What Is Real?: The Unfinished Quest for the Meaning of Quantum Physics

by Adam Becker

“The idea of an objective real world whose smallest parts exist objectively in the same sense as stones or trees exist, independently of whether or not we observe them,” Heisenberg said, “is impossible.” How, then, does our world of stones and trees emerge from the world of atoms and molecules? “The transition from the ‘possible’ to the ‘actual’ takes place during the act of observation,” said Heisenberg. And what happens when we’re not looking? According to Heisenberg, that question can’t even be asked. “If we want to describe what happens in an atomic event, we have to realize that the word ‘happens’ can apply only to the observation, not to the state of affairs between two observations.” And what about the measurement problem? What makes observation so special? Whatever it is, it is “physical,” not “psychical,” said Heisenberg. “The transition from the ‘possible’ to the ‘actual’ takes place as soon as the interaction of the object with the measuring device, and thereby with the rest of the world, has come into play; it is not connected with the act of registration of the result by the mind of the observer.” Yet on the question of what constituted a “measuring device” and why it obeyed different rules than the quantum world, Heisenberg was infuriatingly unclear. Nowhere in his lectures did he propose anything like a solution to the measurement problem.