Did the Big Bang actually make a noise?

Modern cosmology tells us that the universe started 13.8 billion years ago as a point-like source [or singularity] that expanded, exponentially at first, into the cosmos we know today. It is perhaps not surprising that the Big Bang, the mother of all explosions, made a sound. We know this from measurements of the cosmic microwave background (CMB) made by the WMAP and Planck space missions.

Just after the Big Bang, all the matter in the universe was a super-hot plasma confined to the relatively small space of the emerging universe. In that closed space there were vibrations, sound waves of compression and rarefaction that propagated throughout the plasma. The sound persisted as the universe expanded. About 300,000 years after the

Big Bang, the cooling and expanding universe reached the point where electrically neutral hydrogen atoms could form from the free electrons and protons of the hot plasma. When this happened, light, which had been trapped by the electrical charges of the plasma, could pass freely through the neutral hydrogen, and the universe went from opaque to transparent. That released light, which reaches us today as microwaves, has recorded in it the sound waves that were present when it was formed.

In 2003 with WMAP data and again in 2013 with Planck data, I was able to take the sound-wave frequencies and render them as audible sound waves so that we can hear the

sound of the Big Bang with our own ears. John G. Cramer is Professor Emeritus in physics at the University of Washington (UW) in Seattle, United States