On the night of Oct. 29th, 2016, Gravitational Wave - A New Window to Explore the Universe, the 15th session of the "New Worlds, New Horizons" Public Lecture series was held in the iconic Auditorium of Tsinghua University. The lecture was delivered by Professor Rana Adhikari, a member of the LIGO Science Collaboration (LSC) and a professor of Experimental Physics at the California Institute of Technology. The lecture attracted an audience of over 500 students and general public to admire the beauty of gravitational waves.
Beginning with several pictures of our universe in multi-wavelength and an introduction of the curvature of space-time, Prof. Adhikari discussed the first study on gravitational wave (GW) through the detection of energy loss in a binary pulsar, which was followed by a long journey to the direct detection of GW. The audience learned the principle of the Michelson Interferometer and the Laser Interferometric Gravitational-wave Observatory (LIGO). They also learned about the technical details of LIGO, including the control of its flexibility and vibration reduction by multiple stages of pendulum suspension, and efforts to go beyond the "standard" quantum limit by using the "squeezed light", and so on. The signals of the detected gravitational wave of two merging black holes and the future outlook for LIGO were also discussed.
The most striking part of the lecture was several vivid methods Prof. Adhikari used to illustrate gravitational wave. On explaining its propagation and the merging of black holes, Prof. Adhikari used live animations to make the physical concepts clear. To the delight of the audience, Prof. Adhikari demonstrated noises and the sound of real detection by whistling.
The talk aroused great interests and passions among the students and a myriad of questions were raised after the lecture. One student asked whether the wavelength of the laser changes when the gravitational wave signal passes through the detector, while others inquired about the design and technical structure of LIGO (for example, its arm length). Questions were also raised about the differences and similarities of detection techniques for ground-based and space facilities. One student also asked about the implication of GWs in real life. Prof. Adhikari answered these questions with patience and a sense of humor.
While gravitational wave is conceptually simple and beautiful, the speaker pointed out that it has taken generations of astronomers and physicists to actually detect the mysterious ripples of the space-time fabric in the cosmos. Having already spent around 20 years working in this intriguing field, Prof. Rana Adhikari concludes that the most exciting times are still ahead since we have only just detected the first pixel in the dynamic GW sky. In the future, it will enable us to probe the universe when it is only one second old, and answer a set of most fundamental questions of the cosmos and mankind, such as "Where do we come from?" and "Where are we going?"