The imprints of the beginning of our universe
Her eyes open and mouth drops ever so slightly. “The discovery,” Professor Renata Kallosh says in almost a whisper. Her husband, Professor Andrei Linde, stands beside her in complete shock. “What?” he says. Assistant Professor Chao-Lin Kuo tugs at his backpack. “Five sigma,” Kuo says. “Clear as day.”
Champagne is popped and Linde takes a seat. “Let’s just hope that it’s not a trick,” he says. That’s quite the understatement: if it is a trick, we’ll need to come up with another explanation for how our universe was born.
On March 17, four very chuffed scientists – including Stanford University’s Kuo – announced in a press conference at the Harvard-Smithsonian Centre for Astrophysics in Massachusetts that their lonely telescope sitting in the South Pole for three years had detected the first direct evidence for inflation: the theory that describes what happened in a tiny fraction of a second after the birth of the universe. “Five sigma” is a measure of confidence in scientific results, and it meant there was but a 1 in 3.5 million chance that what they caught was a fluke.
Linde, a Russian physicist, also at Stanford, had penned his theory of inflation more than 30 years ago. And now the evidence for it was “clear as day”.
The telescope, called BICEP2, had captured faint ripples in the fabric of space-time, which would have been caused by the Big Bang, the intense explosion that ripped apart the universe when it was a trillionth of a trillionth of a trillionth of a second old. Dubbed “gravitational waves”, they are evidence of the sudden inflation of the universe from nothing – the “bang” in the Big Bang, as Kuo describes it.
Soon after the discovery was made, Kuo went to Linde’s house to tell him. Stanford University filmed the moment, put it on YouTube and in a couple of weeks, a video of three scientists discussing five sigma had almost three million hits.
If the finding is verified by other groups, it will go down as a milestone in the history of science, on the scale of uncovering dark energy and the Big Bang itself. Marc Kamionkowski, of Johns Hopkins University, who was not involved in the research, called it “a grand slam”.
In 1905, Albert Einstein penned the now famous equation E=mc2, which showed that mass and energy are interchangeable. The equation told humanity how to build nuclear weapons, but it also gave us unprecedented insight into the birth of the universe.
When a nuclear bomb explodes a speckle of matter is annihilated and converted into energy. The opposite happened when our universe was born: 13.8 billion years ago, a speck of energy converted into mass. But what happened after that? How did that matter birth galaxies, planets and, eventually, us?
For many years, physicists thought that the foetus of the universe was a rapidly expanding fireball. This idea has problems, though. For one, it can’t explain why everything in the sky is so ridiculously “boring”, explains Chris Lintott, an astrophysicist at the University of Oxford. Looking up at night to see pockmarked, asymmetrical stars, the sky seems quite interesting. But when scientists carve up the universe into cubes of 300 million light years, they find something uncanny: on average, radiation pervading everything has almost exactly the same temperature. “How could parts of the universe that haven’t been in contact since the Big Bang be so similar?” Lintott says.
Another problem with the Big Bang is the fact that the universe is flat. “That’s very difficult to explain if the universe was born in a fireball explosion,” says Lintott. The solution for this problem came from an unlikely place.
On the night of December 6, 1979, Alan Guth, an unknown postdoc at Stanford University who had been struggling to find stable work, was up late sweating over a rather obscure physics problem: why couldn’t he find traces of exotic particles that should have been created in the Big Bang? Scratching his head, Guth found a roundabout answer.
Perhaps, in one savage instant the universe inflated faster than the speed of light, turning a tiny dot of almost nothingness into everythingness. If true, those particles he was desperately looking for weren’t lost, but had been spread so thinly in the immense mass of the growing universe they couldn’t be detected. Quite conveniently, the theory also plugged the holes in the Big Bang Theory. That phenomenal burst of energy could have unified and flattened the universe.
Looking over his work the next day Guth scrawled in capital letters across the page, “Spectacular Realization”. Years later, he wrote, “If inflation is right, the universe can properly be called the ultimate free lunch.” Physicists lapped up the idea, and it quickly became cosmological gospel.
But Guth’s theory wasn’t perfect. In 1983, Linde tweaked it to create “chaotic inflation”. Since then, hundreds of versions of the theory of inflation have been penned. After this new finding, hundreds of those theories have been thrown out. Linde’s work, though, is still on the table.
The scales described for inflation are phenomenal. To create the energy needed to bust out a flat and uniform universe means the speck of space would have been around a trillion trillion times hotter than the surface of the sun. And the universe would have inflated at a ridiculous pace. “Imagine an E. coli bacterium expanding to the size of the galaxy in an instant,” says Dr Julian Berengut, a physicist at the University of New South Wales.
To the uninitiated the idea is crazy. Crazier still, it was treated as truth. “We learned it at university as if it was fact, even though there was no direct evidence for it,” Berengut says.
Some astronomers, like Lintott, were sceptical. “It was a convenient crutch,” he says. “Ordering up a sudden expansion of the universe to get your theory out of a hole seemed rather extravagant.” Now, following the March announcement, Lintott admits, “If the theory holds up, I have words to eat.”
BICEP2 at South Pole
Several years ago an impressive collaboration of astronomers from the cream of the field’s crop – including researchers from Harvard, Stanford and Caltech – came together to build a telescope that they believed would find evidence for inflation. The BICEP2 telescope – short for Background Imaging of Cosmic Extragalactic Polarisation – sat at the South Pole, near the middle of the Antarctic plateau, where it relentlessly observed a patch of space for the footprints of inflation. In particular, it was looking at the oldest light in the universe, called cosmic background radiation.
The gravitational waves it searched for, remnants of the Big Bang, flowed through the early universe, squishing space-time in one direction and stretching it in another. It was believed that their signature would be imprinted forever in the cosmic background radiation.
For three years, light waves streaming in from the early moments of the universe whacked into BICEP2’s sensors, as astronomers pored over the data for that twisted radiation.
When the first inklings came through, no one believed that they were looking at evidence of gravitational waves spawned 13.8 billion years ago. “Basically we were all intensely sceptical,” says co-leader Clem Pryke, from the University of Minnesota, at the press announcement. “We were trying to find … What is it? What’s wrong?” The team searched for other explanations for their findings. Was it dust? Problems with the equipment? Or any other “galactic contamination”? It wasn’t. Gravitational waves were by far the most likely thing that BICEP2 had found.
“It’s mind-boggling to go looking for something like this and actually find it,” Pryke says. “The world of experimental physics is littered with guys who spent decades searching for something which turned out not to exist.”
Science being science, of course, the results need to be verified by other teams before Nobel prizes are rolled out. But, with a dozen other telescopes scouring the skies for evidence of gravitational waves, it shouldn’t be too long before we know if the galactic contamination has tricked us all.
Meanwhile, as Linde and Guth sat in the crowd at the announcement – listening to evidence that they were correct – a question from the press was thrown to them: Can this result tell us about what happened before the Big Bang? They say, “yes”. Both believe this finding supports the so called “multiverse theory” – the idea that the universe is continuously giving birth to other baby universes inside a mushrooming “multiverse”. It’s a cool idea. How long might it be, one wonders, before we find direct evidence for it?
This article was first published in the print edition of The Saturday Paper on Apr 19, 2014 as "New wave physics". Subscribe here.