From an almost perfect universe to the best of both worlds

While the light that our eyes can see is composed of small wavelengths – less than one-thousandth of a millimeter in length – the radiation that Planck detected was spreading over lengths of light. The waves are larger, from a few tenths of a millimeter to a few millimeters. More importantly, it was generated at the very beginning of the Universe

Collectively, this radiation is known as the Cosmic Microwave Background, or CMB. By measuring its tiny differences across the sky, Planck's image had the ability to tell us about the age, the expansion, the history and the content of the story. ;Universe. It was nothing less than the cosmic plan.

Astronomers knew what they hoped to see. Two NASA missions, COBE in the early 1990s and WMAP in the following decade, had already performed an analogous set of sky studies that resulted in similar images. But these images did not have the precision and sharpness of Planck.

The new view would show for the first time the imprint of the primordial Universe in minute detail. And if all was well,

If our model of the Universe was correct, then Planck would confirm it to unprecedented levels of precision. If Planck sent the scientists back to the drawing board, ESA's Planck mission swept the sky at microwave wavelengths to observe the cosmic microwave background, or CMB, which is the most visible light. Ancient. issued in the history of our Universe. Planck's data revealed an "almost perfect Universe": the standard description of a cosmos containing ordinary matter, cold dark matter and dark energy, populated with structures that had been seeded at the beginning of an inflationary expansion, is largely correct. some details remain to be solved. In other words: the best of both worlds. Credit: ESA / Planck Collaboration

When the image was revealed, the data had confirmed the model. The fit to our expectations was too good to draw any other conclusion: Planck had shown us an "almost perfect Universe". Why almost perfect? Because some anomalies remained, and that these would be the object of future researches.

Now, five years later, the Planck consortium has released its final version of the data, known as Legacy Data Publishing. The message remains the same and is even stronger.

"It's the most important legacy of Planck," says Jan Tauber, a scientist of the Planck project from ESA. "Until now, the standard model of cosmology has survived all tests, and Planck has made the measurements that show it."

All cosmological models are based on the theory of general relativity of Albert Einstein. To reconcile general relativistic equations with a wide range of observations, including the cosmic microwave background, the standard model of cosmology includes the action of two unknown components.

First, an attractive material, known as cold dark matter, which, unlike ordinary matter, does not interact with light. Secondly, a repulsive form of energy, known as black energy, which is driving the currently accelerated expansion of the Universe. They have been found to be essential components in explaining our cosmos in addition to the ordinary matter we know. But we do not yet know what these exotic components really are.

Planck was launched in 2009 and collected data until 2013. Its first release – which gave birth to the near-perfect Universe – was made in the spring of this year. It was based solely on the microwave microwave background radiation temperature, and used only the first two sky surveys of the mission.

The data also provided additional evidence of a very early phase of accelerated expansion, called inflation, in the first small fraction of a second in the history of the Universe, at the during which the seeds of all cosmic structures were sown. Producing a quantitative measure of the relative distribution of these primordial fluctuations, Planck provides the best confirmation ever obtained of the inflationary scenario

In addition to mapping the temperature of the cosmic microwave background across the sky with unprecedented accuracy, Planck also measured its polarization. which indicates if the light is vibrating in a preferred direction. The polarization of the cosmic microwave background bears an imprint of the last interaction between particles of radiation and matter in the early Universe, and as such contains additional information, all important, on the history of the cosmos . But it could also contain information on the very first moments of our Universe, and give us clues to understand its birth.

In 2015, a second release of data gathered all the data collected by the mission, eight surveys on the sky. He gave the temperature and the polarization, but came with a warning.

"We felt that the quality of some polarization data was not good enough to be used for cosmology," Jan says. He adds that – of course – that did not stop them from doing cosmology but that some conclusions at that time needed further confirmation and should therefore be treated with caution.

And that's the big change for this data version of 2018 Legacy. The Planck consortium has completed a new data processing. Most of the first signs calling for caution have disappeared. Scientists are now certain that temperature and polarization are accurately determined.

"We are now convinced that we can find a cosmological model based solely on temperature, only on polarization, and based on temperature and polarization." Reno Mandolesi, principal investigator of the LFI instrument on Planck at the University of Ferrara, Italy

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"Planck" puts Einstein to the test