he had once shown a quantum physicist around his laboratory who mistakenly assumed that nerve cells communicate with electromagnetic waves and electrons. It had never occurred to him that they might use chemical neurotransmitters.

A second common criticism was that a quantum level explanation of consciousness was not even necessary. The unique features that seem to demand this type of theory - such as the apparent coherence of subjective experience and freedom of thought - could actually be supplied by the neural connectionist approach. Free will and unity of experience are not the simple, structureless characteristics they are often made out to be, said Christof Koch of the Californian Institute of Technology, who collaborates with Francis Crick in the search for a connectionist model of mind.

Despite such reservations, the Arizona conference does appear to have put the quantum approach on the scientific map. Eric Harth, a physicist from Syracuse University and leading neural connectionist, was moved to comment that however plausible or implausible people might find the various quantum theories, at least testable hypotheses were now being put before the scientific community. Another more critical conference-goer remarked: 'Before it was all just mystical hand-waving. Now they've given us something concrete to shoot at.

the theory vacuum

No scientific pursuit is in more disarray than the study of consciousness. This may sound a harsh judgement, but compare the halting progress of the mind sciences with the rapid rise of physics. Understanding what makes the Universe tick must be every bit as difficult a task as understanding human awareness. But where the mind sciences barely seem to have made a dent on the deep questions in their field, the physical sciences have been on a roller-coaster ride of discovery. Ever since Galileo and Newton set the ball rolling, physics has delivered shock after shock, from the laws of thermodynamics and motion, through general relativity and quantum mechanics, up to the Big Bang and superstring theories of today.

More than this, despite being in a state of almost continual conceptual revolution, the physical sciences have managed to develop a coherence as a scientific discipline. Many kinds of researchers are involved in the quest-astronomers, particle physicists, cosmologists, mathematicians-but over the course of several hundred years, they have evolved a common culture of explanation.

As Professor Frackowiak of the Institute of Neurology's scanner group points out, physicists can justify spending billions on particle accelerators, like CERN's 27-kilometre-long Large Hadron Collider, because there is widespread agreement about the questions that need to be asked and a pretty good idea of the answers to be expected. Indeed, physicists have become so confident about their shared framework that they have taken to calling it the Standard Model of particle physics.

By contrast, there is almost no cohesion to the mind sciences and certainly no track record of solid, cumulative progress. Instead of a Standard Model for the mind, there is a theoretical vacuum, a conceptual void filled only by stale philosophical arguments and creaking computer metaphors. Rather than developing a common culture of explanation, psychology and neurology stand sharply divided, sharing little but a reluctance to tackle the big questions about consciousness head-on.

As has been seen, psychology has busied itself in the foothills of its subject, preferring to create theories of behaviour, or at most, computer models of isolated thought habits and mental sub-systems. Psychologists have measured the mind's performance inventively and exhaustively, but they have yet to get under the covers and account for the machinery that produces our mental experience.

Neurology has been even more cautious. Neurologists deal daily with the brain material that is the stuff of the mind. But for a variety of reasons, it is not the done thing for neurologists to attempt to extend their understanding of brain anatomy and physiology into actual theories of consciousness. The reasons for this are complex. For a long time, so little was known about the brain that there was not much that neurology could usefully say. But also, neurology saw itself as an arm of the medical sciences. As a discipline, its first responsibility was to the alleviation of disease and human suffering. So neurology had to present a sober, practical public face. Researchers could not afford to be seen as being motivated by anything so trivial and vain as personal curiosity or dreams of grand theories.

The severity of this ban should not be underestimated. Quite literally, open speculation about consciousness could be enough to wreck a promising brain scientist's career. Benjamin Libet, the Californian neurophysiologist whose experiments on the half second it takes to "form" consciousness will prove so central to our story, originally made his name with some very straight research-studies of nerve cell discharge mechanisms.

Libet admits he did not dare even begin his controversial experiments on the timing of mental experience until he had safely gained tenure as a professor and so could not be sacked. And even then, the pressure from his peers was such that for thirty years he kept his silence about any theoretical conclusions that might be drawn from his work. Libet just published the bare results, saving any private thoughts he might have about the nature of consciousness for a slim, speculative paper published only in 1994, long after his retirement.

The contrast in attitude with fundamental physics could hardly be greater. There, the field's record of success has bred a confidence that encourages the most freewheeling speculation. Theories of Everything (TOEs) abound. The outrageousness of an idea is almost a badge of honour. But neurology-especially during the 1970s and 1980s-has cultivated an ethic of abstemious self-denial. Only a few neurologists either too old or too famous to care, such as the Nobel prize winner, Sir John Eccles, could risk their standing to talk about how the brain might produce the mind.

To underline this cultural quirk, it is only necessary to consider the names of those best known for putting forward grand brain-based theories of mind. The two most prominent of recent theory-builders, Francis Crick and Gerald Edelman, are not brain scientists by training. They switched to neuroscience only after winning Nobel prizes in other fields-genetics and immunology-and there is little doubt that it was their honours, coupled with a healthy disregard for the stuffy conventions of neurology, that made it possible for them to speak so freely. Likewise, nearly every other academic publicly associated with a big theory of consciousness is an interloper-either a philosopher like Daniel Dennett and Patricia Churchland, or a mathematician and physicist like Roger Penrose.

Neurology's creed of self-denial is important because it raises the question of whether explaining the mind is actually a difficult task-or whether scientists have just not been trying in a particularly organised fashion. But it is also an attitude that has changed fast. The development of brain scanners and other new research techniques has created a sudden buzz of confidence. There is a stirring within the ranks and career brain scientists have started to speculate publicly about the possible global brain processes that might underlie awareness. Theorising about consciousness has become possible, even respectable.

This change in scientific fashion is reflected in a recent flurry of conferences specifically about the mind. Christof Koch, an energetic young German neuroscientist from the California Institute of Technology, who has collaborated with Francis Crick on a "synchronised oscillations" theory of consciousness, says that until about 1992, serious researchers could only mention the C-word late at night-or rather, very late at night and after a great many beers. But Koch points out that by 1994, even the annual conference of the US Society for Neuroscience, which attracts over 20,000 doctors, psychiatrists and brain researchers, was doing the unthinkable and including a session which had consciousness in its title: "Things have loosened up fast. You don't get killed for talking about the mind any more," says Koch.

Yet before looking at the kind of theories that are beginning to take shape, we ought to take a step back and consider existing thinking about the mind. What are the questions that, for historical reasons, academics deem important and what are the kinds of answers that-rightly or wrongly-they expect?

the first Tuscon conference

Perhaps the best opportunity to sample both existing and future currents of thought was presented by a bold interdisciplinary conference held in 1994 at the University of Arizona Health Sciences Center, Tucson. The five day meeting, with the hopeful title "Toward a Scientific Basis for Consciousness", attracted 46 speakers spanning the range from philosophers and complexity theorists to neurobiologists and quantum physicists. To make sure no view was missed, there were even a sprinkling of Jungian analysts and altered states researchers. Then for those who did not get a chance to speak during the official meeting, there were evening poster sessions-of which most of the 300 attendees seemed to want to take advantage.

A welter of ideas were presented to the conference, but out of them a clear divide emerged. Speakers were drawn towards two opposite poles of explanation. Either they conceived of consciousness as some form of special field-a mysterious, reflective presence generated by the brain, or residing soul-like within it-or they treated consciousness as a straightforward brain process-simply the pattern of information created whenever the brain goes to work.

These opposing viewpoints, which obviously both have a long tradition in philosophical thought, led the speakers to very different ideas about what it is about consciousness that needs explaining. In one view, consciousness is seen as something fluid and seamless, an unbroken field of mental energy. This "awareness field" can exist at different strengths-varying in intensity between humans and animals, or even between sleep and wakefulness-but somehow it is always essentially the same thing. The great puzzle, therefore, is what can it be that allows the soggy, three pound lump of flesh and blood that is our brain suddenly to light up with the magical inner glow of subjective experience? There must be some trick, some strange and perhaps supernatural mechanism, that negotiates the transition from inanimate matter to animate mind.

On the other hand, those who take the process view of consciousness are looking for quite a different style of explanation. They see consciousness as not a thing, not a mysterious awareness glow, but as just a fleeting tapestry of nerve connections, a temporary web of information created by the mapping and processing demands of the moment. In this view, talking about consciousness is like talking about the spin of a spinning top or the bounce of a bouncing ball. The word is simply a description of the behaviour of the system, a verb which says what the system is doing. To treat the activity of a system as something with an existence in its own right-to think that spin could exist separate of the top, or "minding" of the brain-is to make a serious linguistic error.

Naturally, exactly the same criticism could be made of the supposed faculties of the mind, such as memory, thought, attention and emotion. Being strictly accurate, we should only ever speak about the actions of remembering, thinking, attending and feeling, because all these are processes which only exist at the moment when the brain is performing them. A sloppy use of language has led to a false distinction between the brain and its actions becoming so ingrained in our culture, we now find it hard to treat consciousness as just "brain output".

Seeing consciousness as merely a neural process means that there is no special need for a psychic light switch, some mysterious power or gimmick, which makes the biological brain switch on with awareness. Consciousness is a self-defining phenomenon, being the sum total of whatever neural activity is taking place in the brain at a particular moment. Far from being a seamless field of awareness - an even sheet of mind stuff rippling with passing thoughts and sensations - the mind becomes a rather ramshackle, make-do affair, constructed out of whatever patterns happen to be bouncing about the circuits of the brain at a particular instant. Thoughts and sensations do not play against a mental backdrop - a view which philosopher, Daniel Dennett, thumpingly dismisses as the Cartesian theatre fallacy. Instead, it is all our thoughts and sensations of a moment, lumped together, which define our consciousness.

Talking about this difference in conceptual styles during one of the lunch-breaks at the Tucson conference, Christof Koch remarked that the contrast lies between the "physicists" and the "biologists". Tall, gangling and hyper, like a college basketballer debating tactics for the big game, Koch smacks the table with a hand to make his point. Koch says the physicists expect to find the secret of consciousness in some grand, fundamental twist on the laws of nature. In keeping with the great breakthroughs in the basic sciences, they believe the answer should have a deep and beautiful simplicity.

The biologically-inclined, however, are used to answers which are complicated, messy even. Just like life, they believe consciousness is not the product of a single process or mechanism but an immense tangle of processes. And just as in biology this complexity demands many levels of explanation, from DNA molecules to ecosystems, so the mind will have to be accounted for in multiple tiers of theory. Eventually, perhaps, it might be possible to boil down a lot of this detail into some cleverly packaged statistical concept-much as the theory of evolution manages to capture the essential dynamics of living systems, and complexity theory is beginning to have something to say about self-organising systems generally. But it is foolish to think of consciousness as having some simple, central mechanism.

Of course, adds Koch, the truth could well turn out to be a bit of both. The mind could be mostly the sum of its parts, the jostle of processing patterns surfing the brain's circuitry at a certain moment, yet there might also be a twist to the story. There could be something special that makes a difference between the brain processes that result in an aware state and the many others that never quite reach this privileged level.

the field~process dichotomy

The two opposing tendencies - the physicist and the biologist, the field view and the process view - are well-entrenched in the history of attempted explanations of the mind. In the 17th Century, the idea of consciousness as something extra to the blind thrum of the physical brain was clear in the dualism of the philosopher, Rene Descartes-and in the Christian view of the human soul that Descartes was seeking to defend-while the British associationist school of philosophy, inspired by Thomas Hobbes and John Locke, tried to account for all mental life in terms of the accumulation of minute organic processes.

In the 20th Century, the division has continued. Various schools of thought, such as Gestalt psychology and the New Age movement, have represented the field view, while Behaviourism, cognitive science and the Functionalist school of philosophy, have been the most obvious champions of the process view.

At Tucson, the two viewpoints were present in their most modern, up-to-date guises. About half of the conference was caught up in an enthusiasm for a quantum mechanical explanation of the mind, in which it was thought that regions of the brain might light up and become introspectively aware through a phenomenon known as quantum coherence. Meanwhile the other half of the conference was equally gripped by the promise of a satisfyingly organic vision of the mind to be found in the new sciences of neural networking and complexity theory. These sciences seemed to show how the surprising order of the mind might spring quite naturally from out of the massive connectedness of the billions of nerve cells in the brain.

Neural connectionism is the great theoretical hope of the mind sciences. If brain scanners are providing the raw experimental evidence, and the long-overdue reproachment between psychology and neurology is creating the necessary social climate for productive research, then neural connectionism - in some form - is expected to be the process-style theory that will finally explain consciousness. However, before picking up the threads of the connectionist story, it is worth dwelling briefly on the recent fashion for quantum-based explanations of the mind-if for no other reason than to see why some scientists might feel that brain scanners will turn out to be almost irrelevant to answering the really deep questions about human awareness.

The Tucson meeting-like several other consciousness conferences that year-was electric with excitement about possible quantum theories of the mind. During the opening session in the dim-lit university hospital auditorium-subdued compared to the dazzling desert light outside-the Washington University philosopher, David Chalmers, neatly summed up the appeal of the quantum connection when he joked: "Consciousness is a mystery, quantum mechanics is a mystery. When you have two mysteries, well maybe there is really only one. Perhaps they are the same thing."

The suggestion that the strange world of the quantum might hold an answer to consciousness is an idea with a long history. Musings on the possibility date back at least as far as a book, Quantum Theory, written by the physicist, David Bohm, in 1951. In recent years, however, the speculation has swelled to the point where it has become almost a popular conviction. What else ask a host of thinkers, including Roger Penrose the Oxford mathematician famed for his work on geometric tiling and black holes, could explain aspects of the mind such as freewill, intuition, creativity and the subjective unity of experience?

Quantum physics paints an odd picture of the universe. According to its equations, matter and energy have two faces, sometimes behaving like particles and sometimes like waves. The particular face they show depends entirely upon the way they are measured. The strange result of this fundamental duality is that matter and energy are indeterminate in their many qualities, such as speed, location and spin, until fixed by an act of measurement. It is as if electrons and photons are smeared across space and time, exploring the full range of possible values open to them, until someone comes along with a probe and collapses them into a definite state of being.

Even more paradoxically, when two quantum objects are the product of the same interaction - such as the pair of gamma rays emitted during the positron-electron annihilation that is the basis of PET scanning measurements-they "stay in touch" so that measuring one will determine all the qualities of the other. It does not matter how far apart the two quanta may fly-a pair of gamma rays from a PET experiment might be left to shoot off in opposite directions across the galaxy for millions of years-somehow measuring one would instantly fix the other. This non-local interaction, or quantum coherence, appears to violate Einstein's theory of relativity and its ban on any event taking place at faster than the speed of light. It is as if the twin particle immediately "knows" about the measurement, or as if the future act of measurement had somehow been foretold at the moment the rays first parted.

While such oddities make quantum physics hard to accept, mathematically it is a view of the Universe that works exceptionally well. Using a statistical tool known as a wave function, it is possible to describe the smeared state of an electron or gamma ray with total accuracy. The wave function provides a map of probabilities so while we cannot say exactly where an unmeasured quantum is at any particular moment, we can say how likely it would be to find it there, and also how fast it would be moving and what sort of spin it would be likely to have. One of the important features of such wave function equations is that they can be used not just to describe the envelope of possibilities containing an individual particle, but to describe whole systems, such as atoms, molecules, and some physicists would argue, even the brain or the entire Universe itself.

There are many ways to interpret the conundrums of quantum physics. In one view, the difficulties stem from trying to preserve the idea of the particle when in reality, the only thing that exists at the sub-atomic level of quantum effects are ripples in the fabric of space/time. Sometimes these ripples appear to behave like particles-their crests intersect, creating what look like movements and collisions. But the energy and mass of such a wave always remains smeared. This is what makes it impossible to measure the position and speed of a "particle" with any exactness.

The measurement problem is something like asking a blind-folded observer to discover the whereabouts of a ripple in a bowl of water. The observer can either stick a finger in the water and wait until the ripple eventually strikes it-this gives an exact location for the ripple, but the timing of event becomes unpredictable-or else the observer can decide that he wants to know immediately, without waiting, whether a ripple is occurring, and so he slaps his whole palm down onto the water's surface. In this case, a precise time can be put on the event, but its location becomes unpredictable. The choice of probe determines which aspect of the ripple can be measured accurately.

However, others have interpreted the oddities of quantum physics quite differently and believe it is not our attempts to preserve the fiction of sub-atomic particles that is at fault, but instead the observer problem has some deep, mysterious link with human consciousness. Quantum physics seems to say that every particle exists as a host of superimposed possibilities-an unresolved smear of energies following every possible path-until there is an act of measurement to "collapse its wave function".

Some physicists believe that an interaction of one particle with another-like a collision or an annihilation event-is enough to count as an observation (with, of course, each collapse opening up a fresh trail of quantum possibilities, described by an entirely new wave function). But a number of physicists believe that particles only become "real" as the result of a human observation. It is only when a human observer knows-has become conscious of-the outcome of a quantum experiment that a wave function actually collapses.

Taking this argument to an extreme, the Universe seems to require human witnesses even to exist. Before the human mind came along, it is presumed that the Universe must have limped along in some unresolved foam of possibilities. But now-thankfully-the evolution of sentient human life has collapsed it into shape!

The free-wheeling, speculative culture encouraged in fundamental physics means that, like the White Queen in Alice Through the Looking Glass, many physicists seem to delight in believing seven impossible things before breakfast. But even those who find it too much to think that the universe might hinge upon the fact of human existence still feel that the paradoxes of quantum theory are suggestive of something about our consciousness.

Just like a quantum system, the creative human mind seems to sample many paths and outcomes, running ahead of itself with hunches and intuitions before collapsing its "wave function" to form the settled state which is our focused, logical stream of thought. It seems plausible that human consciousness might be the result of the brain discovering, during the course of evolution, how to harness subtle quantum effects. While the brain of a lower animal might truly be an automaton, no more than a blind biological computer, with ourselves-and perhaps some of the higher animals-ways were found to form a brain-wide, globally aware, field of quantum coherence.

The appeal of the quantum analogy is obvious. We all have a tremendous desire to understand that most personal of life's mysteries: how we come to find ourselves as a small glow of comprehending, sensing awareness locked inside a mortal construction of flesh, hair and bone. But when we look to the past several hundred years of science and philosophy, we do not get much of an answer. Worse still, the official theories, as far as they go, are dispiritingly mechanistic, treating humans as bundles of reflexes or empty calculating engines. They do not tell us what we really want to know: how do we fit an unbroken panorama of sensations, feelings and ideas inside our heads? What gives us the sense of being a self with feelings, plans and desires?

Not only does quantum physics seem to offer a ready answer for the way the dull, clockwork circuits of the brain could suddenly light up with the fires of consciousness, it also appears automatically to account for some of the special qualities we associate with being human, such as creativity, unpredictability and freedom of action. The more cognitive scientists try to fob us off with computer flow-charts, or neurologists with diagrams of tangled protoplasmic wiring, the more we ache for an explanation that is simple, yet grand in sweep. Forget the fussy details of neural processes, we say, just tell us what the mechanism is that makes consciousness click on inside our heads.

The late 1980s saw an explosion of writers championing the idea of quantum consciousness. In Margins of Reality, published in 1987, Princeton University physicist and parapsychologist, Robert Jahn, claimed that quantum physics could explain not just the mind but psychic powers as well. In 1989, the Oxford philosopher, Michael Lockwood, wrote a dense, influential tome, Mind, Brain and the Quantum. The following year, the English religious writer, Danah Zohar, rode the gathering wave of quantum consciousness theorising to bestsellerdom with her breezily written, The Quantum Self, a book based on theories advanced by her psychiatrist husband, Ninian Marshall. However, the publication which really created wide interest in the idea of quantum consciousness was Roger Penrose's book, The Emperor's New Mind, which appeared in 1989.

A small man in his sixties, with a thick shock of brown hair, rumpled "absent-minded professor" clothes and wary eyes, Penrose made the biggest splash more because of his standing as a scientist than the clarity of his theories. Penrose is widely acknowledged as one of the great mathematicians and cosmologists of the past forty years. So if he thought the mind might be quantum in nature, reviewers and fellow scientists were ready to listen respectfully.

However, like many other champions of quantum consciousness, Penrose's theorising was light on detail. He talked about the suggestive analogies between quantum systems and the mind, but he had little to say about how the biological structure of the brain might actually be harnessing quantum effects to generate a field of creative, human awareness. Without some hypothesis about the mechanism that might bridge the gap between the sub-atomic realm in which quantum effects rule, and the molecular-scale processes that control the firing of brain cells, then the quantum approach amounted to nothing more than vague hand-waving.

The obvious mismatch in scale-a gap of at least a dozen orders of magnitude-is what has led most orthodox scientists to dismiss quantum speculation out of hand. There is no doubt that brain cells are made of atoms and that atoms, in turn, are ruled on a finer scale by the equations of quantum physics. Yet it would seem that quantum-level fluctuations could no more affect the gross metabolic activity of a neuron than our stamping on the ground could deflect the Earth from its orbit.

However, by the time the Tucson consciousness conference came round in 1994, the quantum camp had had time to give a lot of thought to the possible nature of the missing mechanism. Some even felt they had the answer and that the cell structure responsible for amplifying quantum effects was a hollow pipe-shaped protein molecule known as a microtubule.

Microtubules are cylindrical molecules made by gluing together 13 strands of the protein, tubulin, to make a tube 25 nanometres across, with a central channel about 15 nanometres wide. Each microtubule is covered by a fuzz of protein stubs, known as MAPs (microtubule associated proteins), and these can be used to hook clusters of microtubules together into larger lattices. Both microtubules and MAPs seem to be capable of a certain amount of movement, meaning that they can be woven into plastic structures, able to give and bend.

The structural properties of microtubule assemblies make them a valuable building material within cells. For example, a bundle of 20 microtubules form the beating, hair-like cilia that coat the surface of many small single-celled animals, allowing them to swim. However the main use for microtubules appears to be to make an internal skeleton for cells-an intricate scaffolding that gives a cell its shape but also can deform and bend enough to allow it to move.

The existence of the microtubule cytoskeleton was discovered only relatively recently in the 1970s-previously the fixative chemicals used in electron microscopy was having the unfortunate effect of dissolving the tubules-so biologists still have much to learn about what the cytoskeleton does and how it operates. Yet biologists believe that it not only holds a cell in shape but also plays an important role in cell metabolism, acting as a piping system or an internal highway to move plasma and other essential cell products about the cell. Some have suggested microtubules might do this by using their MAP spurs to drag cell protoplasm along, hand over hand, in a miniature bucket brigade running up the sides of a tubule.

There is also evidence that the cytoskeleton could serve as a primitive brain. Biologists have long been puzzled how a simple single-celled animal, like the slipper-shaped paramecium, could behave so intelligently when it has no nervous system. A paramecium is surprisingly nimble as it swims about in pond-bottom detritus, twisting in and out of tight spaces in search of its dinner. Somehow the protozoan manages to respond swiftly to information coming in from a light-sensitive eyespot and its touch-sensitive cilia to co-ordinate its swimming action. Several biologists have speculated that the cytoskeleton could serve as the communication and information processing link needed to organise such relatively complex behaviour.

This suggestion that the cytoskeleton could be a "brain within a brain" has particularly excited the quantum theorists. In casting around for a suitable cell structure to operate as a go-between, connecting the sub-atomic realm with the macroscopic world of firing brain cells, some theorists had considered that the membranes at the synaptic junctions between nerve cells might be the site of quantum interactions.

Others had wondered whether the ion channels down the flanks of neurons could be ruled by quantum effects. But quickly, microtubules began to look a far better bet. While microtubules are not unique to neurons, they are found there in particular abundance (a fact that does not surprise neurologists given that nerve cells are so metabolically-active and microtubules seem essential to metabolic activity).

Furthermore, the speed at which microtubules can switch state between relaxation and contraction is believed to be of the order of a nanosecond. This may be slow by the usual time scales of quantum events, but it is about a million times faster than the cell firing events usually believed to underlie consciousness and so at least appears to get the biology of the system within striking distance of a quantum explanation.

At the Tucson conference, an impressive number of speakers came out arguing the microtubule story. However, as the week went on, it became clear that the person actually behind most of this speculation was in fact the conference organiser, the University of Arizona anaesthesiologist, Stuart Hameroff.

a cast of characters

Hameroff is an unusual type of character to find on the consciousness scene. The extreme reluctance of most mainstream scientists to speculate about the mind means that the academics who do risk their careers and reputations by putting their heads above the parapet tend to have some special hobby horse driving them. They have a single big idea, one overwhelming conviction, that they feel they must convey to the world.

A prime example of this kind of consciousness theorist is the Radford University neuroscientist, Karl Pribram. Pribram is one of the grand old men of neurology, a little pixie-like figure with Father Christmas hair and twinkling eyes. In the 1960s, Pribram was struck by the new invention of holography, a way of storing photographic images which used laser light to collapse a three-dimensional image on to a two-dimensional surface. When a laser was again played over the surface, the image was brought back to startling three-dimensional life.

As a technological invention, holography seemed magic enough. But a special feature of a hologram is that the image is distributed evenly over the whole surface of the film. This means that even if the film is cut into tiny pieces, any one piece can be used to regenerate the whole image. The only thing that happens is that the image gets fuzzier, losing sharpness of detail, as the pieces get smaller.

Pribram thought that this everywhere and nowhere storage of information was just like the brain. It was known both from strokes-nature's lesion experiments-and brain surgery that chopping bits out of the brain seemed to have remarkably little effect. You could degrade the general level of performance, but rarely did the damage appear to destroy specific memories or mental skills.

This has, in fact, since proved to be rather an exaggeration - brain damage can knock out very precise components of conscious experience. The reason why earlier neurologists missed this is that the brain has a certain capacity to repair itself, and also brain-damaged patients usually find ways of masking some of the problems they are having. But at the time, it seemed to Pribram that the mind might be some kind of holographic field generated by the brain and he spent many years searching for ways nerve tissue might store holographic images and memories.

Thirty years on, Pribram was at the Tucson conference, still hammering away at his holographic theory. Brandishing a copy of his 1971 masterwork, Languages of the Brain, Pribram opened his talk by describing himself as infamous for even daring to have a theory of consciousness. He then proceeded to quote a scathing passage by Francis Crick who wrote that holographic theories were taken up only by those who knew very little about either neurology or holograms.

Rolling his eyes at the audience, Pribram sighed: "People like Francis Crick think I'm mad, of course." Clearly, the years of verbal battering from his hard-nosed colleagues had taken their toll, but if anything Pribram seemed even more deeply entrenched in his holographic beliefs.

Several other names on the consciousness scene, hooked on their own big idea, cut similarly lonely figures adrift on the unfriendly seas of orthodoxy. But Hameroff is a very different kind of scientific animal, someone driven more by sheer ambition to succeed than by a fixed idea.

Hameroff makes no secret of the fact that he wants to be seen as a major league player in the hunt for the secrets of consciousness. But as a humble hospital anaesthesiologist, he starts from a rather weak position. The disunited, theory-shy nature of the mind sciences means that it has failed to evolve an orderly meritocracy of ideas. There is no institutional sieve that ensures good theories are promoted and bad theories quickly quashed. Instead, until a few years ago, there has just been a general intolerance of theorising.

In this atmosphere, only the already famous-the Nobel prize winners and a few determined high-ranking psychologists and neurologists-could break through. The system was more feudal than democratic. But by playing the political games of academia skilfully-by cultivating alliances with the right people and seizing on a hot idea-Hameroff has managed to join the privileged few in the limelight.

A stocky figure, casually-dressed and sporting a dapper grey goatee and pony-tail, Hameroff looks hip and laid-back-a person to whom it is easy to warm. Where most academics bristle with insecurity at the merest slight on their pet theories, even blunt attacks seem to roll off Hameroff like water from a duck's back. Hameroff always lays a friendly hand on his opponents' shoulders, seeking to turn critics into honored sparring partners-and, perhaps one day, understanding allies.

Hameroff's political astuteness showed in his organisation of the Tucson conference. Sensibly-but bravely given the bitterness and jealousies that often separate the various branches of science-he brought together a broad sweep of opinion about what consciousness might be.

He invited the old names like Karl Pribram and Benjamin Libet as well as some of the leading lights of the new neural connectionist camp, such as Christof Koch, John Taylor and Walter Freeman. He invited philosophers, brain imagers, molecular biologists and even complexity theorists and mathematicians from the Santa Fe Institute and Los Alamos National Laboratories, across the border in New Mexico. However, the conference also allowed Hameroff to gather together his friends and give the quantum-microtubule approach to explaining consciousness the perfect intellectual showcase.

the quantum microtubule

Hameroff's nose for a hot idea had led him naturally to microtubules and quantum physics. As an ambitious researcher, Hameroff was already interested in microtubules simply for the role they might play in general cell metabolism and anaesthesia. Surprisingly little is known about how medical anaesthetics have their effect. It is believed that drugs like chloroform and ether probably dissolve into the fatty protein of brain cells, temporarily disrupting the operation of the cells and so making a person unconscious. However anaesthesiologists are uncertain which protein structures might be the target. Some think it might be the membranes covering the tips of nerves, but others, like Hameroff, think microtubules are a better candidate.

Hameroff has made a name for himself in medical circles with his microtubule hypothesis. But Hameroff always hungered to be part of a bigger game, and when he raised his sights, wondering whether he might be able to do significant work on the mechanisms of consciousness-rather than just unconsciousness-microtubules were naturally high in his thoughts.

The clincher for Hameroff was the coordinated behaviour shown by the single-celled paramecium. It struck him that by concentrating on the patterns of connections between nerve cells, the rest of science might be missing another level of connectionist computation within each cell. Hameroff was neither the first nor the only person to think along these lines. At the time, at least three other researchers had published speculative papers about how microtubules might perform some sort of information processing inside cells. But the others failed to match Hameroff for the vigour with which he took up the idea.

Once he had started digging deeper into current theories about consciousness, Hameroff soon became intrigued by the quantum analogies being suggested by a great many thinkers. Like others observing mainstream psychological thought from the sidelines during the late 1980s, Hameroff felt it was obvious that cognitive science was barking up the wrong tree in treating the human mind as a mechanistic computation. Consciousness simply did not feel like a bundle of calculations. It had too much coherence, too much sparky wilfulness. There just had to be something extra going on which allowed the dead wiring of the brain to light up with a self-aware glow.

Armed with these basic hunches, Hameroff began casting about for collaborators and energetically publishing papers. One of the first microtubule theories that Hameroff developed (initially with a fellow anaesthesiologist at the University of Arizona, Richard Watts, and later with a larger group including Steen Rasmussen of Los Alamos) turned out not even to have a clear quantum connection at the start. Hameroff's idea was that the surface of microtubules might be capable of rippling in a way that would allow them to act as microscopic cellular automata computers.

A cellular automata is a form of computing familiar to many people as the Game of Life. The display area of a computer screen is divided into a chequer-board grid of squares. Each of these squares, or cells, is either lit up or dark, alive or dead, according to a simple set of rules. In a typical program, a cell will look at the state of its nearest neighbours and decide that if a certain number of them are alive, then it will switch on as well. But if too many neighbours are on, the cell will die of "overcrowding, or if too many are off, it will die of "loneliness". Every cell makes the identical decision at exactly the same time so that with each tick of the computer's internal clock, the cells switch state in unison according to the activity around them.

Such a system sounds ludicrously simple, but if the rules are tuned correctly, the computer screen springs to life, swirling with patterns as waves of on and off messages fan out across its surface. Change the rules ever so slightly and a meandering wave might collapse into a fixed blob. Change them again and the blob might shoot off the screen as an arrow-shaped "glider", or start to suck in surrounding patterns like a black hole. The British mathematician, John Conway, invented the Game of Life in the 1960s, but it soon turned out to be more than just an entertaining party trick. Computer scientists showed how these self-propagating patterns could be used to carry out sophisticated calculations, the gliders representing data and the stationary structures acting as a form of memory storage.

Seeking a way that microtubule lattices might carry out information processing, Hameroff knew that they could not work like nerves, using spikes of electrical depolarisation and the release of neurotransmitter messages at synaptic junctions. Admittedly, it was rather a science fiction leap, but Hameroff wondered whether instead microtubules might be transmitting cellular automata patterns down their flanks?

Hameroff pointed out that the walls of a microtubule were made up of chains of a stubby C-shaped protein, and each of these C-shaped building blocks was, in turn, delicately balanced between an open and closed position. The molecules could snap shut, switching state, in the order of a nanosecond. This flexing movement was thought to be what allowed microtubules to twist and contract, and so to beat when bundled together as cilia. But what if these state-switching molecules did more, coordinating their behaviour in a rule-bound way that allowed them to propagate waves of cellular automata patterns, asked Hameroff?

The idea that chain reactions of activity might wash along microtubule structures seemed plausible as it would certainly help explain how cilia could beat with such regularity, or how the cytoskeleton within cells might push plasma about. But computing was another matter. This idea had a gaping hole because to hold a cellular automata pattern together, every cell would have to switch state on the beat of an internal clock. Unless the activity was exactly synchronised, any pattern would rapidly degenerate into unrecognisable chaos.

This need for a regulating clock led Hameroff to the highly controversial work of the University of Liverpool biophysicist, Herbert Frohlich. In the 1970s, Frohlich suggested that what drove the vibration of a protein molecule might be an internal oscillating dipole. Strategically placed at the hinge point of a large molecule, like the C-shape tubulin molecule, might be a single trapped electron or region of charge.

When this electron made a quantum flip-flop shift of position-a quantum leap across the barrier of the hinge to a point on the other side-the change in the balance of electrostatic forces might be enough to throw the whole protein into a different shape. Frohlich went further and proposed that cell membranes might create a situation where a whole series of such delicately-poised dipoles lined up-like compass needles in a magnetic field-leading to a macro-scale quantum coherent state.

Such long range alignment, producing a single quantum system covered by the same wave function equation, is well known to physics from phenomena such as lasers and superconductivity. But most scientists dismiss the idea that the same kind of coherence can be achieved in the hot, sticky realm of organic molecules. Undeterred however, Hameroff argued that microtubules have the right dimensions and quasi-crystalline structure to generate the fleeting regions of quantum coherence needed to keep vibrating tubulin molecules in step, making the cellular automata idea theoretically possible.

Leaping ahead to how cellular automata computations might lead to conscious-level processes, Hameroff says thoughts and mental images may emerge when the coherence between the patterns rippling along the walls of a network of microtubules reaches a certain critical level. Memories could be stored as frozen standing wave patterns on the surface of microtubules. Creative thought and intuition could be the result of exploiting the bundles of microtubules which are often found running in parallel in nerve cells-a quantum superposition, or smearing, of probabilities allowing the bundle to "explore" many states before eventually collapsing into a favoured solution.

Hameroff agrees that attributing such powers to microtubules leads to the conclusion that even paramecia-or the cells in your big toe-are in some sense conscious. But he says brain cells have unique forms of microtubule organisation and the overall structure of the brain probably also makes a big difference to the general properties of the system. The higher abilities that characterise the human mind might only have emerged once microtubules were put together in the right way.

Penrose adds his twist

To many attending the Tucson conference, Hameroff's cellular automata theory of consciousness sounded plain crazy. Christof Koch complained that Hameroff was just making assumption after assumption. Did anyone know if the C-shaped molecules of tubulin vibrated, let alone whether they vibrated under the control of a quantum hinge, or whether they linked up to send rippling patterns down the flanks of tubules, Koch and others asked? To weld such an unsubstantiated mess of ideas into a super-theory of consciousness was just asking to shot down as a crank.

Reputations are important in science. In a world where research grants and tenured positions are increasingly hard to come by, few researchers can afford to risk being labelled irresponsible. Hameroff's key collaborator on the cellular automata theory, Steen Rasmussen, a hot shot in the new sciences of complexity, adopted a low-key position at the Tucson conference.

Rasmussen appeared to treat the ideas as an interesting technical work-out-an exercise in what could be, rather than a claim of what was. But Hameroff showed little such caution. Indeed, in an almost indecent display of intellectual promiscuity, it turned out that Hameroff was not too bothered if his cellular automata idea fell flat because he had several other quantum-microtubule theories of consciousness up his sleeve-ones he was prepared to advance with equal vigour.

A second equally startling idea of Hameroff's was that the lattice-work of microtubules within cells might behave as an optical computer, using pulses of light to represent information! Again, Frohlich-like states of quantum coherence within microtubules would be needed to create the right conditions. But in this case, the theory was that it would be water molecules inside the central channel of a microtubule-or possibly bound tightly by electrostatic forces to a tubule's outer surface-which became aligned in a quantatised electromagnetic field.

Hameroff claims that there is enough physical theory to suggest that in such a bound or structured state, water will emit photons and these would propagate down the microtubule without absorption. In effect, the protein tubes would squeeze coherent light energy out of trapped water, like tiny organic lasers, and then channel the light down the highways and byways of a cell's cytoskeleton.

Hameroff developed his quantum optical computer theory with a number of collaborators including Mari Jibu and Kunio Yasue of Notre Dame Seishin University in Japan, and Scott Hagan of McGill University in Canada. But again, there is alarmingly little evidence that any of the claimed building blocks of the theory are in place, let alone that microtubule computing can stand as an explanation of consciousness.

Frohlich's theories of large-scale quantum coherence in biological systems are widely disputed and physicists have been searching for evidence of such fields for 20 years. Furthermore, there is good reason to believe from established physics that the delicate alignment of magnetic fields called for by Frohlich's theories would be impossible at the relatively hot temperatures of living tissues.

Large-scale quantum coherence is only found in very cold, highly ordered systems, such as in metals that have been cooled to the temperature of liquid helium and so become super-conducting, or in a powerfully driven pure energy system, such as a laser. It seems certain to most physicists that inside the hot, soupy interior of a cell, the constant bump and jostle of random thermal motions would soon wash away even fleeting moments of quantum alignment.

Physicists can find dozens of other reasons for dismissing Hameroff's optical computer ideas out of hand. There is no evidence that there is structured water inside microtubules. There is no evidence that structured water emits photons. There is no reason to think microtubules could confine such photons and channel them to distant destinations even if they existed. Virtually every link in Hameroff's argument appears to be pure speculation. In corridor meetings and coffee breaks during the conference, skeptics were groaning with disbelief at his uncontained flights of fancy.

Yet undaunted, Hameroff ploughed on. Not only did he bullishly talk up his theories-his address was by far the slickest of the conference, coming complete with computer animations of vibrating tubulin molecules-but he continued to extend his patchwork quilt of speculation, hoping to build fresh alliances by embracing the ideas of others.

In a nod to Karl Pribram's holographic theories, Hameroff argued that holography might be the key to how an optical computing cytoskeleton could carry out mental processes like memory and thought. Photons might be fired through special slits in a microtubule's walls to scribble holographic messages across nearby cytoplasmic gel. Pribram's own belief is that holography is something that takes place between brain cells, rather than within them, and he has created detailed mathematical models of how neurons might store information in fields of electrical potential generated by their bushy dendritic tails. Nevertheless Pribram was clearly soothed to find a friendly face willing to lend general support to him and his holographic approach.

In another skillful manoeuvre, Hameroff managed to ally himself with Roger Penrose. Prior to being invited as an honored speaker at the Tucson conference-and also to be a guest of Hameroff's on an agreeable week-long camping expedition to the Grand Canyon following the meeting - Penrose had not been thinking along microtubule lines.

Indeed, after toying rather half-heartedly with a few possible biological mechanisms by which the brain might harness quantum forces-such as special quantum-sensitive neurons tucked away in the heart of the brain - Penrose had come to feel that even ordinary quantum theory was probably not up to explaining consciousness. Penrose was arguing that a new form of quantum theory, one that married the quantum world of sub-atomic forces with the force of gravity, would have to be developed before science could really take the next step of wondering how the brain might harness quantum effects.

Penrose's general belief was that much of the brain probably did operate like a computer. It behaved as a calculating engine crunching its way through programs to produce predictable, but probably unconscious, results. However, the extra spark that allowed the human mind to be creative and free-willed must stem from some deep quantum uncertainty within its wiring.

He believed that the collapse of a quantum wave function-the transition of a system from a sea of possibilities to a definite outcome-was brought about by the system's own gravitational weight. The smeared energy of a particle would exert a weak but decisive gravitational pull on itself that would serve to collapse it into shape. Applying this kind of "correct quantum gravity" collapse to the wiring of the human brain, Penrose argued that neural circuits might explore many alternative paths of thought for a split second, groping for the best outcome, before reaching some threshold gravitational energy level and collapsing into a settled, conscious state.

Penrose's ideas might be rather sketchy, but as the heavyweight name in quantum consciousness, Hameroff needed him on his side. After some long, friendly discussions Penrose began to lend cautious support to the microtubules idea. At Tucson, Penrose pronounced that his calculations showed that the supposed nanosecond vibration frequency of tubulin molecules would at least put microtubules in the right ballpark to tap quantum effects.

After the conference, his support strengthened. Penrose agreed to co-author a scientific paper with Hameroff and he included warm praise for the microtubule theory in his follow-up book on quantum consciousness, Shadows of the Mind, which was published later that year.

what to believe

The saga of Hameroff and his microtubules tells a lot about the state of the mind sciences in the 1990s. The official mind scientists - the psychologists and neurologists - were failing to satisfy a natural thirst for explanations. In the absence of an accepted standard theory - or even a standard approach to theorising - various populist theories have blossomed.

The quantum hypothesis, in particular, has had all the right ingredients to catch wide attention. It is grand and mysterious. It seems to focus on all that we consider most flatteringly special about the human mind-its inventiveness, its sense of self-determination, its impressive coherence. Quantum consciousness was an idea it was possible to be passionate about. But being attractive does not make something right.

See: Going Inside - A tour around a single moment of consciousness, by John McCrone, 1999.

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