Keio University Team Measures Ancient Cosmic Temperature, Confirming Big Bang Prediction

A Keio University team led by Tatsuya Kotani and Professor Tomoharu Oka measured the cosmic microwave background (CMB) temperature at redshift z = 0.89 (about 7 billion years ago) using ALMA data. They found 5.13 ± 0.06 K, about twice today's 2.7 K. This agrees with the Big Bang prediction that the universe cools as it expands. Published in The Astrophysical Journal, the work is the most precise measurement of this ancient temperature so far.

High-Precision ALMA Measurement

According to the paper, the team relied on historical evidence of the Atacama Large Millimeter/submillimeter Array (ALMA) to see a quasar (PKS1830211) that was very far away and whose radio emission had to traverse a galaxy on the way. The frequency absorption of molecules (especially hydrogen cyanide) in that galaxy placed marks that can be compared to a thermometer to measure the CMB. A CMB temperature of the form 5.13 +- 0.06 K at z = 0.89 was modeled by these absorption lines. It is the most accurate CMB measurement as of this epoch.

Confirming the Big Bang Model

The standard Big Bang theory predicts T ≃ 2.73*(1+z), which at z = 0.89 gives about 5.14 K, essentially in perfect agreement with the measured 5.13K. Keio researchers note the result “reinforces the predicted evolution of temperature over time” and provides a “stringent observational test” of the standard model. Observers comment that this agreement “reinforces confidence that our understanding of cosmological evolution is on solid ground.” In other words, the finding confirms a key Big Bang prediction: that as space expands, the universe cools predictably.