Professor Susan Scott was out shopping at the Boxing Day sales when she received a phone alert telling her that astronomical time and space had just been altered, and she couldn't tell anyone.

"We knew within 70 seconds of it happening that we had a very significant event. I just broke into this big smile," the professor of theoretical physics said.

Professor David McClelland and Professor Susan Scott at the ANU Centre for Gravitational Physics. Credit:Jay Cronan

At 2.39pm on December 26 last year, as most people were watching the first day of the test cricket or bargain shopping, gravitational waves caused by a black hole collision were detected for the second time.

"I was really excited," she said. "It was just so pleasing … to have this second event."