A Century of Debate
The deficiencies at the core of modern physics have long troubled scientists. For a century, dissident physicists have sought alternative interpretations of quantum mechanics that would shed its fraught philosophical baggage. At the beginning, Albert Einstein, Erwin Schrödinger, and other founders critiqued the unrealism and incompleteness of the Copenhagen interpretation. Some critics proposed alternative approaches, while most urged viewing quantum mechanics as a provisional milestone on the path to a more comprehensive, self-consistent, and complete theory.
The history and substance of the foundational debates are summarized in Adam Becker, What is Real? (New York: Basic Books, 2018).
Other founders, most prominently Werner Heisenberg and Niels Bohr, countered that hopes for a successor theory were naive pipedreams. By the late 1920s, as the Copenhagen interpretation—a “tranquilizing philosophy” in Einstein’s phrase—gained hegemony as the dominant paradigm, the debate on foundational questions waned. Philosophically inclined physicists, like Schrödinger and Einstein, departed from the mainstream, while bench physicists focused on the pragmatics of elaborating quantum equations and designing experiments. In 1932, the eminent mathematician John von Neumann’s putative proof of the impossibility of alternative “hidden variable” theories seemed to slam the door shut on heterodox interpretations.
But then in the 1950s, David Bohm refuted von Neumann’s theorem, which had been based on overly restrictive premises, in practice. By producing an actual hidden variable theory, Bohm reopened the debate on the meaning and interpretation of quantum mechanics. Anticipated by Louis de Broglie in the 1920s, Bohm’s “pilot wave theory” repurposed the Schrödinger wave function by reinterpreting certain terms as a real physical force, thereby reproducing quantum mechanics on a realistic, deterministic basis. Schrödinger’s cat is either dead or alive before the chamber is opened.
Unsurprisingly, Bohm’s alternative approach was largely ignored by mainstream physics uninterested in foundational questions, or was met with dismissive pushback, much of it ill-considered and unjustified. In retrospect, his demonstration that quantum theory could be made compatible with philosophical realism stands as a significant contribution to twentieth-century physics. Not least, it led to the formulation of other hidden variable theories, such as the stochastic electron theory (SET) presented here. Still, Bohmian physics itself remains a problematic successor since it only reinterprets the Schrödinger equation, not derive it, transcend it, or make distinguishing predictions.
See Bohm’s scintillating philosophical treatise Causality and Chance in Modern Physics (New York: Harper and Row, 1957).
A very different reinterpretation of quantum mechanics also has roots in the 1950s. The “many-worlds interpretation” audaciously posits that with every observation the universe splits into multiple descendant universes, one for each possible outcome, thereby providing a logical solution to the conundrum of the collapse of the wave function. Thus, when Schrödinger’s cat is observed, the universe bifurcates into one with the cat alive and another with the cat dead, while the human observer bifurcates along with the cat. Since these are parallel, noninteracting realities, this interpretation, like Bohm’s, is untestable. That some philosophers and scientists are drawn to a remedy predicated on proliferating universes is an indication of the gravity of Copenhagen’s defects.
Both the Bohmian and many-worlds schools reinterpret the Schrödinger equation to evade the inscrutable collapse of the wave function that plagues the standard interpretation. By contrast, “objective-collapse theories” modify the equation by adding terms that localize the wave function in a specific state. The source of this mathematical complexification is traced, variously, to gravitational interactions (the Diósi–Penrose model) or to random processes triggering spontaneous collapse (GRW theory and its subsequent developments). These alternatives doctor the Schrödinger equation to recover objective descriptions, but do not derive quantum mechanics from sound first principles.
SET is a descendant of yet another approach to reformulating quantum theory that originated in the 1940s when Imre Fényes noted a formal analogy between quantum mechanics and Brownian motion. The connection was rediscovered in the 1960s by Edward Nelson, who constructed a stochastic process that was mathematically equivalent to Schrödinger but required arbitrary assumptions that ensured the outcome. Still, Nelson’s suggestive work inspired the quest to incorporate Brownian motion in an intuitive, testable model of particle behavior.
As small bands of Copenhagen heretics continue the hunt for a better basis for quantum physics, mainstream practitioners fall into three broad camps. In defense of the standard interpretation, some argue that the purpose of physics is to account for experimental outcomes only, not seek a picture of reality (“logical positivism”). Others question the existence of a material reality independent of human consciousness (“philosophical idealism”). Most working physicists just pursue research within the conventional quantum framework undeterred by its unsatisfactory foundations (“shut up and calculate”).