Until roughly the 20th century, physics was concerned with the realities of ordinary experience: light, heat and sound; motion, acceleration, falling bodies; gases, fluids, solids; electricity, magnetism and so on and so forth through the world of phenomena. Then in 1895, Wilhelm Roentgen discovered X-rays; in 1897, J.J. Thompson discovered the electron; in 1914, Rutherford discovered the proton – and all at once a new branch of physics had come into existence: elementary particle theory, dealing with the hidden realities, the fundamental entities that underlie the observed phenomena of everyday life.
During the 20th century, particle theory developed and grew. It was a continual race between theory and experiment, as new particles showed up in accelerators and new theories arose to accommodate and explain them. Now, near the end of the century, and after almost a hundred years of particle theory, physicists are seriously contemplating the end of their subject. Soon, they think, a Final Theory will be at hand, one that will provide an explanation for absolutely everything that matters in physics. Steven Weinberg’s Dreams of a Final Theory tells us how we got to this point, and urges us to take the next logical step, which might also be our last, since if successful it will give us a complete and lasting theory of nature, ‘one that would be of unlimited validity and entirely satisfying in its completeness and consistency’.
This last step, unfortunately, will be rather expensive, involving the building of the Superconducting Super Collider (or SSC), a 53-mile-long $8 billion particle accelerator underneath the wheat fields of Ellis County, Texas. These last few elementary particles, apparently, are extremely bashful, and do not come cheap. Weinberg’s book is gracefully, even elegantly written. As a history of physics, mainly particle physics, it’s clear and authoritative. It describes the so-called standard model: the currently accepted picture of the elementary particles and the various forces – strong, weak and electromagnetic – that govern their interaction. And it explains one of the major outstanding problems with the standard model, the origin of ‘spontaneous symmetry-breaking’.
Nature, mostly, is symmetrical. On one level this means that objects look the same from different points of view. ‘A sphere looks the same from any direction,’ Weinberg says. ‘Empty space looks the same from all directions and all positions.’ On a deeper level, nature is symmetrical in the sense that its laws and regularities are immune to changes in frames of reference. ‘It makes no difference to our results whether we do our experiments in Texas or Switzerland or on some planet on the other side of the galaxy.’ Nevertheless, nature’s symmetries are often spontaneously broken; an ordinary magnet is an example. ‘The equations that govern the iron atoms and magnetic field in a magnet are perfectly symmetrical with regard to direction in space,’ Weinberg says. ‘Nothing in these equations distinguishes north from south or east or up. Yet, when a piece of iron is cooled below 770°C it spontaneously develops a magnetic field pointing in some specific direction, breaking the symmetry among different directions.’ When such asymmetries appear out of nowhere, an explanation is required. The explanation in the case of the magnet is that during the process of cooling, its atoms spontaneously line up in the same direction, producing a magnetic field. Asymmetries have cropped up in particle theory, too: specifically, there is a breakdown of the symmetry that relates weak and electromagnetic forces. The problem is that the explanation of this asymmetry is currently unknown, and constitutes one of the main theoretical gaps (the other being how to incorporate gravity into the overall picture) which a Final Theory of Nature is designed to bridge. Weinberg suggests what such a theory might be like, and ventures to say what it will mean to physics, and to the world at large, if and when it arrives.
His book is also a pep-talk for building the Superconducting Super Collider; but Weinberg’s account of particle theory is a lot more successful than his pep-talk. Much of the book is a history of physics, tracing the course of humankind’s attempt to discover the true nature of things, and taking us from Thales’ claim that everything is water to the claim that everything is, at base, particles, energy and fields. This is a story that has been told time and again in popular science books, and there is not much new here. What is new is Weinberg’s self-conscious concern for philosophical issues such as the nature of explanation, the sense in which an explanation or theory may be said to be ‘final’, and whether the end-product of science is a nice-sounding, though possibly false, story about nature, or on the contrary a true and valid account of the way things are. Whenever such matters are dealt with in science books, the Kuhnian view reigns supreme: the view that a scientific theory is essentially just a collective Gestalt or vision, a Weltanschauung that a bunch of scientists happen to share at any given moment, but which is no better, epistemologically speaking, than the latest fad or fashion.
The most interesting feature of Weinberg’s book is not his call for yet more money for yet another particle accelerator to discover yet an other elementary particle, but rather his explicit return to an old-fashioned, allegedly long-since superseded conception of science as a search for the objective truth about the world. In a chapter entitled ‘Against Philosophy’, Weinberg advances a sharply anti-Kuhnian viewpoint. Science is a social process, he says, but it does not follow from this that its utterances are equivalent to social trends:
It is simply a logical fallacy to go from the observation that science is a social process to the conclusion that the final product, our scientific theories, is what it is because of the social and historical forces acting in this process. A party of mountain climbers may argue over the best path to the peak, and these arguments may be conditioned by the history and social structure of the expedition, but in the end they either find a good path to the peak of they do not, and when they get there they know it.
In the age of science-as-storytelling, this is refreshing. There is no more laughable spectacle in the late 20th century than that of scientists asymptotically approaching a complete and final understanding of nature while over on the sidelines a bunch of finger-wagging philosophers heckle that all explanations and theories are equally good and that none of them are more than likely stories anyway. The philosophers, of course, always contend that they’re really just being helpful here, offering a much-needed corrective to those naive scientists who would otherwise persist in their mad delusion that they’re actually gaining some objectively true knowledge about the world. Scientists, ironically, do not normally return the favour by issuing matching helpful correctives to philosophers. Weinberg, however, makes no bones about telling the philosophical thought-police to mind their own business. ‘I know of no one,’ he writes, ‘who has participated actively in the advance of physics in the post-war period whose work has been significantly helped by the work of philosophers.’
He also gives a traditional, distinctly unhip account of what a scientific theory is and does. A theory, he says, is not a free construction of the intellect but rather an attempt to explain a given fact or phenomenon in terms of something more basic. A final theory, then, will be one for which there are no more basic entities, laws or phenomena to be found; such a theory ‘will bring to an end a certain sort of science, the ancient search for those principles that cannot be explained in terms of deeper principles’. In particle physics proper, a final theory will be one which successfully accounts for all the fundamental particles and forces, including gravity, that are known to exist; it will also provide an explanation for the phenomenon of electroweak symmetry-breaking.
Currently, the most favoured explanation for the electroweak asymmetry involves the postulation of a new elementary particle, the so-called Higgs boson, whose existence was proposed by Peter Higgs in 1964. One of the reasons why Weinberg and other elementary particle theorists so much want to see the SSC built is that its energies will be high enough to produce the Higgs particle, supposing it exists. The Higgs boson, accordingly, has become the holy grail of physics, the God particle. Weinberg is a master at communicating the excitement of the quest for it, and at giving you the feeling that you’d be a traitor to the human race not to want to see this gigantic intellectual effort continued, no matter what the cost, financial or otherwise. ‘The discovery of the final laws of nature will mark a discontinuity in human intellectual history, the sharpest that has occurred since the beginning of modern science in the 17th century.’
The trouble with all this is that elementary particle theory is the preserve of a priesthood, and a rather small one at that. Particle physicists have always been the high priests of science. The entities they theorise about are so far removed from daily life, so far below the level of direct sensory perception, that they might as well be in another realm. Which, in a sense, they are: sub-atomic particles are not governed by the same laws as those that govern macroscopic bodies; rather, they operate by their own special rules – the laws of quantum mechanics – that have no obvious and intuitive counterpart in the laws of ordinary human experience. Years of arcane training and apprenticeship are required to become familiar with those particles, and to comprehend their idiosyncrasies. Like the high priests of yore, particle physicists have had grand temples built – linear accelerators, cyclotrons, colliding-beam accelerators, and the like – in which their impalpable, hidden and other-worldly entities might fleetingly be glimpsed, in the form of crabbed and cabalistic markings on photographic plates.
One can’t blame particle physicists for coming across as a hermetic cult: it’s not their fault that nature is as complex as it is, and its fundamental realities so obscure. All of the physicists’ marvellous training regimens and mysterious initiation rites are simply the waters they’re forced into by the complexity and recalcitrance of nature itself. The miracle is that these high priests have actually succeeded at their craft; they’ve actually managed to figure out what the world is really made of, and what the laws are by which it operates. Or at least they’ve mostly figured it out: even Weinberg himself, Nobel Prize and all, confesses to some residual bafflement: ‘I admit to some discomfort in working all my life in a theoretical framework that no one fully understands.’
If Steven Weinberg is in such straits, then to the average person particle physics is about as accessible as the Upanishads. Which raises the question of whether the average person should be forced to pay $8 billion so that these same high priests can make yet further advances in theory. Weinberg, for one, thinks the answer is yes, but his reasons are not convincing. There is, for example, his claim that if the United States doesn’t build the SSC, then American physicists will be forced to work abroad. ‘Without the SSC we shall lose a generation of high-energy physicists who will have to do their research in Europe or Japan.’ Is this such a tragedy? Especially when the alternative offered is Waxahachie, Texas?
There is his claim, too, that ‘only with the data from such an accelerator can we be sure that our work will continue’. This is disingenuous: as Weinberg is at pains to point out elsewhere in the book, a final theory will not mean the end of science, nor even the end of physics. ‘About one thing we can be sure – the discovery of a final theory would not end the enterprise of science ... Right now in physics alone there are problems like turbulence and high-temperature superconductivity that are expected to have profound and beautiful explanations. No one knows how galaxies formed or how the genetic mechanism got started or how memories are stored in the brain. None of these problems is likely to be affected by the discovery of a final theory.’ Against the claim that new physics requires new data, Richard Feynman once remarked: ‘I used to think that physics would more or less end as experiments became more expensive and therefore rarer. But it was just the reverse! I underestimated the human tendency to speculate. When there are fewer experimenters, there’s more speculation going on! There are more theories than before, not less.’
Still, physics is more than mere theorising, and the whole point and purpose of the SSC is either to verify or to disprove a small number of relevant theories. But in ordinary human terms, how much is that worth? How many kids will have to do without a computer program, a pair of shoes or a book, so that the SSC can be built and the priesthood find their God particle? How many tenement dwellers who haven’t the least interest in elementary particle theory will have to go without an article of food or clothing in order to get a better picture of the Higgs mechanism as it relates to electroweak symmetry-breaking? How many farmers who have never heard of electroweak symmetry-breaking – and wouldn’t care to, thanks just the same – will have to do without some plants or fertiliser so that some physics post-doc won’t have to leave Texas? How many retired people will have to go without ... well, you get the idea.
Forgive me for asking such questions, but the answer is that all of these people will have to forego something or other for the sake of further progress in particle physics. Weinberg, unfortunately, does not raise the issue but $8 billion has to come from somewhere and the question of where must not be dodged. Especially it must not be dodged in light of the fact that Weinberg doesn’t claim to know for sure that there is a final theory, nor that if there is one, we will he able to devise it. ‘Perhaps there is a final theory ... but we shall never learn what it is.’ His own belief in such a theory, he acknowledges, has the status merely a guess. ‘My own guess is that there is a final theory, and we are capable of discovering it.’ The possibility that the SSC will raise as many questions as it answers is not explored by Weinberg. But what happens if the ‘final’ theory is not final after all? What if the SSC discovers the totally unexpected, what if it opens up a whole new frontier of exotic particles, or provides results that are, even at its enormously high energies, either equivocal or baffling? Weinberg offers no guarantees that this won’t happen.
What is guaranteed is that if the worst occurs – if particle physicists get their SSC and still have questions – a contrite and self-effacing member of the priesthood will again show up one morning on our doorstep, hat in hand, speaking of the glories and wonders of science and asking for yet another contribution – a modest one, certainly: only $82 = $64 billion – for a shiny new particle accelerator, the latest model, one that will completely encircle the state of Arkansas, birthplace of Bill Clinton, so that the high priests and priestesses can produce yet another, a better, a new ‘final theory’.
The time to say no to this absurdist fantasy is right now. My own feeling is that a final theory, even if it is actually realisable, should always remain a dream.