One suggestion that he makes (and one that I would also tend to agree with) is that in a universe with 100 billion galaxies, each containing many hundreds of millions of stars, it is highly unlikely that planet Earth is the only place where life has evolved.
Not rocket science really - more a matter of common sense and logic!
According to Prof Hawking the only real challenge is in working out what the alien life forms might be like - from tiny microbes or little worms, through to something all together more advanced than mankind itself. And we should be warned he says as contact with alien life could spell disaster for the human race!
"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 American Indians"
He could have a point but let's hope not!