Quantum mechanics is the most powerful theory of physics. It was John Bell's view, however, that no formulation of orthodox quantum mechanics is free of fatal flaws. While fully recognising the theory's indisputable utilitarian success, Bell was convinced that its failings meant that “something is rotten in the state of Denmark”. Indeed, as many know from personal experience, he was in the habit of proclaiming that quantum mechanics is “rotten”. What I do not know is whether he chose this particular adjective as a veiled condemnation of the House of Bohr.
Quantum mechanics is the most powerful theory of physics. It was John Bell's view, however, that no formulation of orthodox quantum mechanics is free of fatal flaws. While fully recognising the theory's indisputable utilitarian success, Bell was convinced that its failings meant that “something is rotten in the state of Denmark”. Indeed, as many know from personal experience, he was in the habit of proclaiming that quantum mechanics is “rotten”. What I do not know is whether he chose this particular adjective as a veiled condemnation of the House of Bohr.
Something is rotten in the state of Denmark. Shakespeare , Hamlet, Act 1 Scene 4 The rise and fall of the old quantum theory The principles of the old quantum theory were first articulated by Niels Bohr in 1913 in a three-part paper titled “On the Constitution of Atoms and Molecules.” Bohr had adopted Ernest Rutherford's model of the atom, according to which the mass of the atom is concentrated in a small central nucleus, while the electrons orbit the nucleus in planetary trajectories. The key challenge facing Rutherford's model was that it was unstable: according to classical electrodynamics, the electron, which is a moving charged body, should radiate energy and so eventually collapse into the nucleus. Bohr's solution was to incorporate Max Planck's theory of radiation, according to which “the energy radiation from an atomic system does not take place in the continuous way assumed in ordinary electrodynamics, but that it, on the contrary, takes place in distinctly separated emissions” (Bohr 1913, p. 4; BCW 2, p. 164). In this early paper, and most subsequent accounts, Bohr summarized his quantum theory by means of two assumptions or postulates. According to the first postulate, electrons cannot travel in any path they like around the nucleus, rather atomic systems can only exist in a series of discrete “stationary states,” in which the electron is in a particular allowed stable periodic orbit and is not emitting radiation.
Quantum theory is the most successful scientific theory of all time. Many of the great names of physics are associated with quantum theory. Heisenberg and Schrödinger established the mathematical form of the theory while Einstein and Bohr analysed many of its important features. However, it was John Bell who investigated quantum theory in the greatest depth and established what the theory can tell us about the fundamental nature of the physical world. Moreover, by stimulating experimental tests of the deepest and most profound aspects of quantum theory, Bell's work led to the possibility of exploring seemingly philosophical questions, such as the nature of reality, directly through experiments.
Quantum mechanics is the most powerful of the theories developed by the human beings. In fact, it is able to predict successfully the experimental results with an impressive degree of accuracy. For this reason, the majority of physicists tends to believe that quantum mechanics has no problem and that we are close to finding a real ”theory of everything”. As it has been underlined many times, starting from the famous Bohr–Einstein debate and finally arriving at the writing of John Bell, it is far from being true.
Quantum mechanics occupies a unique position in the history of science. It has survived all experimental tests to date, culminating with the most precise comparison of any measurement to any theory – a 1987 measurement of the electron's magnetic moment, or gyromagnetic ratio g e = 2.002 319 304 39 (Van Dyck et al. 1987), agreeing with QED theory to 12 digits. Despite this and other dramatic successes of quantum mechanics, its foundations are often questioned, owing to the glaring difficulties in reconciling quantum physics with the classical laws of physics that govern macroscopic bodies. If quantum mechanics is indeed a complete theory of nature, why does it not apply to everyday life? Even Richard Feynman (1982), a fierce defender of quantum mechanics, memorably stated that: We have always had a great deal of difficulty in understanding the world view that quantum mechanics represents … Okay, I still get nervous with it … It has not yet become obvious to me that there is no real problem. I cannot define the real problem, therefore I suspect there's no real problem, but I'm not sure there's no real problem. In the dawn of the twenty-first century, John A. Wheeler's big question “Why the quantum?” has returned to the forefront of physics with full steam. Advances in experimental physics are beginning to realize the same thought-experiments that proved helpful to Einstein, Bohr, Heisenberg, Schrödinger, and the other founders of quantum mechanics.
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.
Quantum mechanics emerged in the first decades of the 20th century as a powerful mathematical framework for describing microscopic phenomena. While its predictive success in specific domains is widely acknowledged, its ontological foundations remain deeply problematic nearly a century after its formulation. This paper examines the historical development of quantum mechanics, focusing on the introduction of key concepts such as the collapse of the wave function and quantum entanglement. It argues that these notions did not arise as direct consequences of experimental findings, but were introduced as additional postulates to resolve internal inconsistencies within the theory. The analysis highlights the circular nature of experimental confirmation in quantum mechanics and demonstrates that even the most rigorous tests, including loophole-free Bell inequality experiments, primarily validate mathematical predictions rather than resolve fundamental ontological questions. Multiple alternative interpretations proposed over the decades have failed to achieve consensus, indicating persistent conceptual difficulties. The paper concludes that quantum mechanics, particularly in its standard interpretation, functions more as a speculative mathematical construction than as a coherent and ontologically consistent theory of physical reality. «Keywords:» quantum mechanics, wave function collapse, quantum entanglement, measurement problem, ontology, Copenhagen interpretation, Bell inequalities, alternative interpretations, philosophy of physics