A new study has shown that multiple versions of reality can exist at the same time, at least at the quantum level, the world of subatomic particles.

Researchers were able to show that two people seeing the same particle can come up with different conclusions about its state and still both be correct.

Wigner's Friend

In 1961, Eugene Wigner, winner of the Nobel Prize for Physics in 1963, introduced a thought experiment that later became known as "Wigner's friend."

It involves two people observing a photon, a particle of light. When one observer who is in the isolated laboratory measures the photon, the particle's polarization, or the axis on which it spins, is either vertical or horizontal.

Before the photon is measured, however, the photon displays both polarization at the same time, existing in a superposition of two possible states.

The particle assumes fixed polarization once the person in the lab measures it, but for someone outside of the laboratory who is not aware of the results of the measurements, the unmeasured photon remains in a state of superposition.

This outsider's observation then diverges from the reality of the person inside the lab, but neither of the conflicting observations is wrong, according to the laws of quantum mechanics.

Testing The Wigner's Friend Scenario

In new experiments reported in the preprint journal arXiv on Feb. 13, Martin Ringbauer, from University of Innsbrück in Austria, replicated the conditions described in the thought experiment.

They designated two "laboratories" for the experiments and introduced two pairs of entangled photons, entangled particles linked in a way that actions performed on one affect the other even when the two particles are separated by distances.

The researchers also introduced four observers in the scenario designated as "Alice," "Bob," and a "friend" of each. The friends were the ones located inside the lab, while Alice and Bob were outside the lab.

The interference experiment doubled the scenario in that of the Wigner's friend, and it was able to replicate the results.

"In a state-of-the-art 6-photon experiment, we here realise this extended Wigner's friend scenario, experimentally violating the associated Bell-type inequality by 5 standard deviations. This result lends considerable strength to interpretations of quantum theory already set in an observer-dependent framework and demands for revision of those which are not," the researchers wrote.