Simple But Challenging: The Universe According to Planck
ESA’s Planck satellite has delivered its first all-sky image of the Cosmic Microwave Background (CMB), bringing with it new challenges about our understanding of the origin and evolution of the cosmos. The image has provided the most precise picture of the early Universe so far.
For the most part, the data agree extremely well with the ‘standard model of cosmology’ and allow for a much improved measure of its parameters. In the standard model, the Universe is described as homogeneous and isotropic on very large scales, and cosmic structure is the result of the slow growth of tiny density fluctuations that arose immediately after the Big Bang. At the same time, the extraordinary quality of the Planck data reveals the presence of subtle anomalies in the CMB pattern that might challenge the very foundations of cosmology. The most serious anomaly is a deficit in the signal at large angular scales on the sky, which is about ten per cent weaker than the standard model would like it to be. Other anomalous traits that had been hinted at in the past – a significant discrepancy of the CMB signal as observed in the two opposite hemispheres of the sky and an abnormally large ‘cold spot’ – are confirmed with high confidence. Planck’s new image of the CMB suggests that some aspects of the standard model of cosmology may need a rethink, raising the possibility that the fabric of the cosmos, on the largest scales of the observable Universe, might be more complex than we think.