The Trouble With Physics: The Rise of String Theory, The Fall of a Science, and What Comes Next

by Lee Smolin

  Darwinian evolutionary biology is the prototype for thinking in time, because at its heart is the realization that natural processes developing in time can lead to the creation of genuinely novel structures. Even novel laws can emerge, when the structures to which they apply come into existence. The principles of sexual selection, for example, could not have come to exist before there were sexes. Evolutionary dynamics has no need of vast abstract spaces, like all the possible viable animals, DNA sequences, sets of proteins, or biological laws. Better, as the theoretical biologist Stuart A. Kauffman proposes, to think of evolutionary dynamics as the exploration in time by the biosphere of what can happen next: the “adjacent possible.” The same goes for the evolution of technologies, economies, and societies.

  Thinking in time is not relativism but a form of relationalism—a philosophy that asserts that the truest description of something consists of specifying its relationships to the other parts of the system it is part of. Truth can be both time-bound and objective when it’s about objects that exist once they’ve been invented, either by evolution or human thought.

  On a personal level, to think in time is to accept the uncertainty of life as the necessary price of being alive. To rebel against the precariousness of life, to reject uncertainty, to adopt a zero tolerance to risk, to imagine that life can be organized to completely eliminate danger, is to think outside time. To be human is to live suspended between danger and opportunity.

  We try our best to thrive in an uncertain world, to take care of whom and what we love and now and then enjoy ourselves in the process. We make plans, but we can never anticipate fully either the dangers or the opportunities ahead. The Buddhists say that we live in a house we haven’t yet noticed is on fire. Danger might arise at any time, and in hunter-gatherer societies it was ever present, but in modern life we have organized things so that it’s comparatively rare. The challenge of life is to choose wisely, from the enormous number of possible dangers, what’s worth worrying about. It is also about choosing, from all the opportunities that each moment brings, what to do next. We choose where to devote our energy and attention—always in the face of incomplete knowledge of the consequences.

  Could we do better? Could we overcome the capriciousness of life and achieve a state wherein we knew, if not everything, enough to see all the consequences of our choices—the dangers and the opportunities alike? That is, could we live a truly rational life, without surprises? If time were an illusion, we could imagine this as possible, because in a world in which time was dispensable there would be no fundamental difference between knowledge of the present and knowledge of the future. It would take just a bit more computation to work out. Some number, some formula, could be computed and decoded to tell us all we needed to know.

  But if time is real, the future is not determinable from knowledge of the present. There is no escape from our situation, no redemption from the surprises that come from living in ignorance of most of the consequences of our actions. Surprise is inherent in the structure of the world. Nature can throw us surprises for which no amount of knowledge would have prepared us. Novelty is real. We can create, with our imagination, outcomes not computable from knowledge of the present. This is why it matters for each of us whether time is real or not: The answer can change how we view our situation as seekers of happiness and meaning in a largely unknown universe. I will return to these themes in the Epilogue, where I suggest that the reality of time can help us think about such challenges as climate change and economic crisis.

  Before we begin the main argument of the book, a few words of advice.

  I have tried to make the arguments of this book accessible for the general reader without a background in physics or mathematics. There are no equations, and everything you need to know to follow my arguments is explained. The essential questions are illustrated with the simplest examples possible. As we move on to more sophisticated subjects, readers are advised, if confused, to do what scientists learn to do, which is to skim or skip ahead to a point where the text becomes clearer to them. Readers wanting more background can also consult the several appendices, which are available on-line at www.time reborn.com. The reader may also find it helpful to consult the Notes, which contain citations, helpful remarks either for laypeople or experts, and further discussions that may interest some readers.

  My own journey back to time has taken more than twenty years, from my recognition that laws are to be explained by their having evolved, through my struggles with relativity, quantum foundations, and quantum gravity, which finally led me to the view described here. Collaborations and conversations with several friends and colleagues have been essential to my progress on this road; they are detailed in the Acknowledgments and Notes, as is my use of the results and ideas of others. None of these interactions was more important than a fruitful and provocative collaboration with Roberto Mangabeira Unger, during which we formulated the main argument and many of the key ideas that follow.

  Readers should be aware that there are many points of view about time, quantum theory, cosmology, and other such topics that are not discussed here. There is a vast literature by physicists, cosmologists, and philosophers concerning the issues I touch on. This does not pretend to be an academic book. I have chosen to give readers who may be encountering this area of discussion for the first time one path through its complex terrain, highlighting particular arguments that are its focus. There are (to take one example) bookshelves full of writings analyzing Kant’s views on space and time, which are not mentioned here. Nor do I describe some of the views of contemporary philosophers. I ask forgiveness of my learned friends for these omissions and direct the interested reader to the Bibliography, which contains suggestions for further reading about time.

  LEE SMOLIN

  TORONTO, AUGUST 2012

  Introduction

  THE SCIENTIFIC CASE for time being an illusion is formidable. That is why the consequences of adopting the view that time is real are revolutionary.

  The core of the physicists’ case against time relies on the way we understand what a law of physics is. According to this dominant view, everything that happens in the universe is determined by a law, which dictates precisely how the future evolves out of the present. The law is absolute and, once present conditions are specified, there is no freedom or uncertainty in how the future will evolve.

  As Thomasina, the precocious heroine of Tom Stoppard’s play Arcadia, explains to her tutor: “If you could stop every atom in its position and direction, and if your mind could comprehend all the actions thus suspended, then if you were really, really good at algebra you could write the formula for all the future; and although nobody can be so clever as to do it, the formula must exist just as if one could.”

  I used to believe that my job as a theoretical physicist was to find that formula; I now see my faith in its existence as more mysticism than science.

  Were he writing lines for a modern character, Stoppard would have had Thomasina say that the universe is like a computer. The laws of physics are the program. When you give it an input—the present positions of all the elementary particles in the universe—the computer runs for an appropriate amount of time and gives you the output, which is all the positions of the elementary particles at some future time. Within this view of nature, nothing happens except the rearrangement of particles according to timeless laws, so according to these laws the future is already completely determined by the present, as the present was by the past.

  This view diminishes time in several ways. There can be no surprises, no truly novel phenomena, because all that happens is rearrangement of the atoms. The properties of the atoms themselves are timeless, as are the laws controlling them; neither ever changes. Any feature of the world at a future time can be computed from the configuration of the present. That is, the passage of time can be replaced by a computation, which means that the future is logically a consequence of the present.

  Einstein’s theories of relativity m
ake even stronger arguments that time is inessential to a fundamental description of the world, as I’ll discuss in chapter 6. Relativity strongly suggests that the whole history of the world is a timeless unity; present, past, and future have no meaning apart from human subjectivity. Time is just another dimension of space, and the sense we have of experiencing moments passing is an illusion behind which is a timeless reality.

  These assertions may seem horrifying to anyone whose worldview includes a place for free will or human agency. This is not an argument I will engage in here; my case for the reality of time rests purely on science. My job will be to explain why the usual arguments for a predetermined future are wrong scientifically.

  In Part I, I will present the case from science for believing that time is an illusion. In Part II, I will demolish those arguments and show why time must be taken to be real if fundamental physics and cosmology are to overcome the crises they currently face.

  To frame the argument of Part I, I trace the development of the concepts of time used in physics, from Aristotle and Ptolemy through Galileo, Newton, Einstein, and on to our contemporary quantum cosmologists, and show how our concept of time was diminished, step by step, as physics progressed. Telling the story this way also allows me to gently introduce the material the lay reader needs for an understanding of the argument. Indeed, key points can be introduced by ordinary examples of balls falling and planets orbiting. Part II tells a more contemporary story, since the argument that time must be reinserted into the core of science arose as a result of recent developments.

  My argument starts with a simple observation: The success of scientific theories from Newton through the present day is based on their use of a particular framework of explanation invented by Newton. This framework views nature as consisting of nothing but particles with timeless properties, whose motions and interactions are determined by timeless laws. The properties of the particles, such as their masses and electric charges, never change, and neither do the laws that act on them. This framework is ideally suited to describe small parts of the universe, but it falls apart when we attempt to apply it to the universe as a whole.

  All the major theories of physics are about parts of the universe—a radio, a ball in flight, a biological cell, the Earth, a galaxy. When we describe a part of the universe, we leave ourselves and our measuring tools outside the system. We leave out our role in selecting or preparing the system we study. We leave out the references that serve to establish where the system is. Most crucially for our concern with the nature of time, we leave out the clocks by which we measure change in the system.

  The attempt to extend physics to cosmology brings new challenges that require fresh thinking. A cosmological theory cannot leave anything out. To be complete, it must take into account everything in the universe, including ourselves as observers. It must account for our measuring instruments and clocks. When we do cosmology, we confront a novel circumstance: It is impossible to get outside the system we’re studying when that system is the entire universe.

  Moreover, a cosmological theory must do without two important aspects of the methodology of science. A basic rule of science is that an experiment must be done many times to be sure of the result. But we cannot do this with the universe as a whole—the universe only happens once. Nor can we prepare the system in different ways and study the consequences. These are very real handicaps, which make it much harder to do science at the level of the universe as a whole.

  Nonetheless, we want to extend physics to a science of cosmology. Our first instinct is to take the theories that worked so well when applied to small parts of the universe and scale them up to describe the universe as a whole. As I’ll show in chapters 8 and 9, this cannot work. The Newtonian framework of timeless laws acting on particles with timeless properties is unsuited to the task of describing the entire universe.

  Indeed, as I will show in detail, the very features that make these kinds of theories so successful when applied to small parts of the universe cause them to fail when we attempt to apply them to the universe as a whole.

  I realize that this assertion goes counter to the practice and hopes of many colleagues, but I ask only that the reader pay close attention to the case I make for it in Part II. There I will show in general, and illustrate by specific example, that when we attempt to scale up our standard theories to a cosmological theory, we are rewarded with dilemmas, paradoxes, and unanswerable questions. Among these are the failure of any standard theory to account for the choices made in the early universe—choices of initial conditions and choices of the laws of nature themselves.

  Some of the literature of contemporary cosmology consists of the efforts of very smart people to wrestle with these dilemmas, paradoxes, and unanswerable questions. The notion that our universe is part of a vast or infinite multiverse is popular—and understandably so, because it is based on a methodological error that is easy to fall into. Our current theories can work at the level of the universe only if our universe is a subsystem of a larger system. So we invent a fictional environment and fill it with other universes. This cannot lead to any real scientific progress, because we cannot confirm or falsify any hypothesis about universes causally disconnected from our own.

  The purpose of this book is to suggest that there is another way. We need to make a clean break and embark on a search for a new kind of theory that can be applied to the whole universe—a theory that avoids the confusions and paradoxes, answers the unanswerable questions, and generates genuine physical predictions for cosmological observations.

  I do not have such a theory, but what I can offer is a set of principles to guide the search for it. These are presented in chapter 10. In the chapters that follow it, I will illustrate how the principles can inspire new hypotheses and models of the universe that point the way to a true cosmological theory. The central principle is that time must be real and physical laws must evolve in that real time.

  The idea of evolving laws is not new, nor is the idea that a cosmological science will require them. The American philosopher Charles Sanders Peirce wrote in 1891:

  To suppose universal laws of nature capable of being apprehended by the mind and yet having no reason for their special forms, but standing inexplicable and irrational, is hardly a justifiable position. Uniformities are precisely the sort of facts that need to be accounted for. . . . Law is par excellence the thing that wants a reason.

  Now the only possible way of accounting for the laws of nature and for uniformity in general is to suppose them results of evolution.”

  The contemporary philosopher Roberto Mangabeira Unger has more recently proclaimed:

  You can trace the properties of the present universe back to properties it must have had at its beginning. But you cannot show that these are the only properties that any universe might have had. . . . Earlier or later universes might have had entirely different laws. . . . To state the laws of nature is not to describe or to explain all possible histories of all possible universes. Only a relative distinction exists between lawlike explanation and the narration of a one-time historical sequence.”

  Paul Dirac, who ranks with Einstein and Niels Bohr as one of the most consequential physicists of the 20th century, speculated: “At the beginning of time the laws of Nature were probably very different from what they are now. Thus, we should consider the laws of Nature as continually changing with the epoch, instead of as holding uniformly throughout space-time.” John Archibald Wheeler, one of the great American physicists, also imagined that laws evolved. He proposed that the Big Bang was one of a series of events within which the laws of physics were reprocessed. He also wrote, “There is no law except the law that there is no law.” Even Richard Feynman, another of the great American physicists and Wheeler’s student, once mused in an interview: “The only field which has not admitted any evolutionary question is physics. Here are the laws, we say, . . . but how did they get that way, in time? . . . So, it might turn out that they are not the same [laws]
all the time and that there is a historical, evolutionary, question.”

  In my 1997 book, The Life of the Cosmos, I proposed a mechanism for laws to evolve, which I modeled on biological evolution. I imagined that universes could reproduce by forming baby universes inside black holes, and I posited that whenever this happens, the laws of physics change slightly. In this theory, the laws played the role of genes in biology; a universe was seen as an expression of a choice of laws made at its formation, just as an organism is an expression of its genes. Like the genes, the laws could mutate randomly from generation to generation. Inspired by then-recent results of string theory, I imagined that the search for a fundamental unified theory would lead not to a single Theory of Everything but to a vast space of possible laws. I called this the landscape of theories, taking the language from population genetics, whose practitioners work with fitness landscapes. I will not say more about this here, as it is the subject of chapter 11, except to say that this theory, cosmological natural selection, makes several predictions that, remarkably, have held up despite several opportunities to falsify them in the years since.

  Over the last decade, many string theorists have embraced the concept of a landscape of theories. As a result, the question of how the universe chooses which laws to follow has become especially urgent. This, I will argue, is one of the questions that can be answered only within a new framework for cosmology in which time is real and laws evolve.