I understand that. I just don't understand why he feels the need to start making these unscientific speculations about whether God does or does exist or whether aliens do or don't exist.
I personally think it's unfortunate that the publicity about his book is almost entirely focused on 'Hawking doesn't believe in god' instead of areas such as his improved thought process on the unified field theory.
Wiser theologians should take a step back, bring out that age old trick, and inquire "ah... but who created gravity?"
The problem with an infinite regress is that it's, um, infinite.
It sounds like Hawking is trying to refute the claim that everything that exists must have a creator. That's the claim which allows the snooty "who created gravity" response, and also leads to the self-defeating infinite regress. Whether you believe in a creator or not, you're better off without that argument.