One of the most confounding concepts to emerge from the cauldron of early 20th-century physics was the idea that quantum objects can exist in multiple states simultaneously. A particle could be in many places at once, for example. The math and experimental results were unequivocal about it. And it seemed that the only way for a particle to go from such a “superposition” of states to a single state was for someone or something to observe it, causing the superposition to “collapse.” This bizarre situation raised profound questions about what constitutes an observation or even an observer. Does an observer merely discover the outcome of a collapse or cause it? Is there even an actual collapse? Can an observer be a single photon, or does it have to be a conscious human being?
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