Introducing "model-dependent realism"
Having declared that "philosophy is dead", the authors unwittingly develop a theory familiar to philosophers since the 1980s, namely "perspectivalism". This radical theory holds that there doesn't exist, even in principle, a single comprehensive theory of the universe. Instead, science offers many incomplete windows onto a common reality, one no more "true" than another. In the authors' hands this position bleeds into an alarming anti-realism: not only does science fail to provide a single description of reality, they say, there is no theory-independent reality at all. If either stance is correct, one shouldn't expect to find a final unifying theory like M-theory - only a bunch of separate and sometimes overlapping windows.
I get that measuring things we can't actually perceive is hard, but isn't it premature to declare "we'll never know how reality works?"
Nevermind the admission that we don't really understand what's going on around us - we can still make grand proclamations about the origins of the universe!
M-theory in either sense is far from complete. But that doesn't stop the authors from asserting that it explains the mysteries of existence: why there is something rather than nothing, why this set of laws and not another, and why we exist at all. According to Hawking, enough is known about M-theory to see that God is not needed to answer these questions. Instead, string theory points to the existence of a multiverse, and this multiverse coupled with anthropic reasoning will suffice. Personally, I am doubtful.
Let's just hope that someday quantum physics will advance beyond the "we have no fucking idea, but this concept sounds elegant" stage.