The Varieties of Scientific Experience

Two

All of us grow up with the sense that there is some personal relationship between us, ourselves, and the universe. And there is a natural tendency to project our own knowledge, especially self-knowledge, our own feelings, on others. This is a commonplace in psychology and psychiatry. And so it is with our view of the natural world. Anthropologists and historians of religion sometimes call this animism and attribute it to so-called primitive tribes-that is, ones who have not constructed instruments of mass destruction. This is the idea that every tree and brook has a kind of actuating spirit-that, as Thales, the first scientist, said in one of the few surviving fragments of his work, "There are gods in everything." It's a natural idea. But it's not restricted to animists, of whom there are many millions on the planet today. Physicists, for example, do it all the time, except where nature does not oblige. It is the commonest thing in the world in, say, the kinetic theory of gases, to imagine each of these little molecules of air that are busily colliding in front of us as, maybe, billiard balls. Well, that's not exactly projection, since physicists are not strictly speaking of billiard balls, but it is taking something from everyday experience and projecting it into a different realm. It's very common for physicists to refer to molecules or asteroids as "guys." You can more easily imagine what a molecule or an asteroid is like if you imagine them as beings something like us. And this, I believe, reveals the prevalence in this day of these ancient modes of thinking.

Yet you cannot carry this projection too far, because sooner or later you bump your nose. For example, when we get to relativity or quantum mechanics, we discover realms that are alien to our everyday experience, and suddenly the laws of nature turn out to be astonishingly different. The idea that as I walk in this direction my watch goes slightly slower and I am contracted in the direction of motion and my mass has increased slightly does not correspond to everyday experience. Nevertheless, that is an absolutely certain consequence of special relativity, and the reason it does not conform to common sense is that we are not in the habit of traveling close to the speed of light. We may one day be in that habit, and then the Lorentz transformations [1] will be natural, intuitive. But they aren't yet.

The idea that there is a cosmic speed limit, the speed of light, beyond which no material object can travel, again seems counterintuitive, even though it can be demonstrated, as Einstein did, from an astonishingly simple and basic analysis of what we mean by space, time, simultaneity, and so on.

Or if I were to propose to you that my arm could be in this position or in that position but it would be forbidden by the laws of nature to be in some intermediate position, that would likely strike you as absurd, as contrary to experience. And yet on the subatomic level, there is quantization of energy and position and momentum. The reason it seems counterintuitive is that we are not ordinarily down at the level of the very small, where quantum effects dominate.

So the history of science-especially physics-has in part been the tension between the natural tendency to project our everyday experience on the universe and the universe's noncompliance with this human tendency.

Now, there is another tendency from the psychological or social sphere projected upon the natural world. And that is the idea of privilege. Ever since the invention of civilization, there have been privileged classes in societies. There have been some groups that oppress others and that work to maintain these hierarchies of power. The children of the privileged grow up expecting that, through no particular effort of their own, they will retain a privileged position. At birth all of us imagine that we are the universe, and we don't distinguish the boundaries between ourselves and those around us. This is well established in infants. As we grow up, we discover that there are others who are apparently autonomous and that we're only one among many other people. And then, at least in some social situations, there is the sense that we are central, important. Other social groups, of course, don't have that view. But it is generally those with privilege and status, especially in ancient times, who became the scientists, and there was a natural projection of those attitudes upon the universe.

So, for example, Aristotle provided powerful arguments, none of them instantly dismissible, that the heavens moved and not the Earth, that the Earth is stationary and that the Sun, the Moon, the planets, the stars, rise and set by physically moving once around the Earth every day. With the exception of this kind of motion, the heavens were thought to be changeless. The Earth, while stationary, had all the corruption of the universe localized here.

Up there was matter, which was perfect, unchanging, a special kind of celestial matter that is, by the way, the origin of our word "quintessential." There were four essences down here, the imagined four elements of earth, water, fire, and air, and then there was that fifth element, that fifth essence out of which the heaven stuff was made. And that's why the word "quintessential"-"fifth essence"-comes about. It's interesting to see a kind of linguistic artifact of the previous worldview still present in the Oxford Unabridged. But it's amazing what's in the Oxford Unabridged

Now, in the fifteenth century, Nicolaus Copernicus suggested a different view. He proposed that it was the Earth that rotated and that the stars were in effect motionless. He proposed moreover that in order to explain these apparent movements of the planets against the background of more distant stars, the planets and the Earth, in addition to rotating, revolved around the Sun. That is, the Earth was demoted. You know the phrase- another linguistic artifact-the world, or the Earth. What is the definite article saying? It's saying there is only one. And that also goes straight back to pre-Copernican times, as does the phrase, natural as it is, of the Sun rising and the Sun setting.

Copernicus, by the way, felt his idea to be so dangerous that it was not published until he was on his deathbed, and even then it had an outrageous introduction by a man named Osiander, who was worried that it was too incendiary, too radical. Osiander wrote, in effect, "Copernicus doesn't really believe this. This is just a means of calculating. And don't anybody think he's saying anything contrary to doctrine." This was an important issue.

Aristotle's views had been accepted fully by the medieval church-Thomas Aquinas played a major role in that-and therefore by the time of Copernicus a serious objection to a geocentric universe was a theological offense. And you can see why, because if Copernicus were right, then the Earth would be demoted, no longer the Earth, the world, but just a world, an earth, one of many.

And then came the still more unsettling possibility, the idea that the stars were distant suns and that they also had planets going around them and that, after all, you can see thousands of stars with the naked eye. Suddenly the Earth is not only not central to this solar system but no longer central to any solar system. Well, there was a period in which we hoped that we were at the center of the Milky Way Galaxy. If we weren't at the center of our solar system, at least our solar system was at the center of the Milky Way Galaxy. And the definitive disproof of that occurred only in the 1920s, to give you an idea of how long it took for Copernican ideas to reach galactic astronomy.

And then there was the hope that, well, at least maybe our galaxy was at the center of all the other galaxies, all those many billions of other galaxies. But modern views have it that there is no such thing as a center of the universe, at least not in ordinary three-dimensional space, and we are certainly not at it.

So those who wished for some central cosmic purpose for us, or at least our world, or at least our solar system, or at least our galaxy, have been disappointed, progressively disappointed. The universe is not responsive to our ambitious expectations. A grinding of heels can be heard screeching across the last five centuries as scientists have revealed the noncentrality of our position and as many others have fought to resist that insight to the bitter end. The Catholic Church threatened Galileo with torture if he persisted in the heresy that it was the Earth that moved and not the Sun and the rest of the celestial bodies. It was serious business.

Now, at the same time, another of the Aristotelian precepts was challenged. That was the idea that except for the moving of crystal spheres into which the planets were embedded, nothing changes up in the heavens. In 1572 there was a supernova explosion in the constellation Cassiopeia. A star that had previously been invisible suddenly became so bright that it could be seen by the naked eye. The Danish astronomer Tycho Brahe noticed it. Well, if nothing changes up there, how is it that suddenly a star appeared-I mean suddenly, in a period of a week or less, from invisibility to something easily seen-and then stayed for some months before fading away? Something was wrong.

Just a few years later, there was an impressive comet, the Comet of 1577, and Tycho Brahe-decades after Copernicus- had the presence of mind to organize an international set of observations of that comet. The idea was to see if it was down here in the Earth's atmosphere, as Aristotle had insisted it must be, or up there among the planets. Part of the reason that Aristotle had insisted that the comets were meteorological phenomena was his belief in an unchanging heaven.

So Brahe thought, if the comet is close to the Earth, then two observers far from each other will see it against different background stars. This is called parallax, which you easily can demonstrate by simply winking your eye, first the left and then the right, with a finger propped up about a foot in front of your nose. The finger seems to move as you blink.

Brahe reasoned that if the comet was very far away, then the two observers who were far apart would see it in almost exactly the same part of the sky. You could determine how far away it was by how much it moved between those two different vantage points, how much the parallax was. And Brahe determined it was surely farther away than the Moon and, therefore, up there, in the planetary realm, and not down here, where the weather is. That was another upsetting discovery for the institutionalized Aristotelian wisdom.

Now, as science has progressed, there have been-one after another-a series of assaults on human vainglory. One of them, for example, is the discovery that the Earth is much older than anyone had expected. Human history goes back only a few thousand years. Many people believed that the world was not much older than human history. And there was no sense of evolution, no sense of vast vistas of time. And then the geological and pa-leontological evidence began to accumulate, making it very difficult to see how the geological forms and the fossils of now-extinct plants and animals could have come into being, unless the Earth were enormously older than the few thousand years that had been projected. That is a battle still being fought. In the United States, for example, there are people who are called "creationists," the more radical of whom insist that the Earth is less than ten thousand years old. The shorter the age of the Earth, the greater the relative role of humans in the history of the Earth is. If the Earth is, as we certainly know it to be, 4,500 million years old and the human species at most a few million years old, probably less than that, then we have been here for only an instant of geological time, for less than one one-thousandth of the history of the Earth, and therefore in time, as in space, we have been demoted from the central to an incidental aspect.

And then evolution itself was still a further disquieting discovery, because at least it had been hoped that humans were separate from the rest of the natural world, that we had been specifically put here in a way different from petunias, let's say. And yet Darwin's historic work showed that we were very likely related in an evolutionary sense with all the other beasts and vegetables on the planet. And there remain many people who are enormously offended by this idea.

This sense of offense has-I'm only speculating-deep psychological roots. Part of it is, I believe, an unwillingness to come to grips with the more instinctive aspects of human nature. But I believe it is essential to understand this if we wish to survive. I think ignoring that, imagining all humans are rational actors in the present phase, is enormously dangerous in an age of nuclear weapons. I think the discomfort that some people feel in going to the monkey cages at the zoo is a warning sign.

Then, in the early part of this century, there was still another such assault, which came with special relativity. Because one of the central points of special relativity is that there are no privileged frames of reference, that we are not in an important position or state of motion. There is nothing privileged about the velocity that we have or the acceleration that we have; the universe can be understood precisely if it is true that we do not have a special frame of reference.

Now, it's certainly true that there is something special about our position in time. The universe has changed. A microsecond after the Big Bang, it was quite different from how it is right now. So no one maintains these days that there is not something special about our epoch in the sense that the universe itself evolves. But in terms of position, velocity, and acceleration, there is nothing privileged about where we are. This insight was obtained by a young man who was opposed to privilege in the social sphere. If you look at Einstein's autobiographical writings, I think it is quite clear that his opposition to privilege in the social world was connected with his opposition to privilege in fundamental physics.

Well, if we don't have a distinctive position or velocity or acceleration, or a separate origin from the other plants and animals, then at least, maybe, we are the smartest beings in the entire universe. And that is our uniqueness. So today the battle, the Copernican battle, is, in somewhat covert form, being waged on the issue of extraterrestrial intelligence. Now, this doesn't guarantee that there is extraterrestrial intelligence. It may be that the Copernican insights-the principle of mediocrity, if you wish to call it that-worked for all these other things, but on extraterrestrial life it doesn't, and we are unique. I will come back to that later, but I believe that the ongoing Copernican revolution is relevant to this debate as well.

There is today another battlefield on which the Copernican insights are being attacked. It is connected with one of the classic arguments for the existence of God, that is, the Western kind of God, namely, the argument from design.

The idea of the argument from design goes like this: Suppose you know nothing about watches and you come upon an elegantly tooled pocketwatch. And you open it and everything is going tick-tick-tick-tick, and there are all those gears and levers and burnished brass, and such things are not made in nature. Therefore the existence of such a complex mechanism, the existence of the watch, implies a watchmaker. Now we go and look at an organism. Let's take a very modest organism, a bacterium. Well, you look in there and you find a much more complex mechanism than a pocketwatch. A bacterium has many more moving parts, much more information than what you would have to write down in order to describe how to make a pocket-watch. And yet the world is full of bacteria. They're everywhere, enormous quantities of them. And is it possible that this being, far more complex than a watch, arose spontaneously out of who knows what sort of collisions of atoms? Isn't it more likely that this "watch" also implies a watchmaker? That is one example of the argument from design, and you can imagine that every part of nature might be vulnerable to such an interpretation. Everything, that is, except utter chaos.

Well, Darwin showed, through natural selection, that there was a way other than the existence of a Watchmaker, a way in which it was possible for enormous order to emerge from a more disordered natural world without the interposition of any capital-W Watchmaker. That was natural selection.

The ideas behind natural selection were that there was such a thing as a hereditary material, that there were spontaneous changes in the hereditary material, that those changes were expressed in the external form and function of the organism, that organisms made many more copies of themselves than the environment could support, and therefore that some selection among various natural experiments was made by the environment for reproductive success, that some organisms, by pure accident, were better suited to leaving offspring than others.

Now, an essential aspect of this idea is that you need to have enough time. If the universe is only a few thousand years old, then Darwinian evolution is nonsense. There isn't time. On the other hand, if the Earth is a few thousand million years old, then there is enormous time, and we can at least contemplate that this is the source, as certainly all of modern biology suggests, of the complexity and beauty of the biological world.

This sort of argument from design we can find in other aspects of nature. And I'd like to discuss two of them. One is Isaac Newton's understanding of the order within the solar system, and the other is a most interesting although, I believe, flawed approach to the laws of nature, put forth in recent times, called the "anthropic principle."

One of Newton's many extraordinary accomplishments was to show that, granting a few simple and highly nonarbitrary laws of nature, he could deduce to high precision the motion of the planets in the solar system. The Newtonian method has remained valid from that time to this. It is precisely Newtonian physics that is used routinely in my line of work, sending spacecraft to the planets, something that you might be tempted to say was far beyond Newton's expectations. But he in fact did envision at least the launching of objects into Earth orbit.

What Newton found is that there is a distinctive plane to the solar system. Copernicus had essentially proposed this, but Newton showed in detail how it worked. The orbits of the planets circle the Sun, all of them very close to the ecliptic plane, also called the zodiacal plane (because the constellations of the zodiac are arrayed around this plane). And that's why the planets and the Sun and the Moon apparently move through the zodiac. "Why is everything so regular?" Newton asked. "Why are all the planets in the same plane? Why do they all go around the Sun in the same direction?" It's not that Mercury goes around one way while Venus goes around in another way. All of the planets go around in the same sense. And, as far as he knew then, they all rotated in the same sense. The planets had something astonishingly regular about them. On the other hand, the comets that were known in his day were helter-skelter. Their orbits were at every possible angle to the ecliptic plane. Some went around in the direct sense; some went around in the retrograde sense. And they were tilted in all sorts of directions.

Newton believed that the distribution of cometary orbits was the state of nature and that is how the planets would have moved had there not been an intervening hand. He believed that God established the initial conditions for the planets that made them all go around the Sun in the same direction, in the same plane, and rotating in a compatible sense.

Now, in fact, this is not a strong conclusion. And Newton, who was extraordinarily perceptive in so many areas, was clearly not here.

The outline of a general solution of this problem was provided, independently as far as we can tell, by both Immanuel Kant and by Pierre-Simon, the marquis de Laplace.

Newton, Laplace, and Kant all lived after the invention of the telescope and therefore after the discovery that Saturn has an exquisite ring system that goes around it, a portion of which you see here in this far-encounter photograph. It is a flat plane of clearly fine particles. The first clear demonstration that it's made of many particles, that it isn't a solid sheet, was made by a Scottish physicist, James Clerk Maxwell.

Here's a closer view of the rings of Saturn. And you can see an enormous sequence of such rings and a gap-the so-called Cassini Division in the rings.

fig. 15

fig. 16

If you take a close-up look at this portion, you can see a succession of rings. We now know that there are many hundreds of these rings, all in a flat plane, and we now know, as both Kant and Laplace guessed, that they're made of tumbling boulders and dust particles. The rings of Saturn, by the way, are thinner compared to their lateral extent than is a piece of paper.

Kant also knew about objects that were then called nebulae. It was not clear whether they 'were within our Milky Way or beyond-we now know, of course, most of them are beyond. Some of the nebulae were again flattened systems made, we now know, of stars.

So Kant and Laplace, both of them explicitly mentioning the rings of Saturn, and Kant explicitly mentioning the elliptical nebulae, proposed that the solar system came from such a flattened disk and that somehow the planets condensed out of the disk. But if that's the case, the disk, after all, has some rotation. Everything that condenses out of it will be going around in the same direction. And if you think about it for a moment, you will see that as the particles come together and make larger objects, they will have a common sense of rotation as well.

What Kant and Laplace proposed is what we now call a solar nebula, or accretion disk, whose flattened form was the ancestor of the planets, and that it is perfectly easy to understand how it is that the planets are in the same plane with the same direction of revolution and the same sense of rotation.

What is more, we now know that the random orientation of the comets is not primordial and that very likely the comets began in the solar nebula, all going around the Sun in the same sense, were ejected by gravitational interactions with the major planets, and then, by the gravitational perturbations of passing stars, had their orbits randomized.

So Newton was wrong in both senses: (a) in the sense of believing that the chaotic distribution of cometary orbits is what you would expect in a primordial system and (b) in assuming that there was no natural way in which the regularities of planetary motion could be understood without divine intervention, from which he deduced the existence of a Creator.

Well, if Newton could be fooled, this is something worth paying attention to. It suggests that we, of doubtless inferior intellectual accomplishment, might be vulnerable to the same sort of error.

I would just like to lock in what I've been saying about the solar nebula with three more images.

Here is an attempt to illustrate what I've just been saying. An originally irregular interstellar cloud is rotating. It gravita-tionally contracts; that is, the self-gravity pulls it in. Because of the conservation of angular momentum, it flattens into a disk. A way to think of it is that centrifugal force does not oppose the contraction along the axis of rotation but does in the plane of rotation. So you can see that the net result will be a disk. Through processes that need not detain us here (although remarkable progress has been made in our understanding during the last twenty years), there are gravitational instabilities that produce a large number of objects, which then fall together by collision and produce a smaller number of objects. It's clear that

fig. 17

if there were a huge number of objects with crossing orbits, they would eventually collide, and you would wind up with fewer and fewer objects. So the idea here is that there is a kind of collisional natural selection-the evolutionary idea as applied to astronomy-in which you must eventually wind up with a small number of objects in orbits that do not cross each other. And that is certainly the present configuration of the planetary system shown up here.

This is just another artist's conception of an early stage in the origin of our solar system, showing some of the multitude of small objects a few kilometers across, from which the planets were formed. And that this is not solely a theoretical construct has been made clear in recent years by the discovery of a number of flattened disks around nearby stars.

fig. 18

fig. 19

This one is around the star Beta Pictoris. It's in a Southern Hemisphere constellation. But Vega, one of the brightest stars in the Northern sky, also has such a flattened disk of dust and maybe a little gas around it. And many people think that it is in the final stages of sweeping up a solar nebula, that planets have already formed there, and that if you come back in only a few tens of millions of years you will find the disk entirely dissipated and a fully formed planetary system.

So I would like now to come to what is called the anthropic principle. If you study history, it's almost irresistible to ask the question, what if something had gone in a different direction? What if George III had been a nice guy? There are many questions; that's not the deepest, but you understand what I'm saying. There are many such apparently random events that could just as easily have gone another way, and the history of the world would be significantly different. Maybe-I don't know that this is the case-but maybe Napoleon's mother sneezed and Napoleon's father said, "Gesundheit," and that's how they met. And so a single particle of dust was responsible for that deviation in human history. And you can think of still more significant possibilities. It's a natural thing to think about.

Now, here we are. We're alive; we have some modest degree of intelligence; there is a universe around us that clearly permits the evolution of life and intelligence. That's an unremarkable and, I think, as secure a remark as can be made in this subject: that the universe is consistent with the evolution of life, at least here. But what is interesting is that in a number of respects the universe is very fine-tuned, so that if things were a little different, if the laws of nature were a little different, if the constants that determine the action of these laws of nature were a little different, then the universe might be so different as to be incompatible with life.

For example, we know that the galaxies are all running away from each other (the so-called expanding universe). We can measure the rate of expansion (it is not strictly constant with time). We can even extrapolate back and ask how long ago were all the galaxies so close that they were in effect touching. And that will surely be, if not the origin of the universe, at least an anomalous or singular circumstance from which we can begin dating. And that number varies according to a number of estimates, but it's roughly 14,000 million years.

Now, the period of time that was required for the evolution of intelligent life in the universe-if we are unique and we define ourselves immodestly as the carriers of intelligent life (a case could be made, you know, for other primates and dolphins, whales, and so on)-but for any of those cases it took something like 14,000 million years for intelligence to arrive. Well, how come? Why are those two numbers the same? Put another way: If we were at a much earlier stage or a much later stage in the expansion of the universe, would things be very different? If we were at a much earlier stage, then there would not be, according to this view, enough time for the random aspects of the evolutionary process to proceed, and so intelligent life would not be here, and so there would be nobody to make this argument or debate about it. Therefore the very fact that we can talk about this demonstrates, it is argued, that the universe must be a certain number of years old. So if only we had been wise enough to have thought of this argument before Edwin Hubble, we could have made this spectacular discovery about the expansion of the universe just by contemplating our navels.

There is to my mind a very curious ex post facto aspect of this argument. Let's take another example. Newtonian gravitation is an inverse square law. Take two self-gravitating objects, move them twice as far apart, the gravitational attraction is one-quarter; move them ten times farther apart, the gravitational attraction is one-hundredth, and so on. It turns out that virtually any deviation from an exact inverse square law produces planetary orbits that are, in one way or another, unstable. An inverse cube law, for example, and higher powers of the negative exponent mean that the planets would rapidly spiral into the Sun and be destroyed.

Imagine a device with a dial for changing the law of gravity (I wish there were such a device, but there isn't). We could dial in any exponent, including the number 2 for the universe we live in. And when we do this, we find that a large subset of possible exponents leads to a universe in which stable planetary orbits are impossible. And even a tiny deviation from 2-2.0001, for example-might, over the period of time of the history of the universe, be enough to make our existence today impossible.

So, one may ask, how is it that it's exactly an inverse square law? How did it come about? Here is a law that applies to the entire cosmos that we can see. Distant binary galaxies going around each other follow exactly an inverse square law. Why not some other sort of law? Is it just an accident, or is there an inverse square law so that we could be here?

In the same Newtonian equation, there is the gravitational coupling constant called "big G." It turns out that if big G were ten times larger (its value in the centimeter-gram-second system is about 6.67 x 10^-8), if it were 10 times larger (6.67 x 10^-7), then it turns out the only kind of stars we would have in the sky would be blue giant stars, which expend their nuclear fuel so rapidly that they would not persist long enough for life to evolve on any of their planets (that is, if the timescales for the evolution of life on our planet are typical).

Or if the Newtonian gravitational constant were ten times less, then we would have only red dwarf stars. What's wrong with a universe made with red dwarf stars? Well, it is argued, they're around for a long time because they burn their nuclear fuel slowly, but they are such feeble sources of light that to be warmed to the temperatures of liquid water, let's say, [2] then the planets would have to be very close to the star in order to be at this temperature. But if you put the planets very close to the star, there is a tidal pull that the star exerts on the planet so that the planet always keeps the same face to the star, and therefore, it is said, the near side will be too hot and the far side will be too cold and it's inconsistent with life. So isn't it remarkable that big G has the value it does? I'll come back to this.

Or consider the stability of atoms. An electron with something like one eighteen-hundredth the mass of a proton has precisely the same electrical charge. Precisely. If it were even a little different, the atoms would not be stable. How come the electrical charges are exactly the same? Is it so that 14 billion years later we, who are made of atoms, could be around?

Or if the strong nuclear force coupling constant were only a little weaker than it is, you can show that only hydrogen would be stable in the universe and all the other atoms, which surely are required for life, we would say, would never have been made.

Or if certain specific nuclear resonances in the nuclear physics of carbon and oxygen were a little different, then you could not build up in the interiors of red giant stars the heavier elements and again you would have only hydrogen and helium in the universe and life would be impossible. How is it that everything works out so well to permit life when it's possible to imagine quite different universes?

(What I'm about to say now is not an answer to the question I've just posed.) It is not difficult to see teleology hiding in this sequence of arguments. And, in fact, the very phrase "anthropic principle" is a giveaway as to at least the emotional if not the logical underpinnings of the argument. It says something central about us; we're the anthropos. And that's the reason I am saying that this is another ground, somewhat covert, on which the Copernican conflict is being worked out in our time. J. D. Barrow, one of the authors and promoters of the anthropic principle, is quite straightforward about it. He says that the universe is "designed with the goal of generating and sustaining observers"-namely, us.

Now, what can we say about this? Let me make, in conclusion, a few critical remarks. First of all, in at least parts of this argument there is a failure of the imagination. Let's take that red dwarf argument, in which if the gravitational constant were an order of magnitude less, then we would only have those red giants. Is it true that you could not have life in that situation for the reasons I mentioned? It turns out it isn't, for two different reasons. Let's look again at that tidal locking argument. Yes, for a close-in planet and the star, it seems possible that the net result would be the same kind of situation as for the Moon and the Earth, namely, that the secondary body makes one rotation per revolution, therefore always keeping the same face to the primary. That's why we always just see one Man in the Moon and not some Woman in the Moon on the back that we see as well. But if you look at Mercury and the Sun, you find a close-in planet not in a one-to-one resonance, but it's a three-to-two resonance. There are many more than just this one kind of resonance that are possible. What is more, if we're talking about planets that have life, we're talking about planets with atmospheres. A planet with an atmosphere carries the heat from the illuminated to the unilluminated hemisphere and redistributes the temperature. So it's not just the hot side and the cold side. It is much more moderate than that.

And then let's take a look at the more distant planets that you might imagine were too cold to support life. This neglects what is called the greenhouse effect, the keeping in of infrared emission by the atmospheres of the planet. Let's take Neptune, at thirty astronomical units from the Sun, so you would figure that it has almost a thousand times less sunlight. And yet there is a place we can see with radio waves in the atmosphere of Neptune that is as warm as it is in the cozy room I'm in. So what has happened here is that an argument has been put forward, but in insufficient detail. It has not been looked at closely enough. And I bet that will turn out to be the case in some of the other examples I present.

The second possibility is that there is some new principle hitherto undiscovered, which connects various apparently unconnected aspects of the universe in the same way that natural selection provided a wholly unexpected solution to a problem that seemed to have no conceivable solution whatever.

And thirdly, there is the so-called many worlds or, better, many universes idea. And this is what I had in mind when I was talking about history at the beginning. Namely, that if at every microinstant of time the universe splits into alternate universes in which things go differently, and that if there is at the same moment an enormously, tremendously large, perhaps infinitely large array of other universes with other laws of nature and other constants, then our existence is not really that remarkable. There are all those other universes in which there isn't any life. We just, by accident, happen to be in the one that has life. It's a little bit like a winning hand at bridge. The chance of, let's say, being dealt twelve spades is an absurdly low probability. But it is as likely as getting any other hand, and therefore, eventually, if you play long enough, some universe has to have our laws of nature.

Well, I believe that we are seeing a still largely unexplored area of physics being projected upon by the same sorts of human hopes and fears that have characterized the entire history of the Copernican debate.

I wanted to say just two final things. One is, if the very strong version of the anthropic principle is true, that is, that God-we might as well call a spade a spade-created the universe so that humans would eventually come about, then we have to ask the question, what happens if humans destroy themselves? That would make the whole exercise sort of pointless. So if only we could believe the strong version, we would have to conclude either (a) that an omnipotent and omniscient God did not create the universe, that is, that He was an inexpert cosmic engineer, or (b) that human beings will not self-destruct. Either alternative, it seems to me, is a matter of some interest, would be worth knowing. But there is a dangerous fatalism lurking here in the second branch of that fork in this road.

Well, I would like to conclude, then, by just a few lines of poetry, this one from Rupert Brooke, called "Heaven."

FISH (fly-replete, in depth of June, Dawdling away their wat'ry noon) Ponder deep wisdom, dark or clear, Each secret fishy hope or fear.

Fish say, they have their Stream and Pond; But is there anything Beyond? This life cannot be All, they swear, For how unpleasant, if it were!

One may not doubt that, somehow, Good Shall come of Water and of Mud; And, sure, the reverent eye must see A Purpose in Liquidity.

We darkly know, by Faith we cry, The future is not Wholly Dry. Mud unto mud!-Death eddies near- Not here the appointed End, not here!

But somewhere, beyond Space and Time, Is wetter water, slimier slime! And there (they trust) there swimmeth One, Who swam ere rivers were begun,

Immense, of fishy form and mind, Squamous, omnipotent, and kind; And under that Almighty Fin, The littlest fish may enter in.