The Varieties of Scientific Experience: A Personal View of the Search for God

by Carl Sagan

  This says that life is not guaranteed, that life requires something special, something improbable. I'm not for a moment suggesting it requires miraculous, divine, mystical intervention. But in a natural world, you can have probable events and you can have improbable events. And I'm sure this depends on the nature of the environments of the other planets. But there isn't any other planet that's just like the Earth, and, so far as we know so far, there isn't any other planet that has life on it. There are certainly premonitions and stirrings of life, the kind of organic chemistry on Titan, the big moon of Saturn that I referred to earlier. But that's still not the same as life. And so, by performing a first cursory inspection of our solar system, one realizes something important about where we come from.

  When you investigate the vistas of time, you find something very similar. Because it is clear from the fossil record that almost every species that has ever existed is extinct; extinction is the rule, survival is the exception. And no species is guaranteed its tenure on this planet. I would like to describe to you one event that I've already referred to as central to the origin of the human species, because it is connected with the main topic of this talk. This is the worldwide extinction event that happened 65 million years ago, at the boundary between the Cretaceous and Tertiary periods of geological time, which also corresponds to the end of the Mesozoic age and the beginning of more recent times.

  This is a close-up of a cliff base on a roadside near Gubbio in northern Italy. You can make out the scale of the image from the edge of a five-hundred-lire piece right up at the top. The surface crust has been scraped away a little bit, and the white material is calcium carbonate, essentially chalk, similar to the composition of the White Cliffs of Dover. These are the remains of countless small microorganisms that lived in the Cretaceous seas, forming little calcium carbonate shells that slowly fell through the warm waters of those seas and built up, during

  fig. 35

  Cretaceous time, for many millions of years. This deposit, as you can see, comes to an abrupt end. Time is increasing toward upper left. A layer of reddish brown rock lies above the older white carbonate, separated by a sharp boundary. And it's below this boundary that you find the last dinosaurs, and above the boundary you find an astonishing rate of proliferation of the small mammals into larger mammals, the events that are prerequisite for our own origins.

  The sharpness of this boundary worldwide suggests some quite recent catastrophic event. The boundary is that thin layer of gray clay running diagonally across the picture. The clay- this is also true worldwide-has a quite high concentration, an anomalously high concentration, of a chemical element called iridium and other elements like it in the platinum group of metals. It is known that asteroids, and presumably cometary nuclei as well, have much higher abundances of iridium than do ordinary rocks on the Earth. And this iridium anomaly, now supported by a wide range of other data, is generally taken to be evidence for what happened to extinguish the dinosaurs and most of the other species of life on the Earth 65 million years ago.

  This is an artist's conception of an object, maybe an asteroid, maybe a cometary nucleus, impacting the Cretaceous oceans. It's about ten kilometers across. It is bigger than the thickness of the ocean, so it is the same as impacting on land. The net result is to carve out in the ocean floor an immense crater and propel the fine particles thus generated into high orbit, making a vast

  fig. 36

  cloud of pulverized ocean bottom and pulverized impacting object that takes some years to settle out from the Earth's high atmosphere. During that period of time, sunlight is impeded from reaching the surface of the Earth, and the net result is a darkened and cold surface worldwide, which led, because of the differences in mammalian and reptilian physiology, to the extinction of the dinosaurs and many other kinds of life.

  That is what happened to the dinosaurs. They were powerless to anticipate it and certainly to prevent it. What I would like now to describe is a catastrophe that in some respects is quite similar, one that endangers the future of our own species. It is very different in one respect: Unlike the dinosaurs, we ourselves, at enormous cost in treasure, have created this danger. We are solely responsible for its existence, and we have the means of preventing it, if we are sufficiently courageous and sufficiently willing to reconsider the conventional wisdom. That problem is nuclear war.

  The bombs that destroyed Hiroshima and Nagasaki-everybody's read about them, we know something about what they did-killed some quarter of a million people, making no distinctions according to age, sex, class, occupation, or anything else. The planet Earth today has fifty-five thousand nuclear weapons, almost all of which are more powerful than the bombs that destroyed Hiroshima and Nagasaki and some of which are, each of them, a thousand times more powerful. [7] Some twenty to twenty-two thousand of these weapons are called strategic weapons, and they are poised for as rapid delivery as possible, essentially halfway across the world to someone else's homeland.

  The ballistic missiles are sufficiently capable that typical transit times are less than half an hour. Twenty thousand strategic weapons in the world is a very large number. For example, let's ask how many cities there are on the planet Earth. If you define a city as having more than one hundred thousand people in it, there are twenty-three hundred cities on the Earth. So the United States and the Soviet Union could, if they wished, destroy every city on the Earth and have eighteen thousand strategic weapons left over to do something else with.

  It is my thesis that it is not only imprudent but foolish to an extreme unprecedented in the events of the human species to have so large an arsenal of weapons of such destructive power simply available. Now, the prompt effects of nuclear war are reasonably well known. I will say a few words about them, but I want to concentrate mainly on the more recently discovered, more poorly known, delayed longer-term and global effects.

  Imagine the destruction of New York City by two one-megaton nuclear explosions in a global war. You could choose any other city on the planet, and in a nuclear war you can be reasonably confident that that city would suffer some similar fate. Starting at the World Trade Center and continuing about ten miles in all directions, the effects would play out. You know about the fireball and the shock waves, the prompt neutrons and gamma rays, the fires, the collapsing buildings, the sorts of thing that were responsible for most of the deaths at Hiroshima and Nagasaki. But the bomb light also sets fires, some of which are blown out by the shock wave as the mushroom cloud rises. Others are not.

  And these conflagrations can grow. And in many cases, although certainly not all, the conflagrations merge to produce a firestorm. Recent work suggests that firestorms should be much more common and much more severe than had been expected in earlier research, producing the kind of fire as in a well-tended fireplace with an excellent draft. The net result, as advertised: No cities are left standing. But that's the least of the problem.

  Beyond the obliteration of the cities is the production of a pall of sooty smoke sitting not just above the city but carried by the fire to quite high altitudes, where this dark smoke is heated by the Sun, which then makes it expand still more. This happens, obviously, not just above one target but above many or most targets.

  Cities and petrochemical facilities would be preferentially targeted. Prevailing winds would blow the fine particles in the same direction, from west to east. In anything like a full exchange something like ten thousand nuclear weapons would be detonated.

  Some ten days later, there would still be a few nuclear explosions from, I don't know, nuclear-submarine commanders who have not been told that the war was over. The smoke and dust would circulate all around the planet in longitude and spread poleward and equatorward in latitude. The Northern Hemisphere would be almost entirely socked in with smoke and dust. You would see outriders, plumes of smoke in the Southern Hemisphere. The cloud would then cross the equator well into the Southern Hemisphere. And while the effects would be somewhat less in the Southern Hemisphere
, sunlight would dim and the temperatures would fall there as 'well.

  Some calculations have been done at the National Center for Atmospheric Research in which a five-thousand-megaton war occurs in July. The widespread distribution of smoke twenty days after the war is over would produce temperature declines as much as fifteen to twenty-five centigrade degrees below normal.

  The net result, as you might imagine, is bad. The effects are global. It appears that they last for months, possibly years. Imagine what disastrous worldwide consequences the destruction of agriculture alone would have. The northern midlatitude target zone is precisely the region that is the principal source of food exports (and experts) to the rest of the world. Even countries nowhere near malnutrition today-Japan, for example- could utterly collapse in a nuclear war from the clouds blown eastward from China, an almost certain target in a nuclear war. Even apart from that, if there were no climatic effects in Japan, and not a single nuclear weapon dropped on Japan, it turns out that more than half the food that people eat there is imported. That alone would kill enormous numbers of people in Japan, and the actual effects would be much worse.

  When scientists try to estimate what the consequences of a nuclear war would be, you have to worry not just about the prompt effects. They would be bad enough. The World Health Organization calculates that in an especially nasty nuclear war the prompt effects might kill almost half the people on the planet. You also have to worry about nuclear winter, the cold and the dark that I've just been describing; you have to worry about such facts that those conditions kill not just people and agricultural plants and domesticated animals but the natural ecosystem as well. At just the point that survivors might want to go to the natural ecosystem to live off it, it would be severely stressed.

  There is a kind of witches' brew of effects that have been very poorly studied by the various defense establishments, some more than others. These include, for example, pyrotoxins, the smogs of poison gas produced from the burning of modern synthetics in cities, increased ultraviolet light from the partial destruction of the protective ozone layer, and the intermediate timescale radioactive fallout, which turns out to be some ten times more than confident assurances by miscellaneous governments have had it. And so on. The net result of the simultaneous imposition of these independently severe stresses on the environment will certainly be the destruction of our global civilization, including Southern Hemisphere nations, nations far removed from the conflict-nations, if you can find any, that had no part of the quarrel between the United States and the Soviet Union-and, of course, northern midlatitude nations, it goes without saying.

  Beyond that, many biologists believe that massive extinctions are likely of plants, of animals, of microorganisms, the possibility of a wholesale restructuring of the kind of life we have on Earth.

  It would probably not be as severe as the Cretaceous-Tertiary catastrophe, but possibly approaching it. A number of scientists have said that under those circumstances they cannot exclude the extinction of the human species.

  Now, extinction seems to me serious. Hard to think of something more serious, more worthy of our attention, more crying out to be prevented. Extinction is forever. Extinction undoes the human enterprise. Extinction makes pointless the activities of all of our ancestors back those hundreds of thousands or millions of years. Because surely if they struggled for anything, it was for the continuance of our species. And yet the paleonto-logical record is absolutely clear. Most species become extinct. There's nothing that guarantees it won't happen to us. In the ordinary course of events, it might happen to us. Just wait long enough. A million years is quite young for a species. But we are a peculiar species. We have invented the means of our own self-destruction. And it can be argued that we show only modest disinclination to use it.

  This is what in a number of Christian theologies is called crimes against Creation: the massive destruction of beings on the planet, the disruption of the exquisitely balanced ecology that has tortuously grown up through the evolutionary process on this planet. So, since this is clearly recognized as such a theological crime as well as all the other kinds of crimes, it is reasonable to ask where are the religions-the established religions, the incidental independent-thinker religionists-on nuclear war?

  It seems to me this is the issue above all others on which religions can be calibrated, can be judged. Because certainly the preservation of life is essential if the religion is to continue. Or anything else. And for me personally, I believe there is simply no more pressing issue. Whatever else we're interested in, it is fundamentally compromised by nuclear war. Whatever personal hopes we have for the future, ambitions for children and grandchildren, generalized expectations for future generations-they are all fundamentally threatened by the danger of nuclear war.

  It seems to me that there are many respects in which religions can play a benign, useful, salutary, practical, functional role in the prevention of nuclear war. And there are still other ways that are maybe longer shots but, considering the stakes, are well worth considering. One has to do with perspective.

  Now, not all religions have this perspective on the stewardship of the Earth by men and women, but they could. The idea is that this world is not here for us only. It is for all human generations to come. And not just for humans. Or even if you took only a very narrow view of the world, if you were a speciesist in the same sense as being a racist or a sexist, still you would have to be very careful about all those other nonhuman species, because in many intricate ways our lives depend on them. I remind you of the elementary fact that we breathe the waste products of plants and plants breathe the waste products of humans. A very intimate relationship if you think about it. And that relationship is responsible for every breath you take. We in fact depend on the plants, it turns out, a lot more than the plants depend on us. So that sense that this is a world that is worth taking care of is, it seems to me, something that could be at the heart of religions that wished to make a significant contribution to the human future.

  Then there are more direct kinds of political activity. For example, religious people played a role in the abolition of slavery in the United States, and elsewhere. Religions played a fundamental role in the independence movement in India and in other countries and the civil rights movement in the United States. Religions and religious leaders have played very important roles in getting the human species out of situations that we should never have gotten into that profoundly compromised our ability to survive, and there is no reason religions could not in the future take on similar roles. There are, of course, occasional circumstances, individual clergypersons who have taken that role in this particular crisis, but it is hard to see any major religion that has made this kind of political activity its foremost objective.

  There is also the issue of moral courage. Religions, because they are institutionalized and have many adherents, are able to provide role models, to demonstrate that acts of conscience are creditable, are respectable. They can raise awkward possibilities. The pope, for example, has raised (although not answered) the question about the moral responsibility of workers who develop and produce weapons of mass destruction.

  Or is it okay as long as there is a local excuse? Are some excuses better than other excuses? What are the implications for scientists? For corporate executives? For those who invest in such companies? For military personnel? The archbishop of Amarillo has urged workers at a nuclear-weapons facility in his diocese to quit. So far as I know, no one has quit. Religions can remind us of unpopular truths. Religions can speak truth to power. It's a very important function that is often not carried out by all the other sectors of society.

  Religions can also speak to their own sectarian eschatologies, especially where they run contrary to human survival. I'm thinking, for example, about the Christian fundamentalist view in the United States that the end of the world is unerringly predicted in the book of Revelation, that the details in the book of Revelation are sufficiently similar to those of a nu
clear war that it is the duty of a Christian not to prevent nuclear war. The Christian who does so would be interfering with God's plan. Now, I know I have stated this somewhat more baldly than the advocates of such views, but I believe that is what it comes down to. Christians can play a useful role in providing a steadying hand on people with such eschatologies, because they're very dangerous.

  Suppose someone with such a view were in a position of power, and there was a critical decision that had to be made in a moment, and that person had a little sense that maybe this was the fulfillment of biblical prophecy. Maybe he shouldn't make the effort to avoid this, especially if he believed that he himself will be one of the first people to leave the Earth and appear at the right hand of God. He might be interested to see what that would be like. Why slow it down?

  Religion has a long history of brilliant creativity in myth and metaphor. This is a field crying out for apposite myth and metaphor. Religions can combat fatalism. They can engender hope. They can clarify our bonds with other human beings all over the planet. They can remind us that we are all in this together. There are many functions that religion can serve in trying to prevent this ultimate catastrophe. Ultimate for us-I want to stress that we're not talking about the elimination of all life on Earth. Doubtless roaches and grass and sulfur-metabolizing worms that live in hot vents in the ocean bottoms would survive nuclear war. It is not the Earth that is at stake, it is not life on Earth that's at stake, it is merely us and all we stand for that is at stake.

  Now, along these lines I should also say that at least some religions have specific suggestions on standards of moral behavior that conceivably could be relevant to this problem. (I don't guarantee it; I don't know. The experiment has not been carried out.) And in particular there is the issue of the Golden Rule. Christianity says that you should love your enemy. It certainly doesn't say that you should vaporize his children. But it goes much further than that. It says not just abide your enemy, not just tolerate him, love him.