Stephen Hawking, 68, has long suffered from a motor neurone disease that has extremely limited his powers of communication and movement, but that has never stopped him from  making important contributions to scientific theory.  Hawking just finished up a three-year project, a TV series called Stephen Hawking's Universe, which will air on Sunday May 9 at 9 p.m. on the Discovery Channel.

In the show he will offer up some controversial assessments on extraterrestrial life and what it might be like.  

Hawking is a firm believer that alien life does exist.  The universe contains hundreds of billions of galaxies, each with hundreds of millions of stars, many which have been shown to have planets in orbit.  Numbers virtually guarantee that life has evolved elsewhere, Hawking believes.  He states, "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."

So what might these extraterrestrial species be like?  Hawking believes that most are likely "simple" species, similar to those that have evolved on Earth; ranging from microbes to land animals.

However, Hawking believes there is likely intelligent life out there.  And he's frightened by that possibility.

The aliens in Hawking's vision would be much like the malefic beasties in the blockbuster science-fiction flick Independence Day.  He describes, "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."

He says that humans should try to avoid alien contact as we colonize space.  He states that such contact would be "a little too risky".  What would result?  He states, "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."

In addition to his theories about vicious aliens, Hawking suggests that based on examples of life surviving on Earth in extreme environments, life could be found in unbelievable places, such as in the center of stars or even floating in interplanetary space.

Hawking's colleagues concur on this point.  Lord Martin Rees, a British royal astrophysicist, told his students in lecture earlier this year that humans might not be able to recognize or understand forms of life they stumble across in space.  He states, "I suspect there could be life and intelligence out there in forms we can’t conceive.  Just as a chimpanzee can’t understand quantum theory, it could be there are aspects of reality that are beyond the capacity of our brains."

How close could primitive life be?  Professor Brian Cox, University of Manchester's "rockstar physicist" suggests we look in our own solar backyard.  He says that Mars, Europa (a moon of Jupiter), and Titan (a moon of Saturn) are likely places to find it.