David Kaiser. American Scientist. Volume 95, Issue 6. Nov/Dec 2007.

For nearly two centuries, talk of “evolution” has stirred controversy. Even before the publication of Charles Darwin’s The Origin of Species (1859)-and with greater ferocity since then-most debate over evolution has focused on geology and biology. Is our planet thousands or billions of years old? Did slow-acting, natural processes carve out stark features like the Grand Canyon, or were they produced by the biblical flood? Have humans evolved from less complicated animals?

Although they have invited less scrutiny, significant debates have also raged over the meaning of cosmic evolution, both within the scientific community and beyond it. Indeed, controversial questions about the evolution of the universe have haunted scientific cosmology for a century. Recent developments in physics, the politics of science and electronic communications have turned up the rhetorical heat on these long-simmering questions.

Einstein and Evolution

In a flurry of brief lectures before the Prussian Academy of Sciences in November 1915, Einstein changed forever how physicists view the universe. After almost a decade of false starts and feverish activity, Einstein at last presented the governing equations of his general theory of relativity, more or less as physicists still use them today.

In Einstein’s view, gravity is nothing but geometry. Pace Newton, Einstein declared that there is no “force” of gravity. Rather, objects simply follow the shortest paths they can, moving through a warped and curved spacetime. Earth orbits the Sun, explained Einstein, not because of any mutual forces of attraction, but because the Sun’s large mass makes a significant “dent” in the surrounding spacetime.

Soon Einstein and a small circle of colleagues began to apply general relativity to the universe as a whole. A young Russian mathematical physicist, Alexander Friedmann, demonstrated that Einstein’s equations could describe universes that evolve over time, expanding from a minute speck to supergalactic scales. In some situations, the universe would halt its expansion and collapse back on itself (if it had a large amount of matter and energy per unit volume). Universes of lower density would continue expanding forever. In each case, Friedmann found that the model universes of Einstein’s equations would change their behavior over time.

Einstein liked these options not one bit. He loathed the idea of cosmic expansion-or indeed of any macro-scale evolution. Such changes over time lacked a certain aesthetic satisfaction, Einstein complained; he preferred the pristine symmetry of a universe that always was and always shall be. Even as Einstein was dismissing Friedmann’s solutions, however, a young Belgian mathematical physicist, Georges Lemaître, was busy reproducing them. And Lemaître pressed further. In 1931, he published a paper arguing that if the universe is expanding today, it must have been smaller in the past. Some finite time ago, all the matter in the universe must have been concentrated at a single point. The universe, Lemaître concluded, must have begun in a very hot, dense state-he called it the “primeval atom”-and has been expanding ever since.

Alongside his studies of physics and mathematics, Lemaître had pursued his other great passion: theology. He was ordained as a Catholic priest in 1923, and, at least in these early days, his cosmology and theology seemed well integrated. In a draft of his article on the primeval atom, he rhapsodized, “I think that everyone who believes in a supreme being” would be “glad” to see such congruence between science and religion. He struck out this passage just prior to publication-perhaps recognizing that articles in Nature rarely included invocations of God-and thereafter argued strongly against mixing theology and cosmology. He was an especially outspoken critic of biblical literalism, returning time and again to a position that Galileo had spelled out in his famous letter to the Grand Duchess Christina back in 1615, to wit: The Bible teaches us how to go to Heaven, not how the heavens go.

Lemaître’s newfound care notwithstanding, several of his colleagues continued to advise caution-not just about mixing science and religion, but about believing in a universe that had a beginning and has been evolving ever since. To some, such a scenario smacked too much of the account in the book of Genesis. Arthur Eddington-devoted Quaker, giant of British astrophysics and one-time teacher of Lemaître-argued that a universe that had a beginning in time might be physically possible, but “philosophically it is repugnant to me.” Richard Tolman, an accomplished mathematical physicist and physical chemist at the California Institute of Technology, and one of the earliest champions of relativistic cosmology within the United States, went further still. He cautioned his colleagues in 1934, “We must be especially careful to keep our judgments unaffected by the demands of theology and unswerved by human hopes and fears.”

Many of these early cosmologists became best-selling authors. In their popular books, they freely debated one another’s conclusions, scientific, aesthetic, religious and otherwise. Yet their discussions received little pushback from nonscientists at the time. In short, there was no equivalent of the Sturm und Drang surrounding the Scopes trial of 1925. Indeed, the cosmologists inspired more laughter than fear or anger from the wider public. Consider these snippets of advice from the New York Times: “Einsteinism: just ignore it as of no concern to us” (1923); readers should file modern physics under “things you needn’t worry about just yet” (1928); modern cosmologists are just as quaint as medieval theologians counting the number of angels who can sit on the head of a pin (1931); modern physics fails to answer life’s most important questions (1939); and so on. While Einstein and his colleagues battled over the idea of an evolving cosmos, few outside their circle felt compelled to weigh in.

Big Bangs

Soon after World War II, a trio of physicists working in the United States returned to Lemaître’s ideas, now armed with new concepts and information about nuclear physics-information obtained from the wartime Manhattan Project, from the postwar efforts to design hydrogen bombs and from the ongoing development of nuclear reactors. The moving force behind the new work was Russian émigré George Gamow, who had first learned Einstein’s general relativity from Friedmann in the 1920s. Joining Gamow were Robert Herman and Ralph Alpher, two young physicists at the Johns Hopkins Applied Physics Laboratory. Together the three sought to flesh out Lemaître’s picture of a universe beginning in time and evolving through various stages. Their main question: Where did the elements come from?

Their answer, which formed the basis of Alpher’s dissertation under Gamow’s tutelage in 1948, came to be known as “nucleosynthesis.” At the earliest moments after the beginning of the universe, Gamow and company calculated, ambient temperatures would have been unimaginably high. Energetic photons (quanta of light) from the hot surroundings would each carry so much energy that they would blast apart collections of nuclear particles, such as neutrons and protons, when they began to stick together. That is, the photons’ energy would overwhelm the binding energy of the strong nuclear force, which would otherwise make the nuclear particles clump.

As the universe expanded, however, it also cooled. So the photons present later were less energetic than those that came before. At a calculable moment-roughly one second after the beginning-the force of nuclear attraction would begin to win out over the reduced-energy photons, and neutrons and protons would begin to form stable deuterium nuclei. As the universe continued to expand and cool, additional nuclear particles would glom onto these light nuclei, building up heavier ones.

Never shy about his findings, Gamow trumpeted his group’s work in playful terms. He wrote to Einstein about this new account of “the Days of Creation,” and titled one of his popular books The Creation of the Universe (1952), echoing the biblical term “creation.” Late in 1951, Pope Pius XII delivered a lecture before the Pontifical Academy of Sciences. Impressed by the easy fit between Gamow’s developing model and scriptural accounts, the pope declared that the physicists’ work “invokes no new ideas even for the simplest of the faithful. It introduces nothing different from the opening words of Genesis, ‘In the beginning God created heaven and earth.’“ An inveterate jokester, Gamow considered the pope’s offering too good to be true. Three months later he submitted a brief article to Physical Review in which he quoted extensively from the pope’s lecture, citing it as an authority for his latest research.

One colleague who did not find Gamow’s pranks amusing was British astrophysicist Fred Hoyle, based at the University of Cambridge. Hoyle, who had learned his general relativity during the 1930s from Arthur Eddington, also sought to build a coherent cosmological model soon after the war. Together with the Austrian transplants Hermann Bondi and Thomas Gold-both of whom had left the Continent to study at Cambridge before the Nazis overran Austria-Hoyle developed a rival cosmology to Gamow’s. Hoyle, Bondi and Gold argued that all astronomical observations to date could be accounted for by a steady-state universe, which had no beginning in time and which has always been expanding. If a trace amount of new matter were constantly created-far less than could have been experimentally measured-then on average the universe would look the same at any given moment. That is, there would be no evolution. In place of early-universe nucleosynthesis, Hoyle and company hypothesized that all atomic nuclei had been cooked inside stars and then distributed by supernova explosions.

More than physics seemed to be at stake. Hoyle spoke out vigorously against any theological incursions into physics. In his 1950 popular book, The Nature of the Universe, which was based on a series of radio lectures for the British Broadcasting Company, Hoyle charged that the very notion of a universe beginning in time was “quite characteristic of the outlook of primitive peoples,” who turn to gods to explain physical phenomena. Ironically, Hoyle himself coined the term “big bang” to describe Gamow’s program during these radio lectures; it was meant to sound childish and dismissive. Moreover, Hoyle and his colleagues insisted, physical laws (whether general relativity or nuclear physics) could not be trusted in the extreme extrapolations required by Gamow, Alpher and Herman, who applied equations to conditions radically different from any under which they had been empirically tested. Big-bang advocates who stuck stubbornly to such calculations, Hoyle charged, behaved just like Catholics and communists: Each, he said, were blind believers, too easily swayed by dogma.

Although most physicists ignored Gamow’s and Hoyle’s colorful exchanges at the time, popular news media did cover the debate. Whereas the New York Times had once playfully chided physicists and cosmologists for their utter irrelevance, few people drew the same conclusions after World War II. In the wake of wartime projects like radar and the atomic bomb, physics filled a special-and unprecedented-cultural niche, especially in the United States. Indeed, the overwhelming majority of times that the phrase “big bang” appeared in major newspapers during the 1940s and 1950s, it referred not to Gamow’s cosmology but to nuclear weapons testing or to Cold War brinksmanship with the Soviet Union.

Perhaps the intertwining of cosmology, nuclear physics and geopolitics explains another curious reaction to postwar scientific research. Although those decades saw a resurgence in the United States of strident opposition by evangelical Christians to Darwinian evolution, few but the most hardcore biblical literalists rose to challenge the big bang. Even the most influential advocates of “creation science” after the war drew distinctions between Earth’s age-which they took to be roughly 6,000 years, based on lifespans and geneologies described in the Bible-and the age of the universe at large. John Whitcomb, Jr., and Henry Morris’s runaway bestseller, The Genesis Flood (1961), for example, which sold more than 200,000 copies during its first 25 years, argued that the biblical account of creation applied to the solar system but not to the entire cosmos. Even as they argued passionately against standard geology and biology, these leading creationists issued physics and cosmology a free pass. In the nuclear age, physics seemed untouchable.

A Stringy World?

Scientific consensus in favor of the big bang emerged during the mid-1960s, after several astrophysical observations lent strong support to the model’s predictions while seeming irreconcilable with a steady-state universe. Not long after that, a small group of physicists began to wonder whether Einstein’s framework for all these cosmological discussions-general relativity-was itself only an approximation. What if the universe were not built out of pointlike particles dancing on a curved spacetime, but out of tiny one-dimensional strings? General relativity might then be demoted from a fundamental theory to a merely effective description, covering distance scales that are large compared with the strings. That is, general relativity might be to string theory what Newtonian mechanics is to Einstein’s relativity.

At best a marginal curiosity for several years, string theory burst onto center stage in the mid-1980s when two groups demonstrated that string theory might make gravity compatible with quantum mechanics while avoiding many of the traps that had marred earlier efforts to combine the two. Such unification had long been the Holy Grail of theoretical physics: Only a quantum theory of gravity could possibly be merged with the other known forces of nature, each of which is clearly quantum-mechanical in origin. String theory’s champions began to proclaim it a “theory of everything.”

Today string theory is undeniably at the forefront of high-energy physics. Within the past five years, physicists have published about 10,000 articles on the topic. Yet as physicist Lee Smolin has recently argued, string theory is something of a “package deal”: It combines many features that physicists want with others that are far less desirable. For starters, string theory requires a so-far undetected symmetry among the known particles. More troubling, the theory can only be formulated in a minimum of 10 spacetime dimensions, rather than the four in which we seem to live: one dimension of time, plus the three spatial dimensions. Worst of all, at least according to some critics, string theory leads to a huge number of possible universes, with no way to choose among them. It has gone, in effect, from a “theory of everything” to a “theory of anything.”

Physicists have long recognized that more than just knowledge of the governing laws of string theory is needed to make definite predictions about our observable universe. We also need to know how the extra dimensions are arranged: Are they curled up like tiny soda straws or twisted in some more complicated shape? Every quantitative prediction from string theory depends on the (unknown) topology of the extra dimensions. For two decades, physicists thought the number of topologically distinct possibilities numbered in the hundreds of thousands.

The situation became exacerbated in 2000, when leading string theorists Joseph Polchinski (University of California, Santa Barbara) and Raphael Bousso (then a postdoctoral fellow at Stanford, now a professor at U. C. Berkeley) recognized that other topological structures-fluxes and membranes-could wrap around these extra dimensions. Instead of 105 possibilities, there now appear to be upward of 101000 distinct low-energy states in string theory, in any one of which our observable universe could be residing. Every single observable quantity in our universe, from the masses of elementary particles to the strengths of the fundamental forces to the expansion rate of our universe and more, would depend on precisely which of these stringy states our universe happened to be in. And yet string theorists to date have no way to explain why our universe is in one of these many possibilities.

Pause for a moment to consider that number: 10^sup 1000^. It is utterly removed from our everyday experience, all out of proportion to other numbers that scientists usually encounter. In fact, it is difficult to generate a number that large using familiar quantities. Let us start with the earthly and mundane: the ratio of Bill Gates’s personal wealth (if Internet accounts are to be believed) to my own is a measly 105-which might be either encouraging or depressing, but which is nowhere near 10¹⁰⁰⁰ cosmic numbers likewise fail to come close. The age of our observable universe is about 10¹⁷ seconds; the ratio of the mass of the Milky Way galaxy to the mass of an electron is roughly 10⁷¹.

The story gets still more bizarre. Building on the now-standard supplement to the big bang-inflationary cosmology, which posits a brief burst of exponential expansion early in our universe’s history-some string theorists now argue that these 10¹⁰⁰⁰ states are not just theoretical possibilities, but are actually realized in island universes all their own. Central to the argument is that once inflation begins somewhere, it will continue forever. (This process has been dubbed “eternal inflation.”) In any given region of spacetime, the exponential expansion will halt after a characteristic period of time, much like the half-life of radioactive substances. But in most inflationary models, this half-life is longer than the expansion doubling-time-the time it takes for a volume of spacetime to double in size. So the volume of spacetime that is inflating will always win out over the pockets mat stop inflating. In this view, we live within one “pocket” or “island” universe within a much larger “megaverse.”

As theorists such as Stanford University’s Leonard Susskind and Tufts University’s Alex Vilenkin see it, if one combines the “landscape” of string possibilities with eternal inflation, the relevant question becomes not why one unique state got picked out of the huge number, but why we happen to live in the particular island universe that we do. To answer it, Susskind, Vilenkin and growing numbers of their colleagues have turned to something called the “anthropic principle.” The natural constants in our observable universe-all those particle masses, force-strengths, expansion rates and so on that depend on which string state our universe occupies-must fall within rather narrow ranges for life as we know it to exist. Presumably, these constants would not be conducive to life (at least not life like us) in the vast majority of the other string states, and hence in the vast majority of island universes out there. With each of these 10¹⁰⁰⁰ states realized in an infinite number of island universes, pure random chance might be enough to “explain” why we happened to evolve where we did. Put another way, the fact that we are here to ponder such questions “selects” the configuration our particular island universe must have taken.

Three-quarters of this argument is of quite venerable vintage. Back in the 17th century, natural philosophers such as Bernard le Bovier de Fontenelle in France and Newton in England argued that the constants of nature had to be set just where they are to support life. Fontenelle, Newton and their contemporaries considered such finetuning to be scientific proof that God must exist. The sensitivity of human existence to these physical conditions appeared to be proof of design-of an omnipotent Master Architect at work, designing the universe just for people to inhabit. Fontenelle and Newton, in other words, were charter members of the “intelligent design” club.

On this last issue, Susskind parts company with Fontenelle and Newton. The subtitle to his recent popular book, The Cosmic Landscape: String Theory and the Illusion of Intelligent Design (2005), taunts today’s adherents of “intelligent design.” Susskind and many of his colleagues have planted their staff firmly in the Darwinians’ turf: Given enough time and ample possibilities, natural evolution took its cosmic course, and here we are.

The string landscape and its anthropic interpretation are by no means universally acclaimed even among cutting-edge physicists. Critics-including Nobel laureates such as U. C. Santa Barbara’s David J. Gross-have labeled the anthropic turn “dangerous,” “disappointing,” even “an abdication” of physicists’ proper explanatory goals.

Parallel Universes

While physicists continue to debate string theory and the landscape, many nonscientists have drawn their own conclusions. One response has been a resurgent biblical literalism. Unlike earlier creationists, however, today’s advocates no longer excuse physics and cosmology from their purview. For example, despite a raft of highprecision astrophysical observations that have verified a central tenet of the big bang-that our observable universe is 14 billion years old-newly emboldened creationists readily dismiss such timescales. “I wasn’t there [at the big bang], and neither were they [cosmologists] exclaimed accountant and Kansas State Board of Education member John W. Bacon a few years ago. Bacon was explaining to journalists why he had voted with a majority of board members to remove the big bang as well as biological evolution from statewide high school curricula. “Based on that,” he went on, “whatever explanation they may arrive at is a theory and it should be taught that way.” Several other states followed Kansas’s lead in the late 1990s. Since that time, the teaching bans have ebbed and flowed with various election cycles; the issue is far from settled.

If these education board members need any additional encouragement, they have dozens of new “authoritative” texts to turn to. Books such as D. Russell Humphreys’s Starlight and Time: Solving the Puzzle of Distant Starlight in a Young Universe (1994) have been joined by a raft of recent publications, including Donald DeYoung’s Thousands, Not Billions: Challenging an Icon of Evolution, Questioning the Age of the Earth (2005), Alex Williams and John Hartnett’s Dismantling the Big Bang (2005) and Jason Lisle’s Taking Astronomy Back: The Heavens Declare Creation (2006). Several of these authors sport advanced degrees in the physical sciences and are supported by a robust institutional network, such as the “Answers in Genesis” ministry, complete with its own lecture circuit and educational museum. Much like the island universes dotting Susskind’s string landscape, in other words, today’s creationists have carved out a parallel universe all their own. Most of their books have a sales rank on amazon.com an order of magnitude better than the one I wrote about postwar physics.

Alongside biblical literalism, a second response has come from devotees of “intelligent design.” Although coverage of intelligent design has concentrated on fights over biological evolution in the classroom-such as the headline-grabbing legal showdown in Dover, Pennsylvania, during 2005-the issue has cropped up in other surprising places as well. In February 2006, for example, the story broke of a young public-affairs officer at NASA named George Deutsch, who had circulated an internal memorandum stipulating that the word “theory” be appended to “big bang” in all NASA documents, especially educational Web sites. “The big bang is not proven fact; it is opinion,” began Deutsch’s memo, a copy of which was leaked to the New York Times. “It is not NASA’s place, nor should it be, to make a declaration such as this about the existence of the universe that discounts intelligent design by a creator.” Although the 24 year-old political appointee was forced out of NASA soon after the memo was leaked (for having puffed up his résumé with fake degrees he never earned), the episode makes plain just how wellplaced today’s advocates of intelligent design have become.

So after many years of peaceful coexistence, religious convictions have begun to clash openly with the scientific study of the cosmos. Why have the evolution debates played out so differently in biology and cosmology? Looking back over the past century, two features seem especially salient: pedagogy and prestige.

Unlike biological evolution, the big bang has never been a central part of high school curricula. Modern cosmology draws on material-such as general relativity, let alone string theory-which lies beyond the scope of secondary-school instruction. Thus while Darwinian natural selection has long provided an obvious target for critics of evolution in the classroom, until recently cosmic evolution has been something of a nonissue.

The recent bans on teaching the big bang might not disrupt many lesson plans, but they remain potent symbolically. They signal a sea change in relative prestige. Physicists emerged from World War 2 as national heroes. Their wartime projects had delivered the goods the nation needed, and they found themselves feted like no other group of academics before or since. Biologists enjoyed no such culminating moment at mid-century. Indeed, some historians have argued that American biologists’ zeal to use the centennial of Darwin’s Origin of Species in 1959 to reassert their own cultural importance might have backfired, awakening the sleeping giant of antievolution creationists.

Since the end of the Cold War, physicists’ cultural standing has changed dramatically. The era of limitless funding came to a sudden halt in the early 1990s. Congress provided a clear indication of the change in 1993 when it cancelled the $15-billion Superconducting Super Collider (then under construction near Dallas), which would have been the world’s largest particle accelerator. Since that time, federal funding for basic physics has continued to slide. The changing fortunes of physics, combined with physicists’ own internal divisions and the obviously speculative nature of recent work, has opened the door for a concerted attack. And today’s critics of cosmology have learned to leverage the power of the Internet.

I stumbled onto this thriving, wired network two years ago, after my colleague Alan H. Guth and I published a review of recent cosmological research in Science. About a week after our article appeared, Guth received an e-mail message directing him to a rebuttal of our piece, posted on a creationist Web site. That response included dozens of hyperlinks to like-minded “refutations” of the big bang, inflationary cosmology, string theory and the rest. These sites boasted high production values and good graphics. With a single click, one could zoom to the homepages of the Bible-Science Association, the Creation Science Association, the Center for Scientific Creation, the Institute for Creation Research, the Answers in Genesis ministry or dozens of similar groups. And one could purchase any of the recent anti-big bang books, along with DVDs such as “The Privileged Planet,” proffering “evidence” of supernatural intelligent design. Separate links revealed detailed “alternative” science lesson plans available for download. Or one could sign up for special nature tours to places like the Grand Canyon, to go sightseeing with a specially trained creationist tour guide. (The Web site offering this package is certainly ecumenical: It includes equal parts biblical literalism and intelligent design.)

Back I clicked to the original Web site. After quoting extensively from our article, the commentator switched gears:

We had to show you in their own words what these MIT eggheads are saying … Guth and Kaiser need to take up truck driving. That would get them out of their ivory towers at MIT and into the real world, where they would be forced to look at trees, mountains, weather, ecology, and all the other observable things on our privileged planet that are inexplicable by chance: realities that proclaim design, purpose, intention.

Well, at least someone is still reading Science with a passion. As for the rest of us in the cosmic-evolution business, we’ll just have to keep on truckin’.