The exponential expansion, a consequence of a supercool idea at the right place and at the right time to get rid of a model of the universe too perfectly tuned...‏

Alan Guth: Waiting for 
the Big Bang

Three decades ago, the innovative physicist had a eureka moment that explained the universe.

National Geographic, June 2014

At the end of a quiet, carpeted hallway in MIT's physics department, a display case stands empty outside the office of physicist Alan Guth.
Framed in blond wood and clear glass, the empty cube waits for the world to fill nothing with something.
"It would be nice if it happens," says Guth, a rumpled 67-year-old, who sits in his respectably cluttered office, sunlight brightening piles of papers scattered over a desk and table.
"It" is not just any prize but one thing in particular: a citation for the Nobel Prize in physics. Ever since his remarkable work analyzing the gravitational ripples after the big bang, Guth's perhaps inevitable acceptance of a Swedish-accented phone call from the Nobel committee is now the talk of the physics world.
All for explaining how something small—an apple-size blip in an otherwise empty eternity—inflated almost instantaneously, becoming something much bigger, perhaps endless, a universe. Ours.
Inflation basically suggests that at very early instants in the life of the universe, within a trillionth of a trillionth of a second, gravity acted as a strongly repulsive force, stretching the boundaries of the sky across hundreds of thousands of light-years. Essentially this was the bang in the big bang, the nearly instantaneous expansion of a tiny volume of space into an entire cosmos that started some 13.82 billion years ago.
The appearance of the first subatomic particles at the climax of this event marked the end of cosmological inflation. Gravity then took its familiar apple-falling-from-the-tree form, leaving us to inherit a universe filled with stars, galaxies, planets—and the physicists to ponder how it all came about.


Guth brushes back the bangs of his mop-top haircut, raises his hands and spreads them wide. "I always knew it was a pretty good idea," he says.
Picture of Alan Guth

Guth, a theoretical physicist at MIT, proposed a new cosmological model he called "inflation."PHOTOGRAPH BY DEANNE FITZMAURICE, NATIONAL GEOGRAPHIC  Cosmic Ripples

In March, Guth sat in the auditorium of the Harvard-Smithsonian Center for Astrophysics, a storied center of astronomy on the other side of Cambridge, Massachusetts, from MIT.
He waited in the audience, along with Stanford's Andrei Linde, 66, another inflation theorist, to hear from the BICEP2 astrophysics team that had spent three years looking with an unblinking telescope at one small patch of sky above the frozen waste of Antarctica.
They had looked inside that patch at the most distant thing observable in the cosmos, the so-called cosmic microwave background, or CMB. The CMB emanates from every corner of the sky—leftover heat from the first 380,000 years of the universe's history after the big bang.
"I never thought I would see these measurements made in my lifetime," Guth said.
On the podium that day, the BICEP2 team, led by Harvard's John Kovac, presented the results of their CMB observations: detection of gravitational wave signals of "precisely" the size that Guth's inflationary theory predicted.

These gravitational waves are "ripples" in matter triggered by inflation stretching the boundaries of the early universe faster than the speed of light. (While nothing can travel faster than light, the dimensions of space aren't a solid thing, so the waves can exceed this speed limit when they shift, according to Einstein's explanation of gravity.) A particular "curl" in the BICEP2 team's observed gravitational waves marked them as inflationary relics.
At the event, Johns Hopkins University physicist Marc Kamionkowskicalled the result "the smoking gun for inflation."
Of course, nothing is ever simple in science, and the result faced scrutiny from the physics community, including from theorists whose own explanations of the origin of the universe are threatened by inflation. When Kovac's team published their results in the journal Physical Review Letters in June, they added a note cautioning that interstellar dust may explain the gravitational waves they saw and that they await more telescope observations for confirmation.
"It will be very reassuring to see the result confirmed," Guth told National Geographic at the time of the announcement. "I never thought I would see these measurements made in my lifetime," he added.
Pride of Highland Park
Guth's story begins in Highland Park, New Jersey, where he grew up and attended public school. "Neither of my parents went to college," he says. His father was a grocer and, after a fire destroyed the store, ran a dry-cleaners.
"It was sort of assumed, from the time I was born, really, that I would go to college," he says. "That's sort of the way that Jewish families in New Jersey handled things; that was the norm."
"What always fascinated me about science was the desire to understand what underlies it all, and I think physics is basically the study of that," Guth says.

In the early 1960s, when he was in high school, physics was at the height of its Cold War prestige. A precocious student, he left high school a year early for MIT. "The chemistry teacher I would have had the following year suggested that they get rid of me."
He already had an older sister attending Lesley College in Cambridge, Massachusetts, when he arrived there in 1964. "She was dating guys from MIT and not Harvard, so I didn't end up at Harvard," he says.
"I think I always wanted to go into physics," Guth says, gesturing at the papers in his room. "What always fascinated me about science was the desire to understand what underlies it all, and I think physics is basically the study of that."
The Vietnam War was under way at the time, and a five-year degree leading to a master's degree in physics added a year to Guth's draft deferment status. "I found the transition [to college] very easy," he says. Physics students, he found, largely study both the impossibly small, or the doings of subatomic particles, and the impossibly large, or gravity's construction of space and time.
"It turned out they came together for me," Guth says. "That is really the story with inflation."
He completed his doctorate in physics at MIT; his thesis was "a failure," Guth says. It rested on the then-popular notion that the subatomic particles called quarks were very heavy, a notion disproved in large part by Nobel Prize-winning work in the 1970s performed by MIT physicist Frank Wilczek, whose office is down the hall from Guth's.
"It was starting to be a tough time," Guth says. "But I didn't become discouraged ... Physics was fun, and I was at least in good places all of that time."
Married to his high school sweetheart, Susan, Guth moved from Princeton to Columbia to Cornell in "postdoctoral" positions short of a professorship for nine years. More moves, he says, "than just about anybody I know."

While at Stanford's SLAC National Accelerator Laboratory, Guth conceived of the idea of cosmological inflation. In his wanderings, he had moved from studying quarks to analyzing primordial cosmic defects called magnetic monopoles to pondering problems with the big bang itself.
"For me, everything was being at the right place at the right time," Guth says.
In 1978, he learned in a talk by Princeton physicist Bob Dicke of a problem with the universe—it was too perfect. All sorts of factors, from the workings of atoms to the gravity holding stars together, seem too exquisitely fine-tuned for creating a cosmos in defiance of both rational explanation and what chance would predict.
"One second after the big bang—and I'm pretty sure that is the example he used—the expansion rate had to be just right to an accuracy of 14 decimal places or our universe would look nothing like it does now." Just a smidge more expansion and the universe would have blasted itself apart. A tiny bit less and it would have fallen in on itself. Instead it had unfolded just right, balanced on a universe-friendly knife-edge, seemingly for no reason.
Guth filed away this "flatness" problem in his mind as interesting but too big to tackle. "It just stuck in the back of my mind."
Next, a colleague at Cornell named Henry Tye asked him to examine how many cosmological defects would have been spawned by the big bang. Guth figured out that it should have produced magnetic monopoles, theoretical objects that no one has ever seen.
"I told Henry to forget about it," Guth says. "I thought it was a ridiculous way to waste time. But he continued to needle me."
In the spring of 1979, Guth attended two lectures by physics Nobelist Steven Weinberg, then at Harvard, about problems with the big bang in its first instants, less than a trillionth of a trillionth of a second. "I decided that if Steve was willing to work on these crazy things, maybe they weren't so crazy."


Guth lays on the floor of the atrium of MIT's physics department on artist Sol LeWitt's "Bars of Color Within Space," which gives the illusion of gravitational forces. PHOTOGRAPH BY DEANNE FITZMAURICE, NATIONAL GEOGRAPHIC  
Small World
The answer that Guth and Tye found that year, however, was still crazy: The universe should be swimming with cosmic defects.
In fact, these defects should have been so numerous and so massive that if they actually existed, the age of the universe "would turn out to be about 10,000 years," Guth says, with a laugh. "This doesn't turn out to be the case, scientifically."
So, they turned to exploring whether the early universe (we are still in its first trillionth of a trillionth of a second) "supercooled" as it expanded. A 100,000-fold drop in temperature might have given the forces inside the early universe a bit more time to line up nicely with each other, essentially producing fewer defective cracks in creation.
"This was a eureka moment," Guth says, with amusement and utter certainty. "On that notebook page, I wrote 'spectacular realization' in a double box."
"Once you write down the equations, it is not a hard problem at all. It is really kind of obvious," Guth says. The supercooling does dramatically affect the expansion rate of the universe. "It drives the universe into a period of exponential expansion," he says, now called cosmological inflation.
Sitting at a desk in a study in his rented home on the same night he made this discovery, Guth realized this exponential expansion would solve the "flatness" problem of the Goldilocks-perfect universe that neither collapsed nor exploded in its first instant. This relentless expansion drove the initial conditions of the universe inevitably toward its present state, a realm of vast emptiness filled with stars.

"This was a eureka moment," Guth says, with amusement and utter certainty. "On that notebook page, I wrote 'spectacular realization' in a double box."
Over lunch in Stanford's SLAC cafeteria, Guth soon learned of another big problem in cosmology, the "horizon" problem. The problem is explaining the startling uniformity of conditions across the universe, where galaxies and the cosmic microwave background seem to be evenly distributed across the horizon, instead of clumping up in one corner or another of the sky.
"I soon realized that inflation would solve that too," Guth says. If everything in the universe was packed together closely at its beginning and underwent exponential expansion in an instant, then no wonder everything looked similar across the sky and across the CMB. Once upon a time it was all packed together cheek by jowl at subatomic distances before expanding wildly in scale. Inflation neatly bridged the world of the very small and the world of the unimaginably large, tying them together.
Expanding Universe
Guth was suddenly in high demand, which was good because he needed a job. "That was very much on my mind," he says.
He had two problems, however. "I'm pretty slow at writing papers," Guth says. Plus, he could explain how inflation started, but couldn't explain how it ended.
So beginning in January 1980 at SLAC, he gave talks on inflation for months at universities around the country. At the same time, he was preparing a paper on his finding, looking for a job, and wrestling with how inflation ends. Sidney Coleman, a prominent Harvard physicist, heard the talk at SLAC, got excited, and began spreading the news to others in the field—"incredibly valuable help," Guth says.
Inflation compelled the interest of physicists because it kept all the advantages of the big bang as an explanation for the origin of the universe while filling in a uncharted spot in explaining how it actually started—in other words, what put the bang in the big bang.

"And then the job offers started to come in," he says. On a trip in April 1980 to the University of Maryland, he ate the traditional meal offered to aspiring physics professors at the end of a day of job interviews—dinner at a Chinese restaurant. His fortune cookie read:
An exciting opportunity awaits you if you are not too timid.
Laughing, he says, "I thought, What have I got to lose?" So he wrote to a friend at MIT, where he longed to return, but which wasn't advertising a job that year. "I told them that if they offered me a job, I would like that."
MIT called him back the the next day and did just that. "My wife was very happy," he says.
Then in June, he figured out how inflation ended: unhappily. His version of inflation saw the process ending with a transition resembling water boiling away in a pot to become steam, changing from a dense liquid to a thin vapor. In this analogy, if the bubbles of matter boiling away in inflation were small enough, the result would be a smooth universe after the transition. But that turned out not to be the case.
Instead, he found that big bubbles would cluster away from each other, creating a clumpy universe.
"So I had this unhappy ending, but I still thought it was a good idea," Guth says. "So I did publish it." The study published in 1981 was very frank about the unhappy ending. He was very hopeful still, he says, about someone else coming along and supplying another ending.
And at the end of the year, Stanford's Linde did find another answer, and he was followed shortly afterward by other researchers. The wholesale makeover of inflation, called "chaotic inflation" or "eternal" inflation, produced by Linde and colleagues in 1983 has become a standard for the field. In this model, inflation is occurring somewhere in the universe all the time, far beyond the 92 billion light-year expanse of the cosmos we can now see.

Most often the model also sees inflation producing a proliferation of universes, a multiverse filled with a cornucopia of realities.
Swedish Lessons
Despite the current hoopla over inflation, the idea enjoyed a somewhat lonely existence for more than a decade, Guth explained at a recent symposium on inflation at MIT, where he has enjoyed teaching since 1980.
Onstage, Guth's slouched demeanor gives way to that of a speaker fully engaged with his topic, one hand held behind his back as he paces. He pauses only to raise both hands to make a point as he explains his discovery to a packed audience.
The reason for those lonely decades was that other astronomers did not see the exact kind of "flatness" in the universe predicted by the theory. When others tallied up the weight of observable galaxies and cosmic dust clouds, our cosmos looked a little on the light side.
Back in his office, Guth smiles and shrugs. "My career got off to a slow start."
Tentative observations of the CMB, however, pointed to inflation being on the right track. "Each time they found better and better evidence," Guth says, of this time. "I was ecstatic and impressed they could even make the measurements."
In 1998, researchers discovered that the universe was expanding at an accelerating rate, revealed by observations of distant exploding stars flinging themselves farther and farther away from us at an always increasing rate. They found that the accelerating expansion of the universe was driven by "dark energy," a seeming anti-gravity force pulling the cosmos apart.

Confirmed by other observations, the discovery later earned Saul Perlmutter, Brian Schmidt, and Adam Riess a Nobel Prize in physics.
The dark energy discovery was also "a bombshell" that boosted inflation, as Guth explained at an April symposium on the BICEP2 findings, where the experiment's leader, Kovac, also spoke. "It was pretty clear that dark energy solved the problem" of the stuff that astronomers hadn't been able to see before, Guth said.
Physicist Max Tegmark, a colleague of Guth's, says that, ultimately, one effect of inflation's success may be to do away with the whole concept of a big bang. Physicists can't quite agree at the moment what part of the universe's origin was big and what was the bang. "It was more of a big 'swoosh,'" Tegmark proposed at the April talk.
Either way, Tegmark closed by suggesting that he would try to teach Guth "a little Swedish," for the seemingly inevitable day when a Nobel Prize committee member would call him with a prize announcement.
Gravitational Waves
Back in his office, Guth smiles and shrugs. "My career got off to a slow start." His thesis was a bust, he wandered (studying cosmic defects, no less) in positions short of a professorship for almost a decade, and his job search led him—the man who seems to have figured out where the universe came from—to take career advice from a cookie.
Now, he bicycles to work in the morning to an office overlooking the university where his career took wing. With his just-married son a full professor in mathematics in a nearby building, and his daughter living at home with him and his wife, he says, "I feel enormously lucky. And blessed."
"He was a tremendously fun, supportive father," says his son, Larry, who chimed in at the April symposium to clarify a technical question about inflation asked from the audience. "He did like to talk about physics, no doubt. Maybe not your typical dad."

"I think science is going to require more and more patience from society than it has in the past," Guth says, pointing to the 30 years between his theorizing and the BICEP2 results.
While counting his blessings, Guth waits a little longer for inflation to be validated. Both an earlier indirect look at the CMB by Europe's Planck satellite and the new BICEP2 gravitational wave results support inflation. However, they don't agree on the details.
Guth pronounces himself agnostic on what flavor of inflation emerges from the face-off between Planck and the successor to BICEP2, with more observations expected this fall. "Meanwhile, people have fun with the models," he says. (In June, after this interview, Guth expressed some doubts about the BICEP2 results after the questions about its treatment of cosmic dust. "I hope that the result will hold up, but I think we will need more data before the question is settled," he says.)
The prize cabinet outside his office may not have to wait too long, regardless. In May, the one-million-dollar Kavli Prize, a Norwegian rival to the Nobel, was awarded to Guth, Linde, and Alexei Starobinskyof the Russian Academy of Sciences, who earlier in the 1970s had worked on theories of universal expansion that informed Linde's later work on inflation. The King of Norway will award the prize to the theorists in September.
"I think science is going to require more and more patience from society than it has in the past," Guth says, pointing to the 30 years between his theorizing and the BICEP2 results, as well as the recent experimental work at Europe's CERN lab confirming the existence of a subatomic particle called the Higgs boson, first proposed in the 1960s.

"I do worry about the fact that science is becoming a slower process as society is becoming less patient," he says. "Hopefully some of the excitement about these BICEP2 results will carry over and people see that we still have so much to wait for."

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