simulation lay exactly over the diagonal line created from the results of the experiment itself. What she had witnessed in the little crystal was not an artefact, but something real that she had now reproduced in her computer simulation. She had even mapped out where the atoms should have been on the graph, had they been obeying the usual laws of physics. But there they were in a line: a law completely unto themselves.
She wrote Rosenbaum a guarded email late that evening: ‘I’ve got something interesting to show you in the morning.’ The following day, they examined her graph. There was no other possibility, they both realized; the atoms had been ignoring her and instead were controlled by the activity of their neighbours. No matter whether she blasted the crystal with a strong magnetic field or an increase in temperature, the atoms overrode this outside disturbance.
The only explanation was that the atoms in the sample crystal were internally organizing and behaving like one single giant atom. All the atoms, they realized with some alarm, must be entangled.
One of the strangest aspects of quantum physics is a feature called ‘non-locality’, also poetically referred to as ‘quantum entanglement’. The Danish physicist Niels Bohr discovered that once subatomic particles such as electrons or photons are in contact, they remain cognizant of and influenced by each other instantaneously over any distance forever, despite the absence of the usual things that physicists understand are responsible for influence, such as an exchange of force or energy. When entangled, the actions – for instance, the magnetic orientation – of one will always influence the other in the same or the opposite direction, no matter how far they are separated. Erwin Schrödinger, another one of the original architects of quantum theory, believed that the discovery of non-locality represented no less than quantum theory’s defining moment – its central property and premise.
The activity of entangled particles is analogous to a set of twins being separated at birth, but retaining identical interests and a telepathic connection forever. One lives in Colorado, and the other in London. Although they never meet again, both like the colour blue. Both take a job in engineering. Both like to ski; in fact when one falls down and breaks his right leg at Vale, his twin breaks his right leg at precisely that moment, even though he is 4000 miles away, sipping a latte at Starbucks.4 Albert Einstein refused to accept non-locality, referring to it disparagingly as ‘spukhafte Fernwirkungen’ or ‘spooky action at a distance’. This type of instantaneous connection would require information travelling faster than the speed of light, he argued through a famous thought experiment, which would violate his own special relativity theory.5 Since the formulation of Einstein’s theory, the speed of light (299,792,458 metres per second) has been used as the absolute limiting factor on how quickly one thing can affect something else. Things are not supposed to be able to affect other things faster than the time it would take the first thing to travel to the second thing at the speed of light.
Nevertheless, modern physicists, such as Alain Aspect and his colleagues in Paris, have demonstrated decisively that the speed of light is not an absolute outer boundary in the subatomic world. Aspect’s experiment, which concerned two photons fired off from a single atom, showed that the measurement of one photon instantaneously affected the position of the second photon6 so that it has the same or opposite spin or position (as IBM physicist Charles H. Bennett once put it, ‘opposite luck’).7 The two photons continued to talk to each other and whatever happened to one was identical to, or the very opposite of, what happened to the other. Today, even the most conservative physicists accept non-locality as a strange feature of subatomic reality.8
Most quantum experiments incorporate some test of Bell’s Inequality. This famous experiment in quantum physics was carried out by John Bell, an Irish physicist who developed a practical means to test how quantum particles really behaved.9 This simple test required that you get two quantum particles that had once been in contact, separate them and then take measurements of the two. It is analogous to a couple named Daphne and Ted who have once been together but are now separated. Daphne can choose one of two possible directions to go in and so can Ted. According to our commonsense view of reality, Daphne’s choice should be utterly independent of Ted’s.
When Bell carried out his experiment, the expectation was that one of the measurements would be larger than the other – a demonstration of ‘inequality’. However, a comparison of the measurements showed that both were the same and so his inequality was ‘violated’. Some invisible wire appeared to be connecting these quantum particles across space, to make them follow each other. Ever since, physicists have understood that when a violation of Bell’s Inequality occurs, it means that two things are entangled.
Bell’s Inequality has enormous implications for our understanding of the universe. By accepting non-locality as a natural facet of nature we are acknowledging that two of the bedrocks on which our world view rests are wrong: that influence only occurs over time and distance, and that particles like Daphne and Ted, and indeed the things that are made up of particles, only exist independently of each other.
Although modern physicists now accept non-locality as a given feature of the quantum world, they console themselves by maintaining that this strange, counter-intuitive property of the subatomic universe does not apply to anything bigger than a photon or electron. Once things got to the level of atoms and molecules, which in the world of physics is considered ‘macroscopic’, or large, the universe started behaving itself again, according to predictable, measurable, Newtonian laws.
With one tiny thumbnail’s worth of crystal, Rosenbaum and his graduate student demolished that delineation. They had demonstrated that big things like atoms were non-locally connected, even in matter so large you could hold it in your hand. Never before had quantum non-locality been demonstrated on such a scale. Although the specimen had been only a tiny chip of salt, to the subatomic particle, it was a palatial country mansion, housing a billion billion (1,000,000,000,000,000,000 or 1018) atoms. Rosenbaum, ordinarily loathe to speculate about what he could not yet explain, realized that they had uncovered something extraordinary about the nature of the universe. And I realized they had discovered a mechanism for intention: they had demonstrated that atoms, the essential constituents of matter, could be affected by non-local influence. Large things like crystals were not playing by the grand rules of the game, but by the anarchic rules of the quantum world, maintaining invisible connections without obvious cause.
In 2002, after Sai wrote up their findings, Rosenbaum polished up the wording and sent off their paper to Nature, a journal notorious for conservatism and exacting peer review. After four months of responding to the suggestions of reviewers, Ghosh finally got her paper published in the world’s premier scientific journal, a laudatory feat for a 26-year-old graduate student.10
One of the reviewers, Vlatko Vedral, noted the experiment with a mix of interest and frustration.11 A Yugoslav who had studied at Imperial College, London, during his country’s civil war and subsequent collapse, Vedral had distinguished himself in his adopted country and been chosen to head up quantum information science at the University of Leeds. Vedral, who was tall and leonine, was part of a small group in Vienna working on frontier quantum physics, including entanglement.
Vedral first theoretically predicted the effect that Ghosh and Rosenbaum eventually found three years later. He had submitted the paper to Nature in 2001, but the journal, which preferred experiment to theory, had rejected it. Eventually, Vedral managed to publish his paper in Physical Review Letters, the premier physics journal.
