In what has been hailed as one of the most important discoveries of a generation, astronomers working on the BICEP2 telescope at the South Pole have announced that they have detected gravitational tremors from the birth of our Universe imprinted across the sky. The result is the first direct evidence for inflation, the theory that the Universe expanded unimaginably fast, an infinitesimal instant after time zero.
The theory of inflation states that the Universe grew in volume by about a factor of at least 1078, a number so vast that it’s impossible to comprehend (its roughly equal to the number of atoms in the universe). This phenomenal expansion took place in an incredibly short time, in about ten billionths of a trillionth of a trillionth of a second, at a time when the Universe was cold, dark and empty. To put this in context, if the full stop at the end of this sentence were to grow by the same factor, it would end up about a hundred times larger than our galaxy.
Inflation is a crucial part of modern cosmological theories and solves many serious problems with the traditional Big Bang model, but so far there has been no direct evidence that it actually happened. However, inflationary theories predict that this violent expansion would have created ripples in space and time known as gravitational waves. These ripples would then have echoed through the cosmos, leaving a mark on the oldest light in the Universe, the Cosmic Microwave Background (CMB).
Discovered fifty years ago by the American radio astronomers Arno Penzias and Robert Wilson (who at first mistook it for pigeon poo in their receiver), the CMB is the remnant of the light emitted 380,000 years after the Big Bang, when the Universe cooled enough for atoms to form and for light to travel freely across space. The discovery of the CMB was one of the most important events in the history of science, providing convincing evidence that the Universe began in a violent hot expansion known as the Big Bang. This ancient light has been stretched from a searing hot 3000 Kelvin to a freezing 2.7 Kelvin by the expansion of space, leaving it as a faint microwave signal coming from the entire sky.
The BICEP2 telescope is based at the Amundsen-Scott station at the geographic South Pole, where temperatures plummet to below minus 70 degrees Celsius in the Antarctic winter and the base is buffeted by blizzards and gale force winds. Despite these incredibly hostile conditions, the BICEP2 telescope is in the perfect location to study the CMB.
The South Pole is around 3000 metres above sea level, and the driest place on Earth, meaning that there is relatively little atmospheric water vapour that would otherwise screen out the CMB signal. This comes with the added advantage that BICEP2 is able to scan the same small piece of sky all year round, by effectively looking straight down from the bottom of the planet to the point known as the celestial south pole.
BICEP2 astronomers spent almost three years scanning the CMB in incredible detail, but yesterday the freezing conditions and hard work paid off spectacularly as they revealed subtle twists in the CMB, a smoking gun for gravitational waves from inflation. In fact, the BICEP2 astronomers were surprised by just how strong the signal was. “This has been like looking for a needle in a haystack, but instead we found a crowbar,” said co-leader Clem Pryke.
Although the result hasn’t been peer reviewed or published in a scientific journal yet, most astronomers agree that the findings look solid. The fifty-strong BICEP2 team have been sitting on their historic result since the end of 2012, and have spent more than a year checking and rechecking to ensure they have taken account of every possible effect, from gravitational lensing to space dust, which might have given a false result.
So what does this mean for our understanding of our Universe? The BICEP2 result is really three Nobel Prize-worthy discoveries in one. They have found the first convincing evidence that inflation really happened, giving science its first glimpse of the moment in which the universe came into being. Second, they have found the strongest evidence yet for gravitational waves, the last prediction of Einstein’s theory of general relativity to be verified, and something that astronomers have been searching for for decades. Third, and by no means least, this discovery demonstrates a deep connection between quantum mechanics and gravity, giving hope that we may one day find evidence of a theory of everything, a theory that would unite our theory of particles and forces with our theory of cosmology and gravity. This would undoubtedly be the greatest prize in science.
If confirmed by other observatories, this incredible result will go down in history as one of the most important scientific discoveries of the 21st century, eclipsing even CERN’s discovery of the Higgs boson in 2012. Nobel Prizes will almost certainly follow. More importantly, this result opens up a new window through which astronomers and cosmologists may, for the first time, glimpse the very moment of creation.