Physicist recounts developments in gravitational waves discovery research
Ysin-Yu Chen spoke to the Brandeis Physics Department on Thursday about the discovery of gravitational waves and the future of gravitational research. Chen, who completed her Ph.D. at the University of Chicago and began postdoctoral work at Harvard University this past fall, is a member of the Laser Interferometer Gravitational-Wave Observatory.
The discovery of gravitational waves led to Nobel Prizes for researchers from three universities, including the Massachusetts Institute of Technology and California Technical School. Gravitational waves were predicted by Albert Einstein’s general theory of relativity, which states that all mass distorts the fabric of the universe, affecting the measurement of time and distance.
It often helps to visualize this fabric, called space-time, as a thin, elastic fabric, like a trampoline, which is distorted when heavy objects are placed on it. General relativity predicts that, just as pushing and pulling the trampoline can produce waves on its elastic surface, massive objects like black holes should be able to produce waves in space-time.
Researchers at LIGO measured the gravitational waves generated by two black holes orbiting each other 1.3 billion light-years away in February 2016, making headlines across the world. It was not until October 2017 that researchers measured gravitational waves from a different pair of equally heavy objects, Chen explained. The waves were produced by a pair of neutron stars, which are made of the densely packed nuclei of atoms. For a sense of scale, one teaspoon of a neutron star would weigh approximately 10 million tons.
Chen recounted the process of this more recent discovery in her lecture. Researchers’ first exposure to the measurement came from an automated phone alert sent by the observatory. As researchers learned more of the discovery from other parts of the world, their picture of the event became clearer, Chen explained.
For instance, at the Virgo interferometer, located near Pisa, Italy, researchers had almost no record of the event, which initially puzzled the physicists, according to Chen. After several hours, it became clear to them why. Chen explained that the Virgo detector has a “dead spot” when it measures waves that move in the same direction its arms point.
The LIGO researchers were able to deduce how the gravitational wave propagated and determined more of its characteristics from this. What first seemed like a problem became a useful tool, Chen noted.
Chen went on to explain the significance of the observation in measurements of the Hubble Constant, a variable that describes the rate at which the universe is expanding and accelerating.
Since the scientists were effectively measuring how two massive objects distorted the fabric of the universe, their data helped improve the precision of the constant, giving more insight into the nature of the universe, according to Chen.
The lecture concluded with Chen describing LIGO’s efforts to expand and construct more detectors, including plans to build another observatory in India and a detector currently under construction in Japan.