Inflation of a different kind
BANG! And so the universe was born.
Edwin Hubble had first observed the expansion of the universe, leading to the hypothesis that the universe must have had a beginning, the so-called Big Bang. This was also predicted by General Relativity.
More recently, the Big Bang was confirmed by the COBE satellite experiment (1992), which had observed ripples in the Cosmic Microwave Background (CMB). Those ripples are responsible for the structures we observe in the universe today, and those observations earned George Smoot and John Mather the Nobel Prize in Physics in 2006. The CMB, the remnant of the Big Bang, was first observed in 1964 by Arno Penzias and Robert Wilson of Bell Labs quite accidentally in an experiment involving microwave reception, and that happy accident had earned them the 1978 Nobel Prize.
But what exactly happened immediately after the Big Bang?
In order to explain the universe as we now see it, as "flat, homogeneous, and isotropic", which basically means that it appears the same in every direction we look, Alan Guth in 1980 suggested that the universe expanded at a much faster rate than the speed of light. (Special Relativity asserts that nothing can proceed faster than light.) This 'inflation' occurred between 10-36 and 10-32 seconds immediately after the Big Bang. (To imagine how short a time scale that is, consider that 10-32 seconds is 0.(insert 31 zeros)1 seconds. Think of a blink of a blink of a blink of a blink of an eye - the time at which Inflation occurred is far, far, far quicker than that!
Normal expansion, which Hubble had observed and which continues to this day, began after Inflation. The universe could be thought of as the blowing up of a balloon. The Big Bang and Inflation phases would correspond to the long initial breath with the fast expansion of the balloon, with "normal expansion" being the subsequent breaths and slower expansions of the balloon.
The notion of Inflation, while a largely hypothetical scenario, has been accepted. Yet a new experiment, known as BICEP2 (Background Imagining of Cosmic Extragalactic Polarisation), now has claimed to have found evidence for Inflation.
BICEP2 is an experiment based in Antarctica, which is looking for polarisation in the CMB that could lead to new information about the origins of the universe. (Think of this as the microwave equivalent of looking at light through polarising sunglasses.)
The astronomers, headed by John Kovac of the Harvard-Smithsonian Centre for Astrophysics, and including researchers from Canada, the USA, UK, and Chile, have improved the resolution and sensitivity of the detection from previous measurements (the first measurement of the polarisation was in 2002 by the DASI experiment).
With this much-improved sensitivity, the team has claimed to have found evidence of gravitational waves in the primordial B-mode of the polarisation of the CMB, corresponding to Inflation. Gravitational waves are predicted also by General Relativity, as the "ringing" of the universe, much like the sound waves produced by the ringing of a bell.
The consequences of such a discovery are astounding. First, it would put the last piece in the puzzle in our understanding of how the universe began. Second, Inflation implies the existence of the "multiverse". The idea is that there are many universes, comprising the multiverse, of which ours is only one. Those universes, which were together prior to Inflation, forming as possible bubbles in spacetime, became separated as the result of Inflation.
The results are still preliminary, and the evidence has to go through the peer-review process, but if found to be correct, this will be as important as the CMB measurements from Penzias and Wilson, as well as the results from the COBE satellite.
The key word is "if". The results have to be independently verified by another experiment, first and foremost, if it is to pass the test of "reproducibility". (To give an analogous example, the Higgs announcement was the result of independent detection by both the ATLAS and CMS experiments at CERN.)
Neil Turok, the South African cosmologist who is the director of the Perimeter Institute in Canada (and son of Ben Turok), in an interview with Physics World (the industry magazine for the Institute of Physics, UK), has urged caution in accepting these results. Results from the Planck and WMAP telescopes suggest that the results from BICEP2 may be too large, and the data from those experiments must be reconciled. In fact, Turok suggested that if the results of Planck and BICEP2 agree, then those would represent significant evidence against Inflation. This view is also shared by astrophysicist Peter Coles (Sussex), in an interview with Physics World.
The problem is in precisely what may influence the polarisation of the primordial microwave photons from the CMB as detected by BICEP2. As those photons move through space on their way to Earth to be observed, their polarisation may change, depending on what they pass through. This "contamination" of the polarisation may be caused by gravitational lensing, as the photons are observed through galactic clusters, or the photons may be signals from galactic dust (synchrotron radiation). The BICEP2 team has ruled out synchrotron radiation, at a statistical significance of 2.3-sigma, which is an indication of how reliable the true signal is. Turok would prefer that the evidence be reflected in the 5-sigma limit. (One should note that the Higgs discovery was not made public until the 5-sigma limit was reached independently in both experiments.)
There is still much to be done in order to verify the results coming from BICEP2. If found to be correct, then the evolution of the universe as we understand it - Big Bang, Inflation, Normal Expansion - will be complete. If this smoking gun for the inflationary phase of the universe is to be verified, there can be no questions surrounding the findings of the experiment. Time will tell, and the physics community worldwide will be waiting with as much anticipation as that which greeted the discovery of the Higgs.
Professor Steven Karataglidis is a theoretical physicist working at the University of Johannesburg.