According to standard Big Bang model, our Universe started out very small and very hot. The so-called cosmic microwave background radiation (CMBR) that permeates the local Universe, astronomers believe, is a remnant glow from that infernal time. In theory, the temperature of the CMBR should increase steadily as researchers look back to earlier times. But recent measurements of the CMBR have focused on the microwave radiation near the Earth. Now new research, described today in the journal Nature, reveals the CMBR in a distant cloud, allowing astronomers to take the temperature of the young Universe for the first time. Their results provide strong support to the Big Bang theory.
Raghunathan Srianand of the Inter University Centre for Astronomy and Astrophysics in Pune, India, and his colleagues studied light from a far off quasar that had been absorbed by molecules in a gas cloud when the Universe was just a fifth of its current age. Some of the cloud's carbon atoms, they found, are in "fine-structured states"-- that is, they are slightly more energetic than the lowest energy states of carbon. Explaining such states requires that the cloud be surrounded by a warmer radiation field--one corresponding to a temperature between 6 and 14 degrees above absolute zero, as compared with the CMBR's present temperature of about 2.7 degrees. This, it turns out, accords well with theory's prediction of 9 degrees.
"The Big Bang theory has survived a crucial test," John Bahcall of the Institute for Advanced Study in Princeton, N.J., writes in a commentary accompanying the Nature report. "I am happy that the Big Bang theory passed this test, but it would have been more exciting if the theory had failed and we had to start looking for a new model of the evolution of the Universe.