any of us are old enough to remember the scientific excitement that existed during the early days of brain science, when it seemed that connectionist neural network models might explain how the brain, and maybe even consciousness, worked. Those hopes were dashed twice: first in the 1960s when mathematicians published a book showing that certain computations could not be carried out by the early models, and then again twenty years later when a phenomenon that might be called "claim inflation" began to chew away at the respectability of the field.

Claim inflation occurs because, in the fight for limited journal space, each new paper had to make more grandiose and unsupportable claims than the previous one. One model, for example, asserted that each individual neuron was capable of carrying out every known function of the mind known to psychologists. Another model claimed that, with only N neurons, it was possible to identify all possible 2^N patterns with with 100% accuracy. To compete with these extravagant claims, researchers had to make comparable or superior claims for their own models. Soon the requirements for publication exceeded the limits of physical possibility, and the whole field collapsed. Neural networks are now the almost exclusive domain of statisticians and computer programmers.

Something very similar is happening today in the field of consciousness studies. While we have so far avoided claim inflation, we have on the one hand ultra-reductionists who say they believe that conscious awareness doesn't really exist--it's just an illusion that our brains have created to trick us into wanting to survive. On the other, we have widespread confusion about the difference between consciousness and perception. Against this trend, we have physicists like Henry P. Stapp of the Lawrence Berkeley Laboratory in California, who believe that quantum mechanics may be the key to understanding consciousness.

In this new book, written for a nonscientific audience, Stapp lays out his ideas about why he believes that quantum mechanics is an essential component of any explanation of consciousness. Since there are many scientists out there who don't even believe that conscious awareness exists, Stapp's book is also an attempt to convince people that consciousness is a real phenomenon, and not just some bizarre illusion.

Stapp's theory is based on rigorous physics. To reach a wide lay audience, the mathematical physics that underlies his theory has been completely omitted from this book. Unfortunately, without mathematics, he is to some extent reduced to hand-waving, which probably will make the subject seem even more incomprehensible and even mystical to the layman. In fact, there is nothing mystical about Stapp's theory. Some understanding of quantum mechanics is needed, not to understand what Stapp says, but to enable the reader to evaluate whether it is plausible. To help explain Stapp's theory, it is first necessary to explain some basic quantum physics.

Stapp's theory is based on what physicists call "the role of the observer in wavefunction collapse." For example, when a photon passes through a slit, it exists as a wave and exhibits wavelike behavior until it strikes a detector. While it is acting as a wave, the photon occupies a large volume of space. This is not just because of experimental uncertainty about its location; the photon is actually present throughout the entire volume, and interacts with itself in the same way that different parts of the same water wave interact in the ocean. This interference of single photons has been observed many times: a two-slit apparatus in which only one single photon is present at a time will produce, over time, a complete interference pattern. This could only happen if a photon is spread over a large volume of space, and travels through both slits simultaneously.

When it reaches the detector, however, the photon is forced to interact with matter. It can only do this at a single point in space, and is therefore forced to choose randomly the precise point in space where it will interact. This is called "wavefunction collapse." Stapp, and some other physicists, believe that the act of detecting a photon or other quantum event is an "observation"--an act of consciousness.

This is by no means universally accepted. Calling the event an "observation" instead of an "interaction" creates impression that wavefunction collapse can only occur when an "observer" is present. This has led to some strange speculation about what constitutes an observer. What if the researcher who performed the experiment didn't notice the event? Does that mean it doesn't collapse until an astute reader of the researcher's paper first notices it? It may be simpler to stick to the noncommittal term "decoherence" instead. However, if the theory were true, it would have many profound implications:

1. The observer would be intimately connected to the thing being observed, to the extent that he or she controls where the photon lands by observing it.
2. If there is nobody there to see the photon land, it does not land, but remains in its indeterminate state forever, waiting for someone to observe it.
3. Therefore, because we can prove that photons that we have never observed have in fact landed, the universe itself must be conscious, because it is clearly impossible for humans to have observed all of the quantum events in the universe. (Hence the appropriateness of Stapp's title, "Mindful Universe").

Stapp uses this basis to make the following assertions about the brain:

1. Each nerve terminal exists in a mixture of quantum states, because calcium ions are small enough to require quantum theory to fully describe their behavior. Therefore, says Stapp, the entire brain contains a cloudlike mixture of mixed quantum states.
2. Classical physics precludes any possible explanation of consciousness, because it leads to dualism. Dualism is no longer an issue when quantum mechanics is reintroduced into the problem.
3. A conscious thought is associated with the reduction of a set of quantum possibilities, which causes a corresponding increment in knowledge.
4. Because the decoherence time for ions in aqueous solution, even at a single synapse, is many orders of magnitude too short for quantum effects to play any significant role, Stapp relies heavily on the "quantum Zeno effect" to lengthen the time before decoherence.

This is all interesting stuff, and Stapp deserves credit along with Penrose, Hameroff, and others, for the imagination, rigor, and open-mindedness with which they have pursued these ideas.

This is one of the most interesting works on the subject of consciousness since Penrose's paper relating consciousness to quantum gravity. The lack of detail in this book and the non-technical language may force some readers to turn to Stapp's original papers for details, but will expose these important ideas to a wider audience. The only other problem with this book is that Stapp does not seem to consider the possibility that quantum mechanics may in fact have very little to do with consciousness; he gives the impression of having an unshakeable, almost evangelical belief in the idea that wavefunction collapse = consciousness. To a large extent, that may be unavoidable; it is, after all, only a theory that is still awaiting definitive experimental confirmation, and therefore needs an advocate. Whether you agree with Stapp's ideas or not, Stapp's background as a serious physicist means that they must be taken seriously.