The essence of quantum physics is unpredictability. At every instant, the objects in our physical environment—the atoms in our lungs and the light in our eyes—are making unpredictable choices, deciding what to do next. According to Everett and Deutsch, the multiverse contains a universe for every combination of choices. There are so many universes that every possible sequence of choices occurs in at least one of them. Each universe is constantly splitting into many alternative universes, and the alternatives are recombining when they arrive at the same final state by different routes. The multiverse is a huge network of possible histories diverging and reconverging as time goes on. The “quantum weirdness” that we observe in the behavior of atoms, the “spooky action at a distance” that Einstein famously disliked, is the result of universes recombining in unexpected ways.
According to Deutsch, each of us exists in the multiverse as a crowd of almost identical creatures, traveling together through time along closely related histories, splitting and recombining constantly like the atoms of which we are composed. He does not claim to have an answer to the question “Why does the multiverse exist?” or to the easier question “What is the nature of consciousness?” He sees ahead of us a long future of slow exploration, answering philosophical questions that we do not yet know how to ask. One of the questions that we know how to ask but not to answer is: “Does quantum computing play an essential role in our consciousness?” For Deutsch, the physics of quantum computing is the most promising clue that may lead us to a deeper understanding of our existence. He theorizes, Holt tells us, that “all the different parallel universes in the multiverse” could “be coaxed into collaborating on a single computation.”
There are many other kinds of multiverse besides the Everett version. Multiverse models are fashionable in recent theories of cosmology. Holt went to see the Russian cosmologist Alex Vilenkin at Tufts University in Boston. Unlike Deutsch, Vilenkin has multiple universes disconnected and widely separated from each other. Each arises out of nothing by a process known as quantum tunneling, spontaneously crossing the barrier between nonexistence and existence with no expenditure of energy. Universes spring into existence with precisely zero total energy, the positive energy of matter being equal and opposite to the negative energy of gravitation. Mass comes free because energy is zero.
The title of the Vilenkin chapter is “The Ultimate Free Lunch?” Holt describes a conversation between the young physicist George Gamow and the old physicist Albert Einstein when both of them were in Princeton. Gamow, the original inventor of the idea of quantum tunneling, explained to Einstein the possibility of the free lunch. Einstein was so astonished that he stopped in the middle of the street and was almost run over by a car.
Opinions vary widely concerning the proper limits of science. For me, the multiverse is philosophy and not science. Science is about facts that can be tested and mysteries that can be explored, and I see no way of testing hypotheses of the multiverse. Philosophy is about ideas that can be imagined and stories that can be told. I put narrow limits on science, but I recognize other sources of human wisdom going beyond science. Other sources of wisdom are literature, art, history, religion, and philosophy. The multiverse has its place in philosophy and in literature.
My favorite version of the multiverse is a story told by the philosopher Olaf Stapledon, who died in 1950. He taught philosophy at the University of Liverpool. In 1937 he published a novel, Star Maker, describing his vision of the multiverse. The book was marketed as science fiction, but it has more to do with theology than with science. The narrator has a vision in which he travels through space visiting alien civilizations from the past and the future, his mind merging telepathically with some of their inhabitants who join him on his journey. Finally, this “cosmical mind” encounters the Star Maker, an “eternal and absolute spirit” who has created all of these worlds in a succession of experiments. Each experiment is a universe, and as each experiment fails he learns how to design the next experiment a little better. His first experiment is a simple piece of music, a rhythmic drumbeat exploring the texture of time. After that come many more works of art, exploring the possibilities of space and time with gradually increasing complexity.
Our own universe comes somewhere in the middle, a big improvement on its predecessors but still destined for failure. Its flaws will bring it to a tragic end. Far outside the range of our understanding will be the later experiments, avoiding the mistakes that the Star Maker made with our own universe, and leading the way to ultimate perfection. Stapledon’s multiverse, conceived in the shadow of the approaching horrors of World War II, is an imaginative attempt to grapple with the problem of good and evil.
For most of the twenty-five centuries since written history began, philosophers were important. Two groups of philosophers, Confucius and Lao Tse in China, and Socrates, Plato, and Aristotle in Greece, were dominant figures in the cultures of Asia and Europe for two thousand years. Confucius and Aristotle set the style of thinking for Eastern and Western civilizations. They not only spoke to scholars but also to rulers. They had a deep influence in the practical worlds of politics and morality as well as in the intellectual worlds of science and scholarship.
In more recent centuries, philosophers were still leaders of human destiny. Descartes and Montesquieu in France, Spinoza in Holland, Hobbes and Locke in England, Hegel and Nietzsche in Germany, set their stamp on the divergent styles of nations as nationalism became the driving force in the history of Europe. Through all the vicissitudes of history, from classical Greece and China until the end of the nineteenth century, philosophers were giants playing a dominant role in the kingdom of the mind.
Holt’s philosophers belong to the twentieth and twenty-first centuries. Compared with the giants of the past, they are a sorry bunch of dwarfs. They are thinking deep thoughts and giving scholarly lectures to academic audiences, but hardly anybody in the world outside is listening. They are historically insignificant. At some time toward the end of the nineteenth century, philosophers faded from public life. Like the snark in Lewis Carroll’s poem, they suddenly and silently vanished. So far as the general public was concerned, philosophers became invisible.
The fading of philosophy came to my attention in 1979, when I was involved in the planning of a conference to celebrate the hundredth birthday of Einstein. The conference was held in Princeton, where Einstein had lived, and our largest meeting hall was too small for all the people who wanted to come. A committee was set up to decide who should be invited. When the membership of the committee was announced, there were loud protests from people who were excluded. After acrimonious discussions, we agreed to have three committees, each empowered to invite one third of the participants. One committee was for scientists, one for historians of science, and one for philosophers of science.
After the three committees had made their selections, we had three lists of names of people to be invited. I looked at the lists of names and was immediately struck by their disconnection. With a few exceptions, I knew personally all the people on the science list. On the history list, I knew the names, but I did not know the people personally. On the philosophy list, I did not even know the names.
In earlier centuries, scientists and historians and philosophers would have known one another. Newton and Locke were friends and colleagues in the English parliament of 1689, helping to establish constitutional government in England after the bloodless revolution of 1688. The bloody passions of the English Civil War were finally quieted by establishing a constitutional monarchy with limited powers. Constitutional monarchy was a system of government invented by philosophers. But in the twentieth century, science and history and philosophy had become separate cultures. We were three groups of specialists, living in separate communities and rarely speaking to each other.
When and why did philosophy lose its bite? How did it become a toothless relic of past glories? These are the ugly questions that Jim Holt’s book compels us to ask. Philosophers became insignificant when philosophy became a separate academic discipline, distinct from science and history and literature and religion. The great philosophers of the past covered all these disciplines. Until the nineteenth century, science was called natural philosophy and officially recognized as a branch of philosophy. The word “scientist” was invented by William Whewell, a nineteenth-century Cambridge philosopher who became master of Trinity College and put his name on the building where Wittgenstein and I were living in 1946. Whewell introduced the word in the year 1833. He was waging a deliberate campaign to establish science as a professional discipline distinct from philosophy.
Whewell’s campaign succeeded. As a result, science grew to a dominant position in public life, and philosophy shrank. Philosophy shrank even further when it became detached from religion and from literature. The great philosophers of the past wrote literary masterpieces such as the Book of Job and the Confessions of Saint Augustine. The latest masterpieces written by a philosopher were probably Friedrich Nietzsche’s Thus Spoke Zarathustra in 1885 and Beyond Good and Evil in 1886. Modern departments of philosophy have no place for the mystical.