The central mystery of quantum mechanics is that small chunks¹ of matter sometimes seem to behave like particles, sometimes like waves. For most of the past century, the prevailing² explanation of this conundrum³ has been what's called the "Copenhagen interpretation⁴" -- which holds that, in some sense, a single particle really is a wave, smeared⁵ out across the universe, that collapses⁶ into a determinate location only when observed. But some founders⁷ of quantum physics -- notably⁸ Louis de Broglie -- championed an alternative interpretation, known as "pilot-wave theory," which posits⁹ that quantum particles are borne along on some type of wave. According to pilot-wave theory, the particles have definite trajectories¹⁰, but because of the pilot wave's influence, they still exhibit wavelike statistics.

 

John Bush, a professor of applied¹¹ mathematics at MIT, believes that pilot-wave theory deserves a second look. That's because Yves Couder, Emmanuel Fort, and colleagues at the University of Paris Diderot have recently discovered a macroscopic pilot-wave system whose statistical¹² behavior, in certain circumstances, recalls that of quantum systems.

 

Couder and Fort's system consists of a bath of fluid vibrating at a rate just below the threshold at which waves would start to form on its surface. A droplet¹³ of the same fluid is released above the bath; where it strikes the surface, it causes waves to radiate outward. The droplet then begins moving across the bath, propelled by the very waves it creates.

 

"This system is undoubtedly¹⁴ quantitatively¹⁵ different from quantum mechanics," Bush says. "It's also qualitatively¹⁶ different: There are some features of quantum mechanics that we can't capture, some features of this system that we know aren't present in quantum mechanics. But are they philosophically¹⁷ distinct?"

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