Tversky and I were participants in the cognitive revolution, to which we initially contributed the idea that significant errors of intuitive judgment can arise from the mechanism of cognition, rather than from wishful thinking or other emotional distortions. We also had a glimmer of what later became the two-system idea. Our first joint paper, which documented mistakes in the statistical decisions of researchers, informally distinguished intuitive judgment from deliberate computation. The detailed study of contrasts between automatic and controlled processes began some years later in an Indiana laboratory, and many psychologists have refined and extended that distinction in the intervening decades. In my recent attempt to describe the interactions between fast intuitive thinking and the deliberate self, I draw both on the work of these predecessors and on recent advances in the study of associative memory.
Scientists operate mostly in disciplinary silos, and it is rare for research in one field to influence work in other disciplines. My research with Tversky crossed some of these boundaries, in large part because of our use of demonstrations that were accessible to everyone: we engaged readers in simple problems in which they could observe errors in their own intuitions. Our work has therefore been more visible to outsiders than many other advances in psychological research, but it is best seen as a contribution to the thriving collective enterprise of modern experimental psychology.
This letter does not respond to my suggestion that psychology lives on both sides of the boundary between science and literature, combining the emotional insights of Freud and James with the experimental discoveries of Tversky and Kahneman. As I said in the review, the time for reconciliation has not yet come.
*Farrar, Straus and Giroux, 2011.
17
WHAT CAN YOU REALLY KNOW?
JIM HOLT’S Why Does the World Exist?: An Existential Detective Story is a portrait gallery of leading modern philosophers.* He visited each of them in turn, warning them in advance that he was coming to discuss with them a single question: Why is there something rather than nothing? He reports their reactions to this question, and embellishes their words with descriptions of their habits and personalities. Their answers give us vivid glimpses of the speakers but do not solve the riddle of existence.
The philosophers are more interesting than the philosophy. Most of them are eccentric characters who have risen to the top of their profession. They think their deep thoughts in places of unusual beauty such as Paris and Oxford. They are heirs to an ancient tradition of academic hierarchy, in which disciples sat at the feet of sages, and sages enlightened disciples with Delphic utterances. The universities of Paris and Oxford have maintained this tradition for eight hundred years. The great world religions have maintained it even longer. Universities and religions are the most durable of human institutions.
According to Holt, the two most influential philosophers of the twentieth century were Martin Heidegger and Ludwig Wittgenstein: Heidegger supreme in continental Europe, Wittgenstein in the English-speaking world. Heidegger was one of the founders of existentialism, a school of philosophy that was especially attractive to French intellectuals. Heidegger himself lost his credibility in 1933 when he accepted the position of rector of the University of Freiburg under the newly established Hitler government and became a member of the Nazi Party. Existentialism continued to flourish in France after it faded in Germany.
Wittgenstein, unlike Heidegger, did not establish an ism. He wrote very little, and everything that he wrote was simple and clear. The only book that he published during his lifetime was Tractatus Logico-Philosophicus, written in Vienna in 1918 and published in England with a long introduction by Bertrand Russell in 1922. It fills less than two hundred small pages, even though the original German and the English translation are printed side by side. I was lucky to be given a copy of the Tractatus as a prize when I was in high school. I read it through in one night, in an ecstasy of adolescent enthusiasm. Most of it is about mathematical logic. Only the last five pages deal with human problems. The text is divided into numbered sections, each consisting of one or two sentences. For example, section 6.521 says: “The solution of the problem of life is seen in the vanishing of this problem. Is not this the reason why men, to whom after long doubting the sense of life became clear, could not then say wherein this sense consisted?” The most famous sentence in the book is the final section 7: “Wherof one cannot speak, thereof one must be silent.”
I found the book enlightening and liberating. It said that philosophy is simple and has limited scope. Philosophy is concerned with logic and the correct use of language. All speculations outside this limited area are mysticism. Section 6.522 says: “There is indeed the inexpressible. This shows itself. It is the mystical.” Since the mystical is inexpressible, there is nothing more to be said. Holt summarizes the difference between Heidegger and Wittgenstein in nine words: “Wittgenstein was brave and ascetic, Heidegger treacherous and vain.” These words apply equally to their characters as human beings and to their intellectual output.
Wittgenstein’s intellectual asceticism had a great influence on the philosophers of the English-speaking world. It narrowed the scope of philosophy by excluding ethics and aesthetics. At the same time, his personal asceticism enhanced his credibility. During World War II, he wanted to serve his adopted country in a practical way. Being too old for military service, he took a leave of absence from his academic position in Cambridge and served in a menial job, as a hospital orderly taking care of patients. When I arrived at Cambridge University in 1946, Wittgenstein had just returned from his six years of duty at the hospital. I held him in the highest respect and was delighted to find him living in a room above mine on the same staircase. I frequently met him walking up or down the stairs, but I was too shy to start a conversation. Several times I heard him muttering to himself: “I get stupider and stupider every day.”
Finally, toward the end of my time in Cambridge, I ventured to speak to him. I told him I had enjoyed reading the Tractatus, and I asked him whether he still held the same views that he had expressed twenty-eight years earlier. He remained silent for a long time and then said, “Which newspaper do you represent?” I told him I was a student and not a journalist, but he never answered my question.
Wittgenstein’s response to me was humiliating, and his response to female students who tried to attend his lectures was even worse. If a woman appeared in the audience, he would remain standing silent until she left the room. I decided that he was a charlatan using outrageous behavior to attract attention. I hated him for his rudeness. Fifty years later, walking through a churchyard on the outskirts of Cambridge on a sunny morning in winter, I came by chance upon his tombstone, a massive block of stone lightly covered with fresh snow. On the stone was written a single word: WITTGENSTEIN. To my surprise, I found that the old hatred was gone, replaced by a deeper understanding. He was at peace, and I was at peace too, in the white silence. He was no longer an ill-tempered charlatan. He was a tortured soul, the last survivor of a family with a tragic history, living a lonely life among strangers, trying until the end to express the inexpressible.
The philosophers that Holt interviewed wander over a wide landscape. The main theme of their discussions is a disagreement between two groups that I call materialists and Platonists. Materialists imagine a world built out of atoms. Platonists imagine a world built out of ideas. This division into two categories is a gross simplification, lumping together people with a great variety of opinions. Like taxonomists who name species of plants and animals, observers of the philosophical scene may be splitters or lumpers. Splitters like to name many species; lumpers like to name few.
Holt is a splitter and I am a lumper. Philosophers are mostly splitters, dividing their ways of thinking into narrow specialties such as theism or deism or humanism or panpsychism or axiarchism. Examples of each of these isms are to be seen in Holt’s collection. I find it more convenient to lump them into two big groups: one obsessed with matter and the other ob
sessed with mind. Holt asks them to explain why the world exists. For the materialists, the question concerns the origin of space and time and particles and fields, and the relevant branch of science is physics. For the Platonists, the question concerns the origin of meaning and purpose and consciousness, and the relevant science is psychology.
The most impressive of the Platonists is John Leslie, who spent most of his life teaching philosophy at the University of Guelph and is now living in retirement on the west coast of Canada. He calls himself an extreme axiarchist. The word “axiarchism” is Greek for “value rules,” meaning that the world is built out of ideas, and the Platonic idea of the Good gives value to everything that exists. Leslie takes seriously Plato’s image of the cave as a metaphor of human life. We live in a cave, seeing only shadows cast on the wall by light streaming in from the entrance. The real objects outside the cave are ideas, and all the things that we perceive inside are imperfect images of ideas. Evil exists because our images are distorted. The ultimate reality hidden from our view is Goodness. Goodness is a strong enough force to pull the universe into existence. Leslie understands that this explanation of existence is a poetic fantasy rather than a logical argument. Fantasy comes to the rescue when logic fails. The whole range of Plato’s thinking is embodied in his dialogues, which are dramatic reconstructions of the conversations of his master Socrates. They are based on imagination, not on logic.
In 1996 Leslie published a book, The End of the World, taking a gloomy view of the human situation. He was calculating the probable future duration of the human species, basing his argument on the Copernican principle, which says that the situation of the human observer in the cosmos should be in no way exceptional. Copernicus gave his name to this principle when he moved the earth from its position at the center of the Aristotelian universe and put it into a more modest position as one of the planets orbiting around the sun.
Leslie argued that the Copernican principle should apply to our position in time as well as to our position in space. As observers of the passage of time, we should not put ourselves into a privileged position at the beginning of the history of our species. As Copernican observers, we should expect to be in an average position in our history, rather than close to the beginning. Therefore, we should expect the future duration of our species to be not much longer than its past. Since we know that our species originated about a hundred thousand years ago, we should expect it to become extinct about a hundred thousand years from now.
When Leslie published this prognostication, I protested strongly against it, claiming that it was a technically wrong use of the theory of probability. In fact Leslie’s argument was technically correct. The reason I did not like the argument was that I did not like the conclusion. I thought that the universe had a purpose, and that our minds were a part of that purpose. Since the goodness of the universe was revealed in our existence as observers, we could rely on the goodness of the universe to allow us to continue to exist. I opposed Leslie’s argument because I was a better Platonist than he was.
The antithesis of John Leslie is David Deutsch, whose book The Beginning of Infinity I discuss in chapter 12. Holt visited Deutsch at his home in a village a few miles from Oxford. The chapter describing the visit is entitled “The Magus of the Multiverse.” Deutsch is a professional physicist who uses physics as a basis for philosophical speculation. Unlike most philosophers, he understands quantum mechanics and feels at home in a quantum universe. He likes the many-universe interpretation of quantum mechanics, invented in the 1950s by Hugh Everett, who was then a student in Princeton. Everett imagined the quantum universe as an infinite assemblage of ordinary universes all existing simultaneously. He called the assemblage “the multiverse.”
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 recon-verging 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 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 pr
edecessors 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 spoke not only 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 baker in Lewis Carroll’s poem “The Hunting of the Snark,” they suddenly and silently vanished. So far as the general public was concerned, philosophers became invisible.
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