“Aliens almost certainly exist but humans should avoid making contact, Professor Stephen Hawking has warned.
“In a series for the Discovery Channel the renowned astrophysicist said it was ‘perfectly rational’ to assume intelligent life exists elsewhere.
“But he warned that aliens might simply raid Earth for resources, then move on.
“‘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,’ he said.
“Prof Hawking thinks that, rather than actively trying to communicate with extra-terrestrials, humans should do everything possible to avoid contact.” [BBC Science]
I’d say two things in reply. First, human treatment of weaker cultures has improved steadily since the days of Columbus. Second, any aliens capable of visiting us – never mind invading – would almost certainly know we existed and would have been likely to have watched the rise of our civilisation.
Current human technology could send an unmanned probe to another star, if we were willing to invest billions in such a project. For now it is not worth doing: the last estimate I saw said it would take a thousand years to reach the Alpha Centauri system, our nearest neighbour. In another century or possibly sooner, we are almost certain to be able to send a much faster probe that would get there much sooner. But with what we have now, we can already see other planets out to dozens of light-years. In the next few years, better telescopes are likely to detect Earth-like planets.
If we can see them, they can see us. If we will soon be detecting Earth-like planets, then they can just as easily detect us. Any aliens within a thousand light-years who might theoretically reach Earth would already know that Earth had a flourishing biosphere. It is likely that they would also pick up radio signals as these crossed the intervening light-years.
It is also likely that there are many worlds without intelligent beings. Also many that have no complex life but could be adapted for civilisation, and with no ethical problems. Or artificial habitats in space – human technology might already be able to build them, there is just no need for now.