Can you be in two places at once? Yes, according to quantum physicists
FPI / March 21, 2019
Is it possible for two versions of reality to exist at the same time? Indeed it is – at the quantum level – physicists say.
Of course political scientists can attest that the election of President Donald Trump has produced a proof of the hypothesis: His supporters and his opponents live in two separate and contrasting realities as demonstrated by innumerable polls and news reports and analyses.
The experiment “proposed that two individuals observing the same photon could arrive at different conclusions about that photon’s state – and yet both of their observations would be correct,” Live Science reported on March 20.
Scientists who replicated conditions described in the thought experiment published their results on Feb. 13 in the preprint journal arXiv.
“You can verify both of them,” study co-author Martin Ringbauer, a postdoctoral researcher with the Department of Experimental Physics at the University of Innsbruck in Austria, told Live Science.
The thought experiment was first introduced in 1961 by Eugene Wigner, who won the Nobel Prize for Physics in 1963.
Live Science noted that the initial experiment, known as “Wigner’s friend,” begins with a photon – a particle of light. When an observer in an isolated laboratory measures the photon, they find that the particle’s polarization – the axis on which it spins – is either vertical or horizontal.
However, before the photon is measured, the photon displays both polarizations at once, as dictated by the laws of quantum mechanics; it exists in a “superposition” of two possible states.
Once the person in the lab measures the photon, the particle assumes a fixed polarization. But for someone outside that closed laboratory who doesn’t know the result of the measurements, the unmeasured photon is still in a state of superposition.
That outsider’s observation – their reality – therefore diverges from the reality of the person in the lab who measured the photon. Yet, neither of those conflicting observations is thought to be wrong, according to quantum mechanics.
For decades, Wigner’s mind-bending proposal was just an interesting thought experiment. But in recent years, important advances in physics finally enabled experts to put Wigner’s proposal to the test, Ringbauer said.
“Theoretical advances were needed to formulate the problem in a way that is testable. Then, the experimental side needed developments on the control of quantum systems to implement something like that,” Ringbauer said.
Ringbauer and his colleagues tested Wigner’s original idea with an even more rigorous experiment which doubled the scenario. They designated two “laboratories” where the experiments would take place and introduced two pairs of entangled photons, meaning that their fates were linked, so that knowing the state of one automatically tells you the state of the other. (The photons in the setup were real. Four “people” in the scenario – “Alice,” “Bob” and a “friend” of each – were not real, but instead represented observers of the experiment).
The authors of the new study found that even in their doubled scenario, the results described by Wigner held. Alice and Bob could arrive at conclusions about the photons that were correct and provable and that yet still differed from the observations of their friends – which were also correct and provable, according to the study.
Quantum mechanics describes how the world works at a scale so small that the normal rules of physics no longer apply; over many decades, experts who study the field have offered numerous interpretations of what that means, Ringbauer said.
However, if measurements themselves aren’t absolutes – as these new findings suggest – that 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,” he said.
FPI, Free Press International