Jeff Tollaksen may well believe he was destined to be here at this point in time. We’re on a boat in the Atlantic, and it’s not a pleasant trip. The torrential rain obscures the otherwise majestic backdrop of the volcanic Azorean islands, and the choppy waters are causing the boat to lurch. The rough sea has little effect on Tollaksen, barely bringing color to his Nordic complexion. This is second nature to him; he grew up around boats. Everyone would agree that events in his past have prepared him for today’s excursion. But Tollaksen and his colleagues are investigating a far stranger possibility: It may be not only his past that has led him here today, but his future as well.
Tollaksen’s group is looking into the notion that time might flow backward, allowing the future to influence the past. By extension, the universe might have a destiny that reaches back and conspires with the past to bring the present into view. On a cosmic scale, this idea could help explain how life arose in the universe against tremendous odds. On a personal scale, it may make us question whether fate is pulling us forward and whether we have free will.
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The boat trip has been organized as part of a conference sponsored by the Foundational Questions Institute to highlight some of the most controversial areas in physics. Tollaksen’s idea certainly meets that criterion. And yet, as crazy as it sounds, this notion of reverse causality is gaining ground. A succession of quantum experiments confirm its predictions—showing, bafflingly, that measurements performed in the future can influence results that happened before those measurements were ever made.
As the waves pound, it’s tough to decide what is more unsettling: the boat’s incessant rocking or the mounting evidence that the arrow of time—the flow that defines the essential narrative of our lives—may be not just an illusion but a lie.
Tollaksen, currently at Chapman University in Orange County, California, developed an early taste for quantum mechanics, the theory that governs the motion of particles in the subatomic world. He skipped his final year of high school, instead attending physics lectures by the charismatic Nobel laureate Richard Feynman at Caltech in Pasadena and learning of the paradoxes that still fascinate and frustrate physicists today.
Primary among those oddities was the famous uncertainty principle, which states that you can never know all the properties of a particle at the same time. For instance, it is impossible to measure both where the particle is and how fast it is moving; the more accurately you determine one aspect, the less precisely you can measure the other. At the quantum scale, particles also have curiously split personalities that allow them to exist in more than one place at the same time—until you take a look and check up on them. This fragile state, in which the particle can possess multiple contradictory attributes, is called a superposition. According to the standard view of quantum mechanics, measuring a particle’s properties is a violent process that instantly snaps the particle out of superposition and collapses it into a single identity. Why and how this happens is one of the central mysteries of quantum mechanics.
“The textbook view of measurements in quantum mechanics is inspired by biology,” Tollaksen tells me on the boat. “It’s similar to the idea that you can’t observe a system of animals without affecting them.” The rain is clearing, and the captain receives radio notification that some dolphins have been spotted a few minutes away; soon we’re heading toward them. Our attempts to spy on these animals serve as the zoological equivalent of what Tollaksen terms “strong measurements”—the standard type in quantum mechanics —because they are anything but unobtrusive. The boat is loud; it churns up water as it speeds to the location. When the dolphins finally show themselves, they swim close to the boat, arcing through the air and playing to their audience. According to conventional quantum mechanics, it is similarly impossible to observe a quantum system without interacting with the particles and destroying the fragile quantum behavior that existed before you looked.
Most physicists accept these peculiar restrictions as part and parcel of the theory. Tollaksen was not so easily appeased. “I was smitten, and I knew there was no chance I was ever going to do anything else with my life,” he recalls. On Feynman’s advice, the teenager moved to Boston to study physics at MIT. But he missed the ocean. “For the first time in my life, I lost the background sound of surf,” he says. “That was actually traumatic.”
Mindful that a job in esoteric physics might not be the best way to put food on his family’s table, Tollaksen worked on a computing start-up company while pursuing his Ph.D. But if the young man wasn’t sure of his calling, fate quickly gave him a nudge when a physicist named Yakir Aharonov visited the neighboring Boston University. Aharonov, now at Chapman with Tollaksen, was renowned for having codiscovered a bizarre quantum mechanical effect in which particles can be affected by electric and magnetic fields, even in regions where those fields should have no reach. But Tollaksen was most taken by another area of Aharonov’s research: a time-twisting interpretation of quantum mechanics.
“Aharonov was one of the first to take seriously the idea that if you want to understand what is happening at any point in time, it’s not just the past that is relevant. It’s also the future,” Tollaksen says. In particular, Aharonov reanalyzed the indeterminism that forms the backbone of quantum mechanics. Before quantum mechanics arrived on the scene, physicists believed that the laws of physics could be used to determine the future of the universe and every object within it. By this thinking, if we knew the properties of every particle on the planet we could, in principle, calculate any person’s fate; we could even calculate all the thoughts in his or her head.