The first light emitted after the Big Bang is still all around us. We can’t see it with our own eyes because the expansion of the universe has stretched the photons into the microwave portion of the electromagnetic spectrum. But it is there, and using telescopes we have studied it in detail.
The most accurate measurement of the Cosmic Microwave Background (CMB) radiation, which this light is called, was taken by the European Space Agency’s telescope, Planck. It produced exquisite measurements – a temperature map of the universe – but also gave us something of a puzzle. Certain regions of this map suggested the presence of anomalies in the universe. Anomalies that we could not explain with current theories.
The anomalies could either be statistical flukes, due to rare fluctuations in the CMB, or they could be hinting at new physics beyond the standard model of cosmology. Researchers haven’t got a new CMB map to study but they cleverly reanalyzed the data to produce a new one, focusing on the polarization of light.
Polarization is a property of light, related to how the electromagnetic field oscillates. Many phenomena can affect the polarization of photons, so by studying it, researchers can work out more of the properties of the early universe. Their findings, reported in Astronomy & Astrophysics, revealed that the polarization data doesn’t show any significant traces of anomalies.
That doesn’t mean that the anomalies are not there, just that this latest map couldn’t confirm or deny their origin. But if they are real physical effects, then there are constraints to these anomalies, meaning we can rule out some hypotheses.
“We said at the time of the first release that Planck would be testing the anomalies using its polarisation data. The first set of polarisation maps which are clean enough for this purpose were released in 2018, now we have the results,” Krzysztof M. Górski, one of the authors of the new paper, from the Jet Propulsion Laboratory, said in a statement.
According to the CMB map, regions are hotter or colder depending on the amount of matter that was present there when it was emitted 380,000 years after the Big Bang. The map at large scale is 10 percent weaker than expected and it has a curious feature known as the cold spot.
Further analysis of the Planck data is unlikely to produce an answer on the origin of the anomalies. A dedicated mission designed to study the CMB polarization is in the planning phase but it is still 10 to 15 years into the future.