Stephen Hawking's warnings on Alien contact.

The universe, he points out, has 100 billion galaxies, each containing hundreds of millions of stars. In such a big place, Earth is unlikely to be the only planet where life has evolved.

To my mathematical brain, the numbers alone make thinking about aliens perfectly rational. The real challenge is to work out what aliens might actually be like. The answer will be the equivalent of microbes or simple animals — the sort of life that has dominated Earth for most of its history.

A few life forms could be intelligent and pose a threat. I believe that contact with such a species could be devastating for humanity.

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 colonize whatever planets they can reach.

Trying to make contact with alien races is “a little too risky”. 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.

Source : http://www.timesonline.co.uk/tol/news/science/space/article7107207.ece