For more than half a century, scientists have entertained the thought that each of us may be able to experience totally different realities.
It’s strange to think about – the idea that two people could experience an identical situation entirely differently– but advances in quantum mechanics mean scientists are now more certain than ever that subjective reality is a very real thing.
Last year, a team at Heriot-Watt University in Edinburgh performed a quantum experiment allowing them to produce and compare different realities, and came to the conclusion that it was possible for two irreconcilable realities to be unable to agree on objective facts about the same experiment.
The test was based on ‘Wigner’s Friend’, a thought experiment outlined by Nobel Prize-winning physicist Eugene Wigner in 1961.
Wigner imagined a friend measuring the state of a single polarised photon. When measured, the photon can have either a horizontal or vertical polarisation, but according to the laws of quantum mechanics, before it is measured, the photon exists in both polarisation states at the same time – known as a superposition.
In the experiment, Wigner himself has no information about what his friend has measured, and so must assume that the photon and the measurement of it are in this superposition. Wigner performs an ‘interference experiment’ that shows that this is the case.
As a result, Wigner sees the superposition of the photon as an objective fact, which means the measurement cannot have taken place. But the friend, who did in fact measure the photon and record its specific polarisation, sees things completely differently, creating two irreconcilable realities.
By conducting a real-life version of this experiment, the Heriot-Watt team were able to prove Wigner right, a result they say ‘calls into question the objective status of the facts established by the two observers’.
The team used six entangled photons to create two alternate realities – one representing Wigner and one representing Wigner’s friend – and the results conclusively showed that both realities were able to coexist, even while producing mutually exclusive outcomes.
Given that scientists build their whole careers and beliefs around establishing objective facts, it seems like this experiment could throw up some pretty existential questions, especially for the team that conducted it. The study has raised far more questions than it has answered, and looks set to force physicists to consider that everything they understood about our shared reality could be wrong.
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MIT Technology Review
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