It was the scientific equivalent of a heavyweight title fight, but less conclusive. During the 1920s and ’30s, two of the century’s greatest physicists, Albert Einstein and Niels Bohr, locked brains in a series of debates. Bohr argued that physicists must learn to accept the weird behavior of subatomic particles: Their essential unpredictability even under completely controlled conditions, and a still stranger effect called entanglement, in which two particles, no matter how far apart, behave in ways that, while individually random, are too strongly correlated for the particles to be acting independently.
Einstein was deeply troubled by these phenomena, disparaging the former as "God playing dice" and the latter as "spooky action at a distance." He spent his remaining years searching unsuccessfully for a more naturalistic theory, where every effect would have a cause, and influences would act locally. Newton’s physics, Maxwell’s electromagnetism and Einstein's own theory of relativity share this common-sense property, which he deemed essential to any lawful and orderly explanation of nature.
Meanwhile, the rest of the physics community, including greats like Schrödinger, Heisenberg and Dirac, followed Bohr’s advice and accepted these disturbing phenomena, and the mathematics that explained them, as the new normal.
Now, 90 years later, it’s pretty clear that the greatest scientific mind of the 20th century, flexible enough to bend space and time, wasn’t flexible enough. Quantum randomness and entanglement are real, confirmed by innumerable experiments, and explained in meticulous detail the theory Einstein rejected. Moreover, quantum theory has played an essential role in technologies such as the laser and the transistor, which could not have been developed on the pre-quantum physics of Newton, Maxwell and Einstein.
But Einstein’s uneasiness lives on. Even the physicists who use quantum theory every day, and who all agree on how to use its mathematics to explain and predict the results of experiments, can’t agree on words to say what’s happening, or on how to fit quantum phenomena into some new and expanded version of common sense. Many concluded that this disconnect between mathematics and intuition was permanent, and that since it was fruitless to try to explain quantum phenomena in everyday language, physicists should just "shut up and calculate."
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