Study in darkness shedding light on cosmos

A 20,000-metric-ton sphere, filled with liquid and submerged in a 12-story-tall tank 700 meters below the ground in South China, is being used by scientists to study the mysteries of the universe and how our world first came into being.

The Jiangmen Underground Neutrino Observatory, known as JUNO for short, is located in Jiangmen, Guangdong province, and is tasked with detecting neutrinos, one of the fundamental particles that make up the universe and that are key to scientists understanding it.

Since they were first detected in 1956, neutrinos have been the most challenging particles to study, and significant breakthroughs in neutrino research have been associated with four Nobel Prizes in Physics.

As a neutral elementary particle, neutrinos hardly interact with other matter, making their detection extremely difficult, earning them the nickname "ghost particles".

Neutrinos are everywhere, however, with billions passing through our bodies every second. They move super fast, too, as scientists predict that even a massive entity like Earth can be traversed by neutrinos in just 0.04 seconds.

During the Big Bang, countless neutrinos were generated within the first second, carrying information about the universe earlier than light, scientists say.

"The primary scientific goal of JUNO is to measure the neutrino mass hierarchy and oscillation parameters, which will play a crucial role in testing supernova explosion mechanisms, exploring the origins and evolution of the universe, and discovering new physical phenomena," said Wang Yifang, former director of the Institute of High Energy Physics at the Chinese Academy of Sciences.

Wang said the birth of neutrinos is often related to extreme events in the universe such as the Big Bang, supernova explosions, neutron star mergers and black hole eruptions, with high-energy neutrinos mainly originating from collisions between cosmic rays and dust or gas.

Although neutrinos have existed since the early universe, it wasn't until 1930 that scientists proposed the hypothesis of their existence. It took another 26 years for physicists to experiment with a nuclear reactor and detect the presence of neutrinos.

The plethora of neutrinos remains a mystery to this day. Whether they are massless or have mass directly impacts the evolution laws of the universe, scientists say.

In 2007, China began constructing the Daya Bay Reactor Neutrino Experiment. In 2012, the experiment discovered the third oscillation mode of neutrinos, praised by the international particle physics community as "opening the door to future neutrino physics research" and cementing China's important position in global neutrino research, Wang said.

Neutrino oscillation is a quantum mechanical phenomenon accompanying the generation of neutrinos and is a crucial basis for detecting neutrino mass.