The Many-Worlds Interpretation of Quantum Mechanics: How One of the Most Daring Ideas Was Born

The Many-Worlds Interpretation of Quantum Mechanics: How One of the Most Daring Ideas Was Born
The Many-Worlds Interpretation of Quantum Mechanics: How One of the Most Daring Ideas Was Born
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The idea of ​​parallel universes excites the human mind. But few people know that the author of one of the most popular and widespread ideas about parallel worlds was a modest and stubborn graduate student from Princeton.

quantum mechanics

One evening in Princeton in 1955, over a glass or two of sherry, the Danish physicist Aage Petersen discussed with two of his graduate students, Charles Misner and Hugh Everett, the mysteries at the heart of quantum mechanics. Petersen defended the ideas of his mentor Niels Bohr, who was one of the authors of the so-called Copenhagen Interpretation - the standard way of understanding quantum physics. The Copenhagen Interpretation states that the quantum world is completely separate from our daily experience.

Petersen said that quantum physics is applicable only to ultra-small-scale reality, where isolated and very strange subatomic particles reign. He noted that this area of ​​science cannot be used to describe the world of people, chairs and other objects, consisting of trillions and trillions of such particles: this world can only be described by the classical physics of Isaac Newton. In addition, Petersen argued that the mathematics of quantum physics itself reduces to the mathematics of Newtonian physics as soon as the number of particles increases and becomes large enough.

However, Everett was not shy about attacking the traditional position that Petersen defended. Everett noted that quantum physics, in fact, does not go into classical physics with a large number of particles. According to quantum physics, even objects of ordinary sizes - like chairs - can be found in two different places at the same time - the principle of quantum superposition. He also stressed that it is wrong to turn to classical physics to save the day, as quantum physics should be the more fundamental theory underlying classical physics.

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Some time after this conversation, Everett reconsidered his position and decided to raise the rates. He expanded on the arguments and turned his blow at quantum orthodoxy into a Ph.D. thesis.

“The time has come to take [quantum physics] as a fundamental theory, without any dependence on classical physics,” he wrote in a letter to Petersen.

To solve the problem of superposition, Everett proposed a truly radical concept that at first glance was more suitable for science fiction: he said that quantum physics implies the existence of an infinite number of almost identical parallel universes, constantly separating from each other every time a quantum experiment is performed. This strange idea, which Everett discovered in the mathematics of quantum physics, eventually became known as the many-worlds interpretation.

The multi-world interpretation almost immediately came across a checkpoint in the person of Everett's dissertation curator, physicist John Wheeler. He was not well known outside the scientific community, but he knew all the important people in his field. He was Bohr's protégé and also knew Albert Einstein. 15 years before Everett appeared at its door, Wheeler oversaw the dissertation of young Richard Feynman, and later oversaw theses of dozens of other prominent physicists, including Kip Thorne, winner of the 2018 Nobel Prize in Physics.

Everett's strange ideas were initially fascinating to Wheeler, as he found them useful for applying quantum theory to describe the universe. However, Wheeler was a political man and knew about Bohr's resentment at his departure from the quantum orthodoxy that was preached in Copenhagen. He made it as straightforward as possible: Wheeler traveled to Copenhagen to try to get Bohr's blessing for Everett's work as an extension of the official Copenhagen understanding of the nature of quantum theory.

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It didn't go very well. In his letter to Everett, Wheeler stated that resolving Bohr's criticism of the former "would take a lot of time, a lot of hard arguments with a practical and stubborn person like Bohr, and a lot of writing and rewriting." Wheeler pleaded with Everett to personally come to Copenhagen to "fight the greatest fighter," meaning Bohr.

Everett was not particularly interested in fighting or rewriting anything. He was confident in his ideas, and the intellectual charm of an academic career did not affect him much. He was more interested in money and what could be done with it: good food and drink, material luxury, and women. He wanted to live in style, and not sit in the professor's office. By the time Wheeler's letter was received, Everett had already found a job that could provide him with all this: he got a job as a researcher at the Pentagon, where he considered the consequences of hypothetical nuclear strikes at the height of the Cold War.

Upon his return from Europe, Wheeler forced Everett to revise his dissertation and remove almost all references to "dividing worlds." Once this was done, Everett left Princeton and never returned to academia. In his later career at the Pentagon, Everett examined the worst effects of nuclear war and co-authored one of the earliest and most influential reports on fallout.

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True, in the end he still got to Copenhagen. In March 1959, he traveled to Denmark and presented his ideas to Niels Bohr while he was visiting Europe on other matters. As Everett later wrote, the meeting was "doomed from the start." Neither Bohr nor Everett wavered in their views.

"Bohr's view of quantum mechanics as a whole was accepted around the world by thousands of physicists who study it every day," said Misner, who was also in Copenhagen at the time. “It was absolutely unrealistic to expect that as a result of an hour-long conversation with a guy he would completely change his point of view.”

Everett's work disappeared from the radar. She was remembered only in the 70s, but even then she did not become particularly popular. Everett ended up being wedged once in an academic controversy over his work. Wheeler and colleague Bryce DeWitt invited Everett to talk about their work at the University of Texas in 1977. Among the young physicists from Austin was David Deutsch, who later became a staunch defender of the many-worlds interpretation.

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“He was full of nervous energy, very tense and incredibly intelligent,” Deutsch recalls. "He was enthusiastic about multiple universes and very sane and subtly defended her [the many-worlds interpretation]."

The work of DeWitt, Deutsch, and others has made many worlds interpretations of one of the most popular hypotheses over the past few decades. However, Everett was unable to see how his hypothesis reached its current status, becoming one of the most notable competitors of the Copenhagen interpretation. He died of a massive heart attack in 1982 at the age of 51. His family cremated the body, and the ashes were thrown into the trash, in accordance with his last will. Nevertheless, Everett's argumentation and courage continues to live in his theory, born during a drunken conversation more than 60 years ago, and is increasingly becoming the subject of controversy between physicists today.

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