The word “predictable” first entered the English language two centuries ago. Its début came in neither a farmer’s almanac nor a cardsharp’s manual but in The Monthly Repository of Theology and General Literature, a Unitarian periodical. In 1820, one Stephen Freeman wrote a dense treatise in which he criticized the notion that human behavior—seemingly manifest “amidst the conflicting, boisterous, unreasonable wills of men, all acting, as they feel they do, their various parts with complete freedom of choice”—somehow existed outside the domain of cause and effect. Freeman (“free man,” no less!) argued, instead, that human consciousness and our perception of free will must be subject to chains of causation. “What but this certainty, this necessity, can render any event, even such as depends on the free-will of intelligent agents, predictable?” he asked.

This week, in the journal Nature, a collaboration of more than a hundred quantum physicists, distributed across twelve laboratories in eleven countries on five continents, turned Freeman’s formulation on its head. With the help of high-powered lasers, superconducting magnets, and state-of-the-art machine-learning algorithms, they concluded that “if human will is free, there are physical events . . . that are intrinsically random, that is, impossible to predict.” The group dubbed their experiment the Big Bell Test, after the renowned twentieth-century physicist John S. Bell.

The question at the center of Bell’s work is whether objects in the real world, including elementary particles, have definite properties of their own, independent of whether anyone happens to measure them. Quantum theory holds that they do not—that the act of performing a measurement doesn’t so much reveal a preëxisting value as summon it forth. (It as though you had no definite weight until you stepped on your bathroom scale.) The Danish physicist Niels Bohr, writing in the nineteen-thirties, argued that the outcomes of quantum measurements were thus truly, inherently random.

The idea rankled Albert Einstein. He had particular trouble with the notion of quantum entanglement, which posits that two particles, if prepared in a certain way, remain linked with each other, no matter how far apart they roam; measure the properties of one and you know the properties of the other. Einstein argued that this should be impossible, since, according to his own theory of relativity, nothing—not even secret messages between particles—can travel faster than light. The entangled particles, he explained, must carry certain hidden instructions that govern their activity; anything else would be “spooky action at a distance.” And, if the particles had definite properties of their own, then there was a limit to how similar their measurements could be. Bell, on the other hand, demonstrated that quantum physics predicts scenarios that exceed this limit. He also showed that the inequality between the two paradigms—Einstein’s and Bohr’s—could be explored in the laboratory.

Since Bell did his critical work, physicists have tested his inequality in dozens and dozens of experiments. In every published case, the results have agreed with the predictions of quantum physics, putting tremendous strain on the commonsense notion that objects have properties all on their own. But, as Bell himself conceded, these results wouldn’t be so surprising if the measurements to be performed on each entangled particle could be predicted ahead of time. As the physicist Erwin Schrödinger remarked, in 1935, one would hardly be surprised that “a schoolboy under examination” had aced a test if he had the list of questions in advance. But how to make the selection of measurements as random as possible?

Some groups, including my own at the Massachusetts Institute of Technology (in collaboration with colleagues in Vienna and California), have turned to the stars, performing real-time astronomical observations of distant objects to determine which measurements to perform on Earth-bound entangled particles. In our recent test, the properties of the starlight that determined each measurement had been fixed hundreds of years before, quadrillions of miles from Earth.

For the Big Bell Test, the physicists gathered random inputs from online volunteers, whom they called Bellsters. The team first developed an original video game, which the Bellsters could play on a variety of platforms. The volunteers’ task was to exercise their free will by producing an unpredictable string of zeroes and ones; while they played, a machine-learning algorithm analyzed each Bellster’s first few entries and tried to predict what the next one would be. With real-time feedback from the algorithm, the players could improve their scores by making their selections less predictable. Some of the Bellsters’ ones and zeroes were directed to the participating laboratories via high-speed networks, where the numbers determined which measurements would be performed, right then and there, on various particles. In the course of a single day—November 30, 2016—the volunteers generated nearly a hundred million entries.

Every experiment performed as part of the Big Bell Test, using these creatively crowd-sourced inputs, found statistically significant violations of Bell’s inequality, precisely as quantum theory predicts. Moreover, the groups subjected seven different types of entangled systems to the test. Several used entangled photons, or particles of light, while others performed measurements on entangled photon-atom systems or other, more exotic arrangements.

Which brings us back to Stephen Freeman and the question of free will. If humans really can make choices that are not predetermined, then some large fraction of those hundred million game-generated zeroes and ones should qualify as appropriately free and independent of the other elements of the experiments. And, if that freedom is granted, then this super-collection of experiments—conducted in labs from Australia to Shanghai, Vienna to Barcelona, Buenos Aires to Boulder, Colorado—indeed demonstrated that the outcomes of those measurements were intrinsically random, inherently unpredictable. Any alternative explanation of the results, along the lines that Einstein and Schrödinger would have preferred, would need to posit both that the activities of a large fraction of the Bellsters were somehow swayed by some unseen force and that the same mechanism was able to affect the outcomes of measurements on different types of particles, in different laboratories, dotted clear around the Earth. Given those odds, I’ll take my chances with quantum theory.