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Science is based on facts that are established by independent observations agreed by everyone.

But scientists at Heriot-Watt University's Mostly Quantum Lab have now shown that, in the quantum world, facts may depend on who observes them.

Imagine tossing a coin. A quantum coin can exist in a of both 'heads' and 'tails', until a definite outcome 'heads' or 'tails' is observed, which is considered a fact.

In the 1960s, the renowned scientist, Eugene Wigner, proposed an intriguing thought experiment. An observer, Wigner's friend, tosses a quantum coin inside a closed laboratory, observing as a fact one of the two outcomes. From the outside, we cannot tell what happened, and the rules of quantum mechanics allow us to describe both friend and coin as one single system. 

Massimiliano Proietti, lead author of the study and PhD student at Heriot-Watt, said, "From outside the laboratory, Wigner's friend and the coin become "entangled", which means they are in a superposition where both outcomes, 'heads' and 'tails' are still present — a fact that can be established by the outside observer. This brings about a paradoxical situation where the fact established inside the laboratory seemingly contradicts the fact observed on the outside."

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Category: Science