In a new short film from CuriosityStream, Stephen Hawking explores a beautiful, digitally rendered version of the universe and talks about the wondrous, weird variety of planets lurking outside of our galaxy.

Despite the extreme conditions, he says, there might be planets similar to ours, which means there may be life outside of humanity. But if they try to contact us, he warns us, we should think twice before answering.

It’s a paradoxical warning, considering Hawking is one of the minds behind Breakthrough Initiatives. Here’s how the Initiatives organization describes itself:

Circling one star among hundreds of billions, in one galaxy among a hundred billion more, in a Universe that is vast and expanding ever faster – perhaps toward infinity. In the granular details of daily life, it’s easy to forget that we live in a place of astonishing grandeur and mystery.

The Breakthrough Initiatives are a program of scientific and technological exploration, probing the big questions of life in the Universe: Are we alone? Are there habitable worlds in our galactic neighborhood? Can we make the great leap to the stars? And can we think and act together – as one world in the cosmos?

One of the Initiatives is Breakthrough Listening, which represents the largest attempt to date aimed at searching for contact from extraterrestrials. It surveys one million of the stars closest to Earth, as well as the center of the Milky Way and “the entire galactic plane”:

The instruments used are among the world’s most powerful. They are 50 times more sensitive than existing telescopes dedicated to the search for intelligence.

The radio surveys cover 10 times more of the sky than previous programs. They also cover at least 5 times more of the radio spectrum – and do it 100 times faster. They are sensitive enough to hear a common aircraft radar transmitting to us from any of the 1000 nearest stars.

That’s a lot of horsepower to find alien intelligence that we shouldn’t be contacting. Scientists have already made a couple attempts to send out messages to the stars, including the famous Arecibo message, Pioneer Plaque, and Golden Voyager Records, but according to Hawking, we should be listening and keeping our mouths shut, lest we attract hostile attention:

“We should be wary of answering back,” Stephen warned. “Meeting an advanced civilization could be like Native Americans encountering Columbus – that didn’t turn out so well.”

But even if we don’t speak with extraterrestrials, just discovering their signals and confirming their existence would change everything. Hawking says it would “force us to change” and “give up the idea that we are unique and start acting with more compassion and humility.”

The philosophical, cultural, and psychological ramifications of finding life on other worlds has been the bread and butter of science fiction for decades, with the most recent example being Cixin Liu’s The Three Body Problem. In the book, humanity ends up establishing contact with a race of extraterrestrials called the Trisolarans. Over the course of the book, Liu brings in real-world writings on the dangers of extraterrestrial contact, including Bill Mathers:

This was the theory of “contact as symbol” proposed by sociologist Bill Mathers of RAND Corporation in his book, The 100,000-Light-Year Iron Curtain: SETI Sociology. Mathers believed that contact with an alien civilization is only a symbol or a switch. Regardless of the content of the encounter, the results would be the same. Suppose that the nature of the contact is such that only the existence of extraterrestrial intelligence is confirmed, with no other substantive information-what Mathers called elementary contact. The impact would be magnified by the lens of human mass psychology and culture until it resulted in huge, substantive influences on the progress of civilization. If such contact were monopolized by one country or political force, the significance would be comparable to an overwhelming advantage in economic and military power.

At the heart of The Three Body Problem is the question of whether human society is worth saving at all. The book imagines a colonizing force coming to Earth to wipe out, not redeem, the human race, and many of the characters express the belief that humanity should be destroyed. Strangely enough, Hawking echoes the sentiment in the film: he believes that humanity’s greed and ignorance have spurred climate change and overpopulation, forces that will lead to our own destruction if left unchecked.

Another question is brought up in Michael Crichton’s classic sci-fi novel The Andromeda Strain, which deals with a constantly changing bacteria that comes to Earth in a meteorite. Crichton draws attention to the limits of our imagination when it comes to our conception of extraterrestrials by describing a series of exercises in which people were asked to draw what they thought aliens might look like. Inevitably, all the pictures resembled humans on some level: eyes, limbs, symmetrical bodies, etc. If aliens turned out to be unlike anything we could imagine, what does that say about estimating their motives?

Scientists and sci-fi fans alike would love for the first words from extraterrestrials to be “We come in peace,” but the danger, as Hawking sees it, lies in rushing into the unknown and opening a door we can never shut again.