Where did Hawkins get his science acccredition on to be considered an expert on "the meaning of life"?

'To understand the universe at the deepest level, we need to know not only how the universe behaves, but why. Why is there something rather than nothing? Why do we exist? Why this particular set of laws and not some other?

This is the Ultimate Question of Life, the Universe and Everything. We shall attempt to answer it in this book. Unlike the answer given in The Hitchhiker's Guide to the Galaxy, ours won't be simply "42".'

Stephen Hawking, The Grand Design, 2011.