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Physics + MathPhysics & Math

Big Idea of 2014: BICEP2 and Cosmic Inflation

ByAllison EckNOVA NextNOVA Next

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In March, a clunky metal machine on the frigid underside of the Earth detected what most experts believed was the first direct evidence of cosmic inflation—the theory that space-time ballooned by more than 20 orders of magnitude almost immediately following the Big Bang.

The Antarctic-based instrument, called

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BICEP2 , began taking measurements of the universe’s cosmic microwave background radiation (CMB) in 2010. The CMB is presumed to be thermal energy leftover from our universe’s earliest moments—a dim background glow in the microwave region of the radio spectrum emanating. The CMB is nearly homogeneously distributed across all of the space, which, in the days before the theory of inflation, posed two mathematical impossibilities: first, the universe isn’t old enough for light to have spread all the way across the universe in this way; second, it’s also not old enough for all pockets of space to have settled into a balanced, even temperature like we see in the cosmos today.

Inflation explains how everything from galaxies to dust may have come about.

Inflationary theory—devised by physicist Alan Guth of MIT, Andrei Linde of Stanford, and others—resolves these paradoxes by predicting that the early universe’s exponential growth smoothed out most of the irregularities in the CMB, creating the more or less uniform universe we live in today. Any remaining irregularities would have to have been caused by either tiny temperature fluctuations that gave rise to the planets and stars or primordial gravity waves—quantum fluctuations of space-time that evidence of the inflationary event itself.

In 2003, NASA produced a map measuring the temperature fluctuations—a significant achievement for the theory of inflation. And then in March of this year , Harvard scientists leading the BICEP2 team claimed to have found evidence of the latter, called B-mode polarization. They reported that ripples in the polarization of these microwave photons were evidence that light was bent by the gravitational influence of massive objects accelerating through the fabric of space-time.

B-mode polarization was an extraordinary finding, with huge ramifications for physicists’ understanding of cosmic evolution, quantum gravity, and the Big Bang itself. Unfortunately, though, the celebrations were short-lived. In October, maps produced by the European Space Agency’s Planck satellite indicated that the B-mode signal may have been entirely due to dust, which can polarize photons and mimic the effect of gravity waves. But the scientists involved weren’t deterred; they now plan to direct even more energy into BICEP3, which is being deployed in the coming months. The new-and-improved instrument will attempt to differentiate gravity waves from dust. Meanwhile, theorists like Guth and Linde will continue writing, thinking, and dreaming about inflation.

In her extensively reported story for NOVA Next , science writer Amanda Gefter tracks the story of the BICEP2 team’s almost discovery in unprecedented detail, writing:

Funny, the difference between experiment and theory. Theory is the stuff of great drama, littered with “aha” moments. It’s Archimedes shouting, “eureka!” in the bathtub, it’s Guth writing, “spectacular realization” in his notebook, it’s Linde waking his wife to tell her, “I think I know how the universe was created.” But experiment—experiment is more like life. It’s messy and it happens gradually after a good amount of soldering and shivering and the turning of screws. Sometimes the results are null—and sometimes the results are dust—but little by little it adds up to something tangible and true.

The BICEP2 saga is arguably this year’s most beautiful example of the trials, tribulations, and latent triumphs of the scientific method. Don’t miss Gefter’s equally delightful narrative .

Photo Credit: NASA/ESA