Stephen Hawking on Alien Life, Extraterrestrials and the Possibility of UFOs Visiting Earth

Physicist Stephen Hawking died at his home in Cambridge, England, on Wednesday.

Hawking's earliest astrophysics work posited the existence of singularities, mathematically conforming black holes with Albert Einstein's general theory of relativity. Hawking established, along with Roger Penrose, the universe's origin as a singularity, i.e., a point in spacetime where traditional physical laws break down and gravity becomes infinite. His later work in quantum mechanics, inspired by collaboration with Soviet scientists Yakov Zel'dovich and Alexei Starobinsky, would mathematically indicate the finite entropy and evaporation of black holes as they emitted particles that came to be known as Hawking radiation. Though widely accepted as a breakthrough in theoretical physics, Hawking radiation and its resulting micro black holes have yet to be observed in experiments at CERN's Large Hadron Collider.

His work in theoretical astrophysics (and the 1988 publication of his bestselling book A Brief History of Time) made Hawking a celebrity—including appearances on Star Trek: The Next Generation, The Simpsons and Futurama—which allowed Hawking a prominent public platform for his beliefs outside of physics. An atheist, anti-war activist, BDS supporter and anti-capitalist, the overlap between Hawking's humanist politics and scientific interests found expression in his repeated public statements on the possibility of contact with extraterrestrial life.

Hawking took a conflicted position on alien life, at once promoting the search for extraterrestrial life and warning about the potential dangers of first contact with an alien species. His position on extraterrestrial life advocates two approaches: collecting intel and keeping as quiet as possible.

"There is no bigger question," Hawking said, while announcing his support for Breakthrough Listen, a $100 million program to search for alien communications via radio wave and visible light observations of 1 million nearby stars and 100 galactic centers. "It is time to commit to finding the answer, to search for life beyond Earth."

In 2010, Hawking worried what that answer would bring, describing the dangers of first contact with aliens in a Discovery Channel documentary. "If aliens visit us, the outcome would be much as when Columbus landed in America, which didn't turn out well for the Native Americans," Hawking says. "We only have to look at ourselves to see how intelligent life might develop into something we wouldn't want to meet."

"Such advanced aliens would perhaps become nomads, looking to conquer and colonize whatever planets they can reach," Hawking said in the documentary, Into the Universe with Stephen Hawking.

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Stephen Hawking speaks on stage during a Breakthrough Starshot press conference at One World Observatory in New York City on April 12, 2016. Breakthrough Starshot is one of a number of projects by the Breakthrough Initiative, who also organised Breakthrough Listen. Bryan Bedder/Stringer/Getty Images

Absent knowledge about alien life, Hawking urged documentary viewers to analogize their likely behavior to ours. Hawking noted that first encounters throughout our own history rarely begin with: "I'll pop the kettle on. Milk? Sugar?"

He would reiterate this theme in a later documentary. "One day, we might receive a signal from a planet like this," he says in Stephen Hawking's Favorite Places of the newly discovered world of Gliese 832c. "But we should be wary of answering back."

During the announcement for Breakthrough Listen, Hawking said: "We don't know much about aliens, but we know about humans. If you look at history, contact between humans and less intelligent organisms have often been disastrous from their point of view, and encounters between civilizations with advanced versus primitive technologies have gone badly for the less advanced. A civilization reading one of our messages could be billions of years ahead of us. If so, they will be vastly more powerful, and may not see us as any more valuable than we see bacteria."

While Hawking expresses near certainty that alien life exists in the universe, he does not believe aliens have visited Earth in UFOs or at any point in history. "Why hasn't the Earth been visited, and even colonised?" Hawking wrote on his official website. "I discount suggestions that UFOs contain beings from outer space. I think any visits by aliens, would be much more obvious, and probably also, much more unpleasant."

In the essay Hawking describes some of the possibilities for the universe's seeming silence, speculating that intelligence may be one of many possible evolutionary outcomes or, mostly darkly of all, the possibility that "intelligent life destroys itself."

"I very much hope it isn't true," Hawking wrote.