Observed Observers and the Consistency of Quantum Theory
Alexios P. Polychronakos (CUNY New York)
The special role that observers play in Quantum Mechanics leads to conceptual and interpretational issues when observers become part of the quantum state. This was recently elevated to a contradiction by Frauchiger and Renner, thus casting doubt at the logical consistency of quantum theory.
I argue that unitary quantum mechanics implies that observers who will themselves be subjected to « cat » measurements cannot, in general, apply the standard Born rules to deduce the results of experiments, and thus can neither make reliable predictions nor communicate reliable information to other observers. This restores the logical consistency of quantum mechanics, at the price of introducing an additional element of uncertainty when cat measurements are a possibility. I discuss the feasibility of cat measurements and speculate that thermodynamics and/or quantum field theory may make them physically unattainable.
I argue that unitary quantum mechanics implies that observers who will themselves be subjected to « cat » measurements cannot, in general, apply the standard Born rules to deduce the results of experiments, and thus can neither make reliable predictions nor communicate reliable information to other observers. This restores the logical consistency of quantum mechanics, at the price of introducing an additional element of uncertainty when cat measurements are a possibility. I discuss the feasibility of cat measurements and speculate that thermodynamics and/or quantum field theory may make them physically unattainable.