COSMOS | February 2015
Working late one night, Alan Guth solved a baffling riddle about the beginnings of the cosmos. Wilson da Silva profiles the giant of astrophysics ... a man who once had trouble holding down a job.
ALAN GUTH still finds it amazing that he can understand anything about the first few moments of the Big Bang. But he shouldn’t – he was there.
About 13.8 billion years ago, when the universe was a hundredth of a billionth of a trillionth of a trillionth of a second old, it underwent an incredible growth spurt, doubling in size more than 60 times in a split second. This cosmic fireball quickly slowed, and after about 380,000 years, cooled enough for electrons to combine with nuclei and form atoms; this liberated photons of light from surrounding interference and made the universe suddenly visible.
Somewhere between 150 million and 1 billion years later, gravity drove enough clumps of gas to collapse inward that they formed the first stars. The intense heat and pressure deep within stars acted like thermonuclear furnaces, converting the only matter that existed – hydrogen, helium and lithium – into heavier elements like carbon, iron and nickel. And Alan Guth, of course.
For a giant of astrophysics, the 67-year-old is subdued and unassuming, who considers his PhD a failure.
Not the astrophysicist himself – who sits before me in a checked blue shirt, light green chinos and tussled grey hair with a casual, toothy half-grin – but all of the oxygen, carbon, hydrogen, nitrogen, calcium, phosphorus and trace elements that make up the man. The protons, neutrons and electrons of which those elements are made – themselves composed of subatomic fermions like quarks and leptons – were made in that early universe.
“I find it absolutely amazing,” Guth, a professor of physics at the Massachusetts Institute of Technology in Boston, tells COSMOS. “I mean, we’re making theories about what was happening in the universe at 10-38 seconds, which is totally off scale, way beyond our experience. And nonetheless these predictions turned out to describe the fluctuations of the cosmic background radiation to incredible precision.”
For a giant of astrophysics who was in September recognised with the prestigious US$1 million Kavli Prize, the 67-year-old is subdued and unassuming. It’s not just his shaggy haircut that dates from the 1970s; so does the theory that made him famous. Our universe today is remarkably even. Guth’s explanation? A titanic growth spurt in the split second after its birth that inflated it like a balloon, leaving it smooth and even. He dubbed his theory “cosmic inflation.”
The universe was just too perfect. The density of matter and energy needed to be a precise value – to 15 decimal places – or else the universe would either blast itself apart or collapse on itself.
And yet, this is a man who considers his PhD a failure; even at the time he made his astounding discovery, he’d been stuck in the lower echelons as an untenured post-doc for years. “I would say my future was somewhat uncertain at that point,” he says, adjusting his gold-rimmed glasses.
Thanks to doing his doctorate at MIT, Guth avoided being drafted into the Vietnam War. His thesis was delivered in 1972, the same year conscription ended. It described how quarks combine to form elementary particles and was built on the then-popular belief that subatomic quarks were extremely heavy. Unfortunately the new theory of quantum chromodynamics emerged shortly after, rendering the idea of heavy quarks and Guth’s PhD thesis obsolete.
He had a hard time landing a permanent job. Now married to his high school sweetheart, Susan Tisch, he had a hard time landing a permanent job: over the next nine years, he took post-doctoral research positions at Princeton University, then Columbia, then Cornell, eventually ending up at Stanford University’s SLAC National Accelerator Laboratory near San Francisco. Over all of that time, his work – mostly on abstract mathematical problems – had nevertheless ranged widely, from describing the maths of subatomic particles to the Big Bang. But it was at SLAC, that all of this came together in his own personal big bang. Hitting on the idea of cosmic inflation, he modestly describes it as “being at the right place at the right time”.
THE UNIVERSE WAS just too perfect. This was the problem plaguing physicists in the 1970s. The Big Bang was a compelling description of how it began, but for this to lead to what we see today, the density of matter and energy needed to be a very precise value – to an accuracy of 15 decimal places – or else the universe would either blast itself apart or collapse on itself. This was known as the ‘flatness problem’.
Another difficulty was the ‘horizon problem’: the two edges of the universe are almost 28 billion light-years apart, yet across that distance, the temperature is remarkably uniform, to within 0.007%. Since nothing can move faster than light, heat radiation could not have traveled between these horizons to even out the difference. Physicists were stumped.
Neither of these problems were on the mind of Henry Tye, a fellow postdoctoral physicist at Cornell, who convinced Guth to work on equations that might predict the number of magnetic monopoles in the early universe. Magnets have two poles, but exotic beasts with a single pole are theoretically possible, according to the famous equations of Scottish physicist James Clerk Maxwell. However, monopoles have yet to be seen in the real universe – but if the early universe was superhot, many monopoles would likely have been produced.
In his notebook that night, he wrote “spectacular realisation” and two bold rectangles around it.
Guth and Tye set about calculating how many. Their answer was surprising: even today, the universe should be littered with magnetic monopoles What’s more, the monopoles would be so gargantuan that the universe would slow down extremely fast after the Big Bang. If their calculations were right, the universe would have been just 10,000 years old. That told them they were on the wrong path, because the universe cannot be younger than the Earth. “So that was clearly an impossible prediction,” Guth recalls.
He and Tye began to search for explanations that avoided the overproduction of monopoles. What if the universe cooled extremely quickly after the Big Bang, reducing the emergence of so many monopoles, they wondered? Working in the study of his rented house one night in late 1979, Guth set about doing the numbers, and found that this did indeed skirt the monopoles and the age of the universe problem.
But at 2am that same night, he had a flash of insight. “Such a large amount of supercooling would cause the universe to expand exponentially. And I realised that this would solve the flatness problem,” he recalls. In his notebook that night, he wrote “spectacular realisation” and two bold rectangles around it.
It was the birth of the theory of cosmic inflation. The next morning, he cycled to SLAC in record time. “I was very worried that there’d be some gigantic flaw, so I was very anxious to bounce the idea off colleagues to see if people could poke holes in it.”
However, his idea held up. In fact, from discussions with physicists in the SLAC cafeteria over the following weeks, it became obvious that inflation not only had legs, but also nicely solved the horizon problem. “It was all packed together cheek-by-jowl at subatomic distances before expanding wildly, so inflation neatly bridged the world of the very small and the world of the unimaginably large, tying them together. So I became all the more excited,” he says.
After a day of job interviews, he had dinner at a Chinese restaurant. His fortune cookie read: ‘An exciting opportunity awaits you if you are not too timid.’
Guth was suddenly in demand. From January 1980, he began speaking about his idea at universities and research institutes, inviting comment and criticism from the audience. He has always been slow to write a scientific paper, but in this case, he had good cause: while he could explain how inflation began, he couldn’t make it end in a way that allowed stars and galaxies to form.
Plus, his postdoc was coming to and end and he needed to find a job again – although this time the offers began coming to him. In April, after a day of job interviews, he had dinner at a Chinese restaurant. His fortune cookie read: ‘An exciting opportunity awaits you if you are not too timid.’
Guth really wanted to go back at MIT, but there were no jobs on offer. He contacted a friend at his alma mater, letting him know he was entertaining a host of job offers but would really prefer to work in Boston. A day later, Guth had his job offer “My wife was very happy,” he smiles.
By June, he’d finally completed his calculations on how inflation ended, but he wasn’t pleased – it predicted a lumpy universe, which is not what astronomers were seeing. He decided to publish his paper in January 1981, arguing that it was a powerful explanation despite the unsatisfying ending, and urged others to find ways to make the idea of cosmic inflation work.
There was already a lot of excitement – reports of his talks on inflation had been circulating in the physics community – but no-one had a ready answer. There were several attempts, but it actually took years for Guth’s challenge to be answered. It was Russian physicist Andrei Linde, then at the Lebedev Physical Institute in Moscow, who in 1983 proposed a revamped approach in which the universe gracefully exits from the exponential expansion without producing a wildly clumpy structure. It electrified physicists, and soon became the prototype of modern inflationary models. It also suggested that our universe is just one of many inflationary universes that have sprouted into being – that there is a multiverse of all possible types existing, and still being created.
Guth gushed about how Linde closed the loop: “My version of inflation did not work. Andrei made it work.”
In cracking the problem, Linde was inspired by the work of fellow Russian Alexei Starobinsky of the Landau Institute of Theoretical Physics in Moscow, who in 1980 independently postulated exponential expansion, although driven by a different mechanism: quantum gravity effects. Published in Russian, Starobinsky’s paper was unknown to Guth and others in the West, and had not addressed the flatness and horizon problems. Nevertheless, it was pivotal.
Today inflation theory has been validated many times over through measurements taken by the WMAP spacecraft and other experiments that map the cosmic microwave background – the ancient echo of the light released from the Big Bang. This September all three men were recognised with the US$1 million Kavli Prize in Astrophysics, awarded by Norway’s king at a ceremony in Oslo.
That was where I caught up with Guth and Linde. Over coffee at the Grand Hotel in Oslo, the same place where playwright Henrik Ibsen used to eat every day, Guth gushed about how Linde closed the loop: “My version of inflation did not work. Andrei made it work,” he said.
Now a professor at Stanford, Linde is an ebullient man with windswept white hair and a wide grin, who credits Guth with “a tremendous change in perspective” in physics. “Before the theory of inflation, everyone thought that quantum mechanics had an effect at very small scales, but at large scales it was considered not to be relevant,” he told me. “But we learned that the largest objects in the universe – galaxies – were produced by quantum fluctuations.” Not so long ago, “this would have sounded like a crazy idea, one that's good for science fiction books but not for physics. Yet you go and measure, and everything just fits into this science fiction picture. It’s just amazing.”
All three admit to still being astounded that humans can understand anything about what the universe was like when it was “less than 0.0000000000000000000000000001 centimetres across.”
Starobinksy, a greying and bespectacled man with bushy eyebrows and a more reserved bearing, whom I also met after the Kavli ceremony, agrees. “With this theory, cosmology becomes more like other areas of physics, it becomes predictive – we can predict what we see today with great accuracy. That’s very exciting.”
All three admit to still being astounded that humans can understand anything about what the universe was like when it was, as Starobinsky put it, “unimaginably small, less than 0.0000000000000000000000000001 centimetres across. That’s that’s 27 zeros between the decimal point and the 1!”
IN MARCH THIS year, a team led by Harvard astrophysicist John Kovac announced it had discovered gravitational waves using an Antarctica-based telescope, BICEP2 (for Background Imaging of Cosmic Extragalactic Polarisation 2). The imprint of gravitational waves, they claimed, was detectable as swirling patterns, dubbed B modes, in the polarised ancient light waves left over from the Big Bang.
The news rocked the physics world, and excited Guth, Linde and Starobinsky, as those very swirls were the telltale signs of inflation in action. Space-time would have ‘bounced’ in response to the shock, producing the gravity waves.
“Detection of gravity waves could point to the unification of several forces of nature. It might even provide compelling – though indirect – evidence of the existence of other universes.”
Gravitational waves were predicted by Albert Einstein’s 1916 Theory of General Relativity but are exceptionally feeble and difficult to detect, requiring instruments sensitive enough to detect a ripple smaller than the width of an atomic nucleus. Despite decades of searches using increasingly sophisticated instrumentation, no conclusive evidence of them had been discovered.
Shortly after the BICEP2 announcement, doubts emerged. Critics suggested the tiny swirls seen by the team may have been caused by dust particles looping around the Milky Way’s magnetic field, which might also polarise light and create similar patterns. Kovac’s team countered that they used six different models to predict what dust patterns might look like, then subtracted the six patterns, one at a time, from the raw data – theoretically, the signals left over would be those of bona fide gravitational waves.
In September, a new paper based on data collected by the European Space Agency’s Planck space observatory found that there’s a lot more dust than the BICEP2 team had anticipated in their models. In fact, enough to account for the swirls Kovac’s team measured – although the authors of the Planck paper stressed their analysis did not rule out BICEP2’s gravitational waves.
“When people said gravitational waves would be the smoking gun for inflation, my response was that I thought the room was pretty filled with smoke already.”
The news was disheartening, since measuring the primordial gravitational waves would not only be further validation of inflation theory, it offered hard numbers to explain how the universe operates from the cosmic to the quantum scale. “Detection of gravity waves could point to the unification of several forces of nature,” says cosmologist Lawrence Krauss of Arizona State University. “It might even provide compelling – though indirect – evidence of the existence of other universes.”
Guth is unperturbed that the BICEP2 data might be a mirage. What ruffles him is journalists dubbing the putative discovery as the only real proof cosmic inflation existed. “When people said that gravitational waves would be the smoking gun for inflation, my response was that I thought the room was pretty filled with smoke already,” he quipped.
But then Guth is not one to worry. For a man whose academic journey began with a failed PhD and years of insecurity from revolving postdoc positions, Guth nevertheless struck upon a solution that makes sense of the mess that was cosmology when he began in the field.
Which is ironic, really, considering his office is famously messy: among the smattering of awards he’s picked up over the years is one given by The Boston Globe for the messiest office in town, nominated by colleagues who hoped it would shame him into tidying up. “It’s still pretty messy,” he admitted. He seemed amused by the honour. Perhaps he needs the chaos for order to arise.
Wilson da Silva is a science writer in Sydney, and the former editor-in-chief of COSMOS.