THE COSMOLOGICAL argument emerges from a simple question and its answer.

Some form of this argument has appeared in every human culture. It is universal. For all men, this argument sometimes appears sound, and for some men, always. Is this a surprise? We are talking, after all, about the existence of God, and if the issue were easily decided, we would not be talking. The medieval Arabic argument known as the kalam is an example of the genre.

Its first premise:

Everything that begins to exist has a cause.

And its second:

The universe began to exist.

And its conclusion:

So the universe had a cause.

This is not by itself an argument for the existence of God. It is suggestive without being conclusive. Even so, it is an argument that in a rush covers a good deal of ground carelessly denied by atheists. It is one thing to deny that there is a God; it is quite another to deny that the universe has a cause. What remains, if the universe does have a cause, is the gap between what brought the universe into existence and traditional conceptions of the deity. This is no trivial matter. Nonetheless, the cosmological argument succeeds in displacing the burden of proof from its starting point (Is there a God?) to a place much later in the argument (Is it right and proper to think that the cause of the universe is God?).

THOMAS AQUINAS

The most powerful statement of the cosmological argument is due to Thomas Aquinas, the largest intellectual personality of the thirteenth century. A master of the high scholastic method—Latin, liturgy, and logic—Aquinas synthesized Aristotelian philosophy and the doctrines of the Catholic Church so successfully that to this day, the style of argument adopted by the Vatican represents his influence. Nonetheless, Aquinas is not an easy philosopher to read, and he is not fashionable. This is not a decisive point in his favor, but it is difficult to ignore.

Aquinas was born in 1225 in southern Italy and died fifty years later in a Cistercian monastery in northern Italy. His life coincided with a period of great brilliance in European art, architecture, law, poetry, philosophy, and theology. Commentators who today talk of the dark ages, when faith instead of reason was said ruthlessly to rule, have for their animadversions only the excuse of perfect ignorance.

Both Aquinas’s intellectual gifts and his religious nature were of a kind that is no longer commonly seen in the Western world. Devoted and obedient, he approached the mansion of the Catholic faith with the confidence of someone sure of his welcome at the door and of his comfort within its rooms. The natural world did not attract his attention. He was not curious. He neither conducted experiments nor imagined that it would be worthwhile to do so. His genius was organizational and logical and even, in its largest aspect, legal. His masterpiece and his monument, the Summa Theologica, contains 38 treatises, and deals with 612 separate questions, subdivided into 3,120 separate sections. In all, the work asks and answers ten thousand questions. It is a cathedral in thought, inviting admiration but not affection. Those who reject atheism still find it difficult to accept Aquinas. He is in his sensibility now alien.

On December 6, 1273, Aquinas, while attending mass, fell into a prolonged and rapturous mystical state. Thereafter, he ceased to write. When urged by officials of the Catholic Church to continue his work on the Summa, which he had left unfinished, he replied, “I can do no more. Such secrets have been revealed to me that all I have written now appears to be of little value.”

Aquinas addresses the cosmological argument in Article 3 of Question 2 of the first part of the Summa. Question 2 is called “The Existence of God,” and Article 3 asks the question whether God exists. Aquinas begins by offering a powerful and lucid defense of atheism.

“It is superfluous to suppose,” Aquinas argues, “that what can be accounted for by a few principles has been produced by many.” This constraint is now familiar as Occam’s Razor, even though William of Occam lived and wrote after Aquinas’s death.

“But it seems,” Aquinas at once adds, “that everything we see in the world can be accounted for by other principles, supposing that God did not exist.”

Other principles?

Just so. “All natural things can be reduced to one principle, which is nature, and all voluntary things can be reduced to one principle, which is human reason, or will.”

It follows, Aquinas concludes provisionally, that “[t]here is no reason to suppose God’s existence.”

This is a conclusion that Aquinas is prepared to reject with all the force of his faith and genius. The existence of God may be demonstrated; it is subject to proof, and if not proof, then to argument. It follows that not everything in nature can be accounted for by “other principles.”

The economies of thought offered by Occam’s Razor are an illusion.

We understand things in nature, Aquinas observes, by grasping as best we can causes and their effects: the match that lights the fire, the chill that sets one’s teeth to chattering, the water that slakes thirst. “In the world of sense,” as Aquinas says, “there is an order of efficient causes.” But just as no man can be his own father, no effect can be its own cause. A series of effects preceded by their causes forms a luminous metaphysical trail going backward into the past, because, as Aquinas argues, causes must precede their effects.

Can a series of this sort be infinitely continued, so that it simply disappears into the loom of time?

Aquinas argues that when it comes to causes, “it is not possible to go on to infinity, because in all . . . causes following in order, the first is the cause of the intermediate cause, and the intermediate is the cause of the ultimate cause.”

If a series of causes does not start, it cannot get going, and if it does not get going, then there will be no intermediate causes, and if there are no intermediate causes, then over here, where we have just noticed that a blow has caused a bruise, there is no explanation for what is before our eyes. Either there is a first cause or there is no cause at all, and since there are causes at work in nature, there must be a first. The first cause, Aquinas identified with God, because in at least one respect, a first cause exhibits an important property of the divine: It is uncaused.

This is a weak but not an absurd argument, and while Aquinas’s conclusion may not be true, objections to his argument are frequently inept. Thus Richard Dawkins writes that Aquinas “makes the entirely unwarranted assumption that God is immune to the regress.” It is a commonly made criticism. Lumbering dutifully in Dawkins’s turbulent wake, Victor Stenger makes it as well. But Aquinas makes no such assumption, and thus none that could be unwarranted. It is the conclusion of his argument that causes in nature cannot form an infinite series.

A far better objection has long been common in the philosophical literature: While an infinite series of causes has no first cause, it does not follow (does it?) that any specified effect is without a cause. Never mind the first cause. This blow has caused that bruise. The chain of causes starting with the blow may be chased into the past to any finite extent, but no matter how far back it is chased, effects will always have causes. Why, then, is that first cause so very important?

But this is a counterargument at which common sense is inclined to scruple. Seeing an endless row of dominoes toppling before our eyes, would we without pause say that no first domino set the other dominoes to toppling?

Really?

The give-and-take of these arguments is worthy of respect, but it no longer compels attention. In the eight hundred years following the publication of the Summa, the philosophers have had their say, but they have been overtaken by events. The argument that Aquinas wished to make on metaphysical grounds has been made in other terms and in other ways, and in particular a form of the cosmological argument has appeared in the very place one might least expect it to appear: contemporary physical cosmology.

THE THRESHOLD OF THEOLOGY

The universe, orthodox cosmologists believe, came into existence as the expression of an explosion—what is now called the Big Bang. The word explosion is a sign that words have failed us, as they so often do, for it suggests a humanly comprehensible event—a gigantic explosion or a stupendous eruption. This is absurd. The Big Bang was not an event taking place at a time or in a place. Space and time were themselves created by the Big Bang, the measure along with the measured. If the image of an ordinary explosion is inadequate to the Big Bang, the words themselves—the Big Bang—have by themselves a disturbing power. They suggest the most ancient of human intuitions, and that is the connection between sexual and cosmic energies. The words may have been chosen whimsically; they were not chosen accidentally.

Whatever its name, as far as most physicists are concerned, the Big Bang is now a part of the established structure of modern physics. From time to time, it is true, the astrophysical journals report the failure of observation to confirm the grand design. It hardly matters. The physicists have not only persuaded themselves of the merits of Big Bang cosmology, they have persuaded everyone else as well. The Big Bang has come to signify virtually a universal creed, men and women who know nothing of cosmology convinced that the rumble of creation lies within reach of their collective memory.

If the Big Bang expresses a new idea in physics, it suggests an old idea in thought: In the beginning God created the heaven and the earth. This unwelcome juxtaposition of physical and biblical ideas persuaded the astrophysicist Fred Hoyle, an ardent atheist, to dismiss the Big Bang after he had named it. In this he was not alone. Many physicists have found the idea that the universe had a beginning alarming. “So long as the universe had a beginning,” Stephen Hawking has written, “we could suppose it had a creator.” God forbid! Nonetheless, there is a very natural connection between the fact that the universe had a beginning and the hypothesis that it had a creator. It is a connection so plain that, glowing with its own energy, it may be seen in the dark. Although questions may be raised about what it means, the connection itself cannot be ignored. “The best data we have concerning the big bang,” the Nobel laureate Arno Penzias remarked, “are exactly what I would have predicted, had I nothing to go on but the five books of Moses, the Psalms, the Bible as a whole.”

Remarks such as this traveled far afield. They were repeated gratefully by men and women persuaded that at last cosmology had made some sort of sense. They appeared in the New York Times. Physicists quickly came to their senses. They discovered elaborate reasons to avoid the obvious, not least of which, the fact that the obvious was obvious. For more than a century, physicists had taken a manful pride in the fact that theirs was a discipline that celebrated the weird, the bizarre, the unexpected, the mind-bending, and the recondite. Here was a connection that any intellectual primitive could at once grasp: The universe had a beginning, thus something must have caused it to begin. Where would physics be, physicists asked themselves, if we had paid the slightest attention to the obvious?

In this, the physicists were immeasurably assisted by the philosophers, their traditional enemies, of course, who aided in the work at hand by writing very elegant papers demonstrating that if the universe had a beginning, it was not a beginning that really began. The philosopher Adolf Grünbaum of the University of Pittsburgh was a master of this approach. If the universe did not have a beginning, his papers did not have an end. Fair is fair. Physicists who had been struggling to make precisely the same point welcomed such philosophical efforts with the relief a stutterer might show on having his interlocutor blurt out the stammered word.

All might have been well, or at least better than it turned out to be, had the Big Bang been another one of those tedious ideas that flicker luridly for a moment and then wink out. There are so many of them. But quite the contrary proved to be the case. Over the course of more than half a century—a very long time in the history of the physical sciences—inferences gathered strength separately, and when combined they gathered strength in virtue of their combination.

One line of inference was observational; the second, theoretical; the two together, irresistible.

The observations that made the hypothesis of the Big Bang plausible were derived from a study of the heavens. They had some of the brute power of something seen. This is an exaggeration, of course. Observations themselves depend on a network of theoretical assumptions, but in the case of these observations, their theoretical structure belonged to a part of physics that was well understood. No astronomer scanning the cosmos, for example, doubted much the plainest of plain facts about light. No matter how it appears, light represents an undulation of the electromagnetic field. Its source is the excitable atom itself, with electrons bouncing from one orbit to another and releasing energy as a result. If this is so, it follows that each atom has a spectral signature, a distinctive electromagnetic frequency. The light that streams in from space thus must reveal something about the composition of the galaxies from which it was sent. In the early years of the twentieth century, the characteristic signature of hydrogen was detected in various far-off galaxies. Examining a very small sample of twenty or so galaxies, the American astronomer Vesto Slipher observed that the frequency of their hydrogen atoms was shifted to the red portion of the spectrum. Using a far more sophisticated telescope than any at Slipher’s disposal, Edwin Hubble made the same discovery in the early 1930s, and unlike poor Slipher, he knew he had struck gold.

The galactic redshift, Hubble realized, was an exceptionally vivid cosmic clue, a bit of evidence from far away and long ago, and as with all clues its value lay in the questions it prompted. Why should galactic light be shifted to the red and not the blue portions of the spectrum? Why, for that matter, should it be shifted at all?

These very simple questions received an equally simple answer, with neither question nor answer ever transgressing the margins of plain physical sense. The pitch of a siren is altered as a police car disappears down the street, the sound waves carrying the noise stretched by the speed of the car itself. This is the familiar Doppler effect. Something similar explains the redshift of the galaxies. Distortions in their spectral signature arise because these monsters of the night are receding into the depths. But a universe whose galaxies are receding is one that is expanding.

The inference to the Big Bang now follows. A universe that is expanding is a universe with a clear path into the past. If things are now far apart, they must at one point have been close together; and if things were once close together, they must at one point have been hotter than they are now, the contraction of space acting to compress its constituents like a vise, and so increase their energy. The retreat into the past ends in a state in which material particles are at no distance from one another and the temperature, density, and curvature of the universe are infinite. Such a state is known as a singularity, and in the case of the cosmos it is known as the Big Bang singularity.

The cone tapering into the past must end. The lines of sight converge. The universe had a beginning.

When the facts about an expanding universe became known, physicists at once realized that they had become known in the right place and at the right time. In 1915, Albert Einstein had published his theory of general relativity. The theory represented the culmination of a revolution in physical thought that he had initiated in 1905 with the publication of his theory of special relativity. The general theory of relativity encompassed Einstein’s account of gravitation, but because gravitation extends throughout space and time as a universal force, his theory was simultaneously a kind of cosmic blueprint, a way of grasping by mathematical means the ultimate structure of the cosmos.

General relativity forges a far-flung connection between the geometry of space and time and the presence of matter. Events within Einstein’s majestic theory are designated by four numbers. Three of these numbers indicate where the event is, and the fourth measures when it is there. Physicists very much enjoy suggesting that the world of four dimensions is so inaccessible that entrance is generally denied the mathematically uninitiated. But although those four dimensions are important, the underlying concept is simple. After all, we locate an event in terms of both where it took place and when it took place. Where was JFK assassinated? Three numbers provide the answer (longitude, latitude, and height). And when? One number is sufficient. To have grasped this much is to have grasped everything. (And as long as secrets are being imparted, when physicists talk of ten-dimensional or eleven-dimensional spaces, nothing deeper is at issue.) To a fused form of space and time in which points are identified by four numbers, Einstein assigned a variable geometrical structure. Squeezing a solid rubber ball produces the same effect, although not, of course, on the same scale. Now it is perfectly round. A squeeze is administered, and then it becomes deformed. With the release that follows, its shape changes again, and with its shape, its geometry.

If the geometry of space and time is variable, Einstein conjectured, this must affect the way in which material objects move through the medium of space and time. A beam of light crossing an otherwise empty universe travels in a straight line. If a massive star is placed in its path, the light beam will curve, almost as if its graceful swerve were intended to avoid a collision. By the same token, an observer falling toward the earth, his failed parachute dangling uselessly behind him and an ignominious plop forthcoming, is doing nothing more than traveling along his natural path through space and time. He appears to be accelerating because the earth has distorted the geometry through which he is falling.

Einstein’s theory of general relativity involves the cohabitation of these conceptual partners. Material objects influence space and time by deforming their geometry. Space and time influence material objects by changing their path. The relationship goes both ways.

The field equation that Einstein introduced in 1915 is a majestic identity in which curvature, on the one side, and mass, on the other, are placed in the balance and found equal. Einstein had hoped that the equations of general relativity would determine a single world model, and like virtually every other physicist, he believed that his cosmic blueprint would reveal a universe that had neither a beginning nor an end. Searching for what he wished to find, Einstein discovered a solution to his own equations that specified just such a universe, the great thing having been there from the infinite past and destined to be there into the infinite future. For reasons that he could never make clear, Einstein found a universe so conceived particularly satisfying. Friends of his who knew him well have suggested (to me) that to the end of his life, Einstein regarded an expanding universe with a certain fastidious distaste.

Einstein had hoped that the equations of his great theory would specify only one cosmic blueprint. In this he was destined to be disappointed. Months after he discovered one solution of the field equations, Willem de Sitter discovered another. In de Sitter’s universe, there is no matter whatsoever, the place looking rather like a dance hall in which the music can be heard but no dancers seen. Dismissed at the time, the de Sitter universe has recently enjoyed a revival in quantum cosmology. It is easy to describe, easy to find, and like the diligent Dutch themselves, endlessly useful.

In the 1920s, both Aleksandr Friedmann and Georges Lemaître discovered the solutions to the field equations that have dominated cosmology ever since, their work coming to amalgamate itself into a single denomination as Friedmann-Lemaître (FL) cosmology. To Einstein’s pained surprise, FL cosmology indicated that the universe was either expanding or contracting, a conclusion nicely in accord with Hubble’s observation but profoundly in conflict with models of the universe in which the universe remained resolutely unchanging.

Having been joined at the fulcrum of observation and theory, Big Bang cosmology has been confirmed by additional evidence, some of it astonishing. In 1963, the physicists Arno Penzias and Robert Wilson observed what seemed to be the living remnants of the Big Bang—and after 14 billion years!—when in 1962 they detected, by means of a hum in their equipment, a signal in the night sky they could only explain as the remnants of the microwave radiation background left over from the Big Bang itself.

More than anything else, this observation, and the inference it provoked, persuaded physicists that the structure of Big Bang cosmology was anchored into fact.

The wheel had come full circle.

THE INESCAPABLE BEGINNING

If both theory and evidence suggested that the universe had a beginning, it was natural for physicists to imagine that by tweaking the evidence and adjusting the theory, they could get rid of what they did not want. Perhaps the true and the good universe—the one without a beginning—might be reached by skirting the Big Bang singularity, or bouncing off it in some way? But in the mid-1960s, Roger Penrose and Stephen Hawking demonstrated that insofar as the backward contraction of the universe was controlled by the equations of general relativity, almost all lines of conveyance came to an end.

The singularity was inescapable.

This conclusion encouraged the theologians but did little to ease physicists in their own minds, for while it strengthened the unwholesome conclusions that Big Bang cosmology had already established, it left a good deal else in a fog. In many ways, this was the worst of all possible worlds. Religious believers had emerged from their seminars well satisfied with what they could understand; the physicists themselves could understand nothing very well.

The fog that attended the Penrose-Hawking singularity theorems (there is more than one) arose spontaneously whenever physicists tried to determine just what the singularity signified. At the singularity itself, a great many physical parameters zoom to infinity. Just what is one to make of infinite temperature? Or particles that are no distance from one another. The idea of a singularity, as the astronomer Joseph Silk observed, is “completely unacceptable as a physical description of the universe.. . . An infinitely dense universe [is] where the laws of physics, and even space and time, break down.”

Does the singularity describe a physical state of affairs or not?

Tell us.

If it does, the description is uninformative by virtue of being “completely unacceptable.” If it does not, the description is uninformative by virtue of being completely irrelevant. But if the description is either unacceptable or irrelevant, what reason is there to believe that the universe began in an initial singularity? Absent an initial singularity, what reason is there to believe that the universe began?

If the universe did not begin, but had nonetheless only a finite temporal extent, what on earth are we to think at all?

It may seem that a conclusion has been reached that will appeal to physicists and religious believers alike: Nothing can be said. Those who believe in God and those who do not may resolve their differences by agreeing to say nothing. There is nonetheless a striking point at which Big Bang cosmology and traditional theological claims intersect. The universe has not proceeded from the everlasting to the everlasting. The cosmological beginning may be obscure, but the universe is finite in time. This is something that until the twentieth century was not known. When it became known, it astonished the community of physicists—and everyone else. If nothing else, the facts of Big Bang cosmology indicate that one objection to the argument that Thomas Aquinas offered is empirically unfounded: Causes in nature do come to an end. If science has shown that God does not exist, it has not been by appealing to Big Bang cosmology. The hypothesis of God’s existence and the facts of contemporary cosmology are consistent.

The uncertainties surrounding the origin of the universe have led certain writers to find comfort in a companionship with Aquinas they would not otherwise dream of enjoying. In writing about the first cause to which Aquinas appealed, and which he identified with God, Richard Dawkins argues that “it is more parsimonious to conjure up, say, a ‘Big Bang singularity,’ or some other physical concept as yet unknown” to account for the existence of the universe. The word parsimonious is meaningless in context: Whatever it might denote, how could it be measured? But conjure is the right verb, suggesting as it does both misdirection and inattention. Misdirection: The Big Bang singularity does not represent a physical concept, because it cannot be accommodated by a physical theory. It is a point at which physical theories give way. Inattention: The concept in which Dawkins has placed his confidence is something that is either infinite and inscrutable, or otherwise unknown. Men have come to faith on the basis of far less. This is, I suppose, not surprising. His atheism notwithstanding, Dawkins believes that he is a “deeply religious man.” He simply prefers an alien cult.

“Perhaps the best argument in favor of the thesis that the Big Bang supports theism,” the astrophysicist Christopher Isham has observed, “is the obvious unease with which it is greeted by some atheist physicists. At times this has led to scientific ideas, such as continuous creation or an oscillating universe, being advanced with a tenacity which so exceeds their intrinsic worth that one can only suspect the operation of psychological forces lying very much deeper than the usual academic desire of a theorist to support his or her theory.”