“If you make a measurement, you get an entanglement between the system and the apparatus and the observer,” Zeh said. “The observer sees only one component [of the Schrödinger’s cat state] and not the superposition of all the others. So, that solves the measurement problem.” Zeh had unknowingly reinvented Everett’s many-worlds interpretation from scratch—and, along the way, he had also developed a mathematically sophisticated account of the interactions between small quantum systems, like atoms, and the relatively large quantum objects around them, like rocks and trees and measurement devices.
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Decoherence
