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.... If aliens visit us, the outcome would be much as when Columbus landed in America, which didn't turn out well for the Native Americans.
What a strange set of beliefs must motivate these claims... In the first place, the idea that we wouldn't want to meet a species like ourselves is close to incoherent. I for one have enjoyed meeting Africans, Americans, Europeans, Japanese and Chinese people, all of who belong to a genetic and cultural lineage quite distinct from my own. Yet I not only wanted to meet them, I enjoyed meeting them. Hawking's observation seems to rest on the assumption that we judge international relations by its worst historical instances. If we judge his own field of physics by a similar rubric, it is a murderous slayer of innocents and a poisoner of worlds. Surely a more balanced perspective is called for.
Furthermore, Hawking seems to believe that the ability to colonise interstellar space could be something accessible to creatures who might have used up all the resources at home. This, as Lynn Margulis has hinted at, is a rather odd perspective. Surely, any species which is going to survive long enough to develop the awesome technologies required to explore a galaxy must first master the problem of managing the resources of its home planet sensibly? Any species that does not has very little chance of making it further afield. Mary Midgley makes a similar point in more poetic terms, as she dismisses fears of “alien demons” as a preposterous distraction:
...the idea of space travel itself acts as a symbol for the storming of Heaven. Man, having “conquered” his own world, is supposed to rise up and conquer the sky as well, thus putting down all his rivals, divine as well as terrestrial. But if God is alive, will ray guns bother him? And if he is dead, why dress up in his clothes?
Hawking says if aliens reach us the result would be a colonial invasion... It is difficult to understand the huge tangled knot of assumptions that underlie this conclusion. The only thing we can say with any confidence about intelligent alien life is that we cannot know anything about it. We do not know if its chemistry would be carbon-based, and if so if it would be encoded upon DNA, or if it would be based on a different chemical substrate (or for that matter, a non-chemical substrate). We cannot even know if it could visit our planet and live, let alone if it might be interested in this world or could enter into any kind of relationship with us, colonial or otherwise.
We cannot rule out Hawking's claim. But neither can we rule out the possibility that the species best adapted to interstellar exploration is the one who perfects social or spiritual harmony, a claim I personally find marginally more plausible than the idea of successful intergalactic marauders who somehow manage to develop the ultra high tech equipment requisite for the job despite carelessly exhausting their homeworld. And in either case, the vastly more likely proposition is that we aren't going to meet alien life in anything like a time scale that could matter to us as this time, and that it might be more prudent to focus on the real problems we face right here, right now, on our own planet.
All that we know about alien life is that we know nothing at all about it. We know far more about life upon our own world, and our ability to remain here as inhabitants is far more urgently threatened by our own appalling attitudes than by putative alien raiders. Rather than being afraid of unstoppable space invaders, perhaps we should instead be concerned by what we will do to ourselves if we do not find a way to rein in our worst excesses.
With apologies to Dr. Hawking who was, after all, just giving his opinions in an interview.