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The universe is not locally real

By Daniel Garisto

One of the most unsettling discoveries in the past half a century is that the universe is not locally real. In this context, "real" means that objects have definite properties independent of observation - an apple can be red even when no one is looldng. "Local" means that objects can be influenced only by their surroundings and that any influence cannot travel faster than the light. Investigations at the frontier of quantum physics have found that these things cannot both be true. Instead the evidence shows that objects are not influenced solely by their surroundings, and they may also lack definite properties prior to measurement.

This is, of course, deeply contrary to our everyday experiences. As Albert Einstein once bemoaned to a friend, "Do you really believe the moon is not there when you are not looldng at it?" To adapt a phrase from author Douglas Adams, the demise of local realism has made a lot of people very angry and has been widely regarded as a bad move.

Blame for this achievement has now been laid squarely on the shoulders of three physicists: John Clauser, Alain Aspect and Anton Zeilinger. They equally split the 2022 Nobel Prize in Physics "for experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science ("Bell inequalities" refers to the pioneering work of Northern Ireland physicist John Stewart Bell, who laid the foundations for the 2022 Physics Nobel in the early l960s). Colleagues agreed that the trio had it coming, deserving this reckoning for overthrowing reality as we know it. "It was long overdue," says Sandu Popescu, a quantum physicist at the University of Bristol in England. "Without any doubt, the prize is well deserved."

"The experiments beginning with the earliest one of Clauser and continuing along show that this stuffisn'tjust philosophical, it's real- and like other real things, potentially useful," says Charles H. Bennett, and eminent quantum researcher at IBM "Each Year I thought, 'Oh, maybe this is the year,"' says David Kaiser, a physicist and historian at the Massachusetts Institute of Technology. In 2022 "it really was. It was very emotional- and very thrilling."

The journey from fringe to favor was a long one. From about 1940 until as late as 1990, studies of so-called quantum foundations were often treated as philosophy at best and crackpottery at worst. Many scientific journals refused to publish papers on the topic, and academic positions indulging such investigations were nearly impossible to come by. In 1985 Popescu's adviser warned him against a Ph.D. in the subject. "He said, 'Look, if you do that, you will have fun for five years, and then you will be jobless,"' Popescu says. Today quantum information science is among the most vibrant subfields in all ofphysics.

(Adapted from: Scientific American, 2023)