I am getting a little behind schedule, so let us start by summarizing the last talk given yesterday by Jean-François Cardoso.


Big Bang, Big Data

Jean-François gave a wonderful introduction to the Planck mission. For those who don’t know Planck, it is in my opinion one of the most amazing feat of human intelligence in this century. Planck is an ESA satellite measuring with unprecendented precision the Cosmic Microwave Background (CMB). The CMB is in some sense the very first picture of the universe: right after the big bang, the universe was a very hot plasma of charged particles in which light could not travel freely – any photon was constantly scattered by interactions with these charged particles. But roughly after 380000 years, because of expansion, the universe cooled down to a critical temperature at which electrons and nuclei can bind into neutral atoms. At that point, photons were allowed to travel uninjured and we are still receiving them today in the form of a 3K microwave radition that was first detected by Penzas and Wilson in the 60s (although it had been predicted by Gamow I believe). This CMB is an amazingly important object because it carries a lot of information about the universe in its early stage, but also about what happened afterwards. Indeed, Jean-François explained that tiny temperature fluctuations (of only 10^-5 relative amplitude) in the CMB are related to little density inhomogeneities in the plasma that are responsible, by gravitational effects, for the formation of galaxies and the structure of the universe as we know it. Simply put, this is our cosmic DNA. There are many challenges in processing the CMB as explained by Cardoso. Jean-François focused on his work that aimed at using the various frequency bands of the observations to separate the CMB from various pesky foreground contamination. Jean-François used a source separation technique that works so well it is now the de facto technique used to create CMB maps. At the heart of the technique is the use of Fourier techniques to exploit the knowledge of the CMB power spectral density and separate it from contamination.