I hope you're wide awake, caffeinated, well-fed and of a clear mind, because we're about to dive into a fascinating breakthrough in quantum entanglement.
First, it's best to start with a definition: Quantum entanglement is a physical phenomenon where two linked particles share the same state. So for example, if you observe a particle in one state, the other particle — even if separated by light-years of distance — will instantly change its own state to reflect its twin. This mysterious communication channel is bizarre for a number of reasons, one of the biggest being that it appears to involve messaging from a mass that somehow travels faster than the speed of light, a clear violation of Einstein's Special Theory of Relativity.
In a private letter to German physicist Max Born, Einstein expressed discomfort with the idea of quantum entanglement by calling it "spooky action at a distance."
"I cannot seriously believe in it because the theory cannot be reconciled with the idea that physics should represent a reality in time and space, free from spooky actions at a distance," he wrote at the age of 68. "[…] I am quite convinced that someone will eventually come up with a theory whose objects, connected by laws, are not probabilities but considered facts, as used to be taken for granted until quite recently. I cannot, however, base this conviction on logical reasons."
Humans vs. 'local realism'
In a paper published this week in the journal Nature, a collaborative effort between physicists from 12 laboratories across five continents and more than 100,000 volunteer gamers has placed more weight behind the idea that quantum behavior is not governed by the rules of classical physics.
According to study co-author Morgan Mitchell, a physicist at the Institut de Ciències Fotòniques in Spain, the findings contradict Einstein's description of a state known as "local realism."
"We showed that Einstein’s world-view of local realism, in which things have properties whether or not you observe them, and no influence travels faster than light, cannot be true — at least one of those things must be false," he told Live Science.
Since the 1970s, researchers have used Bell tests, developed by the Irish physicist John Bell, to gauge the plausibility of local realism as it relates to quantum mechanics. The problem is that entanglement can only be measured indirectly through statistics.
Writing for Wired, Sophia Chen offers an analogy that puts the concept in perspective:
"It’s sort of like finding out whether a die is loaded by throwing it thousands of times, if you couldn’t directly measure its weight distribution. In a similar way, you don’t actually ever measure entanglement itself: You measure other properties, like a photon’s orientation, to look for statistical evidence of it.
In order to close bias loopholes from data collected from a Bell test, which require fast and high-efficiency detection and unpredictable measurement settings, the researchers turned to human volunteers to generate a massive amount of random information.
The Big Bell Test
On Nov. 30, 2016, more than 100,000 gamers went online to participate in The Big Bell Test, a game that required players to tap two buttons with values of one and zero. The more random their button pushes, the more points the gamers earned.
"People are unpredictable, and when using smartphones even more so," said team member Andrew White from the University of Queensland in Australia. "We asked folk to contribute unpredictable numbers, using smartphones and so on."
According to the study, 97,347,490 binary choices were streamed to 12 labs, where 13 experiments tested local realism using photons, single atoms, atomic ensembles and superconducting devices. The experiments used the mass of human-generated data to choose each measurement setting, closing the bias loophole and producing results that "strongly contradict local realism."
"We showed that a key property of entanglement in space, so-called monogamy of entanglement, does not hold in the temporal domain," said Dr. Martin Ringbauer of the University of Queensland. "There are still many open questions, and this experiment is a first step towards exploring quantum correlations in time: one suggested application is in quantum blockchain."
While this specific study has concluded, the game is still available for people to play and help contribute random data for future quantum physics experiments.
"We know that the Higgs boson and gravitational waves exist thanks to amazing machines, physical systems built to test the laws of physics," said Mitchell. "But local realism is a question we can't fully answer with a machine. It seems we ourselves must be part of the experiment, to keep the Universe honest."