April 01, 2013
Cosmologists are thrilled with the new map of the cosmic microwave background (CMB) generated by Europe's Planck spaceborne observatory, not because it has completely validated the so-called standard model of cosmology, but because it has not. The most accurate map yet of the Big Bang's echo reveals some unexplained anomalies, which are the fuel of scientific advances.
“The fact that Planck has made such a significant detection of these anomalies erases any doubts about their reality,” states Paolo Natoli of the University of Ferrara, Italy. “They are real and we have to look for a credible explanation.”
Just as Copernicus, Kepler and Galileo moved the Earth out of the center of the sky, with improved observations and better measuring tools such as the telescope, improved measurements of the CMB from space are refining our view of just how—or at least when—all that stuff filled up the sky in the first place.
Using the Hubble Space Telescope, astronomers had calculated that the universe appeared 13.7 billion years ago. Now, based on the most accurate measurements yet of the tiny temperature fluctuations in the CMB by the Planck instruments, that age has been pushed back 100 million years. The universe isn't expanding as rapidly as was thought on the basis of Hubble data, which also means there is less of the mysterious dark energy than was thought to be accelerating that expansion at a particular pace. The Planck data also show there is more matter—normal and dark—than was calculated from Hubble data.
In its first 15.5 months of operation, Planck has validated and tipped the standard model, which holds that the universe has very similar properties everywhere, at very large scales, and that it has maintained those properties in every direction as it has expanded.
Planck scientists have been surprised by the disconnect between the CMB temperatures that the standard model predicts should be coming from the smaller-scale structures Planck has mapped, and by an asymmetry in average CMB temperatures across the sky. The Planck measurements also have confirmed there is a cold spot in the CMB that is much larger than the standard model would allow, a suspicion raised by earlier CMB measurements and now confirmed as more than an artifact of the instruments.
Planck's High Frequency Instrument and Low Frequency Instrument collect microwave and radio wavelengths to map temperature variations in the CMB across the sky (inset). That light originated 380,000 years after the Big Bang (illustration), when the primordial protons and electrons joined to form hydrogen atoms as the temperature fell below 2,700C. Now it averages 2.7K—barely above absolute zero. The instruments are sensitive enough to measure tiny differences across space in that temperature region.