Inflation flexes its biceps

Last week saw the announcement of a major discovery in Physics. Researchers at the Harvard Smithsonian Center for Astrophysics announced the discovery of the signature of gravitational waves in studies of the polarisation of the cosmic wave background data registered at the  Background Imaging of Cosmic Extragalactic Polarization 2 (Bicep2) experiment at the South Pole. The observations are also consist with scenarios called `inflation', which postulate that the universe underwent rapid expansion shortly after its creation in the big bang. The scenario goes as follows: gravitational waves are created due to quantum fluctuations in the structure of space time, right after the big bang. These were magnified to observable levels due to the rapid expansion that occurred during the inflationary epoch and imposed their signature on the cosmic microwave background in the form of a characteristic polarisation pattern. The BICEP2 experiment observed a distinctive twisting pattern called a curl or B-mode in the polarisation of the cosmic microwave background. Such a pattern had been observed before due to the effect of gravitational lensing (a warping of light due to the presence of nearby massive objects) but  this effect has been ruled out here. Measurements also indicate that the contribution of the gravitational waves to the signal is quite large compared to the contributions of the density fluctuations, increasing confidence in the reliability of the discovery. However, the cautious look forward to support of this discovery from other experiments, such as those carried out by the Planck satellite.

The excitement generated by the discovery is comparable to the excitement generated by the discovery of the cosmic microwave background by Penzias and Wilson, even though indirect evidence of gravitational waves has been obtained before in measurements from pulsars, and even resulted in the 1993 Nobel prize. This discovery supports the inflationary models of cosmology first proposed in the 1980-s by Alan Guth, Linde and others, and further analysis of the data may be able to support some inflationary models, and rule out others, and will keep astronomers and cosmologists busy and happy for several years!

This blog post is by Neelima Gupte and Sumathi Rao.