Wave/Particle Duality Living Large

Wave/particle duality is usually a quantum phenomenon confined to photons, electrons, protons, and other ultra-tiny objects.

Quantum mechanics shows that such objects sometimes behave like particles, sometimes behave like waves, and sometimes like a little of both. All objects exhibit wave/particle duality to some extent, but the larger the object the harder it is to observe. Even individual molecules are often too large to show the quantum mechanical behavior.

Now physicists at the Université de Paris have demonstrated a classical version of wave/particle duality with a droplet made of trillions of molecules.

The experiment involved an oil droplet bouncing on the surface of layer of oil that was vibrated vertically. (Check out some pretty pictures of a bouncing oil droplet from a previous, related experiment by the same researchers in a press release put out by the French National Center for Experimental Science last year.) The droplet created waves on the surface, which in turn affected the motion of the droplet. As a result, the droplet and waves formed a single entity that consisted of a hybrid of wave-like and particle-like characteristics.

When the wave/droplet bounced its way through a slit, the waves allowed it to interfere with its own motion, much as a single photon can interfere with itself via quantum mechanics. Although the wave/droplet is clearly a denizen of the classical world, the experiment provides a clever analog of quantum weirdness at a scale that is much easier to study and visualize than is typical of many true quantum experiments.

A paper describing the research, Single-Particle Diffraction and Interference at a Macroscopic Scale, was published in the October 13, 2006 issue of Physical Review Letters.

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