Despite Hawking’s extraordinary effort to find intelligent life in the Universe, he is one of the most outspoken critics of actually trying to communicate with them, an act that he says would potentially endanger humanity, because a distant alien civilisation might view us as inferior, weak, and perfect to conquer.
"If so, they will be vastly more powerful and may not see us as any more valuable than we see bacteria," he says in the film.
Hawking often uses the example of Columbus’ expedition to the America’s to describe what could happen if an advanced civilisation gets word of our existence, saying that that initial meeting "didn’t turn out so well".
Hawking’s warning is rooted in the idea that an alien civilisation, especially one that can pick up our signals and understand where they’re coming from, has the potential to be billions of years more advanced than us, making us an easy target to overthrow or invade.