A team led by a Harvard astronomer announced Monday that it had detected a pattern in the distant cosmos that reveals what happened in the first known moments after the Big Bang 13 billion years ago: a hyper-expansion of our universe known as inflation.
The scientists have also for the first time directly detected gravitational waves, which have been long predicted by Albert Einstein’s general theory of relativity but never directly observed.
“Detecting this signal is one of the most important goals in cosmology today,” John Kovac, associate professor of astronomy at the Harvard-Smithsonian Center for Astrophysics who led the team, said in a statement.
For more than three decades, inflation, first proposed by Massachusetts Institute of Technology physicist Alan Guth, has been an attractive, but unproven theory for the rapid expansion of the early universe. Guth describes it as the “bang” of the Big Bang.
Inflation proposes that the initial expansion was caused by a repulsive form of gravity. The initial patch of the universe that underwent inflation would have been unbelievably small, about the billionth the size of a proton, and then expanded exponentially. It was proposed because simpler models of the Big Bang could not explain some features of the universe.
As Guth’s idea has been refined and developed further 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 direct proof to bolster it. The energy needed to recreate the conditions in a particle accelerator were so high that it was unfeasible to think about recreating it. What inflation did predict, however, was a particular polarization pattern in the cosmic microwave background -- the faint light that is the afterglow of the Big Bang.
Using a telescope called BICEP2 based at the South Pole, the Harvard-led team claims to have detected a polarization pattern in the faint light left over from the Big Bang that will, if confirmed by other experiments, be strong evidence in favor of inflation.
Guth said he learned the results when Kovac, the astrophysicist at the Harvard-Smithsonian Center for Astrophysics, e-mailed him to tell him he had some urgent news. Kovac 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, it must be repeated. If true, he said, the measurement 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 discovery also comes at a historic time -- a half-century after a pair of scientists at Bell Labs used a horn-shaped antennae on top of a hill in New Jersey to make measurements and realized that what appeared to be a noisy background signal 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 really seems to make a pretty tight story from very early time to now, and that’s very satisfying,” said Bob 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.”