Scientists staring at the faint afterglow from the universe’s birth 13.8 billion years ago have discovered the first direct evidence for the theory of cosmic inflation — the mysterious and violent expansion after the big bang.
The findings, made using radio telescopes at the South Pole, support the idea that our known cosmos make up just a tiny fragment in a much larger, unknown frontier that extends far beyond the reaches of light.
During this period of inflation, which happened just a fraction of a second after the big bang, the universe ballooned from smaller than an atom to 100 trillion trillion times its original size, at a rate faster than the speed of light.
The research, submitted to the journal Nature for publication, also provides direct evidence of ripples in the structure of space-time made by gravitational waves, and it affirms the often tense link between quantum mechanics and Albert Einstein’s theory of general relativity.
The findings open “a new window on what we believe to be a new regime of physics,” said John Kovac, a radio astronomer at the Harvard-Smithsonian Center for Astrophysics and one of the project’s lead scientists.
The project, known as BICEP2 for Background Imaging of Cosmic Extragalactic Polarization, also included researchers from Caltech, the Jet Propulsion Laboratory, Stanford University and the University of Minnesota.
Its discovery is potentially worthy of a Nobel Prize, said researchers who were not involved in the project.
“It’s amazing,” said experimental cosmologist John Carlstrom of the University of Chicago, who leads the competing South Pole Telescope project. “Everyone in my field, what we’re thinking of doing in the future, we have to all rethink. This is an amazing milestone.”
The researchers used radio telescopes at the South Pole to stare at the cosmic microwave background radiation — a faint afterglow left over from the big bang that permeates the universe.
Scientists have long wondered why this faint background light is so uniform across the sky, Carlstrom said. Stars clump into galaxies, and galaxies cluster together unevenly across the heavens. But no matter where you look, the cosmic microwave background seems to look essentially the same.
Why was the cosmic microwave background so smooth while all the stuff that came after it looked so lumpy?
In 1980, theoretical physicist Alan Guth of MIT came up with an answer: All that stuff from the early universe had originally been in a single tiny spot when it was ripped outward in a violent expansion.
Because the universe was compressed and experienced a single sudden expansion, the characteristics of the background radiation would be roughly the same.
It would require a massive spurt of inflation that scientists could barely comprehend. In less than a trillionth of a trillionth of a trillionth of a second after the universe popped into existence, the newborn cosmos expanded from the size of a tiny subatomic particle to roughly the size of a basketball.
As the universe continued to expand at a slower rate and then cool, it carried with it the signature of this early trauma.
Guth’s inflation theory became a cornerstone of our understanding of the early universe — but scientists had thought it would be difficult, if not impossible, to prove.
The signal from the cosmic background microwave has weakened over time, making it exceedingly difficult to find the signature of this ancient inflation behind all the cosmic “noise.”
The only hints could come from distortion in the fabric of space-time, created by the trauma of inflation. That could be detected by looking for a particular pattern of polarized light in the cosmic microwave background, known as B-mode polarization.
The theory was that sudden inflation, based on Einstein’s theory of relativity, should cause an onslaught of gravitational waves that ultimately would change the polarity of the background radiation, leaving behind a distinctive swirling pattern.
More than a decade ago, Caltech astrophysicist Jamie Bock, one of the lead scientists on the BICEP2 collaboration, came up with the idea for a telescope to search only for B-mode polarization from gravitational waves. It would be placed at the South Pole where the thin, cold air would allow for a clear signal.
This experiment, BICEP, was the first of its kind to focus solely on this signal, and there was no guarantee of success for such a costly project, Bock said.
The task was not easy. The scientists were using a small, 26-centimeter telescope but surrounded it with material cooled to a few degrees above absolute zero so that it would be sensitive enough to measure subtle patterns in the incredibly weak background radiation.
The researchers discovered the swirling patterns left in the faint polarized light.
The theory of inflation is rooted in quantum mechanics, which operates on the subatomic scale. The new discoveries show that the gravitational waves predicted by Einstein’s theory of relativity, which governs very large-scale phenomena, are also quantum phenomena.
“This is a watershed moment,” Bock said.
Much remains unknown. Scientists still don’t agree on exactly what triggered inflation in the first place. Whatever it was, they do think that it was a mysterious, repulsive force — rather like the dark energy that pervades the universe today and is causing it to expand, but far more powerful.
The discovery lends support to the idea that what we typically think of as the universe is just a tiny part of the much larger cosmos. Parts of the universe could have been hurled well beyond the range of light and thus far beyond the observable fringes, Bock pointed out.
The findings also leave open the idea that there could be multiple universes, not just the one we inhabit.
“It’s hard to build models of inflation that don’t [involve] a multiverse,” said Guth, who was among the first to propose the idea of cosmic inflation.
The landmark findings ultimately have raised as many questions as they answer, scientists said, and would require a lot more work to confirm and then push the research forward.
“We’ll certainly go and have some drinks tonight,” said Clem Pryke, one of the lead scientists on the project based out of the University of Minnesota, “but we’re not completely done.... This is not the end. This is the beginning.”