CUHK Research: Changing the world

Gravitational-wave Observatory (LIGO) detectors. Three international scientists who contributed decisively to the project were awarded the 2017 Nobel Prize in Physics. Professor Li is leading the only group in Hong Kong involved with the work of LIGO. “The LIGO and Virgo detectors are unique L-shaped interferometers that can measure things we did not think were possible. The groundbreaking detection of gravitational waves by these advanced detectors is a technological marvel, able to measure small changes in spacetime. The experiments involved more than 80 institutes around the world, and is a testimony of what humans can achieve when we work together across borders, languages and cultures.” Hearing the universe’s voice I n add i t i on , i t i s a l so cha l l eng i ng t o differentiate gravitational waves from noises. “We spent a lot of time trying to understand the source and doing calculations, hoping to find out what kinds of unique signals we expect from these waves,” says Professor Li. The breakthrough came in 2015 as scientists, for the first time, observed gravitational waves arriving at the Earth from colliding black holes in the distant universe. “The first day I joined CUHK was actually the day when the hints of detection appeared,” says Professor Li. The detection has opened a new window to the universe, revolutionising the study of the cosmos and its content. “Understanding the universe has been a persistent desire throughout the history of mankind,” says Professor Li. The universe’s darkness will never be observable with conven t i ona l a s t ronomy us i ng l i gh t . Gravitational waves bring scientists to better understanding the universe. “To me, the theory behind gravitational waves, that is Einstein’s general relativity, is one of the most beautiful theories in physics. By doing research in this seemingly mysterious field, I am confident it has a tremendous potential to inspire future generations in doing research in STEM sciences,” he adds. Interpreting the universe’s signals Following the discovery of gravitational waves, the CUHK team seeks to interpret interesting signs within. “The current challenge is to map out what is in the universe by observing it on a larger scale,” he notes. “Our next step is to extract signals carrying crucial sub-structures and extra information.” For instance, the team is looking into gravitational lensing where the signal itself gets deformed by a massive object between the source and the observer. By being able to disentangle that from the signal, our understanding of the universe can go beyond what is shown on detectors. “We really need gravitational waves as the avenue to bring us to the next stage of the understanding of the universe. I believe gravitational waves can broaden our understanding about the cosmos in the upcoming decades and centuries of mankind,” says Professor Li. “There is so much more to be done.” We really need gravitational waves as the avenue to bring us to the next stage of the understanding of the universe. 75