Legendary physicist Stephen Hawking is a bit nervous about aliens. So much so that he is warning mankind to be wary about making contact with alien civilizations.

Surprisingly, Hawking is afraid of sort of the Hollywood stereotype of aliens: that they could be Viking-like invaders, roaming the universe and pillaging any civilization they find. That’s based on a new documentary currently streaming on CuriosityStream called “Stephen Hawking’s Favorite Places.”

Hawking warns that we may one day get a signal from another planet indicating a habitable alien world, but perhaps mankind shouldn’t be so quick to answer back. It could be like when the Native Americans welcomed Christopher Columbus to the New World, he said.

Of course, not everyone shares this view. After all, aliens capable of reaching Earth would surely at this point already know of Earth’s existence by now.

The statement reads. “In the 25-minute film, premiering exclusively on CuriosityStream, Hawking leads viewers in his own CGI spaceship (the S.S. Hawking) to five extraordinary locations across the cosmos as he shares his own story of inspiration, curiosity, perseverance and ambition. The journey starts fittingly at The Big Bang, the birthplace of time and space and to which Hawking has devoted the majority of his life’s work, exploring exactly how the Universe formed. From there, Hawking takes viewers deep into a super massive black hole, Sagittarius A, where he explains his theory of matter with a taste of his signature charm and wit, infused with inspiration and humor.”