Theoretical Physicist and Cosmologist Stephen Hawking has, once again, warned of the dangers associated with extraterrestrial life contacting Earth in a half-hour program on CuriosityStream, reports CNET. The renowned scientist has explained the reasoning behind his cautious outlook and it has to do with how things played out on Earth.

In the segment, titled Stephen Hawking’s Favorite Places, the scientist takes viewers to Gliese 832c—a potentially habitable Earth-like extrasolar planet located 16 light-years away—in a CGI spaceship. While passing the “super-Earth,” Hawking gives his take on alien life on the planet.

"If intelligent life has evolved (on Gliese 832c), we should be able to hear it," says Hawking of the planet, which is at least five times the mass of Earth. "One day we might receive a signal from a planet like this, but we should be wary of answering back. Meeting an advanced civilization could be like Native Americans encountering Columbus. That didn't turn out so well."

Gliese832c_phl_960 Located 16 light years away, exoplanet Gliese 832 c may be capable of hosting life. Photo: The Planetary Habitability Laboratory @ UPR Arecibo

Hawking’s pessimistic take on alien life is nothing new. In his 2010 Discovery Channel documentary, Stephen Hawking’s Universe, he explains the risk.

"I imagine they might exist in massive ships, having used up all the resources from their home planet,” said Hawking. “Such advanced aliens would perhaps become nomads, looking to conquer and colonize whatever planets they can reach. If so, it makes sense for them to exploit each new planet for material to build more spaceships so they could move on. Who knows what the limits would be?"

Ultimately, his views come from looking at the trajectory of intelligent life on Earth. According to Hawking, if a similar trajectory takes place between aliens and humans, then mankind will be the likely underdog.

"We don't know much about aliens, but we know about humans,” said Hawking. “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."

But that’s not to say Hawking is against looking for alien life. In fact, he launched a 10-year effort in 2015, funded by the Royal Society in London, to listen for broadcast signals from stars near Earth using powerful telescopes.

"Somewhere in the cosmos, perhaps, intelligent life may be watching these lights of ours, aware of what they mean,” said Hawking at the launch, reports the BBC. "Or do our lights wander a lifeless cosmos - unseen beacons, announcing that here, on one rock, the Universe discovered its existence. Either way, there is no bigger question. It's time to commit to finding the answer - to search for life beyond Earth. We are alive. We are intelligent. We must know."