The Moon isn’t necessarily there if you don’t view it. So says quantum mechanics, which states that what exists depends on what you calculate. Proving reality is just like that usually involves the comparison of arcane probabilities, but physicists in China have made the point in understandable way. They executed a matching game in which two players leverage quantum effects to win every time—which they can’t if measurements only reveal reality as it already exists.

Albert Einstein, who anticipated that something like a photon’s polarization should have estimated independent of whether it is measured. He proposed particles might carry “hidden variables” that deciding how a two-way state will collapse. However, in 1964, British theorist John Bell found a method to prove experimentally that such hidden variables cannot exist by using a phenomenon known as entanglement.

If hidden variables predetermine the outcomes of the measurements, Alice and Bob can’t win every round. Each viable set of values for the hidden variables effectively specifies a grid already filled out with –1s and 1s. The outcomes of the actual measurements just tell Alice which one to pick. The same goes for Bob. But, as is easily express with pencil and paper, no single mesh can satisfy both Alice’s and Bob’s parity rules. So, their mesh must disagree in at least one square, and on average, they can win at most eight out of nine rounds.

Quantum mechanics gives them win every time. To do that, they must utilize a set of measurements devised in 1990 by David Mermin, a senior theorist at Cornell University, and Asher Peres, a onetime theorist at the Israel Institute of Technology. Alice makes the measurements linked with the squares in the row specified by the referee, and Bob, those for the squares in the specified column.

Entanglement guarantees they got agree on the number in the key square and that their measurements also obey the equality rules. The whole plan works because the values emerge only as the measurements are made. The rest of the grid is unimportant, as values don’t exist for measurements that Alice and Bob never make

Xi-Lin Wang says this experiment was to signify mainly to show the potential of the team’s own favorite technology—photons tangled in both polarization and angular momentum. “We hope for to increase the quality of these entangled photons.”

This article has been published by Science

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