Essay: A physicist talks to theologians

My brother is a Lutheran theologian teaching at Concordia Seminary in St. Louis. Every month, the seminary brings in a speaker from beyond the confines of theology to give a talk to the faculty -- basically, to stir things up a bit and spark some interesting conversations. A couple of years ago, my brother was in charge of this speaker series, so he decided to invite me. I said sure, why not -- little suspecting what I was getting myself into! This essay is a rough version of what I said.

I. Ignorance and doubt

The subject for my talk to you is "What I wish my pastor knew about Physics" -- a title and topic, I should add, that has been helpfully supplied by my brother. (Thanks.) It seems to me that there are two presuppositions in this title. First, there is something that my pastor may not know. Second, there is something that I wish that my pastor did know.

My theme therefore is ignorance. There is much to be said for ignorance. It can be a useful thing. Do you remember your Sherlock Holmes? Soon after Dr. Watson meets him for the first time, he is shocked to discover that Holmes is ignorant of the Copernican theory of the Solar System.

"You appear to be astonished," he said, smiling at my expression of surprise. "Now that I do know it I shall do my best to forget it."

"To forget it!"

"You see," he explained, "I consider that a man's brain originally is like a little empty attic, and you have to stock it with such furniture as you choose. A fool takes in all the lumber of every sort that he comes across, so that the knowledge which might be useful to him gets crowded out, or at best is jumbled up with a lot of other things so that he has a difficulty in laying his hands upon it. Now the skilful workman is very careful indeed as to what he takes into his brain-attic. He will have nothing but the tools which may help him in doing his work, but of these he has a large assortment, and all in the most perfect order. It is a mistake to think that that little room has elastic walls and can distend to any extent. Depend upon it there comes a time when for every addition of knowledge you forget something that you knew before. It is of the highest importance, therefore, not to have useless facts elbowing out the useful ones."

"But the Solar System!" I protested.

"What the deuce is it to me?" he interrupted impatiently; "you say that we go round the sun. If we went round the moon it would not make a pennyworth of difference to me or to my work." (A Study in Scarlet, Chapter 2)

An extreme example, maybe, but it illustrates the point!

The first thing we have to realize about ignorance is that it is inevitable. There is simply too much worth knowing for one person to take in within the span of a lifetime. Nowadays, it is even impossible for one person to have a complete knowledge of a fairly restricted field of study, like theoretical physics. We simply must be ignorant about lots of things. Luckily, ignorance is cheap and requires little time and energy to obtain.

Of course, there are problems with ignorance. To begin with, it requires a considerable effort of the imagination to be really aware of your own ignorance. It is something like the blind spot in your eye. If you use just one eye, there is actually a place a little to one side in your field of vision in which you cannot see anything. You are usually not aware of the gap, because your brain just sort of skips over that part. In the same way, we are generally not even aware of most of the gaps in our knowledge. You have to be fairly sophisticated to realize that they are there.

Another more serious problem with ignorance is that it produces what I call a dysfunction of doubt. I think that doubt is a necessary faculty of reason. It should not be a "universal solvent" for dissolving every belief, but it does help us distinguish between beliefs that are pretty certain and things that are merely very likely. If you are ignorant of a subject, though, this helpful faculty does not work properly.

Ignorance can lead to undue credulity, to believing nonsense and speculation as if it were solid fact. For instance, there are all too many people in the world who think that the Protocols of the Elders of Zion, the vicious anti-Semitic forgery cooked up in Czarist Russia, is an actual historical document about the plans of the Jews for world domination. That is a credulous belief based on historical ignorance, a dysfunction of doubt. Ignorance can also lead to undue skepticism, to disbelieving things that are pretty well established. There are people who do not believe that the Holocaust in Nazi Germany ever happened, despite the overwhelming historical evidence and personal testimony. This is undue skepticism based on historical ignorance, likewise a dysfunction of doubt. And my example shows that these two dysfunctions of doubt can actually reinforce one another in a truly diabolical way.

If the effects of ignorance were strictly confined, then we still might be okay. But the natural world, human civilization and our own lives are all extremely interconnected. Errors and nonsense in one realm can lead to serious misjudgments in others. Ignorance of economics can lead to bad laws. Ignorance of medical facts can lead to bad ethical reasoning. So ignorance of something like physics might really be a problem for my pastor.

II. The nature of science

So what do I wish that my pastor knew about physics?

First, I wish that my pastor understood something about science as an intellectual enterprise -- how it works and why we believe its results. Given how much science is done in our civilization, it is amazing how ignorant people are about the whole process. The accounts of "the scientific method" that we learn from 7th grade textbooks are not very good. And in my personal opinion, the philosophers of science are not much better.

Take a couple of famous examples. Thomas Kuhn described the development of science as a series of reigning paradigms, which grow and develop and guide scientific thinking until they are overthrown and replaced in a scientific revolution. Karl Popper focused on the logic of the falsifiability of theories. The idea here is that a theory cannot be proven by an experiment, but it might be disproven. Our science is made of theories that could in principle be falsified, but have not been falsified yet.

My objection to these ideas is not that they are wrong, but that they tend to take one aspect of science and exaggerate it. The reality is much more interactive and dialectical that the static formulas suggest. Let me instead suggest an informal model of science that works tolerably well, but is not intended to be the last word on the subject.

Basically, I see science as composed of three elements, arranged in a cycle: Observation, Theory and Prediction.

Each of these elements requires some commentary. The observations in science are special, because we want these observations to be observer-independent. This means that, in the same situation, any observer would observe the same thing. They are in that way objective. This is what people get at when they talk about "repeatable" observations or the need for "controlled experiments". But these phrases aren't really adequate. A measurement of the magnitude of an earthquake is certainly a scientific observation, but it is neither repeatable (since the earthquake is an event that happens once and does not repeat itself later) nor a part of a controlled laboratory experiment.

Poetry has been defined as the refraction of experience through an individual personality. In other words, it not only matters what happened, it matters who observed it. Scientific observations, then, are not poetry!

What about theories? A theory is a rational structure for making inferences, and the key requirement is that scientific theories must be user-independent. That is, two different people using the same theory in the same situation should make the same inferences. This is, in fact, the reason that mathematics plays such a big role in science. The concepts of mathematics are extremely clear and distinct. Unlike many less formal ideas, there is no equivocation involved. Consequently, mathematical concepts can support chains of reasoning that are both arbitrarily long and extremely reliable.

Finally, there is prediction. Predictions are the logical results of the theories. And here is where the circle closes. In science, we require predictions to be accurate -- that is, to agree with observation. If our theory makes predictions that do not agree with observation, we need a new theory.

Now, lots of people get tangled up in the "future tense" of prediction. A prediction is supposed to be an inference about an observation that is not yet made. That is all well and good, since that is how we really test our theories in new areas. But remember, the future tense is about the observation, not the phenomenon itself. I can make a prediction about the kind of fossil I will find in a certain layer of rock, and that counts as a prediction even though the fossil has been there for millions of years. The key thing is that the new observation is outside the data set that we used to build the theory with.

Some people also get tangled up in the idea that the "scientific method" is a relatively new way of thinking, but it isn't, really. And to prove my point, let me read you a passage from Augustine's Confessions. Augustine is considering the claims of astrology.

I then turned my thoughts to those that are born twins, who generally come out of the womb so near the one to the other that the short interval between them -- whatever importance they may ascribe to it in the nature of things -- cannot be noted by human observation or expressed in those tables which the astrologer uses to examine when he undertakes to pronounce the truth. But such pronouncements cannot be true. For looking into the same horoscopes, he must have foretold the same future for Esau and Jacob, whereas the same future did not turn out for them. He must therefore speak falsely. If he is to speak truly, then he must read contrary predictions into the same horoscopes. But this would mean that it was not by art, but by chance, that he would speak truly. (Confessions, Book VII, Chapter 6)

See how it works? Augustine says that astrology would make the same prediction for Jacob and Esau -- otherwise it isn't really a well-defined, user-independent theory. But since this prediction does not agree with observation about the actual lives of Jacob and Esau, the theory cannot hold. A beautiful example of scientific thinking.

Where is human creativity in all this? We use it to construct and understand new theories, of course. Even if we aren't inventing a new theory, though, there is often plenty of creativity and ingenuity required to tease out the predictions in a given circumstance. Furthermore, we are always searching for ways to make new and better observations. There is a lot of room for creativity in science.

Of course, science is not as cut-and-dried and neat as my little picture. It is rife with real-life complications -- not least of which is that it is done by human scientists. But this is the sort of picture I'd like my pastor to appreciate.

I want to say a final word about theories. Sometimes, unscientific people will say (in a dismissive tone of voice) that such-and-such is "just a theory". That is a rather unhelpful remark. "Just a theory" -- the same description would apply both to the latest speculation of a sociobiologist and also to the idea that the Earth's gravitation steers the Moon in its orbit. Of course it is just a theory. The question is, what kind of theory is it?

My favorite classification of theories comes from physicist Charles Misner. He said that there were four kinds of theories, which I will paraphrase here:

1. Discarded theories are those that have been proven wrong and which nobody thinks about any more. A classic example of this is the phlogiston theory of combustion, which was knocked on the head by the 18th Century discovery of oxygen.
2. Best theories embody our best current battle-tested understandings of the world. These theories may have some flaws, but they are the best we have. A good example of this would be quantum mechancis.
3. Speculative theories are the cutting-edge ideas that go beyond what we know well. At any given time, we may have several incompatible speculative theories in play, and most of them will turn out to be wrong. But this is where a lot of excitement is.
4. Archival theories are no theories that are no longer the best theories available, but they are still kept around and studied for their insight and utility. Newton's theory of gravity is an example. We have a better gravity theory, due to Einstein, but we still teach Newtonian gravity because it is so clear and useful. In some ways, Newton's theory is a better theory than ever, because we know something about its limitations.

Some people seem to think that all theories are speculative, but that is not the case. That's an example of undue skepticism -- a dysfunction of doubt, brought on by ignorance.

III. The structure of the physical world

I also wish that my pastor understood something about the structure of the physical world. I suppose that sounds like a bit of special pleading. Gardeners wish that their pastors knew about horticulture, etc. But I do think that, in our present age, there is something important for a theological person to know about how the world is put together. To put it briefly, the structure of the physical world is highly rational and marvelous. It is also very surprising, strange and elusive -- very far removed from everyday "common sense". I hope I may be forgiven for sketching a little something of what I mean.

Since time immemorial, there have been essentially two different ideas about the nature of nature. Either nature is made of stuff, or nature is made of things. Greek natural philosophy can be roughly divided between atomists (who believed that everything was made of indivisible things called atoms) and others like the Eleatics, who thought that reality was smooth and continuous. By the end of the 19th Century, physicists and chemists had achieved a very remarkable synthesis using both ideas. Basically, they had decided that matter is made of atoms -- that is, matter is "thing-like" -- but that light is a continuous electromagnetic wave -- wavy stuff, but still stuff. The essential distinction was this. You can have one atom or two or three, but not 4.72116 atoms. They are discrete things. On the other hand, you can have a light wave of any intensity, and its energy would be spread out in space. It is continuous stuff.

This picture worked really, really well until the beginning of the 20th Century, when we learned that it was all wrong -- or at least, terribly incomplete. Planck and Einstein showed that the energy in light comes in discrete lumps called quanta of a determinate size. In other words, light was in some ways thing-like. Then Bohr, de Broglie, Schrodinger and the rest demonstrated that matter could show wave behavior. That is, the particles behaved like things that were spread out smoothly in space.

Now, it wasn't that we were just wrong. All of the lines of reasoning that 19th Century science had followed still applied. But somehow, just because light behaved as a wave in one set of circumstances (like the famous two-slit interference experiment) did not prevent it from behaving as a swarm of particles in another situation (like the photoelectric effect). Both the wave and particle pictures are partial descriptions of a reality that is more subtle than either. Each picture is necessary in some circumstance, but each is inadequate by itself. We might describe the resulting quantum theory as the "Mohammed Ali" theory of the world. Light propagates from place to place as a wave, but interacts as if it were made of particles. It floats like a butterfly, but stings like a bee.

Let me emphasize that the situation is not ambiguous or confused. The mathematical ideas are clear and we know how to use them. But they express a reality that is a tough match to ordinary language, so the informal description sounds a bit kooky. And we aren't talking about a side-issue here; this wave-particle duality is at the heart of the rational structure of physical law.

Why do I think that my pastor needs to know anything about this? Because the theories of physics are often misused to serve ideological ends, and my pastor needs to be defended against undue credulity for these claims. Let me give three examples.

• Einstein's theory of relativity has been used to justify philosophical or moral relativism. This sounds reasonable, unless you know something about relativity. The basic tenet of relativity is that the laws of physics are the same for every observer, in every coordinate system. This is about as far from "everything is relative" as you can get!
• People often try to draw a connection between quantum physics and eastern mysticism. The Buddhists or the Taoists, it is claimed, have understood for centuries these strange ideas that modern physics is just revealing to us. (As it turns out, I have an interesting perspective on this question. One summer in Innsbruck -- it's a long story -- I got to sit in on a two-day symposium in which quantum physicists and Buddhist scholars met with the Dalai Lama and tried to find connections. It was instructive. When the quantum physicists finally got across the real peculiar nature of the quantum world, the Dalai Lama was just as amazed as anybody. He did not have some kind of "private line" to quantum enlightenment. I found this very reassuring!)
• The Second Law of Thermodynamics (the law of the increase of entropy in isolated systems) has been used to argue that Darwinian evolution by natural selection is impossible. Complex systems cannot arise by natural processes, the argument goes, since they involve a decrease in entropy. (The same argument, of course, can be used to "prove" that snowflake crystals cannot form spontaneously.)

All of these arguments, in fact, turn out to be nonsense. They depend on misrepresentations of the physics involved. But without some basic knowledge of the physical world, my pastor might believe one or the other of them.

IV. The experience of science

So far, I have wished that my pastor knew something about the process of science and the amazing nature of the physical world. But even more importantly, I wish that he understood something about physics as a human experience. This is something very little discussed.

The experience of physics, of learning and using and doing physics, is an important one, and for some it is a thing that profoundly shapes their lives. It is also a very widespread experience. What I say about physics actually applies to all "hard" sciences. Most of the scientists who have ever lived are alive today, and there are many more in the "penumbra" of science -- physicians, engineers, teachers, and people with technical occupations of all sorts. Although they are not scientists themselves, they get close enough to science to have some of the experience themselves. It sets them apart.

What is this experience? I would describe it as one of illumination -- of coming to understand some important aspect of the natural world. It is hard to describe to outsiders. For one thing, it is often very wide in scope. When you come to understand the Second Law of Thermodynamics, you don't just understand steam engines or chemical reactions or the motions of fluids; you understand something about all of them at once. The world opens before you. And this illumination is a continuing source of insight, and opens the door to deeper and more encompassing ways of understanding.

One vital aspect of this experience is that it is widely shared. There are lots of people who have closely related experiences of illumination. This means that there is the possibility of exchanging insights with people of very wide cultural backgrounds. A physicist from India may have a very different outlook from mine on many things. A discussion of family or religion might lead to many misunderstandings, but when we talk about quantum mechanics we can communicate very well indeed. The fact that one's own illumination is not an altogether private experience makes it all the more powerful.

It is tempting to contrast this with the humanities. It seems like we are wrangling over the same human questions that Aristotle and Aeschylus were. But physics has moved on to new territory. How did we manage that? In physics, we have a contact with an external reality. Nature, as it were, is a participant in the conversation. Instead of endless human argument, chasing ideas round in circles for centuries, we can actually get somewhere.

The experience of understanding nature in a significant way often brings awe and wonder. The world is magnificently intelligible, and it is a delight to uncover its secrets. This experience can be extremely intense and exciting in a research setting, of course, where you might be the first to get a glimpse of some marvelous new thing. But it is communicated to some extent even to students. After all, understanding relativity theory is the next best thing to discovering it.

Does the experience I'm trying to describe have a moral dimension? Hardly any, as far as I can see, but that does not prevent it from being a powerful force in one's life.

What I am saying is this. The experience of science is profound and potent, and I think my pastor ought to be aware of it, even if he cannot share it. He needs to be aware of it because it affects the attitudes and thought-processes that many scientific people share. It is to these characteristics that I will turn next.

V. Habits of thought

There are certain habits of thought that are natural to a practitioner of science. I will list a few.

Philosophical realism. Regardless of what the official position is, all scientists are at root philosophical realists. They believe that the rational structure they uncover in the physical world is a real thing "out there". The world is real and its rationality is real.

Reductionism. Scientists are by habit reductionist thinkers. To understand something at a fundamental level means, more or less, to understand what the atoms are doing. There is a sort of "great chain of knowledge", with psychology on top, biology beneath it, chemistry under that and physics at the bottom. The further down you are, the more fundamental you are. Lower levels give causal explanations for things at higher levels. Regardless of one's philosophical position, this is simply how one thinks 99% of the time.

Authority. Scientists have a peculiar relation to the idea of authority. They tend to be both conservative and radical. They will strongly defend the status quo against unworthy challenges. If someone proposes a new theory of gravity, the first job is to try to disprove it. On the other hand, scientists reserve their greatest rewards for those who make the most profound innovations.

This is a strange mixture, if you think about it. Part of the way it works is that authority in science is not personal. Einstein is revered among physicists; on the other hand, most of them believe that Einstein's critique of quantum theory was wrong-headed. Einstein is a hero, but the fact that Einstein believed something is really no reason in itself to agree with him. Also -- and you theologians may need to hear this -- scientists have very little interest in the careful reading of authoritative texts. There is no holy writ. I was once at a conference in which we were discussing some tricky issue about quantum theory. Someone made a point, and someone else wondered aloud if this could help us understand something that Niels Bohr had written. (Bohr was famously subtle, not to say obscure, in his writings.) A Nobel laureate spoke up and said, "I don't think we want to discuss literary criticism." In other words, who cares what Bohr said? The point is to try to understand quantum physics!

Wariness. Scientists have a heightened awareness of the possibility that one's prejudices will interfere with one's understanding. There are some notorious examples. Einstein, as I've already mentioned, never really accepted quantum mechanics, in part because of a philosophical commitment to a deterministic universe. But an infinitely worse example comes from the history of biology in the Soviet Union. Because the crackpot theories of Lysenko gained political favor, orthodox genetics essentially died in the USSR until the 1960's. Ideology is suspect. One of the worst criticisms you can make of a scientist is to say that his opinions are tainted by his philosophical ideas.

This wariness expresses itself in a kind of scientific "conscience", an inner sensitivity about whether a given line of thinking is tainted by outside forces. One of my favorite expressions of this is due to Tony Rothman, who coined "Rothman's Law": Thou shalt not covet thine own hypothesis. Just because an idea is yours does not mean you should not subject it to great scrutiny. In fact, if it is yours, you have all the more reason to be skeptical!

Of course, this is often observed in the breach! Scientists are plagued with the same sins and imperfections as anybody: stubbornness, blindness, ambition, jealousy, personal malice. Yet what I describe is, I think, seriously held as an ideal.

Copernican sensibility. Almost all scientists are thoroughgoing Copernicans. The universe is big! It's old! It's full of wonderful stuff that has nothing to do with us! Consequently, a world view that puts human beings at the center of creation may seem a little wrong-headed. Now, I should mention that there are significant dissenting minorities here. Some physicists, in particular, are impressed with the so-called anthropic coincidences, which describe how "fine-tuned" the Universe must be to permit intelligent life like us. Maybe our existence, therefore, has something to do with how those properties came into being. This is an intriguing idea which may or may not make sense. It is a minority view, though.

[Search for elegance. This is a point brought up in questions to my lecture. It is a truism, especially among theoretical physicists like me, that the quest for "elegance" is an important motivation. This is not only a truism, it is also true. I think that it is less true in many other disciplines in science, but it remains a good point. Scientists share a faith that the universe is not only intelligible, but superbly so, that many disparate things are comprehensible on the basis of a few powerful ideas. This is in part motivated very great success we have had at comprehending a wider and wider range of phenomena on the basis of a more and more compact set of concepts.]

VI. The scientist-Christian

It is unfortunate that Mary Baker Eddy co-opted the term Christian Scientist to describe someone who might, arguably, be neither one. This forces me to use the more awkward term scientist-Christian to describe someone who is both a Christian and a practitioner of science. What is the situation of such a person? That is, after all, a subject of some interest to me.

Christians in the world have a sort of dual citizenship, in the world and in heaven, and this poses complex challenges in everyday life. The scientist-Christian, I would argue, has something very much like triple citizenship. This poses challenges that may be even more complex. On the one hand, he deals with scientific work and scientific thinking. On the other, he deals with faith and doctrine. He also lives in the world. How does he reconcile it all?


There are, of course, significant and meaningful harmonies between science and faith, especially when compared to the social and cultural environment in which we live. Neither science nor orthodox faith, for instance, propose that you should believe something because you wish it to be true. Each of them is about encountering a reality, conceived as rational, that exists outside of ourselves and to which we must conform ourselves. I think that science and theology could be natural allies against the superstitions and anti-rational movements of our own age.

But we must not disguise the fact that there are significant tensions as well. For instance, matters of faith are almost always presented in ways that "set off" the scientific conscience. Faith, we are told, must precede understanding. Much religious thinking is based on an understanding of human beings that is thoroughly prescientific. Obstinate belief, belief in the face of terrible obstacles, is praised as a virtue. And so much is based on a simple assertion of Scriptural authority -- with an emphasis on exegesis, close attention to the meanings of Greek words, etc. All of this would seem bad if put in the context of scientific practice, and it is a real obstacle to those with a well-developed scientific conscience.

What is the solution? I don't know the whole solution, but I am sure that we should not try to make the Christian faith more "scientific". My pastor does need to understand what is going on, and he needs to be ready, when necessary, to help the scientific people in his flock understand why other approaches are necessary and valid and appropriate and not a betrayal of conscience. The scientific conscience really is a part of our faculty for telling right from wrong. Perhaps my conscience needs some education, but it is no good simply to ask me to set it aside when I walk into church. How can I hope to come closer to Christ by acting or thinking in a way that I secretly believe to be wrong?

Scientist-Christians are mostly working all of this out on their own, in isolation. Even if many of their fellow-scientists are Christians, they may not have many spiritual friendships among them. Most books on the subject are marred by crummy science, crummy theology, or both. There are some interesting exceptions; I often recommend books by Ian Barbour, Arthur Peacocke, and (my favorite) John Polkinghorne to friends and students who are wrestling with these issues. It would be nice if my pastor knew enough about physics to help -- or at least to appreciate that this process is going on.

Most scientists are not Christians. What about them? Well, there is a work of evangelism to be done. Some of this will have to be apologetic in character. Where to begin? We might think to start with the magnificent intelligibility of the universe. What does this say about the universe? What does this say about us? I think that there may be some open doors in that direction.

What is the importance of all this for you folks, the theologians? Very great, I think. There will be many challenges to theology based on scientific ideas. Genetics and neuroscience will challenge the theological understanding of human nature. Many of the theories will be highly speculative, and many of the challenges will be ill-founded. But theological people will need to know enough science to separate wheat from chaff. True faith can have nothing to fear from true science. But there is nothing so pitiful as a heresy founded to appease a short-lived scientific fad -- or to oppose an enduring scientific truth.

Einstein said, "The only way to teach is to be an example -- if one can't help it, a warning example." I think this might describe my situation here! My faults as a lecturer may therefore be balanced by my usefulness as an instructive specimen -- if only a specimen of the kind of confusion that a layman of scientific background might fall into. But in any case, I am also a specimen of gratitude, both for your kind invitation and your patient attention.