The Cosmic Landscape (3 page)

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.”
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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,
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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 about 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.

The controversy detailed in
The Cosmic Landscape
is a real one: physicists and cosmologists feel passionately about their own views, whatever they happen to be. Chapter 13 takes a look at the current opinions of many of the world’s leading theoretical physicists and cosmologists and how they individually view the controversy. I also discuss the various ways that experiment and observation can guide us toward consensus.

To Victor’s question, “Was it not God’s infinite kindness and love that permitted our existence?” I would have to answer with Laplace’s reply to Napoléon: “I have no need of this hypothesis.”
The Cosmic Landscape
is my answer, as well as the answer of a growing number of physicists and cosmologists, to the paradox of a benevolent universe.

N
o doubt we’ll never know the name of the first cosmologist to look to the sky and ask, “What is all this? How did it get here? What am
I
doing here?” What we do know is that it occurred deep in the prehistoric past, probably in Africa. The first cosmologies, creation myths, were nothing like today’s scientific cosmology, but they were born of the same human curiosity. Not surprisingly these myths were about earth, water, sky, and living creatures. And of course they featured the supernatural creator: how else to explain the existence of such complex and intricate creatures as humans, not to mention rain, sun, edible animals, and plants that seemed to be placed on earth just for our benefit?

The idea that precise laws of nature govern both the celestial and terrestrial world dates back to Isaac Newton. Before Newton, there was no concept of universal laws that applied both to astronomical objects like planets and to ordinary earthly objects like falling rain and flying arrows. Newton’s laws of motion were the first example of such universal laws. But even for the mighty Sir Isaac, it was far too much of a stretch to suppose that the same laws led to the creation of human beings: he spent more time on theology than physics.

I’m not a historian, but I’ll venture an opinion: modern cosmology really began with Darwin and Wallace.
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Unlike anyone before them, they provided explanations of our existence that completely rejected supernatural agents. Two natural laws underlie Darwinian evolution. The first is that copying information is never perfect. Even the best reproduction mechanisms from time to time make small errors. DNA replication is no exception. Although it would take a century for Crick and Watson to uncover the double helix, Darwin intuitively understood that accumulated random mutations constitute the engine that drives evolution. Most mutations are bad, but Darwin understood enough about probability to know that every now and then, by pure chance, a beneficial mutation occurs.

The second pillar of Darwin’s intuitive theory was a principle of competition: the winner gets to reproduce. Better genes prosper; inferior genes come to a dead end. These two simple ideas explained how complex and even intelligent life could form without any supernatural intervention. In today’s world of computer viruses and Internet worms, it’s easy to imagine similar principles applying to completely inanimate objects. Once the magic was removed from the origin of living creatures, the way lay open to a purely scientific explanation of creation.

Darwin and Wallace set a standard not only for the life sciences but for cosmology as well. The laws that govern the birth and evolution of the universe must be the same laws that govern the falling of stones, the chemistry and nuclear physics of the elements and the physics of elementary particles. They freed us from the supernatural by showing that complex and even intelligent life could arise from chance, competition, and natural causes. Cosmologists would have to do as well: the basis for cosmology would have to be impersonal rules that are the same throughout the universe and whose origin has nothing to do with our own existence. The only god permitted to cosmologists would be Richard Dawkins’s “blind watchmaker.”
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