Theories of Everything

Sir John Maddox was for almost a quarter of a century, until 1995, the editor-in-chief of Nature , one of the world’s premier scientific journals. In this ambitious book he attempts nothing less than an overview of what has been discovered about the natural world in the last three centuries, and what is likely to be discovered in the century ahead.

It is clear that Maddox intended this to be a rebuttal of John Horgan’s provocative book, The End of Science , published in 1996. Horgan’s thesis was that science is entering “an era of diminishing returns.” He noted that many fields of research, such as human anatomy or geography, are limited simply by the boundedness of their subject matter. Even chemistry, being based on the periodic table, is bounded. Although the number of compounds that can be built up from these elements is vast, there is a sense in which the problems in chemistry become less and less fundamental as time goes on. In any finite field of inquiry one expects that at some point all the basic principles that are humanly discoverable will be known. There are some who hope-or fear-that we may already be close to that point in fundamental physics. Many leading particle physicists believe that in “superstring theory” they have already hit upon what will turn out to be the ultimate theory of physics- the laws of nature.

Even if we are not close to achieving the final theory in physics or other sciences, we may, according to Horgan, be running up against limits to what we can discover. Some of these limits are imposed by nature itself. For example, in astronomy there is a distance beyond which it is impossible to observe because of the finite speed of light. Other limits are practical: a few years ago the U.S. Congress cancelled in mid-construction what was to be the world’s largest particle accelerator. Finally, there may be limits imposed by human intellectual capacity. The mathematics of superstring theory, for instance, is of such prodigious depth that after a decade and a half of remarkable progress researchers feel that they are very far from coming to grips with its central principles.

As evidence of his thesis, Horgan argued that there have been no truly revolutionary discoveries in the last several decades. What, he asked, has been done recently that can compare in magnitude to the discovery of evolution, the principles of genetics, and the structure of DNA, or to the discovery of Newton’s laws, Einstein’s theory of gravity, and quantum mechanics?

Maddox attempts to answer Horgan, although, curiously, he never mentions his name. Maddox makes his purpose clear in the preface: “And [my] message? Despite assertions to the contrary, the lode of discovery is far from worked out. This book provides an agenda for several decades, even centuries, of constructive discovery that will undoubtedly change our view of our place in the world as radically as it has been changed since the time of Copernicus.” To answer Horgan, Maddox surveys what is currently known, primarily in cosmology, physics, and biology, indicating along the way which unsolved problems in each field he regards as the major ones.

In biology, Maddox has no trouble coming up with a list of profound issues about which little if anything is known: how life originated from nonliving chemicals four billion years ago; how a single cell is able to assemble itself into a complex multicellular organism; the way in which speciation occurs; how and why sexual reproduction evolved; the way in which the human brain works; and the nature of consciousness. Maddox argues persuasively that great progress is likely to be made in the next century (or at least is achievable) in some of these areas.

His optimism is less plausible, however, when it comes to the deepest questions, such as how the human brain works. He concedes that “progress in this field will not be quick.” The complexity of the brain’s circuitry is just staggering: “[It] probably contains many times as many neurons as our galaxy contains stars . . . . The complexity of connections between neurons is similarly gargantuan; cells of the cortex may be in a position to signal to as many as ten thousand others, either in the cortex or elsewhere in the head. The combinatorial possibilities are immense.” Moreover, even the most sophisticated means that are presently used to study the living human brain are comparatively crude: “What remains to be seen is whether the detail that can be identified by these means will be fine enough to answer the questions being asked about the function of the brain as a computer.” In spite of all this, Maddox asserts that the “circuitry of consciousness” will be understood. “Perhaps new techniques will be required before the goal is truly in sight. But that the goal is attainable seems now to be plain.” On what does Maddox base this last confident assertion? As far as I can tell, on nothing at all.

The difficulties that must be faced in understanding the mechanisms of evolution are no less daunting. In discussing one evolutionary puzzle, Maddox admits that “complex questions such as these cannot be tackled with the information now available.” In another place he remarks “how little has yet been done to found even rudimentary evolutionary speculation on laboratory investigations.” He notes that thorny questions such as “the causes of the rapid appearance of novel species at the Cambrian Explosion” will be answerable only at some possibly distant date “when the process of speciation is fully understood in modern genetic language.” And yet, in some miraculous manner, Maddox already knows what this far-off research will reveal: “Heritable variation and natural selection, the central tenets of Darwinism, will then be found to account for what is known of the patterns of evolution.”

When it comes to particle physics and cosmology, Maddox has somewhat less mastery of his material. He makes a disconcerting number of minor technical errors. More seriously, he does not have a very clear picture of what the major unsolved problems in cosmology and particle physics really are. He mentions as puzzles several things that never were or no longer are such, while failing to mention some of the truly great and difficult questions that confront present-day theory. Maddox also has some quirky prejudices, such as a particular dislike of black holes.

More understandable is his hostility to the idea that physics may be close to a “Theory of Everything” in the form of superstring theory. This idea is very controversial even among particle physicists themselves, many of whom complain that there is not a shred of direct experimental evidence for it, and that after years of serious work superstring theorists still cannot make a single testable prediction.

Given these facts, why do so many of the most brilliant people in the field continue to work on superstring theory and regard it as such a promising candidate for the ultimate theory of nature? To understand this one has to have some appreciation of the great trends in the history of physics. One trend has been toward an ever more unified picture of nature, beginning when Newton showed that the same laws govern terrestrial and celestial phenomena. As time went on, Newtonian mechanics was able to explain phenomena as diverse as the motion of fluids, the propagation of sound, and the flow of heat. In the nineteenth century the Newtonian framework was extended to describe electrical and magnetic phenomena, as well; and with the equations written down by James Clerk Maxwell in 1865 it was realized that electricity, magnetism, and optics are all different aspects of a single force called “electromagnetism.” In 1905, Einstein showed that space and time form a single, four-dimensional whole, and that mass and energy are really the same thing. Quantum theory showed that force fields, wave phenomena, and particles are all manifestations of something called a “quantum field,” so that there was no longer any fundamental distinction between matter and the forces that influence matter.

In the 1970s, another enormous unifying step was achieved when it was found that two of the four known forces of nature, electromagnetism and the “weak nuclear force,” are really pieces of a single force. Powerful circumstantial evidence also emerged at that time (still not conclusive, however) that a third force, the “strong nuclear force,” was unified with these in an analogous way.

Everything that is now known about the physical world can be described by two theoretical structures: Einstein’s theory of gravity, and a quantum field theory called “the Standard Model,” which incorporates everything except gravity. It is clear to almost everyone that these are but two pieces of a grander whole. For decades physicists tried to bring Einstein’s theory of gravity under the umbrella of “quantum field theory,” but the umbrella was not big enough. All attempts to bring together Einsteinian gravity and quantum theory failed-until superstrings came along. Astonishingly, superstring theory not only could accommodate them both, but actually needed them both for its own completeness and consistency.

The other great trend that has culminated in superstring theory is the increasing role of powerful principles of “symmetry” in our understanding of the laws of physics. Since ancient times people have been impressed by the harmony and order they saw in nature, manifested most clearly in the grand cyclic motions of the heavenly bodies. They pointed to this order as evidence of a cosmic design-and a Designer.

What science has shown is that this order runs far deeper than anyone had imagined. In the phenomena around us we catch mere fragmentary glimpses of order amidst much apparent haphazardness and chaos. But modern physics gives us eyes to see down to the very roots of the world’s structure, to the deepest layers of physical law, and what is seen there is an orderliness of the most pristine mathematical purity.

This order is reflected in principles of symmetry of wonderful richness and beauty. It was a new principle of symmetry that led Einstein to his theory of gravity, and a new principle of symmetry that allowed the unification of forces achieved in the 1970s. What scientists have stumbled upon, in superstrings, is a mathematical structure of such towering grandeur that they cannot help but call it “miraculous.” It is of a beauty that only a few mathematicians are able to discern, and even the greatest experts feel that they are seeing only a small part of it. Edward Witten, the greatest of all the experts, grew exasperated with John Horgan’s lack of appreciation: “I don’t think I’ve succeeded in conveying to you,” he said, “its wonder, its incredible consistency, remarkable elegance, and beauty.”

If the laws of nature should prove to form a unified and coherent structure of great beauty, that would hardly surprise the religious among us. But would that mathematical structure amount to a “Theory of Everything”? It would certainly be a theory of everything physical . But is everything physical? In particular is man, made in the image of God, entirely physical? This brings us out of the realm of particle physics and into the realm of the human mind. It is here that one encounters among certain contemporary scientists an attempt at a unification far bolder than anything ever contemplated by physics.

In this greater unification, all mental phenomena will be explained in physical terms. In the words of Francis Crick, the Nobel-laureate biologist, we humans are “nothing but a pack of neurons.” Strangely, Maddox has no qualms in accepting this kind of theory of everything. He assures us, with calm confidence, that “an explanation of the mind . . . must ultimately be an explanation in terms of the way neurons function.”

What neither Maddox nor the authorities he follows seem to appreciate is how profoundly different this mind-equals-neurons theory is from all scientific theories that have gone before. All scientific theories up till now have been attempts by the human mind to grasp the nature of physical reality. The new theory is an attempt to show that the human mind, as such, is a fiction, and that only the physical reality exists. This is the suicide of theory.

Scientific theories are built up of ideas, and ideas exist in the mind. The ideas of modern science are, notoriously, very abstract. Chemistry, for example, uses such concepts as “atomic bond” and “valency” and “activation energy.” These concepts rest on yet more abstract concepts in physics, such as “electromagnetic field” and “energy level.” These, in turn, entail all of the recondite mathematical ideas of relativistic quantum field theory, which take years of study to comprehend.

We are supposed to believe that these ideas are nothing more than various patterns of neurons “firing” or discharging in human brains. A certain pattern of neurons firing is the concept “energy level.” Another pattern of neurons firing is the concept “square root of 2.” And so on. Not, mind you, just that a certain pattern of neurons firing accompanies the concept “square root of 2,” or causes that concept to be present to the mind. That concept is supposed to be nothing other than the firing of the neurons. To “understand” the physical world using scientific and mathematical concepts would mean, then, nothing else than that the neurons in one’s brain were discharging in particular patterns and sequences.

The concept “neuron” itself, in fact, is on this account nothing other than a certain pattern of neurons firing in the brain. Is there not something here to make us vaguely uneasy? Is not the snake of scientific theory eating its own tail-or rather its own head? Traditionally, we explained the physical world, including the brain, using concepts. Now we are to explain the concepts themselves as being mere physical events in brains. In fact, this whole theory according to which the mind and all conceptual understanding are nothing but electro-chemical discharges of nerve cells is itself , by its own account, nothing but a discharging of nerve cells. This makes it, as far as I can see, no more significant or interesting than a toothache. We should listen to great scientific minds because they are great scientific minds. However, when they begin to tell us that they really have no minds at all, we are entitled to ignore them.

For all that, Maddox has written a most valuable book, and he is certainly right in his main point. There is a long road of scientific adventure ahead of us, and surely many remarkable things await us along that road. The great discoveries, when they come, will commend themselves to us, as they always have, by their “wonder, incredible consistency, remarkable elegance, and beauty,” as Witten says. But as for the neuroscientists’ “theory of everything,” I find no wonder in it.

Stephen M. Barr is Associate Professor of Physics at the Bartol Reseach Institute, University of Delaware.