Researchers claim they can prove that it is possible for two versions of reality to exist at the same time, but only at the quantum level.

The belief that there are multiple versions of ourselves in an infinite number of dimensions has long been a staple of science fiction, but has so far remained only that. However, within the weird world of quantum mechanics, scientists are now coming to terms with the possibility that something vaguely similar could indeed be true in the real world.

According to Live Science, researchers in Austria recently published a paper appearing to confirm a decades-old theoretical question posed by the 1963 winner of the Nobel Prize in Physics, Eugene Wigner. In 1961, the physicist proposed the question that became known as ‘Wigner’s friend’, whereby it could be possible for two people to observe the same photon and see them existing in two different states, with both being technically correct.

When observed, the particle of light’s polarisation should be either vertical or horizontal, but before it is measured the laws of quantum mechanics state that it should exist in a ‘superposition’ where it is both polarisations at once.

Therefore, if ‘person A’ in the lab sees a fixed polarisation, ‘person B’ – who has no idea about the results of the lab measurements as they are outside the process – would then see it in a state of superposition. This results in two people seeing two different realities of the same thing.

Since Wigner first proposed it decades ago, the thought experiment has remained just that, but major advances in our understanding of physics in recent years have helped us actually put it to the test.

“Theoretical advances were needed to formulate the problem in a way that is testable,” said Martin Ringbauer, a postdoctoral researcher at the University of Innsbrück. “Then, the experimental side needed developments on the control of quantum systems to implement something like that.”

Bob, Alice and friends

To conduct their experiment, the researchers took things even further by doubling the scenario: two labs with two pairs of entangled photons, meaning that knowing the state of one photon would automatically tell you the state of the other.

The photons were represented by names including ‘Bob’, ‘Alice’ and two ‘friends’, with the latter two split between both labs and each measuring one photon in an entangled pair. This resulted in the breaking of superposition, forcing the photon measured by the friends to be in a fixed polarisation.

The results of the experiments showed that even when the scenario was doubled, Wigner’s theory held up as both Alice and Bob would arrive at a conclusion that differed from their friends. If this is causing you headaches, spare a thought for quantum physicists who have to come to terms with the fact that this challenges the very meaning of quantum mechanics.

“It seems that, in contrast to classical physics, measurement results cannot be considered absolute truth but must be understood relative to the observer who performed the measurement,” Ringbauer said. “The stories we tell about quantum mechanics have to adapt to that.”