"The Grand Design" by Hawking and Mlodinow

I have just finished reading The Grand Design, by Stephen Hawking and Leonard Mlodinow (New York:  Random House).  The book was originally published in 2010, and I acquired a glossy-paged edition in 2013, but it sat on my shelf unread, until a few months ago.  I have been meaning to read it for a long time.  Hawking died in 2018, so this book belongs to the final decade of his career, and I regret not getting to it until long after his passing.

Sadly, since the book was published, both authors (as well as many, many top physicists) have been associated with Jeffrey Epstein.  However as far as can be determined at this time, any allegations of improper or illegal conduct by either Hawking or Mlodinow have not been substantiated.  

On to the book itself.  Much of it is science popularization, and though I am conversant in the more familiar parts of physics exposited, the book did clarify a couple things for me, which I appreciated.  For example, I have often been confused by the use of the term "effective theory" in physics, and the book explained it in layman's terms.

The important point made by the book is a strong endorsement of supersymmetry and M-theory.  On the final page, the authors write that "M-theory is the only candidate for a complete theory of the universe"(italics original).  They also advocate the multiverse concept, and the strong anthropic principle.  Along with these, they present a metaphysical principle, "model-dependent realism", which superficially appears to be a hybrid of instrumentalism and realism.  However, I'm not sure if you can really eat your cake and have it too.  The principle appears to be crafted specifically to accommodate M-theory, which is actually an infinite number of theories, each with its own domain of applicability, though where the domains overlap, the theories make the same predictions.  I don't see what is realist about "model-dependent realism"; it appears to me to be a variant of instrumentalism.

A key passage is this (p. 58):

Regarding the laws that govern the universe, what we can say is this:  There seems to be no single mathematical model or theory that can describe every aspect of the universe.  Instead...there seems to be the network of theories called M-theory.  Each theory in the M-theory network is good at describing phenomena within a certain range.  Wherever their ranges overlap, the various theories in the network agree, so they can all be said to be parts of the same theory.  But no single theory within the network can describe every aspect of the universe--all the forces of nature, the particles that feel those forces, and the framework of space and time in which it all plays out.  Though this situation does not fulfill the traditional physicist's dream of a single unified theory, it is acceptable within the framework of model-dependent realism.

Later, they write (p. 143):  "We seem to be at a critical point in the history of science, in which we must alter our conception of goals and of what makes a physical theory acceptable". 

I am glad that I read this book after I read Jim Baggott's Farewell to Reality, which was published in 2013 (by Pegasus Books), and which I acquired less than a year after acquiring The Grand Design.  I read it within a year, and reviewed it on this blog in 2014.  In the decade since, I think it is fair to say that empirical evidence for supersymmetry has not yet been found, though back then, expectations were high that such evidence would be found within a decade.  This has weakened the case for The Grand Design and strengthened the critique given by Baggott.  Indeed, Baggott uses the phrase "Grand Delusion", which sounds like direct mockery of The Grand Design.  

On balance, reading The Grand Design was not a waste of my time.  It was important for me to know the views of one of the greatest physicists of my lifetime, and I did learn a few things.  However I am doubtful about its main conclusions, though I have a benefit of hindsight -- 15 years of physics progress since the book was published -- to reinforce my doubts.  If you're interested, don't let me stop you from reading The Grand Design, but if you do, do yourself the favor of also reading Baggott's Farewell to Reality in conjunction, to get a more balanced perspective.