After nearly a year of debate, it seems that the much heralded experimental evidence of inflationary physics was actually nothing more than dust. It is a bit of a disappointment for cosmologists, and especially for those who work in the field of cosmic inflation, but as with all of science the facts and the evidence must always take precedence over popular theories.

One year ago I wrote about an interesting new result from the BICEP experiment (original article), in which measurements of the polarization of the cosmic microwave background photons seemed to show primordial gravitational waves generated by a period of inflation during the first second of the Universe's existence. This proved a theory that has been developed by the theory community for thirty years, as well as providing a potential information on the nature of gravity at high energies and small spatial scales, and was met with much excitement. 

Then the rival experiment PLANCK countered the claim in September, with the suggestion that the BICEP team had misinterpreted the effects of dust particles in the Universe (original article). Their data showed a high level of interaction between these dust particles and microwave photons, and they claimed that no polarization from inflation had actually been observed.

Now a new set of data has been released which, in the true spirit of scientific inquiry and cooperation, was produced and analysed by the PLANCK and BICEP team work together. The BICEP experiment had focused on a 150GHz signal which is sensitive to the CMB, but which doesn't allow for studying the effects of dust. The PLANCK data covered nine different frequencies ranging from 30GHz to 350GHz, which allowed them to see how the polarization changes at different frequencies. In our galaxy (and probably others) the effects at 350GHz are more than twenty times stronger than at 150Ghz, so it can be used to map out where there is dust and its density. 

The final conclusion is that at least half of the signal that BICEP had reported was in fact dust. But that doesn't exclude inflation, and some of the BICEP and PLANCK data is still (possibly) the result of primordial gravitational waves. It does however exclude some of the more violent, high energy theories of inflation, and suggests that theories now focus on a smaller class of models of both inflation and quantum gravity.

The result is not as exciting as the one announced last year, but it is a tribute to the scientific process that rival teams quickly united to resolve their discrepancies, and to provide a transparent and open answer to this mystery.