When the quantum dog doesn’t bark

Allan Brewer

George S. Greenstein

Sara Imari Walker, P. C. W. Davies, Prasant Samantray +1 more

Quantum weak measurements with states both pre- and post-selected offer a window into a hitherto neglected sector of quantum mechanics. A class of such systems involves time dependent evolution with transitions possible. In this paper we explore two very simple systems in this class. The first is a toy model representing the decay of an excited atom. The second is the tunneling of a particle through a barrier. The post-selection criteria are chosen as follows: at the final time, the atom remains in its initial excited state for the first example and the particle remains behind the barrier for the second. We then ask what weak values are predicted in the physical environment of the atom (to which no net energy has been transferred) and in the region beyond the barrier (to which the particle has not tunneled). Thus, just as the dog that didnʼt bark in Arthur Conan Doyleʼs story Silver Blaze gave Sherlock Holmes meaningful information about the dogʼs non-canine environment, here we probe whether the particle that has not decayed or has not tunneled can provide measurable information about physical changes in the environment. Previous work suggests that very large weak values might arise in these regions for long durations between pre- and post-selection times. Our calculations reveal some distinct differences between the two model systems.

Peter Woit

David Waldner

Alexander Wendt’s Quantum Mind and Social Science reopens the question of the relevance of quantum mechanics to the social sciences. In response, I argue that due to “quantum decoherence,” the macroscopic world filters out quantum effects. Moreover, quantum decoherence makes it unlikely that the theory of quantum brains, on which Wendt relies, is true. Finally, while quantum decision theory is a potentially revolutionary field, it has not clearly accounted for alleged anomalies in classical understandings of decision making. However, the logic of quantum decoherence can motivate a new approach to the structure-agent problem.

Shishir Kumar Shandilya, Agni Datta, Yash Kartik +1 more