Cosmological Big Bang Or Damp Squib?
There is a disturbance in the cosmological community as to whether ripples in the space-time continuum have actually been found. Two months ago scientists claimed to have found signs of gravitational waves from the first second of the universe, which if true would confirm the inflationary model of the universe. Some critics are now saying their work was flawed in a way that may invalidate it. However, the team that made the initial announcement are holding their ground, and discussion has got a little nasty.
Back in March a team using the Background Imaging of Cosmic Extragalactic Polarization (BICEP) detector at the South Pole released a study of the polarization of the cosmic background radiation (CMB for Cosmic Microwave Background). What they reported was consistent with the radiation being affected by a gravitational wave released from a surge in the expansion of the universe (referred to as inflation) an unimaginably short time after the Big Bang.
The news generated its own wave of excitement, including charming footage of one of inflationary theory’s inventors getting the news
and a handy demonstration using a towel, apple and ping pong ball.
However, the CMB is affected by many things. In order to get a picture of the influence from the dawn of time, the BICEP2 team had to remove polarization caused by dust within our own galaxy. In order to do this they used a map from the European Space Agency’s Plank telescope. The problem is that they may have misunderstood what the map really showed.
The BICEP team didn’t need to map the whole sky to find polarization. Instead they used an area 15° by 60°, pictured in the now famous image above. The area was deliberately chosen as being away from the galactic plane, in order to minimize distortion from within our galaxy it is not possible to avoid this entirely. As with other parts of the sky, the cosmic background is mixed with microwave emissions from other galaxies and from dust within our own galaxy.
According to Laboratory of theoretical physics, Orsay, physicist and blogger Adam Falkowski BICEP believed the map only represented the last of these, when in fact it was made up of the both effects from our own galaxy and from others.
If Falkowski is right, BICEP subtracted both sorts of interference, thinking they were only removing one, which meant they still thought they needed to take account of the influence of other galaxies. However, if these were included in the Planck data then BICEP effectively eliminated them twice. Since these other galaxies produce largely unpolarized microwave radiation they lower the average polarization of what we see. If their effect is taken out the polarization. Take it out twice and you end up with a map with a picture of more polarization than really exists.
BICEP also took their own measurements, but Falkowski says they only did this at one frequency, 150 GHz, and that higher frequencies would have been more appropriate in this situation.
The above discussion represents science working exactly as it should. A team make an announcement, it gets scrutinized. If it survives others’ attention it is added to the canon of human knowledge. If not it is hoped we learn something about how to do these experiments better in future.
However, two aspects reveal the way science sometimes falls short of its lofty goals. Falkowski claimed the BICEP2 team had admitted to a mistake. Harvard University’s John Kovac, principal investigator of the BICEP team has categorically denied it, telling New Scientist “We’ve done no such thing.” It’s unclear whether Falkowski is spreading false rumors or if BICEP know they are wrong but are refusing to publicly admit defeat, but either way someone is going to come out of this looking bad.
A further uncomfortable aspect is the reason why the problems, if real, might have arisen. Although the Planck data is necessary for BICEP2’s work, and is considered the most likely tool to confirm their findings, the team working on Planck are also to some extent BICEP2’s rivals. Planck chose not to share their data on local effects with BICEP, forcing the BICEP2 team to rely on a scan of a PDF map presented at a conference. Clement Pryke, a BICEP2 team member from the University of Minnesota told Science “It’s unclear what that plot shows.”
This is hardly the first time competing teams have delayed the advancement of science by failing to share their work. However, since the race to be the first to make great discoveries is one of the great motivators for scientific activity it is hard to see a way around this problem.
Meanwhile, the Planck team are expected to release their own results in October.