Thirty years ago, when scientists first developed the cosmic theory of inflation, many thought it could not be more than a beautiful story.
Gravitational waves from inflation generate a faint but distinctive twisting pattern in the polarization of the cosmic microwave background, known as a “curl” or B-mode pattern.(Image courtesy of BICEP2 Collaboration)
CIFAR Associate in the program in Cosmology & Gravity Andrei Linde (Stanford University) was one of the original authors of inflationary theory. This week he received the news that researchers had found powerful, though unconfirmed, evidence supporting his decades of research.
“I was stunned,” he says.
Linde says that if the results are verified they would rule out alternative theories about the birth of our universe, including most versions of inflation — favouring a handful of the simplest models. However, the theory has had a long journey since it was first conceived in the 1980s.
“Experts knew that we were dealing with something exquisite, something very interesting. On the other hand, it was looking like science fiction,” says Linde.
“Inflationary theory essentially tells you that you take one milligram of matter in a special state, and then you produce the whole universe …This all looked like a magic trick.”
The theory says that from this speck emerged a flat, uniform universe, with quantum fluctuations that produced galaxies, and possibly a chain reaction that created multiple universes.
The results of the new experiment, called BICEP2 and carried out at the South Pole, are consistent with inflation. A collaboration of researchers including CIFAR Senior Fellows in Cosmology & Gravity Barth Netterfield (University of Toronto) and Mark Halpern (University of British Columbia) conducted the study of the oldest light in the universe, called the cosmic microwave background.
Following Harvard University’s announcement of the results at a press conference March 17, the scientific community has bubbled with discussion, with several members of CIFAR’s Cosmology & Gravity program expressing excitement, skepticism and wonder at how the evidence could fundamentally change cosmology.
“It’s just crazily important. It is as important as the discovery of the Higgs Boson — I would say much more important,” Linde says.
The researchers reported that BICEP2 had detected gravitational waves, which were caused by the universe’s rapid growth a trillionth of a trillionth of a trillionth of a second after it was born, from smaller than a proton to about the size of a grapefruit. Afterward, the theory states that the universe continued to expand more slowly.
“What we believe is that during this inflation, all kinds of ripples and wrinkles in the universe became larger and smoother,” says Halpern. “It’s a little bit like you’ve got a wrinkled tarp and you’re stretching it out, and all these wrinkles become smaller and smaller. And then if it ends suddenly, you’re left with some residual wrinkles.”
Halpern built the detector readout system for the BICEP2 radio telescope’s new, ultra-sensitive cameras, which allowed it to detect these residual wrinkles and show that they appear to include gravitational radiation.
However, Halpern says that when the data first arrived, he couldn’t believe his own readout system.
“We’ve had these results for well over a year. And my first reaction was — I think like many of our scientific colleagues — wow this just has to be wrong.”
The particular signature of gravitational radiation is very faint and difficult to detect. Halpern says researchers feared for years they simply wouldn’t be able to see the signal, and once they had detected it, they spent a year studying the data for potential errors.
Netterfield, whose lab provided electronics and helped with analysis on BICEP2, says he had guessed the signature would be too small to measure, but he’s ecstatic that he seems to have been incorrect.
“It’s like a dream,” Netterfield says. “If it hadn’t been measurable, we would have been stuck.”
Sorting out whether the data really showed gravitational waves, and not noise or some other error, is an intricate process. The wavelengths of gravitational waves are incredibly long, meaning researchers cannot watch their movement; they can only detect a snapshot of their distortion in space.
The BICEP2 researchers compared the data to how the cosmic microwave background should look if the waves were absent, and found the wave signature they detected was similar in size to what inflation predicted.
But given the complexity of the experiment, the technology and the analysis, CIFAR Senior Fellow in Cosmology & Gravity Neil Turok (Perimeter Institute for Theoretical Physics) remains skeptical. He says there are still factors that could complicate or disprove the BICEP2 results.
Turok says detecting a signature so faint could be complicated by noise from the Earth’s atmosphere, the galaxy, light distortions in the universe or other factors. In addition, he says the BICEP2 papers contain some signals that remain unexplained.
“All these are reasons for concern. But I don’t think they’re reasons for pessimism in the slightest,” Turok says.
Turok is one of the authors of cyclic universe theory, which posits that the universe cycles through repeated big bangs. The original version of that theory states that the Big Bang would not have formed long wavelength gravitational waves like those BICEP2 seems to have detected. The new evidence, if it is verified, would disprove that version of cyclic universe theory, though Turok says newer versions might still be able to explain the results. It would also make him the loser in a wager with Stephen Hawking — but that’s a bet Turok says he would be happy to lose.
“It sounds a funny thing to say, but I certainly hope he wins the bet,” he says.
If the BICEP2 evidence is proven true, it means there are observable, quantum effects in the universe. Furthermore, it means the Big Bang left a clear mark on the sky.
“This is just extremely exciting for fundamental theory and for our prospect of understanding what happened at the Big Bang,” Turok says.
“And who better could I lose a bet to than Stephen Hawking?” he says with a laugh.
A number of experiments, including the European Space Agency’s Planck Space Telescope, on which several CIFAR researchers are collaborators, are positioned to verify the results of BICEP2 within the next year or two. Planck’s most recent results from 2013, however, contradict BICEP2, and the new data brings us to the frontier of knowledge.
Halpern says debates like the one taking place in the scientific community happened within the BICEP2 team, and that’s exactly how it should be.
“It’s a perfectly wonderful, healthy thing for them to be doing,” Halpern says.
“If I’m going to rethink how physics works, I need to be very, very sure of the data through which I’m doing that.”
While the wait for more evidence has begun, Netterfield says the BICEP2 data renews hope for many members of the Cosmology & Gravity program who study the B-mode polarization — distortion of light from the cosmic microwave background — that the story they’re trying to tell isn’t fiction after all.
“In one sense, what it says is the goals we’ve had in the CIFAR program of detecting and then characterizing the B-modes is not chasing after a ghost. It’s really there,” Netterfield says.