by Lee Smolin
ALSO BY LEE SMOLIN
The Singular Universe and the Reality of Time
(with Roberto Mangabeira Unger)
Time Reborn
The Trouble with Physics
Three Roads to Quantum Gravity
The Life of the Cosmos
PENGUIN PRESS
An imprint of Penguin Random House LLC
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Copyright © 2019 by Lee Smolin
Illustrations copyright © 2019 by Kaća Bradonjić
Penguin supports copyright. Copyright fuels creativity, encourages diverse voices, promotes free speech, and creates a vibrant culture. Thank you for buying an authorized edition of this book and for complying with copyright laws by not reproducing, scanning, or distributing any part of it in any form without permission. You are supporting writers and allowing Penguin to continue to publish books for every reader.
Library of Congress Cataloging-in-Publication Data
Names: Smolin, Lee, 1955- author. | Bradonjic, Kaca, illustrator.
Title: Einstein’s unfinished revolution : the search for what lies beyond the quantum / Lee Smolin ; illustrations by Kaca Bradonjic.
Description: New York : Penguin Press, 2019. | Includes bibliographical references and index.
Identifiers: LCCN 2018045679 (print) | LCCN 2018060769 (ebook) | ISBN 9780698169135 (ebook) | ISBN 9781594206191 (hardcover)
Subjects: LCSH: Quantum theory. | Physics--Research.
Classification: LCC QC174.13 (ebook) | LCC QC174.13 .S6545 2019 (print) | DDC 530.12--dc23
LC record available at https://lccn.loc.gov/2018045679
Version_2
For Dina and Kai
All a musician can do is to get closer to the sources of nature, and so feel that he is in communion with the natural laws.
—JOHN COLTRANE
I can safely say that nobody understands quantum mechanics.
—RICHARD FEYNMAN
Contents
Also by Lee Smolin
Title Page
Copyright
Dedication
Epigraph
Preface
PART 1. AN ORTHODOXY OF THE UNREAL
ONE Nature Loves to Hide
TWO Quanta
THREE How Quanta Change
FOUR How Quanta Share
FIVE What Quantum Mechanics Doesn’t Explain
SIX The Triumph of Anti-Realism
PART 2. REALISM REBORN
SEVEN The Challenge of Realism: de Broglie and Einstein
EIGHT Bohm: Realism Tries Again
NINE Physical Collapse of the Quantum State
TEN Magical Realism
ELEVEN Critical Realism
PART 3. BEYOND THE QUANTUM
TWELVE Alternatives to Revolution
THIRTEEN Lessons
FOURTEEN First, Principles
FIFTEEN A Causal Theory of Views
Epilogue/Revolutions: Note to Self
Acknowledgments
Notes
Glossary
Further Reading
Index
About the Author
Preface
We human beings have always had a problem with the boundary between reality and fantasy. To explain the world to ourselves we make up stories and then, because we are good storytellers, we get infatuated by them and confuse our representations of the world with the world itself. This confusion afflicts scientists as much as laypeople; indeed, it affects us more, because we have such powerful stories in our tool kits.
As we go deeper into our understanding of the natural world, moving to smaller and more elementary phenomena, our successes impose barriers to further progress. To avoid getting stuck, we must balance our well-justified confidence in the power of established knowledge with an acute consciousness of just how hypothetical even our most successful hypotheses are. A hard lesson to learn is that our sensations are partly caused by reality, but are fully constructed by our brains to present the world to us in just the form we need to make our way in nature. Beyond those sensations, nature hovers, fundamentally mysterious and just at the edge of what we can know.
The most important features of nature, as we understand them now, were not perceived. The simplest general facts we know about the world—that matter is made of atoms, for example, or that the Earth is a spherical shell of rock surrounding a molten core and enveloped within a thin atmosphere, which moves, suspended in a near vacuum, as it orbits a natural thermonuclear reactor—these plain facts we learn just out of our cribs are the result of centuries of intense effort by scholars and scientists. Each of these facts arose as an almost crazy idea in conflict with a much more obvious and reasonable—but wrong—hypothesis.
To have a scientific mind is to respect the consensus facts, which are the resolution of generations of dispute, while maintaining an open mind about the still unknown. It helps to have a humble sense of the essential mystery of the world, for the aspects that are known become even more mysterious when we examine them further. The more we know, the more curious it all is. There is not a thing in nature so ordinary that its contemplation cannot be a route to a wordless sense of wonder and gratitude just to be a part of it all.
This spring morning the air coming through the open window carries fresh smells from the garden—but by what miracle does that happen? How are molecules wafted by a breeze turned by a nose into that happy scent? We see vivid colors, and we recall that there is a story about how different wavelengths of light excite different neurons. But how could the sensations of redness or blueness possibly be caused by different neurons being excited? What kinds of things are the sensations, the qualia, as the philosophers call them, of the different colors, or the different scents? In what way are scents different from colors, and why do they differ, if it is all electrical impulses in neurons? Who is the I that wakes and what is the universe that surrounds me when I open my eyes? The simplest facts about our existence and our relationship to the world are mysteries.
Let us tiptoe past the hard question of consciousness to simpler questions. As a scientist, I believe that is the best way to get somewhere. Let’s start with one very basic question: What is matter? My son has left a rock on the table. I pick it up; its weight and shape fit comfortably in my hand—surely an ancient feeling.
But what is a rock?
We know what the rock looks like, what it feels like. But these are at least as much about us as they are about the rock. Little in a rock’s feel or appearance gives a hint as to what, essentially, constitutes the existence—the rockness—of a rock. We know most of the rock is empty space in which atoms are arranged. The solidity and hardness of the rock is a construction of our minds, which integrate perceptions on scales very coarse compared to the sizes of the atoms.
Matter comes in many forms, some of which, like the rock, like the organic material woven into our blankets, sheets, and clothes, we know must be complex. So let’s consider first a simpler form of matter: the water in our glass. What is it?
To our eyes and to our touch, water appears to be smooth, continuous. Until relatively recently, a bit more than a century ago, physicists thought that matter was entirely continuous. Early in the twentieth century, Albert Einstein showed that was wrong and that water is made of myriad atoms. In water, these are organized into triplets, bound together into molecules, each consisting of two hydrogen and an oxygen.
Yes, but what is an atom? It took less than a decade after Einstein for it to be understood that each atom
is like a tiny solar system, with a nucleus in the center in place of the Sun and the planets represented by electrons.
So far so good, but then what is an electron? We know that electrons come in discrete units, each one carrying a certain quantity of mass and charge. An electron can have a location in space. It can move: when we first look it is here; when we look again it is there.
Beyond those attributes it is not easy to give a picture of what an electron is. It will take much of this book.
The best understanding of what rocks are, what water is, what molecules and atoms and electrons are, is expressed by the branch of science called quantum physics. But, as it seems everyone knows by now, that is a realm full of paradox and mystery. Quantum physics describes a world in which nothing has a stable existence: an atom or an electron may be a wave or a particle, depending on how you look at it; cats are both alive and dead. This is great for popular culture, which has made “quantum” a buzzword for cool, geek mystification. But it’s terrible for those of us who want to understand the world we live in, for there seems to be no easy answer to the simple question, “What is a rock?”
In the first quarter of the twentieth century a theory called quantum mechanics was developed to explain quantum physics. This theory has been, ever since its inception, the golden child of science. It is the basis of our understanding of atoms, radiation, and so much else, from the elementary particles and basic forces to the behavior of materials. It also has been, for just as long, a troubled child. From the beginning, its inventors were deeply split over what to make of it. Some expressed shock and misgivings, even outrage. Others declared it a revolutionary new kind of science, which shattered the metaphysical assumptions about nature and our relationship to it that previous generations had thought essential for the success of science.
In these chapters I hope to convince you that the conceptual problems and raging disagreements that have bedeviled quantum mechanics since its inception are unsolved and unsolvable, for the simple reason that the theory is wrong. It is highly successful, but incomplete. Our task—if we are to have simple answers to our simple questions about what rocks are—must be to go beyond quantum mechanics to a description of the world on an atomic scale that makes sense.
This task might seem overwhelmingly difficult, were it not for one almost forgotten and long-ignored aspect of the history of quantum mechanics. Since the very beginning of the quantum era, in the 1920s, there has been an alternative version of quantum physics that does make complete sense. This shadow theory resolves the apparent paradoxes and mysteries of the quantum domain. The scandal—and I believe that term is warranted—is that this alternative form of quantum theory is rarely taught. It is seldom mentioned, either in textbooks for budding physicists or in popularizations for laypeople.
There are several alternative formulations of quantum physics that make consistent sense. The challenge now is to build on these to find the right way to understand quantum physics—the one that nature uses. I believe this will have wide repercussions, because the new form of quantum physics will be the basis of the solutions to many of the outstanding problems in physics. Problems such as quantum gravity and the unification of the forces, on which we have made little definitive progress, are, I believe, foundering because at the foundations of our theorizing is an incorrect theory.
Physicists agree about how the quantum world behaves. We agree that atoms and radiation behave differently than rocks and cats, and we agree that quantum mechanics works to predict some aspects of that behavior. But we don’t agree about what it means that our world is a quantum world. It is clear that some radical change in our understanding of nature is required, but we disagree as to what that change needs to be. Some argue that we must give up holding any picture of reality and settle for a theory which describes only the knowledge we can have of the world. Others claim that our notion of reality must be vastly extended to embrace an infinitude of parallel realities.
In fact, neither is necessary. The alternative ways of understanding the quantum world do not require us to give up the idea that physics describes a reality independent of our knowledge of it. Nor do they require that we expand that reality beyond the commonsense notion that there is one world and it is what we see when we look around us. As I’ll explain in these pages, commonsense realism, according to which science can aspire to give a complete picture of the natural world as it is, or would be in our absence, is not actually threatened by anything we know about quantum physics.
It is thus both unfortunate and unnecessary that the quantum realm has been presented as mysterious and counterintuitive. One of the aims of this book is to present the alternative quantum theories to laypeople and, by doing so, to lift the mystery and present the quantum world in a way that is intuitive and accessible to people who are not specialists in physics.
I imagine my reader as someone with a strong curiosity about nature, who may follow science through news, blogs, and popular books, but whose education has not included the mathematics usually assumed as the language of physics. Instead I use words and pictures to convey the basic phenomena we find in the quantum world as well as the principles their study has inspired. After an introduction, the book starts with three short chapters which describe the bare-bones basics of quantum physics. These will equip us to explore the diverse conceptual universes which arise from the different forms of quantum theory that have been proposed.
* * *
—
WHAT IS AT STAKE in the argument over quantum mechanics? Why does it matter if our fundamental theory of the natural world is mysterious and paradoxical?
Behind the century-long argument over quantum mechanics is a fundamental disagreement about the nature of reality—a disagreement which, unresolved, escalates into an argument about the nature of science.
Two questions underlie the schism.
First off, does the natural world exist independently of our minds? More precisely, does matter have a stable set of properties in and of itself, without regard to our perceptions and knowledge?
Second, can those properties be comprehended and described by us? Can we understand enough about the laws of nature to explain the history of our universe and predict its future?
The answers we give to these two questions have implications for larger questions about the nature and aim of science, and the role of science in the larger human project. These are, indeed, questions about the boundary between reality and fantasy.
People who answer yes to these two questions are called realists. Einstein was a realist. I am also a realist. We realists believe that there is a real world out there, whose properties in no way depend on our knowledge or perception of it. This is nature—as it would be, and mostly is, in our absence. We also believe that the world may be understood and described precisely enough to explain how any system in the natural world behaves.
If you are a realist, you believe that science is the systematic search for that explanation. This is based on a naive notion of truth. Assertions about objects or systems in nature are true to the extent that they correspond to genuine properties of nature.
If you answer no to one or both of these questions, you are an anti-realist.
Most scientists are realists about everyday objects on the human scale. Things we can see, pick up, and throw around have simple and easily comprehended properties. They exist at each moment somewhere in space. When they move, they follow a trajectory, and that trajectory has, relative to someone describing them, a definite speed. They have mass and weight.
When we tell our partner that the red notebook they are looking for is on the table, we expect that this is simply true or false, absolutely independent of our knowledge or perception.
The description of matter at this level, from the smallest scales we can see with our eyes up to stars and planets, is called classical physics. It was invented by Galileo, Kepler, and Newton. Einstein�
�s theories of relativity are its crowning achievements.
But it is not easy, or obvious, for us to be realists about matter on the scale of individual atoms. This is because of quantum mechanics.
Quantum mechanics is presently our best theory of nature at the atomic scale. That theory has, as I have alluded to, certain very puzzling features. It is widely believed that those features preclude realism. That is, quantum mechanics requires that we say no to one or both of the two questions I asked above. To the extent that quantum mechanics is the correct description of nature, we are forced to give up realism.
Most physicists are not realists about atoms, radiation, and elementary particles. Their belief, for the most part, does not stem from a desire to reject realism on the basis of radical philosophical positions. Instead, it is because they are convinced quantum mechanics is correct and they believe, as they have been taught, that quantum mechanics precludes realism.
If it is true that quantum mechanics requires that we give up realism, then, if you are a realist, you must believe that quantum mechanics is false. It may be temporarily successful, but it cannot be the fully correct description of nature at an atomic scale. This led Einstein to reject quantum mechanics as anything more than a temporary expedient.
Einstein and other realists believe that quantum mechanics gives us an incomplete description of nature, which is missing features necessary for a full understanding of the world. Einstein sometimes imagined that there were “hidden variables” which would complete the description of the world given by quantum theory. He believed that the full description, including those missing features, would be consistent with realism.
Thus, if you are a realist and a physicist, there is one overriding imperative, which is to go beyond quantum mechanics to discover those missing features and use that knowledge to construct a true theory of the atoms. This was Einstein’s unfinished mission, and it is mine.