When my son was three years old he liked to crawl into my bed in the early morning and talk about the problems of life. One morning he said abruptly, “You know there are two Gods.” I was surprised and asked him, “What are their names?” He replied, “One is called Jesus and he makes people, and the other is called Bacchus and he makes wine.” I suppose my son must have picked up from his surroundings a tendency to polytheism. Anybody who has read or seen a performance of that intensely religious drama, the Bacchae of Euripides, will be aware that Bacchus is a formidable deity, making extreme demands upon his followers. In the tragedies and exaltations of the modern drug culture, Bacchus is alive. I doubt whether my three-year-old son was conscious of all this, any more than he was conscious of the fine points of the doctrine of the divinity of Jesus. His statement showed, in my opinion, a certain innate religious feeling, expressed in language appropriate for the child of a physicist.

Adam Gifford in his will establishing the Gifford Lectures ordained that the subject should be “Natural Theology.” The words “Natural Theology” have a technical meaning. According to Christian doctrine, God gave us two books in which his actions are recorded. One book is the Bible, the other is the Book of Nature. By reading the Book of Nature we can obtain knowledge of God’s work, whether or not we also read the Bible. This is what Adam Gifford meant when he wrote his will. Natural Theology is the reading of God’s mind as expressed in the works of Nature.

My own attitude to religion is closer to the attitude of my three-year-old son than to the attitude of Lord Gifford. I do not claim to be reading the Book of Nature when I do a scientific calculation. I do not claim to be an earnest enquirer after truth when I talk about Jesus and Bacchus. Science and religion are two windows through which we can look out at the world around us. We are free to choose. As the Swiss proverb says, “Some people like to go to church and some people like cherries.” One may have a friendly respect for religion without being pious. The way of truth is not necessarily paved with earnestness.

The Gifford Lectures are supposed to be an occasion for an elderly theologian or scientist to express in polished prose the sum total of his life’s wisdom. They were given in times past by William James and Alfred North Whitehead and by other distinguished philosophers. The lectures of William James were published in his classic volume The Varieties of Religious Experience; those of Whitehead in his equally classic but less readable Process and Reality. In the biography of William James we read that he took a two-year leave of absence from his position at Harvard in order to collect materials and concentrate his thoughts for the preparation of the Gifford Lectures. The effort of preparation was so intense that it caused a temporary breakdown of his health. After this effort, his health restored, he arrived in Edinburgh with the manuscript of a literary masterpiece in his briefcase. My situation, alas, was different. I had no masterpiece in my briefcase. I am a working scientist with no pretensions to being a deep philosophical thinker. I took no leave of absence to prepare the lectures. Whatever philosophical thinking I do is done in brief snatches, at odd times, and is usually not worth recording. Confronted with the fact that I was not William James or Alfred Whitehead, I decided to make a virtue of necessity. I talked about things which interested me. I did not try to fit the things which interested me into any grand design.

The lectures were given in two series, and this book is accordingly divided into two parts. Part 1 is about life as a scientific phenomenon, about our efforts to understand the nature of life and its place in the universe. Part 2 is about ethics and politics, about the local problems introduced by our species into the existence of life on this planet. The two parts do not come in logical sequence. I do not pretend that the scientific understanding of life will help us to solve political problems. Nevertheless, the two parts are not entirely disconnected. The connecting link is a general point of view. I look both at scientific and at human problems from the point of view of a lover of diversity. Diversity is the great gift which life has brought to our planet and may one day bring to the rest of the universe. The preservation and fostering of diversity is the great goal which I would like to see embodied in our ethical principles and in our political actions.

This first chapter is concerned with the relation between science and religion. The rest of the book touches upon religion only occasionally. When I talk about religion, I speak for myself alone. Any statement which attempted to express a consensus of scientists about religious and philosophical questions would miss the main point. There is no consensus among us. The voice of science is a Babel of diverse languages and cultures. That is to me the joy and charm of science. Science is a free creation of the human mind, and at the same time it is an international club cutting across barriers of race and nationality and creed. Many first-rate scientists are Christians, Moslems, Buddhists or Jews, many are Marxists, many are militant atheists, many are like me, loosely attached to Christian beliefs by birth and habit but not committed to any particular dogma.

Science and religion are two human enterprises sharing many common features. They share these features also with other enterprises such as art, literature and music. The most salient features of all these enterprises are discipline and diversity. Discipline to submerge the individual fantasy in a greater whole. Diversity to give scope to the infinite variety of human souls and temperaments. Without discipline there can be no greatness. Without diversity there can be no freedom. Greatness for the enterprise, freedom for the individual—these are the two themes, contrasting but not incompatible, that make up the history of science and the history of religion.

My own field of physics is passing today through a phase of exuberant freedom, a phase of passionate prodigality. Sometimes as I listen to the conversation of my young colleagues at Princeton, I feel as if I am lost in a rain forest, with insects and birds and flowers growing all around me in intricate profusion, growing too abundantly for my sixty-year-old brain to comprehend. But the young people are at home in the rain forest and walk confidently along trails which to me are almost invisible. They have their own discipline, different from the discipline which I was taught forty years ago, but still as strict in its way as mine. They are not wandering aimlessly. They are explorers, mapping out the ground, finding the ways that will lead them out of the jungle up to the mountain peaks.

There is a curious parallel here between the history of physics and the history of geographical exploration. At the beginning the explorers had their eyes on the mountain peaks. George Everest, the organizer of the geological survey of India, left his name on the highest mountain. The intervening jungles were only obstacles to be overcome. And so it was also in physics. Maxwell’s equations of the electromagnetic field, Einstein’s theory of general relativity, these were the great mountain peaks which dominated our vision for a hundred years. But God did not only create mountains, he also created jungles. And today we are beginning to understand that the jungles are the richest and most vibrant part of his creation. The modern explorer in South America or in Africa is not looking for mountains. She is looking into the depths of the jungles to observe and understand the creatures who live there in all their intricate variety. We ourselves came out of the jungle a few million years ago, and we are now becoming aware that we need to understand and preserve the jungle if we are to remain alive and healthy on this planet.

Likewise, in physics, it turned out that God’s creation was richer than either Maxwell or Einstein had imagined. There was a time in the 1920s and 1930s when it seemed that the landscape of physics was almost fully mapped. The world of physics looked simple. There were the mountains explored by Maxwell and Einstein and Rutherford and Bohr, the theories of relativity and the quantum, great landmarks standing clear and cold and clean in the sunlight, and between them only a few unimportant valleys still to be surveyed. Now we know better. After we began seriously to explore the valleys in the 1950s, we found in them flora and fauna as strange and unexpected as anything to be seen in the valleys of the Amazon. Instead of the three species of elementary particle which were known in the 1920s, we now have sixty-one. Instead of three states of matter, solid, liquid, and gas, we have six or more. Instead of a few succinct equations to summarize the universe of physics, we have a luxuriant growth of mathematical structures, as diverse as the phenomena that they attempt to describe. So we have come back to the rain forest, intellectually as well as geographically.

What philosophical lessons arise from the recent discoveries in physics? The main lesson to be learned is that nature is complicated. There is no such thing as a simple material universe. The old vision which Einstein maintained until the end of his life, of an objective world of space and time and matter independent of human thought and observation, is no longer ours. Einstein hoped to find a universe possessing what he called “objective reality,” a universe of mountaintops which he could comprehend by means of a finite set of equations. Nature, it turns out, lives not on the mountaintops but in the valleys.

I recently listened to a talk by a famous biologist. He spoke about two philosophical viewpoints which he called scientific materialism and religious transcendentalism. He said, “At bedrock they are incompatible and mutually exclusive.” This seems to be a widely accepted view, both among biologists and among Christian fundamentalists. I do not share it. I do not know what the word “materialism” means. Speaking as a physicist, I judge matter to be an imprecise and rather old-fashioned concept. Roughly speaking, matter is the way particles behave when a large number of them are lumped together. When we examine matter in the finest detail in the experiments of particle physics, we see it behaving as an active agent rather than as an inert substance. Its actions are in the strict sense unpredictable. It makes what appear to be arbitrary choices between alternative possibilities. Between matter as we observe it in the laboratory and mind as we observe it in our own consciousness, there seems to be only a difference in degree but not in kind. If God exists and is accessible to us, then his mind and ours may likewise differ from each other only in degree and not in kind. We stand, in a manner of speaking, midway between the unpredictability of matter and the unpredictability of God. Our minds may receive inputs equally from matter and from God. This view of our place in the cosmos may not be true, but it is at least logically consistent and compatible with the active nature of matter as revealed in the experiments of modern physics. Therefore, I say, speaking as a physicist, scientific materialism and religious transcendentalism are neither incompatible nor mutually exclusive. We have learned that matter is weird stuff. It is weird enough, so that it does not limit God’s freedom to make it do what he pleases.

Another phrase which occurs frequently in the propaganda of Christian fundamentalists is “scientific humanism.” Scientific humanism is supposed to be a philosophy standing in opposition to Christian faith. Fundamentalists like to pretend that we have only two alternatives, either scientific humanism or their version of Christianity. But scientific humanism has as many different meanings as scientific materialism. Roughly speaking, a scientific humanist is somebody who believes in science and in humanity but not in God. If that is the correct definition, I do not qualify as a scientific humanist. I cannot regard humanity as a final goal of God’s creation. Humanity looks to me like a magnificent beginning but not the last word. Small children often have a better grasp of these questions than grown-ups. It happened to me that I adopted a stepdaughter. I moved into her family when she was five years old. Before that, she had been living alone with her mother. Soon after I moved in, she saw me for the first time naked. “Did God really make you like that?” she asked with some astonishment. “Couldn’t he have made you better?” That is a question which every scientific humanist should be confronted with, at least once in a lifetime. The only honest answer is, of course, yes.

My personal brand of scientific humanism is influenced by the writings of H. G. Wells, and especially by Wells’s Outline of History, a lucid account of the history of mankind, written in 1920. First, two sentences at the beginning to set the stage for his history:

“Not only is Space from the point of view of life and humanity empty, but Time is empty also. Life is like a little glow, scarcely kindled yet, in these void immensities.”

It was important for Wells, and for me, that the stage is large and humanity is small. An awareness of our smallness may help to redeem us from the arrogance which is the besetting sin of scientists.

Halfway through his history, when he comes to the life and teachings of Jesus, Wells puts in a paragraph addressed explicitly to the relation between science and religion:

Perhaps the humanism of Wells sits more easily with religion because he was by nature an artist rather than a scientist. He was trained as a biologist but he made his living as a writer. He cared more for the turmoil and travail of the individual human soul than for the biology of the human species. As a scientist he knew that human passions and feelings, love and brotherhood and the fear of God, have a longer history and deeper roots in men’s minds than science.

I quoted from Wells because he is a prime example of a scientific humanist sympathetic to Christianity. He was sympathetic because his science left room for the transcendental. He was himself a preacher, preaching the moral regeneration of mankind through education. He was a revolutionary, believing in the evanescence of all earthly kingdoms. He stood firmly in the tradition of Christian millenarianism. He taught the coming of a future of hope and glory for mankind, just as Jesus taught the coming of the Kingdom of Heaven.

Wells represents the version of scientific humanism which I find congenial. There are many other versions, some friendly to religion, some indifferent, some hostile. Science is not a monolithic body of doctrine. Science is a culture, constantly growing and changing. The science of today has broken out of the molds of classical nineteenth-century science, just as the paintings of Pablo Picasso and Jackson Pollock broke out of the molds of nineteenth-century art. Science has as many competing styles as painting or poetry.

The diversity of science also finds a parallel in the diversity of religion. Once, when I was a child, walking with my mother through the English cathedral town of Winchester, I asked her: “Why are there so many different churches?” My mother gave me a wise answer: “Because God likes it that way. If he had wanted us all to worship him in one church, he would not have made so many different kinds of people.” That was an answer invented on the spur of the moment to satisfy the curiosity of a five-year-old. Now, almost sixty years later, it still has the ring of truth. In the nature of God and in the nature of man there is a far greater diversity of spirit than any one church can encompass. Just as in the nature of the universe there is a far greater diversity of structure and behavior than any one discipline of science can elucidate.

Religion and science can live harmoniously together in the human soul so long as each respects the other’s autonomy, so long as neither claims infallibility. Conflicts occur when organized science or organized religion claims a monopoly of truth. The ethic of science is supposed to be based on a fundamental open-mindedness, a willingness to subject every belief and every theory to analytical scrutiny and experimental test. The Royal Society of London in 1660 proudly took as its motto the phrase Nullius in Verba, meaning “No man’s word shall be final.” The assertion of papal infallibility, even in questions of faith and morals having nothing to do with science, grates harshly upon a scientist’s ear. We scientists are by training and temperament jealous of our freedom. We do not in principle allow any statement whatever to be immune to doubt.

On the other hand, as I listen to the arguments raging in recent years between biologists and creationists over the teaching of biology in American schools, I am shocked to hear voices among the scientists sounding as arrogant as the voices of the creationists. In these arguments, the parents of school-children are complaining that the public schools use taxpayers’ money to destroy the religious faith of their children. The parents have a legitimate complaint. The tragedy of their situation lies in the fact that their religious beliefs are in conflict with the evolutionary doctrines of modern biology. But the scientists, by and large, show no respect or understanding for the human anguish of the parents.

There is no easy solution to the conflict between fundamentalist Christian dogma and the facts of biological evolution. I am not saying that the conflict could have been altogether avoided. I am saying only that the conflict was made more bitter and more damaging, both to religion and to science, by the dogmatic self-righteousness of scientists. What was needed was a little more human charity, a little more willingness to listen rather than to lay down the law, a little more humility. Scientists stand in need of these Christian virtues just as much as preachers do. The children, over whose hearts and minds the battle is fought, need to see that there is good on both sides, that both their parents’ faith and the wider vision of science are worthy of respect.

Fortunately, the battle over creationism involves only a small minority of religious believers and of scientists. Far more important is the vast area of social and political action within which religion and science are finding common concerns and opportunities for fruitful collaboration. Religion and science have one essential quality in common. Both are truly international enterprises. Both are international, not only in spirit but in the details of daily work and organization. Both stand opposed to the selfish nationalism which would cut them off from their international roots. Both see the human race as one. Both render unto Caesar the things that are Caesar’s, but both reach around the world in the conviction that the essential core of human achievement and human dignity has nothing to do with Caesar.

In recent years, science and religion have come more and more into alliance through their common striving for peace. Chapters 11–15 of this book are concerned with the ethical problems of nuclear weapons and military strategy. Scientists have written a great deal about nuclear strategy, but nothing we have written is as thoughtful as the Pastoral Letter on War and Peace, “The Challenge of Peace: God’s Promise and Our Response,” which the Catholic Bishops of America hammered out and issued to the world in 1983. That Letter is indeed a challenge, a challenge to us scientists as well as to everybody else. It expresses a fundamental rejection of the idea that permanent peace on earth can be achieved with nuclear weapons. It challenges scientists to put our skills to work in more hopeful directions, in directions leading to peace and reconciliation rather than to a precarious balance of terror.

To end this chapter I give a brief synopsis of the remainder of Part 1. Chapter 2 is a one-hour tour of the universe, emphasizing the diversity of viewpoints from which the universe can be encountered as well as the diversity of objects which it contains. Chapter 3 is concerned with the history of science. It describes two contrasting styles in science, one welcoming diversity and the other deploring it, one trying to diversify and the other trying to unify. The names of two cities, Manchester and Athens, are symbols of the two ways of approaching science. This choice of symbols is borrowed from Benjamin Disraeli. After I am finished, you will understand why butterflies belong to Manchester and superstrings to Athens. Chapter 4 is concerned with the origin of life. It describes the ideas of six illustrious scientists who have struggled to understand the nature of life from various points of view. Chapter 5 continues the discussion of the nature and evolution of life. The question, why life characteristically tends toward extremes of diversity, remains central in all attempts to understand life’s place in the universe. Chapter 6 is an exercise in eschatology, trying to define possible futures for life and for the universe, going all the way from here to infinity. In that chapter I will be crossing the border between science and science fiction. At the end, in deference to Lord Gifford’s wishes, I put my speculations into a slightly theological context.