The Cosmic Landscape Read online

  But the controversy among scientists does have repercussions for the broader public debate. Not surprisingly, it does overflow the seminar rooms and scientific journals into the political debates about design and creationism. Christian Internet sites have leapt into the fray:

  The Bible says:

  “From the time the world was created, people have seen the earth and the sky and all that God made. They can clearly see His invisible qualities—His eternal power and divine nature. So they have no excuse whatsoever for not knowing God.”

  This is as true today as it ever has been—in some ways, with the discovery of the Anthropic Principle, it is more true now than ever before. So the first kind of evidence that we have is the creation itself—a universe that carries God’s signature—a universe “just right” for us to live in.

  And from another religious site:

  In his book “The Cosmic Blueprint,” the astronomer professor Paul Davies concludes that the evidence for design is overwhelming:

  Professor Sir Fred Hoyle—no sympathizer with Christianity—says that it looks as if a super-intellect has monkeyed with physics as well as with chemistry and biology.

  And the astronomer George Greenstein says:

  As we survey all the evidence, the thought insistently arises that some supernatural agency, or rather Agency, must be involved. Is it possible that suddenly, without intending to, we have stumbled upon scientific proof of the existence of a supreme being? Was it God who stepped in and so providentially created the cosmos for our benefit?*

  Is it any wonder that the Anthropic Principle makes many physicists very uncomfortable?

  Davies and Greenstein are serious scholars, and Hoyle was one of the great scientists of the twentieth century. As they point out, the appearance of intelligent design is undeniable.† Extraordinary coincidences are required for life to be possible. It will take us a few chapters to fully understand this “elephant in the room,” but let’s begin with a sneak preview.

  The world as we know it is very precarious, in a sense that is of special interest to physicists. There are many ways it could go bad—so bad that life as we know it would be totally impossible. The requirements that the world be similar enough to our own to support conventional life fall into three broad classes. The first class involves the raw materials of life: chemicals. Life is, of course, a chemical process. Something about the way atoms are constructed makes them stick together in the most bizarre combinations: the giant crazy Tinkertoy molecules of life—DNA, RNA, hundreds of proteins, and all the rest. Chemistry is really a branch of physics: the physics of the valence electrons, i.e., those that orbit the nucleus at the outer edges of the atom. It’s the valence electrons hopping back and forth or being shared between atoms that gives the atoms their amazing abilities.

  The Laws of Physics begin with a list of elementary particles like electrons, quarks, and photons, each with special properties such as mass and electric charge. These are the objects that everything else is built out of. No one knows why the list is what it is or why the properties of these particles are exactly what they are. An infinite number of other lists is equally possible. But a universe filled with life is by no means a generic expectation. Eliminating any of these particles (electrons, quarks, or photons), or even changing their properties a modest amount, would cause conventional chemistry to collapse. This is obviously so for the electrons and for the quarks that make up protons and neutrons. Without these there could be no atoms at all. But the importance of the photon may be less obvious. In later chapters we will learn about the origin of forces like electric and gravitational forces, but for now it’s enough to know that the electric forces that hold the atom together are consequences of the photon and its special properties.

  If the laws of nature seem well chosen for chemistry, they are also well chosen for the second set of requirements, namely, that the evolution of the universe provided us with a comfortable home to live in. The large-scale properties of the universe—its size; how fast it grows; the existence of galaxies, stars, and planets—are mainly governed by the force of gravity. It’s Einstein’s theory of gravity—the General Theory of Relativity—that explains how the universe expanded from the initial hot Big Bang to its present large size. The properties of gravity, especially its strength, could easily have been different. In fact it is an unexplained miracle that gravity is as weak as it is.* The gravitational force between electrons and the atomic nucleus is ten thousand billion billion billion billion times weaker than the electrical attraction. Were the gravitational forces even a little stronger, the universe would have evolved so quickly that there would have been no time for intelligent life to arise.

  But gravity plays a very dramatic role in the unfolding of the universe. Its pull causes the material in the universe—hydrogen, helium, and the so-called dark matter—to clump, into galaxies, stars, and finally planets. However, for this to happen, the very early universe must have been a bit lumpy. If the original material of the universe had been smoothly distributed, it would have stayed that way for all time. In fact, fourteen billion years ago, the universe was just lumpy enough—a bit lumpier or a bit less lumpy, and there would have been no galaxies, stars, or planets for life to evolve on.

  Finally, there is the actual chemical composition of the universe. In the beginning there were only hydrogen and helium: certainly not sufficient for the formation of life. Carbon, oxygen, and all the others came later. They were formed in the nuclear reactors in the interiors of stars. But the ability of stars to transmute hydrogen and helium into the all-important carbon nuclei was a very delicate affair. Small changes in the laws of electricity and nuclear physics could have prevented the formation of carbon.

  Even if the carbon, oxygen, and other biologically important elements were formed inside stars, they had to get out in order to provide the material for planets and life. Obviously we cannot live in the intensely hot cores of stars. How did the material escape the stellar interior? The answer is that it was violently ejected in cataclysmic supernova explosions.

  Supernova explosions themselves are remarkable phenomena. In addition to protons, neutrons, electrons, photons, and gravity, supernovae require yet another particle—the ghostly neutrino previously mentioned. The neutrinos, as they escape from the collapsing star, create a pressure that pushes the elements in front of them. And, fortunately, the list of elementary particles happens to include neutrinos with the right properties.

  As I said, a world full of biological phenomena is by no means a generic expectation. From the point of view of picking elementary-particle lists and strengths of forces, it is the very rare exception. But how exceptional—exceptional enough to warrant a radically new paradigm including the Anthropic Principle? If we were to base our opinions on only the things that I’ve explained so far, opinions would be mixed, even among those who are open to anthropic ideas. Most of the individual fine-tunings needed for life are not so very precise that they couldn’t just be lucky accidents. Perhaps, as physicists have always believed, a mathematical principle will be discovered that explains the list of particles and constants of nature and a lot of lucky accidents will prove to be just that: a lot of lucky accidents. But there is one fine-tuning of nature that I will explain in chapter 2 that is incredibly unlikely. Its occurrence has been a stupendous puzzle to physicists for more than half a century. The only explanation, if it can be called that, is the Anthropic Principle.

  A paradox then: how can we ever hope to explain the extraordinarily benevolent properties of the Laws of Physics, and our own world, without appeal to a supernatural intelligence? The Anthropic Principle, with its placement of intelligent life at the center of the explanation for our universe, would seem to suggest that someone, some Agent, is looking out for humankind. This book is about the emerging physical paradigm that does make use of the Anthropic Principle but in a way that offers a wholly scientific explanation of the apparent benevolence of the universe. I think of it as the physicist
’s Darwinism.

  What are these Laws of Physics of which I’ve spoken? How are they formulated? Until Richard Feynman came along, the only tools that physicists had for expressing Laws of Physics were the arcane, impenetrable equations of quantum field theory—a subject so difficult that even mathematicians have trouble understanding it. But Feynman’s uncanny ability to visualize physical phenomena changed all that. He made it possible to summarize the laws of elementary particles by drawing a few simple pictures. Feynman’s pictures and the laws of elementary-particle physics, known to physicists as the Standard Model, are the subjects of chapter 1.

  Is it really true that the universe and its laws are very delicately balanced? The second chapter, “The Mother of All Physics Problems,” could also be called “The Mother of All Balancing Acts.” When the laws of elementary particles meet the laws of gravity, the result is a potential catastrophe: a world of such violence that astronomical bodies, as well as elementary particles, would be torn asunder by the most destructive force imaginable. The only way out is for one particular constant of nature—Einstein’s cosmological constant—to be so incredibly finely tuned that no one could possibly think it accidental. First introduced by Einstein soon after the completion of his theory of gravity, the cosmological constant has been the greatest enigma of theoretical physics for almost ninety years. It represents a universal repulsive force—a kind of antigravity—that would instantly destroy the universe if it were not astonishingly small. The problem is that all our modern theories imply that the cosmological constant should not be small. The modern principles of physics are based on two foundations: the Theory of Relativity and quantum mechanics. The generic result of a world based on these principles is a universe that would very quickly self-destruct. But for reasons that have been completely incomprehensible, the cosmological constant is fine-tuned to an astonishing degree. This, more than any other lucky “accident,” leads some people to conclude that the universe must be the result of a design.

  Is the Standard Model of particle physics “written in stone”? Are other laws possible? In the third chapter of this book, I explain why our particular laws are not at all unique—how they could change from place to place or from time to time. The Laws of Physics are much like the weather: they are controlled by invisible influences in space almost the same way that temperature, humidity, air pressure, and wind velocity control how rain and snow and hail form. The invisible influences are called fields. Some of them, like the magnetic field, are fairly familiar. Many others are unfamiliar, even to physicists. But they are there, filling space and controlling the behavior of elementary particles. The Landscape is the term that I coined to describe the entire extent of these theoretical environments. The Landscape is the space of possibilities—a schematic representation of all the possible environments permitted by theory. Over the last couple of years, the existence of a rich Landscape of possibilities has become the central question of String Theory.

  The controversy is not only scientific. In chapter 4 we will talk about the aesthetic side of the debate. Physicists, particularly theoretical physicists, have a very strong sense of beauty, elegance, and uniqueness. They have always believed that the laws of nature are the unique inevitable consequence of some elegant mathematical principle. The belief is so deeply ingrained that most of my colleagues would feel an immense sense of loss and disappointment if this uniqueness and elegance turned out to be absent—if the Laws of Physics are “ugly.” But are the Laws of Physics elegant in the physicist’s sense? If the only criterion for how the universe works is that it should support life, it may well be that the whole structure is a clumsy, ungainly “Rube Goldberg machine.”* Despite the protestations of physicists that the laws of elementary particles are elegant, the empirical evidence points much more convincingly to the opposite conclusion. The universe has more in common with a Rube Goldberg machine than with a unique consequence of mathematical symmetry. We cannot fully understand the controversy and the shifting paradigms without also understanding the notions of beauty and elegance in physics, how they originated, and how they compare with the real world.

  This book is about a conceptual “earthquake,” but it is not the work of only theorists. Much of what we know comes from experimental cosmology and modern astronomy. Two key discoveries are driving the paradigm shift—the success of inflationary cosmology and the existence of a small cosmological constant. Inflation refers to the brief period of rapid exponential expansion that initially set the stage for the Big Bang. Without it the universe would probably have been a tiny Little Pop, no bigger than an elementary particle. With it, the universe grew to proportions vastly bigger than anything we can detect with the most powerful telescopes. When Alan Guth first suggested inflation, in 1980, there seemed to be very little chance that astronomical observations would ever be able to test it. But astronomy has advanced by orders of magnitude since 1980: so much so that what seemed inconceivable then is accomplished fact today.

  The enormous advances in astronomy led to a second discovery that came as a thunderbolt to physicists, something so shocking that we are still reeling from the impact. The infamous cosmological constant,* which almost everyone was sure was exactly zero, isn’t. It seems that the laws of nature were fine-tuned just enough to keep the cosmological constant from being a deadly danger to the formation of life, but no more than that. Chapter 5 is devoted to these discoveries. This chapter also explains all the basic astronomical and cosmological background that the reader will need.

  The cosmological constant may be the “mother of all balancing acts,” but there are many additional delicate conditions that seem like fantastically lucky coincidences. Chapter 6, “On Frozen Fish and Boiled Fish,” is all about these lesser balancing acts. They range from the cosmological to the microscopic, from the way the universe expands to the masses of elementary particles like the proton and neutron. Once again the lesson is not that the universe is simple but that it is full of surprising, unexplained, lucky coincidences.

  Until very recently, the Anthropic Principle was considered by almost all physicists to be unscientific, religious, and generally a goofy misguided idea. According to physicists it was a creation of inebriated cosmologists, drunk on their own mystical ideas. Real theories like String Theory would explain all the properties of nature in a unique way that has nothing to do with our own existence. But a stunning reversal of fortune has put string theorists in an embarrassing position: their own cherished theory is pushing them right into the waiting arms of the enemy. String Theory is turning out to be the enemy’s strongest weapon. Instead of producing a single unique elegant construct, it gives rise to a colossal landscape of Rube Goldberg machines. The result of the reversal is that many string theorists have switched sides. Chapters 7, 8, 9, and 10 are about String Theory and how it is changing the paradigm.

  Chapters 11 and 12 are about the startling new view of the universe that is emerging out of the combined work of astronomers, cosmologists, and theoretical physicists: the world—according to cosmologists such as Andrei Linde, Alexander Vilenkin, and Alan Guth—consists of a virtually infinite collection of “pocket universes” of enormous diversity. Each pocket has its own “weather”: its own list of elementary particles, forces, and constants of physics. The consequences of such a rich view of the universe are profound for physics and cosmology. The question, “Why is the universe the way it is?” may be replaced by, “Is there a pocket in this vast diversity in which conditions match our own?” How the mechanism called Eternal Inflation caused this diversity to evolve from primordial chaos and how it revolutionizes the debates over the Anthropic Principle and the design of the universe are the subjects of chapter 11.

  This cosmological paradigm shift is not the only one taking place in the foundations of physics. Chapter 12 concerns another titanic battle, a conflict I call the Black Hole War. The Black Hole War has played out over the last thirty years and has radically changed the way theoretical physicists think abou
t gravity and black holes. The fierce battle was over the fate of information that falls behind the horizon of a black hole: is it permanently lost, totally beyond the knowledge of observers on the outside, or is there some subtle way in which the details are conveyed back out as the black hole evaporates? Hawking’s view was that all information behind the horizon is irretrievably lost. Not even the slightest shred of information about the objects that are on the other side can ever be reconstructed. But that has turned out to be wrong. The laws of quantum mechanics prevent even a single bit from being lost. In order to understand how information escapes the prison of a black hole, it was necessary to completely rebuild our most basic concepts of space.

  What does the Black Hole War have to do with the concerns of this book? Because the universe is expanding under the influence of the cosmological constant, cosmology also has its horizons. Our cosmic horizon is about fifteen billion light-years away, where things are moving so rapidly away from us that light from there can never reach us, nor can any other signal. It is exactly the same as a black hole horizon—a point of no return. The only difference is that the cosmic horizon surrounds us, whereas we surround a black hole horizon. In either case nothing from beyond the horizon can influence us, or so it was thought. Furthermore, the other pocket universes—the gigantic sea of diversity—are all beyond our reach behind the horizon! According to classical physics, those other worlds are forever completely sealed off from our world. But the very same arguments that won the Black Hole War can be adapted to cosmological horizons. The existence and details of all the other pocket universes are contained in the subtle features of the cosmic radiation that constantly bathes all parts of our observable universe. Chapter 12 is an introduction to the Black Hole War, how it was won, and its implications for cosmology.