Russell Stannard in The Huffington Post [h/t: Namit Arora]:
[E]ven if the M-theory hypothesis is correct, does it in fact answer the question of “Why is there something rather than nothing?” It would certainly account for the existence of the world. But would it not raise a fresh question: “Where did M-theory come from? What is responsible for its existence?”
This brings us up against what one suspects is a fundamental limitation of the scientific enterprise. The job of science is to describe the world we find ourselves in — what it consists of, and how it operates. But it appears to fall short of explaining why we are presented with this kind of world rather than some other — or why there should be a world at all.
Indeed, there is cause to wonder whether science even gets as far as describing the world. For instance, what is the world made of? One might answer in terms of the electrons, protons, and neutrons that make up atoms. But what are electrons, protons and neutrons? Quantum physics shows how they are observed to behave like waves as they move about. But on reaching their destination and giving up their energy and momentum they behave like tiny particles. But how can something be both a spread out wave with humps and troughs, and at the same time be a tiny localized particle? This is the famous wave/particle paradox. It afflicts everything, including light.
The solution given by the Danish physicist Neils Bohr was that one has to stop trying to explain what something, such as an electron, is. Instead, we are confined to explaining how something behaves in the context of a certain kind of observation being made on it — whether we are observing it moving from one place to another (in which case the language of waves is appropriate), or alternatively observing it interacting on reaching its destination (requiring the language of particles).