Einstein’s Struggles with Quantum Theory: A Reappraisal , Dipankar Home and Andrew Whitaker , Springer, New York, 2007. $149.00 (372 pp.). ISBN 978-0-387-71519-3
In 1986 John Stachel, founding editor of the ongoing series The Collected Papers of Albert Einstein (Princeton University Press, 1987), wrote the article “Einstein and the Quantum: Fifty Years of Struggle,” which also appeared later in his book Einstein from “B” to “Z” (Birkhäuser, 2002). He started with the following quote from a letter Einstein had written late in his life to his friend Michele Besso: “The whole fifty years of conscious brooding have not brought me nearer to the answer to the question ‘What are light quanta?’ Nowadays every scalawag believes that he knows what they are, but he deceives himself.”
More than 20 years and 10 volumes of Einstein’s collected papers later, I was expecting that a book with a title similar to Stachel’s article would offer an update on our current understanding of the physicist’s broodings on the quantum. Yet that is not what Einstein’s Struggles with Quantum Theory: A Reappraisal is about. Apart from a passing reference to the first volume of the collected papers, authors Dipankar Home, a professor of physics at Bose Institute in Kolkata, India, and Andrew Whitaker, a professor of physics at Queen’s University Belfast in Northern Ireland, make no use of the published volumes of Einstein’s papers and mention very little of the pertinent, specialized history-of-science literature on the subject. Nor did they do any research in the Albert Einstein Archives at the Hebrew University in Jerusalem. “Fifty years of conscious brooding” has left its traces in unpublished manuscripts, correspondence, and other documents, analysis of which would make for an interesting read. I should expect that such an account would put Einstein’s response to the physics of his time in a broader historical context. But the authors are not historians, and their focus is not on Einstein as a historical figure.
Nevertheless, despite the misleading first part of its title, the book is serious, competent, and most engaging. Its declared aim is a reappraisal of Einstein’s critical attitude toward quantum theory. The authors argue against the widely shared view that Einstein’s refusal to accept the orthodox Copenhagen interpretation is merely an expression of a stubborn unwillingness to accept the results of modern physical research. Quite to the contrary, they argue, the case can be made that much of the most interesting, cutting-edge research in quantum physics today vindicates Einstein’s critical insistence on questioning the conventional Copenhagen dogma. What they see as Einstein’s crucial legacy is mostly the famous Einstein-Podolsky-Rosen incompleteness argument.
Home and Whitaker also discuss some of his earlier work and especially the famous Einstein–Bohr debate. They agree with historians and philosophers of science who recently have been debunking the myth of the grand victory of Niels Bohr and his followers in their standoff with Einstein. The authors evaluate Einstein’s position on the basis of his published works and some of his published correspondence. Despite their not-so-much historical yet systematic interest, they give a fair characterization of his position, although their analysis of his realism as pragmatic seems excessively benign. A more detailed historical evaluation may have revealed his position to be more nuanced, one that also changed over time and was perhaps not always consistent. The authors’ historical claim that Einstein’s critique of quantum theory was justifiable does not derive from an assessment of the physics of Einstein’s day. It rests on identifying a line of development that leads from David Bohm and John Stewart Bell to today’s research in quantum information theory, quantum computation, quantum cryptography, and efforts to test quantum mechanical effects on mesoscopic and macroscopic scales. In fact, the book’s full strength unfolds in its later chapters, where the authors discuss recent developments in those fields in light of their earlier treatment of Einstein’s criticisms. A crucial observation emphasized by the authors is that the ubiquitous notion of entanglement traced back to Einstein’s earlier interventions is now being explored as a rich resource rather than as a stumbling block for the standard interpretation.
Home and Whitaker give expert overviews and brief characterizations of various nonstandard quantum interpretations, the development and current status of the field of quantum information theory, and attempts to bridge the quantum–classical divide. For the most part, they avoid equations. Nevertheless, the arguments require some prior knowledge of quantum theory. Each chapter offers many references to the relevant literature that will help students read further.
The reappraisal suggested in the book provides a fresh perspective on Einstein’s work in light of researchers’ current best understanding of quantum physics. It also justifies the authors’ passionate plea for an “open spirit of tolerance.” With their goals set between a rock and a hard place, between history and ongoing science, the authors have won my full support. I recommend Einstein’s Struggles with Quantum Theory to physicists who are interested in their past and to historians and philosophers who are curious about today’s quantum physics.
