Why is there something rather than nothing?

'Even if there is only one possible unified theory, it is just a set of rules and equations. What is it that breathes fire into the equations and makes a universe for them to describe? The usual approach of science of constructing a mathematical model cannot answer the questions of why there should be a universe for the model to describe? Why does the universe go to all the bother of existing? Is the unified theory so compelling that it brings about its own existence? Or does it need a creator, and, if so, does he have any other effect on the universe? And who created him?'

(Stephen W. Hawking, A Brief History of Time: From the Big Bang to Black Holes, London 1988, p.174.)

Stephen Hawking is a scientist who recognises there is a distinction between questions which ask what exists in the universe and those that concern why the universe exists, even if his subsequent, and notorious, comment about knowing the mind of God is forgetful of this.