16Comments
Two scientists claim to have found evidence of something evenly distributed throughout the universe polarizing the afterglow of the Big Bang. If the effect is real it will force a radical readjustment of many of the things physicists think they know, and possibly give us our first real insights into the nature of dark energy. For the moment, however, most cosmologists who have commented consider the evidence interesting, but not strong enough to get really excited.
Theoretical physicists have toyed with the idea of a quintessence, an exotic substance sort of like an updated version of the ether whose overthrow inspired Einstein's discovery of relativity. The quintessence is proposed to exist throughout the universe, rather than being clumped in galaxies like both visible and dark matter, and might be an explanation for dark energy.
Within galaxies, the effects of a quintessence would be almost impossible to spot, because everything else would overwhelm its influence. Consequently, a good place to look for it is in the cosmic microwave background (CMB) radiation, the ancient light left over from the Big Bang. Given the vast distance it has traveled to get to us, the CMB has had more opportunity to be affected by something evenly distributed through the universe than anything else we can study. Now a paper in Physical Review Letters claims to have found something is twisting the CMB, and dark energy might be it.
Astronomers have examined the CMB for signs of a change in the angle of polarization induced by anything it has passed in its travels, known as the cosmic birefringence angle (β). Under the standard model of particle physics β should be zero. If it's anything else it means something is twisting the CMB, the standard model needs reworking, and we might even have found dark energy.
CMB measurements have produced estimates of β that aren't zero, but with margins of error large enough that β=0 is a distinct possibility. An error in measurement well within expected uncertainties seems a much safer explanation than something that overthrows the standard model. However, Dr Yuto Minami of Japan's High Energy Accelerator Organization and Professor Eiichiro Komatsu of the Max Plank Institute for Astrophysics claim to have narrowed the uncertainties to the point where β=0 now falls outside them.
Minami and Komatsu correlated CMB measurements by the Plank Space Telescope with polarization from dust within our galaxy, for which β should be insignificant. This way they claim to have removed systematic errors in Plank's detecting devices (since these would apply to the local sources as well), halving the uncertainty in estimates of β in the process. As a result they claim a 99.2 percent confidence that β is not zero (their estimate is 0.35±0.14 degrees).
If it exists the quintessence would certainly take some explaining, and the most exciting possibility is that it is dark energy, the mysterious force pushing the universe to expand ever faster. Two decades after dark energy's existence was confirmed we've learned almost nothing more about what it is or how it behaves.
Professor Sean Carroll of the California Institute of Technology proposed using CMB polarization to test for quintessence in 1998. In response to Minami and Komatsu's work Carroll told Nature News if dark energy is a quintessence it will challenge our assumptions about it and “We’re back to a situation where we have zero idea about how the Universe is going to end.”
However, even the authors are cautious."It is clear that we have not found definitive evidence for new physics yet; higher statistical significance is needed to confirm this signal,” Prof. Komatsu said in a statement.
