A Quick Guide to Cosmic Inflation
One of the most important scientific discoveries of the 20th century was the idea of the inflationary cosmos: that in the very first moments of the Big Bang, space underwent a period of rapid and unprecedented expansion, doubling in size about every 10-37 second. Before the universe was even a second old, it was already quite massive. Although this isn't completely proven yet, the implications are enormous. Inflation explains one of the most unusual features of the universe: that it appears remarkably flat and uniform on very large scales. That's because space inflated rapidly and smoothed out most of the small wrinkles and irregularities left over from the Big Bang. Another possible prediction of inflationary theory is the existence of a multiverse — an infinite number of universes beside our own, each of which may contain their own unique laws and conditions.
Last March, a team of astrophysicists, working on a satellite array known as BICEP2, announced that they had discovered evidence for cosmic inflation for the first time. Needless to say, this would be a huge deal; it's the kind of result for which Nobel prizes are won. When physicist Alan Guth first proposed the idea of cosmic inflation back in 1979, he thought it would be difficult, perhaps impossible, to prove1. To him it was just a "game"; a theoretician's romantic yet futile attempt to explain the origins of the universe. More than 35 years after Guth's discovery, inflation has become a huge, sprawling branch of physics, which encompasses multiple theories and ideas. And yet, for all its importance, the one thing it lacks is direct, discernible evidence. A far more elegant view of the universe would emerge if scientists ever found the "smoking gun" for cosmic inflation.
We are now much closer to finding this smoking gun thanks to the somewhat mad obsession of the BICEP2 team. In order to reconstruct what occurred in the early moments of the universe, the astrophysicists of BICEP2 looked for patterns in the "cosmic microwave background" radiation (CMB for short), which is the oldest known light in the universe, first imprinted on the cosmos when it was just 380,000 years old. Back then, the universe was suffused with a hot, dense fog of plasma, which congealed into the galaxies and stars we see today. The CMB is the radiation left over from this early stage of the universe.
Between 2010 and 2012, the BICEP2 satellite began looking for patterns embedded in the CMB around the South Pole. Because of the thin atmosphere and the absence of water vapor, Antarctica contains an ideal environment for detecting radiation at very small wavelengths. The purpose was to detect a phenomenon known as gravitational waves. First postulated by Albert Einstein in 1916, these are ancient ripples in the fabric of space originating from the very first moments of the universe during its rapid expansion. Gravitational waves would have left a faint polarization pattern in the CMB. The detection of this pattern led physicists to believe that they had discovered direct evidence for cosmic inflation.
But soon after the BICEP2 team published its results, doubts began to emerge. The problem wasn't the data, but instead their interpretation. Skeptics noted that gravitational waves were not the only possible cause of polarization. Interstellar dust drifting in space could also produce the same pattern. Normally, astrophysicists would utilize maps of interstellar dust to distinguish between gravitational waves and residual "noise" in the background of space. But the most detailed maps were unavailable to the BICEP2 team by the time they made their announcement. In their initial paper, they may have underestimated the degree to which cosmic dust interfered in the contamination their data.
The collapse of the BICEP2 results doesn't necessarily mark the end of the search for gravitational waves. But it does lead to the inevitable question about what, if anything, the scientists should have done differently. After the recent furor over similar controversies, like the arsenic-based bacteria and the Darwinius masillae fossil, skeptics are sensibly worried that, by substituting manufactured hype and sensationalism in place of scientific objectivity, these news stories could undermine the vital link between scientific communication and public awareness.
But regardless of the hype that preceded the announcement, the results of BICEP2 still provided an invaluable source of information. Jamie Bock, who's one of the leaders of BICEP2, defended his team's decision to promulgate the results online instead of waiting for the peer-reviewed process by saying that other physicists "needed to be able to react to our data and test the results independently."2 According to Bock, the real problem is that scientists' ability to measure galactic dust emissions is "frustratingly limited."
Before the controversy of BICEP2 had even settled, astrophysicists were already looking for evidence of gravitational waves at different frequencies. SPIDER, a balloon experiment that floats above the atmosphere, made its first flight in January, and the next stage of the BICEP experiment, known as BICEP3, is still ongoing. If the newer generation of experiments cannot find evidence for gravitational waves, then the picture of the early universe is likely more complicated than current models would otherwise suggest, perhaps involving more exotic ideas and theories.