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Author: Sabina Sokol- USA Ambassador of girls in quantum.

The War on Quantum Theory: Albert Einstein and Niels Bohr

Terms to Know

  • Scientific Realism – theories that accurately describe the world 
  • Deterministic – the belief that all events are caused by prior events (chain reaction)
  • Anti-Realism/Instrumentalism – the belief that scientific theories don’t give absolute truths (can be separate from nature)
  • Probabilistic – the belief that everything ultimately behaves in uncertainty (the most you can do is predict the probability that the event will occur)

The Story

In 1920, Niels Bohr, a quantum physicist that believed in instrumentalist (anti-realistic) and probabilistic theories, proposed the Copenhagen Interpretation. It formed the basis of instrumentalist theory, which argued that scientific conclusions should be based on experimental measurements and observations, meaning that scientific theory doesn’t necessarily have to explain everything in nature. Bohr presented this idea at the 1927 Solvay Conference, a convention for the most brilliant minds in the world, most of which won Nobel Peace Prizes.

Members of the 1927 Solvay Conference.

Albert Einstein, who believed in scientific realistic and deterministic theories, completely disagreed with the Copenhagen Interpretation. He believed that something must govern everything in nature, and that scientific conclusions should reflect that. He told Niels Bohr that “God does not play dice”, to which Bohr responded with, “Stop telling God what to do.” Einstein was using “God” as a metaphor for the entity who creates the laws of nature, which in this case was the scientific community present at this conference. He believed that nature did “not play dice”, meaning that every event occurring in nature is caused by something else and is therefore not based on probabilities, which Bohr believed to be the case.

The two continued to battle it out in what is known as the “Great Debate”, and Bohr ended up winning because more scientists backed his ideas. However, Einstein’s theories were later picked up by a new generation of physicists.

During World War II, The United States government formed the Manhattan Project, which involved hiring large groups of physicists across different prestigious universities to build the first hydrogen bomb. One notable faction was at the Berkeley Radiation Laboratory (“Rad Lab”), where Robert J. Oppenhiemer, who is considered the “father” of the atomic bomb, worked for some time. Because this was a top secret project, the Military Intelligence Defense (MID) along with the separate Manhattan Project Security (MPS) forces were tasked with making sure that the information and resources utilized in the labs remained hidden from foreign entities. This meant that the physicists’ backgrounds were heavily investigated and their connections were monitored to ensure that none were double agents. 

The Berkeley Radiation Lab during World War II.

Many members of the Berkeley Radiation Lab were part of the Federation of Architects, Engineers, Chemists, and Technicians (FAECT), a union that the MID suspected of having ties to the American Communist Party. Steve Nelson, a known Soviet spy who had a direct connection to this party, was friends with Joseph Wienberg, a quantum physicist who worked in the Rad Lab under Oppenhiemer at the time. Weinberg, like many others, was part of FAECT; among them was David Bohm, another physicist in the Rad Lab. At one point, Oppenheimer, who feared that MPS would discover his own questionable actions, decided to throw them off his scent by claiming that Bohm, one of his brightest students, was a dangerous communist. He pointed to Bohm’s association to FAECT as his link to the American Communist Party. MPS immediately jumped into an investigation, but to Oppenhiemer’s dismay, they found that membership of the union was not sufficient evidence of being a communist. However, this investigation was still recorded in MPS’ files.

Around the same time, the FBI — who was sent in by MID to patrol the lab premises as an extra precaution — got wind that Wienberg was selling secrets about the atomic bomb to his friend Nelson. Apparently, two FBI officers had overheard the two talking about something related to quantum and assumed that it had to be some new concept being utilized in the “Rad Lab”. In reality, Nelson and Wienberg were merely discussing content in a published quantum textbook that was available to the public, so there were no secrets spilled in the conversation. But the two FBI officers ran back to MID, fearing that the Soviets were getting some top secret information, and caused a major panic through the US government. MID was so afraid of the Soviet “threat” that it had President Rooselvet himself call up the head of FAECT, Paul Murray and ask him to shut the Berkeley faction down completely. Murray obliged immediately and the entire incident was recorded in MID’s files. 

Due to the nature of the Manhattan Project, MID and MPS did not communicate with each other, and thus had separate investigations and records about FAECT and its members at the Rad Lab. Ultimately, the shutdown of the union was forgotten by MID during this tumultuous time.

The web of connections during the World War II era.

Shortly after the war ended, many of the Manhattan Project physicists were hired to university physics departments all over the country. But as the fear of communism in America rose with the start of the Cold War, the US government formed the House of Un-American Activities Committee (HUAC), which was tasked with investigating suspected communists. This organization later got its hands on the files about FAECT from MID and MPS, and began to worry about the former members, like Joseph Wienberg and David Bohm. Both were called to trial before the HUAC in the late 1940s. During this time, rumors of a “Scientist X”, a figure that both the government and press claimed to be sending information about the construction of an atomic bomb back to the Soviet Union, started circulating. As Wienberg was put on trial, the HUAC convicted him of being this individual and sentenced him to prison. The entire incident that came out of his unrelated conversation with Steve Nelson had been rediscovered, and with the Red Scare in full swing, it became enough evidence of a direct connection to the communists. Other physicists, like David Bohm, were not sentenced but experienced extreme marginalization and isolation by the American scientific community. Being put on trial alone was enough for Princeton University to fire him from his position as a physics department head and professor. It was really a matter of protecting an image; nobody wanted to be labeled as a friend or associate of a suspected communist.

House of Un-American Activities Committee holding a trial.

As the Red Scare continued, more and more teachers and scientists were put on trial by the HUAC for presenting an idea that didn’t comply with the norm; students, mentore, and peers were pointing fingers at each other, afraid that someone in their midst was a communist. Albert Einstein openly criticized Senator McCarthy — who championed this movement against the Soviet threat — in a public letter, stating that people in the realm of education were being shut up by the government. This, of course, angered McCarthy greatly, but he couldn’t really do anything about it because Einstein was such a big name in the global scientific community. Instead, he kept going after other quantum physicists for their involvement in unions like FAECT that might have had some tie to the American Communist Party.

As mentioned before, physicists like David Bohm were cast out of the scientific community and were left on their own; many fled the country in hopes of finding a job elsewhere. In 1957, Bohm published a paper on the “Hidden Variables” theory, which supported Einstein’s notion that there has to be something to explain the behavior of quantum particles. Bohm had originally conformed with many of Bohr’s ideas before his isolation, mainly because that was what he and most physicists who worked in the Manhattan Project were exposed to; Bohr’s ideas dominated the quantum physics used in the development of the atomic bomb. But Bohm slowly started warming up to Einstein’s ideas after the project was over, and came up with a theory that supported it. In the end, Einstein himself didn’t even support it despite the fact that it fully supported his ideas, but the critical blow was the lack of response by the American scientific community. Because of Bohm’s status as a “HUAC trial-er”, his ideas were largely ignored. Discussions about fundamental quantum principles had faded out by the mid-1950s, and scientists had already moved onto applications in electromagnetism. 

As the Red Scare started fading out in the 1970s, Bohm’s papers suddenly gained popularity by the same community that had ignored him just a decade earlier. The number of citations for his “Hidden Variables” theory grew exponentially as scientists suddenly started revisiting those quantum fundamentals once more. Though support for Einstein’s ideas continued to grow with new ideas and mathematical proofs, Bohr’s ideas continue to prevail in the realm of quantum mechanics. The compelling history of early quantum physicists from the 1920s reflects the huge role that domestic politics and public interests played with deciding who ultimately won the war on quantum theory.

Number of citations of David Bohm’s “Hidden Variables” paper from the 1950s until 1990s.


Halpern, P. (2017). This Man Was Einstein and Bohr’s Relationship Counselor. Scientific American. 

Kaiser, D. (1994). Bringing the human actors back on stage: the personal context of the Einstein-Bohr debate. BJHS, (27), 129-152. 

Mirsky, S. (Host). (2015, June 19). Einstein–Bohr Friendship Recounted by Bohr’s Grandson [Audio podcast episode]. In 60-Second Science. Scientific American. 

**Murray, S. (1954, November 11). [Letter to Albert Einstein]. 

Olwell, R. (1999). Physical Isolation and Marginalization in Physics: David Bohm’s Cold War Exile. The University of Chicago Press, 90(4), 738-756. 

Skibba, R. (2018, March 27). Einstein, Bohr and the war over quantum theory. nature.,Albert%20Einstein%20and%20Niels%20Bohr.&text=Propounded%20by%20Bohr%20and%20Werner,%2C%20until%20they’re%20measured 

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