As the most recognizable face of the "Star Trek" franchise, actor William Shatner is probably used to fielding questions about his extraterrestrial beliefs. But in a 2010 interview for Montreal Gazette, the man who brought Captain Kirk of the Starship Enterprise to life explained why he thinks intelligent beings must be out there.
"There is no doubt that there is life out there; the mathematics of it lead you to that absolute conclusion. In my mind, there is no doubt that the universe teems — teems! — with life in all its forms."
Stephen Hawking has repeatedly warned that humans should be wary of contacting alien civilizations. In 2016, in a documentary called "Stephen Hawking's Favorite Places," the famed theoretical physicist said humanity may one day receive a signal from a potentially habitable alien world, such as Gliese 832c.
"But we should be wary of answering back," Hawking said in the 26-minute documentary. "Meeting an advanced civilization could be like Native Americans encountering Columbus. That didn't turn out so well."
That's not the first time Hawking has expressed such a concern. In 2015, he cautioned that visiting aliens may be in search of resources to plunder, as they roam the cosmos colonizing other worlds.
"Such advanced aliens would perhaps become nomads, looking to conquer and colonize whatever planets they can reach," he said in an interview with El País at the time.
Still, Hawking said it's not likely that humanity will find intelligent alien life in the next 20 years. "The probability is low, probably," said Hawking, who has amyotrophic lateral sclerosis (ALS) and is paralyzed, but "speaks" with the assistance of a computer.
During an appearance on the talk show "Late Night with Seth Myers," singer Demi Lovato insisted that aliens are real. "How self-centered would we be, as humans, to believe that we are the only living things in the universe?" she said.
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Denise Chow was the assistant managing editor at Live Science before moving to NBC News as a science reporter, where she focuses on general science and climate change. Before joining the Live Science team in 2013, she spent two years as a staff writer for Space.com, writing about rocket launches and covering NASA's final three space shuttle missions. A Canadian transplant, Denise has a bachelor's degree from the University of Toronto, and a master's degree in journalism from New York University.