In “New pursuit of Schrödinger’s cat” (Prospect , 21st September 2011) Philip Ball:
“Quantum theory is reliable but fraught with paradox. Philip Ball asks if scientists will now find an object existing in two places at once,”
At some scale, the quantum-ness of the microscopic world gives way to classical, Newtonian physics. Why? The generally accepted answer is the process of decoherence. Crudely speaking, interactions of a quantum entity with its teeming environment act like a measurement, collapsing superpositions into a well-defined state. So, large objects obey classical physics not because of their size per se but because they contain more particles and thus experience more interactions, so decohering instantly.
But that doesn’t fully resolve the issue—as shown by Schrödinger’s famous cat. In his thought experiment, Schrödinger imagined a cat that is poisoned, or not, depending on the outcome of a quantum event. The experiment is concealed inside a box. Since the outcome of the event is undetermined until observation collapses the wavefunction, quantum theory seemed to insist that, until the box is opened, the cat would be both alive and dead. Physicists used to evade that absurdity by insisting that somehow the bigness of the cat would bring about decoherence even without observation, so that it would be either alive or dead but not both.
Ball hopes Darwin will solve the problem.