0348 GMT February 29, 2020
Hawking made the prediction on April 12 during the Breakthrough Starshot announcement in New York City. At the news conference, Hawking, along with Russian billionaire investor Yuri Milner and a group of scientists, detailed a new project that aims to send a multitude of tiny, wafer-size spaceships into space to the neighboring star system Alpha Centauri, space.com wrote.
If these tiny spaceships travel at 20 percent the speed of light, they'll be able to reach Alpha Centauri in just 20 years, Milner said. Once there, the spacecraft will be able to do a one-hour flyby of Alpha Centauri and collect data that's impossible to gather from Earth, such as taking close-up photos of the star system, probing space dust molecules and measuring magnetic fields, said Avi Loeb, chairman of the Breakthrough Starshot Advisory Committee and a professor of science at Harvard University.
In addition to learning about space technology, the audience wanted to hear about aliens — specifically, when scientists might find them.
Hawking took questions from reporters in advance so that he would have time to prepare his answers. (Hawking, who has amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease, is paralyzed but ‘speaks’ with the assistance of a computer.)
Hawking said it's not likely that scientists will find intelligent alien life in the next 20 years. "The probability is low, probably," he said.
But the cosmologist did mention one caveat.
"The discoveries of the [NASA] Kepler mission suggest that there are billions of habitable planets in our galaxy alone," Hawking said. "There are at least a hundred billion galaxies in the visible universe, so it seems likely that there are others out there."
Hawking has famously predicted that intelligent aliens might threaten humankind. Indeed, when asked about what Earthlings should do if we come across intelligent alien life, he said, "We should hope that they don't find us."