The universe could just come into being out of nothing, Mr. Hawking suggested, as long as there are physical laws to mediate the process. I'm reluctant to disagree with the late Mr. Hawking because he truly was a genius, but geniuses often become ordinary thinkers when they step outside their rightful domain, which Mr. Hawking did in The Grand Design.
Early in the book he famously declared that, "Philosophy is dead," and that science no longer has need of it. He received a lot of criticism for this claim, not least because it is itself a philosophical assertion, but also because The Grand Design is filled with philosophical conjectures. For example, he speculates in the book about the existence of God which is clearly not a scientific, but rather a philosophical, musing.
Had Hawking been a bit less cavalier about philosophy he might've avoided the sloppy thinking involved in the statement that "Because there is a law such as gravity, the universe can and will create itself from nothing," an asseveration that suffers from several philosophical shortcomings.
First, if gravity, or merely the law of gravity, exists then that's not nothing. Physical laws are existing somethings, but where, exactly, do such laws exist before* there's a universe?
They can't exist in matter because there is no matter until there's a universe. They can only exist either as abstract "objects" or they exist as ideas in a mind. If they're abstractions they cannot have produced the universe because abstractions - like, say, numbers - can't produce anything. Indeed, physical laws have no creative power, they're simply descriptions of how matter and energy behave.
If, though, these physical laws exist as ideas in a mind it must be a mind that precedes or transcends the universe which means it's not material, spatial, nor temporal because neither matter nor space nor time exist until there's a universe. In other words, it's a mind which possesses at least some of the attributes of the immaterial, spaceless, atemporal transcendent God.
Second, the idea that anything, universes included, can somehow create themselves is incoherent. In order for something to create itself it has to exist before it exists which is nonsense. Pace Hawking and physicist Lawrence Krauss in his book A Universe from Nothing, if there was a "time" when there was literally nothing then there never could be anything now. Ex nihilo nihil fit (Out of nothing nothing comes) is one of the oldest principles in philosophy.
Folks like Hawking and Krauss are essentially asking us to choose between belief that God created the universe or the belief that physics created the universe, but it's a silly choice. It's almost like asking us to choose between the belief that Thomas Edison created the light bulb or that the laws of physics created the light bulb.
Celebrated physicist and author of a number of popular books on science, Paul Davies, falls into the same error. Davies writes,
There's no need to invoke anything supernatural in the origins of the universe or of life. I never liked the idea of divine tinkering: for me it is much more inspiring to believe that a set of mathematical laws can be so clever as to bring all these things into being.This makes no sense. The laws of mathematics are not "clever," they're not intelligent minds, and moreover they don't bring anything into being. If you have an apple in each hand the laws of mathematics tell you that you'll have two apples, but those laws don't put the apples in your hands, and they certainly don't bring the apples into being.
Stephen Hawking was, and the others are, very smart men, but very smart men sometimes say very foolish things, especially when they're trying to do away with God.
* Technically, it's inappropriate to use temporal prepositions like before and until when talking about the origin of the universe because time came into being with the universe. Even so, it's awkward not to use them so in this post I do.