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One of the most mind-bending revelations of quantum physics over the past century has been that properties of particles are possibly not real until they are measured. Now a new thought experiment suggests that conclusion may be too tame: it seems that particles’ properties—their spin, for instance—may not even belong to them. This possibility is akin to saying that your personality does not belong to you.

The new study claims to demonstrate this paradoxical disconnect between particles and their properties via a new version of the so-called quantum Cheshire cat experiment. First performed in 2013, the experiment draws its name from the disappearing feline in Lewis Carroll’s Alice’s Adventures in Wonderland and involves the ostensible separation of a cat (actually, a particle) from its grin (some property of the particle).

The new version of the experiment starts with two grinning Cheshire cats and ends with the grin of one cat gracing the other cat’s face, and vice versa. In quantum terminology, it shows how two particles could end up exchanging their properties, or physical attributes.

“Niels Bohr’s view [was] that until you do a measurement on a quantum system, you cannot say that the physical attribute actually exists. That questions the reality of physical attributes,” says Arun Kumar Pati of the Harish-Chandra Research Institute (HRI) in India, who co-authored the new work. “Our thought experiment takes that view a step ahead. Not only are the attributes not real, but they could not be yours. It questions the reality at a much deeper level.”

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Category: Science