The Cosmic Landscape (4 page)

The modern cosmological paradigm is not very old. When I was a young graduate student at Cornell University, in the early 1960s, the Big Bang theory of the universe was still in hot competition with another serious contender. The Steady State theory was, in a sense, the logical opposite of the Big Bang. If the Big Bang said that the universe began at some time, the Steady State said that it had always existed. The Steady State theory was the brainchild of three of the world’s most famous cosmologists—Fred Hoyle, Herman Bondi, and Thomas Gold—who thought that the explosive creation of the universe a mere ten billion years ago was too unlikely a possibility. Gold was a professor at Cornell and had his office a few doors down from mine. At the time he was tirelessly preaching the virtue of an infinitely old (and also infinitely big) universe. I barely knew him well enough to say good morning to him, but one day, very uncharacteristically, he sat down to coffee with a few graduate students, and I was able to ask him something that had been bothering me: “If the universe is eternally unchanging, how is it that the galaxies are all receding away from one another? Doesn’t it mean that in the past they were more closely packed?” Gold’s explanation was simple: “The galaxies are indeed moving apart, but as they separate, new matter is created to fill the space between them.” It was a clever answer, but it made no mathematical sense. Within a year or two, the Steady State universe had given way to the Big Bang and was soon forgotten. The victorious Big Bang paradigm asserted that the expanding universe was only about ten billion years old and about ten billion light-years big.
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But one thing that both theories shared was a belief that the universe is homogeneous, which means that it is everywhere the same: governed by the same universal Laws of Physics throughout. Moreover, those Laws of Physics are the same ones that we discover in terrestrial laboratories.

It’s been very exciting, over the last forty years, to watch experimental cosmology mature from a crude, qualitative art to a very precise, quantitative science. But it is only recently that the basic framework of George Gamow’s Big Bang theory has started to yield to a more powerful idea. As the new century dawns, we are finding ourselves at a watershed that is likely to permanently change our understanding of the universe. Something is happening that is much more than the discovery of new facts or new equations. Our entire outlook and framework for thinking, the whole epistemology of physics and cosmology, are undergoing upheaval. The narrow twentieth-century paradigm of a single universe about ten billion years old and ten billion light-years across with a unique set of physical laws is giving way to something much bigger and pregnant with new possibilities. Gradually cosmologists and physicists like myself are coming to see our ten billion light-years as an infinitesimal pocket of a stupendous
megaverse.
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At the same time, theoretical physicists are proposing theories that demote our ordinary laws of nature to a tiny corner of a gigantic Landscape of mathematical possibilities.

The word
Landscape,
in the present context, is fewer than three years old, but since I introduced it in 2003, it has become part of the cosmologist’s vocabulary. It denotes a mathematical space representing all of the possible environments that theory allows. Each possible environment has its own Laws of Physics, its own elementary particles, and its own constants of nature. Some environments are similar to our own but slightly different. For example, they may have electrons, quarks, and all the usual particles but with gravity a billion times stronger than ours. Others have gravity like ours but contain electrons that are heavier than atomic nuclei.
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Still others may resemble our world except for a violent repulsive force (called the cosmological constant) that rips apart galaxies, molecules, and even atoms. Not even the three dimensions of space are sacred; regions of the Landscape describe worlds of four, five, six, and even more dimensions.

According to modern cosmological theories, the diversity of the Landscape is paralleled by a corresponding diversity in ordinary space. Inflationary cosmology, which is our best theory of the universe, is leading us, sometimes unwillingly, to a concept of a megaverse, filled with a prodigious number of what Alan Guth calls “pocket universes.” Some pockets are microscopically small and never get big. Others are big like ours but totally empty. And each lies in its own little valley of the Landscape. The old twentieth-century question, “What can you find in the universe?” is giving way to, “What can you not find?”

Man’s place in the universe is also being reexamined and challenged. A megaverse of such diversity is unlikely to support intelligent life anywhere but in a tiny fraction of its expanse. According to this view, many questions such as, “Why is a certain constant of nature one number, instead of another?” will have answers that are entirely different from what physicists had hoped. No unique value will be picked out by mathematical consistency, since the Landscape permits an enormous variety of possible values. Instead, the answer will be, “Somewhere in the megaverse, the constant equals
this
number; somewhere else it is
that
number. We live in one tiny pocket where the value of the constant is consistent with our kind of life. That’s it! That’s all! There is no other answer to the question.”

Many coincidences occur in the laws and constants of nature that have no explanation other than, “If it were otherwise, intelligent life could not exist.” To some it seems as though the Laws of Physics were chosen, at least in part, to permit our existence. Called the Anthropic Principle
,
this idea is hated by most physicists, as I noted in my introduction. To some it smells of supernatural creation myths, religion, or intelligent design. Others feel that it represents surrender, a giving up of the noble quest for rational answers. But because of unprecedented new developments in physics, astronomy, and cosmology, these same physicists are being forced to reevaluate their prejudices. There are four principal developments driving this sea change: two from theoretical physics and two from observational astronomy. On the theoretical side an outgrowth of inflationary theory called Eternal Inflation is demanding that the world be a megaverse, full of pocket universes that have bubbled up out of inflating space, like bubbles in an uncorked bottle of champagne. At the same time, String Theory is producing a Landscape of enormous diversity. The best estimates are that 10
⁵⁰⁰
distinct kinds of environments are possible. This number (one followed by five hundred zeros) is far beyond being “unimaginably large,” but even it may not be big enough to count the possibilities.

Very recent astronomical discoveries exactly parallel the theoretical advances. The newest astronomical data about the size and shape of the universe provide confirmation that the universe exponentially “inflated” to a stupendous size much bigger than the standard ten or fifteen billion light-years. There is very little doubt that we are embedded in a vastly bigger megaverse. But the biggest news is that in our pocket of space, the notorious cosmological constant (a mathematical term that Einstein originally introduced into his equations and later rejected in disgust) is not quite zero as it was thought to be. This discovery has rocked the boat more than any other. The cosmological constant represents an extra gravitational repulsion, a kind of antigravity that was believed to be absolutely absent from the real world. The fact that it is not absent is a cataclysm for physicists, and the only way that we know how to make any sense of it is through the reviled and despised Anthropic Principle.

I don’t know what strange and unimaginable twists our view of the universe will undergo while exploring the vastness of this Landscape. But I would bet that at the turn of the twenty-second century, philosophers and physicists will look back to the present as a time when the twentieth-century concept of the universe gave way to a megaverse, populating a Landscape of mind-boggling proportions.

“Anyone who is not shocked by quantum theory has not understood it.”

— NIELS BOHR

The idea that the Laws of Physics can vary throughout the universe is as meaningless as the idea that there can be more than one universe. The universe is all there is; it may be the one noun in the English language that logically should have no plural. The laws governing the universe as a whole cannot change. What laws would govern those changes? Are they not also part of the Laws of Physics?

But I mean something much more modest by the Laws of Physics than the grand, overarching laws that regulate all aspects of the megaverse. I mean the things that an ordinary twentieth-century physicist, a physicist more interested in the laboratory than the universe, would have meant: the laws governing the building blocks of ordinary matter.

This book is about these Laws of Physics—not
what
they are but
why
they are. But before we can discuss the why, we need to know the what. Exactly what are these laws? What do they say, and how are they expressed? The task of this first chapter is to bring you up to speed on the Laws of Physics as they were understood circa the year 2000.

To Isaac Newton and those who came after him, the physical world was a precise deterministic machine whose past determined its future “as sure as night follows day.” The laws of nature were rules (equations) that expressed this determinism in precise mathematical language. For example, one could determine how objects move along precise trajectories given their initial starting points (including their velocities). The great French eighteenth-century physicist and mathematician Pierre-Simon de Laplace expressed it this way:

We may regard the present state of the universe as the effect of its past and the cause of its future. An intellect which at a certain moment would know all forces that set nature in motion, and all positions of all items of which nature is composed, if this intellect were also vast enough to submit these data to analysis, it would embrace in a single formula the movements of the greatest bodies of the universe and those of the tiniest atom; for such an intellect nothing would be uncertain and the future just like the past would be present before its eyes.

Just in case the translation from the French is unclear, Laplace was saying that if, at some instant, you (some superintellect) knew the position and velocity of every particle in the universe, you could forever after predict the exact future of the world. This ultra-deterministic view of nature was the prevailing paradigm until, at the beginning of the twentieth century, that subversive thinker Albert Einstein came along and changed everything. Although Einstein is most famous for the Theory of Relativity, his boldest and most radical move—his most subversive move—had to do with the strange world of quantum mechanics, not the Theory of Relativity. Since that time physicists have understood that the Laws of Physics are quantum laws. For that reason, I have chosen to begin this first chapter with a short course on “thinking quantum-mechanically.”

You are about to enter the bizarre Alice in Wonderland world of modern physics, where nothing is what it seems, everything fluctuates and shimmers, and uncertainty reigns supreme. Forget the predictable clockwork universe of Newtonian physics. The world of quantum mechanics is anything but predictable. The early-twentieth-century revolutions in physics were not “velvet revolutions.” They not only changed the equations and Laws of Physics, but they destroyed the epistemological foundations of much of classical science and philosophy. Many physicists were unable to cope with the new ways of relating to phenomena and were left behind. But a younger, more flexible generation reveled in the bizarre modern ideas and developed new intuitions and powers of visualization. So complete was the change that many theoretical physicists of my generation find it easier to think quantum-mechanically or relativistically than in the old classical ways.

Quantum mechanics was the biggest shock. At the quantum level the world is a jittery, fluctuating place of probabilities and uncertainty. But the electron does not just stagger around like a drunken sailor. There is a subtler pattern to the randomness that is best described in the arcane symbolism of abstract mathematics. However, with a little effort on my part and some patience on your part, the most important things can be translated into common language.

Since the nineteenth century, physicists have used the metaphor of a billiard table to represent the physical world of interacting, colliding particles. James Clerk Maxwell used the analogy; so did Ludwig Boltzmann. By now it’s been used by scores of physicists to explain the quantum world. The first time I heard it used was by Richard Feynman, who explained things this way:

Imagine a billiard table that is so perfectly constructed that it has no friction at all. The balls and cushions are so elastic (bouncy) that whenever a collision occurs, the balls bounce with no loss of kinetic energy. Let’s also remove the pockets so that once the balls are set into motion, they will continue moving forever, colliding, bouncing off the cushions, and moving on. The game starts with fifteen balls arranged in a triangle like a two-dimensional version of a stack of cannon balls. The cue ball is sent rocketing toward the pack.

What happens next is too complicated and unpredictable to follow. But why is it so unpredictable? It’s because each collision magnifies minute differences in the starting positions and velocities of the balls, so that even the tiniest deviation eventually leads to an entirely different outcome. [This kind of ultra-sensitivity to initial conditions is called chaos, and it is a ubiquitous feature of nature.] Trying to reproduce a pool game is not like reproducing a chess game. It would take almost infinite precision. Nevertheless, in classical physics the balls move along perfectly precise trajectories, and the motion is completely predictable, if only we know the initial positions and velocities of the balls with infinite precision. Of course, the longer we want to predict the motion, the more accurately we need to know the initial data. But there is no limit to the precision of this data and no limit to our ability to predict the future from the past.