Where did everything come from? Don't say, "the Big Bang." To say that everything came from the Big Bang is like saying babies come from maternity wards—true in a narrow sense, but it hardly goes back far enough. Where did the stuff that went "bang" come from? What was it? Why did it bang?

Inflationary universes need not be natural, argues Guth (plotting the curving boundaries of hypothetical artificial universes against a space-time axis). In his view, an advanced race could harness the engines of inflation and create a whole cosmos from scratch. Indeed, our universe could be such a creation.

Before Alan Guth came along, cosmologists seldom dared to guess.

The Big Bang theory, based on speculations dating back to 1922 and confirmed by astronomers in the 1960s, posited that the universe began as a minuscule fireball of extreme density and temperature and that it has been expanding and cooling ever since. But the theory said nothing about what came before or even during the split second when everything went bang. In December 1979 Guth, then 32 and an obscure physicist at the Stanford Linear Accelerator Center, emerged as the first scientist to offer a plausible description of the universe when it was less than one-hundredth of a second old. During an unimaginably explosive period between 10-37 second and 10-34 second after its birth, Guth said, the universe expanded at a rate that kept doubling before beginning to settle down to the more sedate expansion originally described by the Big Bang theory.

Guth's theory of inflation—the name he coined for this superfast early-universe expansion—has since vanquished every theoretical challenge and grown stronger with each new cosmological finding, including the latest, largest one: that the universe's expansion rate, long thought to be slowing, is actually accelerating. "There's no competition, but that's not for lack of trying," says cosmologist Alexander Vilenkin of Tufts University. "Many people have tried to develop a model that addresses the same problems, and they have failed." Guth's reputation has ascended with the theory: He has gone from an underemployed postdoc to cosmology's leading man. In April of last year, he received the Benjamin Franklin Medal in physics, often a precursor to the Nobel Prize.

Meanwhile, the time has come to contemplate inflation's largest implication, one that seemed overreaching for an unproved theory in 1979 but that now must be faced squarely. The whole universe may be, to use Guth's phrase, "a free lunch." The primordial "stuff" of inflation, he and other cosmologists contend, is very likely a spontaneous creation, a no-strings gift that boiled out of absolutely nowhere by means of an utterly random but nonetheless scientifically possible process. Now that inflation theory is approaching dogma, it is bringing science to the brink of answering one of the largest questions of all: Why is there something rather than nothing?

To find out, I walk across campus at the Massachusetts Institute of Technology, where Guth is the V. F. Weisskopf Professor of Physics. His office is in building 6—at aggressively utilitarian MIT, buildings are numbered, not named—at the end of a quarter-mile connector that students call "the infinite hallway." I knock. Guth isn't there. "He's always late," a passing professor says helpfully. Guth's assistant unlocks the door for me.

It looks like something went bang in Guth's office: Even by distracted-genius standards, it is a terrific mess. A pile of 39 empty soda bottles, mostly Diet Pepsi, leans against the wall. The litter includes a half-finished grande coffee, empty computer-parts boxes, and other debris. Covering all the horizontal surfaces is seemingly every paper or book ever written about cosmology, astrophysics, or particle physics. The piles on Guth's desk are higher than his computer monitor. It's a big office by academic standards, maybe 15 by 20 feet, but one must hop between the few clear spaces on the carpet to get anywhere.

And here comes Guth, apologizing for his lateness, hand extended. He is shortish at 5 feet 7 inches and energetic, sort of bouncy. It's easy to believe he was once the champion long jumper at his high school in Highland Park, New Jersey. His neck projects forward at about a 45-degree angle from his shoulders, giving the impression that he is fascinated by everything, which is true. His graying hair covers his ears. He wears gold-rimmed glasses, a blue button-down shirt with no tie, khaki pants, casual brown leather shoes, and one of those nerd watches with a numeric keypad. He talks quickly, with a strong Jersey accent. He is 55, the son of a dry cleaner. He is a family man, with a son in college and a daughter in high school, and he is pleasantly down-to-earth, laughing loudly and often as we discuss the impossible parking situation at MIT.

As Guth talks, he seems naturally to drift back 15 billion years, to the moment when most cosmologists agree the universe began. Soon we are among the nascent stars.

"It's not a coincidence that the Bible starts with Genesis," he says as we leave the building and hustle up Vassar Street, through a chill autumn wind blowing off the Charles River. "Most people really want to know where we came from and where everything around us came from. I like to strongly push the scientific answer. We have evidence. We no longer have to rely on stories we were told when we were young."

We enter a small Italian restaurant on MIT's north side. There is no such thing as a free lunch here. Guth's breaded sole is $10.95—good, he says, and worth the price.

An Inflationary UniverseThe universe according to Guth began in the era of quantum gravity, a time when all four forces of the universe—gravity, electromagnetism, the strong (nuclear) and weak forces—may have been unified. Energy boiling out of this unstable stew grew during the brief inflationary period at an ever-doubling rate, then decayed into an electron-quark soup as those forces began splitting apart. The soup's fundamental particles combined into ever-more-complex forms as the universe cooled and expanded. Graphic by Matt Zang

So if eight ounces of fish costs 11 bucks, and if, in a larger sense, nothing in this universe is ever "purchased" without an exchange of energy, how can the whole universe be free?

Start, Guth says, by imagining nothing, a pure vacuum. Be careful. Don't imagine outer space without matter in it. Imagine no space at all and no matter at all. Good luck.

To the average person it might seem obvious that nothing can happen in nothing. But to a quantum physicist, nothing is, in fact, something. Quantum theory holds that probability, not absolutes, rules any physical system. It is impossible, even in principle, to predict the behavior of any single atom; all physicists can do is predict the average properties of a large collection of atoms. Quantum theory also holds that a vacuum, like atoms, is subject to quantum uncertainties. This means that things can materialize out of the vacuum, although they tend to vanish back into it quickly. While this phenomenon has never been observed directly, measurements of the electron's magnetic strength strongly imply that it is real and happening in the vacuum of space even now.

Theoretically, anything—a dog, a house, a planet—can pop into existence by means of this quantum quirk, which physicists call a vacuum fluctuation. Probability, however, dictates that pairs of subatomic particles—one positive, one negative, so that conservation laws are not violated—are by far the most likely creations and that they will last extremely briefly, typically for only 10-21 second. The spontaneous, persistent creation of something even as large as a molecule is profoundly unlikely.

Nonetheless, in 1973 an assistant professor at Columbia University named Edward Tryon suggested that the entire universe might have come into existence this way. In a paper titled "Is the Universe a Vacuum Fluctuation?" he stated, "I offer the modest proposal that our Universe is simply one of those things which happen from time to time." Others scoffed at the idea. If a from-nothing, briefly existing molecule is absurdly unlikely, physicists reasoned, a from-nothing, 15-billion-year-old universe is vastly less likely.

So the situation remained for about five years. Then, on November 13, 1978, Guth, while doing postdoctoral research in particle physics at Cornell University, chanced to stroll into a lecture on the Big Bang given by Princeton cosmologist Robert Dicke. At the time, Guth thought the field of cosmology was irritatingly vague, a sandbox of speculative indulgence compared with the mathematically clean world of particle physics. "If the week had been just a bit more hectic, I would have skipped the lecture," he says.

But it wasn't, and he didn't.

Dicke's topic was the flatness problem, one of the Big Bang theory's biggest mysteries. Dicke explained that somehow the universe seems to be extremely "flat," which means matter, velocity, and gravity all balance to put space-time precisely on the dividing line between a "closed" and an "open" geometry. In a closed universe, space-time curves back on itself, such that light beams that start out parallel will actually meet. In an open universe the beams will diverge. The value of omega describes the ratio between the average density of matter in space and what that density would need to be to make the universe perfectly flat. If omega equals one, the universe is flat.

Now back in Guth's office (explaining omega took much longer than the summary above suggests), he hunches forward on his dorm-issue orange couch, his excitement about this subject palpable. "According to classic Big Bang theory, as the universe evolves, the value of omega is always driven away from one," he says. So if the universe starts out with an omega value of less than one, omega gets rapidly smaller as the universe ages. If it starts with omega greater than one, omega gets rapidly larger. The fact that omega is very close to one today—microwave background radiation measurements indicate it is within 10 percent of one—means that, according to classic Big Bang theory, one second after the bang, omega would have had to be between .999999999999999 and 1.000000000000001. But why? "I was intrigued," says Guth. "How could that number start out so finely tuned?"

On December 6, 1979, after more than a full year of mulling over this and other Big Bang mysteries, Guth sat down at his desk and came up with the breakthrough that he called inflation. He realized that omega did not have to be preposterously fine-tuned from the start. An exponentially expanding early universe, which he would come to call the inflationary universe, would drive omega toward one, not away from it, making a flat universe inevitable.

Some cosmologists are as remote as their subject matter, but not Guth, who eagerly strides to the podium for a public lecture at MIT. "It's fun to see what kind of impact these ideas have on people who have not heard them," he says. "It rejuvenates my excitement."

Huh?

Return to that primordial vacuum, a boiling stew from which pairs of positive and negative subatomic particles bubble into being for the briefest of instants. Inflationary theory suggests that what erupted was a "false vacuum," a peculiar form of matter predicted to exist by many particle theorists, although the real article has never been observed.

A false vacuum is characterized by a repulsive gravitational field, one so strong it can explode into a universe. Another peculiarity of the false vacuum is that it does not "thin out" during expansion as, say, a gas does—the density of the energy within it remains constant even as it grows. So the false vacuum's expansion, accelerating exponentially as its repulsive force compounded, actually created vast quantities of ever-doubling energy, which decayed into a seething plasma of particles such as electrons, positrons, and neutrinos. As the early universe went along doubling every microsecond, the stuff in it doubled, too—out of nowhere. The electrons, positrons, and neutrinos became a sort of hot soup, which 300,000 years later neutralized to form simple atoms. The simple atoms, like hydrogen, helium, and lithium, were ripped apart and crushed together to form more complex, heavier atoms inside stars. Exploded into space by supernovas, they became the matter we see—and are—today.

The initial bit of false vacuum required by Guth's calculations turned out to be mind-bendingly small: A patch one-billionth the size of a proton would do. And the required period of exponential growth was very short. In perhaps just 10-34 second, he suggested, the universe expanded by 25 orders of magnitude, to roughly the size of a marble, an increase equivalent to a pea growing to the size of the Milky Way.

The inflationary process, Guth discovered, would push omega toward one with incredible swiftness. The reason is best expressed by analogy. The universe appears to be virtually flat for the same reason that Earth's surface appears to be virtually flat to a person standing on that surface. The very fabric of space becomes relatively "stretched" so that in as few as 100 doublings in size, its curvature is effectively canceled.

And what about the conservation of energy? According to Einstein's theory of relativity, the energy of a gravitational field is negative. The energy of matter, however, is positive. So the entire universe-creation scenario could unfold without breaking conservation-of-energy laws. The positive energy of all matter in the universe could be precisely counterbalanced by the negative energy of all the gravity in the universe.

This also is more than theory. Observations are consistent with the idea, and calculations totaling up all the matter and all the gravity in the observable universe indicate that the two values seem to precisely counterbalance. All matter plus all gravity equals zero. So the universe could come from nothing because it is, fundamentally, nothing.

"It is rather fantastic to realize that the laws of physics can describe how everything was created in a random quantum fluctuation out of nothing, and how over the course of 15 billion years, matter could organize in such complex ways that we have human beings sitting here, talking, doing things intentionally," says Guth, leaning, if possible, even farther forward.

Three weeks later I attend a lecture Guth gives to the New York Academy of Sciences. It's an august gathering, sold-out, and Guth handles questions with aplomb, even an off-the-wall query about "negative consciousness waves" stemming from the September 11 terrorist attacks (Guth suggests that rational thought, such as what cosmology brings to bear on the origin of the universe, could make the world a more peaceful place).

But how do we know if any of this is true?

"There really are tests," Guth says. Readings from the Cosmic Background Explorer satellite, launched in 1989, show that the temperature of the radiation that pervades the universe is astoundingly uniform. Standard Big Bang cosmology theory without inflation offers no explanation. Some mechanism would have to transmit energy and information at about 100 times the speed of light for these vastly distant parts of the background radiation to "know" and reflect one another's temperature. Inflation, expanding at faster-than-light speed, is the only known way such uniformity could be spread so widely. (Incidentally, such expansion does not violate the cosmic speed limit. Einstein correctly asserted that nothing in the universe could exceed light's speed, but even as the cosmos grew at faster-than-light speeds, no particle within it could ever win a race with a beam of light.)

Inflation theory also predicts what are called density perturbations—small ripples in this uniformity that become seeds for galaxy formation. The galaxies we observe today are just what inflation theory suggests should have been created. "The theories we have developed so far seem to be working shockingly well," Guth says.

Still, cosmologists busily fiddle. Roughly 50 forms of inflation have been proposed, named, and studied, including double, triple, and hybrid inflation, tilted hybrid inflation, hyperextended inflation, and inflation that is "warm," "soft," "tepid," and "natural." In 1997 Guth tallied 3,000 published papers devoted to the subject; he has since stopped counting. Guth in particular credits cosmologists, including Stanford's Andrei Linde and Princeton's Paul Steinhardt, with refining the theory, but each variation preserves the essential elements of Guth's original brainstorm: Some state plays the role of the false vacuum and its repulsive gravity, and some decay of that state leads to the formation of matter. The details, Guth believes, will tumble out of university labs, particle accelerators, and deep-space satellite readings for decades, if not centuries.

The latest wrinkle is that observations by two teams of astronomers in 1998 show that the rate of cosmic expansion is accelerating, not slowing as had previously been thought. If these observations are right, Guth says, they offer proof that gravity can act repulsively. In fact, the same type of repulsive force that originally powered inflation probably drives the universe's current acceleration. Since energy and mass are equivalent, this repulsive energy must also exert gravity, and if there were enough of it, it would preserve the original mass-gravity balance required to make the universe flat. Inflation theory triumphs again.

"Whenever I try to organize the office, I get interrupted, so I never get anywhere," says Guth, awash in the paper sea. "I'm also a saver. I would rather keep a pile of junk, assuming there is something there I want, than throw the whole thing away and regret it."

Guth is pursuing this and other cosmic investigations, but I frankly wonder how much headway he can make. As we speak in his office, constant phone calls, urgent e-mails, and bureaucratic folderol assail the poor guy. A confused freshman raps on the door, seeking approval for a transfer. A fellow physics professor returns Guth's call: The "right" answer in the freshman physics quiz, Guth contends, isn't right enough, and they debate this for a while. It's odd. If Alan Guth is the man who answered the central question of human existence—the origin of the universe—neither he nor those around him seem terribly awed by the fact.

Or perhaps that shouldn't be surprising. Human beings have evolved to survive in this universe, not necessarily to be able to understand it. A false vacuum, jittering from nothing into actuality and then erupting into a universe—or according to some newer variants of inflationary theory, an infinity of universes—is the kind of knowledge that tends to slide off the brain. Guth remains obscure among the public at large because the theory itself remains rather inaccessible. Large sections of his 1997 book, The Inflationary Universe, are very heavy sledding, despite Guth's earnest efforts to make the underlying physics clear.

Guth admits that some aspects of his work are challenging even for him. In one of the most charming sections of the book, he describes his first attempt as a particle physicist to explain inflation to a group of astrophysicists. "I understood very little of what they were saying, so I had no idea why we were disagreeing," he wrote.

So let's be clear. Is Guth saying that cosmology can crack the ultimate mystery? That creation can be just another physical process that science has rendered prosaic, like the discovery that germs cause disease or Earth circles the sun?

Guth smiles and puts his fingertips together.

"I like to be careful how I put that," he says. "The way I like to say it is that we are approaching a scenario for the creation of the universe that is compatible with the laws of physics. That raises the question: 'Where do the laws of physics come from?'" He pauses. "We are a long way from being able to answer that one."

WHERE DO RULES COME FROM?Alan Guth's inflation theory explains the creation of the universe in a way that's compatible with the laws of physics. But where did the laws of physics come from? "One theory is that there are no laws of physics, that there are only properties of matter," Guth says. "According to this view, if there is no matter, then there are no properties."

If that's true then Guth's speculations about how a universe might have started from nothing are absurd. But Guth argues that quantum theory, the best theory yet for describing the physical world, seems to require independent laws. "If you bang two electrons together with enough energy, you produce protons. If there are no independent laws, then all the properties of protons must somehow be 'known' by the electrons. By extension every elementary particle must carry around enough information to produce the entire universe. I find that difficult to believe." Guth adds that quantum theory holds that objects can appear and disappear according to specific laws, and the behavior of an absent object is just as predictable as the behavior of a present one. "If laws are just properties of objects," he says, "how can those laws continue to operate when the object is not really there?" — B. L.

INFINITE INFLATING UNIVERSESSo far, what inflation theory predicts, the observable universe has reflected. But cosmologists Andrei Linde, Alexander Vilenkin, and others have run with inflation's premises to step beyond the bounds of what we can see or measure. They speculate that the decay of the false vacuum—which, according to the inflation theory, created the matter of our universe—does not happen all at once. While some regions decay into universes, other regions keep expanding and creating other universes. Residual false vacuum from the creation of those universes creates still others, indefinitely. Linde and Vilenkin call this "the eternally existing, self-reproducing inflationary universe." Guth contends that this scenario is not only possible, it seems like a sure thing. "If a biologist discovered a bacterium that belonged to no known species, she would presumably invent a new species in which to classify it," Guth wrote in his 1997 book, The Inflationary Universe. "However, even though only a single specimen of the new species had been found, she would undoubtedly assume that it was the offspring of a bacterial parent cell." Guth predicts that "any cosmological theory that does not lead to the eternal reproduction of universes will be considered as unimaginable as a species of bacteria that cannot reproduce."— B. L.

For a complete guide to the Big Bang theory and related concepts, check out the Web site for NASA's Microwave Anisotropy Probe: map.gsfc.nasa.gov/m_uni.html.