Research press release


Nature Communications

Quantum physics: Quantum mechanics fails in consistently describing macroscopic systems



今回、Renato RennerとDaniela Frauchigerは、複数の観測者が関与する状況において、これらの量子力学の解釈の多くが現実を矛盾なく記述できないことを明らかにした。今回の研究で行われた思考実験では、4人の異なるエージェントが関与し、それぞれ異なる数量の測定を行った。全てのエージェントが量子論を使って自らの観測結果のモデル化をし、それぞれの観測者が単一の測定結果を得ると仮定した上でお互いの観測結果を予測すると、それぞれの観測者の観測結果は、他の観測者の予測と反対の結果になった。


When multiple agents use quantum mechanics to predict each other’s observations they will invariably end up with inconsistent results, according to a thought experiment reported in Nature Communications. The findings suggest that current interpretations of quantum theory cannot be extrapolated to consistently describe complex, macroscopic (large enough to be visible with the naked eye) systems.

Quantum mechanics can be successfully used to describe the microscopic world, where particles can exist ‘in superposition’ between different states at the same time. However, to be universally valid, the theory should in principle be able to model complex systems that include agents who are themselves using quantum theory. It has been unclear how to reconcile this with the fact that in the laboratory a scientist will experience a single, specific value each time they measure one of the superposed states. There are currently many interpretations of quantum mechanics to provide an answer to this question.

Renato Renner and Daniela Frauchiger show that there are situations involving multiple observers where many of these interpretations of quantum mechanics invariably fail to give a consistent description of reality. Their thought experiment involves four different agents, each one measuring a different quantity. If all the agents use quantum theory to model what they observe and to predict each other’s observation (and if we assume that each observer sees a single measurement outcome), then each observer’s outcome will be opposite to what the other would have expected.

This result suggests that the extension of quantum theory to include macroscopic systems is even less straightforward than was previously thought, and needs further development.

doi: 10.1038/s41467-018-05739-8

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