On Wednesday, November 30, 2016, crowds of Cubans took to the streets of Havana to pay their last respects to Fidel Castro. On the same day, fans gathered to watch Spanish football stalwart Hercules surprise Barcelona one-on-one in their Copa del Rey match. And to test a central feature of quantum mechanics, a crowd of 100,000 people around the world came together to type in a series of 0s and 1s on an online video game, flying as fast as their fingers could.
The gamers were part of a one-day experiment called the Big Bell Test, the results of which are described in this issue of Nature (The Big Bell Test Collaboration. Nature 557, 212–216; 2018). The findings were formulated in an unusual way and, with the symmetry one would expect from a beautiful physics theory, they were also reviewed for publication in an unusual way.
Less than a year after testing, the Big Bell test paper landed on the desk of physicist Sabrina Manisalko of the University of Turku in Finland for review from Nature. Given the crowded public input involved, Maniscalco decided to crowdsource the requested review — well, up to a point.
He showed it to seven of his senior PhD students, and then invited them to discuss it with him over a day of brainstorming, literature searching, and pizza. She incorporated the resulting comments and criticisms into the referee’s report which she submitted, and which all seven students revisited before submitting.
There was no breach of trust during the review process: the students agreed to strict confidentiality, and Maniscalco opted for our referee-recognition test scheme, meaning that her name, along with the participating students, would eventually be a The statement appears in the research paper. Two other reviewers presented their views on the paper in the usual way.
It is not uncommon for a lab head to entrust a peer review of a paper to a junior colleague, or to collaborate with one – and, unfortunately, the colleague’s contribution is not always acknowledged. It is unusual, as far as we know, to make peer review a team exercise and openly state how it was done.
This is not an experiment that we expect to be repeated often. Yet, contrary to popular belief, our editors are, in principle, happy to involve others in the review process by referees, as long as confidentiality is assured and editors are kept in the loop. It’s okay for everyone involved in peer review to be accepted. At its best, such collaboration can enrich the review process and help junior researchers develop the skills needed to become effective referees themselves.
In this case, the paper explores the tension between quantum physics and local realism. The latter brings together two principles: localism – according to which, the observation of a particle in one physical location may not have an immediate effect on the properties of a particle at a different location – and realism, which expresses that the observable properties of particles How features exist, even if we don’t actively measure them.
But in quantum mechanics, the connections between distant particles are so strong that they violate local realism. In other words, it is possible in quantum theory to have two correlated particles very far from each other, to measure the first and, consequently, learn something about the second without looking directly at them.
So here’s the riddle: does quantum mechanics actually violate local realism, or could it be that some unknown factor will satisfy the theory and explain these apparent violations? In the 1960s, physicist John Bell introduced a way to tackle the problem in the laboratory, by studying quantum correlations in the form of entanglement. In these experiments, a sequence of spatially separated measurements on entangled particles calculates a quantity whose values may not be possible in terms of local and realistic theories.
Bell tests have at times confirmed the validity of quantum theory, but they contain assumptions that leave room for non-quantum explanations as to why local realism is violated, and so physicists try to close these loopholes. Looking for ways.
In 2015, physicists showed that successful Bell tests could not be due to motion-of-light communication between particles, or to inefficient detection processes during measurements. But another, more subtle, loophole was still open. The Bell test also assumes that experimenters have free choice about which measurements they make on each particle. And yet, hidden parameters can influence the correlations these choices give the illusion of entanglement.
The Big Bell Test closes the loophole of this freedom-of-choice. The different experimental groups did not have a say on which measurement setting to use. Instead, he made his measurements according to the unpredictable streams of bits he received from 100,000 gamers.