Aliens exist ?? But don't talk to them ?? Says Stephen Hawking ?

British theoretical physicist Stephen Hawking has warned of the dangers of attempting to contact extra-terrestrial life. One of the world's leading scientists, he says that aliens almost certainly exist but mankind should be doing everything they can to avoid contact.

"To my mathematical brain, the numbers alone make thinking about aliens perfectly rational," he said. "The real challenge is to work out what aliens might actually be like."

His views are expressed in a new documentary made for the Discovery Channel. In it he points out that the universe has more than 100 billion galaxies, each containing hundreds of millions of stars. In such circumstances, Earth is unlikely to be the only planet where life has evolved, Hawking claims.

While many forms of life may be little more than microbes, Hawking says a few life forms could be intelligent and pose a threat to the human race. 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," Hawking says.

"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," the scientist says. While there may be benign aliens out there, Hawkings says trying to make contact is "a little too risky".

It took three years to complete the documentary which was a major challenge as well as a triumph for 68 year old Hawking who is paralysed by motor neurone disease and has very limited powers of communication.

John Smithson, executive producer for Discovery, said, "He wanted to make a programme that was entertaining for a general audience as well as scientific and that’s a tough job, given the complexity of the ideas involved." 'Into The Universe with Stephen Hawking' started on the Discovery Channel yesterday [Sunday April 25]. The broadcaster has described the programme as a new kind of cosmology series.

"It takes the world's most famous scientific mind and sets it free, powered by the limitless possibilities of computer animation. Hawking gives us the ultimate guide to the universe, a ripping yarn based on real science, spanning the whole of space and time -- from the nature of the universe itself, to the chances of alien life, and the real possibility of time travel."