Science in Mind

Harvard-led team detects gravitational waves, evidence of cosmic inflation

Graduate student Justus Brevik tests the BICEP2 readout electronics.
Physicist Justus Brevik tests the readout electronics of BICEP2, the South Pole-based telescope that has detected direct evidence of cosmic inflation.Steffen Richter / VagabondPix.co

CAMBRIDGE—In a landmark discovery about the first moments of the universe, a team led by a Harvard astronomer announced Monday it had found proof of what happened just after the Big Bang 13.8 billion years ago:

Using a telescope at the South Pole, the scientists detected a distinct pattern in the distant cosmos that reveals there was a hyper-expansion of our universe known as inflation.

The scientists also captured the first images of gravitational waves, which were predicted a century ago by Albert Einstein’s general theory of relativity. And they made the first measurement of a type of radiation predicted by famed British cosmologist Stephen Hawking.

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Scientists hailed the discovery as a transformative event that will provide deep and complicated questions for physicists to explore as well as transfix the imagination to the broader public, because it gives insight into a foundational question in physics: how did the universe begin?

“This is one of the most important scientific discoveries of all time,” said Max Tegmark, a physicist from the Massachusetts Institute of Technology who was not involved in the work but attended the announcement in a packed auditorium at the Harvard-Smithsonian Center for Astrophysics. “It’s just like when something big happens in your personal life and you keep waking up and saying, ‘Whoa!’ I keep having these ‘whoa!’ moments. This is absolutely spectacular.”

The theory of cosmic inflation was proposed by MIT physicist Alan Guth in 1980, because simpler models of the Big Bang could not explain some features of the universe as it appears today, such as how uniform it is across the sky. Guth describes inflation as the “bang” of the Big Bang.

Inflation proposes that the initial expansion of the universe was caused by a repulsive form of gravity—opposite the normal way of thinking about gravity as an attractive force. The initial patch of the universe that underwent inflation would have been unbelievably small, about one-billionth of the size of a proton, and then it would have expanded exponentially. In the slightest fraction of a second, the universe would have doubled in size 100 times.

As the university continues to expand today, “what we see now is still a coasting expansion, originating from the Big Bang,” Guth said.

As Guth’s initial idea has been refined and developed by other scientists over the years, its predictions seemed to be bearing out. But there was still no direct evidence for inflation and it was unclear whether the theory would ever have proof to bolster it. The energy needed to recreate the conditions of the early universe in a particle accelerator—10 trillion times higher than what is produced at the Large Hadron Collider in Switzerland—were so high that it was unfeasible.

The Harvard-led team took a different approach. One prediction of the theory is that the rapid expansion would have left behind a fingerprint—a particular pattern of polarized light in the cosmic microwave background. The pattern is created when the faint light all across the sky that is the afterglow of the Big Bang, emitted 380,000 years after the explosion, interacted with gravitational waves.

Using a telescope called BICEP2 at the South Pole, the team claims to have detected that swirly polarization pattern, called B-mode polarization. If confirmed by other experiments, it will be strong evidence of inflation and help guide scientists to which particular version of inflation is the correct one.

“I think we can think of this measurement today as opening a new window up on what we believe to be a new regime of physics, the physics of what happens in the first unbelievably tiny fraction of a second in the universe, and at extremely high energies,” said John Kovac, the team leader and an associate professor of astronomy at the Harvard-Smithsonian Center.

He and other team members wore matching T-shirts with a map of the South Pole on the back. Outside the auditorium, an image of Rosie the Riveter was left near copies of the scientific papers, with the motto “We can do it!” replaced by “We detected it!”

Guth said Kovac e-mailed him to tell him he had some urgent news, then came to Guth’s office at MIT and disclosed the results last week.

“I was ecstatic,” said Guth. “I hope this will sort of put the nail in the coffin, and define inflation as being the theory.”

Andrei Linde, a Stanford University physicist who developed Guth’s theory further and put forth a version of inflation called chaotic inflation, said he was cautious because the discovery was so profound. He said the team that made the measurements is extremely strong, but as with all science, the work must be repeated by others. If true, he said, the finding is worthy of a Nobel Prize.

“The signal is compatible with models which I proposed a long time ago, so for me, this is fantastic news,” Linde said. “For the general theory of relativity, for Einstein’s theory, it’s fantastic news because the gravitational waves is part of Einstein’s theory, never seen—just like the discovery of the Higgs boson was necessary for proving the standard model of particles.”

The scientists emphasized that they were eager to see other competing experiments confirm their results, and that a faster and more powerful version of the telescope called BICEP 3 now being built will allow them to probe even further the polarization pattern to learn more about inflation.

Marc Kamionkowski, a physics and astronomy professor from Johns Hopkins University, called the new data “cosmology’s missing link” and was like hitting a grand slam in baseball.

The discovery comes at a historic time—a half-century after a pair of scientists at Bell Labs used a horn-shaped antenna on top of a hill in New Jersey to make measurements of microwave radiation. They saw a stubborn, noisy background signal in their data, and despite efforts to get rid of it, it remained. Eventually, they realized it wasn’t due to faulty equipment, but was actually the faint afterglow of the Big Bang.

That measurement spurred a revolution in cosmology, finally confirming that the universe had a discrete beginning—and allowing scientists to discard the longstanding “Steady State theory,” which said that the universe had always existed. It also sparked careful study of the cosmic microwave background, which has provided new insight into the structure and formation of our universe.

“I guess one can never rule out some other theory coming along which does something better, but this [discovery] really seems to make a pretty tight story from very early time to now, and that’s very satisfying,” said Robert W. Wilson, a Harvard astronomer who co-discovered the cosmic microwave background in 1964 at Bell Labs and shared the Nobel Prize for the work. “I was a little bit skeptical of inflation, but now it looks like it’s really a pretty tight fit.”

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