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Planck: Shining a light on the origin of the Universe

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Planck: Shining a light on the origin of the Universe



François Bouchet is a CNRS research director at the Paris Astrophysics Institute (IAP, UPMC/CNRS) and scientific co-manager of the HFI instrument, which is on board the Planck satellite. This is a project to uncover the origins of the Universe by observing light emitted 380,000 years after the Big Bang. Responsible for the global processing of hundreds of billions of data sent by the satellite, Bouchet revealed the first results of the mission.




What is the Planck mission and how did it start?


François Bouchet: In the early 20th century, we discovered the cosmic microwave background, the oldest emitted by the universe, which let us better understand its history.

In 1992, the COBE satellite announced one of the most important discoveries of the century: the detection of anisotropy of the cosmic black body, that is to say the background temperature of the sky changes depending on the direction of observation. But as we go further back in time, the Universe is hotter, denser and less evolved. The further we look into the distance, the more our exploration brings us to the origins of the Universe at a time when its structures (galaxies, galaxy clusters, etc.) are less developed: it turns out that the light from the bottom of sky was issued about 380,000 years after the Big Bang, which is 13.8 billion years ago. By measuring the background radiation of the sky, we see a portion of the Universe in a very primitive state.

To look at this light, Jean-Loup Puget, Jean-Michel Lamarre, Richard Gispert1 and I have worked to develop the Planck satellite project, which is much more accurate than its predecessor launched in 2001 by NASA, called the WMAP. In 1996, we were selected by the European Space Agency (ESA) after a first version of the project by the National Space Studies Centre (CNES ) was accepted. It was a little less ambitious. In 2009, the Planck was launched from the Kourou base in French Guiana with the HFI instrument onboard. Its mission is to observe the sky’s background with the accuracy required to gather all the information contained in its radiation.


How have you analyzed the data and what do they reveal?


F.B : The satellite scanned the sky for 30 months, regularly sending valuable observations for processing stored in the basement of the IPA. The HFI instrument, managed by France, reached the end of its lifecycle in January after sending more than 800 billion points of measurement. The results announced in March correspond to a first analysis of half of the measuring points. During this process, we have transformed this flood of data into six maps, showing the intensity of the radiation in different colors corresponding to different wavelengths. The other instrument on the Planck provided three additional cards, which are useful for certain analyzes. We pulled the sky’s background temperature chart, whose texture revealed certain important cosmological parameters. Two parameters describe the creation of the Universe: one shows the rate of expansion of the Universe and the other the influence of the first stars. Finally, two other parameters provided information about the physical mechanisms that led to the anisotropy, providing unique information about what happened in the first moments of the Universe. Indeed, the best explanation we now have makes reference to an inflationary phase, in which the quantum vacuum fluctuations initiated the growth of structures. In other words, we must look at that first fraction of a second behind the development of complexity in the Universe: we are born from a void! 


The first data are well described by the theory of the Big Bang and inflation.


Will these results challenge current understanding of the Universe?


F.B : The Planck satellite observations have some surprises. The Universe's expansion rate is slower than previously thought, and the Universe is a little older. On the other hand, the satellite’s information slightly changes the composition of the universe, with a little less dark energy and a bit more dark matter. Many models of the generation of primordial lumps have been eliminated. Planck also raises questions in terms of galaxy clusters for which we do not currently have answers. More fundamentally, we also found a number of anomalies, whose existence is unlikely within the minimum theoretical framework, especially the larger angular scales of the map.


Coincidence or not, we hope that the results of the second half of the data will bring further clarification. Who knows, a new physics could possibly emerge. That's all we can say at the end of this first analysis. In any case, the dream that began in 1992 is now widespread because we achieved our most optimistic forecasts. We will focus in particular on the analysis of light polarization (electric and magnetic behavior of vectors in the spread of a light wave), which may justify the construction of a new instrument and several generations of UPMC students will be able to dream of bringing new information to this topic!





The CMB map achieved thanks to the Planck satellite data.

Credits: ESA - Planck Collaboration.











(1)Jean-Loup Puget is a research director at the CNRS and Director of the Space Astrophysics Institute (IAS).

Jean-Michel Lamarre is a research director at the CNRS and head of the instrumental part of the Planck project.

Richard Gispert was a CNRS research director at the Institute of Space Astrophysics at Orsay.


Crédits photo : Pierre Kitmacher - UPMC


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