When I first told Wilczek that I was writing this book, he related a somewhat disconcerting story to me about a time when he tried to explain the remarkable aspects of the strong interaction between quarks to a public audience (before the Nobel committee anointed this work as being important). After the talk, a member of the audience raised his hand and asked: “Why should I care about all of this? Isn’t it just the fourdimensional manifestation of the far more fundamental predictions made by string theory in ten dimensions?”
This reminded both of us of an earlier time when we were working together to advise the Smithsonian Institution on several projects it was sponsoring, supported by the Defense Advanced Research Projects Agency (DARPA, a national security funding group), on the detection of neutrinos. DARPA was interested in detecting neutrinos because they are emitted by nuclear reactors, and nuclear reactors are on submarines, and detecting submarines is of vital strategic importance. Thus, even far-out schemes seemed to DARPA to be worth throwing a bit of money at, because if any of them worked, it could easily have tipped the Cold War strategic balance in our favor.
Of the projects we examined, all were rather fanciful, but one was at least marginally plausible. It was a proposal to detect neutrinos from possible nearby nuclear weapons tests using a large ton-sized detector. However, when we informed DARPA of our choice, we were told that they had already been supporting the work of a well-known (but misguided) scientist, who claimed he had a bread box–sized device that could detect neutrinos from every nuclear reactor and nuclear weapon on Earth. How could DARPA therefore justify funding a ton-sized detector near a nuclear weapons test when it was spending millions on a far smaller detector that was argued to be far more sensitive?
This is the problem that often arises when speculative science is valued more than the remarkable achievements of empirically tested science. The moral for our present discussions is, I hope, clear. The tremendous intellectual efforts over the past century to formulate a candidate theory that might unify quantum mechanics and gravity in a higher-dimensional framework should not be minimized. The theoretical and mathematical results that have been developed are fascinating. But neither should they be celebrated for more than they yet are.
It does a disservice to the most remarkable century in the history of human intellectual investigation to diminish the profound theoretical and experimental discoveries we have made in favor of what is at the present time essentially well-motivated, educated speculation. It is also simply disingenuous to claim that there is any definitive evidence that any of the ideas associated with string theory yet bear a clear connection to reality, or that they will even survive in their present form for very much longer. Perhaps more to the point, the deeper we probe these theories, the hazier they seem to have become.
Which brings us to Edward Witten, who has been the leading force driving string theory since the mid 1980s. Ed is not only an incredible intellect, but he is also a refreshingly honest one. He says what he means, and he always has a sound reason for saying what he does. Edward is also the attributed author of the infamous statement regarding twenty-first-century physics in the twentieth century, which is probably one reason it is so often repeated. But one should not read more into that observation than I believe Ed intended. Ed may be a “true believer” in string theory, but that simply reflects the very nature of his position on the theoretical forefront. It is, as I have stressed, very difficult to devote the incredible intellectual energy and focus that are required over long periods of time in the attempt to unravel the hidden realities of nature if one does not have great personal conviction that one has a good chance of being on the right track. As Edward said succinctly at a recent meeting on the future of physics, regarding why one should study string theory: “I don’t consider it plausible that a completely wrong theory would generate so many good ideas.”
The same level of personal conviction is required of artists and writers, as well. But what makes science somewhat different, I believe, is that great scientists are prepared to follow an idea for as long as decades, but at the same time are equally prepared to dispense with all of this effort in a New York minute if a better idea or a contradictory experimental result comes along.
With this in mind, a number of other statements that Edward made at this recent meeting are quite telling and, I believe, validate the gestalt I have tried to characterize here. Summarizing the essential progress of the theory he has devoted much of the past two decades to studying, he said:
“It [string theory] is a remarkably simple way of getting a rough draft of particle physics unified with gravity. There are, however, uncomfortably many ways to reach such a rough draft, and it is frustratingly difficult to get a second draft.” He next reiterated that while we lack any understanding of the core idea—equivalent to the Equivalence Principle (between gravity and acceleration) that was at the heart of general relativity—behind string theory, at its heart is the notion that space-time is an “emergent” and not a fundamental concept. Thus, the whole notion of what an extra spatial dimension may mean within the context of string theory is not clear. More interesting still, he argued that even strings themselves are not likely to be fundamental, but that they, too, would prove to be an emergent concept based on something more fundamental. Finally, Witten stressed what I believe, given the current situation in string theory after more than twenty years of research, is an eminently reasonable position: That it is at best plausible that we will manage to ever understand what string theory is all about, and, whether or not we do, that it is not at all clear whether we will be able to use it to understand nature. This will depend upon factors beyond our control, including how complex the ultimate answer may be, and what clues we might be lucky enough to derive from experiment. I reiterate that these were statements made not by a skeptic, but by someone who passionately believes that string theory contains a germ of truth.
I have debated this very point on stage twice with Brian Greene, who has worked as hard as anyone to popularize and celebrate string theory. Brian earnestly and successfully communicates the excitement of the theory in a way that can inspire lay people. Brian is an honest popularizer and prefaces his remarks about string theory with qualifications about its present speculative and unproven state. However, he is so convincing and enthusiastic that I have argued with him that when such things as animations of strings within elementary particles are presented, even if the intent is merely illustrative, it tends to give the impression that string theory is a better defined construct than it currently is, and also suggests it gives definite predictions about the properties of observed elementary particles in four dimensions. This is of course a subjective issue, and I know Brian disagrees with me about this. Ultimately, from my perspective, this enthusiasm is unwarranted at the present time, given what might be described as the current impotence of the theory.
In order to dramatize my own concerns about the dangers of conveying enthusiasm as truth, I have claimed that string theory is in some sense the least successful great idea in twentieth-century physics, a statement that The New York Times kindly quoted out of context. At a recent event celebrating Einstein, I pointed out that it is somewhat incongruous to, on one hand, portray as tragic the past thirty years of Einstein’s life, during which he worked on his own on an unsuccessful unified field theory, while at the same time celebrate at scientific meetings and in the popular media perhaps three thousand man-years of full-time intellectual activity by a brigade of some of the most talented young theoretical minds around the world on a proposed unified theory that has thus far been largely fruitless in its predictions, and has yet to be properly understood. I believe both extreme viewpoints are inappropriate. Einstein’s efforts were no more tragic than the recent string program has been an unqualified success. Both are part of the search for underlying order in the natural world that proceeds by fits and starts, and is full of far more blind alleys than awakenings.
And I want to reiterate once again, per
haps even more strongly, that these efforts, even if they do not produce the results we wish, will not have been wasted. Ed Witten wrote me a frank letter after I asked him to read a draft of this book. He described how, when he was a student in the 1970s, he was obsessed with trying to understand, on the basis of simple analytical physical calculations, exactly why quarks are confined together. He gave up, because he thought the problem was too hard. Now, almost thirty years later, he is working on the problem again, this time using the tools of string theory, and he feels he is making progress. As he put it: “Being able to develop these models in the last decade, fifteen years after giving up on quark confinement as too hard, has been a lot of fun.” Moreover, after arguing that the many developments I have discussed are evidence that our understanding of string theory is reaching a deeper level, he nevertheless emphasized that this most recent work, on using string methods to attack quark confinement and not quantum gravity, as originally intended, has “maybe been the most fun for me.”
One never knows where insights will come from, or where they may lead. The pleasure of research is discovering the unexpected. Ed’s poignant remark underscores that ultimately the driving force behind all human inquiry is the satisfaction of the quest itself. We may or may not be hardwired to long for hidden realities, but we are most certainly hardwired to enjoy solving puzzles, especially when their resolution is far from what one may initially have expected.
I would also be less than candid if I did not reveal that there is other, more personal evidence I now have that the string effort has already borne some fruit. After The New York Times published my supposed statement on the failures of string theory, I received a package in the mail from California. Upon opening it, I found a fruit basket from John Schwarz with a note, which read: “Dear Lawrence: Now maybe you won’t feel it’s all been so fruitless.”
This finally brings me to David Gross, who has played the most interesting sociological role in the story I have told. You will recall that David was a student at Berkeley in the 1960s, the era of bootstrap models and dual string models as applied to strongly interacting elementary particles. He thus received his scientific grounding in theories that turned out to be footnotes in scientific history. But it was ultimately his own work on asymptotic freedom, for which he has shared the Nobel Prize, that turned them into footnotes.
In another poetic example of the ironies of scientific progress, over a decade later David became a key part of the new string revolution, which reinstated the very ideas he had earlier killed, but this time in a new context. His work on heterotic strings, and the possibility of explaining all the phenomenology of elementary particle physics in four dimensions via an underlying theory in ten and twenty-six dimensions, helped to create the fervor that motivated Witten’s statement about the incursion of twentyfirst-century physics into the twentieth century. But, as Ed Witten has admitted, these ideas ultimately just produced a “rough draft” that has yet to ever go beyond this stage. One might think that having witnessed the demise of a similar rough draft in the 1970s that Gross might temper his statements about the ultimate truth of the new string theory. But it is an interesting facet of the human condition that revolutionaries sometimes replicate certain features of the regimes they set out to overthrow. In this case the former young rebel has become something of a defender of the faith.
In many forums David has argued forcefully—and, of course, brilliantly, because his is a powerful intellect—that the theory is simply too beautiful not to be true. As such, every new result tends to merely reinforce its truth, even without the luxury of experiment. As I have described, this attitude has been adopted by many of the younger researchers in this field, who are, of course, strongly influenced by their senior mentors, as well as the mathematical appeal of the subject.
I do not mean to cast aspersion on David’s scientific work, which has been impeccable and important. And as I said, it is perfectly reasonable to expect those theorists who have devoted decades to exploring a theory to be driven by an expectation of its inherent validity. The problem, however, is that this viewpoint strikes some, including me, as sounding like religion more than science. At other times in this century, science may have been able to more easily tolerate such confusion. Perhaps I am oversensitive on this subject, but I have spent much of the past several years fighting attacks on science, from the classroom to the White House. The aim of both these sets of challenges has been to replace the hard-won results of the scientific process with ideological dogma. In the former case, where individuals have been attempting to impugn a well-tested scientific theory that is the foundation of all of modern biology, I have often been told that science itself is merely another kind of religion. I believe that nothing should be further from the truth, and anything that confuses this issue is regressive. Still, the convergence of truth and beauty, at least as we behold it, is a notion that is in some sense central to almost everything I have discussed in this book. Indeed, I began with a discussion of the mysterious fact that nature and beautiful mathematics seem inextricably united. Recall Bertrand Russell’s description of mathematics as possessing “not only truth, but supreme beauty.” With that in mind it is, I believe, generally appropriate to give the last word to a mathematician whose work played a central role in the earliest developments that I have described here. I refer to Hermann Weyl, the brilliant mathematical physicist whose results originally inspired Kaluza to ponder extra dimensions, and who first exposed the fundamental symmetry of nature that we now call gauge invariance, which is at the heart of the description of all the known forces in nature, including gravity. Weyl was a student of Hilbert, one of the fathers of higher-dimensional geometry, and, as you may also recall, a competitor of Einstein’s on the road to developing general relativity. And Weyl ended his career at the Institute for Advanced Study at Princeton along with Einstein. So it is, in fact, particularly appropriate to turn to Weyl for enlightenment as we reach the end of our own journey through the looking glass. Upon reflecting upon his work, which clearly touched not only on mathematics but on the physical world, Weyl made a profoundly insightful confession that appeared in his own obituary, written by the physicist Freeman Dyson in 1956. Nothing I can think of better captures the dilemma exemplified by our ongoing, and remarkably timely, love affair with extra dimensions. Referring to his research, Weyl admitted:
My work always tried to unite the true with the beautiful, but when I had to choose one or the other, I usually chose the beautiful. So it is that mathematicians, poets, writers, and artists almost always choose beauty over truth. Scientists, alas, do not have this luxury, and can only hope that we do not have to make a choice.
A C K N O W L E D G M E N T S
Each of my books has been a tremendous learning experience. I depend greatly both on previous authors with their accumulated wisdom and on generous colleagues from a variety of areas who help steer me in the right direction as I begin to grapple with sometimes totally new subjects. Thinking about the cultural and social legacy associated with the notion of extra dimensions, I am enormously grateful to my Case colleague Henry Adams, professor of art history and former curator at the Cleveland Museum of Art. He and a student of his provided me with a wonderful bibliography of twentieth-century artists whose work related to the notion of a fourth dimension.
One of the most important books that I initially turned to was Linda Dalrymple Henderson’s The Fourth Dimension and Non-Euclidean Geometry in Modern Art, a wonderfully broad and complex discussion of the notion of a fourth dimension in modern art. I owe a great debt to her scholarship, which pointed me in the direction of numerous important sources, and which has inevitably strongly influenced my own thinking. I also owe thanks to several individuals in the science fiction community, notably Charles Brown and several other of my colleagues on the board of the Science Fiction Experience in Seattle, who helped direct me to the appropriate literature, in particular to the fiction and nonfiction work of Rudy Rucker on the fourth dimensi
on.
I want to thank the librarians at the Case Western Reserve University for providing me with great assistance, including a room to work and store books in, as I tried to devour the appropriate literature and write in a quiet place away from my office.
I thank numerous colleagues for discussions and illuminations related to the physics and historical ideas discussed here. I learned a great deal from the informative introduction in the book Modern Kaluza Klein Theory, by Tom Appelquist, Alan Chodos, and Peter Freund, as well as the comprehensive two-volume opus Superstring Theory by Michael Green, John Schwarz, and Edward Witten, and the more recent two-volume work String Theory by Joe Polchinski, as well as, of course, the numerous papers in the literature so easily accessible thanks to the physics Web archive created by Paul Ginsparg. I owe a personal great debt to my Case colleague and friend Cyrus Taylor, who spent many hours introducing me to the intricacies of string theory, and who directed me to appropriate places in the literature. Gia Dvali helped me first tackle large extra dimensions, and continues to provoke my imagination. My friend and colleague Frank Wilczek has shared many of his physics and philosophical insights with me over the years, and I appreciate his willingness to provide feedback on some of the issues I raised in the final chapters. Lastly, I want to thank all of my colleagues who have looked at this manuscript and provided comments and feedback. In particular, I want to thank Glenn Starkman for general suggestions, and John Schwarz and Edward Witten for carefully reading the sections on string theory and making comments.
Finally, I want to thank once again my wife Kate and daughter Lilli for putting up with and supporting me through yet another book project, and for being joyful reminders that physics is just one part of a fascinating world.
Hiding in the Mirror: The Quest for Alternate Realities, From Plato to String Theory (By Way of Alicein Wonderland, Einstein, and the Twilight Zone) Page 28