In 1927, when Albert Einstein began his famous series of battles at the Solvay conference in Brussels with Danish physicist Niels Bohr on the meaning of quantum mechanics, John Wheeler just a teenager. Quantum mechanics is the physical description of the behavior of atoms. Unlike classical Newtonian physics, it involves instantaneous transitions, established by probabilistic rules rather than exact mechanical laws. Einstein opposed nervousness, random elements and other undetermined aspects of quantum theory, while Bohr found them acceptable. While Wheeler became a middle physicist in the late 1930s, he became friends with both debaters, appreciated their well-argued arguments, and hoped to find a way to reconcile their conflicting views.
Wheeler shared with Einstein and Bohr a deep appreciation for the philosophical underpinnings of theoretical physics. Einstein's readings on Baruch Spinoza and Ernst Mach had led to objective, deterministic and, in principle, directly measurable theories for all components at all times by local observers. By contrast, Bohr, a fan of Eastern philosophy, including Taoism with his Yin-Yang union of opposites, has embraced the contradictions in his theory of complementarity. According to this notion, the behavior of a quantum entity, whether wave-shaped or particle-shaped, depends on how it is measured. While many American physicists shy away from philosophy, Wheeler, the son of two librarians, embraces him. Therefore, while leaning towards the interpretation of Bohr, he found merit in the perspectives of both thinkers.
At Solvay, Einstein had argued, through thought experiments that he had presented to Bohr and others, that even though quantum mechanics corresponded to experimental data, it was fundamentally incomplete. According to Einstein, this was not sufficient to include situations in which the choice of methods and devices by experimenters affected the fact that some parameters had definite values or were unclear. Moreover (as underlined by the concept of entanglement introduced in 1935), it was non-local, which means that a quantum state can include two things that have connected properties even if they are physically separated, can -being even at a great distance. Whenever Bohr reversed one of his thought experiments, Einstein proposed another. The failures of quantum mechanics to provide a complete plan of nature, Einstein reasoned, suggested the need for a deeper and more complete theory that could do just that. He is therefore looking for a mechanistic and unified theory that would replace quantum mechanics. It was a quest that would last the rest of his life.
Wheeler met Bohr for the first time during a research stay in 1934 at his Institute of Theoretical Physics in Copenhagen. In January 1939, after Wheeler was appointed assistant professor at Princeton University, Bohr arrived there for a research stay of several months. Together, Bohr and Wheeler have developed a model of nuclear fission activation energy that predicts which isotopes of uranium and plutonium would be the most easily fissile. At this point, Wheeler's focus was more practical than philosophical.
Einstein was, at that time, Wheeler's neighbor, both at work and at home. The German physicist in exile worked at the Institute for Advanced Study, which was originally located at Princeton's Fine Hall until a dedicated facility could be built . Wheeler's office was also at Fine Hall, on the same floor as Einstein's (and Bohr's when he was temporarily in Princeton). Einstein's home on Mercer Street was only a few blocks from Wheeler's on Battle Road. Wheeler could speak German and had a pleasant and pleasant personality that exuded friendly respect - just the right ingredients to make Einstein love himself.
Since Wheeler knew Bohr and Einstein very well and viewed them as his mentors, he was beginning to think of ways to reconcile their radically different points of view. While Wheeler embraced Bohr's complementarity, he was in agreement with Einstein on the fact that the role of a human observer - as a separate entity making a decision that triggers a "roll of the dice" - was vague and perhaps even paradoxical. Are humans not governed at a deep level by quantum rules?
Richard Wheeler's student, Richard Feynman, developed a radical alternative to the classical methods of quantum mechanics. In the so-called Integral Feynman Path Formalism, nicknamed by Wheeler "Sum on Stories," quantum computations are performed via a weighted sum of probability magnitudes for the different alternative paths in which an interaction might occur . It's like if we calculate the overall effort of a commute to get to work by relying on the alternatives of taking a bus, a train, a taxi and walking in tandem as if everything were done at the same time, instead of considering them separately. The classic path was simply the most likely.
Wheeler, armed with what he thought was a superior way to look at quantum mechanics, stopped in front of Einstein's house and engaged him in a deep discussion about Feynman's methods. Nevertheless, the stubborn older physicist has not been persuaded. "I can not believe God is playing dice," Einstein said. "But maybe I've earned the right to make my mistakes."
After Einstein died in 1955, Wheeler went on to try to find a common ground among the various perspectives on quantum mechanics. He was intrigued when another of his students, Hugh Everett III, eliminated the direct role of observers with his concept of a universal wave function (later nicknamed by Bryce DeWitt "the interpretation of multiple worlds "). quantum physics would be entirely deterministic. The only problem is that at each quantum measure, the universe would divide into a myriad of alternatives. Unlike the "sum over stories", with its mix of possibilities in one reality, they would be disparate realities in their own right. The conscious existence of an observer would also bifurcate, allowing different copies to have different results. Therefore, human and particle fates would be linked together, avoiding the need for independent observers.
In the case of Everett 's hypothesis, it was Bohr who would not budge. Although Wheeler tried to persuade Bohr that it was a more complete theory, Bohr did not see the need to move away from complementarity. Wheeler tried to paint Everett's theory in his least radical light, but Bohr had little interest.
Wheeler's latest attempt to pave the rift dates back to the late 1970s, more than a decade after Bohr's death. Wheeler sought self-consistency through a "participatory universe" in which human observation in the present could affect quantum results in the past. Thus, complementarity becomes a closed loop in which what is observed in the past shapes the entirety of the story and ultimately the observer himself. Wheeler called it a "self-excited circuit". The only missing element, he realized, was a reason for observers to exist. "How is the existence?" Became the ultimate question of Wheeler. He remained unanswered when he died in 2008 at the age of 96.
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