Review of: Becker, Adam. What Is Real?: The Unfinished Quest for the Meaning of Quantum Physics, 2018.
The book is organized in three parts: Part I: A Tranquilizing Philosophy, Part II: Quantum Dissidents, and Part III The Great Enterprise. It also includes an Appendix that includes views via different interpretations regarding Wheeler’s Smoky Dragon experiment. The book begins with the history of the development of quantum theory from Schrödinger, von Neumann, Bohr, Einstein, Heisenberg, and others. Dissidents such as David Bohm are discussed as well as “the most profound discovery” of non-locality by J. Bell. Later Clauser, Aspect and Bertlemann are also discussed as well as the viewpoints of Everett, DeWitt, Zeilinger, and others.
Becker provides a well-written description of the Schrödinger-Cat problem as originally put forward by Schrödinger. Related issues such as Bell’s inequality are explained and intertwined with substantial and interesting history as well. The book is easy to read and has a nice flow. Several of the leading quantum measurement theories are described in laymen’s terms.
The book lacks a sufficiently detailed quantum analysis that is required to fully understand the quantum measurement problem to the point of beginning to conduct research. This incomplete picture leads to statements such as:
It’s certainly true that we’ll get the same answers when doing quantum-mechanical calculations whether we prefer the Copenhagen interpretation, the many-worlds interpretation, the pilot-wave interpretation, or anything else. Even alternatives to quantum physics, like spontaneous-collapse theories, will give the same answers in nearly every situation. (p. 283 Kindle Edition.)
But the devil is in the details, and this statement indicates to us that Becker, while understanding the basics of the problem as understood by many philosophers, does not have a complete understanding of the measurement problem. If one assumes that one knows what constitutes a measurement device, then it is correct that all theories will give the same result as the Copenhagen interpretation. We call this the philosophers’ measurement problem because (1) the problem is put into the realm of a philosophical problem and not a problem that will have any bearing on making new predictions, and (2) many (but not all) philosophers contend that in-fact this is the measurement problem. However, the QMP more generally is the problem that the Schrödinger predicted quantum state is different than encountered under measurement. Quantum mechanical calculations would yield an entangled state whereas a physical measurement theory would diverge from this and yield a product state. And as described in our book The Quantum Measurement Problem, these differences are experimentally distinguishable within the current Copenhagen formalism. The problem is that the current von Neumann theory, as it stands, assumes one knows a priori what a measurement device consists of. This allows the current theory to be self-consistent. The point is, that we do not currently know what physically constitutes a measurement device and if one removes the knowledge of what a measurement device consists of, the theory is no longer self-consistent. We call this problem, the physical measurement problem. The resolution of the physical measurement problem will necessarily require going beyond the current theory, as you cannot assume knowledge of what constitutes a measurement, nor the measurement basis.
But if you’re an instrumentalist—if you think that science is merely a tool for predicting the outcomes of experiments and nothing more—then this kind of hopping around isn’t a problem, because questions of interpretation are pointless and unscientific anyhow. (p.271 Kindle edition)
Contrary to Becker’s impressions, it is not the case that all theories that address the physical measurement problem will predict the same answer. With the ability of entanglement experimentation approaching the mesoscopic and even in some cases the macroscopic regimes, the physical measurement problem is the modern-day measurement problem, not the problem of developing YAI (yet another interpretation) while assuming a priori what constitutes a measurement device and the measurement basis. The concept behind the investigation of this problem is to develop theories and experiments that give different answers under the conditions of measurement. Only then, will a solution eventually be found.