More Than One Reality Exists (in Quantum Physics)

Scientists have confirmed that multiple versions of reality exist and can be experimentally tested.

Before the hype machine takes hold – this is confirmed at the sub-atomic quantum level. And while the result is stunning, and has implications at the real world level we don’t know what those will be. It doesn’t mean we’ll be reality hopping anytime soon.

Researchers conducted experiments to test a theory first put forward by Nobel Prize winning Physicist Eugene Wigner. He proposed that two individuals measuring the same photon could discover different results about the photon’s state – and vitally – both results would be correct.

This is like measuring a spinning football to decide if it spins horizontally (like Earth) or vertically (rolling end over end, such as a bowling ball). And finding that it is doing both, exclusively, at the same time.

For the first time scientists have managed to recreate the conditions of the theory and test it in real laboratory conditions. The results of the experiment confirm that even when multiple (not just two) observers describe different states in the same photon, the conflicting realities revealed by the different states are all true.

Eugene Wigner, Nobel Laureate in Physics
Eugene Wigner, Nobel Laureate Physics 1963

Wigner’s experiment

In 1961, two years before he won the Nobel Prize, Wigner devised a thought experiment that became known as “Wigner’s friend.” It begins with a photon — a particle of light. Light is made up of tiny packets known as photons. When an observer in an isolated laboratory measures a photon, they see that the photon’s polarisation — the axis on which it spins like a football— is either vertical or horizontal.

Yet, before any photon is measured, it shows both polarisations at once due to the deterministic laws of quantum physics. In physics this is known as a “superposition” of two possible states. In effect before you observe the photon, the polarisation is ‘blurred’.

When an observer measures a photon, it assumes a fixed polarisation. Either horizontal or vertical. But for someone observing outside that closed laboratory who doesn’t know the result of the measurements, the unmeasured photon is still in a state of superposition.

That outside person’s observation — their reality — thus differs significantly from the reality of the person in the lab who measured the photon. The key is that neither of those conflicting observations of reality is false. They are both physically real, and physically different.

Altered states

Since its creation, Wigner’s experiment was a cornerstone thought experiment, but un-testable. However, in recent years, with advances in quantum teleportation and quantum computing the technology finally caught up to enable scientists to test Wigner’s proposal. Put simply it was not possible to control quantum systems well enough until recently to be able to setup and run the experiment reliably.

In the paper Ringbauer describe how they test Wigner’s original idea with a rigorous experiment in which they assign two “laboratories” where the experiments occur and introduce two pairs of entangled photons. When photons are entangled measurement of one automatically lets one know the state of the other. To accompany the photons four experimental observers Alice, Bob and a friend each were installed.

Wigner’s Friend – Experiment Setup. Credit: MIT Labs.

The two friends were located inside each of the labs, each measured one photon in an entangled pair.

Alice and Bob, working outside the black-box environment of the labs, could then decide how to measure the state of the photon.

They could either:

  1. measure their friends’ results already stored in quantum memory and so agree with them about the polarised photons spin state.
  2. Run their own experiment, and they would see if the photon is still in ‘superposition’ by observing it’s interference pattern.

In an interference experiment, if the photons still exist in a superposition of states, then Alice and Bob will see a characteristic pattern of light and dark fringes, where the peaks and valleys of the light waves add up or cancel each other out.

On the other hand, if photons have fixed their spin state, Alice and Bob will see a different patter. Wigner’s suggested that reviewing this pattern would reveal if photons were still in an entangled state.

The experiment produces a definitive result. The study found that even in the multiple observer setup, the results anticipated by Wigner were shown. It is the case that both realities exist despite producing conflicting outcomes, just as Wigner predicted.

Alice and Bob can arrive at conclusions about the photons which are entirely correct and provable which differ from the observations of their friends — which were also correct and provable, according to the study.

That result is stunning, and has far reaching implications for our understanding of reality and measurement. However we know already that the quantum world at the sub-atomic scale behaves very differently from the larger scale world of every day reality. This result isn’t magic, it doesn’t break our day to day world experience – but it does show us that we have some way to go before truly claiming to understand our reality.

As an author of the study, Ringbauer put it: “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,”.

The work has important implications for the work of scientists. “The scientific method relies on facts, established through repeated measurements and agreed upon universally, independently of who observed them,” say Proietti and co. However their work challenges that very idea – perhaps putting it aside forever.

We are entering a new age where quantum computing and quantum physics will shape our technology in unexpected ways. Science can illuminate new pathways and new ways of understanding, and part of that is the risk it reveals our existing assumptions fail to hold under new conditions.

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