One of a human’s earliest developmental milestones is an understanding of object permanence. It generally takes less than a year for a baby to realize that when an adult hides their face behind their hands in a game of peek-a-boo, they don’t cease to exist. There’s more to the world around us than what we perceive.
This suggests — or at least, it suggested to Albert Einstein — that the world is “real,” in the sense that things in the world have properties that are intrinsically true no matter what anyone thinks. A red billiard ball is red, even in the dark, and even if no one is checking its color. The redness is a property belonging to the ball, not to some device measuring the ball, and not to the mind of some person operating the measuring device.
Yet quantum mechanics, a thoroughly validated theory of how the world works, seems to suggest otherwise. The theory’s math assigns redness to the billiard ball at the moment you measure it. Before then, the theory gives you only a set of probabilities telling you what color the ball might be.
Key founders of quantum mechanics suggested that this math reflects the nature of reality — that in some sense, a single, objective reality doesn’t really exist. In 1935, Einstein rebelled against this surreal reading of quantum theory, proposing one of the 20th century’s most famous thought experiments. But his rebellion was doomed.
In 1964, the physicist John Stewart Bell showed with a thought experiment of his own that reality had to be stranger than Einstein assumed. Subsequent work would put Bell’s thought experiment to the test — and prove him right. Then, 50 years after Bell, Matthew Pusey, at the time a graduate student at Imperial College London, took on what remained of Einstein’s notion of reality and — without originally intending to — delivered the killing blow.
The paradigm-shifting theorem became known as PBR, for Pusey and his academic accomplices, Jonathan Barrett and Terry Rudolph. Since the publication of PBR in 2012, many theorists have come to accept that it rules out our most commonsense understanding of reality. At the time, Pienaar, like Pusey, had been walking in Einstein’s footsteps, dabbling in theories designed to show that objective reality exists and that quantum mechanics merely describes our incomplete knowledge of it.
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