Planck calls into question BICEP2 gravitational waves finding


Data released by the BICEP2 consortium shows the CMB from a patch of sky over the South Pole. The colours show slight temperature variations and the lines represent swirling patterns of light polarisation, the hallmarks of gravitational wave disturbances.
NSF/BICEP2 COLLABORATION/S PL

The European Space Agency’s Planck mission has called into question the dramatic announcement earlier this year that astronomers had found evidence of gravitational waves. The Planck scientists say the observation could be just an effect of space dust.

The announcement is a bitter blow to the scientists, led by Harvard astrophysicist John Kovac who used the Background Imaging of Cosmic Extragalactic Polarisation (BICEP2) telescope at the South Pole to make their observations.

Many, including respected physicist Paul Davies who wrote about the finding in Cosmos, had reservations about the discovery from the beginning.

But so dramatic was the apparent discovery of gravitational waves, first predicted by Einstein in 1916 as part of his Theory of General Relativity, that it captivated the scientific community worldwide.

Not only did the discovery appear to prove Einstein right but it provided the “smoking gun for inflation”, a 1980 refinement of the Big Bang theory.

The BICEP2 astronomers claimed to have seen the first evidence for the primordial “B-mode” polarisation of the cosmic microwave background (CMB) – effectively ripples that could be caused by gravitational waves, which squeeze and expand space as they expand.

But, in a process that raised some eyebrows, Kovac made his announcement before receiving vital data from Planck on space dust. And it now appears they might have underestimated how much they were looking at.

Doubts were first raised in June by Raphael Flauger, a researcher at Princeton's Institute for Advanced Study, who revealed the devil in the detail. He suggested the swirls, or ripples, may be caused by space dust looping the loop in the Milky Way’s magnetic field.

As we reported, he pointed out that dust – tiny particles ejected from supernovae and other material – can also polarise light and create swirly patterns.

The latest paper from the Planck team does not rule out that BICEP2 did pick up evidence of gravitational waves, but it points out that space dust alone could account for its finding.

Perhaps the more serious question is one of process and the blow to the credibility of science that a too-hasty release of data threatens to cause.

We cautioned about this issue back in June.

The problem was getting the right data on the cosmic dust in the first place. The Planck space telescope, which mapped the CMB from space and also looked at the effects of space dust - was the best source but its data had not yet been formally released. So the BICEP2 team got the next best thing. The Planck team had presented their preliminary results on a slide at a conference. The BICEP2 team extracted that preliminary data – “a valid approach”, according to Flauger. “To make progress, you have to either wait – which no one wants to do right now – or one has to be creative. And that’s what the BICEP2 team did.”

We must now seriously question whether Kovac would not have been better to wait until the full Planck data was revealed before making his announcement.

Bill condie 2014.png?ixlib=rails 2.1
Bill Condie is head of publishing at The Royal Institution of Australia and former publisher of Cosmos.
  1. https://beta.cosmosmagazine.com/physical-sciences/ripples-fabric-space-time
  2. https://beta.cosmosmagazine.com/physical-sciences/news-update-reviewers-claim-cmb-analysis-was-flawed
  3. http://lanl.arxiv.org/abs/1409.5738v1
  4. https://beta.cosmosmagazine.com/physical-sciences/news-update-reviewers-claim-cmb-analysis-was-flawed
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