Copenhagen vs. Many Worlds: And the Winner Is...

The conundrum over the quantum to classical transition appeared on the horizon soon after the discovery of quantum mechanics. In the 1920s, quantum behemoths Niels Bohr and Werner Heisenberg, and others, met in Copenhagen and arrived upon the standard interpretation of quantum mechanics: Prior to observation, a quantum object exists as a wavefunction that accommodates the superposition of multiple states. The act of observing the system "collapses" the wavefunction and we end up with a classical state.

The problem with the Copenhagen Interpretation is that it doesn’t describe how this collapse occurs. It also raises the uncomfortable philosophical question of whether an objective reality exists in the absence of observers.

Then in the 1950s, Hugh Everett III—a student of John Wheeler’s—came up with an even more radical solution that did away with collapse entirely. He suggested that the entire universe is a quantum object, with every possible outcome of a measurement realized—just in different realities. This leads to a mind-boggling scenario, in which every possible quantum state exists in its own world, a scenario of parallel universes rather simplistically called the "many worlds" interpretation.

So which alternative does Zurek back? He favors decoherence theory, which describes how interaction with the environment gradually destroys a quantum state. But Zurek is quick to point out that decoherence is compatible with both interpretations.

"Collapse has metaphysical connotations. It begins to touch on whether you think like Bohr or Everett," says Zurek. "What I am trying to do, among other things, is to try and stay away from taking a side."

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