“Gravitational waves emitted at the time of the big bang can tell us how the Universe came to exist. The BICEP experiment has today announced the detection of evidence for these primordial waves. If these results prove correct, we will have new key information on the very early Universe, information that is hard to get from any other source.”
Dr Ed Daw from the University of Sheffield’s Department of Physics and Astronomy
The universe is, to many a scientist and philosopher, a puzzle – a grand cosmic riddle. Here, sitting on our pale blue dot suspended in a sunbeam, humanity has set its sights to solving this riddle and searched far and wide through the grand cosmic fog to find clues to do it. Today, it has been announced that one such clue has been found and it may lead to a huge breakthrough in answering one of the riddle’s most important components: how the universe came to be.
It’s all thanks to the sleuthing abilities of a US-led team of astronomers who have been using a radio telescope based at the Amundsen-Scott Research Station in the South Pole to glimpse back into the very early stages of the universe. Their goal: to detect ripples in space-time, the gravitational waves foreshadowed by Einstein’s last untested prediction.
Not only do these cosmic ripples add one final piece in the puzzle that is General Relativity, they also serve as proof for inflation, one of the most convincing, yet ultimately unproven, models of the universe. First stated by the physicist Alan Guth in 1980, the idea of inflation is that at just approximately one hundred million, billion, billion, billionth of a second after the big bang (10^-35 of a second, which is a decimal point with 34 zeros after it), the universe began experiencing a period of rapid growth. After this initial blow-up, the universe continued to expand, but at a much calmer rate. The universe continues to expand today, as Georges Lemaitre discovered in 1927 in his equations of General Relativity, which were verified by the observations Edward Hubble made two years later. (The rate of the universe’s expansion was subsequently labelled the Hubble Constant.)
“Modern cosmology is based on three underlying assumptions – inflation, dark matter and dark energy. We don’t know what any of them actually are, but over the last few years we have seen increasingly strong evidence that they are real.”
Professor John Womersley, Chief Executive of the Science and Technology Facilities Council (STFC) which funds UK research into cosmology
Though compelling, the theory needed proof. At the initial rate of inflation, the universe needed to expand violently, a tiny sliver of space-time booming much faster and more aggressively than its surroundings – like a balloon. This baptism of fire for our universe would have to have left a massive signature on space-time itself – a wobble. A better way of putting it is to imagine space-time as a rather large elastic membrane that has been stretched out instantaneously by a violent explosion, leaving the elastic ringing like a bell. The ringing would would appear like a wave or a ripple in the elastic material.
Though the existence of gravitational waves was implied by the inflationary model, the closest we’ve come to finding proof of them was in 1989 when astronomers observed the time of arrival on Earth of light from binary pulsars (a pair of orbiting dead hyper-dense stars), finding that it was consistent with General Relativity’s predictions of gravitational radiation.
This is where the observations from the South Pole radio telescope come in. The experiment conducted there, named BICEP2 (Background Imaging of Cosmic Extragalactic Polarization), involves measuring the light polarisation of the cosmic microwave background (CMB), the radiation left over from the big bang. The light waves of this radiation have been stretched out so far that they have become longer wavelengths which today exist in the microwave region of the electromagnetic spectrum. This is the furthest into the spectrum that our technological capabilities currently permit us to look into, but it still provides a picture of a very, very early point in the universe’s history.
Early enough, in fact, that the BICEP researchers believe they are able to detect the existence of ancient gravitational waves by observing how the light is polarised there. Just as sunlight is scattered by atoms in the atmosphere, the light in the CMB is also scattered by atoms and electrons. Tiny fluctuations in these polarisations provide clues to conditions in the early universe. And according to the experiment’s co-leaders, they have found the type of light polarisation consistent with the presence of gravitational waves. This type of polarisation, called “B-modes“, manifests itself in a vortex-like, curly pattern in the CMB, which is supposed to represent the passage of gravitational waves.
“Finding this would be the most significant cosmological discovery in nearly two decades, and a huge triumph for physics. It’s like all our Christmases at once – I doubt many cosmologists will get much sleep tonight.”
Dr Chris Lintott, Astrophysicist at the University of Oxford
The research still needs to be verified of course. Rumors of the discovery leaked well before the announcement, generating considerable debate, as there is still a lot of skepticism that this kind of signal could be detected with confidence. Some scientists argue that not even the inflationary model can predict a gravitational wave as long and polarising enough to be detected by BICEP. In due time, we will know more about the acceptability of the discovery, however.
What is for sure is that this is an extremely exciting time to be a physicist… or a cosmologist… or a philosopher… or alive at all. With the recent confirmation of the Higgs boson, the capture of the CMB and now this new proof of inflation, there is a lot of new information to work with to solve the mysteries of the universe. As for me, I’m just pleased that I was alive when humans first peered into the very depths of the cosmos to get that little bit closer to finding out how it all began…
“Gravitational waves are a key prediction of Einstein’s General Relativity and their existence is still not conclusively confirmed. Even so, gravitational waves are getting second billing to what we will learn about the early universe: we will know that inflation is a compelling answer to cosmology’s initial-conditions problems, and humankind will have looked directly into the cosmic dawn.”
Professor Richard Easther, Head of Department of physics at the University of Auckland (read his blog here)