Quantum mechanics is the most fundamental, and most successful, branch of physics. It was discovered from the experiment and forged with the experiment. And yet, given its unique indeterministic perspective of Nature, it is also the most criticized branch of physics. Famous critics, such as Einstein, and Schrödinger, called it ‘not complete’ and even ‘repugnant’, respectively. On the other hand, for those of us who have been in contact with quantum mechanics for nearly 50 years, and made a living out of it for the last 45 plus years, quantum is like a benevolent teacher and generous provider that is misunderstood by many and unappreciated by others. The ineffability of quantum mechanics is a direct consequence of quantum mechanic's proximity to Nature. Indeed, Nature is a lot more subtle, a lot more richer, than what our linguistic abilities can describe and our philosophies can assimilate. In Quantum Clear we set out to explain the foundations of quantum mechanics and to clarify many of the misunderstandings that surround it.
Quantum mechanics is the most fundamental, and most successful, branch of physics. It was discovered from the experiment and forged with the experiment. And yet, given its unique indeterministic perspective of Nature, it is also the most criticized branch of physics. Famous critics, such as Einstein, and Schrödinger, called it ‘not complete’ and even ‘repugnant’, respectively. On the other hand, for those of us who have been in contact with quantum mechanics for nearly 50 years, and made a living out of it for the last 45 plus years, quantum is like a benevolent teacher and generous provider that is misunderstood by many and unappreciated by others. The ineffability of quantum mechanics is a direct consequence of quantum mechanic's proximity to Nature. Indeed, Nature is a lot more subtle, a lot more richer, than what our linguistic abilities can describe and our philosophies can assimilate. In Quantum Clear we set out to explain the foundations of quantum mechanics and to clarify many of the misunderstandings that surround it.
Quantum mechanics is our most successful physical theory. It underlies our very detailed understanding of atomic physics, chemistry, and nuclear physics, and the many technologies to which physical systems in these regimes give rise. Additionally, relativistic quantum mechanics is the basis for the standard model of elementary particles, which very successfully gives a partial unification of the forces operating at the atomic, nuclear, and subnuclear levels. However, from its inception the probabilistic nature of quantum mechanics, and the fact that “quantum measurements” in the orthodox formulation appear to require the intervention of non-quantum mechanical “classical systems,” have led to speculations by many physicists, mathematicians, and philosophers of science that quantum mechanics may be incomplete. Among the Founding Fathers of quantum theory, Einstein and Schrödinger were both of the opinion that quantum mechanics is in some way unsatisfactory, and this view has been amplified in more recent profound work of John Bell, among others. In an opposing camp, many others in the physics, mathematics, and philosophy communities have attempted to provide an interpretational foundation in which quantum mechanics remains a complete and self-contained system. Among the Founding Fathers, Bohr, Born, and Heisenberg maintained that quantum mechanics is a complete system, and a number of recent proposals have been made to improve upon or to provide alternatives to their “Copenhagen Interpretation.” The debate continues, and has spawned an enormous literature.
The founding fathers of quantum mechanics had already perceived the essence of the difficulties of quantum mechanics; today, after almost a century, the discussions are still lively and, if some very interesting new aspects have emerged, at a deeper level the questions have not changed so much. What is more recent, nevertheless, is a general change of attitude among physicists: until about 1970 or 1980, most physicists thought that the essential questions had been settled, and that “Bohr was right and proved his opponents to be wrong”. This was probably a consequence of the famous discussions between Bohr, Einstein, Schrödinger, Heisenberg, Pauli, de Broglie, and others (in particular at the Solvay meetings [1–3], where Bohr's point of view had successfully resisted Einstein's extremely clever attacks). The majority of physicists did not know the details of the arguments. They nevertheless thought that the standard “Copenhagen interpretation” had clearly emerged from the infancy of quantum mechanics as the only sensible attitude for good scientists. This interpretation includes the idea that modern physics must contain indeterminacy as an essential ingredient: it is fundamentally impossible to predict the outcome of single microscopical events; it is impossible to go beyond the formalism of the wave function (or its generalization, the state vector ∣ψ) and complete it.
Introduction Despite its extraordinary predictive successes, quantum mechanics has, since its inception some seventy years ago, been plagued by conceptual difficulties. The basic problem, plainly put, is this: It is not at all clear what quantum mechanics is about. What, in fact, does quantum mechanics describe? It might seem, since it is widely agreed that the state of any quantum mechanical system is completely specified by its wave function, that quantum mechanics is fundamentally about the behavior of wave functions. Quite naturally, no physicist wanted this to be true more than did Erwin Schrodinger, the father of the wave function. Nonetheless, Schrodinger ultimately found this impossible to believe. His difficulty was not so much with the novelty of the wave function [2, page 156 of [3]]: "That it is an abstract, unintuitive mathematical construct is a scruple that almost always surfaces against new aids to thought and that carries no great message." Rather, it was that
In this chapter we assume a critical perspective of the previous 36 chapters and the 7 appendices that integrate this work. We also go beyond Quantum Clear the book and explore the meaning of the concept, quantum clear, in view of the transparent mathematics and principles that integrate the whole of quantum physics – principles that give us working tools to explain and predict experimental phenomena. As a counter balance, we also go beyond Quantum Clear the book and explore the meaning of Feynman's statement, in regard to the perception that ‘nobody understands quantum mechanics.’ From this perspective we also return to mention some of the major misunderstandings surrounding quantum mechanics and their unnecessariness and unnaturalness. In a brief detour we also pay attention to ‘consistency’ in physics. Finally, we explore the meaning of understanding quantum mechanics and the possible future of quantum physics.
The Einstein-Podolsky-Rosen (EPR) paradox was enunciated in 1935 and since then it has made a lot of ink flow. Being a subtle result, it has also been largely misunderstood. Indeed, if questioned about its solution, many physicists will still affirm today that the paradox has been solved by the Bell-test experimental results, which have shown that entangled states are real. However, this remains a wrong view, as the validity of the EPR ex-absurdum reasoning is independent from the Bell-test experiments, and the possible structural shortcomings it evidenced cannot be eliminated. These were correctly identified by the Belgian physicist Diederik Aerts, in the eighties of last century, and are about the inability of the quantum formalism to describe separate physical systems. The purpose of the present article is to bring Aerts' overlooked result to the attention again of the physics' community, explaining its content and implications.
Quantum mechanics is one of the crowning achievements of human thought. There is no theory that is more successful in predicting phenomena over such a wide range of situations—and with such accuracy—than quantum mechanics. From the basic principles of chemistry to the working of the semiconductors in your mobile phone, and from the Big Bang to atomic clocks, quantum mechanics comes up with the goods. At the same time, we still have trouble pinpointing exactly what the theory tells us about nature. Quantum mechanics is hard, but perhaps not as hard as you think.