Only five percent of the universe is currently known to the human race. According to scientists from NASA, 68 percent of the universe is dark energy and 27 percent is dark matter – both invisible to human eye, and so far undetected. In southwest China's Liangshan Yi Autonomous Prefecture, the Yalong River flows in scenic valleys. Inside one of the mountains – the unknown awaits, to be found.

It's a 10-minute drive in the tunnels before we can reach the Jinping Underground Laboratory, where China's dark matter experiment is taking place. The tunnels were once dug by the local hydropower company for its employees' commute. It's now a near-perfect location for dark matter research.

What is dark matter really? Dark matter is physics' Holy Grail. Scientists around the world are racing to find evidence that might change the existing understanding of physics.

About 2,400 meters below the Jinping Mountain, scientists from China's top universities are working around the clock. A lot of the researches here are classified and very hard to understand for laymen.  

Xiao Xiang, an associate professor from China's Sun Yat-sen University, is leading a team participating in the PandaX experiment inside the mountain's tunnels.

PandaX is short for Particle and Astrophysical Xenon TPC. It is a series of experimental projects that utilizes Xenon detectors to search for elusive dark matter particles. The experiment involves several top Chinese universities and also those from around the world.

"Dark matter is a kind of non-luminous particle that is blackened out from astronomical observation. Scientists observed the movement and speed of galaxies in the universe, and found that the mass of these observable substances in the universe could not provide such great gravity to enable the galaxies to move so fast," said Xiao.

Xiao has been studying dark matter for over a decade. He told me the reason he chose this path is that he wanted to know more.

The primary evidence for dark matter is the calculations behind galaxy behavior. Scientists believe there must be unseen energy and matter that make movement of galaxies possible.

The reason why scientists here chose to work inside the mountains is to reduce noise as much as possible. The Jinping Mountain is mainly marble – already low in radiation. But still, the metals in the soil break down and release radioactive radon gas. Walls in the tunnels have been treated to help reduce radiation that might affect research into dark matter.

"We adopted a special waterproof structure of ten layers to block moisture and radon gas. So, we are creating a low-radiation environment for the laboratory. All our materials are low-radiation materials," said Wang Wei, a project supervisor from China Station Construction.  

Wang oversees the construction of the second phase of the lab. One of the treatments the construction team used is liquid rubber. It is sprayed on and only needs four seconds to form. And the layer can last for 50 years.

The Jinping Underground Laboratory is now the world's deepest underground lab. The second phase of the Jinping Underground Lab will be completed in 2024. And the plan is to invite scientists from around the world for joint research into the unknown.

In the past decade, China has been increasing its focus on frontier sciences such as dark matter research, quantum technology and artificial intelligence. Investment into research and development more than doubled from $143 billion in 2012 to $388 billion. And it is still expanding.

China has made technological innovation a top priority, and believes through technological innovation, we can better understand humanity's existence and hence create a better life for all mankind.