“Such scenes are speculative, but Hawking uses them to lead on to a serious point: that a few life forms could be intelligent and pose a threat. Hawking believes that contact with such a species could be devastating for humanity.

“He suggests that aliens might simply raid Earth for its resources and then move on: ‘We only have to look at ourselves to see how intelligent life might develop into something we wouldn’t want to meet. I imagine they might exist in massive ships, having used up all the resources from their home planet. Such advanced aliens would perhaps become nomads, looking to conquer and colonise whatever planets they can reach.’

“He concludes that trying to make contact with alien races is ‘a little too risky’. He said: ‘If aliens ever visit us, I think the outcome would be much as when Christopher Columbus first landed in America, which didn’t turn out very well for the Native Americans.'”

***
“1) In space, does anybody understand the security dilemma? In international relations, there is at least full information about who the other actors are and where they are located. Clearly, we lack this kind of information about the known universe.

“What Hawking is suggesting, however, is that efforts to collect such information
would in and of themselves be dangerous, because they would announce our presence to others. He might be right. But shouldn’t that risk be weighed against the cost of possessing a less robust early warning system? Isn’t it in Earth’s interests to enhance its intelligence-gathering activities?…

“3) Why would aliens go after the inhabited planets? Ceteris paribus, I’m assuming that aliens would prefer to strip-mine an uninhabited planet abundant with natural resources than an inhabited one. Three hundred planets have already been discovered in the Milky Way, and there are ‘likely many billions.’ Even rapacious aliens might try some of them first before looking at Earth, since we are mostly harmless.”