An extremely faint glow, a relic left over from the dawn of the universe, permeates all known space, between stars and galaxies. This is the cosmic microwave background (CMB), the first light that can travel through the universe when it cools enough about 380,000 years after the Big Bang to combine ions and electrons into atoms.
But now scientists have discovered something special about CMB. A new measurement technique has revealed hints of a reversal in light – something that could be a sign of a parity symmetry violation, hinting at physics outside the standard model.
According to the Standard Model of Physics, if we are to turn the universe as if it were a mirror image of itself, the laws of physics must be rigid. Subatomic interactions must occur in exactly the same way in the mirror as in the real universe. This is called parity symmetry.
As far as we have been able to measure so far, there is only one basic interaction that breaks the symmetry of parity; it is the weak interaction between subatomic particles that is responsible for radioactive decay. But finding another place where the symmetry of parity is broken can potentially lead us to a new physics outside the standard model.
And two physicists ̵
Polarization occurs when light is scattered, causing its waves to propagate at a certain orientation.
Reflective surfaces such as glass and water polarize light. You are probably familiar with polarized sunglasses designed to block certain orientations to reduce the amount of light reaching the eye.
Even water and particles in the atmosphere can scatter and polarize light; the rainbow is a good example of this.
The early universe, for the first 380,000 years, was so hot and dense that atoms could not exist. Protons and electrons flew around like ionized plasma, and the universe was opaque, like a thick smoky mist.
Only after the universe cooled enough for these protons and electrons to combine into neutral gas hydrogen atoms did space become clear, allowing photons to travel freely.
As the ionized plasma turns into a neutral gas, the photons are scattered by the electrons, causing the CMB to polarize. The polarization of CMB can tell us a lot about the universe. Especially if it is rotated at an angle.
This angle, described as β, can indicate a CMB interaction with dark matter or dark energy, the mysterious inner and outer forces that seem to dominate the universe but that we cannot directly detect.
“If dark matter or dark energy interacts with the light of the cosmic microwave background in a way that breaks the symmetry of parity, we can find its signature in the polarization data,” Minami explained.
The problem with identifying β with some certainty is in the technology we use to detect the polarization of CMB. The European Space Agency’s Planck satellite, which published its latest CMB observations in 2018, is equipped with polarization-sensitive detectors.
But unless you know exactly how these detectors are oriented toward the sky, it’s impossible to tell if what you’re looking at is actually β or a rotation in the detector that just looks like β.
The team’s technique relies on studying a different source of polarized light and comparing the two to extract the false signal.
“We have developed a new method for determining artificial rotation using polarized light emitted by dust in our Milky Way,” Minami said. “With this method, we have achieved an accuracy that is twice that of the previous work, and we can finally measure β.”
The sources of radiation from the Milky Way are much closer than CMB, so they are not affected by dark matter or dark energy. Therefore, any rotation in the polarization must be the result of rotation in the detector only.
CMB is affected by both β and artificial rotation – so if you subtract the artificial rotation observed in the sources of the Milky Way from CMB observations, you should only be left with β.
Using this technique, the team determined that β was not zero, with 99.2% certainty. This seems quite high, but it is still not quite enough to claim the discovery of new physics. This requires a confidence level of 99.99995 percent.
But the finding certainly shows that CMB is worth examining more closely.
“Clearly, we have not yet found conclusive evidence for new physics; higher statistical significance is needed to confirm this signal,” said astrophysicist Eichiro Komatsu of the Kavli Institute of Physics and Mathematics.
“But we’re excited because our new method has finally allowed us to make this ‘impossible’ measurement, which may point to a new physics.”
The study was published in Physical examination letters.