The universe is not silent. It has a faint but persistent hum that pervades the cosmos, even in the absence of any detectable sources of sound. This hum, known as the cosmological background noise, is a relic of the early stages of the universe, when it was filled with hot plasma and sound waves.

The cosmological background noise is not audible to human ears, but it can be measured by sensitive instruments that detect tiny fluctuations in the cosmic microwave background (CMB), the radiation left over from the Big Bang. The CMB is a snapshot of the universe when it was about 380,000 years old, and it contains information about the primordial sound waves that propagated through the plasma.

For particularly regular pulsars, those pulses are as regular as, or more regular than, our best atomic clocks! Now a gravitational wave arrives. You might have seen animations of what gravitational waves do. If you make a circle out of freely floating particles, then a 4/

— Markus Pössel (@mpoessel) June 25, 2023

Physicists have been trying to detect the cosmological background noise for decades, but it has been elusive because of its extremely low amplitude and frequency. The noise is estimated to have a frequency of about 10^-16 Hertz, which is much lower than the lowest frequency that humans can hear, which is about 20 Hertz. The noise is also drowned out by other sources of noise in the universe, such as galaxies, stars, and black holes.

However, a team of physicists from the University of California, Berkeley, and Lawrence Berkeley National Laboratory has recently reported a breakthrough in detecting the cosmological background noise. They used data from the Planck satellite, which mapped the CMB with unprecedented precision from 2009 to 2013. They applied a novel statistical technique to filter out the noise from other sources and isolate the signal from the primordial sound waves.

The team found that the cosmological background noise has an amplitude of about 10^-18 times the CMB temperature fluctuations, which are already very small. This means that the noise is extremely faint, but still detectable with Planck’s data. The team also confirmed that the noise has a characteristic spectrum that matches the theoretical predictions based on the standard model of cosmology.

The detection of the cosmological background noise is a remarkable achievement that sheds new light on the early history of the universe. It also opens up new possibilities for testing alternative models of cosmology that may deviate from the standard model. The cosmological background noise is a new window into the secrets of the universe, and it may reveal more surprises in the future.