Gravitational waves: a big bungle?

Updated - November 17, 2021 04:35 am IST

Published - June 12, 2014 12:44 am IST

In this 2007 photo provided by Steffen Richter, the sun sets behind the BICEP2 telescope, foreground, and the South Pole Telescope in Antarctica.

In this 2007 photo provided by Steffen Richter, the sun sets behind the BICEP2 telescope, foreground, and the South Pole Telescope in Antarctica.

An announcement made earlier this year prior to publication, which was purported to be the cosmology world’s finding of the year, may well prove to be flawed, as viewed by two independent analyses.

This was the discovery of gravitational waves by a Harvard University group led by John Kovac, seen as an evidence for the theory of cosmic inflation (which is the concept that the cosmos ballooned in size during the first few instants after the big bang).

The problem has been pointed out in an article by Paul Steinhardt, published in the journal Nature. Announcement of these results seem premature now, as a new study, led by David Spergel of Princeton University, and another study by Seljak and Michael Mortonson, of University of California, Berkeley, raise doubts on their validity.

The Harvard group, working at BICEP2 (Background Imaging of Cosmic Extragalactic Polarisation) telescope, had reported that they had observed a twist in the polarisation of ancient light that goes back to the time of the big bang. This twist was seen as the evidence for gravitational waves (ripples in the fabric of space-time generated in the early universe, close to the big bang) which were predicted by Einstein.

On the other hand, the study led by David Spergel argues that this effect of twisting the polarisation of the light could be produced by dust which is present both within the Milky Way and outside it. Their contention is that ultrafine dust can absorb starlight and re-emit it as infrared or radio waves and because of their uneven shape, could end up twisting the light.

According to Spergel, the entire effect could be caused by dust alone and therefore Kovac’s group could not claim that they had made a definitive measurement of gravitational waves, and while the Harvard group had taken into account the effect of dust in polarising the light, they had seriously underestimated the effect of dust in the Milky Way.

The other study, points out another point of debate. In small spatial scales, “gravitational lensing,” a process by which light curves around massive objects in space, can have the same effect of twisting the polarisation of light.

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