Mr. Becker’s book is largely a historic narrative describing in great detail, the circumstances surrounding the development of the prevailing interpretation of QM—The Copenhagen Interpretation, alongside the stories of the many physicists that worked on the subject. As Mr. Becker points out, the Copenhagen interpretation is not a single viewpoint—there is no single accepted definition. But by and large it refers to an approach best summarized in the edict “Shut up and Calculate”—one that willfully chooses to ignore the validity of the question of reality in the absence of measurement. Albert Einstein was famously deeply uncomfortable with this line of thinking. 

What is Real? describes the history of how this interpretation came to hold sway, including the prevailing Logical Positivism movement/philosophy that Niels Bohr and other QM ‘Fathers’ were influenced by. The hegemony of the Copenhagen interpretation applied intense pressure on scientists everywhere to conform to its line of thinking and for a great while this made any attempts at alternative explanations, an exercise in career suicide. Despite this vitiating atmosphere, physicists like Bohm and Everett did make headway with plausible alternative theories, but these seldom received much attention from the QM cognoscenti—until recently at least—given the sway the Copenhagen proponents have had. The intellectual climate in America that prized practical success over theory also did not help.