Copyright
Copyright © 2006 by Leonard Susskind
All rights reserved. No part of this book may be reproduced in any form or by any electronic or mechanical means, including information storage and retrieval systems, without permission in writing from the publisher, except by a reviewer who may quote brief passages in a review.
Hachette Book Group
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First eBook Edition: December 2005
Illustration credits (page numbers refer to the print edition): Einstein (p. 70), California Institute of Technology Archives; Rube Goldberg machine (p. 112), Rube Goldberg is the ® and © of Rube Goldberg Inc.; Kepler’s model (p. 120), from J. Kepler, Mysterium Cosmographicum (1596); Crab Nebula (p. 181), ESO—European Southern Observatory; eclipse (p. 188), Fred Esperak; snowflake (p. 242), Kenneth G. Libbrecht, Professor of Physics, Cal Tech; Calabi Yau (p. 290), Jean-François Colonna, CMAP (Centre de Mathématiques Appliquées); Mercator projection (p. 311), An Album of Map Projections, USGS Professional Paper 1453, by John P. Snyder and Phillip M. Voxland (USGPO, 1989); Escher (p. 312), M. C. Escher’s Limit Circle IV, © 2005 The M. C. Escher Company—Holland. All rights reserved.
ISBN: 978-0-316-05558-1
The “Little, Brown and Company” name and logo are trademarks of Hachette Book Group, Inc.
Contents
Copyright
Preface
Introduction
CHAPTER ONE: The World According to Feynman
CHAPTER TWO: The Mother of All Physics Problems
CHAPTER THREE: The Lay of the Land
CHAPTER FOUR: The Myth of Uniqueness and Elegance
CHAPTER FIVE: Thunderbolt from Heaven
CHAPTER SIX: On Frozen Fish and Boiled Fish
CHAPTER SEVEN: A Rubber Band-Powered World
CHAPTER EIGHT: Reincarnation
CHAPTER NINE: On Our Own?
CHAPTER TEN: The Branes behind Rube Goldberg’s Greatest Machine
CHAPTER ELEVEN: A Bubble Bath Universe
CHAPTER TWELVE: The Black Hole War
CHAPTER THIRTEEN: Summing Up
Epilogue
A Word on the Distinction between Landscape and Megaverse
Note on Terminology
Glossary
About the Author
“Your Highness, I have no need of this hypothesis.”
— Pierre-Simon de Laplace (1749-1827), reply made to Napoléon when asked why his celestial mechanics had no mention of God
Preface
I have always enjoyed explaining physics. In fact it’s more than just enjoyment: I need to explain physics. A lot of my research time is spent daydreaming—telling an imaginary admiring audience of laymen how to understand some difficult scientific idea. I suppose I am a bit of a ham, but it’s more than that. It’s part of the way I think: a mental tool for organizing my ideas and even creating new ways of thinking about problems. So it was natural that at some point I would decide to try my hand at writing a book for a general audience. A couple of years ago I decided to take the plunge and write a book about the twenty-year debate between myself and Stephen Hawking concerning the fate of information that fell into a black hole.
But just about that time, I found myself in the eye of a huge scientific hurricane. The issues involve not only the origin of the universe but also the origin of the laws that govern it. In my scientific article “The Anthropic Landscape of String Theory,” I called attention to the new emerging concept that I had christened the Landscape. The paper stirred up an enormous fuss in the physics and cosmology communities that by now has spread to philosophers and even theologians. The Landscape represents an idea that cuts across boundaries and touches not only on current paradigm shifts in physics and cosmology, but also on the profound cultural questions that are rocking our social and political landscape: can science explain the extraordinary fact that the universe appears to be uncannily, nay, spectacularly, well designed for our own existence? I decided to put the black hole book on the back burner for the moment and write a popular book about this extraordinary story. Thus was born The Cosmic Landscape.
Some readers of this book will be aware that in the past few years the science sections of newspapers have been reporting that cosmologists are mystified by two astonishing “dark” discoveries. The first is that 90 percent of the matter in the universe is made of some shadowy, mysterious substance called dark matter. The other is that 70 percent of the energy in the universe is composed of an even more ghostly mysterious stuff called dark energy. The words mystery, mysterious, and mystified get a very thorough workout in these articles.
I have to admit I find neither discovery all that mysterious. To me, the word mystery conveys something that completely eludes rational explanation. The discoveries of dark matter and energy were surprises but not mysteries. Elementary-particle physicists (I am one of them) have always known that their theories were incomplete and that many particles remain to be discovered. The tradition of postulating new, hard-to-detect particles began when Wolfgang Pauli correctly guessed that one form of radioactivity involved an almost invisible particle called the neutrino. Dark matter is not made of neutrinos, but by now physicists have postulated plenty of particles that could easily form the invisible stuff. There is no mystery there—only the difficulties of identifying and detecting those particles.
Dark energy has more of a claim to being called mysterious, but the mystery has much more to do with its absence than its presence. Physicists have known for seventy-five years or more that there is every reason for space to be filled with dark energy. The mystery is not why dark energy exists but why so little of it exists. But one thing is clear: even a little more dark energy would have been fatal to our own existence.
The real mystery raised by modern cosmology concerns a silent “elephant in the room,” an elephant, I might add, that has been a huge embarrassment to physicists: why is it that the universe has all of the appearances of having been specially designed just so that life forms like us can exist? This has puzzled scientists and at the same time encouraged those who prefer the false comfort of a creationist myth. The situation in many ways resembles biology before Darwin, when thoughtful people were unable to understand how, without the guiding hand of a deity, natural processes of physics and chemistry could possibly create anything as complex as the human eye. Like the eye, the special properties of the physical universe are so surprisingly fine-tuned that they demand explanation.
Let me be up front and state my own prejudices right here. I thoroughly believe that real science requires explanations that do not involve supernatural agents. I believe that the eye evolved by Darwinian mechanisms. Furthermore, I believe that physicists and cosmologists must also find a natural explanation of our world, including the amazing lucky accidents that conspired to make our own existence possible. I believe that when people substitute magic for rational explanation, they are not doing science no matter how loudly they claim otherwise.
In the past most physicists (including me) have chosen to ignore the elephant—even to deny its existence. They preferred to believe that nature’s laws follow from some elegant mathematical principle and that the apparent design of the universe is merely a lucky accident. But recent discoveries in astronomy, cosmology, and above all, String Theory have left theoretical physicists little choice but to think about these things. Surprisingly, we may be starting to see the reasons for this pattern of coincidences. Evidence has been accumulating for an explanation of the “illusion of intelligent design” that depends only on the principles of physics, mathematics, and the laws of large numbers. This is what The Cosmic Landscape is abou
t: the scientific explanation of the apparent miracles of physics and cosmology and its philosophical implications.
Who are the intended readers of this book? The answer is anyone with a lively interest in science and a curiosity about how the world came to be the way it is. But although the book is aimed at a lay audience, it is not aimed at the “lightweight” who is afraid to stretch his or her mind. I have kept the book free of equations and jargon but not of challenging concepts. I have avoided mathematical formulas, but on the other hand, I have striven to give accurate and clear explanations of the principles and mechanisms that underlie the new emerging paradigm. Understanding this new paradigm will be critical for anyone hoping to follow the further developments in answering the “big questions.”
I am indebted to many people, some who didn’t even know that they were helping me write this book. Among them are all the physicists and cosmologists whose ideas I have drawn on—Steven Weinberg, Gerard ’t Hooft, Martin Rees, Joseph Polchinski, Raphael Bousso, Alan Guth, Alex Vilenkin, Shamit Kachru, Renata Kallosh, and above all, Andrei Linde, who has been generously sharing his ideas with me for many years.
The actual writing of the book would not have been possible without the support of my agent, John Brockman, and my friend Malcolm Griffith, who read and criticized the early mess of a manuscript that I sent him and taught me how to “juggle more than three balls” (Malcolm’s way of describing the difficulties of writing a coherent book). To all the people at Little, Brown—Steve Lamont, Carolyn O’Keefe, and especially my editor, and now friend, Liz Nagle—I owe a huge debt of gratitude for her extraordinary contribution to the writing of this book. Liz’s patient guidance was way beyond the call of duty.
And finally to my wife, Anne, I am grateful, beyond measure, for her continuous loving support and help.
Introduction
The air is very cold and still: except for the sound of my own breathing, the silence is absolute. The dry, powdery snow crackles whenever my boot touches down. Its perfect whiteness, lit by starlight, gives the terrain a luminous, eerie brilliance, while the stars fade into a continuous glow across the black celestial dome. The night is brighter on this desolate planet than on my own home world. Beauty, but of a cold and lifeless kind: a place for metaphysical contemplation if ever there was one.
Alone, I’d left the safety of the base, to think about the day’s events and to watch the sky for meteors. But it was impossible to think of anything other than the sheer enormousness and impersonal nature of the universe. The pinwheeling of galaxies, the endless expansion of the universe, the infinite coldness of space, the heat of stars being born, and their final death throes as red giants: surely this must be the point of existence. Man—life in general—seems irrelevant to the workings of the universe: a mere smudge of water, grease, and carbon on a pinpoint planet circling a star of no special consequence.
Earlier, during the short stingy sunlight hours, Curt, Kip, and I had hiked about a mile to the Russian compound to see if we could find some Ivans to talk to. Stephen had wanted to come with us but his wheelchair could not navigate the snowdrifts. The derelict compound, just a few low rusted corrugated-metal buildings, looked deserted. We banged on the doors, but no life appeared. I cracked open the door and peered into the spooky interior darkness, then decided to brave entry and have a look around. As cold inside as it was outside, the compound was completely abandoned. The hundred or so dormitory rooms were unlocked but deserted. How did a hundred men disappear so completely? In silence we hiked back to our own base.
At the bar, we found our Russian, drinking and laughing—Victor. Victor, it seems, was one of the last three Russians left on the planet. Supplies from Russia had ceased more than a year ago. They would have starved but for the fact that our own people adopted them. We never saw the other two Russians, but Victor assured us they were alive.
Victor insisted on buying me a drink, “for the cold,” and asked, “How do you like this %#&*^ place?” I told him in all my travels only once had I seen the night sky even remotely as beautiful as here. Ironically, that other alien planet was so hot that the rocks would fry anything that touched them.
Of course we were not really on another planet. It only seemed that way. Antarctica is truly alien. Stephen Hawking, Curt Callan, Kip Thorne, Stan Deser, Claudio Teitelboim, myself, our wives, and a few other theoretical physicists were there for fun—as a lark—a reward for coming to Chile for a conference on black holes. Claudio, an eminent Chilean physicist, had arranged for the Chilean Air Force to fly us in one of its giant Hercules cargo planes to their Antarctic base for a couple of days.
It was August 1997—winter in the southern hemisphere—and we were expecting the worst. The coldest I had ever experienced was 20 below zero Fahrenheit, and I was worried about how well I would handle the 60 below that can grip the base in midwinter. When the plane landed, we anxiously zipped up the heavy Arctic gear that the military had provided and prepared for the fearful cold.
Then the cargo hold opened, and Curt’s wife, Chantal, bounded out of the plane, threw up her arms, and joyously yelled back, “It’s about as cold as a winter day in New Jersey.” And so it was. It stayed that way for the whole day while we frolicked in the snow.
Sometime during that night the beast awoke. By morning Antarctica had unleashed its fury. I went outside for a couple of minutes to get a taste of what Shackleton and his shipwrecked men had endured. Why hadn’t they all perished? Not a single member of the expedition was lost. Freezing cold and soaking wet for more than a year, why didn’t they all die of pneumonia? Out there in the blast of the storm, I knew the answer: nothing survives—not even the microbes that give men colds.
The other alien “planet” I’d mentioned to Victor was Death Valley—another lifeless place. No, not quite lifeless. But I wondered how much hotter it would have to get to fry all protoplasm. What Antarctica has in common with Death Valley is extreme dryness. It’s too cold for much water vapor to be suspended in the air—that and the complete lack of light pollution make it possible, in both extremes, to see the stars in a way that modern man rarely can. Standing there in the Antarctic starlight, it occurred to me how lucky we humans are. Life is fragile: it thrives only in a narrow range of temperatures between freezing and boiling. How lucky that our planet is just the right distance from the sun: a little farther, and the death of the perpetual Antarctic winter—or worse—would prevail; a little closer, and the surface would truly fry anything that touched it. Victor, being Russian, took a spiritual view of the question. “Was it not,” he asked, “God’s infinite kindness and love that permitted our existence?” My own “mindless” explanation will become clear in good time.
In fact we have much more to be thankful for than just the earth’s temperature. Without the right amount of carbon, oxygen, nitrogen, and other elements, a temperate climate would be wasted. If the sun at the center of our solar system were replaced by the more common binary star system,* planetary orbits would be too chaotic and unstable for life to have evolved. There are endless dangers of this kind. But on top of all these are the laws of nature themselves. All it takes is a small change in Newton’s laws, or the rules of atomic physics, and poof—life would either be instantly extinguished or would never have formed. It seems that our guardian angel not only provided us with a very benign planet to live on but also made the rules of existence—the laws of physics and cosmology—just right for us. This is one of the greatest mysteries of nature. Is it luck? Is it intelligent and benevolent design? Is it at all a topic for science—for metaphysics—for religion?
This book is about a debate that is stirring the passions of physicists and cosmologists but is also part of a broader controversy, especially in the United States, where it has entered the partisan political discourse. On one side are the people who are convinced that the world must have been created or designed by an intelligent agent with a benevolent purpose. On the other side are the hard-nosed, scientific types who feel certai
n that the universe is the product of impersonal, disinterested laws of physics, mathematics, and probability—a world without a purpose, so to speak. By the first group, I don’t mean the biblical literalists who believe the world was created six thousand years ago and are ready to fight about it. I am talking about thoughtful, intelligent people who look around at the world and have a hard time believing that it was just dumb luck that made the world so accommodating to human beings. I don’t think these people are being stupid; they have a real point.
The advocates of intelligent design generally argue that it is incredible that anything as complex as the human visual system could have evolved by purely random processes. It is incredible! But biologists are armed with a very powerful tool—the Principle of Natural Selection—whose explanatory power is so great that almost all biologists believe the weight of evidence is strongly in favor of Darwin. The miracle of the eye is only an apparent miracle.
I think the design enthusiasts are on better ground when it comes to physics and cosmology. Biology is only part of the story of creation. The Laws of Physics and the origin of the universe are the other part, and here again, incredible miracles appear to abound. It seems hopelessly improbable that any particular rules accidentally led to the miracle of intelligent life. Nevertheless, this is exactly what most physicists have believed: intelligent life is a purely serendipitous consequence of physical principles that have nothing to do with our own existence. Here I share the skepticism of the intelligent-design crowd: I think that the dumb luck needs an explanation. But the explanation that is emerging from modern physics is every bit as different from intelligent design as Darwin’s was from “Soapy” Sam Wilberforce’s.*
The debate that this book is concerned with is not the bitter political controversy between science and creationism. Unlike the debate between “Darwin’s Bulldog” Thomas Huxley and Wilberforce, the present argument is not between religion and science but between two warring factions of science—those who believe, on the one hand, that the laws of nature are determined by mathematical relations, which by mere chance happen to allow life, and those who believe that the Laws of Physics have, in some way, been determined by the requirement that intelligent life be possible. The bitterness and rancor of the controversy have crystallized around a single phrase—the Anthropic Principle—a hypothetical principle that says that the world is fine-tuned so that we can be here to observe it! By itself I would have to say that this is a silly, half-baked notion. It makes no more sense than saying that the reason the eye evolved is so that someone can exist to read this book. But it is really shorthand for a much richer set of concepts that I will make clear in the chapters that follow.
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