What is Real? The Bohr-Einstein Debate

In 1927 during the Fifth Solvay Congress in Brussels, two super-heavyweight sumo wrestlers in quantum physics, Bohr and Einstein, grappled and puttied their theory against each other. Spectators were animated to watch the two scientific titans collide to shake the relationship between theory and reality's nature to finally answer the question, what is real?

In one corner was Albert Einstein, who reconfigured the Newtonian Universe to give birth to the Theory of Relativity. Einstein was at the height of his popularity and was the gold standard for a genius. He helped establish quantum theory, discovering that light has dual citizenship as both a wave and a particle. On the opposite side was Niels Bohr with his hybrid physics-philosophical "complementarity" treatise, which proclaimed: that it depends on how the observer sees the light that can depict the characteristics of a wave or particle. Inanely, the glass can be half empty or half full, depending on the observer. They were not alone in their corner. Broglie, who sided with Einstein, claimed, based on his Ph.D. thesis, that if light particles could behave like waves conceivably, waves can also act like particles.

Later, Schrödinger presented a concept he called "matter waves," which he attempted to describe as a "rippling sea of smeared-out particles." Naturally, people listening to his explanation cannot understand his hypothesis. It took another scientist, Max Born, to show that Schrödinger's "matter waves" are "waves of probability," which further baffled the scientific community. Roughly, let us say you have a gun particle that shoots electrons that behave like a wave and later like a particle that allows you to see the electron appear in a specific position in the target. Thus, they converted the quantum science from a complicated to strange to weird theory.

Further experiments in quantum particles revealed that mere observing significantly influences the particle's momentum, making it impossible to accurately measure the particle's position. Thus Werner Heisenberg, who first discovered the phenomena proposed the "uncertainty principle." During the conference, Bohr presented the "Copenhagen interpretation," named in honor of the town where he came from, for the first time, establishing the idea of particle-wave complementarity as a confirmation of both Born's and Heisenberg's principles. Confused? If your head is spinning like an electron around a nucleus, do not worry, there are plenty of us.

Like in the super-heavyweight championship, the conference participants showered adulation to the presentation of Bohr, except for the challenger in the corner, who was unimpressed with the interpretation. Einstein contested that the "rippling sea of smeared-out particles" observed is similar to the "jittery motion of pollen" in still water and was attributable to the random motion of water molecules following Newton's law of motion. Therefore, predictable, and the finding was not new. Contrarily, the Copenhagen principle maintained that chance ruled the subatomic particles.

During the rematch in 1930 at Sixth Solvay Congress, Einstein, sure to get Bohr with his two-punch combination, argued that the logical route of quantum theory leads to an absurd outcome. Bohr ducked and rolled with the suppositions from Einstein, who was sure to convince him that the quantum theory was incomplete. He remembered a previous statement of Einstein, "God does not play dice with the universe," in which he replied, "stop telling God what to do with his dice." The outcome was a draw, setting the stage for a second rematch.

Like a hungry boxer eager to win the unification bout to become the undefeated, undisputed super-heavyweight champion of physics, Einstein, while in Princeton in 1935, collaborated with two physicists to propose the Einstein-Podolsky-Rosen paradox or EPR for short, the theory was deceptively simple. Let me illustrate. Suppose you have a pair of slippers that you separately put inside a sealed box. If you ask a friend to open the box and inform you that it is the right pair, you know that inside is the left pair even without opening the other box. Thus, the two are "entangled." Even if the other box with the right pair was brought to the moon, you know that the left pair is inside the other box.

Applying the principle to the electron demonstrates an intrinsic property called "spin." If two electrons are produced in the same event and if one electron spins up, the other is sure to spin down. They are entangled, similar to a pair of slippers. Therefore, nothing is strange with the quantum theory proposed by the entanglement principle. It is that, to begin with, they are like a pair of slippers.

Take that Bohr, so it seems Einstein won the day. But unknowingly, it was a pyrrhic victory. The EPR implies that even if your friend moved the box to another galaxy, your electron must "know" that it must depict the opposite spin immediately after your friend opened it. If the two electrons "communicate," the action violates the Theory of Relativity that nothing travels faster than light. Einstein painted himself in the corner and awkwardly proposed that the event was a "spooky action at a distance."

Wait, there was more. EPR depicted that your electron, to begin with, does not have its own identity until your friend decides to observe his electron. In other words, the physical nature of your electron depends on the way your friend observes his electron. As if to give Bohr the coup de grace, Einstein stated, "Do you really believe the Moon is there only when you look at it?" Thus according to Einstein et Al., the quantum theory had a major problem. It is incomplete. Yet quantum theory brought esoteric philosophy into the mainstream of society.

The EPR jolted Bohr. He rejected the idea that the mere act of measuring influences the particle's state. Bohr strongly believed that uncertainty is the primary principle behind quantum mechanics. More level-headed, Bohr declared that we could only document what we observe at the beginning and end of the quantum experiments. We can only guess what happened in between.

Though Einstein and Bohr are on the opposite side of the fence, they remain friends. It is the nature of reality that is the bone of their contention. Bohr believed that nature was basically random, while Einstein fervently opposed the idea. Most quantum theorists considered Bohr was accurately describing reality's nature until John Bell convincingly proved Einstein wrong. Who?