Does the universe exist as a concrete structure if there is no one to observe it? Or, is the cosmos a fluid, infinite amount of possible realities until the moment it is measured? This is one of the subjects of a series of great debates between Danish physicist Niels Bohr and Albert Einstein, and as a new episode of PBS's wonderful series Space Time explores, it is central to the mysteries of quantum mechanics to this day.
Bohr, citing new discoveries in quantum mechanics that mathematically define particles in superposition—where they exist in two or more quantum states at once, represented by a wave function until observations are made and the wave function collapses—argued that the entire atomic structure of the universe must adhere to this same principle. Until the universe is measured, it exists as a conglomerate of all possible realities, as defined by Bohr's Copenhagen interpretation.
But this interpretation throws a wrench into Einstein's theory of relativity because it violates the principal of locality—the concept that events can only affect matter in the same vicinity—which is central to Einstein's idea that nothing, not even information, can travel faster than the speed of light. The legendary theoretical physicist countered that there must be an objective reality to the universe independent of any observation or measurement. Quantum mechanics, he argued, is an incomplete scientific theory, and yet-to-be-discovered underlying physical variables would ultimately explain the phenomenon of superposition.
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